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 286227 2015-08-03 12:13:54Z jch $");
   52 
   53 #include "opt_ipfw.h"           /* for ipfw_fwd */
   54 #include "opt_inet.h"
   55 #include "opt_inet6.h"
   56 #include "opt_ipsec.h"
   57 #include "opt_tcpdebug.h"
   58 
   59 #include <sys/param.h>
   60 #include <sys/kernel.h>
   61 #include <sys/hhook.h>
   62 #include <sys/malloc.h>
   63 #include <sys/mbuf.h>
   64 #include <sys/proc.h>           /* for proc0 declaration */
   65 #include <sys/protosw.h>
   66 #include <sys/sdt.h>
   67 #include <sys/signalvar.h>
   68 #include <sys/socket.h>
   69 #include <sys/socketvar.h>
   70 #include <sys/sysctl.h>
   71 #include <sys/syslog.h>
   72 #include <sys/systm.h>
   73 
   74 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
   75 
   76 #include <vm/uma.h>
   77 
   78 #include <net/if.h>
   79 #include <net/if_var.h>
   80 #include <net/route.h>
   81 #include <net/vnet.h>
   82 
   83 #define TCPSTATES               /* for logging */
   84 
   85 #include <netinet/cc.h>
   86 #include <netinet/in.h>
   87 #include <netinet/in_kdtrace.h>
   88 #include <netinet/in_pcb.h>
   89 #include <netinet/in_systm.h>
   90 #include <netinet/in_var.h>
   91 #include <netinet/ip.h>
   92 #include <netinet/ip_icmp.h>    /* required for icmp_var.h */
   93 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
   94 #include <netinet/ip_var.h>
   95 #include <netinet/ip_options.h>
   96 #include <netinet/ip6.h>
   97 #include <netinet/icmp6.h>
   98 #include <netinet6/in6_pcb.h>
   99 #include <netinet6/ip6_var.h>
  100 #include <netinet6/nd6.h>
  101 #include <netinet/tcp_fsm.h>
  102 #include <netinet/tcp_seq.h>
  103 #include <netinet/tcp_timer.h>
  104 #include <netinet/tcp_var.h>
  105 #include <netinet6/tcp6_var.h>
  106 #include <netinet/tcpip.h>
  107 #include <netinet/tcp_syncache.h>
  108 #ifdef TCPDEBUG
  109 #include <netinet/tcp_debug.h>
  110 #endif /* TCPDEBUG */
  111 #ifdef TCP_OFFLOAD
  112 #include <netinet/tcp_offload.h>
  113 #endif
  114 
  115 #ifdef IPSEC
  116 #include <netipsec/ipsec.h>
  117 #include <netipsec/ipsec6.h>
  118 #endif /*IPSEC*/
  119 
  120 #include <machine/in_cksum.h>
  121 
  122 #include <security/mac/mac_framework.h>
  123 
  124 const int tcprexmtthresh = 3;
  125 
  126 int tcp_log_in_vain = 0;
  127 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
  128     &tcp_log_in_vain, 0,
  129     "Log all incoming TCP segments to closed ports");
  130 
  131 VNET_DEFINE(int, blackhole) = 0;
  132 #define V_blackhole             VNET(blackhole)
  133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_VNET | CTLFLAG_RW,
  134     &VNET_NAME(blackhole), 0,
  135     "Do not send RST on segments to closed ports");
  136 
  137 VNET_DEFINE(int, tcp_delack_enabled) = 1;
  138 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_VNET | CTLFLAG_RW,
  139     &VNET_NAME(tcp_delack_enabled), 0,
  140     "Delay ACK to try and piggyback it onto a data packet");
  141 
  142 VNET_DEFINE(int, drop_synfin) = 0;
  143 #define V_drop_synfin           VNET(drop_synfin)
  144 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_VNET | CTLFLAG_RW,
  145     &VNET_NAME(drop_synfin), 0,
  146     "Drop TCP packets with SYN+FIN set");
  147 
  148 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
  149 #define V_tcp_do_rfc3042        VNET(tcp_do_rfc3042)
  150 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_VNET | CTLFLAG_RW,
  151     &VNET_NAME(tcp_do_rfc3042), 0,
  152     "Enable RFC 3042 (Limited Transmit)");
  153 
  154 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
  155 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_VNET | CTLFLAG_RW,
  156     &VNET_NAME(tcp_do_rfc3390), 0,
  157     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
  158 
  159 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, experimental, CTLFLAG_RW, 0,
  160     "Experimental TCP extensions");
  161 
  162 VNET_DEFINE(int, tcp_do_initcwnd10) = 1;
  163 SYSCTL_INT(_net_inet_tcp_experimental, OID_AUTO, initcwnd10, CTLFLAG_VNET | CTLFLAG_RW,
  164     &VNET_NAME(tcp_do_initcwnd10), 0,
  165     "Enable RFC 6928 (Increasing initial CWND to 10)");
  166 
  167 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
  168 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_VNET | CTLFLAG_RW,
  169     &VNET_NAME(tcp_do_rfc3465), 0,
  170     "Enable RFC 3465 (Appropriate Byte Counting)");
  171 
  172 VNET_DEFINE(int, tcp_abc_l_var) = 2;
  173 SYSCTL_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_VNET | CTLFLAG_RW,
  174     &VNET_NAME(tcp_abc_l_var), 2,
  175     "Cap the max cwnd increment during slow-start to this number of segments");
  176 
  177 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
  178 
  179 VNET_DEFINE(int, tcp_do_ecn) = 0;
  180 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
  181     &VNET_NAME(tcp_do_ecn), 0,
  182     "TCP ECN support");
  183 
  184 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
  185 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_VNET | CTLFLAG_RW,
  186     &VNET_NAME(tcp_ecn_maxretries), 0,
  187     "Max retries before giving up on ECN");
  188 
  189 VNET_DEFINE(int, tcp_insecure_syn) = 0;
  190 #define V_tcp_insecure_syn      VNET(tcp_insecure_syn)
  191 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
  192     &VNET_NAME(tcp_insecure_syn), 0,
  193     "Follow RFC793 instead of RFC5961 criteria for accepting SYN packets");
  194 
  195 VNET_DEFINE(int, tcp_insecure_rst) = 0;
  196 #define V_tcp_insecure_rst      VNET(tcp_insecure_rst)
  197 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_VNET | CTLFLAG_RW,
  198     &VNET_NAME(tcp_insecure_rst), 0,
  199     "Follow RFC793 instead of RFC5961 criteria for accepting RST packets");
  200 
  201 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
  202 #define V_tcp_recvspace VNET(tcp_recvspace)
  203 SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_VNET | CTLFLAG_RW,
  204     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
  205 
  206 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
  207 #define V_tcp_do_autorcvbuf     VNET(tcp_do_autorcvbuf)
  208 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
  209     &VNET_NAME(tcp_do_autorcvbuf), 0,
  210     "Enable automatic receive buffer sizing");
  211 
  212 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
  213 #define V_tcp_autorcvbuf_inc    VNET(tcp_autorcvbuf_inc)
  214 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
  215     &VNET_NAME(tcp_autorcvbuf_inc), 0,
  216     "Incrementor step size of automatic receive buffer");
  217 
  218 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
  219 #define V_tcp_autorcvbuf_max    VNET(tcp_autorcvbuf_max)
  220 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
  221     &VNET_NAME(tcp_autorcvbuf_max), 0,
  222     "Max size of automatic receive buffer");
  223 
  224 VNET_DEFINE(struct inpcbhead, tcb);
  225 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
  226 VNET_DEFINE(struct inpcbinfo, tcbinfo);
  227 
  228 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
  229 static void      tcp_do_segment(struct mbuf *, struct tcphdr *,
  230                      struct socket *, struct tcpcb *, int, int, uint8_t,
  231                      int);
  232 static void      tcp_dropwithreset(struct mbuf *, struct tcphdr *,
  233                      struct tcpcb *, int, int);
  234 static void      tcp_pulloutofband(struct socket *,
  235                      struct tcphdr *, struct mbuf *, int);
  236 static void      tcp_xmit_timer(struct tcpcb *, int);
  237 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
  238 static void inline      cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
  239                             uint16_t type);
  240 static void inline      cc_conn_init(struct tcpcb *tp);
  241 static void inline      cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
  242 static void inline      hhook_run_tcp_est_in(struct tcpcb *tp,
  243                             struct tcphdr *th, struct tcpopt *to);
  244 
  245 /*
  246  * TCP statistics are stored in an "array" of counter(9)s.
  247  */
  248 VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
  249 VNET_PCPUSTAT_SYSINIT(tcpstat);
  250 SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
  251     tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
  252 
  253 #ifdef VIMAGE
  254 VNET_PCPUSTAT_SYSUNINIT(tcpstat);
  255 #endif /* VIMAGE */
  256 /*
  257  * Kernel module interface for updating tcpstat.  The argument is an index
  258  * into tcpstat treated as an array.
  259  */
  260 void
  261 kmod_tcpstat_inc(int statnum)
  262 {
  263 
  264         counter_u64_add(VNET(tcpstat)[statnum], 1);
  265 }
  266 
  267 /*
  268  * Wrapper for the TCP established input helper hook.
  269  */
  270 static void inline
  271 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
  272 {
  273         struct tcp_hhook_data hhook_data;
  274 
  275         if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
  276                 hhook_data.tp = tp;
  277                 hhook_data.th = th;
  278                 hhook_data.to = to;
  279 
  280                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
  281                     tp->osd);
  282         }
  283 }
  284 
  285 /*
  286  * CC wrapper hook functions
  287  */
  288 static void inline
  289 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type)
  290 {
  291         INP_WLOCK_ASSERT(tp->t_inpcb);
  292 
  293         tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
  294         if (tp->snd_cwnd <= tp->snd_wnd)
  295                 tp->ccv->flags |= CCF_CWND_LIMITED;
  296         else
  297                 tp->ccv->flags &= ~CCF_CWND_LIMITED;
  298 
  299         if (type == CC_ACK) {
  300                 if (tp->snd_cwnd > tp->snd_ssthresh) {
  301                         tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
  302                              V_tcp_abc_l_var * tp->t_maxseg);
  303                         if (tp->t_bytes_acked >= tp->snd_cwnd) {
  304                                 tp->t_bytes_acked -= tp->snd_cwnd;
  305                                 tp->ccv->flags |= CCF_ABC_SENTAWND;
  306                         }
  307                 } else {
  308                                 tp->ccv->flags &= ~CCF_ABC_SENTAWND;
  309                                 tp->t_bytes_acked = 0;
  310                 }
  311         }
  312 
  313         if (CC_ALGO(tp)->ack_received != NULL) {
  314                 /* XXXLAS: Find a way to live without this */
  315                 tp->ccv->curack = th->th_ack;
  316                 CC_ALGO(tp)->ack_received(tp->ccv, type);
  317         }
  318 }
  319 
  320 static void inline
  321 cc_conn_init(struct tcpcb *tp)
  322 {
  323         struct hc_metrics_lite metrics;
  324         struct inpcb *inp = tp->t_inpcb;
  325         int rtt;
  326 
  327         INP_WLOCK_ASSERT(tp->t_inpcb);
  328 
  329         tcp_hc_get(&inp->inp_inc, &metrics);
  330 
  331         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
  332                 tp->t_srtt = rtt;
  333                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
  334                 TCPSTAT_INC(tcps_usedrtt);
  335                 if (metrics.rmx_rttvar) {
  336                         tp->t_rttvar = metrics.rmx_rttvar;
  337                         TCPSTAT_INC(tcps_usedrttvar);
  338                 } else {
  339                         /* default variation is +- 1 rtt */
  340                         tp->t_rttvar =
  341                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
  342                 }
  343                 TCPT_RANGESET(tp->t_rxtcur,
  344                     ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
  345                     tp->t_rttmin, TCPTV_REXMTMAX);
  346         }
  347         if (metrics.rmx_ssthresh) {
  348                 /*
  349                  * There's some sort of gateway or interface
  350                  * buffer limit on the path.  Use this to set
  351                  * the slow start threshhold, but set the
  352                  * threshold to no less than 2*mss.
  353                  */
  354                 tp->snd_ssthresh = max(2 * tp->t_maxseg, metrics.rmx_ssthresh);
  355                 TCPSTAT_INC(tcps_usedssthresh);
  356         }
  357 
  358         /*
  359          * Set the initial slow-start flight size.
  360          *
  361          * RFC5681 Section 3.1 specifies the default conservative values.
  362          * RFC3390 specifies slightly more aggressive values.
  363          * RFC6928 increases it to ten segments.
  364          *
  365          * If a SYN or SYN/ACK was lost and retransmitted, we have to
  366          * reduce the initial CWND to one segment as congestion is likely
  367          * requiring us to be cautious.
  368          */
  369         if (tp->snd_cwnd == 1)
  370                 tp->snd_cwnd = tp->t_maxseg;            /* SYN(-ACK) lost */
  371         else if (V_tcp_do_initcwnd10)
  372                 tp->snd_cwnd = min(10 * tp->t_maxseg,
  373                     max(2 * tp->t_maxseg, 14600));
  374         else if (V_tcp_do_rfc3390)
  375                 tp->snd_cwnd = min(4 * tp->t_maxseg,
  376                     max(2 * tp->t_maxseg, 4380));
  377         else {
  378                 /* Per RFC5681 Section 3.1 */
  379                 if (tp->t_maxseg > 2190)
  380                         tp->snd_cwnd = 2 * tp->t_maxseg;
  381                 else if (tp->t_maxseg > 1095)
  382                         tp->snd_cwnd = 3 * tp->t_maxseg;
  383                 else
  384                         tp->snd_cwnd = 4 * tp->t_maxseg;
  385         }
  386 
  387         if (CC_ALGO(tp)->conn_init != NULL)
  388                 CC_ALGO(tp)->conn_init(tp->ccv);
  389 }
  390 
  391 void inline
  392 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
  393 {
  394         INP_WLOCK_ASSERT(tp->t_inpcb);
  395 
  396         switch(type) {
  397         case CC_NDUPACK:
  398                 if (!IN_FASTRECOVERY(tp->t_flags)) {
  399                         tp->snd_recover = tp->snd_max;
  400                         if (tp->t_flags & TF_ECN_PERMIT)
  401                                 tp->t_flags |= TF_ECN_SND_CWR;
  402                 }
  403                 break;
  404         case CC_ECN:
  405                 if (!IN_CONGRECOVERY(tp->t_flags)) {
  406                         TCPSTAT_INC(tcps_ecn_rcwnd);
  407                         tp->snd_recover = tp->snd_max;
  408                         if (tp->t_flags & TF_ECN_PERMIT)
  409                                 tp->t_flags |= TF_ECN_SND_CWR;
  410                 }
  411                 break;
  412         case CC_RTO:
  413                 tp->t_dupacks = 0;
  414                 tp->t_bytes_acked = 0;
  415                 EXIT_RECOVERY(tp->t_flags);
  416                 tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
  417                     tp->t_maxseg) * tp->t_maxseg;
  418                 tp->snd_cwnd = tp->t_maxseg;
  419                 break;
  420         case CC_RTO_ERR:
  421                 TCPSTAT_INC(tcps_sndrexmitbad);
  422                 /* RTO was unnecessary, so reset everything. */
  423                 tp->snd_cwnd = tp->snd_cwnd_prev;
  424                 tp->snd_ssthresh = tp->snd_ssthresh_prev;
  425                 tp->snd_recover = tp->snd_recover_prev;
  426                 if (tp->t_flags & TF_WASFRECOVERY)
  427                         ENTER_FASTRECOVERY(tp->t_flags);
  428                 if (tp->t_flags & TF_WASCRECOVERY)
  429                         ENTER_CONGRECOVERY(tp->t_flags);
  430                 tp->snd_nxt = tp->snd_max;
  431                 tp->t_flags &= ~TF_PREVVALID;
  432                 tp->t_badrxtwin = 0;
  433                 break;
  434         }
  435 
  436         if (CC_ALGO(tp)->cong_signal != NULL) {
  437                 if (th != NULL)
  438                         tp->ccv->curack = th->th_ack;
  439                 CC_ALGO(tp)->cong_signal(tp->ccv, type);
  440         }
  441 }
  442 
  443 static void inline
  444 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
  445 {
  446         INP_WLOCK_ASSERT(tp->t_inpcb);
  447 
  448         /* XXXLAS: KASSERT that we're in recovery? */
  449 
  450         if (CC_ALGO(tp)->post_recovery != NULL) {
  451                 tp->ccv->curack = th->th_ack;
  452                 CC_ALGO(tp)->post_recovery(tp->ccv);
  453         }
  454         /* XXXLAS: EXIT_RECOVERY ? */
  455         tp->t_bytes_acked = 0;
  456 }
  457 
  458 #ifdef TCP_SIGNATURE
  459 static inline int
  460 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
  461     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
  462 {
  463         int ret;
  464 
  465         tcp_fields_to_net(th);
  466         ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
  467         tcp_fields_to_host(th);
  468         return (ret);
  469 }
  470 #endif
  471 
  472 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
  473 #ifdef INET6
  474 #define ND6_HINT(tp) \
  475 do { \
  476         if ((tp) && (tp)->t_inpcb && \
  477             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
  478                 nd6_nud_hint(NULL, NULL, 0); \
  479 } while (0)
  480 #else
  481 #define ND6_HINT(tp)
  482 #endif
  483 
  484 /*
  485  * Indicate whether this ack should be delayed.  We can delay the ack if
  486  * following conditions are met:
  487  *      - There is no delayed ack timer in progress.
  488  *      - Our last ack wasn't a 0-sized window. We never want to delay
  489  *        the ack that opens up a 0-sized window.
  490  *      - LRO wasn't used for this segment. We make sure by checking that the
  491  *        segment size is not larger than the MSS.
  492  *      - Delayed acks are enabled or this is a half-synchronized T/TCP
  493  *        connection.
  494  */
  495 #define DELAY_ACK(tp, tlen)                                             \
  496         ((!tcp_timer_active(tp, TT_DELACK) &&                           \
  497             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
  498             (tlen <= tp->t_maxopd) &&                                   \
  499             (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
  500 
  501 static void inline
  502 cc_ecnpkt_handler(struct tcpcb *tp, struct tcphdr *th, uint8_t iptos)
  503 {
  504         INP_WLOCK_ASSERT(tp->t_inpcb);
  505 
  506         if (CC_ALGO(tp)->ecnpkt_handler != NULL) {
  507                 switch (iptos & IPTOS_ECN_MASK) {
  508                 case IPTOS_ECN_CE:
  509                     tp->ccv->flags |= CCF_IPHDR_CE;
  510                     break;
  511                 case IPTOS_ECN_ECT0:
  512                     tp->ccv->flags &= ~CCF_IPHDR_CE;
  513                     break;
  514                 case IPTOS_ECN_ECT1:
  515                     tp->ccv->flags &= ~CCF_IPHDR_CE;
  516                     break;
  517                 }
  518 
  519                 if (th->th_flags & TH_CWR)
  520                         tp->ccv->flags |= CCF_TCPHDR_CWR;
  521                 else
  522                         tp->ccv->flags &= ~CCF_TCPHDR_CWR;
  523 
  524                 if (tp->t_flags & TF_DELACK)
  525                         tp->ccv->flags |= CCF_DELACK;
  526                 else
  527                         tp->ccv->flags &= ~CCF_DELACK;
  528 
  529                 CC_ALGO(tp)->ecnpkt_handler(tp->ccv);
  530 
  531                 if (tp->ccv->flags & CCF_ACKNOW)
  532                         tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
  533         }
  534 }
  535 
  536 /*
  537  * TCP input handling is split into multiple parts:
  538  *   tcp6_input is a thin wrapper around tcp_input for the extended
  539  *      ip6_protox[] call format in ip6_input
  540  *   tcp_input handles primary segment validation, inpcb lookup and
  541  *      SYN processing on listen sockets
  542  *   tcp_do_segment processes the ACK and text of the segment for
  543  *      establishing, established and closing connections
  544  */
  545 #ifdef INET6
  546 int
  547 tcp6_input(struct mbuf **mp, int *offp, int proto)
  548 {
  549         struct mbuf *m = *mp;
  550         struct in6_ifaddr *ia6;
  551         struct ip6_hdr *ip6;
  552 
  553         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
  554 
  555         /*
  556          * draft-itojun-ipv6-tcp-to-anycast
  557          * better place to put this in?
  558          */
  559         ip6 = mtod(m, struct ip6_hdr *);
  560         ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */);
  561         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
  562                 struct ip6_hdr *ip6;
  563 
  564                 ifa_free(&ia6->ia_ifa);
  565                 ip6 = mtod(m, struct ip6_hdr *);
  566                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
  567                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
  568                 return (IPPROTO_DONE);
  569         }
  570         if (ia6)
  571                 ifa_free(&ia6->ia_ifa);
  572 
  573         return (tcp_input(mp, offp, proto));
  574 }
  575 #endif /* INET6 */
  576 
  577 int
  578 tcp_input(struct mbuf **mp, int *offp, int proto)
  579 {
  580         struct mbuf *m = *mp;
  581         struct tcphdr *th = NULL;
  582         struct ip *ip = NULL;
  583         struct inpcb *inp = NULL;
  584         struct tcpcb *tp = NULL;
  585         struct socket *so = NULL;
  586         u_char *optp = NULL;
  587         int off0;
  588         int optlen = 0;
  589 #ifdef INET
  590         int len;
  591 #endif
  592         int tlen = 0, off;
  593         int drop_hdrlen;
  594         int thflags;
  595         int rstreason = 0;      /* For badport_bandlim accounting purposes */
  596 #ifdef TCP_SIGNATURE
  597         uint8_t sig_checked = 0;
  598 #endif
  599         uint8_t iptos = 0;
  600         struct m_tag *fwd_tag = NULL;
  601 #ifdef INET6
  602         struct ip6_hdr *ip6 = NULL;
  603         int isipv6;
  604 #else
  605         const void *ip6 = NULL;
  606 #endif /* INET6 */
  607         struct tcpopt to;               /* options in this segment */
  608         char *s = NULL;                 /* address and port logging */
  609         int ti_locked;
  610 #define TI_UNLOCKED     1
  611 #define TI_RLOCKED      2
  612 
  613 #ifdef TCPDEBUG
  614         /*
  615          * The size of tcp_saveipgen must be the size of the max ip header,
  616          * now IPv6.
  617          */
  618         u_char tcp_saveipgen[IP6_HDR_LEN];
  619         struct tcphdr tcp_savetcp;
  620         short ostate = 0;
  621 #endif
  622 
  623 #ifdef INET6
  624         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
  625 #endif
  626 
  627         off0 = *offp;
  628         m = *mp;
  629         *mp = NULL;
  630         to.to_flags = 0;
  631         TCPSTAT_INC(tcps_rcvtotal);
  632 
  633 #ifdef INET6
  634         if (isipv6) {
  635                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
  636 
  637                 if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
  638                         m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
  639                         if (m == NULL) {
  640                                 TCPSTAT_INC(tcps_rcvshort);
  641                                 return (IPPROTO_DONE);
  642                         }
  643                 }
  644 
  645                 ip6 = mtod(m, struct ip6_hdr *);
  646                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
  647                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
  648                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
  649                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  650                                 th->th_sum = m->m_pkthdr.csum_data;
  651                         else
  652                                 th->th_sum = in6_cksum_pseudo(ip6, tlen,
  653                                     IPPROTO_TCP, m->m_pkthdr.csum_data);
  654                         th->th_sum ^= 0xffff;
  655                 } else
  656                         th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
  657                 if (th->th_sum) {
  658                         TCPSTAT_INC(tcps_rcvbadsum);
  659                         goto drop;
  660                 }
  661 
  662                 /*
  663                  * Be proactive about unspecified IPv6 address in source.
  664                  * As we use all-zero to indicate unbounded/unconnected pcb,
  665                  * unspecified IPv6 address can be used to confuse us.
  666                  *
  667                  * Note that packets with unspecified IPv6 destination is
  668                  * already dropped in ip6_input.
  669                  */
  670                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
  671                         /* XXX stat */
  672                         goto drop;
  673                 }
  674         }
  675 #endif
  676 #if defined(INET) && defined(INET6)
  677         else
  678 #endif
  679 #ifdef INET
  680         {
  681                 /*
  682                  * Get IP and TCP header together in first mbuf.
  683                  * Note: IP leaves IP header in first mbuf.
  684                  */
  685                 if (off0 > sizeof (struct ip)) {
  686                         ip_stripoptions(m);
  687                         off0 = sizeof(struct ip);
  688                 }
  689                 if (m->m_len < sizeof (struct tcpiphdr)) {
  690                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
  691                             == NULL) {
  692                                 TCPSTAT_INC(tcps_rcvshort);
  693                                 return (IPPROTO_DONE);
  694                         }
  695                 }
  696                 ip = mtod(m, struct ip *);
  697                 th = (struct tcphdr *)((caddr_t)ip + off0);
  698                 tlen = ntohs(ip->ip_len) - off0;
  699 
  700                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
  701                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  702                                 th->th_sum = m->m_pkthdr.csum_data;
  703                         else
  704                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
  705                                     ip->ip_dst.s_addr,
  706                                     htonl(m->m_pkthdr.csum_data + tlen +
  707                                     IPPROTO_TCP));
  708                         th->th_sum ^= 0xffff;
  709                 } else {
  710                         struct ipovly *ipov = (struct ipovly *)ip;
  711 
  712                         /*
  713                          * Checksum extended TCP header and data.
  714                          */
  715                         len = off0 + tlen;
  716                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
  717                         ipov->ih_len = htons(tlen);
  718                         th->th_sum = in_cksum(m, len);
  719                         /* Reset length for SDT probes. */
  720                         ip->ip_len = htons(tlen + off0);
  721                 }
  722 
  723                 if (th->th_sum) {
  724                         TCPSTAT_INC(tcps_rcvbadsum);
  725                         goto drop;
  726                 }
  727                 /* Re-initialization for later version check */
  728                 ip->ip_v = IPVERSION;
  729         }
  730 #endif /* INET */
  731 
  732 #ifdef INET6
  733         if (isipv6)
  734                 iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
  735 #endif
  736 #if defined(INET) && defined(INET6)
  737         else
  738 #endif
  739 #ifdef INET
  740                 iptos = ip->ip_tos;
  741 #endif
  742 
  743         /*
  744          * Check that TCP offset makes sense,
  745          * pull out TCP options and adjust length.              XXX
  746          */
  747         off = th->th_off << 2;
  748         if (off < sizeof (struct tcphdr) || off > tlen) {
  749                 TCPSTAT_INC(tcps_rcvbadoff);
  750                 goto drop;
  751         }
  752         tlen -= off;    /* tlen is used instead of ti->ti_len */
  753         if (off > sizeof (struct tcphdr)) {
  754 #ifdef INET6
  755                 if (isipv6) {
  756                         IP6_EXTHDR_CHECK(m, off0, off, IPPROTO_DONE);
  757                         ip6 = mtod(m, struct ip6_hdr *);
  758                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
  759                 }
  760 #endif
  761 #if defined(INET) && defined(INET6)
  762                 else
  763 #endif
  764 #ifdef INET
  765                 {
  766                         if (m->m_len < sizeof(struct ip) + off) {
  767                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
  768                                     == NULL) {
  769                                         TCPSTAT_INC(tcps_rcvshort);
  770                                         return (IPPROTO_DONE);
  771                                 }
  772                                 ip = mtod(m, struct ip *);
  773                                 th = (struct tcphdr *)((caddr_t)ip + off0);
  774                         }
  775                 }
  776 #endif
  777                 optlen = off - sizeof (struct tcphdr);
  778                 optp = (u_char *)(th + 1);
  779         }
  780         thflags = th->th_flags;
  781 
  782         /*
  783          * Convert TCP protocol specific fields to host format.
  784          */
  785         tcp_fields_to_host(th);
  786 
  787         /*
  788          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
  789          */
  790         drop_hdrlen = off0 + off;
  791 
  792         /*
  793          * Locate pcb for segment; if we're likely to add or remove a
  794          * connection then first acquire pcbinfo lock.  There are three cases
  795          * where we might discover later we need a write lock despite the
  796          * flags: ACKs moving a connection out of the syncache, ACKs for a
  797          * connection in TIMEWAIT and SYNs not targeting a listening socket.
  798          */
  799         if ((thflags & (TH_FIN | TH_RST)) != 0) {
  800                 INP_INFO_RLOCK(&V_tcbinfo);
  801                 ti_locked = TI_RLOCKED;
  802         } else
  803                 ti_locked = TI_UNLOCKED;
  804 
  805         /*
  806          * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
  807          */
  808         if (
  809 #ifdef INET6
  810             (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
  811 #ifdef INET
  812             || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
  813 #endif
  814 #endif
  815 #if defined(INET) && !defined(INET6)
  816             (m->m_flags & M_IP_NEXTHOP)
  817 #endif
  818             )
  819                 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
  820 
  821 findpcb:
  822 #ifdef INVARIANTS
  823         if (ti_locked == TI_RLOCKED) {
  824                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  825         } else {
  826                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
  827         }
  828 #endif
  829 #ifdef INET6
  830         if (isipv6 && fwd_tag != NULL) {
  831                 struct sockaddr_in6 *next_hop6;
  832 
  833                 next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
  834                 /*
  835                  * Transparently forwarded. Pretend to be the destination.
  836                  * Already got one like this?
  837                  */
  838                 inp = in6_pcblookup_mbuf(&V_tcbinfo,
  839                     &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
  840                     INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
  841                 if (!inp) {
  842                         /*
  843                          * It's new.  Try to find the ambushing socket.
  844                          * Because we've rewritten the destination address,
  845                          * any hardware-generated hash is ignored.
  846                          */
  847                         inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
  848                             th->th_sport, &next_hop6->sin6_addr,
  849                             next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
  850                             th->th_dport, INPLOOKUP_WILDCARD |
  851                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  852                 }
  853         } else if (isipv6) {
  854                 inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
  855                     th->th_sport, &ip6->ip6_dst, th->th_dport,
  856                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  857                     m->m_pkthdr.rcvif, m);
  858         }
  859 #endif /* INET6 */
  860 #if defined(INET6) && defined(INET)
  861         else
  862 #endif
  863 #ifdef INET
  864         if (fwd_tag != NULL) {
  865                 struct sockaddr_in *next_hop;
  866 
  867                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
  868                 /*
  869                  * Transparently forwarded. Pretend to be the destination.
  870                  * already got one like this?
  871                  */
  872                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
  873                     ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
  874                     m->m_pkthdr.rcvif, m);
  875                 if (!inp) {
  876                         /*
  877                          * It's new.  Try to find the ambushing socket.
  878                          * Because we've rewritten the destination address,
  879                          * any hardware-generated hash is ignored.
  880                          */
  881                         inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
  882                             th->th_sport, next_hop->sin_addr,
  883                             next_hop->sin_port ? ntohs(next_hop->sin_port) :
  884                             th->th_dport, INPLOOKUP_WILDCARD |
  885                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  886                 }
  887         } else
  888                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
  889                     th->th_sport, ip->ip_dst, th->th_dport,
  890                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  891                     m->m_pkthdr.rcvif, m);
  892 #endif /* INET */
  893 
  894         /*
  895          * If the INPCB does not exist then all data in the incoming
  896          * segment is discarded and an appropriate RST is sent back.
  897          * XXX MRT Send RST using which routing table?
  898          */
  899         if (inp == NULL) {
  900                 /*
  901                  * Log communication attempts to ports that are not
  902                  * in use.
  903                  */
  904                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
  905                     tcp_log_in_vain == 2) {
  906                         if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
  907                                 log(LOG_INFO, "%s; %s: Connection attempt "
  908                                     "to closed port\n", s, __func__);
  909                 }
  910                 /*
  911                  * When blackholing do not respond with a RST but
  912                  * completely ignore the segment and drop it.
  913                  */
  914                 if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
  915                     V_blackhole == 2)
  916                         goto dropunlock;
  917 
  918                 rstreason = BANDLIM_RST_CLOSEDPORT;
  919                 goto dropwithreset;
  920         }
  921         INP_WLOCK_ASSERT(inp);
  922         if ((inp->inp_flowtype == M_HASHTYPE_NONE) &&
  923             (M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) &&
  924             ((inp->inp_socket == NULL) ||
  925             (inp->inp_socket->so_options & SO_ACCEPTCONN) == 0)) {
  926                 inp->inp_flowid = m->m_pkthdr.flowid;
  927                 inp->inp_flowtype = M_HASHTYPE_GET(m);
  928         }
  929 #ifdef IPSEC
  930 #ifdef INET6
  931         if (isipv6 && ipsec6_in_reject(m, inp)) {
  932                 goto dropunlock;
  933         } else
  934 #endif /* INET6 */
  935         if (ipsec4_in_reject(m, inp) != 0) {
  936                 goto dropunlock;
  937         }
  938 #endif /* IPSEC */
  939 
  940         /*
  941          * Check the minimum TTL for socket.
  942          */
  943         if (inp->inp_ip_minttl != 0) {
  944 #ifdef INET6
  945                 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
  946                         goto dropunlock;
  947                 else
  948 #endif
  949                 if (inp->inp_ip_minttl > ip->ip_ttl)
  950                         goto dropunlock;
  951         }
  952 
  953         /*
  954          * A previous connection in TIMEWAIT state is supposed to catch stray
  955          * or duplicate segments arriving late.  If this segment was a
  956          * legitimate new connection attempt, the old INPCB gets removed and
  957          * we can try again to find a listening socket.
  958          *
  959          * At this point, due to earlier optimism, we may hold only an inpcb
  960          * lock, and not the inpcbinfo write lock.  If so, we need to try to
  961          * acquire it, or if that fails, acquire a reference on the inpcb,
  962          * drop all locks, acquire a global write lock, and then re-acquire
  963          * the inpcb lock.  We may at that point discover that another thread
  964          * has tried to free the inpcb, in which case we need to loop back
  965          * and try to find a new inpcb to deliver to.
  966          *
  967          * XXXRW: It may be time to rethink timewait locking.
  968          */
  969 relocked:
  970         if (inp->inp_flags & INP_TIMEWAIT) {
  971                 if (ti_locked == TI_UNLOCKED) {
  972                         if (INP_INFO_TRY_RLOCK(&V_tcbinfo) == 0) {
  973                                 in_pcbref(inp);
  974                                 INP_WUNLOCK(inp);
  975                                 INP_INFO_RLOCK(&V_tcbinfo);
  976                                 ti_locked = TI_RLOCKED;
  977                                 INP_WLOCK(inp);
  978                                 if (in_pcbrele_wlocked(inp)) {
  979                                         inp = NULL;
  980                                         goto findpcb;
  981                                 }
  982                         } else
  983                                 ti_locked = TI_RLOCKED;
  984                 }
  985                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  986 
  987                 if (thflags & TH_SYN)
  988                         tcp_dooptions(&to, optp, optlen, TO_SYN);
  989                 /*
  990                  * NB: tcp_twcheck unlocks the INP and frees the mbuf.
  991                  */
  992                 if (tcp_twcheck(inp, &to, th, m, tlen))
  993                         goto findpcb;
  994                 INP_INFO_RUNLOCK(&V_tcbinfo);
  995                 return (IPPROTO_DONE);
  996         }
  997         /*
  998          * The TCPCB may no longer exist if the connection is winding
  999          * down or it is in the CLOSED state.  Either way we drop the
 1000          * segment and send an appropriate response.
 1001          */
 1002         tp = intotcpcb(inp);
 1003         if (tp == NULL || tp->t_state == TCPS_CLOSED) {
 1004                 rstreason = BANDLIM_RST_CLOSEDPORT;
 1005                 goto dropwithreset;
 1006         }
 1007 
 1008 #ifdef TCP_OFFLOAD
 1009         if (tp->t_flags & TF_TOE) {
 1010                 tcp_offload_input(tp, m);
 1011                 m = NULL;       /* consumed by the TOE driver */
 1012                 goto dropunlock;
 1013         }
 1014 #endif
 1015 
 1016         /*
 1017          * We've identified a valid inpcb, but it could be that we need an
 1018          * inpcbinfo write lock but don't hold it.  In this case, attempt to
 1019          * acquire using the same strategy as the TIMEWAIT case above.  If we
 1020          * relock, we have to jump back to 'relocked' as the connection might
 1021          * now be in TIMEWAIT.
 1022          */
 1023 #ifdef INVARIANTS
 1024         if ((thflags & (TH_FIN | TH_RST)) != 0)
 1025                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1026 #endif
 1027         if (!((tp->t_state == TCPS_ESTABLISHED && (thflags & TH_SYN) == 0) ||
 1028             (tp->t_state == TCPS_LISTEN && (thflags & TH_SYN)))) {
 1029                 if (ti_locked == TI_UNLOCKED) {
 1030                         if (INP_INFO_TRY_RLOCK(&V_tcbinfo) == 0) {
 1031                                 in_pcbref(inp);
 1032                                 INP_WUNLOCK(inp);
 1033                                 INP_INFO_RLOCK(&V_tcbinfo);
 1034                                 ti_locked = TI_RLOCKED;
 1035                                 INP_WLOCK(inp);
 1036                                 if (in_pcbrele_wlocked(inp)) {
 1037                                         inp = NULL;
 1038                                         goto findpcb;
 1039                                 }
 1040                                 goto relocked;
 1041                         } else
 1042                                 ti_locked = TI_RLOCKED;
 1043                 }
 1044                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1045         }
 1046 
 1047 #ifdef MAC
 1048         INP_WLOCK_ASSERT(inp);
 1049         if (mac_inpcb_check_deliver(inp, m))
 1050                 goto dropunlock;
 1051 #endif
 1052         so = inp->inp_socket;
 1053         KASSERT(so != NULL, ("%s: so == NULL", __func__));
 1054 #ifdef TCPDEBUG
 1055         if (so->so_options & SO_DEBUG) {
 1056                 ostate = tp->t_state;
 1057 #ifdef INET6
 1058                 if (isipv6) {
 1059                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 1060                 } else
 1061 #endif
 1062                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 1063                 tcp_savetcp = *th;
 1064         }
 1065 #endif /* TCPDEBUG */
 1066         /*
 1067          * When the socket is accepting connections (the INPCB is in LISTEN
 1068          * state) we look into the SYN cache if this is a new connection
 1069          * attempt or the completion of a previous one.
 1070          */
 1071         if (so->so_options & SO_ACCEPTCONN) {
 1072                 struct in_conninfo inc;
 1073 
 1074                 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
 1075                     "tp not listening", __func__));
 1076                 bzero(&inc, sizeof(inc));
 1077 #ifdef INET6
 1078                 if (isipv6) {
 1079                         inc.inc_flags |= INC_ISIPV6;
 1080                         inc.inc6_faddr = ip6->ip6_src;
 1081                         inc.inc6_laddr = ip6->ip6_dst;
 1082                 } else
 1083 #endif
 1084                 {
 1085                         inc.inc_faddr = ip->ip_src;
 1086                         inc.inc_laddr = ip->ip_dst;
 1087                 }
 1088                 inc.inc_fport = th->th_sport;
 1089                 inc.inc_lport = th->th_dport;
 1090                 inc.inc_fibnum = so->so_fibnum;
 1091 
 1092                 /*
 1093                  * Check for an existing connection attempt in syncache if
 1094                  * the flag is only ACK.  A successful lookup creates a new
 1095                  * socket appended to the listen queue in SYN_RECEIVED state.
 1096                  */
 1097                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 1098 
 1099                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1100                         /*
 1101                          * Parse the TCP options here because
 1102                          * syncookies need access to the reflected
 1103                          * timestamp.
 1104                          */
 1105                         tcp_dooptions(&to, optp, optlen, 0);
 1106                         /*
 1107                          * NB: syncache_expand() doesn't unlock
 1108                          * inp and tcpinfo locks.
 1109                          */
 1110                         if (!syncache_expand(&inc, &to, th, &so, m)) {
 1111                                 /*
 1112                                  * No syncache entry or ACK was not
 1113                                  * for our SYN/ACK.  Send a RST.
 1114                                  * NB: syncache did its own logging
 1115                                  * of the failure cause.
 1116                                  */
 1117                                 rstreason = BANDLIM_RST_OPENPORT;
 1118                                 goto dropwithreset;
 1119                         }
 1120                         if (so == NULL) {
 1121                                 /*
 1122                                  * We completed the 3-way handshake
 1123                                  * but could not allocate a socket
 1124                                  * either due to memory shortage,
 1125                                  * listen queue length limits or
 1126                                  * global socket limits.  Send RST
 1127                                  * or wait and have the remote end
 1128                                  * retransmit the ACK for another
 1129                                  * try.
 1130                                  */
 1131                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1132                                         log(LOG_DEBUG, "%s; %s: Listen socket: "
 1133                                             "Socket allocation failed due to "
 1134                                             "limits or memory shortage, %s\n",
 1135                                             s, __func__,
 1136                                             V_tcp_sc_rst_sock_fail ?
 1137                                             "sending RST" : "try again");
 1138                                 if (V_tcp_sc_rst_sock_fail) {
 1139                                         rstreason = BANDLIM_UNLIMITED;
 1140                                         goto dropwithreset;
 1141                                 } else
 1142                                         goto dropunlock;
 1143                         }
 1144                         /*
 1145                          * Socket is created in state SYN_RECEIVED.
 1146                          * Unlock the listen socket, lock the newly
 1147                          * created socket and update the tp variable.
 1148                          */
 1149                         INP_WUNLOCK(inp);       /* listen socket */
 1150                         inp = sotoinpcb(so);
 1151                         /*
 1152                          * New connection inpcb is already locked by
 1153                          * syncache_expand().
 1154                          */
 1155                         INP_WLOCK_ASSERT(inp);
 1156                         tp = intotcpcb(inp);
 1157                         KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
 1158                             ("%s: ", __func__));
 1159 #ifdef TCP_SIGNATURE
 1160                         if (sig_checked == 0)  {
 1161                                 tcp_dooptions(&to, optp, optlen,
 1162                                     (thflags & TH_SYN) ? TO_SYN : 0);
 1163                                 if (!tcp_signature_verify_input(m, off0, tlen,
 1164                                     optlen, &to, th, tp->t_flags)) {
 1165 
 1166                                         /*
 1167                                          * In SYN_SENT state if it receives an
 1168                                          * RST, it is allowed for further
 1169                                          * processing.
 1170                                          */
 1171                                         if ((thflags & TH_RST) == 0 ||
 1172                                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1173                                                 goto dropunlock;
 1174                                 }
 1175                                 sig_checked = 1;
 1176                         }
 1177 #endif
 1178 
 1179                         /*
 1180                          * Process the segment and the data it
 1181                          * contains.  tcp_do_segment() consumes
 1182                          * the mbuf chain and unlocks the inpcb.
 1183                          */
 1184                         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
 1185                             iptos, ti_locked);
 1186                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1187                         return (IPPROTO_DONE);
 1188                 }
 1189                 /*
 1190                  * Segment flag validation for new connection attempts:
 1191                  *
 1192                  * Our (SYN|ACK) response was rejected.
 1193                  * Check with syncache and remove entry to prevent
 1194                  * retransmits.
 1195                  *
 1196                  * NB: syncache_chkrst does its own logging of failure
 1197                  * causes.
 1198                  */
 1199                 if (thflags & TH_RST) {
 1200                         syncache_chkrst(&inc, th);
 1201                         goto dropunlock;
 1202                 }
 1203                 /*
 1204                  * We can't do anything without SYN.
 1205                  */
 1206                 if ((thflags & TH_SYN) == 0) {
 1207                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1208                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1209                                     "SYN is missing, segment ignored\n",
 1210                                     s, __func__);
 1211                         TCPSTAT_INC(tcps_badsyn);
 1212                         goto dropunlock;
 1213                 }
 1214                 /*
 1215                  * (SYN|ACK) is bogus on a listen socket.
 1216                  */
 1217                 if (thflags & TH_ACK) {
 1218                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1219                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1220                                     "SYN|ACK invalid, segment rejected\n",
 1221                                     s, __func__);
 1222                         syncache_badack(&inc);  /* XXX: Not needed! */
 1223                         TCPSTAT_INC(tcps_badsyn);
 1224                         rstreason = BANDLIM_RST_OPENPORT;
 1225                         goto dropwithreset;
 1226                 }
 1227                 /*
 1228                  * If the drop_synfin option is enabled, drop all
 1229                  * segments with both the SYN and FIN bits set.
 1230                  * This prevents e.g. nmap from identifying the
 1231                  * TCP/IP stack.
 1232                  * XXX: Poor reasoning.  nmap has other methods
 1233                  * and is constantly refining its stack detection
 1234                  * strategies.
 1235                  * XXX: This is a violation of the TCP specification
 1236                  * and was used by RFC1644.
 1237                  */
 1238                 if ((thflags & TH_FIN) && V_drop_synfin) {
 1239                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1240                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1241                                     "SYN|FIN segment ignored (based on "
 1242                                     "sysctl setting)\n", s, __func__);
 1243                         TCPSTAT_INC(tcps_badsyn);
 1244                         goto dropunlock;
 1245                 }
 1246                 /*
 1247                  * Segment's flags are (SYN) or (SYN|FIN).
 1248                  *
 1249                  * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
 1250                  * as they do not affect the state of the TCP FSM.
 1251                  * The data pointed to by TH_URG and th_urp is ignored.
 1252                  */
 1253                 KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
 1254                     ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
 1255                 KASSERT(thflags & (TH_SYN),
 1256                     ("%s: Listen socket: TH_SYN not set", __func__));
 1257 #ifdef INET6
 1258                 /*
 1259                  * If deprecated address is forbidden,
 1260                  * we do not accept SYN to deprecated interface
 1261                  * address to prevent any new inbound connection from
 1262                  * getting established.
 1263                  * When we do not accept SYN, we send a TCP RST,
 1264                  * with deprecated source address (instead of dropping
 1265                  * it).  We compromise it as it is much better for peer
 1266                  * to send a RST, and RST will be the final packet
 1267                  * for the exchange.
 1268                  *
 1269                  * If we do not forbid deprecated addresses, we accept
 1270                  * the SYN packet.  RFC2462 does not suggest dropping
 1271                  * SYN in this case.
 1272                  * If we decipher RFC2462 5.5.4, it says like this:
 1273                  * 1. use of deprecated addr with existing
 1274                  *    communication is okay - "SHOULD continue to be
 1275                  *    used"
 1276                  * 2. use of it with new communication:
 1277                  *   (2a) "SHOULD NOT be used if alternate address
 1278                  *        with sufficient scope is available"
 1279                  *   (2b) nothing mentioned otherwise.
 1280                  * Here we fall into (2b) case as we have no choice in
 1281                  * our source address selection - we must obey the peer.
 1282                  *
 1283                  * The wording in RFC2462 is confusing, and there are
 1284                  * multiple description text for deprecated address
 1285                  * handling - worse, they are not exactly the same.
 1286                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 1287                  */
 1288                 if (isipv6 && !V_ip6_use_deprecated) {
 1289                         struct in6_ifaddr *ia6;
 1290 
 1291                         ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */);
 1292                         if (ia6 != NULL &&
 1293                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 1294                                 ifa_free(&ia6->ia_ifa);
 1295                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1296                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1297                                         "Connection attempt to deprecated "
 1298                                         "IPv6 address rejected\n",
 1299                                         s, __func__);
 1300                                 rstreason = BANDLIM_RST_OPENPORT;
 1301                                 goto dropwithreset;
 1302                         }
 1303                         if (ia6)
 1304                                 ifa_free(&ia6->ia_ifa);
 1305                 }
 1306 #endif /* INET6 */
 1307                 /*
 1308                  * Basic sanity checks on incoming SYN requests:
 1309                  *   Don't respond if the destination is a link layer
 1310                  *      broadcast according to RFC1122 4.2.3.10, p. 104.
 1311                  *   If it is from this socket it must be forged.
 1312                  *   Don't respond if the source or destination is a
 1313                  *      global or subnet broad- or multicast address.
 1314                  *   Note that it is quite possible to receive unicast
 1315                  *      link-layer packets with a broadcast IP address. Use
 1316                  *      in_broadcast() to find them.
 1317                  */
 1318                 if (m->m_flags & (M_BCAST|M_MCAST)) {
 1319                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1320                             log(LOG_DEBUG, "%s; %s: Listen socket: "
 1321                                 "Connection attempt from broad- or multicast "
 1322                                 "link layer address ignored\n", s, __func__);
 1323                         goto dropunlock;
 1324                 }
 1325 #ifdef INET6
 1326                 if (isipv6) {
 1327                         if (th->th_dport == th->th_sport &&
 1328                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
 1329                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1330                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1331                                         "Connection attempt to/from self "
 1332                                         "ignored\n", s, __func__);
 1333                                 goto dropunlock;
 1334                         }
 1335                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 1336                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
 1337                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1338                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1339                                         "Connection attempt from/to multicast "
 1340                                         "address ignored\n", s, __func__);
 1341                                 goto dropunlock;
 1342                         }
 1343                 }
 1344 #endif
 1345 #if defined(INET) && defined(INET6)
 1346                 else
 1347 #endif
 1348 #ifdef INET
 1349                 {
 1350                         if (th->th_dport == th->th_sport &&
 1351                             ip->ip_dst.s_addr == ip->ip_src.s_addr) {
 1352                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1353                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1354                                         "Connection attempt from/to self "
 1355                                         "ignored\n", s, __func__);
 1356                                 goto dropunlock;
 1357                         }
 1358                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 1359                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 1360                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 1361                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
 1362                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1363                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1364                                         "Connection attempt from/to broad- "
 1365                                         "or multicast address ignored\n",
 1366                                         s, __func__);
 1367                                 goto dropunlock;
 1368                         }
 1369                 }
 1370 #endif
 1371                 /*
 1372                  * SYN appears to be valid.  Create compressed TCP state
 1373                  * for syncache.
 1374                  */
 1375 #ifdef TCPDEBUG
 1376                 if (so->so_options & SO_DEBUG)
 1377                         tcp_trace(TA_INPUT, ostate, tp,
 1378                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1379 #endif
 1380                 tcp_dooptions(&to, optp, optlen, TO_SYN);
 1381                 syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
 1382                 /*
 1383                  * Entry added to syncache and mbuf consumed.
 1384                  * Only the listen socket is unlocked by syncache_add().
 1385                  */
 1386                 if (ti_locked == TI_RLOCKED) {
 1387                         INP_INFO_RUNLOCK(&V_tcbinfo);
 1388                         ti_locked = TI_UNLOCKED;
 1389                 }
 1390                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1391                 return (IPPROTO_DONE);
 1392         } else if (tp->t_state == TCPS_LISTEN) {
 1393                 /*
 1394                  * When a listen socket is torn down the SO_ACCEPTCONN
 1395                  * flag is removed first while connections are drained
 1396                  * from the accept queue in a unlock/lock cycle of the
 1397                  * ACCEPT_LOCK, opening a race condition allowing a SYN
 1398                  * attempt go through unhandled.
 1399                  */
 1400                 goto dropunlock;
 1401         }
 1402 
 1403 #ifdef TCP_SIGNATURE
 1404         if (sig_checked == 0)  {
 1405                 tcp_dooptions(&to, optp, optlen,
 1406                     (thflags & TH_SYN) ? TO_SYN : 0);
 1407                 if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
 1408                     th, tp->t_flags)) {
 1409 
 1410                         /*
 1411                          * In SYN_SENT state if it receives an RST, it is
 1412                          * allowed for further processing.
 1413                          */
 1414                         if ((thflags & TH_RST) == 0 ||
 1415                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1416                                 goto dropunlock;
 1417                 }
 1418                 sig_checked = 1;
 1419         }
 1420 #endif
 1421 
 1422         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1423 
 1424         /*
 1425          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
 1426          * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
 1427          * the inpcb, and unlocks pcbinfo.
 1428          */
 1429         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
 1430         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1431         return (IPPROTO_DONE);
 1432 
 1433 dropwithreset:
 1434         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1435 
 1436         if (ti_locked == TI_RLOCKED) {
 1437                 INP_INFO_RUNLOCK(&V_tcbinfo);
 1438                 ti_locked = TI_UNLOCKED;
 1439         }
 1440 #ifdef INVARIANTS
 1441         else {
 1442                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
 1443                     "ti_locked: %d", __func__, ti_locked));
 1444                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1445         }
 1446 #endif
 1447 
 1448         if (inp != NULL) {
 1449                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 1450                 INP_WUNLOCK(inp);
 1451         } else
 1452                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 1453         m = NULL;       /* mbuf chain got consumed. */
 1454         goto drop;
 1455 
 1456 dropunlock:
 1457         if (m != NULL)
 1458                 TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1459 
 1460         if (ti_locked == TI_RLOCKED) {
 1461                 INP_INFO_RUNLOCK(&V_tcbinfo);
 1462                 ti_locked = TI_UNLOCKED;
 1463         }
 1464 #ifdef INVARIANTS
 1465         else {
 1466                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
 1467                     "ti_locked: %d", __func__, ti_locked));
 1468                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1469         }
 1470 #endif
 1471 
 1472         if (inp != NULL)
 1473                 INP_WUNLOCK(inp);
 1474 
 1475 drop:
 1476         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1477         if (s != NULL)
 1478                 free(s, M_TCPLOG);
 1479         if (m != NULL)
 1480                 m_freem(m);
 1481         return (IPPROTO_DONE);
 1482 }
 1483 
 1484 static void
 1485 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 1486     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
 1487     int ti_locked)
 1488 {
 1489         int thflags, acked, ourfinisacked, needoutput = 0;
 1490         int rstreason, todrop, win;
 1491         u_long tiwin;
 1492         char *s;
 1493         struct in_conninfo *inc;
 1494         struct mbuf *mfree;
 1495         struct tcpopt to;
 1496 
 1497 #ifdef TCPDEBUG
 1498         /*
 1499          * The size of tcp_saveipgen must be the size of the max ip header,
 1500          * now IPv6.
 1501          */
 1502         u_char tcp_saveipgen[IP6_HDR_LEN];
 1503         struct tcphdr tcp_savetcp;
 1504         short ostate = 0;
 1505 #endif
 1506         thflags = th->th_flags;
 1507         inc = &tp->t_inpcb->inp_inc;
 1508         tp->sackhint.last_sack_ack = 0;
 1509 
 1510         /*
 1511          * If this is either a state-changing packet or current state isn't
 1512          * established, we require a write lock on tcbinfo.  Otherwise, we
 1513          * allow the tcbinfo to be in either alocked or unlocked, as the
 1514          * caller may have unnecessarily acquired a write lock due to a race.
 1515          */
 1516         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
 1517             tp->t_state != TCPS_ESTABLISHED) {
 1518                 KASSERT(ti_locked == TI_RLOCKED, ("%s ti_locked %d for "
 1519                     "SYN/FIN/RST/!EST", __func__, ti_locked));
 1520                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1521         } else {
 1522 #ifdef INVARIANTS
 1523                 if (ti_locked == TI_RLOCKED)
 1524                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1525                 else {
 1526                         KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
 1527                             "ti_locked: %d", __func__, ti_locked));
 1528                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1529                 }
 1530 #endif
 1531         }
 1532         INP_WLOCK_ASSERT(tp->t_inpcb);
 1533         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
 1534             __func__));
 1535         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
 1536             __func__));
 1537 
 1538         /*
 1539          * Segment received on connection.
 1540          * Reset idle time and keep-alive timer.
 1541          * XXX: This should be done after segment
 1542          * validation to ignore broken/spoofed segs.
 1543          */
 1544         tp->t_rcvtime = ticks;
 1545         if (TCPS_HAVEESTABLISHED(tp->t_state))
 1546                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 1547 
 1548         /*
 1549          * Scale up the window into a 32-bit value.
 1550          * For the SYN_SENT state the scale is zero.
 1551          */
 1552         tiwin = th->th_win << tp->snd_scale;
 1553 
 1554         /*
 1555          * TCP ECN processing.
 1556          */
 1557         if (tp->t_flags & TF_ECN_PERMIT) {
 1558                 if (thflags & TH_CWR)
 1559                         tp->t_flags &= ~TF_ECN_SND_ECE;
 1560                 switch (iptos & IPTOS_ECN_MASK) {
 1561                 case IPTOS_ECN_CE:
 1562                         tp->t_flags |= TF_ECN_SND_ECE;
 1563                         TCPSTAT_INC(tcps_ecn_ce);
 1564                         break;
 1565                 case IPTOS_ECN_ECT0:
 1566                         TCPSTAT_INC(tcps_ecn_ect0);
 1567                         break;
 1568                 case IPTOS_ECN_ECT1:
 1569                         TCPSTAT_INC(tcps_ecn_ect1);
 1570                         break;
 1571                 }
 1572 
 1573                 /* Process a packet differently from RFC3168. */
 1574                 cc_ecnpkt_handler(tp, th, iptos);
 1575 
 1576                 /* Congestion experienced. */
 1577                 if (thflags & TH_ECE) {
 1578                         cc_cong_signal(tp, th, CC_ECN);
 1579                 }
 1580         }
 1581 
 1582         /*
 1583          * Parse options on any incoming segment.
 1584          */
 1585         tcp_dooptions(&to, (u_char *)(th + 1),
 1586             (th->th_off << 2) - sizeof(struct tcphdr),
 1587             (thflags & TH_SYN) ? TO_SYN : 0);
 1588 
 1589         /*
 1590          * If echoed timestamp is later than the current time,
 1591          * fall back to non RFC1323 RTT calculation.  Normalize
 1592          * timestamp if syncookies were used when this connection
 1593          * was established.
 1594          */
 1595         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
 1596                 to.to_tsecr -= tp->ts_offset;
 1597                 if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
 1598                         to.to_tsecr = 0;
 1599         }
 1600         /*
 1601          * If timestamps were negotiated during SYN/ACK they should
 1602          * appear on every segment during this session and vice versa.
 1603          */
 1604         if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
 1605                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1606                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1607                             "no action\n", s, __func__);
 1608                         free(s, M_TCPLOG);
 1609                 }
 1610         }
 1611         if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
 1612                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1613                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1614                             "no action\n", s, __func__);
 1615                         free(s, M_TCPLOG);
 1616                 }
 1617         }
 1618 
 1619         /*
 1620          * Process options only when we get SYN/ACK back. The SYN case
 1621          * for incoming connections is handled in tcp_syncache.
 1622          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
 1623          * or <SYN,ACK>) segment itself is never scaled.
 1624          * XXX this is traditional behavior, may need to be cleaned up.
 1625          */
 1626         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
 1627                 if ((to.to_flags & TOF_SCALE) &&
 1628                     (tp->t_flags & TF_REQ_SCALE)) {
 1629                         tp->t_flags |= TF_RCVD_SCALE;
 1630                         tp->snd_scale = to.to_wscale;
 1631                 }
 1632                 /*
 1633                  * Initial send window.  It will be updated with
 1634                  * the next incoming segment to the scaled value.
 1635                  */
 1636                 tp->snd_wnd = th->th_win;
 1637                 if (to.to_flags & TOF_TS) {
 1638                         tp->t_flags |= TF_RCVD_TSTMP;
 1639                         tp->ts_recent = to.to_tsval;
 1640                         tp->ts_recent_age = tcp_ts_getticks();
 1641                 }
 1642                 if (to.to_flags & TOF_MSS)
 1643                         tcp_mss(tp, to.to_mss);
 1644                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 1645                     (to.to_flags & TOF_SACKPERM) == 0)
 1646                         tp->t_flags &= ~TF_SACK_PERMIT;
 1647         }
 1648 
 1649         /*
 1650          * Header prediction: check for the two common cases
 1651          * of a uni-directional data xfer.  If the packet has
 1652          * no control flags, is in-sequence, the window didn't
 1653          * change and we're not retransmitting, it's a
 1654          * candidate.  If the length is zero and the ack moved
 1655          * forward, we're the sender side of the xfer.  Just
 1656          * free the data acked & wake any higher level process
 1657          * that was blocked waiting for space.  If the length
 1658          * is non-zero and the ack didn't move, we're the
 1659          * receiver side.  If we're getting packets in-order
 1660          * (the reassembly queue is empty), add the data to
 1661          * the socket buffer and note that we need a delayed ack.
 1662          * Make sure that the hidden state-flags are also off.
 1663          * Since we check for TCPS_ESTABLISHED first, it can only
 1664          * be TH_NEEDSYN.
 1665          */
 1666         if (tp->t_state == TCPS_ESTABLISHED &&
 1667             th->th_seq == tp->rcv_nxt &&
 1668             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 1669             tp->snd_nxt == tp->snd_max &&
 1670             tiwin && tiwin == tp->snd_wnd && 
 1671             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 1672             LIST_EMPTY(&tp->t_segq) &&
 1673             ((to.to_flags & TOF_TS) == 0 ||
 1674              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
 1675 
 1676                 /*
 1677                  * If last ACK falls within this segment's sequence numbers,
 1678                  * record the timestamp.
 1679                  * NOTE that the test is modified according to the latest
 1680                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 1681                  */
 1682                 if ((to.to_flags & TOF_TS) != 0 &&
 1683                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 1684                         tp->ts_recent_age = tcp_ts_getticks();
 1685                         tp->ts_recent = to.to_tsval;
 1686                 }
 1687 
 1688                 if (tlen == 0) {
 1689                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 1690                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 1691                             !IN_RECOVERY(tp->t_flags) &&
 1692                             (to.to_flags & TOF_SACK) == 0 &&
 1693                             TAILQ_EMPTY(&tp->snd_holes)) {
 1694                                 /*
 1695                                  * This is a pure ack for outstanding data.
 1696                                  */
 1697                                 if (ti_locked == TI_RLOCKED)
 1698                                         INP_INFO_RUNLOCK(&V_tcbinfo);
 1699                                 ti_locked = TI_UNLOCKED;
 1700 
 1701                                 TCPSTAT_INC(tcps_predack);
 1702 
 1703                                 /*
 1704                                  * "bad retransmit" recovery.
 1705                                  */
 1706                                 if (tp->t_rxtshift == 1 &&
 1707                                     tp->t_flags & TF_PREVVALID &&
 1708                                     (int)(ticks - tp->t_badrxtwin) < 0) {
 1709                                         cc_cong_signal(tp, th, CC_RTO_ERR);
 1710                                 }
 1711 
 1712                                 /*
 1713                                  * Recalculate the transmit timer / rtt.
 1714                                  *
 1715                                  * Some boxes send broken timestamp replies
 1716                                  * during the SYN+ACK phase, ignore
 1717                                  * timestamps of 0 or we could calculate a
 1718                                  * huge RTT and blow up the retransmit timer.
 1719                                  */
 1720                                 if ((to.to_flags & TOF_TS) != 0 &&
 1721                                     to.to_tsecr) {
 1722                                         u_int t;
 1723 
 1724                                         t = tcp_ts_getticks() - to.to_tsecr;
 1725                                         if (!tp->t_rttlow || tp->t_rttlow > t)
 1726                                                 tp->t_rttlow = t;
 1727                                         tcp_xmit_timer(tp,
 1728                                             TCP_TS_TO_TICKS(t) + 1);
 1729                                 } else if (tp->t_rtttime &&
 1730                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
 1731                                         if (!tp->t_rttlow ||
 1732                                             tp->t_rttlow > ticks - tp->t_rtttime)
 1733                                                 tp->t_rttlow = ticks - tp->t_rtttime;
 1734                                         tcp_xmit_timer(tp,
 1735                                                         ticks - tp->t_rtttime);
 1736                                 }
 1737                                 acked = BYTES_THIS_ACK(tp, th);
 1738 
 1739                                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 1740                                 hhook_run_tcp_est_in(tp, th, &to);
 1741 
 1742                                 TCPSTAT_INC(tcps_rcvackpack);
 1743                                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 1744                                 sbdrop(&so->so_snd, acked);
 1745                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
 1746                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 1747                                         tp->snd_recover = th->th_ack - 1;
 1748                                 
 1749                                 /*
 1750                                  * Let the congestion control algorithm update
 1751                                  * congestion control related information. This
 1752                                  * typically means increasing the congestion
 1753                                  * window.
 1754                                  */
 1755                                 cc_ack_received(tp, th, CC_ACK);
 1756 
 1757                                 tp->snd_una = th->th_ack;
 1758                                 /*
 1759                                  * Pull snd_wl2 up to prevent seq wrap relative
 1760                                  * to th_ack.
 1761                                  */
 1762                                 tp->snd_wl2 = th->th_ack;
 1763                                 tp->t_dupacks = 0;
 1764                                 m_freem(m);
 1765                                 ND6_HINT(tp); /* Some progress has been made. */
 1766 
 1767                                 /*
 1768                                  * If all outstanding data are acked, stop
 1769                                  * retransmit timer, otherwise restart timer
 1770                                  * using current (possibly backed-off) value.
 1771                                  * If process is waiting for space,
 1772                                  * wakeup/selwakeup/signal.  If data
 1773                                  * are ready to send, let tcp_output
 1774                                  * decide between more output or persist.
 1775                                  */
 1776 #ifdef TCPDEBUG
 1777                                 if (so->so_options & SO_DEBUG)
 1778                                         tcp_trace(TA_INPUT, ostate, tp,
 1779                                             (void *)tcp_saveipgen,
 1780                                             &tcp_savetcp, 0);
 1781 #endif
 1782                                 if (tp->snd_una == tp->snd_max)
 1783                                         tcp_timer_activate(tp, TT_REXMT, 0);
 1784                                 else if (!tcp_timer_active(tp, TT_PERSIST))
 1785                                         tcp_timer_activate(tp, TT_REXMT,
 1786                                                       tp->t_rxtcur);
 1787                                 sowwakeup(so);
 1788                                 if (sbavail(&so->so_snd))
 1789                                         (void) tcp_output(tp);
 1790                                 goto check_delack;
 1791                         }
 1792                 } else if (th->th_ack == tp->snd_una &&
 1793                     tlen <= sbspace(&so->so_rcv)) {
 1794                         int newsize = 0;        /* automatic sockbuf scaling */
 1795 
 1796                         /*
 1797                          * This is a pure, in-sequence data packet with
 1798                          * nothing on the reassembly queue and we have enough
 1799                          * buffer space to take it.
 1800                          */
 1801                         if (ti_locked == TI_RLOCKED)
 1802                                 INP_INFO_RUNLOCK(&V_tcbinfo);
 1803                         ti_locked = TI_UNLOCKED;
 1804 
 1805                         /* Clean receiver SACK report if present */
 1806                         if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
 1807                                 tcp_clean_sackreport(tp);
 1808                         TCPSTAT_INC(tcps_preddat);
 1809                         tp->rcv_nxt += tlen;
 1810                         /*
 1811                          * Pull snd_wl1 up to prevent seq wrap relative to
 1812                          * th_seq.
 1813                          */
 1814                         tp->snd_wl1 = th->th_seq;
 1815                         /*
 1816                          * Pull rcv_up up to prevent seq wrap relative to
 1817                          * rcv_nxt.
 1818                          */
 1819                         tp->rcv_up = tp->rcv_nxt;
 1820                         TCPSTAT_INC(tcps_rcvpack);
 1821                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 1822                         ND6_HINT(tp);   /* Some progress has been made */
 1823 #ifdef TCPDEBUG
 1824                         if (so->so_options & SO_DEBUG)
 1825                                 tcp_trace(TA_INPUT, ostate, tp,
 1826                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1827 #endif
 1828                 /*
 1829                  * Automatic sizing of receive socket buffer.  Often the send
 1830                  * buffer size is not optimally adjusted to the actual network
 1831                  * conditions at hand (delay bandwidth product).  Setting the
 1832                  * buffer size too small limits throughput on links with high
 1833                  * bandwidth and high delay (eg. trans-continental/oceanic links).
 1834                  *
 1835                  * On the receive side the socket buffer memory is only rarely
 1836                  * used to any significant extent.  This allows us to be much
 1837                  * more aggressive in scaling the receive socket buffer.  For
 1838                  * the case that the buffer space is actually used to a large
 1839                  * extent and we run out of kernel memory we can simply drop
 1840                  * the new segments; TCP on the sender will just retransmit it
 1841                  * later.  Setting the buffer size too big may only consume too
 1842                  * much kernel memory if the application doesn't read() from
 1843                  * the socket or packet loss or reordering makes use of the
 1844                  * reassembly queue.
 1845                  *
 1846                  * The criteria to step up the receive buffer one notch are:
 1847                  *  1. Application has not set receive buffer size with
 1848                  *     SO_RCVBUF. Setting SO_RCVBUF clears SB_AUTOSIZE.
 1849                  *  2. the number of bytes received during the time it takes
 1850                  *     one timestamp to be reflected back to us (the RTT);
 1851                  *  3. received bytes per RTT is within seven eighth of the
 1852                  *     current socket buffer size;
 1853                  *  4. receive buffer size has not hit maximal automatic size;
 1854                  *
 1855                  * This algorithm does one step per RTT at most and only if
 1856                  * we receive a bulk stream w/o packet losses or reorderings.
 1857                  * Shrinking the buffer during idle times is not necessary as
 1858                  * it doesn't consume any memory when idle.
 1859                  *
 1860                  * TODO: Only step up if the application is actually serving
 1861                  * the buffer to better manage the socket buffer resources.
 1862                  */
 1863                         if (V_tcp_do_autorcvbuf &&
 1864                             (to.to_flags & TOF_TS) &&
 1865                             to.to_tsecr &&
 1866                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
 1867                                 if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
 1868                                     to.to_tsecr - tp->rfbuf_ts < hz) {
 1869                                         if (tp->rfbuf_cnt >
 1870                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
 1871                                             so->so_rcv.sb_hiwat <
 1872                                             V_tcp_autorcvbuf_max) {
 1873                                                 newsize =
 1874                                                     min(so->so_rcv.sb_hiwat +
 1875                                                     V_tcp_autorcvbuf_inc,
 1876                                                     V_tcp_autorcvbuf_max);
 1877                                         }
 1878                                         /* Start over with next RTT. */
 1879                                         tp->rfbuf_ts = 0;
 1880                                         tp->rfbuf_cnt = 0;
 1881                                 } else
 1882                                         tp->rfbuf_cnt += tlen;  /* add up */
 1883                         }
 1884 
 1885                         /* Add data to socket buffer. */
 1886                         SOCKBUF_LOCK(&so->so_rcv);
 1887                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 1888                                 m_freem(m);
 1889                         } else {
 1890                                 /*
 1891                                  * Set new socket buffer size.
 1892                                  * Give up when limit is reached.
 1893                                  */
 1894                                 if (newsize)
 1895                                         if (!sbreserve_locked(&so->so_rcv,
 1896                                             newsize, so, NULL))
 1897                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
 1898                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 1899                                 sbappendstream_locked(&so->so_rcv, m, 0);
 1900                         }
 1901                         /* NB: sorwakeup_locked() does an implicit unlock. */
 1902                         sorwakeup_locked(so);
 1903                         if (DELAY_ACK(tp, tlen)) {
 1904                                 tp->t_flags |= TF_DELACK;
 1905                         } else {
 1906                                 tp->t_flags |= TF_ACKNOW;
 1907                                 tcp_output(tp);
 1908                         }
 1909                         goto check_delack;
 1910                 }
 1911         }
 1912 
 1913         /*
 1914          * Calculate amount of space in receive window,
 1915          * and then do TCP input processing.
 1916          * Receive window is amount of space in rcv queue,
 1917          * but not less than advertised window.
 1918          */
 1919         win = sbspace(&so->so_rcv);
 1920         if (win < 0)
 1921                 win = 0;
 1922         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 1923 
 1924         /* Reset receive buffer auto scaling when not in bulk receive mode. */
 1925         tp->rfbuf_ts = 0;
 1926         tp->rfbuf_cnt = 0;
 1927 
 1928         switch (tp->t_state) {
 1929 
 1930         /*
 1931          * If the state is SYN_RECEIVED:
 1932          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
 1933          */
 1934         case TCPS_SYN_RECEIVED:
 1935                 if ((thflags & TH_ACK) &&
 1936                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
 1937                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1938                                 rstreason = BANDLIM_RST_OPENPORT;
 1939                                 goto dropwithreset;
 1940                 }
 1941                 break;
 1942 
 1943         /*
 1944          * If the state is SYN_SENT:
 1945          *      if seg contains an ACK, but not for our SYN, drop the input.
 1946          *      if seg contains a RST, then drop the connection.
 1947          *      if seg does not contain SYN, then drop it.
 1948          * Otherwise this is an acceptable SYN segment
 1949          *      initialize tp->rcv_nxt and tp->irs
 1950          *      if seg contains ack then advance tp->snd_una
 1951          *      if seg contains an ECE and ECN support is enabled, the stream
 1952          *          is ECN capable.
 1953          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
 1954          *      arrange for segment to be acked (eventually)
 1955          *      continue processing rest of data/controls, beginning with URG
 1956          */
 1957         case TCPS_SYN_SENT:
 1958                 if ((thflags & TH_ACK) &&
 1959                     (SEQ_LEQ(th->th_ack, tp->iss) ||
 1960                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1961                         rstreason = BANDLIM_UNLIMITED;
 1962                         goto dropwithreset;
 1963                 }
 1964                 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
 1965                         TCP_PROBE5(connect__refused, NULL, tp,
 1966                             mtod(m, const char *), tp, th);
 1967                         tp = tcp_drop(tp, ECONNREFUSED);
 1968                 }
 1969                 if (thflags & TH_RST)
 1970                         goto drop;
 1971                 if (!(thflags & TH_SYN))
 1972                         goto drop;
 1973 
 1974                 tp->irs = th->th_seq;
 1975                 tcp_rcvseqinit(tp);
 1976                 if (thflags & TH_ACK) {
 1977                         TCPSTAT_INC(tcps_connects);
 1978                         soisconnected(so);
 1979 #ifdef MAC
 1980                         mac_socketpeer_set_from_mbuf(m, so);
 1981 #endif
 1982                         /* Do window scaling on this connection? */
 1983                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 1984                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 1985                                 tp->rcv_scale = tp->request_r_scale;
 1986                         }
 1987                         tp->rcv_adv += imin(tp->rcv_wnd,
 1988                             TCP_MAXWIN << tp->rcv_scale);
 1989                         tp->snd_una++;          /* SYN is acked */
 1990                         /*
 1991                          * If there's data, delay ACK; if there's also a FIN
 1992                          * ACKNOW will be turned on later.
 1993                          */
 1994                         if (DELAY_ACK(tp, tlen) && tlen != 0)
 1995                                 tcp_timer_activate(tp, TT_DELACK,
 1996                                     tcp_delacktime);
 1997                         else
 1998                                 tp->t_flags |= TF_ACKNOW;
 1999 
 2000                         if ((thflags & TH_ECE) && V_tcp_do_ecn) {
 2001                                 tp->t_flags |= TF_ECN_PERMIT;
 2002                                 TCPSTAT_INC(tcps_ecn_shs);
 2003                         }
 2004                         
 2005                         /*
 2006                          * Received <SYN,ACK> in SYN_SENT[*] state.
 2007                          * Transitions:
 2008                          *      SYN_SENT  --> ESTABLISHED
 2009                          *      SYN_SENT* --> FIN_WAIT_1
 2010                          */
 2011                         tp->t_starttime = ticks;
 2012                         if (tp->t_flags & TF_NEEDFIN) {
 2013                                 tcp_state_change(tp, TCPS_FIN_WAIT_1);
 2014                                 tp->t_flags &= ~TF_NEEDFIN;
 2015                                 thflags &= ~TH_SYN;
 2016                         } else {
 2017                                 tcp_state_change(tp, TCPS_ESTABLISHED);
 2018                                 TCP_PROBE5(connect__established, NULL, tp,
 2019                                     mtod(m, const char *), tp, th);
 2020                                 cc_conn_init(tp);
 2021                                 tcp_timer_activate(tp, TT_KEEP,
 2022                                     TP_KEEPIDLE(tp));
 2023                         }
 2024                 } else {
 2025                         /*
 2026                          * Received initial SYN in SYN-SENT[*] state =>
 2027                          * simultaneous open.
 2028                          * If it succeeds, connection is * half-synchronized.
 2029                          * Otherwise, do 3-way handshake:
 2030                          *        SYN-SENT -> SYN-RECEIVED
 2031                          *        SYN-SENT* -> SYN-RECEIVED*
 2032                          */
 2033                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 2034                         tcp_timer_activate(tp, TT_REXMT, 0);
 2035                         tcp_state_change(tp, TCPS_SYN_RECEIVED);
 2036                 }
 2037 
 2038                 KASSERT(ti_locked == TI_RLOCKED, ("%s: trimthenstep6: "
 2039                     "ti_locked %d", __func__, ti_locked));
 2040                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2041                 INP_WLOCK_ASSERT(tp->t_inpcb);
 2042 
 2043                 /*
 2044                  * Advance th->th_seq to correspond to first data byte.
 2045                  * If data, trim to stay within window,
 2046                  * dropping FIN if necessary.
 2047                  */
 2048                 th->th_seq++;
 2049                 if (tlen > tp->rcv_wnd) {
 2050                         todrop = tlen - tp->rcv_wnd;
 2051                         m_adj(m, -todrop);
 2052                         tlen = tp->rcv_wnd;
 2053                         thflags &= ~TH_FIN;
 2054                         TCPSTAT_INC(tcps_rcvpackafterwin);
 2055                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2056                 }
 2057                 tp->snd_wl1 = th->th_seq - 1;
 2058                 tp->rcv_up = th->th_seq;
 2059                 /*
 2060                  * Client side of transaction: already sent SYN and data.
 2061                  * If the remote host used T/TCP to validate the SYN,
 2062                  * our data will be ACK'd; if so, enter normal data segment
 2063                  * processing in the middle of step 5, ack processing.
 2064                  * Otherwise, goto step 6.
 2065                  */
 2066                 if (thflags & TH_ACK)
 2067                         goto process_ACK;
 2068 
 2069                 goto step6;
 2070 
 2071         /*
 2072          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
 2073          *      do normal processing.
 2074          *
 2075          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
 2076          */
 2077         case TCPS_LAST_ACK:
 2078         case TCPS_CLOSING:
 2079                 break;  /* continue normal processing */
 2080         }
 2081 
 2082         /*
 2083          * States other than LISTEN or SYN_SENT.
 2084          * First check the RST flag and sequence number since reset segments
 2085          * are exempt from the timestamp and connection count tests.  This
 2086          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
 2087          * below which allowed reset segments in half the sequence space
 2088          * to fall though and be processed (which gives forged reset
 2089          * segments with a random sequence number a 50 percent chance of
 2090          * killing a connection).
 2091          * Then check timestamp, if present.
 2092          * Then check the connection count, if present.
 2093          * Then check that at least some bytes of segment are within
 2094          * receive window.  If segment begins before rcv_nxt,
 2095          * drop leading data (and SYN); if nothing left, just ack.
 2096          */
 2097         if (thflags & TH_RST) {
 2098                 /*
 2099                  * RFC5961 Section 3.2
 2100                  *
 2101                  * - RST drops connection only if SEG.SEQ == RCV.NXT.
 2102                  * - If RST is in window, we send challenge ACK.
 2103                  *
 2104                  * Note: to take into account delayed ACKs, we should
 2105                  *   test against last_ack_sent instead of rcv_nxt.
 2106                  * Note 2: we handle special case of closed window, not
 2107                  *   covered by the RFC.
 2108                  */
 2109                 if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
 2110                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) ||
 2111                     (tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
 2112 
 2113                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2114                         KASSERT(ti_locked == TI_RLOCKED,
 2115                             ("%s: TH_RST ti_locked %d, th %p tp %p",
 2116                             __func__, ti_locked, th, tp));
 2117                         KASSERT(tp->t_state != TCPS_SYN_SENT,
 2118                             ("%s: TH_RST for TCPS_SYN_SENT th %p tp %p",
 2119                             __func__, th, tp));
 2120 
 2121                         if (V_tcp_insecure_rst ||
 2122                             tp->last_ack_sent == th->th_seq) {
 2123                                 TCPSTAT_INC(tcps_drops);
 2124                                 /* Drop the connection. */
 2125                                 switch (tp->t_state) {
 2126                                 case TCPS_SYN_RECEIVED:
 2127                                         so->so_error = ECONNREFUSED;
 2128                                         goto close;
 2129                                 case TCPS_ESTABLISHED:
 2130                                 case TCPS_FIN_WAIT_1:
 2131                                 case TCPS_FIN_WAIT_2:
 2132                                 case TCPS_CLOSE_WAIT:
 2133                                         so->so_error = ECONNRESET;
 2134                                 close:
 2135                                         tcp_state_change(tp, TCPS_CLOSED);
 2136                                         /* FALLTHROUGH */
 2137                                 default:
 2138                                         tp = tcp_close(tp);
 2139                                 }
 2140                         } else {
 2141                                 TCPSTAT_INC(tcps_badrst);
 2142                                 /* Send challenge ACK. */
 2143                                 tcp_respond(tp, mtod(m, void *), th, m,
 2144                                     tp->rcv_nxt, tp->snd_nxt, TH_ACK);
 2145                                 tp->last_ack_sent = tp->rcv_nxt;
 2146                                 m = NULL;
 2147                         }
 2148                 }
 2149                 goto drop;
 2150         }
 2151 
 2152         /*
 2153          * RFC5961 Section 4.2
 2154          * Send challenge ACK for any SYN in synchronized state.
 2155          */
 2156         if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT) {
 2157                 KASSERT(ti_locked == TI_RLOCKED,
 2158                     ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
 2159                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2160 
 2161                 TCPSTAT_INC(tcps_badsyn);
 2162                 if (V_tcp_insecure_syn &&
 2163                     SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
 2164                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
 2165                         tp = tcp_drop(tp, ECONNRESET);
 2166                         rstreason = BANDLIM_UNLIMITED;
 2167                 } else {
 2168                         /* Send challenge ACK. */
 2169                         tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
 2170                             tp->snd_nxt, TH_ACK);
 2171                         tp->last_ack_sent = tp->rcv_nxt;
 2172                         m = NULL;
 2173                 }
 2174                 goto drop;
 2175         }
 2176 
 2177         /*
 2178          * RFC 1323 PAWS: If we have a timestamp reply on this segment
 2179          * and it's less than ts_recent, drop it.
 2180          */
 2181         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
 2182             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
 2183 
 2184                 /* Check to see if ts_recent is over 24 days old.  */
 2185                 if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
 2186                         /*
 2187                          * Invalidate ts_recent.  If this segment updates
 2188                          * ts_recent, the age will be reset later and ts_recent
 2189                          * will get a valid value.  If it does not, setting
 2190                          * ts_recent to zero will at least satisfy the
 2191                          * requirement that zero be placed in the timestamp
 2192                          * echo reply when ts_recent isn't valid.  The
 2193                          * age isn't reset until we get a valid ts_recent
 2194                          * because we don't want out-of-order segments to be
 2195                          * dropped when ts_recent is old.
 2196                          */
 2197                         tp->ts_recent = 0;
 2198                 } else {
 2199                         TCPSTAT_INC(tcps_rcvduppack);
 2200                         TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
 2201                         TCPSTAT_INC(tcps_pawsdrop);
 2202                         if (tlen)
 2203                                 goto dropafterack;
 2204                         goto drop;
 2205                 }
 2206         }
 2207 
 2208         /*
 2209          * In the SYN-RECEIVED state, validate that the packet belongs to
 2210          * this connection before trimming the data to fit the receive
 2211          * window.  Check the sequence number versus IRS since we know
 2212          * the sequence numbers haven't wrapped.  This is a partial fix
 2213          * for the "LAND" DoS attack.
 2214          */
 2215         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
 2216                 rstreason = BANDLIM_RST_OPENPORT;
 2217                 goto dropwithreset;
 2218         }
 2219 
 2220         todrop = tp->rcv_nxt - th->th_seq;
 2221         if (todrop > 0) {
 2222                 if (thflags & TH_SYN) {
 2223                         thflags &= ~TH_SYN;
 2224                         th->th_seq++;
 2225                         if (th->th_urp > 1)
 2226                                 th->th_urp--;
 2227                         else
 2228                                 thflags &= ~TH_URG;
 2229                         todrop--;
 2230                 }
 2231                 /*
 2232                  * Following if statement from Stevens, vol. 2, p. 960.
 2233                  */
 2234                 if (todrop > tlen
 2235                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
 2236                         /*
 2237                          * Any valid FIN must be to the left of the window.
 2238                          * At this point the FIN must be a duplicate or out
 2239                          * of sequence; drop it.
 2240                          */
 2241                         thflags &= ~TH_FIN;
 2242 
 2243                         /*
 2244                          * Send an ACK to resynchronize and drop any data.
 2245                          * But keep on processing for RST or ACK.
 2246                          */
 2247                         tp->t_flags |= TF_ACKNOW;
 2248                         todrop = tlen;
 2249                         TCPSTAT_INC(tcps_rcvduppack);
 2250                         TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
 2251                 } else {
 2252                         TCPSTAT_INC(tcps_rcvpartduppack);
 2253                         TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
 2254                 }
 2255                 drop_hdrlen += todrop;  /* drop from the top afterwards */
 2256                 th->th_seq += todrop;
 2257                 tlen -= todrop;
 2258                 if (th->th_urp > todrop)
 2259                         th->th_urp -= todrop;
 2260                 else {
 2261                         thflags &= ~TH_URG;
 2262                         th->th_urp = 0;
 2263                 }
 2264         }
 2265 
 2266         /*
 2267          * If new data are received on a connection after the
 2268          * user processes are gone, then RST the other end.
 2269          */
 2270         if ((so->so_state & SS_NOFDREF) &&
 2271             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
 2272                 KASSERT(ti_locked == TI_RLOCKED, ("%s: SS_NOFDEREF && "
 2273                     "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
 2274                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2275 
 2276                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 2277                         log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
 2278                             "after socket was closed, "
 2279                             "sending RST and removing tcpcb\n",
 2280                             s, __func__, tcpstates[tp->t_state], tlen);
 2281                         free(s, M_TCPLOG);
 2282                 }
 2283                 tp = tcp_close(tp);
 2284                 TCPSTAT_INC(tcps_rcvafterclose);
 2285                 rstreason = BANDLIM_UNLIMITED;
 2286                 goto dropwithreset;
 2287         }
 2288 
 2289         /*
 2290          * If segment ends after window, drop trailing data
 2291          * (and PUSH and FIN); if nothing left, just ACK.
 2292          */
 2293         todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
 2294         if (todrop > 0) {
 2295                 TCPSTAT_INC(tcps_rcvpackafterwin);
 2296                 if (todrop >= tlen) {
 2297                         TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
 2298                         /*
 2299                          * If window is closed can only take segments at
 2300                          * window edge, and have to drop data and PUSH from
 2301                          * incoming segments.  Continue processing, but
 2302                          * remember to ack.  Otherwise, drop segment
 2303                          * and ack.
 2304                          */
 2305                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
 2306                                 tp->t_flags |= TF_ACKNOW;
 2307                                 TCPSTAT_INC(tcps_rcvwinprobe);
 2308                         } else
 2309                                 goto dropafterack;
 2310                 } else
 2311                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2312                 m_adj(m, -todrop);
 2313                 tlen -= todrop;
 2314                 thflags &= ~(TH_PUSH|TH_FIN);
 2315         }
 2316 
 2317         /*
 2318          * If last ACK falls within this segment's sequence numbers,
 2319          * record its timestamp.
 2320          * NOTE: 
 2321          * 1) That the test incorporates suggestions from the latest
 2322          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
 2323          * 2) That updating only on newer timestamps interferes with
 2324          *    our earlier PAWS tests, so this check should be solely
 2325          *    predicated on the sequence space of this segment.
 2326          * 3) That we modify the segment boundary check to be 
 2327          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len  
 2328          *    instead of RFC1323's
 2329          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
 2330          *    This modified check allows us to overcome RFC1323's
 2331          *    limitations as described in Stevens TCP/IP Illustrated
 2332          *    Vol. 2 p.869. In such cases, we can still calculate the
 2333          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
 2334          */
 2335         if ((to.to_flags & TOF_TS) != 0 &&
 2336             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
 2337             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
 2338                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
 2339                 tp->ts_recent_age = tcp_ts_getticks();
 2340                 tp->ts_recent = to.to_tsval;
 2341         }
 2342 
 2343         /*
 2344          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
 2345          * flag is on (half-synchronized state), then queue data for
 2346          * later processing; else drop segment and return.
 2347          */
 2348         if ((thflags & TH_ACK) == 0) {
 2349                 if (tp->t_state == TCPS_SYN_RECEIVED ||
 2350                     (tp->t_flags & TF_NEEDSYN))
 2351                         goto step6;
 2352                 else if (tp->t_flags & TF_ACKNOW)
 2353                         goto dropafterack;
 2354                 else
 2355                         goto drop;
 2356         }
 2357 
 2358         /*
 2359          * Ack processing.
 2360          */
 2361         switch (tp->t_state) {
 2362 
 2363         /*
 2364          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
 2365          * ESTABLISHED state and continue processing.
 2366          * The ACK was checked above.
 2367          */
 2368         case TCPS_SYN_RECEIVED:
 2369 
 2370                 TCPSTAT_INC(tcps_connects);
 2371                 soisconnected(so);
 2372                 /* Do window scaling? */
 2373                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2374                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2375                         tp->rcv_scale = tp->request_r_scale;
 2376                         tp->snd_wnd = tiwin;
 2377                 }
 2378                 /*
 2379                  * Make transitions:
 2380                  *      SYN-RECEIVED  -> ESTABLISHED
 2381                  *      SYN-RECEIVED* -> FIN-WAIT-1
 2382                  */
 2383                 tp->t_starttime = ticks;
 2384                 if (tp->t_flags & TF_NEEDFIN) {
 2385                         tcp_state_change(tp, TCPS_FIN_WAIT_1);
 2386                         tp->t_flags &= ~TF_NEEDFIN;
 2387                 } else {
 2388                         tcp_state_change(tp, TCPS_ESTABLISHED);
 2389                         TCP_PROBE5(accept__established, NULL, tp,
 2390                             mtod(m, const char *), tp, th);
 2391                         cc_conn_init(tp);
 2392                         tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 2393                 }
 2394                 /*
 2395                  * If segment contains data or ACK, will call tcp_reass()
 2396                  * later; if not, do so now to pass queued data to user.
 2397                  */
 2398                 if (tlen == 0 && (thflags & TH_FIN) == 0)
 2399                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
 2400                             (struct mbuf *)0);
 2401                 tp->snd_wl1 = th->th_seq - 1;
 2402                 /* FALLTHROUGH */
 2403 
 2404         /*
 2405          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
 2406          * ACKs.  If the ack is in the range
 2407          *      tp->snd_una < th->th_ack <= tp->snd_max
 2408          * then advance tp->snd_una to th->th_ack and drop
 2409          * data from the retransmission queue.  If this ACK reflects
 2410          * more up to date window information we update our window information.
 2411          */
 2412         case TCPS_ESTABLISHED:
 2413         case TCPS_FIN_WAIT_1:
 2414         case TCPS_FIN_WAIT_2:
 2415         case TCPS_CLOSE_WAIT:
 2416         case TCPS_CLOSING:
 2417         case TCPS_LAST_ACK:
 2418                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
 2419                         TCPSTAT_INC(tcps_rcvacktoomuch);
 2420                         goto dropafterack;
 2421                 }
 2422                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 2423                     ((to.to_flags & TOF_SACK) ||
 2424                      !TAILQ_EMPTY(&tp->snd_holes)))
 2425                         tcp_sack_doack(tp, &to, th->th_ack);
 2426 
 2427                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 2428                 hhook_run_tcp_est_in(tp, th, &to);
 2429 
 2430                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
 2431                         if (tlen == 0 && tiwin == tp->snd_wnd) {
 2432                                 /*
 2433                                  * If this is the first time we've seen a
 2434                                  * FIN from the remote, this is not a
 2435                                  * duplicate and it needs to be processed
 2436                                  * normally.  This happens during a
 2437                                  * simultaneous close.
 2438                                  */
 2439                                 if ((thflags & TH_FIN) &&
 2440                                     (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
 2441                                         tp->t_dupacks = 0;
 2442                                         break;
 2443                                 }
 2444                                 TCPSTAT_INC(tcps_rcvdupack);
 2445                                 /*
 2446                                  * If we have outstanding data (other than
 2447                                  * a window probe), this is a completely
 2448                                  * duplicate ack (ie, window info didn't
 2449                                  * change and FIN isn't set),
 2450                                  * the ack is the biggest we've
 2451                                  * seen and we've seen exactly our rexmt
 2452                                  * threshhold of them, assume a packet
 2453                                  * has been dropped and retransmit it.
 2454                                  * Kludge snd_nxt & the congestion
 2455                                  * window so we send only this one
 2456                                  * packet.
 2457                                  *
 2458                                  * We know we're losing at the current
 2459                                  * window size so do congestion avoidance
 2460                                  * (set ssthresh to half the current window
 2461                                  * and pull our congestion window back to
 2462                                  * the new ssthresh).
 2463                                  *
 2464                                  * Dup acks mean that packets have left the
 2465                                  * network (they're now cached at the receiver)
 2466                                  * so bump cwnd by the amount in the receiver
 2467                                  * to keep a constant cwnd packets in the
 2468                                  * network.
 2469                                  *
 2470                                  * When using TCP ECN, notify the peer that
 2471                                  * we reduced the cwnd.
 2472                                  */
 2473                                 if (!tcp_timer_active(tp, TT_REXMT) ||
 2474                                     th->th_ack != tp->snd_una)
 2475                                         tp->t_dupacks = 0;
 2476                                 else if (++tp->t_dupacks > tcprexmtthresh ||
 2477                                      IN_FASTRECOVERY(tp->t_flags)) {
 2478                                         cc_ack_received(tp, th, CC_DUPACK);
 2479                                         if ((tp->t_flags & TF_SACK_PERMIT) &&
 2480                                             IN_FASTRECOVERY(tp->t_flags)) {
 2481                                                 int awnd;
 2482                                                 
 2483                                                 /*
 2484                                                  * Compute the amount of data in flight first.
 2485                                                  * We can inject new data into the pipe iff 
 2486                                                  * we have less than 1/2 the original window's
 2487                                                  * worth of data in flight.
 2488                                                  */
 2489                                                 awnd = (tp->snd_nxt - tp->snd_fack) +
 2490                                                         tp->sackhint.sack_bytes_rexmit;
 2491                                                 if (awnd < tp->snd_ssthresh) {
 2492                                                         tp->snd_cwnd += tp->t_maxseg;
 2493                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
 2494                                                                 tp->snd_cwnd = tp->snd_ssthresh;
 2495                                                 }
 2496                                         } else
 2497                                                 tp->snd_cwnd += tp->t_maxseg;
 2498                                         (void) tcp_output(tp);
 2499                                         goto drop;
 2500                                 } else if (tp->t_dupacks == tcprexmtthresh) {
 2501                                         tcp_seq onxt = tp->snd_nxt;
 2502 
 2503                                         /*
 2504                                          * If we're doing sack, check to
 2505                                          * see if we're already in sack
 2506                                          * recovery. If we're not doing sack,
 2507                                          * check to see if we're in newreno
 2508                                          * recovery.
 2509                                          */
 2510                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2511                                                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2512                                                         tp->t_dupacks = 0;
 2513                                                         break;
 2514                                                 }
 2515                                         } else {
 2516                                                 if (SEQ_LEQ(th->th_ack,
 2517                                                     tp->snd_recover)) {
 2518                                                         tp->t_dupacks = 0;
 2519                                                         break;
 2520                                                 }
 2521                                         }
 2522                                         /* Congestion signal before ack. */
 2523                                         cc_cong_signal(tp, th, CC_NDUPACK);
 2524                                         cc_ack_received(tp, th, CC_DUPACK);
 2525                                         tcp_timer_activate(tp, TT_REXMT, 0);
 2526                                         tp->t_rtttime = 0;
 2527                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2528                                                 TCPSTAT_INC(
 2529                                                     tcps_sack_recovery_episode);
 2530                                                 tp->sack_newdata = tp->snd_nxt;
 2531                                                 tp->snd_cwnd = tp->t_maxseg;
 2532                                                 (void) tcp_output(tp);
 2533                                                 goto drop;
 2534                                         }
 2535                                         tp->snd_nxt = th->th_ack;
 2536                                         tp->snd_cwnd = tp->t_maxseg;
 2537                                         (void) tcp_output(tp);
 2538                                         KASSERT(tp->snd_limited <= 2,
 2539                                             ("%s: tp->snd_limited too big",
 2540                                             __func__));
 2541                                         tp->snd_cwnd = tp->snd_ssthresh +
 2542                                              tp->t_maxseg *
 2543                                              (tp->t_dupacks - tp->snd_limited);
 2544                                         if (SEQ_GT(onxt, tp->snd_nxt))
 2545                                                 tp->snd_nxt = onxt;
 2546                                         goto drop;
 2547                                 } else if (V_tcp_do_rfc3042) {
 2548                                         cc_ack_received(tp, th, CC_DUPACK);
 2549                                         u_long oldcwnd = tp->snd_cwnd;
 2550                                         tcp_seq oldsndmax = tp->snd_max;
 2551                                         u_int sent;
 2552                                         int avail;
 2553 
 2554                                         KASSERT(tp->t_dupacks == 1 ||
 2555                                             tp->t_dupacks == 2,
 2556                                             ("%s: dupacks not 1 or 2",
 2557                                             __func__));
 2558                                         if (tp->t_dupacks == 1)
 2559                                                 tp->snd_limited = 0;
 2560                                         tp->snd_cwnd =
 2561                                             (tp->snd_nxt - tp->snd_una) +
 2562                                             (tp->t_dupacks - tp->snd_limited) *
 2563                                             tp->t_maxseg;
 2564                                         /*
 2565                                          * Only call tcp_output when there
 2566                                          * is new data available to be sent.
 2567                                          * Otherwise we would send pure ACKs.
 2568                                          */
 2569                                         SOCKBUF_LOCK(&so->so_snd);
 2570                                         avail = sbavail(&so->so_snd) -
 2571                                             (tp->snd_nxt - tp->snd_una);
 2572                                         SOCKBUF_UNLOCK(&so->so_snd);
 2573                                         if (avail > 0)
 2574                                                 (void) tcp_output(tp);
 2575                                         sent = tp->snd_max - oldsndmax;
 2576                                         if (sent > tp->t_maxseg) {
 2577                                                 KASSERT((tp->t_dupacks == 2 &&
 2578                                                     tp->snd_limited == 0) ||
 2579                                                    (sent == tp->t_maxseg + 1 &&
 2580                                                     tp->t_flags & TF_SENTFIN),
 2581                                                     ("%s: sent too much",
 2582                                                     __func__));
 2583                                                 tp->snd_limited = 2;
 2584                                         } else if (sent > 0)
 2585                                                 ++tp->snd_limited;
 2586                                         tp->snd_cwnd = oldcwnd;
 2587                                         goto drop;
 2588                                 }
 2589                         } else
 2590                                 tp->t_dupacks = 0;
 2591                         break;
 2592                 }
 2593 
 2594                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
 2595                     ("%s: th_ack <= snd_una", __func__));
 2596 
 2597                 /*
 2598                  * If the congestion window was inflated to account
 2599                  * for the other side's cached packets, retract it.
 2600                  */
 2601                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2602                         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
 2603                                 if (tp->t_flags & TF_SACK_PERMIT)
 2604                                         tcp_sack_partialack(tp, th);
 2605                                 else
 2606                                         tcp_newreno_partial_ack(tp, th);
 2607                         } else
 2608                                 cc_post_recovery(tp, th);
 2609                 }
 2610                 tp->t_dupacks = 0;
 2611                 /*
 2612                  * If we reach this point, ACK is not a duplicate,
 2613                  *     i.e., it ACKs something we sent.
 2614                  */
 2615                 if (tp->t_flags & TF_NEEDSYN) {
 2616                         /*
 2617                          * T/TCP: Connection was half-synchronized, and our
 2618                          * SYN has been ACK'd (so connection is now fully
 2619                          * synchronized).  Go to non-starred state,
 2620                          * increment snd_una for ACK of SYN, and check if
 2621                          * we can do window scaling.
 2622                          */
 2623                         tp->t_flags &= ~TF_NEEDSYN;
 2624                         tp->snd_una++;
 2625                         /* Do window scaling? */
 2626                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2627                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2628                                 tp->rcv_scale = tp->request_r_scale;
 2629                                 /* Send window already scaled. */
 2630                         }
 2631                 }
 2632 
 2633 process_ACK:
 2634                 INP_WLOCK_ASSERT(tp->t_inpcb);
 2635 
 2636                 acked = BYTES_THIS_ACK(tp, th);
 2637                 TCPSTAT_INC(tcps_rcvackpack);
 2638                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 2639 
 2640                 /*
 2641                  * If we just performed our first retransmit, and the ACK
 2642                  * arrives within our recovery window, then it was a mistake
 2643                  * to do the retransmit in the first place.  Recover our
 2644                  * original cwnd and ssthresh, and proceed to transmit where
 2645                  * we left off.
 2646                  */
 2647                 if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
 2648                     (int)(ticks - tp->t_badrxtwin) < 0)
 2649                         cc_cong_signal(tp, th, CC_RTO_ERR);
 2650 
 2651                 /*
 2652                  * If we have a timestamp reply, update smoothed
 2653                  * round trip time.  If no timestamp is present but
 2654                  * transmit timer is running and timed sequence
 2655                  * number was acked, update smoothed round trip time.
 2656                  * Since we now have an rtt measurement, cancel the
 2657                  * timer backoff (cf., Phil Karn's retransmit alg.).
 2658                  * Recompute the initial retransmit timer.
 2659                  *
 2660                  * Some boxes send broken timestamp replies
 2661                  * during the SYN+ACK phase, ignore
 2662                  * timestamps of 0 or we could calculate a
 2663                  * huge RTT and blow up the retransmit timer.
 2664                  */
 2665                 if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
 2666                         u_int t;
 2667 
 2668                         t = tcp_ts_getticks() - to.to_tsecr;
 2669                         if (!tp->t_rttlow || tp->t_rttlow > t)
 2670                                 tp->t_rttlow = t;
 2671                         tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
 2672                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
 2673                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
 2674                                 tp->t_rttlow = ticks - tp->t_rtttime;
 2675                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
 2676                 }
 2677 
 2678                 /*
 2679                  * If all outstanding data is acked, stop retransmit
 2680                  * timer and remember to restart (more output or persist).
 2681                  * If there is more data to be acked, restart retransmit
 2682                  * timer, using current (possibly backed-off) value.
 2683                  */
 2684                 if (th->th_ack == tp->snd_max) {
 2685                         tcp_timer_activate(tp, TT_REXMT, 0);
 2686                         needoutput = 1;
 2687                 } else if (!tcp_timer_active(tp, TT_PERSIST))
 2688                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 2689 
 2690                 /*
 2691                  * If no data (only SYN) was ACK'd,
 2692                  *    skip rest of ACK processing.
 2693                  */
 2694                 if (acked == 0)
 2695                         goto step6;
 2696 
 2697                 /*
 2698                  * Let the congestion control algorithm update congestion
 2699                  * control related information. This typically means increasing
 2700                  * the congestion window.
 2701                  */
 2702                 cc_ack_received(tp, th, CC_ACK);
 2703 
 2704                 SOCKBUF_LOCK(&so->so_snd);
 2705                 if (acked > sbavail(&so->so_snd)) {
 2706                         tp->snd_wnd -= sbavail(&so->so_snd);
 2707                         mfree = sbcut_locked(&so->so_snd,
 2708                             (int)sbavail(&so->so_snd));
 2709                         ourfinisacked = 1;
 2710                 } else {
 2711                         mfree = sbcut_locked(&so->so_snd, acked);
 2712                         tp->snd_wnd -= acked;
 2713                         ourfinisacked = 0;
 2714                 }
 2715                 /* NB: sowwakeup_locked() does an implicit unlock. */
 2716                 sowwakeup_locked(so);
 2717                 m_freem(mfree);
 2718                 /* Detect una wraparound. */
 2719                 if (!IN_RECOVERY(tp->t_flags) &&
 2720                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
 2721                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 2722                         tp->snd_recover = th->th_ack - 1;
 2723                 /* XXXLAS: Can this be moved up into cc_post_recovery? */
 2724                 if (IN_RECOVERY(tp->t_flags) &&
 2725                     SEQ_GEQ(th->th_ack, tp->snd_recover)) {
 2726                         EXIT_RECOVERY(tp->t_flags);
 2727                 }
 2728                 tp->snd_una = th->th_ack;
 2729                 if (tp->t_flags & TF_SACK_PERMIT) {
 2730                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
 2731                                 tp->snd_recover = tp->snd_una;
 2732                 }
 2733                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 2734                         tp->snd_nxt = tp->snd_una;
 2735 
 2736                 switch (tp->t_state) {
 2737 
 2738                 /*
 2739                  * In FIN_WAIT_1 STATE in addition to the processing
 2740                  * for the ESTABLISHED state if our FIN is now acknowledged
 2741                  * then enter FIN_WAIT_2.
 2742                  */
 2743                 case TCPS_FIN_WAIT_1:
 2744                         if (ourfinisacked) {
 2745                                 /*
 2746                                  * If we can't receive any more
 2747                                  * data, then closing user can proceed.
 2748                                  * Starting the timer is contrary to the
 2749                                  * specification, but if we don't get a FIN
 2750                                  * we'll hang forever.
 2751                                  *
 2752                                  * XXXjl:
 2753                                  * we should release the tp also, and use a
 2754                                  * compressed state.
 2755                                  */
 2756                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 2757                                         soisdisconnected(so);
 2758                                         tcp_timer_activate(tp, TT_2MSL,
 2759                                             (tcp_fast_finwait2_recycle ?
 2760                                             tcp_finwait2_timeout :
 2761                                             TP_MAXIDLE(tp)));
 2762                                 }
 2763                                 tcp_state_change(tp, TCPS_FIN_WAIT_2);
 2764                         }
 2765                         break;
 2766 
 2767                 /*
 2768                  * In CLOSING STATE in addition to the processing for
 2769                  * the ESTABLISHED state if the ACK acknowledges our FIN
 2770                  * then enter the TIME-WAIT state, otherwise ignore
 2771                  * the segment.
 2772                  */
 2773                 case TCPS_CLOSING:
 2774                         if (ourfinisacked) {
 2775                                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2776                                 tcp_twstart(tp);
 2777                                 INP_INFO_RUNLOCK(&V_tcbinfo);
 2778                                 m_freem(m);
 2779                                 return;
 2780                         }
 2781                         break;
 2782 
 2783                 /*
 2784                  * In LAST_ACK, we may still be waiting for data to drain
 2785                  * and/or to be acked, as well as for the ack of our FIN.
 2786                  * If our FIN is now acknowledged, delete the TCB,
 2787                  * enter the closed state and return.
 2788                  */
 2789                 case TCPS_LAST_ACK:
 2790                         if (ourfinisacked) {
 2791                                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 2792                                 tp = tcp_close(tp);
 2793                                 goto drop;
 2794                         }
 2795                         break;
 2796                 }
 2797         }
 2798 
 2799 step6:
 2800         INP_WLOCK_ASSERT(tp->t_inpcb);
 2801 
 2802         /*
 2803          * Update window information.
 2804          * Don't look at window if no ACK: TAC's send garbage on first SYN.
 2805          */
 2806         if ((thflags & TH_ACK) &&
 2807             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
 2808             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
 2809              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
 2810                 /* keep track of pure window updates */
 2811                 if (tlen == 0 &&
 2812                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
 2813                         TCPSTAT_INC(tcps_rcvwinupd);
 2814                 tp->snd_wnd = tiwin;
 2815                 tp->snd_wl1 = th->th_seq;
 2816                 tp->snd_wl2 = th->th_ack;
 2817                 if (tp->snd_wnd > tp->max_sndwnd)
 2818                         tp->max_sndwnd = tp->snd_wnd;
 2819                 needoutput = 1;
 2820         }
 2821 
 2822         /*
 2823          * Process segments with URG.
 2824          */
 2825         if ((thflags & TH_URG) && th->th_urp &&
 2826             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2827                 /*
 2828                  * This is a kludge, but if we receive and accept
 2829                  * random urgent pointers, we'll crash in
 2830                  * soreceive.  It's hard to imagine someone
 2831                  * actually wanting to send this much urgent data.
 2832                  */
 2833                 SOCKBUF_LOCK(&so->so_rcv);
 2834                 if (th->th_urp + sbavail(&so->so_rcv) > sb_max) {
 2835                         th->th_urp = 0;                 /* XXX */
 2836                         thflags &= ~TH_URG;             /* XXX */
 2837                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
 2838                         goto dodata;                    /* XXX */
 2839                 }
 2840                 /*
 2841                  * If this segment advances the known urgent pointer,
 2842                  * then mark the data stream.  This should not happen
 2843                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
 2844                  * a FIN has been received from the remote side.
 2845                  * In these states we ignore the URG.
 2846                  *
 2847                  * According to RFC961 (Assigned Protocols),
 2848                  * the urgent pointer points to the last octet
 2849                  * of urgent data.  We continue, however,
 2850                  * to consider it to indicate the first octet
 2851                  * of data past the urgent section as the original
 2852                  * spec states (in one of two places).
 2853                  */
 2854                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
 2855                         tp->rcv_up = th->th_seq + th->th_urp;
 2856                         so->so_oobmark = sbavail(&so->so_rcv) +
 2857                             (tp->rcv_up - tp->rcv_nxt) - 1;
 2858                         if (so->so_oobmark == 0)
 2859                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
 2860                         sohasoutofband(so);
 2861                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
 2862                 }
 2863                 SOCKBUF_UNLOCK(&so->so_rcv);
 2864                 /*
 2865                  * Remove out of band data so doesn't get presented to user.
 2866                  * This can happen independent of advancing the URG pointer,
 2867                  * but if two URG's are pending at once, some out-of-band
 2868                  * data may creep in... ick.
 2869                  */
 2870                 if (th->th_urp <= (u_long)tlen &&
 2871                     !(so->so_options & SO_OOBINLINE)) {
 2872                         /* hdr drop is delayed */
 2873                         tcp_pulloutofband(so, th, m, drop_hdrlen);
 2874                 }
 2875         } else {
 2876                 /*
 2877                  * If no out of band data is expected,
 2878                  * pull receive urgent pointer along
 2879                  * with the receive window.
 2880                  */
 2881                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
 2882                         tp->rcv_up = tp->rcv_nxt;
 2883         }
 2884 dodata:                                                 /* XXX */
 2885         INP_WLOCK_ASSERT(tp->t_inpcb);
 2886 
 2887         /*
 2888          * Process the segment text, merging it into the TCP sequencing queue,
 2889          * and arranging for acknowledgment of receipt if necessary.
 2890          * This process logically involves adjusting tp->rcv_wnd as data
 2891          * is presented to the user (this happens in tcp_usrreq.c,
 2892          * case PRU_RCVD).  If a FIN has already been received on this
 2893          * connection then we just ignore the text.
 2894          */
 2895         if ((tlen || (thflags & TH_FIN)) &&
 2896             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2897                 tcp_seq save_start = th->th_seq;
 2898                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 2899                 /*
 2900                  * Insert segment which includes th into TCP reassembly queue
 2901                  * with control block tp.  Set thflags to whether reassembly now
 2902                  * includes a segment with FIN.  This handles the common case
 2903                  * inline (segment is the next to be received on an established
 2904                  * connection, and the queue is empty), avoiding linkage into
 2905                  * and removal from the queue and repetition of various
 2906                  * conversions.
 2907                  * Set DELACK for segments received in order, but ack
 2908                  * immediately when segments are out of order (so
 2909                  * fast retransmit can work).
 2910                  */
 2911                 if (th->th_seq == tp->rcv_nxt &&
 2912                     LIST_EMPTY(&tp->t_segq) &&
 2913                     TCPS_HAVEESTABLISHED(tp->t_state)) {
 2914                         if (DELAY_ACK(tp, tlen))
 2915                                 tp->t_flags |= TF_DELACK;
 2916                         else
 2917                                 tp->t_flags |= TF_ACKNOW;
 2918                         tp->rcv_nxt += tlen;
 2919                         thflags = th->th_flags & TH_FIN;
 2920                         TCPSTAT_INC(tcps_rcvpack);
 2921                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 2922                         ND6_HINT(tp);
 2923                         SOCKBUF_LOCK(&so->so_rcv);
 2924                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
 2925                                 m_freem(m);
 2926                         else
 2927                                 sbappendstream_locked(&so->so_rcv, m, 0);
 2928                         /* NB: sorwakeup_locked() does an implicit unlock. */
 2929                         sorwakeup_locked(so);
 2930                 } else {
 2931                         /*
 2932                          * XXX: Due to the header drop above "th" is
 2933                          * theoretically invalid by now.  Fortunately
 2934                          * m_adj() doesn't actually frees any mbufs
 2935                          * when trimming from the head.
 2936                          */
 2937                         thflags = tcp_reass(tp, th, &tlen, m);
 2938                         tp->t_flags |= TF_ACKNOW;
 2939                 }
 2940                 if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
 2941                         tcp_update_sack_list(tp, save_start, save_start + tlen);
 2942 #if 0
 2943                 /*
 2944                  * Note the amount of data that peer has sent into
 2945                  * our window, in order to estimate the sender's
 2946                  * buffer size.
 2947                  * XXX: Unused.
 2948                  */
 2949                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
 2950                         len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
 2951                 else
 2952                         len = so->so_rcv.sb_hiwat;
 2953 #endif
 2954         } else {
 2955                 m_freem(m);
 2956                 thflags &= ~TH_FIN;
 2957         }
 2958 
 2959         /*
 2960          * If FIN is received ACK the FIN and let the user know
 2961          * that the connection is closing.
 2962          */
 2963         if (thflags & TH_FIN) {
 2964                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2965                         socantrcvmore(so);
 2966                         /*
 2967                          * If connection is half-synchronized
 2968                          * (ie NEEDSYN flag on) then delay ACK,
 2969                          * so it may be piggybacked when SYN is sent.
 2970                          * Otherwise, since we received a FIN then no
 2971                          * more input can be expected, send ACK now.
 2972                          */
 2973                         if (tp->t_flags & TF_NEEDSYN)
 2974                                 tp->t_flags |= TF_DELACK;
 2975                         else
 2976                                 tp->t_flags |= TF_ACKNOW;
 2977                         tp->rcv_nxt++;
 2978                 }
 2979                 switch (tp->t_state) {
 2980 
 2981                 /*
 2982                  * In SYN_RECEIVED and ESTABLISHED STATES
 2983                  * enter the CLOSE_WAIT state.
 2984                  */
 2985                 case TCPS_SYN_RECEIVED:
 2986                         tp->t_starttime = ticks;
 2987                         /* FALLTHROUGH */
 2988                 case TCPS_ESTABLISHED:
 2989                         tcp_state_change(tp, TCPS_CLOSE_WAIT);
 2990                         break;
 2991 
 2992                 /*
 2993                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
 2994                  * enter the CLOSING state.
 2995                  */
 2996                 case TCPS_FIN_WAIT_1:
 2997                         tcp_state_change(tp, TCPS_CLOSING);
 2998                         break;
 2999 
 3000                 /*
 3001                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
 3002                  * starting the time-wait timer, turning off the other
 3003                  * standard timers.
 3004                  */
 3005                 case TCPS_FIN_WAIT_2:
 3006                         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 3007                         KASSERT(ti_locked == TI_RLOCKED, ("%s: dodata "
 3008                             "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
 3009                             ti_locked));
 3010 
 3011                         tcp_twstart(tp);
 3012                         INP_INFO_RUNLOCK(&V_tcbinfo);
 3013                         return;
 3014                 }
 3015         }
 3016         if (ti_locked == TI_RLOCKED)
 3017                 INP_INFO_RUNLOCK(&V_tcbinfo);
 3018         ti_locked = TI_UNLOCKED;
 3019 
 3020 #ifdef TCPDEBUG
 3021         if (so->so_options & SO_DEBUG)
 3022                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
 3023                           &tcp_savetcp, 0);
 3024 #endif
 3025 
 3026         /*
 3027          * Return any desired output.
 3028          */
 3029         if (needoutput || (tp->t_flags & TF_ACKNOW))
 3030                 (void) tcp_output(tp);
 3031 
 3032 check_delack:
 3033         KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
 3034             __func__, ti_locked));
 3035         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3036         INP_WLOCK_ASSERT(tp->t_inpcb);
 3037 
 3038         if (tp->t_flags & TF_DELACK) {
 3039                 tp->t_flags &= ~TF_DELACK;
 3040                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
 3041         }
 3042         INP_WUNLOCK(tp->t_inpcb);
 3043         return;
 3044 
 3045 dropafterack:
 3046         /*
 3047          * Generate an ACK dropping incoming segment if it occupies
 3048          * sequence space, where the ACK reflects our state.
 3049          *
 3050          * We can now skip the test for the RST flag since all
 3051          * paths to this code happen after packets containing
 3052          * RST have been dropped.
 3053          *
 3054          * In the SYN-RECEIVED state, don't send an ACK unless the
 3055          * segment we received passes the SYN-RECEIVED ACK test.
 3056          * If it fails send a RST.  This breaks the loop in the
 3057          * "LAND" DoS attack, and also prevents an ACK storm
 3058          * between two listening ports that have been sent forged
 3059          * SYN segments, each with the source address of the other.
 3060          */
 3061         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
 3062             (SEQ_GT(tp->snd_una, th->th_ack) ||
 3063              SEQ_GT(th->th_ack, tp->snd_max)) ) {
 3064                 rstreason = BANDLIM_RST_OPENPORT;
 3065                 goto dropwithreset;
 3066         }
 3067 #ifdef TCPDEBUG
 3068         if (so->so_options & SO_DEBUG)
 3069                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3070                           &tcp_savetcp, 0);
 3071 #endif
 3072         if (ti_locked == TI_RLOCKED)
 3073                 INP_INFO_RUNLOCK(&V_tcbinfo);
 3074         ti_locked = TI_UNLOCKED;
 3075 
 3076         tp->t_flags |= TF_ACKNOW;
 3077         (void) tcp_output(tp);
 3078         INP_WUNLOCK(tp->t_inpcb);
 3079         m_freem(m);
 3080         return;
 3081 
 3082 dropwithreset:
 3083         if (ti_locked == TI_RLOCKED)
 3084                 INP_INFO_RUNLOCK(&V_tcbinfo);
 3085         ti_locked = TI_UNLOCKED;
 3086 
 3087         if (tp != NULL) {
 3088                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 3089                 INP_WUNLOCK(tp->t_inpcb);
 3090         } else
 3091                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 3092         return;
 3093 
 3094 drop:
 3095         if (ti_locked == TI_RLOCKED) {
 3096                 INP_INFO_RUNLOCK(&V_tcbinfo);
 3097                 ti_locked = TI_UNLOCKED;
 3098         }
 3099 #ifdef INVARIANTS
 3100         else
 3101                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3102 #endif
 3103 
 3104         /*
 3105          * Drop space held by incoming segment and return.
 3106          */
 3107 #ifdef TCPDEBUG
 3108         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 3109                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3110                           &tcp_savetcp, 0);
 3111 #endif
 3112         if (tp != NULL)
 3113                 INP_WUNLOCK(tp->t_inpcb);
 3114         m_freem(m);
 3115 }
 3116 
 3117 /*
 3118  * Issue RST and make ACK acceptable to originator of segment.
 3119  * The mbuf must still include the original packet header.
 3120  * tp may be NULL.
 3121  */
 3122 static void
 3123 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
 3124     int tlen, int rstreason)
 3125 {
 3126 #ifdef INET
 3127         struct ip *ip;
 3128 #endif
 3129 #ifdef INET6
 3130         struct ip6_hdr *ip6;
 3131 #endif
 3132 
 3133         if (tp != NULL) {
 3134                 INP_WLOCK_ASSERT(tp->t_inpcb);
 3135         }
 3136 
 3137         /* Don't bother if destination was broadcast/multicast. */
 3138         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
 3139                 goto drop;
 3140 #ifdef INET6
 3141         if (mtod(m, struct ip *)->ip_v == 6) {
 3142                 ip6 = mtod(m, struct ip6_hdr *);
 3143                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 3144                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 3145                         goto drop;
 3146                 /* IPv6 anycast check is done at tcp6_input() */
 3147         }
 3148 #endif
 3149 #if defined(INET) && defined(INET6)
 3150         else
 3151 #endif
 3152 #ifdef INET
 3153         {
 3154                 ip = mtod(m, struct ip *);
 3155                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 3156                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 3157                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 3158                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 3159                         goto drop;
 3160         }
 3161 #endif
 3162 
 3163         /* Perform bandwidth limiting. */
 3164         if (badport_bandlim(rstreason) < 0)
 3165                 goto drop;
 3166 
 3167         /* tcp_respond consumes the mbuf chain. */
 3168         if (th->th_flags & TH_ACK) {
 3169                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
 3170                     th->th_ack, TH_RST);
 3171         } else {
 3172                 if (th->th_flags & TH_SYN)
 3173                         tlen++;
 3174                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
 3175                     (tcp_seq)0, TH_RST|TH_ACK);
 3176         }
 3177         return;
 3178 drop:
 3179         m_freem(m);
 3180 }
 3181 
 3182 /*
 3183  * Parse TCP options and place in tcpopt.
 3184  */
 3185 static void
 3186 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
 3187 {
 3188         int opt, optlen;
 3189 
 3190         to->to_flags = 0;
 3191         for (; cnt > 0; cnt -= optlen, cp += optlen) {
 3192                 opt = cp[0];
 3193                 if (opt == TCPOPT_EOL)
 3194                         break;
 3195                 if (opt == TCPOPT_NOP)
 3196                         optlen = 1;
 3197                 else {
 3198                         if (cnt < 2)
 3199                                 break;
 3200                         optlen = cp[1];
 3201                         if (optlen < 2 || optlen > cnt)
 3202                                 break;
 3203                 }
 3204                 switch (opt) {
 3205                 case TCPOPT_MAXSEG:
 3206                         if (optlen != TCPOLEN_MAXSEG)
 3207                                 continue;
 3208                         if (!(flags & TO_SYN))
 3209                                 continue;
 3210                         to->to_flags |= TOF_MSS;
 3211                         bcopy((char *)cp + 2,
 3212                             (char *)&to->to_mss, sizeof(to->to_mss));
 3213                         to->to_mss = ntohs(to->to_mss);
 3214                         break;
 3215                 case TCPOPT_WINDOW:
 3216                         if (optlen != TCPOLEN_WINDOW)
 3217                                 continue;
 3218                         if (!(flags & TO_SYN))
 3219                                 continue;
 3220                         to->to_flags |= TOF_SCALE;
 3221                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
 3222                         break;
 3223                 case TCPOPT_TIMESTAMP:
 3224                         if (optlen != TCPOLEN_TIMESTAMP)
 3225                                 continue;
 3226                         to->to_flags |= TOF_TS;
 3227                         bcopy((char *)cp + 2,
 3228                             (char *)&to->to_tsval, sizeof(to->to_tsval));
 3229                         to->to_tsval = ntohl(to->to_tsval);
 3230                         bcopy((char *)cp + 6,
 3231                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
 3232                         to->to_tsecr = ntohl(to->to_tsecr);
 3233                         break;
 3234 #ifdef TCP_SIGNATURE
 3235                 /*
 3236                  * XXX In order to reply to a host which has set the
 3237                  * TCP_SIGNATURE option in its initial SYN, we have to
 3238                  * record the fact that the option was observed here
 3239                  * for the syncache code to perform the correct response.
 3240                  */
 3241                 case TCPOPT_SIGNATURE:
 3242                         if (optlen != TCPOLEN_SIGNATURE)
 3243                                 continue;
 3244                         to->to_flags |= TOF_SIGNATURE;
 3245                         to->to_signature = cp + 2;
 3246                         break;
 3247 #endif
 3248                 case TCPOPT_SACK_PERMITTED:
 3249                         if (optlen != TCPOLEN_SACK_PERMITTED)
 3250                                 continue;
 3251                         if (!(flags & TO_SYN))
 3252                                 continue;
 3253                         if (!V_tcp_do_sack)
 3254                                 continue;
 3255                         to->to_flags |= TOF_SACKPERM;
 3256                         break;
 3257                 case TCPOPT_SACK:
 3258                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
 3259                                 continue;
 3260                         if (flags & TO_SYN)
 3261                                 continue;
 3262                         to->to_flags |= TOF_SACK;
 3263                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
 3264                         to->to_sacks = cp + 2;
 3265                         TCPSTAT_INC(tcps_sack_rcv_blocks);
 3266                         break;
 3267                 default:
 3268                         continue;
 3269                 }
 3270         }
 3271 }
 3272 
 3273 /*
 3274  * Pull out of band byte out of a segment so
 3275  * it doesn't appear in the user's data queue.
 3276  * It is still reflected in the segment length for
 3277  * sequencing purposes.
 3278  */
 3279 static void
 3280 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
 3281     int off)
 3282 {
 3283         int cnt = off + th->th_urp - 1;
 3284 
 3285         while (cnt >= 0) {
 3286                 if (m->m_len > cnt) {
 3287                         char *cp = mtod(m, caddr_t) + cnt;
 3288                         struct tcpcb *tp = sototcpcb(so);
 3289 
 3290                         INP_WLOCK_ASSERT(tp->t_inpcb);
 3291 
 3292                         tp->t_iobc = *cp;
 3293                         tp->t_oobflags |= TCPOOB_HAVEDATA;
 3294                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
 3295                         m->m_len--;
 3296                         if (m->m_flags & M_PKTHDR)
 3297                                 m->m_pkthdr.len--;
 3298                         return;
 3299                 }
 3300                 cnt -= m->m_len;
 3301                 m = m->m_next;
 3302                 if (m == NULL)
 3303                         break;
 3304         }
 3305         panic("tcp_pulloutofband");
 3306 }
 3307 
 3308 /*
 3309  * Collect new round-trip time estimate
 3310  * and update averages and current timeout.
 3311  */
 3312 static void
 3313 tcp_xmit_timer(struct tcpcb *tp, int rtt)
 3314 {
 3315         int delta;
 3316 
 3317         INP_WLOCK_ASSERT(tp->t_inpcb);
 3318 
 3319         TCPSTAT_INC(tcps_rttupdated);
 3320         tp->t_rttupdated++;
 3321         if (tp->t_srtt != 0) {
 3322                 /*
 3323                  * srtt is stored as fixed point with 5 bits after the
 3324                  * binary point (i.e., scaled by 8).  The following magic
 3325                  * is equivalent to the smoothing algorithm in rfc793 with
 3326                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
 3327                  * point).  Adjust rtt to origin 0.
 3328                  */
 3329                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
 3330                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
 3331 
 3332                 if ((tp->t_srtt += delta) <= 0)
 3333                         tp->t_srtt = 1;
 3334 
 3335                 /*
 3336                  * We accumulate a smoothed rtt variance (actually, a
 3337                  * smoothed mean difference), then set the retransmit
 3338                  * timer to smoothed rtt + 4 times the smoothed variance.
 3339                  * rttvar is stored as fixed point with 4 bits after the
 3340                  * binary point (scaled by 16).  The following is
 3341                  * equivalent to rfc793 smoothing with an alpha of .75
 3342                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
 3343                  * rfc793's wired-in beta.
 3344                  */
 3345                 if (delta < 0)
 3346                         delta = -delta;
 3347                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
 3348                 if ((tp->t_rttvar += delta) <= 0)
 3349                         tp->t_rttvar = 1;
 3350                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
 3351                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3352         } else {
 3353                 /*
 3354                  * No rtt measurement yet - use the unsmoothed rtt.
 3355                  * Set the variance to half the rtt (so our first
 3356                  * retransmit happens at 3*rtt).
 3357                  */
 3358                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
 3359                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
 3360                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3361         }
 3362         tp->t_rtttime = 0;
 3363         tp->t_rxtshift = 0;
 3364 
 3365         /*
 3366          * the retransmit should happen at rtt + 4 * rttvar.
 3367          * Because of the way we do the smoothing, srtt and rttvar
 3368          * will each average +1/2 tick of bias.  When we compute
 3369          * the retransmit timer, we want 1/2 tick of rounding and
 3370          * 1 extra tick because of +-1/2 tick uncertainty in the
 3371          * firing of the timer.  The bias will give us exactly the
 3372          * 1.5 tick we need.  But, because the bias is
 3373          * statistical, we have to test that we don't drop below
 3374          * the minimum feasible timer (which is 2 ticks).
 3375          */
 3376         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
 3377                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
 3378 
 3379         /*
 3380          * We received an ack for a packet that wasn't retransmitted;
 3381          * it is probably safe to discard any error indications we've
 3382          * received recently.  This isn't quite right, but close enough
 3383          * for now (a route might have failed after we sent a segment,
 3384          * and the return path might not be symmetrical).
 3385          */
 3386         tp->t_softerror = 0;
 3387 }
 3388 
 3389 /*
 3390  * Determine a reasonable value for maxseg size.
 3391  * If the route is known, check route for mtu.
 3392  * If none, use an mss that can be handled on the outgoing interface
 3393  * without forcing IP to fragment.  If no route is found, route has no mtu,
 3394  * or the destination isn't local, use a default, hopefully conservative
 3395  * size (usually 512 or the default IP max size, but no more than the mtu
 3396  * of the interface), as we can't discover anything about intervening
 3397  * gateways or networks.  We also initialize the congestion/slow start
 3398  * window to be a single segment if the destination isn't local.
 3399  * While looking at the routing entry, we also initialize other path-dependent
 3400  * parameters from pre-set or cached values in the routing entry.
 3401  *
 3402  * Also take into account the space needed for options that we
 3403  * send regularly.  Make maxseg shorter by that amount to assure
 3404  * that we can send maxseg amount of data even when the options
 3405  * are present.  Store the upper limit of the length of options plus
 3406  * data in maxopd.
 3407  *
 3408  * NOTE that this routine is only called when we process an incoming
 3409  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
 3410  * settings are handled in tcp_mssopt().
 3411  */
 3412 void
 3413 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
 3414     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
 3415 {
 3416         int mss = 0;
 3417         u_long maxmtu = 0;
 3418         struct inpcb *inp = tp->t_inpcb;
 3419         struct hc_metrics_lite metrics;
 3420         int origoffer;
 3421 #ifdef INET6
 3422         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
 3423         size_t min_protoh = isipv6 ?
 3424                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
 3425                             sizeof (struct tcpiphdr);
 3426 #else
 3427         const size_t min_protoh = sizeof(struct tcpiphdr);
 3428 #endif
 3429 
 3430         INP_WLOCK_ASSERT(tp->t_inpcb);
 3431 
 3432         if (mtuoffer != -1) {
 3433                 KASSERT(offer == -1, ("%s: conflict", __func__));
 3434                 offer = mtuoffer - min_protoh;
 3435         }
 3436         origoffer = offer;
 3437 
 3438         /* Initialize. */
 3439 #ifdef INET6
 3440         if (isipv6) {
 3441                 maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
 3442                 tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
 3443         }
 3444 #endif
 3445 #if defined(INET) && defined(INET6)
 3446         else
 3447 #endif
 3448 #ifdef INET
 3449         {
 3450                 maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
 3451                 tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
 3452         }
 3453 #endif
 3454 
 3455         /*
 3456          * No route to sender, stay with default mss and return.
 3457          */
 3458         if (maxmtu == 0) {
 3459                 /*
 3460                  * In case we return early we need to initialize metrics
 3461                  * to a defined state as tcp_hc_get() would do for us
 3462                  * if there was no cache hit.
 3463                  */
 3464                 if (metricptr != NULL)
 3465                         bzero(metricptr, sizeof(struct hc_metrics_lite));
 3466                 return;
 3467         }
 3468 
 3469         /* What have we got? */
 3470         switch (offer) {
 3471                 case 0:
 3472                         /*
 3473                          * Offer == 0 means that there was no MSS on the SYN
 3474                          * segment, in this case we use tcp_mssdflt as
 3475                          * already assigned to t_maxopd above.
 3476                          */
 3477                         offer = tp->t_maxopd;
 3478                         break;
 3479 
 3480                 case -1:
 3481                         /*
 3482                          * Offer == -1 means that we didn't receive SYN yet.
 3483                          */
 3484                         /* FALLTHROUGH */
 3485 
 3486                 default:
 3487                         /*
 3488                          * Prevent DoS attack with too small MSS. Round up
 3489                          * to at least minmss.
 3490                          */
 3491                         offer = max(offer, V_tcp_minmss);
 3492         }
 3493 
 3494         /*
 3495          * rmx information is now retrieved from tcp_hostcache.
 3496          */
 3497         tcp_hc_get(&inp->inp_inc, &metrics);
 3498         if (metricptr != NULL)
 3499                 bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
 3500 
 3501         /*
 3502          * If there's a discovered mtu in tcp hostcache, use it.
 3503          * Else, use the link mtu.
 3504          */
 3505         if (metrics.rmx_mtu)
 3506                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
 3507         else {
 3508 #ifdef INET6
 3509                 if (isipv6) {
 3510                         mss = maxmtu - min_protoh;
 3511                         if (!V_path_mtu_discovery &&
 3512                             !in6_localaddr(&inp->in6p_faddr))
 3513                                 mss = min(mss, V_tcp_v6mssdflt);
 3514                 }
 3515 #endif
 3516 #if defined(INET) && defined(INET6)
 3517                 else
 3518 #endif
 3519 #ifdef INET
 3520                 {
 3521                         mss = maxmtu - min_protoh;
 3522                         if (!V_path_mtu_discovery &&
 3523                             !in_localaddr(inp->inp_faddr))
 3524                                 mss = min(mss, V_tcp_mssdflt);
 3525                 }
 3526 #endif
 3527                 /*
 3528                  * XXX - The above conditional (mss = maxmtu - min_protoh)
 3529                  * probably violates the TCP spec.
 3530                  * The problem is that, since we don't know the
 3531                  * other end's MSS, we are supposed to use a conservative
 3532                  * default.  But, if we do that, then MTU discovery will
 3533                  * never actually take place, because the conservative
 3534                  * default is much less than the MTUs typically seen
 3535                  * on the Internet today.  For the moment, we'll sweep
 3536                  * this under the carpet.
 3537                  *
 3538                  * The conservative default might not actually be a problem
 3539                  * if the only case this occurs is when sending an initial
 3540                  * SYN with options and data to a host we've never talked
 3541                  * to before.  Then, they will reply with an MSS value which
 3542                  * will get recorded and the new parameters should get
 3543                  * recomputed.  For Further Study.
 3544                  */
 3545         }
 3546         mss = min(mss, offer);
 3547 
 3548         /*
 3549          * Sanity check: make sure that maxopd will be large
 3550          * enough to allow some data on segments even if the
 3551          * all the option space is used (40bytes).  Otherwise
 3552          * funny things may happen in tcp_output.
 3553          */
 3554         mss = max(mss, 64);
 3555 
 3556         /*
 3557          * maxopd stores the maximum length of data AND options
 3558          * in a segment; maxseg is the amount of data in a normal
 3559          * segment.  We need to store this value (maxopd) apart
 3560          * from maxseg, because now every segment carries options
 3561          * and thus we normally have somewhat less data in segments.
 3562          */
 3563         tp->t_maxopd = mss;
 3564 
 3565         /*
 3566          * origoffer==-1 indicates that no segments were received yet.
 3567          * In this case we just guess.
 3568          */
 3569         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
 3570             (origoffer == -1 ||
 3571              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
 3572                 mss -= TCPOLEN_TSTAMP_APPA;
 3573 
 3574         tp->t_maxseg = mss;
 3575 }
 3576 
 3577 void
 3578 tcp_mss(struct tcpcb *tp, int offer)
 3579 {
 3580         int mss;
 3581         u_long bufsize;
 3582         struct inpcb *inp;
 3583         struct socket *so;
 3584         struct hc_metrics_lite metrics;
 3585         struct tcp_ifcap cap;
 3586 
 3587         KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
 3588 
 3589         bzero(&cap, sizeof(cap));
 3590         tcp_mss_update(tp, offer, -1, &metrics, &cap);
 3591 
 3592         mss = tp->t_maxseg;
 3593         inp = tp->t_inpcb;
 3594 
 3595         /*
 3596          * If there's a pipesize, change the socket buffer to that size,
 3597          * don't change if sb_hiwat is different than default (then it
 3598          * has been changed on purpose with setsockopt).
 3599          * Make the socket buffers an integral number of mss units;
 3600          * if the mss is larger than the socket buffer, decrease the mss.
 3601          */
 3602         so = inp->inp_socket;
 3603         SOCKBUF_LOCK(&so->so_snd);
 3604         if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
 3605                 bufsize = metrics.rmx_sendpipe;
 3606         else
 3607                 bufsize = so->so_snd.sb_hiwat;
 3608         if (bufsize < mss)
 3609                 mss = bufsize;
 3610         else {
 3611                 bufsize = roundup(bufsize, mss);
 3612                 if (bufsize > sb_max)
 3613                         bufsize = sb_max;
 3614                 if (bufsize > so->so_snd.sb_hiwat)
 3615                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
 3616         }
 3617         SOCKBUF_UNLOCK(&so->so_snd);
 3618         tp->t_maxseg = mss;
 3619 
 3620         SOCKBUF_LOCK(&so->so_rcv);
 3621         if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
 3622                 bufsize = metrics.rmx_recvpipe;
 3623         else
 3624                 bufsize = so->so_rcv.sb_hiwat;
 3625         if (bufsize > mss) {
 3626                 bufsize = roundup(bufsize, mss);
 3627                 if (bufsize > sb_max)
 3628                         bufsize = sb_max;
 3629                 if (bufsize > so->so_rcv.sb_hiwat)
 3630                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
 3631         }
 3632         SOCKBUF_UNLOCK(&so->so_rcv);
 3633 
 3634         /* Check the interface for TSO capabilities. */
 3635         if (cap.ifcap & CSUM_TSO) {
 3636                 tp->t_flags |= TF_TSO;
 3637                 tp->t_tsomax = cap.tsomax;
 3638                 tp->t_tsomaxsegcount = cap.tsomaxsegcount;
 3639                 tp->t_tsomaxsegsize = cap.tsomaxsegsize;
 3640         }
 3641 }
 3642 
 3643 /*
 3644  * Determine the MSS option to send on an outgoing SYN.
 3645  */
 3646 int
 3647 tcp_mssopt(struct in_conninfo *inc)
 3648 {
 3649         int mss = 0;
 3650         u_long maxmtu = 0;
 3651         u_long thcmtu = 0;
 3652         size_t min_protoh;
 3653 
 3654         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
 3655 
 3656 #ifdef INET6
 3657         if (inc->inc_flags & INC_ISIPV6) {
 3658                 mss = V_tcp_v6mssdflt;
 3659                 maxmtu = tcp_maxmtu6(inc, NULL);
 3660                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
 3661         }
 3662 #endif
 3663 #if defined(INET) && defined(INET6)
 3664         else
 3665 #endif
 3666 #ifdef INET
 3667         {
 3668                 mss = V_tcp_mssdflt;
 3669                 maxmtu = tcp_maxmtu(inc, NULL);
 3670                 min_protoh = sizeof(struct tcpiphdr);
 3671         }
 3672 #endif
 3673 #if defined(INET6) || defined(INET)
 3674         thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
 3675 #endif
 3676 
 3677         if (maxmtu && thcmtu)
 3678                 mss = min(maxmtu, thcmtu) - min_protoh;
 3679         else if (maxmtu || thcmtu)
 3680                 mss = max(maxmtu, thcmtu) - min_protoh;
 3681 
 3682         return (mss);
 3683 }
 3684 
 3685 
 3686 /*
 3687  * On a partial ack arrives, force the retransmission of the
 3688  * next unacknowledged segment.  Do not clear tp->t_dupacks.
 3689  * By setting snd_nxt to ti_ack, this forces retransmission timer to
 3690  * be started again.
 3691  */
 3692 static void
 3693 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
 3694 {
 3695         tcp_seq onxt = tp->snd_nxt;
 3696         u_long  ocwnd = tp->snd_cwnd;
 3697 
 3698         INP_WLOCK_ASSERT(tp->t_inpcb);
 3699 
 3700         tcp_timer_activate(tp, TT_REXMT, 0);
 3701         tp->t_rtttime = 0;
 3702         tp->snd_nxt = th->th_ack;
 3703         /*
 3704          * Set snd_cwnd to one segment beyond acknowledged offset.
 3705          * (tp->snd_una has not yet been updated when this function is called.)
 3706          */
 3707         tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th);
 3708         tp->t_flags |= TF_ACKNOW;
 3709         (void) tcp_output(tp);
 3710         tp->snd_cwnd = ocwnd;
 3711         if (SEQ_GT(onxt, tp->snd_nxt))
 3712                 tp->snd_nxt = onxt;
 3713         /*
 3714          * Partial window deflation.  Relies on fact that tp->snd_una
 3715          * not updated yet.
 3716          */
 3717         if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
 3718                 tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
 3719         else
 3720                 tp->snd_cwnd = 0;
 3721         tp->snd_cwnd += tp->t_maxseg;
 3722 }

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