The Design and Implementation of the FreeBSD Operating System, Second Edition
[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]

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

Version: -  FREEBSD  -  FREEBSD10  -  FREEBSD9  -  FREEBSD92  -  FREEBSD91  -  FREEBSD90  -  FREEBSD8  -  FREEBSD82  -  FREEBSD81  -  FREEBSD80  -  FREEBSD7  -  FREEBSD74  -  FREEBSD73  -  FREEBSD72  -  FREEBSD71  -  FREEBSD70  -  FREEBSD6  -  FREEBSD64  -  FREEBSD63  -  FREEBSD62  -  FREEBSD61  -  FREEBSD60  -  FREEBSD5  -  FREEBSD55  -  FREEBSD54  -  FREEBSD53  -  FREEBSD52  -  FREEBSD51  -  FREEBSD50  -  FREEBSD4  -  FREEBSD3  -  FREEBSD22  -  cheribsd  -  linux-2.6  -  linux-2.4.22  -  MK83  -  MK84  -  PLAN9  -  DFBSD  -  NETBSD  -  NETBSD5  -  NETBSD4  -  NETBSD3  -  NETBSD20  -  OPENBSD  -  xnu-517  -  xnu-792  -  xnu-792.6.70  -  xnu-1228  -  xnu-1456.1.26  -  xnu-1699.24.8  -  xnu-2050.18.24  -  OPENSOLARIS  -  minix-3-1-1  -  FREEBSD-LIBC  -  FREEBSD8-LIBC  -  FREEBSD7-LIBC  -  FREEBSD6-LIBC  -  GLIBC27 
SearchContext: -  none  -  3  -  10 

    1 /*-
    2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
    3  *      The Regents of the University of California.  All rights reserved.
    4  * Copyright (c) 2007-2008,2010
    5  *      Swinburne University of Technology, Melbourne, Australia.
    6  * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
    7  * Copyright (c) 2010 The FreeBSD Foundation
    8  * Copyright (c) 2010-2011 Juniper Networks, Inc.
    9  * All rights reserved.
   10  *
   11  * Portions of this software were developed at the Centre for Advanced Internet
   12  * Architectures, Swinburne University of Technology, by Lawrence Stewart,
   13  * James Healy and David Hayes, made possible in part by a grant from the Cisco
   14  * University Research Program Fund at Community Foundation Silicon Valley.
   15  *
   16  * Portions of this software were developed at the Centre for Advanced
   17  * Internet Architectures, Swinburne University of Technology, Melbourne,
   18  * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
   19  *
   20  * Portions of this software were developed by Robert N. M. Watson under
   21  * contract to Juniper Networks, Inc.
   22  *
   23  * Redistribution and use in source and binary forms, with or without
   24  * modification, are permitted provided that the following conditions
   25  * are met:
   26  * 1. Redistributions of source code must retain the above copyright
   27  *    notice, this list of conditions and the following disclaimer.
   28  * 2. Redistributions in binary form must reproduce the above copyright
   29  *    notice, this list of conditions and the following disclaimer in the
   30  *    documentation and/or other materials provided with the distribution.
   31  * 4. Neither the name of the University nor the names of its contributors
   32  *    may be used to endorse or promote products derived from this software
   33  *    without specific prior written permission.
   34  *
   35  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   36  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   37  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   38  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   39  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   40  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   41  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   42  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   43  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   44  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   45  * SUCH DAMAGE.
   46  *
   47  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
   48  */
   49 
   50 #include <sys/cdefs.h>
   51 __FBSDID("$FreeBSD: head/sys/netinet/tcp_input.c 269766 2014-08-09 21:01:24Z hiren $");
   52 
   53 #include "opt_ipfw.h"           /* for ipfw_fwd */
   54 #include "opt_inet.h"
   55 #include "opt_inet6.h"
   56 #include "opt_ipsec.h"
   57 #include "opt_tcpdebug.h"
   58 
   59 #include <sys/param.h>
   60 #include <sys/kernel.h>
   61 #include <sys/hhook.h>
   62 #include <sys/malloc.h>
   63 #include <sys/mbuf.h>
   64 #include <sys/proc.h>           /* for proc0 declaration */
   65 #include <sys/protosw.h>
   66 #include <sys/sdt.h>
   67 #include <sys/signalvar.h>
   68 #include <sys/socket.h>
   69 #include <sys/socketvar.h>
   70 #include <sys/sysctl.h>
   71 #include <sys/syslog.h>
   72 #include <sys/systm.h>
   73 
   74 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
   75 
   76 #include <vm/uma.h>
   77 
   78 #include <net/if.h>
   79 #include <net/if_var.h>
   80 #include <net/route.h>
   81 #include <net/vnet.h>
   82 
   83 #define TCPSTATES               /* for logging */
   84 
   85 #include <netinet/cc.h>
   86 #include <netinet/in.h>
   87 #include <netinet/in_kdtrace.h>
   88 #include <netinet/in_pcb.h>
   89 #include <netinet/in_systm.h>
   90 #include <netinet/in_var.h>
   91 #include <netinet/ip.h>
   92 #include <netinet/ip_icmp.h>    /* required for icmp_var.h */
   93 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
   94 #include <netinet/ip_var.h>
   95 #include <netinet/ip_options.h>
   96 #include <netinet/ip6.h>
   97 #include <netinet/icmp6.h>
   98 #include <netinet6/in6_pcb.h>
   99 #include <netinet6/ip6_var.h>
  100 #include <netinet6/nd6.h>
  101 #include <netinet/tcp_fsm.h>
  102 #include <netinet/tcp_seq.h>
  103 #include <netinet/tcp_timer.h>
  104 #include <netinet/tcp_var.h>
  105 #include <netinet6/tcp6_var.h>
  106 #include <netinet/tcpip.h>
  107 #include <netinet/tcp_syncache.h>
  108 #ifdef TCPDEBUG
  109 #include <netinet/tcp_debug.h>
  110 #endif /* TCPDEBUG */
  111 #ifdef TCP_OFFLOAD
  112 #include <netinet/tcp_offload.h>
  113 #endif
  114 
  115 #ifdef IPSEC
  116 #include <netipsec/ipsec.h>
  117 #include <netipsec/ipsec6.h>
  118 #endif /*IPSEC*/
  119 
  120 #include <machine/in_cksum.h>
  121 
  122 #include <security/mac/mac_framework.h>
  123 
  124 const int tcprexmtthresh = 3;
  125 
  126 int tcp_log_in_vain = 0;
  127 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
  128     &tcp_log_in_vain, 0,
  129     "Log all incoming TCP segments to closed ports");
  130 
  131 VNET_DEFINE(int, blackhole) = 0;
  132 #define V_blackhole             VNET(blackhole)
  133 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
  134     &VNET_NAME(blackhole), 0,
  135     "Do not send RST on segments to closed ports");
  136 
  137 VNET_DEFINE(int, tcp_delack_enabled) = 1;
  138 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
  139     &VNET_NAME(tcp_delack_enabled), 0,
  140     "Delay ACK to try and piggyback it onto a data packet");
  141 
  142 VNET_DEFINE(int, drop_synfin) = 0;
  143 #define V_drop_synfin           VNET(drop_synfin)
  144 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
  145     &VNET_NAME(drop_synfin), 0,
  146     "Drop TCP packets with SYN+FIN set");
  147 
  148 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
  149 #define V_tcp_do_rfc3042        VNET(tcp_do_rfc3042)
  150 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
  151     &VNET_NAME(tcp_do_rfc3042), 0,
  152     "Enable RFC 3042 (Limited Transmit)");
  153 
  154 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
  155 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
  156     &VNET_NAME(tcp_do_rfc3390), 0,
  157     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
  158 
  159 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, experimental, CTLFLAG_RW, 0,
  160     "Experimental TCP extensions");
  161 
  162 VNET_DEFINE(int, tcp_do_initcwnd10) = 1;
  163 SYSCTL_VNET_INT(_net_inet_tcp_experimental, OID_AUTO, initcwnd10, CTLFLAG_RW,
  164     &VNET_NAME(tcp_do_initcwnd10), 0,
  165     "Enable RFC 6928 (Increasing initial CWND to 10)");
  166 
  167 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
  168 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_RW,
  169     &VNET_NAME(tcp_do_rfc3465), 0,
  170     "Enable RFC 3465 (Appropriate Byte Counting)");
  171 
  172 VNET_DEFINE(int, tcp_abc_l_var) = 2;
  173 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_RW,
  174     &VNET_NAME(tcp_abc_l_var), 2,
  175     "Cap the max cwnd increment during slow-start to this number of segments");
  176 
  177 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
  178 
  179 VNET_DEFINE(int, tcp_do_ecn) = 0;
  180 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_RW,
  181     &VNET_NAME(tcp_do_ecn), 0,
  182     "TCP ECN support");
  183 
  184 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
  185 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_RW,
  186     &VNET_NAME(tcp_ecn_maxretries), 0,
  187     "Max retries before giving up on ECN");
  188 
  189 VNET_DEFINE(int, tcp_insecure_rst) = 0;
  190 #define V_tcp_insecure_rst      VNET(tcp_insecure_rst)
  191 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
  192     &VNET_NAME(tcp_insecure_rst), 0,
  193     "Follow the old (insecure) criteria for accepting RST packets");
  194 
  195 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
  196 #define V_tcp_recvspace VNET(tcp_recvspace)
  197 SYSCTL_VNET_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_RW,
  198     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
  199 
  200 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
  201 #define V_tcp_do_autorcvbuf     VNET(tcp_do_autorcvbuf)
  202 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
  203     &VNET_NAME(tcp_do_autorcvbuf), 0,
  204     "Enable automatic receive buffer sizing");
  205 
  206 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
  207 #define V_tcp_autorcvbuf_inc    VNET(tcp_autorcvbuf_inc)
  208 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
  209     &VNET_NAME(tcp_autorcvbuf_inc), 0,
  210     "Incrementor step size of automatic receive buffer");
  211 
  212 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
  213 #define V_tcp_autorcvbuf_max    VNET(tcp_autorcvbuf_max)
  214 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
  215     &VNET_NAME(tcp_autorcvbuf_max), 0,
  216     "Max size of automatic receive buffer");
  217 
  218 VNET_DEFINE(struct inpcbhead, tcb);
  219 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
  220 VNET_DEFINE(struct inpcbinfo, tcbinfo);
  221 
  222 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
  223 static void      tcp_do_segment(struct mbuf *, struct tcphdr *,
  224                      struct socket *, struct tcpcb *, int, int, uint8_t,
  225                      int);
  226 static void      tcp_dropwithreset(struct mbuf *, struct tcphdr *,
  227                      struct tcpcb *, int, int);
  228 static void      tcp_pulloutofband(struct socket *,
  229                      struct tcphdr *, struct mbuf *, int);
  230 static void      tcp_xmit_timer(struct tcpcb *, int);
  231 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
  232 static void inline      cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
  233                             uint16_t type);
  234 static void inline      cc_conn_init(struct tcpcb *tp);
  235 static void inline      cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
  236 static void inline      hhook_run_tcp_est_in(struct tcpcb *tp,
  237                             struct tcphdr *th, struct tcpopt *to);
  238 
  239 /*
  240  * TCP statistics are stored in an "array" of counter(9)s.
  241  */
  242 VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
  243 VNET_PCPUSTAT_SYSINIT(tcpstat);
  244 SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
  245     tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
  246 
  247 #ifdef VIMAGE
  248 VNET_PCPUSTAT_SYSUNINIT(tcpstat);
  249 #endif /* VIMAGE */
  250 /*
  251  * Kernel module interface for updating tcpstat.  The argument is an index
  252  * into tcpstat treated as an array.
  253  */
  254 void
  255 kmod_tcpstat_inc(int statnum)
  256 {
  257 
  258         counter_u64_add(VNET(tcpstat)[statnum], 1);
  259 }
  260 
  261 /*
  262  * Wrapper for the TCP established input helper hook.
  263  */
  264 static void inline
  265 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
  266 {
  267         struct tcp_hhook_data hhook_data;
  268 
  269         if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
  270                 hhook_data.tp = tp;
  271                 hhook_data.th = th;
  272                 hhook_data.to = to;
  273 
  274                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
  275                     tp->osd);
  276         }
  277 }
  278 
  279 /*
  280  * CC wrapper hook functions
  281  */
  282 static void inline
  283 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type)
  284 {
  285         INP_WLOCK_ASSERT(tp->t_inpcb);
  286 
  287         tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
  288         if (tp->snd_cwnd <= tp->snd_wnd)
  289                 tp->ccv->flags |= CCF_CWND_LIMITED;
  290         else
  291                 tp->ccv->flags &= ~CCF_CWND_LIMITED;
  292 
  293         if (type == CC_ACK) {
  294                 if (tp->snd_cwnd > tp->snd_ssthresh) {
  295                         tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
  296                              V_tcp_abc_l_var * tp->t_maxseg);
  297                         if (tp->t_bytes_acked >= tp->snd_cwnd) {
  298                                 tp->t_bytes_acked -= tp->snd_cwnd;
  299                                 tp->ccv->flags |= CCF_ABC_SENTAWND;
  300                         }
  301                 } else {
  302                                 tp->ccv->flags &= ~CCF_ABC_SENTAWND;
  303                                 tp->t_bytes_acked = 0;
  304                 }
  305         }
  306 
  307         if (CC_ALGO(tp)->ack_received != NULL) {
  308                 /* XXXLAS: Find a way to live without this */
  309                 tp->ccv->curack = th->th_ack;
  310                 CC_ALGO(tp)->ack_received(tp->ccv, type);
  311         }
  312 }
  313 
  314 static void inline
  315 cc_conn_init(struct tcpcb *tp)
  316 {
  317         struct hc_metrics_lite metrics;
  318         struct inpcb *inp = tp->t_inpcb;
  319         int rtt;
  320 
  321         INP_WLOCK_ASSERT(tp->t_inpcb);
  322 
  323         tcp_hc_get(&inp->inp_inc, &metrics);
  324 
  325         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
  326                 tp->t_srtt = rtt;
  327                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
  328                 TCPSTAT_INC(tcps_usedrtt);
  329                 if (metrics.rmx_rttvar) {
  330                         tp->t_rttvar = metrics.rmx_rttvar;
  331                         TCPSTAT_INC(tcps_usedrttvar);
  332                 } else {
  333                         /* default variation is +- 1 rtt */
  334                         tp->t_rttvar =
  335                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
  336                 }
  337                 TCPT_RANGESET(tp->t_rxtcur,
  338                     ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
  339                     tp->t_rttmin, TCPTV_REXMTMAX);
  340         }
  341         if (metrics.rmx_ssthresh) {
  342                 /*
  343                  * There's some sort of gateway or interface
  344                  * buffer limit on the path.  Use this to set
  345                  * the slow start threshhold, but set the
  346                  * threshold to no less than 2*mss.
  347                  */
  348                 tp->snd_ssthresh = max(2 * tp->t_maxseg, metrics.rmx_ssthresh);
  349                 TCPSTAT_INC(tcps_usedssthresh);
  350         }
  351 
  352         /*
  353          * Set the initial slow-start flight size.
  354          *
  355          * RFC5681 Section 3.1 specifies the default conservative values.
  356          * RFC3390 specifies slightly more aggressive values.
  357          * RFC6928 increases it to ten segments.
  358          *
  359          * If a SYN or SYN/ACK was lost and retransmitted, we have to
  360          * reduce the initial CWND to one segment as congestion is likely
  361          * requiring us to be cautious.
  362          */
  363         if (tp->snd_cwnd == 1)
  364                 tp->snd_cwnd = tp->t_maxseg;            /* SYN(-ACK) lost */
  365         else if (V_tcp_do_initcwnd10)
  366                 tp->snd_cwnd = min(10 * tp->t_maxseg,
  367                     max(2 * tp->t_maxseg, 14600));
  368         else if (V_tcp_do_rfc3390)
  369                 tp->snd_cwnd = min(4 * tp->t_maxseg,
  370                     max(2 * tp->t_maxseg, 4380));
  371         else {
  372                 /* Per RFC5681 Section 3.1 */
  373                 if (tp->t_maxseg > 2190)
  374                         tp->snd_cwnd = 2 * tp->t_maxseg;
  375                 else if (tp->t_maxseg > 1095)
  376                         tp->snd_cwnd = 3 * tp->t_maxseg;
  377                 else
  378                         tp->snd_cwnd = 4 * tp->t_maxseg;
  379         }
  380 
  381         if (CC_ALGO(tp)->conn_init != NULL)
  382                 CC_ALGO(tp)->conn_init(tp->ccv);
  383 }
  384 
  385 void inline
  386 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
  387 {
  388         INP_WLOCK_ASSERT(tp->t_inpcb);
  389 
  390         switch(type) {
  391         case CC_NDUPACK:
  392                 if (!IN_FASTRECOVERY(tp->t_flags)) {
  393                         tp->snd_recover = tp->snd_max;
  394                         if (tp->t_flags & TF_ECN_PERMIT)
  395                                 tp->t_flags |= TF_ECN_SND_CWR;
  396                 }
  397                 break;
  398         case CC_ECN:
  399                 if (!IN_CONGRECOVERY(tp->t_flags)) {
  400                         TCPSTAT_INC(tcps_ecn_rcwnd);
  401                         tp->snd_recover = tp->snd_max;
  402                         if (tp->t_flags & TF_ECN_PERMIT)
  403                                 tp->t_flags |= TF_ECN_SND_CWR;
  404                 }
  405                 break;
  406         case CC_RTO:
  407                 tp->t_dupacks = 0;
  408                 tp->t_bytes_acked = 0;
  409                 EXIT_RECOVERY(tp->t_flags);
  410                 tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
  411                     tp->t_maxseg) * tp->t_maxseg;
  412                 tp->snd_cwnd = tp->t_maxseg;
  413                 break;
  414         case CC_RTO_ERR:
  415                 TCPSTAT_INC(tcps_sndrexmitbad);
  416                 /* RTO was unnecessary, so reset everything. */
  417                 tp->snd_cwnd = tp->snd_cwnd_prev;
  418                 tp->snd_ssthresh = tp->snd_ssthresh_prev;
  419                 tp->snd_recover = tp->snd_recover_prev;
  420                 if (tp->t_flags & TF_WASFRECOVERY)
  421                         ENTER_FASTRECOVERY(tp->t_flags);
  422                 if (tp->t_flags & TF_WASCRECOVERY)
  423                         ENTER_CONGRECOVERY(tp->t_flags);
  424                 tp->snd_nxt = tp->snd_max;
  425                 tp->t_flags &= ~TF_PREVVALID;
  426                 tp->t_badrxtwin = 0;
  427                 break;
  428         }
  429 
  430         if (CC_ALGO(tp)->cong_signal != NULL) {
  431                 if (th != NULL)
  432                         tp->ccv->curack = th->th_ack;
  433                 CC_ALGO(tp)->cong_signal(tp->ccv, type);
  434         }
  435 }
  436 
  437 static void inline
  438 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
  439 {
  440         INP_WLOCK_ASSERT(tp->t_inpcb);
  441 
  442         /* XXXLAS: KASSERT that we're in recovery? */
  443 
  444         if (CC_ALGO(tp)->post_recovery != NULL) {
  445                 tp->ccv->curack = th->th_ack;
  446                 CC_ALGO(tp)->post_recovery(tp->ccv);
  447         }
  448         /* XXXLAS: EXIT_RECOVERY ? */
  449         tp->t_bytes_acked = 0;
  450 }
  451 
  452 #ifdef TCP_SIGNATURE
  453 static inline int
  454 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
  455     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
  456 {
  457         int ret;
  458 
  459         tcp_fields_to_net(th);
  460         ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
  461         tcp_fields_to_host(th);
  462         return (ret);
  463 }
  464 #endif
  465 
  466 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
  467 #ifdef INET6
  468 #define ND6_HINT(tp) \
  469 do { \
  470         if ((tp) && (tp)->t_inpcb && \
  471             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
  472                 nd6_nud_hint(NULL, NULL, 0); \
  473 } while (0)
  474 #else
  475 #define ND6_HINT(tp)
  476 #endif
  477 
  478 /*
  479  * Indicate whether this ack should be delayed.  We can delay the ack if
  480  * following conditions are met:
  481  *      - There is no delayed ack timer in progress.
  482  *      - Our last ack wasn't a 0-sized window. We never want to delay
  483  *        the ack that opens up a 0-sized window.
  484  *      - LRO wasn't used for this segment. We make sure by checking that the
  485  *        segment size is not larger than the MSS.
  486  *      - Delayed acks are enabled or this is a half-synchronized T/TCP
  487  *        connection.
  488  */
  489 #define DELAY_ACK(tp, tlen)                                             \
  490         ((!tcp_timer_active(tp, TT_DELACK) &&                           \
  491             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
  492             (tlen <= tp->t_maxopd) &&                                   \
  493             (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
  494 
  495 /*
  496  * TCP input handling is split into multiple parts:
  497  *   tcp6_input is a thin wrapper around tcp_input for the extended
  498  *      ip6_protox[] call format in ip6_input
  499  *   tcp_input handles primary segment validation, inpcb lookup and
  500  *      SYN processing on listen sockets
  501  *   tcp_do_segment processes the ACK and text of the segment for
  502  *      establishing, established and closing connections
  503  */
  504 #ifdef INET6
  505 int
  506 tcp6_input(struct mbuf **mp, int *offp, int proto)
  507 {
  508         struct mbuf *m = *mp;
  509         struct in6_ifaddr *ia6;
  510 
  511         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
  512 
  513         /*
  514          * draft-itojun-ipv6-tcp-to-anycast
  515          * better place to put this in?
  516          */
  517         ia6 = ip6_getdstifaddr(m);
  518         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
  519                 struct ip6_hdr *ip6;
  520 
  521                 ifa_free(&ia6->ia_ifa);
  522                 ip6 = mtod(m, struct ip6_hdr *);
  523                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
  524                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
  525                 return (IPPROTO_DONE);
  526         }
  527         if (ia6)
  528                 ifa_free(&ia6->ia_ifa);
  529 
  530         return (tcp_input(mp, offp, proto));
  531 }
  532 #endif /* INET6 */
  533 
  534 int
  535 tcp_input(struct mbuf **mp, int *offp, int proto)
  536 {
  537         struct mbuf *m = *mp;
  538         struct tcphdr *th = NULL;
  539         struct ip *ip = NULL;
  540         struct inpcb *inp = NULL;
  541         struct tcpcb *tp = NULL;
  542         struct socket *so = NULL;
  543         u_char *optp = NULL;
  544         int off0;
  545         int optlen = 0;
  546 #ifdef INET
  547         int len;
  548 #endif
  549         int tlen = 0, off;
  550         int drop_hdrlen;
  551         int thflags;
  552         int rstreason = 0;      /* For badport_bandlim accounting purposes */
  553 #ifdef TCP_SIGNATURE
  554         uint8_t sig_checked = 0;
  555 #endif
  556         uint8_t iptos = 0;
  557         struct m_tag *fwd_tag = NULL;
  558 #ifdef INET6
  559         struct ip6_hdr *ip6 = NULL;
  560         int isipv6;
  561 #else
  562         const void *ip6 = NULL;
  563 #endif /* INET6 */
  564         struct tcpopt to;               /* options in this segment */
  565         char *s = NULL;                 /* address and port logging */
  566         int ti_locked;
  567 #define TI_UNLOCKED     1
  568 #define TI_WLOCKED      2
  569 
  570 #ifdef TCPDEBUG
  571         /*
  572          * The size of tcp_saveipgen must be the size of the max ip header,
  573          * now IPv6.
  574          */
  575         u_char tcp_saveipgen[IP6_HDR_LEN];
  576         struct tcphdr tcp_savetcp;
  577         short ostate = 0;
  578 #endif
  579 
  580 #ifdef INET6
  581         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
  582 #endif
  583 
  584         off0 = *offp;
  585         m = *mp;
  586         *mp = NULL;
  587         to.to_flags = 0;
  588         TCPSTAT_INC(tcps_rcvtotal);
  589 
  590 #ifdef INET6
  591         if (isipv6) {
  592                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
  593 
  594                 if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
  595                         m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
  596                         if (m == NULL) {
  597                                 TCPSTAT_INC(tcps_rcvshort);
  598                                 return (IPPROTO_DONE);
  599                         }
  600                 }
  601 
  602                 ip6 = mtod(m, struct ip6_hdr *);
  603                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
  604                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
  605                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
  606                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  607                                 th->th_sum = m->m_pkthdr.csum_data;
  608                         else
  609                                 th->th_sum = in6_cksum_pseudo(ip6, tlen,
  610                                     IPPROTO_TCP, m->m_pkthdr.csum_data);
  611                         th->th_sum ^= 0xffff;
  612                 } else
  613                         th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
  614                 if (th->th_sum) {
  615                         TCPSTAT_INC(tcps_rcvbadsum);
  616                         goto drop;
  617                 }
  618 
  619                 /*
  620                  * Be proactive about unspecified IPv6 address in source.
  621                  * As we use all-zero to indicate unbounded/unconnected pcb,
  622                  * unspecified IPv6 address can be used to confuse us.
  623                  *
  624                  * Note that packets with unspecified IPv6 destination is
  625                  * already dropped in ip6_input.
  626                  */
  627                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
  628                         /* XXX stat */
  629                         goto drop;
  630                 }
  631         }
  632 #endif
  633 #if defined(INET) && defined(INET6)
  634         else
  635 #endif
  636 #ifdef INET
  637         {
  638                 /*
  639                  * Get IP and TCP header together in first mbuf.
  640                  * Note: IP leaves IP header in first mbuf.
  641                  */
  642                 if (off0 > sizeof (struct ip)) {
  643                         ip_stripoptions(m);
  644                         off0 = sizeof(struct ip);
  645                 }
  646                 if (m->m_len < sizeof (struct tcpiphdr)) {
  647                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
  648                             == NULL) {
  649                                 TCPSTAT_INC(tcps_rcvshort);
  650                                 return (IPPROTO_DONE);
  651                         }
  652                 }
  653                 ip = mtod(m, struct ip *);
  654                 th = (struct tcphdr *)((caddr_t)ip + off0);
  655                 tlen = ntohs(ip->ip_len) - off0;
  656 
  657                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
  658                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
  659                                 th->th_sum = m->m_pkthdr.csum_data;
  660                         else
  661                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
  662                                     ip->ip_dst.s_addr,
  663                                     htonl(m->m_pkthdr.csum_data + tlen +
  664                                     IPPROTO_TCP));
  665                         th->th_sum ^= 0xffff;
  666                 } else {
  667                         struct ipovly *ipov = (struct ipovly *)ip;
  668 
  669                         /*
  670                          * Checksum extended TCP header and data.
  671                          */
  672                         len = off0 + tlen;
  673                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
  674                         ipov->ih_len = htons(tlen);
  675                         th->th_sum = in_cksum(m, len);
  676                         /* Reset length for SDT probes. */
  677                         ip->ip_len = htons(tlen + off0);
  678                 }
  679 
  680                 if (th->th_sum) {
  681                         TCPSTAT_INC(tcps_rcvbadsum);
  682                         goto drop;
  683                 }
  684                 /* Re-initialization for later version check */
  685                 ip->ip_v = IPVERSION;
  686         }
  687 #endif /* INET */
  688 
  689 #ifdef INET6
  690         if (isipv6)
  691                 iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
  692 #endif
  693 #if defined(INET) && defined(INET6)
  694         else
  695 #endif
  696 #ifdef INET
  697                 iptos = ip->ip_tos;
  698 #endif
  699 
  700         /*
  701          * Check that TCP offset makes sense,
  702          * pull out TCP options and adjust length.              XXX
  703          */
  704         off = th->th_off << 2;
  705         if (off < sizeof (struct tcphdr) || off > tlen) {
  706                 TCPSTAT_INC(tcps_rcvbadoff);
  707                 goto drop;
  708         }
  709         tlen -= off;    /* tlen is used instead of ti->ti_len */
  710         if (off > sizeof (struct tcphdr)) {
  711 #ifdef INET6
  712                 if (isipv6) {
  713                         IP6_EXTHDR_CHECK(m, off0, off, IPPROTO_DONE);
  714                         ip6 = mtod(m, struct ip6_hdr *);
  715                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
  716                 }
  717 #endif
  718 #if defined(INET) && defined(INET6)
  719                 else
  720 #endif
  721 #ifdef INET
  722                 {
  723                         if (m->m_len < sizeof(struct ip) + off) {
  724                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
  725                                     == NULL) {
  726                                         TCPSTAT_INC(tcps_rcvshort);
  727                                         return (IPPROTO_DONE);
  728                                 }
  729                                 ip = mtod(m, struct ip *);
  730                                 th = (struct tcphdr *)((caddr_t)ip + off0);
  731                         }
  732                 }
  733 #endif
  734                 optlen = off - sizeof (struct tcphdr);
  735                 optp = (u_char *)(th + 1);
  736         }
  737         thflags = th->th_flags;
  738 
  739         /*
  740          * Convert TCP protocol specific fields to host format.
  741          */
  742         tcp_fields_to_host(th);
  743 
  744         /*
  745          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
  746          */
  747         drop_hdrlen = off0 + off;
  748 
  749         /*
  750          * Locate pcb for segment; if we're likely to add or remove a
  751          * connection then first acquire pcbinfo lock.  There are two cases
  752          * where we might discover later we need a write lock despite the
  753          * flags: ACKs moving a connection out of the syncache, and ACKs for
  754          * a connection in TIMEWAIT.
  755          */
  756         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0) {
  757                 INP_INFO_WLOCK(&V_tcbinfo);
  758                 ti_locked = TI_WLOCKED;
  759         } else
  760                 ti_locked = TI_UNLOCKED;
  761 
  762         /*
  763          * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
  764          */
  765         if (
  766 #ifdef INET6
  767             (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
  768 #ifdef INET
  769             || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
  770 #endif
  771 #endif
  772 #if defined(INET) && !defined(INET6)
  773             (m->m_flags & M_IP_NEXTHOP)
  774 #endif
  775             )
  776                 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
  777 
  778 findpcb:
  779 #ifdef INVARIANTS
  780         if (ti_locked == TI_WLOCKED) {
  781                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  782         } else {
  783                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
  784         }
  785 #endif
  786 #ifdef INET6
  787         if (isipv6 && fwd_tag != NULL) {
  788                 struct sockaddr_in6 *next_hop6;
  789 
  790                 next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
  791                 /*
  792                  * Transparently forwarded. Pretend to be the destination.
  793                  * Already got one like this?
  794                  */
  795                 inp = in6_pcblookup_mbuf(&V_tcbinfo,
  796                     &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
  797                     INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
  798                 if (!inp) {
  799                         /*
  800                          * It's new.  Try to find the ambushing socket.
  801                          * Because we've rewritten the destination address,
  802                          * any hardware-generated hash is ignored.
  803                          */
  804                         inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
  805                             th->th_sport, &next_hop6->sin6_addr,
  806                             next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
  807                             th->th_dport, INPLOOKUP_WILDCARD |
  808                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  809                 }
  810         } else if (isipv6) {
  811                 inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
  812                     th->th_sport, &ip6->ip6_dst, th->th_dport,
  813                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  814                     m->m_pkthdr.rcvif, m);
  815         }
  816 #endif /* INET6 */
  817 #if defined(INET6) && defined(INET)
  818         else
  819 #endif
  820 #ifdef INET
  821         if (fwd_tag != NULL) {
  822                 struct sockaddr_in *next_hop;
  823 
  824                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
  825                 /*
  826                  * Transparently forwarded. Pretend to be the destination.
  827                  * already got one like this?
  828                  */
  829                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
  830                     ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
  831                     m->m_pkthdr.rcvif, m);
  832                 if (!inp) {
  833                         /*
  834                          * It's new.  Try to find the ambushing socket.
  835                          * Because we've rewritten the destination address,
  836                          * any hardware-generated hash is ignored.
  837                          */
  838                         inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
  839                             th->th_sport, next_hop->sin_addr,
  840                             next_hop->sin_port ? ntohs(next_hop->sin_port) :
  841                             th->th_dport, INPLOOKUP_WILDCARD |
  842                             INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
  843                 }
  844         } else
  845                 inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
  846                     th->th_sport, ip->ip_dst, th->th_dport,
  847                     INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
  848                     m->m_pkthdr.rcvif, m);
  849 #endif /* INET */
  850 
  851         /*
  852          * If the INPCB does not exist then all data in the incoming
  853          * segment is discarded and an appropriate RST is sent back.
  854          * XXX MRT Send RST using which routing table?
  855          */
  856         if (inp == NULL) {
  857                 /*
  858                  * Log communication attempts to ports that are not
  859                  * in use.
  860                  */
  861                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
  862                     tcp_log_in_vain == 2) {
  863                         if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
  864                                 log(LOG_INFO, "%s; %s: Connection attempt "
  865                                     "to closed port\n", s, __func__);
  866                 }
  867                 /*
  868                  * When blackholing do not respond with a RST but
  869                  * completely ignore the segment and drop it.
  870                  */
  871                 if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
  872                     V_blackhole == 2)
  873                         goto dropunlock;
  874 
  875                 rstreason = BANDLIM_RST_CLOSEDPORT;
  876                 goto dropwithreset;
  877         }
  878         INP_WLOCK_ASSERT(inp);
  879         if (!(inp->inp_flags & INP_HW_FLOWID)
  880             && (m->m_flags & M_FLOWID)
  881             && ((inp->inp_socket == NULL)
  882                 || !(inp->inp_socket->so_options & SO_ACCEPTCONN))) {
  883                 inp->inp_flags |= INP_HW_FLOWID;
  884                 inp->inp_flags &= ~INP_SW_FLOWID;
  885                 inp->inp_flowid = m->m_pkthdr.flowid;
  886                 inp->inp_flowtype = M_HASHTYPE_GET(m);
  887         }
  888 #ifdef IPSEC
  889 #ifdef INET6
  890         if (isipv6 && ipsec6_in_reject(m, inp)) {
  891                 IPSEC6STAT_INC(ips_in_polvio);
  892                 goto dropunlock;
  893         } else
  894 #endif /* INET6 */
  895         if (ipsec4_in_reject(m, inp) != 0) {
  896                 IPSECSTAT_INC(ips_in_polvio);
  897                 goto dropunlock;
  898         }
  899 #endif /* IPSEC */
  900 
  901         /*
  902          * Check the minimum TTL for socket.
  903          */
  904         if (inp->inp_ip_minttl != 0) {
  905 #ifdef INET6
  906                 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
  907                         goto dropunlock;
  908                 else
  909 #endif
  910                 if (inp->inp_ip_minttl > ip->ip_ttl)
  911                         goto dropunlock;
  912         }
  913 
  914         /*
  915          * A previous connection in TIMEWAIT state is supposed to catch stray
  916          * or duplicate segments arriving late.  If this segment was a
  917          * legitimate new connection attempt, the old INPCB gets removed and
  918          * we can try again to find a listening socket.
  919          *
  920          * At this point, due to earlier optimism, we may hold only an inpcb
  921          * lock, and not the inpcbinfo write lock.  If so, we need to try to
  922          * acquire it, or if that fails, acquire a reference on the inpcb,
  923          * drop all locks, acquire a global write lock, and then re-acquire
  924          * the inpcb lock.  We may at that point discover that another thread
  925          * has tried to free the inpcb, in which case we need to loop back
  926          * and try to find a new inpcb to deliver to.
  927          *
  928          * XXXRW: It may be time to rethink timewait locking.
  929          */
  930 relocked:
  931         if (inp->inp_flags & INP_TIMEWAIT) {
  932                 if (ti_locked == TI_UNLOCKED) {
  933                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
  934                                 in_pcbref(inp);
  935                                 INP_WUNLOCK(inp);
  936                                 INP_INFO_WLOCK(&V_tcbinfo);
  937                                 ti_locked = TI_WLOCKED;
  938                                 INP_WLOCK(inp);
  939                                 if (in_pcbrele_wlocked(inp)) {
  940                                         inp = NULL;
  941                                         goto findpcb;
  942                                 }
  943                         } else
  944                                 ti_locked = TI_WLOCKED;
  945                 }
  946                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  947 
  948                 if (thflags & TH_SYN)
  949                         tcp_dooptions(&to, optp, optlen, TO_SYN);
  950                 /*
  951                  * NB: tcp_twcheck unlocks the INP and frees the mbuf.
  952                  */
  953                 if (tcp_twcheck(inp, &to, th, m, tlen))
  954                         goto findpcb;
  955                 INP_INFO_WUNLOCK(&V_tcbinfo);
  956                 return (IPPROTO_DONE);
  957         }
  958         /*
  959          * The TCPCB may no longer exist if the connection is winding
  960          * down or it is in the CLOSED state.  Either way we drop the
  961          * segment and send an appropriate response.
  962          */
  963         tp = intotcpcb(inp);
  964         if (tp == NULL || tp->t_state == TCPS_CLOSED) {
  965                 rstreason = BANDLIM_RST_CLOSEDPORT;
  966                 goto dropwithreset;
  967         }
  968 
  969 #ifdef TCP_OFFLOAD
  970         if (tp->t_flags & TF_TOE) {
  971                 tcp_offload_input(tp, m);
  972                 m = NULL;       /* consumed by the TOE driver */
  973                 goto dropunlock;
  974         }
  975 #endif
  976 
  977         /*
  978          * We've identified a valid inpcb, but it could be that we need an
  979          * inpcbinfo write lock but don't hold it.  In this case, attempt to
  980          * acquire using the same strategy as the TIMEWAIT case above.  If we
  981          * relock, we have to jump back to 'relocked' as the connection might
  982          * now be in TIMEWAIT.
  983          */
  984 #ifdef INVARIANTS
  985         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0)
  986                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  987 #endif
  988         if (tp->t_state != TCPS_ESTABLISHED) {
  989                 if (ti_locked == TI_UNLOCKED) {
  990                         if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
  991                                 in_pcbref(inp);
  992                                 INP_WUNLOCK(inp);
  993                                 INP_INFO_WLOCK(&V_tcbinfo);
  994                                 ti_locked = TI_WLOCKED;
  995                                 INP_WLOCK(inp);
  996                                 if (in_pcbrele_wlocked(inp)) {
  997                                         inp = NULL;
  998                                         goto findpcb;
  999                                 }
 1000                                 goto relocked;
 1001                         } else
 1002                                 ti_locked = TI_WLOCKED;
 1003                 }
 1004                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1005         }
 1006 
 1007 #ifdef MAC
 1008         INP_WLOCK_ASSERT(inp);
 1009         if (mac_inpcb_check_deliver(inp, m))
 1010                 goto dropunlock;
 1011 #endif
 1012         so = inp->inp_socket;
 1013         KASSERT(so != NULL, ("%s: so == NULL", __func__));
 1014 #ifdef TCPDEBUG
 1015         if (so->so_options & SO_DEBUG) {
 1016                 ostate = tp->t_state;
 1017 #ifdef INET6
 1018                 if (isipv6) {
 1019                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 1020                 } else
 1021 #endif
 1022                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 1023                 tcp_savetcp = *th;
 1024         }
 1025 #endif /* TCPDEBUG */
 1026         /*
 1027          * When the socket is accepting connections (the INPCB is in LISTEN
 1028          * state) we look into the SYN cache if this is a new connection
 1029          * attempt or the completion of a previous one.  Because listen
 1030          * sockets are never in TCPS_ESTABLISHED, the V_tcbinfo lock will be
 1031          * held in this case.
 1032          */
 1033         if (so->so_options & SO_ACCEPTCONN) {
 1034                 struct in_conninfo inc;
 1035 
 1036                 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
 1037                     "tp not listening", __func__));
 1038                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1039 
 1040                 bzero(&inc, sizeof(inc));
 1041 #ifdef INET6
 1042                 if (isipv6) {
 1043                         inc.inc_flags |= INC_ISIPV6;
 1044                         inc.inc6_faddr = ip6->ip6_src;
 1045                         inc.inc6_laddr = ip6->ip6_dst;
 1046                 } else
 1047 #endif
 1048                 {
 1049                         inc.inc_faddr = ip->ip_src;
 1050                         inc.inc_laddr = ip->ip_dst;
 1051                 }
 1052                 inc.inc_fport = th->th_sport;
 1053                 inc.inc_lport = th->th_dport;
 1054                 inc.inc_fibnum = so->so_fibnum;
 1055 
 1056                 /*
 1057                  * Check for an existing connection attempt in syncache if
 1058                  * the flag is only ACK.  A successful lookup creates a new
 1059                  * socket appended to the listen queue in SYN_RECEIVED state.
 1060                  */
 1061                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 1062                         /*
 1063                          * Parse the TCP options here because
 1064                          * syncookies need access to the reflected
 1065                          * timestamp.
 1066                          */
 1067                         tcp_dooptions(&to, optp, optlen, 0);
 1068                         /*
 1069                          * NB: syncache_expand() doesn't unlock
 1070                          * inp and tcpinfo locks.
 1071                          */
 1072                         if (!syncache_expand(&inc, &to, th, &so, m)) {
 1073                                 /*
 1074                                  * No syncache entry or ACK was not
 1075                                  * for our SYN/ACK.  Send a RST.
 1076                                  * NB: syncache did its own logging
 1077                                  * of the failure cause.
 1078                                  */
 1079                                 rstreason = BANDLIM_RST_OPENPORT;
 1080                                 goto dropwithreset;
 1081                         }
 1082                         if (so == NULL) {
 1083                                 /*
 1084                                  * We completed the 3-way handshake
 1085                                  * but could not allocate a socket
 1086                                  * either due to memory shortage,
 1087                                  * listen queue length limits or
 1088                                  * global socket limits.  Send RST
 1089                                  * or wait and have the remote end
 1090                                  * retransmit the ACK for another
 1091                                  * try.
 1092                                  */
 1093                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1094                                         log(LOG_DEBUG, "%s; %s: Listen socket: "
 1095                                             "Socket allocation failed due to "
 1096                                             "limits or memory shortage, %s\n",
 1097                                             s, __func__,
 1098                                             V_tcp_sc_rst_sock_fail ?
 1099                                             "sending RST" : "try again");
 1100                                 if (V_tcp_sc_rst_sock_fail) {
 1101                                         rstreason = BANDLIM_UNLIMITED;
 1102                                         goto dropwithreset;
 1103                                 } else
 1104                                         goto dropunlock;
 1105                         }
 1106                         /*
 1107                          * Socket is created in state SYN_RECEIVED.
 1108                          * Unlock the listen socket, lock the newly
 1109                          * created socket and update the tp variable.
 1110                          */
 1111                         INP_WUNLOCK(inp);       /* listen socket */
 1112                         inp = sotoinpcb(so);
 1113                         INP_WLOCK(inp);         /* new connection */
 1114                         tp = intotcpcb(inp);
 1115                         KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
 1116                             ("%s: ", __func__));
 1117 #ifdef TCP_SIGNATURE
 1118                         if (sig_checked == 0)  {
 1119                                 tcp_dooptions(&to, optp, optlen,
 1120                                     (thflags & TH_SYN) ? TO_SYN : 0);
 1121                                 if (!tcp_signature_verify_input(m, off0, tlen,
 1122                                     optlen, &to, th, tp->t_flags)) {
 1123 
 1124                                         /*
 1125                                          * In SYN_SENT state if it receives an
 1126                                          * RST, it is allowed for further
 1127                                          * processing.
 1128                                          */
 1129                                         if ((thflags & TH_RST) == 0 ||
 1130                                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1131                                                 goto dropunlock;
 1132                                 }
 1133                                 sig_checked = 1;
 1134                         }
 1135 #endif
 1136 
 1137                         /*
 1138                          * Process the segment and the data it
 1139                          * contains.  tcp_do_segment() consumes
 1140                          * the mbuf chain and unlocks the inpcb.
 1141                          */
 1142                         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
 1143                             iptos, ti_locked);
 1144                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1145                         return (IPPROTO_DONE);
 1146                 }
 1147                 /*
 1148                  * Segment flag validation for new connection attempts:
 1149                  *
 1150                  * Our (SYN|ACK) response was rejected.
 1151                  * Check with syncache and remove entry to prevent
 1152                  * retransmits.
 1153                  *
 1154                  * NB: syncache_chkrst does its own logging of failure
 1155                  * causes.
 1156                  */
 1157                 if (thflags & TH_RST) {
 1158                         syncache_chkrst(&inc, th);
 1159                         goto dropunlock;
 1160                 }
 1161                 /*
 1162                  * We can't do anything without SYN.
 1163                  */
 1164                 if ((thflags & TH_SYN) == 0) {
 1165                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1166                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1167                                     "SYN is missing, segment ignored\n",
 1168                                     s, __func__);
 1169                         TCPSTAT_INC(tcps_badsyn);
 1170                         goto dropunlock;
 1171                 }
 1172                 /*
 1173                  * (SYN|ACK) is bogus on a listen socket.
 1174                  */
 1175                 if (thflags & TH_ACK) {
 1176                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1177                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1178                                     "SYN|ACK invalid, segment rejected\n",
 1179                                     s, __func__);
 1180                         syncache_badack(&inc);  /* XXX: Not needed! */
 1181                         TCPSTAT_INC(tcps_badsyn);
 1182                         rstreason = BANDLIM_RST_OPENPORT;
 1183                         goto dropwithreset;
 1184                 }
 1185                 /*
 1186                  * If the drop_synfin option is enabled, drop all
 1187                  * segments with both the SYN and FIN bits set.
 1188                  * This prevents e.g. nmap from identifying the
 1189                  * TCP/IP stack.
 1190                  * XXX: Poor reasoning.  nmap has other methods
 1191                  * and is constantly refining its stack detection
 1192                  * strategies.
 1193                  * XXX: This is a violation of the TCP specification
 1194                  * and was used by RFC1644.
 1195                  */
 1196                 if ((thflags & TH_FIN) && V_drop_synfin) {
 1197                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1198                                 log(LOG_DEBUG, "%s; %s: Listen socket: "
 1199                                     "SYN|FIN segment ignored (based on "
 1200                                     "sysctl setting)\n", s, __func__);
 1201                         TCPSTAT_INC(tcps_badsyn);
 1202                         goto dropunlock;
 1203                 }
 1204                 /*
 1205                  * Segment's flags are (SYN) or (SYN|FIN).
 1206                  *
 1207                  * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
 1208                  * as they do not affect the state of the TCP FSM.
 1209                  * The data pointed to by TH_URG and th_urp is ignored.
 1210                  */
 1211                 KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
 1212                     ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
 1213                 KASSERT(thflags & (TH_SYN),
 1214                     ("%s: Listen socket: TH_SYN not set", __func__));
 1215 #ifdef INET6
 1216                 /*
 1217                  * If deprecated address is forbidden,
 1218                  * we do not accept SYN to deprecated interface
 1219                  * address to prevent any new inbound connection from
 1220                  * getting established.
 1221                  * When we do not accept SYN, we send a TCP RST,
 1222                  * with deprecated source address (instead of dropping
 1223                  * it).  We compromise it as it is much better for peer
 1224                  * to send a RST, and RST will be the final packet
 1225                  * for the exchange.
 1226                  *
 1227                  * If we do not forbid deprecated addresses, we accept
 1228                  * the SYN packet.  RFC2462 does not suggest dropping
 1229                  * SYN in this case.
 1230                  * If we decipher RFC2462 5.5.4, it says like this:
 1231                  * 1. use of deprecated addr with existing
 1232                  *    communication is okay - "SHOULD continue to be
 1233                  *    used"
 1234                  * 2. use of it with new communication:
 1235                  *   (2a) "SHOULD NOT be used if alternate address
 1236                  *        with sufficient scope is available"
 1237                  *   (2b) nothing mentioned otherwise.
 1238                  * Here we fall into (2b) case as we have no choice in
 1239                  * our source address selection - we must obey the peer.
 1240                  *
 1241                  * The wording in RFC2462 is confusing, and there are
 1242                  * multiple description text for deprecated address
 1243                  * handling - worse, they are not exactly the same.
 1244                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 1245                  */
 1246                 if (isipv6 && !V_ip6_use_deprecated) {
 1247                         struct in6_ifaddr *ia6;
 1248 
 1249                         ia6 = ip6_getdstifaddr(m);
 1250                         if (ia6 != NULL &&
 1251                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 1252                                 ifa_free(&ia6->ia_ifa);
 1253                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1254                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1255                                         "Connection attempt to deprecated "
 1256                                         "IPv6 address rejected\n",
 1257                                         s, __func__);
 1258                                 rstreason = BANDLIM_RST_OPENPORT;
 1259                                 goto dropwithreset;
 1260                         }
 1261                         if (ia6)
 1262                                 ifa_free(&ia6->ia_ifa);
 1263                 }
 1264 #endif /* INET6 */
 1265                 /*
 1266                  * Basic sanity checks on incoming SYN requests:
 1267                  *   Don't respond if the destination is a link layer
 1268                  *      broadcast according to RFC1122 4.2.3.10, p. 104.
 1269                  *   If it is from this socket it must be forged.
 1270                  *   Don't respond if the source or destination is a
 1271                  *      global or subnet broad- or multicast address.
 1272                  *   Note that it is quite possible to receive unicast
 1273                  *      link-layer packets with a broadcast IP address. Use
 1274                  *      in_broadcast() to find them.
 1275                  */
 1276                 if (m->m_flags & (M_BCAST|M_MCAST)) {
 1277                         if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1278                             log(LOG_DEBUG, "%s; %s: Listen socket: "
 1279                                 "Connection attempt from broad- or multicast "
 1280                                 "link layer address ignored\n", s, __func__);
 1281                         goto dropunlock;
 1282                 }
 1283 #ifdef INET6
 1284                 if (isipv6) {
 1285                         if (th->th_dport == th->th_sport &&
 1286                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
 1287                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1288                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1289                                         "Connection attempt to/from self "
 1290                                         "ignored\n", s, __func__);
 1291                                 goto dropunlock;
 1292                         }
 1293                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 1294                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
 1295                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1296                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1297                                         "Connection attempt from/to multicast "
 1298                                         "address ignored\n", s, __func__);
 1299                                 goto dropunlock;
 1300                         }
 1301                 }
 1302 #endif
 1303 #if defined(INET) && defined(INET6)
 1304                 else
 1305 #endif
 1306 #ifdef INET
 1307                 {
 1308                         if (th->th_dport == th->th_sport &&
 1309                             ip->ip_dst.s_addr == ip->ip_src.s_addr) {
 1310                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1311                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1312                                         "Connection attempt from/to self "
 1313                                         "ignored\n", s, __func__);
 1314                                 goto dropunlock;
 1315                         }
 1316                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 1317                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 1318                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 1319                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
 1320                                 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
 1321                                     log(LOG_DEBUG, "%s; %s: Listen socket: "
 1322                                         "Connection attempt from/to broad- "
 1323                                         "or multicast address ignored\n",
 1324                                         s, __func__);
 1325                                 goto dropunlock;
 1326                         }
 1327                 }
 1328 #endif
 1329                 /*
 1330                  * SYN appears to be valid.  Create compressed TCP state
 1331                  * for syncache.
 1332                  */
 1333 #ifdef TCPDEBUG
 1334                 if (so->so_options & SO_DEBUG)
 1335                         tcp_trace(TA_INPUT, ostate, tp,
 1336                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1337 #endif
 1338                 tcp_dooptions(&to, optp, optlen, TO_SYN);
 1339                 syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
 1340                 /*
 1341                  * Entry added to syncache and mbuf consumed.
 1342                  * Everything already unlocked by syncache_add().
 1343                  */
 1344                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1345                 return (IPPROTO_DONE);
 1346         } else if (tp->t_state == TCPS_LISTEN) {
 1347                 /*
 1348                  * When a listen socket is torn down the SO_ACCEPTCONN
 1349                  * flag is removed first while connections are drained
 1350                  * from the accept queue in a unlock/lock cycle of the
 1351                  * ACCEPT_LOCK, opening a race condition allowing a SYN
 1352                  * attempt go through unhandled.
 1353                  */
 1354                 goto dropunlock;
 1355         }
 1356 
 1357 #ifdef TCP_SIGNATURE
 1358         if (sig_checked == 0)  {
 1359                 tcp_dooptions(&to, optp, optlen,
 1360                     (thflags & TH_SYN) ? TO_SYN : 0);
 1361                 if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
 1362                     th, tp->t_flags)) {
 1363 
 1364                         /*
 1365                          * In SYN_SENT state if it receives an RST, it is
 1366                          * allowed for further processing.
 1367                          */
 1368                         if ((thflags & TH_RST) == 0 ||
 1369                             (tp->t_state == TCPS_SYN_SENT) == 0)
 1370                                 goto dropunlock;
 1371                 }
 1372                 sig_checked = 1;
 1373         }
 1374 #endif
 1375 
 1376         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1377 
 1378         /*
 1379          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
 1380          * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
 1381          * the inpcb, and unlocks pcbinfo.
 1382          */
 1383         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
 1384         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1385         return (IPPROTO_DONE);
 1386 
 1387 dropwithreset:
 1388         TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1389 
 1390         if (ti_locked == TI_WLOCKED) {
 1391                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1392                 ti_locked = TI_UNLOCKED;
 1393         }
 1394 #ifdef INVARIANTS
 1395         else {
 1396                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
 1397                     "ti_locked: %d", __func__, ti_locked));
 1398                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1399         }
 1400 #endif
 1401 
 1402         if (inp != NULL) {
 1403                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 1404                 INP_WUNLOCK(inp);
 1405         } else
 1406                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 1407         m = NULL;       /* mbuf chain got consumed. */
 1408         goto drop;
 1409 
 1410 dropunlock:
 1411         if (m != NULL)
 1412                 TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
 1413 
 1414         if (ti_locked == TI_WLOCKED) {
 1415                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1416                 ti_locked = TI_UNLOCKED;
 1417         }
 1418 #ifdef INVARIANTS
 1419         else {
 1420                 KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
 1421                     "ti_locked: %d", __func__, ti_locked));
 1422                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1423         }
 1424 #endif
 1425 
 1426         if (inp != NULL)
 1427                 INP_WUNLOCK(inp);
 1428 
 1429 drop:
 1430         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1431         if (s != NULL)
 1432                 free(s, M_TCPLOG);
 1433         if (m != NULL)
 1434                 m_freem(m);
 1435         return (IPPROTO_DONE);
 1436 }
 1437 
 1438 static void
 1439 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 1440     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
 1441     int ti_locked)
 1442 {
 1443         int thflags, acked, ourfinisacked, needoutput = 0;
 1444         int rstreason, todrop, win;
 1445         u_long tiwin;
 1446         char *s;
 1447         struct in_conninfo *inc;
 1448         struct mbuf *mfree;
 1449         struct tcpopt to;
 1450 
 1451 #ifdef TCPDEBUG
 1452         /*
 1453          * The size of tcp_saveipgen must be the size of the max ip header,
 1454          * now IPv6.
 1455          */
 1456         u_char tcp_saveipgen[IP6_HDR_LEN];
 1457         struct tcphdr tcp_savetcp;
 1458         short ostate = 0;
 1459 #endif
 1460         thflags = th->th_flags;
 1461         inc = &tp->t_inpcb->inp_inc;
 1462         tp->sackhint.last_sack_ack = 0;
 1463 
 1464         /*
 1465          * If this is either a state-changing packet or current state isn't
 1466          * established, we require a write lock on tcbinfo.  Otherwise, we
 1467          * allow the tcbinfo to be in either alocked or unlocked, as the
 1468          * caller may have unnecessarily acquired a write lock due to a race.
 1469          */
 1470         if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
 1471             tp->t_state != TCPS_ESTABLISHED) {
 1472                 KASSERT(ti_locked == TI_WLOCKED, ("%s ti_locked %d for "
 1473                     "SYN/FIN/RST/!EST", __func__, ti_locked));
 1474                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1475         } else {
 1476 #ifdef INVARIANTS
 1477                 if (ti_locked == TI_WLOCKED)
 1478                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1479                 else {
 1480                         KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
 1481                             "ti_locked: %d", __func__, ti_locked));
 1482                         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 1483                 }
 1484 #endif
 1485         }
 1486         INP_WLOCK_ASSERT(tp->t_inpcb);
 1487         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
 1488             __func__));
 1489         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
 1490             __func__));
 1491 
 1492         /*
 1493          * Segment received on connection.
 1494          * Reset idle time and keep-alive timer.
 1495          * XXX: This should be done after segment
 1496          * validation to ignore broken/spoofed segs.
 1497          */
 1498         tp->t_rcvtime = ticks;
 1499         if (TCPS_HAVEESTABLISHED(tp->t_state))
 1500                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 1501 
 1502         /*
 1503          * Unscale the window into a 32-bit value.
 1504          * For the SYN_SENT state the scale is zero.
 1505          */
 1506         tiwin = th->th_win << tp->snd_scale;
 1507 
 1508         /*
 1509          * TCP ECN processing.
 1510          */
 1511         if (tp->t_flags & TF_ECN_PERMIT) {
 1512                 if (thflags & TH_CWR)
 1513                         tp->t_flags &= ~TF_ECN_SND_ECE;
 1514                 switch (iptos & IPTOS_ECN_MASK) {
 1515                 case IPTOS_ECN_CE:
 1516                         tp->t_flags |= TF_ECN_SND_ECE;
 1517                         TCPSTAT_INC(tcps_ecn_ce);
 1518                         break;
 1519                 case IPTOS_ECN_ECT0:
 1520                         TCPSTAT_INC(tcps_ecn_ect0);
 1521                         break;
 1522                 case IPTOS_ECN_ECT1:
 1523                         TCPSTAT_INC(tcps_ecn_ect1);
 1524                         break;
 1525                 }
 1526                 /* Congestion experienced. */
 1527                 if (thflags & TH_ECE) {
 1528                         cc_cong_signal(tp, th, CC_ECN);
 1529                 }
 1530         }
 1531 
 1532         /*
 1533          * Parse options on any incoming segment.
 1534          */
 1535         tcp_dooptions(&to, (u_char *)(th + 1),
 1536             (th->th_off << 2) - sizeof(struct tcphdr),
 1537             (thflags & TH_SYN) ? TO_SYN : 0);
 1538 
 1539         /*
 1540          * If echoed timestamp is later than the current time,
 1541          * fall back to non RFC1323 RTT calculation.  Normalize
 1542          * timestamp if syncookies were used when this connection
 1543          * was established.
 1544          */
 1545         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
 1546                 to.to_tsecr -= tp->ts_offset;
 1547                 if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
 1548                         to.to_tsecr = 0;
 1549         }
 1550         /*
 1551          * If timestamps were negotiated during SYN/ACK they should
 1552          * appear on every segment during this session and vice versa.
 1553          */
 1554         if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
 1555                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1556                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1557                             "no action\n", s, __func__);
 1558                         free(s, M_TCPLOG);
 1559                 }
 1560         }
 1561         if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
 1562                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1563                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1564                             "no action\n", s, __func__);
 1565                         free(s, M_TCPLOG);
 1566                 }
 1567         }
 1568 
 1569         /*
 1570          * Process options only when we get SYN/ACK back. The SYN case
 1571          * for incoming connections is handled in tcp_syncache.
 1572          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
 1573          * or <SYN,ACK>) segment itself is never scaled.
 1574          * XXX this is traditional behavior, may need to be cleaned up.
 1575          */
 1576         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
 1577                 if ((to.to_flags & TOF_SCALE) &&
 1578                     (tp->t_flags & TF_REQ_SCALE)) {
 1579                         tp->t_flags |= TF_RCVD_SCALE;
 1580                         tp->snd_scale = to.to_wscale;
 1581                 }
 1582                 /*
 1583                  * Initial send window.  It will be updated with
 1584                  * the next incoming segment to the scaled value.
 1585                  */
 1586                 tp->snd_wnd = th->th_win;
 1587                 if (to.to_flags & TOF_TS) {
 1588                         tp->t_flags |= TF_RCVD_TSTMP;
 1589                         tp->ts_recent = to.to_tsval;
 1590                         tp->ts_recent_age = tcp_ts_getticks();
 1591                 }
 1592                 if (to.to_flags & TOF_MSS)
 1593                         tcp_mss(tp, to.to_mss);
 1594                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 1595                     (to.to_flags & TOF_SACKPERM) == 0)
 1596                         tp->t_flags &= ~TF_SACK_PERMIT;
 1597         }
 1598 
 1599         /*
 1600          * Header prediction: check for the two common cases
 1601          * of a uni-directional data xfer.  If the packet has
 1602          * no control flags, is in-sequence, the window didn't
 1603          * change and we're not retransmitting, it's a
 1604          * candidate.  If the length is zero and the ack moved
 1605          * forward, we're the sender side of the xfer.  Just
 1606          * free the data acked & wake any higher level process
 1607          * that was blocked waiting for space.  If the length
 1608          * is non-zero and the ack didn't move, we're the
 1609          * receiver side.  If we're getting packets in-order
 1610          * (the reassembly queue is empty), add the data to
 1611          * the socket buffer and note that we need a delayed ack.
 1612          * Make sure that the hidden state-flags are also off.
 1613          * Since we check for TCPS_ESTABLISHED first, it can only
 1614          * be TH_NEEDSYN.
 1615          */
 1616         if (tp->t_state == TCPS_ESTABLISHED &&
 1617             th->th_seq == tp->rcv_nxt &&
 1618             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 1619             tp->snd_nxt == tp->snd_max &&
 1620             tiwin && tiwin == tp->snd_wnd && 
 1621             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 1622             tp->t_segq == NULL && ((to.to_flags & TOF_TS) == 0 ||
 1623              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
 1624 
 1625                 /*
 1626                  * If last ACK falls within this segment's sequence numbers,
 1627                  * record the timestamp.
 1628                  * NOTE that the test is modified according to the latest
 1629                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 1630                  */
 1631                 if ((to.to_flags & TOF_TS) != 0 &&
 1632                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 1633                         tp->ts_recent_age = tcp_ts_getticks();
 1634                         tp->ts_recent = to.to_tsval;
 1635                 }
 1636 
 1637                 if (tlen == 0) {
 1638                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 1639                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 1640                             !IN_RECOVERY(tp->t_flags) &&
 1641                             (to.to_flags & TOF_SACK) == 0 &&
 1642                             TAILQ_EMPTY(&tp->snd_holes)) {
 1643                                 /*
 1644                                  * This is a pure ack for outstanding data.
 1645                                  */
 1646                                 if (ti_locked == TI_WLOCKED)
 1647                                         INP_INFO_WUNLOCK(&V_tcbinfo);
 1648                                 ti_locked = TI_UNLOCKED;
 1649 
 1650                                 TCPSTAT_INC(tcps_predack);
 1651 
 1652                                 /*
 1653                                  * "bad retransmit" recovery.
 1654                                  */
 1655                                 if (tp->t_rxtshift == 1 &&
 1656                                     tp->t_flags & TF_PREVVALID &&
 1657                                     (int)(ticks - tp->t_badrxtwin) < 0) {
 1658                                         cc_cong_signal(tp, th, CC_RTO_ERR);
 1659                                 }
 1660 
 1661                                 /*
 1662                                  * Recalculate the transmit timer / rtt.
 1663                                  *
 1664                                  * Some boxes send broken timestamp replies
 1665                                  * during the SYN+ACK phase, ignore
 1666                                  * timestamps of 0 or we could calculate a
 1667                                  * huge RTT and blow up the retransmit timer.
 1668                                  */
 1669                                 if ((to.to_flags & TOF_TS) != 0 &&
 1670                                     to.to_tsecr) {
 1671                                         u_int t;
 1672 
 1673                                         t = tcp_ts_getticks() - to.to_tsecr;
 1674                                         if (!tp->t_rttlow || tp->t_rttlow > t)
 1675                                                 tp->t_rttlow = t;
 1676                                         tcp_xmit_timer(tp,
 1677                                             TCP_TS_TO_TICKS(t) + 1);
 1678                                 } else if (tp->t_rtttime &&
 1679                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
 1680                                         if (!tp->t_rttlow ||
 1681                                             tp->t_rttlow > ticks - tp->t_rtttime)
 1682                                                 tp->t_rttlow = ticks - tp->t_rtttime;
 1683                                         tcp_xmit_timer(tp,
 1684                                                         ticks - tp->t_rtttime);
 1685                                 }
 1686                                 acked = BYTES_THIS_ACK(tp, th);
 1687 
 1688                                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 1689                                 hhook_run_tcp_est_in(tp, th, &to);
 1690 
 1691                                 TCPSTAT_INC(tcps_rcvackpack);
 1692                                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 1693                                 sbdrop(&so->so_snd, acked);
 1694                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
 1695                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 1696                                         tp->snd_recover = th->th_ack - 1;
 1697                                 
 1698                                 /*
 1699                                  * Let the congestion control algorithm update
 1700                                  * congestion control related information. This
 1701                                  * typically means increasing the congestion
 1702                                  * window.
 1703                                  */
 1704                                 cc_ack_received(tp, th, CC_ACK);
 1705 
 1706                                 tp->snd_una = th->th_ack;
 1707                                 /*
 1708                                  * Pull snd_wl2 up to prevent seq wrap relative
 1709                                  * to th_ack.
 1710                                  */
 1711                                 tp->snd_wl2 = th->th_ack;
 1712                                 tp->t_dupacks = 0;
 1713                                 m_freem(m);
 1714                                 ND6_HINT(tp); /* Some progress has been made. */
 1715 
 1716                                 /*
 1717                                  * If all outstanding data are acked, stop
 1718                                  * retransmit timer, otherwise restart timer
 1719                                  * using current (possibly backed-off) value.
 1720                                  * If process is waiting for space,
 1721                                  * wakeup/selwakeup/signal.  If data
 1722                                  * are ready to send, let tcp_output
 1723                                  * decide between more output or persist.
 1724                                  */
 1725 #ifdef TCPDEBUG
 1726                                 if (so->so_options & SO_DEBUG)
 1727                                         tcp_trace(TA_INPUT, ostate, tp,
 1728                                             (void *)tcp_saveipgen,
 1729                                             &tcp_savetcp, 0);
 1730 #endif
 1731                                 if (tp->snd_una == tp->snd_max)
 1732                                         tcp_timer_activate(tp, TT_REXMT, 0);
 1733                                 else if (!tcp_timer_active(tp, TT_PERSIST))
 1734                                         tcp_timer_activate(tp, TT_REXMT,
 1735                                                       tp->t_rxtcur);
 1736                                 sowwakeup(so);
 1737                                 if (so->so_snd.sb_cc)
 1738                                         (void) tcp_output(tp);
 1739                                 goto check_delack;
 1740                         }
 1741                 } else if (th->th_ack == tp->snd_una &&
 1742                     tlen <= sbspace(&so->so_rcv)) {
 1743                         int newsize = 0;        /* automatic sockbuf scaling */
 1744 
 1745                         /*
 1746                          * This is a pure, in-sequence data packet with
 1747                          * nothing on the reassembly queue and we have enough
 1748                          * buffer space to take it.
 1749                          */
 1750                         if (ti_locked == TI_WLOCKED)
 1751                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1752                         ti_locked = TI_UNLOCKED;
 1753 
 1754                         /* Clean receiver SACK report if present */
 1755                         if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
 1756                                 tcp_clean_sackreport(tp);
 1757                         TCPSTAT_INC(tcps_preddat);
 1758                         tp->rcv_nxt += tlen;
 1759                         /*
 1760                          * Pull snd_wl1 up to prevent seq wrap relative to
 1761                          * th_seq.
 1762                          */
 1763                         tp->snd_wl1 = th->th_seq;
 1764                         /*
 1765                          * Pull rcv_up up to prevent seq wrap relative to
 1766                          * rcv_nxt.
 1767                          */
 1768                         tp->rcv_up = tp->rcv_nxt;
 1769                         TCPSTAT_INC(tcps_rcvpack);
 1770                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 1771                         ND6_HINT(tp);   /* Some progress has been made */
 1772 #ifdef TCPDEBUG
 1773                         if (so->so_options & SO_DEBUG)
 1774                                 tcp_trace(TA_INPUT, ostate, tp,
 1775                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
 1776 #endif
 1777                 /*
 1778                  * Automatic sizing of receive socket buffer.  Often the send
 1779                  * buffer size is not optimally adjusted to the actual network
 1780                  * conditions at hand (delay bandwidth product).  Setting the
 1781                  * buffer size too small limits throughput on links with high
 1782                  * bandwidth and high delay (eg. trans-continental/oceanic links).
 1783                  *
 1784                  * On the receive side the socket buffer memory is only rarely
 1785                  * used to any significant extent.  This allows us to be much
 1786                  * more aggressive in scaling the receive socket buffer.  For
 1787                  * the case that the buffer space is actually used to a large
 1788                  * extent and we run out of kernel memory we can simply drop
 1789                  * the new segments; TCP on the sender will just retransmit it
 1790                  * later.  Setting the buffer size too big may only consume too
 1791                  * much kernel memory if the application doesn't read() from
 1792                  * the socket or packet loss or reordering makes use of the
 1793                  * reassembly queue.
 1794                  *
 1795                  * The criteria to step up the receive buffer one notch are:
 1796                  *  1. Application has not set receive buffer size with
 1797                  *     SO_RCVBUF. Setting SO_RCVBUF clears SB_AUTOSIZE.
 1798                  *  2. the number of bytes received during the time it takes
 1799                  *     one timestamp to be reflected back to us (the RTT);
 1800                  *  3. received bytes per RTT is within seven eighth of the
 1801                  *     current socket buffer size;
 1802                  *  4. receive buffer size has not hit maximal automatic size;
 1803                  *
 1804                  * This algorithm does one step per RTT at most and only if
 1805                  * we receive a bulk stream w/o packet losses or reorderings.
 1806                  * Shrinking the buffer during idle times is not necessary as
 1807                  * it doesn't consume any memory when idle.
 1808                  *
 1809                  * TODO: Only step up if the application is actually serving
 1810                  * the buffer to better manage the socket buffer resources.
 1811                  */
 1812                         if (V_tcp_do_autorcvbuf &&
 1813                             to.to_tsecr &&
 1814                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
 1815                                 if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
 1816                                     to.to_tsecr - tp->rfbuf_ts < hz) {
 1817                                         if (tp->rfbuf_cnt >
 1818                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
 1819                                             so->so_rcv.sb_hiwat <
 1820                                             V_tcp_autorcvbuf_max) {
 1821                                                 newsize =
 1822                                                     min(so->so_rcv.sb_hiwat +
 1823                                                     V_tcp_autorcvbuf_inc,
 1824                                                     V_tcp_autorcvbuf_max);
 1825                                         }
 1826                                         /* Start over with next RTT. */
 1827                                         tp->rfbuf_ts = 0;
 1828                                         tp->rfbuf_cnt = 0;
 1829                                 } else
 1830                                         tp->rfbuf_cnt += tlen;  /* add up */
 1831                         }
 1832 
 1833                         /* Add data to socket buffer. */
 1834                         SOCKBUF_LOCK(&so->so_rcv);
 1835                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 1836                                 m_freem(m);
 1837                         } else {
 1838                                 /*
 1839                                  * Set new socket buffer size.
 1840                                  * Give up when limit is reached.
 1841                                  */
 1842                                 if (newsize)
 1843                                         if (!sbreserve_locked(&so->so_rcv,
 1844                                             newsize, so, NULL))
 1845                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
 1846                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 1847                                 sbappendstream_locked(&so->so_rcv, m);
 1848                         }
 1849                         /* NB: sorwakeup_locked() does an implicit unlock. */
 1850                         sorwakeup_locked(so);
 1851                         if (DELAY_ACK(tp, tlen)) {
 1852                                 tp->t_flags |= TF_DELACK;
 1853                         } else {
 1854                                 tp->t_flags |= TF_ACKNOW;
 1855                                 tcp_output(tp);
 1856                         }
 1857                         goto check_delack;
 1858                 }
 1859         }
 1860 
 1861         /*
 1862          * Calculate amount of space in receive window,
 1863          * and then do TCP input processing.
 1864          * Receive window is amount of space in rcv queue,
 1865          * but not less than advertised window.
 1866          */
 1867         win = sbspace(&so->so_rcv);
 1868         if (win < 0)
 1869                 win = 0;
 1870         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 1871 
 1872         /* Reset receive buffer auto scaling when not in bulk receive mode. */
 1873         tp->rfbuf_ts = 0;
 1874         tp->rfbuf_cnt = 0;
 1875 
 1876         switch (tp->t_state) {
 1877 
 1878         /*
 1879          * If the state is SYN_RECEIVED:
 1880          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
 1881          */
 1882         case TCPS_SYN_RECEIVED:
 1883                 if ((thflags & TH_ACK) &&
 1884                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
 1885                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1886                                 rstreason = BANDLIM_RST_OPENPORT;
 1887                                 goto dropwithreset;
 1888                 }
 1889                 break;
 1890 
 1891         /*
 1892          * If the state is SYN_SENT:
 1893          *      if seg contains an ACK, but not for our SYN, drop the input.
 1894          *      if seg contains a RST, then drop the connection.
 1895          *      if seg does not contain SYN, then drop it.
 1896          * Otherwise this is an acceptable SYN segment
 1897          *      initialize tp->rcv_nxt and tp->irs
 1898          *      if seg contains ack then advance tp->snd_una
 1899          *      if seg contains an ECE and ECN support is enabled, the stream
 1900          *          is ECN capable.
 1901          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
 1902          *      arrange for segment to be acked (eventually)
 1903          *      continue processing rest of data/controls, beginning with URG
 1904          */
 1905         case TCPS_SYN_SENT:
 1906                 if ((thflags & TH_ACK) &&
 1907                     (SEQ_LEQ(th->th_ack, tp->iss) ||
 1908                      SEQ_GT(th->th_ack, tp->snd_max))) {
 1909                         rstreason = BANDLIM_UNLIMITED;
 1910                         goto dropwithreset;
 1911                 }
 1912                 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
 1913                         TCP_PROBE5(connect__refused, NULL, tp,
 1914                             mtod(m, const char *), tp, th);
 1915                         tp = tcp_drop(tp, ECONNREFUSED);
 1916                 }
 1917                 if (thflags & TH_RST)
 1918                         goto drop;
 1919                 if (!(thflags & TH_SYN))
 1920                         goto drop;
 1921 
 1922                 tp->irs = th->th_seq;
 1923                 tcp_rcvseqinit(tp);
 1924                 if (thflags & TH_ACK) {
 1925                         TCPSTAT_INC(tcps_connects);
 1926                         soisconnected(so);
 1927 #ifdef MAC
 1928                         mac_socketpeer_set_from_mbuf(m, so);
 1929 #endif
 1930                         /* Do window scaling on this connection? */
 1931                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 1932                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 1933                                 tp->rcv_scale = tp->request_r_scale;
 1934                         }
 1935                         tp->rcv_adv += imin(tp->rcv_wnd,
 1936                             TCP_MAXWIN << tp->rcv_scale);
 1937                         tp->snd_una++;          /* SYN is acked */
 1938                         /*
 1939                          * If there's data, delay ACK; if there's also a FIN
 1940                          * ACKNOW will be turned on later.
 1941                          */
 1942                         if (DELAY_ACK(tp, tlen) && tlen != 0)
 1943                                 tcp_timer_activate(tp, TT_DELACK,
 1944                                     tcp_delacktime);
 1945                         else
 1946                                 tp->t_flags |= TF_ACKNOW;
 1947 
 1948                         if ((thflags & TH_ECE) && V_tcp_do_ecn) {
 1949                                 tp->t_flags |= TF_ECN_PERMIT;
 1950                                 TCPSTAT_INC(tcps_ecn_shs);
 1951                         }
 1952                         
 1953                         /*
 1954                          * Received <SYN,ACK> in SYN_SENT[*] state.
 1955                          * Transitions:
 1956                          *      SYN_SENT  --> ESTABLISHED
 1957                          *      SYN_SENT* --> FIN_WAIT_1
 1958                          */
 1959                         tp->t_starttime = ticks;
 1960                         if (tp->t_flags & TF_NEEDFIN) {
 1961                                 tcp_state_change(tp, TCPS_FIN_WAIT_1);
 1962                                 tp->t_flags &= ~TF_NEEDFIN;
 1963                                 thflags &= ~TH_SYN;
 1964                         } else {
 1965                                 tcp_state_change(tp, TCPS_ESTABLISHED);
 1966                                 TCP_PROBE5(connect__established, NULL, tp,
 1967                                     mtod(m, const char *), tp, th);
 1968                                 cc_conn_init(tp);
 1969                                 tcp_timer_activate(tp, TT_KEEP,
 1970                                     TP_KEEPIDLE(tp));
 1971                         }
 1972                 } else {
 1973                         /*
 1974                          * Received initial SYN in SYN-SENT[*] state =>
 1975                          * simultaneous open.
 1976                          * If it succeeds, connection is * half-synchronized.
 1977                          * Otherwise, do 3-way handshake:
 1978                          *        SYN-SENT -> SYN-RECEIVED
 1979                          *        SYN-SENT* -> SYN-RECEIVED*
 1980                          */
 1981                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 1982                         tcp_timer_activate(tp, TT_REXMT, 0);
 1983                         tcp_state_change(tp, TCPS_SYN_RECEIVED);
 1984                 }
 1985 
 1986                 KASSERT(ti_locked == TI_WLOCKED, ("%s: trimthenstep6: "
 1987                     "ti_locked %d", __func__, ti_locked));
 1988                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1989                 INP_WLOCK_ASSERT(tp->t_inpcb);
 1990 
 1991                 /*
 1992                  * Advance th->th_seq to correspond to first data byte.
 1993                  * If data, trim to stay within window,
 1994                  * dropping FIN if necessary.
 1995                  */
 1996                 th->th_seq++;
 1997                 if (tlen > tp->rcv_wnd) {
 1998                         todrop = tlen - tp->rcv_wnd;
 1999                         m_adj(m, -todrop);
 2000                         tlen = tp->rcv_wnd;
 2001                         thflags &= ~TH_FIN;
 2002                         TCPSTAT_INC(tcps_rcvpackafterwin);
 2003                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2004                 }
 2005                 tp->snd_wl1 = th->th_seq - 1;
 2006                 tp->rcv_up = th->th_seq;
 2007                 /*
 2008                  * Client side of transaction: already sent SYN and data.
 2009                  * If the remote host used T/TCP to validate the SYN,
 2010                  * our data will be ACK'd; if so, enter normal data segment
 2011                  * processing in the middle of step 5, ack processing.
 2012                  * Otherwise, goto step 6.
 2013                  */
 2014                 if (thflags & TH_ACK)
 2015                         goto process_ACK;
 2016 
 2017                 goto step6;
 2018 
 2019         /*
 2020          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
 2021          *      do normal processing.
 2022          *
 2023          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
 2024          */
 2025         case TCPS_LAST_ACK:
 2026         case TCPS_CLOSING:
 2027                 break;  /* continue normal processing */
 2028         }
 2029 
 2030         /*
 2031          * States other than LISTEN or SYN_SENT.
 2032          * First check the RST flag and sequence number since reset segments
 2033          * are exempt from the timestamp and connection count tests.  This
 2034          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
 2035          * below which allowed reset segments in half the sequence space
 2036          * to fall though and be processed (which gives forged reset
 2037          * segments with a random sequence number a 50 percent chance of
 2038          * killing a connection).
 2039          * Then check timestamp, if present.
 2040          * Then check the connection count, if present.
 2041          * Then check that at least some bytes of segment are within
 2042          * receive window.  If segment begins before rcv_nxt,
 2043          * drop leading data (and SYN); if nothing left, just ack.
 2044          *
 2045          *
 2046          * If the RST bit is set, check the sequence number to see
 2047          * if this is a valid reset segment.
 2048          * RFC 793 page 37:
 2049          *   In all states except SYN-SENT, all reset (RST) segments
 2050          *   are validated by checking their SEQ-fields.  A reset is
 2051          *   valid if its sequence number is in the window.
 2052          * Note: this does not take into account delayed ACKs, so
 2053          *   we should test against last_ack_sent instead of rcv_nxt.
 2054          *   The sequence number in the reset segment is normally an
 2055          *   echo of our outgoing acknowlegement numbers, but some hosts
 2056          *   send a reset with the sequence number at the rightmost edge
 2057          *   of our receive window, and we have to handle this case.
 2058          * Note 2: Paul Watson's paper "Slipping in the Window" has shown
 2059          *   that brute force RST attacks are possible.  To combat this,
 2060          *   we use a much stricter check while in the ESTABLISHED state,
 2061          *   only accepting RSTs where the sequence number is equal to
 2062          *   last_ack_sent.  In all other states (the states in which a
 2063          *   RST is more likely), the more permissive check is used.
 2064          * If we have multiple segments in flight, the initial reset
 2065          * segment sequence numbers will be to the left of last_ack_sent,
 2066          * but they will eventually catch up.
 2067          * In any case, it never made sense to trim reset segments to
 2068          * fit the receive window since RFC 1122 says:
 2069          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
 2070          *
 2071          *    A TCP SHOULD allow a received RST segment to include data.
 2072          *
 2073          *    DISCUSSION
 2074          *         It has been suggested that a RST segment could contain
 2075          *         ASCII text that encoded and explained the cause of the
 2076          *         RST.  No standard has yet been established for such
 2077          *         data.
 2078          *
 2079          * If the reset segment passes the sequence number test examine
 2080          * the state:
 2081          *    SYN_RECEIVED STATE:
 2082          *      If passive open, return to LISTEN state.
 2083          *      If active open, inform user that connection was refused.
 2084          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
 2085          *      Inform user that connection was reset, and close tcb.
 2086          *    CLOSING, LAST_ACK STATES:
 2087          *      Close the tcb.
 2088          *    TIME_WAIT STATE:
 2089          *      Drop the segment - see Stevens, vol. 2, p. 964 and
 2090          *      RFC 1337.
 2091          */
 2092         if (thflags & TH_RST) {
 2093                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
 2094                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
 2095                         switch (tp->t_state) {
 2096 
 2097                         case TCPS_SYN_RECEIVED:
 2098                                 so->so_error = ECONNREFUSED;
 2099                                 goto close;
 2100 
 2101                         case TCPS_ESTABLISHED:
 2102                                 if (V_tcp_insecure_rst == 0 &&
 2103                                     !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
 2104                                     SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
 2105                                     !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
 2106                                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
 2107                                         TCPSTAT_INC(tcps_badrst);
 2108                                         goto drop;
 2109                                 }
 2110                                 /* FALLTHROUGH */
 2111                         case TCPS_FIN_WAIT_1:
 2112                         case TCPS_FIN_WAIT_2:
 2113                         case TCPS_CLOSE_WAIT:
 2114                                 so->so_error = ECONNRESET;
 2115                         close:
 2116                                 KASSERT(ti_locked == TI_WLOCKED,
 2117                                     ("tcp_do_segment: TH_RST 1 ti_locked %d",
 2118                                     ti_locked));
 2119                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2120 
 2121                                 tcp_state_change(tp, TCPS_CLOSED);
 2122                                 TCPSTAT_INC(tcps_drops);
 2123                                 tp = tcp_close(tp);
 2124                                 break;
 2125 
 2126                         case TCPS_CLOSING:
 2127                         case TCPS_LAST_ACK:
 2128                                 KASSERT(ti_locked == TI_WLOCKED,
 2129                                     ("tcp_do_segment: TH_RST 2 ti_locked %d",
 2130                                     ti_locked));
 2131                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2132 
 2133                                 tp = tcp_close(tp);
 2134                                 break;
 2135                         }
 2136                 }
 2137                 goto drop;
 2138         }
 2139 
 2140         /*
 2141          * RFC 1323 PAWS: If we have a timestamp reply on this segment
 2142          * and it's less than ts_recent, drop it.
 2143          */
 2144         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
 2145             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
 2146 
 2147                 /* Check to see if ts_recent is over 24 days old.  */
 2148                 if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
 2149                         /*
 2150                          * Invalidate ts_recent.  If this segment updates
 2151                          * ts_recent, the age will be reset later and ts_recent
 2152                          * will get a valid value.  If it does not, setting
 2153                          * ts_recent to zero will at least satisfy the
 2154                          * requirement that zero be placed in the timestamp
 2155                          * echo reply when ts_recent isn't valid.  The
 2156                          * age isn't reset until we get a valid ts_recent
 2157                          * because we don't want out-of-order segments to be
 2158                          * dropped when ts_recent is old.
 2159                          */
 2160                         tp->ts_recent = 0;
 2161                 } else {
 2162                         TCPSTAT_INC(tcps_rcvduppack);
 2163                         TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
 2164                         TCPSTAT_INC(tcps_pawsdrop);
 2165                         if (tlen)
 2166                                 goto dropafterack;
 2167                         goto drop;
 2168                 }
 2169         }
 2170 
 2171         /*
 2172          * In the SYN-RECEIVED state, validate that the packet belongs to
 2173          * this connection before trimming the data to fit the receive
 2174          * window.  Check the sequence number versus IRS since we know
 2175          * the sequence numbers haven't wrapped.  This is a partial fix
 2176          * for the "LAND" DoS attack.
 2177          */
 2178         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
 2179                 rstreason = BANDLIM_RST_OPENPORT;
 2180                 goto dropwithreset;
 2181         }
 2182 
 2183         todrop = tp->rcv_nxt - th->th_seq;
 2184         if (todrop > 0) {
 2185                 /*
 2186                  * If this is a duplicate SYN for our current connection,
 2187                  * advance over it and pretend and it's not a SYN.
 2188                  */
 2189                 if (thflags & TH_SYN && th->th_seq == tp->irs) {
 2190                         thflags &= ~TH_SYN;
 2191                         th->th_seq++;
 2192                         if (th->th_urp > 1)
 2193                                 th->th_urp--;
 2194                         else
 2195                                 thflags &= ~TH_URG;
 2196                         todrop--;
 2197                 }
 2198                 /*
 2199                  * Following if statement from Stevens, vol. 2, p. 960.
 2200                  */
 2201                 if (todrop > tlen
 2202                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
 2203                         /*
 2204                          * Any valid FIN must be to the left of the window.
 2205                          * At this point the FIN must be a duplicate or out
 2206                          * of sequence; drop it.
 2207                          */
 2208                         thflags &= ~TH_FIN;
 2209 
 2210                         /*
 2211                          * Send an ACK to resynchronize and drop any data.
 2212                          * But keep on processing for RST or ACK.
 2213                          */
 2214                         tp->t_flags |= TF_ACKNOW;
 2215                         todrop = tlen;
 2216                         TCPSTAT_INC(tcps_rcvduppack);
 2217                         TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
 2218                 } else {
 2219                         TCPSTAT_INC(tcps_rcvpartduppack);
 2220                         TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
 2221                 }
 2222                 drop_hdrlen += todrop;  /* drop from the top afterwards */
 2223                 th->th_seq += todrop;
 2224                 tlen -= todrop;
 2225                 if (th->th_urp > todrop)
 2226                         th->th_urp -= todrop;
 2227                 else {
 2228                         thflags &= ~TH_URG;
 2229                         th->th_urp = 0;
 2230                 }
 2231         }
 2232 
 2233         /*
 2234          * If new data are received on a connection after the
 2235          * user processes are gone, then RST the other end.
 2236          */
 2237         if ((so->so_state & SS_NOFDREF) &&
 2238             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
 2239                 KASSERT(ti_locked == TI_WLOCKED, ("%s: SS_NOFDEREF && "
 2240                     "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
 2241                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2242 
 2243                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 2244                         log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
 2245                             "after socket was closed, "
 2246                             "sending RST and removing tcpcb\n",
 2247                             s, __func__, tcpstates[tp->t_state], tlen);
 2248                         free(s, M_TCPLOG);
 2249                 }
 2250                 tp = tcp_close(tp);
 2251                 TCPSTAT_INC(tcps_rcvafterclose);
 2252                 rstreason = BANDLIM_UNLIMITED;
 2253                 goto dropwithreset;
 2254         }
 2255 
 2256         /*
 2257          * If segment ends after window, drop trailing data
 2258          * (and PUSH and FIN); if nothing left, just ACK.
 2259          */
 2260         todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
 2261         if (todrop > 0) {
 2262                 TCPSTAT_INC(tcps_rcvpackafterwin);
 2263                 if (todrop >= tlen) {
 2264                         TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
 2265                         /*
 2266                          * If window is closed can only take segments at
 2267                          * window edge, and have to drop data and PUSH from
 2268                          * incoming segments.  Continue processing, but
 2269                          * remember to ack.  Otherwise, drop segment
 2270                          * and ack.
 2271                          */
 2272                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
 2273                                 tp->t_flags |= TF_ACKNOW;
 2274                                 TCPSTAT_INC(tcps_rcvwinprobe);
 2275                         } else
 2276                                 goto dropafterack;
 2277                 } else
 2278                         TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
 2279                 m_adj(m, -todrop);
 2280                 tlen -= todrop;
 2281                 thflags &= ~(TH_PUSH|TH_FIN);
 2282         }
 2283 
 2284         /*
 2285          * If last ACK falls within this segment's sequence numbers,
 2286          * record its timestamp.
 2287          * NOTE: 
 2288          * 1) That the test incorporates suggestions from the latest
 2289          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
 2290          * 2) That updating only on newer timestamps interferes with
 2291          *    our earlier PAWS tests, so this check should be solely
 2292          *    predicated on the sequence space of this segment.
 2293          * 3) That we modify the segment boundary check to be 
 2294          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len  
 2295          *    instead of RFC1323's
 2296          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
 2297          *    This modified check allows us to overcome RFC1323's
 2298          *    limitations as described in Stevens TCP/IP Illustrated
 2299          *    Vol. 2 p.869. In such cases, we can still calculate the
 2300          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
 2301          */
 2302         if ((to.to_flags & TOF_TS) != 0 &&
 2303             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
 2304             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
 2305                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
 2306                 tp->ts_recent_age = tcp_ts_getticks();
 2307                 tp->ts_recent = to.to_tsval;
 2308         }
 2309 
 2310         /*
 2311          * If a SYN is in the window, then this is an
 2312          * error and we send an RST and drop the connection.
 2313          */
 2314         if (thflags & TH_SYN) {
 2315                 KASSERT(ti_locked == TI_WLOCKED,
 2316                     ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
 2317                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2318 
 2319                 tp = tcp_drop(tp, ECONNRESET);
 2320                 rstreason = BANDLIM_UNLIMITED;
 2321                 goto drop;
 2322         }
 2323 
 2324         /*
 2325          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
 2326          * flag is on (half-synchronized state), then queue data for
 2327          * later processing; else drop segment and return.
 2328          */
 2329         if ((thflags & TH_ACK) == 0) {
 2330                 if (tp->t_state == TCPS_SYN_RECEIVED ||
 2331                     (tp->t_flags & TF_NEEDSYN))
 2332                         goto step6;
 2333                 else if (tp->t_flags & TF_ACKNOW)
 2334                         goto dropafterack;
 2335                 else
 2336                         goto drop;
 2337         }
 2338 
 2339         /*
 2340          * Ack processing.
 2341          */
 2342         switch (tp->t_state) {
 2343 
 2344         /*
 2345          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
 2346          * ESTABLISHED state and continue processing.
 2347          * The ACK was checked above.
 2348          */
 2349         case TCPS_SYN_RECEIVED:
 2350 
 2351                 TCPSTAT_INC(tcps_connects);
 2352                 soisconnected(so);
 2353                 /* Do window scaling? */
 2354                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2355                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2356                         tp->rcv_scale = tp->request_r_scale;
 2357                         tp->snd_wnd = tiwin;
 2358                 }
 2359                 /*
 2360                  * Make transitions:
 2361                  *      SYN-RECEIVED  -> ESTABLISHED
 2362                  *      SYN-RECEIVED* -> FIN-WAIT-1
 2363                  */
 2364                 tp->t_starttime = ticks;
 2365                 if (tp->t_flags & TF_NEEDFIN) {
 2366                         tcp_state_change(tp, TCPS_FIN_WAIT_1);
 2367                         tp->t_flags &= ~TF_NEEDFIN;
 2368                 } else {
 2369                         tcp_state_change(tp, TCPS_ESTABLISHED);
 2370                         TCP_PROBE5(accept__established, NULL, tp,
 2371                             mtod(m, const char *), tp, th);
 2372                         cc_conn_init(tp);
 2373                         tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 2374                 }
 2375                 /*
 2376                  * If segment contains data or ACK, will call tcp_reass()
 2377                  * later; if not, do so now to pass queued data to user.
 2378                  */
 2379                 if (tlen == 0 && (thflags & TH_FIN) == 0)
 2380                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
 2381                             (struct mbuf *)0);
 2382                 tp->snd_wl1 = th->th_seq - 1;
 2383                 /* FALLTHROUGH */
 2384 
 2385         /*
 2386          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
 2387          * ACKs.  If the ack is in the range
 2388          *      tp->snd_una < th->th_ack <= tp->snd_max
 2389          * then advance tp->snd_una to th->th_ack and drop
 2390          * data from the retransmission queue.  If this ACK reflects
 2391          * more up to date window information we update our window information.
 2392          */
 2393         case TCPS_ESTABLISHED:
 2394         case TCPS_FIN_WAIT_1:
 2395         case TCPS_FIN_WAIT_2:
 2396         case TCPS_CLOSE_WAIT:
 2397         case TCPS_CLOSING:
 2398         case TCPS_LAST_ACK:
 2399                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
 2400                         TCPSTAT_INC(tcps_rcvacktoomuch);
 2401                         goto dropafterack;
 2402                 }
 2403                 if ((tp->t_flags & TF_SACK_PERMIT) &&
 2404                     ((to.to_flags & TOF_SACK) ||
 2405                      !TAILQ_EMPTY(&tp->snd_holes)))
 2406                         tcp_sack_doack(tp, &to, th->th_ack);
 2407 
 2408                 /* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
 2409                 hhook_run_tcp_est_in(tp, th, &to);
 2410 
 2411                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
 2412                         if (tlen == 0 && tiwin == tp->snd_wnd) {
 2413                                 /*
 2414                                  * If this is the first time we've seen a
 2415                                  * FIN from the remote, this is not a
 2416                                  * duplicate and it needs to be processed
 2417                                  * normally.  This happens during a
 2418                                  * simultaneous close.
 2419                                  */
 2420                                 if ((thflags & TH_FIN) &&
 2421                                     (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
 2422                                         tp->t_dupacks = 0;
 2423                                         break;
 2424                                 }
 2425                                 TCPSTAT_INC(tcps_rcvdupack);
 2426                                 /*
 2427                                  * If we have outstanding data (other than
 2428                                  * a window probe), this is a completely
 2429                                  * duplicate ack (ie, window info didn't
 2430                                  * change and FIN isn't set),
 2431                                  * the ack is the biggest we've
 2432                                  * seen and we've seen exactly our rexmt
 2433                                  * threshhold of them, assume a packet
 2434                                  * has been dropped and retransmit it.
 2435                                  * Kludge snd_nxt & the congestion
 2436                                  * window so we send only this one
 2437                                  * packet.
 2438                                  *
 2439                                  * We know we're losing at the current
 2440                                  * window size so do congestion avoidance
 2441                                  * (set ssthresh to half the current window
 2442                                  * and pull our congestion window back to
 2443                                  * the new ssthresh).
 2444                                  *
 2445                                  * Dup acks mean that packets have left the
 2446                                  * network (they're now cached at the receiver)
 2447                                  * so bump cwnd by the amount in the receiver
 2448                                  * to keep a constant cwnd packets in the
 2449                                  * network.
 2450                                  *
 2451                                  * When using TCP ECN, notify the peer that
 2452                                  * we reduced the cwnd.
 2453                                  */
 2454                                 if (!tcp_timer_active(tp, TT_REXMT) ||
 2455                                     th->th_ack != tp->snd_una)
 2456                                         tp->t_dupacks = 0;
 2457                                 else if (++tp->t_dupacks > tcprexmtthresh ||
 2458                                      IN_FASTRECOVERY(tp->t_flags)) {
 2459                                         cc_ack_received(tp, th, CC_DUPACK);
 2460                                         if ((tp->t_flags & TF_SACK_PERMIT) &&
 2461                                             IN_FASTRECOVERY(tp->t_flags)) {
 2462                                                 int awnd;
 2463                                                 
 2464                                                 /*
 2465                                                  * Compute the amount of data in flight first.
 2466                                                  * We can inject new data into the pipe iff 
 2467                                                  * we have less than 1/2 the original window's
 2468                                                  * worth of data in flight.
 2469                                                  */
 2470                                                 awnd = (tp->snd_nxt - tp->snd_fack) +
 2471                                                         tp->sackhint.sack_bytes_rexmit;
 2472                                                 if (awnd < tp->snd_ssthresh) {
 2473                                                         tp->snd_cwnd += tp->t_maxseg;
 2474                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
 2475                                                                 tp->snd_cwnd = tp->snd_ssthresh;
 2476                                                 }
 2477                                         } else
 2478                                                 tp->snd_cwnd += tp->t_maxseg;
 2479                                         (void) tcp_output(tp);
 2480                                         goto drop;
 2481                                 } else if (tp->t_dupacks == tcprexmtthresh) {
 2482                                         tcp_seq onxt = tp->snd_nxt;
 2483 
 2484                                         /*
 2485                                          * If we're doing sack, check to
 2486                                          * see if we're already in sack
 2487                                          * recovery. If we're not doing sack,
 2488                                          * check to see if we're in newreno
 2489                                          * recovery.
 2490                                          */
 2491                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2492                                                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2493                                                         tp->t_dupacks = 0;
 2494                                                         break;
 2495                                                 }
 2496                                         } else {
 2497                                                 if (SEQ_LEQ(th->th_ack,
 2498                                                     tp->snd_recover)) {
 2499                                                         tp->t_dupacks = 0;
 2500                                                         break;
 2501                                                 }
 2502                                         }
 2503                                         /* Congestion signal before ack. */
 2504                                         cc_cong_signal(tp, th, CC_NDUPACK);
 2505                                         cc_ack_received(tp, th, CC_DUPACK);
 2506                                         tcp_timer_activate(tp, TT_REXMT, 0);
 2507                                         tp->t_rtttime = 0;
 2508                                         if (tp->t_flags & TF_SACK_PERMIT) {
 2509                                                 TCPSTAT_INC(
 2510                                                     tcps_sack_recovery_episode);
 2511                                                 tp->sack_newdata = tp->snd_nxt;
 2512                                                 tp->snd_cwnd = tp->t_maxseg;
 2513                                                 (void) tcp_output(tp);
 2514                                                 goto drop;
 2515                                         }
 2516                                         tp->snd_nxt = th->th_ack;
 2517                                         tp->snd_cwnd = tp->t_maxseg;
 2518                                         (void) tcp_output(tp);
 2519                                         KASSERT(tp->snd_limited <= 2,
 2520                                             ("%s: tp->snd_limited too big",
 2521                                             __func__));
 2522                                         tp->snd_cwnd = tp->snd_ssthresh +
 2523                                              tp->t_maxseg *
 2524                                              (tp->t_dupacks - tp->snd_limited);
 2525                                         if (SEQ_GT(onxt, tp->snd_nxt))
 2526                                                 tp->snd_nxt = onxt;
 2527                                         goto drop;
 2528                                 } else if (V_tcp_do_rfc3042) {
 2529                                         cc_ack_received(tp, th, CC_DUPACK);
 2530                                         u_long oldcwnd = tp->snd_cwnd;
 2531                                         tcp_seq oldsndmax = tp->snd_max;
 2532                                         u_int sent;
 2533                                         int avail;
 2534 
 2535                                         KASSERT(tp->t_dupacks == 1 ||
 2536                                             tp->t_dupacks == 2,
 2537                                             ("%s: dupacks not 1 or 2",
 2538                                             __func__));
 2539                                         if (tp->t_dupacks == 1)
 2540                                                 tp->snd_limited = 0;
 2541                                         tp->snd_cwnd =
 2542                                             (tp->snd_nxt - tp->snd_una) +
 2543                                             (tp->t_dupacks - tp->snd_limited) *
 2544                                             tp->t_maxseg;
 2545                                         /*
 2546                                          * Only call tcp_output when there
 2547                                          * is new data available to be sent.
 2548                                          * Otherwise we would send pure ACKs.
 2549                                          */
 2550                                         SOCKBUF_LOCK(&so->so_snd);
 2551                                         avail = so->so_snd.sb_cc -
 2552                                             (tp->snd_nxt - tp->snd_una);
 2553                                         SOCKBUF_UNLOCK(&so->so_snd);
 2554                                         if (avail > 0)
 2555                                                 (void) tcp_output(tp);
 2556                                         sent = tp->snd_max - oldsndmax;
 2557                                         if (sent > tp->t_maxseg) {
 2558                                                 KASSERT((tp->t_dupacks == 2 &&
 2559                                                     tp->snd_limited == 0) ||
 2560                                                    (sent == tp->t_maxseg + 1 &&
 2561                                                     tp->t_flags & TF_SENTFIN),
 2562                                                     ("%s: sent too much",
 2563                                                     __func__));
 2564                                                 tp->snd_limited = 2;
 2565                                         } else if (sent > 0)
 2566                                                 ++tp->snd_limited;
 2567                                         tp->snd_cwnd = oldcwnd;
 2568                                         goto drop;
 2569                                 }
 2570                         } else
 2571                                 tp->t_dupacks = 0;
 2572                         break;
 2573                 }
 2574 
 2575                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
 2576                     ("%s: th_ack <= snd_una", __func__));
 2577 
 2578                 /*
 2579                  * If the congestion window was inflated to account
 2580                  * for the other side's cached packets, retract it.
 2581                  */
 2582                 if (IN_FASTRECOVERY(tp->t_flags)) {
 2583                         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
 2584                                 if (tp->t_flags & TF_SACK_PERMIT)
 2585                                         tcp_sack_partialack(tp, th);
 2586                                 else
 2587                                         tcp_newreno_partial_ack(tp, th);
 2588                         } else
 2589                                 cc_post_recovery(tp, th);
 2590                 }
 2591                 tp->t_dupacks = 0;
 2592                 /*
 2593                  * If we reach this point, ACK is not a duplicate,
 2594                  *     i.e., it ACKs something we sent.
 2595                  */
 2596                 if (tp->t_flags & TF_NEEDSYN) {
 2597                         /*
 2598                          * T/TCP: Connection was half-synchronized, and our
 2599                          * SYN has been ACK'd (so connection is now fully
 2600                          * synchronized).  Go to non-starred state,
 2601                          * increment snd_una for ACK of SYN, and check if
 2602                          * we can do window scaling.
 2603                          */
 2604                         tp->t_flags &= ~TF_NEEDSYN;
 2605                         tp->snd_una++;
 2606                         /* Do window scaling? */
 2607                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
 2608                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
 2609                                 tp->rcv_scale = tp->request_r_scale;
 2610                                 /* Send window already scaled. */
 2611                         }
 2612                 }
 2613 
 2614 process_ACK:
 2615                 INP_WLOCK_ASSERT(tp->t_inpcb);
 2616 
 2617                 acked = BYTES_THIS_ACK(tp, th);
 2618                 TCPSTAT_INC(tcps_rcvackpack);
 2619                 TCPSTAT_ADD(tcps_rcvackbyte, acked);
 2620 
 2621                 /*
 2622                  * If we just performed our first retransmit, and the ACK
 2623                  * arrives within our recovery window, then it was a mistake
 2624                  * to do the retransmit in the first place.  Recover our
 2625                  * original cwnd and ssthresh, and proceed to transmit where
 2626                  * we left off.
 2627                  */
 2628                 if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
 2629                     (int)(ticks - tp->t_badrxtwin) < 0)
 2630                         cc_cong_signal(tp, th, CC_RTO_ERR);
 2631 
 2632                 /*
 2633                  * If we have a timestamp reply, update smoothed
 2634                  * round trip time.  If no timestamp is present but
 2635                  * transmit timer is running and timed sequence
 2636                  * number was acked, update smoothed round trip time.
 2637                  * Since we now have an rtt measurement, cancel the
 2638                  * timer backoff (cf., Phil Karn's retransmit alg.).
 2639                  * Recompute the initial retransmit timer.
 2640                  *
 2641                  * Some boxes send broken timestamp replies
 2642                  * during the SYN+ACK phase, ignore
 2643                  * timestamps of 0 or we could calculate a
 2644                  * huge RTT and blow up the retransmit timer.
 2645                  */
 2646                 if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
 2647                         u_int t;
 2648 
 2649                         t = tcp_ts_getticks() - to.to_tsecr;
 2650                         if (!tp->t_rttlow || tp->t_rttlow > t)
 2651                                 tp->t_rttlow = t;
 2652                         tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
 2653                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
 2654                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
 2655                                 tp->t_rttlow = ticks - tp->t_rtttime;
 2656                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
 2657                 }
 2658 
 2659                 /*
 2660                  * If all outstanding data is acked, stop retransmit
 2661                  * timer and remember to restart (more output or persist).
 2662                  * If there is more data to be acked, restart retransmit
 2663                  * timer, using current (possibly backed-off) value.
 2664                  */
 2665                 if (th->th_ack == tp->snd_max) {
 2666                         tcp_timer_activate(tp, TT_REXMT, 0);
 2667                         needoutput = 1;
 2668                 } else if (!tcp_timer_active(tp, TT_PERSIST))
 2669                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 2670 
 2671                 /*
 2672                  * If no data (only SYN) was ACK'd,
 2673                  *    skip rest of ACK processing.
 2674                  */
 2675                 if (acked == 0)
 2676                         goto step6;
 2677 
 2678                 /*
 2679                  * Let the congestion control algorithm update congestion
 2680                  * control related information. This typically means increasing
 2681                  * the congestion window.
 2682                  */
 2683                 cc_ack_received(tp, th, CC_ACK);
 2684 
 2685                 SOCKBUF_LOCK(&so->so_snd);
 2686                 if (acked > so->so_snd.sb_cc) {
 2687                         tp->snd_wnd -= so->so_snd.sb_cc;
 2688                         mfree = sbcut_locked(&so->so_snd,
 2689                             (int)so->so_snd.sb_cc);
 2690                         ourfinisacked = 1;
 2691                 } else {
 2692                         mfree = sbcut_locked(&so->so_snd, acked);
 2693                         tp->snd_wnd -= acked;
 2694                         ourfinisacked = 0;
 2695                 }
 2696                 /* NB: sowwakeup_locked() does an implicit unlock. */
 2697                 sowwakeup_locked(so);
 2698                 m_freem(mfree);
 2699                 /* Detect una wraparound. */
 2700                 if (!IN_RECOVERY(tp->t_flags) &&
 2701                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
 2702                     SEQ_LEQ(th->th_ack, tp->snd_recover))
 2703                         tp->snd_recover = th->th_ack - 1;
 2704                 /* XXXLAS: Can this be moved up into cc_post_recovery? */
 2705                 if (IN_RECOVERY(tp->t_flags) &&
 2706                     SEQ_GEQ(th->th_ack, tp->snd_recover)) {
 2707                         EXIT_RECOVERY(tp->t_flags);
 2708                 }
 2709                 tp->snd_una = th->th_ack;
 2710                 if (tp->t_flags & TF_SACK_PERMIT) {
 2711                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
 2712                                 tp->snd_recover = tp->snd_una;
 2713                 }
 2714                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 2715                         tp->snd_nxt = tp->snd_una;
 2716 
 2717                 switch (tp->t_state) {
 2718 
 2719                 /*
 2720                  * In FIN_WAIT_1 STATE in addition to the processing
 2721                  * for the ESTABLISHED state if our FIN is now acknowledged
 2722                  * then enter FIN_WAIT_2.
 2723                  */
 2724                 case TCPS_FIN_WAIT_1:
 2725                         if (ourfinisacked) {
 2726                                 /*
 2727                                  * If we can't receive any more
 2728                                  * data, then closing user can proceed.
 2729                                  * Starting the timer is contrary to the
 2730                                  * specification, but if we don't get a FIN
 2731                                  * we'll hang forever.
 2732                                  *
 2733                                  * XXXjl:
 2734                                  * we should release the tp also, and use a
 2735                                  * compressed state.
 2736                                  */
 2737                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 2738                                         soisdisconnected(so);
 2739                                         tcp_timer_activate(tp, TT_2MSL,
 2740                                             (tcp_fast_finwait2_recycle ?
 2741                                             tcp_finwait2_timeout :
 2742                                             TP_MAXIDLE(tp)));
 2743                                 }
 2744                                 tcp_state_change(tp, TCPS_FIN_WAIT_2);
 2745                         }
 2746                         break;
 2747 
 2748                 /*
 2749                  * In CLOSING STATE in addition to the processing for
 2750                  * the ESTABLISHED state if the ACK acknowledges our FIN
 2751                  * then enter the TIME-WAIT state, otherwise ignore
 2752                  * the segment.
 2753                  */
 2754                 case TCPS_CLOSING:
 2755                         if (ourfinisacked) {
 2756                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2757                                 tcp_twstart(tp);
 2758                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 2759                                 m_freem(m);
 2760                                 return;
 2761                         }
 2762                         break;
 2763 
 2764                 /*
 2765                  * In LAST_ACK, we may still be waiting for data to drain
 2766                  * and/or to be acked, as well as for the ack of our FIN.
 2767                  * If our FIN is now acknowledged, delete the TCB,
 2768                  * enter the closed state and return.
 2769                  */
 2770                 case TCPS_LAST_ACK:
 2771                         if (ourfinisacked) {
 2772                                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2773                                 tp = tcp_close(tp);
 2774                                 goto drop;
 2775                         }
 2776                         break;
 2777                 }
 2778         }
 2779 
 2780 step6:
 2781         INP_WLOCK_ASSERT(tp->t_inpcb);
 2782 
 2783         /*
 2784          * Update window information.
 2785          * Don't look at window if no ACK: TAC's send garbage on first SYN.
 2786          */
 2787         if ((thflags & TH_ACK) &&
 2788             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
 2789             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
 2790              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
 2791                 /* keep track of pure window updates */
 2792                 if (tlen == 0 &&
 2793                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
 2794                         TCPSTAT_INC(tcps_rcvwinupd);
 2795                 tp->snd_wnd = tiwin;
 2796                 tp->snd_wl1 = th->th_seq;
 2797                 tp->snd_wl2 = th->th_ack;
 2798                 if (tp->snd_wnd > tp->max_sndwnd)
 2799                         tp->max_sndwnd = tp->snd_wnd;
 2800                 needoutput = 1;
 2801         }
 2802 
 2803         /*
 2804          * Process segments with URG.
 2805          */
 2806         if ((thflags & TH_URG) && th->th_urp &&
 2807             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2808                 /*
 2809                  * This is a kludge, but if we receive and accept
 2810                  * random urgent pointers, we'll crash in
 2811                  * soreceive.  It's hard to imagine someone
 2812                  * actually wanting to send this much urgent data.
 2813                  */
 2814                 SOCKBUF_LOCK(&so->so_rcv);
 2815                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
 2816                         th->th_urp = 0;                 /* XXX */
 2817                         thflags &= ~TH_URG;             /* XXX */
 2818                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
 2819                         goto dodata;                    /* XXX */
 2820                 }
 2821                 /*
 2822                  * If this segment advances the known urgent pointer,
 2823                  * then mark the data stream.  This should not happen
 2824                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
 2825                  * a FIN has been received from the remote side.
 2826                  * In these states we ignore the URG.
 2827                  *
 2828                  * According to RFC961 (Assigned Protocols),
 2829                  * the urgent pointer points to the last octet
 2830                  * of urgent data.  We continue, however,
 2831                  * to consider it to indicate the first octet
 2832                  * of data past the urgent section as the original
 2833                  * spec states (in one of two places).
 2834                  */
 2835                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
 2836                         tp->rcv_up = th->th_seq + th->th_urp;
 2837                         so->so_oobmark = so->so_rcv.sb_cc +
 2838                             (tp->rcv_up - tp->rcv_nxt) - 1;
 2839                         if (so->so_oobmark == 0)
 2840                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
 2841                         sohasoutofband(so);
 2842                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
 2843                 }
 2844                 SOCKBUF_UNLOCK(&so->so_rcv);
 2845                 /*
 2846                  * Remove out of band data so doesn't get presented to user.
 2847                  * This can happen independent of advancing the URG pointer,
 2848                  * but if two URG's are pending at once, some out-of-band
 2849                  * data may creep in... ick.
 2850                  */
 2851                 if (th->th_urp <= (u_long)tlen &&
 2852                     !(so->so_options & SO_OOBINLINE)) {
 2853                         /* hdr drop is delayed */
 2854                         tcp_pulloutofband(so, th, m, drop_hdrlen);
 2855                 }
 2856         } else {
 2857                 /*
 2858                  * If no out of band data is expected,
 2859                  * pull receive urgent pointer along
 2860                  * with the receive window.
 2861                  */
 2862                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
 2863                         tp->rcv_up = tp->rcv_nxt;
 2864         }
 2865 dodata:                                                 /* XXX */
 2866         INP_WLOCK_ASSERT(tp->t_inpcb);
 2867 
 2868         /*
 2869          * Process the segment text, merging it into the TCP sequencing queue,
 2870          * and arranging for acknowledgment of receipt if necessary.
 2871          * This process logically involves adjusting tp->rcv_wnd as data
 2872          * is presented to the user (this happens in tcp_usrreq.c,
 2873          * case PRU_RCVD).  If a FIN has already been received on this
 2874          * connection then we just ignore the text.
 2875          */
 2876         if ((tlen || (thflags & TH_FIN)) &&
 2877             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2878                 tcp_seq save_start = th->th_seq;
 2879                 m_adj(m, drop_hdrlen);  /* delayed header drop */
 2880                 /*
 2881                  * Insert segment which includes th into TCP reassembly queue
 2882                  * with control block tp.  Set thflags to whether reassembly now
 2883                  * includes a segment with FIN.  This handles the common case
 2884                  * inline (segment is the next to be received on an established
 2885                  * connection, and the queue is empty), avoiding linkage into
 2886                  * and removal from the queue and repetition of various
 2887                  * conversions.
 2888                  * Set DELACK for segments received in order, but ack
 2889                  * immediately when segments are out of order (so
 2890                  * fast retransmit can work).
 2891                  */
 2892                 if (th->th_seq == tp->rcv_nxt && tp->t_segq == NULL &&
 2893                     TCPS_HAVEESTABLISHED(tp->t_state)) {
 2894                         if (DELAY_ACK(tp, tlen))
 2895                                 tp->t_flags |= TF_DELACK;
 2896                         else
 2897                                 tp->t_flags |= TF_ACKNOW;
 2898                         tp->rcv_nxt += tlen;
 2899                         thflags = th->th_flags & TH_FIN;
 2900                         TCPSTAT_INC(tcps_rcvpack);
 2901                         TCPSTAT_ADD(tcps_rcvbyte, tlen);
 2902                         ND6_HINT(tp);
 2903                         SOCKBUF_LOCK(&so->so_rcv);
 2904                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
 2905                                 m_freem(m);
 2906                         else
 2907                                 sbappendstream_locked(&so->so_rcv, m);
 2908                         /* NB: sorwakeup_locked() does an implicit unlock. */
 2909                         sorwakeup_locked(so);
 2910                 } else {
 2911                         /*
 2912                          * XXX: Due to the header drop above "th" is
 2913                          * theoretically invalid by now.  Fortunately
 2914                          * m_adj() doesn't actually frees any mbufs
 2915                          * when trimming from the head.
 2916                          */
 2917                         thflags = tcp_reass(tp, th, &tlen, m);
 2918                         tp->t_flags |= TF_ACKNOW;
 2919                 }
 2920                 if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
 2921                         tcp_update_sack_list(tp, save_start, save_start + tlen);
 2922 #if 0
 2923                 /*
 2924                  * Note the amount of data that peer has sent into
 2925                  * our window, in order to estimate the sender's
 2926                  * buffer size.
 2927                  * XXX: Unused.
 2928                  */
 2929                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
 2930                         len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
 2931                 else
 2932                         len = so->so_rcv.sb_hiwat;
 2933 #endif
 2934         } else {
 2935                 m_freem(m);
 2936                 thflags &= ~TH_FIN;
 2937         }
 2938 
 2939         /*
 2940          * If FIN is received ACK the FIN and let the user know
 2941          * that the connection is closing.
 2942          */
 2943         if (thflags & TH_FIN) {
 2944                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 2945                         socantrcvmore(so);
 2946                         /*
 2947                          * If connection is half-synchronized
 2948                          * (ie NEEDSYN flag on) then delay ACK,
 2949                          * so it may be piggybacked when SYN is sent.
 2950                          * Otherwise, since we received a FIN then no
 2951                          * more input can be expected, send ACK now.
 2952                          */
 2953                         if (tp->t_flags & TF_NEEDSYN)
 2954                                 tp->t_flags |= TF_DELACK;
 2955                         else
 2956                                 tp->t_flags |= TF_ACKNOW;
 2957                         tp->rcv_nxt++;
 2958                 }
 2959                 switch (tp->t_state) {
 2960 
 2961                 /*
 2962                  * In SYN_RECEIVED and ESTABLISHED STATES
 2963                  * enter the CLOSE_WAIT state.
 2964                  */
 2965                 case TCPS_SYN_RECEIVED:
 2966                         tp->t_starttime = ticks;
 2967                         /* FALLTHROUGH */
 2968                 case TCPS_ESTABLISHED:
 2969                         tcp_state_change(tp, TCPS_CLOSE_WAIT);
 2970                         break;
 2971 
 2972                 /*
 2973                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
 2974                  * enter the CLOSING state.
 2975                  */
 2976                 case TCPS_FIN_WAIT_1:
 2977                         tcp_state_change(tp, TCPS_CLOSING);
 2978                         break;
 2979 
 2980                 /*
 2981                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
 2982                  * starting the time-wait timer, turning off the other
 2983                  * standard timers.
 2984                  */
 2985                 case TCPS_FIN_WAIT_2:
 2986                         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 2987                         KASSERT(ti_locked == TI_WLOCKED, ("%s: dodata "
 2988                             "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
 2989                             ti_locked));
 2990 
 2991                         tcp_twstart(tp);
 2992                         INP_INFO_WUNLOCK(&V_tcbinfo);
 2993                         return;
 2994                 }
 2995         }
 2996         if (ti_locked == TI_WLOCKED)
 2997                 INP_INFO_WUNLOCK(&V_tcbinfo);
 2998         ti_locked = TI_UNLOCKED;
 2999 
 3000 #ifdef TCPDEBUG
 3001         if (so->so_options & SO_DEBUG)
 3002                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
 3003                           &tcp_savetcp, 0);
 3004 #endif
 3005 
 3006         /*
 3007          * Return any desired output.
 3008          */
 3009         if (needoutput || (tp->t_flags & TF_ACKNOW))
 3010                 (void) tcp_output(tp);
 3011 
 3012 check_delack:
 3013         KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
 3014             __func__, ti_locked));
 3015         INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3016         INP_WLOCK_ASSERT(tp->t_inpcb);
 3017 
 3018         if (tp->t_flags & TF_DELACK) {
 3019                 tp->t_flags &= ~TF_DELACK;
 3020                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
 3021         }
 3022         INP_WUNLOCK(tp->t_inpcb);
 3023         return;
 3024 
 3025 dropafterack:
 3026         /*
 3027          * Generate an ACK dropping incoming segment if it occupies
 3028          * sequence space, where the ACK reflects our state.
 3029          *
 3030          * We can now skip the test for the RST flag since all
 3031          * paths to this code happen after packets containing
 3032          * RST have been dropped.
 3033          *
 3034          * In the SYN-RECEIVED state, don't send an ACK unless the
 3035          * segment we received passes the SYN-RECEIVED ACK test.
 3036          * If it fails send a RST.  This breaks the loop in the
 3037          * "LAND" DoS attack, and also prevents an ACK storm
 3038          * between two listening ports that have been sent forged
 3039          * SYN segments, each with the source address of the other.
 3040          */
 3041         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
 3042             (SEQ_GT(tp->snd_una, th->th_ack) ||
 3043              SEQ_GT(th->th_ack, tp->snd_max)) ) {
 3044                 rstreason = BANDLIM_RST_OPENPORT;
 3045                 goto dropwithreset;
 3046         }
 3047 #ifdef TCPDEBUG
 3048         if (so->so_options & SO_DEBUG)
 3049                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3050                           &tcp_savetcp, 0);
 3051 #endif
 3052         if (ti_locked == TI_WLOCKED)
 3053                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3054         ti_locked = TI_UNLOCKED;
 3055 
 3056         tp->t_flags |= TF_ACKNOW;
 3057         (void) tcp_output(tp);
 3058         INP_WUNLOCK(tp->t_inpcb);
 3059         m_freem(m);
 3060         return;
 3061 
 3062 dropwithreset:
 3063         if (ti_locked == TI_WLOCKED)
 3064                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3065         ti_locked = TI_UNLOCKED;
 3066 
 3067         if (tp != NULL) {
 3068                 tcp_dropwithreset(m, th, tp, tlen, rstreason);
 3069                 INP_WUNLOCK(tp->t_inpcb);
 3070         } else
 3071                 tcp_dropwithreset(m, th, NULL, tlen, rstreason);
 3072         return;
 3073 
 3074 drop:
 3075         if (ti_locked == TI_WLOCKED) {
 3076                 INP_INFO_WUNLOCK(&V_tcbinfo);
 3077                 ti_locked = TI_UNLOCKED;
 3078         }
 3079 #ifdef INVARIANTS
 3080         else
 3081                 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 3082 #endif
 3083 
 3084         /*
 3085          * Drop space held by incoming segment and return.
 3086          */
 3087 #ifdef TCPDEBUG
 3088         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 3089                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
 3090                           &tcp_savetcp, 0);
 3091 #endif
 3092         if (tp != NULL)
 3093                 INP_WUNLOCK(tp->t_inpcb);
 3094         m_freem(m);
 3095 }
 3096 
 3097 /*
 3098  * Issue RST and make ACK acceptable to originator of segment.
 3099  * The mbuf must still include the original packet header.
 3100  * tp may be NULL.
 3101  */
 3102 static void
 3103 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
 3104     int tlen, int rstreason)
 3105 {
 3106 #ifdef INET
 3107         struct ip *ip;
 3108 #endif
 3109 #ifdef INET6
 3110         struct ip6_hdr *ip6;
 3111 #endif
 3112 
 3113         if (tp != NULL) {
 3114                 INP_WLOCK_ASSERT(tp->t_inpcb);
 3115         }
 3116 
 3117         /* Don't bother if destination was broadcast/multicast. */
 3118         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
 3119                 goto drop;
 3120 #ifdef INET6
 3121         if (mtod(m, struct ip *)->ip_v == 6) {
 3122                 ip6 = mtod(m, struct ip6_hdr *);
 3123                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 3124                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 3125                         goto drop;
 3126                 /* IPv6 anycast check is done at tcp6_input() */
 3127         }
 3128 #endif
 3129 #if defined(INET) && defined(INET6)
 3130         else
 3131 #endif
 3132 #ifdef INET
 3133         {
 3134                 ip = mtod(m, struct ip *);
 3135                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 3136                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 3137                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 3138                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 3139                         goto drop;
 3140         }
 3141 #endif
 3142 
 3143         /* Perform bandwidth limiting. */
 3144         if (badport_bandlim(rstreason) < 0)
 3145                 goto drop;
 3146 
 3147         /* tcp_respond consumes the mbuf chain. */
 3148         if (th->th_flags & TH_ACK) {
 3149                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
 3150                     th->th_ack, TH_RST);
 3151         } else {
 3152                 if (th->th_flags & TH_SYN)
 3153                         tlen++;
 3154                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
 3155                     (tcp_seq)0, TH_RST|TH_ACK);
 3156         }
 3157         return;
 3158 drop:
 3159         m_freem(m);
 3160 }
 3161 
 3162 /*
 3163  * Parse TCP options and place in tcpopt.
 3164  */
 3165 static void
 3166 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
 3167 {
 3168         int opt, optlen;
 3169 
 3170         to->to_flags = 0;
 3171         for (; cnt > 0; cnt -= optlen, cp += optlen) {
 3172                 opt = cp[0];
 3173                 if (opt == TCPOPT_EOL)
 3174                         break;
 3175                 if (opt == TCPOPT_NOP)
 3176                         optlen = 1;
 3177                 else {
 3178                         if (cnt < 2)
 3179                                 break;
 3180                         optlen = cp[1];
 3181                         if (optlen < 2 || optlen > cnt)
 3182                                 break;
 3183                 }
 3184                 switch (opt) {
 3185                 case TCPOPT_MAXSEG:
 3186                         if (optlen != TCPOLEN_MAXSEG)
 3187                                 continue;
 3188                         if (!(flags & TO_SYN))
 3189                                 continue;
 3190                         to->to_flags |= TOF_MSS;
 3191                         bcopy((char *)cp + 2,
 3192                             (char *)&to->to_mss, sizeof(to->to_mss));
 3193                         to->to_mss = ntohs(to->to_mss);
 3194                         break;
 3195                 case TCPOPT_WINDOW:
 3196                         if (optlen != TCPOLEN_WINDOW)
 3197                                 continue;
 3198                         if (!(flags & TO_SYN))
 3199                                 continue;
 3200                         to->to_flags |= TOF_SCALE;
 3201                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
 3202                         break;
 3203                 case TCPOPT_TIMESTAMP:
 3204                         if (optlen != TCPOLEN_TIMESTAMP)
 3205                                 continue;
 3206                         to->to_flags |= TOF_TS;
 3207                         bcopy((char *)cp + 2,
 3208                             (char *)&to->to_tsval, sizeof(to->to_tsval));
 3209                         to->to_tsval = ntohl(to->to_tsval);
 3210                         bcopy((char *)cp + 6,
 3211                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
 3212                         to->to_tsecr = ntohl(to->to_tsecr);
 3213                         break;
 3214 #ifdef TCP_SIGNATURE
 3215                 /*
 3216                  * XXX In order to reply to a host which has set the
 3217                  * TCP_SIGNATURE option in its initial SYN, we have to
 3218                  * record the fact that the option was observed here
 3219                  * for the syncache code to perform the correct response.
 3220                  */
 3221                 case TCPOPT_SIGNATURE:
 3222                         if (optlen != TCPOLEN_SIGNATURE)
 3223                                 continue;
 3224                         to->to_flags |= TOF_SIGNATURE;
 3225                         to->to_signature = cp + 2;
 3226                         break;
 3227 #endif
 3228                 case TCPOPT_SACK_PERMITTED:
 3229                         if (optlen != TCPOLEN_SACK_PERMITTED)
 3230                                 continue;
 3231                         if (!(flags & TO_SYN))
 3232                                 continue;
 3233                         if (!V_tcp_do_sack)
 3234                                 continue;
 3235                         to->to_flags |= TOF_SACKPERM;
 3236                         break;
 3237                 case TCPOPT_SACK:
 3238                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
 3239                                 continue;
 3240                         if (flags & TO_SYN)
 3241                                 continue;
 3242                         to->to_flags |= TOF_SACK;
 3243                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
 3244                         to->to_sacks = cp + 2;
 3245                         TCPSTAT_INC(tcps_sack_rcv_blocks);
 3246                         break;
 3247                 default:
 3248                         continue;
 3249                 }
 3250         }
 3251 }
 3252 
 3253 /*
 3254  * Pull out of band byte out of a segment so
 3255  * it doesn't appear in the user's data queue.
 3256  * It is still reflected in the segment length for
 3257  * sequencing purposes.
 3258  */
 3259 static void
 3260 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
 3261     int off)
 3262 {
 3263         int cnt = off + th->th_urp - 1;
 3264 
 3265         while (cnt >= 0) {
 3266                 if (m->m_len > cnt) {
 3267                         char *cp = mtod(m, caddr_t) + cnt;
 3268                         struct tcpcb *tp = sototcpcb(so);
 3269 
 3270                         INP_WLOCK_ASSERT(tp->t_inpcb);
 3271 
 3272                         tp->t_iobc = *cp;
 3273                         tp->t_oobflags |= TCPOOB_HAVEDATA;
 3274                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
 3275                         m->m_len--;
 3276                         if (m->m_flags & M_PKTHDR)
 3277                                 m->m_pkthdr.len--;
 3278                         return;
 3279                 }
 3280                 cnt -= m->m_len;
 3281                 m = m->m_next;
 3282                 if (m == NULL)
 3283                         break;
 3284         }
 3285         panic("tcp_pulloutofband");
 3286 }
 3287 
 3288 /*
 3289  * Collect new round-trip time estimate
 3290  * and update averages and current timeout.
 3291  */
 3292 static void
 3293 tcp_xmit_timer(struct tcpcb *tp, int rtt)
 3294 {
 3295         int delta;
 3296 
 3297         INP_WLOCK_ASSERT(tp->t_inpcb);
 3298 
 3299         TCPSTAT_INC(tcps_rttupdated);
 3300         tp->t_rttupdated++;
 3301         if (tp->t_srtt != 0) {
 3302                 /*
 3303                  * srtt is stored as fixed point with 5 bits after the
 3304                  * binary point (i.e., scaled by 8).  The following magic
 3305                  * is equivalent to the smoothing algorithm in rfc793 with
 3306                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
 3307                  * point).  Adjust rtt to origin 0.
 3308                  */
 3309                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
 3310                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
 3311 
 3312                 if ((tp->t_srtt += delta) <= 0)
 3313                         tp->t_srtt = 1;
 3314 
 3315                 /*
 3316                  * We accumulate a smoothed rtt variance (actually, a
 3317                  * smoothed mean difference), then set the retransmit
 3318                  * timer to smoothed rtt + 4 times the smoothed variance.
 3319                  * rttvar is stored as fixed point with 4 bits after the
 3320                  * binary point (scaled by 16).  The following is
 3321                  * equivalent to rfc793 smoothing with an alpha of .75
 3322                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
 3323                  * rfc793's wired-in beta.
 3324                  */
 3325                 if (delta < 0)
 3326                         delta = -delta;
 3327                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
 3328                 if ((tp->t_rttvar += delta) <= 0)
 3329                         tp->t_rttvar = 1;
 3330                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
 3331                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3332         } else {
 3333                 /*
 3334                  * No rtt measurement yet - use the unsmoothed rtt.
 3335                  * Set the variance to half the rtt (so our first
 3336                  * retransmit happens at 3*rtt).
 3337                  */
 3338                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
 3339                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
 3340                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
 3341         }
 3342         tp->t_rtttime = 0;
 3343         tp->t_rxtshift = 0;
 3344 
 3345         /*
 3346          * the retransmit should happen at rtt + 4 * rttvar.
 3347          * Because of the way we do the smoothing, srtt and rttvar
 3348          * will each average +1/2 tick of bias.  When we compute
 3349          * the retransmit timer, we want 1/2 tick of rounding and
 3350          * 1 extra tick because of +-1/2 tick uncertainty in the
 3351          * firing of the timer.  The bias will give us exactly the
 3352          * 1.5 tick we need.  But, because the bias is
 3353          * statistical, we have to test that we don't drop below
 3354          * the minimum feasible timer (which is 2 ticks).
 3355          */
 3356         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
 3357                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
 3358 
 3359         /*
 3360          * We received an ack for a packet that wasn't retransmitted;
 3361          * it is probably safe to discard any error indications we've
 3362          * received recently.  This isn't quite right, but close enough
 3363          * for now (a route might have failed after we sent a segment,
 3364          * and the return path might not be symmetrical).
 3365          */
 3366         tp->t_softerror = 0;
 3367 }
 3368 
 3369 /*
 3370  * Determine a reasonable value for maxseg size.
 3371  * If the route is known, check route for mtu.
 3372  * If none, use an mss that can be handled on the outgoing interface
 3373  * without forcing IP to fragment.  If no route is found, route has no mtu,
 3374  * or the destination isn't local, use a default, hopefully conservative
 3375  * size (usually 512 or the default IP max size, but no more than the mtu
 3376  * of the interface), as we can't discover anything about intervening
 3377  * gateways or networks.  We also initialize the congestion/slow start
 3378  * window to be a single segment if the destination isn't local.
 3379  * While looking at the routing entry, we also initialize other path-dependent
 3380  * parameters from pre-set or cached values in the routing entry.
 3381  *
 3382  * Also take into account the space needed for options that we
 3383  * send regularly.  Make maxseg shorter by that amount to assure
 3384  * that we can send maxseg amount of data even when the options
 3385  * are present.  Store the upper limit of the length of options plus
 3386  * data in maxopd.
 3387  *
 3388  * NOTE that this routine is only called when we process an incoming
 3389  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
 3390  * settings are handled in tcp_mssopt().
 3391  */
 3392 void
 3393 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
 3394     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
 3395 {
 3396         int mss = 0;
 3397         u_long maxmtu = 0;
 3398         struct inpcb *inp = tp->t_inpcb;
 3399         struct hc_metrics_lite metrics;
 3400         int origoffer;
 3401 #ifdef INET6
 3402         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
 3403         size_t min_protoh = isipv6 ?
 3404                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
 3405                             sizeof (struct tcpiphdr);
 3406 #else
 3407         const size_t min_protoh = sizeof(struct tcpiphdr);
 3408 #endif
 3409 
 3410         INP_WLOCK_ASSERT(tp->t_inpcb);
 3411 
 3412         if (mtuoffer != -1) {
 3413                 KASSERT(offer == -1, ("%s: conflict", __func__));
 3414                 offer = mtuoffer - min_protoh;
 3415         }
 3416         origoffer = offer;
 3417 
 3418         /* Initialize. */
 3419 #ifdef INET6
 3420         if (isipv6) {
 3421                 maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
 3422                 tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
 3423         }
 3424 #endif
 3425 #if defined(INET) && defined(INET6)
 3426         else
 3427 #endif
 3428 #ifdef INET
 3429         {
 3430                 maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
 3431                 tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
 3432         }
 3433 #endif
 3434 
 3435         /*
 3436          * No route to sender, stay with default mss and return.
 3437          */
 3438         if (maxmtu == 0) {
 3439                 /*
 3440                  * In case we return early we need to initialize metrics
 3441                  * to a defined state as tcp_hc_get() would do for us
 3442                  * if there was no cache hit.
 3443                  */
 3444                 if (metricptr != NULL)
 3445                         bzero(metricptr, sizeof(struct hc_metrics_lite));
 3446                 return;
 3447         }
 3448 
 3449         /* What have we got? */
 3450         switch (offer) {
 3451                 case 0:
 3452                         /*
 3453                          * Offer == 0 means that there was no MSS on the SYN
 3454                          * segment, in this case we use tcp_mssdflt as
 3455                          * already assigned to t_maxopd above.
 3456                          */
 3457                         offer = tp->t_maxopd;
 3458                         break;
 3459 
 3460                 case -1:
 3461                         /*
 3462                          * Offer == -1 means that we didn't receive SYN yet.
 3463                          */
 3464                         /* FALLTHROUGH */
 3465 
 3466                 default:
 3467                         /*
 3468                          * Prevent DoS attack with too small MSS. Round up
 3469                          * to at least minmss.
 3470                          */
 3471                         offer = max(offer, V_tcp_minmss);
 3472         }
 3473 
 3474         /*
 3475          * rmx information is now retrieved from tcp_hostcache.
 3476          */
 3477         tcp_hc_get(&inp->inp_inc, &metrics);
 3478         if (metricptr != NULL)
 3479                 bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
 3480 
 3481         /*
 3482          * If there's a discovered mtu in tcp hostcache, use it.
 3483          * Else, use the link mtu.
 3484          */
 3485         if (metrics.rmx_mtu)
 3486                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
 3487         else {
 3488 #ifdef INET6
 3489                 if (isipv6) {
 3490                         mss = maxmtu - min_protoh;
 3491                         if (!V_path_mtu_discovery &&
 3492                             !in6_localaddr(&inp->in6p_faddr))
 3493                                 mss = min(mss, V_tcp_v6mssdflt);
 3494                 }
 3495 #endif
 3496 #if defined(INET) && defined(INET6)
 3497                 else
 3498 #endif
 3499 #ifdef INET
 3500                 {
 3501                         mss = maxmtu - min_protoh;
 3502                         if (!V_path_mtu_discovery &&
 3503                             !in_localaddr(inp->inp_faddr))
 3504                                 mss = min(mss, V_tcp_mssdflt);
 3505                 }
 3506 #endif
 3507                 /*
 3508                  * XXX - The above conditional (mss = maxmtu - min_protoh)
 3509                  * probably violates the TCP spec.
 3510                  * The problem is that, since we don't know the
 3511                  * other end's MSS, we are supposed to use a conservative
 3512                  * default.  But, if we do that, then MTU discovery will
 3513                  * never actually take place, because the conservative
 3514                  * default is much less than the MTUs typically seen
 3515                  * on the Internet today.  For the moment, we'll sweep
 3516                  * this under the carpet.
 3517                  *
 3518                  * The conservative default might not actually be a problem
 3519                  * if the only case this occurs is when sending an initial
 3520                  * SYN with options and data to a host we've never talked
 3521                  * to before.  Then, they will reply with an MSS value which
 3522                  * will get recorded and the new parameters should get
 3523                  * recomputed.  For Further Study.
 3524                  */
 3525         }
 3526         mss = min(mss, offer);
 3527 
 3528         /*
 3529          * Sanity check: make sure that maxopd will be large
 3530          * enough to allow some data on segments even if the
 3531          * all the option space is used (40bytes).  Otherwise
 3532          * funny things may happen in tcp_output.
 3533          */
 3534         mss = max(mss, 64);
 3535 
 3536         /*
 3537          * maxopd stores the maximum length of data AND options
 3538          * in a segment; maxseg is the amount of data in a normal
 3539          * segment.  We need to store this value (maxopd) apart
 3540          * from maxseg, because now every segment carries options
 3541          * and thus we normally have somewhat less data in segments.
 3542          */
 3543         tp->t_maxopd = mss;
 3544 
 3545         /*
 3546          * origoffer==-1 indicates that no segments were received yet.
 3547          * In this case we just guess.
 3548          */
 3549         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
 3550             (origoffer == -1 ||
 3551              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
 3552                 mss -= TCPOLEN_TSTAMP_APPA;
 3553 
 3554         tp->t_maxseg = mss;
 3555 }
 3556 
 3557 void
 3558 tcp_mss(struct tcpcb *tp, int offer)
 3559 {
 3560         int mss;
 3561         u_long bufsize;
 3562         struct inpcb *inp;
 3563         struct socket *so;
 3564         struct hc_metrics_lite metrics;
 3565         struct tcp_ifcap cap;
 3566 
 3567         KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
 3568 
 3569         bzero(&cap, sizeof(cap));
 3570         tcp_mss_update(tp, offer, -1, &metrics, &cap);
 3571 
 3572         mss = tp->t_maxseg;
 3573         inp = tp->t_inpcb;
 3574 
 3575         /*
 3576          * If there's a pipesize, change the socket buffer to that size,
 3577          * don't change if sb_hiwat is different than default (then it
 3578          * has been changed on purpose with setsockopt).
 3579          * Make the socket buffers an integral number of mss units;
 3580          * if the mss is larger than the socket buffer, decrease the mss.
 3581          */
 3582         so = inp->inp_socket;
 3583         SOCKBUF_LOCK(&so->so_snd);
 3584         if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
 3585                 bufsize = metrics.rmx_sendpipe;
 3586         else
 3587                 bufsize = so->so_snd.sb_hiwat;
 3588         if (bufsize < mss)
 3589                 mss = bufsize;
 3590         else {
 3591                 bufsize = roundup(bufsize, mss);
 3592                 if (bufsize > sb_max)
 3593                         bufsize = sb_max;
 3594                 if (bufsize > so->so_snd.sb_hiwat)
 3595                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
 3596         }
 3597         SOCKBUF_UNLOCK(&so->so_snd);
 3598         tp->t_maxseg = mss;
 3599 
 3600         SOCKBUF_LOCK(&so->so_rcv);
 3601         if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
 3602                 bufsize = metrics.rmx_recvpipe;
 3603         else
 3604                 bufsize = so->so_rcv.sb_hiwat;
 3605         if (bufsize > mss) {
 3606                 bufsize = roundup(bufsize, mss);
 3607                 if (bufsize > sb_max)
 3608                         bufsize = sb_max;
 3609                 if (bufsize > so->so_rcv.sb_hiwat)
 3610                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
 3611         }
 3612         SOCKBUF_UNLOCK(&so->so_rcv);
 3613 
 3614         /* Check the interface for TSO capabilities. */
 3615         if (cap.ifcap & CSUM_TSO) {
 3616                 tp->t_flags |= TF_TSO;
 3617                 tp->t_tsomax = cap.tsomax;
 3618         }
 3619 }
 3620 
 3621 /*
 3622  * Determine the MSS option to send on an outgoing SYN.
 3623  */
 3624 int
 3625 tcp_mssopt(struct in_conninfo *inc)
 3626 {
 3627         int mss = 0;
 3628         u_long maxmtu = 0;
 3629         u_long thcmtu = 0;
 3630         size_t min_protoh;
 3631 
 3632         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
 3633 
 3634 #ifdef INET6
 3635         if (inc->inc_flags & INC_ISIPV6) {
 3636                 mss = V_tcp_v6mssdflt;
 3637                 maxmtu = tcp_maxmtu6(inc, NULL);
 3638                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
 3639         }
 3640 #endif
 3641 #if defined(INET) && defined(INET6)
 3642         else
 3643 #endif
 3644 #ifdef INET
 3645         {
 3646                 mss = V_tcp_mssdflt;
 3647                 maxmtu = tcp_maxmtu(inc, NULL);
 3648                 min_protoh = sizeof(struct tcpiphdr);
 3649         }
 3650 #endif
 3651 #if defined(INET6) || defined(INET)
 3652         thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
 3653 #endif
 3654 
 3655         if (maxmtu && thcmtu)
 3656                 mss = min(maxmtu, thcmtu) - min_protoh;
 3657         else if (maxmtu || thcmtu)
 3658                 mss = max(maxmtu, thcmtu) - min_protoh;
 3659 
 3660         return (mss);
 3661 }
 3662 
 3663 
 3664 /*
 3665  * On a partial ack arrives, force the retransmission of the
 3666  * next unacknowledged segment.  Do not clear tp->t_dupacks.
 3667  * By setting snd_nxt to ti_ack, this forces retransmission timer to
 3668  * be started again.
 3669  */
 3670 static void
 3671 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
 3672 {
 3673         tcp_seq onxt = tp->snd_nxt;
 3674         u_long  ocwnd = tp->snd_cwnd;
 3675 
 3676         INP_WLOCK_ASSERT(tp->t_inpcb);
 3677 
 3678         tcp_timer_activate(tp, TT_REXMT, 0);
 3679         tp->t_rtttime = 0;
 3680         tp->snd_nxt = th->th_ack;
 3681         /*
 3682          * Set snd_cwnd to one segment beyond acknowledged offset.
 3683          * (tp->snd_una has not yet been updated when this function is called.)
 3684          */
 3685         tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th);
 3686         tp->t_flags |= TF_ACKNOW;
 3687         (void) tcp_output(tp);
 3688         tp->snd_cwnd = ocwnd;
 3689         if (SEQ_GT(onxt, tp->snd_nxt))
 3690                 tp->snd_nxt = onxt;
 3691         /*
 3692          * Partial window deflation.  Relies on fact that tp->snd_una
 3693          * not updated yet.
 3694          */
 3695         if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
 3696                 tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
 3697         else
 3698                 tp->snd_cwnd = 0;
 3699         tp->snd_cwnd += tp->t_maxseg;
 3700 }

Cache object: ba32a0a0af587b917cdb87102e1e7267


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]


This page is part of the FreeBSD/Linux Linux Kernel Cross-Reference, and was automatically generated using a modified version of the LXR engine.