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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 261244 2014-01-28 21:13:15Z peter $");
   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_VNET_INT(_net_inet_tcp, OID_AUTO, blackhole, 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_VNET_INT(_net_inet_tcp, OID_AUTO, delayed_ack, 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_VNET_INT(_net_inet_tcp, OID_AUTO, drop_synfin, 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_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3042, 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_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3390, 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_VNET_INT(_net_inet_tcp_experimental, OID_AUTO, initcwnd10, 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_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3465, 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_VNET_INT(_net_inet_tcp, OID_AUTO, abc_l_var, 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_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_RW,
  181     &VNET_NAME(tcp_do_ecn), 0,
  182     "TCP ECN support");
  183 
  184 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
  185 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_RW,
  186     &VNET_NAME(tcp_ecn_maxretries), 0,
  187     "Max retries before giving up on ECN");
  188 
  189 VNET_DEFINE(int, tcp_insecure_rst) = 0;
  190 #define V_tcp_insecure_rst      VNET(tcp_insecure_rst)
  191 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
  192     &VNET_NAME(tcp_insecure_rst), 0,
  193     "Follow the old (insecure) criteria for accepting RST packets");
  194 
  195 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
  196 #define V_tcp_recvspace VNET(tcp_recvspace)
  197 SYSCTL_VNET_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_RW,
  198     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
  199 
  200 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
  201 #define V_tcp_do_autorcvbuf     VNET(tcp_do_autorcvbuf)
  202 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
  203     &VNET_NAME(tcp_do_autorcvbuf), 0,
  204     "Enable automatic receive buffer sizing");
  205 
  206 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
  207 #define V_tcp_autorcvbuf_inc    VNET(tcp_autorcvbuf_inc)
  208 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
  209     &VNET_NAME(tcp_autorcvbuf_inc), 0,
  210     "Incrementor step size of automatic receive buffer");
  211 
  212 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
  213 #define V_tcp_autorcvbuf_max    VNET(tcp_autorcvbuf_max)
  214 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
  215     &VNET_NAME(tcp_autorcvbuf_max), 0,
  216     "Max size of automatic receive buffer");
  217 
  218 VNET_DEFINE(struct inpcbhead, tcb);
  219 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
  220 VNET_DEFINE(struct inpcbinfo, tcbinfo);
  221 
  222 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
  223 static void      tcp_do_segment(struct mbuf *, struct tcphdr *,
  224                      struct socket *, struct tcpcb *, int, int, uint8_t,
  225                      int);
  226 static void      tcp_dropwithreset(struct mbuf *, struct tcphdr *,
  227                      struct tcpcb *, int, int);
  228 static void      tcp_pulloutofband(struct socket *,
  229                      struct tcphdr *, struct mbuf *, int);
  230 static void      tcp_xmit_timer(struct tcpcb *, int);
  231 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
  232 static void inline      tcp_fields_to_host(struct tcphdr *);
  233 #ifdef TCP_SIGNATURE
  234 static void inline      tcp_fields_to_net(struct tcphdr *);
  235 static int inline       tcp_signature_verify_input(struct mbuf *, int, int,
  236                             int, struct tcpopt *, struct tcphdr *, u_int);
  237 #endif
  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 static inline void
  459 tcp_fields_to_host(struct tcphdr *th)
  460 {
  461 
  462         th->th_seq = ntohl(th->th_seq);
  463         th->th_ack = ntohl(th->th_ack);
  464         th->th_win = ntohs(th->th_win);
  465         th->th_urp = ntohs(th->th_urp);
  466 }
  467 
  468 #ifdef TCP_SIGNATURE
  469 static inline void
  470 tcp_fields_to_net(struct tcphdr *th)
  471 {
  472 
  473         th->th_seq = htonl(th->th_seq);
  474         th->th_ack = htonl(th->th_ack);
  475         th->th_win = htons(th->th_win);
  476         th->th_urp = htons(th->th_urp);
  477 }
  478 
  479 static inline int
  480 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
  481     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
  482 {
  483         int ret;
  484 
  485         tcp_fields_to_net(th);
  486         ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
  487         tcp_fields_to_host(th);
  488         return (ret);
  489 }
  490 #endif
  491 
  492 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
  493 #ifdef INET6
  494 #define ND6_HINT(tp) \
  495 do { \
  496         if ((tp) && (tp)->t_inpcb && \
  497             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
  498                 nd6_nud_hint(NULL, NULL, 0); \
  499 } while (0)
  500 #else
  501 #define ND6_HINT(tp)
  502 #endif
  503 
  504 /*
  505  * Indicate whether this ack should be delayed.  We can delay the ack if
  506  *      - there is no delayed ack timer in progress and
  507  *      - our last ack wasn't a 0-sized window.  We never want to delay
  508  *        the ack that opens up a 0-sized window and
  509  *              - delayed acks are enabled or
  510  *              - this is a half-synchronized T/TCP connection.
  511  *      - the segment size is not larger than the MSS and LRO wasn't used
  512  *        for this segment.
  513  */
  514 #define DELAY_ACK(tp, tlen)                                             \
  515         ((!tcp_timer_active(tp, TT_DELACK) &&                           \
  516             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
  517             (tlen <= tp->t_maxopd) &&                                   \
  518             (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
  519 
  520 /*
  521  * TCP input handling is split into multiple parts:
  522  *   tcp6_input is a thin wrapper around tcp_input for the extended
  523  *      ip6_protox[] call format in ip6_input
  524  *   tcp_input handles primary segment validation, inpcb lookup and
  525  *      SYN processing on listen sockets
  526  *   tcp_do_segment processes the ACK and text of the segment for
  527  *      establishing, established and closing connections
  528  */
  529 #ifdef INET6
  530 int
  531 tcp6_input(struct mbuf **mp, int *offp, int proto)
  532 {
  533         struct mbuf *m = *mp;
  534         struct in6_ifaddr *ia6;
  535 
  536         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
  537 
  538         /*
  539          * draft-itojun-ipv6-tcp-to-anycast
  540          * better place to put this in?
  541          */
  542         ia6 = ip6_getdstifaddr(m);
  543         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
  544                 struct ip6_hdr *ip6;
  545 
  546                 ifa_free(&ia6->ia_ifa);
  547                 ip6 = mtod(m, struct ip6_hdr *);
  548                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
  549                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
  550                 return IPPROTO_DONE;
  551         }
  552         if (ia6)
  553                 ifa_free(&ia6->ia_ifa);
  554 
  555         tcp_input(m, *offp);
  556         return IPPROTO_DONE;
  557 }
  558 #endif /* INET6 */
  559 
  560 void
  561 tcp_input(struct mbuf *m, int off0)
  562 {
  563         struct tcphdr *th = NULL;
  564         struct ip *ip = NULL;
  565         struct inpcb *inp = NULL;
  566         struct tcpcb *tp = NULL;
  567         struct socket *so = NULL;
  568         u_char *optp = NULL;
  569         int optlen = 0;
  570 #ifdef INET
  571         int len;
  572 #endif
  573         int tlen = 0, off;
  574         int drop_hdrlen;
  575         int thflags;
  576         int rstreason = 0;      /* For badport_bandlim accounting purposes */
  577 #ifdef TCP_SIGNATURE
  578         uint8_t sig_checked = 0;
  579 #endif
  580         uint8_t iptos = 0;
  581         struct m_tag *fwd_tag = NULL;
  582 #ifdef INET6
  583         struct ip6_hdr *ip6 = NULL;
  584         int isipv6;
  585 #else
  586         const void *ip6 = NULL;
  587 #endif /* INET6 */
  588         struct tcpopt to;               /* options in this segment */
  589         char *s = NULL;                 /* address and port logging */
  590         int ti_locked;
  591 #define TI_UNLOCKED     1
  592 #define TI_WLOCKED      2
  593 
  594 #ifdef TCPDEBUG
  595         /*
  596          * The size of tcp_saveipgen must be the size of the max ip header,
  597          * now IPv6.
  598          */
  599         u_char tcp_saveipgen[IP6_HDR_LEN];
  600         struct tcphdr tcp_savetcp;
  601         short ostate = 0;
  602 #endif
  603 
  604 #ifdef INET6
  605         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
  606 #endif
  607 
  608         to.to_flags = 0;
  609         TCPSTAT_INC(tcps_rcvtotal);
  610 
  611 #ifdef INET6
  612         if (isipv6) {
  613                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
  614 
  615                 if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
  616                         m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
  617                         if (m == NULL) {
  618                                 TCPSTAT_INC(tcps_rcvshort);
  619                                 return;
  620                         }
  621                 }
  622 
  623                 ip6 = mtod(m, struct ip6_hdr *);
  624                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
  625                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
  626                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
  627                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  628                                 th->th_sum = m->m_pkthdr.csum_data;
  629                         else
  630                                 th->th_sum = in6_cksum_pseudo(ip6, tlen,
  631                                     IPPROTO_TCP, m->m_pkthdr.csum_data);
  632                         th->th_sum ^= 0xffff;
  633                 } else
  634                         th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
  635                 if (th->th_sum) {
  636                         TCPSTAT_INC(tcps_rcvbadsum);
  637                         goto drop;
  638                 }
  639 
  640                 /*
  641                  * Be proactive about unspecified IPv6 address in source.
  642                  * As we use all-zero to indicate unbounded/unconnected pcb,
  643                  * unspecified IPv6 address can be used to confuse us.
  644                  *
  645                  * Note that packets with unspecified IPv6 destination is
  646                  * already dropped in ip6_input.
  647                  */
  648                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
  649                         /* XXX stat */
  650                         goto drop;
  651                 }
  652         }
  653 #endif
  654 #if defined(INET) && defined(INET6)
  655         else
  656 #endif
  657 #ifdef INET
  658         {
  659                 /*
  660                  * Get IP and TCP header together in first mbuf.
  661                  * Note: IP leaves IP header in first mbuf.
  662                  */
  663                 if (off0 > sizeof (struct ip)) {
  664                         ip_stripoptions(m);
  665                         off0 = sizeof(struct ip);
  666                 }
  667                 if (m->m_len < sizeof (struct tcpiphdr)) {
  668                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
  669                             == NULL) {
  670                                 TCPSTAT_INC(tcps_rcvshort);
  671                                 return;
  672                         }
  673                 }
  674                 ip = mtod(m, struct ip *);
  675                 th = (struct tcphdr *)((caddr_t)ip + off0);
  676                 tlen = ntohs(ip->ip_len) - off0;
  677 
  678                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
  679                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  680                                 th->th_sum = m->m_pkthdr.csum_data;
  681                         else
  682                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
  683                                     ip->ip_dst.s_addr,
  684                                     htonl(m->m_pkthdr.csum_data + tlen +
  685                                     IPPROTO_TCP));
  686                         th->th_sum ^= 0xffff;
  687                 } else {
  688                         struct ipovly *ipov = (struct ipovly *)ip;
  689 
  690                         /*
  691                          * Checksum extended TCP header and data.
  692                          */
  693                         len = off0 + tlen;
  694                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
  695                         ipov->ih_len = htons(tlen);
  696                         th->th_sum = in_cksum(m, len);
  697                         /* Reset length for SDT probes. */
  698                         ip->ip_len = htons(tlen + off0);
  699                 }
  700 
  701                 if (th->th_sum) {
  702                         TCPSTAT_INC(tcps_rcvbadsum);
  703                         goto drop;
  704                 }
  705                 /* Re-initialization for later version check */
  706                 ip->ip_v = IPVERSION;
  707         }
  708 #endif /* INET */
  709 
  710 #ifdef INET6
  711         if (isipv6)
  712                 iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
  713 #endif
  714 #if defined(INET) && defined(INET6)
  715         else
  716 #endif
  717 #ifdef INET
  718                 iptos = ip->ip_tos;
  719 #endif
  720 
  721         /*
  722          * Check that TCP offset makes sense,
  723          * pull out TCP options and adjust length.              XXX
  724          */
  725         off = th->th_off << 2;
  726         if (off < sizeof (struct tcphdr) || off > tlen) {
  727                 TCPSTAT_INC(tcps_rcvbadoff);
  728                 goto drop;
  729         }
  730         tlen -= off;    /* tlen is used instead of ti->ti_len */
  731         if (off > sizeof (struct tcphdr)) {
  732 #ifdef INET6
  733                 if (isipv6) {
  734                         IP6_EXTHDR_CHECK(m, off0, off, );
  735                         ip6 = mtod(m, struct ip6_hdr *);
  736                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
  737                 }
  738 #endif
  739 #if defined(INET) && defined(INET6)
  740                 else
  741 #endif
  742 #ifdef INET
  743                 {
  744                         if (m->m_len < sizeof(struct ip) + off) {
  745                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
  746                                     == NULL) {
  747                                         TCPSTAT_INC(tcps_rcvshort);
  748                                         return;
  749                                 }
  750                                 ip = mtod(m, struct ip *);
  751                                 th = (struct tcphdr *)((caddr_t)ip + off0);
  752                         }
  753                 }
  754 #endif
  755                 optlen = off - sizeof (struct tcphdr);
  756                 optp = (u_char *)(th + 1);
  757         }
  758         thflags = th->th_flags;
  759 
  760         /*
  761          * Convert TCP protocol specific fields to host format.
  762          */
  763         tcp_fields_to_host(th);
  764 
  765         /*
  766          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
  767          */
  768         drop_hdrlen = off0 + off;
  769 
  770         /*
  771          * Locate pcb for segment; if we're likely to add or remove a
  772          * connection then first acquire pcbinfo lock.  There are two cases
  773          * where we might discover later we need a write lock despite the
  774          * flags: ACKs moving a connection out of the syncache, and ACKs for
  775          * a connection in TIMEWAIT.
  776          */
  777         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0) {
  778                 INP_INFO_WLOCK(&V_tcbinfo);
  779                 ti_locked = TI_WLOCKED;
  780         } else
  781                 ti_locked = TI_UNLOCKED;
  782 
  783         /*
  784          * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
  785          */
  786         if (
  787 #ifdef INET6
  788             (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
  789 #ifdef INET
  790             || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
  791 #endif
  792 #endif
  793 #if defined(INET) && !defined(INET6)
  794             (m->m_flags & M_IP_NEXTHOP)
  795 #endif
  796             )
  797                 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
  798 
  799 findpcb:
  800 #ifdef INVARIANTS
  801         if (ti_locked == TI_WLOCKED) {
  802                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  803         } else {
  804                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
  805         }
  806 #endif
  807 #ifdef INET6
  808         if (isipv6 && fwd_tag != NULL) {
  809                 struct sockaddr_in6 *next_hop6;
  810 
  811                 next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
  812                 /*
  813                  * Transparently forwarded. Pretend to be the destination.
  814                  * Already got one like this?
  815                  */
  816                 inp = in6_pcblookup_mbuf(&V_tcbinfo,
  817                     &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
  818                     INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
  819                 if (!inp) {
  820                         /*
  821                          * It's new.  Try to find the ambushing socket.
  822                          * Because we've rewritten the destination address,
  823                          * any hardware-generated hash is ignored.
  824                          */
  825                         inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
  826                             th->th_sport, &next_hop6->sin6_addr,
  827                             next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
  828                             th->th_dport, INPLOOKUP_WILDCARD |
  829                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  830                 }
  831         } else if (isipv6) {
  832                 inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
  833                     th->th_sport, &ip6->ip6_dst, th->th_dport,
  834                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  835                     m->m_pkthdr.rcvif, m);
  836         }
  837 #endif /* INET6 */
  838 #if defined(INET6) && defined(INET)
  839         else
  840 #endif
  841 #ifdef INET
  842         if (fwd_tag != NULL) {
  843                 struct sockaddr_in *next_hop;
  844 
  845                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
  846                 /*
  847                  * Transparently forwarded. Pretend to be the destination.
  848                  * already got one like this?
  849                  */
  850                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
  851                     ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
  852                     m->m_pkthdr.rcvif, m);
  853                 if (!inp) {
  854                         /*
  855                          * It's new.  Try to find the ambushing socket.
  856                          * Because we've rewritten the destination address,
  857                          * any hardware-generated hash is ignored.
  858                          */
  859                         inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
  860                             th->th_sport, next_hop->sin_addr,
  861                             next_hop->sin_port ? ntohs(next_hop->sin_port) :
  862                             th->th_dport, INPLOOKUP_WILDCARD |
  863                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  864                 }
  865         } else
  866                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
  867                     th->th_sport, ip->ip_dst, th->th_dport,
  868                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  869                     m->m_pkthdr.rcvif, m);
  870 #endif /* INET */
  871 
  872         /*
  873          * If the INPCB does not exist then all data in the incoming
  874          * segment is discarded and an appropriate RST is sent back.
  875          * XXX MRT Send RST using which routing table?
  876          */
  877         if (inp == NULL) {
  878                 /*
  879                  * Log communication attempts to ports that are not
  880                  * in use.
  881                  */
  882                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
  883                     tcp_log_in_vain == 2) {
  884                         if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
  885                                 log(LOG_INFO, "%s; %s: Connection attempt "
  886                                     "to closed port\n", s, __func__);
  887                 }
  888                 /*
  889                  * When blackholing do not respond with a RST but
  890                  * completely ignore the segment and drop it.
  891                  */
  892                 if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
  893                     V_blackhole == 2)
  894                         goto dropunlock;
  895 
  896                 rstreason = BANDLIM_RST_CLOSEDPORT;
  897                 goto dropwithreset;
  898         }
  899         INP_WLOCK_ASSERT(inp);
  900         if (!(inp->inp_flags & INP_HW_FLOWID)
  901             && (m->m_flags & M_FLOWID)
  902             && ((inp->inp_socket == NULL)
  903                 || !(inp->inp_socket->so_options & SO_ACCEPTCONN))) {
  904                 inp->inp_flags |= INP_HW_FLOWID;
  905                 inp->inp_flags &= ~INP_SW_FLOWID;
  906                 inp->inp_flowid = m->m_pkthdr.flowid;
  907         }
  908 #ifdef IPSEC
  909 #ifdef INET6
  910         if (isipv6 && ipsec6_in_reject(m, inp)) {
  911                 IPSEC6STAT_INC(ips_in_polvio);
  912                 goto dropunlock;
  913         } else
  914 #endif /* INET6 */
  915         if (ipsec4_in_reject(m, inp) != 0) {
  916                 IPSECSTAT_INC(ips_in_polvio);
  917                 goto dropunlock;
  918         }
  919 #endif /* IPSEC */
  920 
  921         /*
  922          * Check the minimum TTL for socket.
  923          */
  924         if (inp->inp_ip_minttl != 0) {
  925 #ifdef INET6
  926                 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
  927                         goto dropunlock;
  928                 else
  929 #endif
  930                 if (inp->inp_ip_minttl > ip->ip_ttl)
  931                         goto dropunlock;
  932         }
  933 
  934         /*
  935          * A previous connection in TIMEWAIT state is supposed to catch stray
  936          * or duplicate segments arriving late.  If this segment was a
  937          * legitimate new connection attempt, the old INPCB gets removed and
  938          * we can try again to find a listening socket.
  939          *
  940          * At this point, due to earlier optimism, we may hold only an inpcb
  941          * lock, and not the inpcbinfo write lock.  If so, we need to try to
  942          * acquire it, or if that fails, acquire a reference on the inpcb,
  943          * drop all locks, acquire a global write lock, and then re-acquire
  944          * the inpcb lock.  We may at that point discover that another thread
  945          * has tried to free the inpcb, in which case we need to loop back
  946          * and try to find a new inpcb to deliver to.
  947          *
  948          * XXXRW: It may be time to rethink timewait locking.
  949          */
  950 relocked:
  951         if (inp->inp_flags & INP_TIMEWAIT) {
  952                 if (ti_locked == TI_UNLOCKED) {
  953                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
  954                                 in_pcbref(inp);
  955                                 INP_WUNLOCK(inp);
  956                                 INP_INFO_WLOCK(&V_tcbinfo);
  957                                 ti_locked = TI_WLOCKED;
  958                                 INP_WLOCK(inp);
  959                                 if (in_pcbrele_wlocked(inp)) {
  960                                         inp = NULL;
  961                                         goto findpcb;
  962                                 }
  963                         } else
  964                                 ti_locked = TI_WLOCKED;
  965                 }
  966                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  967 
  968                 if (thflags & TH_SYN)
  969                         tcp_dooptions(&to, optp, optlen, TO_SYN);
  970                 /*
  971                  * NB: tcp_twcheck unlocks the INP and frees the mbuf.
  972                  */
  973                 if (tcp_twcheck(inp, &to, th, m, tlen))
  974                         goto findpcb;
  975                 INP_INFO_WUNLOCK(&V_tcbinfo);
  976                 return;
  977         }
  978         /*
  979          * The TCPCB may no longer exist if the connection is winding
  980          * down or it is in the CLOSED state.  Either way we drop the
  981          * segment and send an appropriate response.
  982          */
  983         tp = intotcpcb(inp);
  984         if (tp == NULL || tp->t_state == TCPS_CLOSED) {
  985                 rstreason = BANDLIM_RST_CLOSEDPORT;
  986                 goto dropwithreset;
  987         }
  988 
  989 #ifdef TCP_OFFLOAD
  990         if (tp->t_flags & TF_TOE) {
  991                 tcp_offload_input(tp, m);
  992                 m = NULL;       /* consumed by the TOE driver */
  993                 goto dropunlock;
  994         }
  995 #endif
  996 
  997         /*
  998          * We've identified a valid inpcb, but it could be that we need an
  999          * inpcbinfo write lock but don't hold it.  In this case, attempt to
 1000          * acquire using the same strategy as the TIMEWAIT case above.  If we
 1001          * relock, we have to jump back to 'relocked' as the connection might
 1002          * now be in TIMEWAIT.
 1003          */
 1004 #ifdef INVARIANTS
 1005         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0)
 1006                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1007 #endif
 1008         if (tp->t_state != TCPS_ESTABLISHED) {
 1009                 if (ti_locked == TI_UNLOCKED) {
 1010                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
 1011                                 in_pcbref(inp);
 1012                                 INP_WUNLOCK(inp);
 1013                                 INP_INFO_WLOCK(&V_tcbinfo);
 1014                                 ti_locked = TI_WLOCKED;
 1015                                 INP_WLOCK(inp);
 1016                                 if (in_pcbrele_wlocked(inp)) {
 1017                                         inp = NULL;
 1018                                         goto findpcb;
 1019                                 }
 1020                                 goto relocked;
 1021                         } else
 1022                                 ti_locked = TI_WLOCKED;
 1023                 }
 1024                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1025         }
 1026 
 1027 #ifdef MAC
 1028         INP_WLOCK_ASSERT(inp);
 1029         if (mac_inpcb_check_deliver(inp, m))
 1030                 goto dropunlock;
 1031 #endif
 1032         so = inp->inp_socket;
 1033         KASSERT(so != NULL, ("%s: so == NULL", __func__));
 1034 #ifdef TCPDEBUG
 1035         if (so->so_options & SO_DEBUG) {
 1036                 ostate = tp->t_state;
 1037 #ifdef INET6
 1038                 if (isipv6) {
 1039                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 1040                 } else
 1041 #endif
 1042                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 1043                 tcp_savetcp = *th;
 1044         }
 1045 #endif /* TCPDEBUG */
 1046         /*
 1047          * When the socket is accepting connections (the INPCB is in LISTEN
 1048          * state) we look into the SYN cache if this is a new connection
 1049          * attempt or the completion of a previous one.  Because listen
 1050          * sockets are never in TCPS_ESTABLISHED, the V_tcbinfo lock will be
 1051          * held in this case.
 1052          */
 1053         if (so->so_options & SO_ACCEPTCONN) {
 1054                 struct in_conninfo inc;
 1055 
 1056                 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
 1057                     "tp not listening", __func__));
 1058                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1059 
 1060                 bzero(&inc, sizeof(inc));
 1061 #ifdef INET6
 1062                 if (isipv6) {
 1063                         inc.inc_flags |= INC_ISIPV6;
 1064                         inc.inc6_faddr = ip6->ip6_src;
 1065                         inc.inc6_laddr = ip6->ip6_dst;
 1066                 } else
 1067 #endif
 1068                 {
 1069                         inc.inc_faddr = ip->ip_src;
 1070                         inc.inc_laddr = ip->ip_dst;
 1071                 }
 1072                 inc.inc_fport = th->th_sport;
 1073                 inc.inc_lport = th->th_dport;
 1074                 inc.inc_fibnum = so->so_fibnum;
 1075 
 1076                 /*
 1077                  * Check for an existing connection attempt in syncache if
 1078                  * the flag is only ACK.  A successful lookup creates a new
 1079                  * socket appended to the listen queue in SYN_RECEIVED state.
 1080                  */
 1081                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 1082                         /*
 1083                          * Parse the TCP options here because
 1084                          * syncookies need access to the reflected
 1085                          * timestamp.
 1086                          */
 1087                         tcp_dooptions(&to, optp, optlen, 0);
 1088                         /*
 1089                          * NB: syncache_expand() doesn't unlock
 1090                          * inp and tcpinfo locks.
 1091                          */
 1092                         if (!syncache_expand(&inc, &to, th, &so, m)) {
 1093                                 /*
 1094                                  * No syncache entry or ACK was not
 1095                                  * for our SYN/ACK.  Send a RST.
 1096                                  * NB: syncache did its own logging
 1097                                  * of the failure cause.
 1098                                  */
 1099                                 rstreason = BANDLIM_RST_OPENPORT;
 1100                                 goto dropwithreset;
 1101                         }
 1102                         if (so == NULL) {
 1103                                 /*
 1104                                  * We completed the 3-way handshake
 1105                                  * but could not allocate a socket
 1106                                  * either due to memory shortage,
 1107                                  * listen queue length limits or
 1108                                  * global socket limits.  Send RST
 1109                                  * or wait and have the remote end
 1110                                  * retransmit the ACK for another
 1111                                  * try.
 1112                                  */
 1113                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1114                                         log(LOG_DEBUG, "%s; %s: Listen socket: "
 1115                                             "Socket allocation failed due to "
 1116                                             "limits or memory shortage, %s\n",
 1117                                             s, __func__,
 1118                                             V_tcp_sc_rst_sock_fail ?
 1119                                             "sending RST" : "try again");
 1120                                 if (V_tcp_sc_rst_sock_fail) {
 1121                                         rstreason = BANDLIM_UNLIMITED;
 1122                                         goto dropwithreset;
 1123                                 } else
 1124                                         goto dropunlock;
 1125                         }
 1126                         /*
 1127                          * Socket is created in state SYN_RECEIVED.
 1128                          * Unlock the listen socket, lock the newly
 1129                          * created socket and update the tp variable.
 1130                          */
 1131                         INP_WUNLOCK(inp);       /* listen socket */
 1132                         inp = sotoinpcb(so);
 1133                         INP_WLOCK(inp);         /* new connection */
 1134                         tp = intotcpcb(inp);
 1135                         KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
 1136                             ("%s: ", __func__));
 1137 #ifdef TCP_SIGNATURE
 1138                         if (sig_checked == 0)  {
 1139                                 tcp_dooptions(&to, optp, optlen,
 1140                                     (thflags & TH_SYN) ? TO_SYN : 0);
 1141                                 if (!tcp_signature_verify_input(m, off0, tlen,
 1142                                     optlen, &to, th, tp->t_flags)) {
 1143 
 1144                                         /*
 1145                                          * In SYN_SENT state if it receives an
 1146                                          * RST, it is allowed for further
 1147                                          * processing.
 1148                                          */
 1149                                         if ((thflags & TH_RST) == 0 ||
 1150                                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1151                                                 goto dropunlock;
 1152                                 }
 1153                                 sig_checked = 1;
 1154                         }
 1155 #endif
 1156 
 1157                         /*
 1158                          * Process the segment and the data it
 1159                          * contains.  tcp_do_segment() consumes
 1160                          * the mbuf chain and unlocks the inpcb.
 1161                          */
 1162                         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
 1163                             iptos, ti_locked);
 1164                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1165                         return;
 1166                 }
 1167                 /*
 1168                  * Segment flag validation for new connection attempts:
 1169                  *
 1170                  * Our (SYN|ACK) response was rejected.
 1171                  * Check with syncache and remove entry to prevent
 1172                  * retransmits.
 1173                  *
 1174                  * NB: syncache_chkrst does its own logging of failure
 1175                  * causes.
 1176                  */
 1177                 if (thflags & TH_RST) {
 1178                         syncache_chkrst(&inc, th);
 1179                         goto dropunlock;
 1180                 }
 1181                 /*
 1182                  * We can't do anything without SYN.
 1183                  */
 1184                 if ((thflags & TH_SYN) == 0) {
 1185                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1186                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1187                                     "SYN is missing, segment ignored\n",
 1188                                     s, __func__);
 1189                         TCPSTAT_INC(tcps_badsyn);
 1190                         goto dropunlock;
 1191                 }
 1192                 /*
 1193                  * (SYN|ACK) is bogus on a listen socket.
 1194                  */
 1195                 if (thflags & TH_ACK) {
 1196                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1197                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1198                                     "SYN|ACK invalid, segment rejected\n",
 1199                                     s, __func__);
 1200                         syncache_badack(&inc);  /* XXX: Not needed! */
 1201                         TCPSTAT_INC(tcps_badsyn);
 1202                         rstreason = BANDLIM_RST_OPENPORT;
 1203                         goto dropwithreset;
 1204                 }
 1205                 /*
 1206                  * If the drop_synfin option is enabled, drop all
 1207                  * segments with both the SYN and FIN bits set.
 1208                  * This prevents e.g. nmap from identifying the
 1209                  * TCP/IP stack.
 1210                  * XXX: Poor reasoning.  nmap has other methods
 1211                  * and is constantly refining its stack detection
 1212                  * strategies.
 1213                  * XXX: This is a violation of the TCP specification
 1214                  * and was used by RFC1644.
 1215                  */
 1216                 if ((thflags & TH_FIN) && V_drop_synfin) {
 1217                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1218                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1219                                     "SYN|FIN segment ignored (based on "
 1220                                     "sysctl setting)\n", s, __func__);
 1221                         TCPSTAT_INC(tcps_badsyn);
 1222                         goto dropunlock;
 1223                 }
 1224                 /*
 1225                  * Segment's flags are (SYN) or (SYN|FIN).
 1226                  *
 1227                  * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
 1228                  * as they do not affect the state of the TCP FSM.
 1229                  * The data pointed to by TH_URG and th_urp is ignored.
 1230                  */
 1231                 KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
 1232                     ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
 1233                 KASSERT(thflags & (TH_SYN),
 1234                     ("%s: Listen socket: TH_SYN not set", __func__));
 1235 #ifdef INET6
 1236                 /*
 1237                  * If deprecated address is forbidden,
 1238                  * we do not accept SYN to deprecated interface
 1239                  * address to prevent any new inbound connection from
 1240                  * getting established.
 1241                  * When we do not accept SYN, we send a TCP RST,
 1242                  * with deprecated source address (instead of dropping
 1243                  * it).  We compromise it as it is much better for peer
 1244                  * to send a RST, and RST will be the final packet
 1245                  * for the exchange.
 1246                  *
 1247                  * If we do not forbid deprecated addresses, we accept
 1248                  * the SYN packet.  RFC2462 does not suggest dropping
 1249                  * SYN in this case.
 1250                  * If we decipher RFC2462 5.5.4, it says like this:
 1251                  * 1. use of deprecated addr with existing
 1252                  *    communication is okay - "SHOULD continue to be
 1253                  *    used"
 1254                  * 2. use of it with new communication:
 1255                  *   (2a) "SHOULD NOT be used if alternate address
 1256                  *        with sufficient scope is available"
 1257                  *   (2b) nothing mentioned otherwise.
 1258                  * Here we fall into (2b) case as we have no choice in
 1259                  * our source address selection - we must obey the peer.
 1260                  *
 1261                  * The wording in RFC2462 is confusing, and there are
 1262                  * multiple description text for deprecated address
 1263                  * handling - worse, they are not exactly the same.
 1264                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 1265                  */
 1266                 if (isipv6 && !V_ip6_use_deprecated) {
 1267                         struct in6_ifaddr *ia6;
 1268 
 1269                         ia6 = ip6_getdstifaddr(m);
 1270                         if (ia6 != NULL &&
 1271                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 1272                                 ifa_free(&ia6->ia_ifa);
 1273                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1274                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1275                                         "Connection attempt to deprecated "
 1276                                         "IPv6 address rejected\n",
 1277                                         s, __func__);
 1278                                 rstreason = BANDLIM_RST_OPENPORT;
 1279                                 goto dropwithreset;
 1280                         }
 1281                         if (ia6)
 1282                                 ifa_free(&ia6->ia_ifa);
 1283                 }
 1284 #endif /* INET6 */
 1285                 /*
 1286                  * Basic sanity checks on incoming SYN requests:
 1287                  *   Don't respond if the destination is a link layer
 1288                  *      broadcast according to RFC1122 4.2.3.10, p. 104.
 1289                  *   If it is from this socket it must be forged.
 1290                  *   Don't respond if the source or destination is a
 1291                  *      global or subnet broad- or multicast address.
 1292                  *   Note that it is quite possible to receive unicast
 1293                  *      link-layer packets with a broadcast IP address. Use
 1294                  *      in_broadcast() to find them.
 1295                  */
 1296                 if (m->m_flags & (M_BCAST|M_MCAST)) {
 1297                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1298                             log(LOG_DEBUG, "%s; %s: Listen socket: "
 1299                                 "Connection attempt from broad- or multicast "
 1300                                 "link layer address ignored\n", s, __func__);
 1301                         goto dropunlock;
 1302                 }
 1303 #ifdef INET6
 1304                 if (isipv6) {
 1305                         if (th->th_dport == th->th_sport &&
 1306                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
 1307                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1308                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1309                                         "Connection attempt to/from self "
 1310                                         "ignored\n", s, __func__);
 1311                                 goto dropunlock;
 1312                         }
 1313                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 1314                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
 1315                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1316                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1317                                         "Connection attempt from/to multicast "
 1318                                         "address ignored\n", s, __func__);
 1319                                 goto dropunlock;
 1320                         }
 1321                 }
 1322 #endif
 1323 #if defined(INET) && defined(INET6)
 1324                 else
 1325 #endif
 1326 #ifdef INET
 1327                 {
 1328                         if (th->th_dport == th->th_sport &&
 1329                             ip->ip_dst.s_addr == ip->ip_src.s_addr) {
 1330                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1331                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1332                                         "Connection attempt from/to self "
 1333                                         "ignored\n", s, __func__);
 1334                                 goto dropunlock;
 1335                         }
 1336                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 1337                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 1338                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 1339                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
 1340                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1341                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1342                                         "Connection attempt from/to broad- "
 1343                                         "or multicast address ignored\n",
 1344                                         s, __func__);
 1345                                 goto dropunlock;
 1346                         }
 1347                 }
 1348 #endif
 1349                 /*
 1350                  * SYN appears to be valid.  Create compressed TCP state
 1351                  * for syncache.
 1352                  */
 1353 #ifdef TCPDEBUG
 1354                 if (so->so_options & SO_DEBUG)
 1355                         tcp_trace(TA_INPUT, ostate, tp,
 1356                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1357 #endif
 1358                 tcp_dooptions(&to, optp, optlen, TO_SYN);
 1359                 syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
 1360                 /*
 1361                  * Entry added to syncache and mbuf consumed.
 1362                  * Everything already unlocked by syncache_add().
 1363                  */
 1364                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1365                 return;
 1366         } else if (tp->t_state == TCPS_LISTEN) {
 1367                 /*
 1368                  * When a listen socket is torn down the SO_ACCEPTCONN
 1369                  * flag is removed first while connections are drained
 1370                  * from the accept queue in a unlock/lock cycle of the
 1371                  * ACCEPT_LOCK, opening a race condition allowing a SYN
 1372                  * attempt go through unhandled.
 1373                  */
 1374                 goto dropunlock;
 1375         }
 1376 
 1377 #ifdef TCP_SIGNATURE
 1378         if (sig_checked == 0)  {
 1379                 tcp_dooptions(&to, optp, optlen,
 1380                     (thflags & TH_SYN) ? TO_SYN : 0);
 1381                 if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
 1382                     th, tp->t_flags)) {
 1383 
 1384                         /*
 1385                          * In SYN_SENT state if it receives an RST, it is
 1386                          * allowed for further processing.
 1387                          */
 1388                         if ((thflags & TH_RST) == 0 ||
 1389                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1390                                 goto dropunlock;
 1391                 }
 1392                 sig_checked = 1;
 1393         }
 1394 #endif
 1395 
 1396         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1397 
 1398         /*
 1399          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
 1400          * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
 1401          * the inpcb, and unlocks pcbinfo.
 1402          */
 1403         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
 1404         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1405         return;
 1406 
 1407 dropwithreset:
 1408         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1409 
 1410         if (ti_locked == TI_WLOCKED) {
 1411                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1412                 ti_locked = TI_UNLOCKED;
 1413         }
 1414 #ifdef INVARIANTS
 1415         else {
 1416                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
 1417                     "ti_locked: %d", __func__, ti_locked));
 1418                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1419         }
 1420 #endif
 1421 
 1422         if (inp != NULL) {
 1423                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 1424                 INP_WUNLOCK(inp);
 1425         } else
 1426                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 1427         m = NULL;       /* mbuf chain got consumed. */
 1428         goto drop;
 1429 
 1430 dropunlock:
 1431         if (m != NULL)
 1432                 TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1433 
 1434         if (ti_locked == TI_WLOCKED) {
 1435                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1436                 ti_locked = TI_UNLOCKED;
 1437         }
 1438 #ifdef INVARIANTS
 1439         else {
 1440                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
 1441                     "ti_locked: %d", __func__, ti_locked));
 1442                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1443         }
 1444 #endif
 1445 
 1446         if (inp != NULL)
 1447                 INP_WUNLOCK(inp);
 1448 
 1449 drop:
 1450         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1451         if (s != NULL)
 1452                 free(s, M_TCPLOG);
 1453         if (m != NULL)
 1454                 m_freem(m);
 1455 }
 1456 
 1457 static void
 1458 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 1459     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
 1460     int ti_locked)
 1461 {
 1462         int thflags, acked, ourfinisacked, needoutput = 0;
 1463         int rstreason, todrop, win;
 1464         u_long tiwin;
 1465         char *s;
 1466         struct in_conninfo *inc;
 1467         struct mbuf *mfree;
 1468         struct tcpopt to;
 1469 
 1470 #ifdef TCPDEBUG
 1471         /*
 1472          * The size of tcp_saveipgen must be the size of the max ip header,
 1473          * now IPv6.
 1474          */
 1475         u_char tcp_saveipgen[IP6_HDR_LEN];
 1476         struct tcphdr tcp_savetcp;
 1477         short ostate = 0;
 1478 #endif
 1479         thflags = th->th_flags;
 1480         inc = &tp->t_inpcb->inp_inc;
 1481         tp->sackhint.last_sack_ack = 0;
 1482 
 1483         /*
 1484          * If this is either a state-changing packet or current state isn't
 1485          * established, we require a write lock on tcbinfo.  Otherwise, we
 1486          * allow the tcbinfo to be in either alocked or unlocked, as the
 1487          * caller may have unnecessarily acquired a write lock due to a race.
 1488          */
 1489         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
 1490             tp->t_state != TCPS_ESTABLISHED) {
 1491                 KASSERT(ti_locked == TI_WLOCKED, ("%s ti_locked %d for "
 1492                     "SYN/FIN/RST/!EST", __func__, ti_locked));
 1493                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1494         } else {
 1495 #ifdef INVARIANTS
 1496                 if (ti_locked == TI_WLOCKED)
 1497                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1498                 else {
 1499                         KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
 1500                             "ti_locked: %d", __func__, ti_locked));
 1501                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1502                 }
 1503 #endif
 1504         }
 1505         INP_WLOCK_ASSERT(tp->t_inpcb);
 1506         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
 1507             __func__));
 1508         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
 1509             __func__));
 1510 
 1511         /*
 1512          * Segment received on connection.
 1513          * Reset idle time and keep-alive timer.
 1514          * XXX: This should be done after segment
 1515          * validation to ignore broken/spoofed segs.
 1516          */
 1517         tp->t_rcvtime = ticks;
 1518         if (TCPS_HAVEESTABLISHED(tp->t_state))
 1519                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 1520 
 1521         /*
 1522          * Unscale the window into a 32-bit value.
 1523          * For the SYN_SENT state the scale is zero.
 1524          */
 1525         tiwin = th->th_win << tp->snd_scale;
 1526 
 1527         /*
 1528          * TCP ECN processing.
 1529          */
 1530         if (tp->t_flags & TF_ECN_PERMIT) {
 1531                 if (thflags & TH_CWR)
 1532                         tp->t_flags &= ~TF_ECN_SND_ECE;
 1533                 switch (iptos & IPTOS_ECN_MASK) {
 1534                 case IPTOS_ECN_CE:
 1535                         tp->t_flags |= TF_ECN_SND_ECE;
 1536                         TCPSTAT_INC(tcps_ecn_ce);
 1537                         break;
 1538                 case IPTOS_ECN_ECT0:
 1539                         TCPSTAT_INC(tcps_ecn_ect0);
 1540                         break;
 1541                 case IPTOS_ECN_ECT1:
 1542                         TCPSTAT_INC(tcps_ecn_ect1);
 1543                         break;
 1544                 }
 1545                 /* Congestion experienced. */
 1546                 if (thflags & TH_ECE) {
 1547                         cc_cong_signal(tp, th, CC_ECN);
 1548                 }
 1549         }
 1550 
 1551         /*
 1552          * Parse options on any incoming segment.
 1553          */
 1554         tcp_dooptions(&to, (u_char *)(th + 1),
 1555             (th->th_off << 2) - sizeof(struct tcphdr),
 1556             (thflags & TH_SYN) ? TO_SYN : 0);
 1557 
 1558         /*
 1559          * If echoed timestamp is later than the current time,
 1560          * fall back to non RFC1323 RTT calculation.  Normalize
 1561          * timestamp if syncookies were used when this connection
 1562          * was established.
 1563          */
 1564         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
 1565                 to.to_tsecr -= tp->ts_offset;
 1566                 if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
 1567                         to.to_tsecr = 0;
 1568         }
 1569         /*
 1570          * If timestamps were negotiated during SYN/ACK they should
 1571          * appear on every segment during this session and vice versa.
 1572          */
 1573         if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
 1574                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1575                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1576                             "no action\n", s, __func__);
 1577                         free(s, M_TCPLOG);
 1578                 }
 1579         }
 1580         if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
 1581                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1582                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1583                             "no action\n", s, __func__);
 1584                         free(s, M_TCPLOG);
 1585                 }
 1586         }
 1587 
 1588         /*
 1589          * Process options only when we get SYN/ACK back. The SYN case
 1590          * for incoming connections is handled in tcp_syncache.
 1591          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
 1592          * or <SYN,ACK>) segment itself is never scaled.
 1593          * XXX this is traditional behavior, may need to be cleaned up.
 1594          */
 1595         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
 1596                 if ((to.to_flags & TOF_SCALE) &&
 1597                     (tp->t_flags & TF_REQ_SCALE)) {
 1598                         tp->t_flags |= TF_RCVD_SCALE;
 1599                         tp->snd_scale = to.to_wscale;
 1600                 }
 1601                 /*
 1602                  * Initial send window.  It will be updated with
 1603                  * the next incoming segment to the scaled value.
 1604                  */
 1605                 tp->snd_wnd = th->th_win;
 1606                 if (to.to_flags & TOF_TS) {
 1607                         tp->t_flags |= TF_RCVD_TSTMP;
 1608                         tp->ts_recent = to.to_tsval;
 1609                         tp->ts_recent_age = tcp_ts_getticks();
 1610                 }
 1611                 if (to.to_flags & TOF_MSS)
 1612                         tcp_mss(tp, to.to_mss);
 1613                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 1614                     (to.to_flags & TOF_SACKPERM) == 0)
 1615                         tp->t_flags &= ~TF_SACK_PERMIT;
 1616         }
 1617 
 1618         /*
 1619          * Header prediction: check for the two common cases
 1620          * of a uni-directional data xfer.  If the packet has
 1621          * no control flags, is in-sequence, the window didn't
 1622          * change and we're not retransmitting, it's a
 1623          * candidate.  If the length is zero and the ack moved
 1624          * forward, we're the sender side of the xfer.  Just
 1625          * free the data acked & wake any higher level process
 1626          * that was blocked waiting for space.  If the length
 1627          * is non-zero and the ack didn't move, we're the
 1628          * receiver side.  If we're getting packets in-order
 1629          * (the reassembly queue is empty), add the data to
 1630          * the socket buffer and note that we need a delayed ack.
 1631          * Make sure that the hidden state-flags are also off.
 1632          * Since we check for TCPS_ESTABLISHED first, it can only
 1633          * be TH_NEEDSYN.
 1634          */
 1635         if (tp->t_state == TCPS_ESTABLISHED &&
 1636             th->th_seq == tp->rcv_nxt &&
 1637             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 1638             tp->snd_nxt == tp->snd_max &&
 1639             tiwin && tiwin == tp->snd_wnd && 
 1640             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 1641             LIST_EMPTY(&tp->t_segq) &&
 1642             ((to.to_flags & TOF_TS) == 0 ||
 1643              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
 1644 
 1645                 /*
 1646                  * If last ACK falls within this segment's sequence numbers,
 1647                  * record the timestamp.
 1648                  * NOTE that the test is modified according to the latest
 1649                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 1650                  */
 1651                 if ((to.to_flags & TOF_TS) != 0 &&
 1652                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 1653                         tp->ts_recent_age = tcp_ts_getticks();
 1654                         tp->ts_recent = to.to_tsval;
 1655                 }
 1656 
 1657                 if (tlen == 0) {
 1658                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 1659                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 1660                             !IN_RECOVERY(tp->t_flags) &&
 1661                             (to.to_flags & TOF_SACK) == 0 &&
 1662                             TAILQ_EMPTY(&tp->snd_holes)) {
 1663                                 /*
 1664                                  * This is a pure ack for outstanding data.
 1665                                  */
 1666                                 if (ti_locked == TI_WLOCKED)
 1667                                         INP_INFO_WUNLOCK(&V_tcbinfo);
 1668                                 ti_locked = TI_UNLOCKED;
 1669 
 1670                                 TCPSTAT_INC(tcps_predack);
 1671 
 1672                                 /*
 1673                                  * "bad retransmit" recovery.
 1674                                  */
 1675                                 if (tp->t_rxtshift == 1 &&
 1676                                     tp->t_flags & TF_PREVVALID &&
 1677                                     (int)(ticks - tp->t_badrxtwin) < 0) {
 1678                                         cc_cong_signal(tp, th, CC_RTO_ERR);
 1679                                 }
 1680 
 1681                                 /*
 1682                                  * Recalculate the transmit timer / rtt.
 1683                                  *
 1684                                  * Some boxes send broken timestamp replies
 1685                                  * during the SYN+ACK phase, ignore
 1686                                  * timestamps of 0 or we could calculate a
 1687                                  * huge RTT and blow up the retransmit timer.
 1688                                  */
 1689                                 if ((to.to_flags & TOF_TS) != 0 &&
 1690                                     to.to_tsecr) {
 1691                                         u_int t;
 1692 
 1693                                         t = tcp_ts_getticks() - to.to_tsecr;
 1694                                         if (!tp->t_rttlow || tp->t_rttlow > t)
 1695                                                 tp->t_rttlow = t;
 1696                                         tcp_xmit_timer(tp,
 1697                                             TCP_TS_TO_TICKS(t) + 1);
 1698                                 } else if (tp->t_rtttime &&
 1699                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
 1700                                         if (!tp->t_rttlow ||
 1701                                             tp->t_rttlow > ticks - tp->t_rtttime)
 1702                                                 tp->t_rttlow = ticks - tp->t_rtttime;
 1703                                         tcp_xmit_timer(tp,
 1704                                                         ticks - tp->t_rtttime);
 1705                                 }
 1706                                 acked = BYTES_THIS_ACK(tp, th);
 1707 
 1708                                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 1709                                 hhook_run_tcp_est_in(tp, th, &to);
 1710 
 1711                                 TCPSTAT_INC(tcps_rcvackpack);
 1712                                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 1713                                 sbdrop(&so->so_snd, acked);
 1714                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
 1715                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 1716                                         tp->snd_recover = th->th_ack - 1;
 1717                                 
 1718                                 /*
 1719                                  * Let the congestion control algorithm update
 1720                                  * congestion control related information. This
 1721                                  * typically means increasing the congestion
 1722                                  * window.
 1723                                  */
 1724                                 cc_ack_received(tp, th, CC_ACK);
 1725 
 1726                                 tp->snd_una = th->th_ack;
 1727                                 /*
 1728                                  * Pull snd_wl2 up to prevent seq wrap relative
 1729                                  * to th_ack.
 1730                                  */
 1731                                 tp->snd_wl2 = th->th_ack;
 1732                                 tp->t_dupacks = 0;
 1733                                 m_freem(m);
 1734                                 ND6_HINT(tp); /* Some progress has been made. */
 1735 
 1736                                 /*
 1737                                  * If all outstanding data are acked, stop
 1738                                  * retransmit timer, otherwise restart timer
 1739                                  * using current (possibly backed-off) value.
 1740                                  * If process is waiting for space,
 1741                                  * wakeup/selwakeup/signal.  If data
 1742                                  * are ready to send, let tcp_output
 1743                                  * decide between more output or persist.
 1744                                  */
 1745 #ifdef TCPDEBUG
 1746                                 if (so->so_options & SO_DEBUG)
 1747                                         tcp_trace(TA_INPUT, ostate, tp,
 1748                                             (void *)tcp_saveipgen,
 1749                                             &tcp_savetcp, 0);
 1750 #endif
 1751                                 if (tp->snd_una == tp->snd_max)
 1752                                         tcp_timer_activate(tp, TT_REXMT, 0);
 1753                                 else if (!tcp_timer_active(tp, TT_PERSIST))
 1754                                         tcp_timer_activate(tp, TT_REXMT,
 1755                                                       tp->t_rxtcur);
 1756                                 sowwakeup(so);
 1757                                 if (so->so_snd.sb_cc)
 1758                                         (void) tcp_output(tp);
 1759                                 goto check_delack;
 1760                         }
 1761                 } else if (th->th_ack == tp->snd_una &&
 1762                     tlen <= sbspace(&so->so_rcv)) {
 1763                         int newsize = 0;        /* automatic sockbuf scaling */
 1764 
 1765                         /*
 1766                          * This is a pure, in-sequence data packet with
 1767                          * nothing on the reassembly queue and we have enough
 1768                          * buffer space to take it.
 1769                          */
 1770                         if (ti_locked == TI_WLOCKED)
 1771                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1772                         ti_locked = TI_UNLOCKED;
 1773 
 1774                         /* Clean receiver SACK report if present */
 1775                         if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
 1776                                 tcp_clean_sackreport(tp);
 1777                         TCPSTAT_INC(tcps_preddat);
 1778                         tp->rcv_nxt += tlen;
 1779                         /*
 1780                          * Pull snd_wl1 up to prevent seq wrap relative to
 1781                          * th_seq.
 1782                          */
 1783                         tp->snd_wl1 = th->th_seq;
 1784                         /*
 1785                          * Pull rcv_up up to prevent seq wrap relative to
 1786                          * rcv_nxt.
 1787                          */
 1788                         tp->rcv_up = tp->rcv_nxt;
 1789                         TCPSTAT_INC(tcps_rcvpack);
 1790                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 1791                         ND6_HINT(tp);   /* Some progress has been made */
 1792 #ifdef TCPDEBUG
 1793                         if (so->so_options & SO_DEBUG)
 1794                                 tcp_trace(TA_INPUT, ostate, tp,
 1795                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1796 #endif
 1797                 /*
 1798                  * Automatic sizing of receive socket buffer.  Often the send
 1799                  * buffer size is not optimally adjusted to the actual network
 1800                  * conditions at hand (delay bandwidth product).  Setting the
 1801                  * buffer size too small limits throughput on links with high
 1802                  * bandwidth and high delay (eg. trans-continental/oceanic links).
 1803                  *
 1804                  * On the receive side the socket buffer memory is only rarely
 1805                  * used to any significant extent.  This allows us to be much
 1806                  * more aggressive in scaling the receive socket buffer.  For
 1807                  * the case that the buffer space is actually used to a large
 1808                  * extent and we run out of kernel memory we can simply drop
 1809                  * the new segments; TCP on the sender will just retransmit it
 1810                  * later.  Setting the buffer size too big may only consume too
 1811                  * much kernel memory if the application doesn't read() from
 1812                  * the socket or packet loss or reordering makes use of the
 1813                  * reassembly queue.
 1814                  *
 1815                  * The criteria to step up the receive buffer one notch are:
 1816                  *  1. the number of bytes received during the time it takes
 1817                  *     one timestamp to be reflected back to us (the RTT);
 1818                  *  2. received bytes per RTT is within seven eighth of the
 1819                  *     current socket buffer size;
 1820                  *  3. receive buffer size has not hit maximal automatic size;
 1821                  *
 1822                  * This algorithm does one step per RTT at most and only if
 1823                  * we receive a bulk stream w/o packet losses or reorderings.
 1824                  * Shrinking the buffer during idle times is not necessary as
 1825                  * it doesn't consume any memory when idle.
 1826                  *
 1827                  * TODO: Only step up if the application is actually serving
 1828                  * the buffer to better manage the socket buffer resources.
 1829                  */
 1830                         if (V_tcp_do_autorcvbuf &&
 1831                             to.to_tsecr &&
 1832                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
 1833                                 if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
 1834                                     to.to_tsecr - tp->rfbuf_ts < hz) {
 1835                                         if (tp->rfbuf_cnt >
 1836                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
 1837                                             so->so_rcv.sb_hiwat <
 1838                                             V_tcp_autorcvbuf_max) {
 1839                                                 newsize =
 1840                                                     min(so->so_rcv.sb_hiwat +
 1841                                                     V_tcp_autorcvbuf_inc,
 1842                                                     V_tcp_autorcvbuf_max);
 1843                                         }
 1844                                         /* Start over with next RTT. */
 1845                                         tp->rfbuf_ts = 0;
 1846                                         tp->rfbuf_cnt = 0;
 1847                                 } else
 1848                                         tp->rfbuf_cnt += tlen;  /* add up */
 1849                         }
 1850 
 1851                         /* Add data to socket buffer. */
 1852                         SOCKBUF_LOCK(&so->so_rcv);
 1853                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 1854                                 m_freem(m);
 1855                         } else {
 1856                                 /*
 1857                                  * Set new socket buffer size.
 1858                                  * Give up when limit is reached.
 1859                                  */
 1860                                 if (newsize)
 1861                                         if (!sbreserve_locked(&so->so_rcv,
 1862                                             newsize, so, NULL))
 1863                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
 1864                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 1865                                 sbappendstream_locked(&so->so_rcv, m);
 1866                         }
 1867                         /* NB: sorwakeup_locked() does an implicit unlock. */
 1868                         sorwakeup_locked(so);
 1869                         if (DELAY_ACK(tp, tlen)) {
 1870                                 tp->t_flags |= TF_DELACK;
 1871                         } else {
 1872                                 tp->t_flags |= TF_ACKNOW;
 1873                                 tcp_output(tp);
 1874                         }
 1875                         goto check_delack;
 1876                 }
 1877         }
 1878 
 1879         /*
 1880          * Calculate amount of space in receive window,
 1881          * and then do TCP input processing.
 1882          * Receive window is amount of space in rcv queue,
 1883          * but not less than advertised window.
 1884          */
 1885         win = sbspace(&so->so_rcv);
 1886         if (win < 0)
 1887                 win = 0;
 1888         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 1889 
 1890         /* Reset receive buffer auto scaling when not in bulk receive mode. */
 1891         tp->rfbuf_ts = 0;
 1892         tp->rfbuf_cnt = 0;
 1893 
 1894         switch (tp->t_state) {
 1895 
 1896         /*
 1897          * If the state is SYN_RECEIVED:
 1898          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
 1899          */
 1900         case TCPS_SYN_RECEIVED:
 1901                 if ((thflags & TH_ACK) &&
 1902                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
 1903                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1904                                 rstreason = BANDLIM_RST_OPENPORT;
 1905                                 goto dropwithreset;
 1906                 }
 1907                 break;
 1908 
 1909         /*
 1910          * If the state is SYN_SENT:
 1911          *      if seg contains an ACK, but not for our SYN, drop the input.
 1912          *      if seg contains a RST, then drop the connection.
 1913          *      if seg does not contain SYN, then drop it.
 1914          * Otherwise this is an acceptable SYN segment
 1915          *      initialize tp->rcv_nxt and tp->irs
 1916          *      if seg contains ack then advance tp->snd_una
 1917          *      if seg contains an ECE and ECN support is enabled, the stream
 1918          *          is ECN capable.
 1919          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
 1920          *      arrange for segment to be acked (eventually)
 1921          *      continue processing rest of data/controls, beginning with URG
 1922          */
 1923         case TCPS_SYN_SENT:
 1924                 if ((thflags & TH_ACK) &&
 1925                     (SEQ_LEQ(th->th_ack, tp->iss) ||
 1926                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1927                         rstreason = BANDLIM_UNLIMITED;
 1928                         goto dropwithreset;
 1929                 }
 1930                 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
 1931                         TCP_PROBE5(connect__refused, NULL, tp,
 1932                             mtod(m, const char *), tp, th);
 1933                         tp = tcp_drop(tp, ECONNREFUSED);
 1934                 }
 1935                 if (thflags & TH_RST)
 1936                         goto drop;
 1937                 if (!(thflags & TH_SYN))
 1938                         goto drop;
 1939 
 1940                 tp->irs = th->th_seq;
 1941                 tcp_rcvseqinit(tp);
 1942                 if (thflags & TH_ACK) {
 1943                         TCPSTAT_INC(tcps_connects);
 1944                         soisconnected(so);
 1945 #ifdef MAC
 1946                         mac_socketpeer_set_from_mbuf(m, so);
 1947 #endif
 1948                         /* Do window scaling on this connection? */
 1949                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 1950                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 1951                                 tp->rcv_scale = tp->request_r_scale;
 1952                         }
 1953                         tp->rcv_adv += imin(tp->rcv_wnd,
 1954                             TCP_MAXWIN << tp->rcv_scale);
 1955                         tp->snd_una++;          /* SYN is acked */
 1956                         /*
 1957                          * If there's data, delay ACK; if there's also a FIN
 1958                          * ACKNOW will be turned on later.
 1959                          */
 1960                         if (DELAY_ACK(tp, tlen) && tlen != 0)
 1961                                 tcp_timer_activate(tp, TT_DELACK,
 1962                                     tcp_delacktime);
 1963                         else
 1964                                 tp->t_flags |= TF_ACKNOW;
 1965 
 1966                         if ((thflags & TH_ECE) && V_tcp_do_ecn) {
 1967                                 tp->t_flags |= TF_ECN_PERMIT;
 1968                                 TCPSTAT_INC(tcps_ecn_shs);
 1969                         }
 1970                         
 1971                         /*
 1972                          * Received <SYN,ACK> in SYN_SENT[*] state.
 1973                          * Transitions:
 1974                          *      SYN_SENT  --> ESTABLISHED
 1975                          *      SYN_SENT* --> FIN_WAIT_1
 1976                          */
 1977                         tp->t_starttime = ticks;
 1978                         if (tp->t_flags & TF_NEEDFIN) {
 1979                                 tcp_state_change(tp, TCPS_FIN_WAIT_1);
 1980                                 tp->t_flags &= ~TF_NEEDFIN;
 1981                                 thflags &= ~TH_SYN;
 1982                         } else {
 1983                                 tcp_state_change(tp, TCPS_ESTABLISHED);
 1984                                 TCP_PROBE5(connect__established, NULL, tp,
 1985                                     mtod(m, const char *), tp, th);
 1986                                 cc_conn_init(tp);
 1987                                 tcp_timer_activate(tp, TT_KEEP,
 1988                                     TP_KEEPIDLE(tp));
 1989                         }
 1990                 } else {
 1991                         /*
 1992                          * Received initial SYN in SYN-SENT[*] state =>
 1993                          * simultaneous open.  If segment contains CC option
 1994                          * and there is a cached CC, apply TAO test.
 1995                          * If it succeeds, connection is * half-synchronized.
 1996                          * Otherwise, do 3-way handshake:
 1997                          *        SYN-SENT -> SYN-RECEIVED
 1998                          *        SYN-SENT* -> SYN-RECEIVED*
 1999                          * If there was no CC option, clear cached CC value.
 2000                          */
 2001                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 2002                         tcp_timer_activate(tp, TT_REXMT, 0);
 2003                         tcp_state_change(tp, TCPS_SYN_RECEIVED);
 2004                 }
 2005 
 2006                 KASSERT(ti_locked == TI_WLOCKED, ("%s: trimthenstep6: "
 2007                     "ti_locked %d", __func__, ti_locked));
 2008                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2009                 INP_WLOCK_ASSERT(tp->t_inpcb);
 2010 
 2011                 /*
 2012                  * Advance th->th_seq to correspond to first data byte.
 2013                  * If data, trim to stay within window,
 2014                  * dropping FIN if necessary.
 2015                  */
 2016                 th->th_seq++;
 2017                 if (tlen > tp->rcv_wnd) {
 2018                         todrop = tlen - tp->rcv_wnd;
 2019                         m_adj(m, -todrop);
 2020                         tlen = tp->rcv_wnd;
 2021                         thflags &= ~TH_FIN;
 2022                         TCPSTAT_INC(tcps_rcvpackafterwin);
 2023                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2024                 }
 2025                 tp->snd_wl1 = th->th_seq - 1;
 2026                 tp->rcv_up = th->th_seq;
 2027                 /*
 2028                  * Client side of transaction: already sent SYN and data.
 2029                  * If the remote host used T/TCP to validate the SYN,
 2030                  * our data will be ACK'd; if so, enter normal data segment
 2031                  * processing in the middle of step 5, ack processing.
 2032                  * Otherwise, goto step 6.
 2033                  */
 2034                 if (thflags & TH_ACK)
 2035                         goto process_ACK;
 2036 
 2037                 goto step6;
 2038 
 2039         /*
 2040          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
 2041          *      do normal processing.
 2042          *
 2043          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
 2044          */
 2045         case TCPS_LAST_ACK:
 2046         case TCPS_CLOSING:
 2047                 break;  /* continue normal processing */
 2048         }
 2049 
 2050         /*
 2051          * States other than LISTEN or SYN_SENT.
 2052          * First check the RST flag and sequence number since reset segments
 2053          * are exempt from the timestamp and connection count tests.  This
 2054          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
 2055          * below which allowed reset segments in half the sequence space
 2056          * to fall though and be processed (which gives forged reset
 2057          * segments with a random sequence number a 50 percent chance of
 2058          * killing a connection).
 2059          * Then check timestamp, if present.
 2060          * Then check the connection count, if present.
 2061          * Then check that at least some bytes of segment are within
 2062          * receive window.  If segment begins before rcv_nxt,
 2063          * drop leading data (and SYN); if nothing left, just ack.
 2064          *
 2065          *
 2066          * If the RST bit is set, check the sequence number to see
 2067          * if this is a valid reset segment.
 2068          * RFC 793 page 37:
 2069          *   In all states except SYN-SENT, all reset (RST) segments
 2070          *   are validated by checking their SEQ-fields.  A reset is
 2071          *   valid if its sequence number is in the window.
 2072          * Note: this does not take into account delayed ACKs, so
 2073          *   we should test against last_ack_sent instead of rcv_nxt.
 2074          *   The sequence number in the reset segment is normally an
 2075          *   echo of our outgoing acknowlegement numbers, but some hosts
 2076          *   send a reset with the sequence number at the rightmost edge
 2077          *   of our receive window, and we have to handle this case.
 2078          * Note 2: Paul Watson's paper "Slipping in the Window" has shown
 2079          *   that brute force RST attacks are possible.  To combat this,
 2080          *   we use a much stricter check while in the ESTABLISHED state,
 2081          *   only accepting RSTs where the sequence number is equal to
 2082          *   last_ack_sent.  In all other states (the states in which a
 2083          *   RST is more likely), the more permissive check is used.
 2084          * If we have multiple segments in flight, the initial reset
 2085          * segment sequence numbers will be to the left of last_ack_sent,
 2086          * but they will eventually catch up.
 2087          * In any case, it never made sense to trim reset segments to
 2088          * fit the receive window since RFC 1122 says:
 2089          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
 2090          *
 2091          *    A TCP SHOULD allow a received RST segment to include data.
 2092          *
 2093          *    DISCUSSION
 2094          *         It has been suggested that a RST segment could contain
 2095          *         ASCII text that encoded and explained the cause of the
 2096          *         RST.  No standard has yet been established for such
 2097          *         data.
 2098          *
 2099          * If the reset segment passes the sequence number test examine
 2100          * the state:
 2101          *    SYN_RECEIVED STATE:
 2102          *      If passive open, return to LISTEN state.
 2103          *      If active open, inform user that connection was refused.
 2104          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
 2105          *      Inform user that connection was reset, and close tcb.
 2106          *    CLOSING, LAST_ACK STATES:
 2107          *      Close the tcb.
 2108          *    TIME_WAIT STATE:
 2109          *      Drop the segment - see Stevens, vol. 2, p. 964 and
 2110          *      RFC 1337.
 2111          */
 2112         if (thflags & TH_RST) {
 2113                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
 2114                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
 2115                         switch (tp->t_state) {
 2116 
 2117                         case TCPS_SYN_RECEIVED:
 2118                                 so->so_error = ECONNREFUSED;
 2119                                 goto close;
 2120 
 2121                         case TCPS_ESTABLISHED:
 2122                                 if (V_tcp_insecure_rst == 0 &&
 2123                                     !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
 2124                                     SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
 2125                                     !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
 2126                                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
 2127                                         TCPSTAT_INC(tcps_badrst);
 2128                                         goto drop;
 2129                                 }
 2130                                 /* FALLTHROUGH */
 2131                         case TCPS_FIN_WAIT_1:
 2132                         case TCPS_FIN_WAIT_2:
 2133                         case TCPS_CLOSE_WAIT:
 2134                                 so->so_error = ECONNRESET;
 2135                         close:
 2136                                 KASSERT(ti_locked == TI_WLOCKED,
 2137                                     ("tcp_do_segment: TH_RST 1 ti_locked %d",
 2138                                     ti_locked));
 2139                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2140 
 2141                                 tcp_state_change(tp, TCPS_CLOSED);
 2142                                 TCPSTAT_INC(tcps_drops);
 2143                                 tp = tcp_close(tp);
 2144                                 break;
 2145 
 2146                         case TCPS_CLOSING:
 2147                         case TCPS_LAST_ACK:
 2148                                 KASSERT(ti_locked == TI_WLOCKED,
 2149                                     ("tcp_do_segment: TH_RST 2 ti_locked %d",
 2150                                     ti_locked));
 2151                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2152 
 2153                                 tp = tcp_close(tp);
 2154                                 break;
 2155                         }
 2156                 }
 2157                 goto drop;
 2158         }
 2159 
 2160         /*
 2161          * RFC 1323 PAWS: If we have a timestamp reply on this segment
 2162          * and it's less than ts_recent, drop it.
 2163          */
 2164         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
 2165             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
 2166 
 2167                 /* Check to see if ts_recent is over 24 days old.  */
 2168                 if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
 2169                         /*
 2170                          * Invalidate ts_recent.  If this segment updates
 2171                          * ts_recent, the age will be reset later and ts_recent
 2172                          * will get a valid value.  If it does not, setting
 2173                          * ts_recent to zero will at least satisfy the
 2174                          * requirement that zero be placed in the timestamp
 2175                          * echo reply when ts_recent isn't valid.  The
 2176                          * age isn't reset until we get a valid ts_recent
 2177                          * because we don't want out-of-order segments to be
 2178                          * dropped when ts_recent is old.
 2179                          */
 2180                         tp->ts_recent = 0;
 2181                 } else {
 2182                         TCPSTAT_INC(tcps_rcvduppack);
 2183                         TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
 2184                         TCPSTAT_INC(tcps_pawsdrop);
 2185                         if (tlen)
 2186                                 goto dropafterack;
 2187                         goto drop;
 2188                 }
 2189         }
 2190 
 2191         /*
 2192          * In the SYN-RECEIVED state, validate that the packet belongs to
 2193          * this connection before trimming the data to fit the receive
 2194          * window.  Check the sequence number versus IRS since we know
 2195          * the sequence numbers haven't wrapped.  This is a partial fix
 2196          * for the "LAND" DoS attack.
 2197          */
 2198         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
 2199                 rstreason = BANDLIM_RST_OPENPORT;
 2200                 goto dropwithreset;
 2201         }
 2202 
 2203         todrop = tp->rcv_nxt - th->th_seq;
 2204         if (todrop > 0) {
 2205                 /*
 2206                  * If this is a duplicate SYN for our current connection,
 2207                  * advance over it and pretend and it's not a SYN.
 2208                  */
 2209                 if (thflags & TH_SYN && th->th_seq == tp->irs) {
 2210                         thflags &= ~TH_SYN;
 2211                         th->th_seq++;
 2212                         if (th->th_urp > 1)
 2213                                 th->th_urp--;
 2214                         else
 2215                                 thflags &= ~TH_URG;
 2216                         todrop--;
 2217                 }
 2218                 /*
 2219                  * Following if statement from Stevens, vol. 2, p. 960.
 2220                  */
 2221                 if (todrop > tlen
 2222                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
 2223                         /*
 2224                          * Any valid FIN must be to the left of the window.
 2225                          * At this point the FIN must be a duplicate or out
 2226                          * of sequence; drop it.
 2227                          */
 2228                         thflags &= ~TH_FIN;
 2229 
 2230                         /*
 2231                          * Send an ACK to resynchronize and drop any data.
 2232                          * But keep on processing for RST or ACK.
 2233                          */
 2234                         tp->t_flags |= TF_ACKNOW;
 2235                         todrop = tlen;
 2236                         TCPSTAT_INC(tcps_rcvduppack);
 2237                         TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
 2238                 } else {
 2239                         TCPSTAT_INC(tcps_rcvpartduppack);
 2240                         TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
 2241                 }
 2242                 drop_hdrlen += todrop;  /* drop from the top afterwards */
 2243                 th->th_seq += todrop;
 2244                 tlen -= todrop;
 2245                 if (th->th_urp > todrop)
 2246                         th->th_urp -= todrop;
 2247                 else {
 2248                         thflags &= ~TH_URG;
 2249                         th->th_urp = 0;
 2250                 }
 2251         }
 2252 
 2253         /*
 2254          * If new data are received on a connection after the
 2255          * user processes are gone, then RST the other end.
 2256          */
 2257         if ((so->so_state & SS_NOFDREF) &&
 2258             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
 2259                 KASSERT(ti_locked == TI_WLOCKED, ("%s: SS_NOFDEREF && "
 2260                     "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
 2261                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2262 
 2263                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 2264                         log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
 2265                             "after socket was closed, "
 2266                             "sending RST and removing tcpcb\n",
 2267                             s, __func__, tcpstates[tp->t_state], tlen);
 2268                         free(s, M_TCPLOG);
 2269                 }
 2270                 tp = tcp_close(tp);
 2271                 TCPSTAT_INC(tcps_rcvafterclose);
 2272                 rstreason = BANDLIM_UNLIMITED;
 2273                 goto dropwithreset;
 2274         }
 2275 
 2276         /*
 2277          * If segment ends after window, drop trailing data
 2278          * (and PUSH and FIN); if nothing left, just ACK.
 2279          */
 2280         todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
 2281         if (todrop > 0) {
 2282                 TCPSTAT_INC(tcps_rcvpackafterwin);
 2283                 if (todrop >= tlen) {
 2284                         TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
 2285                         /*
 2286                          * If window is closed can only take segments at
 2287                          * window edge, and have to drop data and PUSH from
 2288                          * incoming segments.  Continue processing, but
 2289                          * remember to ack.  Otherwise, drop segment
 2290                          * and ack.
 2291                          */
 2292                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
 2293                                 tp->t_flags |= TF_ACKNOW;
 2294                                 TCPSTAT_INC(tcps_rcvwinprobe);
 2295                         } else
 2296                                 goto dropafterack;
 2297                 } else
 2298                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2299                 m_adj(m, -todrop);
 2300                 tlen -= todrop;
 2301                 thflags &= ~(TH_PUSH|TH_FIN);
 2302         }
 2303 
 2304         /*
 2305          * If last ACK falls within this segment's sequence numbers,
 2306          * record its timestamp.
 2307          * NOTE: 
 2308          * 1) That the test incorporates suggestions from the latest
 2309          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
 2310          * 2) That updating only on newer timestamps interferes with
 2311          *    our earlier PAWS tests, so this check should be solely
 2312          *    predicated on the sequence space of this segment.
 2313          * 3) That we modify the segment boundary check to be 
 2314          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len  
 2315          *    instead of RFC1323's
 2316          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
 2317          *    This modified check allows us to overcome RFC1323's
 2318          *    limitations as described in Stevens TCP/IP Illustrated
 2319          *    Vol. 2 p.869. In such cases, we can still calculate the
 2320          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
 2321          */
 2322         if ((to.to_flags & TOF_TS) != 0 &&
 2323             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
 2324             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
 2325                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
 2326                 tp->ts_recent_age = tcp_ts_getticks();
 2327                 tp->ts_recent = to.to_tsval;
 2328         }
 2329 
 2330         /*
 2331          * If a SYN is in the window, then this is an
 2332          * error and we send an RST and drop the connection.
 2333          */
 2334         if (thflags & TH_SYN) {
 2335                 KASSERT(ti_locked == TI_WLOCKED,
 2336                     ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
 2337                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2338 
 2339                 tp = tcp_drop(tp, ECONNRESET);
 2340                 rstreason = BANDLIM_UNLIMITED;
 2341                 goto drop;
 2342         }
 2343 
 2344         /*
 2345          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
 2346          * flag is on (half-synchronized state), then queue data for
 2347          * later processing; else drop segment and return.
 2348          */
 2349         if ((thflags & TH_ACK) == 0) {
 2350                 if (tp->t_state == TCPS_SYN_RECEIVED ||
 2351                     (tp->t_flags & TF_NEEDSYN))
 2352                         goto step6;
 2353                 else if (tp->t_flags & TF_ACKNOW)
 2354                         goto dropafterack;
 2355                 else
 2356                         goto drop;
 2357         }
 2358 
 2359         /*
 2360          * Ack processing.
 2361          */
 2362         switch (tp->t_state) {
 2363 
 2364         /*
 2365          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
 2366          * ESTABLISHED state and continue processing.
 2367          * The ACK was checked above.
 2368          */
 2369         case TCPS_SYN_RECEIVED:
 2370 
 2371                 TCPSTAT_INC(tcps_connects);
 2372                 soisconnected(so);
 2373                 /* Do window scaling? */
 2374                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2375                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2376                         tp->rcv_scale = tp->request_r_scale;
 2377                         tp->snd_wnd = tiwin;
 2378                 }
 2379                 /*
 2380                  * Make transitions:
 2381                  *      SYN-RECEIVED  -> ESTABLISHED
 2382                  *      SYN-RECEIVED* -> FIN-WAIT-1
 2383                  */
 2384                 tp->t_starttime = ticks;
 2385                 if (tp->t_flags & TF_NEEDFIN) {
 2386                         tcp_state_change(tp, TCPS_FIN_WAIT_1);
 2387                         tp->t_flags &= ~TF_NEEDFIN;
 2388                 } else {
 2389                         tcp_state_change(tp, TCPS_ESTABLISHED);
 2390                         TCP_PROBE5(accept__established, NULL, tp,
 2391                             mtod(m, const char *), tp, th);
 2392                         cc_conn_init(tp);
 2393                         tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 2394                 }
 2395                 /*
 2396                  * If segment contains data or ACK, will call tcp_reass()
 2397                  * later; if not, do so now to pass queued data to user.
 2398                  */
 2399                 if (tlen == 0 && (thflags & TH_FIN) == 0)
 2400                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
 2401                             (struct mbuf *)0);
 2402                 tp->snd_wl1 = th->th_seq - 1;
 2403                 /* FALLTHROUGH */
 2404 
 2405         /*
 2406          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
 2407          * ACKs.  If the ack is in the range
 2408          *      tp->snd_una < th->th_ack <= tp->snd_max
 2409          * then advance tp->snd_una to th->th_ack and drop
 2410          * data from the retransmission queue.  If this ACK reflects
 2411          * more up to date window information we update our window information.
 2412          */
 2413         case TCPS_ESTABLISHED:
 2414         case TCPS_FIN_WAIT_1:
 2415         case TCPS_FIN_WAIT_2:
 2416         case TCPS_CLOSE_WAIT:
 2417         case TCPS_CLOSING:
 2418         case TCPS_LAST_ACK:
 2419                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
 2420                         TCPSTAT_INC(tcps_rcvacktoomuch);
 2421                         goto dropafterack;
 2422                 }
 2423                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 2424                     ((to.to_flags & TOF_SACK) ||
 2425                      !TAILQ_EMPTY(&tp->snd_holes)))
 2426                         tcp_sack_doack(tp, &to, th->th_ack);
 2427 
 2428                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 2429                 hhook_run_tcp_est_in(tp, th, &to);
 2430 
 2431                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
 2432                         if (tlen == 0 && tiwin == tp->snd_wnd) {
 2433                                 /*
 2434                                  * If this is the first time we've seen a
 2435                                  * FIN from the remote, this is not a
 2436                                  * duplicate and it needs to be processed
 2437                                  * normally.  This happens during a
 2438                                  * simultaneous close.
 2439                                  */
 2440                                 if ((thflags & TH_FIN) &&
 2441                                     (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
 2442                                         tp->t_dupacks = 0;
 2443                                         break;
 2444                                 }
 2445                                 TCPSTAT_INC(tcps_rcvdupack);
 2446                                 /*
 2447                                  * If we have outstanding data (other than
 2448                                  * a window probe), this is a completely
 2449                                  * duplicate ack (ie, window info didn't
 2450                                  * change and FIN isn't set),
 2451                                  * the ack is the biggest we've
 2452                                  * seen and we've seen exactly our rexmt
 2453                                  * threshhold of them, assume a packet
 2454                                  * has been dropped and retransmit it.
 2455                                  * Kludge snd_nxt & the congestion
 2456                                  * window so we send only this one
 2457                                  * packet.
 2458                                  *
 2459                                  * We know we're losing at the current
 2460                                  * window size so do congestion avoidance
 2461                                  * (set ssthresh to half the current window
 2462                                  * and pull our congestion window back to
 2463                                  * the new ssthresh).
 2464                                  *
 2465                                  * Dup acks mean that packets have left the
 2466                                  * network (they're now cached at the receiver)
 2467                                  * so bump cwnd by the amount in the receiver
 2468                                  * to keep a constant cwnd packets in the
 2469                                  * network.
 2470                                  *
 2471                                  * When using TCP ECN, notify the peer that
 2472                                  * we reduced the cwnd.
 2473                                  */
 2474                                 if (!tcp_timer_active(tp, TT_REXMT) ||
 2475                                     th->th_ack != tp->snd_una)
 2476                                         tp->t_dupacks = 0;
 2477                                 else if (++tp->t_dupacks > tcprexmtthresh ||
 2478                                      IN_FASTRECOVERY(tp->t_flags)) {
 2479                                         cc_ack_received(tp, th, CC_DUPACK);
 2480                                         if ((tp->t_flags & TF_SACK_PERMIT) &&
 2481                                             IN_FASTRECOVERY(tp->t_flags)) {
 2482                                                 int awnd;
 2483                                                 
 2484                                                 /*
 2485                                                  * Compute the amount of data in flight first.
 2486                                                  * We can inject new data into the pipe iff 
 2487                                                  * we have less than 1/2 the original window's
 2488                                                  * worth of data in flight.
 2489                                                  */
 2490                                                 awnd = (tp->snd_nxt - tp->snd_fack) +
 2491                                                         tp->sackhint.sack_bytes_rexmit;
 2492                                                 if (awnd < tp->snd_ssthresh) {
 2493                                                         tp->snd_cwnd += tp->t_maxseg;
 2494                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
 2495                                                                 tp->snd_cwnd = tp->snd_ssthresh;
 2496                                                 }
 2497                                         } else
 2498                                                 tp->snd_cwnd += tp->t_maxseg;
 2499                                         (void) tcp_output(tp);
 2500                                         goto drop;
 2501                                 } else if (tp->t_dupacks == tcprexmtthresh) {
 2502                                         tcp_seq onxt = tp->snd_nxt;
 2503 
 2504                                         /*
 2505                                          * If we're doing sack, check to
 2506                                          * see if we're already in sack
 2507                                          * recovery. If we're not doing sack,
 2508                                          * check to see if we're in newreno
 2509                                          * recovery.
 2510                                          */
 2511                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2512                                                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2513                                                         tp->t_dupacks = 0;
 2514                                                         break;
 2515                                                 }
 2516                                         } else {
 2517                                                 if (SEQ_LEQ(th->th_ack,
 2518                                                     tp->snd_recover)) {
 2519                                                         tp->t_dupacks = 0;
 2520                                                         break;
 2521                                                 }
 2522                                         }
 2523                                         /* Congestion signal before ack. */
 2524                                         cc_cong_signal(tp, th, CC_NDUPACK);
 2525                                         cc_ack_received(tp, th, CC_DUPACK);
 2526                                         tcp_timer_activate(tp, TT_REXMT, 0);
 2527                                         tp->t_rtttime = 0;
 2528                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2529                                                 TCPSTAT_INC(
 2530                                                     tcps_sack_recovery_episode);
 2531                                                 tp->sack_newdata = tp->snd_nxt;
 2532                                                 tp->snd_cwnd = tp->t_maxseg;
 2533                                                 (void) tcp_output(tp);
 2534                                                 goto drop;
 2535                                         }
 2536                                         tp->snd_nxt = th->th_ack;
 2537                                         tp->snd_cwnd = tp->t_maxseg;
 2538                                         (void) tcp_output(tp);
 2539                                         KASSERT(tp->snd_limited <= 2,
 2540                                             ("%s: tp->snd_limited too big",
 2541                                             __func__));
 2542                                         tp->snd_cwnd = tp->snd_ssthresh +
 2543                                              tp->t_maxseg *
 2544                                              (tp->t_dupacks - tp->snd_limited);
 2545                                         if (SEQ_GT(onxt, tp->snd_nxt))
 2546                                                 tp->snd_nxt = onxt;
 2547                                         goto drop;
 2548                                 } else if (V_tcp_do_rfc3042) {
 2549                                         cc_ack_received(tp, th, CC_DUPACK);
 2550                                         u_long oldcwnd = tp->snd_cwnd;
 2551                                         tcp_seq oldsndmax = tp->snd_max;
 2552                                         u_int sent;
 2553                                         int avail;
 2554 
 2555                                         KASSERT(tp->t_dupacks == 1 ||
 2556                                             tp->t_dupacks == 2,
 2557                                             ("%s: dupacks not 1 or 2",
 2558                                             __func__));
 2559                                         if (tp->t_dupacks == 1)
 2560                                                 tp->snd_limited = 0;
 2561                                         tp->snd_cwnd =
 2562                                             (tp->snd_nxt - tp->snd_una) +
 2563                                             (tp->t_dupacks - tp->snd_limited) *
 2564                                             tp->t_maxseg;
 2565                                         /*
 2566                                          * Only call tcp_output when there
 2567                                          * is new data available to be sent.
 2568                                          * Otherwise we would send pure ACKs.
 2569                                          */
 2570                                         SOCKBUF_LOCK(&so->so_snd);
 2571                                         avail = so->so_snd.sb_cc -
 2572                                             (tp->snd_nxt - tp->snd_una);
 2573                                         SOCKBUF_UNLOCK(&so->so_snd);
 2574                                         if (avail > 0)
 2575                                                 (void) tcp_output(tp);
 2576                                         sent = tp->snd_max - oldsndmax;
 2577                                         if (sent > tp->t_maxseg) {
 2578                                                 KASSERT((tp->t_dupacks == 2 &&
 2579                                                     tp->snd_limited == 0) ||
 2580                                                    (sent == tp->t_maxseg + 1 &&
 2581                                                     tp->t_flags & TF_SENTFIN),
 2582                                                     ("%s: sent too much",
 2583                                                     __func__));
 2584                                                 tp->snd_limited = 2;
 2585                                         } else if (sent > 0)
 2586                                                 ++tp->snd_limited;
 2587                                         tp->snd_cwnd = oldcwnd;
 2588                                         goto drop;
 2589                                 }
 2590                         } else
 2591                                 tp->t_dupacks = 0;
 2592                         break;
 2593                 }
 2594 
 2595                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
 2596                     ("%s: th_ack <= snd_una", __func__));
 2597 
 2598                 /*
 2599                  * If the congestion window was inflated to account
 2600                  * for the other side's cached packets, retract it.
 2601                  */
 2602                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2603                         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
 2604                                 if (tp->t_flags & TF_SACK_PERMIT)
 2605                                         tcp_sack_partialack(tp, th);
 2606                                 else
 2607                                         tcp_newreno_partial_ack(tp, th);
 2608                         } else
 2609                                 cc_post_recovery(tp, th);
 2610                 }
 2611                 tp->t_dupacks = 0;
 2612                 /*
 2613                  * If we reach this point, ACK is not a duplicate,
 2614                  *     i.e., it ACKs something we sent.
 2615                  */
 2616                 if (tp->t_flags & TF_NEEDSYN) {
 2617                         /*
 2618                          * T/TCP: Connection was half-synchronized, and our
 2619                          * SYN has been ACK'd (so connection is now fully
 2620                          * synchronized).  Go to non-starred state,
 2621                          * increment snd_una for ACK of SYN, and check if
 2622                          * we can do window scaling.
 2623                          */
 2624                         tp->t_flags &= ~TF_NEEDSYN;
 2625                         tp->snd_una++;
 2626                         /* Do window scaling? */
 2627                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2628                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2629                                 tp->rcv_scale = tp->request_r_scale;
 2630                                 /* Send window already scaled. */
 2631                         }
 2632                 }
 2633 
 2634 process_ACK:
 2635                 INP_WLOCK_ASSERT(tp->t_inpcb);
 2636 
 2637                 acked = BYTES_THIS_ACK(tp, th);
 2638                 TCPSTAT_INC(tcps_rcvackpack);
 2639                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 2640 
 2641                 /*
 2642                  * If we just performed our first retransmit, and the ACK
 2643                  * arrives within our recovery window, then it was a mistake
 2644                  * to do the retransmit in the first place.  Recover our
 2645                  * original cwnd and ssthresh, and proceed to transmit where
 2646                  * we left off.
 2647                  */
 2648                 if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
 2649                     (int)(ticks - tp->t_badrxtwin) < 0)
 2650                         cc_cong_signal(tp, th, CC_RTO_ERR);
 2651 
 2652                 /*
 2653                  * If we have a timestamp reply, update smoothed
 2654                  * round trip time.  If no timestamp is present but
 2655                  * transmit timer is running and timed sequence
 2656                  * number was acked, update smoothed round trip time.
 2657                  * Since we now have an rtt measurement, cancel the
 2658                  * timer backoff (cf., Phil Karn's retransmit alg.).
 2659                  * Recompute the initial retransmit timer.
 2660                  *
 2661                  * Some boxes send broken timestamp replies
 2662                  * during the SYN+ACK phase, ignore
 2663                  * timestamps of 0 or we could calculate a
 2664                  * huge RTT and blow up the retransmit timer.
 2665                  */
 2666                 if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
 2667                         u_int t;
 2668 
 2669                         t = tcp_ts_getticks() - to.to_tsecr;
 2670                         if (!tp->t_rttlow || tp->t_rttlow > t)
 2671                                 tp->t_rttlow = t;
 2672                         tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
 2673                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
 2674                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
 2675                                 tp->t_rttlow = ticks - tp->t_rtttime;
 2676                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
 2677                 }
 2678 
 2679                 /*
 2680                  * If all outstanding data is acked, stop retransmit
 2681                  * timer and remember to restart (more output or persist).
 2682                  * If there is more data to be acked, restart retransmit
 2683                  * timer, using current (possibly backed-off) value.
 2684                  */
 2685                 if (th->th_ack == tp->snd_max) {
 2686                         tcp_timer_activate(tp, TT_REXMT, 0);
 2687                         needoutput = 1;
 2688                 } else if (!tcp_timer_active(tp, TT_PERSIST))
 2689                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 2690 
 2691                 /*
 2692                  * If no data (only SYN) was ACK'd,
 2693                  *    skip rest of ACK processing.
 2694                  */
 2695                 if (acked == 0)
 2696                         goto step6;
 2697 
 2698                 /*
 2699                  * Let the congestion control algorithm update congestion
 2700                  * control related information. This typically means increasing
 2701                  * the congestion window.
 2702                  */
 2703                 cc_ack_received(tp, th, CC_ACK);
 2704 
 2705                 SOCKBUF_LOCK(&so->so_snd);
 2706                 if (acked > so->so_snd.sb_cc) {
 2707                         tp->snd_wnd -= so->so_snd.sb_cc;
 2708                         mfree = sbcut_locked(&so->so_snd,
 2709                             (int)so->so_snd.sb_cc);
 2710                         ourfinisacked = 1;
 2711                 } else {
 2712                         mfree = sbcut_locked(&so->so_snd, acked);
 2713                         tp->snd_wnd -= acked;
 2714                         ourfinisacked = 0;
 2715                 }
 2716                 /* NB: sowwakeup_locked() does an implicit unlock. */
 2717                 sowwakeup_locked(so);
 2718                 m_freem(mfree);
 2719                 /* Detect una wraparound. */
 2720                 if (!IN_RECOVERY(tp->t_flags) &&
 2721                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
 2722                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 2723                         tp->snd_recover = th->th_ack - 1;
 2724                 /* XXXLAS: Can this be moved up into cc_post_recovery? */
 2725                 if (IN_RECOVERY(tp->t_flags) &&
 2726                     SEQ_GEQ(th->th_ack, tp->snd_recover)) {
 2727                         EXIT_RECOVERY(tp->t_flags);
 2728                 }
 2729                 tp->snd_una = th->th_ack;
 2730                 if (tp->t_flags & TF_SACK_PERMIT) {
 2731                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
 2732                                 tp->snd_recover = tp->snd_una;
 2733                 }
 2734                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 2735                         tp->snd_nxt = tp->snd_una;
 2736 
 2737                 switch (tp->t_state) {
 2738 
 2739                 /*
 2740                  * In FIN_WAIT_1 STATE in addition to the processing
 2741                  * for the ESTABLISHED state if our FIN is now acknowledged
 2742                  * then enter FIN_WAIT_2.
 2743                  */
 2744                 case TCPS_FIN_WAIT_1:
 2745                         if (ourfinisacked) {
 2746                                 /*
 2747                                  * If we can't receive any more
 2748                                  * data, then closing user can proceed.
 2749                                  * Starting the timer is contrary to the
 2750                                  * specification, but if we don't get a FIN
 2751                                  * we'll hang forever.
 2752                                  *
 2753                                  * XXXjl:
 2754                                  * we should release the tp also, and use a
 2755                                  * compressed state.
 2756                                  */
 2757                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 2758                                         soisdisconnected(so);
 2759                                         tcp_timer_activate(tp, TT_2MSL,
 2760                                             (tcp_fast_finwait2_recycle ?
 2761                                             tcp_finwait2_timeout :
 2762                                             TP_MAXIDLE(tp)));
 2763                                 }
 2764                                 tcp_state_change(tp, TCPS_FIN_WAIT_2);
 2765                         }
 2766                         break;
 2767 
 2768                 /*
 2769                  * In CLOSING STATE in addition to the processing for
 2770                  * the ESTABLISHED state if the ACK acknowledges our FIN
 2771                  * then enter the TIME-WAIT state, otherwise ignore
 2772                  * the segment.
 2773                  */
 2774                 case TCPS_CLOSING:
 2775                         if (ourfinisacked) {
 2776                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2777                                 tcp_twstart(tp);
 2778                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 2779                                 m_freem(m);
 2780                                 return;
 2781                         }
 2782                         break;
 2783 
 2784                 /*
 2785                  * In LAST_ACK, we may still be waiting for data to drain
 2786                  * and/or to be acked, as well as for the ack of our FIN.
 2787                  * If our FIN is now acknowledged, delete the TCB,
 2788                  * enter the closed state and return.
 2789                  */
 2790                 case TCPS_LAST_ACK:
 2791                         if (ourfinisacked) {
 2792                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2793                                 tp = tcp_close(tp);
 2794                                 goto drop;
 2795                         }
 2796                         break;
 2797                 }
 2798         }
 2799 
 2800 step6:
 2801         INP_WLOCK_ASSERT(tp->t_inpcb);
 2802 
 2803         /*
 2804          * Update window information.
 2805          * Don't look at window if no ACK: TAC's send garbage on first SYN.
 2806          */
 2807         if ((thflags & TH_ACK) &&
 2808             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
 2809             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
 2810              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
 2811                 /* keep track of pure window updates */
 2812                 if (tlen == 0 &&
 2813                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
 2814                         TCPSTAT_INC(tcps_rcvwinupd);
 2815                 tp->snd_wnd = tiwin;
 2816                 tp->snd_wl1 = th->th_seq;
 2817                 tp->snd_wl2 = th->th_ack;
 2818                 if (tp->snd_wnd > tp->max_sndwnd)
 2819                         tp->max_sndwnd = tp->snd_wnd;
 2820                 needoutput = 1;
 2821         }
 2822 
 2823         /*
 2824          * Process segments with URG.
 2825          */
 2826         if ((thflags & TH_URG) && th->th_urp &&
 2827             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2828                 /*
 2829                  * This is a kludge, but if we receive and accept
 2830                  * random urgent pointers, we'll crash in
 2831                  * soreceive.  It's hard to imagine someone
 2832                  * actually wanting to send this much urgent data.
 2833                  */
 2834                 SOCKBUF_LOCK(&so->so_rcv);
 2835                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
 2836                         th->th_urp = 0;                 /* XXX */
 2837                         thflags &= ~TH_URG;             /* XXX */
 2838                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
 2839                         goto dodata;                    /* XXX */
 2840                 }
 2841                 /*
 2842                  * If this segment advances the known urgent pointer,
 2843                  * then mark the data stream.  This should not happen
 2844                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
 2845                  * a FIN has been received from the remote side.
 2846                  * In these states we ignore the URG.
 2847                  *
 2848                  * According to RFC961 (Assigned Protocols),
 2849                  * the urgent pointer points to the last octet
 2850                  * of urgent data.  We continue, however,
 2851                  * to consider it to indicate the first octet
 2852                  * of data past the urgent section as the original
 2853                  * spec states (in one of two places).
 2854                  */
 2855                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
 2856                         tp->rcv_up = th->th_seq + th->th_urp;
 2857                         so->so_oobmark = so->so_rcv.sb_cc +
 2858                             (tp->rcv_up - tp->rcv_nxt) - 1;
 2859                         if (so->so_oobmark == 0)
 2860                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
 2861                         sohasoutofband(so);
 2862                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
 2863                 }
 2864                 SOCKBUF_UNLOCK(&so->so_rcv);
 2865                 /*
 2866                  * Remove out of band data so doesn't get presented to user.
 2867                  * This can happen independent of advancing the URG pointer,
 2868                  * but if two URG's are pending at once, some out-of-band
 2869                  * data may creep in... ick.
 2870                  */
 2871                 if (th->th_urp <= (u_long)tlen &&
 2872                     !(so->so_options & SO_OOBINLINE)) {
 2873                         /* hdr drop is delayed */
 2874                         tcp_pulloutofband(so, th, m, drop_hdrlen);
 2875                 }
 2876         } else {
 2877                 /*
 2878                  * If no out of band data is expected,
 2879                  * pull receive urgent pointer along
 2880                  * with the receive window.
 2881                  */
 2882                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
 2883                         tp->rcv_up = tp->rcv_nxt;
 2884         }
 2885 dodata:                                                 /* XXX */
 2886         INP_WLOCK_ASSERT(tp->t_inpcb);
 2887 
 2888         /*
 2889          * Process the segment text, merging it into the TCP sequencing queue,
 2890          * and arranging for acknowledgment of receipt if necessary.
 2891          * This process logically involves adjusting tp->rcv_wnd as data
 2892          * is presented to the user (this happens in tcp_usrreq.c,
 2893          * case PRU_RCVD).  If a FIN has already been received on this
 2894          * connection then we just ignore the text.
 2895          */
 2896         if ((tlen || (thflags & TH_FIN)) &&
 2897             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2898                 tcp_seq save_start = th->th_seq;
 2899                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 2900                 /*
 2901                  * Insert segment which includes th into TCP reassembly queue
 2902                  * with control block tp.  Set thflags to whether reassembly now
 2903                  * includes a segment with FIN.  This handles the common case
 2904                  * inline (segment is the next to be received on an established
 2905                  * connection, and the queue is empty), avoiding linkage into
 2906                  * and removal from the queue and repetition of various
 2907                  * conversions.
 2908                  * Set DELACK for segments received in order, but ack
 2909                  * immediately when segments are out of order (so
 2910                  * fast retransmit can work).
 2911                  */
 2912                 if (th->th_seq == tp->rcv_nxt &&
 2913                     LIST_EMPTY(&tp->t_segq) &&
 2914                     TCPS_HAVEESTABLISHED(tp->t_state)) {
 2915                         if (DELAY_ACK(tp, tlen))
 2916                                 tp->t_flags |= TF_DELACK;
 2917                         else
 2918                                 tp->t_flags |= TF_ACKNOW;
 2919                         tp->rcv_nxt += tlen;
 2920                         thflags = th->th_flags & TH_FIN;
 2921                         TCPSTAT_INC(tcps_rcvpack);
 2922                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 2923                         ND6_HINT(tp);
 2924                         SOCKBUF_LOCK(&so->so_rcv);
 2925                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
 2926                                 m_freem(m);
 2927                         else
 2928                                 sbappendstream_locked(&so->so_rcv, m);
 2929                         /* NB: sorwakeup_locked() does an implicit unlock. */
 2930                         sorwakeup_locked(so);
 2931                 } else {
 2932                         /*
 2933                          * XXX: Due to the header drop above "th" is
 2934                          * theoretically invalid by now.  Fortunately
 2935                          * m_adj() doesn't actually frees any mbufs
 2936                          * when trimming from the head.
 2937                          */
 2938                         thflags = tcp_reass(tp, th, &tlen, m);
 2939                         tp->t_flags |= TF_ACKNOW;
 2940                 }
 2941                 if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
 2942                         tcp_update_sack_list(tp, save_start, save_start + tlen);
 2943 #if 0
 2944                 /*
 2945                  * Note the amount of data that peer has sent into
 2946                  * our window, in order to estimate the sender's
 2947                  * buffer size.
 2948                  * XXX: Unused.
 2949                  */
 2950                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
 2951                         len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
 2952                 else
 2953                         len = so->so_rcv.sb_hiwat;
 2954 #endif
 2955         } else {
 2956                 m_freem(m);
 2957                 thflags &= ~TH_FIN;
 2958         }
 2959 
 2960         /*
 2961          * If FIN is received ACK the FIN and let the user know
 2962          * that the connection is closing.
 2963          */
 2964         if (thflags & TH_FIN) {
 2965                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2966                         socantrcvmore(so);
 2967                         /*
 2968                          * If connection is half-synchronized
 2969                          * (ie NEEDSYN flag on) then delay ACK,
 2970                          * so it may be piggybacked when SYN is sent.
 2971                          * Otherwise, since we received a FIN then no
 2972                          * more input can be expected, send ACK now.
 2973                          */
 2974                         if (tp->t_flags & TF_NEEDSYN)
 2975                                 tp->t_flags |= TF_DELACK;
 2976                         else
 2977                                 tp->t_flags |= TF_ACKNOW;
 2978                         tp->rcv_nxt++;
 2979                 }
 2980                 switch (tp->t_state) {
 2981 
 2982                 /*
 2983                  * In SYN_RECEIVED and ESTABLISHED STATES
 2984                  * enter the CLOSE_WAIT state.
 2985                  */
 2986                 case TCPS_SYN_RECEIVED:
 2987                         tp->t_starttime = ticks;
 2988                         /* FALLTHROUGH */
 2989                 case TCPS_ESTABLISHED:
 2990                         tcp_state_change(tp, TCPS_CLOSE_WAIT);
 2991                         break;
 2992 
 2993                 /*
 2994                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
 2995                  * enter the CLOSING state.
 2996                  */
 2997                 case TCPS_FIN_WAIT_1:
 2998                         tcp_state_change(tp, TCPS_CLOSING);
 2999                         break;
 3000 
 3001                 /*
 3002                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
 3003                  * starting the time-wait timer, turning off the other
 3004                  * standard timers.
 3005                  */
 3006                 case TCPS_FIN_WAIT_2:
 3007                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 3008                         KASSERT(ti_locked == TI_WLOCKED, ("%s: dodata "
 3009                             "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
 3010                             ti_locked));
 3011 
 3012                         tcp_twstart(tp);
 3013                         INP_INFO_WUNLOCK(&V_tcbinfo);
 3014                         return;
 3015                 }
 3016         }
 3017         if (ti_locked == TI_WLOCKED)
 3018                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3019         ti_locked = TI_UNLOCKED;
 3020 
 3021 #ifdef TCPDEBUG
 3022         if (so->so_options & SO_DEBUG)
 3023                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
 3024                           &tcp_savetcp, 0);
 3025 #endif
 3026 
 3027         /*
 3028          * Return any desired output.
 3029          */
 3030         if (needoutput || (tp->t_flags & TF_ACKNOW))
 3031                 (void) tcp_output(tp);
 3032 
 3033 check_delack:
 3034         KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
 3035             __func__, ti_locked));
 3036         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3037         INP_WLOCK_ASSERT(tp->t_inpcb);
 3038 
 3039         if (tp->t_flags & TF_DELACK) {
 3040                 tp->t_flags &= ~TF_DELACK;
 3041                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
 3042         }
 3043         INP_WUNLOCK(tp->t_inpcb);
 3044         return;
 3045 
 3046 dropafterack:
 3047         /*
 3048          * Generate an ACK dropping incoming segment if it occupies
 3049          * sequence space, where the ACK reflects our state.
 3050          *
 3051          * We can now skip the test for the RST flag since all
 3052          * paths to this code happen after packets containing
 3053          * RST have been dropped.
 3054          *
 3055          * In the SYN-RECEIVED state, don't send an ACK unless the
 3056          * segment we received passes the SYN-RECEIVED ACK test.
 3057          * If it fails send a RST.  This breaks the loop in the
 3058          * "LAND" DoS attack, and also prevents an ACK storm
 3059          * between two listening ports that have been sent forged
 3060          * SYN segments, each with the source address of the other.
 3061          */
 3062         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
 3063             (SEQ_GT(tp->snd_una, th->th_ack) ||
 3064              SEQ_GT(th->th_ack, tp->snd_max)) ) {
 3065                 rstreason = BANDLIM_RST_OPENPORT;
 3066                 goto dropwithreset;
 3067         }
 3068 #ifdef TCPDEBUG
 3069         if (so->so_options & SO_DEBUG)
 3070                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3071                           &tcp_savetcp, 0);
 3072 #endif
 3073         if (ti_locked == TI_WLOCKED)
 3074                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3075         ti_locked = TI_UNLOCKED;
 3076 
 3077         tp->t_flags |= TF_ACKNOW;
 3078         (void) tcp_output(tp);
 3079         INP_WUNLOCK(tp->t_inpcb);
 3080         m_freem(m);
 3081         return;
 3082 
 3083 dropwithreset:
 3084         if (ti_locked == TI_WLOCKED)
 3085                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3086         ti_locked = TI_UNLOCKED;
 3087 
 3088         if (tp != NULL) {
 3089                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 3090                 INP_WUNLOCK(tp->t_inpcb);
 3091         } else
 3092                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 3093         return;
 3094 
 3095 drop:
 3096         if (ti_locked == TI_WLOCKED) {
 3097                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3098                 ti_locked = TI_UNLOCKED;
 3099         }
 3100 #ifdef INVARIANTS
 3101         else
 3102                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3103 #endif
 3104 
 3105         /*
 3106          * Drop space held by incoming segment and return.
 3107          */
 3108 #ifdef TCPDEBUG
 3109         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 3110                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3111                           &tcp_savetcp, 0);
 3112 #endif
 3113         if (tp != NULL)
 3114                 INP_WUNLOCK(tp->t_inpcb);
 3115         m_freem(m);
 3116 }
 3117 
 3118 /*
 3119  * Issue RST and make ACK acceptable to originator of segment.
 3120  * The mbuf must still include the original packet header.
 3121  * tp may be NULL.
 3122  */
 3123 static void
 3124 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
 3125     int tlen, int rstreason)
 3126 {
 3127 #ifdef INET
 3128         struct ip *ip;
 3129 #endif
 3130 #ifdef INET6
 3131         struct ip6_hdr *ip6;
 3132 #endif
 3133 
 3134         if (tp != NULL) {
 3135                 INP_WLOCK_ASSERT(tp->t_inpcb);
 3136         }
 3137 
 3138         /* Don't bother if destination was broadcast/multicast. */
 3139         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
 3140                 goto drop;
 3141 #ifdef INET6
 3142         if (mtod(m, struct ip *)->ip_v == 6) {
 3143                 ip6 = mtod(m, struct ip6_hdr *);
 3144                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 3145                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 3146                         goto drop;
 3147                 /* IPv6 anycast check is done at tcp6_input() */
 3148         }
 3149 #endif
 3150 #if defined(INET) && defined(INET6)
 3151         else
 3152 #endif
 3153 #ifdef INET
 3154         {
 3155                 ip = mtod(m, struct ip *);
 3156                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 3157                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 3158                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 3159                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 3160                         goto drop;
 3161         }
 3162 #endif
 3163 
 3164         /* Perform bandwidth limiting. */
 3165         if (badport_bandlim(rstreason) < 0)
 3166                 goto drop;
 3167 
 3168         /* tcp_respond consumes the mbuf chain. */
 3169         if (th->th_flags & TH_ACK) {
 3170                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
 3171                     th->th_ack, TH_RST);
 3172         } else {
 3173                 if (th->th_flags & TH_SYN)
 3174                         tlen++;
 3175                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
 3176                     (tcp_seq)0, TH_RST|TH_ACK);
 3177         }
 3178         return;
 3179 drop:
 3180         m_freem(m);
 3181 }
 3182 
 3183 /*
 3184  * Parse TCP options and place in tcpopt.
 3185  */
 3186 static void
 3187 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
 3188 {
 3189         int opt, optlen;
 3190 
 3191         to->to_flags = 0;
 3192         for (; cnt > 0; cnt -= optlen, cp += optlen) {
 3193                 opt = cp[0];
 3194                 if (opt == TCPOPT_EOL)
 3195                         break;
 3196                 if (opt == TCPOPT_NOP)
 3197                         optlen = 1;
 3198                 else {
 3199                         if (cnt < 2)
 3200                                 break;
 3201                         optlen = cp[1];
 3202                         if (optlen < 2 || optlen > cnt)
 3203                                 break;
 3204                 }
 3205                 switch (opt) {
 3206                 case TCPOPT_MAXSEG:
 3207                         if (optlen != TCPOLEN_MAXSEG)
 3208                                 continue;
 3209                         if (!(flags & TO_SYN))
 3210                                 continue;
 3211                         to->to_flags |= TOF_MSS;
 3212                         bcopy((char *)cp + 2,
 3213                             (char *)&to->to_mss, sizeof(to->to_mss));
 3214                         to->to_mss = ntohs(to->to_mss);
 3215                         break;
 3216                 case TCPOPT_WINDOW:
 3217                         if (optlen != TCPOLEN_WINDOW)
 3218                                 continue;
 3219                         if (!(flags & TO_SYN))
 3220                                 continue;
 3221                         to->to_flags |= TOF_SCALE;
 3222                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
 3223                         break;
 3224                 case TCPOPT_TIMESTAMP:
 3225                         if (optlen != TCPOLEN_TIMESTAMP)
 3226                                 continue;
 3227                         to->to_flags |= TOF_TS;
 3228                         bcopy((char *)cp + 2,
 3229                             (char *)&to->to_tsval, sizeof(to->to_tsval));
 3230                         to->to_tsval = ntohl(to->to_tsval);
 3231                         bcopy((char *)cp + 6,
 3232                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
 3233                         to->to_tsecr = ntohl(to->to_tsecr);
 3234                         break;
 3235 #ifdef TCP_SIGNATURE
 3236                 /*
 3237                  * XXX In order to reply to a host which has set the
 3238                  * TCP_SIGNATURE option in its initial SYN, we have to
 3239                  * record the fact that the option was observed here
 3240                  * for the syncache code to perform the correct response.
 3241                  */
 3242                 case TCPOPT_SIGNATURE:
 3243                         if (optlen != TCPOLEN_SIGNATURE)
 3244                                 continue;
 3245                         to->to_flags |= TOF_SIGNATURE;
 3246                         to->to_signature = cp + 2;
 3247                         break;
 3248 #endif
 3249                 case TCPOPT_SACK_PERMITTED:
 3250                         if (optlen != TCPOLEN_SACK_PERMITTED)
 3251                                 continue;
 3252                         if (!(flags & TO_SYN))
 3253                                 continue;
 3254                         if (!V_tcp_do_sack)
 3255                                 continue;
 3256                         to->to_flags |= TOF_SACKPERM;
 3257                         break;
 3258                 case TCPOPT_SACK:
 3259                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
 3260                                 continue;
 3261                         if (flags & TO_SYN)
 3262                                 continue;
 3263                         to->to_flags |= TOF_SACK;
 3264                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
 3265                         to->to_sacks = cp + 2;
 3266                         TCPSTAT_INC(tcps_sack_rcv_blocks);
 3267                         break;
 3268                 default:
 3269                         continue;
 3270                 }
 3271         }
 3272 }
 3273 
 3274 /*
 3275  * Pull out of band byte out of a segment so
 3276  * it doesn't appear in the user's data queue.
 3277  * It is still reflected in the segment length for
 3278  * sequencing purposes.
 3279  */
 3280 static void
 3281 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
 3282     int off)
 3283 {
 3284         int cnt = off + th->th_urp - 1;
 3285 
 3286         while (cnt >= 0) {
 3287                 if (m->m_len > cnt) {
 3288                         char *cp = mtod(m, caddr_t) + cnt;
 3289                         struct tcpcb *tp = sototcpcb(so);
 3290 
 3291                         INP_WLOCK_ASSERT(tp->t_inpcb);
 3292 
 3293                         tp->t_iobc = *cp;
 3294                         tp->t_oobflags |= TCPOOB_HAVEDATA;
 3295                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
 3296                         m->m_len--;
 3297                         if (m->m_flags & M_PKTHDR)
 3298                                 m->m_pkthdr.len--;
 3299                         return;
 3300                 }
 3301                 cnt -= m->m_len;
 3302                 m = m->m_next;
 3303                 if (m == NULL)
 3304                         break;
 3305         }
 3306         panic("tcp_pulloutofband");
 3307 }
 3308 
 3309 /*
 3310  * Collect new round-trip time estimate
 3311  * and update averages and current timeout.
 3312  */
 3313 static void
 3314 tcp_xmit_timer(struct tcpcb *tp, int rtt)
 3315 {
 3316         int delta;
 3317 
 3318         INP_WLOCK_ASSERT(tp->t_inpcb);
 3319 
 3320         TCPSTAT_INC(tcps_rttupdated);
 3321         tp->t_rttupdated++;
 3322         if (tp->t_srtt != 0) {
 3323                 /*
 3324                  * srtt is stored as fixed point with 5 bits after the
 3325                  * binary point (i.e., scaled by 8).  The following magic
 3326                  * is equivalent to the smoothing algorithm in rfc793 with
 3327                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
 3328                  * point).  Adjust rtt to origin 0.
 3329                  */
 3330                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
 3331                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
 3332 
 3333                 if ((tp->t_srtt += delta) <= 0)
 3334                         tp->t_srtt = 1;
 3335 
 3336                 /*
 3337                  * We accumulate a smoothed rtt variance (actually, a
 3338                  * smoothed mean difference), then set the retransmit
 3339                  * timer to smoothed rtt + 4 times the smoothed variance.
 3340                  * rttvar is stored as fixed point with 4 bits after the
 3341                  * binary point (scaled by 16).  The following is
 3342                  * equivalent to rfc793 smoothing with an alpha of .75
 3343                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
 3344                  * rfc793's wired-in beta.
 3345                  */
 3346                 if (delta < 0)
 3347                         delta = -delta;
 3348                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
 3349                 if ((tp->t_rttvar += delta) <= 0)
 3350                         tp->t_rttvar = 1;
 3351                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
 3352                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3353         } else {
 3354                 /*
 3355                  * No rtt measurement yet - use the unsmoothed rtt.
 3356                  * Set the variance to half the rtt (so our first
 3357                  * retransmit happens at 3*rtt).
 3358                  */
 3359                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
 3360                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
 3361                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3362         }
 3363         tp->t_rtttime = 0;
 3364         tp->t_rxtshift = 0;
 3365 
 3366         /*
 3367          * the retransmit should happen at rtt + 4 * rttvar.
 3368          * Because of the way we do the smoothing, srtt and rttvar
 3369          * will each average +1/2 tick of bias.  When we compute
 3370          * the retransmit timer, we want 1/2 tick of rounding and
 3371          * 1 extra tick because of +-1/2 tick uncertainty in the
 3372          * firing of the timer.  The bias will give us exactly the
 3373          * 1.5 tick we need.  But, because the bias is
 3374          * statistical, we have to test that we don't drop below
 3375          * the minimum feasible timer (which is 2 ticks).
 3376          */
 3377         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
 3378                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
 3379 
 3380         /*
 3381          * We received an ack for a packet that wasn't retransmitted;
 3382          * it is probably safe to discard any error indications we've
 3383          * received recently.  This isn't quite right, but close enough
 3384          * for now (a route might have failed after we sent a segment,
 3385          * and the return path might not be symmetrical).
 3386          */
 3387         tp->t_softerror = 0;
 3388 }
 3389 
 3390 /*
 3391  * Determine a reasonable value for maxseg size.
 3392  * If the route is known, check route for mtu.
 3393  * If none, use an mss that can be handled on the outgoing interface
 3394  * without forcing IP to fragment.  If no route is found, route has no mtu,
 3395  * or the destination isn't local, use a default, hopefully conservative
 3396  * size (usually 512 or the default IP max size, but no more than the mtu
 3397  * of the interface), as we can't discover anything about intervening
 3398  * gateways or networks.  We also initialize the congestion/slow start
 3399  * window to be a single segment if the destination isn't local.
 3400  * While looking at the routing entry, we also initialize other path-dependent
 3401  * parameters from pre-set or cached values in the routing entry.
 3402  *
 3403  * Also take into account the space needed for options that we
 3404  * send regularly.  Make maxseg shorter by that amount to assure
 3405  * that we can send maxseg amount of data even when the options
 3406  * are present.  Store the upper limit of the length of options plus
 3407  * data in maxopd.
 3408  *
 3409  * NOTE that this routine is only called when we process an incoming
 3410  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
 3411  * settings are handled in tcp_mssopt().
 3412  */
 3413 void
 3414 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
 3415     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
 3416 {
 3417         int mss = 0;
 3418         u_long maxmtu = 0;
 3419         struct inpcb *inp = tp->t_inpcb;
 3420         struct hc_metrics_lite metrics;
 3421         int origoffer;
 3422 #ifdef INET6
 3423         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
 3424         size_t min_protoh = isipv6 ?
 3425                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
 3426                             sizeof (struct tcpiphdr);
 3427 #else
 3428         const size_t min_protoh = sizeof(struct tcpiphdr);
 3429 #endif
 3430 
 3431         INP_WLOCK_ASSERT(tp->t_inpcb);
 3432 
 3433         if (mtuoffer != -1) {
 3434                 KASSERT(offer == -1, ("%s: conflict", __func__));
 3435                 offer = mtuoffer - min_protoh;
 3436         }
 3437         origoffer = offer;
 3438 
 3439         /* Initialize. */
 3440 #ifdef INET6
 3441         if (isipv6) {
 3442                 maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
 3443                 tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
 3444         }
 3445 #endif
 3446 #if defined(INET) && defined(INET6)
 3447         else
 3448 #endif
 3449 #ifdef INET
 3450         {
 3451                 maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
 3452                 tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
 3453         }
 3454 #endif
 3455 
 3456         /*
 3457          * No route to sender, stay with default mss and return.
 3458          */
 3459         if (maxmtu == 0) {
 3460                 /*
 3461                  * In case we return early we need to initialize metrics
 3462                  * to a defined state as tcp_hc_get() would do for us
 3463                  * if there was no cache hit.
 3464                  */
 3465                 if (metricptr != NULL)
 3466                         bzero(metricptr, sizeof(struct hc_metrics_lite));
 3467                 return;
 3468         }
 3469 
 3470         /* What have we got? */
 3471         switch (offer) {
 3472                 case 0:
 3473                         /*
 3474                          * Offer == 0 means that there was no MSS on the SYN
 3475                          * segment, in this case we use tcp_mssdflt as
 3476                          * already assigned to t_maxopd above.
 3477                          */
 3478                         offer = tp->t_maxopd;
 3479                         break;
 3480 
 3481                 case -1:
 3482                         /*
 3483                          * Offer == -1 means that we didn't receive SYN yet.
 3484                          */
 3485                         /* FALLTHROUGH */
 3486 
 3487                 default:
 3488                         /*
 3489                          * Prevent DoS attack with too small MSS. Round up
 3490                          * to at least minmss.
 3491                          */
 3492                         offer = max(offer, V_tcp_minmss);
 3493         }
 3494 
 3495         /*
 3496          * rmx information is now retrieved from tcp_hostcache.
 3497          */
 3498         tcp_hc_get(&inp->inp_inc, &metrics);
 3499         if (metricptr != NULL)
 3500                 bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
 3501 
 3502         /*
 3503          * If there's a discovered mtu int tcp hostcache, use it
 3504          * else, use the link mtu.
 3505          */
 3506         if (metrics.rmx_mtu)
 3507                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
 3508         else {
 3509 #ifdef INET6
 3510                 if (isipv6) {
 3511                         mss = maxmtu - min_protoh;
 3512                         if (!V_path_mtu_discovery &&
 3513                             !in6_localaddr(&inp->in6p_faddr))
 3514                                 mss = min(mss, V_tcp_v6mssdflt);
 3515                 }
 3516 #endif
 3517 #if defined(INET) && defined(INET6)
 3518                 else
 3519 #endif
 3520 #ifdef INET
 3521                 {
 3522                         mss = maxmtu - min_protoh;
 3523                         if (!V_path_mtu_discovery &&
 3524                             !in_localaddr(inp->inp_faddr))
 3525                                 mss = min(mss, V_tcp_mssdflt);
 3526                 }
 3527 #endif
 3528                 /*
 3529                  * XXX - The above conditional (mss = maxmtu - min_protoh)
 3530                  * probably violates the TCP spec.
 3531                  * The problem is that, since we don't know the
 3532                  * other end's MSS, we are supposed to use a conservative
 3533                  * default.  But, if we do that, then MTU discovery will
 3534                  * never actually take place, because the conservative
 3535                  * default is much less than the MTUs typically seen
 3536                  * on the Internet today.  For the moment, we'll sweep
 3537                  * this under the carpet.
 3538                  *
 3539                  * The conservative default might not actually be a problem
 3540                  * if the only case this occurs is when sending an initial
 3541                  * SYN with options and data to a host we've never talked
 3542                  * to before.  Then, they will reply with an MSS value which
 3543                  * will get recorded and the new parameters should get
 3544                  * recomputed.  For Further Study.
 3545                  */
 3546         }
 3547         mss = min(mss, offer);
 3548 
 3549         /*
 3550          * Sanity check: make sure that maxopd will be large
 3551          * enough to allow some data on segments even if the
 3552          * all the option space is used (40bytes).  Otherwise
 3553          * funny things may happen in tcp_output.
 3554          */
 3555         mss = max(mss, 64);
 3556 
 3557         /*
 3558          * maxopd stores the maximum length of data AND options
 3559          * in a segment; maxseg is the amount of data in a normal
 3560          * segment.  We need to store this value (maxopd) apart
 3561          * from maxseg, because now every segment carries options
 3562          * and thus we normally have somewhat less data in segments.
 3563          */
 3564         tp->t_maxopd = mss;
 3565 
 3566         /*
 3567          * origoffer==-1 indicates that no segments were received yet.
 3568          * In this case we just guess.
 3569          */
 3570         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
 3571             (origoffer == -1 ||
 3572              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
 3573                 mss -= TCPOLEN_TSTAMP_APPA;
 3574 
 3575         tp->t_maxseg = mss;
 3576 }
 3577 
 3578 void
 3579 tcp_mss(struct tcpcb *tp, int offer)
 3580 {
 3581         int mss;
 3582         u_long bufsize;
 3583         struct inpcb *inp;
 3584         struct socket *so;
 3585         struct hc_metrics_lite metrics;
 3586         struct tcp_ifcap cap;
 3587 
 3588         KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
 3589 
 3590         bzero(&cap, sizeof(cap));
 3591         tcp_mss_update(tp, offer, -1, &metrics, &cap);
 3592 
 3593         mss = tp->t_maxseg;
 3594         inp = tp->t_inpcb;
 3595 
 3596         /*
 3597          * If there's a pipesize, change the socket buffer to that size,
 3598          * don't change if sb_hiwat is different than default (then it
 3599          * has been changed on purpose with setsockopt).
 3600          * Make the socket buffers an integral number of mss units;
 3601          * if the mss is larger than the socket buffer, decrease the mss.
 3602          */
 3603         so = inp->inp_socket;
 3604         SOCKBUF_LOCK(&so->so_snd);
 3605         if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
 3606                 bufsize = metrics.rmx_sendpipe;
 3607         else
 3608                 bufsize = so->so_snd.sb_hiwat;
 3609         if (bufsize < mss)
 3610                 mss = bufsize;
 3611         else {
 3612                 bufsize = roundup(bufsize, mss);
 3613                 if (bufsize > sb_max)
 3614                         bufsize = sb_max;
 3615                 if (bufsize > so->so_snd.sb_hiwat)
 3616                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
 3617         }
 3618         SOCKBUF_UNLOCK(&so->so_snd);
 3619         tp->t_maxseg = mss;
 3620 
 3621         SOCKBUF_LOCK(&so->so_rcv);
 3622         if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
 3623                 bufsize = metrics.rmx_recvpipe;
 3624         else
 3625                 bufsize = so->so_rcv.sb_hiwat;
 3626         if (bufsize > mss) {
 3627                 bufsize = roundup(bufsize, mss);
 3628                 if (bufsize > sb_max)
 3629                         bufsize = sb_max;
 3630                 if (bufsize > so->so_rcv.sb_hiwat)
 3631                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
 3632         }
 3633         SOCKBUF_UNLOCK(&so->so_rcv);
 3634 
 3635         /* Check the interface for TSO capabilities. */
 3636         if (cap.ifcap & CSUM_TSO) {
 3637                 tp->t_flags |= TF_TSO;
 3638                 tp->t_tsomax = cap.tsomax;
 3639         }
 3640 }
 3641 
 3642 /*
 3643  * Determine the MSS option to send on an outgoing SYN.
 3644  */
 3645 int
 3646 tcp_mssopt(struct in_conninfo *inc)
 3647 {
 3648         int mss = 0;
 3649         u_long maxmtu = 0;
 3650         u_long thcmtu = 0;
 3651         size_t min_protoh;
 3652 
 3653         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
 3654 
 3655 #ifdef INET6
 3656         if (inc->inc_flags & INC_ISIPV6) {
 3657                 mss = V_tcp_v6mssdflt;
 3658                 maxmtu = tcp_maxmtu6(inc, NULL);
 3659                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
 3660         }
 3661 #endif
 3662 #if defined(INET) && defined(INET6)
 3663         else
 3664 #endif
 3665 #ifdef INET
 3666         {
 3667                 mss = V_tcp_mssdflt;
 3668                 maxmtu = tcp_maxmtu(inc, NULL);
 3669                 min_protoh = sizeof(struct tcpiphdr);
 3670         }
 3671 #endif
 3672 #if defined(INET6) || defined(INET)
 3673         thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
 3674 #endif
 3675 
 3676         if (maxmtu && thcmtu)
 3677                 mss = min(maxmtu, thcmtu) - min_protoh;
 3678         else if (maxmtu || thcmtu)
 3679                 mss = max(maxmtu, thcmtu) - min_protoh;
 3680 
 3681         return (mss);
 3682 }
 3683 
 3684 
 3685 /*
 3686  * On a partial ack arrives, force the retransmission of the
 3687  * next unacknowledged segment.  Do not clear tp->t_dupacks.
 3688  * By setting snd_nxt to ti_ack, this forces retransmission timer to
 3689  * be started again.
 3690  */
 3691 static void
 3692 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
 3693 {
 3694         tcp_seq onxt = tp->snd_nxt;
 3695         u_long  ocwnd = tp->snd_cwnd;
 3696 
 3697         INP_WLOCK_ASSERT(tp->t_inpcb);
 3698 
 3699         tcp_timer_activate(tp, TT_REXMT, 0);
 3700         tp->t_rtttime = 0;
 3701         tp->snd_nxt = th->th_ack;
 3702         /*
 3703          * Set snd_cwnd to one segment beyond acknowledged offset.
 3704          * (tp->snd_una has not yet been updated when this function is called.)
 3705          */
 3706         tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th);
 3707         tp->t_flags |= TF_ACKNOW;
 3708         (void) tcp_output(tp);
 3709         tp->snd_cwnd = ocwnd;
 3710         if (SEQ_GT(onxt, tp->snd_nxt))
 3711                 tp->snd_nxt = onxt;
 3712         /*
 3713          * Partial window deflation.  Relies on fact that tp->snd_una
 3714          * not updated yet.
 3715          */
 3716         if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
 3717                 tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
 3718         else
 3719                 tp->snd_cwnd = 0;
 3720         tp->snd_cwnd += tp->t_maxseg;
 3721 }

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