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


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

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
    3  *      The Regents of the University of California.  All rights reserved.
    4  * Copyright (c) 2007-2008,2010
    5  *      Swinburne University of Technology, Melbourne, Australia.
    6  * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
    7  * Copyright (c) 2010 The FreeBSD Foundation
    8  * Copyright (c) 2010-2011 Juniper Networks, Inc.
    9  * All rights reserved.
   10  *
   11  * Portions of this software were developed at the Centre for Advanced Internet
   12  * Architectures, Swinburne University of Technology, by Lawrence Stewart,
   13  * James Healy and David Hayes, made possible in part by a grant from the Cisco
   14  * University Research Program Fund at Community Foundation Silicon Valley.
   15  *
   16  * Portions of this software were developed at the Centre for Advanced
   17  * Internet Architectures, Swinburne University of Technology, Melbourne,
   18  * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
   19  *
   20  * Portions of this software were developed by Robert N. M. Watson under
   21  * contract to Juniper Networks, Inc.
   22  *
   23  * Redistribution and use in source and binary forms, with or without
   24  * modification, are permitted provided that the following conditions
   25  * are met:
   26  * 1. Redistributions of source code must retain the above copyright
   27  *    notice, this list of conditions and the following disclaimer.
   28  * 2. Redistributions in binary form must reproduce the above copyright
   29  *    notice, this list of conditions and the following disclaimer in the
   30  *    documentation and/or other materials provided with the distribution.
   31  * 4. Neither the name of the University nor the names of its contributors
   32  *    may be used to endorse or promote products derived from this software
   33  *    without specific prior written permission.
   34  *
   35  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   36  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   37  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   38  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   39  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   40  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   41  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   42  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   43  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   44  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   45  * SUCH DAMAGE.
   46  *
   47  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
   48  */
   49 
   50 #include <sys/cdefs.h>
   51 __FBSDID("$FreeBSD: releng/10.1/sys/netinet/tcp_input.c 271667 2014-09-16 09:48:35Z delphij $");
   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_kdtrace.h"
   58 #include "opt_tcpdebug.h"
   59 
   60 #include <sys/param.h>
   61 #include <sys/kernel.h>
   62 #include <sys/hhook.h>
   63 #include <sys/malloc.h>
   64 #include <sys/mbuf.h>
   65 #include <sys/proc.h>           /* for proc0 declaration */
   66 #include <sys/protosw.h>
   67 #include <sys/sdt.h>
   68 #include <sys/signalvar.h>
   69 #include <sys/socket.h>
   70 #include <sys/socketvar.h>
   71 #include <sys/sysctl.h>
   72 #include <sys/syslog.h>
   73 #include <sys/systm.h>
   74 
   75 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
   76 
   77 #include <vm/uma.h>
   78 
   79 #include <net/if.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      cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
  233                             uint16_t type);
  234 static void inline      cc_conn_init(struct tcpcb *tp);
  235 static void inline      cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
  236 static void inline      hhook_run_tcp_est_in(struct tcpcb *tp,
  237                             struct tcphdr *th, struct tcpopt *to);
  238 
  239 /*
  240  * TCP statistics are stored in an "array" of counter(9)s.
  241  */
  242 VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
  243 VNET_PCPUSTAT_SYSINIT(tcpstat);
  244 SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
  245     tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
  246 
  247 #ifdef VIMAGE
  248 VNET_PCPUSTAT_SYSUNINIT(tcpstat);
  249 #endif /* VIMAGE */
  250 /*
  251  * Kernel module interface for updating tcpstat.  The argument is an index
  252  * into tcpstat treated as an array.
  253  */
  254 void
  255 kmod_tcpstat_inc(int statnum)
  256 {
  257 
  258         counter_u64_add(VNET(tcpstat)[statnum], 1);
  259 }
  260 
  261 /*
  262  * Wrapper for the TCP established input helper hook.
  263  */
  264 static void inline
  265 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
  266 {
  267         struct tcp_hhook_data hhook_data;
  268 
  269         if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
  270                 hhook_data.tp = tp;
  271                 hhook_data.th = th;
  272                 hhook_data.to = to;
  273 
  274                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
  275                     tp->osd);
  276         }
  277 }
  278 
  279 /*
  280  * CC wrapper hook functions
  281  */
  282 static void inline
  283 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type)
  284 {
  285         INP_WLOCK_ASSERT(tp->t_inpcb);
  286 
  287         tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
  288         if (tp->snd_cwnd <= tp->snd_wnd)
  289                 tp->ccv->flags |= CCF_CWND_LIMITED;
  290         else
  291                 tp->ccv->flags &= ~CCF_CWND_LIMITED;
  292 
  293         if (type == CC_ACK) {
  294                 if (tp->snd_cwnd > tp->snd_ssthresh) {
  295                         tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
  296                              V_tcp_abc_l_var * tp->t_maxseg);
  297                         if (tp->t_bytes_acked >= tp->snd_cwnd) {
  298                                 tp->t_bytes_acked -= tp->snd_cwnd;
  299                                 tp->ccv->flags |= CCF_ABC_SENTAWND;
  300                         }
  301                 } else {
  302                                 tp->ccv->flags &= ~CCF_ABC_SENTAWND;
  303                                 tp->t_bytes_acked = 0;
  304                 }
  305         }
  306 
  307         if (CC_ALGO(tp)->ack_received != NULL) {
  308                 /* XXXLAS: Find a way to live without this */
  309                 tp->ccv->curack = th->th_ack;
  310                 CC_ALGO(tp)->ack_received(tp->ccv, type);
  311         }
  312 }
  313 
  314 static void inline
  315 cc_conn_init(struct tcpcb *tp)
  316 {
  317         struct hc_metrics_lite metrics;
  318         struct inpcb *inp = tp->t_inpcb;
  319         int rtt;
  320 
  321         INP_WLOCK_ASSERT(tp->t_inpcb);
  322 
  323         tcp_hc_get(&inp->inp_inc, &metrics);
  324 
  325         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
  326                 tp->t_srtt = rtt;
  327                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
  328                 TCPSTAT_INC(tcps_usedrtt);
  329                 if (metrics.rmx_rttvar) {
  330                         tp->t_rttvar = metrics.rmx_rttvar;
  331                         TCPSTAT_INC(tcps_usedrttvar);
  332                 } else {
  333                         /* default variation is +- 1 rtt */
  334                         tp->t_rttvar =
  335                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
  336                 }
  337                 TCPT_RANGESET(tp->t_rxtcur,
  338                     ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
  339                     tp->t_rttmin, TCPTV_REXMTMAX);
  340         }
  341         if (metrics.rmx_ssthresh) {
  342                 /*
  343                  * There's some sort of gateway or interface
  344                  * buffer limit on the path.  Use this to set
  345                  * the slow start threshhold, but set the
  346                  * threshold to no less than 2*mss.
  347                  */
  348                 tp->snd_ssthresh = max(2 * tp->t_maxseg, metrics.rmx_ssthresh);
  349                 TCPSTAT_INC(tcps_usedssthresh);
  350         }
  351 
  352         /*
  353          * Set the initial slow-start flight size.
  354          *
  355          * RFC5681 Section 3.1 specifies the default conservative values.
  356          * RFC3390 specifies slightly more aggressive values.
  357          * RFC6928 increases it to ten segments.
  358          *
  359          * If a SYN or SYN/ACK was lost and retransmitted, we have to
  360          * reduce the initial CWND to one segment as congestion is likely
  361          * requiring us to be cautious.
  362          */
  363         if (tp->snd_cwnd == 1)
  364                 tp->snd_cwnd = tp->t_maxseg;            /* SYN(-ACK) lost */
  365         else if (V_tcp_do_initcwnd10)
  366                 tp->snd_cwnd = min(10 * tp->t_maxseg,
  367                     max(2 * tp->t_maxseg, 14600));
  368         else if (V_tcp_do_rfc3390)
  369                 tp->snd_cwnd = min(4 * tp->t_maxseg,
  370                     max(2 * tp->t_maxseg, 4380));
  371         else {
  372                 /* Per RFC5681 Section 3.1 */
  373                 if (tp->t_maxseg > 2190)
  374                         tp->snd_cwnd = 2 * tp->t_maxseg;
  375                 else if (tp->t_maxseg > 1095)
  376                         tp->snd_cwnd = 3 * tp->t_maxseg;
  377                 else
  378                         tp->snd_cwnd = 4 * tp->t_maxseg;
  379         }
  380 
  381         if (CC_ALGO(tp)->conn_init != NULL)
  382                 CC_ALGO(tp)->conn_init(tp->ccv);
  383 }
  384 
  385 void inline
  386 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
  387 {
  388         INP_WLOCK_ASSERT(tp->t_inpcb);
  389 
  390         switch(type) {
  391         case CC_NDUPACK:
  392                 if (!IN_FASTRECOVERY(tp->t_flags)) {
  393                         tp->snd_recover = tp->snd_max;
  394                         if (tp->t_flags & TF_ECN_PERMIT)
  395                                 tp->t_flags |= TF_ECN_SND_CWR;
  396                 }
  397                 break;
  398         case CC_ECN:
  399                 if (!IN_CONGRECOVERY(tp->t_flags)) {
  400                         TCPSTAT_INC(tcps_ecn_rcwnd);
  401                         tp->snd_recover = tp->snd_max;
  402                         if (tp->t_flags & TF_ECN_PERMIT)
  403                                 tp->t_flags |= TF_ECN_SND_CWR;
  404                 }
  405                 break;
  406         case CC_RTO:
  407                 tp->t_dupacks = 0;
  408                 tp->t_bytes_acked = 0;
  409                 EXIT_RECOVERY(tp->t_flags);
  410                 tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
  411                     tp->t_maxseg) * tp->t_maxseg;
  412                 tp->snd_cwnd = tp->t_maxseg;
  413                 break;
  414         case CC_RTO_ERR:
  415                 TCPSTAT_INC(tcps_sndrexmitbad);
  416                 /* RTO was unnecessary, so reset everything. */
  417                 tp->snd_cwnd = tp->snd_cwnd_prev;
  418                 tp->snd_ssthresh = tp->snd_ssthresh_prev;
  419                 tp->snd_recover = tp->snd_recover_prev;
  420                 if (tp->t_flags & TF_WASFRECOVERY)
  421                         ENTER_FASTRECOVERY(tp->t_flags);
  422                 if (tp->t_flags & TF_WASCRECOVERY)
  423                         ENTER_CONGRECOVERY(tp->t_flags);
  424                 tp->snd_nxt = tp->snd_max;
  425                 tp->t_flags &= ~TF_PREVVALID;
  426                 tp->t_badrxtwin = 0;
  427                 break;
  428         }
  429 
  430         if (CC_ALGO(tp)->cong_signal != NULL) {
  431                 if (th != NULL)
  432                         tp->ccv->curack = th->th_ack;
  433                 CC_ALGO(tp)->cong_signal(tp->ccv, type);
  434         }
  435 }
  436 
  437 static void inline
  438 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
  439 {
  440         INP_WLOCK_ASSERT(tp->t_inpcb);
  441 
  442         /* XXXLAS: KASSERT that we're in recovery? */
  443 
  444         if (CC_ALGO(tp)->post_recovery != NULL) {
  445                 tp->ccv->curack = th->th_ack;
  446                 CC_ALGO(tp)->post_recovery(tp->ccv);
  447         }
  448         /* XXXLAS: EXIT_RECOVERY ? */
  449         tp->t_bytes_acked = 0;
  450 }
  451 
  452 #ifdef TCP_SIGNATURE
  453 static inline int
  454 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
  455     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
  456 {
  457         int ret;
  458 
  459         tcp_fields_to_net(th);
  460         ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
  461         tcp_fields_to_host(th);
  462         return (ret);
  463 }
  464 #endif
  465 
  466 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
  467 #ifdef INET6
  468 #define ND6_HINT(tp) \
  469 do { \
  470         if ((tp) && (tp)->t_inpcb && \
  471             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
  472                 nd6_nud_hint(NULL, NULL, 0); \
  473 } while (0)
  474 #else
  475 #define ND6_HINT(tp)
  476 #endif
  477 
  478 /*
  479  * Indicate whether this ack should be delayed.  We can delay the ack if
  480  *      - there is no delayed ack timer in progress and
  481  *      - our last ack wasn't a 0-sized window.  We never want to delay
  482  *        the ack that opens up a 0-sized window and
  483  *              - delayed acks are enabled or
  484  *              - this is a half-synchronized T/TCP connection.
  485  *      - the segment size is not larger than the MSS and LRO wasn't used
  486  *        for this segment.
  487  */
  488 #define DELAY_ACK(tp, tlen)                                             \
  489         ((!tcp_timer_active(tp, TT_DELACK) &&                           \
  490             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
  491             (tlen <= tp->t_maxopd) &&                                   \
  492             (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
  493 
  494 /*
  495  * TCP input handling is split into multiple parts:
  496  *   tcp6_input is a thin wrapper around tcp_input for the extended
  497  *      ip6_protox[] call format in ip6_input
  498  *   tcp_input handles primary segment validation, inpcb lookup and
  499  *      SYN processing on listen sockets
  500  *   tcp_do_segment processes the ACK and text of the segment for
  501  *      establishing, established and closing connections
  502  */
  503 #ifdef INET6
  504 int
  505 tcp6_input(struct mbuf **mp, int *offp, int proto)
  506 {
  507         struct mbuf *m = *mp;
  508         struct in6_ifaddr *ia6;
  509 
  510         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
  511 
  512         /*
  513          * draft-itojun-ipv6-tcp-to-anycast
  514          * better place to put this in?
  515          */
  516         ia6 = ip6_getdstifaddr(m);
  517         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
  518                 struct ip6_hdr *ip6;
  519 
  520                 ifa_free(&ia6->ia_ifa);
  521                 ip6 = mtod(m, struct ip6_hdr *);
  522                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
  523                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
  524                 return IPPROTO_DONE;
  525         }
  526         if (ia6)
  527                 ifa_free(&ia6->ia_ifa);
  528 
  529         tcp_input(m, *offp);
  530         return IPPROTO_DONE;
  531 }
  532 #endif /* INET6 */
  533 
  534 void
  535 tcp_input(struct mbuf *m, int off0)
  536 {
  537         struct tcphdr *th = NULL;
  538         struct ip *ip = NULL;
  539         struct inpcb *inp = NULL;
  540         struct tcpcb *tp = NULL;
  541         struct socket *so = NULL;
  542         u_char *optp = NULL;
  543         int optlen = 0;
  544 #ifdef INET
  545         int len;
  546 #endif
  547         int tlen = 0, off;
  548         int drop_hdrlen;
  549         int thflags;
  550         int rstreason = 0;      /* For badport_bandlim accounting purposes */
  551 #ifdef TCP_SIGNATURE
  552         uint8_t sig_checked = 0;
  553 #endif
  554         uint8_t iptos = 0;
  555         struct m_tag *fwd_tag = NULL;
  556 #ifdef INET6
  557         struct ip6_hdr *ip6 = NULL;
  558         int isipv6;
  559 #else
  560         const void *ip6 = NULL;
  561 #endif /* INET6 */
  562         struct tcpopt to;               /* options in this segment */
  563         char *s = NULL;                 /* address and port logging */
  564         int ti_locked;
  565 #define TI_UNLOCKED     1
  566 #define TI_WLOCKED      2
  567 
  568 #ifdef TCPDEBUG
  569         /*
  570          * The size of tcp_saveipgen must be the size of the max ip header,
  571          * now IPv6.
  572          */
  573         u_char tcp_saveipgen[IP6_HDR_LEN];
  574         struct tcphdr tcp_savetcp;
  575         short ostate = 0;
  576 #endif
  577 
  578 #ifdef INET6
  579         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
  580 #endif
  581 
  582         to.to_flags = 0;
  583         TCPSTAT_INC(tcps_rcvtotal);
  584 
  585 #ifdef INET6
  586         if (isipv6) {
  587                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
  588 
  589                 if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
  590                         m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
  591                         if (m == NULL) {
  592                                 TCPSTAT_INC(tcps_rcvshort);
  593                                 return;
  594                         }
  595                 }
  596 
  597                 ip6 = mtod(m, struct ip6_hdr *);
  598                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
  599                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
  600                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
  601                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  602                                 th->th_sum = m->m_pkthdr.csum_data;
  603                         else
  604                                 th->th_sum = in6_cksum_pseudo(ip6, tlen,
  605                                     IPPROTO_TCP, m->m_pkthdr.csum_data);
  606                         th->th_sum ^= 0xffff;
  607                 } else
  608                         th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
  609                 if (th->th_sum) {
  610                         TCPSTAT_INC(tcps_rcvbadsum);
  611                         goto drop;
  612                 }
  613 
  614                 /*
  615                  * Be proactive about unspecified IPv6 address in source.
  616                  * As we use all-zero to indicate unbounded/unconnected pcb,
  617                  * unspecified IPv6 address can be used to confuse us.
  618                  *
  619                  * Note that packets with unspecified IPv6 destination is
  620                  * already dropped in ip6_input.
  621                  */
  622                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
  623                         /* XXX stat */
  624                         goto drop;
  625                 }
  626         }
  627 #endif
  628 #if defined(INET) && defined(INET6)
  629         else
  630 #endif
  631 #ifdef INET
  632         {
  633                 /*
  634                  * Get IP and TCP header together in first mbuf.
  635                  * Note: IP leaves IP header in first mbuf.
  636                  */
  637                 if (off0 > sizeof (struct ip)) {
  638                         ip_stripoptions(m);
  639                         off0 = sizeof(struct ip);
  640                 }
  641                 if (m->m_len < sizeof (struct tcpiphdr)) {
  642                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
  643                             == NULL) {
  644                                 TCPSTAT_INC(tcps_rcvshort);
  645                                 return;
  646                         }
  647                 }
  648                 ip = mtod(m, struct ip *);
  649                 th = (struct tcphdr *)((caddr_t)ip + off0);
  650                 tlen = ntohs(ip->ip_len) - off0;
  651 
  652                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
  653                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  654                                 th->th_sum = m->m_pkthdr.csum_data;
  655                         else
  656                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
  657                                     ip->ip_dst.s_addr,
  658                                     htonl(m->m_pkthdr.csum_data + tlen +
  659                                     IPPROTO_TCP));
  660                         th->th_sum ^= 0xffff;
  661                 } else {
  662                         struct ipovly *ipov = (struct ipovly *)ip;
  663 
  664                         /*
  665                          * Checksum extended TCP header and data.
  666                          */
  667                         len = off0 + tlen;
  668                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
  669                         ipov->ih_len = htons(tlen);
  670                         th->th_sum = in_cksum(m, len);
  671                         /* Reset length for SDT probes. */
  672                         ip->ip_len = htons(tlen + off0);
  673                 }
  674 
  675                 if (th->th_sum) {
  676                         TCPSTAT_INC(tcps_rcvbadsum);
  677                         goto drop;
  678                 }
  679                 /* Re-initialization for later version check */
  680                 ip->ip_v = IPVERSION;
  681         }
  682 #endif /* INET */
  683 
  684 #ifdef INET6
  685         if (isipv6)
  686                 iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
  687 #endif
  688 #if defined(INET) && defined(INET6)
  689         else
  690 #endif
  691 #ifdef INET
  692                 iptos = ip->ip_tos;
  693 #endif
  694 
  695         /*
  696          * Check that TCP offset makes sense,
  697          * pull out TCP options and adjust length.              XXX
  698          */
  699         off = th->th_off << 2;
  700         if (off < sizeof (struct tcphdr) || off > tlen) {
  701                 TCPSTAT_INC(tcps_rcvbadoff);
  702                 goto drop;
  703         }
  704         tlen -= off;    /* tlen is used instead of ti->ti_len */
  705         if (off > sizeof (struct tcphdr)) {
  706 #ifdef INET6
  707                 if (isipv6) {
  708                         IP6_EXTHDR_CHECK(m, off0, off, );
  709                         ip6 = mtod(m, struct ip6_hdr *);
  710                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
  711                 }
  712 #endif
  713 #if defined(INET) && defined(INET6)
  714                 else
  715 #endif
  716 #ifdef INET
  717                 {
  718                         if (m->m_len < sizeof(struct ip) + off) {
  719                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
  720                                     == NULL) {
  721                                         TCPSTAT_INC(tcps_rcvshort);
  722                                         return;
  723                                 }
  724                                 ip = mtod(m, struct ip *);
  725                                 th = (struct tcphdr *)((caddr_t)ip + off0);
  726                         }
  727                 }
  728 #endif
  729                 optlen = off - sizeof (struct tcphdr);
  730                 optp = (u_char *)(th + 1);
  731         }
  732         thflags = th->th_flags;
  733 
  734         /*
  735          * Convert TCP protocol specific fields to host format.
  736          */
  737         tcp_fields_to_host(th);
  738 
  739         /*
  740          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
  741          */
  742         drop_hdrlen = off0 + off;
  743 
  744         /*
  745          * Locate pcb for segment; if we're likely to add or remove a
  746          * connection then first acquire pcbinfo lock.  There are two cases
  747          * where we might discover later we need a write lock despite the
  748          * flags: ACKs moving a connection out of the syncache, and ACKs for
  749          * a connection in TIMEWAIT.
  750          */
  751         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0) {
  752                 INP_INFO_WLOCK(&V_tcbinfo);
  753                 ti_locked = TI_WLOCKED;
  754         } else
  755                 ti_locked = TI_UNLOCKED;
  756 
  757         /*
  758          * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
  759          */
  760         if (
  761 #ifdef INET6
  762             (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
  763 #ifdef INET
  764             || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
  765 #endif
  766 #endif
  767 #if defined(INET) && !defined(INET6)
  768             (m->m_flags & M_IP_NEXTHOP)
  769 #endif
  770             )
  771                 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
  772 
  773 findpcb:
  774 #ifdef INVARIANTS
  775         if (ti_locked == TI_WLOCKED) {
  776                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  777         } else {
  778                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
  779         }
  780 #endif
  781 #ifdef INET6
  782         if (isipv6 && fwd_tag != NULL) {
  783                 struct sockaddr_in6 *next_hop6;
  784 
  785                 next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
  786                 /*
  787                  * Transparently forwarded. Pretend to be the destination.
  788                  * Already got one like this?
  789                  */
  790                 inp = in6_pcblookup_mbuf(&V_tcbinfo,
  791                     &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
  792                     INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
  793                 if (!inp) {
  794                         /*
  795                          * It's new.  Try to find the ambushing socket.
  796                          * Because we've rewritten the destination address,
  797                          * any hardware-generated hash is ignored.
  798                          */
  799                         inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
  800                             th->th_sport, &next_hop6->sin6_addr,
  801                             next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
  802                             th->th_dport, INPLOOKUP_WILDCARD |
  803                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  804                 }
  805         } else if (isipv6) {
  806                 inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
  807                     th->th_sport, &ip6->ip6_dst, th->th_dport,
  808                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  809                     m->m_pkthdr.rcvif, m);
  810         }
  811 #endif /* INET6 */
  812 #if defined(INET6) && defined(INET)
  813         else
  814 #endif
  815 #ifdef INET
  816         if (fwd_tag != NULL) {
  817                 struct sockaddr_in *next_hop;
  818 
  819                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
  820                 /*
  821                  * Transparently forwarded. Pretend to be the destination.
  822                  * already got one like this?
  823                  */
  824                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
  825                     ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
  826                     m->m_pkthdr.rcvif, m);
  827                 if (!inp) {
  828                         /*
  829                          * It's new.  Try to find the ambushing socket.
  830                          * Because we've rewritten the destination address,
  831                          * any hardware-generated hash is ignored.
  832                          */
  833                         inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
  834                             th->th_sport, next_hop->sin_addr,
  835                             next_hop->sin_port ? ntohs(next_hop->sin_port) :
  836                             th->th_dport, INPLOOKUP_WILDCARD |
  837                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  838                 }
  839         } else
  840                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
  841                     th->th_sport, ip->ip_dst, th->th_dport,
  842                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  843                     m->m_pkthdr.rcvif, m);
  844 #endif /* INET */
  845 
  846         /*
  847          * If the INPCB does not exist then all data in the incoming
  848          * segment is discarded and an appropriate RST is sent back.
  849          * XXX MRT Send RST using which routing table?
  850          */
  851         if (inp == NULL) {
  852                 /*
  853                  * Log communication attempts to ports that are not
  854                  * in use.
  855                  */
  856                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
  857                     tcp_log_in_vain == 2) {
  858                         if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
  859                                 log(LOG_INFO, "%s; %s: Connection attempt "
  860                                     "to closed port\n", s, __func__);
  861                 }
  862                 /*
  863                  * When blackholing do not respond with a RST but
  864                  * completely ignore the segment and drop it.
  865                  */
  866                 if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
  867                     V_blackhole == 2)
  868                         goto dropunlock;
  869 
  870                 rstreason = BANDLIM_RST_CLOSEDPORT;
  871                 goto dropwithreset;
  872         }
  873         INP_WLOCK_ASSERT(inp);
  874         if (!(inp->inp_flags & INP_HW_FLOWID)
  875             && (m->m_flags & M_FLOWID)
  876             && ((inp->inp_socket == NULL)
  877                 || !(inp->inp_socket->so_options & SO_ACCEPTCONN))) {
  878                 inp->inp_flags |= INP_HW_FLOWID;
  879                 inp->inp_flags &= ~INP_SW_FLOWID;
  880                 inp->inp_flowid = m->m_pkthdr.flowid;
  881         }
  882 #ifdef IPSEC
  883 #ifdef INET6
  884         if (isipv6 && ipsec6_in_reject(m, inp)) {
  885                 IPSEC6STAT_INC(ips_in_polvio);
  886                 goto dropunlock;
  887         } else
  888 #endif /* INET6 */
  889         if (ipsec4_in_reject(m, inp) != 0) {
  890                 IPSECSTAT_INC(ips_in_polvio);
  891                 goto dropunlock;
  892         }
  893 #endif /* IPSEC */
  894 
  895         /*
  896          * Check the minimum TTL for socket.
  897          */
  898         if (inp->inp_ip_minttl != 0) {
  899 #ifdef INET6
  900                 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
  901                         goto dropunlock;
  902                 else
  903 #endif
  904                 if (inp->inp_ip_minttl > ip->ip_ttl)
  905                         goto dropunlock;
  906         }
  907 
  908         /*
  909          * A previous connection in TIMEWAIT state is supposed to catch stray
  910          * or duplicate segments arriving late.  If this segment was a
  911          * legitimate new connection attempt, the old INPCB gets removed and
  912          * we can try again to find a listening socket.
  913          *
  914          * At this point, due to earlier optimism, we may hold only an inpcb
  915          * lock, and not the inpcbinfo write lock.  If so, we need to try to
  916          * acquire it, or if that fails, acquire a reference on the inpcb,
  917          * drop all locks, acquire a global write lock, and then re-acquire
  918          * the inpcb lock.  We may at that point discover that another thread
  919          * has tried to free the inpcb, in which case we need to loop back
  920          * and try to find a new inpcb to deliver to.
  921          *
  922          * XXXRW: It may be time to rethink timewait locking.
  923          */
  924 relocked:
  925         if (inp->inp_flags & INP_TIMEWAIT) {
  926                 if (ti_locked == TI_UNLOCKED) {
  927                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
  928                                 in_pcbref(inp);
  929                                 INP_WUNLOCK(inp);
  930                                 INP_INFO_WLOCK(&V_tcbinfo);
  931                                 ti_locked = TI_WLOCKED;
  932                                 INP_WLOCK(inp);
  933                                 if (in_pcbrele_wlocked(inp)) {
  934                                         inp = NULL;
  935                                         goto findpcb;
  936                                 }
  937                         } else
  938                                 ti_locked = TI_WLOCKED;
  939                 }
  940                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  941 
  942                 if (thflags & TH_SYN)
  943                         tcp_dooptions(&to, optp, optlen, TO_SYN);
  944                 /*
  945                  * NB: tcp_twcheck unlocks the INP and frees the mbuf.
  946                  */
  947                 if (tcp_twcheck(inp, &to, th, m, tlen))
  948                         goto findpcb;
  949                 INP_INFO_WUNLOCK(&V_tcbinfo);
  950                 return;
  951         }
  952         /*
  953          * The TCPCB may no longer exist if the connection is winding
  954          * down or it is in the CLOSED state.  Either way we drop the
  955          * segment and send an appropriate response.
  956          */
  957         tp = intotcpcb(inp);
  958         if (tp == NULL || tp->t_state == TCPS_CLOSED) {
  959                 rstreason = BANDLIM_RST_CLOSEDPORT;
  960                 goto dropwithreset;
  961         }
  962 
  963 #ifdef TCP_OFFLOAD
  964         if (tp->t_flags & TF_TOE) {
  965                 tcp_offload_input(tp, m);
  966                 m = NULL;       /* consumed by the TOE driver */
  967                 goto dropunlock;
  968         }
  969 #endif
  970 
  971         /*
  972          * We've identified a valid inpcb, but it could be that we need an
  973          * inpcbinfo write lock but don't hold it.  In this case, attempt to
  974          * acquire using the same strategy as the TIMEWAIT case above.  If we
  975          * relock, we have to jump back to 'relocked' as the connection might
  976          * now be in TIMEWAIT.
  977          */
  978 #ifdef INVARIANTS
  979         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0)
  980                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  981 #endif
  982         if (tp->t_state != TCPS_ESTABLISHED) {
  983                 if (ti_locked == TI_UNLOCKED) {
  984                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
  985                                 in_pcbref(inp);
  986                                 INP_WUNLOCK(inp);
  987                                 INP_INFO_WLOCK(&V_tcbinfo);
  988                                 ti_locked = TI_WLOCKED;
  989                                 INP_WLOCK(inp);
  990                                 if (in_pcbrele_wlocked(inp)) {
  991                                         inp = NULL;
  992                                         goto findpcb;
  993                                 }
  994                                 goto relocked;
  995                         } else
  996                                 ti_locked = TI_WLOCKED;
  997                 }
  998                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  999         }
 1000 
 1001 #ifdef MAC
 1002         INP_WLOCK_ASSERT(inp);
 1003         if (mac_inpcb_check_deliver(inp, m))
 1004                 goto dropunlock;
 1005 #endif
 1006         so = inp->inp_socket;
 1007         KASSERT(so != NULL, ("%s: so == NULL", __func__));
 1008 #ifdef TCPDEBUG
 1009         if (so->so_options & SO_DEBUG) {
 1010                 ostate = tp->t_state;
 1011 #ifdef INET6
 1012                 if (isipv6) {
 1013                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 1014                 } else
 1015 #endif
 1016                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 1017                 tcp_savetcp = *th;
 1018         }
 1019 #endif /* TCPDEBUG */
 1020         /*
 1021          * When the socket is accepting connections (the INPCB is in LISTEN
 1022          * state) we look into the SYN cache if this is a new connection
 1023          * attempt or the completion of a previous one.  Because listen
 1024          * sockets are never in TCPS_ESTABLISHED, the V_tcbinfo lock will be
 1025          * held in this case.
 1026          */
 1027         if (so->so_options & SO_ACCEPTCONN) {
 1028                 struct in_conninfo inc;
 1029 
 1030                 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
 1031                     "tp not listening", __func__));
 1032                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1033 
 1034                 bzero(&inc, sizeof(inc));
 1035 #ifdef INET6
 1036                 if (isipv6) {
 1037                         inc.inc_flags |= INC_ISIPV6;
 1038                         inc.inc6_faddr = ip6->ip6_src;
 1039                         inc.inc6_laddr = ip6->ip6_dst;
 1040                 } else
 1041 #endif
 1042                 {
 1043                         inc.inc_faddr = ip->ip_src;
 1044                         inc.inc_laddr = ip->ip_dst;
 1045                 }
 1046                 inc.inc_fport = th->th_sport;
 1047                 inc.inc_lport = th->th_dport;
 1048                 inc.inc_fibnum = so->so_fibnum;
 1049 
 1050                 /*
 1051                  * Check for an existing connection attempt in syncache if
 1052                  * the flag is only ACK.  A successful lookup creates a new
 1053                  * socket appended to the listen queue in SYN_RECEIVED state.
 1054                  */
 1055                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 1056                         /*
 1057                          * Parse the TCP options here because
 1058                          * syncookies need access to the reflected
 1059                          * timestamp.
 1060                          */
 1061                         tcp_dooptions(&to, optp, optlen, 0);
 1062                         /*
 1063                          * NB: syncache_expand() doesn't unlock
 1064                          * inp and tcpinfo locks.
 1065                          */
 1066                         if (!syncache_expand(&inc, &to, th, &so, m)) {
 1067                                 /*
 1068                                  * No syncache entry or ACK was not
 1069                                  * for our SYN/ACK.  Send a RST.
 1070                                  * NB: syncache did its own logging
 1071                                  * of the failure cause.
 1072                                  */
 1073                                 rstreason = BANDLIM_RST_OPENPORT;
 1074                                 goto dropwithreset;
 1075                         }
 1076                         if (so == NULL) {
 1077                                 /*
 1078                                  * We completed the 3-way handshake
 1079                                  * but could not allocate a socket
 1080                                  * either due to memory shortage,
 1081                                  * listen queue length limits or
 1082                                  * global socket limits.  Send RST
 1083                                  * or wait and have the remote end
 1084                                  * retransmit the ACK for another
 1085                                  * try.
 1086                                  */
 1087                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1088                                         log(LOG_DEBUG, "%s; %s: Listen socket: "
 1089                                             "Socket allocation failed due to "
 1090                                             "limits or memory shortage, %s\n",
 1091                                             s, __func__,
 1092                                             V_tcp_sc_rst_sock_fail ?
 1093                                             "sending RST" : "try again");
 1094                                 if (V_tcp_sc_rst_sock_fail) {
 1095                                         rstreason = BANDLIM_UNLIMITED;
 1096                                         goto dropwithreset;
 1097                                 } else
 1098                                         goto dropunlock;
 1099                         }
 1100                         /*
 1101                          * Socket is created in state SYN_RECEIVED.
 1102                          * Unlock the listen socket, lock the newly
 1103                          * created socket and update the tp variable.
 1104                          */
 1105                         INP_WUNLOCK(inp);       /* listen socket */
 1106                         inp = sotoinpcb(so);
 1107                         INP_WLOCK(inp);         /* new connection */
 1108                         tp = intotcpcb(inp);
 1109                         KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
 1110                             ("%s: ", __func__));
 1111 #ifdef TCP_SIGNATURE
 1112                         if (sig_checked == 0)  {
 1113                                 tcp_dooptions(&to, optp, optlen,
 1114                                     (thflags & TH_SYN) ? TO_SYN : 0);
 1115                                 if (!tcp_signature_verify_input(m, off0, tlen,
 1116                                     optlen, &to, th, tp->t_flags)) {
 1117 
 1118                                         /*
 1119                                          * In SYN_SENT state if it receives an
 1120                                          * RST, it is allowed for further
 1121                                          * processing.
 1122                                          */
 1123                                         if ((thflags & TH_RST) == 0 ||
 1124                                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1125                                                 goto dropunlock;
 1126                                 }
 1127                                 sig_checked = 1;
 1128                         }
 1129 #endif
 1130 
 1131                         /*
 1132                          * Process the segment and the data it
 1133                          * contains.  tcp_do_segment() consumes
 1134                          * the mbuf chain and unlocks the inpcb.
 1135                          */
 1136                         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
 1137                             iptos, ti_locked);
 1138                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1139                         return;
 1140                 }
 1141                 /*
 1142                  * Segment flag validation for new connection attempts:
 1143                  *
 1144                  * Our (SYN|ACK) response was rejected.
 1145                  * Check with syncache and remove entry to prevent
 1146                  * retransmits.
 1147                  *
 1148                  * NB: syncache_chkrst does its own logging of failure
 1149                  * causes.
 1150                  */
 1151                 if (thflags & TH_RST) {
 1152                         syncache_chkrst(&inc, th);
 1153                         goto dropunlock;
 1154                 }
 1155                 /*
 1156                  * We can't do anything without SYN.
 1157                  */
 1158                 if ((thflags & TH_SYN) == 0) {
 1159                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1160                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1161                                     "SYN is missing, segment ignored\n",
 1162                                     s, __func__);
 1163                         TCPSTAT_INC(tcps_badsyn);
 1164                         goto dropunlock;
 1165                 }
 1166                 /*
 1167                  * (SYN|ACK) is bogus on a listen socket.
 1168                  */
 1169                 if (thflags & TH_ACK) {
 1170                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1171                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1172                                     "SYN|ACK invalid, segment rejected\n",
 1173                                     s, __func__);
 1174                         syncache_badack(&inc);  /* XXX: Not needed! */
 1175                         TCPSTAT_INC(tcps_badsyn);
 1176                         rstreason = BANDLIM_RST_OPENPORT;
 1177                         goto dropwithreset;
 1178                 }
 1179                 /*
 1180                  * If the drop_synfin option is enabled, drop all
 1181                  * segments with both the SYN and FIN bits set.
 1182                  * This prevents e.g. nmap from identifying the
 1183                  * TCP/IP stack.
 1184                  * XXX: Poor reasoning.  nmap has other methods
 1185                  * and is constantly refining its stack detection
 1186                  * strategies.
 1187                  * XXX: This is a violation of the TCP specification
 1188                  * and was used by RFC1644.
 1189                  */
 1190                 if ((thflags & TH_FIN) && V_drop_synfin) {
 1191                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1192                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1193                                     "SYN|FIN segment ignored (based on "
 1194                                     "sysctl setting)\n", s, __func__);
 1195                         TCPSTAT_INC(tcps_badsyn);
 1196                         goto dropunlock;
 1197                 }
 1198                 /*
 1199                  * Segment's flags are (SYN) or (SYN|FIN).
 1200                  *
 1201                  * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
 1202                  * as they do not affect the state of the TCP FSM.
 1203                  * The data pointed to by TH_URG and th_urp is ignored.
 1204                  */
 1205                 KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
 1206                     ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
 1207                 KASSERT(thflags & (TH_SYN),
 1208                     ("%s: Listen socket: TH_SYN not set", __func__));
 1209 #ifdef INET6
 1210                 /*
 1211                  * If deprecated address is forbidden,
 1212                  * we do not accept SYN to deprecated interface
 1213                  * address to prevent any new inbound connection from
 1214                  * getting established.
 1215                  * When we do not accept SYN, we send a TCP RST,
 1216                  * with deprecated source address (instead of dropping
 1217                  * it).  We compromise it as it is much better for peer
 1218                  * to send a RST, and RST will be the final packet
 1219                  * for the exchange.
 1220                  *
 1221                  * If we do not forbid deprecated addresses, we accept
 1222                  * the SYN packet.  RFC2462 does not suggest dropping
 1223                  * SYN in this case.
 1224                  * If we decipher RFC2462 5.5.4, it says like this:
 1225                  * 1. use of deprecated addr with existing
 1226                  *    communication is okay - "SHOULD continue to be
 1227                  *    used"
 1228                  * 2. use of it with new communication:
 1229                  *   (2a) "SHOULD NOT be used if alternate address
 1230                  *        with sufficient scope is available"
 1231                  *   (2b) nothing mentioned otherwise.
 1232                  * Here we fall into (2b) case as we have no choice in
 1233                  * our source address selection - we must obey the peer.
 1234                  *
 1235                  * The wording in RFC2462 is confusing, and there are
 1236                  * multiple description text for deprecated address
 1237                  * handling - worse, they are not exactly the same.
 1238                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 1239                  */
 1240                 if (isipv6 && !V_ip6_use_deprecated) {
 1241                         struct in6_ifaddr *ia6;
 1242 
 1243                         ia6 = ip6_getdstifaddr(m);
 1244                         if (ia6 != NULL &&
 1245                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 1246                                 ifa_free(&ia6->ia_ifa);
 1247                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1248                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1249                                         "Connection attempt to deprecated "
 1250                                         "IPv6 address rejected\n",
 1251                                         s, __func__);
 1252                                 rstreason = BANDLIM_RST_OPENPORT;
 1253                                 goto dropwithreset;
 1254                         }
 1255                         if (ia6)
 1256                                 ifa_free(&ia6->ia_ifa);
 1257                 }
 1258 #endif /* INET6 */
 1259                 /*
 1260                  * Basic sanity checks on incoming SYN requests:
 1261                  *   Don't respond if the destination is a link layer
 1262                  *      broadcast according to RFC1122 4.2.3.10, p. 104.
 1263                  *   If it is from this socket it must be forged.
 1264                  *   Don't respond if the source or destination is a
 1265                  *      global or subnet broad- or multicast address.
 1266                  *   Note that it is quite possible to receive unicast
 1267                  *      link-layer packets with a broadcast IP address. Use
 1268                  *      in_broadcast() to find them.
 1269                  */
 1270                 if (m->m_flags & (M_BCAST|M_MCAST)) {
 1271                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1272                             log(LOG_DEBUG, "%s; %s: Listen socket: "
 1273                                 "Connection attempt from broad- or multicast "
 1274                                 "link layer address ignored\n", s, __func__);
 1275                         goto dropunlock;
 1276                 }
 1277 #ifdef INET6
 1278                 if (isipv6) {
 1279                         if (th->th_dport == th->th_sport &&
 1280                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
 1281                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1282                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1283                                         "Connection attempt to/from self "
 1284                                         "ignored\n", s, __func__);
 1285                                 goto dropunlock;
 1286                         }
 1287                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 1288                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
 1289                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1290                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1291                                         "Connection attempt from/to multicast "
 1292                                         "address ignored\n", s, __func__);
 1293                                 goto dropunlock;
 1294                         }
 1295                 }
 1296 #endif
 1297 #if defined(INET) && defined(INET6)
 1298                 else
 1299 #endif
 1300 #ifdef INET
 1301                 {
 1302                         if (th->th_dport == th->th_sport &&
 1303                             ip->ip_dst.s_addr == ip->ip_src.s_addr) {
 1304                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1305                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1306                                         "Connection attempt from/to self "
 1307                                         "ignored\n", s, __func__);
 1308                                 goto dropunlock;
 1309                         }
 1310                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 1311                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 1312                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 1313                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
 1314                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1315                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1316                                         "Connection attempt from/to broad- "
 1317                                         "or multicast address ignored\n",
 1318                                         s, __func__);
 1319                                 goto dropunlock;
 1320                         }
 1321                 }
 1322 #endif
 1323                 /*
 1324                  * SYN appears to be valid.  Create compressed TCP state
 1325                  * for syncache.
 1326                  */
 1327 #ifdef TCPDEBUG
 1328                 if (so->so_options & SO_DEBUG)
 1329                         tcp_trace(TA_INPUT, ostate, tp,
 1330                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1331 #endif
 1332                 tcp_dooptions(&to, optp, optlen, TO_SYN);
 1333                 syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
 1334                 /*
 1335                  * Entry added to syncache and mbuf consumed.
 1336                  * Everything already unlocked by syncache_add().
 1337                  */
 1338                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1339                 return;
 1340         } else if (tp->t_state == TCPS_LISTEN) {
 1341                 /*
 1342                  * When a listen socket is torn down the SO_ACCEPTCONN
 1343                  * flag is removed first while connections are drained
 1344                  * from the accept queue in a unlock/lock cycle of the
 1345                  * ACCEPT_LOCK, opening a race condition allowing a SYN
 1346                  * attempt go through unhandled.
 1347                  */
 1348                 goto dropunlock;
 1349         }
 1350 
 1351 #ifdef TCP_SIGNATURE
 1352         if (sig_checked == 0)  {
 1353                 tcp_dooptions(&to, optp, optlen,
 1354                     (thflags & TH_SYN) ? TO_SYN : 0);
 1355                 if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
 1356                     th, tp->t_flags)) {
 1357 
 1358                         /*
 1359                          * In SYN_SENT state if it receives an RST, it is
 1360                          * allowed for further processing.
 1361                          */
 1362                         if ((thflags & TH_RST) == 0 ||
 1363                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1364                                 goto dropunlock;
 1365                 }
 1366                 sig_checked = 1;
 1367         }
 1368 #endif
 1369 
 1370         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1371 
 1372         /*
 1373          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
 1374          * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
 1375          * the inpcb, and unlocks pcbinfo.
 1376          */
 1377         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
 1378         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1379         return;
 1380 
 1381 dropwithreset:
 1382         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1383 
 1384         if (ti_locked == TI_WLOCKED) {
 1385                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1386                 ti_locked = TI_UNLOCKED;
 1387         }
 1388 #ifdef INVARIANTS
 1389         else {
 1390                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
 1391                     "ti_locked: %d", __func__, ti_locked));
 1392                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1393         }
 1394 #endif
 1395 
 1396         if (inp != NULL) {
 1397                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 1398                 INP_WUNLOCK(inp);
 1399         } else
 1400                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 1401         m = NULL;       /* mbuf chain got consumed. */
 1402         goto drop;
 1403 
 1404 dropunlock:
 1405         if (m != NULL)
 1406                 TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1407 
 1408         if (ti_locked == TI_WLOCKED) {
 1409                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1410                 ti_locked = TI_UNLOCKED;
 1411         }
 1412 #ifdef INVARIANTS
 1413         else {
 1414                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
 1415                     "ti_locked: %d", __func__, ti_locked));
 1416                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1417         }
 1418 #endif
 1419 
 1420         if (inp != NULL)
 1421                 INP_WUNLOCK(inp);
 1422 
 1423 drop:
 1424         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1425         if (s != NULL)
 1426                 free(s, M_TCPLOG);
 1427         if (m != NULL)
 1428                 m_freem(m);
 1429 }
 1430 
 1431 static void
 1432 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 1433     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
 1434     int ti_locked)
 1435 {
 1436         int thflags, acked, ourfinisacked, needoutput = 0;
 1437         int rstreason, todrop, win;
 1438         u_long tiwin;
 1439         char *s;
 1440         struct in_conninfo *inc;
 1441         struct mbuf *mfree;
 1442         struct tcpopt to;
 1443 
 1444 #ifdef TCPDEBUG
 1445         /*
 1446          * The size of tcp_saveipgen must be the size of the max ip header,
 1447          * now IPv6.
 1448          */
 1449         u_char tcp_saveipgen[IP6_HDR_LEN];
 1450         struct tcphdr tcp_savetcp;
 1451         short ostate = 0;
 1452 #endif
 1453         thflags = th->th_flags;
 1454         inc = &tp->t_inpcb->inp_inc;
 1455         tp->sackhint.last_sack_ack = 0;
 1456 
 1457         /*
 1458          * If this is either a state-changing packet or current state isn't
 1459          * established, we require a write lock on tcbinfo.  Otherwise, we
 1460          * allow the tcbinfo to be in either alocked or unlocked, as the
 1461          * caller may have unnecessarily acquired a write lock due to a race.
 1462          */
 1463         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
 1464             tp->t_state != TCPS_ESTABLISHED) {
 1465                 KASSERT(ti_locked == TI_WLOCKED, ("%s ti_locked %d for "
 1466                     "SYN/FIN/RST/!EST", __func__, ti_locked));
 1467                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1468         } else {
 1469 #ifdef INVARIANTS
 1470                 if (ti_locked == TI_WLOCKED)
 1471                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1472                 else {
 1473                         KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
 1474                             "ti_locked: %d", __func__, ti_locked));
 1475                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1476                 }
 1477 #endif
 1478         }
 1479         INP_WLOCK_ASSERT(tp->t_inpcb);
 1480         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
 1481             __func__));
 1482         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
 1483             __func__));
 1484 
 1485         /*
 1486          * Segment received on connection.
 1487          * Reset idle time and keep-alive timer.
 1488          * XXX: This should be done after segment
 1489          * validation to ignore broken/spoofed segs.
 1490          */
 1491         tp->t_rcvtime = ticks;
 1492         if (TCPS_HAVEESTABLISHED(tp->t_state))
 1493                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 1494 
 1495         /*
 1496          * Unscale the window into a 32-bit value.
 1497          * For the SYN_SENT state the scale is zero.
 1498          */
 1499         tiwin = th->th_win << tp->snd_scale;
 1500 
 1501         /*
 1502          * TCP ECN processing.
 1503          */
 1504         if (tp->t_flags & TF_ECN_PERMIT) {
 1505                 if (thflags & TH_CWR)
 1506                         tp->t_flags &= ~TF_ECN_SND_ECE;
 1507                 switch (iptos & IPTOS_ECN_MASK) {
 1508                 case IPTOS_ECN_CE:
 1509                         tp->t_flags |= TF_ECN_SND_ECE;
 1510                         TCPSTAT_INC(tcps_ecn_ce);
 1511                         break;
 1512                 case IPTOS_ECN_ECT0:
 1513                         TCPSTAT_INC(tcps_ecn_ect0);
 1514                         break;
 1515                 case IPTOS_ECN_ECT1:
 1516                         TCPSTAT_INC(tcps_ecn_ect1);
 1517                         break;
 1518                 }
 1519                 /* Congestion experienced. */
 1520                 if (thflags & TH_ECE) {
 1521                         cc_cong_signal(tp, th, CC_ECN);
 1522                 }
 1523         }
 1524 
 1525         /*
 1526          * Parse options on any incoming segment.
 1527          */
 1528         tcp_dooptions(&to, (u_char *)(th + 1),
 1529             (th->th_off << 2) - sizeof(struct tcphdr),
 1530             (thflags & TH_SYN) ? TO_SYN : 0);
 1531 
 1532         /*
 1533          * If echoed timestamp is later than the current time,
 1534          * fall back to non RFC1323 RTT calculation.  Normalize
 1535          * timestamp if syncookies were used when this connection
 1536          * was established.
 1537          */
 1538         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
 1539                 to.to_tsecr -= tp->ts_offset;
 1540                 if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
 1541                         to.to_tsecr = 0;
 1542         }
 1543         /*
 1544          * If timestamps were negotiated during SYN/ACK they should
 1545          * appear on every segment during this session and vice versa.
 1546          */
 1547         if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
 1548                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1549                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1550                             "no action\n", s, __func__);
 1551                         free(s, M_TCPLOG);
 1552                 }
 1553         }
 1554         if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
 1555                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1556                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1557                             "no action\n", s, __func__);
 1558                         free(s, M_TCPLOG);
 1559                 }
 1560         }
 1561 
 1562         /*
 1563          * Process options only when we get SYN/ACK back. The SYN case
 1564          * for incoming connections is handled in tcp_syncache.
 1565          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
 1566          * or <SYN,ACK>) segment itself is never scaled.
 1567          * XXX this is traditional behavior, may need to be cleaned up.
 1568          */
 1569         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
 1570                 if ((to.to_flags & TOF_SCALE) &&
 1571                     (tp->t_flags & TF_REQ_SCALE)) {
 1572                         tp->t_flags |= TF_RCVD_SCALE;
 1573                         tp->snd_scale = to.to_wscale;
 1574                 }
 1575                 /*
 1576                  * Initial send window.  It will be updated with
 1577                  * the next incoming segment to the scaled value.
 1578                  */
 1579                 tp->snd_wnd = th->th_win;
 1580                 if (to.to_flags & TOF_TS) {
 1581                         tp->t_flags |= TF_RCVD_TSTMP;
 1582                         tp->ts_recent = to.to_tsval;
 1583                         tp->ts_recent_age = tcp_ts_getticks();
 1584                 }
 1585                 if (to.to_flags & TOF_MSS)
 1586                         tcp_mss(tp, to.to_mss);
 1587                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 1588                     (to.to_flags & TOF_SACKPERM) == 0)
 1589                         tp->t_flags &= ~TF_SACK_PERMIT;
 1590         }
 1591 
 1592         /*
 1593          * Header prediction: check for the two common cases
 1594          * of a uni-directional data xfer.  If the packet has
 1595          * no control flags, is in-sequence, the window didn't
 1596          * change and we're not retransmitting, it's a
 1597          * candidate.  If the length is zero and the ack moved
 1598          * forward, we're the sender side of the xfer.  Just
 1599          * free the data acked & wake any higher level process
 1600          * that was blocked waiting for space.  If the length
 1601          * is non-zero and the ack didn't move, we're the
 1602          * receiver side.  If we're getting packets in-order
 1603          * (the reassembly queue is empty), add the data to
 1604          * the socket buffer and note that we need a delayed ack.
 1605          * Make sure that the hidden state-flags are also off.
 1606          * Since we check for TCPS_ESTABLISHED first, it can only
 1607          * be TH_NEEDSYN.
 1608          */
 1609         if (tp->t_state == TCPS_ESTABLISHED &&
 1610             th->th_seq == tp->rcv_nxt &&
 1611             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 1612             tp->snd_nxt == tp->snd_max &&
 1613             tiwin && tiwin == tp->snd_wnd && 
 1614             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 1615             LIST_EMPTY(&tp->t_segq) &&
 1616             ((to.to_flags & TOF_TS) == 0 ||
 1617              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
 1618 
 1619                 /*
 1620                  * If last ACK falls within this segment's sequence numbers,
 1621                  * record the timestamp.
 1622                  * NOTE that the test is modified according to the latest
 1623                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 1624                  */
 1625                 if ((to.to_flags & TOF_TS) != 0 &&
 1626                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 1627                         tp->ts_recent_age = tcp_ts_getticks();
 1628                         tp->ts_recent = to.to_tsval;
 1629                 }
 1630 
 1631                 if (tlen == 0) {
 1632                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 1633                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 1634                             !IN_RECOVERY(tp->t_flags) &&
 1635                             (to.to_flags & TOF_SACK) == 0 &&
 1636                             TAILQ_EMPTY(&tp->snd_holes)) {
 1637                                 /*
 1638                                  * This is a pure ack for outstanding data.
 1639                                  */
 1640                                 if (ti_locked == TI_WLOCKED)
 1641                                         INP_INFO_WUNLOCK(&V_tcbinfo);
 1642                                 ti_locked = TI_UNLOCKED;
 1643 
 1644                                 TCPSTAT_INC(tcps_predack);
 1645 
 1646                                 /*
 1647                                  * "bad retransmit" recovery.
 1648                                  */
 1649                                 if (tp->t_rxtshift == 1 &&
 1650                                     tp->t_flags & TF_PREVVALID &&
 1651                                     (int)(ticks - tp->t_badrxtwin) < 0) {
 1652                                         cc_cong_signal(tp, th, CC_RTO_ERR);
 1653                                 }
 1654 
 1655                                 /*
 1656                                  * Recalculate the transmit timer / rtt.
 1657                                  *
 1658                                  * Some boxes send broken timestamp replies
 1659                                  * during the SYN+ACK phase, ignore
 1660                                  * timestamps of 0 or we could calculate a
 1661                                  * huge RTT and blow up the retransmit timer.
 1662                                  */
 1663                                 if ((to.to_flags & TOF_TS) != 0 &&
 1664                                     to.to_tsecr) {
 1665                                         u_int t;
 1666 
 1667                                         t = tcp_ts_getticks() - to.to_tsecr;
 1668                                         if (!tp->t_rttlow || tp->t_rttlow > t)
 1669                                                 tp->t_rttlow = t;
 1670                                         tcp_xmit_timer(tp,
 1671                                             TCP_TS_TO_TICKS(t) + 1);
 1672                                 } else if (tp->t_rtttime &&
 1673                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
 1674                                         if (!tp->t_rttlow ||
 1675                                             tp->t_rttlow > ticks - tp->t_rtttime)
 1676                                                 tp->t_rttlow = ticks - tp->t_rtttime;
 1677                                         tcp_xmit_timer(tp,
 1678                                                         ticks - tp->t_rtttime);
 1679                                 }
 1680                                 acked = BYTES_THIS_ACK(tp, th);
 1681 
 1682                                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 1683                                 hhook_run_tcp_est_in(tp, th, &to);
 1684 
 1685                                 TCPSTAT_INC(tcps_rcvackpack);
 1686                                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 1687                                 sbdrop(&so->so_snd, acked);
 1688                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
 1689                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 1690                                         tp->snd_recover = th->th_ack - 1;
 1691                                 
 1692                                 /*
 1693                                  * Let the congestion control algorithm update
 1694                                  * congestion control related information. This
 1695                                  * typically means increasing the congestion
 1696                                  * window.
 1697                                  */
 1698                                 cc_ack_received(tp, th, CC_ACK);
 1699 
 1700                                 tp->snd_una = th->th_ack;
 1701                                 /*
 1702                                  * Pull snd_wl2 up to prevent seq wrap relative
 1703                                  * to th_ack.
 1704                                  */
 1705                                 tp->snd_wl2 = th->th_ack;
 1706                                 tp->t_dupacks = 0;
 1707                                 m_freem(m);
 1708                                 ND6_HINT(tp); /* Some progress has been made. */
 1709 
 1710                                 /*
 1711                                  * If all outstanding data are acked, stop
 1712                                  * retransmit timer, otherwise restart timer
 1713                                  * using current (possibly backed-off) value.
 1714                                  * If process is waiting for space,
 1715                                  * wakeup/selwakeup/signal.  If data
 1716                                  * are ready to send, let tcp_output
 1717                                  * decide between more output or persist.
 1718                                  */
 1719 #ifdef TCPDEBUG
 1720                                 if (so->so_options & SO_DEBUG)
 1721                                         tcp_trace(TA_INPUT, ostate, tp,
 1722                                             (void *)tcp_saveipgen,
 1723                                             &tcp_savetcp, 0);
 1724 #endif
 1725                                 if (tp->snd_una == tp->snd_max)
 1726                                         tcp_timer_activate(tp, TT_REXMT, 0);
 1727                                 else if (!tcp_timer_active(tp, TT_PERSIST))
 1728                                         tcp_timer_activate(tp, TT_REXMT,
 1729                                                       tp->t_rxtcur);
 1730                                 sowwakeup(so);
 1731                                 if (so->so_snd.sb_cc)
 1732                                         (void) tcp_output(tp);
 1733                                 goto check_delack;
 1734                         }
 1735                 } else if (th->th_ack == tp->snd_una &&
 1736                     tlen <= sbspace(&so->so_rcv)) {
 1737                         int newsize = 0;        /* automatic sockbuf scaling */
 1738 
 1739                         /*
 1740                          * This is a pure, in-sequence data packet with
 1741                          * nothing on the reassembly queue and we have enough
 1742                          * buffer space to take it.
 1743                          */
 1744                         if (ti_locked == TI_WLOCKED)
 1745                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1746                         ti_locked = TI_UNLOCKED;
 1747 
 1748                         /* Clean receiver SACK report if present */
 1749                         if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
 1750                                 tcp_clean_sackreport(tp);
 1751                         TCPSTAT_INC(tcps_preddat);
 1752                         tp->rcv_nxt += tlen;
 1753                         /*
 1754                          * Pull snd_wl1 up to prevent seq wrap relative to
 1755                          * th_seq.
 1756                          */
 1757                         tp->snd_wl1 = th->th_seq;
 1758                         /*
 1759                          * Pull rcv_up up to prevent seq wrap relative to
 1760                          * rcv_nxt.
 1761                          */
 1762                         tp->rcv_up = tp->rcv_nxt;
 1763                         TCPSTAT_INC(tcps_rcvpack);
 1764                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 1765                         ND6_HINT(tp);   /* Some progress has been made */
 1766 #ifdef TCPDEBUG
 1767                         if (so->so_options & SO_DEBUG)
 1768                                 tcp_trace(TA_INPUT, ostate, tp,
 1769                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1770 #endif
 1771                 /*
 1772                  * Automatic sizing of receive socket buffer.  Often the send
 1773                  * buffer size is not optimally adjusted to the actual network
 1774                  * conditions at hand (delay bandwidth product).  Setting the
 1775                  * buffer size too small limits throughput on links with high
 1776                  * bandwidth and high delay (eg. trans-continental/oceanic links).
 1777                  *
 1778                  * On the receive side the socket buffer memory is only rarely
 1779                  * used to any significant extent.  This allows us to be much
 1780                  * more aggressive in scaling the receive socket buffer.  For
 1781                  * the case that the buffer space is actually used to a large
 1782                  * extent and we run out of kernel memory we can simply drop
 1783                  * the new segments; TCP on the sender will just retransmit it
 1784                  * later.  Setting the buffer size too big may only consume too
 1785                  * much kernel memory if the application doesn't read() from
 1786                  * the socket or packet loss or reordering makes use of the
 1787                  * reassembly queue.
 1788                  *
 1789                  * The criteria to step up the receive buffer one notch are:
 1790                  *  1. the number of bytes received during the time it takes
 1791                  *     one timestamp to be reflected back to us (the RTT);
 1792                  *  2. received bytes per RTT is within seven eighth of the
 1793                  *     current socket buffer size;
 1794                  *  3. receive buffer size has not hit maximal automatic size;
 1795                  *
 1796                  * This algorithm does one step per RTT at most and only if
 1797                  * we receive a bulk stream w/o packet losses or reorderings.
 1798                  * Shrinking the buffer during idle times is not necessary as
 1799                  * it doesn't consume any memory when idle.
 1800                  *
 1801                  * TODO: Only step up if the application is actually serving
 1802                  * the buffer to better manage the socket buffer resources.
 1803                  */
 1804                         if (V_tcp_do_autorcvbuf &&
 1805                             to.to_tsecr &&
 1806                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
 1807                                 if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
 1808                                     to.to_tsecr - tp->rfbuf_ts < hz) {
 1809                                         if (tp->rfbuf_cnt >
 1810                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
 1811                                             so->so_rcv.sb_hiwat <
 1812                                             V_tcp_autorcvbuf_max) {
 1813                                                 newsize =
 1814                                                     min(so->so_rcv.sb_hiwat +
 1815                                                     V_tcp_autorcvbuf_inc,
 1816                                                     V_tcp_autorcvbuf_max);
 1817                                         }
 1818                                         /* Start over with next RTT. */
 1819                                         tp->rfbuf_ts = 0;
 1820                                         tp->rfbuf_cnt = 0;
 1821                                 } else
 1822                                         tp->rfbuf_cnt += tlen;  /* add up */
 1823                         }
 1824 
 1825                         /* Add data to socket buffer. */
 1826                         SOCKBUF_LOCK(&so->so_rcv);
 1827                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 1828                                 m_freem(m);
 1829                         } else {
 1830                                 /*
 1831                                  * Set new socket buffer size.
 1832                                  * Give up when limit is reached.
 1833                                  */
 1834                                 if (newsize)
 1835                                         if (!sbreserve_locked(&so->so_rcv,
 1836                                             newsize, so, NULL))
 1837                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
 1838                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 1839                                 sbappendstream_locked(&so->so_rcv, m);
 1840                         }
 1841                         /* NB: sorwakeup_locked() does an implicit unlock. */
 1842                         sorwakeup_locked(so);
 1843                         if (DELAY_ACK(tp, tlen)) {
 1844                                 tp->t_flags |= TF_DELACK;
 1845                         } else {
 1846                                 tp->t_flags |= TF_ACKNOW;
 1847                                 tcp_output(tp);
 1848                         }
 1849                         goto check_delack;
 1850                 }
 1851         }
 1852 
 1853         /*
 1854          * Calculate amount of space in receive window,
 1855          * and then do TCP input processing.
 1856          * Receive window is amount of space in rcv queue,
 1857          * but not less than advertised window.
 1858          */
 1859         win = sbspace(&so->so_rcv);
 1860         if (win < 0)
 1861                 win = 0;
 1862         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 1863 
 1864         /* Reset receive buffer auto scaling when not in bulk receive mode. */
 1865         tp->rfbuf_ts = 0;
 1866         tp->rfbuf_cnt = 0;
 1867 
 1868         switch (tp->t_state) {
 1869 
 1870         /*
 1871          * If the state is SYN_RECEIVED:
 1872          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
 1873          */
 1874         case TCPS_SYN_RECEIVED:
 1875                 if ((thflags & TH_ACK) &&
 1876                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
 1877                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1878                                 rstreason = BANDLIM_RST_OPENPORT;
 1879                                 goto dropwithreset;
 1880                 }
 1881                 break;
 1882 
 1883         /*
 1884          * If the state is SYN_SENT:
 1885          *      if seg contains an ACK, but not for our SYN, drop the input.
 1886          *      if seg contains a RST, then drop the connection.
 1887          *      if seg does not contain SYN, then drop it.
 1888          * Otherwise this is an acceptable SYN segment
 1889          *      initialize tp->rcv_nxt and tp->irs
 1890          *      if seg contains ack then advance tp->snd_una
 1891          *      if seg contains an ECE and ECN support is enabled, the stream
 1892          *          is ECN capable.
 1893          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
 1894          *      arrange for segment to be acked (eventually)
 1895          *      continue processing rest of data/controls, beginning with URG
 1896          */
 1897         case TCPS_SYN_SENT:
 1898                 if ((thflags & TH_ACK) &&
 1899                     (SEQ_LEQ(th->th_ack, tp->iss) ||
 1900                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1901                         rstreason = BANDLIM_UNLIMITED;
 1902                         goto dropwithreset;
 1903                 }
 1904                 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
 1905                         TCP_PROBE5(connect__refused, NULL, tp,
 1906                             mtod(m, const char *), tp, th);
 1907                         tp = tcp_drop(tp, ECONNREFUSED);
 1908                 }
 1909                 if (thflags & TH_RST)
 1910                         goto drop;
 1911                 if (!(thflags & TH_SYN))
 1912                         goto drop;
 1913 
 1914                 tp->irs = th->th_seq;
 1915                 tcp_rcvseqinit(tp);
 1916                 if (thflags & TH_ACK) {
 1917                         TCPSTAT_INC(tcps_connects);
 1918                         soisconnected(so);
 1919 #ifdef MAC
 1920                         mac_socketpeer_set_from_mbuf(m, so);
 1921 #endif
 1922                         /* Do window scaling on this connection? */
 1923                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 1924                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 1925                                 tp->rcv_scale = tp->request_r_scale;
 1926                         }
 1927                         tp->rcv_adv += imin(tp->rcv_wnd,
 1928                             TCP_MAXWIN << tp->rcv_scale);
 1929                         tp->snd_una++;          /* SYN is acked */
 1930                         /*
 1931                          * If there's data, delay ACK; if there's also a FIN
 1932                          * ACKNOW will be turned on later.
 1933                          */
 1934                         if (DELAY_ACK(tp, tlen) && tlen != 0)
 1935                                 tcp_timer_activate(tp, TT_DELACK,
 1936                                     tcp_delacktime);
 1937                         else
 1938                                 tp->t_flags |= TF_ACKNOW;
 1939 
 1940                         if ((thflags & TH_ECE) && V_tcp_do_ecn) {
 1941                                 tp->t_flags |= TF_ECN_PERMIT;
 1942                                 TCPSTAT_INC(tcps_ecn_shs);
 1943                         }
 1944                         
 1945                         /*
 1946                          * Received <SYN,ACK> in SYN_SENT[*] state.
 1947                          * Transitions:
 1948                          *      SYN_SENT  --> ESTABLISHED
 1949                          *      SYN_SENT* --> FIN_WAIT_1
 1950                          */
 1951                         tp->t_starttime = ticks;
 1952                         if (tp->t_flags & TF_NEEDFIN) {
 1953                                 tcp_state_change(tp, TCPS_FIN_WAIT_1);
 1954                                 tp->t_flags &= ~TF_NEEDFIN;
 1955                                 thflags &= ~TH_SYN;
 1956                         } else {
 1957                                 tcp_state_change(tp, TCPS_ESTABLISHED);
 1958                                 TCP_PROBE5(connect__established, NULL, tp,
 1959                                     mtod(m, const char *), tp, th);
 1960                                 cc_conn_init(tp);
 1961                                 tcp_timer_activate(tp, TT_KEEP,
 1962                                     TP_KEEPIDLE(tp));
 1963                         }
 1964                 } else {
 1965                         /*
 1966                          * Received initial SYN in SYN-SENT[*] state =>
 1967                          * simultaneous open.  If segment contains CC option
 1968                          * and there is a cached CC, apply TAO test.
 1969                          * If it succeeds, connection is * half-synchronized.
 1970                          * Otherwise, do 3-way handshake:
 1971                          *        SYN-SENT -> SYN-RECEIVED
 1972                          *        SYN-SENT* -> SYN-RECEIVED*
 1973                          * If there was no CC option, clear cached CC value.
 1974                          */
 1975                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 1976                         tcp_timer_activate(tp, TT_REXMT, 0);
 1977                         tcp_state_change(tp, TCPS_SYN_RECEIVED);
 1978                 }
 1979 
 1980                 KASSERT(ti_locked == TI_WLOCKED, ("%s: trimthenstep6: "
 1981                     "ti_locked %d", __func__, ti_locked));
 1982                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1983                 INP_WLOCK_ASSERT(tp->t_inpcb);
 1984 
 1985                 /*
 1986                  * Advance th->th_seq to correspond to first data byte.
 1987                  * If data, trim to stay within window,
 1988                  * dropping FIN if necessary.
 1989                  */
 1990                 th->th_seq++;
 1991                 if (tlen > tp->rcv_wnd) {
 1992                         todrop = tlen - tp->rcv_wnd;
 1993                         m_adj(m, -todrop);
 1994                         tlen = tp->rcv_wnd;
 1995                         thflags &= ~TH_FIN;
 1996                         TCPSTAT_INC(tcps_rcvpackafterwin);
 1997                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 1998                 }
 1999                 tp->snd_wl1 = th->th_seq - 1;
 2000                 tp->rcv_up = th->th_seq;
 2001                 /*
 2002                  * Client side of transaction: already sent SYN and data.
 2003                  * If the remote host used T/TCP to validate the SYN,
 2004                  * our data will be ACK'd; if so, enter normal data segment
 2005                  * processing in the middle of step 5, ack processing.
 2006                  * Otherwise, goto step 6.
 2007                  */
 2008                 if (thflags & TH_ACK)
 2009                         goto process_ACK;
 2010 
 2011                 goto step6;
 2012 
 2013         /*
 2014          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
 2015          *      do normal processing.
 2016          *
 2017          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
 2018          */
 2019         case TCPS_LAST_ACK:
 2020         case TCPS_CLOSING:
 2021                 break;  /* continue normal processing */
 2022         }
 2023 
 2024         /*
 2025          * States other than LISTEN or SYN_SENT.
 2026          * First check the RST flag and sequence number since reset segments
 2027          * are exempt from the timestamp and connection count tests.  This
 2028          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
 2029          * below which allowed reset segments in half the sequence space
 2030          * to fall though and be processed (which gives forged reset
 2031          * segments with a random sequence number a 50 percent chance of
 2032          * killing a connection).
 2033          * Then check timestamp, if present.
 2034          * Then check the connection count, if present.
 2035          * Then check that at least some bytes of segment are within
 2036          * receive window.  If segment begins before rcv_nxt,
 2037          * drop leading data (and SYN); if nothing left, just ack.
 2038          *
 2039          *
 2040          * If the RST bit is set, check the sequence number to see
 2041          * if this is a valid reset segment.
 2042          * RFC 793 page 37:
 2043          *   In all states except SYN-SENT, all reset (RST) segments
 2044          *   are validated by checking their SEQ-fields.  A reset is
 2045          *   valid if its sequence number is in the window.
 2046          * Note: this does not take into account delayed ACKs, so
 2047          *   we should test against last_ack_sent instead of rcv_nxt.
 2048          *   The sequence number in the reset segment is normally an
 2049          *   echo of our outgoing acknowlegement numbers, but some hosts
 2050          *   send a reset with the sequence number at the rightmost edge
 2051          *   of our receive window, and we have to handle this case.
 2052          * Note 2: Paul Watson's paper "Slipping in the Window" has shown
 2053          *   that brute force RST attacks are possible.  To combat this,
 2054          *   we use a much stricter check while in the ESTABLISHED state,
 2055          *   only accepting RSTs where the sequence number is equal to
 2056          *   last_ack_sent.  In all other states (the states in which a
 2057          *   RST is more likely), the more permissive check is used.
 2058          * If we have multiple segments in flight, the initial reset
 2059          * segment sequence numbers will be to the left of last_ack_sent,
 2060          * but they will eventually catch up.
 2061          * In any case, it never made sense to trim reset segments to
 2062          * fit the receive window since RFC 1122 says:
 2063          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
 2064          *
 2065          *    A TCP SHOULD allow a received RST segment to include data.
 2066          *
 2067          *    DISCUSSION
 2068          *         It has been suggested that a RST segment could contain
 2069          *         ASCII text that encoded and explained the cause of the
 2070          *         RST.  No standard has yet been established for such
 2071          *         data.
 2072          *
 2073          * If the reset segment passes the sequence number test examine
 2074          * the state:
 2075          *    SYN_RECEIVED STATE:
 2076          *      If passive open, return to LISTEN state.
 2077          *      If active open, inform user that connection was refused.
 2078          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
 2079          *      Inform user that connection was reset, and close tcb.
 2080          *    CLOSING, LAST_ACK STATES:
 2081          *      Close the tcb.
 2082          *    TIME_WAIT STATE:
 2083          *      Drop the segment - see Stevens, vol. 2, p. 964 and
 2084          *      RFC 1337.
 2085          */
 2086         if (thflags & TH_RST) {
 2087                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
 2088                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
 2089                         switch (tp->t_state) {
 2090 
 2091                         case TCPS_SYN_RECEIVED:
 2092                                 so->so_error = ECONNREFUSED;
 2093                                 goto close;
 2094 
 2095                         case TCPS_ESTABLISHED:
 2096                                 if (V_tcp_insecure_rst == 0 &&
 2097                                     !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
 2098                                     SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
 2099                                     !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
 2100                                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
 2101                                         TCPSTAT_INC(tcps_badrst);
 2102                                         goto drop;
 2103                                 }
 2104                                 /* FALLTHROUGH */
 2105                         case TCPS_FIN_WAIT_1:
 2106                         case TCPS_FIN_WAIT_2:
 2107                         case TCPS_CLOSE_WAIT:
 2108                                 so->so_error = ECONNRESET;
 2109                         close:
 2110                                 KASSERT(ti_locked == TI_WLOCKED,
 2111                                     ("tcp_do_segment: TH_RST 1 ti_locked %d",
 2112                                     ti_locked));
 2113                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2114 
 2115                                 tcp_state_change(tp, TCPS_CLOSED);
 2116                                 TCPSTAT_INC(tcps_drops);
 2117                                 tp = tcp_close(tp);
 2118                                 break;
 2119 
 2120                         case TCPS_CLOSING:
 2121                         case TCPS_LAST_ACK:
 2122                                 KASSERT(ti_locked == TI_WLOCKED,
 2123                                     ("tcp_do_segment: TH_RST 2 ti_locked %d",
 2124                                     ti_locked));
 2125                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2126 
 2127                                 tp = tcp_close(tp);
 2128                                 break;
 2129                         }
 2130                 }
 2131                 goto drop;
 2132         }
 2133 
 2134         /*
 2135          * RFC 1323 PAWS: If we have a timestamp reply on this segment
 2136          * and it's less than ts_recent, drop it.
 2137          */
 2138         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
 2139             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
 2140 
 2141                 /* Check to see if ts_recent is over 24 days old.  */
 2142                 if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
 2143                         /*
 2144                          * Invalidate ts_recent.  If this segment updates
 2145                          * ts_recent, the age will be reset later and ts_recent
 2146                          * will get a valid value.  If it does not, setting
 2147                          * ts_recent to zero will at least satisfy the
 2148                          * requirement that zero be placed in the timestamp
 2149                          * echo reply when ts_recent isn't valid.  The
 2150                          * age isn't reset until we get a valid ts_recent
 2151                          * because we don't want out-of-order segments to be
 2152                          * dropped when ts_recent is old.
 2153                          */
 2154                         tp->ts_recent = 0;
 2155                 } else {
 2156                         TCPSTAT_INC(tcps_rcvduppack);
 2157                         TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
 2158                         TCPSTAT_INC(tcps_pawsdrop);
 2159                         if (tlen)
 2160                                 goto dropafterack;
 2161                         goto drop;
 2162                 }
 2163         }
 2164 
 2165         /*
 2166          * In the SYN-RECEIVED state, validate that the packet belongs to
 2167          * this connection before trimming the data to fit the receive
 2168          * window.  Check the sequence number versus IRS since we know
 2169          * the sequence numbers haven't wrapped.  This is a partial fix
 2170          * for the "LAND" DoS attack.
 2171          */
 2172         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
 2173                 rstreason = BANDLIM_RST_OPENPORT;
 2174                 goto dropwithreset;
 2175         }
 2176 
 2177         todrop = tp->rcv_nxt - th->th_seq;
 2178         if (todrop > 0) {
 2179                 if (thflags & TH_SYN) {
 2180                         thflags &= ~TH_SYN;
 2181                         th->th_seq++;
 2182                         if (th->th_urp > 1)
 2183                                 th->th_urp--;
 2184                         else
 2185                                 thflags &= ~TH_URG;
 2186                         todrop--;
 2187                 }
 2188                 /*
 2189                  * Following if statement from Stevens, vol. 2, p. 960.
 2190                  */
 2191                 if (todrop > tlen
 2192                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
 2193                         /*
 2194                          * Any valid FIN must be to the left of the window.
 2195                          * At this point the FIN must be a duplicate or out
 2196                          * of sequence; drop it.
 2197                          */
 2198                         thflags &= ~TH_FIN;
 2199 
 2200                         /*
 2201                          * Send an ACK to resynchronize and drop any data.
 2202                          * But keep on processing for RST or ACK.
 2203                          */
 2204                         tp->t_flags |= TF_ACKNOW;
 2205                         todrop = tlen;
 2206                         TCPSTAT_INC(tcps_rcvduppack);
 2207                         TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
 2208                 } else {
 2209                         TCPSTAT_INC(tcps_rcvpartduppack);
 2210                         TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
 2211                 }
 2212                 drop_hdrlen += todrop;  /* drop from the top afterwards */
 2213                 th->th_seq += todrop;
 2214                 tlen -= todrop;
 2215                 if (th->th_urp > todrop)
 2216                         th->th_urp -= todrop;
 2217                 else {
 2218                         thflags &= ~TH_URG;
 2219                         th->th_urp = 0;
 2220                 }
 2221         }
 2222 
 2223         /*
 2224          * If new data are received on a connection after the
 2225          * user processes are gone, then RST the other end.
 2226          */
 2227         if ((so->so_state & SS_NOFDREF) &&
 2228             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
 2229                 KASSERT(ti_locked == TI_WLOCKED, ("%s: SS_NOFDEREF && "
 2230                     "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
 2231                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2232 
 2233                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 2234                         log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
 2235                             "after socket was closed, "
 2236                             "sending RST and removing tcpcb\n",
 2237                             s, __func__, tcpstates[tp->t_state], tlen);
 2238                         free(s, M_TCPLOG);
 2239                 }
 2240                 tp = tcp_close(tp);
 2241                 TCPSTAT_INC(tcps_rcvafterclose);
 2242                 rstreason = BANDLIM_UNLIMITED;
 2243                 goto dropwithreset;
 2244         }
 2245 
 2246         /*
 2247          * If segment ends after window, drop trailing data
 2248          * (and PUSH and FIN); if nothing left, just ACK.
 2249          */
 2250         todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
 2251         if (todrop > 0) {
 2252                 TCPSTAT_INC(tcps_rcvpackafterwin);
 2253                 if (todrop >= tlen) {
 2254                         TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
 2255                         /*
 2256                          * If window is closed can only take segments at
 2257                          * window edge, and have to drop data and PUSH from
 2258                          * incoming segments.  Continue processing, but
 2259                          * remember to ack.  Otherwise, drop segment
 2260                          * and ack.
 2261                          */
 2262                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
 2263                                 tp->t_flags |= TF_ACKNOW;
 2264                                 TCPSTAT_INC(tcps_rcvwinprobe);
 2265                         } else
 2266                                 goto dropafterack;
 2267                 } else
 2268                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2269                 m_adj(m, -todrop);
 2270                 tlen -= todrop;
 2271                 thflags &= ~(TH_PUSH|TH_FIN);
 2272         }
 2273 
 2274         /*
 2275          * If last ACK falls within this segment's sequence numbers,
 2276          * record its timestamp.
 2277          * NOTE: 
 2278          * 1) That the test incorporates suggestions from the latest
 2279          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
 2280          * 2) That updating only on newer timestamps interferes with
 2281          *    our earlier PAWS tests, so this check should be solely
 2282          *    predicated on the sequence space of this segment.
 2283          * 3) That we modify the segment boundary check to be 
 2284          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len  
 2285          *    instead of RFC1323's
 2286          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
 2287          *    This modified check allows us to overcome RFC1323's
 2288          *    limitations as described in Stevens TCP/IP Illustrated
 2289          *    Vol. 2 p.869. In such cases, we can still calculate the
 2290          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
 2291          */
 2292         if ((to.to_flags & TOF_TS) != 0 &&
 2293             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
 2294             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
 2295                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
 2296                 tp->ts_recent_age = tcp_ts_getticks();
 2297                 tp->ts_recent = to.to_tsval;
 2298         }
 2299 
 2300         /*
 2301          * If a SYN is in the window, then this is an
 2302          * error and we send an RST and drop the connection.
 2303          */
 2304         if (thflags & TH_SYN) {
 2305                 KASSERT(ti_locked == TI_WLOCKED,
 2306                     ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
 2307                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2308 
 2309                 tp = tcp_drop(tp, ECONNRESET);
 2310                 rstreason = BANDLIM_UNLIMITED;
 2311                 goto drop;
 2312         }
 2313 
 2314         /*
 2315          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
 2316          * flag is on (half-synchronized state), then queue data for
 2317          * later processing; else drop segment and return.
 2318          */
 2319         if ((thflags & TH_ACK) == 0) {
 2320                 if (tp->t_state == TCPS_SYN_RECEIVED ||
 2321                     (tp->t_flags & TF_NEEDSYN))
 2322                         goto step6;
 2323                 else if (tp->t_flags & TF_ACKNOW)
 2324                         goto dropafterack;
 2325                 else
 2326                         goto drop;
 2327         }
 2328 
 2329         /*
 2330          * Ack processing.
 2331          */
 2332         switch (tp->t_state) {
 2333 
 2334         /*
 2335          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
 2336          * ESTABLISHED state and continue processing.
 2337          * The ACK was checked above.
 2338          */
 2339         case TCPS_SYN_RECEIVED:
 2340 
 2341                 TCPSTAT_INC(tcps_connects);
 2342                 soisconnected(so);
 2343                 /* Do window scaling? */
 2344                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2345                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2346                         tp->rcv_scale = tp->request_r_scale;
 2347                         tp->snd_wnd = tiwin;
 2348                 }
 2349                 /*
 2350                  * Make transitions:
 2351                  *      SYN-RECEIVED  -> ESTABLISHED
 2352                  *      SYN-RECEIVED* -> FIN-WAIT-1
 2353                  */
 2354                 tp->t_starttime = ticks;
 2355                 if (tp->t_flags & TF_NEEDFIN) {
 2356                         tcp_state_change(tp, TCPS_FIN_WAIT_1);
 2357                         tp->t_flags &= ~TF_NEEDFIN;
 2358                 } else {
 2359                         tcp_state_change(tp, TCPS_ESTABLISHED);
 2360                         TCP_PROBE5(accept__established, NULL, tp,
 2361                             mtod(m, const char *), tp, th);
 2362                         cc_conn_init(tp);
 2363                         tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 2364                 }
 2365                 /*
 2366                  * If segment contains data or ACK, will call tcp_reass()
 2367                  * later; if not, do so now to pass queued data to user.
 2368                  */
 2369                 if (tlen == 0 && (thflags & TH_FIN) == 0)
 2370                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
 2371                             (struct mbuf *)0);
 2372                 tp->snd_wl1 = th->th_seq - 1;
 2373                 /* FALLTHROUGH */
 2374 
 2375         /*
 2376          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
 2377          * ACKs.  If the ack is in the range
 2378          *      tp->snd_una < th->th_ack <= tp->snd_max
 2379          * then advance tp->snd_una to th->th_ack and drop
 2380          * data from the retransmission queue.  If this ACK reflects
 2381          * more up to date window information we update our window information.
 2382          */
 2383         case TCPS_ESTABLISHED:
 2384         case TCPS_FIN_WAIT_1:
 2385         case TCPS_FIN_WAIT_2:
 2386         case TCPS_CLOSE_WAIT:
 2387         case TCPS_CLOSING:
 2388         case TCPS_LAST_ACK:
 2389                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
 2390                         TCPSTAT_INC(tcps_rcvacktoomuch);
 2391                         goto dropafterack;
 2392                 }
 2393                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 2394                     ((to.to_flags & TOF_SACK) ||
 2395                      !TAILQ_EMPTY(&tp->snd_holes)))
 2396                         tcp_sack_doack(tp, &to, th->th_ack);
 2397 
 2398                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 2399                 hhook_run_tcp_est_in(tp, th, &to);
 2400 
 2401                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
 2402                         if (tlen == 0 && tiwin == tp->snd_wnd) {
 2403                                 TCPSTAT_INC(tcps_rcvdupack);
 2404                                 /*
 2405                                  * If we have outstanding data (other than
 2406                                  * a window probe), this is a completely
 2407                                  * duplicate ack (ie, window info didn't
 2408                                  * change), the ack is the biggest we've
 2409                                  * seen and we've seen exactly our rexmt
 2410                                  * threshhold of them, assume a packet
 2411                                  * has been dropped and retransmit it.
 2412                                  * Kludge snd_nxt & the congestion
 2413                                  * window so we send only this one
 2414                                  * packet.
 2415                                  *
 2416                                  * We know we're losing at the current
 2417                                  * window size so do congestion avoidance
 2418                                  * (set ssthresh to half the current window
 2419                                  * and pull our congestion window back to
 2420                                  * the new ssthresh).
 2421                                  *
 2422                                  * Dup acks mean that packets have left the
 2423                                  * network (they're now cached at the receiver)
 2424                                  * so bump cwnd by the amount in the receiver
 2425                                  * to keep a constant cwnd packets in the
 2426                                  * network.
 2427                                  *
 2428                                  * When using TCP ECN, notify the peer that
 2429                                  * we reduced the cwnd.
 2430                                  */
 2431                                 if (!tcp_timer_active(tp, TT_REXMT) ||
 2432                                     th->th_ack != tp->snd_una)
 2433                                         tp->t_dupacks = 0;
 2434                                 else if (++tp->t_dupacks > tcprexmtthresh ||
 2435                                      IN_FASTRECOVERY(tp->t_flags)) {
 2436                                         cc_ack_received(tp, th, CC_DUPACK);
 2437                                         if ((tp->t_flags & TF_SACK_PERMIT) &&
 2438                                             IN_FASTRECOVERY(tp->t_flags)) {
 2439                                                 int awnd;
 2440                                                 
 2441                                                 /*
 2442                                                  * Compute the amount of data in flight first.
 2443                                                  * We can inject new data into the pipe iff 
 2444                                                  * we have less than 1/2 the original window's
 2445                                                  * worth of data in flight.
 2446                                                  */
 2447                                                 awnd = (tp->snd_nxt - tp->snd_fack) +
 2448                                                         tp->sackhint.sack_bytes_rexmit;
 2449                                                 if (awnd < tp->snd_ssthresh) {
 2450                                                         tp->snd_cwnd += tp->t_maxseg;
 2451                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
 2452                                                                 tp->snd_cwnd = tp->snd_ssthresh;
 2453                                                 }
 2454                                         } else
 2455                                                 tp->snd_cwnd += tp->t_maxseg;
 2456                                         if ((thflags & TH_FIN) &&
 2457                                             (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
 2458                                                 /* 
 2459                                                  * If its a fin we need to process
 2460                                                  * it to avoid a race where both
 2461                                                  * sides enter FIN-WAIT and send FIN|ACK
 2462                                                  * at the same time.
 2463                                                  */
 2464                                                 break;
 2465                                         }
 2466                                         (void) tcp_output(tp);
 2467                                         goto drop;
 2468                                 } else if (tp->t_dupacks == tcprexmtthresh) {
 2469                                         tcp_seq onxt = tp->snd_nxt;
 2470 
 2471                                         /*
 2472                                          * If we're doing sack, check to
 2473                                          * see if we're already in sack
 2474                                          * recovery. If we're not doing sack,
 2475                                          * check to see if we're in newreno
 2476                                          * recovery.
 2477                                          */
 2478                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2479                                                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2480                                                         tp->t_dupacks = 0;
 2481                                                         break;
 2482                                                 }
 2483                                         } else {
 2484                                                 if (SEQ_LEQ(th->th_ack,
 2485                                                     tp->snd_recover)) {
 2486                                                         tp->t_dupacks = 0;
 2487                                                         break;
 2488                                                 }
 2489                                         }
 2490                                         /* Congestion signal before ack. */
 2491                                         cc_cong_signal(tp, th, CC_NDUPACK);
 2492                                         cc_ack_received(tp, th, CC_DUPACK);
 2493                                         tcp_timer_activate(tp, TT_REXMT, 0);
 2494                                         tp->t_rtttime = 0;
 2495                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2496                                                 TCPSTAT_INC(
 2497                                                     tcps_sack_recovery_episode);
 2498                                                 tp->sack_newdata = tp->snd_nxt;
 2499                                                 tp->snd_cwnd = tp->t_maxseg;
 2500                                                 (void) tcp_output(tp);
 2501                                                 goto drop;
 2502                                         }
 2503                                         tp->snd_nxt = th->th_ack;
 2504                                         tp->snd_cwnd = tp->t_maxseg;
 2505                                         if ((thflags & TH_FIN) &&
 2506                                             (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
 2507                                                 /* 
 2508                                                  * If its a fin we need to process
 2509                                                  * it to avoid a race where both
 2510                                                  * sides enter FIN-WAIT and send FIN|ACK
 2511                                                  * at the same time.
 2512                                                  */
 2513                                                 break;
 2514                                         }
 2515                                         (void) tcp_output(tp);
 2516                                         KASSERT(tp->snd_limited <= 2,
 2517                                             ("%s: tp->snd_limited too big",
 2518                                             __func__));
 2519                                         tp->snd_cwnd = tp->snd_ssthresh +
 2520                                              tp->t_maxseg *
 2521                                              (tp->t_dupacks - tp->snd_limited);
 2522                                         if (SEQ_GT(onxt, tp->snd_nxt))
 2523                                                 tp->snd_nxt = onxt;
 2524                                         goto drop;
 2525                                 } else if (V_tcp_do_rfc3042) {
 2526                                         cc_ack_received(tp, th, CC_DUPACK);
 2527                                         u_long oldcwnd = tp->snd_cwnd;
 2528                                         tcp_seq oldsndmax = tp->snd_max;
 2529                                         u_int sent;
 2530                                         int avail;
 2531 
 2532                                         KASSERT(tp->t_dupacks == 1 ||
 2533                                             tp->t_dupacks == 2,
 2534                                             ("%s: dupacks not 1 or 2",
 2535                                             __func__));
 2536                                         if (tp->t_dupacks == 1)
 2537                                                 tp->snd_limited = 0;
 2538                                         tp->snd_cwnd =
 2539                                             (tp->snd_nxt - tp->snd_una) +
 2540                                             (tp->t_dupacks - tp->snd_limited) *
 2541                                             tp->t_maxseg;
 2542                                         if ((thflags & TH_FIN) &&
 2543                                             (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
 2544                                                 /* 
 2545                                                  * If its a fin we need to process
 2546                                                  * it to avoid a race where both
 2547                                                  * sides enter FIN-WAIT and send FIN|ACK
 2548                                                  * at the same time.
 2549                                                  */
 2550                                                 break;
 2551                                         }
 2552                                         /*
 2553                                          * Only call tcp_output when there
 2554                                          * is new data available to be sent.
 2555                                          * Otherwise we would send pure ACKs.
 2556                                          */
 2557                                         SOCKBUF_LOCK(&so->so_snd);
 2558                                         avail = so->so_snd.sb_cc -
 2559                                             (tp->snd_nxt - tp->snd_una);
 2560                                         SOCKBUF_UNLOCK(&so->so_snd);
 2561                                         if (avail > 0)
 2562                                                 (void) tcp_output(tp);
 2563                                         sent = tp->snd_max - oldsndmax;
 2564                                         if (sent > tp->t_maxseg) {
 2565                                                 KASSERT((tp->t_dupacks == 2 &&
 2566                                                     tp->snd_limited == 0) ||
 2567                                                    (sent == tp->t_maxseg + 1 &&
 2568                                                     tp->t_flags & TF_SENTFIN),
 2569                                                     ("%s: sent too much",
 2570                                                     __func__));
 2571                                                 tp->snd_limited = 2;
 2572                                         } else if (sent > 0)
 2573                                                 ++tp->snd_limited;
 2574                                         tp->snd_cwnd = oldcwnd;
 2575                                         goto drop;
 2576                                 }
 2577                         } else
 2578                                 tp->t_dupacks = 0;
 2579                         break;
 2580                 }
 2581 
 2582                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
 2583                     ("%s: th_ack <= snd_una", __func__));
 2584 
 2585                 /*
 2586                  * If the congestion window was inflated to account
 2587                  * for the other side's cached packets, retract it.
 2588                  */
 2589                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2590                         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
 2591                                 if (tp->t_flags & TF_SACK_PERMIT)
 2592                                         tcp_sack_partialack(tp, th);
 2593                                 else
 2594                                         tcp_newreno_partial_ack(tp, th);
 2595                         } else
 2596                                 cc_post_recovery(tp, th);
 2597                 }
 2598                 tp->t_dupacks = 0;
 2599                 /*
 2600                  * If we reach this point, ACK is not a duplicate,
 2601                  *     i.e., it ACKs something we sent.
 2602                  */
 2603                 if (tp->t_flags & TF_NEEDSYN) {
 2604                         /*
 2605                          * T/TCP: Connection was half-synchronized, and our
 2606                          * SYN has been ACK'd (so connection is now fully
 2607                          * synchronized).  Go to non-starred state,
 2608                          * increment snd_una for ACK of SYN, and check if
 2609                          * we can do window scaling.
 2610                          */
 2611                         tp->t_flags &= ~TF_NEEDSYN;
 2612                         tp->snd_una++;
 2613                         /* Do window scaling? */
 2614                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2615                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2616                                 tp->rcv_scale = tp->request_r_scale;
 2617                                 /* Send window already scaled. */
 2618                         }
 2619                 }
 2620 
 2621 process_ACK:
 2622                 INP_WLOCK_ASSERT(tp->t_inpcb);
 2623 
 2624                 acked = BYTES_THIS_ACK(tp, th);
 2625                 TCPSTAT_INC(tcps_rcvackpack);
 2626                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 2627 
 2628                 /*
 2629                  * If we just performed our first retransmit, and the ACK
 2630                  * arrives within our recovery window, then it was a mistake
 2631                  * to do the retransmit in the first place.  Recover our
 2632                  * original cwnd and ssthresh, and proceed to transmit where
 2633                  * we left off.
 2634                  */
 2635                 if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
 2636                     (int)(ticks - tp->t_badrxtwin) < 0)
 2637                         cc_cong_signal(tp, th, CC_RTO_ERR);
 2638 
 2639                 /*
 2640                  * If we have a timestamp reply, update smoothed
 2641                  * round trip time.  If no timestamp is present but
 2642                  * transmit timer is running and timed sequence
 2643                  * number was acked, update smoothed round trip time.
 2644                  * Since we now have an rtt measurement, cancel the
 2645                  * timer backoff (cf., Phil Karn's retransmit alg.).
 2646                  * Recompute the initial retransmit timer.
 2647                  *
 2648                  * Some boxes send broken timestamp replies
 2649                  * during the SYN+ACK phase, ignore
 2650                  * timestamps of 0 or we could calculate a
 2651                  * huge RTT and blow up the retransmit timer.
 2652                  */
 2653                 if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
 2654                         u_int t;
 2655 
 2656                         t = tcp_ts_getticks() - to.to_tsecr;
 2657                         if (!tp->t_rttlow || tp->t_rttlow > t)
 2658                                 tp->t_rttlow = t;
 2659                         tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
 2660                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
 2661                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
 2662                                 tp->t_rttlow = ticks - tp->t_rtttime;
 2663                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
 2664                 }
 2665 
 2666                 /*
 2667                  * If all outstanding data is acked, stop retransmit
 2668                  * timer and remember to restart (more output or persist).
 2669                  * If there is more data to be acked, restart retransmit
 2670                  * timer, using current (possibly backed-off) value.
 2671                  */
 2672                 if (th->th_ack == tp->snd_max) {
 2673                         tcp_timer_activate(tp, TT_REXMT, 0);
 2674                         needoutput = 1;
 2675                 } else if (!tcp_timer_active(tp, TT_PERSIST))
 2676                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 2677 
 2678                 /*
 2679                  * If no data (only SYN) was ACK'd,
 2680                  *    skip rest of ACK processing.
 2681                  */
 2682                 if (acked == 0)
 2683                         goto step6;
 2684 
 2685                 /*
 2686                  * Let the congestion control algorithm update congestion
 2687                  * control related information. This typically means increasing
 2688                  * the congestion window.
 2689                  */
 2690                 cc_ack_received(tp, th, CC_ACK);
 2691 
 2692                 SOCKBUF_LOCK(&so->so_snd);
 2693                 if (acked > so->so_snd.sb_cc) {
 2694                         tp->snd_wnd -= so->so_snd.sb_cc;
 2695                         mfree = sbcut_locked(&so->so_snd,
 2696                             (int)so->so_snd.sb_cc);
 2697                         ourfinisacked = 1;
 2698                 } else {
 2699                         mfree = sbcut_locked(&so->so_snd, acked);
 2700                         tp->snd_wnd -= acked;
 2701                         ourfinisacked = 0;
 2702                 }
 2703                 /* NB: sowwakeup_locked() does an implicit unlock. */
 2704                 sowwakeup_locked(so);
 2705                 m_freem(mfree);
 2706                 /* Detect una wraparound. */
 2707                 if (!IN_RECOVERY(tp->t_flags) &&
 2708                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
 2709                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 2710                         tp->snd_recover = th->th_ack - 1;
 2711                 /* XXXLAS: Can this be moved up into cc_post_recovery? */
 2712                 if (IN_RECOVERY(tp->t_flags) &&
 2713                     SEQ_GEQ(th->th_ack, tp->snd_recover)) {
 2714                         EXIT_RECOVERY(tp->t_flags);
 2715                 }
 2716                 tp->snd_una = th->th_ack;
 2717                 if (tp->t_flags & TF_SACK_PERMIT) {
 2718                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
 2719                                 tp->snd_recover = tp->snd_una;
 2720                 }
 2721                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 2722                         tp->snd_nxt = tp->snd_una;
 2723 
 2724                 switch (tp->t_state) {
 2725 
 2726                 /*
 2727                  * In FIN_WAIT_1 STATE in addition to the processing
 2728                  * for the ESTABLISHED state if our FIN is now acknowledged
 2729                  * then enter FIN_WAIT_2.
 2730                  */
 2731                 case TCPS_FIN_WAIT_1:
 2732                         if (ourfinisacked) {
 2733                                 /*
 2734                                  * If we can't receive any more
 2735                                  * data, then closing user can proceed.
 2736                                  * Starting the timer is contrary to the
 2737                                  * specification, but if we don't get a FIN
 2738                                  * we'll hang forever.
 2739                                  *
 2740                                  * XXXjl:
 2741                                  * we should release the tp also, and use a
 2742                                  * compressed state.
 2743                                  */
 2744                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 2745                                         soisdisconnected(so);
 2746                                         tcp_timer_activate(tp, TT_2MSL,
 2747                                             (tcp_fast_finwait2_recycle ?
 2748                                             tcp_finwait2_timeout :
 2749                                             TP_MAXIDLE(tp)));
 2750                                 }
 2751                                 tcp_state_change(tp, TCPS_FIN_WAIT_2);
 2752                         }
 2753                         break;
 2754 
 2755                 /*
 2756                  * In CLOSING STATE in addition to the processing for
 2757                  * the ESTABLISHED state if the ACK acknowledges our FIN
 2758                  * then enter the TIME-WAIT state, otherwise ignore
 2759                  * the segment.
 2760                  */
 2761                 case TCPS_CLOSING:
 2762                         if (ourfinisacked) {
 2763                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2764                                 tcp_twstart(tp);
 2765                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 2766                                 m_freem(m);
 2767                                 return;
 2768                         }
 2769                         break;
 2770 
 2771                 /*
 2772                  * In LAST_ACK, we may still be waiting for data to drain
 2773                  * and/or to be acked, as well as for the ack of our FIN.
 2774                  * If our FIN is now acknowledged, delete the TCB,
 2775                  * enter the closed state and return.
 2776                  */
 2777                 case TCPS_LAST_ACK:
 2778                         if (ourfinisacked) {
 2779                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2780                                 tp = tcp_close(tp);
 2781                                 goto drop;
 2782                         }
 2783                         break;
 2784                 }
 2785         }
 2786 
 2787 step6:
 2788         INP_WLOCK_ASSERT(tp->t_inpcb);
 2789 
 2790         /*
 2791          * Update window information.
 2792          * Don't look at window if no ACK: TAC's send garbage on first SYN.
 2793          */
 2794         if ((thflags & TH_ACK) &&
 2795             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
 2796             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
 2797              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
 2798                 /* keep track of pure window updates */
 2799                 if (tlen == 0 &&
 2800                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
 2801                         TCPSTAT_INC(tcps_rcvwinupd);
 2802                 tp->snd_wnd = tiwin;
 2803                 tp->snd_wl1 = th->th_seq;
 2804                 tp->snd_wl2 = th->th_ack;
 2805                 if (tp->snd_wnd > tp->max_sndwnd)
 2806                         tp->max_sndwnd = tp->snd_wnd;
 2807                 needoutput = 1;
 2808         }
 2809 
 2810         /*
 2811          * Process segments with URG.
 2812          */
 2813         if ((thflags & TH_URG) && th->th_urp &&
 2814             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2815                 /*
 2816                  * This is a kludge, but if we receive and accept
 2817                  * random urgent pointers, we'll crash in
 2818                  * soreceive.  It's hard to imagine someone
 2819                  * actually wanting to send this much urgent data.
 2820                  */
 2821                 SOCKBUF_LOCK(&so->so_rcv);
 2822                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
 2823                         th->th_urp = 0;                 /* XXX */
 2824                         thflags &= ~TH_URG;             /* XXX */
 2825                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
 2826                         goto dodata;                    /* XXX */
 2827                 }
 2828                 /*
 2829                  * If this segment advances the known urgent pointer,
 2830                  * then mark the data stream.  This should not happen
 2831                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
 2832                  * a FIN has been received from the remote side.
 2833                  * In these states we ignore the URG.
 2834                  *
 2835                  * According to RFC961 (Assigned Protocols),
 2836                  * the urgent pointer points to the last octet
 2837                  * of urgent data.  We continue, however,
 2838                  * to consider it to indicate the first octet
 2839                  * of data past the urgent section as the original
 2840                  * spec states (in one of two places).
 2841                  */
 2842                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
 2843                         tp->rcv_up = th->th_seq + th->th_urp;
 2844                         so->so_oobmark = so->so_rcv.sb_cc +
 2845                             (tp->rcv_up - tp->rcv_nxt) - 1;
 2846                         if (so->so_oobmark == 0)
 2847                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
 2848                         sohasoutofband(so);
 2849                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
 2850                 }
 2851                 SOCKBUF_UNLOCK(&so->so_rcv);
 2852                 /*
 2853                  * Remove out of band data so doesn't get presented to user.
 2854                  * This can happen independent of advancing the URG pointer,
 2855                  * but if two URG's are pending at once, some out-of-band
 2856                  * data may creep in... ick.
 2857                  */
 2858                 if (th->th_urp <= (u_long)tlen &&
 2859                     !(so->so_options & SO_OOBINLINE)) {
 2860                         /* hdr drop is delayed */
 2861                         tcp_pulloutofband(so, th, m, drop_hdrlen);
 2862                 }
 2863         } else {
 2864                 /*
 2865                  * If no out of band data is expected,
 2866                  * pull receive urgent pointer along
 2867                  * with the receive window.
 2868                  */
 2869                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
 2870                         tp->rcv_up = tp->rcv_nxt;
 2871         }
 2872 dodata:                                                 /* XXX */
 2873         INP_WLOCK_ASSERT(tp->t_inpcb);
 2874 
 2875         /*
 2876          * Process the segment text, merging it into the TCP sequencing queue,
 2877          * and arranging for acknowledgment of receipt if necessary.
 2878          * This process logically involves adjusting tp->rcv_wnd as data
 2879          * is presented to the user (this happens in tcp_usrreq.c,
 2880          * case PRU_RCVD).  If a FIN has already been received on this
 2881          * connection then we just ignore the text.
 2882          */
 2883         if ((tlen || (thflags & TH_FIN)) &&
 2884             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2885                 tcp_seq save_start = th->th_seq;
 2886                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 2887                 /*
 2888                  * Insert segment which includes th into TCP reassembly queue
 2889                  * with control block tp.  Set thflags to whether reassembly now
 2890                  * includes a segment with FIN.  This handles the common case
 2891                  * inline (segment is the next to be received on an established
 2892                  * connection, and the queue is empty), avoiding linkage into
 2893                  * and removal from the queue and repetition of various
 2894                  * conversions.
 2895                  * Set DELACK for segments received in order, but ack
 2896                  * immediately when segments are out of order (so
 2897                  * fast retransmit can work).
 2898                  */
 2899                 if (th->th_seq == tp->rcv_nxt &&
 2900                     LIST_EMPTY(&tp->t_segq) &&
 2901                     TCPS_HAVEESTABLISHED(tp->t_state)) {
 2902                         if (DELAY_ACK(tp, tlen))
 2903                                 tp->t_flags |= TF_DELACK;
 2904                         else
 2905                                 tp->t_flags |= TF_ACKNOW;
 2906                         tp->rcv_nxt += tlen;
 2907                         thflags = th->th_flags & TH_FIN;
 2908                         TCPSTAT_INC(tcps_rcvpack);
 2909                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 2910                         ND6_HINT(tp);
 2911                         SOCKBUF_LOCK(&so->so_rcv);
 2912                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
 2913                                 m_freem(m);
 2914                         else
 2915                                 sbappendstream_locked(&so->so_rcv, m);
 2916                         /* NB: sorwakeup_locked() does an implicit unlock. */
 2917                         sorwakeup_locked(so);
 2918                 } else {
 2919                         /*
 2920                          * XXX: Due to the header drop above "th" is
 2921                          * theoretically invalid by now.  Fortunately
 2922                          * m_adj() doesn't actually frees any mbufs
 2923                          * when trimming from the head.
 2924                          */
 2925                         thflags = tcp_reass(tp, th, &tlen, m);
 2926                         tp->t_flags |= TF_ACKNOW;
 2927                 }
 2928                 if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
 2929                         tcp_update_sack_list(tp, save_start, save_start + tlen);
 2930 #if 0
 2931                 /*
 2932                  * Note the amount of data that peer has sent into
 2933                  * our window, in order to estimate the sender's
 2934                  * buffer size.
 2935                  * XXX: Unused.
 2936                  */
 2937                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
 2938                         len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
 2939                 else
 2940                         len = so->so_rcv.sb_hiwat;
 2941 #endif
 2942         } else {
 2943                 m_freem(m);
 2944                 thflags &= ~TH_FIN;
 2945         }
 2946 
 2947         /*
 2948          * If FIN is received ACK the FIN and let the user know
 2949          * that the connection is closing.
 2950          */
 2951         if (thflags & TH_FIN) {
 2952                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2953                         socantrcvmore(so);
 2954                         /*
 2955                          * If connection is half-synchronized
 2956                          * (ie NEEDSYN flag on) then delay ACK,
 2957                          * so it may be piggybacked when SYN is sent.
 2958                          * Otherwise, since we received a FIN then no
 2959                          * more input can be expected, send ACK now.
 2960                          */
 2961                         if (tp->t_flags & TF_NEEDSYN)
 2962                                 tp->t_flags |= TF_DELACK;
 2963                         else
 2964                                 tp->t_flags |= TF_ACKNOW;
 2965                         tp->rcv_nxt++;
 2966                 }
 2967                 switch (tp->t_state) {
 2968 
 2969                 /*
 2970                  * In SYN_RECEIVED and ESTABLISHED STATES
 2971                  * enter the CLOSE_WAIT state.
 2972                  */
 2973                 case TCPS_SYN_RECEIVED:
 2974                         tp->t_starttime = ticks;
 2975                         /* FALLTHROUGH */
 2976                 case TCPS_ESTABLISHED:
 2977                         tcp_state_change(tp, TCPS_CLOSE_WAIT);
 2978                         break;
 2979 
 2980                 /*
 2981                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
 2982                  * enter the CLOSING state.
 2983                  */
 2984                 case TCPS_FIN_WAIT_1:
 2985                         tcp_state_change(tp, TCPS_CLOSING);
 2986                         break;
 2987 
 2988                 /*
 2989                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
 2990                  * starting the time-wait timer, turning off the other
 2991                  * standard timers.
 2992                  */
 2993                 case TCPS_FIN_WAIT_2:
 2994                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2995                         KASSERT(ti_locked == TI_WLOCKED, ("%s: dodata "
 2996                             "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
 2997                             ti_locked));
 2998 
 2999                         tcp_twstart(tp);
 3000                         INP_INFO_WUNLOCK(&V_tcbinfo);
 3001                         return;
 3002                 }
 3003         }
 3004         if (ti_locked == TI_WLOCKED)
 3005                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3006         ti_locked = TI_UNLOCKED;
 3007 
 3008 #ifdef TCPDEBUG
 3009         if (so->so_options & SO_DEBUG)
 3010                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
 3011                           &tcp_savetcp, 0);
 3012 #endif
 3013 
 3014         /*
 3015          * Return any desired output.
 3016          */
 3017         if (needoutput || (tp->t_flags & TF_ACKNOW))
 3018                 (void) tcp_output(tp);
 3019 
 3020 check_delack:
 3021         KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
 3022             __func__, ti_locked));
 3023         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3024         INP_WLOCK_ASSERT(tp->t_inpcb);
 3025 
 3026         if (tp->t_flags & TF_DELACK) {
 3027                 tp->t_flags &= ~TF_DELACK;
 3028                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
 3029         }
 3030         INP_WUNLOCK(tp->t_inpcb);
 3031         return;
 3032 
 3033 dropafterack:
 3034         /*
 3035          * Generate an ACK dropping incoming segment if it occupies
 3036          * sequence space, where the ACK reflects our state.
 3037          *
 3038          * We can now skip the test for the RST flag since all
 3039          * paths to this code happen after packets containing
 3040          * RST have been dropped.
 3041          *
 3042          * In the SYN-RECEIVED state, don't send an ACK unless the
 3043          * segment we received passes the SYN-RECEIVED ACK test.
 3044          * If it fails send a RST.  This breaks the loop in the
 3045          * "LAND" DoS attack, and also prevents an ACK storm
 3046          * between two listening ports that have been sent forged
 3047          * SYN segments, each with the source address of the other.
 3048          */
 3049         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
 3050             (SEQ_GT(tp->snd_una, th->th_ack) ||
 3051              SEQ_GT(th->th_ack, tp->snd_max)) ) {
 3052                 rstreason = BANDLIM_RST_OPENPORT;
 3053                 goto dropwithreset;
 3054         }
 3055 #ifdef TCPDEBUG
 3056         if (so->so_options & SO_DEBUG)
 3057                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3058                           &tcp_savetcp, 0);
 3059 #endif
 3060         if (ti_locked == TI_WLOCKED)
 3061                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3062         ti_locked = TI_UNLOCKED;
 3063 
 3064         tp->t_flags |= TF_ACKNOW;
 3065         (void) tcp_output(tp);
 3066         INP_WUNLOCK(tp->t_inpcb);
 3067         m_freem(m);
 3068         return;
 3069 
 3070 dropwithreset:
 3071         if (ti_locked == TI_WLOCKED)
 3072                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3073         ti_locked = TI_UNLOCKED;
 3074 
 3075         if (tp != NULL) {
 3076                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 3077                 INP_WUNLOCK(tp->t_inpcb);
 3078         } else
 3079                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 3080         return;
 3081 
 3082 drop:
 3083         if (ti_locked == TI_WLOCKED) {
 3084                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3085                 ti_locked = TI_UNLOCKED;
 3086         }
 3087 #ifdef INVARIANTS
 3088         else
 3089                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3090 #endif
 3091 
 3092         /*
 3093          * Drop space held by incoming segment and return.
 3094          */
 3095 #ifdef TCPDEBUG
 3096         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 3097                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3098                           &tcp_savetcp, 0);
 3099 #endif
 3100         if (tp != NULL)
 3101                 INP_WUNLOCK(tp->t_inpcb);
 3102         m_freem(m);
 3103 }
 3104 
 3105 /*
 3106  * Issue RST and make ACK acceptable to originator of segment.
 3107  * The mbuf must still include the original packet header.
 3108  * tp may be NULL.
 3109  */
 3110 static void
 3111 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
 3112     int tlen, int rstreason)
 3113 {
 3114 #ifdef INET
 3115         struct ip *ip;
 3116 #endif
 3117 #ifdef INET6
 3118         struct ip6_hdr *ip6;
 3119 #endif
 3120 
 3121         if (tp != NULL) {
 3122                 INP_WLOCK_ASSERT(tp->t_inpcb);
 3123         }
 3124 
 3125         /* Don't bother if destination was broadcast/multicast. */
 3126         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
 3127                 goto drop;
 3128 #ifdef INET6
 3129         if (mtod(m, struct ip *)->ip_v == 6) {
 3130                 ip6 = mtod(m, struct ip6_hdr *);
 3131                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 3132                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 3133                         goto drop;
 3134                 /* IPv6 anycast check is done at tcp6_input() */
 3135         }
 3136 #endif
 3137 #if defined(INET) && defined(INET6)
 3138         else
 3139 #endif
 3140 #ifdef INET
 3141         {
 3142                 ip = mtod(m, struct ip *);
 3143                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 3144                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 3145                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 3146                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 3147                         goto drop;
 3148         }
 3149 #endif
 3150 
 3151         /* Perform bandwidth limiting. */
 3152         if (badport_bandlim(rstreason) < 0)
 3153                 goto drop;
 3154 
 3155         /* tcp_respond consumes the mbuf chain. */
 3156         if (th->th_flags & TH_ACK) {
 3157                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
 3158                     th->th_ack, TH_RST);
 3159         } else {
 3160                 if (th->th_flags & TH_SYN)
 3161                         tlen++;
 3162                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
 3163                     (tcp_seq)0, TH_RST|TH_ACK);
 3164         }
 3165         return;
 3166 drop:
 3167         m_freem(m);
 3168 }
 3169 
 3170 /*
 3171  * Parse TCP options and place in tcpopt.
 3172  */
 3173 static void
 3174 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
 3175 {
 3176         int opt, optlen;
 3177 
 3178         to->to_flags = 0;
 3179         for (; cnt > 0; cnt -= optlen, cp += optlen) {
 3180                 opt = cp[0];
 3181                 if (opt == TCPOPT_EOL)
 3182                         break;
 3183                 if (opt == TCPOPT_NOP)
 3184                         optlen = 1;
 3185                 else {
 3186                         if (cnt < 2)
 3187                                 break;
 3188                         optlen = cp[1];
 3189                         if (optlen < 2 || optlen > cnt)
 3190                                 break;
 3191                 }
 3192                 switch (opt) {
 3193                 case TCPOPT_MAXSEG:
 3194                         if (optlen != TCPOLEN_MAXSEG)
 3195                                 continue;
 3196                         if (!(flags & TO_SYN))
 3197                                 continue;
 3198                         to->to_flags |= TOF_MSS;
 3199                         bcopy((char *)cp + 2,
 3200                             (char *)&to->to_mss, sizeof(to->to_mss));
 3201                         to->to_mss = ntohs(to->to_mss);
 3202                         break;
 3203                 case TCPOPT_WINDOW:
 3204                         if (optlen != TCPOLEN_WINDOW)
 3205                                 continue;
 3206                         if (!(flags & TO_SYN))
 3207                                 continue;
 3208                         to->to_flags |= TOF_SCALE;
 3209                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
 3210                         break;
 3211                 case TCPOPT_TIMESTAMP:
 3212                         if (optlen != TCPOLEN_TIMESTAMP)
 3213                                 continue;
 3214                         to->to_flags |= TOF_TS;
 3215                         bcopy((char *)cp + 2,
 3216                             (char *)&to->to_tsval, sizeof(to->to_tsval));
 3217                         to->to_tsval = ntohl(to->to_tsval);
 3218                         bcopy((char *)cp + 6,
 3219                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
 3220                         to->to_tsecr = ntohl(to->to_tsecr);
 3221                         break;
 3222 #ifdef TCP_SIGNATURE
 3223                 /*
 3224                  * XXX In order to reply to a host which has set the
 3225                  * TCP_SIGNATURE option in its initial SYN, we have to
 3226                  * record the fact that the option was observed here
 3227                  * for the syncache code to perform the correct response.
 3228                  */
 3229                 case TCPOPT_SIGNATURE:
 3230                         if (optlen != TCPOLEN_SIGNATURE)
 3231                                 continue;
 3232                         to->to_flags |= TOF_SIGNATURE;
 3233                         to->to_signature = cp + 2;
 3234                         break;
 3235 #endif
 3236                 case TCPOPT_SACK_PERMITTED:
 3237                         if (optlen != TCPOLEN_SACK_PERMITTED)
 3238                                 continue;
 3239                         if (!(flags & TO_SYN))
 3240                                 continue;
 3241                         if (!V_tcp_do_sack)
 3242                                 continue;
 3243                         to->to_flags |= TOF_SACKPERM;
 3244                         break;
 3245                 case TCPOPT_SACK:
 3246                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
 3247                                 continue;
 3248                         if (flags & TO_SYN)
 3249                                 continue;
 3250                         to->to_flags |= TOF_SACK;
 3251                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
 3252                         to->to_sacks = cp + 2;
 3253                         TCPSTAT_INC(tcps_sack_rcv_blocks);
 3254                         break;
 3255                 default:
 3256                         continue;
 3257                 }
 3258         }
 3259 }
 3260 
 3261 /*
 3262  * Pull out of band byte out of a segment so
 3263  * it doesn't appear in the user's data queue.
 3264  * It is still reflected in the segment length for
 3265  * sequencing purposes.
 3266  */
 3267 static void
 3268 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
 3269     int off)
 3270 {
 3271         int cnt = off + th->th_urp - 1;
 3272 
 3273         while (cnt >= 0) {
 3274                 if (m->m_len > cnt) {
 3275                         char *cp = mtod(m, caddr_t) + cnt;
 3276                         struct tcpcb *tp = sototcpcb(so);
 3277 
 3278                         INP_WLOCK_ASSERT(tp->t_inpcb);
 3279 
 3280                         tp->t_iobc = *cp;
 3281                         tp->t_oobflags |= TCPOOB_HAVEDATA;
 3282                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
 3283                         m->m_len--;
 3284                         if (m->m_flags & M_PKTHDR)
 3285                                 m->m_pkthdr.len--;
 3286                         return;
 3287                 }
 3288                 cnt -= m->m_len;
 3289                 m = m->m_next;
 3290                 if (m == NULL)
 3291                         break;
 3292         }
 3293         panic("tcp_pulloutofband");
 3294 }
 3295 
 3296 /*
 3297  * Collect new round-trip time estimate
 3298  * and update averages and current timeout.
 3299  */
 3300 static void
 3301 tcp_xmit_timer(struct tcpcb *tp, int rtt)
 3302 {
 3303         int delta;
 3304 
 3305         INP_WLOCK_ASSERT(tp->t_inpcb);
 3306 
 3307         TCPSTAT_INC(tcps_rttupdated);
 3308         tp->t_rttupdated++;
 3309         if (tp->t_srtt != 0) {
 3310                 /*
 3311                  * srtt is stored as fixed point with 5 bits after the
 3312                  * binary point (i.e., scaled by 8).  The following magic
 3313                  * is equivalent to the smoothing algorithm in rfc793 with
 3314                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
 3315                  * point).  Adjust rtt to origin 0.
 3316                  */
 3317                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
 3318                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
 3319 
 3320                 if ((tp->t_srtt += delta) <= 0)
 3321                         tp->t_srtt = 1;
 3322 
 3323                 /*
 3324                  * We accumulate a smoothed rtt variance (actually, a
 3325                  * smoothed mean difference), then set the retransmit
 3326                  * timer to smoothed rtt + 4 times the smoothed variance.
 3327                  * rttvar is stored as fixed point with 4 bits after the
 3328                  * binary point (scaled by 16).  The following is
 3329                  * equivalent to rfc793 smoothing with an alpha of .75
 3330                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
 3331                  * rfc793's wired-in beta.
 3332                  */
 3333                 if (delta < 0)
 3334                         delta = -delta;
 3335                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
 3336                 if ((tp->t_rttvar += delta) <= 0)
 3337                         tp->t_rttvar = 1;
 3338                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
 3339                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3340         } else {
 3341                 /*
 3342                  * No rtt measurement yet - use the unsmoothed rtt.
 3343                  * Set the variance to half the rtt (so our first
 3344                  * retransmit happens at 3*rtt).
 3345                  */
 3346                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
 3347                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
 3348                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3349         }
 3350         tp->t_rtttime = 0;
 3351         tp->t_rxtshift = 0;
 3352 
 3353         /*
 3354          * the retransmit should happen at rtt + 4 * rttvar.
 3355          * Because of the way we do the smoothing, srtt and rttvar
 3356          * will each average +1/2 tick of bias.  When we compute
 3357          * the retransmit timer, we want 1/2 tick of rounding and
 3358          * 1 extra tick because of +-1/2 tick uncertainty in the
 3359          * firing of the timer.  The bias will give us exactly the
 3360          * 1.5 tick we need.  But, because the bias is
 3361          * statistical, we have to test that we don't drop below
 3362          * the minimum feasible timer (which is 2 ticks).
 3363          */
 3364         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
 3365                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
 3366 
 3367         /*
 3368          * We received an ack for a packet that wasn't retransmitted;
 3369          * it is probably safe to discard any error indications we've
 3370          * received recently.  This isn't quite right, but close enough
 3371          * for now (a route might have failed after we sent a segment,
 3372          * and the return path might not be symmetrical).
 3373          */
 3374         tp->t_softerror = 0;
 3375 }
 3376 
 3377 /*
 3378  * Determine a reasonable value for maxseg size.
 3379  * If the route is known, check route for mtu.
 3380  * If none, use an mss that can be handled on the outgoing interface
 3381  * without forcing IP to fragment.  If no route is found, route has no mtu,
 3382  * or the destination isn't local, use a default, hopefully conservative
 3383  * size (usually 512 or the default IP max size, but no more than the mtu
 3384  * of the interface), as we can't discover anything about intervening
 3385  * gateways or networks.  We also initialize the congestion/slow start
 3386  * window to be a single segment if the destination isn't local.
 3387  * While looking at the routing entry, we also initialize other path-dependent
 3388  * parameters from pre-set or cached values in the routing entry.
 3389  *
 3390  * Also take into account the space needed for options that we
 3391  * send regularly.  Make maxseg shorter by that amount to assure
 3392  * that we can send maxseg amount of data even when the options
 3393  * are present.  Store the upper limit of the length of options plus
 3394  * data in maxopd.
 3395  *
 3396  * NOTE that this routine is only called when we process an incoming
 3397  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
 3398  * settings are handled in tcp_mssopt().
 3399  */
 3400 void
 3401 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
 3402     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
 3403 {
 3404         int mss = 0;
 3405         u_long maxmtu = 0;
 3406         struct inpcb *inp = tp->t_inpcb;
 3407         struct hc_metrics_lite metrics;
 3408         int origoffer;
 3409 #ifdef INET6
 3410         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
 3411         size_t min_protoh = isipv6 ?
 3412                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
 3413                             sizeof (struct tcpiphdr);
 3414 #else
 3415         const size_t min_protoh = sizeof(struct tcpiphdr);
 3416 #endif
 3417 
 3418         INP_WLOCK_ASSERT(tp->t_inpcb);
 3419 
 3420         if (mtuoffer != -1) {
 3421                 KASSERT(offer == -1, ("%s: conflict", __func__));
 3422                 offer = mtuoffer - min_protoh;
 3423         }
 3424         origoffer = offer;
 3425 
 3426         /* Initialize. */
 3427 #ifdef INET6
 3428         if (isipv6) {
 3429                 maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
 3430                 tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
 3431         }
 3432 #endif
 3433 #if defined(INET) && defined(INET6)
 3434         else
 3435 #endif
 3436 #ifdef INET
 3437         {
 3438                 maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
 3439                 tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
 3440         }
 3441 #endif
 3442 
 3443         /*
 3444          * No route to sender, stay with default mss and return.
 3445          */
 3446         if (maxmtu == 0) {
 3447                 /*
 3448                  * In case we return early we need to initialize metrics
 3449                  * to a defined state as tcp_hc_get() would do for us
 3450                  * if there was no cache hit.
 3451                  */
 3452                 if (metricptr != NULL)
 3453                         bzero(metricptr, sizeof(struct hc_metrics_lite));
 3454                 return;
 3455         }
 3456 
 3457         /* What have we got? */
 3458         switch (offer) {
 3459                 case 0:
 3460                         /*
 3461                          * Offer == 0 means that there was no MSS on the SYN
 3462                          * segment, in this case we use tcp_mssdflt as
 3463                          * already assigned to t_maxopd above.
 3464                          */
 3465                         offer = tp->t_maxopd;
 3466                         break;
 3467 
 3468                 case -1:
 3469                         /*
 3470                          * Offer == -1 means that we didn't receive SYN yet.
 3471                          */
 3472                         /* FALLTHROUGH */
 3473 
 3474                 default:
 3475                         /*
 3476                          * Prevent DoS attack with too small MSS. Round up
 3477                          * to at least minmss.
 3478                          */
 3479                         offer = max(offer, V_tcp_minmss);
 3480         }
 3481 
 3482         /*
 3483          * rmx information is now retrieved from tcp_hostcache.
 3484          */
 3485         tcp_hc_get(&inp->inp_inc, &metrics);
 3486         if (metricptr != NULL)
 3487                 bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
 3488 
 3489         /*
 3490          * If there's a discovered mtu int tcp hostcache, use it
 3491          * else, use the link mtu.
 3492          */
 3493         if (metrics.rmx_mtu)
 3494                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
 3495         else {
 3496 #ifdef INET6
 3497                 if (isipv6) {
 3498                         mss = maxmtu - min_protoh;
 3499                         if (!V_path_mtu_discovery &&
 3500                             !in6_localaddr(&inp->in6p_faddr))
 3501                                 mss = min(mss, V_tcp_v6mssdflt);
 3502                 }
 3503 #endif
 3504 #if defined(INET) && defined(INET6)
 3505                 else
 3506 #endif
 3507 #ifdef INET
 3508                 {
 3509                         mss = maxmtu - min_protoh;
 3510                         if (!V_path_mtu_discovery &&
 3511                             !in_localaddr(inp->inp_faddr))
 3512                                 mss = min(mss, V_tcp_mssdflt);
 3513                 }
 3514 #endif
 3515                 /*
 3516                  * XXX - The above conditional (mss = maxmtu - min_protoh)
 3517                  * probably violates the TCP spec.
 3518                  * The problem is that, since we don't know the
 3519                  * other end's MSS, we are supposed to use a conservative
 3520                  * default.  But, if we do that, then MTU discovery will
 3521                  * never actually take place, because the conservative
 3522                  * default is much less than the MTUs typically seen
 3523                  * on the Internet today.  For the moment, we'll sweep
 3524                  * this under the carpet.
 3525                  *
 3526                  * The conservative default might not actually be a problem
 3527                  * if the only case this occurs is when sending an initial
 3528                  * SYN with options and data to a host we've never talked
 3529                  * to before.  Then, they will reply with an MSS value which
 3530                  * will get recorded and the new parameters should get
 3531                  * recomputed.  For Further Study.
 3532                  */
 3533         }
 3534         mss = min(mss, offer);
 3535 
 3536         /*
 3537          * Sanity check: make sure that maxopd will be large
 3538          * enough to allow some data on segments even if the
 3539          * all the option space is used (40bytes).  Otherwise
 3540          * funny things may happen in tcp_output.
 3541          */
 3542         mss = max(mss, 64);
 3543 
 3544         /*
 3545          * maxopd stores the maximum length of data AND options
 3546          * in a segment; maxseg is the amount of data in a normal
 3547          * segment.  We need to store this value (maxopd) apart
 3548          * from maxseg, because now every segment carries options
 3549          * and thus we normally have somewhat less data in segments.
 3550          */
 3551         tp->t_maxopd = mss;
 3552 
 3553         /*
 3554          * origoffer==-1 indicates that no segments were received yet.
 3555          * In this case we just guess.
 3556          */
 3557         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
 3558             (origoffer == -1 ||
 3559              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
 3560                 mss -= TCPOLEN_TSTAMP_APPA;
 3561 
 3562         tp->t_maxseg = mss;
 3563 }
 3564 
 3565 void
 3566 tcp_mss(struct tcpcb *tp, int offer)
 3567 {
 3568         int mss;
 3569         u_long bufsize;
 3570         struct inpcb *inp;
 3571         struct socket *so;
 3572         struct hc_metrics_lite metrics;
 3573         struct tcp_ifcap cap;
 3574 
 3575         KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
 3576 
 3577         bzero(&cap, sizeof(cap));
 3578         tcp_mss_update(tp, offer, -1, &metrics, &cap);
 3579 
 3580         mss = tp->t_maxseg;
 3581         inp = tp->t_inpcb;
 3582 
 3583         /*
 3584          * If there's a pipesize, change the socket buffer to that size,
 3585          * don't change if sb_hiwat is different than default (then it
 3586          * has been changed on purpose with setsockopt).
 3587          * Make the socket buffers an integral number of mss units;
 3588          * if the mss is larger than the socket buffer, decrease the mss.
 3589          */
 3590         so = inp->inp_socket;
 3591         SOCKBUF_LOCK(&so->so_snd);
 3592         if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
 3593                 bufsize = metrics.rmx_sendpipe;
 3594         else
 3595                 bufsize = so->so_snd.sb_hiwat;
 3596         if (bufsize < mss)
 3597                 mss = bufsize;
 3598         else {
 3599                 bufsize = roundup(bufsize, mss);
 3600                 if (bufsize > sb_max)
 3601                         bufsize = sb_max;
 3602                 if (bufsize > so->so_snd.sb_hiwat)
 3603                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
 3604         }
 3605         SOCKBUF_UNLOCK(&so->so_snd);
 3606         tp->t_maxseg = mss;
 3607 
 3608         SOCKBUF_LOCK(&so->so_rcv);
 3609         if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
 3610                 bufsize = metrics.rmx_recvpipe;
 3611         else
 3612                 bufsize = so->so_rcv.sb_hiwat;
 3613         if (bufsize > mss) {
 3614                 bufsize = roundup(bufsize, mss);
 3615                 if (bufsize > sb_max)
 3616                         bufsize = sb_max;
 3617                 if (bufsize > so->so_rcv.sb_hiwat)
 3618                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
 3619         }
 3620         SOCKBUF_UNLOCK(&so->so_rcv);
 3621 
 3622         /* Check the interface for TSO capabilities. */
 3623         if (cap.ifcap & CSUM_TSO) {
 3624                 tp->t_flags |= TF_TSO;
 3625                 tp->t_tsomax = cap.tsomax;
 3626         }
 3627 }
 3628 
 3629 /*
 3630  * Determine the MSS option to send on an outgoing SYN.
 3631  */
 3632 int
 3633 tcp_mssopt(struct in_conninfo *inc)
 3634 {
 3635         int mss = 0;
 3636         u_long maxmtu = 0;
 3637         u_long thcmtu = 0;
 3638         size_t min_protoh;
 3639 
 3640         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
 3641 
 3642 #ifdef INET6
 3643         if (inc->inc_flags & INC_ISIPV6) {
 3644                 mss = V_tcp_v6mssdflt;
 3645                 maxmtu = tcp_maxmtu6(inc, NULL);
 3646                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
 3647         }
 3648 #endif
 3649 #if defined(INET) && defined(INET6)
 3650         else
 3651 #endif
 3652 #ifdef INET
 3653         {
 3654                 mss = V_tcp_mssdflt;
 3655                 maxmtu = tcp_maxmtu(inc, NULL);
 3656                 min_protoh = sizeof(struct tcpiphdr);
 3657         }
 3658 #endif
 3659 #if defined(INET6) || defined(INET)
 3660         thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
 3661 #endif
 3662 
 3663         if (maxmtu && thcmtu)
 3664                 mss = min(maxmtu, thcmtu) - min_protoh;
 3665         else if (maxmtu || thcmtu)
 3666                 mss = max(maxmtu, thcmtu) - min_protoh;
 3667 
 3668         return (mss);
 3669 }
 3670 
 3671 
 3672 /*
 3673  * On a partial ack arrives, force the retransmission of the
 3674  * next unacknowledged segment.  Do not clear tp->t_dupacks.
 3675  * By setting snd_nxt to ti_ack, this forces retransmission timer to
 3676  * be started again.
 3677  */
 3678 static void
 3679 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
 3680 {
 3681         tcp_seq onxt = tp->snd_nxt;
 3682         u_long  ocwnd = tp->snd_cwnd;
 3683 
 3684         INP_WLOCK_ASSERT(tp->t_inpcb);
 3685 
 3686         tcp_timer_activate(tp, TT_REXMT, 0);
 3687         tp->t_rtttime = 0;
 3688         tp->snd_nxt = th->th_ack;
 3689         /*
 3690          * Set snd_cwnd to one segment beyond acknowledged offset.
 3691          * (tp->snd_una has not yet been updated when this function is called.)
 3692          */
 3693         tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th);
 3694         tp->t_flags |= TF_ACKNOW;
 3695         (void) tcp_output(tp);
 3696         tp->snd_cwnd = ocwnd;
 3697         if (SEQ_GT(onxt, tp->snd_nxt))
 3698                 tp->snd_nxt = onxt;
 3699         /*
 3700          * Partial window deflation.  Relies on fact that tp->snd_una
 3701          * not updated yet.
 3702          */
 3703         if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
 3704                 tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
 3705         else
 3706                 tp->snd_cwnd = 0;
 3707         tp->snd_cwnd += tp->t_maxseg;
 3708 }

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