The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_input.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
    3  *      The Regents of the University of California.  All rights reserved.
    4  * Copyright (c) 2007-2008,2010
    5  *      Swinburne University of Technology, Melbourne, Australia.
    6  * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
    7  * Copyright (c) 2010 The FreeBSD Foundation
    8  * Copyright (c) 2010-2011 Juniper Networks, Inc.
    9  * All rights reserved.
   10  *
   11  * Portions of this software were developed at the Centre for Advanced Internet
   12  * Architectures, Swinburne University of Technology, by Lawrence Stewart,
   13  * James Healy and David Hayes, made possible in part by a grant from the Cisco
   14  * University Research Program Fund at Community Foundation Silicon Valley.
   15  *
   16  * Portions of this software were developed at the Centre for Advanced
   17  * Internet Architectures, Swinburne University of Technology, Melbourne,
   18  * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
   19  *
   20  * Portions of this software were developed by Robert N. M. Watson under
   21  * contract to Juniper Networks, Inc.
   22  *
   23  * Redistribution and use in source and binary forms, with or without
   24  * modification, are permitted provided that the following conditions
   25  * are met:
   26  * 1. Redistributions of source code must retain the above copyright
   27  *    notice, this list of conditions and the following disclaimer.
   28  * 2. Redistributions in binary form must reproduce the above copyright
   29  *    notice, this list of conditions and the following disclaimer in the
   30  *    documentation and/or other materials provided with the distribution.
   31  * 4. Neither the name of the University nor the names of its contributors
   32  *    may be used to endorse or promote products derived from this software
   33  *    without specific prior written permission.
   34  *
   35  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   36  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   37  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   38  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   39  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   40  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   41  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   42  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   43  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   44  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   45  * SUCH DAMAGE.
   46  *
   47  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
   48  */
   49 
   50 #include <sys/cdefs.h>
   51 __FBSDID("$FreeBSD: head/sys/netinet/tcp_input.c 301717 2016-06-09 05:48:34Z ae $");
   52 
   53 #include "opt_inet.h"
   54 #include "opt_inet6.h"
   55 #include "opt_ipsec.h"
   56 #include "opt_tcpdebug.h"
   57 
   58 #include <sys/param.h>
   59 #include <sys/kernel.h>
   60 #include <sys/hhook.h>
   61 #include <sys/malloc.h>
   62 #include <sys/mbuf.h>
   63 #include <sys/proc.h>           /* for proc0 declaration */
   64 #include <sys/protosw.h>
   65 #include <sys/sdt.h>
   66 #include <sys/signalvar.h>
   67 #include <sys/socket.h>
   68 #include <sys/socketvar.h>
   69 #include <sys/sysctl.h>
   70 #include <sys/syslog.h>
   71 #include <sys/systm.h>
   72 
   73 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
   74 
   75 #include <vm/uma.h>
   76 
   77 #include <net/if.h>
   78 #include <net/if_var.h>
   79 #include <net/route.h>
   80 #include <net/vnet.h>
   81 
   82 #define TCPSTATES               /* for logging */
   83 
   84 #include <netinet/in.h>
   85 #include <netinet/in_kdtrace.h>
   86 #include <netinet/in_pcb.h>
   87 #include <netinet/in_systm.h>
   88 #include <netinet/ip.h>
   89 #include <netinet/ip_icmp.h>    /* required for icmp_var.h */
   90 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
   91 #include <netinet/ip_var.h>
   92 #include <netinet/ip_options.h>
   93 #include <netinet/ip6.h>
   94 #include <netinet/icmp6.h>
   95 #include <netinet6/in6_pcb.h>
   96 #include <netinet6/in6_var.h>
   97 #include <netinet6/ip6_var.h>
   98 #include <netinet6/nd6.h>
   99 #ifdef TCP_RFC7413
  100 #include <netinet/tcp_fastopen.h>
  101 #endif
  102 #include <netinet/tcp.h>
  103 #include <netinet/tcp_fsm.h>
  104 #include <netinet/tcp_seq.h>
  105 #include <netinet/tcp_timer.h>
  106 #include <netinet/tcp_var.h>
  107 #include <netinet6/tcp6_var.h>
  108 #include <netinet/tcpip.h>
  109 #include <netinet/cc/cc.h>
  110 #ifdef TCPPCAP
  111 #include <netinet/tcp_pcap.h>
  112 #endif
  113 #include <netinet/tcp_syncache.h>
  114 #ifdef TCPDEBUG
  115 #include <netinet/tcp_debug.h>
  116 #endif /* TCPDEBUG */
  117 #ifdef TCP_OFFLOAD
  118 #include <netinet/tcp_offload.h>
  119 #endif
  120 
  121 #ifdef IPSEC
  122 #include <netipsec/ipsec.h>
  123 #include <netipsec/ipsec6.h>
  124 #endif /*IPSEC*/
  125 
  126 #include <machine/in_cksum.h>
  127 
  128 #include <security/mac/mac_framework.h>
  129 
  130 const int tcprexmtthresh = 3;
  131 
  132 int tcp_log_in_vain = 0;
  133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
  134     &tcp_log_in_vain, 0,
  135     "Log all incoming TCP segments to closed ports");
  136 
  137 VNET_DEFINE(int, blackhole) = 0;
  138 #define V_blackhole             VNET(blackhole)
  139 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_VNET | CTLFLAG_RW,
  140     &VNET_NAME(blackhole), 0,
  141     "Do not send RST on segments to closed ports");
  142 
  143 VNET_DEFINE(int, tcp_delack_enabled) = 1;
  144 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_VNET | CTLFLAG_RW,
  145     &VNET_NAME(tcp_delack_enabled), 0,
  146     "Delay ACK to try and piggyback it onto a data packet");
  147 
  148 VNET_DEFINE(int, drop_synfin) = 0;
  149 #define V_drop_synfin           VNET(drop_synfin)
  150 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_VNET | CTLFLAG_RW,
  151     &VNET_NAME(drop_synfin), 0,
  152     "Drop TCP packets with SYN+FIN set");
  153 
  154 VNET_DEFINE(int, tcp_do_rfc6675_pipe) = 0;
  155 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc6675_pipe, CTLFLAG_VNET | CTLFLAG_RW,
  156     &VNET_NAME(tcp_do_rfc6675_pipe), 0,
  157     "Use calculated pipe/in-flight bytes per RFC 6675");
  158 
  159 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
  160 #define V_tcp_do_rfc3042        VNET(tcp_do_rfc3042)
  161 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_VNET | CTLFLAG_RW,
  162     &VNET_NAME(tcp_do_rfc3042), 0,
  163     "Enable RFC 3042 (Limited Transmit)");
  164 
  165 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
  166 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_VNET | CTLFLAG_RW,
  167     &VNET_NAME(tcp_do_rfc3390), 0,
  168     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
  169 
  170 VNET_DEFINE(int, tcp_initcwnd_segments) = 10;
  171 SYSCTL_INT(_net_inet_tcp, OID_AUTO, initcwnd_segments,
  172     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_initcwnd_segments), 0,
  173     "Slow-start flight size (initial congestion window) in number of segments");
  174 
  175 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
  176 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_VNET | CTLFLAG_RW,
  177     &VNET_NAME(tcp_do_rfc3465), 0,
  178     "Enable RFC 3465 (Appropriate Byte Counting)");
  179 
  180 VNET_DEFINE(int, tcp_abc_l_var) = 2;
  181 SYSCTL_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_VNET | CTLFLAG_RW,
  182     &VNET_NAME(tcp_abc_l_var), 2,
  183     "Cap the max cwnd increment during slow-start to this number of segments");
  184 
  185 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
  186 
  187 VNET_DEFINE(int, tcp_do_ecn) = 2;
  188 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
  189     &VNET_NAME(tcp_do_ecn), 0,
  190     "TCP ECN support");
  191 
  192 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
  193 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_VNET | CTLFLAG_RW,
  194     &VNET_NAME(tcp_ecn_maxretries), 0,
  195     "Max retries before giving up on ECN");
  196 
  197 VNET_DEFINE(int, tcp_insecure_syn) = 0;
  198 #define V_tcp_insecure_syn      VNET(tcp_insecure_syn)
  199 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
  200     &VNET_NAME(tcp_insecure_syn), 0,
  201     "Follow RFC793 instead of RFC5961 criteria for accepting SYN packets");
  202 
  203 VNET_DEFINE(int, tcp_insecure_rst) = 0;
  204 #define V_tcp_insecure_rst      VNET(tcp_insecure_rst)
  205 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_VNET | CTLFLAG_RW,
  206     &VNET_NAME(tcp_insecure_rst), 0,
  207     "Follow RFC793 instead of RFC5961 criteria for accepting RST packets");
  208 
  209 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
  210 #define V_tcp_recvspace VNET(tcp_recvspace)
  211 SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_VNET | CTLFLAG_RW,
  212     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
  213 
  214 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
  215 #define V_tcp_do_autorcvbuf     VNET(tcp_do_autorcvbuf)
  216 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
  217     &VNET_NAME(tcp_do_autorcvbuf), 0,
  218     "Enable automatic receive buffer sizing");
  219 
  220 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
  221 #define V_tcp_autorcvbuf_inc    VNET(tcp_autorcvbuf_inc)
  222 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
  223     &VNET_NAME(tcp_autorcvbuf_inc), 0,
  224     "Incrementor step size of automatic receive buffer");
  225 
  226 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
  227 #define V_tcp_autorcvbuf_max    VNET(tcp_autorcvbuf_max)
  228 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
  229     &VNET_NAME(tcp_autorcvbuf_max), 0,
  230     "Max size of automatic receive buffer");
  231 
  232 VNET_DEFINE(struct inpcbhead, tcb);
  233 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
  234 VNET_DEFINE(struct inpcbinfo, tcbinfo);
  235 
  236 /*
  237  * TCP statistics are stored in an array of counter(9)s, which size matches
  238  * size of struct tcpstat.  TCP running connection count is a regular array.
  239  */
  240 VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
  241 SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
  242     tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
  243 VNET_DEFINE(counter_u64_t, tcps_states[TCP_NSTATES]);
  244 SYSCTL_COUNTER_U64_ARRAY(_net_inet_tcp, TCPCTL_STATES, states, CTLFLAG_RD |
  245     CTLFLAG_VNET, &VNET_NAME(tcps_states)[0], TCP_NSTATES,
  246     "TCP connection counts by TCP state");
  247 
  248 static void
  249 tcp_vnet_init(const void *unused)
  250 {
  251 
  252         COUNTER_ARRAY_ALLOC(V_tcps_states, TCP_NSTATES, M_WAITOK);
  253         VNET_PCPUSTAT_ALLOC(tcpstat, M_WAITOK);
  254 }
  255 VNET_SYSINIT(tcp_vnet_init, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
  256     tcp_vnet_init, NULL);
  257 
  258 #ifdef VIMAGE
  259 static void
  260 tcp_vnet_uninit(const void *unused)
  261 {
  262 
  263         COUNTER_ARRAY_FREE(V_tcps_states, TCP_NSTATES);
  264         VNET_PCPUSTAT_FREE(tcpstat);
  265 }
  266 VNET_SYSUNINIT(tcp_vnet_uninit, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
  267     tcp_vnet_uninit, NULL);
  268 #endif /* VIMAGE */
  269 
  270 /*
  271  * Kernel module interface for updating tcpstat.  The argument is an index
  272  * into tcpstat treated as an array.
  273  */
  274 void
  275 kmod_tcpstat_inc(int statnum)
  276 {
  277 
  278         counter_u64_add(VNET(tcpstat)[statnum], 1);
  279 }
  280 
  281 /*
  282  * Wrapper for the TCP established input helper hook.
  283  */
  284 void
  285 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
  286 {
  287         struct tcp_hhook_data hhook_data;
  288 
  289         if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
  290                 hhook_data.tp = tp;
  291                 hhook_data.th = th;
  292                 hhook_data.to = to;
  293 
  294                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
  295                     tp->osd);
  296         }
  297 }
  298 
  299 /*
  300  * CC wrapper hook functions
  301  */
  302 void
  303 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type)
  304 {
  305         INP_WLOCK_ASSERT(tp->t_inpcb);
  306 
  307         tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
  308         if (tp->snd_cwnd <= tp->snd_wnd)
  309                 tp->ccv->flags |= CCF_CWND_LIMITED;
  310         else
  311                 tp->ccv->flags &= ~CCF_CWND_LIMITED;
  312 
  313         if (type == CC_ACK) {
  314                 if (tp->snd_cwnd > tp->snd_ssthresh) {
  315                         tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
  316                              V_tcp_abc_l_var * tcp_maxseg(tp));
  317                         if (tp->t_bytes_acked >= tp->snd_cwnd) {
  318                                 tp->t_bytes_acked -= tp->snd_cwnd;
  319                                 tp->ccv->flags |= CCF_ABC_SENTAWND;
  320                         }
  321                 } else {
  322                                 tp->ccv->flags &= ~CCF_ABC_SENTAWND;
  323                                 tp->t_bytes_acked = 0;
  324                 }
  325         }
  326 
  327         if (CC_ALGO(tp)->ack_received != NULL) {
  328                 /* XXXLAS: Find a way to live without this */
  329                 tp->ccv->curack = th->th_ack;
  330                 CC_ALGO(tp)->ack_received(tp->ccv, type);
  331         }
  332 }
  333 
  334 void 
  335 cc_conn_init(struct tcpcb *tp)
  336 {
  337         struct hc_metrics_lite metrics;
  338         struct inpcb *inp = tp->t_inpcb;
  339         u_int maxseg;
  340         int rtt;
  341 
  342         INP_WLOCK_ASSERT(tp->t_inpcb);
  343 
  344         tcp_hc_get(&inp->inp_inc, &metrics);
  345         maxseg = tcp_maxseg(tp);
  346 
  347         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
  348                 tp->t_srtt = rtt;
  349                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
  350                 TCPSTAT_INC(tcps_usedrtt);
  351                 if (metrics.rmx_rttvar) {
  352                         tp->t_rttvar = metrics.rmx_rttvar;
  353                         TCPSTAT_INC(tcps_usedrttvar);
  354                 } else {
  355                         /* default variation is +- 1 rtt */
  356                         tp->t_rttvar =
  357                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
  358                 }
  359                 TCPT_RANGESET(tp->t_rxtcur,
  360                     ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
  361                     tp->t_rttmin, TCPTV_REXMTMAX);
  362         }
  363         if (metrics.rmx_ssthresh) {
  364                 /*
  365                  * There's some sort of gateway or interface
  366                  * buffer limit on the path.  Use this to set
  367                  * the slow start threshold, but set the
  368                  * threshold to no less than 2*mss.
  369                  */
  370                 tp->snd_ssthresh = max(2 * maxseg, metrics.rmx_ssthresh);
  371                 TCPSTAT_INC(tcps_usedssthresh);
  372         }
  373 
  374         /*
  375          * Set the initial slow-start flight size.
  376          *
  377          * RFC5681 Section 3.1 specifies the default conservative values.
  378          * RFC3390 specifies slightly more aggressive values.
  379          * RFC6928 increases it to ten segments.
  380          * Support for user specified value for initial flight size.
  381          *
  382          * If a SYN or SYN/ACK was lost and retransmitted, we have to
  383          * reduce the initial CWND to one segment as congestion is likely
  384          * requiring us to be cautious.
  385          */
  386         if (tp->snd_cwnd == 1)
  387                 tp->snd_cwnd = maxseg;          /* SYN(-ACK) lost */
  388         else if (V_tcp_initcwnd_segments)
  389                 tp->snd_cwnd = min(V_tcp_initcwnd_segments * maxseg,
  390                     max(2 * maxseg, V_tcp_initcwnd_segments * 1460));
  391         else if (V_tcp_do_rfc3390)
  392                 tp->snd_cwnd = min(4 * maxseg, max(2 * maxseg, 4380));
  393         else {
  394                 /* Per RFC5681 Section 3.1 */
  395                 if (maxseg > 2190)
  396                         tp->snd_cwnd = 2 * maxseg;
  397                 else if (maxseg > 1095)
  398                         tp->snd_cwnd = 3 * maxseg;
  399                 else
  400                         tp->snd_cwnd = 4 * maxseg;
  401         }
  402 
  403         if (CC_ALGO(tp)->conn_init != NULL)
  404                 CC_ALGO(tp)->conn_init(tp->ccv);
  405 }
  406 
  407 void inline
  408 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
  409 {
  410         u_int maxseg;
  411 
  412         INP_WLOCK_ASSERT(tp->t_inpcb);
  413 
  414         switch(type) {
  415         case CC_NDUPACK:
  416                 if (!IN_FASTRECOVERY(tp->t_flags)) {
  417                         tp->snd_recover = tp->snd_max;
  418                         if (tp->t_flags & TF_ECN_PERMIT)
  419                                 tp->t_flags |= TF_ECN_SND_CWR;
  420                 }
  421                 break;
  422         case CC_ECN:
  423                 if (!IN_CONGRECOVERY(tp->t_flags)) {
  424                         TCPSTAT_INC(tcps_ecn_rcwnd);
  425                         tp->snd_recover = tp->snd_max;
  426                         if (tp->t_flags & TF_ECN_PERMIT)
  427                                 tp->t_flags |= TF_ECN_SND_CWR;
  428                 }
  429                 break;
  430         case CC_RTO:
  431                 maxseg = tcp_maxseg(tp);
  432                 tp->t_dupacks = 0;
  433                 tp->t_bytes_acked = 0;
  434                 EXIT_RECOVERY(tp->t_flags);
  435                 tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
  436                     maxseg) * maxseg;
  437                 tp->snd_cwnd = maxseg;
  438                 break;
  439         case CC_RTO_ERR:
  440                 TCPSTAT_INC(tcps_sndrexmitbad);
  441                 /* RTO was unnecessary, so reset everything. */
  442                 tp->snd_cwnd = tp->snd_cwnd_prev;
  443                 tp->snd_ssthresh = tp->snd_ssthresh_prev;
  444                 tp->snd_recover = tp->snd_recover_prev;
  445                 if (tp->t_flags & TF_WASFRECOVERY)
  446                         ENTER_FASTRECOVERY(tp->t_flags);
  447                 if (tp->t_flags & TF_WASCRECOVERY)
  448                         ENTER_CONGRECOVERY(tp->t_flags);
  449                 tp->snd_nxt = tp->snd_max;
  450                 tp->t_flags &= ~TF_PREVVALID;
  451                 tp->t_badrxtwin = 0;
  452                 break;
  453         }
  454 
  455         if (CC_ALGO(tp)->cong_signal != NULL) {
  456                 if (th != NULL)
  457                         tp->ccv->curack = th->th_ack;
  458                 CC_ALGO(tp)->cong_signal(tp->ccv, type);
  459         }
  460 }
  461 
  462 void inline
  463 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
  464 {
  465         INP_WLOCK_ASSERT(tp->t_inpcb);
  466 
  467         /* XXXLAS: KASSERT that we're in recovery? */
  468 
  469         if (CC_ALGO(tp)->post_recovery != NULL) {
  470                 tp->ccv->curack = th->th_ack;
  471                 CC_ALGO(tp)->post_recovery(tp->ccv);
  472         }
  473         /* XXXLAS: EXIT_RECOVERY ? */
  474         tp->t_bytes_acked = 0;
  475 }
  476 
  477 #ifdef TCP_SIGNATURE
  478 static inline int
  479 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
  480     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
  481 {
  482         int ret;
  483 
  484         tcp_fields_to_net(th);
  485         ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
  486         tcp_fields_to_host(th);
  487         return (ret);
  488 }
  489 #endif
  490 
  491 /*
  492  * Indicate whether this ack should be delayed.  We can delay the ack if
  493  * following conditions are met:
  494  *      - There is no delayed ack timer in progress.
  495  *      - Our last ack wasn't a 0-sized window. We never want to delay
  496  *        the ack that opens up a 0-sized window.
  497  *      - LRO wasn't used for this segment. We make sure by checking that the
  498  *        segment size is not larger than the MSS.
  499  */
  500 #define DELAY_ACK(tp, tlen)                                             \
  501         ((!tcp_timer_active(tp, TT_DELACK) &&                           \
  502             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
  503             (tlen <= tp->t_maxseg) &&                                   \
  504             (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
  505 
  506 static void inline
  507 cc_ecnpkt_handler(struct tcpcb *tp, struct tcphdr *th, uint8_t iptos)
  508 {
  509         INP_WLOCK_ASSERT(tp->t_inpcb);
  510 
  511         if (CC_ALGO(tp)->ecnpkt_handler != NULL) {
  512                 switch (iptos & IPTOS_ECN_MASK) {
  513                 case IPTOS_ECN_CE:
  514                     tp->ccv->flags |= CCF_IPHDR_CE;
  515                     break;
  516                 case IPTOS_ECN_ECT0:
  517                     tp->ccv->flags &= ~CCF_IPHDR_CE;
  518                     break;
  519                 case IPTOS_ECN_ECT1:
  520                     tp->ccv->flags &= ~CCF_IPHDR_CE;
  521                     break;
  522                 }
  523 
  524                 if (th->th_flags & TH_CWR)
  525                         tp->ccv->flags |= CCF_TCPHDR_CWR;
  526                 else
  527                         tp->ccv->flags &= ~CCF_TCPHDR_CWR;
  528 
  529                 if (tp->t_flags & TF_DELACK)
  530                         tp->ccv->flags |= CCF_DELACK;
  531                 else
  532                         tp->ccv->flags &= ~CCF_DELACK;
  533 
  534                 CC_ALGO(tp)->ecnpkt_handler(tp->ccv);
  535 
  536                 if (tp->ccv->flags & CCF_ACKNOW)
  537                         tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
  538         }
  539 }
  540 
  541 /*
  542  * TCP input handling is split into multiple parts:
  543  *   tcp6_input is a thin wrapper around tcp_input for the extended
  544  *      ip6_protox[] call format in ip6_input
  545  *   tcp_input handles primary segment validation, inpcb lookup and
  546  *      SYN processing on listen sockets
  547  *   tcp_do_segment processes the ACK and text of the segment for
  548  *      establishing, established and closing connections
  549  */
  550 #ifdef INET6
  551 int
  552 tcp6_input(struct mbuf **mp, int *offp, int proto)
  553 {
  554         struct mbuf *m = *mp;
  555         struct in6_ifaddr *ia6;
  556         struct ip6_hdr *ip6;
  557 
  558         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
  559 
  560         /*
  561          * draft-itojun-ipv6-tcp-to-anycast
  562          * better place to put this in?
  563          */
  564         ip6 = mtod(m, struct ip6_hdr *);
  565         ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */);
  566         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
  567                 struct ip6_hdr *ip6;
  568 
  569                 ifa_free(&ia6->ia_ifa);
  570                 ip6 = mtod(m, struct ip6_hdr *);
  571                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
  572                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
  573                 return (IPPROTO_DONE);
  574         }
  575         if (ia6)
  576                 ifa_free(&ia6->ia_ifa);
  577 
  578         return (tcp_input(mp, offp, proto));
  579 }
  580 #endif /* INET6 */
  581 
  582 int
  583 tcp_input(struct mbuf **mp, int *offp, int proto)
  584 {
  585         struct mbuf *m = *mp;
  586         struct tcphdr *th = NULL;
  587         struct ip *ip = NULL;
  588         struct inpcb *inp = NULL;
  589         struct tcpcb *tp = NULL;
  590         struct socket *so = NULL;
  591         u_char *optp = NULL;
  592         int off0;
  593         int optlen = 0;
  594 #ifdef INET
  595         int len;
  596 #endif
  597         int tlen = 0, off;
  598         int drop_hdrlen;
  599         int thflags;
  600         int rstreason = 0;      /* For badport_bandlim accounting purposes */
  601 #ifdef TCP_SIGNATURE
  602         uint8_t sig_checked = 0;
  603 #endif
  604         uint8_t iptos = 0;
  605         struct m_tag *fwd_tag = NULL;
  606 #ifdef INET6
  607         struct ip6_hdr *ip6 = NULL;
  608         int isipv6;
  609 #else
  610         const void *ip6 = NULL;
  611 #endif /* INET6 */
  612         struct tcpopt to;               /* options in this segment */
  613         char *s = NULL;                 /* address and port logging */
  614         int ti_locked;
  615 #ifdef TCPDEBUG
  616         /*
  617          * The size of tcp_saveipgen must be the size of the max ip header,
  618          * now IPv6.
  619          */
  620         u_char tcp_saveipgen[IP6_HDR_LEN];
  621         struct tcphdr tcp_savetcp;
  622         short ostate = 0;
  623 #endif
  624 
  625 #ifdef INET6
  626         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
  627 #endif
  628 
  629         off0 = *offp;
  630         m = *mp;
  631         *mp = NULL;
  632         to.to_flags = 0;
  633         TCPSTAT_INC(tcps_rcvtotal);
  634 
  635 #ifdef INET6
  636         if (isipv6) {
  637                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
  638 
  639                 if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
  640                         m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
  641                         if (m == NULL) {
  642                                 TCPSTAT_INC(tcps_rcvshort);
  643                                 return (IPPROTO_DONE);
  644                         }
  645                 }
  646 
  647                 ip6 = mtod(m, struct ip6_hdr *);
  648                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
  649                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
  650                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
  651                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  652                                 th->th_sum = m->m_pkthdr.csum_data;
  653                         else
  654                                 th->th_sum = in6_cksum_pseudo(ip6, tlen,
  655                                     IPPROTO_TCP, m->m_pkthdr.csum_data);
  656                         th->th_sum ^= 0xffff;
  657                 } else
  658                         th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
  659                 if (th->th_sum) {
  660                         TCPSTAT_INC(tcps_rcvbadsum);
  661                         goto drop;
  662                 }
  663 
  664                 /*
  665                  * Be proactive about unspecified IPv6 address in source.
  666                  * As we use all-zero to indicate unbounded/unconnected pcb,
  667                  * unspecified IPv6 address can be used to confuse us.
  668                  *
  669                  * Note that packets with unspecified IPv6 destination is
  670                  * already dropped in ip6_input.
  671                  */
  672                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
  673                         /* XXX stat */
  674                         goto drop;
  675                 }
  676         }
  677 #endif
  678 #if defined(INET) && defined(INET6)
  679         else
  680 #endif
  681 #ifdef INET
  682         {
  683                 /*
  684                  * Get IP and TCP header together in first mbuf.
  685                  * Note: IP leaves IP header in first mbuf.
  686                  */
  687                 if (off0 > sizeof (struct ip)) {
  688                         ip_stripoptions(m);
  689                         off0 = sizeof(struct ip);
  690                 }
  691                 if (m->m_len < sizeof (struct tcpiphdr)) {
  692                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
  693                             == NULL) {
  694                                 TCPSTAT_INC(tcps_rcvshort);
  695                                 return (IPPROTO_DONE);
  696                         }
  697                 }
  698                 ip = mtod(m, struct ip *);
  699                 th = (struct tcphdr *)((caddr_t)ip + off0);
  700                 tlen = ntohs(ip->ip_len) - off0;
  701 
  702                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
  703                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  704                                 th->th_sum = m->m_pkthdr.csum_data;
  705                         else
  706                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
  707                                     ip->ip_dst.s_addr,
  708                                     htonl(m->m_pkthdr.csum_data + tlen +
  709                                     IPPROTO_TCP));
  710                         th->th_sum ^= 0xffff;
  711                 } else {
  712                         struct ipovly *ipov = (struct ipovly *)ip;
  713 
  714                         /*
  715                          * Checksum extended TCP header and data.
  716                          */
  717                         len = off0 + tlen;
  718                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
  719                         ipov->ih_len = htons(tlen);
  720                         th->th_sum = in_cksum(m, len);
  721                         /* Reset length for SDT probes. */
  722                         ip->ip_len = htons(tlen + off0);
  723                 }
  724 
  725                 if (th->th_sum) {
  726                         TCPSTAT_INC(tcps_rcvbadsum);
  727                         goto drop;
  728                 }
  729                 /* Re-initialization for later version check */
  730                 ip->ip_v = IPVERSION;
  731         }
  732 #endif /* INET */
  733 
  734 #ifdef INET6
  735         if (isipv6)
  736                 iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
  737 #endif
  738 #if defined(INET) && defined(INET6)
  739         else
  740 #endif
  741 #ifdef INET
  742                 iptos = ip->ip_tos;
  743 #endif
  744 
  745         /*
  746          * Check that TCP offset makes sense,
  747          * pull out TCP options and adjust length.              XXX
  748          */
  749         off = th->th_off << 2;
  750         if (off < sizeof (struct tcphdr) || off > tlen) {
  751                 TCPSTAT_INC(tcps_rcvbadoff);
  752                 goto drop;
  753         }
  754         tlen -= off;    /* tlen is used instead of ti->ti_len */
  755         if (off > sizeof (struct tcphdr)) {
  756 #ifdef INET6
  757                 if (isipv6) {
  758                         IP6_EXTHDR_CHECK(m, off0, off, IPPROTO_DONE);
  759                         ip6 = mtod(m, struct ip6_hdr *);
  760                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
  761                 }
  762 #endif
  763 #if defined(INET) && defined(INET6)
  764                 else
  765 #endif
  766 #ifdef INET
  767                 {
  768                         if (m->m_len < sizeof(struct ip) + off) {
  769                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
  770                                     == NULL) {
  771                                         TCPSTAT_INC(tcps_rcvshort);
  772                                         return (IPPROTO_DONE);
  773                                 }
  774                                 ip = mtod(m, struct ip *);
  775                                 th = (struct tcphdr *)((caddr_t)ip + off0);
  776                         }
  777                 }
  778 #endif
  779                 optlen = off - sizeof (struct tcphdr);
  780                 optp = (u_char *)(th + 1);
  781         }
  782         thflags = th->th_flags;
  783 
  784         /*
  785          * Convert TCP protocol specific fields to host format.
  786          */
  787         tcp_fields_to_host(th);
  788 
  789         /*
  790          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
  791          */
  792         drop_hdrlen = off0 + off;
  793 
  794         /*
  795          * Locate pcb for segment; if we're likely to add or remove a
  796          * connection then first acquire pcbinfo lock.  There are three cases
  797          * where we might discover later we need a write lock despite the
  798          * flags: ACKs moving a connection out of the syncache, ACKs for a
  799          * connection in TIMEWAIT and SYNs not targeting a listening socket.
  800          */
  801         if ((thflags & (TH_FIN | TH_RST)) != 0) {
  802                 INP_INFO_RLOCK(&V_tcbinfo);
  803                 ti_locked = TI_RLOCKED;
  804         } else
  805                 ti_locked = TI_UNLOCKED;
  806 
  807         /*
  808          * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
  809          */
  810         if (
  811 #ifdef INET6
  812             (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
  813 #ifdef INET
  814             || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
  815 #endif
  816 #endif
  817 #if defined(INET) && !defined(INET6)
  818             (m->m_flags & M_IP_NEXTHOP)
  819 #endif
  820             )
  821                 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
  822 
  823 findpcb:
  824 #ifdef INVARIANTS
  825         if (ti_locked == TI_RLOCKED) {
  826                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  827         } else {
  828                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
  829         }
  830 #endif
  831 #ifdef INET6
  832         if (isipv6 && fwd_tag != NULL) {
  833                 struct sockaddr_in6 *next_hop6;
  834 
  835                 next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
  836                 /*
  837                  * Transparently forwarded. Pretend to be the destination.
  838                  * Already got one like this?
  839                  */
  840                 inp = in6_pcblookup_mbuf(&V_tcbinfo,
  841                     &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
  842                     INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
  843                 if (!inp) {
  844                         /*
  845                          * It's new.  Try to find the ambushing socket.
  846                          * Because we've rewritten the destination address,
  847                          * any hardware-generated hash is ignored.
  848                          */
  849                         inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
  850                             th->th_sport, &next_hop6->sin6_addr,
  851                             next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
  852                             th->th_dport, INPLOOKUP_WILDCARD |
  853                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  854                 }
  855         } else if (isipv6) {
  856                 inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
  857                     th->th_sport, &ip6->ip6_dst, th->th_dport,
  858                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  859                     m->m_pkthdr.rcvif, m);
  860         }
  861 #endif /* INET6 */
  862 #if defined(INET6) && defined(INET)
  863         else
  864 #endif
  865 #ifdef INET
  866         if (fwd_tag != NULL) {
  867                 struct sockaddr_in *next_hop;
  868 
  869                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
  870                 /*
  871                  * Transparently forwarded. Pretend to be the destination.
  872                  * already got one like this?
  873                  */
  874                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
  875                     ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
  876                     m->m_pkthdr.rcvif, m);
  877                 if (!inp) {
  878                         /*
  879                          * It's new.  Try to find the ambushing socket.
  880                          * Because we've rewritten the destination address,
  881                          * any hardware-generated hash is ignored.
  882                          */
  883                         inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
  884                             th->th_sport, next_hop->sin_addr,
  885                             next_hop->sin_port ? ntohs(next_hop->sin_port) :
  886                             th->th_dport, INPLOOKUP_WILDCARD |
  887                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  888                 }
  889         } else
  890                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
  891                     th->th_sport, ip->ip_dst, th->th_dport,
  892                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  893                     m->m_pkthdr.rcvif, m);
  894 #endif /* INET */
  895 
  896         /*
  897          * If the INPCB does not exist then all data in the incoming
  898          * segment is discarded and an appropriate RST is sent back.
  899          * XXX MRT Send RST using which routing table?
  900          */
  901         if (inp == NULL) {
  902                 /*
  903                  * Log communication attempts to ports that are not
  904                  * in use.
  905                  */
  906                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
  907                     tcp_log_in_vain == 2) {
  908                         if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
  909                                 log(LOG_INFO, "%s; %s: Connection attempt "
  910                                     "to closed port\n", s, __func__);
  911                 }
  912                 /*
  913                  * When blackholing do not respond with a RST but
  914                  * completely ignore the segment and drop it.
  915                  */
  916                 if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
  917                     V_blackhole == 2)
  918                         goto dropunlock;
  919 
  920                 rstreason = BANDLIM_RST_CLOSEDPORT;
  921                 goto dropwithreset;
  922         }
  923         INP_WLOCK_ASSERT(inp);
  924         if ((inp->inp_flowtype == M_HASHTYPE_NONE) &&
  925             (M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) &&
  926             ((inp->inp_socket == NULL) ||
  927             (inp->inp_socket->so_options & SO_ACCEPTCONN) == 0)) {
  928                 inp->inp_flowid = m->m_pkthdr.flowid;
  929                 inp->inp_flowtype = M_HASHTYPE_GET(m);
  930         }
  931 #ifdef IPSEC
  932 #ifdef INET6
  933         if (isipv6 && ipsec6_in_reject(m, inp)) {
  934                 goto dropunlock;
  935         } else
  936 #endif /* INET6 */
  937         if (ipsec4_in_reject(m, inp) != 0) {
  938                 goto dropunlock;
  939         }
  940 #endif /* IPSEC */
  941 
  942         /*
  943          * Check the minimum TTL for socket.
  944          */
  945         if (inp->inp_ip_minttl != 0) {
  946 #ifdef INET6
  947                 if (isipv6) {
  948                         if (inp->inp_ip_minttl > ip6->ip6_hlim)
  949                                 goto dropunlock;
  950                 } else
  951 #endif
  952                 if (inp->inp_ip_minttl > ip->ip_ttl)
  953                         goto dropunlock;
  954         }
  955 
  956         /*
  957          * A previous connection in TIMEWAIT state is supposed to catch stray
  958          * or duplicate segments arriving late.  If this segment was a
  959          * legitimate new connection attempt, the old INPCB gets removed and
  960          * we can try again to find a listening socket.
  961          *
  962          * At this point, due to earlier optimism, we may hold only an inpcb
  963          * lock, and not the inpcbinfo write lock.  If so, we need to try to
  964          * acquire it, or if that fails, acquire a reference on the inpcb,
  965          * drop all locks, acquire a global write lock, and then re-acquire
  966          * the inpcb lock.  We may at that point discover that another thread
  967          * has tried to free the inpcb, in which case we need to loop back
  968          * and try to find a new inpcb to deliver to.
  969          *
  970          * XXXRW: It may be time to rethink timewait locking.
  971          */
  972 relocked:
  973         if (inp->inp_flags & INP_TIMEWAIT) {
  974                 if (ti_locked == TI_UNLOCKED) {
  975                         if (INP_INFO_TRY_RLOCK(&V_tcbinfo) == 0) {
  976                                 in_pcbref(inp);
  977                                 INP_WUNLOCK(inp);
  978                                 INP_INFO_RLOCK(&V_tcbinfo);
  979                                 ti_locked = TI_RLOCKED;
  980                                 INP_WLOCK(inp);
  981                                 if (in_pcbrele_wlocked(inp)) {
  982                                         inp = NULL;
  983                                         goto findpcb;
  984                                 }
  985                         } else
  986                                 ti_locked = TI_RLOCKED;
  987                 }
  988                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  989 
  990                 if (thflags & TH_SYN)
  991                         tcp_dooptions(&to, optp, optlen, TO_SYN);
  992                 /*
  993                  * NB: tcp_twcheck unlocks the INP and frees the mbuf.
  994                  */
  995                 if (tcp_twcheck(inp, &to, th, m, tlen))
  996                         goto findpcb;
  997                 INP_INFO_RUNLOCK(&V_tcbinfo);
  998                 return (IPPROTO_DONE);
  999         }
 1000         /*
 1001          * The TCPCB may no longer exist if the connection is winding
 1002          * down or it is in the CLOSED state.  Either way we drop the
 1003          * segment and send an appropriate response.
 1004          */
 1005         tp = intotcpcb(inp);
 1006         if (tp == NULL || tp->t_state == TCPS_CLOSED) {
 1007                 rstreason = BANDLIM_RST_CLOSEDPORT;
 1008                 goto dropwithreset;
 1009         }
 1010 
 1011 #ifdef TCP_OFFLOAD
 1012         if (tp->t_flags & TF_TOE) {
 1013                 tcp_offload_input(tp, m);
 1014                 m = NULL;       /* consumed by the TOE driver */
 1015                 goto dropunlock;
 1016         }
 1017 #endif
 1018 
 1019         /*
 1020          * We've identified a valid inpcb, but it could be that we need an
 1021          * inpcbinfo write lock but don't hold it.  In this case, attempt to
 1022          * acquire using the same strategy as the TIMEWAIT case above.  If we
 1023          * relock, we have to jump back to 'relocked' as the connection might
 1024          * now be in TIMEWAIT.
 1025          */
 1026 #ifdef INVARIANTS
 1027         if ((thflags & (TH_FIN | TH_RST)) != 0)
 1028                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1029 #endif
 1030         if (!((tp->t_state == TCPS_ESTABLISHED && (thflags & TH_SYN) == 0) ||
 1031               (tp->t_state == TCPS_LISTEN && (thflags & TH_SYN) &&
 1032                !(tp->t_flags & TF_FASTOPEN)))) {
 1033                 if (ti_locked == TI_UNLOCKED) {
 1034                         if (INP_INFO_TRY_RLOCK(&V_tcbinfo) == 0) {
 1035                                 in_pcbref(inp);
 1036                                 INP_WUNLOCK(inp);
 1037                                 INP_INFO_RLOCK(&V_tcbinfo);
 1038                                 ti_locked = TI_RLOCKED;
 1039                                 INP_WLOCK(inp);
 1040                                 if (in_pcbrele_wlocked(inp)) {
 1041                                         inp = NULL;
 1042                                         goto findpcb;
 1043                                 }
 1044                                 goto relocked;
 1045                         } else
 1046                                 ti_locked = TI_RLOCKED;
 1047                 }
 1048                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1049         }
 1050 
 1051 #ifdef MAC
 1052         INP_WLOCK_ASSERT(inp);
 1053         if (mac_inpcb_check_deliver(inp, m))
 1054                 goto dropunlock;
 1055 #endif
 1056         so = inp->inp_socket;
 1057         KASSERT(so != NULL, ("%s: so == NULL", __func__));
 1058 #ifdef TCPDEBUG
 1059         if (so->so_options & SO_DEBUG) {
 1060                 ostate = tp->t_state;
 1061 #ifdef INET6
 1062                 if (isipv6) {
 1063                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 1064                 } else
 1065 #endif
 1066                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 1067                 tcp_savetcp = *th;
 1068         }
 1069 #endif /* TCPDEBUG */
 1070         /*
 1071          * When the socket is accepting connections (the INPCB is in LISTEN
 1072          * state) we look into the SYN cache if this is a new connection
 1073          * attempt or the completion of a previous one.
 1074          */
 1075         if (so->so_options & SO_ACCEPTCONN) {
 1076                 struct in_conninfo inc;
 1077 
 1078                 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
 1079                     "tp not listening", __func__));
 1080                 bzero(&inc, sizeof(inc));
 1081 #ifdef INET6
 1082                 if (isipv6) {
 1083                         inc.inc_flags |= INC_ISIPV6;
 1084                         inc.inc6_faddr = ip6->ip6_src;
 1085                         inc.inc6_laddr = ip6->ip6_dst;
 1086                 } else
 1087 #endif
 1088                 {
 1089                         inc.inc_faddr = ip->ip_src;
 1090                         inc.inc_laddr = ip->ip_dst;
 1091                 }
 1092                 inc.inc_fport = th->th_sport;
 1093                 inc.inc_lport = th->th_dport;
 1094                 inc.inc_fibnum = so->so_fibnum;
 1095 
 1096                 /*
 1097                  * Check for an existing connection attempt in syncache if
 1098                  * the flag is only ACK.  A successful lookup creates a new
 1099                  * socket appended to the listen queue in SYN_RECEIVED state.
 1100                  */
 1101                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 1102 
 1103                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1104                         /*
 1105                          * Parse the TCP options here because
 1106                          * syncookies need access to the reflected
 1107                          * timestamp.
 1108                          */
 1109                         tcp_dooptions(&to, optp, optlen, 0);
 1110                         /*
 1111                          * NB: syncache_expand() doesn't unlock
 1112                          * inp and tcpinfo locks.
 1113                          */
 1114                         if (!syncache_expand(&inc, &to, th, &so, m)) {
 1115                                 /*
 1116                                  * No syncache entry or ACK was not
 1117                                  * for our SYN/ACK.  Send a RST.
 1118                                  * NB: syncache did its own logging
 1119                                  * of the failure cause.
 1120                                  */
 1121                                 rstreason = BANDLIM_RST_OPENPORT;
 1122                                 goto dropwithreset;
 1123                         }
 1124 #ifdef TCP_RFC7413
 1125 new_tfo_socket:
 1126 #endif
 1127                         if (so == NULL) {
 1128                                 /*
 1129                                  * We completed the 3-way handshake
 1130                                  * but could not allocate a socket
 1131                                  * either due to memory shortage,
 1132                                  * listen queue length limits or
 1133                                  * global socket limits.  Send RST
 1134                                  * or wait and have the remote end
 1135                                  * retransmit the ACK for another
 1136                                  * try.
 1137                                  */
 1138                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1139                                         log(LOG_DEBUG, "%s; %s: Listen socket: "
 1140                                             "Socket allocation failed due to "
 1141                                             "limits or memory shortage, %s\n",
 1142                                             s, __func__,
 1143                                             V_tcp_sc_rst_sock_fail ?
 1144                                             "sending RST" : "try again");
 1145                                 if (V_tcp_sc_rst_sock_fail) {
 1146                                         rstreason = BANDLIM_UNLIMITED;
 1147                                         goto dropwithreset;
 1148                                 } else
 1149                                         goto dropunlock;
 1150                         }
 1151                         /*
 1152                          * Socket is created in state SYN_RECEIVED.
 1153                          * Unlock the listen socket, lock the newly
 1154                          * created socket and update the tp variable.
 1155                          */
 1156                         INP_WUNLOCK(inp);       /* listen socket */
 1157                         inp = sotoinpcb(so);
 1158                         /*
 1159                          * New connection inpcb is already locked by
 1160                          * syncache_expand().
 1161                          */
 1162                         INP_WLOCK_ASSERT(inp);
 1163                         tp = intotcpcb(inp);
 1164                         KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
 1165                             ("%s: ", __func__));
 1166 #ifdef TCP_SIGNATURE
 1167                         if (sig_checked == 0)  {
 1168                                 tcp_dooptions(&to, optp, optlen,
 1169                                     (thflags & TH_SYN) ? TO_SYN : 0);
 1170                                 if (!tcp_signature_verify_input(m, off0, tlen,
 1171                                     optlen, &to, th, tp->t_flags)) {
 1172 
 1173                                         /*
 1174                                          * In SYN_SENT state if it receives an
 1175                                          * RST, it is allowed for further
 1176                                          * processing.
 1177                                          */
 1178                                         if ((thflags & TH_RST) == 0 ||
 1179                                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1180                                                 goto dropunlock;
 1181                                 }
 1182                                 sig_checked = 1;
 1183                         }
 1184 #endif
 1185 
 1186                         /*
 1187                          * Process the segment and the data it
 1188                          * contains.  tcp_do_segment() consumes
 1189                          * the mbuf chain and unlocks the inpcb.
 1190                          */
 1191                         tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
 1192                             iptos, ti_locked);
 1193                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1194                         return (IPPROTO_DONE);
 1195                 }
 1196                 /*
 1197                  * Segment flag validation for new connection attempts:
 1198                  *
 1199                  * Our (SYN|ACK) response was rejected.
 1200                  * Check with syncache and remove entry to prevent
 1201                  * retransmits.
 1202                  *
 1203                  * NB: syncache_chkrst does its own logging of failure
 1204                  * causes.
 1205                  */
 1206                 if (thflags & TH_RST) {
 1207                         syncache_chkrst(&inc, th);
 1208                         goto dropunlock;
 1209                 }
 1210                 /*
 1211                  * We can't do anything without SYN.
 1212                  */
 1213                 if ((thflags & TH_SYN) == 0) {
 1214                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1215                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1216                                     "SYN is missing, segment ignored\n",
 1217                                     s, __func__);
 1218                         TCPSTAT_INC(tcps_badsyn);
 1219                         goto dropunlock;
 1220                 }
 1221                 /*
 1222                  * (SYN|ACK) is bogus on a listen socket.
 1223                  */
 1224                 if (thflags & TH_ACK) {
 1225                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1226                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1227                                     "SYN|ACK invalid, segment rejected\n",
 1228                                     s, __func__);
 1229                         syncache_badack(&inc);  /* XXX: Not needed! */
 1230                         TCPSTAT_INC(tcps_badsyn);
 1231                         rstreason = BANDLIM_RST_OPENPORT;
 1232                         goto dropwithreset;
 1233                 }
 1234                 /*
 1235                  * If the drop_synfin option is enabled, drop all
 1236                  * segments with both the SYN and FIN bits set.
 1237                  * This prevents e.g. nmap from identifying the
 1238                  * TCP/IP stack.
 1239                  * XXX: Poor reasoning.  nmap has other methods
 1240                  * and is constantly refining its stack detection
 1241                  * strategies.
 1242                  * XXX: This is a violation of the TCP specification
 1243                  * and was used by RFC1644.
 1244                  */
 1245                 if ((thflags & TH_FIN) && V_drop_synfin) {
 1246                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1247                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1248                                     "SYN|FIN segment ignored (based on "
 1249                                     "sysctl setting)\n", s, __func__);
 1250                         TCPSTAT_INC(tcps_badsyn);
 1251                         goto dropunlock;
 1252                 }
 1253                 /*
 1254                  * Segment's flags are (SYN) or (SYN|FIN).
 1255                  *
 1256                  * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
 1257                  * as they do not affect the state of the TCP FSM.
 1258                  * The data pointed to by TH_URG and th_urp is ignored.
 1259                  */
 1260                 KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
 1261                     ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
 1262                 KASSERT(thflags & (TH_SYN),
 1263                     ("%s: Listen socket: TH_SYN not set", __func__));
 1264 #ifdef INET6
 1265                 /*
 1266                  * If deprecated address is forbidden,
 1267                  * we do not accept SYN to deprecated interface
 1268                  * address to prevent any new inbound connection from
 1269                  * getting established.
 1270                  * When we do not accept SYN, we send a TCP RST,
 1271                  * with deprecated source address (instead of dropping
 1272                  * it).  We compromise it as it is much better for peer
 1273                  * to send a RST, and RST will be the final packet
 1274                  * for the exchange.
 1275                  *
 1276                  * If we do not forbid deprecated addresses, we accept
 1277                  * the SYN packet.  RFC2462 does not suggest dropping
 1278                  * SYN in this case.
 1279                  * If we decipher RFC2462 5.5.4, it says like this:
 1280                  * 1. use of deprecated addr with existing
 1281                  *    communication is okay - "SHOULD continue to be
 1282                  *    used"
 1283                  * 2. use of it with new communication:
 1284                  *   (2a) "SHOULD NOT be used if alternate address
 1285                  *        with sufficient scope is available"
 1286                  *   (2b) nothing mentioned otherwise.
 1287                  * Here we fall into (2b) case as we have no choice in
 1288                  * our source address selection - we must obey the peer.
 1289                  *
 1290                  * The wording in RFC2462 is confusing, and there are
 1291                  * multiple description text for deprecated address
 1292                  * handling - worse, they are not exactly the same.
 1293                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 1294                  */
 1295                 if (isipv6 && !V_ip6_use_deprecated) {
 1296                         struct in6_ifaddr *ia6;
 1297 
 1298                         ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */);
 1299                         if (ia6 != NULL &&
 1300                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 1301                                 ifa_free(&ia6->ia_ifa);
 1302                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1303                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1304                                         "Connection attempt to deprecated "
 1305                                         "IPv6 address rejected\n",
 1306                                         s, __func__);
 1307                                 rstreason = BANDLIM_RST_OPENPORT;
 1308                                 goto dropwithreset;
 1309                         }
 1310                         if (ia6)
 1311                                 ifa_free(&ia6->ia_ifa);
 1312                 }
 1313 #endif /* INET6 */
 1314                 /*
 1315                  * Basic sanity checks on incoming SYN requests:
 1316                  *   Don't respond if the destination is a link layer
 1317                  *      broadcast according to RFC1122 4.2.3.10, p. 104.
 1318                  *   If it is from this socket it must be forged.
 1319                  *   Don't respond if the source or destination is a
 1320                  *      global or subnet broad- or multicast address.
 1321                  *   Note that it is quite possible to receive unicast
 1322                  *      link-layer packets with a broadcast IP address. Use
 1323                  *      in_broadcast() to find them.
 1324                  */
 1325                 if (m->m_flags & (M_BCAST|M_MCAST)) {
 1326                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1327                             log(LOG_DEBUG, "%s; %s: Listen socket: "
 1328                                 "Connection attempt from broad- or multicast "
 1329                                 "link layer address ignored\n", s, __func__);
 1330                         goto dropunlock;
 1331                 }
 1332 #ifdef INET6
 1333                 if (isipv6) {
 1334                         if (th->th_dport == th->th_sport &&
 1335                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
 1336                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1337                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1338                                         "Connection attempt to/from self "
 1339                                         "ignored\n", s, __func__);
 1340                                 goto dropunlock;
 1341                         }
 1342                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 1343                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
 1344                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1345                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1346                                         "Connection attempt from/to multicast "
 1347                                         "address ignored\n", s, __func__);
 1348                                 goto dropunlock;
 1349                         }
 1350                 }
 1351 #endif
 1352 #if defined(INET) && defined(INET6)
 1353                 else
 1354 #endif
 1355 #ifdef INET
 1356                 {
 1357                         if (th->th_dport == th->th_sport &&
 1358                             ip->ip_dst.s_addr == ip->ip_src.s_addr) {
 1359                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1360                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1361                                         "Connection attempt from/to self "
 1362                                         "ignored\n", s, __func__);
 1363                                 goto dropunlock;
 1364                         }
 1365                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 1366                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 1367                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 1368                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
 1369                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1370                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1371                                         "Connection attempt from/to broad- "
 1372                                         "or multicast address ignored\n",
 1373                                         s, __func__);
 1374                                 goto dropunlock;
 1375                         }
 1376                 }
 1377 #endif
 1378                 /*
 1379                  * SYN appears to be valid.  Create compressed TCP state
 1380                  * for syncache.
 1381                  */
 1382 #ifdef TCPDEBUG
 1383                 if (so->so_options & SO_DEBUG)
 1384                         tcp_trace(TA_INPUT, ostate, tp,
 1385                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1386 #endif
 1387                 TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
 1388                 tcp_dooptions(&to, optp, optlen, TO_SYN);
 1389 #ifdef TCP_RFC7413
 1390                 if (syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL))
 1391                         goto new_tfo_socket;
 1392 #else
 1393                 syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
 1394 #endif
 1395                 /*
 1396                  * Entry added to syncache and mbuf consumed.
 1397                  * Only the listen socket is unlocked by syncache_add().
 1398                  */
 1399                 if (ti_locked == TI_RLOCKED) {
 1400                         INP_INFO_RUNLOCK(&V_tcbinfo);
 1401                         ti_locked = TI_UNLOCKED;
 1402                 }
 1403                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1404                 return (IPPROTO_DONE);
 1405         } else if (tp->t_state == TCPS_LISTEN) {
 1406                 /*
 1407                  * When a listen socket is torn down the SO_ACCEPTCONN
 1408                  * flag is removed first while connections are drained
 1409                  * from the accept queue in a unlock/lock cycle of the
 1410                  * ACCEPT_LOCK, opening a race condition allowing a SYN
 1411                  * attempt go through unhandled.
 1412                  */
 1413                 goto dropunlock;
 1414         }
 1415 
 1416 #ifdef TCP_SIGNATURE
 1417         if (sig_checked == 0)  {
 1418                 tcp_dooptions(&to, optp, optlen,
 1419                     (thflags & TH_SYN) ? TO_SYN : 0);
 1420                 if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
 1421                     th, tp->t_flags)) {
 1422 
 1423                         /*
 1424                          * In SYN_SENT state if it receives an RST, it is
 1425                          * allowed for further processing.
 1426                          */
 1427                         if ((thflags & TH_RST) == 0 ||
 1428                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1429                                 goto dropunlock;
 1430                 }
 1431                 sig_checked = 1;
 1432         }
 1433 #endif
 1434 
 1435         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1436 
 1437         /*
 1438          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
 1439          * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
 1440          * the inpcb, and unlocks pcbinfo.
 1441          */
 1442         tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
 1443         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1444         return (IPPROTO_DONE);
 1445 
 1446 dropwithreset:
 1447         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1448 
 1449         if (ti_locked == TI_RLOCKED) {
 1450                 INP_INFO_RUNLOCK(&V_tcbinfo);
 1451                 ti_locked = TI_UNLOCKED;
 1452         }
 1453 #ifdef INVARIANTS
 1454         else {
 1455                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
 1456                     "ti_locked: %d", __func__, ti_locked));
 1457                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1458         }
 1459 #endif
 1460 
 1461         if (inp != NULL) {
 1462                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 1463                 INP_WUNLOCK(inp);
 1464         } else
 1465                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 1466         m = NULL;       /* mbuf chain got consumed. */
 1467         goto drop;
 1468 
 1469 dropunlock:
 1470         if (m != NULL)
 1471                 TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1472 
 1473         if (ti_locked == TI_RLOCKED) {
 1474                 INP_INFO_RUNLOCK(&V_tcbinfo);
 1475                 ti_locked = TI_UNLOCKED;
 1476         }
 1477 #ifdef INVARIANTS
 1478         else {
 1479                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
 1480                     "ti_locked: %d", __func__, ti_locked));
 1481                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1482         }
 1483 #endif
 1484 
 1485         if (inp != NULL)
 1486                 INP_WUNLOCK(inp);
 1487 
 1488 drop:
 1489         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1490         if (s != NULL)
 1491                 free(s, M_TCPLOG);
 1492         if (m != NULL)
 1493                 m_freem(m);
 1494         return (IPPROTO_DONE);
 1495 }
 1496 
 1497 void
 1498 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 1499     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
 1500     int ti_locked)
 1501 {
 1502         int thflags, acked, ourfinisacked, needoutput = 0, sack_changed;
 1503         int rstreason, todrop, win;
 1504         u_long tiwin;
 1505         char *s;
 1506         struct in_conninfo *inc;
 1507         struct mbuf *mfree;
 1508         struct tcpopt to;
 1509         int tfo_syn;
 1510         
 1511 #ifdef TCPDEBUG
 1512         /*
 1513          * The size of tcp_saveipgen must be the size of the max ip header,
 1514          * now IPv6.
 1515          */
 1516         u_char tcp_saveipgen[IP6_HDR_LEN];
 1517         struct tcphdr tcp_savetcp;
 1518         short ostate = 0;
 1519 #endif
 1520         thflags = th->th_flags;
 1521         inc = &tp->t_inpcb->inp_inc;
 1522         tp->sackhint.last_sack_ack = 0;
 1523         sack_changed = 0;
 1524 
 1525         /*
 1526          * If this is either a state-changing packet or current state isn't
 1527          * established, we require a write lock on tcbinfo.  Otherwise, we
 1528          * allow the tcbinfo to be in either alocked or unlocked, as the
 1529          * caller may have unnecessarily acquired a write lock due to a race.
 1530          */
 1531         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
 1532             tp->t_state != TCPS_ESTABLISHED) {
 1533                 KASSERT(ti_locked == TI_RLOCKED, ("%s ti_locked %d for "
 1534                     "SYN/FIN/RST/!EST", __func__, ti_locked));
 1535                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1536         } else {
 1537 #ifdef INVARIANTS
 1538                 if (ti_locked == TI_RLOCKED)
 1539                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1540                 else {
 1541                         KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
 1542                             "ti_locked: %d", __func__, ti_locked));
 1543                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1544                 }
 1545 #endif
 1546         }
 1547         INP_WLOCK_ASSERT(tp->t_inpcb);
 1548         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
 1549             __func__));
 1550         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
 1551             __func__));
 1552 
 1553 #ifdef TCPPCAP
 1554         /* Save segment, if requested. */
 1555         tcp_pcap_add(th, m, &(tp->t_inpkts));
 1556 #endif
 1557 
 1558         /*
 1559          * Segment received on connection.
 1560          * Reset idle time and keep-alive timer.
 1561          * XXX: This should be done after segment
 1562          * validation to ignore broken/spoofed segs.
 1563          */
 1564         tp->t_rcvtime = ticks;
 1565         if (TCPS_HAVEESTABLISHED(tp->t_state))
 1566                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 1567 
 1568         /*
 1569          * Scale up the window into a 32-bit value.
 1570          * For the SYN_SENT state the scale is zero.
 1571          */
 1572         tiwin = th->th_win << tp->snd_scale;
 1573 
 1574         /*
 1575          * TCP ECN processing.
 1576          */
 1577         if (tp->t_flags & TF_ECN_PERMIT) {
 1578                 if (thflags & TH_CWR)
 1579                         tp->t_flags &= ~TF_ECN_SND_ECE;
 1580                 switch (iptos & IPTOS_ECN_MASK) {
 1581                 case IPTOS_ECN_CE:
 1582                         tp->t_flags |= TF_ECN_SND_ECE;
 1583                         TCPSTAT_INC(tcps_ecn_ce);
 1584                         break;
 1585                 case IPTOS_ECN_ECT0:
 1586                         TCPSTAT_INC(tcps_ecn_ect0);
 1587                         break;
 1588                 case IPTOS_ECN_ECT1:
 1589                         TCPSTAT_INC(tcps_ecn_ect1);
 1590                         break;
 1591                 }
 1592 
 1593                 /* Process a packet differently from RFC3168. */
 1594                 cc_ecnpkt_handler(tp, th, iptos);
 1595 
 1596                 /* Congestion experienced. */
 1597                 if (thflags & TH_ECE) {
 1598                         cc_cong_signal(tp, th, CC_ECN);
 1599                 }
 1600         }
 1601 
 1602         /*
 1603          * Parse options on any incoming segment.
 1604          */
 1605         tcp_dooptions(&to, (u_char *)(th + 1),
 1606             (th->th_off << 2) - sizeof(struct tcphdr),
 1607             (thflags & TH_SYN) ? TO_SYN : 0);
 1608 
 1609         /*
 1610          * If echoed timestamp is later than the current time,
 1611          * fall back to non RFC1323 RTT calculation.  Normalize
 1612          * timestamp if syncookies were used when this connection
 1613          * was established.
 1614          */
 1615         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
 1616                 to.to_tsecr -= tp->ts_offset;
 1617                 if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
 1618                         to.to_tsecr = 0;
 1619         }
 1620         /*
 1621          * If timestamps were negotiated during SYN/ACK they should
 1622          * appear on every segment during this session and vice versa.
 1623          */
 1624         if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
 1625                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1626                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1627                             "no action\n", s, __func__);
 1628                         free(s, M_TCPLOG);
 1629                 }
 1630         }
 1631         if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
 1632                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1633                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1634                             "no action\n", s, __func__);
 1635                         free(s, M_TCPLOG);
 1636                 }
 1637         }
 1638 
 1639         /*
 1640          * Process options only when we get SYN/ACK back. The SYN case
 1641          * for incoming connections is handled in tcp_syncache.
 1642          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
 1643          * or <SYN,ACK>) segment itself is never scaled.
 1644          * XXX this is traditional behavior, may need to be cleaned up.
 1645          */
 1646         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
 1647                 if ((to.to_flags & TOF_SCALE) &&
 1648                     (tp->t_flags & TF_REQ_SCALE)) {
 1649                         tp->t_flags |= TF_RCVD_SCALE;
 1650                         tp->snd_scale = to.to_wscale;
 1651                 }
 1652                 /*
 1653                  * Initial send window.  It will be updated with
 1654                  * the next incoming segment to the scaled value.
 1655                  */
 1656                 tp->snd_wnd = th->th_win;
 1657                 if (to.to_flags & TOF_TS) {
 1658                         tp->t_flags |= TF_RCVD_TSTMP;
 1659                         tp->ts_recent = to.to_tsval;
 1660                         tp->ts_recent_age = tcp_ts_getticks();
 1661                 }
 1662                 if (to.to_flags & TOF_MSS)
 1663                         tcp_mss(tp, to.to_mss);
 1664                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 1665                     (to.to_flags & TOF_SACKPERM) == 0)
 1666                         tp->t_flags &= ~TF_SACK_PERMIT;
 1667         }
 1668 
 1669         /*
 1670          * Header prediction: check for the two common cases
 1671          * of a uni-directional data xfer.  If the packet has
 1672          * no control flags, is in-sequence, the window didn't
 1673          * change and we're not retransmitting, it's a
 1674          * candidate.  If the length is zero and the ack moved
 1675          * forward, we're the sender side of the xfer.  Just
 1676          * free the data acked & wake any higher level process
 1677          * that was blocked waiting for space.  If the length
 1678          * is non-zero and the ack didn't move, we're the
 1679          * receiver side.  If we're getting packets in-order
 1680          * (the reassembly queue is empty), add the data to
 1681          * the socket buffer and note that we need a delayed ack.
 1682          * Make sure that the hidden state-flags are also off.
 1683          * Since we check for TCPS_ESTABLISHED first, it can only
 1684          * be TH_NEEDSYN.
 1685          */
 1686         if (tp->t_state == TCPS_ESTABLISHED &&
 1687             th->th_seq == tp->rcv_nxt &&
 1688             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 1689             tp->snd_nxt == tp->snd_max &&
 1690             tiwin && tiwin == tp->snd_wnd && 
 1691             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 1692             LIST_EMPTY(&tp->t_segq) &&
 1693             ((to.to_flags & TOF_TS) == 0 ||
 1694              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
 1695 
 1696                 /*
 1697                  * If last ACK falls within this segment's sequence numbers,
 1698                  * record the timestamp.
 1699                  * NOTE that the test is modified according to the latest
 1700                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 1701                  */
 1702                 if ((to.to_flags & TOF_TS) != 0 &&
 1703                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 1704                         tp->ts_recent_age = tcp_ts_getticks();
 1705                         tp->ts_recent = to.to_tsval;
 1706                 }
 1707 
 1708                 if (tlen == 0) {
 1709                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 1710                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 1711                             !IN_RECOVERY(tp->t_flags) &&
 1712                             (to.to_flags & TOF_SACK) == 0 &&
 1713                             TAILQ_EMPTY(&tp->snd_holes)) {
 1714                                 /*
 1715                                  * This is a pure ack for outstanding data.
 1716                                  */
 1717                                 if (ti_locked == TI_RLOCKED)
 1718                                         INP_INFO_RUNLOCK(&V_tcbinfo);
 1719                                 ti_locked = TI_UNLOCKED;
 1720 
 1721                                 TCPSTAT_INC(tcps_predack);
 1722 
 1723                                 /*
 1724                                  * "bad retransmit" recovery.
 1725                                  */
 1726                                 if (tp->t_rxtshift == 1 &&
 1727                                     tp->t_flags & TF_PREVVALID &&
 1728                                     (int)(ticks - tp->t_badrxtwin) < 0) {
 1729                                         cc_cong_signal(tp, th, CC_RTO_ERR);
 1730                                 }
 1731 
 1732                                 /*
 1733                                  * Recalculate the transmit timer / rtt.
 1734                                  *
 1735                                  * Some boxes send broken timestamp replies
 1736                                  * during the SYN+ACK phase, ignore
 1737                                  * timestamps of 0 or we could calculate a
 1738                                  * huge RTT and blow up the retransmit timer.
 1739                                  */
 1740                                 if ((to.to_flags & TOF_TS) != 0 &&
 1741                                     to.to_tsecr) {
 1742                                         u_int t;
 1743 
 1744                                         t = tcp_ts_getticks() - to.to_tsecr;
 1745                                         if (!tp->t_rttlow || tp->t_rttlow > t)
 1746                                                 tp->t_rttlow = t;
 1747                                         tcp_xmit_timer(tp,
 1748                                             TCP_TS_TO_TICKS(t) + 1);
 1749                                 } else if (tp->t_rtttime &&
 1750                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
 1751                                         if (!tp->t_rttlow ||
 1752                                             tp->t_rttlow > ticks - tp->t_rtttime)
 1753                                                 tp->t_rttlow = ticks - tp->t_rtttime;
 1754                                         tcp_xmit_timer(tp,
 1755                                                         ticks - tp->t_rtttime);
 1756                                 }
 1757                                 acked = BYTES_THIS_ACK(tp, th);
 1758 
 1759                                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 1760                                 hhook_run_tcp_est_in(tp, th, &to);
 1761 
 1762                                 TCPSTAT_INC(tcps_rcvackpack);
 1763                                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 1764                                 sbdrop(&so->so_snd, acked);
 1765                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
 1766                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 1767                                         tp->snd_recover = th->th_ack - 1;
 1768                                 
 1769                                 /*
 1770                                  * Let the congestion control algorithm update
 1771                                  * congestion control related information. This
 1772                                  * typically means increasing the congestion
 1773                                  * window.
 1774                                  */
 1775                                 cc_ack_received(tp, th, CC_ACK);
 1776 
 1777                                 tp->snd_una = th->th_ack;
 1778                                 /*
 1779                                  * Pull snd_wl2 up to prevent seq wrap relative
 1780                                  * to th_ack.
 1781                                  */
 1782                                 tp->snd_wl2 = th->th_ack;
 1783                                 tp->t_dupacks = 0;
 1784                                 m_freem(m);
 1785 
 1786                                 /*
 1787                                  * If all outstanding data are acked, stop
 1788                                  * retransmit timer, otherwise restart timer
 1789                                  * using current (possibly backed-off) value.
 1790                                  * If process is waiting for space,
 1791                                  * wakeup/selwakeup/signal.  If data
 1792                                  * are ready to send, let tcp_output
 1793                                  * decide between more output or persist.
 1794                                  */
 1795 #ifdef TCPDEBUG
 1796                                 if (so->so_options & SO_DEBUG)
 1797                                         tcp_trace(TA_INPUT, ostate, tp,
 1798                                             (void *)tcp_saveipgen,
 1799                                             &tcp_savetcp, 0);
 1800 #endif
 1801                                 TCP_PROBE3(debug__input, tp, th,
 1802                                         mtod(m, const char *));
 1803                                 if (tp->snd_una == tp->snd_max)
 1804                                         tcp_timer_activate(tp, TT_REXMT, 0);
 1805                                 else if (!tcp_timer_active(tp, TT_PERSIST))
 1806                                         tcp_timer_activate(tp, TT_REXMT,
 1807                                                       tp->t_rxtcur);
 1808                                 sowwakeup(so);
 1809                                 if (sbavail(&so->so_snd))
 1810                                         (void) tp->t_fb->tfb_tcp_output(tp);
 1811                                 goto check_delack;
 1812                         }
 1813                 } else if (th->th_ack == tp->snd_una &&
 1814                     tlen <= sbspace(&so->so_rcv)) {
 1815                         int newsize = 0;        /* automatic sockbuf scaling */
 1816 
 1817                         /*
 1818                          * This is a pure, in-sequence data packet with
 1819                          * nothing on the reassembly queue and we have enough
 1820                          * buffer space to take it.
 1821                          */
 1822                         if (ti_locked == TI_RLOCKED)
 1823                                 INP_INFO_RUNLOCK(&V_tcbinfo);
 1824                         ti_locked = TI_UNLOCKED;
 1825 
 1826                         /* Clean receiver SACK report if present */
 1827                         if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
 1828                                 tcp_clean_sackreport(tp);
 1829                         TCPSTAT_INC(tcps_preddat);
 1830                         tp->rcv_nxt += tlen;
 1831                         /*
 1832                          * Pull snd_wl1 up to prevent seq wrap relative to
 1833                          * th_seq.
 1834                          */
 1835                         tp->snd_wl1 = th->th_seq;
 1836                         /*
 1837                          * Pull rcv_up up to prevent seq wrap relative to
 1838                          * rcv_nxt.
 1839                          */
 1840                         tp->rcv_up = tp->rcv_nxt;
 1841                         TCPSTAT_INC(tcps_rcvpack);
 1842                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 1843 #ifdef TCPDEBUG
 1844                         if (so->so_options & SO_DEBUG)
 1845                                 tcp_trace(TA_INPUT, ostate, tp,
 1846                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1847 #endif
 1848                         TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
 1849 
 1850                 /*
 1851                  * Automatic sizing of receive socket buffer.  Often the send
 1852                  * buffer size is not optimally adjusted to the actual network
 1853                  * conditions at hand (delay bandwidth product).  Setting the
 1854                  * buffer size too small limits throughput on links with high
 1855                  * bandwidth and high delay (eg. trans-continental/oceanic links).
 1856                  *
 1857                  * On the receive side the socket buffer memory is only rarely
 1858                  * used to any significant extent.  This allows us to be much
 1859                  * more aggressive in scaling the receive socket buffer.  For
 1860                  * the case that the buffer space is actually used to a large
 1861                  * extent and we run out of kernel memory we can simply drop
 1862                  * the new segments; TCP on the sender will just retransmit it
 1863                  * later.  Setting the buffer size too big may only consume too
 1864                  * much kernel memory if the application doesn't read() from
 1865                  * the socket or packet loss or reordering makes use of the
 1866                  * reassembly queue.
 1867                  *
 1868                  * The criteria to step up the receive buffer one notch are:
 1869                  *  1. Application has not set receive buffer size with
 1870                  *     SO_RCVBUF. Setting SO_RCVBUF clears SB_AUTOSIZE.
 1871                  *  2. the number of bytes received during the time it takes
 1872                  *     one timestamp to be reflected back to us (the RTT);
 1873                  *  3. received bytes per RTT is within seven eighth of the
 1874                  *     current socket buffer size;
 1875                  *  4. receive buffer size has not hit maximal automatic size;
 1876                  *
 1877                  * This algorithm does one step per RTT at most and only if
 1878                  * we receive a bulk stream w/o packet losses or reorderings.
 1879                  * Shrinking the buffer during idle times is not necessary as
 1880                  * it doesn't consume any memory when idle.
 1881                  *
 1882                  * TODO: Only step up if the application is actually serving
 1883                  * the buffer to better manage the socket buffer resources.
 1884                  */
 1885                         if (V_tcp_do_autorcvbuf &&
 1886                             (to.to_flags & TOF_TS) &&
 1887                             to.to_tsecr &&
 1888                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
 1889                                 if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
 1890                                     to.to_tsecr - tp->rfbuf_ts < hz) {
 1891                                         if (tp->rfbuf_cnt >
 1892                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
 1893                                             so->so_rcv.sb_hiwat <
 1894                                             V_tcp_autorcvbuf_max) {
 1895                                                 newsize =
 1896                                                     min(so->so_rcv.sb_hiwat +
 1897                                                     V_tcp_autorcvbuf_inc,
 1898                                                     V_tcp_autorcvbuf_max);
 1899                                         }
 1900                                         /* Start over with next RTT. */
 1901                                         tp->rfbuf_ts = 0;
 1902                                         tp->rfbuf_cnt = 0;
 1903                                 } else
 1904                                         tp->rfbuf_cnt += tlen;  /* add up */
 1905                         }
 1906 
 1907                         /* Add data to socket buffer. */
 1908                         SOCKBUF_LOCK(&so->so_rcv);
 1909                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 1910                                 m_freem(m);
 1911                         } else {
 1912                                 /*
 1913                                  * Set new socket buffer size.
 1914                                  * Give up when limit is reached.
 1915                                  */
 1916                                 if (newsize)
 1917                                         if (!sbreserve_locked(&so->so_rcv,
 1918                                             newsize, so, NULL))
 1919                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
 1920                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 1921                                 sbappendstream_locked(&so->so_rcv, m, 0);
 1922                         }
 1923                         /* NB: sorwakeup_locked() does an implicit unlock. */
 1924                         sorwakeup_locked(so);
 1925                         if (DELAY_ACK(tp, tlen)) {
 1926                                 tp->t_flags |= TF_DELACK;
 1927                         } else {
 1928                                 tp->t_flags |= TF_ACKNOW;
 1929                                 tp->t_fb->tfb_tcp_output(tp);
 1930                         }
 1931                         goto check_delack;
 1932                 }
 1933         }
 1934 
 1935         /*
 1936          * Calculate amount of space in receive window,
 1937          * and then do TCP input processing.
 1938          * Receive window is amount of space in rcv queue,
 1939          * but not less than advertised window.
 1940          */
 1941         win = sbspace(&so->so_rcv);
 1942         if (win < 0)
 1943                 win = 0;
 1944         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 1945 
 1946         /* Reset receive buffer auto scaling when not in bulk receive mode. */
 1947         tp->rfbuf_ts = 0;
 1948         tp->rfbuf_cnt = 0;
 1949 
 1950         switch (tp->t_state) {
 1951 
 1952         /*
 1953          * If the state is SYN_RECEIVED:
 1954          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
 1955          */
 1956         case TCPS_SYN_RECEIVED:
 1957                 if ((thflags & TH_ACK) &&
 1958                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
 1959                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1960                                 rstreason = BANDLIM_RST_OPENPORT;
 1961                                 goto dropwithreset;
 1962                 }
 1963 #ifdef TCP_RFC7413
 1964                 if (tp->t_flags & TF_FASTOPEN) {
 1965                         /*
 1966                          * When a TFO connection is in SYN_RECEIVED, the
 1967                          * only valid packets are the initial SYN, a
 1968                          * retransmit/copy of the initial SYN (possibly with
 1969                          * a subset of the original data), a valid ACK, a
 1970                          * FIN, or a RST.
 1971                          */
 1972                         if ((thflags & (TH_SYN|TH_ACK)) == (TH_SYN|TH_ACK)) {
 1973                                 rstreason = BANDLIM_RST_OPENPORT;
 1974                                 goto dropwithreset;
 1975                         } else if (thflags & TH_SYN) {
 1976                                 /* non-initial SYN is ignored */
 1977                                 if ((tcp_timer_active(tp, TT_DELACK) || 
 1978                                      tcp_timer_active(tp, TT_REXMT)))
 1979                                         goto drop;
 1980                         } else if (!(thflags & (TH_ACK|TH_FIN|TH_RST))) {
 1981                                 goto drop;
 1982                         }
 1983                 }
 1984 #endif
 1985                 break;
 1986 
 1987         /*
 1988          * If the state is SYN_SENT:
 1989          *      if seg contains an ACK, but not for our SYN, drop the input.
 1990          *      if seg contains a RST, then drop the connection.
 1991          *      if seg does not contain SYN, then drop it.
 1992          * Otherwise this is an acceptable SYN segment
 1993          *      initialize tp->rcv_nxt and tp->irs
 1994          *      if seg contains ack then advance tp->snd_una
 1995          *      if seg contains an ECE and ECN support is enabled, the stream
 1996          *          is ECN capable.
 1997          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
 1998          *      arrange for segment to be acked (eventually)
 1999          *      continue processing rest of data/controls, beginning with URG
 2000          */
 2001         case TCPS_SYN_SENT:
 2002                 if ((thflags & TH_ACK) &&
 2003                     (SEQ_LEQ(th->th_ack, tp->iss) ||
 2004                      SEQ_GT(th->th_ack, tp->snd_max))) {
 2005                         rstreason = BANDLIM_UNLIMITED;
 2006                         goto dropwithreset;
 2007                 }
 2008                 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
 2009                         TCP_PROBE5(connect__refused, NULL, tp,
 2010                             mtod(m, const char *), tp, th);
 2011                         tp = tcp_drop(tp, ECONNREFUSED);
 2012                 }
 2013                 if (thflags & TH_RST)
 2014                         goto drop;
 2015                 if (!(thflags & TH_SYN))
 2016                         goto drop;
 2017 
 2018                 tp->irs = th->th_seq;
 2019                 tcp_rcvseqinit(tp);
 2020                 if (thflags & TH_ACK) {
 2021                         TCPSTAT_INC(tcps_connects);
 2022                         soisconnected(so);
 2023 #ifdef MAC
 2024                         mac_socketpeer_set_from_mbuf(m, so);
 2025 #endif
 2026                         /* Do window scaling on this connection? */
 2027                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2028                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2029                                 tp->rcv_scale = tp->request_r_scale;
 2030                         }
 2031                         tp->rcv_adv += imin(tp->rcv_wnd,
 2032                             TCP_MAXWIN << tp->rcv_scale);
 2033                         tp->snd_una++;          /* SYN is acked */
 2034                         /*
 2035                          * If there's data, delay ACK; if there's also a FIN
 2036                          * ACKNOW will be turned on later.
 2037                          */
 2038                         if (DELAY_ACK(tp, tlen) && tlen != 0)
 2039                                 tcp_timer_activate(tp, TT_DELACK,
 2040                                     tcp_delacktime);
 2041                         else
 2042                                 tp->t_flags |= TF_ACKNOW;
 2043 
 2044                         if ((thflags & TH_ECE) && V_tcp_do_ecn) {
 2045                                 tp->t_flags |= TF_ECN_PERMIT;
 2046                                 TCPSTAT_INC(tcps_ecn_shs);
 2047                         }
 2048                         
 2049                         /*
 2050                          * Received <SYN,ACK> in SYN_SENT[*] state.
 2051                          * Transitions:
 2052                          *      SYN_SENT  --> ESTABLISHED
 2053                          *      SYN_SENT* --> FIN_WAIT_1
 2054                          */
 2055                         tp->t_starttime = ticks;
 2056                         if (tp->t_flags & TF_NEEDFIN) {
 2057                                 tcp_state_change(tp, TCPS_FIN_WAIT_1);
 2058                                 tp->t_flags &= ~TF_NEEDFIN;
 2059                                 thflags &= ~TH_SYN;
 2060                         } else {
 2061                                 tcp_state_change(tp, TCPS_ESTABLISHED);
 2062                                 TCP_PROBE5(connect__established, NULL, tp,
 2063                                     mtod(m, const char *), tp, th);
 2064                                 cc_conn_init(tp);
 2065                                 tcp_timer_activate(tp, TT_KEEP,
 2066                                     TP_KEEPIDLE(tp));
 2067                         }
 2068                 } else {
 2069                         /*
 2070                          * Received initial SYN in SYN-SENT[*] state =>
 2071                          * simultaneous open.
 2072                          * If it succeeds, connection is * half-synchronized.
 2073                          * Otherwise, do 3-way handshake:
 2074                          *        SYN-SENT -> SYN-RECEIVED
 2075                          *        SYN-SENT* -> SYN-RECEIVED*
 2076                          */
 2077                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 2078                         tcp_timer_activate(tp, TT_REXMT, 0);
 2079                         tcp_state_change(tp, TCPS_SYN_RECEIVED);
 2080                 }
 2081 
 2082                 KASSERT(ti_locked == TI_RLOCKED, ("%s: trimthenstep6: "
 2083                     "ti_locked %d", __func__, ti_locked));
 2084                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2085                 INP_WLOCK_ASSERT(tp->t_inpcb);
 2086 
 2087                 /*
 2088                  * Advance th->th_seq to correspond to first data byte.
 2089                  * If data, trim to stay within window,
 2090                  * dropping FIN if necessary.
 2091                  */
 2092                 th->th_seq++;
 2093                 if (tlen > tp->rcv_wnd) {
 2094                         todrop = tlen - tp->rcv_wnd;
 2095                         m_adj(m, -todrop);
 2096                         tlen = tp->rcv_wnd;
 2097                         thflags &= ~TH_FIN;
 2098                         TCPSTAT_INC(tcps_rcvpackafterwin);
 2099                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2100                 }
 2101                 tp->snd_wl1 = th->th_seq - 1;
 2102                 tp->rcv_up = th->th_seq;
 2103                 /*
 2104                  * Client side of transaction: already sent SYN and data.
 2105                  * If the remote host used T/TCP to validate the SYN,
 2106                  * our data will be ACK'd; if so, enter normal data segment
 2107                  * processing in the middle of step 5, ack processing.
 2108                  * Otherwise, goto step 6.
 2109                  */
 2110                 if (thflags & TH_ACK)
 2111                         goto process_ACK;
 2112 
 2113                 goto step6;
 2114 
 2115         /*
 2116          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
 2117          *      do normal processing.
 2118          *
 2119          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
 2120          */
 2121         case TCPS_LAST_ACK:
 2122         case TCPS_CLOSING:
 2123                 break;  /* continue normal processing */
 2124         }
 2125 
 2126         /*
 2127          * States other than LISTEN or SYN_SENT.
 2128          * First check the RST flag and sequence number since reset segments
 2129          * are exempt from the timestamp and connection count tests.  This
 2130          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
 2131          * below which allowed reset segments in half the sequence space
 2132          * to fall though and be processed (which gives forged reset
 2133          * segments with a random sequence number a 50 percent chance of
 2134          * killing a connection).
 2135          * Then check timestamp, if present.
 2136          * Then check the connection count, if present.
 2137          * Then check that at least some bytes of segment are within
 2138          * receive window.  If segment begins before rcv_nxt,
 2139          * drop leading data (and SYN); if nothing left, just ack.
 2140          */
 2141         if (thflags & TH_RST) {
 2142                 /*
 2143                  * RFC5961 Section 3.2
 2144                  *
 2145                  * - RST drops connection only if SEG.SEQ == RCV.NXT.
 2146                  * - If RST is in window, we send challenge ACK.
 2147                  *
 2148                  * Note: to take into account delayed ACKs, we should
 2149                  *   test against last_ack_sent instead of rcv_nxt.
 2150                  * Note 2: we handle special case of closed window, not
 2151                  *   covered by the RFC.
 2152                  */
 2153                 if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
 2154                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) ||
 2155                     (tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
 2156 
 2157                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2158                         KASSERT(ti_locked == TI_RLOCKED,
 2159                             ("%s: TH_RST ti_locked %d, th %p tp %p",
 2160                             __func__, ti_locked, th, tp));
 2161                         KASSERT(tp->t_state != TCPS_SYN_SENT,
 2162                             ("%s: TH_RST for TCPS_SYN_SENT th %p tp %p",
 2163                             __func__, th, tp));
 2164 
 2165                         if (V_tcp_insecure_rst ||
 2166                             tp->last_ack_sent == th->th_seq) {
 2167                                 TCPSTAT_INC(tcps_drops);
 2168                                 /* Drop the connection. */
 2169                                 switch (tp->t_state) {
 2170                                 case TCPS_SYN_RECEIVED:
 2171                                         so->so_error = ECONNREFUSED;
 2172                                         goto close;
 2173                                 case TCPS_ESTABLISHED:
 2174                                 case TCPS_FIN_WAIT_1:
 2175                                 case TCPS_FIN_WAIT_2:
 2176                                 case TCPS_CLOSE_WAIT:
 2177                                         so->so_error = ECONNRESET;
 2178                                 close:
 2179                                         tcp_state_change(tp, TCPS_CLOSED);
 2180                                         /* FALLTHROUGH */
 2181                                 default:
 2182                                         tp = tcp_close(tp);
 2183                                 }
 2184                         } else {
 2185                                 TCPSTAT_INC(tcps_badrst);
 2186                                 /* Send challenge ACK. */
 2187                                 tcp_respond(tp, mtod(m, void *), th, m,
 2188                                     tp->rcv_nxt, tp->snd_nxt, TH_ACK);
 2189                                 tp->last_ack_sent = tp->rcv_nxt;
 2190                                 m = NULL;
 2191                         }
 2192                 }
 2193                 goto drop;
 2194         }
 2195 
 2196         /*
 2197          * RFC5961 Section 4.2
 2198          * Send challenge ACK for any SYN in synchronized state.
 2199          */
 2200         if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT &&
 2201             tp->t_state != TCPS_SYN_RECEIVED) {
 2202                 KASSERT(ti_locked == TI_RLOCKED,
 2203                     ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
 2204                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2205 
 2206                 TCPSTAT_INC(tcps_badsyn);
 2207                 if (V_tcp_insecure_syn &&
 2208                     SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
 2209                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
 2210                         tp = tcp_drop(tp, ECONNRESET);
 2211                         rstreason = BANDLIM_UNLIMITED;
 2212                 } else {
 2213                         /* Send challenge ACK. */
 2214                         tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
 2215                             tp->snd_nxt, TH_ACK);
 2216                         tp->last_ack_sent = tp->rcv_nxt;
 2217                         m = NULL;
 2218                 }
 2219                 goto drop;
 2220         }
 2221 
 2222         /*
 2223          * RFC 1323 PAWS: If we have a timestamp reply on this segment
 2224          * and it's less than ts_recent, drop it.
 2225          */
 2226         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
 2227             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
 2228 
 2229                 /* Check to see if ts_recent is over 24 days old.  */
 2230                 if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
 2231                         /*
 2232                          * Invalidate ts_recent.  If this segment updates
 2233                          * ts_recent, the age will be reset later and ts_recent
 2234                          * will get a valid value.  If it does not, setting
 2235                          * ts_recent to zero will at least satisfy the
 2236                          * requirement that zero be placed in the timestamp
 2237                          * echo reply when ts_recent isn't valid.  The
 2238                          * age isn't reset until we get a valid ts_recent
 2239                          * because we don't want out-of-order segments to be
 2240                          * dropped when ts_recent is old.
 2241                          */
 2242                         tp->ts_recent = 0;
 2243                 } else {
 2244                         TCPSTAT_INC(tcps_rcvduppack);
 2245                         TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
 2246                         TCPSTAT_INC(tcps_pawsdrop);
 2247                         if (tlen)
 2248                                 goto dropafterack;
 2249                         goto drop;
 2250                 }
 2251         }
 2252 
 2253         /*
 2254          * In the SYN-RECEIVED state, validate that the packet belongs to
 2255          * this connection before trimming the data to fit the receive
 2256          * window.  Check the sequence number versus IRS since we know
 2257          * the sequence numbers haven't wrapped.  This is a partial fix
 2258          * for the "LAND" DoS attack.
 2259          */
 2260         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
 2261                 rstreason = BANDLIM_RST_OPENPORT;
 2262                 goto dropwithreset;
 2263         }
 2264 
 2265         todrop = tp->rcv_nxt - th->th_seq;
 2266         if (todrop > 0) {
 2267                 if (thflags & TH_SYN) {
 2268                         thflags &= ~TH_SYN;
 2269                         th->th_seq++;
 2270                         if (th->th_urp > 1)
 2271                                 th->th_urp--;
 2272                         else
 2273                                 thflags &= ~TH_URG;
 2274                         todrop--;
 2275                 }
 2276                 /*
 2277                  * Following if statement from Stevens, vol. 2, p. 960.
 2278                  */
 2279                 if (todrop > tlen
 2280                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
 2281                         /*
 2282                          * Any valid FIN must be to the left of the window.
 2283                          * At this point the FIN must be a duplicate or out
 2284                          * of sequence; drop it.
 2285                          */
 2286                         thflags &= ~TH_FIN;
 2287 
 2288                         /*
 2289                          * Send an ACK to resynchronize and drop any data.
 2290                          * But keep on processing for RST or ACK.
 2291                          */
 2292                         tp->t_flags |= TF_ACKNOW;
 2293                         todrop = tlen;
 2294                         TCPSTAT_INC(tcps_rcvduppack);
 2295                         TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
 2296                 } else {
 2297                         TCPSTAT_INC(tcps_rcvpartduppack);
 2298                         TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
 2299                 }
 2300                 drop_hdrlen += todrop;  /* drop from the top afterwards */
 2301                 th->th_seq += todrop;
 2302                 tlen -= todrop;
 2303                 if (th->th_urp > todrop)
 2304                         th->th_urp -= todrop;
 2305                 else {
 2306                         thflags &= ~TH_URG;
 2307                         th->th_urp = 0;
 2308                 }
 2309         }
 2310 
 2311         /*
 2312          * If new data are received on a connection after the
 2313          * user processes are gone, then RST the other end.
 2314          */
 2315         if ((so->so_state & SS_NOFDREF) &&
 2316             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
 2317                 KASSERT(ti_locked == TI_RLOCKED, ("%s: SS_NOFDEREF && "
 2318                     "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
 2319                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2320 
 2321                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 2322                         log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
 2323                             "after socket was closed, "
 2324                             "sending RST and removing tcpcb\n",
 2325                             s, __func__, tcpstates[tp->t_state], tlen);
 2326                         free(s, M_TCPLOG);
 2327                 }
 2328                 tp = tcp_close(tp);
 2329                 TCPSTAT_INC(tcps_rcvafterclose);
 2330                 rstreason = BANDLIM_UNLIMITED;
 2331                 goto dropwithreset;
 2332         }
 2333 
 2334         /*
 2335          * If segment ends after window, drop trailing data
 2336          * (and PUSH and FIN); if nothing left, just ACK.
 2337          */
 2338         todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
 2339         if (todrop > 0) {
 2340                 TCPSTAT_INC(tcps_rcvpackafterwin);
 2341                 if (todrop >= tlen) {
 2342                         TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
 2343                         /*
 2344                          * If window is closed can only take segments at
 2345                          * window edge, and have to drop data and PUSH from
 2346                          * incoming segments.  Continue processing, but
 2347                          * remember to ack.  Otherwise, drop segment
 2348                          * and ack.
 2349                          */
 2350                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
 2351                                 tp->t_flags |= TF_ACKNOW;
 2352                                 TCPSTAT_INC(tcps_rcvwinprobe);
 2353                         } else
 2354                                 goto dropafterack;
 2355                 } else
 2356                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2357                 m_adj(m, -todrop);
 2358                 tlen -= todrop;
 2359                 thflags &= ~(TH_PUSH|TH_FIN);
 2360         }
 2361 
 2362         /*
 2363          * If last ACK falls within this segment's sequence numbers,
 2364          * record its timestamp.
 2365          * NOTE: 
 2366          * 1) That the test incorporates suggestions from the latest
 2367          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
 2368          * 2) That updating only on newer timestamps interferes with
 2369          *    our earlier PAWS tests, so this check should be solely
 2370          *    predicated on the sequence space of this segment.
 2371          * 3) That we modify the segment boundary check to be 
 2372          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len  
 2373          *    instead of RFC1323's
 2374          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
 2375          *    This modified check allows us to overcome RFC1323's
 2376          *    limitations as described in Stevens TCP/IP Illustrated
 2377          *    Vol. 2 p.869. In such cases, we can still calculate the
 2378          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
 2379          */
 2380         if ((to.to_flags & TOF_TS) != 0 &&
 2381             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
 2382             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
 2383                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
 2384                 tp->ts_recent_age = tcp_ts_getticks();
 2385                 tp->ts_recent = to.to_tsval;
 2386         }
 2387 
 2388         /*
 2389          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
 2390          * flag is on (half-synchronized state), then queue data for
 2391          * later processing; else drop segment and return.
 2392          */
 2393         if ((thflags & TH_ACK) == 0) {
 2394                 if (tp->t_state == TCPS_SYN_RECEIVED ||
 2395                     (tp->t_flags & TF_NEEDSYN)) {
 2396 #ifdef TCP_RFC7413
 2397                         if (tp->t_state == TCPS_SYN_RECEIVED &&
 2398                             tp->t_flags & TF_FASTOPEN) {
 2399                                 tp->snd_wnd = tiwin;
 2400                                 cc_conn_init(tp);
 2401                         }
 2402 #endif
 2403                         goto step6;
 2404                 } else if (tp->t_flags & TF_ACKNOW)
 2405                         goto dropafterack;
 2406                 else
 2407                         goto drop;
 2408         }
 2409 
 2410         /*
 2411          * Ack processing.
 2412          */
 2413         switch (tp->t_state) {
 2414 
 2415         /*
 2416          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
 2417          * ESTABLISHED state and continue processing.
 2418          * The ACK was checked above.
 2419          */
 2420         case TCPS_SYN_RECEIVED:
 2421 
 2422                 TCPSTAT_INC(tcps_connects);
 2423                 soisconnected(so);
 2424                 /* Do window scaling? */
 2425                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2426                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2427                         tp->rcv_scale = tp->request_r_scale;
 2428                         tp->snd_wnd = tiwin;
 2429                 }
 2430                 /*
 2431                  * Make transitions:
 2432                  *      SYN-RECEIVED  -> ESTABLISHED
 2433                  *      SYN-RECEIVED* -> FIN-WAIT-1
 2434                  */
 2435                 tp->t_starttime = ticks;
 2436                 if (tp->t_flags & TF_NEEDFIN) {
 2437                         tcp_state_change(tp, TCPS_FIN_WAIT_1);
 2438                         tp->t_flags &= ~TF_NEEDFIN;
 2439                 } else {
 2440                         tcp_state_change(tp, TCPS_ESTABLISHED);
 2441                         TCP_PROBE5(accept__established, NULL, tp,
 2442                             mtod(m, const char *), tp, th);
 2443 #ifdef TCP_RFC7413
 2444                         if (tp->t_tfo_pending) {
 2445                                 tcp_fastopen_decrement_counter(tp->t_tfo_pending);
 2446                                 tp->t_tfo_pending = NULL;
 2447 
 2448                                 /*
 2449                                  * Account for the ACK of our SYN prior to
 2450                                  * regular ACK processing below.
 2451                                  */ 
 2452                                 tp->snd_una++;
 2453                         }
 2454                         /*
 2455                          * TFO connections call cc_conn_init() during SYN
 2456                          * processing.  Calling it again here for such
 2457                          * connections is not harmless as it would undo the
 2458                          * snd_cwnd reduction that occurs when a TFO SYN|ACK
 2459                          * is retransmitted.
 2460                          */
 2461                         if (!(tp->t_flags & TF_FASTOPEN))
 2462 #endif
 2463                                 cc_conn_init(tp);
 2464                         tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 2465                 }
 2466                 /*
 2467                  * If segment contains data or ACK, will call tcp_reass()
 2468                  * later; if not, do so now to pass queued data to user.
 2469                  */
 2470                 if (tlen == 0 && (thflags & TH_FIN) == 0)
 2471                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
 2472                             (struct mbuf *)0);
 2473                 tp->snd_wl1 = th->th_seq - 1;
 2474                 /* FALLTHROUGH */
 2475 
 2476         /*
 2477          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
 2478          * ACKs.  If the ack is in the range
 2479          *      tp->snd_una < th->th_ack <= tp->snd_max
 2480          * then advance tp->snd_una to th->th_ack and drop
 2481          * data from the retransmission queue.  If this ACK reflects
 2482          * more up to date window information we update our window information.
 2483          */
 2484         case TCPS_ESTABLISHED:
 2485         case TCPS_FIN_WAIT_1:
 2486         case TCPS_FIN_WAIT_2:
 2487         case TCPS_CLOSE_WAIT:
 2488         case TCPS_CLOSING:
 2489         case TCPS_LAST_ACK:
 2490                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
 2491                         TCPSTAT_INC(tcps_rcvacktoomuch);
 2492                         goto dropafterack;
 2493                 }
 2494                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 2495                     ((to.to_flags & TOF_SACK) ||
 2496                      !TAILQ_EMPTY(&tp->snd_holes)))
 2497                         sack_changed = tcp_sack_doack(tp, &to, th->th_ack);
 2498                 else
 2499                         /*
 2500                          * Reset the value so that previous (valid) value
 2501                          * from the last ack with SACK doesn't get used.
 2502                          */
 2503                         tp->sackhint.sacked_bytes = 0;
 2504 
 2505                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 2506                 hhook_run_tcp_est_in(tp, th, &to);
 2507 
 2508                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
 2509                         u_int maxseg;
 2510 
 2511                         maxseg = tcp_maxseg(tp);
 2512                         if (tlen == 0 &&
 2513                             (tiwin == tp->snd_wnd ||
 2514                             (tp->t_flags & TF_SACK_PERMIT))) {
 2515                                 /*
 2516                                  * If this is the first time we've seen a
 2517                                  * FIN from the remote, this is not a
 2518                                  * duplicate and it needs to be processed
 2519                                  * normally.  This happens during a
 2520                                  * simultaneous close.
 2521                                  */
 2522                                 if ((thflags & TH_FIN) &&
 2523                                     (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
 2524                                         tp->t_dupacks = 0;
 2525                                         break;
 2526                                 }
 2527                                 TCPSTAT_INC(tcps_rcvdupack);
 2528                                 /*
 2529                                  * If we have outstanding data (other than
 2530                                  * a window probe), this is a completely
 2531                                  * duplicate ack (ie, window info didn't
 2532                                  * change and FIN isn't set),
 2533                                  * the ack is the biggest we've
 2534                                  * seen and we've seen exactly our rexmt
 2535                                  * threshold of them, assume a packet
 2536                                  * has been dropped and retransmit it.
 2537                                  * Kludge snd_nxt & the congestion
 2538                                  * window so we send only this one
 2539                                  * packet.
 2540                                  *
 2541                                  * We know we're losing at the current
 2542                                  * window size so do congestion avoidance
 2543                                  * (set ssthresh to half the current window
 2544                                  * and pull our congestion window back to
 2545                                  * the new ssthresh).
 2546                                  *
 2547                                  * Dup acks mean that packets have left the
 2548                                  * network (they're now cached at the receiver)
 2549                                  * so bump cwnd by the amount in the receiver
 2550                                  * to keep a constant cwnd packets in the
 2551                                  * network.
 2552                                  *
 2553                                  * When using TCP ECN, notify the peer that
 2554                                  * we reduced the cwnd.
 2555                                  */
 2556                                 /*
 2557                                  * Following 2 kinds of acks should not affect
 2558                                  * dupack counting:
 2559                                  * 1) Old acks
 2560                                  * 2) Acks with SACK but without any new SACK
 2561                                  * information in them. These could result from
 2562                                  * any anomaly in the network like a switch
 2563                                  * duplicating packets or a possible DoS attack.
 2564                                  */
 2565                                 if (th->th_ack != tp->snd_una ||
 2566                                     ((tp->t_flags & TF_SACK_PERMIT) &&
 2567                                     !sack_changed))
 2568                                         break;
 2569                                 else if (!tcp_timer_active(tp, TT_REXMT))
 2570                                         tp->t_dupacks = 0;
 2571                                 else if (++tp->t_dupacks > tcprexmtthresh ||
 2572                                      IN_FASTRECOVERY(tp->t_flags)) {
 2573                                         cc_ack_received(tp, th, CC_DUPACK);
 2574                                         if ((tp->t_flags & TF_SACK_PERMIT) &&
 2575                                             IN_FASTRECOVERY(tp->t_flags)) {
 2576                                                 int awnd;
 2577                                                 
 2578                                                 /*
 2579                                                  * Compute the amount of data in flight first.
 2580                                                  * We can inject new data into the pipe iff 
 2581                                                  * we have less than 1/2 the original window's
 2582                                                  * worth of data in flight.
 2583                                                  */
 2584                                                 if (V_tcp_do_rfc6675_pipe)
 2585                                                         awnd = tcp_compute_pipe(tp);
 2586                                                 else
 2587                                                         awnd = (tp->snd_nxt - tp->snd_fack) +
 2588                                                                 tp->sackhint.sack_bytes_rexmit;
 2589 
 2590                                                 if (awnd < tp->snd_ssthresh) {
 2591                                                         tp->snd_cwnd += maxseg;
 2592                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
 2593                                                                 tp->snd_cwnd = tp->snd_ssthresh;
 2594                                                 }
 2595                                         } else
 2596                                                 tp->snd_cwnd += maxseg;
 2597                                         (void) tp->t_fb->tfb_tcp_output(tp);
 2598                                         goto drop;
 2599                                 } else if (tp->t_dupacks == tcprexmtthresh) {
 2600                                         tcp_seq onxt = tp->snd_nxt;
 2601 
 2602                                         /*
 2603                                          * If we're doing sack, check to
 2604                                          * see if we're already in sack
 2605                                          * recovery. If we're not doing sack,
 2606                                          * check to see if we're in newreno
 2607                                          * recovery.
 2608                                          */
 2609                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2610                                                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2611                                                         tp->t_dupacks = 0;
 2612                                                         break;
 2613                                                 }
 2614                                         } else {
 2615                                                 if (SEQ_LEQ(th->th_ack,
 2616                                                     tp->snd_recover)) {
 2617                                                         tp->t_dupacks = 0;
 2618                                                         break;
 2619                                                 }
 2620                                         }
 2621                                         /* Congestion signal before ack. */
 2622                                         cc_cong_signal(tp, th, CC_NDUPACK);
 2623                                         cc_ack_received(tp, th, CC_DUPACK);
 2624                                         tcp_timer_activate(tp, TT_REXMT, 0);
 2625                                         tp->t_rtttime = 0;
 2626                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2627                                                 TCPSTAT_INC(
 2628                                                     tcps_sack_recovery_episode);
 2629                                                 tp->sack_newdata = tp->snd_nxt;
 2630                                                 tp->snd_cwnd = maxseg;
 2631                                                 (void) tp->t_fb->tfb_tcp_output(tp);
 2632                                                 goto drop;
 2633                                         }
 2634                                         tp->snd_nxt = th->th_ack;
 2635                                         tp->snd_cwnd = maxseg;
 2636                                         (void) tp->t_fb->tfb_tcp_output(tp);
 2637                                         KASSERT(tp->snd_limited <= 2,
 2638                                             ("%s: tp->snd_limited too big",
 2639                                             __func__));
 2640                                         tp->snd_cwnd = tp->snd_ssthresh +
 2641                                              maxseg *
 2642                                              (tp->t_dupacks - tp->snd_limited);
 2643                                         if (SEQ_GT(onxt, tp->snd_nxt))
 2644                                                 tp->snd_nxt = onxt;
 2645                                         goto drop;
 2646                                 } else if (V_tcp_do_rfc3042) {
 2647                                         /*
 2648                                          * Process first and second duplicate
 2649                                          * ACKs. Each indicates a segment
 2650                                          * leaving the network, creating room
 2651                                          * for more. Make sure we can send a
 2652                                          * packet on reception of each duplicate
 2653                                          * ACK by increasing snd_cwnd by one
 2654                                          * segment. Restore the original
 2655                                          * snd_cwnd after packet transmission.
 2656                                          */
 2657                                         cc_ack_received(tp, th, CC_DUPACK);
 2658                                         u_long oldcwnd = tp->snd_cwnd;
 2659                                         tcp_seq oldsndmax = tp->snd_max;
 2660                                         u_int sent;
 2661                                         int avail;
 2662 
 2663                                         KASSERT(tp->t_dupacks == 1 ||
 2664                                             tp->t_dupacks == 2,
 2665                                             ("%s: dupacks not 1 or 2",
 2666                                             __func__));
 2667                                         if (tp->t_dupacks == 1)
 2668                                                 tp->snd_limited = 0;
 2669                                         tp->snd_cwnd =
 2670                                             (tp->snd_nxt - tp->snd_una) +
 2671                                             (tp->t_dupacks - tp->snd_limited) *
 2672                                             maxseg;
 2673                                         /*
 2674                                          * Only call tcp_output when there
 2675                                          * is new data available to be sent.
 2676                                          * Otherwise we would send pure ACKs.
 2677                                          */
 2678                                         SOCKBUF_LOCK(&so->so_snd);
 2679                                         avail = sbavail(&so->so_snd) -
 2680                                             (tp->snd_nxt - tp->snd_una);
 2681                                         SOCKBUF_UNLOCK(&so->so_snd);
 2682                                         if (avail > 0)
 2683                                                 (void) tp->t_fb->tfb_tcp_output(tp);
 2684                                         sent = tp->snd_max - oldsndmax;
 2685                                         if (sent > maxseg) {
 2686                                                 KASSERT((tp->t_dupacks == 2 &&
 2687                                                     tp->snd_limited == 0) ||
 2688                                                    (sent == maxseg + 1 &&
 2689                                                     tp->t_flags & TF_SENTFIN),
 2690                                                     ("%s: sent too much",
 2691                                                     __func__));
 2692                                                 tp->snd_limited = 2;
 2693                                         } else if (sent > 0)
 2694                                                 ++tp->snd_limited;
 2695                                         tp->snd_cwnd = oldcwnd;
 2696                                         goto drop;
 2697                                 }
 2698                         }
 2699                         break;
 2700                 } else {
 2701                         /*
 2702                          * This ack is advancing the left edge, reset the
 2703                          * counter.
 2704                          */
 2705                         tp->t_dupacks = 0;
 2706                         /*
 2707                          * If this ack also has new SACK info, increment the
 2708                          * counter as per rfc6675.
 2709                          */
 2710                         if ((tp->t_flags & TF_SACK_PERMIT) && sack_changed)
 2711                                 tp->t_dupacks++;
 2712                 }
 2713 
 2714                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
 2715                     ("%s: th_ack <= snd_una", __func__));
 2716 
 2717                 /*
 2718                  * If the congestion window was inflated to account
 2719                  * for the other side's cached packets, retract it.
 2720                  */
 2721                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2722                         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
 2723                                 if (tp->t_flags & TF_SACK_PERMIT)
 2724                                         tcp_sack_partialack(tp, th);
 2725                                 else
 2726                                         tcp_newreno_partial_ack(tp, th);
 2727                         } else
 2728                                 cc_post_recovery(tp, th);
 2729                 }
 2730                 /*
 2731                  * If we reach this point, ACK is not a duplicate,
 2732                  *     i.e., it ACKs something we sent.
 2733                  */
 2734                 if (tp->t_flags & TF_NEEDSYN) {
 2735                         /*
 2736                          * T/TCP: Connection was half-synchronized, and our
 2737                          * SYN has been ACK'd (so connection is now fully
 2738                          * synchronized).  Go to non-starred state,
 2739                          * increment snd_una for ACK of SYN, and check if
 2740                          * we can do window scaling.
 2741                          */
 2742                         tp->t_flags &= ~TF_NEEDSYN;
 2743                         tp->snd_una++;
 2744                         /* Do window scaling? */
 2745                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2746                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2747                                 tp->rcv_scale = tp->request_r_scale;
 2748                                 /* Send window already scaled. */
 2749                         }
 2750                 }
 2751 
 2752 process_ACK:
 2753                 INP_WLOCK_ASSERT(tp->t_inpcb);
 2754 
 2755                 acked = BYTES_THIS_ACK(tp, th);
 2756                 KASSERT(acked >= 0, ("%s: acked unexepectedly negative "
 2757                     "(tp->snd_una=%u, th->th_ack=%u, tp=%p, m=%p)", __func__,
 2758                     tp->snd_una, th->th_ack, tp, m));
 2759                 TCPSTAT_INC(tcps_rcvackpack);
 2760                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 2761 
 2762                 /*
 2763                  * If we just performed our first retransmit, and the ACK
 2764                  * arrives within our recovery window, then it was a mistake
 2765                  * to do the retransmit in the first place.  Recover our
 2766                  * original cwnd and ssthresh, and proceed to transmit where
 2767                  * we left off.
 2768                  */
 2769                 if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
 2770                     (int)(ticks - tp->t_badrxtwin) < 0)
 2771                         cc_cong_signal(tp, th, CC_RTO_ERR);
 2772 
 2773                 /*
 2774                  * If we have a timestamp reply, update smoothed
 2775                  * round trip time.  If no timestamp is present but
 2776                  * transmit timer is running and timed sequence
 2777                  * number was acked, update smoothed round trip time.
 2778                  * Since we now have an rtt measurement, cancel the
 2779                  * timer backoff (cf., Phil Karn's retransmit alg.).
 2780                  * Recompute the initial retransmit timer.
 2781                  *
 2782                  * Some boxes send broken timestamp replies
 2783                  * during the SYN+ACK phase, ignore
 2784                  * timestamps of 0 or we could calculate a
 2785                  * huge RTT and blow up the retransmit timer.
 2786                  */
 2787                 if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
 2788                         u_int t;
 2789 
 2790                         t = tcp_ts_getticks() - to.to_tsecr;
 2791                         if (!tp->t_rttlow || tp->t_rttlow > t)
 2792                                 tp->t_rttlow = t;
 2793                         tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
 2794                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
 2795                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
 2796                                 tp->t_rttlow = ticks - tp->t_rtttime;
 2797                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
 2798                 }
 2799 
 2800                 /*
 2801                  * If all outstanding data is acked, stop retransmit
 2802                  * timer and remember to restart (more output or persist).
 2803                  * If there is more data to be acked, restart retransmit
 2804                  * timer, using current (possibly backed-off) value.
 2805                  */
 2806                 if (th->th_ack == tp->snd_max) {
 2807                         tcp_timer_activate(tp, TT_REXMT, 0);
 2808                         needoutput = 1;
 2809                 } else if (!tcp_timer_active(tp, TT_PERSIST))
 2810                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 2811 
 2812                 /*
 2813                  * If no data (only SYN) was ACK'd,
 2814                  *    skip rest of ACK processing.
 2815                  */
 2816                 if (acked == 0)
 2817                         goto step6;
 2818 
 2819                 /*
 2820                  * Let the congestion control algorithm update congestion
 2821                  * control related information. This typically means increasing
 2822                  * the congestion window.
 2823                  */
 2824                 cc_ack_received(tp, th, CC_ACK);
 2825 
 2826                 SOCKBUF_LOCK(&so->so_snd);
 2827                 if (acked > sbavail(&so->so_snd)) {
 2828                         if (tp->snd_wnd >= sbavail(&so->so_snd))
 2829                                 tp->snd_wnd -= sbavail(&so->so_snd);
 2830                         else
 2831                                 tp->snd_wnd = 0;
 2832                         mfree = sbcut_locked(&so->so_snd,
 2833                             (int)sbavail(&so->so_snd));
 2834                         ourfinisacked = 1;
 2835                 } else {
 2836                         mfree = sbcut_locked(&so->so_snd, acked);
 2837                         if (tp->snd_wnd >= (u_long) acked)
 2838                                 tp->snd_wnd -= acked;
 2839                         else
 2840                                 tp->snd_wnd = 0;
 2841                         ourfinisacked = 0;
 2842                 }
 2843                 /* NB: sowwakeup_locked() does an implicit unlock. */
 2844                 sowwakeup_locked(so);
 2845                 m_freem(mfree);
 2846                 /* Detect una wraparound. */
 2847                 if (!IN_RECOVERY(tp->t_flags) &&
 2848                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
 2849                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 2850                         tp->snd_recover = th->th_ack - 1;
 2851                 /* XXXLAS: Can this be moved up into cc_post_recovery? */
 2852                 if (IN_RECOVERY(tp->t_flags) &&
 2853                     SEQ_GEQ(th->th_ack, tp->snd_recover)) {
 2854                         EXIT_RECOVERY(tp->t_flags);
 2855                 }
 2856                 tp->snd_una = th->th_ack;
 2857                 if (tp->t_flags & TF_SACK_PERMIT) {
 2858                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
 2859                                 tp->snd_recover = tp->snd_una;
 2860                 }
 2861                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 2862                         tp->snd_nxt = tp->snd_una;
 2863 
 2864                 switch (tp->t_state) {
 2865 
 2866                 /*
 2867                  * In FIN_WAIT_1 STATE in addition to the processing
 2868                  * for the ESTABLISHED state if our FIN is now acknowledged
 2869                  * then enter FIN_WAIT_2.
 2870                  */
 2871                 case TCPS_FIN_WAIT_1:
 2872                         if (ourfinisacked) {
 2873                                 /*
 2874                                  * If we can't receive any more
 2875                                  * data, then closing user can proceed.
 2876                                  * Starting the timer is contrary to the
 2877                                  * specification, but if we don't get a FIN
 2878                                  * we'll hang forever.
 2879                                  *
 2880                                  * XXXjl:
 2881                                  * we should release the tp also, and use a
 2882                                  * compressed state.
 2883                                  */
 2884                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 2885                                         soisdisconnected(so);
 2886                                         tcp_timer_activate(tp, TT_2MSL,
 2887                                             (tcp_fast_finwait2_recycle ?
 2888                                             tcp_finwait2_timeout :
 2889                                             TP_MAXIDLE(tp)));
 2890                                 }
 2891                                 tcp_state_change(tp, TCPS_FIN_WAIT_2);
 2892                         }
 2893                         break;
 2894 
 2895                 /*
 2896                  * In CLOSING STATE in addition to the processing for
 2897                  * the ESTABLISHED state if the ACK acknowledges our FIN
 2898                  * then enter the TIME-WAIT state, otherwise ignore
 2899                  * the segment.
 2900                  */
 2901                 case TCPS_CLOSING:
 2902                         if (ourfinisacked) {
 2903                                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2904                                 tcp_twstart(tp);
 2905                                 INP_INFO_RUNLOCK(&V_tcbinfo);
 2906                                 m_freem(m);
 2907                                 return;
 2908                         }
 2909                         break;
 2910 
 2911                 /*
 2912                  * In LAST_ACK, we may still be waiting for data to drain
 2913                  * and/or to be acked, as well as for the ack of our FIN.
 2914                  * If our FIN is now acknowledged, delete the TCB,
 2915                  * enter the closed state and return.
 2916                  */
 2917                 case TCPS_LAST_ACK:
 2918                         if (ourfinisacked) {
 2919                                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2920                                 tp = tcp_close(tp);
 2921                                 goto drop;
 2922                         }
 2923                         break;
 2924                 }
 2925         }
 2926 
 2927 step6:
 2928         INP_WLOCK_ASSERT(tp->t_inpcb);
 2929 
 2930         /*
 2931          * Update window information.
 2932          * Don't look at window if no ACK: TAC's send garbage on first SYN.
 2933          */
 2934         if ((thflags & TH_ACK) &&
 2935             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
 2936             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
 2937              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
 2938                 /* keep track of pure window updates */
 2939                 if (tlen == 0 &&
 2940                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
 2941                         TCPSTAT_INC(tcps_rcvwinupd);
 2942                 tp->snd_wnd = tiwin;
 2943                 tp->snd_wl1 = th->th_seq;
 2944                 tp->snd_wl2 = th->th_ack;
 2945                 if (tp->snd_wnd > tp->max_sndwnd)
 2946                         tp->max_sndwnd = tp->snd_wnd;
 2947                 needoutput = 1;
 2948         }
 2949 
 2950         /*
 2951          * Process segments with URG.
 2952          */
 2953         if ((thflags & TH_URG) && th->th_urp &&
 2954             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2955                 /*
 2956                  * This is a kludge, but if we receive and accept
 2957                  * random urgent pointers, we'll crash in
 2958                  * soreceive.  It's hard to imagine someone
 2959                  * actually wanting to send this much urgent data.
 2960                  */
 2961                 SOCKBUF_LOCK(&so->so_rcv);
 2962                 if (th->th_urp + sbavail(&so->so_rcv) > sb_max) {
 2963                         th->th_urp = 0;                 /* XXX */
 2964                         thflags &= ~TH_URG;             /* XXX */
 2965                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
 2966                         goto dodata;                    /* XXX */
 2967                 }
 2968                 /*
 2969                  * If this segment advances the known urgent pointer,
 2970                  * then mark the data stream.  This should not happen
 2971                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
 2972                  * a FIN has been received from the remote side.
 2973                  * In these states we ignore the URG.
 2974                  *
 2975                  * According to RFC961 (Assigned Protocols),
 2976                  * the urgent pointer points to the last octet
 2977                  * of urgent data.  We continue, however,
 2978                  * to consider it to indicate the first octet
 2979                  * of data past the urgent section as the original
 2980                  * spec states (in one of two places).
 2981                  */
 2982                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
 2983                         tp->rcv_up = th->th_seq + th->th_urp;
 2984                         so->so_oobmark = sbavail(&so->so_rcv) +
 2985                             (tp->rcv_up - tp->rcv_nxt) - 1;
 2986                         if (so->so_oobmark == 0)
 2987                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
 2988                         sohasoutofband(so);
 2989                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
 2990                 }
 2991                 SOCKBUF_UNLOCK(&so->so_rcv);
 2992                 /*
 2993                  * Remove out of band data so doesn't get presented to user.
 2994                  * This can happen independent of advancing the URG pointer,
 2995                  * but if two URG's are pending at once, some out-of-band
 2996                  * data may creep in... ick.
 2997                  */
 2998                 if (th->th_urp <= (u_long)tlen &&
 2999                     !(so->so_options & SO_OOBINLINE)) {
 3000                         /* hdr drop is delayed */
 3001                         tcp_pulloutofband(so, th, m, drop_hdrlen);
 3002                 }
 3003         } else {
 3004                 /*
 3005                  * If no out of band data is expected,
 3006                  * pull receive urgent pointer along
 3007                  * with the receive window.
 3008                  */
 3009                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
 3010                         tp->rcv_up = tp->rcv_nxt;
 3011         }
 3012 dodata:                                                 /* XXX */
 3013         INP_WLOCK_ASSERT(tp->t_inpcb);
 3014 
 3015         /*
 3016          * Process the segment text, merging it into the TCP sequencing queue,
 3017          * and arranging for acknowledgment of receipt if necessary.
 3018          * This process logically involves adjusting tp->rcv_wnd as data
 3019          * is presented to the user (this happens in tcp_usrreq.c,
 3020          * case PRU_RCVD).  If a FIN has already been received on this
 3021          * connection then we just ignore the text.
 3022          */
 3023         tfo_syn = ((tp->t_state == TCPS_SYN_RECEIVED) &&
 3024                    (tp->t_flags & TF_FASTOPEN));
 3025         if ((tlen || (thflags & TH_FIN) || tfo_syn) &&
 3026             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 3027                 tcp_seq save_start = th->th_seq;
 3028                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 3029                 /*
 3030                  * Insert segment which includes th into TCP reassembly queue
 3031                  * with control block tp.  Set thflags to whether reassembly now
 3032                  * includes a segment with FIN.  This handles the common case
 3033                  * inline (segment is the next to be received on an established
 3034                  * connection, and the queue is empty), avoiding linkage into
 3035                  * and removal from the queue and repetition of various
 3036                  * conversions.
 3037                  * Set DELACK for segments received in order, but ack
 3038                  * immediately when segments are out of order (so
 3039                  * fast retransmit can work).
 3040                  */
 3041                 if (th->th_seq == tp->rcv_nxt &&
 3042                     LIST_EMPTY(&tp->t_segq) &&
 3043                     (TCPS_HAVEESTABLISHED(tp->t_state) ||
 3044                      tfo_syn)) {
 3045                         if (DELAY_ACK(tp, tlen) || tfo_syn)
 3046                                 tp->t_flags |= TF_DELACK;
 3047                         else
 3048                                 tp->t_flags |= TF_ACKNOW;
 3049                         tp->rcv_nxt += tlen;
 3050                         thflags = th->th_flags & TH_FIN;
 3051                         TCPSTAT_INC(tcps_rcvpack);
 3052                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 3053                         SOCKBUF_LOCK(&so->so_rcv);
 3054                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
 3055                                 m_freem(m);
 3056                         else
 3057                                 sbappendstream_locked(&so->so_rcv, m, 0);
 3058                         /* NB: sorwakeup_locked() does an implicit unlock. */
 3059                         sorwakeup_locked(so);
 3060                 } else {
 3061                         /*
 3062                          * XXX: Due to the header drop above "th" is
 3063                          * theoretically invalid by now.  Fortunately
 3064                          * m_adj() doesn't actually frees any mbufs
 3065                          * when trimming from the head.
 3066                          */
 3067                         thflags = tcp_reass(tp, th, &tlen, m);
 3068                         tp->t_flags |= TF_ACKNOW;
 3069                 }
 3070                 if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
 3071                         tcp_update_sack_list(tp, save_start, save_start + tlen);
 3072 #if 0
 3073                 /*
 3074                  * Note the amount of data that peer has sent into
 3075                  * our window, in order to estimate the sender's
 3076                  * buffer size.
 3077                  * XXX: Unused.
 3078                  */
 3079                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
 3080                         len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
 3081                 else
 3082                         len = so->so_rcv.sb_hiwat;
 3083 #endif
 3084         } else {
 3085                 m_freem(m);
 3086                 thflags &= ~TH_FIN;
 3087         }
 3088 
 3089         /*
 3090          * If FIN is received ACK the FIN and let the user know
 3091          * that the connection is closing.
 3092          */
 3093         if (thflags & TH_FIN) {
 3094                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 3095                         socantrcvmore(so);
 3096                         /*
 3097                          * If connection is half-synchronized
 3098                          * (ie NEEDSYN flag on) then delay ACK,
 3099                          * so it may be piggybacked when SYN is sent.
 3100                          * Otherwise, since we received a FIN then no
 3101                          * more input can be expected, send ACK now.
 3102                          */
 3103                         if (tp->t_flags & TF_NEEDSYN)
 3104                                 tp->t_flags |= TF_DELACK;
 3105                         else
 3106                                 tp->t_flags |= TF_ACKNOW;
 3107                         tp->rcv_nxt++;
 3108                 }
 3109                 switch (tp->t_state) {
 3110 
 3111                 /*
 3112                  * In SYN_RECEIVED and ESTABLISHED STATES
 3113                  * enter the CLOSE_WAIT state.
 3114                  */
 3115                 case TCPS_SYN_RECEIVED:
 3116                         tp->t_starttime = ticks;
 3117                         /* FALLTHROUGH */
 3118                 case TCPS_ESTABLISHED:
 3119                         tcp_state_change(tp, TCPS_CLOSE_WAIT);
 3120                         break;
 3121 
 3122                 /*
 3123                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
 3124                  * enter the CLOSING state.
 3125                  */
 3126                 case TCPS_FIN_WAIT_1:
 3127                         tcp_state_change(tp, TCPS_CLOSING);
 3128                         break;
 3129 
 3130                 /*
 3131                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
 3132                  * starting the time-wait timer, turning off the other
 3133                  * standard timers.
 3134                  */
 3135                 case TCPS_FIN_WAIT_2:
 3136                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 3137                         KASSERT(ti_locked == TI_RLOCKED, ("%s: dodata "
 3138                             "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
 3139                             ti_locked));
 3140 
 3141                         tcp_twstart(tp);
 3142                         INP_INFO_RUNLOCK(&V_tcbinfo);
 3143                         return;
 3144                 }
 3145         }
 3146         if (ti_locked == TI_RLOCKED)
 3147                 INP_INFO_RUNLOCK(&V_tcbinfo);
 3148         ti_locked = TI_UNLOCKED;
 3149 
 3150 #ifdef TCPDEBUG
 3151         if (so->so_options & SO_DEBUG)
 3152                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
 3153                           &tcp_savetcp, 0);
 3154 #endif
 3155         TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
 3156 
 3157         /*
 3158          * Return any desired output.
 3159          */
 3160         if (needoutput || (tp->t_flags & TF_ACKNOW))
 3161                 (void) tp->t_fb->tfb_tcp_output(tp);
 3162 
 3163 check_delack:
 3164         KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
 3165             __func__, ti_locked));
 3166         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3167         INP_WLOCK_ASSERT(tp->t_inpcb);
 3168 
 3169         if (tp->t_flags & TF_DELACK) {
 3170                 tp->t_flags &= ~TF_DELACK;
 3171                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
 3172         }
 3173         INP_WUNLOCK(tp->t_inpcb);
 3174         return;
 3175 
 3176 dropafterack:
 3177         /*
 3178          * Generate an ACK dropping incoming segment if it occupies
 3179          * sequence space, where the ACK reflects our state.
 3180          *
 3181          * We can now skip the test for the RST flag since all
 3182          * paths to this code happen after packets containing
 3183          * RST have been dropped.
 3184          *
 3185          * In the SYN-RECEIVED state, don't send an ACK unless the
 3186          * segment we received passes the SYN-RECEIVED ACK test.
 3187          * If it fails send a RST.  This breaks the loop in the
 3188          * "LAND" DoS attack, and also prevents an ACK storm
 3189          * between two listening ports that have been sent forged
 3190          * SYN segments, each with the source address of the other.
 3191          */
 3192         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
 3193             (SEQ_GT(tp->snd_una, th->th_ack) ||
 3194              SEQ_GT(th->th_ack, tp->snd_max)) ) {
 3195                 rstreason = BANDLIM_RST_OPENPORT;
 3196                 goto dropwithreset;
 3197         }
 3198 #ifdef TCPDEBUG
 3199         if (so->so_options & SO_DEBUG)
 3200                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3201                           &tcp_savetcp, 0);
 3202 #endif
 3203         TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
 3204         if (ti_locked == TI_RLOCKED)
 3205                 INP_INFO_RUNLOCK(&V_tcbinfo);
 3206         ti_locked = TI_UNLOCKED;
 3207 
 3208         tp->t_flags |= TF_ACKNOW;
 3209         (void) tp->t_fb->tfb_tcp_output(tp);
 3210         INP_WUNLOCK(tp->t_inpcb);
 3211         m_freem(m);
 3212         return;
 3213 
 3214 dropwithreset:
 3215         if (ti_locked == TI_RLOCKED)
 3216                 INP_INFO_RUNLOCK(&V_tcbinfo);
 3217         ti_locked = TI_UNLOCKED;
 3218 
 3219         if (tp != NULL) {
 3220                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 3221                 INP_WUNLOCK(tp->t_inpcb);
 3222         } else
 3223                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 3224         return;
 3225 
 3226 drop:
 3227         if (ti_locked == TI_RLOCKED) {
 3228                 INP_INFO_RUNLOCK(&V_tcbinfo);
 3229                 ti_locked = TI_UNLOCKED;
 3230         }
 3231 #ifdef INVARIANTS
 3232         else
 3233                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3234 #endif
 3235 
 3236         /*
 3237          * Drop space held by incoming segment and return.
 3238          */
 3239 #ifdef TCPDEBUG
 3240         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 3241                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3242                           &tcp_savetcp, 0);
 3243 #endif
 3244         TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
 3245         if (tp != NULL)
 3246                 INP_WUNLOCK(tp->t_inpcb);
 3247         m_freem(m);
 3248 }
 3249 
 3250 /*
 3251  * Issue RST and make ACK acceptable to originator of segment.
 3252  * The mbuf must still include the original packet header.
 3253  * tp may be NULL.
 3254  */
 3255 void
 3256 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
 3257     int tlen, int rstreason)
 3258 {
 3259 #ifdef INET
 3260         struct ip *ip;
 3261 #endif
 3262 #ifdef INET6
 3263         struct ip6_hdr *ip6;
 3264 #endif
 3265 
 3266         if (tp != NULL) {
 3267                 INP_WLOCK_ASSERT(tp->t_inpcb);
 3268         }
 3269 
 3270         /* Don't bother if destination was broadcast/multicast. */
 3271         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
 3272                 goto drop;
 3273 #ifdef INET6
 3274         if (mtod(m, struct ip *)->ip_v == 6) {
 3275                 ip6 = mtod(m, struct ip6_hdr *);
 3276                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 3277                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 3278                         goto drop;
 3279                 /* IPv6 anycast check is done at tcp6_input() */
 3280         }
 3281 #endif
 3282 #if defined(INET) && defined(INET6)
 3283         else
 3284 #endif
 3285 #ifdef INET
 3286         {
 3287                 ip = mtod(m, struct ip *);
 3288                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 3289                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 3290                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 3291                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 3292                         goto drop;
 3293         }
 3294 #endif
 3295 
 3296         /* Perform bandwidth limiting. */
 3297         if (badport_bandlim(rstreason) < 0)
 3298                 goto drop;
 3299 
 3300         /* tcp_respond consumes the mbuf chain. */
 3301         if (th->th_flags & TH_ACK) {
 3302                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
 3303                     th->th_ack, TH_RST);
 3304         } else {
 3305                 if (th->th_flags & TH_SYN)
 3306                         tlen++;
 3307                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
 3308                     (tcp_seq)0, TH_RST|TH_ACK);
 3309         }
 3310         return;
 3311 drop:
 3312         m_freem(m);
 3313 }
 3314 
 3315 /*
 3316  * Parse TCP options and place in tcpopt.
 3317  */
 3318 void
 3319 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
 3320 {
 3321         int opt, optlen;
 3322 
 3323         to->to_flags = 0;
 3324         for (; cnt > 0; cnt -= optlen, cp += optlen) {
 3325                 opt = cp[0];
 3326                 if (opt == TCPOPT_EOL)
 3327                         break;
 3328                 if (opt == TCPOPT_NOP)
 3329                         optlen = 1;
 3330                 else {
 3331                         if (cnt < 2)
 3332                                 break;
 3333                         optlen = cp[1];
 3334                         if (optlen < 2 || optlen > cnt)
 3335                                 break;
 3336                 }
 3337                 switch (opt) {
 3338                 case TCPOPT_MAXSEG:
 3339                         if (optlen != TCPOLEN_MAXSEG)
 3340                                 continue;
 3341                         if (!(flags & TO_SYN))
 3342                                 continue;
 3343                         to->to_flags |= TOF_MSS;
 3344                         bcopy((char *)cp + 2,
 3345                             (char *)&to->to_mss, sizeof(to->to_mss));
 3346                         to->to_mss = ntohs(to->to_mss);
 3347                         break;
 3348                 case TCPOPT_WINDOW:
 3349                         if (optlen != TCPOLEN_WINDOW)
 3350                                 continue;
 3351                         if (!(flags & TO_SYN))
 3352                                 continue;
 3353                         to->to_flags |= TOF_SCALE;
 3354                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
 3355                         break;
 3356                 case TCPOPT_TIMESTAMP:
 3357                         if (optlen != TCPOLEN_TIMESTAMP)
 3358                                 continue;
 3359                         to->to_flags |= TOF_TS;
 3360                         bcopy((char *)cp + 2,
 3361                             (char *)&to->to_tsval, sizeof(to->to_tsval));
 3362                         to->to_tsval = ntohl(to->to_tsval);
 3363                         bcopy((char *)cp + 6,
 3364                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
 3365                         to->to_tsecr = ntohl(to->to_tsecr);
 3366                         break;
 3367 #ifdef TCP_SIGNATURE
 3368                 /*
 3369                  * XXX In order to reply to a host which has set the
 3370                  * TCP_SIGNATURE option in its initial SYN, we have to
 3371                  * record the fact that the option was observed here
 3372                  * for the syncache code to perform the correct response.
 3373                  */
 3374                 case TCPOPT_SIGNATURE:
 3375                         if (optlen != TCPOLEN_SIGNATURE)
 3376                                 continue;
 3377                         to->to_flags |= TOF_SIGNATURE;
 3378                         to->to_signature = cp + 2;
 3379                         break;
 3380 #endif
 3381                 case TCPOPT_SACK_PERMITTED:
 3382                         if (optlen != TCPOLEN_SACK_PERMITTED)
 3383                                 continue;
 3384                         if (!(flags & TO_SYN))
 3385                                 continue;
 3386                         if (!V_tcp_do_sack)
 3387                                 continue;
 3388                         to->to_flags |= TOF_SACKPERM;
 3389                         break;
 3390                 case TCPOPT_SACK:
 3391                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
 3392                                 continue;
 3393                         if (flags & TO_SYN)
 3394                                 continue;
 3395                         to->to_flags |= TOF_SACK;
 3396                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
 3397                         to->to_sacks = cp + 2;
 3398                         TCPSTAT_INC(tcps_sack_rcv_blocks);
 3399                         break;
 3400 #ifdef TCP_RFC7413
 3401                 case TCPOPT_FAST_OPEN:
 3402                         if ((optlen != TCPOLEN_FAST_OPEN_EMPTY) &&
 3403                             (optlen < TCPOLEN_FAST_OPEN_MIN) &&
 3404                             (optlen > TCPOLEN_FAST_OPEN_MAX))
 3405                                 continue;
 3406                         if (!(flags & TO_SYN))
 3407                                 continue;
 3408                         if (!V_tcp_fastopen_enabled)
 3409                                 continue;
 3410                         to->to_flags |= TOF_FASTOPEN;
 3411                         to->to_tfo_len = optlen - 2;
 3412                         to->to_tfo_cookie = to->to_tfo_len ? cp + 2 : NULL;
 3413                         break;
 3414 #endif
 3415                 default:
 3416                         continue;
 3417                 }
 3418         }
 3419 }
 3420 
 3421 /*
 3422  * Pull out of band byte out of a segment so
 3423  * it doesn't appear in the user's data queue.
 3424  * It is still reflected in the segment length for
 3425  * sequencing purposes.
 3426  */
 3427 void
 3428 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
 3429     int off)
 3430 {
 3431         int cnt = off + th->th_urp - 1;
 3432 
 3433         while (cnt >= 0) {
 3434                 if (m->m_len > cnt) {
 3435                         char *cp = mtod(m, caddr_t) + cnt;
 3436                         struct tcpcb *tp = sototcpcb(so);
 3437 
 3438                         INP_WLOCK_ASSERT(tp->t_inpcb);
 3439 
 3440                         tp->t_iobc = *cp;
 3441                         tp->t_oobflags |= TCPOOB_HAVEDATA;
 3442                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
 3443                         m->m_len--;
 3444                         if (m->m_flags & M_PKTHDR)
 3445                                 m->m_pkthdr.len--;
 3446                         return;
 3447                 }
 3448                 cnt -= m->m_len;
 3449                 m = m->m_next;
 3450                 if (m == NULL)
 3451                         break;
 3452         }
 3453         panic("tcp_pulloutofband");
 3454 }
 3455 
 3456 /*
 3457  * Collect new round-trip time estimate
 3458  * and update averages and current timeout.
 3459  */
 3460 void
 3461 tcp_xmit_timer(struct tcpcb *tp, int rtt)
 3462 {
 3463         int delta;
 3464 
 3465         INP_WLOCK_ASSERT(tp->t_inpcb);
 3466 
 3467         TCPSTAT_INC(tcps_rttupdated);
 3468         tp->t_rttupdated++;
 3469         if (tp->t_srtt != 0) {
 3470                 /*
 3471                  * srtt is stored as fixed point with 5 bits after the
 3472                  * binary point (i.e., scaled by 8).  The following magic
 3473                  * is equivalent to the smoothing algorithm in rfc793 with
 3474                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
 3475                  * point).  Adjust rtt to origin 0.
 3476                  */
 3477                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
 3478                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
 3479 
 3480                 if ((tp->t_srtt += delta) <= 0)
 3481                         tp->t_srtt = 1;
 3482 
 3483                 /*
 3484                  * We accumulate a smoothed rtt variance (actually, a
 3485                  * smoothed mean difference), then set the retransmit
 3486                  * timer to smoothed rtt + 4 times the smoothed variance.
 3487                  * rttvar is stored as fixed point with 4 bits after the
 3488                  * binary point (scaled by 16).  The following is
 3489                  * equivalent to rfc793 smoothing with an alpha of .75
 3490                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
 3491                  * rfc793's wired-in beta.
 3492                  */
 3493                 if (delta < 0)
 3494                         delta = -delta;
 3495                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
 3496                 if ((tp->t_rttvar += delta) <= 0)
 3497                         tp->t_rttvar = 1;
 3498                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
 3499                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3500         } else {
 3501                 /*
 3502                  * No rtt measurement yet - use the unsmoothed rtt.
 3503                  * Set the variance to half the rtt (so our first
 3504                  * retransmit happens at 3*rtt).
 3505                  */
 3506                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
 3507                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
 3508                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3509         }
 3510         tp->t_rtttime = 0;
 3511         tp->t_rxtshift = 0;
 3512 
 3513         /*
 3514          * the retransmit should happen at rtt + 4 * rttvar.
 3515          * Because of the way we do the smoothing, srtt and rttvar
 3516          * will each average +1/2 tick of bias.  When we compute
 3517          * the retransmit timer, we want 1/2 tick of rounding and
 3518          * 1 extra tick because of +-1/2 tick uncertainty in the
 3519          * firing of the timer.  The bias will give us exactly the
 3520          * 1.5 tick we need.  But, because the bias is
 3521          * statistical, we have to test that we don't drop below
 3522          * the minimum feasible timer (which is 2 ticks).
 3523          */
 3524         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
 3525                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
 3526 
 3527         /*
 3528          * We received an ack for a packet that wasn't retransmitted;
 3529          * it is probably safe to discard any error indications we've
 3530          * received recently.  This isn't quite right, but close enough
 3531          * for now (a route might have failed after we sent a segment,
 3532          * and the return path might not be symmetrical).
 3533          */
 3534         tp->t_softerror = 0;
 3535 }
 3536 
 3537 /*
 3538  * Determine a reasonable value for maxseg size.
 3539  * If the route is known, check route for mtu.
 3540  * If none, use an mss that can be handled on the outgoing interface
 3541  * without forcing IP to fragment.  If no route is found, route has no mtu,
 3542  * or the destination isn't local, use a default, hopefully conservative
 3543  * size (usually 512 or the default IP max size, but no more than the mtu
 3544  * of the interface), as we can't discover anything about intervening
 3545  * gateways or networks.  We also initialize the congestion/slow start
 3546  * window to be a single segment if the destination isn't local.
 3547  * While looking at the routing entry, we also initialize other path-dependent
 3548  * parameters from pre-set or cached values in the routing entry.
 3549  *
 3550  * NOTE that resulting t_maxseg doesn't include space for TCP options or
 3551  * IP options, e.g. IPSEC data, since length of this data may vary, and
 3552  * thus it is calculated for every segment separately in tcp_output().
 3553  *
 3554  * NOTE that this routine is only called when we process an incoming
 3555  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
 3556  * settings are handled in tcp_mssopt().
 3557  */
 3558 void
 3559 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
 3560     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
 3561 {
 3562         int mss = 0;
 3563         u_long maxmtu = 0;
 3564         struct inpcb *inp = tp->t_inpcb;
 3565         struct hc_metrics_lite metrics;
 3566 #ifdef INET6
 3567         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
 3568         size_t min_protoh = isipv6 ?
 3569                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
 3570                             sizeof (struct tcpiphdr);
 3571 #else
 3572         const size_t min_protoh = sizeof(struct tcpiphdr);
 3573 #endif
 3574 
 3575         INP_WLOCK_ASSERT(tp->t_inpcb);
 3576 
 3577         if (mtuoffer != -1) {
 3578                 KASSERT(offer == -1, ("%s: conflict", __func__));
 3579                 offer = mtuoffer - min_protoh;
 3580         }
 3581 
 3582         /* Initialize. */
 3583 #ifdef INET6
 3584         if (isipv6) {
 3585                 maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
 3586                 tp->t_maxseg = V_tcp_v6mssdflt;
 3587         }
 3588 #endif
 3589 #if defined(INET) && defined(INET6)
 3590         else
 3591 #endif
 3592 #ifdef INET
 3593         {
 3594                 maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
 3595                 tp->t_maxseg = V_tcp_mssdflt;
 3596         }
 3597 #endif
 3598 
 3599         /*
 3600          * No route to sender, stay with default mss and return.
 3601          */
 3602         if (maxmtu == 0) {
 3603                 /*
 3604                  * In case we return early we need to initialize metrics
 3605                  * to a defined state as tcp_hc_get() would do for us
 3606                  * if there was no cache hit.
 3607                  */
 3608                 if (metricptr != NULL)
 3609                         bzero(metricptr, sizeof(struct hc_metrics_lite));
 3610                 return;
 3611         }
 3612 
 3613         /* What have we got? */
 3614         switch (offer) {
 3615                 case 0:
 3616                         /*
 3617                          * Offer == 0 means that there was no MSS on the SYN
 3618                          * segment, in this case we use tcp_mssdflt as
 3619                          * already assigned to t_maxseg above.
 3620                          */
 3621                         offer = tp->t_maxseg;
 3622                         break;
 3623 
 3624                 case -1:
 3625                         /*
 3626                          * Offer == -1 means that we didn't receive SYN yet.
 3627                          */
 3628                         /* FALLTHROUGH */
 3629 
 3630                 default:
 3631                         /*
 3632                          * Prevent DoS attack with too small MSS. Round up
 3633                          * to at least minmss.
 3634                          */
 3635                         offer = max(offer, V_tcp_minmss);
 3636         }
 3637 
 3638         /*
 3639          * rmx information is now retrieved from tcp_hostcache.
 3640          */
 3641         tcp_hc_get(&inp->inp_inc, &metrics);
 3642         if (metricptr != NULL)
 3643                 bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
 3644 
 3645         /*
 3646          * If there's a discovered mtu in tcp hostcache, use it.
 3647          * Else, use the link mtu.
 3648          */
 3649         if (metrics.rmx_mtu)
 3650                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
 3651         else {
 3652 #ifdef INET6
 3653                 if (isipv6) {
 3654                         mss = maxmtu - min_protoh;
 3655                         if (!V_path_mtu_discovery &&
 3656                             !in6_localaddr(&inp->in6p_faddr))
 3657                                 mss = min(mss, V_tcp_v6mssdflt);
 3658                 }
 3659 #endif
 3660 #if defined(INET) && defined(INET6)
 3661                 else
 3662 #endif
 3663 #ifdef INET
 3664                 {
 3665                         mss = maxmtu - min_protoh;
 3666                         if (!V_path_mtu_discovery &&
 3667                             !in_localaddr(inp->inp_faddr))
 3668                                 mss = min(mss, V_tcp_mssdflt);
 3669                 }
 3670 #endif
 3671                 /*
 3672                  * XXX - The above conditional (mss = maxmtu - min_protoh)
 3673                  * probably violates the TCP spec.
 3674                  * The problem is that, since we don't know the
 3675                  * other end's MSS, we are supposed to use a conservative
 3676                  * default.  But, if we do that, then MTU discovery will
 3677                  * never actually take place, because the conservative
 3678                  * default is much less than the MTUs typically seen
 3679                  * on the Internet today.  For the moment, we'll sweep
 3680                  * this under the carpet.
 3681                  *
 3682                  * The conservative default might not actually be a problem
 3683                  * if the only case this occurs is when sending an initial
 3684                  * SYN with options and data to a host we've never talked
 3685                  * to before.  Then, they will reply with an MSS value which
 3686                  * will get recorded and the new parameters should get
 3687                  * recomputed.  For Further Study.
 3688                  */
 3689         }
 3690         mss = min(mss, offer);
 3691 
 3692         /*
 3693          * Sanity check: make sure that maxseg will be large
 3694          * enough to allow some data on segments even if the
 3695          * all the option space is used (40bytes).  Otherwise
 3696          * funny things may happen in tcp_output.
 3697          *
 3698          * XXXGL: shouldn't we reserve space for IP/IPv6 options?
 3699          */
 3700         mss = max(mss, 64);
 3701 
 3702         tp->t_maxseg = mss;
 3703 }
 3704 
 3705 void
 3706 tcp_mss(struct tcpcb *tp, int offer)
 3707 {
 3708         int mss;
 3709         u_long bufsize;
 3710         struct inpcb *inp;
 3711         struct socket *so;
 3712         struct hc_metrics_lite metrics;
 3713         struct tcp_ifcap cap;
 3714 
 3715         KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
 3716 
 3717         bzero(&cap, sizeof(cap));
 3718         tcp_mss_update(tp, offer, -1, &metrics, &cap);
 3719 
 3720         mss = tp->t_maxseg;
 3721         inp = tp->t_inpcb;
 3722 
 3723         /*
 3724          * If there's a pipesize, change the socket buffer to that size,
 3725          * don't change if sb_hiwat is different than default (then it
 3726          * has been changed on purpose with setsockopt).
 3727          * Make the socket buffers an integral number of mss units;
 3728          * if the mss is larger than the socket buffer, decrease the mss.
 3729          */
 3730         so = inp->inp_socket;
 3731         SOCKBUF_LOCK(&so->so_snd);
 3732         if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
 3733                 bufsize = metrics.rmx_sendpipe;
 3734         else
 3735                 bufsize = so->so_snd.sb_hiwat;
 3736         if (bufsize < mss)
 3737                 mss = bufsize;
 3738         else {
 3739                 bufsize = roundup(bufsize, mss);
 3740                 if (bufsize > sb_max)
 3741                         bufsize = sb_max;
 3742                 if (bufsize > so->so_snd.sb_hiwat)
 3743                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
 3744         }
 3745         SOCKBUF_UNLOCK(&so->so_snd);
 3746         tp->t_maxseg = mss;
 3747 
 3748         SOCKBUF_LOCK(&so->so_rcv);
 3749         if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
 3750                 bufsize = metrics.rmx_recvpipe;
 3751         else
 3752                 bufsize = so->so_rcv.sb_hiwat;
 3753         if (bufsize > mss) {
 3754                 bufsize = roundup(bufsize, mss);
 3755                 if (bufsize > sb_max)
 3756                         bufsize = sb_max;
 3757                 if (bufsize > so->so_rcv.sb_hiwat)
 3758                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
 3759         }
 3760         SOCKBUF_UNLOCK(&so->so_rcv);
 3761 
 3762         /* Check the interface for TSO capabilities. */
 3763         if (cap.ifcap & CSUM_TSO) {
 3764                 tp->t_flags |= TF_TSO;
 3765                 tp->t_tsomax = cap.tsomax;
 3766                 tp->t_tsomaxsegcount = cap.tsomaxsegcount;
 3767                 tp->t_tsomaxsegsize = cap.tsomaxsegsize;
 3768         }
 3769 }
 3770 
 3771 /*
 3772  * Determine the MSS option to send on an outgoing SYN.
 3773  */
 3774 int
 3775 tcp_mssopt(struct in_conninfo *inc)
 3776 {
 3777         int mss = 0;
 3778         u_long maxmtu = 0;
 3779         u_long thcmtu = 0;
 3780         size_t min_protoh;
 3781 
 3782         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
 3783 
 3784 #ifdef INET6
 3785         if (inc->inc_flags & INC_ISIPV6) {
 3786                 mss = V_tcp_v6mssdflt;
 3787                 maxmtu = tcp_maxmtu6(inc, NULL);
 3788                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
 3789         }
 3790 #endif
 3791 #if defined(INET) && defined(INET6)
 3792         else
 3793 #endif
 3794 #ifdef INET
 3795         {
 3796                 mss = V_tcp_mssdflt;
 3797                 maxmtu = tcp_maxmtu(inc, NULL);
 3798                 min_protoh = sizeof(struct tcpiphdr);
 3799         }
 3800 #endif
 3801 #if defined(INET6) || defined(INET)
 3802         thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
 3803 #endif
 3804 
 3805         if (maxmtu && thcmtu)
 3806                 mss = min(maxmtu, thcmtu) - min_protoh;
 3807         else if (maxmtu || thcmtu)
 3808                 mss = max(maxmtu, thcmtu) - min_protoh;
 3809 
 3810         return (mss);
 3811 }
 3812 
 3813 
 3814 /*
 3815  * On a partial ack arrives, force the retransmission of the
 3816  * next unacknowledged segment.  Do not clear tp->t_dupacks.
 3817  * By setting snd_nxt to ti_ack, this forces retransmission timer to
 3818  * be started again.
 3819  */
 3820 void
 3821 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
 3822 {
 3823         tcp_seq onxt = tp->snd_nxt;
 3824         u_long ocwnd = tp->snd_cwnd;
 3825         u_int maxseg = tcp_maxseg(tp);
 3826 
 3827         INP_WLOCK_ASSERT(tp->t_inpcb);
 3828 
 3829         tcp_timer_activate(tp, TT_REXMT, 0);
 3830         tp->t_rtttime = 0;
 3831         tp->snd_nxt = th->th_ack;
 3832         /*
 3833          * Set snd_cwnd to one segment beyond acknowledged offset.
 3834          * (tp->snd_una has not yet been updated when this function is called.)
 3835          */
 3836         tp->snd_cwnd = maxseg + BYTES_THIS_ACK(tp, th);
 3837         tp->t_flags |= TF_ACKNOW;
 3838         (void) tp->t_fb->tfb_tcp_output(tp);
 3839         tp->snd_cwnd = ocwnd;
 3840         if (SEQ_GT(onxt, tp->snd_nxt))
 3841                 tp->snd_nxt = onxt;
 3842         /*
 3843          * Partial window deflation.  Relies on fact that tp->snd_una
 3844          * not updated yet.
 3845          */
 3846         if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
 3847                 tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
 3848         else
 3849                 tp->snd_cwnd = 0;
 3850         tp->snd_cwnd += maxseg;
 3851 }
 3852 
 3853 int
 3854 tcp_compute_pipe(struct tcpcb *tp)
 3855 {
 3856         return (tp->snd_max - tp->snd_una +
 3857                 tp->sackhint.sack_bytes_rexmit -
 3858                 tp->sackhint.sacked_bytes);
 3859 }

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