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/9.0/sys/netinet/tcp_input.c 236953 2012-06-12 12:10:10Z bz $");
   52 
   53 #include "opt_ipfw.h"           /* for ipfw_fwd */
   54 #include "opt_inet.h"
   55 #include "opt_inet6.h"
   56 #include "opt_ipsec.h"
   57 #include "opt_tcpdebug.h"
   58 
   59 #include <sys/param.h>
   60 #include <sys/kernel.h>
   61 #include <sys/hhook.h>
   62 #include <sys/malloc.h>
   63 #include <sys/mbuf.h>
   64 #include <sys/proc.h>           /* for proc0 declaration */
   65 #include <sys/protosw.h>
   66 #include <sys/signalvar.h>
   67 #include <sys/socket.h>
   68 #include <sys/socketvar.h>
   69 #include <sys/sysctl.h>
   70 #include <sys/syslog.h>
   71 #include <sys/systm.h>
   72 
   73 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
   74 
   75 #include <vm/uma.h>
   76 
   77 #include <net/if.h>
   78 #include <net/route.h>
   79 #include <net/vnet.h>
   80 
   81 #define TCPSTATES               /* for logging */
   82 
   83 #include <netinet/cc.h>
   84 #include <netinet/in.h>
   85 #include <netinet/in_pcb.h>
   86 #include <netinet/in_systm.h>
   87 #include <netinet/in_var.h>
   88 #include <netinet/ip.h>
   89 #include <netinet/ip_icmp.h>    /* required for icmp_var.h */
   90 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
   91 #include <netinet/ip_var.h>
   92 #include <netinet/ip_options.h>
   93 #include <netinet/ip6.h>
   94 #include <netinet/icmp6.h>
   95 #include <netinet6/in6_pcb.h>
   96 #include <netinet6/ip6_var.h>
   97 #include <netinet6/nd6.h>
   98 #include <netinet/tcp_fsm.h>
   99 #include <netinet/tcp_seq.h>
  100 #include <netinet/tcp_timer.h>
  101 #include <netinet/tcp_var.h>
  102 #include <netinet6/tcp6_var.h>
  103 #include <netinet/tcpip.h>
  104 #include <netinet/tcp_syncache.h>
  105 #ifdef TCPDEBUG
  106 #include <netinet/tcp_debug.h>
  107 #endif /* TCPDEBUG */
  108 
  109 #ifdef IPSEC
  110 #include <netipsec/ipsec.h>
  111 #include <netipsec/ipsec6.h>
  112 #endif /*IPSEC*/
  113 
  114 #include <machine/in_cksum.h>
  115 
  116 #include <security/mac/mac_framework.h>
  117 
  118 const int tcprexmtthresh = 3;
  119 
  120 VNET_DEFINE(struct tcpstat, tcpstat);
  121 SYSCTL_VNET_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
  122     &VNET_NAME(tcpstat), tcpstat,
  123     "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
  124 
  125 int tcp_log_in_vain = 0;
  126 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
  127     &tcp_log_in_vain, 0,
  128     "Log all incoming TCP segments to closed ports");
  129 
  130 VNET_DEFINE(int, blackhole) = 0;
  131 #define V_blackhole             VNET(blackhole)
  132 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
  133     &VNET_NAME(blackhole), 0,
  134     "Do not send RST on segments to closed ports");
  135 
  136 VNET_DEFINE(int, tcp_delack_enabled) = 1;
  137 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
  138     &VNET_NAME(tcp_delack_enabled), 0,
  139     "Delay ACK to try and piggyback it onto a data packet");
  140 
  141 VNET_DEFINE(int, drop_synfin) = 0;
  142 #define V_drop_synfin           VNET(drop_synfin)
  143 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
  144     &VNET_NAME(drop_synfin), 0,
  145     "Drop TCP packets with SYN+FIN set");
  146 
  147 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
  148 #define V_tcp_do_rfc3042        VNET(tcp_do_rfc3042)
  149 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
  150     &VNET_NAME(tcp_do_rfc3042), 0,
  151     "Enable RFC 3042 (Limited Transmit)");
  152 
  153 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
  154 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
  155     &VNET_NAME(tcp_do_rfc3390), 0,
  156     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
  157 
  158 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
  159 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_RW,
  160     &VNET_NAME(tcp_do_rfc3465), 0,
  161     "Enable RFC 3465 (Appropriate Byte Counting)");
  162 
  163 VNET_DEFINE(int, tcp_abc_l_var) = 2;
  164 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_RW,
  165     &VNET_NAME(tcp_abc_l_var), 2,
  166     "Cap the max cwnd increment during slow-start to this number of segments");
  167 
  168 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
  169 
  170 VNET_DEFINE(int, tcp_do_ecn) = 0;
  171 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_RW,
  172     &VNET_NAME(tcp_do_ecn), 0,
  173     "TCP ECN support");
  174 
  175 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
  176 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_RW,
  177     &VNET_NAME(tcp_ecn_maxretries), 0,
  178     "Max retries before giving up on ECN");
  179 
  180 VNET_DEFINE(int, tcp_insecure_rst) = 0;
  181 #define V_tcp_insecure_rst      VNET(tcp_insecure_rst)
  182 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
  183     &VNET_NAME(tcp_insecure_rst), 0,
  184     "Follow the old (insecure) criteria for accepting RST packets");
  185 
  186 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
  187 #define V_tcp_do_autorcvbuf     VNET(tcp_do_autorcvbuf)
  188 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
  189     &VNET_NAME(tcp_do_autorcvbuf), 0,
  190     "Enable automatic receive buffer sizing");
  191 
  192 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
  193 #define V_tcp_autorcvbuf_inc    VNET(tcp_autorcvbuf_inc)
  194 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
  195     &VNET_NAME(tcp_autorcvbuf_inc), 0,
  196     "Incrementor step size of automatic receive buffer");
  197 
  198 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
  199 #define V_tcp_autorcvbuf_max    VNET(tcp_autorcvbuf_max)
  200 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
  201     &VNET_NAME(tcp_autorcvbuf_max), 0,
  202     "Max size of automatic receive buffer");
  203 
  204 VNET_DEFINE(struct inpcbhead, tcb);
  205 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
  206 VNET_DEFINE(struct inpcbinfo, tcbinfo);
  207 
  208 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
  209 static void      tcp_do_segment(struct mbuf *, struct tcphdr *,
  210                      struct socket *, struct tcpcb *, int, int, uint8_t,
  211                      int);
  212 static void      tcp_dropwithreset(struct mbuf *, struct tcphdr *,
  213                      struct tcpcb *, int, int);
  214 static void      tcp_pulloutofband(struct socket *,
  215                      struct tcphdr *, struct mbuf *, int);
  216 static void      tcp_xmit_timer(struct tcpcb *, int);
  217 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
  218 static void inline      tcp_fields_to_host(struct tcphdr *);
  219 #ifdef TCP_SIGNATURE
  220 static void inline      tcp_fields_to_net(struct tcphdr *);
  221 static int inline       tcp_signature_verify_input(struct mbuf *, int, int,
  222                             int, struct tcpopt *, struct tcphdr *, u_int);
  223 #endif
  224 static void inline      cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
  225                             uint16_t type);
  226 static void inline      cc_conn_init(struct tcpcb *tp);
  227 static void inline      cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
  228 static void inline      hhook_run_tcp_est_in(struct tcpcb *tp,
  229                             struct tcphdr *th, struct tcpopt *to);
  230 
  231 /*
  232  * Kernel module interface for updating tcpstat.  The argument is an index
  233  * into tcpstat treated as an array of u_long.  While this encodes the
  234  * general layout of tcpstat into the caller, it doesn't encode its location,
  235  * so that future changes to add, for example, per-CPU stats support won't
  236  * cause binary compatibility problems for kernel modules.
  237  */
  238 void
  239 kmod_tcpstat_inc(int statnum)
  240 {
  241 
  242         (*((u_long *)&V_tcpstat + statnum))++;
  243 }
  244 
  245 /*
  246  * Wrapper for the TCP established input helper hook.
  247  */
  248 static void inline
  249 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
  250 {
  251         struct tcp_hhook_data hhook_data;
  252 
  253         if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
  254                 hhook_data.tp = tp;
  255                 hhook_data.th = th;
  256                 hhook_data.to = to;
  257 
  258                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
  259                     tp->osd);
  260         }
  261 }
  262 
  263 /*
  264  * CC wrapper hook functions
  265  */
  266 static void inline
  267 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type)
  268 {
  269         INP_WLOCK_ASSERT(tp->t_inpcb);
  270 
  271         tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
  272         if (tp->snd_cwnd == min(tp->snd_cwnd, tp->snd_wnd))
  273                 tp->ccv->flags |= CCF_CWND_LIMITED;
  274         else
  275                 tp->ccv->flags &= ~CCF_CWND_LIMITED;
  276 
  277         if (type == CC_ACK) {
  278                 if (tp->snd_cwnd > tp->snd_ssthresh) {
  279                         tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
  280                              V_tcp_abc_l_var * tp->t_maxseg);
  281                         if (tp->t_bytes_acked >= tp->snd_cwnd) {
  282                                 tp->t_bytes_acked -= tp->snd_cwnd;
  283                                 tp->ccv->flags |= CCF_ABC_SENTAWND;
  284                         }
  285                 } else {
  286                                 tp->ccv->flags &= ~CCF_ABC_SENTAWND;
  287                                 tp->t_bytes_acked = 0;
  288                 }
  289         }
  290 
  291         if (CC_ALGO(tp)->ack_received != NULL) {
  292                 /* XXXLAS: Find a way to live without this */
  293                 tp->ccv->curack = th->th_ack;
  294                 CC_ALGO(tp)->ack_received(tp->ccv, type);
  295         }
  296 }
  297 
  298 static void inline
  299 cc_conn_init(struct tcpcb *tp)
  300 {
  301         struct hc_metrics_lite metrics;
  302         struct inpcb *inp = tp->t_inpcb;
  303         int rtt;
  304 #ifdef INET6
  305         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
  306 #endif
  307 
  308         INP_WLOCK_ASSERT(tp->t_inpcb);
  309 
  310         tcp_hc_get(&inp->inp_inc, &metrics);
  311 
  312         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
  313                 tp->t_srtt = rtt;
  314                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
  315                 TCPSTAT_INC(tcps_usedrtt);
  316                 if (metrics.rmx_rttvar) {
  317                         tp->t_rttvar = metrics.rmx_rttvar;
  318                         TCPSTAT_INC(tcps_usedrttvar);
  319                 } else {
  320                         /* default variation is +- 1 rtt */
  321                         tp->t_rttvar =
  322                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
  323                 }
  324                 TCPT_RANGESET(tp->t_rxtcur,
  325                     ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
  326                     tp->t_rttmin, TCPTV_REXMTMAX);
  327         }
  328         if (metrics.rmx_ssthresh) {
  329                 /*
  330                  * There's some sort of gateway or interface
  331                  * buffer limit on the path.  Use this to set
  332                  * the slow start threshhold, but set the
  333                  * threshold to no less than 2*mss.
  334                  */
  335                 tp->snd_ssthresh = max(2 * tp->t_maxseg, metrics.rmx_ssthresh);
  336                 TCPSTAT_INC(tcps_usedssthresh);
  337         }
  338 
  339         /*
  340          * Set the slow-start flight size depending on whether this
  341          * is a local network or not.
  342          *
  343          * Extend this so we cache the cwnd too and retrieve it here.
  344          * Make cwnd even bigger than RFC3390 suggests but only if we
  345          * have previous experience with the remote host. Be careful
  346          * not make cwnd bigger than remote receive window or our own
  347          * send socket buffer. Maybe put some additional upper bound
  348          * on the retrieved cwnd. Should do incremental updates to
  349          * hostcache when cwnd collapses so next connection doesn't
  350          * overloads the path again.
  351          *
  352          * XXXAO: Initializing the CWND from the hostcache is broken
  353          * and in its current form not RFC conformant.  It is disabled
  354          * until fixed or removed entirely.
  355          *
  356          * RFC3390 says only do this if SYN or SYN/ACK didn't got lost.
  357          * We currently check only in syncache_socket for that.
  358          */
  359 /* #define TCP_METRICS_CWND */
  360 #ifdef TCP_METRICS_CWND
  361         if (metrics.rmx_cwnd)
  362                 tp->snd_cwnd = max(tp->t_maxseg, min(metrics.rmx_cwnd / 2,
  363                     min(tp->snd_wnd, so->so_snd.sb_hiwat)));
  364         else
  365 #endif
  366         if (V_tcp_do_rfc3390)
  367                 tp->snd_cwnd = min(4 * tp->t_maxseg,
  368                     max(2 * tp->t_maxseg, 4380));
  369 #ifdef INET6
  370         else if (isipv6 && in6_localaddr(&inp->in6p_faddr))
  371                 tp->snd_cwnd = tp->t_maxseg * V_ss_fltsz_local;
  372 #endif
  373 #if defined(INET) && defined(INET6)
  374         else if (!isipv6 && in_localaddr(inp->inp_faddr))
  375                 tp->snd_cwnd = tp->t_maxseg * V_ss_fltsz_local;
  376 #endif
  377 #ifdef INET
  378         else if (in_localaddr(inp->inp_faddr))
  379                 tp->snd_cwnd = tp->t_maxseg * V_ss_fltsz_local;
  380 #endif
  381         else
  382                 tp->snd_cwnd = tp->t_maxseg * V_ss_fltsz;
  383 
  384         if (CC_ALGO(tp)->conn_init != NULL)
  385                 CC_ALGO(tp)->conn_init(tp->ccv);
  386 }
  387 
  388 void inline
  389 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
  390 {
  391         INP_WLOCK_ASSERT(tp->t_inpcb);
  392 
  393         switch(type) {
  394         case CC_NDUPACK:
  395                 if (!IN_FASTRECOVERY(tp->t_flags)) {
  396                         tp->snd_recover = tp->snd_max;
  397                         if (tp->t_flags & TF_ECN_PERMIT)
  398                                 tp->t_flags |= TF_ECN_SND_CWR;
  399                 }
  400                 break;
  401         case CC_ECN:
  402                 if (!IN_CONGRECOVERY(tp->t_flags)) {
  403                         TCPSTAT_INC(tcps_ecn_rcwnd);
  404                         tp->snd_recover = tp->snd_max;
  405                         if (tp->t_flags & TF_ECN_PERMIT)
  406                                 tp->t_flags |= TF_ECN_SND_CWR;
  407                 }
  408                 break;
  409         case CC_RTO:
  410                 tp->t_dupacks = 0;
  411                 tp->t_bytes_acked = 0;
  412                 EXIT_RECOVERY(tp->t_flags);
  413                 tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
  414                     tp->t_maxseg) * tp->t_maxseg;
  415                 tp->snd_cwnd = tp->t_maxseg;
  416                 break;
  417         case CC_RTO_ERR:
  418                 TCPSTAT_INC(tcps_sndrexmitbad);
  419                 /* RTO was unnecessary, so reset everything. */
  420                 tp->snd_cwnd = tp->snd_cwnd_prev;
  421                 tp->snd_ssthresh = tp->snd_ssthresh_prev;
  422                 tp->snd_recover = tp->snd_recover_prev;
  423                 if (tp->t_flags & TF_WASFRECOVERY)
  424                         ENTER_FASTRECOVERY(tp->t_flags);
  425                 if (tp->t_flags & TF_WASCRECOVERY)
  426                         ENTER_CONGRECOVERY(tp->t_flags);
  427                 tp->snd_nxt = tp->snd_max;
  428                 tp->t_flags &= ~TF_PREVVALID;
  429                 tp->t_badrxtwin = 0;
  430                 break;
  431         }
  432 
  433         if (CC_ALGO(tp)->cong_signal != NULL) {
  434                 if (th != NULL)
  435                         tp->ccv->curack = th->th_ack;
  436                 CC_ALGO(tp)->cong_signal(tp->ccv, type);
  437         }
  438 }
  439 
  440 static void inline
  441 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
  442 {
  443         INP_WLOCK_ASSERT(tp->t_inpcb);
  444 
  445         /* XXXLAS: KASSERT that we're in recovery? */
  446 
  447         if (CC_ALGO(tp)->post_recovery != NULL) {
  448                 tp->ccv->curack = th->th_ack;
  449                 CC_ALGO(tp)->post_recovery(tp->ccv);
  450         }
  451         /* XXXLAS: EXIT_RECOVERY ? */
  452         tp->t_bytes_acked = 0;
  453 }
  454 
  455 static inline void
  456 tcp_fields_to_host(struct tcphdr *th)
  457 {
  458 
  459         th->th_seq = ntohl(th->th_seq);
  460         th->th_ack = ntohl(th->th_ack);
  461         th->th_win = ntohs(th->th_win);
  462         th->th_urp = ntohs(th->th_urp);
  463 }
  464 
  465 #ifdef TCP_SIGNATURE
  466 static inline void
  467 tcp_fields_to_net(struct tcphdr *th)
  468 {
  469 
  470         th->th_seq = htonl(th->th_seq);
  471         th->th_ack = htonl(th->th_ack);
  472         th->th_win = htons(th->th_win);
  473         th->th_urp = htons(th->th_urp);
  474 }
  475 
  476 static inline int
  477 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
  478     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
  479 {
  480         int ret;
  481 
  482         tcp_fields_to_net(th);
  483         ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
  484         tcp_fields_to_host(th);
  485         return (ret);
  486 }
  487 #endif
  488 
  489 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
  490 #ifdef INET6
  491 #define ND6_HINT(tp) \
  492 do { \
  493         if ((tp) && (tp)->t_inpcb && \
  494             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
  495                 nd6_nud_hint(NULL, NULL, 0); \
  496 } while (0)
  497 #else
  498 #define ND6_HINT(tp)
  499 #endif
  500 
  501 /*
  502  * Indicate whether this ack should be delayed.  We can delay the ack if
  503  *      - there is no delayed ack timer in progress and
  504  *      - our last ack wasn't a 0-sized window.  We never want to delay
  505  *        the ack that opens up a 0-sized window and
  506  *              - delayed acks are enabled or
  507  *              - this is a half-synchronized T/TCP connection.
  508  */
  509 #define DELAY_ACK(tp)                                                   \
  510         ((!tcp_timer_active(tp, TT_DELACK) &&                           \
  511             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
  512             (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
  513 
  514 /*
  515  * TCP input handling is split into multiple parts:
  516  *   tcp6_input is a thin wrapper around tcp_input for the extended
  517  *      ip6_protox[] call format in ip6_input
  518  *   tcp_input handles primary segment validation, inpcb lookup and
  519  *      SYN processing on listen sockets
  520  *   tcp_do_segment processes the ACK and text of the segment for
  521  *      establishing, established and closing connections
  522  */
  523 #ifdef INET6
  524 int
  525 tcp6_input(struct mbuf **mp, int *offp, int proto)
  526 {
  527         struct mbuf *m = *mp;
  528         struct in6_ifaddr *ia6;
  529 
  530         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
  531 
  532         /*
  533          * draft-itojun-ipv6-tcp-to-anycast
  534          * better place to put this in?
  535          */
  536         ia6 = ip6_getdstifaddr(m);
  537         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
  538                 struct ip6_hdr *ip6;
  539 
  540                 ifa_free(&ia6->ia_ifa);
  541                 ip6 = mtod(m, struct ip6_hdr *);
  542                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
  543                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
  544                 return IPPROTO_DONE;
  545         }
  546         if (ia6)
  547                 ifa_free(&ia6->ia_ifa);
  548 
  549         tcp_input(m, *offp);
  550         return IPPROTO_DONE;
  551 }
  552 #endif /* INET6 */
  553 
  554 void
  555 tcp_input(struct mbuf *m, int off0)
  556 {
  557         struct tcphdr *th = NULL;
  558         struct ip *ip = NULL;
  559 #ifdef INET
  560         struct ipovly *ipov;
  561 #endif
  562         struct inpcb *inp = NULL;
  563         struct tcpcb *tp = NULL;
  564         struct socket *so = NULL;
  565         u_char *optp = NULL;
  566         int optlen = 0;
  567 #ifdef INET
  568         int len;
  569 #endif
  570         int tlen = 0, off;
  571         int drop_hdrlen;
  572         int thflags;
  573         int rstreason = 0;      /* For badport_bandlim accounting purposes */
  574 #ifdef TCP_SIGNATURE
  575         uint8_t sig_checked = 0;
  576 #endif
  577         uint8_t iptos = 0;
  578 #ifdef IPFIREWALL_FORWARD
  579         struct m_tag *fwd_tag;
  580 #endif
  581 #ifdef INET6
  582         struct ip6_hdr *ip6 = NULL;
  583         int isipv6;
  584 #else
  585         const void *ip6 = NULL;
  586 #endif /* INET6 */
  587         struct tcpopt to;               /* options in this segment */
  588         char *s = NULL;                 /* address and port logging */
  589         int ti_locked;
  590 #define TI_UNLOCKED     1
  591 #define TI_WLOCKED      2
  592 
  593 #ifdef TCPDEBUG
  594         /*
  595          * The size of tcp_saveipgen must be the size of the max ip header,
  596          * now IPv6.
  597          */
  598         u_char tcp_saveipgen[IP6_HDR_LEN];
  599         struct tcphdr tcp_savetcp;
  600         short ostate = 0;
  601 #endif
  602 
  603 #ifdef INET6
  604         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
  605 #endif
  606 
  607         to.to_flags = 0;
  608         TCPSTAT_INC(tcps_rcvtotal);
  609 
  610 #ifdef INET6
  611         if (isipv6) {
  612                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
  613                 ip6 = mtod(m, struct ip6_hdr *);
  614                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
  615                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
  616                         TCPSTAT_INC(tcps_rcvbadsum);
  617                         goto drop;
  618                 }
  619                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
  620 
  621                 /*
  622                  * Be proactive about unspecified IPv6 address in source.
  623                  * As we use all-zero to indicate unbounded/unconnected pcb,
  624                  * unspecified IPv6 address can be used to confuse us.
  625                  *
  626                  * Note that packets with unspecified IPv6 destination is
  627                  * already dropped in ip6_input.
  628                  */
  629                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
  630                         /* XXX stat */
  631                         goto drop;
  632                 }
  633         }
  634 #endif
  635 #if defined(INET) && defined(INET6)
  636         else
  637 #endif
  638 #ifdef INET
  639         {
  640                 /*
  641                  * Get IP and TCP header together in first mbuf.
  642                  * Note: IP leaves IP header in first mbuf.
  643                  */
  644                 if (off0 > sizeof (struct ip)) {
  645                         ip_stripoptions(m, (struct mbuf *)0);
  646                         off0 = sizeof(struct ip);
  647                 }
  648                 if (m->m_len < sizeof (struct tcpiphdr)) {
  649                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
  650                             == NULL) {
  651                                 TCPSTAT_INC(tcps_rcvshort);
  652                                 return;
  653                         }
  654                 }
  655                 ip = mtod(m, struct ip *);
  656                 ipov = (struct ipovly *)ip;
  657                 th = (struct tcphdr *)((caddr_t)ip + off0);
  658                 tlen = ip->ip_len;
  659 
  660                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
  661                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  662                                 th->th_sum = m->m_pkthdr.csum_data;
  663                         else
  664                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
  665                                                 ip->ip_dst.s_addr,
  666                                                 htonl(m->m_pkthdr.csum_data +
  667                                                         ip->ip_len +
  668                                                         IPPROTO_TCP));
  669                         th->th_sum ^= 0xffff;
  670 #ifdef TCPDEBUG
  671                         ipov->ih_len = (u_short)tlen;
  672                         ipov->ih_len = htons(ipov->ih_len);
  673 #endif
  674                 } else {
  675                         /*
  676                          * Checksum extended TCP header and data.
  677                          */
  678                         len = sizeof (struct ip) + tlen;
  679                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
  680                         ipov->ih_len = (u_short)tlen;
  681                         ipov->ih_len = htons(ipov->ih_len);
  682                         th->th_sum = in_cksum(m, len);
  683                 }
  684                 if (th->th_sum) {
  685                         TCPSTAT_INC(tcps_rcvbadsum);
  686                         goto drop;
  687                 }
  688                 /* Re-initialization for later version check */
  689                 ip->ip_v = IPVERSION;
  690         }
  691 #endif /* INET */
  692 
  693 #ifdef INET6
  694         if (isipv6)
  695                 iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
  696 #endif
  697 #if defined(INET) && defined(INET6)
  698         else
  699 #endif
  700 #ifdef INET
  701                 iptos = ip->ip_tos;
  702 #endif
  703 
  704         /*
  705          * Check that TCP offset makes sense,
  706          * pull out TCP options and adjust length.              XXX
  707          */
  708         off = th->th_off << 2;
  709         if (off < sizeof (struct tcphdr) || off > tlen) {
  710                 TCPSTAT_INC(tcps_rcvbadoff);
  711                 goto drop;
  712         }
  713         tlen -= off;    /* tlen is used instead of ti->ti_len */
  714         if (off > sizeof (struct tcphdr)) {
  715 #ifdef INET6
  716                 if (isipv6) {
  717                         IP6_EXTHDR_CHECK(m, off0, off, );
  718                         ip6 = mtod(m, struct ip6_hdr *);
  719                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
  720                 }
  721 #endif
  722 #if defined(INET) && defined(INET6)
  723                 else
  724 #endif
  725 #ifdef INET
  726                 {
  727                         if (m->m_len < sizeof(struct ip) + off) {
  728                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
  729                                     == NULL) {
  730                                         TCPSTAT_INC(tcps_rcvshort);
  731                                         return;
  732                                 }
  733                                 ip = mtod(m, struct ip *);
  734                                 ipov = (struct ipovly *)ip;
  735                                 th = (struct tcphdr *)((caddr_t)ip + off0);
  736                         }
  737                 }
  738 #endif
  739                 optlen = off - sizeof (struct tcphdr);
  740                 optp = (u_char *)(th + 1);
  741         }
  742         thflags = th->th_flags;
  743 
  744         /*
  745          * Convert TCP protocol specific fields to host format.
  746          */
  747         tcp_fields_to_host(th);
  748 
  749         /*
  750          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
  751          */
  752         drop_hdrlen = off0 + off;
  753 
  754         /*
  755          * Locate pcb for segment; if we're likely to add or remove a
  756          * connection then first acquire pcbinfo lock.  There are two cases
  757          * where we might discover later we need a write lock despite the
  758          * flags: ACKs moving a connection out of the syncache, and ACKs for
  759          * a connection in TIMEWAIT.
  760          */
  761         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0) {
  762                 INP_INFO_WLOCK(&V_tcbinfo);
  763                 ti_locked = TI_WLOCKED;
  764         } else
  765                 ti_locked = TI_UNLOCKED;
  766 
  767 findpcb:
  768 #ifdef INVARIANTS
  769         if (ti_locked == TI_WLOCKED) {
  770                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  771         } else {
  772                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
  773         }
  774 #endif
  775 
  776 #ifdef IPFIREWALL_FORWARD
  777         /*
  778          * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
  779          */
  780         fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
  781 #endif /* IPFIREWALL_FORWARD */
  782 
  783 #ifdef INET6
  784 #ifdef IPFIREWALL_FORWARD
  785         if (isipv6 && fwd_tag != NULL) {
  786                 struct sockaddr_in6 *next_hop6;
  787 
  788                 next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
  789                 /*
  790                  * Transparently forwarded. Pretend to be the destination.
  791                  * Already got one like this?
  792                  */
  793                 inp = in6_pcblookup_mbuf(&V_tcbinfo,
  794                     &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
  795                     INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
  796                 if (!inp) {
  797                         /*
  798                          * It's new.  Try to find the ambushing socket.
  799                          * Because we've rewritten the destination address,
  800                          * any hardware-generated hash is ignored.
  801                          */
  802                         inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
  803                             th->th_sport, &next_hop6->sin6_addr,
  804                             next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
  805                             th->th_dport, INPLOOKUP_WILDCARD |
  806                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  807                 }
  808                 /* Remove the tag from the packet.  We don't need it anymore. */
  809                 m_tag_delete(m, fwd_tag);
  810         } else
  811 #endif /* IPFIREWALL_FORWARD */
  812         if (isipv6) {
  813                 inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
  814                     th->th_sport, &ip6->ip6_dst, th->th_dport,
  815                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  816                     m->m_pkthdr.rcvif, m);
  817         }
  818 #endif /* INET6 */
  819 #if defined(INET6) && defined(INET)
  820         else
  821 #endif
  822 #ifdef INET
  823 #ifdef IPFIREWALL_FORWARD
  824         if (fwd_tag != NULL) {
  825                 struct sockaddr_in *next_hop;
  826 
  827                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
  828                 /*
  829                  * Transparently forwarded. Pretend to be the destination.
  830                  * already got one like this?
  831                  */
  832                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
  833                     ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
  834                     m->m_pkthdr.rcvif, m);
  835                 if (!inp) {
  836                         /*
  837                          * It's new.  Try to find the ambushing socket.
  838                          * Because we've rewritten the destination address,
  839                          * any hardware-generated hash is ignored.
  840                          */
  841                         inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
  842                             th->th_sport, next_hop->sin_addr,
  843                             next_hop->sin_port ? ntohs(next_hop->sin_port) :
  844                             th->th_dport, INPLOOKUP_WILDCARD |
  845                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  846                 }
  847                 /* Remove the tag from the packet.  We don't need it anymore. */
  848                 m_tag_delete(m, fwd_tag);
  849         } else
  850 #endif /* IPFIREWALL_FORWARD */
  851                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
  852                     th->th_sport, ip->ip_dst, th->th_dport,
  853                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  854                     m->m_pkthdr.rcvif, m);
  855 #endif /* INET */
  856 
  857         /*
  858          * If the INPCB does not exist then all data in the incoming
  859          * segment is discarded and an appropriate RST is sent back.
  860          * XXX MRT Send RST using which routing table?
  861          */
  862         if (inp == NULL) {
  863                 /*
  864                  * Log communication attempts to ports that are not
  865                  * in use.
  866                  */
  867                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
  868                     tcp_log_in_vain == 2) {
  869                         if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
  870                                 log(LOG_INFO, "%s; %s: Connection attempt "
  871                                     "to closed port\n", s, __func__);
  872                 }
  873                 /*
  874                  * When blackholing do not respond with a RST but
  875                  * completely ignore the segment and drop it.
  876                  */
  877                 if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
  878                     V_blackhole == 2)
  879                         goto dropunlock;
  880 
  881                 rstreason = BANDLIM_RST_CLOSEDPORT;
  882                 goto dropwithreset;
  883         }
  884         INP_WLOCK_ASSERT(inp);
  885         if (!(inp->inp_flags & INP_HW_FLOWID)
  886             && (m->m_flags & M_FLOWID)
  887             && ((inp->inp_socket == NULL)
  888                 || !(inp->inp_socket->so_options & SO_ACCEPTCONN))) {
  889                 inp->inp_flags |= INP_HW_FLOWID;
  890                 inp->inp_flags &= ~INP_SW_FLOWID;
  891                 inp->inp_flowid = m->m_pkthdr.flowid;
  892         }
  893 #ifdef IPSEC
  894 #ifdef INET6
  895         if (isipv6 && ipsec6_in_reject(m, inp)) {
  896                 V_ipsec6stat.in_polvio++;
  897                 goto dropunlock;
  898         } else
  899 #endif /* INET6 */
  900         if (ipsec4_in_reject(m, inp) != 0) {
  901                 V_ipsec4stat.in_polvio++;
  902                 goto dropunlock;
  903         }
  904 #endif /* IPSEC */
  905 
  906         /*
  907          * Check the minimum TTL for socket.
  908          */
  909         if (inp->inp_ip_minttl != 0) {
  910 #ifdef INET6
  911                 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
  912                         goto dropunlock;
  913                 else
  914 #endif
  915                 if (inp->inp_ip_minttl > ip->ip_ttl)
  916                         goto dropunlock;
  917         }
  918 
  919         /*
  920          * A previous connection in TIMEWAIT state is supposed to catch stray
  921          * or duplicate segments arriving late.  If this segment was a
  922          * legitimate new connection attempt the old INPCB gets removed and
  923          * we can try again to find a listening socket.
  924          *
  925          * At this point, due to earlier optimism, we may hold only an inpcb
  926          * lock, and not the inpcbinfo write lock.  If so, we need to try to
  927          * acquire it, or if that fails, acquire a reference on the inpcb,
  928          * drop all locks, acquire a global write lock, and then re-acquire
  929          * the inpcb lock.  We may at that point discover that another thread
  930          * has tried to free the inpcb, in which case we need to loop back
  931          * and try to find a new inpcb to deliver to.
  932          *
  933          * XXXRW: It may be time to rethink timewait locking.
  934          */
  935 relocked:
  936         if (inp->inp_flags & INP_TIMEWAIT) {
  937                 if (ti_locked == TI_UNLOCKED) {
  938                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
  939                                 in_pcbref(inp);
  940                                 INP_WUNLOCK(inp);
  941                                 INP_INFO_WLOCK(&V_tcbinfo);
  942                                 ti_locked = TI_WLOCKED;
  943                                 INP_WLOCK(inp);
  944                                 if (in_pcbrele_wlocked(inp)) {
  945                                         inp = NULL;
  946                                         goto findpcb;
  947                                 }
  948                         } else
  949                                 ti_locked = TI_WLOCKED;
  950                 }
  951                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  952 
  953                 if (thflags & TH_SYN)
  954                         tcp_dooptions(&to, optp, optlen, TO_SYN);
  955                 /*
  956                  * NB: tcp_twcheck unlocks the INP and frees the mbuf.
  957                  */
  958                 if (tcp_twcheck(inp, &to, th, m, tlen))
  959                         goto findpcb;
  960                 INP_INFO_WUNLOCK(&V_tcbinfo);
  961                 return;
  962         }
  963         /*
  964          * The TCPCB may no longer exist if the connection is winding
  965          * down or it is in the CLOSED state.  Either way we drop the
  966          * segment and send an appropriate response.
  967          */
  968         tp = intotcpcb(inp);
  969         if (tp == NULL || tp->t_state == TCPS_CLOSED) {
  970                 rstreason = BANDLIM_RST_CLOSEDPORT;
  971                 goto dropwithreset;
  972         }
  973 
  974         /*
  975          * We've identified a valid inpcb, but it could be that we need an
  976          * inpcbinfo write lock but don't hold it.  In this case, attempt to
  977          * acquire using the same strategy as the TIMEWAIT case above.  If we
  978          * relock, we have to jump back to 'relocked' as the connection might
  979          * now be in TIMEWAIT.
  980          */
  981 #ifdef INVARIANTS
  982         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0)
  983                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  984 #endif
  985         if (tp->t_state != TCPS_ESTABLISHED) {
  986                 if (ti_locked == TI_UNLOCKED) {
  987                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
  988                                 in_pcbref(inp);
  989                                 INP_WUNLOCK(inp);
  990                                 INP_INFO_WLOCK(&V_tcbinfo);
  991                                 ti_locked = TI_WLOCKED;
  992                                 INP_WLOCK(inp);
  993                                 if (in_pcbrele_wlocked(inp)) {
  994                                         inp = NULL;
  995                                         goto findpcb;
  996                                 }
  997                                 goto relocked;
  998                         } else
  999                                 ti_locked = TI_WLOCKED;
 1000                 }
 1001                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1002         }
 1003 
 1004 #ifdef MAC
 1005         INP_WLOCK_ASSERT(inp);
 1006         if (mac_inpcb_check_deliver(inp, m))
 1007                 goto dropunlock;
 1008 #endif
 1009         so = inp->inp_socket;
 1010         KASSERT(so != NULL, ("%s: so == NULL", __func__));
 1011 #ifdef TCPDEBUG
 1012         if (so->so_options & SO_DEBUG) {
 1013                 ostate = tp->t_state;
 1014 #ifdef INET6
 1015                 if (isipv6) {
 1016                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 1017                 } else
 1018 #endif
 1019                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 1020                 tcp_savetcp = *th;
 1021         }
 1022 #endif /* TCPDEBUG */
 1023         /*
 1024          * When the socket is accepting connections (the INPCB is in LISTEN
 1025          * state) we look into the SYN cache if this is a new connection
 1026          * attempt or the completion of a previous one.  Because listen
 1027          * sockets are never in TCPS_ESTABLISHED, the V_tcbinfo lock will be
 1028          * held in this case.
 1029          */
 1030         if (so->so_options & SO_ACCEPTCONN) {
 1031                 struct in_conninfo inc;
 1032 
 1033                 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
 1034                     "tp not listening", __func__));
 1035                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1036 
 1037                 bzero(&inc, sizeof(inc));
 1038 #ifdef INET6
 1039                 if (isipv6) {
 1040                         inc.inc_flags |= INC_ISIPV6;
 1041                         inc.inc6_faddr = ip6->ip6_src;
 1042                         inc.inc6_laddr = ip6->ip6_dst;
 1043                 } else
 1044 #endif
 1045                 {
 1046                         inc.inc_faddr = ip->ip_src;
 1047                         inc.inc_laddr = ip->ip_dst;
 1048                 }
 1049                 inc.inc_fport = th->th_sport;
 1050                 inc.inc_lport = th->th_dport;
 1051                 inc.inc_fibnum = so->so_fibnum;
 1052 
 1053                 /*
 1054                  * Check for an existing connection attempt in syncache if
 1055                  * the flag is only ACK.  A successful lookup creates a new
 1056                  * socket appended to the listen queue in SYN_RECEIVED state.
 1057                  */
 1058                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 1059                         /*
 1060                          * Parse the TCP options here because
 1061                          * syncookies need access to the reflected
 1062                          * timestamp.
 1063                          */
 1064                         tcp_dooptions(&to, optp, optlen, 0);
 1065                         /*
 1066                          * NB: syncache_expand() doesn't unlock
 1067                          * inp and tcpinfo locks.
 1068                          */
 1069                         if (!syncache_expand(&inc, &to, th, &so, m)) {
 1070                                 /*
 1071                                  * No syncache entry or ACK was not
 1072                                  * for our SYN/ACK.  Send a RST.
 1073                                  * NB: syncache did its own logging
 1074                                  * of the failure cause.
 1075                                  */
 1076                                 rstreason = BANDLIM_RST_OPENPORT;
 1077                                 goto dropwithreset;
 1078                         }
 1079                         if (so == NULL) {
 1080                                 /*
 1081                                  * We completed the 3-way handshake
 1082                                  * but could not allocate a socket
 1083                                  * either due to memory shortage,
 1084                                  * listen queue length limits or
 1085                                  * global socket limits.  Send RST
 1086                                  * or wait and have the remote end
 1087                                  * retransmit the ACK for another
 1088                                  * try.
 1089                                  */
 1090                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1091                                         log(LOG_DEBUG, "%s; %s: Listen socket: "
 1092                                             "Socket allocation failed due to "
 1093                                             "limits or memory shortage, %s\n",
 1094                                             s, __func__,
 1095                                             V_tcp_sc_rst_sock_fail ?
 1096                                             "sending RST" : "try again");
 1097                                 if (V_tcp_sc_rst_sock_fail) {
 1098                                         rstreason = BANDLIM_UNLIMITED;
 1099                                         goto dropwithreset;
 1100                                 } else
 1101                                         goto dropunlock;
 1102                         }
 1103                         /*
 1104                          * Socket is created in state SYN_RECEIVED.
 1105                          * Unlock the listen socket, lock the newly
 1106                          * created socket and update the tp variable.
 1107                          */
 1108                         INP_WUNLOCK(inp);       /* listen socket */
 1109                         inp = sotoinpcb(so);
 1110                         INP_WLOCK(inp);         /* new connection */
 1111                         tp = intotcpcb(inp);
 1112                         KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
 1113                             ("%s: ", __func__));
 1114 #ifdef TCP_SIGNATURE
 1115                         if (sig_checked == 0)  {
 1116                                 tcp_dooptions(&to, optp, optlen,
 1117                                     (thflags & TH_SYN) ? TO_SYN : 0);
 1118                                 if (!tcp_signature_verify_input(m, off0, tlen,
 1119                                     optlen, &to, th, tp->t_flags)) {
 1120 
 1121                                         /*
 1122                                          * In SYN_SENT state if it receives an
 1123                                          * RST, it is allowed for further
 1124                                          * processing.
 1125                                          */
 1126                                         if ((thflags & TH_RST) == 0 ||
 1127                                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1128                                                 goto dropunlock;
 1129                                 }
 1130                                 sig_checked = 1;
 1131                         }
 1132 #endif
 1133 
 1134                         /*
 1135                          * Process the segment and the data it
 1136                          * contains.  tcp_do_segment() consumes
 1137                          * the mbuf chain and unlocks the inpcb.
 1138                          */
 1139                         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
 1140                             iptos, ti_locked);
 1141                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1142                         return;
 1143                 }
 1144                 /*
 1145                  * Segment flag validation for new connection attempts:
 1146                  *
 1147                  * Our (SYN|ACK) response was rejected.
 1148                  * Check with syncache and remove entry to prevent
 1149                  * retransmits.
 1150                  *
 1151                  * NB: syncache_chkrst does its own logging of failure
 1152                  * causes.
 1153                  */
 1154                 if (thflags & TH_RST) {
 1155                         syncache_chkrst(&inc, th);
 1156                         goto dropunlock;
 1157                 }
 1158                 /*
 1159                  * We can't do anything without SYN.
 1160                  */
 1161                 if ((thflags & TH_SYN) == 0) {
 1162                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1163                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1164                                     "SYN is missing, segment ignored\n",
 1165                                     s, __func__);
 1166                         TCPSTAT_INC(tcps_badsyn);
 1167                         goto dropunlock;
 1168                 }
 1169                 /*
 1170                  * (SYN|ACK) is bogus on a listen socket.
 1171                  */
 1172                 if (thflags & TH_ACK) {
 1173                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1174                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1175                                     "SYN|ACK invalid, segment rejected\n",
 1176                                     s, __func__);
 1177                         syncache_badack(&inc);  /* XXX: Not needed! */
 1178                         TCPSTAT_INC(tcps_badsyn);
 1179                         rstreason = BANDLIM_RST_OPENPORT;
 1180                         goto dropwithreset;
 1181                 }
 1182                 /*
 1183                  * If the drop_synfin option is enabled, drop all
 1184                  * segments with both the SYN and FIN bits set.
 1185                  * This prevents e.g. nmap from identifying the
 1186                  * TCP/IP stack.
 1187                  * XXX: Poor reasoning.  nmap has other methods
 1188                  * and is constantly refining its stack detection
 1189                  * strategies.
 1190                  * XXX: This is a violation of the TCP specification
 1191                  * and was used by RFC1644.
 1192                  */
 1193                 if ((thflags & TH_FIN) && V_drop_synfin) {
 1194                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1195                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1196                                     "SYN|FIN segment ignored (based on "
 1197                                     "sysctl setting)\n", s, __func__);
 1198                         TCPSTAT_INC(tcps_badsyn);
 1199                         goto dropunlock;
 1200                 }
 1201                 /*
 1202                  * Segment's flags are (SYN) or (SYN|FIN).
 1203                  *
 1204                  * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
 1205                  * as they do not affect the state of the TCP FSM.
 1206                  * The data pointed to by TH_URG and th_urp is ignored.
 1207                  */
 1208                 KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
 1209                     ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
 1210                 KASSERT(thflags & (TH_SYN),
 1211                     ("%s: Listen socket: TH_SYN not set", __func__));
 1212 #ifdef INET6
 1213                 /*
 1214                  * If deprecated address is forbidden,
 1215                  * we do not accept SYN to deprecated interface
 1216                  * address to prevent any new inbound connection from
 1217                  * getting established.
 1218                  * When we do not accept SYN, we send a TCP RST,
 1219                  * with deprecated source address (instead of dropping
 1220                  * it).  We compromise it as it is much better for peer
 1221                  * to send a RST, and RST will be the final packet
 1222                  * for the exchange.
 1223                  *
 1224                  * If we do not forbid deprecated addresses, we accept
 1225                  * the SYN packet.  RFC2462 does not suggest dropping
 1226                  * SYN in this case.
 1227                  * If we decipher RFC2462 5.5.4, it says like this:
 1228                  * 1. use of deprecated addr with existing
 1229                  *    communication is okay - "SHOULD continue to be
 1230                  *    used"
 1231                  * 2. use of it with new communication:
 1232                  *   (2a) "SHOULD NOT be used if alternate address
 1233                  *        with sufficient scope is available"
 1234                  *   (2b) nothing mentioned otherwise.
 1235                  * Here we fall into (2b) case as we have no choice in
 1236                  * our source address selection - we must obey the peer.
 1237                  *
 1238                  * The wording in RFC2462 is confusing, and there are
 1239                  * multiple description text for deprecated address
 1240                  * handling - worse, they are not exactly the same.
 1241                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 1242                  */
 1243                 if (isipv6 && !V_ip6_use_deprecated) {
 1244                         struct in6_ifaddr *ia6;
 1245 
 1246                         ia6 = ip6_getdstifaddr(m);
 1247                         if (ia6 != NULL &&
 1248                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 1249                                 ifa_free(&ia6->ia_ifa);
 1250                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1251                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1252                                         "Connection attempt to deprecated "
 1253                                         "IPv6 address rejected\n",
 1254                                         s, __func__);
 1255                                 rstreason = BANDLIM_RST_OPENPORT;
 1256                                 goto dropwithreset;
 1257                         }
 1258                         if (ia6)
 1259                                 ifa_free(&ia6->ia_ifa);
 1260                 }
 1261 #endif /* INET6 */
 1262                 /*
 1263                  * Basic sanity checks on incoming SYN requests:
 1264                  *   Don't respond if the destination is a link layer
 1265                  *      broadcast according to RFC1122 4.2.3.10, p. 104.
 1266                  *   If it is from this socket it must be forged.
 1267                  *   Don't respond if the source or destination is a
 1268                  *      global or subnet broad- or multicast address.
 1269                  *   Note that it is quite possible to receive unicast
 1270                  *      link-layer packets with a broadcast IP address. Use
 1271                  *      in_broadcast() to find them.
 1272                  */
 1273                 if (m->m_flags & (M_BCAST|M_MCAST)) {
 1274                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1275                             log(LOG_DEBUG, "%s; %s: Listen socket: "
 1276                                 "Connection attempt from broad- or multicast "
 1277                                 "link layer address ignored\n", s, __func__);
 1278                         goto dropunlock;
 1279                 }
 1280 #ifdef INET6
 1281                 if (isipv6) {
 1282                         if (th->th_dport == th->th_sport &&
 1283                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
 1284                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1285                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1286                                         "Connection attempt to/from self "
 1287                                         "ignored\n", s, __func__);
 1288                                 goto dropunlock;
 1289                         }
 1290                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 1291                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
 1292                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1293                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1294                                         "Connection attempt from/to multicast "
 1295                                         "address ignored\n", s, __func__);
 1296                                 goto dropunlock;
 1297                         }
 1298                 }
 1299 #endif
 1300 #if defined(INET) && defined(INET6)
 1301                 else
 1302 #endif
 1303 #ifdef INET
 1304                 {
 1305                         if (th->th_dport == th->th_sport &&
 1306                             ip->ip_dst.s_addr == ip->ip_src.s_addr) {
 1307                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1308                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1309                                         "Connection attempt from/to self "
 1310                                         "ignored\n", s, __func__);
 1311                                 goto dropunlock;
 1312                         }
 1313                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 1314                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 1315                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 1316                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
 1317                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1318                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1319                                         "Connection attempt from/to broad- "
 1320                                         "or multicast address ignored\n",
 1321                                         s, __func__);
 1322                                 goto dropunlock;
 1323                         }
 1324                 }
 1325 #endif
 1326                 /*
 1327                  * SYN appears to be valid.  Create compressed TCP state
 1328                  * for syncache.
 1329                  */
 1330 #ifdef TCPDEBUG
 1331                 if (so->so_options & SO_DEBUG)
 1332                         tcp_trace(TA_INPUT, ostate, tp,
 1333                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1334 #endif
 1335                 tcp_dooptions(&to, optp, optlen, TO_SYN);
 1336                 syncache_add(&inc, &to, th, inp, &so, m);
 1337                 /*
 1338                  * Entry added to syncache and mbuf consumed.
 1339                  * Everything already unlocked by syncache_add().
 1340                  */
 1341                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1342                 return;
 1343         }
 1344 
 1345 #ifdef TCP_SIGNATURE
 1346         if (sig_checked == 0)  {
 1347                 tcp_dooptions(&to, optp, optlen,
 1348                     (thflags & TH_SYN) ? TO_SYN : 0);
 1349                 if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
 1350                     th, tp->t_flags)) {
 1351 
 1352                         /*
 1353                          * In SYN_SENT state if it receives an RST, it is
 1354                          * allowed for further processing.
 1355                          */
 1356                         if ((thflags & TH_RST) == 0 ||
 1357                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1358                                 goto dropunlock;
 1359                 }
 1360                 sig_checked = 1;
 1361         }
 1362 #endif
 1363 
 1364         /*
 1365          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
 1366          * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
 1367          * the inpcb, and unlocks pcbinfo.
 1368          */
 1369         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
 1370         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1371         return;
 1372 
 1373 dropwithreset:
 1374         if (ti_locked == TI_WLOCKED) {
 1375                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1376                 ti_locked = TI_UNLOCKED;
 1377         }
 1378 #ifdef INVARIANTS
 1379         else {
 1380                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
 1381                     "ti_locked: %d", __func__, ti_locked));
 1382                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1383         }
 1384 #endif
 1385 
 1386         if (inp != NULL) {
 1387                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 1388                 INP_WUNLOCK(inp);
 1389         } else
 1390                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 1391         m = NULL;       /* mbuf chain got consumed. */
 1392         goto drop;
 1393 
 1394 dropunlock:
 1395         if (ti_locked == TI_WLOCKED) {
 1396                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1397                 ti_locked = TI_UNLOCKED;
 1398         }
 1399 #ifdef INVARIANTS
 1400         else {
 1401                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
 1402                     "ti_locked: %d", __func__, ti_locked));
 1403                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1404         }
 1405 #endif
 1406 
 1407         if (inp != NULL)
 1408                 INP_WUNLOCK(inp);
 1409 
 1410 drop:
 1411         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1412         if (s != NULL)
 1413                 free(s, M_TCPLOG);
 1414         if (m != NULL)
 1415                 m_freem(m);
 1416 }
 1417 
 1418 static void
 1419 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 1420     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
 1421     int ti_locked)
 1422 {
 1423         int thflags, acked, ourfinisacked, needoutput = 0;
 1424         int rstreason, todrop, win;
 1425         u_long tiwin;
 1426         struct tcpopt to;
 1427 
 1428 #ifdef TCPDEBUG
 1429         /*
 1430          * The size of tcp_saveipgen must be the size of the max ip header,
 1431          * now IPv6.
 1432          */
 1433         u_char tcp_saveipgen[IP6_HDR_LEN];
 1434         struct tcphdr tcp_savetcp;
 1435         short ostate = 0;
 1436 #endif
 1437         thflags = th->th_flags;
 1438         tp->sackhint.last_sack_ack = 0;
 1439 
 1440         /*
 1441          * If this is either a state-changing packet or current state isn't
 1442          * established, we require a write lock on tcbinfo.  Otherwise, we
 1443          * allow either a read lock or a write lock, as we may have acquired
 1444          * a write lock due to a race.
 1445          *
 1446          * Require a global write lock for SYN/FIN/RST segments or
 1447          * non-established connections; otherwise accept either a read or
 1448          * write lock, as we may have conservatively acquired a write lock in
 1449          * certain cases in tcp_input() (is this still true?).  Currently we
 1450          * will never enter with no lock, so we try to drop it quickly in the
 1451          * common pure ack/pure data cases.
 1452          */
 1453         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
 1454             tp->t_state != TCPS_ESTABLISHED) {
 1455                 KASSERT(ti_locked == TI_WLOCKED, ("%s ti_locked %d for "
 1456                     "SYN/FIN/RST/!EST", __func__, ti_locked));
 1457                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1458         } else {
 1459 #ifdef INVARIANTS
 1460                 if (ti_locked == TI_WLOCKED)
 1461                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1462                 else {
 1463                         KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
 1464                             "ti_locked: %d", __func__, ti_locked));
 1465                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1466                 }
 1467 #endif
 1468         }
 1469         INP_WLOCK_ASSERT(tp->t_inpcb);
 1470         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
 1471             __func__));
 1472         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
 1473             __func__));
 1474 
 1475         /*
 1476          * Segment received on connection.
 1477          * Reset idle time and keep-alive timer.
 1478          * XXX: This should be done after segment
 1479          * validation to ignore broken/spoofed segs.
 1480          */
 1481         tp->t_rcvtime = ticks;
 1482         if (TCPS_HAVEESTABLISHED(tp->t_state))
 1483                 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
 1484 
 1485         /*
 1486          * Unscale the window into a 32-bit value.
 1487          * For the SYN_SENT state the scale is zero.
 1488          */
 1489         tiwin = th->th_win << tp->snd_scale;
 1490 
 1491         /*
 1492          * TCP ECN processing.
 1493          */
 1494         if (tp->t_flags & TF_ECN_PERMIT) {
 1495                 if (thflags & TH_CWR)
 1496                         tp->t_flags &= ~TF_ECN_SND_ECE;
 1497                 switch (iptos & IPTOS_ECN_MASK) {
 1498                 case IPTOS_ECN_CE:
 1499                         tp->t_flags |= TF_ECN_SND_ECE;
 1500                         TCPSTAT_INC(tcps_ecn_ce);
 1501                         break;
 1502                 case IPTOS_ECN_ECT0:
 1503                         TCPSTAT_INC(tcps_ecn_ect0);
 1504                         break;
 1505                 case IPTOS_ECN_ECT1:
 1506                         TCPSTAT_INC(tcps_ecn_ect1);
 1507                         break;
 1508                 }
 1509                 /* Congestion experienced. */
 1510                 if (thflags & TH_ECE) {
 1511                         cc_cong_signal(tp, th, CC_ECN);
 1512                 }
 1513         }
 1514 
 1515         /*
 1516          * Parse options on any incoming segment.
 1517          */
 1518         tcp_dooptions(&to, (u_char *)(th + 1),
 1519             (th->th_off << 2) - sizeof(struct tcphdr),
 1520             (thflags & TH_SYN) ? TO_SYN : 0);
 1521 
 1522         /*
 1523          * If echoed timestamp is later than the current time,
 1524          * fall back to non RFC1323 RTT calculation.  Normalize
 1525          * timestamp if syncookies were used when this connection
 1526          * was established.
 1527          */
 1528         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
 1529                 to.to_tsecr -= tp->ts_offset;
 1530                 if (TSTMP_GT(to.to_tsecr, ticks))
 1531                         to.to_tsecr = 0;
 1532         }
 1533 
 1534         /*
 1535          * Process options only when we get SYN/ACK back. The SYN case
 1536          * for incoming connections is handled in tcp_syncache.
 1537          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
 1538          * or <SYN,ACK>) segment itself is never scaled.
 1539          * XXX this is traditional behavior, may need to be cleaned up.
 1540          */
 1541         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
 1542                 if ((to.to_flags & TOF_SCALE) &&
 1543                     (tp->t_flags & TF_REQ_SCALE)) {
 1544                         tp->t_flags |= TF_RCVD_SCALE;
 1545                         tp->snd_scale = to.to_wscale;
 1546                 }
 1547                 /*
 1548                  * Initial send window.  It will be updated with
 1549                  * the next incoming segment to the scaled value.
 1550                  */
 1551                 tp->snd_wnd = th->th_win;
 1552                 if (to.to_flags & TOF_TS) {
 1553                         tp->t_flags |= TF_RCVD_TSTMP;
 1554                         tp->ts_recent = to.to_tsval;
 1555                         tp->ts_recent_age = ticks;
 1556                 }
 1557                 if (to.to_flags & TOF_MSS)
 1558                         tcp_mss(tp, to.to_mss);
 1559                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 1560                     (to.to_flags & TOF_SACKPERM) == 0)
 1561                         tp->t_flags &= ~TF_SACK_PERMIT;
 1562         }
 1563 
 1564         /*
 1565          * Header prediction: check for the two common cases
 1566          * of a uni-directional data xfer.  If the packet has
 1567          * no control flags, is in-sequence, the window didn't
 1568          * change and we're not retransmitting, it's a
 1569          * candidate.  If the length is zero and the ack moved
 1570          * forward, we're the sender side of the xfer.  Just
 1571          * free the data acked & wake any higher level process
 1572          * that was blocked waiting for space.  If the length
 1573          * is non-zero and the ack didn't move, we're the
 1574          * receiver side.  If we're getting packets in-order
 1575          * (the reassembly queue is empty), add the data to
 1576          * the socket buffer and note that we need a delayed ack.
 1577          * Make sure that the hidden state-flags are also off.
 1578          * Since we check for TCPS_ESTABLISHED first, it can only
 1579          * be TH_NEEDSYN.
 1580          */
 1581         if (tp->t_state == TCPS_ESTABLISHED &&
 1582             th->th_seq == tp->rcv_nxt &&
 1583             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 1584             tp->snd_nxt == tp->snd_max &&
 1585             tiwin && tiwin == tp->snd_wnd && 
 1586             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 1587             LIST_EMPTY(&tp->t_segq) &&
 1588             ((to.to_flags & TOF_TS) == 0 ||
 1589              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
 1590 
 1591                 /*
 1592                  * If last ACK falls within this segment's sequence numbers,
 1593                  * record the timestamp.
 1594                  * NOTE that the test is modified according to the latest
 1595                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 1596                  */
 1597                 if ((to.to_flags & TOF_TS) != 0 &&
 1598                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 1599                         tp->ts_recent_age = ticks;
 1600                         tp->ts_recent = to.to_tsval;
 1601                 }
 1602 
 1603                 if (tlen == 0) {
 1604                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 1605                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 1606                             !IN_RECOVERY(tp->t_flags) &&
 1607                             (to.to_flags & TOF_SACK) == 0 &&
 1608                             TAILQ_EMPTY(&tp->snd_holes)) {
 1609                                 /*
 1610                                  * This is a pure ack for outstanding data.
 1611                                  */
 1612                                 if (ti_locked == TI_WLOCKED)
 1613                                         INP_INFO_WUNLOCK(&V_tcbinfo);
 1614                                 ti_locked = TI_UNLOCKED;
 1615 
 1616                                 TCPSTAT_INC(tcps_predack);
 1617 
 1618                                 /*
 1619                                  * "bad retransmit" recovery.
 1620                                  */
 1621                                 if (tp->t_rxtshift == 1 &&
 1622                                     tp->t_flags & TF_PREVVALID &&
 1623                                     (int)(ticks - tp->t_badrxtwin) < 0) {
 1624                                         cc_cong_signal(tp, th, CC_RTO_ERR);
 1625                                 }
 1626 
 1627                                 /*
 1628                                  * Recalculate the transmit timer / rtt.
 1629                                  *
 1630                                  * Some boxes send broken timestamp replies
 1631                                  * during the SYN+ACK phase, ignore
 1632                                  * timestamps of 0 or we could calculate a
 1633                                  * huge RTT and blow up the retransmit timer.
 1634                                  */
 1635                                 if ((to.to_flags & TOF_TS) != 0 &&
 1636                                     to.to_tsecr) {
 1637                                         if (!tp->t_rttlow ||
 1638                                             tp->t_rttlow > ticks - to.to_tsecr)
 1639                                                 tp->t_rttlow = ticks - to.to_tsecr;
 1640                                         tcp_xmit_timer(tp,
 1641                                             ticks - to.to_tsecr + 1);
 1642                                 } else if (tp->t_rtttime &&
 1643                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
 1644                                         if (!tp->t_rttlow ||
 1645                                             tp->t_rttlow > ticks - tp->t_rtttime)
 1646                                                 tp->t_rttlow = ticks - tp->t_rtttime;
 1647                                         tcp_xmit_timer(tp,
 1648                                                         ticks - tp->t_rtttime);
 1649                                 }
 1650                                 acked = BYTES_THIS_ACK(tp, th);
 1651 
 1652                                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 1653                                 hhook_run_tcp_est_in(tp, th, &to);
 1654 
 1655                                 TCPSTAT_INC(tcps_rcvackpack);
 1656                                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 1657                                 sbdrop(&so->so_snd, acked);
 1658                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
 1659                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 1660                                         tp->snd_recover = th->th_ack - 1;
 1661                                 
 1662                                 /*
 1663                                  * Let the congestion control algorithm update
 1664                                  * congestion control related information. This
 1665                                  * typically means increasing the congestion
 1666                                  * window.
 1667                                  */
 1668                                 cc_ack_received(tp, th, CC_ACK);
 1669 
 1670                                 tp->snd_una = th->th_ack;
 1671                                 /*
 1672                                  * Pull snd_wl2 up to prevent seq wrap relative
 1673                                  * to th_ack.
 1674                                  */
 1675                                 tp->snd_wl2 = th->th_ack;
 1676                                 tp->t_dupacks = 0;
 1677                                 m_freem(m);
 1678                                 ND6_HINT(tp); /* Some progress has been made. */
 1679 
 1680                                 /*
 1681                                  * If all outstanding data are acked, stop
 1682                                  * retransmit timer, otherwise restart timer
 1683                                  * using current (possibly backed-off) value.
 1684                                  * If process is waiting for space,
 1685                                  * wakeup/selwakeup/signal.  If data
 1686                                  * are ready to send, let tcp_output
 1687                                  * decide between more output or persist.
 1688                                  */
 1689 #ifdef TCPDEBUG
 1690                                 if (so->so_options & SO_DEBUG)
 1691                                         tcp_trace(TA_INPUT, ostate, tp,
 1692                                             (void *)tcp_saveipgen,
 1693                                             &tcp_savetcp, 0);
 1694 #endif
 1695                                 if (tp->snd_una == tp->snd_max)
 1696                                         tcp_timer_activate(tp, TT_REXMT, 0);
 1697                                 else if (!tcp_timer_active(tp, TT_PERSIST))
 1698                                         tcp_timer_activate(tp, TT_REXMT,
 1699                                                       tp->t_rxtcur);
 1700                                 sowwakeup(so);
 1701                                 if (so->so_snd.sb_cc)
 1702                                         (void) tcp_output(tp);
 1703                                 goto check_delack;
 1704                         }
 1705                 } else if (th->th_ack == tp->snd_una &&
 1706                     tlen <= sbspace(&so->so_rcv)) {
 1707                         int newsize = 0;        /* automatic sockbuf scaling */
 1708 
 1709                         /*
 1710                          * This is a pure, in-sequence data packet with
 1711                          * nothing on the reassembly queue and we have enough
 1712                          * buffer space to take it.
 1713                          */
 1714                         if (ti_locked == TI_WLOCKED)
 1715                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1716                         ti_locked = TI_UNLOCKED;
 1717 
 1718                         /* Clean receiver SACK report if present */
 1719                         if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
 1720                                 tcp_clean_sackreport(tp);
 1721                         TCPSTAT_INC(tcps_preddat);
 1722                         tp->rcv_nxt += tlen;
 1723                         /*
 1724                          * Pull snd_wl1 up to prevent seq wrap relative to
 1725                          * th_seq.
 1726                          */
 1727                         tp->snd_wl1 = th->th_seq;
 1728                         /*
 1729                          * Pull rcv_up up to prevent seq wrap relative to
 1730                          * rcv_nxt.
 1731                          */
 1732                         tp->rcv_up = tp->rcv_nxt;
 1733                         TCPSTAT_INC(tcps_rcvpack);
 1734                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 1735                         ND6_HINT(tp);   /* Some progress has been made */
 1736 #ifdef TCPDEBUG
 1737                         if (so->so_options & SO_DEBUG)
 1738                                 tcp_trace(TA_INPUT, ostate, tp,
 1739                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1740 #endif
 1741                 /*
 1742                  * Automatic sizing of receive socket buffer.  Often the send
 1743                  * buffer size is not optimally adjusted to the actual network
 1744                  * conditions at hand (delay bandwidth product).  Setting the
 1745                  * buffer size too small limits throughput on links with high
 1746                  * bandwidth and high delay (eg. trans-continental/oceanic links).
 1747                  *
 1748                  * On the receive side the socket buffer memory is only rarely
 1749                  * used to any significant extent.  This allows us to be much
 1750                  * more aggressive in scaling the receive socket buffer.  For
 1751                  * the case that the buffer space is actually used to a large
 1752                  * extent and we run out of kernel memory we can simply drop
 1753                  * the new segments; TCP on the sender will just retransmit it
 1754                  * later.  Setting the buffer size too big may only consume too
 1755                  * much kernel memory if the application doesn't read() from
 1756                  * the socket or packet loss or reordering makes use of the
 1757                  * reassembly queue.
 1758                  *
 1759                  * The criteria to step up the receive buffer one notch are:
 1760                  *  1. the number of bytes received during the time it takes
 1761                  *     one timestamp to be reflected back to us (the RTT);
 1762                  *  2. received bytes per RTT is within seven eighth of the
 1763                  *     current socket buffer size;
 1764                  *  3. receive buffer size has not hit maximal automatic size;
 1765                  *
 1766                  * This algorithm does one step per RTT at most and only if
 1767                  * we receive a bulk stream w/o packet losses or reorderings.
 1768                  * Shrinking the buffer during idle times is not necessary as
 1769                  * it doesn't consume any memory when idle.
 1770                  *
 1771                  * TODO: Only step up if the application is actually serving
 1772                  * the buffer to better manage the socket buffer resources.
 1773                  */
 1774                         if (V_tcp_do_autorcvbuf &&
 1775                             to.to_tsecr &&
 1776                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
 1777                                 if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
 1778                                     to.to_tsecr - tp->rfbuf_ts < hz) {
 1779                                         if (tp->rfbuf_cnt >
 1780                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
 1781                                             so->so_rcv.sb_hiwat <
 1782                                             V_tcp_autorcvbuf_max) {
 1783                                                 newsize =
 1784                                                     min(so->so_rcv.sb_hiwat +
 1785                                                     V_tcp_autorcvbuf_inc,
 1786                                                     V_tcp_autorcvbuf_max);
 1787                                         }
 1788                                         /* Start over with next RTT. */
 1789                                         tp->rfbuf_ts = 0;
 1790                                         tp->rfbuf_cnt = 0;
 1791                                 } else
 1792                                         tp->rfbuf_cnt += tlen;  /* add up */
 1793                         }
 1794 
 1795                         /* Add data to socket buffer. */
 1796                         SOCKBUF_LOCK(&so->so_rcv);
 1797                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 1798                                 m_freem(m);
 1799                         } else {
 1800                                 /*
 1801                                  * Set new socket buffer size.
 1802                                  * Give up when limit is reached.
 1803                                  */
 1804                                 if (newsize)
 1805                                         if (!sbreserve_locked(&so->so_rcv,
 1806                                             newsize, so, NULL))
 1807                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
 1808                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 1809                                 sbappendstream_locked(&so->so_rcv, m);
 1810                         }
 1811                         /* NB: sorwakeup_locked() does an implicit unlock. */
 1812                         sorwakeup_locked(so);
 1813                         if (DELAY_ACK(tp)) {
 1814                                 tp->t_flags |= TF_DELACK;
 1815                         } else {
 1816                                 tp->t_flags |= TF_ACKNOW;
 1817                                 tcp_output(tp);
 1818                         }
 1819                         goto check_delack;
 1820                 }
 1821         }
 1822 
 1823         /*
 1824          * Calculate amount of space in receive window,
 1825          * and then do TCP input processing.
 1826          * Receive window is amount of space in rcv queue,
 1827          * but not less than advertised window.
 1828          */
 1829         win = sbspace(&so->so_rcv);
 1830         if (win < 0)
 1831                 win = 0;
 1832         KASSERT(SEQ_GEQ(tp->rcv_adv, tp->rcv_nxt),
 1833             ("tcp_input negative window: tp %p rcv_nxt %u rcv_adv %u", tp,
 1834             tp->rcv_nxt, tp->rcv_adv));
 1835         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 1836 
 1837         /* Reset receive buffer auto scaling when not in bulk receive mode. */
 1838         tp->rfbuf_ts = 0;
 1839         tp->rfbuf_cnt = 0;
 1840 
 1841         switch (tp->t_state) {
 1842 
 1843         /*
 1844          * If the state is SYN_RECEIVED:
 1845          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
 1846          */
 1847         case TCPS_SYN_RECEIVED:
 1848                 if ((thflags & TH_ACK) &&
 1849                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
 1850                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1851                                 rstreason = BANDLIM_RST_OPENPORT;
 1852                                 goto dropwithreset;
 1853                 }
 1854                 break;
 1855 
 1856         /*
 1857          * If the state is SYN_SENT:
 1858          *      if seg contains an ACK, but not for our SYN, drop the input.
 1859          *      if seg contains a RST, then drop the connection.
 1860          *      if seg does not contain SYN, then drop it.
 1861          * Otherwise this is an acceptable SYN segment
 1862          *      initialize tp->rcv_nxt and tp->irs
 1863          *      if seg contains ack then advance tp->snd_una
 1864          *      if seg contains an ECE and ECN support is enabled, the stream
 1865          *          is ECN capable.
 1866          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
 1867          *      arrange for segment to be acked (eventually)
 1868          *      continue processing rest of data/controls, beginning with URG
 1869          */
 1870         case TCPS_SYN_SENT:
 1871                 if ((thflags & TH_ACK) &&
 1872                     (SEQ_LEQ(th->th_ack, tp->iss) ||
 1873                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1874                         rstreason = BANDLIM_UNLIMITED;
 1875                         goto dropwithreset;
 1876                 }
 1877                 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST))
 1878                         tp = tcp_drop(tp, ECONNREFUSED);
 1879                 if (thflags & TH_RST)
 1880                         goto drop;
 1881                 if (!(thflags & TH_SYN))
 1882                         goto drop;
 1883 
 1884                 tp->irs = th->th_seq;
 1885                 tcp_rcvseqinit(tp);
 1886                 if (thflags & TH_ACK) {
 1887                         TCPSTAT_INC(tcps_connects);
 1888                         soisconnected(so);
 1889 #ifdef MAC
 1890                         mac_socketpeer_set_from_mbuf(m, so);
 1891 #endif
 1892                         /* Do window scaling on this connection? */
 1893                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 1894                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 1895                                 tp->rcv_scale = tp->request_r_scale;
 1896                         }
 1897                         tp->rcv_adv += imin(tp->rcv_wnd,
 1898                             TCP_MAXWIN << tp->rcv_scale);
 1899                         tp->snd_una++;          /* SYN is acked */
 1900                         /*
 1901                          * If there's data, delay ACK; if there's also a FIN
 1902                          * ACKNOW will be turned on later.
 1903                          */
 1904                         if (DELAY_ACK(tp) && tlen != 0)
 1905                                 tcp_timer_activate(tp, TT_DELACK,
 1906                                     tcp_delacktime);
 1907                         else
 1908                                 tp->t_flags |= TF_ACKNOW;
 1909 
 1910                         if ((thflags & TH_ECE) && V_tcp_do_ecn) {
 1911                                 tp->t_flags |= TF_ECN_PERMIT;
 1912                                 TCPSTAT_INC(tcps_ecn_shs);
 1913                         }
 1914                         
 1915                         /*
 1916                          * Received <SYN,ACK> in SYN_SENT[*] state.
 1917                          * Transitions:
 1918                          *      SYN_SENT  --> ESTABLISHED
 1919                          *      SYN_SENT* --> FIN_WAIT_1
 1920                          */
 1921                         tp->t_starttime = ticks;
 1922                         if (tp->t_flags & TF_NEEDFIN) {
 1923                                 tp->t_state = TCPS_FIN_WAIT_1;
 1924                                 tp->t_flags &= ~TF_NEEDFIN;
 1925                                 thflags &= ~TH_SYN;
 1926                         } else {
 1927                                 tp->t_state = TCPS_ESTABLISHED;
 1928                                 cc_conn_init(tp);
 1929                                 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
 1930                         }
 1931                 } else {
 1932                         /*
 1933                          * Received initial SYN in SYN-SENT[*] state =>
 1934                          * simultaneous open.  If segment contains CC option
 1935                          * and there is a cached CC, apply TAO test.
 1936                          * If it succeeds, connection is * half-synchronized.
 1937                          * Otherwise, do 3-way handshake:
 1938                          *        SYN-SENT -> SYN-RECEIVED
 1939                          *        SYN-SENT* -> SYN-RECEIVED*
 1940                          * If there was no CC option, clear cached CC value.
 1941                          */
 1942                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 1943                         tcp_timer_activate(tp, TT_REXMT, 0);
 1944                         tp->t_state = TCPS_SYN_RECEIVED;
 1945                 }
 1946 
 1947                 KASSERT(ti_locked == TI_WLOCKED, ("%s: trimthenstep6: "
 1948                     "ti_locked %d", __func__, ti_locked));
 1949                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1950                 INP_WLOCK_ASSERT(tp->t_inpcb);
 1951 
 1952                 /*
 1953                  * Advance th->th_seq to correspond to first data byte.
 1954                  * If data, trim to stay within window,
 1955                  * dropping FIN if necessary.
 1956                  */
 1957                 th->th_seq++;
 1958                 if (tlen > tp->rcv_wnd) {
 1959                         todrop = tlen - tp->rcv_wnd;
 1960                         m_adj(m, -todrop);
 1961                         tlen = tp->rcv_wnd;
 1962                         thflags &= ~TH_FIN;
 1963                         TCPSTAT_INC(tcps_rcvpackafterwin);
 1964                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 1965                 }
 1966                 tp->snd_wl1 = th->th_seq - 1;
 1967                 tp->rcv_up = th->th_seq;
 1968                 /*
 1969                  * Client side of transaction: already sent SYN and data.
 1970                  * If the remote host used T/TCP to validate the SYN,
 1971                  * our data will be ACK'd; if so, enter normal data segment
 1972                  * processing in the middle of step 5, ack processing.
 1973                  * Otherwise, goto step 6.
 1974                  */
 1975                 if (thflags & TH_ACK)
 1976                         goto process_ACK;
 1977 
 1978                 goto step6;
 1979 
 1980         /*
 1981          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
 1982          *      do normal processing.
 1983          *
 1984          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
 1985          */
 1986         case TCPS_LAST_ACK:
 1987         case TCPS_CLOSING:
 1988                 break;  /* continue normal processing */
 1989         }
 1990 
 1991         /*
 1992          * States other than LISTEN or SYN_SENT.
 1993          * First check the RST flag and sequence number since reset segments
 1994          * are exempt from the timestamp and connection count tests.  This
 1995          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
 1996          * below which allowed reset segments in half the sequence space
 1997          * to fall though and be processed (which gives forged reset
 1998          * segments with a random sequence number a 50 percent chance of
 1999          * killing a connection).
 2000          * Then check timestamp, if present.
 2001          * Then check the connection count, if present.
 2002          * Then check that at least some bytes of segment are within
 2003          * receive window.  If segment begins before rcv_nxt,
 2004          * drop leading data (and SYN); if nothing left, just ack.
 2005          *
 2006          *
 2007          * If the RST bit is set, check the sequence number to see
 2008          * if this is a valid reset segment.
 2009          * RFC 793 page 37:
 2010          *   In all states except SYN-SENT, all reset (RST) segments
 2011          *   are validated by checking their SEQ-fields.  A reset is
 2012          *   valid if its sequence number is in the window.
 2013          * Note: this does not take into account delayed ACKs, so
 2014          *   we should test against last_ack_sent instead of rcv_nxt.
 2015          *   The sequence number in the reset segment is normally an
 2016          *   echo of our outgoing acknowlegement numbers, but some hosts
 2017          *   send a reset with the sequence number at the rightmost edge
 2018          *   of our receive window, and we have to handle this case.
 2019          * Note 2: Paul Watson's paper "Slipping in the Window" has shown
 2020          *   that brute force RST attacks are possible.  To combat this,
 2021          *   we use a much stricter check while in the ESTABLISHED state,
 2022          *   only accepting RSTs where the sequence number is equal to
 2023          *   last_ack_sent.  In all other states (the states in which a
 2024          *   RST is more likely), the more permissive check is used.
 2025          * If we have multiple segments in flight, the initial reset
 2026          * segment sequence numbers will be to the left of last_ack_sent,
 2027          * but they will eventually catch up.
 2028          * In any case, it never made sense to trim reset segments to
 2029          * fit the receive window since RFC 1122 says:
 2030          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
 2031          *
 2032          *    A TCP SHOULD allow a received RST segment to include data.
 2033          *
 2034          *    DISCUSSION
 2035          *         It has been suggested that a RST segment could contain
 2036          *         ASCII text that encoded and explained the cause of the
 2037          *         RST.  No standard has yet been established for such
 2038          *         data.
 2039          *
 2040          * If the reset segment passes the sequence number test examine
 2041          * the state:
 2042          *    SYN_RECEIVED STATE:
 2043          *      If passive open, return to LISTEN state.
 2044          *      If active open, inform user that connection was refused.
 2045          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
 2046          *      Inform user that connection was reset, and close tcb.
 2047          *    CLOSING, LAST_ACK STATES:
 2048          *      Close the tcb.
 2049          *    TIME_WAIT STATE:
 2050          *      Drop the segment - see Stevens, vol. 2, p. 964 and
 2051          *      RFC 1337.
 2052          */
 2053         if (thflags & TH_RST) {
 2054                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
 2055                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
 2056                         switch (tp->t_state) {
 2057 
 2058                         case TCPS_SYN_RECEIVED:
 2059                                 so->so_error = ECONNREFUSED;
 2060                                 goto close;
 2061 
 2062                         case TCPS_ESTABLISHED:
 2063                                 if (V_tcp_insecure_rst == 0 &&
 2064                                     !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
 2065                                     SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
 2066                                     !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
 2067                                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
 2068                                         TCPSTAT_INC(tcps_badrst);
 2069                                         goto drop;
 2070                                 }
 2071                                 /* FALLTHROUGH */
 2072                         case TCPS_FIN_WAIT_1:
 2073                         case TCPS_FIN_WAIT_2:
 2074                         case TCPS_CLOSE_WAIT:
 2075                                 so->so_error = ECONNRESET;
 2076                         close:
 2077                                 KASSERT(ti_locked == TI_WLOCKED,
 2078                                     ("tcp_do_segment: TH_RST 1 ti_locked %d",
 2079                                     ti_locked));
 2080                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2081 
 2082                                 tp->t_state = TCPS_CLOSED;
 2083                                 TCPSTAT_INC(tcps_drops);
 2084                                 tp = tcp_close(tp);
 2085                                 break;
 2086 
 2087                         case TCPS_CLOSING:
 2088                         case TCPS_LAST_ACK:
 2089                                 KASSERT(ti_locked == TI_WLOCKED,
 2090                                     ("tcp_do_segment: TH_RST 2 ti_locked %d",
 2091                                     ti_locked));
 2092                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2093 
 2094                                 tp = tcp_close(tp);
 2095                                 break;
 2096                         }
 2097                 }
 2098                 goto drop;
 2099         }
 2100 
 2101         /*
 2102          * RFC 1323 PAWS: If we have a timestamp reply on this segment
 2103          * and it's less than ts_recent, drop it.
 2104          */
 2105         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
 2106             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
 2107 
 2108                 /* Check to see if ts_recent is over 24 days old.  */
 2109                 if (ticks - tp->ts_recent_age > TCP_PAWS_IDLE) {
 2110                         /*
 2111                          * Invalidate ts_recent.  If this segment updates
 2112                          * ts_recent, the age will be reset later and ts_recent
 2113                          * will get a valid value.  If it does not, setting
 2114                          * ts_recent to zero will at least satisfy the
 2115                          * requirement that zero be placed in the timestamp
 2116                          * echo reply when ts_recent isn't valid.  The
 2117                          * age isn't reset until we get a valid ts_recent
 2118                          * because we don't want out-of-order segments to be
 2119                          * dropped when ts_recent is old.
 2120                          */
 2121                         tp->ts_recent = 0;
 2122                 } else {
 2123                         TCPSTAT_INC(tcps_rcvduppack);
 2124                         TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
 2125                         TCPSTAT_INC(tcps_pawsdrop);
 2126                         if (tlen)
 2127                                 goto dropafterack;
 2128                         goto drop;
 2129                 }
 2130         }
 2131 
 2132         /*
 2133          * In the SYN-RECEIVED state, validate that the packet belongs to
 2134          * this connection before trimming the data to fit the receive
 2135          * window.  Check the sequence number versus IRS since we know
 2136          * the sequence numbers haven't wrapped.  This is a partial fix
 2137          * for the "LAND" DoS attack.
 2138          */
 2139         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
 2140                 rstreason = BANDLIM_RST_OPENPORT;
 2141                 goto dropwithreset;
 2142         }
 2143 
 2144         todrop = tp->rcv_nxt - th->th_seq;
 2145         if (todrop > 0) {
 2146                 /*
 2147                  * If this is a duplicate SYN for our current connection,
 2148                  * advance over it and pretend and it's not a SYN.
 2149                  */
 2150                 if (thflags & TH_SYN && th->th_seq == tp->irs) {
 2151                         thflags &= ~TH_SYN;
 2152                         th->th_seq++;
 2153                         if (th->th_urp > 1)
 2154                                 th->th_urp--;
 2155                         else
 2156                                 thflags &= ~TH_URG;
 2157                         todrop--;
 2158                 }
 2159                 /*
 2160                  * Following if statement from Stevens, vol. 2, p. 960.
 2161                  */
 2162                 if (todrop > tlen
 2163                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
 2164                         /*
 2165                          * Any valid FIN must be to the left of the window.
 2166                          * At this point the FIN must be a duplicate or out
 2167                          * of sequence; drop it.
 2168                          */
 2169                         thflags &= ~TH_FIN;
 2170 
 2171                         /*
 2172                          * Send an ACK to resynchronize and drop any data.
 2173                          * But keep on processing for RST or ACK.
 2174                          */
 2175                         tp->t_flags |= TF_ACKNOW;
 2176                         todrop = tlen;
 2177                         TCPSTAT_INC(tcps_rcvduppack);
 2178                         TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
 2179                 } else {
 2180                         TCPSTAT_INC(tcps_rcvpartduppack);
 2181                         TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
 2182                 }
 2183                 drop_hdrlen += todrop;  /* drop from the top afterwards */
 2184                 th->th_seq += todrop;
 2185                 tlen -= todrop;
 2186                 if (th->th_urp > todrop)
 2187                         th->th_urp -= todrop;
 2188                 else {
 2189                         thflags &= ~TH_URG;
 2190                         th->th_urp = 0;
 2191                 }
 2192         }
 2193 
 2194         /*
 2195          * If new data are received on a connection after the
 2196          * user processes are gone, then RST the other end.
 2197          */
 2198         if ((so->so_state & SS_NOFDREF) &&
 2199             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
 2200                 char *s;
 2201 
 2202                 KASSERT(ti_locked == TI_WLOCKED, ("%s: SS_NOFDEREF && "
 2203                     "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
 2204                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2205 
 2206                 if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
 2207                         log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data after socket "
 2208                             "was closed, sending RST and removing tcpcb\n",
 2209                             s, __func__, tcpstates[tp->t_state], tlen);
 2210                         free(s, M_TCPLOG);
 2211                 }
 2212                 tp = tcp_close(tp);
 2213                 TCPSTAT_INC(tcps_rcvafterclose);
 2214                 rstreason = BANDLIM_UNLIMITED;
 2215                 goto dropwithreset;
 2216         }
 2217 
 2218         /*
 2219          * If segment ends after window, drop trailing data
 2220          * (and PUSH and FIN); if nothing left, just ACK.
 2221          */
 2222         todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
 2223         if (todrop > 0) {
 2224                 TCPSTAT_INC(tcps_rcvpackafterwin);
 2225                 if (todrop >= tlen) {
 2226                         TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
 2227                         /*
 2228                          * If window is closed can only take segments at
 2229                          * window edge, and have to drop data and PUSH from
 2230                          * incoming segments.  Continue processing, but
 2231                          * remember to ack.  Otherwise, drop segment
 2232                          * and ack.
 2233                          */
 2234                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
 2235                                 tp->t_flags |= TF_ACKNOW;
 2236                                 TCPSTAT_INC(tcps_rcvwinprobe);
 2237                         } else
 2238                                 goto dropafterack;
 2239                 } else
 2240                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2241                 m_adj(m, -todrop);
 2242                 tlen -= todrop;
 2243                 thflags &= ~(TH_PUSH|TH_FIN);
 2244         }
 2245 
 2246         /*
 2247          * If last ACK falls within this segment's sequence numbers,
 2248          * record its timestamp.
 2249          * NOTE: 
 2250          * 1) That the test incorporates suggestions from the latest
 2251          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
 2252          * 2) That updating only on newer timestamps interferes with
 2253          *    our earlier PAWS tests, so this check should be solely
 2254          *    predicated on the sequence space of this segment.
 2255          * 3) That we modify the segment boundary check to be 
 2256          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len  
 2257          *    instead of RFC1323's
 2258          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
 2259          *    This modified check allows us to overcome RFC1323's
 2260          *    limitations as described in Stevens TCP/IP Illustrated
 2261          *    Vol. 2 p.869. In such cases, we can still calculate the
 2262          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
 2263          */
 2264         if ((to.to_flags & TOF_TS) != 0 &&
 2265             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
 2266             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
 2267                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
 2268                 tp->ts_recent_age = ticks;
 2269                 tp->ts_recent = to.to_tsval;
 2270         }
 2271 
 2272         /*
 2273          * If a SYN is in the window, then this is an
 2274          * error and we send an RST and drop the connection.
 2275          */
 2276         if (thflags & TH_SYN) {
 2277                 KASSERT(ti_locked == TI_WLOCKED,
 2278                     ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
 2279                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2280 
 2281                 tp = tcp_drop(tp, ECONNRESET);
 2282                 rstreason = BANDLIM_UNLIMITED;
 2283                 goto drop;
 2284         }
 2285 
 2286         /*
 2287          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
 2288          * flag is on (half-synchronized state), then queue data for
 2289          * later processing; else drop segment and return.
 2290          */
 2291         if ((thflags & TH_ACK) == 0) {
 2292                 if (tp->t_state == TCPS_SYN_RECEIVED ||
 2293                     (tp->t_flags & TF_NEEDSYN))
 2294                         goto step6;
 2295                 else if (tp->t_flags & TF_ACKNOW)
 2296                         goto dropafterack;
 2297                 else
 2298                         goto drop;
 2299         }
 2300 
 2301         /*
 2302          * Ack processing.
 2303          */
 2304         switch (tp->t_state) {
 2305 
 2306         /*
 2307          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
 2308          * ESTABLISHED state and continue processing.
 2309          * The ACK was checked above.
 2310          */
 2311         case TCPS_SYN_RECEIVED:
 2312 
 2313                 TCPSTAT_INC(tcps_connects);
 2314                 soisconnected(so);
 2315                 /* Do window scaling? */
 2316                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2317                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2318                         tp->rcv_scale = tp->request_r_scale;
 2319                         tp->snd_wnd = tiwin;
 2320                 }
 2321                 /*
 2322                  * Make transitions:
 2323                  *      SYN-RECEIVED  -> ESTABLISHED
 2324                  *      SYN-RECEIVED* -> FIN-WAIT-1
 2325                  */
 2326                 tp->t_starttime = ticks;
 2327                 if (tp->t_flags & TF_NEEDFIN) {
 2328                         tp->t_state = TCPS_FIN_WAIT_1;
 2329                         tp->t_flags &= ~TF_NEEDFIN;
 2330                 } else {
 2331                         tp->t_state = TCPS_ESTABLISHED;
 2332                         cc_conn_init(tp);
 2333                         tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
 2334                 }
 2335                 /*
 2336                  * If segment contains data or ACK, will call tcp_reass()
 2337                  * later; if not, do so now to pass queued data to user.
 2338                  */
 2339                 if (tlen == 0 && (thflags & TH_FIN) == 0)
 2340                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
 2341                             (struct mbuf *)0);
 2342                 tp->snd_wl1 = th->th_seq - 1;
 2343                 /* FALLTHROUGH */
 2344 
 2345         /*
 2346          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
 2347          * ACKs.  If the ack is in the range
 2348          *      tp->snd_una < th->th_ack <= tp->snd_max
 2349          * then advance tp->snd_una to th->th_ack and drop
 2350          * data from the retransmission queue.  If this ACK reflects
 2351          * more up to date window information we update our window information.
 2352          */
 2353         case TCPS_ESTABLISHED:
 2354         case TCPS_FIN_WAIT_1:
 2355         case TCPS_FIN_WAIT_2:
 2356         case TCPS_CLOSE_WAIT:
 2357         case TCPS_CLOSING:
 2358         case TCPS_LAST_ACK:
 2359                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
 2360                         TCPSTAT_INC(tcps_rcvacktoomuch);
 2361                         goto dropafterack;
 2362                 }
 2363                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 2364                     ((to.to_flags & TOF_SACK) ||
 2365                      !TAILQ_EMPTY(&tp->snd_holes)))
 2366                         tcp_sack_doack(tp, &to, th->th_ack);
 2367 
 2368                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 2369                 hhook_run_tcp_est_in(tp, th, &to);
 2370 
 2371                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
 2372                         if (tlen == 0 && tiwin == tp->snd_wnd) {
 2373                                 TCPSTAT_INC(tcps_rcvdupack);
 2374                                 /*
 2375                                  * If we have outstanding data (other than
 2376                                  * a window probe), this is a completely
 2377                                  * duplicate ack (ie, window info didn't
 2378                                  * change), the ack is the biggest we've
 2379                                  * seen and we've seen exactly our rexmt
 2380                                  * threshhold of them, assume a packet
 2381                                  * has been dropped and retransmit it.
 2382                                  * Kludge snd_nxt & the congestion
 2383                                  * window so we send only this one
 2384                                  * packet.
 2385                                  *
 2386                                  * We know we're losing at the current
 2387                                  * window size so do congestion avoidance
 2388                                  * (set ssthresh to half the current window
 2389                                  * and pull our congestion window back to
 2390                                  * the new ssthresh).
 2391                                  *
 2392                                  * Dup acks mean that packets have left the
 2393                                  * network (they're now cached at the receiver)
 2394                                  * so bump cwnd by the amount in the receiver
 2395                                  * to keep a constant cwnd packets in the
 2396                                  * network.
 2397                                  *
 2398                                  * When using TCP ECN, notify the peer that
 2399                                  * we reduced the cwnd.
 2400                                  */
 2401                                 if (!tcp_timer_active(tp, TT_REXMT) ||
 2402                                     th->th_ack != tp->snd_una)
 2403                                         tp->t_dupacks = 0;
 2404                                 else if (++tp->t_dupacks > tcprexmtthresh ||
 2405                                      IN_FASTRECOVERY(tp->t_flags)) {
 2406                                         cc_ack_received(tp, th, CC_DUPACK);
 2407                                         if ((tp->t_flags & TF_SACK_PERMIT) &&
 2408                                             IN_FASTRECOVERY(tp->t_flags)) {
 2409                                                 int awnd;
 2410                                                 
 2411                                                 /*
 2412                                                  * Compute the amount of data in flight first.
 2413                                                  * We can inject new data into the pipe iff 
 2414                                                  * we have less than 1/2 the original window's
 2415                                                  * worth of data in flight.
 2416                                                  */
 2417                                                 awnd = (tp->snd_nxt - tp->snd_fack) +
 2418                                                         tp->sackhint.sack_bytes_rexmit;
 2419                                                 if (awnd < tp->snd_ssthresh) {
 2420                                                         tp->snd_cwnd += tp->t_maxseg;
 2421                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
 2422                                                                 tp->snd_cwnd = tp->snd_ssthresh;
 2423                                                 }
 2424                                         } else
 2425                                                 tp->snd_cwnd += tp->t_maxseg;
 2426                                         (void) tcp_output(tp);
 2427                                         goto drop;
 2428                                 } else if (tp->t_dupacks == tcprexmtthresh) {
 2429                                         tcp_seq onxt = tp->snd_nxt;
 2430 
 2431                                         /*
 2432                                          * If we're doing sack, check to
 2433                                          * see if we're already in sack
 2434                                          * recovery. If we're not doing sack,
 2435                                          * check to see if we're in newreno
 2436                                          * recovery.
 2437                                          */
 2438                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2439                                                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2440                                                         tp->t_dupacks = 0;
 2441                                                         break;
 2442                                                 }
 2443                                         } else {
 2444                                                 if (SEQ_LEQ(th->th_ack,
 2445                                                     tp->snd_recover)) {
 2446                                                         tp->t_dupacks = 0;
 2447                                                         break;
 2448                                                 }
 2449                                         }
 2450                                         /* Congestion signal before ack. */
 2451                                         cc_cong_signal(tp, th, CC_NDUPACK);
 2452                                         cc_ack_received(tp, th, CC_DUPACK);
 2453                                         tcp_timer_activate(tp, TT_REXMT, 0);
 2454                                         tp->t_rtttime = 0;
 2455                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2456                                                 TCPSTAT_INC(
 2457                                                     tcps_sack_recovery_episode);
 2458                                                 tp->sack_newdata = tp->snd_nxt;
 2459                                                 tp->snd_cwnd = tp->t_maxseg;
 2460                                                 (void) tcp_output(tp);
 2461                                                 goto drop;
 2462                                         }
 2463                                         tp->snd_nxt = th->th_ack;
 2464                                         tp->snd_cwnd = tp->t_maxseg;
 2465                                         (void) tcp_output(tp);
 2466                                         KASSERT(tp->snd_limited <= 2,
 2467                                             ("%s: tp->snd_limited too big",
 2468                                             __func__));
 2469                                         tp->snd_cwnd = tp->snd_ssthresh +
 2470                                              tp->t_maxseg *
 2471                                              (tp->t_dupacks - tp->snd_limited);
 2472                                         if (SEQ_GT(onxt, tp->snd_nxt))
 2473                                                 tp->snd_nxt = onxt;
 2474                                         goto drop;
 2475                                 } else if (V_tcp_do_rfc3042) {
 2476                                         cc_ack_received(tp, th, CC_DUPACK);
 2477                                         u_long oldcwnd = tp->snd_cwnd;
 2478                                         tcp_seq oldsndmax = tp->snd_max;
 2479                                         u_int sent;
 2480 
 2481                                         KASSERT(tp->t_dupacks == 1 ||
 2482                                             tp->t_dupacks == 2,
 2483                                             ("%s: dupacks not 1 or 2",
 2484                                             __func__));
 2485                                         if (tp->t_dupacks == 1)
 2486                                                 tp->snd_limited = 0;
 2487                                         tp->snd_cwnd =
 2488                                             (tp->snd_nxt - tp->snd_una) +
 2489                                             (tp->t_dupacks - tp->snd_limited) *
 2490                                             tp->t_maxseg;
 2491                                         (void) tcp_output(tp);
 2492                                         sent = tp->snd_max - oldsndmax;
 2493                                         if (sent > tp->t_maxseg) {
 2494                                                 KASSERT((tp->t_dupacks == 2 &&
 2495                                                     tp->snd_limited == 0) ||
 2496                                                    (sent == tp->t_maxseg + 1 &&
 2497                                                     tp->t_flags & TF_SENTFIN),
 2498                                                     ("%s: sent too much",
 2499                                                     __func__));
 2500                                                 tp->snd_limited = 2;
 2501                                         } else if (sent > 0)
 2502                                                 ++tp->snd_limited;
 2503                                         tp->snd_cwnd = oldcwnd;
 2504                                         goto drop;
 2505                                 }
 2506                         } else
 2507                                 tp->t_dupacks = 0;
 2508                         break;
 2509                 }
 2510 
 2511                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
 2512                     ("%s: th_ack <= snd_una", __func__));
 2513 
 2514                 /*
 2515                  * If the congestion window was inflated to account
 2516                  * for the other side's cached packets, retract it.
 2517                  */
 2518                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2519                         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
 2520                                 if (tp->t_flags & TF_SACK_PERMIT)
 2521                                         tcp_sack_partialack(tp, th);
 2522                                 else
 2523                                         tcp_newreno_partial_ack(tp, th);
 2524                         } else
 2525                                 cc_post_recovery(tp, th);
 2526                 }
 2527                 tp->t_dupacks = 0;
 2528                 /*
 2529                  * If we reach this point, ACK is not a duplicate,
 2530                  *     i.e., it ACKs something we sent.
 2531                  */
 2532                 if (tp->t_flags & TF_NEEDSYN) {
 2533                         /*
 2534                          * T/TCP: Connection was half-synchronized, and our
 2535                          * SYN has been ACK'd (so connection is now fully
 2536                          * synchronized).  Go to non-starred state,
 2537                          * increment snd_una for ACK of SYN, and check if
 2538                          * we can do window scaling.
 2539                          */
 2540                         tp->t_flags &= ~TF_NEEDSYN;
 2541                         tp->snd_una++;
 2542                         /* Do window scaling? */
 2543                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2544                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2545                                 tp->rcv_scale = tp->request_r_scale;
 2546                                 /* Send window already scaled. */
 2547                         }
 2548                 }
 2549 
 2550 process_ACK:
 2551                 INP_WLOCK_ASSERT(tp->t_inpcb);
 2552 
 2553                 acked = BYTES_THIS_ACK(tp, th);
 2554                 TCPSTAT_INC(tcps_rcvackpack);
 2555                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 2556 
 2557                 /*
 2558                  * If we just performed our first retransmit, and the ACK
 2559                  * arrives within our recovery window, then it was a mistake
 2560                  * to do the retransmit in the first place.  Recover our
 2561                  * original cwnd and ssthresh, and proceed to transmit where
 2562                  * we left off.
 2563                  */
 2564                 if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
 2565                     (int)(ticks - tp->t_badrxtwin) < 0)
 2566                         cc_cong_signal(tp, th, CC_RTO_ERR);
 2567 
 2568                 /*
 2569                  * If we have a timestamp reply, update smoothed
 2570                  * round trip time.  If no timestamp is present but
 2571                  * transmit timer is running and timed sequence
 2572                  * number was acked, update smoothed round trip time.
 2573                  * Since we now have an rtt measurement, cancel the
 2574                  * timer backoff (cf., Phil Karn's retransmit alg.).
 2575                  * Recompute the initial retransmit timer.
 2576                  *
 2577                  * Some boxes send broken timestamp replies
 2578                  * during the SYN+ACK phase, ignore
 2579                  * timestamps of 0 or we could calculate a
 2580                  * huge RTT and blow up the retransmit timer.
 2581                  */
 2582                 if ((to.to_flags & TOF_TS) != 0 &&
 2583                     to.to_tsecr) {
 2584                         if (!tp->t_rttlow || tp->t_rttlow > ticks - to.to_tsecr)
 2585                                 tp->t_rttlow = ticks - to.to_tsecr;
 2586                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
 2587                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
 2588                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
 2589                                 tp->t_rttlow = ticks - tp->t_rtttime;
 2590                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
 2591                 }
 2592 
 2593                 /*
 2594                  * If all outstanding data is acked, stop retransmit
 2595                  * timer and remember to restart (more output or persist).
 2596                  * If there is more data to be acked, restart retransmit
 2597                  * timer, using current (possibly backed-off) value.
 2598                  */
 2599                 if (th->th_ack == tp->snd_max) {
 2600                         tcp_timer_activate(tp, TT_REXMT, 0);
 2601                         needoutput = 1;
 2602                 } else if (!tcp_timer_active(tp, TT_PERSIST))
 2603                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 2604 
 2605                 /*
 2606                  * If no data (only SYN) was ACK'd,
 2607                  *    skip rest of ACK processing.
 2608                  */
 2609                 if (acked == 0)
 2610                         goto step6;
 2611 
 2612                 /*
 2613                  * Let the congestion control algorithm update congestion
 2614                  * control related information. This typically means increasing
 2615                  * the congestion window.
 2616                  */
 2617                 cc_ack_received(tp, th, CC_ACK);
 2618 
 2619                 SOCKBUF_LOCK(&so->so_snd);
 2620                 if (acked > so->so_snd.sb_cc) {
 2621                         tp->snd_wnd -= so->so_snd.sb_cc;
 2622                         sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
 2623                         ourfinisacked = 1;
 2624                 } else {
 2625                         sbdrop_locked(&so->so_snd, acked);
 2626                         tp->snd_wnd -= acked;
 2627                         ourfinisacked = 0;
 2628                 }
 2629                 /* NB: sowwakeup_locked() does an implicit unlock. */
 2630                 sowwakeup_locked(so);
 2631                 /* Detect una wraparound. */
 2632                 if (!IN_RECOVERY(tp->t_flags) &&
 2633                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
 2634                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 2635                         tp->snd_recover = th->th_ack - 1;
 2636                 /* XXXLAS: Can this be moved up into cc_post_recovery? */
 2637                 if (IN_RECOVERY(tp->t_flags) &&
 2638                     SEQ_GEQ(th->th_ack, tp->snd_recover)) {
 2639                         EXIT_RECOVERY(tp->t_flags);
 2640                 }
 2641                 tp->snd_una = th->th_ack;
 2642                 if (tp->t_flags & TF_SACK_PERMIT) {
 2643                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
 2644                                 tp->snd_recover = tp->snd_una;
 2645                 }
 2646                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 2647                         tp->snd_nxt = tp->snd_una;
 2648 
 2649                 switch (tp->t_state) {
 2650 
 2651                 /*
 2652                  * In FIN_WAIT_1 STATE in addition to the processing
 2653                  * for the ESTABLISHED state if our FIN is now acknowledged
 2654                  * then enter FIN_WAIT_2.
 2655                  */
 2656                 case TCPS_FIN_WAIT_1:
 2657                         if (ourfinisacked) {
 2658                                 /*
 2659                                  * If we can't receive any more
 2660                                  * data, then closing user can proceed.
 2661                                  * Starting the timer is contrary to the
 2662                                  * specification, but if we don't get a FIN
 2663                                  * we'll hang forever.
 2664                                  *
 2665                                  * XXXjl:
 2666                                  * we should release the tp also, and use a
 2667                                  * compressed state.
 2668                                  */
 2669                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 2670                                         int timeout;
 2671 
 2672                                         soisdisconnected(so);
 2673                                         timeout = (tcp_fast_finwait2_recycle) ? 
 2674                                                 tcp_finwait2_timeout : tcp_maxidle;
 2675                                         tcp_timer_activate(tp, TT_2MSL, timeout);
 2676                                 }
 2677                                 tp->t_state = TCPS_FIN_WAIT_2;
 2678                         }
 2679                         break;
 2680 
 2681                 /*
 2682                  * In CLOSING STATE in addition to the processing for
 2683                  * the ESTABLISHED state if the ACK acknowledges our FIN
 2684                  * then enter the TIME-WAIT state, otherwise ignore
 2685                  * the segment.
 2686                  */
 2687                 case TCPS_CLOSING:
 2688                         if (ourfinisacked) {
 2689                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2690                                 tcp_twstart(tp);
 2691                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 2692                                 m_freem(m);
 2693                                 return;
 2694                         }
 2695                         break;
 2696 
 2697                 /*
 2698                  * In LAST_ACK, we may still be waiting for data to drain
 2699                  * and/or to be acked, as well as for the ack of our FIN.
 2700                  * If our FIN is now acknowledged, delete the TCB,
 2701                  * enter the closed state and return.
 2702                  */
 2703                 case TCPS_LAST_ACK:
 2704                         if (ourfinisacked) {
 2705                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2706                                 tp = tcp_close(tp);
 2707                                 goto drop;
 2708                         }
 2709                         break;
 2710                 }
 2711         }
 2712 
 2713 step6:
 2714         INP_WLOCK_ASSERT(tp->t_inpcb);
 2715 
 2716         /*
 2717          * Update window information.
 2718          * Don't look at window if no ACK: TAC's send garbage on first SYN.
 2719          */
 2720         if ((thflags & TH_ACK) &&
 2721             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
 2722             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
 2723              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
 2724                 /* keep track of pure window updates */
 2725                 if (tlen == 0 &&
 2726                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
 2727                         TCPSTAT_INC(tcps_rcvwinupd);
 2728                 tp->snd_wnd = tiwin;
 2729                 tp->snd_wl1 = th->th_seq;
 2730                 tp->snd_wl2 = th->th_ack;
 2731                 if (tp->snd_wnd > tp->max_sndwnd)
 2732                         tp->max_sndwnd = tp->snd_wnd;
 2733                 needoutput = 1;
 2734         }
 2735 
 2736         /*
 2737          * Process segments with URG.
 2738          */
 2739         if ((thflags & TH_URG) && th->th_urp &&
 2740             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2741                 /*
 2742                  * This is a kludge, but if we receive and accept
 2743                  * random urgent pointers, we'll crash in
 2744                  * soreceive.  It's hard to imagine someone
 2745                  * actually wanting to send this much urgent data.
 2746                  */
 2747                 SOCKBUF_LOCK(&so->so_rcv);
 2748                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
 2749                         th->th_urp = 0;                 /* XXX */
 2750                         thflags &= ~TH_URG;             /* XXX */
 2751                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
 2752                         goto dodata;                    /* XXX */
 2753                 }
 2754                 /*
 2755                  * If this segment advances the known urgent pointer,
 2756                  * then mark the data stream.  This should not happen
 2757                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
 2758                  * a FIN has been received from the remote side.
 2759                  * In these states we ignore the URG.
 2760                  *
 2761                  * According to RFC961 (Assigned Protocols),
 2762                  * the urgent pointer points to the last octet
 2763                  * of urgent data.  We continue, however,
 2764                  * to consider it to indicate the first octet
 2765                  * of data past the urgent section as the original
 2766                  * spec states (in one of two places).
 2767                  */
 2768                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
 2769                         tp->rcv_up = th->th_seq + th->th_urp;
 2770                         so->so_oobmark = so->so_rcv.sb_cc +
 2771                             (tp->rcv_up - tp->rcv_nxt) - 1;
 2772                         if (so->so_oobmark == 0)
 2773                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
 2774                         sohasoutofband(so);
 2775                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
 2776                 }
 2777                 SOCKBUF_UNLOCK(&so->so_rcv);
 2778                 /*
 2779                  * Remove out of band data so doesn't get presented to user.
 2780                  * This can happen independent of advancing the URG pointer,
 2781                  * but if two URG's are pending at once, some out-of-band
 2782                  * data may creep in... ick.
 2783                  */
 2784                 if (th->th_urp <= (u_long)tlen &&
 2785                     !(so->so_options & SO_OOBINLINE)) {
 2786                         /* hdr drop is delayed */
 2787                         tcp_pulloutofband(so, th, m, drop_hdrlen);
 2788                 }
 2789         } else {
 2790                 /*
 2791                  * If no out of band data is expected,
 2792                  * pull receive urgent pointer along
 2793                  * with the receive window.
 2794                  */
 2795                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
 2796                         tp->rcv_up = tp->rcv_nxt;
 2797         }
 2798 dodata:                                                 /* XXX */
 2799         INP_WLOCK_ASSERT(tp->t_inpcb);
 2800 
 2801         /*
 2802          * Process the segment text, merging it into the TCP sequencing queue,
 2803          * and arranging for acknowledgment of receipt if necessary.
 2804          * This process logically involves adjusting tp->rcv_wnd as data
 2805          * is presented to the user (this happens in tcp_usrreq.c,
 2806          * case PRU_RCVD).  If a FIN has already been received on this
 2807          * connection then we just ignore the text.
 2808          */
 2809         if ((tlen || (thflags & TH_FIN)) &&
 2810             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2811                 tcp_seq save_start = th->th_seq;
 2812                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 2813                 /*
 2814                  * Insert segment which includes th into TCP reassembly queue
 2815                  * with control block tp.  Set thflags to whether reassembly now
 2816                  * includes a segment with FIN.  This handles the common case
 2817                  * inline (segment is the next to be received on an established
 2818                  * connection, and the queue is empty), avoiding linkage into
 2819                  * and removal from the queue and repetition of various
 2820                  * conversions.
 2821                  * Set DELACK for segments received in order, but ack
 2822                  * immediately when segments are out of order (so
 2823                  * fast retransmit can work).
 2824                  */
 2825                 if (th->th_seq == tp->rcv_nxt &&
 2826                     LIST_EMPTY(&tp->t_segq) &&
 2827                     TCPS_HAVEESTABLISHED(tp->t_state)) {
 2828                         if (DELAY_ACK(tp))
 2829                                 tp->t_flags |= TF_DELACK;
 2830                         else
 2831                                 tp->t_flags |= TF_ACKNOW;
 2832                         tp->rcv_nxt += tlen;
 2833                         thflags = th->th_flags & TH_FIN;
 2834                         TCPSTAT_INC(tcps_rcvpack);
 2835                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 2836                         ND6_HINT(tp);
 2837                         SOCKBUF_LOCK(&so->so_rcv);
 2838                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
 2839                                 m_freem(m);
 2840                         else
 2841                                 sbappendstream_locked(&so->so_rcv, m);
 2842                         /* NB: sorwakeup_locked() does an implicit unlock. */
 2843                         sorwakeup_locked(so);
 2844                 } else {
 2845                         /*
 2846                          * XXX: Due to the header drop above "th" is
 2847                          * theoretically invalid by now.  Fortunately
 2848                          * m_adj() doesn't actually frees any mbufs
 2849                          * when trimming from the head.
 2850                          */
 2851                         thflags = tcp_reass(tp, th, &tlen, m);
 2852                         tp->t_flags |= TF_ACKNOW;
 2853                 }
 2854                 if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
 2855                         tcp_update_sack_list(tp, save_start, save_start + tlen);
 2856 #if 0
 2857                 /*
 2858                  * Note the amount of data that peer has sent into
 2859                  * our window, in order to estimate the sender's
 2860                  * buffer size.
 2861                  * XXX: Unused.
 2862                  */
 2863                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
 2864                         len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
 2865                 else
 2866                         len = so->so_rcv.sb_hiwat;
 2867 #endif
 2868         } else {
 2869                 m_freem(m);
 2870                 thflags &= ~TH_FIN;
 2871         }
 2872 
 2873         /*
 2874          * If FIN is received ACK the FIN and let the user know
 2875          * that the connection is closing.
 2876          */
 2877         if (thflags & TH_FIN) {
 2878                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2879                         socantrcvmore(so);
 2880                         /*
 2881                          * If connection is half-synchronized
 2882                          * (ie NEEDSYN flag on) then delay ACK,
 2883                          * so it may be piggybacked when SYN is sent.
 2884                          * Otherwise, since we received a FIN then no
 2885                          * more input can be expected, send ACK now.
 2886                          */
 2887                         if (tp->t_flags & TF_NEEDSYN)
 2888                                 tp->t_flags |= TF_DELACK;
 2889                         else
 2890                                 tp->t_flags |= TF_ACKNOW;
 2891                         tp->rcv_nxt++;
 2892                 }
 2893                 switch (tp->t_state) {
 2894 
 2895                 /*
 2896                  * In SYN_RECEIVED and ESTABLISHED STATES
 2897                  * enter the CLOSE_WAIT state.
 2898                  */
 2899                 case TCPS_SYN_RECEIVED:
 2900                         tp->t_starttime = ticks;
 2901                         /* FALLTHROUGH */
 2902                 case TCPS_ESTABLISHED:
 2903                         tp->t_state = TCPS_CLOSE_WAIT;
 2904                         break;
 2905 
 2906                 /*
 2907                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
 2908                  * enter the CLOSING state.
 2909                  */
 2910                 case TCPS_FIN_WAIT_1:
 2911                         tp->t_state = TCPS_CLOSING;
 2912                         break;
 2913 
 2914                 /*
 2915                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
 2916                  * starting the time-wait timer, turning off the other
 2917                  * standard timers.
 2918                  */
 2919                 case TCPS_FIN_WAIT_2:
 2920                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2921                         KASSERT(ti_locked == TI_WLOCKED, ("%s: dodata "
 2922                             "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
 2923                             ti_locked));
 2924 
 2925                         tcp_twstart(tp);
 2926                         INP_INFO_WUNLOCK(&V_tcbinfo);
 2927                         return;
 2928                 }
 2929         }
 2930         if (ti_locked == TI_WLOCKED)
 2931                 INP_INFO_WUNLOCK(&V_tcbinfo);
 2932         ti_locked = TI_UNLOCKED;
 2933 
 2934 #ifdef TCPDEBUG
 2935         if (so->so_options & SO_DEBUG)
 2936                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
 2937                           &tcp_savetcp, 0);
 2938 #endif
 2939 
 2940         /*
 2941          * Return any desired output.
 2942          */
 2943         if (needoutput || (tp->t_flags & TF_ACKNOW))
 2944                 (void) tcp_output(tp);
 2945 
 2946 check_delack:
 2947         KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
 2948             __func__, ti_locked));
 2949         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 2950         INP_WLOCK_ASSERT(tp->t_inpcb);
 2951 
 2952         if (tp->t_flags & TF_DELACK) {
 2953                 tp->t_flags &= ~TF_DELACK;
 2954                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
 2955         }
 2956         INP_WUNLOCK(tp->t_inpcb);
 2957         return;
 2958 
 2959 dropafterack:
 2960         /*
 2961          * Generate an ACK dropping incoming segment if it occupies
 2962          * sequence space, where the ACK reflects our state.
 2963          *
 2964          * We can now skip the test for the RST flag since all
 2965          * paths to this code happen after packets containing
 2966          * RST have been dropped.
 2967          *
 2968          * In the SYN-RECEIVED state, don't send an ACK unless the
 2969          * segment we received passes the SYN-RECEIVED ACK test.
 2970          * If it fails send a RST.  This breaks the loop in the
 2971          * "LAND" DoS attack, and also prevents an ACK storm
 2972          * between two listening ports that have been sent forged
 2973          * SYN segments, each with the source address of the other.
 2974          */
 2975         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
 2976             (SEQ_GT(tp->snd_una, th->th_ack) ||
 2977              SEQ_GT(th->th_ack, tp->snd_max)) ) {
 2978                 rstreason = BANDLIM_RST_OPENPORT;
 2979                 goto dropwithreset;
 2980         }
 2981 #ifdef TCPDEBUG
 2982         if (so->so_options & SO_DEBUG)
 2983                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 2984                           &tcp_savetcp, 0);
 2985 #endif
 2986         if (ti_locked == TI_WLOCKED)
 2987                 INP_INFO_WUNLOCK(&V_tcbinfo);
 2988         ti_locked = TI_UNLOCKED;
 2989 
 2990         tp->t_flags |= TF_ACKNOW;
 2991         (void) tcp_output(tp);
 2992         INP_WUNLOCK(tp->t_inpcb);
 2993         m_freem(m);
 2994         return;
 2995 
 2996 dropwithreset:
 2997         if (ti_locked == TI_WLOCKED)
 2998                 INP_INFO_WUNLOCK(&V_tcbinfo);
 2999         ti_locked = TI_UNLOCKED;
 3000 
 3001         if (tp != NULL) {
 3002                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 3003                 INP_WUNLOCK(tp->t_inpcb);
 3004         } else
 3005                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 3006         return;
 3007 
 3008 drop:
 3009         if (ti_locked == TI_WLOCKED) {
 3010                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3011                 ti_locked = TI_UNLOCKED;
 3012         }
 3013 #ifdef INVARIANTS
 3014         else
 3015                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3016 #endif
 3017 
 3018         /*
 3019          * Drop space held by incoming segment and return.
 3020          */
 3021 #ifdef TCPDEBUG
 3022         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 3023                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3024                           &tcp_savetcp, 0);
 3025 #endif
 3026         if (tp != NULL)
 3027                 INP_WUNLOCK(tp->t_inpcb);
 3028         m_freem(m);
 3029 }
 3030 
 3031 /*
 3032  * Issue RST and make ACK acceptable to originator of segment.
 3033  * The mbuf must still include the original packet header.
 3034  * tp may be NULL.
 3035  */
 3036 static void
 3037 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
 3038     int tlen, int rstreason)
 3039 {
 3040 #ifdef INET
 3041         struct ip *ip;
 3042 #endif
 3043 #ifdef INET6
 3044         struct ip6_hdr *ip6;
 3045 #endif
 3046 
 3047         if (tp != NULL) {
 3048                 INP_WLOCK_ASSERT(tp->t_inpcb);
 3049         }
 3050 
 3051         /* Don't bother if destination was broadcast/multicast. */
 3052         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
 3053                 goto drop;
 3054 #ifdef INET6
 3055         if (mtod(m, struct ip *)->ip_v == 6) {
 3056                 ip6 = mtod(m, struct ip6_hdr *);
 3057                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 3058                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 3059                         goto drop;
 3060                 /* IPv6 anycast check is done at tcp6_input() */
 3061         }
 3062 #endif
 3063 #if defined(INET) && defined(INET6)
 3064         else
 3065 #endif
 3066 #ifdef INET
 3067         {
 3068                 ip = mtod(m, struct ip *);
 3069                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 3070                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 3071                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 3072                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 3073                         goto drop;
 3074         }
 3075 #endif
 3076 
 3077         /* Perform bandwidth limiting. */
 3078         if (badport_bandlim(rstreason) < 0)
 3079                 goto drop;
 3080 
 3081         /* tcp_respond consumes the mbuf chain. */
 3082         if (th->th_flags & TH_ACK) {
 3083                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
 3084                     th->th_ack, TH_RST);
 3085         } else {
 3086                 if (th->th_flags & TH_SYN)
 3087                         tlen++;
 3088                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
 3089                     (tcp_seq)0, TH_RST|TH_ACK);
 3090         }
 3091         return;
 3092 drop:
 3093         m_freem(m);
 3094 }
 3095 
 3096 /*
 3097  * Parse TCP options and place in tcpopt.
 3098  */
 3099 static void
 3100 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
 3101 {
 3102         int opt, optlen;
 3103 
 3104         to->to_flags = 0;
 3105         for (; cnt > 0; cnt -= optlen, cp += optlen) {
 3106                 opt = cp[0];
 3107                 if (opt == TCPOPT_EOL)
 3108                         break;
 3109                 if (opt == TCPOPT_NOP)
 3110                         optlen = 1;
 3111                 else {
 3112                         if (cnt < 2)
 3113                                 break;
 3114                         optlen = cp[1];
 3115                         if (optlen < 2 || optlen > cnt)
 3116                                 break;
 3117                 }
 3118                 switch (opt) {
 3119                 case TCPOPT_MAXSEG:
 3120                         if (optlen != TCPOLEN_MAXSEG)
 3121                                 continue;
 3122                         if (!(flags & TO_SYN))
 3123                                 continue;
 3124                         to->to_flags |= TOF_MSS;
 3125                         bcopy((char *)cp + 2,
 3126                             (char *)&to->to_mss, sizeof(to->to_mss));
 3127                         to->to_mss = ntohs(to->to_mss);
 3128                         break;
 3129                 case TCPOPT_WINDOW:
 3130                         if (optlen != TCPOLEN_WINDOW)
 3131                                 continue;
 3132                         if (!(flags & TO_SYN))
 3133                                 continue;
 3134                         to->to_flags |= TOF_SCALE;
 3135                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
 3136                         break;
 3137                 case TCPOPT_TIMESTAMP:
 3138                         if (optlen != TCPOLEN_TIMESTAMP)
 3139                                 continue;
 3140                         to->to_flags |= TOF_TS;
 3141                         bcopy((char *)cp + 2,
 3142                             (char *)&to->to_tsval, sizeof(to->to_tsval));
 3143                         to->to_tsval = ntohl(to->to_tsval);
 3144                         bcopy((char *)cp + 6,
 3145                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
 3146                         to->to_tsecr = ntohl(to->to_tsecr);
 3147                         break;
 3148 #ifdef TCP_SIGNATURE
 3149                 /*
 3150                  * XXX In order to reply to a host which has set the
 3151                  * TCP_SIGNATURE option in its initial SYN, we have to
 3152                  * record the fact that the option was observed here
 3153                  * for the syncache code to perform the correct response.
 3154                  */
 3155                 case TCPOPT_SIGNATURE:
 3156                         if (optlen != TCPOLEN_SIGNATURE)
 3157                                 continue;
 3158                         to->to_flags |= TOF_SIGNATURE;
 3159                         to->to_signature = cp + 2;
 3160                         break;
 3161 #endif
 3162                 case TCPOPT_SACK_PERMITTED:
 3163                         if (optlen != TCPOLEN_SACK_PERMITTED)
 3164                                 continue;
 3165                         if (!(flags & TO_SYN))
 3166                                 continue;
 3167                         if (!V_tcp_do_sack)
 3168                                 continue;
 3169                         to->to_flags |= TOF_SACKPERM;
 3170                         break;
 3171                 case TCPOPT_SACK:
 3172                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
 3173                                 continue;
 3174                         if (flags & TO_SYN)
 3175                                 continue;
 3176                         to->to_flags |= TOF_SACK;
 3177                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
 3178                         to->to_sacks = cp + 2;
 3179                         TCPSTAT_INC(tcps_sack_rcv_blocks);
 3180                         break;
 3181                 default:
 3182                         continue;
 3183                 }
 3184         }
 3185 }
 3186 
 3187 /*
 3188  * Pull out of band byte out of a segment so
 3189  * it doesn't appear in the user's data queue.
 3190  * It is still reflected in the segment length for
 3191  * sequencing purposes.
 3192  */
 3193 static void
 3194 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
 3195     int off)
 3196 {
 3197         int cnt = off + th->th_urp - 1;
 3198 
 3199         while (cnt >= 0) {
 3200                 if (m->m_len > cnt) {
 3201                         char *cp = mtod(m, caddr_t) + cnt;
 3202                         struct tcpcb *tp = sototcpcb(so);
 3203 
 3204                         INP_WLOCK_ASSERT(tp->t_inpcb);
 3205 
 3206                         tp->t_iobc = *cp;
 3207                         tp->t_oobflags |= TCPOOB_HAVEDATA;
 3208                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
 3209                         m->m_len--;
 3210                         if (m->m_flags & M_PKTHDR)
 3211                                 m->m_pkthdr.len--;
 3212                         return;
 3213                 }
 3214                 cnt -= m->m_len;
 3215                 m = m->m_next;
 3216                 if (m == NULL)
 3217                         break;
 3218         }
 3219         panic("tcp_pulloutofband");
 3220 }
 3221 
 3222 /*
 3223  * Collect new round-trip time estimate
 3224  * and update averages and current timeout.
 3225  */
 3226 static void
 3227 tcp_xmit_timer(struct tcpcb *tp, int rtt)
 3228 {
 3229         int delta;
 3230 
 3231         INP_WLOCK_ASSERT(tp->t_inpcb);
 3232 
 3233         TCPSTAT_INC(tcps_rttupdated);
 3234         tp->t_rttupdated++;
 3235         if (tp->t_srtt != 0) {
 3236                 /*
 3237                  * srtt is stored as fixed point with 5 bits after the
 3238                  * binary point (i.e., scaled by 8).  The following magic
 3239                  * is equivalent to the smoothing algorithm in rfc793 with
 3240                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
 3241                  * point).  Adjust rtt to origin 0.
 3242                  */
 3243                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
 3244                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
 3245 
 3246                 if ((tp->t_srtt += delta) <= 0)
 3247                         tp->t_srtt = 1;
 3248 
 3249                 /*
 3250                  * We accumulate a smoothed rtt variance (actually, a
 3251                  * smoothed mean difference), then set the retransmit
 3252                  * timer to smoothed rtt + 4 times the smoothed variance.
 3253                  * rttvar is stored as fixed point with 4 bits after the
 3254                  * binary point (scaled by 16).  The following is
 3255                  * equivalent to rfc793 smoothing with an alpha of .75
 3256                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
 3257                  * rfc793's wired-in beta.
 3258                  */
 3259                 if (delta < 0)
 3260                         delta = -delta;
 3261                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
 3262                 if ((tp->t_rttvar += delta) <= 0)
 3263                         tp->t_rttvar = 1;
 3264                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
 3265                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3266         } else {
 3267                 /*
 3268                  * No rtt measurement yet - use the unsmoothed rtt.
 3269                  * Set the variance to half the rtt (so our first
 3270                  * retransmit happens at 3*rtt).
 3271                  */
 3272                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
 3273                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
 3274                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3275         }
 3276         tp->t_rtttime = 0;
 3277         tp->t_rxtshift = 0;
 3278 
 3279         /*
 3280          * the retransmit should happen at rtt + 4 * rttvar.
 3281          * Because of the way we do the smoothing, srtt and rttvar
 3282          * will each average +1/2 tick of bias.  When we compute
 3283          * the retransmit timer, we want 1/2 tick of rounding and
 3284          * 1 extra tick because of +-1/2 tick uncertainty in the
 3285          * firing of the timer.  The bias will give us exactly the
 3286          * 1.5 tick we need.  But, because the bias is
 3287          * statistical, we have to test that we don't drop below
 3288          * the minimum feasible timer (which is 2 ticks).
 3289          */
 3290         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
 3291                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
 3292 
 3293         /*
 3294          * We received an ack for a packet that wasn't retransmitted;
 3295          * it is probably safe to discard any error indications we've
 3296          * received recently.  This isn't quite right, but close enough
 3297          * for now (a route might have failed after we sent a segment,
 3298          * and the return path might not be symmetrical).
 3299          */
 3300         tp->t_softerror = 0;
 3301 }
 3302 
 3303 /*
 3304  * Determine a reasonable value for maxseg size.
 3305  * If the route is known, check route for mtu.
 3306  * If none, use an mss that can be handled on the outgoing
 3307  * interface without forcing IP to fragment; if bigger than
 3308  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
 3309  * to utilize large mbufs.  If no route is found, route has no mtu,
 3310  * or the destination isn't local, use a default, hopefully conservative
 3311  * size (usually 512 or the default IP max size, but no more than the mtu
 3312  * of the interface), as we can't discover anything about intervening
 3313  * gateways or networks.  We also initialize the congestion/slow start
 3314  * window to be a single segment if the destination isn't local.
 3315  * While looking at the routing entry, we also initialize other path-dependent
 3316  * parameters from pre-set or cached values in the routing entry.
 3317  *
 3318  * Also take into account the space needed for options that we
 3319  * send regularly.  Make maxseg shorter by that amount to assure
 3320  * that we can send maxseg amount of data even when the options
 3321  * are present.  Store the upper limit of the length of options plus
 3322  * data in maxopd.
 3323  *
 3324  * In case of T/TCP, we call this routine during implicit connection
 3325  * setup as well (offer = -1), to initialize maxseg from the cached
 3326  * MSS of our peer.
 3327  *
 3328  * NOTE that this routine is only called when we process an incoming
 3329  * segment. Outgoing SYN/ACK MSS settings are handled in tcp_mssopt().
 3330  */
 3331 void
 3332 tcp_mss_update(struct tcpcb *tp, int offer,
 3333     struct hc_metrics_lite *metricptr, int *mtuflags)
 3334 {
 3335         int mss = 0;
 3336         u_long maxmtu = 0;
 3337         struct inpcb *inp = tp->t_inpcb;
 3338         struct hc_metrics_lite metrics;
 3339         int origoffer = offer;
 3340 #ifdef INET6
 3341         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
 3342         size_t min_protoh = isipv6 ?
 3343                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
 3344                             sizeof (struct tcpiphdr);
 3345 #else
 3346         const size_t min_protoh = sizeof(struct tcpiphdr);
 3347 #endif
 3348 
 3349         INP_WLOCK_ASSERT(tp->t_inpcb);
 3350 
 3351         /* Initialize. */
 3352 #ifdef INET6
 3353         if (isipv6) {
 3354                 maxmtu = tcp_maxmtu6(&inp->inp_inc, mtuflags);
 3355                 tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
 3356         }
 3357 #endif
 3358 #if defined(INET) && defined(INET6)
 3359         else
 3360 #endif
 3361 #ifdef INET
 3362         {
 3363                 maxmtu = tcp_maxmtu(&inp->inp_inc, mtuflags);
 3364                 tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
 3365         }
 3366 #endif
 3367 
 3368         /*
 3369          * No route to sender, stay with default mss and return.
 3370          */
 3371         if (maxmtu == 0) {
 3372                 /*
 3373                  * In case we return early we need to initialize metrics
 3374                  * to a defined state as tcp_hc_get() would do for us
 3375                  * if there was no cache hit.
 3376                  */
 3377                 if (metricptr != NULL)
 3378                         bzero(metricptr, sizeof(struct hc_metrics_lite));
 3379                 return;
 3380         }
 3381 
 3382         /* What have we got? */
 3383         switch (offer) {
 3384                 case 0:
 3385                         /*
 3386                          * Offer == 0 means that there was no MSS on the SYN
 3387                          * segment, in this case we use tcp_mssdflt as
 3388                          * already assigned to t_maxopd above.
 3389                          */
 3390                         offer = tp->t_maxopd;
 3391                         break;
 3392 
 3393                 case -1:
 3394                         /*
 3395                          * Offer == -1 means that we didn't receive SYN yet.
 3396                          */
 3397                         /* FALLTHROUGH */
 3398 
 3399                 default:
 3400                         /*
 3401                          * Prevent DoS attack with too small MSS. Round up
 3402                          * to at least minmss.
 3403                          */
 3404                         offer = max(offer, V_tcp_minmss);
 3405         }
 3406 
 3407         /*
 3408          * rmx information is now retrieved from tcp_hostcache.
 3409          */
 3410         tcp_hc_get(&inp->inp_inc, &metrics);
 3411         if (metricptr != NULL)
 3412                 bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
 3413 
 3414         /*
 3415          * If there's a discovered mtu int tcp hostcache, use it
 3416          * else, use the link mtu.
 3417          */
 3418         if (metrics.rmx_mtu)
 3419                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
 3420         else {
 3421 #ifdef INET6
 3422                 if (isipv6) {
 3423                         mss = maxmtu - min_protoh;
 3424                         if (!V_path_mtu_discovery &&
 3425                             !in6_localaddr(&inp->in6p_faddr))
 3426                                 mss = min(mss, V_tcp_v6mssdflt);
 3427                 }
 3428 #endif
 3429 #if defined(INET) && defined(INET6)
 3430                 else
 3431 #endif
 3432 #ifdef INET
 3433                 {
 3434                         mss = maxmtu - min_protoh;
 3435                         if (!V_path_mtu_discovery &&
 3436                             !in_localaddr(inp->inp_faddr))
 3437                                 mss = min(mss, V_tcp_mssdflt);
 3438                 }
 3439 #endif
 3440                 /*
 3441                  * XXX - The above conditional (mss = maxmtu - min_protoh)
 3442                  * probably violates the TCP spec.
 3443                  * The problem is that, since we don't know the
 3444                  * other end's MSS, we are supposed to use a conservative
 3445                  * default.  But, if we do that, then MTU discovery will
 3446                  * never actually take place, because the conservative
 3447                  * default is much less than the MTUs typically seen
 3448                  * on the Internet today.  For the moment, we'll sweep
 3449                  * this under the carpet.
 3450                  *
 3451                  * The conservative default might not actually be a problem
 3452                  * if the only case this occurs is when sending an initial
 3453                  * SYN with options and data to a host we've never talked
 3454                  * to before.  Then, they will reply with an MSS value which
 3455                  * will get recorded and the new parameters should get
 3456                  * recomputed.  For Further Study.
 3457                  */
 3458         }
 3459         mss = min(mss, offer);
 3460 
 3461         /*
 3462          * Sanity check: make sure that maxopd will be large
 3463          * enough to allow some data on segments even if the
 3464          * all the option space is used (40bytes).  Otherwise
 3465          * funny things may happen in tcp_output.
 3466          */
 3467         mss = max(mss, 64);
 3468 
 3469         /*
 3470          * maxopd stores the maximum length of data AND options
 3471          * in a segment; maxseg is the amount of data in a normal
 3472          * segment.  We need to store this value (maxopd) apart
 3473          * from maxseg, because now every segment carries options
 3474          * and thus we normally have somewhat less data in segments.
 3475          */
 3476         tp->t_maxopd = mss;
 3477 
 3478         /*
 3479          * origoffer==-1 indicates that no segments were received yet.
 3480          * In this case we just guess.
 3481          */
 3482         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
 3483             (origoffer == -1 ||
 3484              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
 3485                 mss -= TCPOLEN_TSTAMP_APPA;
 3486 
 3487 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
 3488         if (mss > MCLBYTES)
 3489                 mss &= ~(MCLBYTES-1);
 3490 #else
 3491         if (mss > MCLBYTES)
 3492                 mss = mss / MCLBYTES * MCLBYTES;
 3493 #endif
 3494         tp->t_maxseg = mss;
 3495 }
 3496 
 3497 void
 3498 tcp_mss(struct tcpcb *tp, int offer)
 3499 {
 3500         int mss;
 3501         u_long bufsize;
 3502         struct inpcb *inp;
 3503         struct socket *so;
 3504         struct hc_metrics_lite metrics;
 3505         int mtuflags = 0;
 3506 
 3507         KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
 3508         
 3509         tcp_mss_update(tp, offer, &metrics, &mtuflags);
 3510 
 3511         mss = tp->t_maxseg;
 3512         inp = tp->t_inpcb;
 3513 
 3514         /*
 3515          * If there's a pipesize, change the socket buffer to that size,
 3516          * don't change if sb_hiwat is different than default (then it
 3517          * has been changed on purpose with setsockopt).
 3518          * Make the socket buffers an integral number of mss units;
 3519          * if the mss is larger than the socket buffer, decrease the mss.
 3520          */
 3521         so = inp->inp_socket;
 3522         SOCKBUF_LOCK(&so->so_snd);
 3523         if ((so->so_snd.sb_hiwat == tcp_sendspace) && metrics.rmx_sendpipe)
 3524                 bufsize = metrics.rmx_sendpipe;
 3525         else
 3526                 bufsize = so->so_snd.sb_hiwat;
 3527         if (bufsize < mss)
 3528                 mss = bufsize;
 3529         else {
 3530                 bufsize = roundup(bufsize, mss);
 3531                 if (bufsize > sb_max)
 3532                         bufsize = sb_max;
 3533                 if (bufsize > so->so_snd.sb_hiwat)
 3534                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
 3535         }
 3536         SOCKBUF_UNLOCK(&so->so_snd);
 3537         tp->t_maxseg = mss;
 3538 
 3539         SOCKBUF_LOCK(&so->so_rcv);
 3540         if ((so->so_rcv.sb_hiwat == tcp_recvspace) && metrics.rmx_recvpipe)
 3541                 bufsize = metrics.rmx_recvpipe;
 3542         else
 3543                 bufsize = so->so_rcv.sb_hiwat;
 3544         if (bufsize > mss) {
 3545                 bufsize = roundup(bufsize, mss);
 3546                 if (bufsize > sb_max)
 3547                         bufsize = sb_max;
 3548                 if (bufsize > so->so_rcv.sb_hiwat)
 3549                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
 3550         }
 3551         SOCKBUF_UNLOCK(&so->so_rcv);
 3552 
 3553         /* Check the interface for TSO capabilities. */
 3554         if (mtuflags & CSUM_TSO)
 3555                 tp->t_flags |= TF_TSO;
 3556 }
 3557 
 3558 /*
 3559  * Determine the MSS option to send on an outgoing SYN.
 3560  */
 3561 int
 3562 tcp_mssopt(struct in_conninfo *inc)
 3563 {
 3564         int mss = 0;
 3565         u_long maxmtu = 0;
 3566         u_long thcmtu = 0;
 3567         size_t min_protoh;
 3568 
 3569         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
 3570 
 3571 #ifdef INET6
 3572         if (inc->inc_flags & INC_ISIPV6) {
 3573                 mss = V_tcp_v6mssdflt;
 3574                 maxmtu = tcp_maxmtu6(inc, NULL);
 3575                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
 3576                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
 3577         }
 3578 #endif
 3579 #if defined(INET) && defined(INET6)
 3580         else
 3581 #endif
 3582 #ifdef INET
 3583         {
 3584                 mss = V_tcp_mssdflt;
 3585                 maxmtu = tcp_maxmtu(inc, NULL);
 3586                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
 3587                 min_protoh = sizeof(struct tcpiphdr);
 3588         }
 3589 #endif
 3590         if (maxmtu && thcmtu)
 3591                 mss = min(maxmtu, thcmtu) - min_protoh;
 3592         else if (maxmtu || thcmtu)
 3593                 mss = max(maxmtu, thcmtu) - min_protoh;
 3594 
 3595         return (mss);
 3596 }
 3597 
 3598 
 3599 /*
 3600  * On a partial ack arrives, force the retransmission of the
 3601  * next unacknowledged segment.  Do not clear tp->t_dupacks.
 3602  * By setting snd_nxt to ti_ack, this forces retransmission timer to
 3603  * be started again.
 3604  */
 3605 static void
 3606 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
 3607 {
 3608         tcp_seq onxt = tp->snd_nxt;
 3609         u_long  ocwnd = tp->snd_cwnd;
 3610 
 3611         INP_WLOCK_ASSERT(tp->t_inpcb);
 3612 
 3613         tcp_timer_activate(tp, TT_REXMT, 0);
 3614         tp->t_rtttime = 0;
 3615         tp->snd_nxt = th->th_ack;
 3616         /*
 3617          * Set snd_cwnd to one segment beyond acknowledged offset.
 3618          * (tp->snd_una has not yet been updated when this function is called.)
 3619          */
 3620         tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th);
 3621         tp->t_flags |= TF_ACKNOW;
 3622         (void) tcp_output(tp);
 3623         tp->snd_cwnd = ocwnd;
 3624         if (SEQ_GT(onxt, tp->snd_nxt))
 3625                 tp->snd_nxt = onxt;
 3626         /*
 3627          * Partial window deflation.  Relies on fact that tp->snd_una
 3628          * not updated yet.
 3629          */
 3630         if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
 3631                 tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
 3632         else
 3633                 tp->snd_cwnd = 0;
 3634         tp->snd_cwnd += tp->t_maxseg;
 3635 }

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