sys/netinet/tcp_input.c

   1 /*
   2  * Copyright (c) 2002, 2003, 2004 Jeffrey M. Hsu.  All rights reserved.
   3  * Copyright (c) 2002, 2003, 2004 The DragonFly Project.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to The DragonFly Project
   6  * by Jeffrey M. Hsu.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of The DragonFly Project nor the names of its
  17  *    contributors may be used to endorse or promote products derived
  18  *    from this software without specific, prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  21  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  22  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  23  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  24  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  25  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  26  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  27  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  28  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  29  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  30  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 /*
  35  * Copyright (c) 2002, 2003, 2004 Jeffrey M. Hsu.  All rights reserved.
  36  *
  37  * License terms: all terms for the DragonFly license above plus the following:
  38  *
  39  * 4. All advertising materials mentioning features or use of this software
  40  *    must display the following acknowledgement:
  41  *
  42  *      This product includes software developed by Jeffrey M. Hsu
  43  *      for the DragonFly Project.
  44  *
  45  *    This requirement may be waived with permission from Jeffrey Hsu.
  46  *    This requirement will sunset and may be removed on July 8 2005,
  47  *    after which the standard DragonFly license (as shown above) will
  48  *    apply.
  49  */
  50
  51 /*
  52  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
  53  *      The Regents of the University of California.  All rights reserved.
  54  *
  55  * Redistribution and use in source and binary forms, with or without
  56  * modification, are permitted provided that the following conditions
  57  * are met:
  58  * 1. Redistributions of source code must retain the above copyright
  59  *    notice, this list of conditions and the following disclaimer.
  60  * 2. Redistributions in binary form must reproduce the above copyright
  61  *    notice, this list of conditions and the following disclaimer in the
  62  *    documentation and/or other materials provided with the distribution.
  63  * 3. All advertising materials mentioning features or use of this software
  64  *    must display the following acknowledgement:
  65  *      This product includes software developed by the University of
  66  *      California, Berkeley and its contributors.
  67  * 4. Neither the name of the University nor the names of its contributors
  68  *    may be used to endorse or promote products derived from this software
  69  *    without specific prior written permission.
  70  *
  71  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  72  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  73  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  74  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  75  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  76  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  77  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  78  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  79  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  80  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  81  * SUCH DAMAGE.
  82  *
  83  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  84  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
  85  * $DragonFly: src/sys/netinet/tcp_input.c,v 1.32 2004/07/27 17:57:02 drhodus Exp $
  86  */
  87
  88 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  89 #include "opt_inet6.h"
  90 #include "opt_ipsec.h"
  91 #include "opt_tcpdebug.h"
  92 #include "opt_tcp_input.h"
  93
  94 #include <sys/param.h>
  95 #include <sys/systm.h>
  96 #include <sys/kernel.h>
  97 #include <sys/sysctl.h>
  98 #include <sys/malloc.h>
  99 #include <sys/mbuf.h>
 100 #include <sys/proc.h>           /* for proc0 declaration */
 101 #include <sys/protosw.h>
 102 #include <sys/socket.h>
 103 #include <sys/socketvar.h>
 104 #include <sys/syslog.h>
 105 #include <sys/in_cksum.h>
 106
 107 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
 108 #include <machine/stdarg.h>
 109
 110 #include <net/if.h>
 111 #include <net/route.h>
 112
 113 #include <netinet/in.h>
 114 #include <netinet/in_systm.h>
 115 #include <netinet/ip.h>
 116 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM */
 117 #include <netinet/in_var.h>
 118 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
 119 #include <netinet/in_pcb.h>
 120 #include <netinet/ip_var.h>
 121 #include <netinet/ip6.h>
 122 #include <netinet/icmp6.h>
 123 #include <netinet6/nd6.h>
 124 #include <netinet6/ip6_var.h>
 125 #include <netinet6/in6_pcb.h>
 126 #include <netinet/tcp.h>
 127 #include <netinet/tcp_fsm.h>
 128 #include <netinet/tcp_seq.h>
 129 #include <netinet/tcp_timer.h>
 130 #include <netinet/tcp_var.h>
 131 #include <netinet6/tcp6_var.h>
 132 #include <netinet/tcpip.h>
 133
 134 #ifdef TCPDEBUG
 135 #include <netinet/tcp_debug.h>
 136
 137 u_char tcp_saveipgen[40];    /* the size must be of max ip header, now IPv6 */
 138 struct tcphdr tcp_savetcp;
 139 #endif
 140
 141 #ifdef FAST_IPSEC
 142 #include <netipsec/ipsec.h>
 143 #include <netipsec/ipsec6.h>
 144 #endif
 145
 146 #ifdef IPSEC
 147 #include <netinet6/ipsec.h>
 148 #include <netinet6/ipsec6.h>
 149 #include <netproto/key/key.h>
 150 #endif
 151
 152 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
 153
 154 static const int tcprexmtthresh = 3;
 155 tcp_cc  tcp_ccgen;
 156 static int log_in_vain = 0;
 157 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 158     &log_in_vain, 0, "Log all incoming TCP connections");
 159
 160 static int blackhole = 0;
 161 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 162     &blackhole, 0, "Do not send RST when dropping refused connections");
 163
 164 int tcp_delack_enabled = 1;
 165 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 166     &tcp_delack_enabled, 0,
 167     "Delay ACK to try and piggyback it onto a data packet");
 168
 169 #ifdef TCP_DROP_SYNFIN
 170 static int drop_synfin = 0;
 171 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 172     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 173 #endif
 174
 175 static int tcp_do_limitedtransmit = 1;
 176 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
 177     &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
 178
 179 static int tcp_do_early_retransmit = 0;
 180 SYSCTL_INT(_net_inet_tcp, OID_AUTO, earlyretransmit, CTLFLAG_RW,
 181     &tcp_do_early_retransmit, 0, "Early retransmit");
 182
 183 static int tcp_do_rfc3390 = 1;
 184 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 185     &tcp_do_rfc3390, 0,
 186     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 187
 188 static int tcp_do_eifel_detect = 1;
 189 SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel, CTLFLAG_RW,
 190     &tcp_do_eifel_detect, 0, "Eifel detection algorithm (RFC 3522)");
 191
 192 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
 193     "TCP Segment Reassembly Queue");
 194
 195 int tcp_reass_maxseg = 0;
 196 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RD,
 197     &tcp_reass_maxseg, 0,
 198     "Global maximum number of TCP Segments in Reassembly Queue");
 199
 200 int tcp_reass_qsize = 0;
 201 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD,
 202     &tcp_reass_qsize, 0,
 203     "Global number of TCP Segments currently in Reassembly Queue");
 204
 205 static int tcp_reass_overflows = 0;
 206 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD,
 207     &tcp_reass_overflows, 0,
 208     "Global number of TCP Segment Reassembly Queue Overflows");
 209
 210 struct inpcbinfo tcbinfo[MAXCPU];
 211
 212 static void      tcp_dooptions(struct tcpopt *, u_char *, int, boolean_t);
 213 static void      tcp_pulloutofband(struct socket *,
 214                      struct tcphdr *, struct mbuf *, int);
 215 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 216                      struct mbuf *);
 217 static void      tcp_xmit_timer(struct tcpcb *, int);
 218 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 219
 220 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 221 #ifdef INET6
 222 #define ND6_HINT(tp) \
 223 do { \
 224         if ((tp) && (tp)->t_inpcb && \
 225             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 226             (tp)->t_inpcb->in6p_route.ro_rt) \
 227                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 228 } while (0)
 229 #else
 230 #define ND6_HINT(tp)
 231 #endif
 232
 233 /*
 234  * Indicate whether this ack should be delayed.  We can delay the ack if
 235  *      - delayed acks are enabled and
 236  *      - there is no delayed ack timer in progress and
 237  *      - our last ack wasn't a 0-sized window.  We never want to delay
 238  *        the ack that opens up a 0-sized window.
 239  */
 240 #define DELAY_ACK(tp) \
 241         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
 242         (tp->t_flags & TF_RXWIN0SENT) == 0)
 243
 244 static int
 245 tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
 246 {
 247         struct tseg_qent *q;
 248         struct tseg_qent *p = NULL;
 249         struct tseg_qent *nq;
 250         struct tseg_qent *te;
 251         struct socket *so = tp->t_inpcb->inp_socket;
 252         int flags;
 253
 254         /*
 255          * Call with th==0 after become established to
 256          * force pre-ESTABLISHED data up to user socket.
 257          */
 258         if (th == 0)
 259                 goto present;
 260
 261         /*
 262          * Limit the number of segments in the reassembly queue to prevent
 263          * holding on to too many segments (and thus running out of mbufs).
 264          * Make sure to let the missing segment through which caused this
 265          * queue.  Always keep one global queue entry spare to be able to
 266          * process the missing segment.
 267          */
 268         if (th->th_seq != tp->rcv_nxt &&
 269             tcp_reass_qsize + 1 >= tcp_reass_maxseg) {
 270                 tcp_reass_overflows++;
 271                 tcpstat.tcps_rcvmemdrop++;
 272                 m_freem(m);
 273                 return (0);
 274         }
 275
 276         /* Allocate a new queue entry. */
 277         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
 278                M_INTWAIT | M_NULLOK);
 279         if (te == NULL) {
 280                 tcpstat.tcps_rcvmemdrop++;
 281                 m_freem(m);
 282                 return (0);
 283         }
 284         tcp_reass_qsize++;
 285
 286         /*
 287          * Find a segment which begins after this one does.
 288          */
 289         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 290                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 291                         break;
 292                 p = q;
 293         }
 294
 295         /*
 296          * If there is a preceding segment, it may provide some of
 297          * our data already.  If so, drop the data from the incoming
 298          * segment.  If it provides all of our data, drop us.
 299          */
 300         if (p != NULL) {
 301                 int i;
 302                 /* conversion to int (in i) handles seq wraparound */
 303                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 304                 if (i > 0) {
 305                         if (i >= *tlenp) {
 306                                 tcpstat.tcps_rcvduppack++;
 307                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 308                                 m_freem(m);
 309                                 free(te, M_TSEGQ);
 310                                 tcp_reass_qsize--;
 311                                 /*
 312                                  * Try to present any queued data
 313                                  * at the left window edge to the user.
 314                                  * This is needed after the 3-WHS
 315                                  * completes.
 316                                  */
 317                                 goto present;   /* ??? */
 318                         }
 319                         m_adj(m, i);
 320                         *tlenp -= i;
 321                         th->th_seq += i;
 322                 }
 323         }
 324         tcpstat.tcps_rcvoopack++;
 325         tcpstat.tcps_rcvoobyte += *tlenp;
 326
 327         /*
 328          * While we overlap succeeding segments trim them or,
 329          * if they are completely covered, dequeue them.
 330          */
 331         while (q) {
 332                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 333                 if (i <= 0)
 334                         break;
 335                 if (i < q->tqe_len) {
 336                         q->tqe_th->th_seq += i;
 337                         q->tqe_len -= i;
 338                         m_adj(q->tqe_m, i);
 339                         break;
 340                 }
 341
 342                 nq = LIST_NEXT(q, tqe_q);
 343                 LIST_REMOVE(q, tqe_q);
 344                 m_freem(q->tqe_m);
 345                 free(q, M_TSEGQ);
 346                 tcp_reass_qsize--;
 347                 q = nq;
 348         }
 349
 350         /* Insert the new segment queue entry into place. */
 351         te->tqe_m = m;
 352         te->tqe_th = th;
 353         te->tqe_len = *tlenp;
 354
 355         if (p == NULL) {
 356                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 357         } else {
 358                 LIST_INSERT_AFTER(p, te, tqe_q);
 359         }
 360
 361 present:
 362         /*
 363          * Present data to user, advancing rcv_nxt through
 364          * completed sequence space.
 365          */
 366         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 367                 return (0);
 368         q = LIST_FIRST(&tp->t_segq);
 369         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 370                 return (0);
 371         do {
 372                 tp->rcv_nxt += q->tqe_len;
 373                 flags = q->tqe_th->th_flags & TH_FIN;
 374                 nq = LIST_NEXT(q, tqe_q);
 375                 LIST_REMOVE(q, tqe_q);
 376                 if (so->so_state & SS_CANTRCVMORE)
 377                         m_freem(q->tqe_m);
 378                 else
 379                         sbappend(&so->so_rcv, q->tqe_m);
 380                 free(q, M_TSEGQ);
 381                 tcp_reass_qsize--;
 382                 q = nq;
 383         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 384         ND6_HINT(tp);
 385         sorwakeup(so);
 386         return (flags);
 387 }
 388
 389 /*
 390  * TCP input routine, follows pages 65-76 of the
 391  * protocol specification dated September, 1981 very closely.
 392  */
 393 #ifdef INET6
 394 int
 395 tcp6_input(struct mbuf **mp, int *offp, int proto)
 396 {
 397         struct mbuf *m = *mp;
 398         struct in6_ifaddr *ia6;
 399
 400         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 401
 402         /*
 403          * draft-itojun-ipv6-tcp-to-anycast
 404          * better place to put this in?
 405          */
 406         ia6 = ip6_getdstifaddr(m);
 407         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 408                 struct ip6_hdr *ip6;
 409
 410                 ip6 = mtod(m, struct ip6_hdr *);
 411                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 412                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 413                 return (IPPROTO_DONE);
 414         }
 415
 416         tcp_input(m, *offp, proto);
 417         return (IPPROTO_DONE);
 418 }
 419 #endif
 420
 421 void
 422 tcp_input(struct mbuf *m, ...)
 423 {
 424         __va_list ap;
 425         int off0, proto;
 426         struct tcphdr *th;
 427         struct ip *ip = NULL;
 428         struct ipovly *ipov;
 429         struct inpcb *inp = NULL;
 430         u_char *optp = NULL;
 431         int optlen = 0;
 432         int len, tlen, off;
 433         int drop_hdrlen;
 434         struct tcpcb *tp = NULL;
 435         int thflags;
 436         struct socket *so = 0;
 437         int todrop, acked, ourfinisacked, needoutput = 0;
 438         u_long tiwin;
 439         struct tcpopt to;               /* options in this segment */
 440         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 441         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 442         struct sockaddr_in *next_hop = NULL;
 443         int rstreason; /* For badport_bandlim accounting purposes */
 444         int cpu;
 445         struct ip6_hdr *ip6 = NULL;
 446 #ifdef INET6
 447         boolean_t isipv6;
 448 #else
 449         const boolean_t isipv6 = FALSE;
 450 #endif
 451 #ifdef TCPDEBUG
 452         short ostate = 0;
 453 #endif
 454
 455         __va_start(ap, m);
 456         off0 = __va_arg(ap, int);
 457         proto = __va_arg(ap, int);
 458         __va_end(ap);
 459
 460         tcpstat.tcps_rcvtotal++;
 461
 462         /* Grab info from and strip MT_TAG mbufs prepended to the chain. */
 463         while  (m->m_type == MT_TAG) {
 464                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 465                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 466                 m = m->m_next;
 467         }
 468
 469 #ifdef INET6
 470         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? TRUE : FALSE;
 471 #endif
 472
 473         if (isipv6) {
 474                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 475                 ip6 = mtod(m, struct ip6_hdr *);
 476                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 477                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 478                         tcpstat.tcps_rcvbadsum++;
 479                         goto drop;
 480                 }
 481                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 482
 483                 /*
 484                  * Be proactive about unspecified IPv6 address in source.
 485                  * As we use all-zero to indicate unbounded/unconnected pcb,
 486                  * unspecified IPv6 address can be used to confuse us.
 487                  *
 488                  * Note that packets with unspecified IPv6 destination is
 489                  * already dropped in ip6_input.
 490                  */
 491                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 492                         /* XXX stat */
 493                         goto drop;
 494                 }
 495         } else {
 496                 /*
 497                  * Get IP and TCP header together in first mbuf.
 498                  * Note: IP leaves IP header in first mbuf.
 499                  */
 500                 if (off0 > sizeof(struct ip)) {
 501                         ip_stripoptions(m);
 502                         off0 = sizeof(struct ip);
 503                 }
 504                 /* already checked and pulled up in ip_demux() */
 505                 KASSERT(m->m_len >= sizeof(struct tcpiphdr),
 506                     ("TCP header not in one mbuf"));
 507                 ip = mtod(m, struct ip *);
 508                 ipov = (struct ipovly *)ip;
 509                 th = (struct tcphdr *)((caddr_t)ip + off0);
 510                 tlen = ip->ip_len;
 511
 512                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 513                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 514                                 th->th_sum = m->m_pkthdr.csum_data;
 515                         else
 516                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 517                                                 ip->ip_dst.s_addr,
 518                                                 htonl(m->m_pkthdr.csum_data +
 519                                                         ip->ip_len +
 520                                                         IPPROTO_TCP));
 521                         th->th_sum ^= 0xffff;
 522                 } else {
 523                         /*
 524                          * Checksum extended TCP header and data.
 525                          */
 526                         len = sizeof(struct ip) + tlen;
 527                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 528                         ipov->ih_len = (u_short)tlen;
 529                         ipov->ih_len = htons(ipov->ih_len);
 530                         th->th_sum = in_cksum(m, len);
 531                 }
 532                 if (th->th_sum) {
 533                         tcpstat.tcps_rcvbadsum++;
 534                         goto drop;
 535                 }
 536 #ifdef INET6
 537                 /* Re-initialization for later version check */
 538                 ip->ip_v = IPVERSION;
 539 #endif
 540         }
 541
 542         /*
 543          * Check that TCP offset makes sense,
 544          * pull out TCP options and adjust length.              XXX
 545          */
 546         off = th->th_off << 2;
 547         /* already checked and pulled up in ip_demux() */
 548         KASSERT(off >= sizeof(struct tcphdr) && off <= tlen,
 549             ("bad TCP data offset"));
 550         tlen -= off;    /* tlen is used instead of ti->ti_len */
 551         if (off > sizeof(struct tcphdr)) {
 552                 if (isipv6) {
 553                         IP6_EXTHDR_CHECK(m, off0, off, );
 554                         ip6 = mtod(m, struct ip6_hdr *);
 555                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 556                 } else {
 557                         /* already pulled up in ip_demux() */
 558                         KASSERT(m->m_len >= sizeof(struct ip) + off,
 559                             ("TCP header and options not in one mbuf"));
 560                 }
 561                 optlen = off - sizeof(struct tcphdr);
 562                 optp = (u_char *)(th + 1);
 563         }
 564         thflags = th->th_flags;
 565
 566 #ifdef TCP_DROP_SYNFIN
 567         /*
 568          * If the drop_synfin option is enabled, drop all packets with
 569          * both the SYN and FIN bits set. This prevents e.g. nmap from
 570          * identifying the TCP/IP stack.
 571          *
 572          * This is a violation of the TCP specification.
 573          */
 574         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 575                 goto drop;
 576 #endif
 577
 578         /*
 579          * Convert TCP protocol specific fields to host format.
 580          */
 581         th->th_seq = ntohl(th->th_seq);
 582         th->th_ack = ntohl(th->th_ack);
 583         th->th_win = ntohs(th->th_win);
 584         th->th_urp = ntohs(th->th_urp);
 585
 586         /*
 587          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options,
 588          * until after ip6_savecontrol() is called and before other functions
 589          * which don't want those proto headers.
 590          * Because ip6_savecontrol() is going to parse the mbuf to
 591          * search for data to be passed up to user-land, it wants mbuf
 592          * parameters to be unchanged.
 593          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 594          * latest version of the advanced API (20020110).
 595          */
 596         drop_hdrlen = off0 + off;
 597
 598         /*
 599          * Locate pcb for segment.
 600          */
 601 findpcb:
 602         /* IPFIREWALL_FORWARD section */
 603         if (next_hop != NULL && !isipv6) {  /* IPv6 support is not there yet */
 604                 /*
 605                  * Transparently forwarded. Pretend to be the destination.
 606                  * already got one like this?
 607                  */
 608                 cpu = mycpu->gd_cpuid;
 609                 inp = in_pcblookup_hash(&tcbinfo[cpu],
 610                                         ip->ip_src, th->th_sport,
 611                                         ip->ip_dst, th->th_dport,
 612                                         0, m->m_pkthdr.rcvif);
 613                 if (!inp) {
 614                         /*
 615                          * It's new.  Try to find the ambushing socket.
 616                          */
 617
 618                         /*
 619                          * The rest of the ipfw code stores the port in
 620                          * host order.  XXX
 621                          * (The IP address is still in network order.)
 622                          */
 623                         in_port_t dport = next_hop->sin_port ?
 624                                                 htons(next_hop->sin_port) :
 625                                                 th->th_dport;
 626
 627                         cpu = tcp_addrcpu(ip->ip_src.s_addr, th->th_sport,
 628                                           next_hop->sin_addr.s_addr, dport);
 629                         inp = in_pcblookup_hash(&tcbinfo[cpu],
 630                                                 ip->ip_src, th->th_sport,
 631                                                 next_hop->sin_addr, dport,
 632                                                 1, m->m_pkthdr.rcvif);
 633                 }
 634         } else {
 635                 if (isipv6) {
 636                         inp = in6_pcblookup_hash(&tcbinfo[0],
 637                                                  &ip6->ip6_src, th->th_sport,
 638                                                  &ip6->ip6_dst, th->th_dport,
 639                                                  1, m->m_pkthdr.rcvif);
 640                 } else {
 641                         cpu = mycpu->gd_cpuid;
 642                         inp = in_pcblookup_hash(&tcbinfo[cpu],
 643                                                 ip->ip_src, th->th_sport,
 644                                                 ip->ip_dst, th->th_dport,
 645                                                 1, m->m_pkthdr.rcvif);
 646                 }
 647       }
 648
 649 #ifdef IPSEC
 650         if (isipv6) {
 651                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 652                         ipsec6stat.in_polvio++;
 653                         goto drop;
 654                 }
 655         } else {
 656                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 657                         ipsecstat.in_polvio++;
 658                         goto drop;
 659                 }
 660         }
 661 #endif
 662 #ifdef FAST_IPSEC
 663         if (isipv6) {
 664                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 665                         goto drop;
 666                 }
 667         } else {
 668                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 669                         goto drop;
 670                 }
 671         }
 672 #endif
 673
 674         /*
 675          * If the state is CLOSED (i.e., TCB does not exist) then
 676          * all data in the incoming segment is discarded.
 677          * If the TCB exists but is in CLOSED state, it is embryonic,
 678          * but should either do a listen or a connect soon.
 679          */
 680         if (inp == NULL) {
 681                 if (log_in_vain) {
 682 #ifdef INET6
 683                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 684 #else
 685                         char dbuf[4 * sizeof "123"], sbuf[4 * sizeof "123"];
 686 #endif
 687                         if (isipv6) {
 688                                 strcpy(dbuf, "[");
 689                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 690                                 strcat(dbuf, "]");
 691                                 strcpy(sbuf, "[");
 692                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 693                                 strcat(sbuf, "]");
 694                         } else {
 695                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 696                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 697                         }
 698                         switch (log_in_vain) {
 699                         case 1:
 700                                 if ((thflags & TH_SYN) == 0)
 701                                         break;
 702                         case 2:
 703                                 log(LOG_INFO,
 704                                     "Connection attempt to TCP %s:%d "
 705                                     "from %s:%d flags:0x%02x\n",
 706                                     dbuf, ntohs(th->th_dport), sbuf,
 707                                     ntohs(th->th_sport), thflags);
 708                                 break;
 709                         default:
 710                                 break;
 711                         }
 712                 }
 713                 if (blackhole) {
 714                         switch (blackhole) {
 715                         case 1:
 716                                 if (thflags & TH_SYN)
 717                                         goto drop;
 718                                 break;
 719                         case 2:
 720                                 goto drop;
 721                         default:
 722                                 goto drop;
 723                         }
 724                 }
 725                 rstreason = BANDLIM_RST_CLOSEDPORT;
 726                 goto dropwithreset;
 727         }
 728         tp = intotcpcb(inp);
 729         if (tp == NULL) {
 730                 rstreason = BANDLIM_RST_CLOSEDPORT;
 731                 goto dropwithreset;
 732         }
 733         if (tp->t_state == TCPS_CLOSED)
 734                 goto drop;
 735
 736         /* Unscale the window into a 32-bit value. */
 737         if (!(thflags & TH_SYN))
 738                 tiwin = th->th_win << tp->snd_scale;
 739         else
 740                 tiwin = th->th_win;
 741
 742         so = inp->inp_socket;
 743
 744 #ifdef TCPDEBUG
 745         if (so->so_options & SO_DEBUG) {
 746                 ostate = tp->t_state;
 747                 if (isipv6)
 748                         bcopy(ip6, tcp_saveipgen, sizeof(*ip6));
 749                 else
 750                         bcopy(ip, tcp_saveipgen, sizeof(*ip));
 751                 tcp_savetcp = *th;
 752         }
 753 #endif
 754
 755         bzero(&to, sizeof(to));
 756
 757         if (so->so_options & SO_ACCEPTCONN) {
 758                 struct in_conninfo inc;
 759
 760 #ifdef INET6
 761                 inc.inc_isipv6 = (isipv6 == TRUE);
 762 #endif
 763                 if (isipv6) {
 764                         inc.inc6_faddr = ip6->ip6_src;
 765                         inc.inc6_laddr = ip6->ip6_dst;
 766                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 767                 } else {
 768                         inc.inc_faddr = ip->ip_src;
 769                         inc.inc_laddr = ip->ip_dst;
 770                         inc.inc_route.ro_rt = NULL;             /* XXX */
 771                 }
 772                 inc.inc_fport = th->th_sport;
 773                 inc.inc_lport = th->th_dport;
 774
 775                 /*
 776                  * If the state is LISTEN then ignore segment if it contains
 777                  * a RST.  If the segment contains an ACK then it is bad and
 778                  * send a RST.  If it does not contain a SYN then it is not
 779                  * interesting; drop it.
 780                  *
 781                  * If the state is SYN_RECEIVED (syncache) and seg contains
 782                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 783                  * contains a RST, check the sequence number to see if it
 784                  * is a valid reset segment.
 785                  */
 786                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 787                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 788                                 if (!syncache_expand(&inc, th, &so, m)) {
 789                                         /*
 790                                          * No syncache entry, or ACK was not
 791                                          * for our SYN/ACK.  Send a RST.
 792                                          */
 793                                         tcpstat.tcps_badsyn++;
 794                                         rstreason = BANDLIM_RST_OPENPORT;
 795                                         goto dropwithreset;
 796                                 }
 797                                 if (so == NULL)
 798                                         /*
 799                                          * Could not complete 3-way handshake,
 800                                          * connection is being closed down, and
 801                                          * syncache will free mbuf.
 802                                          */
 803                                         return;
 804                                 /*
 805                                  * Socket is created in state SYN_RECEIVED.
 806                                  * Continue processing segment.
 807                                  */
 808                                 inp = sotoinpcb(so);
 809                                 tp = intotcpcb(inp);
 810                                 /*
 811                                  * This is what would have happened in
 812                                  * tcp_output() when the SYN,ACK was sent.
 813                                  */
 814                                 tp->snd_up = tp->snd_una;
 815                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 816                                 tp->last_ack_sent = tp->rcv_nxt;
 817 /*
 818  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 819  * until the _second_ ACK is received:
 820  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 821  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 822  *        move to ESTAB, set snd_wnd to tiwin.
 823  */
 824                                 tp->snd_wnd = tiwin;    /* unscaled */
 825                                 goto after_listen;
 826                         }
 827                         if (thflags & TH_RST) {
 828                                 syncache_chkrst(&inc, th);
 829                                 goto drop;
 830                         }
 831                         if (thflags & TH_ACK) {
 832                                 syncache_badack(&inc);
 833                                 tcpstat.tcps_badsyn++;
 834                                 rstreason = BANDLIM_RST_OPENPORT;
 835                                 goto dropwithreset;
 836                         }
 837                         goto drop;
 838                 }
 839
 840                 /*
 841                  * Segment's flags are (SYN) or (SYN|FIN).
 842                  */
 843 #ifdef INET6
 844                 /*
 845                  * If deprecated address is forbidden,
 846                  * we do not accept SYN to deprecated interface
 847                  * address to prevent any new inbound connection from
 848                  * getting established.
 849                  * When we do not accept SYN, we send a TCP RST,
 850                  * with deprecated source address (instead of dropping
 851                  * it).  We compromise it as it is much better for peer
 852                  * to send a RST, and RST will be the final packet
 853                  * for the exchange.
 854                  *
 855                  * If we do not forbid deprecated addresses, we accept
 856                  * the SYN packet.  RFC2462 does not suggest dropping
 857                  * SYN in this case.
 858                  * If we decipher RFC2462 5.5.4, it says like this:
 859                  * 1. use of deprecated addr with existing
 860                  *    communication is okay - "SHOULD continue to be
 861                  *    used"
 862                  * 2. use of it with new communication:
 863                  *   (2a) "SHOULD NOT be used if alternate address
 864                  *        with sufficient scope is available"
 865                  *   (2b) nothing mentioned otherwise.
 866                  * Here we fall into (2b) case as we have no choice in
 867                  * our source address selection - we must obey the peer.
 868                  *
 869                  * The wording in RFC2462 is confusing, and there are
 870                  * multiple description text for deprecated address
 871                  * handling - worse, they are not exactly the same.
 872                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 873                  */
 874                 if (isipv6 && !ip6_use_deprecated) {
 875                         struct in6_ifaddr *ia6;
 876
 877                         if ((ia6 = ip6_getdstifaddr(m)) &&
 878                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 879                                 tp = NULL;
 880                                 rstreason = BANDLIM_RST_OPENPORT;
 881                                 goto dropwithreset;
 882                         }
 883                 }
 884 #endif
 885                 /*
 886                  * If it is from this socket, drop it, it must be forged.
 887                  * Don't bother responding if the destination was a broadcast.
 888                  */
 889                 if (th->th_dport == th->th_sport) {
 890                         if (isipv6) {
 891                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 892                                                        &ip6->ip6_src))
 893                                         goto drop;
 894                         } else {
 895                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 896                                         goto drop;
 897                         }
 898                 }
 899                 /*
 900                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 901                  *
 902                  * Note that it is quite possible to receive unicast
 903                  * link-layer packets with a broadcast IP address. Use
 904                  * in_broadcast() to find them.
 905                  */
 906                 if (m->m_flags & (M_BCAST|M_MCAST))
 907                         goto drop;
 908                 if (isipv6) {
 909                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 910                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 911                                 goto drop;
 912                 } else {
 913                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 914                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 915                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 916                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 917                                 goto drop;
 918                 }
 919                 /*
 920                  * SYN appears to be valid; create compressed TCP state
 921                  * for syncache, or perform t/tcp connection.
 922                  */
 923                 if (so->so_qlen <= so->so_qlimit) {
 924                         tcp_dooptions(&to, optp, optlen, TRUE);
 925                         if (!syncache_add(&inc, &to, th, &so, m))
 926                                 goto drop;
 927                         if (so == NULL)
 928                                 /*
 929                                  * Entry added to syncache, mbuf used to
 930                                  * send SYN,ACK packet.
 931                                  */
 932                                 return;
 933                         /*
 934                          * Segment passed TAO tests.
 935                          */
 936                         inp = sotoinpcb(so);
 937                         tp = intotcpcb(inp);
 938                         tp->snd_wnd = tiwin;
 939                         tp->t_starttime = ticks;
 940                         tp->t_state = TCPS_ESTABLISHED;
 941
 942                         /*
 943                          * If there is a FIN, or if there is data and the
 944                          * connection is local, then delay SYN,ACK(SYN) in
 945                          * the hope of piggy-backing it on a response
 946                          * segment.  Otherwise must send ACK now in case
 947                          * the other side is slow starting.
 948                          */
 949                         if (DELAY_ACK(tp) &&
 950                             ((thflags & TH_FIN) ||
 951                              (tlen != 0 &&
 952                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 953                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 954                                 callout_reset(tp->tt_delack, tcp_delacktime,
 955                                                 tcp_timer_delack, tp);
 956                                 tp->t_flags |= TF_NEEDSYN;
 957                         } else
 958                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 959
 960                         tcpstat.tcps_connects++;
 961                         soisconnected(so);
 962                         goto trimthenstep6;
 963                 }
 964                 goto drop;
 965         }
 966 after_listen:
 967
 968 /* XXX temp debugging */
 969         /* should not happen - syncache should pick up these connections */
 970         if (tp->t_state == TCPS_LISTEN)
 971                 panic("tcp_input: TCPS_LISTEN");
 972
 973         /*
 974          * Segment received on connection.
 975          * Reset idle time and keep-alive timer.
 976          */
 977         tp->t_rcvtime = ticks;
 978         if (TCPS_HAVEESTABLISHED(tp->t_state))
 979                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 980
 981         /*
 982          * Process options.
 983          * XXX this is tradtitional behavior, may need to be cleaned up.
 984          */
 985         tcp_dooptions(&to, optp, optlen, (thflags & TH_SYN) != 0);
 986         if (thflags & TH_SYN) {
 987                 if (to.to_flags & TOF_SCALE) {
 988                         tp->t_flags |= TF_RCVD_SCALE;
 989                         tp->requested_s_scale = to.to_requested_s_scale;
 990                 }
 991                 if (to.to_flags & TOF_TS) {
 992                         tp->t_flags |= TF_RCVD_TSTMP;
 993                         tp->ts_recent = to.to_tsval;
 994                         tp->ts_recent_age = ticks;
 995                 }
 996                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 997                         tp->t_flags |= TF_RCVD_CC;
 998                 if (to.to_flags & TOF_MSS)
 999                         tcp_mss(tp, to.to_mss);
1000         }
1001
1002         /*
1003          * Header prediction: check for the two common cases
1004          * of a uni-directional data xfer.  If the packet has
1005          * no control flags, is in-sequence, the window didn't
1006          * change and we're not retransmitting, it's a
1007          * candidate.  If the length is zero and the ack moved
1008          * forward, we're the sender side of the xfer.  Just
1009          * free the data acked & wake any higher level process
1010          * that was blocked waiting for space.  If the length
1011          * is non-zero and the ack didn't move, we're the
1012          * receiver side.  If we're getting packets in-order
1013          * (the reassembly queue is empty), add the data to
1014          * the socket buffer and note that we need a delayed ack.
1015          * Make sure that the hidden state-flags are also off.
1016          * Since we check for TCPS_ESTABLISHED above, it can only
1017          * be TH_NEEDSYN.
1018          */
1019         if (tp->t_state == TCPS_ESTABLISHED &&
1020             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1021             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1022             ((to.to_flags & TOF_TS) == 0 ||
1023              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
1024             /*
1025              * Using the CC option is compulsory if once started:
1026              *   the segment is OK if no T/TCP was negotiated or
1027              *   if the segment has a CC option equal to CCrecv
1028              */
1029             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
1030              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
1031             th->th_seq == tp->rcv_nxt &&
1032             tiwin && tiwin == tp->snd_wnd &&
1033             tp->snd_nxt == tp->snd_max) {
1034
1035                 /*
1036                  * If last ACK falls within this segment's sequence numbers,
1037                  * record the timestamp.
1038                  * NOTE that the test is modified according to the latest
1039                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1040                  */
1041                 if ((to.to_flags & TOF_TS) != 0 &&
1042                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1043                         tp->ts_recent_age = ticks;
1044                         tp->ts_recent = to.to_tsval;
1045                 }
1046
1047                 if (tlen == 0) {
1048                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1049                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1050                             tp->snd_cwnd >= tp->snd_wnd &&
1051                             !IN_FASTRECOVERY(tp)) {
1052                                 /*
1053                                  * this is a pure ack for outstanding data.
1054                                  */
1055                                 ++tcpstat.tcps_predack;
1056                                 /*
1057                                  * "bad retransmit" recovery
1058                                  *
1059                                  * If Eifel detection applies, then
1060                                  * it is deterministic, so use it
1061                                  * unconditionally over the old heuristic.
1062                                  * Otherwise, fall back to the old heuristic.
1063                                  */
1064                                 if (tcp_do_eifel_detect &&
1065                                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1066                                     (tp->t_flags & TF_FIRSTACCACK)) {
1067                                         /* Eifel detection applicable. */
1068                                         if (to.to_tsecr < tp->t_rexmtTS) {
1069                                                 tcp_revert_congestion_state(tp);
1070                                                 ++tcpstat.tcps_eifeldetected;
1071                                         }
1072                                 } else if (tp->t_rxtshift == 1 &&
1073                                            ticks < tp->t_badrxtwin) {
1074                                         tcp_revert_congestion_state(tp);
1075                                         ++tcpstat.tcps_rttdetected;
1076                                 }
1077                                 tp->t_flags &= ~(TF_FIRSTACCACK |
1078                                                  TF_FASTREXMT | TF_EARLYREXMT);
1079                                 /*
1080                                  * Recalculate the retransmit timer / rtt.
1081                                  *
1082                                  * Some machines (certain windows boxes)
1083                                  * send broken timestamp replies during the
1084                                  * SYN+ACK phase, ignore timestamps of 0.
1085                                  */
1086                                 if ((to.to_flags & TOF_TS) && to.to_tsecr) {
1087                                         tcp_xmit_timer(tp,
1088                                                        ticks - to.to_tsecr + 1);
1089                                 } else if (tp->t_rtttime &&
1090                                            SEQ_GT(th->th_ack, tp->t_rtseq)) {
1091                                         tcp_xmit_timer(tp,
1092                                                        ticks - tp->t_rtttime);
1093                                 }
1094                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1095                                 acked = th->th_ack - tp->snd_una;
1096                                 tcpstat.tcps_rcvackpack++;
1097                                 tcpstat.tcps_rcvackbyte += acked;
1098                                 sbdrop(&so->so_snd, acked);
1099                                 tp->snd_recover = th->th_ack - 1;
1100                                 tp->snd_una = th->th_ack;
1101                                 tp->t_dupacks = 0;
1102                                 m_freem(m);
1103                                 ND6_HINT(tp); /* some progress has been done */
1104
1105                                 /*
1106                                  * If all outstanding data are acked, stop
1107                                  * retransmit timer, otherwise restart timer
1108                                  * using current (possibly backed-off) value.
1109                                  * If process is waiting for space,
1110                                  * wakeup/selwakeup/signal.  If data
1111                                  * are ready to send, let tcp_output
1112                                  * decide between more output or persist.
1113                                  */
1114                                 if (tp->snd_una == tp->snd_max)
1115                                         callout_stop(tp->tt_rexmt);
1116                                 else if (!callout_active(tp->tt_persist))
1117                                         callout_reset(tp->tt_rexmt,
1118                                                       tp->t_rxtcur,
1119                                                       tcp_timer_rexmt, tp);
1120
1121                                 sowwakeup(so);
1122                                 if (so->so_snd.sb_cc)
1123                                         (void) tcp_output(tp);
1124                                 return;
1125                         }
1126                 } else if (th->th_ack == tp->snd_una &&
1127                     LIST_EMPTY(&tp->t_segq) &&
1128                     tlen <= sbspace(&so->so_rcv)) {
1129                         /*
1130                          * this is a pure, in-sequence data packet
1131                          * with nothing on the reassembly queue and
1132                          * we have enough buffer space to take it.
1133                          */
1134                         ++tcpstat.tcps_preddat;
1135                         tp->rcv_nxt += tlen;
1136                         tcpstat.tcps_rcvpack++;
1137                         tcpstat.tcps_rcvbyte += tlen;
1138                         ND6_HINT(tp);   /* some progress has been done */
1139                         /*
1140                          * Add data to socket buffer.
1141                          */
1142                         if (so->so_state & SS_CANTRCVMORE) {
1143                                 m_freem(m);
1144                         } else {
1145                                 m_adj(m, drop_hdrlen); /* delayed header drop */
1146                                 sbappend(&so->so_rcv, m);
1147                         }
1148                         sorwakeup(so);
1149                         if (DELAY_ACK(tp)) {
1150                                 callout_reset(tp->tt_delack, tcp_delacktime,
1151                                     tcp_timer_delack, tp);
1152                         } else {
1153                                 tp->t_flags |= TF_ACKNOW;
1154                                 tcp_output(tp);
1155                         }
1156                         return;
1157                 }
1158         }
1159
1160         /*
1161          * Calculate amount of space in receive window,
1162          * and then do TCP input processing.
1163          * Receive window is amount of space in rcv queue,
1164          * but not less than advertised window.
1165          */
1166         { int win;
1167
1168         win = sbspace(&so->so_rcv);
1169         if (win < 0)
1170                 win = 0;
1171         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1172         }
1173
1174         switch (tp->t_state) {
1175
1176         /*
1177          * If the state is SYN_RECEIVED:
1178          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1179          */
1180         case TCPS_SYN_RECEIVED:
1181                 if ((thflags & TH_ACK) &&
1182                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1183                      SEQ_GT(th->th_ack, tp->snd_max))) {
1184                                 rstreason = BANDLIM_RST_OPENPORT;
1185                                 goto dropwithreset;
1186                 }
1187                 break;
1188
1189         /*
1190          * If the state is SYN_SENT:
1191          *      if seg contains an ACK, but not for our SYN, drop the input.
1192          *      if seg contains a RST, then drop the connection.
1193          *      if seg does not contain SYN, then drop it.
1194          * Otherwise this is an acceptable SYN segment
1195          *      initialize tp->rcv_nxt and tp->irs
1196          *      if seg contains ack then advance tp->snd_una
1197          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1198          *      arrange for segment to be acked (eventually)
1199          *      continue processing rest of data/controls, beginning with URG
1200          */
1201         case TCPS_SYN_SENT:
1202                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1203                         taop = &tao_noncached;
1204                         bzero(taop, sizeof(*taop));
1205                 }
1206
1207                 if ((thflags & TH_ACK) &&
1208                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1209                      SEQ_GT(th->th_ack, tp->snd_max))) {
1210                         /*
1211                          * If we have a cached CCsent for the remote host,
1212                          * hence we haven't just crashed and restarted,
1213                          * do not send a RST.  This may be a retransmission
1214                          * from the other side after our earlier ACK was lost.
1215                          * Our new SYN, when it arrives, will serve as the
1216                          * needed ACK.
1217                          */
1218                         if (taop->tao_ccsent != 0)
1219                                 goto drop;
1220                         else {
1221                                 rstreason = BANDLIM_UNLIMITED;
1222                                 goto dropwithreset;
1223                         }
1224                 }
1225                 if (thflags & TH_RST) {
1226                         if (thflags & TH_ACK)
1227                                 tp = tcp_drop(tp, ECONNREFUSED);
1228                         goto drop;
1229                 }
1230                 if ((thflags & TH_SYN) == 0)
1231                         goto drop;
1232                 tp->snd_wnd = th->th_win;       /* initial send window */
1233                 tp->cc_recv = to.to_cc;         /* foreign CC */
1234
1235                 tp->irs = th->th_seq;
1236                 tcp_rcvseqinit(tp);
1237                 if (thflags & TH_ACK) {
1238                         /*
1239                          * Our SYN was acked.  If segment contains CC.ECHO
1240                          * option, check it to make sure this segment really
1241                          * matches our SYN.  If not, just drop it as old
1242                          * duplicate, but send an RST if we're still playing
1243                          * by the old rules.  If no CC.ECHO option, make sure
1244                          * we don't get fooled into using T/TCP.
1245                          */
1246                         if (to.to_flags & TOF_CCECHO) {
1247                                 if (tp->cc_send != to.to_ccecho) {
1248                                         if (taop->tao_ccsent != 0)
1249                                                 goto drop;
1250                                         else {
1251                                                 rstreason = BANDLIM_UNLIMITED;
1252                                                 goto dropwithreset;
1253                                         }
1254                                 }
1255                         } else
1256                                 tp->t_flags &= ~TF_RCVD_CC;
1257                         tcpstat.tcps_connects++;
1258                         soisconnected(so);
1259                         /* Do window scaling on this connection? */
1260                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1261                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1262                                 tp->snd_scale = tp->requested_s_scale;
1263                                 tp->rcv_scale = tp->request_r_scale;
1264                         }
1265                         /* Segment is acceptable, update cache if undefined. */
1266                         if (taop->tao_ccsent == 0)
1267                                 taop->tao_ccsent = to.to_ccecho;
1268
1269                         tp->rcv_adv += tp->rcv_wnd;
1270                         tp->snd_una++;          /* SYN is acked */
1271                         /*
1272                          * If there's data, delay ACK; if there's also a FIN
1273                          * ACKNOW will be turned on later.
1274                          */
1275                         if (DELAY_ACK(tp) && tlen != 0)
1276                                 callout_reset(tp->tt_delack, tcp_delacktime,
1277                                     tcp_timer_delack, tp);
1278                         else
1279                                 tp->t_flags |= TF_ACKNOW;
1280                         /*
1281                          * Received <SYN,ACK> in SYN_SENT[*] state.
1282                          * Transitions:
1283                          *      SYN_SENT  --> ESTABLISHED
1284                          *      SYN_SENT* --> FIN_WAIT_1
1285                          */
1286                         tp->t_starttime = ticks;
1287                         if (tp->t_flags & TF_NEEDFIN) {
1288                                 tp->t_state = TCPS_FIN_WAIT_1;
1289                                 tp->t_flags &= ~TF_NEEDFIN;
1290                                 thflags &= ~TH_SYN;
1291                         } else {
1292                                 tp->t_state = TCPS_ESTABLISHED;
1293                                 callout_reset(tp->tt_keep, tcp_keepidle,
1294                                               tcp_timer_keep, tp);
1295                         }
1296                 } else {
1297                         /*
1298                          * Received initial SYN in SYN-SENT[*] state =>
1299                          * simultaneous open.  If segment contains CC option
1300                          * and there is a cached CC, apply TAO test.
1301                          * If it succeeds, connection is * half-synchronized.
1302                          * Otherwise, do 3-way handshake:
1303                          *        SYN-SENT -> SYN-RECEIVED
1304                          *        SYN-SENT* -> SYN-RECEIVED*
1305                          * If there was no CC option, clear cached CC value.
1306                          */
1307                         tp->t_flags |= TF_ACKNOW;
1308                         callout_stop(tp->tt_rexmt);
1309                         if (to.to_flags & TOF_CC) {
1310                                 if (taop->tao_cc != 0 &&
1311                                     CC_GT(to.to_cc, taop->tao_cc)) {
1312                                         /*
1313                                          * update cache and make transition:
1314                                          *        SYN-SENT -> ESTABLISHED*
1315                                          *        SYN-SENT* -> FIN-WAIT-1*
1316                                          */
1317                                         taop->tao_cc = to.to_cc;
1318                                         tp->t_starttime = ticks;
1319                                         if (tp->t_flags & TF_NEEDFIN) {
1320                                                 tp->t_state = TCPS_FIN_WAIT_1;
1321                                                 tp->t_flags &= ~TF_NEEDFIN;
1322                                         } else {
1323                                                 tp->t_state = TCPS_ESTABLISHED;
1324                                                 callout_reset(tp->tt_keep,
1325                                                               tcp_keepidle,
1326                                                               tcp_timer_keep,
1327                                                               tp);
1328                                         }
1329                                         tp->t_flags |= TF_NEEDSYN;
1330                                 } else
1331                                         tp->t_state = TCPS_SYN_RECEIVED;
1332                         } else {
1333                                 /* CC.NEW or no option => invalidate cache */
1334                                 taop->tao_cc = 0;
1335                                 tp->t_state = TCPS_SYN_RECEIVED;
1336                         }
1337                 }
1338
1339 trimthenstep6:
1340                 /*
1341                  * Advance th->th_seq to correspond to first data byte.
1342                  * If data, trim to stay within window,
1343                  * dropping FIN if necessary.
1344                  */
1345                 th->th_seq++;
1346                 if (tlen > tp->rcv_wnd) {
1347                         todrop = tlen - tp->rcv_wnd;
1348                         m_adj(m, -todrop);
1349                         tlen = tp->rcv_wnd;
1350                         thflags &= ~TH_FIN;
1351                         tcpstat.tcps_rcvpackafterwin++;
1352                         tcpstat.tcps_rcvbyteafterwin += todrop;
1353                 }
1354                 tp->snd_wl1 = th->th_seq - 1;
1355                 tp->rcv_up = th->th_seq;
1356                 /*
1357                  * Client side of transaction: already sent SYN and data.
1358                  * If the remote host used T/TCP to validate the SYN,
1359                  * our data will be ACK'd; if so, enter normal data segment
1360                  * processing in the middle of step 5, ack processing.
1361                  * Otherwise, goto step 6.
1362                  */
1363                 if (thflags & TH_ACK)
1364                         goto process_ACK;
1365
1366                 goto step6;
1367
1368         /*
1369          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1370          *      if segment contains a SYN and CC [not CC.NEW] option:
1371          *              if state == TIME_WAIT and connection duration > MSL,
1372          *                  drop packet and send RST;
1373          *
1374          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1375          *                  ack the FIN (and data) in retransmission queue.
1376          *                  Complete close and delete TCPCB.  Then reprocess
1377          *                  segment, hoping to find new TCPCB in LISTEN state;
1378          *
1379          *              else must be old SYN; drop it.
1380          *      else do normal processing.
1381          */
1382         case TCPS_LAST_ACK:
1383         case TCPS_CLOSING:
1384         case TCPS_TIME_WAIT:
1385                 if ((thflags & TH_SYN) &&
1386                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1387                         if (tp->t_state == TCPS_TIME_WAIT &&
1388                                         (ticks - tp->t_starttime) > tcp_msl) {
1389                                 rstreason = BANDLIM_UNLIMITED;
1390                                 goto dropwithreset;
1391                         }
1392                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1393                                 tp = tcp_close(tp);
1394                                 goto findpcb;
1395                         }
1396                         else
1397                                 goto drop;
1398                 }
1399                 break;  /* continue normal processing */
1400         }
1401
1402         /*
1403          * States other than LISTEN or SYN_SENT.
1404          * First check the RST flag and sequence number since reset segments
1405          * are exempt from the timestamp and connection count tests.  This
1406          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1407          * below which allowed reset segments in half the sequence space
1408          * to fall though and be processed (which gives forged reset
1409          * segments with a random sequence number a 50 percent chance of
1410          * killing a connection).
1411          * Then check timestamp, if present.
1412          * Then check the connection count, if present.
1413          * Then check that at least some bytes of segment are within
1414          * receive window.  If segment begins before rcv_nxt,
1415          * drop leading data (and SYN); if nothing left, just ack.
1416          *
1417          *
1418          * If the RST bit is set, check the sequence number to see
1419          * if this is a valid reset segment.
1420          * RFC 793 page 37:
1421          *   In all states except SYN-SENT, all reset (RST) segments
1422          *   are validated by checking their SEQ-fields.  A reset is
1423          *   valid if its sequence number is in the window.
1424          * Note: this does not take into account delayed ACKs, so
1425          *   we should test against last_ack_sent instead of rcv_nxt.
1426          *   The sequence number in the reset segment is normally an
1427          *   echo of our outgoing acknowlegement numbers, but some hosts
1428          *   send a reset with the sequence number at the rightmost edge
1429          *   of our receive window, and we have to handle this case.
1430          * If we have multiple segments in flight, the intial reset
1431          * segment sequence numbers will be to the left of last_ack_sent,
1432          * but they will eventually catch up.
1433          * In any case, it never made sense to trim reset segments to
1434          * fit the receive window since RFC 1122 says:
1435          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1436          *
1437          *    A TCP SHOULD allow a received RST segment to include data.
1438          *
1439          *    DISCUSSION
1440          *         It has been suggested that a RST segment could contain
1441          *         ASCII text that encoded and explained the cause of the
1442          *         RST.  No standard has yet been established for such
1443          *         data.
1444          *
1445          * If the reset segment passes the sequence number test examine
1446          * the state:
1447          *    SYN_RECEIVED STATE:
1448          *      If passive open, return to LISTEN state.
1449          *      If active open, inform user that connection was refused.
1450          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1451          *      Inform user that connection was reset, and close tcb.
1452          *    CLOSING, LAST_ACK STATES:
1453          *      Close the tcb.
1454          *    TIME_WAIT STATE:
1455          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1456          *      RFC 1337.
1457          */
1458         if (thflags & TH_RST) {
1459                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1460                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1461                         switch (tp->t_state) {
1462
1463                         case TCPS_SYN_RECEIVED:
1464                                 so->so_error = ECONNREFUSED;
1465                                 goto close;
1466
1467                         case TCPS_ESTABLISHED:
1468                         case TCPS_FIN_WAIT_1:
1469                         case TCPS_FIN_WAIT_2:
1470                         case TCPS_CLOSE_WAIT:
1471                                 so->so_error = ECONNRESET;
1472                         close:
1473                                 tp->t_state = TCPS_CLOSED;
1474                                 tcpstat.tcps_drops++;
1475                                 tp = tcp_close(tp);
1476                                 break;
1477
1478                         case TCPS_CLOSING:
1479                         case TCPS_LAST_ACK:
1480                                 tp = tcp_close(tp);
1481                                 break;
1482
1483                         case TCPS_TIME_WAIT:
1484                                 break;
1485                         }
1486                 }
1487                 goto drop;
1488         }
1489
1490         /*
1491          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1492          * and it's less than ts_recent, drop it.
1493          */
1494         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1495             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1496
1497                 /* Check to see if ts_recent is over 24 days old.  */
1498                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1499                         /*
1500                          * Invalidate ts_recent.  If this segment updates
1501                          * ts_recent, the age will be reset later and ts_recent
1502                          * will get a valid value.  If it does not, setting
1503                          * ts_recent to zero will at least satisfy the
1504                          * requirement that zero be placed in the timestamp
1505                          * echo reply when ts_recent isn't valid.  The
1506                          * age isn't reset until we get a valid ts_recent
1507                          * because we don't want out-of-order segments to be
1508                          * dropped when ts_recent is old.
1509                          */
1510                         tp->ts_recent = 0;
1511                 } else {
1512                         tcpstat.tcps_rcvduppack++;
1513                         tcpstat.tcps_rcvdupbyte += tlen;
1514                         tcpstat.tcps_pawsdrop++;
1515                         if (tlen)
1516                                 goto dropafterack;
1517                         goto drop;
1518                 }
1519         }
1520
1521         /*
1522          * T/TCP mechanism
1523          *   If T/TCP was negotiated and the segment doesn't have CC,
1524          *   or if its CC is wrong then drop the segment.
1525          *   RST segments do not have to comply with this.
1526          */
1527         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1528             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1529                 goto dropafterack;
1530
1531         /*
1532          * In the SYN-RECEIVED state, validate that the packet belongs to
1533          * this connection before trimming the data to fit the receive
1534          * window.  Check the sequence number versus IRS since we know
1535          * the sequence numbers haven't wrapped.  This is a partial fix
1536          * for the "LAND" DoS attack.
1537          */
1538         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1539                 rstreason = BANDLIM_RST_OPENPORT;
1540                 goto dropwithreset;
1541         }
1542
1543         todrop = tp->rcv_nxt - th->th_seq;
1544         if (todrop > 0) {
1545                 if (thflags & TH_SYN) {
1546                         thflags &= ~TH_SYN;
1547                         th->th_seq++;
1548                         if (th->th_urp > 1)
1549                                 th->th_urp--;
1550                         else
1551                                 thflags &= ~TH_URG;
1552                         todrop--;
1553                 }
1554                 /*
1555                  * Following if statement from Stevens, vol. 2, p. 960.
1556                  */
1557                 if (todrop > tlen
1558                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1559                         /*
1560                          * Any valid FIN must be to the left of the window.
1561                          * At this point the FIN must be a duplicate or out
1562                          * of sequence; drop it.
1563                          */
1564                         thflags &= ~TH_FIN;
1565
1566                         /*
1567                          * Send an ACK to resynchronize and drop any data.
1568                          * But keep on processing for RST or ACK.
1569                          */
1570                         tp->t_flags |= TF_ACKNOW;
1571                         todrop = tlen;
1572                         tcpstat.tcps_rcvduppack++;
1573                         tcpstat.tcps_rcvdupbyte += todrop;
1574                 } else {
1575                         tcpstat.tcps_rcvpartduppack++;
1576                         tcpstat.tcps_rcvpartdupbyte += todrop;
1577                 }
1578                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1579                 th->th_seq += todrop;
1580                 tlen -= todrop;
1581                 if (th->th_urp > todrop)
1582                         th->th_urp -= todrop;
1583                 else {
1584                         thflags &= ~TH_URG;
1585                         th->th_urp = 0;
1586                 }
1587         }
1588
1589         /*
1590          * If new data are received on a connection after the
1591          * user processes are gone, then RST the other end.
1592          */
1593         if ((so->so_state & SS_NOFDREF) &&
1594             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1595                 tp = tcp_close(tp);
1596                 tcpstat.tcps_rcvafterclose++;
1597                 rstreason = BANDLIM_UNLIMITED;
1598                 goto dropwithreset;
1599         }
1600
1601         /*
1602          * If segment ends after window, drop trailing data
1603          * (and PUSH and FIN); if nothing left, just ACK.
1604          */
1605         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1606         if (todrop > 0) {
1607                 tcpstat.tcps_rcvpackafterwin++;
1608                 if (todrop >= tlen) {
1609                         tcpstat.tcps_rcvbyteafterwin += tlen;
1610                         /*
1611                          * If a new connection request is received
1612                          * while in TIME_WAIT, drop the old connection
1613                          * and start over if the sequence numbers
1614                          * are above the previous ones.
1615                          */
1616                         if (thflags & TH_SYN &&
1617                             tp->t_state == TCPS_TIME_WAIT &&
1618                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1619                                 tp = tcp_close(tp);
1620                                 goto findpcb;
1621                         }
1622                         /*
1623                          * If window is closed can only take segments at
1624                          * window edge, and have to drop data and PUSH from
1625                          * incoming segments.  Continue processing, but
1626                          * remember to ack.  Otherwise, drop segment
1627                          * and ack.
1628                          */
1629                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1630                                 tp->t_flags |= TF_ACKNOW;
1631                                 tcpstat.tcps_rcvwinprobe++;
1632                         } else
1633                                 goto dropafterack;
1634                 } else
1635                         tcpstat.tcps_rcvbyteafterwin += todrop;
1636                 m_adj(m, -todrop);
1637                 tlen -= todrop;
1638                 thflags &= ~(TH_PUSH|TH_FIN);
1639         }
1640
1641         /*
1642          * If last ACK falls within this segment's sequence numbers,
1643          * record its timestamp.
1644          * NOTE that the test is modified according to the latest
1645          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1646          */
1647         if ((to.to_flags & TOF_TS) != 0 &&
1648             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1649                 tp->ts_recent_age = ticks;
1650                 tp->ts_recent = to.to_tsval;
1651         }
1652
1653         /*
1654          * If a SYN is in the window, then this is an
1655          * error and we send an RST and drop the connection.
1656          */
1657         if (thflags & TH_SYN) {
1658                 tp = tcp_drop(tp, ECONNRESET);
1659                 rstreason = BANDLIM_UNLIMITED;
1660                 goto dropwithreset;
1661         }
1662
1663         /*
1664          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1665          * flag is on (half-synchronized state), then queue data for
1666          * later processing; else drop segment and return.
1667          */
1668         if ((thflags & TH_ACK) == 0) {
1669                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1670                     (tp->t_flags & TF_NEEDSYN))
1671                         goto step6;
1672                 else
1673                         goto drop;
1674         }
1675
1676         /*
1677          * Ack processing.
1678          */
1679         switch (tp->t_state) {
1680
1681         /*
1682          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1683          * ESTABLISHED state and continue processing.
1684          * The ACK was checked above.
1685          */
1686         case TCPS_SYN_RECEIVED:
1687
1688                 tcpstat.tcps_connects++;
1689                 soisconnected(so);
1690                 /* Do window scaling? */
1691                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1692                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1693                         tp->snd_scale = tp->requested_s_scale;
1694                         tp->rcv_scale = tp->request_r_scale;
1695                 }
1696                 /*
1697                  * Upon successful completion of 3-way handshake,
1698                  * update cache.CC if it was undefined, pass any queued
1699                  * data to the user, and advance state appropriately.
1700                  */
1701                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1702                     taop->tao_cc == 0)
1703                         taop->tao_cc = tp->cc_recv;
1704
1705                 /*
1706                  * Make transitions:
1707                  *      SYN-RECEIVED  -> ESTABLISHED
1708                  *      SYN-RECEIVED* -> FIN-WAIT-1
1709                  */
1710                 tp->t_starttime = ticks;
1711                 if (tp->t_flags & TF_NEEDFIN) {
1712                         tp->t_state = TCPS_FIN_WAIT_1;
1713                         tp->t_flags &= ~TF_NEEDFIN;
1714                 } else {
1715                         tp->t_state = TCPS_ESTABLISHED;
1716                         callout_reset(tp->tt_keep, tcp_keepidle,
1717                                       tcp_timer_keep, tp);
1718                 }
1719                 /*
1720                  * If segment contains data or ACK, will call tcp_reass()
1721                  * later; if not, do so now to pass queued data to user.
1722                  */
1723                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1724                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1725                             (struct mbuf *)0);
1726                 tp->snd_wl1 = th->th_seq - 1;
1727                 /* fall into ... */
1728
1729         /*
1730          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1731          * ACKs.  If the ack is in the range
1732          *      tp->snd_una < th->th_ack <= tp->snd_max
1733          * then advance tp->snd_una to th->th_ack and drop
1734          * data from the retransmission queue.  If this ACK reflects
1735          * more up to date window information we update our window information.
1736          */
1737         case TCPS_ESTABLISHED:
1738         case TCPS_FIN_WAIT_1:
1739         case TCPS_FIN_WAIT_2:
1740         case TCPS_CLOSE_WAIT:
1741         case TCPS_CLOSING:
1742         case TCPS_LAST_ACK:
1743         case TCPS_TIME_WAIT:
1744
1745                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1746                         if (tlen != 0 || tiwin != tp->snd_wnd) {
1747                                 tp->t_dupacks = 0;
1748                                 break;
1749                         }
1750                         tcpstat.tcps_rcvdupack++;
1751                         /*
1752                          * If we have outstanding data (other than
1753                          * a window probe), this is a completely
1754                          * duplicate ack (ie, window info didn't
1755                          * change), the ack is the biggest we've
1756                          * seen and we've seen exactly our rexmt
1757                          * threshhold of them, assume a packet
1758                          * has been dropped and retransmit it.
1759                          * Kludge snd_nxt & the congestion
1760                          * window so we send only this one
1761                          * packet.
1762                          *
1763                          * We know we're losing at the current
1764                          * window size so do congestion avoidance
1765                          * (set ssthresh to half the current window
1766                          * and pull our congestion window back to
1767                          * the new ssthresh).
1768                          *
1769                          * Dup acks mean that packets have left the
1770                          * network (they're now cached at the receiver)
1771                          * so bump cwnd by the amount in the receiver
1772                          * to keep a constant cwnd packets in the
1773                          * network.
1774                          */
1775                         if (!callout_active(tp->tt_rexmt) ||
1776                             th->th_ack != tp->snd_una) {
1777                                 tp->t_dupacks = 0;
1778                                 break;
1779                         }
1780                         if (IN_FASTRECOVERY(tp)) {
1781                                 tp->snd_cwnd += tp->t_maxseg;
1782                                 (void) tcp_output(tp);
1783                         } else if (++tp->t_dupacks == tcprexmtthresh) {
1784                                 tcp_seq onxt;
1785                                 u_int win;
1786
1787                                 if (SEQ_LEQ(th->th_ack, tp->snd_recover)) {
1788                                         tp->t_dupacks = 0;
1789                                         break;
1790                                 }
1791 fastretransmit:
1792                                 if (tcp_do_eifel_detect &&
1793                                     (tp->t_flags & TF_RCVD_TSTMP)) {
1794                                         tcp_save_congestion_state(tp);
1795                                         tp->t_flags |= TF_FASTREXMT;
1796                                 }
1797                                 win = min(tp->snd_wnd, tp->snd_cwnd) / 2 /
1798                                     tp->t_maxseg;
1799                                 if (win < 2)
1800                                         win = 2;
1801                                 tp->snd_ssthresh = win * tp->t_maxseg;
1802                                 ENTER_FASTRECOVERY(tp);
1803                                 tp->snd_recover = tp->snd_max;
1804                                 callout_stop(tp->tt_rexmt);
1805                                 tp->t_rtttime = 0;
1806                                 onxt = tp->snd_nxt;
1807                                 tp->snd_nxt = th->th_ack;
1808                                 tp->snd_cwnd = tp->t_maxseg;
1809                                 (void) tcp_output(tp);
1810                                 ++tcpstat.tcps_sndfastrexmit;
1811                                 KASSERT(tp->snd_limited <= 2,
1812                                     ("tp->snd_limited too big"));
1813                                 tp->snd_cwnd = tp->snd_ssthresh +
1814                                     (tp->t_maxseg *
1815                                      (tp->t_dupacks - tp->snd_limited));
1816                                 if (SEQ_GT(onxt, tp->snd_nxt))
1817                                         tp->snd_nxt = onxt;
1818                         } else if (tcp_do_limitedtransmit) {
1819                                 u_long oldcwnd = tp->snd_cwnd;
1820                                 tcp_seq oldsndmax = tp->snd_max;
1821                                 /* outstanding data */
1822                                 uint32_t ownd = tp->snd_max - tp->snd_una;
1823                                 u_int sent;
1824
1825 #define iceildiv(n, d)          (((n)+(d)-1) / (d))
1826
1827                                 KASSERT(tp->t_dupacks == 1 ||
1828                                         tp->t_dupacks == 2,
1829                                     ("dupacks not 1 or 2"));
1830                                 if (tp->t_dupacks == 1)
1831                                         tp->snd_limited = 0;
1832                                 tp->snd_cwnd = ownd +
1833                                     (tp->t_dupacks - tp->snd_limited) *
1834                                     tp->t_maxseg;
1835                                 (void) tcp_output(tp);
1836                                 tp->snd_cwnd = oldcwnd;
1837                                 sent = tp->snd_max - oldsndmax;
1838                                 if (sent > tp->t_maxseg) {
1839                                         KASSERT((tp->t_dupacks == 2 &&
1840                                                  tp->snd_limited == 0) ||
1841                                                 (sent == tp->t_maxseg + 1 &&
1842                                                  tp->t_flags & TF_SENTFIN),
1843                                             ("sent too much"));
1844                                         KASSERT(sent <= tp->t_maxseg * 2,
1845                                             ("sent too many segments"));
1846                                         tp->snd_limited = 2;
1847                                         tcpstat.tcps_sndlimited += 2;
1848                                 } else if (sent > 0) {
1849                                         ++tp->snd_limited;
1850                                         ++tcpstat.tcps_sndlimited;
1851                                 } else if (tcp_do_early_retransmit &&
1852                                     (tcp_do_eifel_detect &&
1853                                      (tp->t_flags & TF_RCVD_TSTMP)) &&
1854                                     tp->t_dupacks + 1 >=
1855                                       iceildiv(ownd, tp->t_maxseg)) {
1856                                         ++tcpstat.tcps_sndearlyrexmit;
1857                                         tp->t_flags |= TF_EARLYREXMT;
1858                                         goto fastretransmit;
1859                                 }
1860                         }
1861                         goto drop;
1862                 }
1863
1864                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1865
1866                 /*
1867                  * If the congestion window was inflated to account
1868                  * for the other side's cached packets, retract it.
1869                  */
1870                 if (IN_FASTRECOVERY(tp)) {
1871                         if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1872                                 tcp_newreno_partial_ack(tp, th);
1873                         } else {
1874                                 /*
1875                                  * Window inflation should have left us
1876                                  * with approximately snd_ssthresh
1877                                  * outstanding data.
1878                                  * But in case we would be inclined to
1879                                  * send a burst, better to do it via
1880                                  * the slow start mechanism.
1881                                  */
1882                                 if (SEQ_GT(th->th_ack + tp->snd_ssthresh,
1883                                            tp->snd_max))
1884                                         tp->snd_cwnd = tp->snd_max -
1885                                             th->th_ack + tp->t_maxseg;
1886                                 else
1887                                         tp->snd_cwnd = tp->snd_ssthresh;
1888                         }
1889                 }
1890                 tp->t_dupacks = 0;
1891                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1892                         /*
1893                          * Detected optimistic ACK attack.
1894                          * Force slow-start to de-synchronize attack.
1895                          */
1896                         tp->snd_cwnd = tp->t_maxseg;
1897
1898                         tcpstat.tcps_rcvacktoomuch++;
1899                         goto dropafterack;
1900                 }
1901                 /*
1902                  * If we reach this point, ACK is not a duplicate,
1903                  *     i.e., it ACKs something we sent.
1904                  */
1905                 if (tp->t_flags & TF_NEEDSYN) {
1906                         /*
1907                          * T/TCP: Connection was half-synchronized, and our
1908                          * SYN has been ACK'd (so connection is now fully
1909                          * synchronized).  Go to non-starred state,
1910                          * increment snd_una for ACK of SYN, and check if
1911                          * we can do window scaling.
1912                          */
1913                         tp->t_flags &= ~TF_NEEDSYN;
1914                         tp->snd_una++;
1915                         /* Do window scaling? */
1916                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1917                             (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1918                                 tp->snd_scale = tp->requested_s_scale;
1919                                 tp->rcv_scale = tp->request_r_scale;
1920                         }
1921                 }
1922
1923 process_ACK:
1924                 acked = th->th_ack - tp->snd_una;
1925                 tcpstat.tcps_rcvackpack++;
1926                 tcpstat.tcps_rcvackbyte += acked;
1927
1928                 /*
1929                  * If we just performed our first retransmit, and the ACK
1930                  * arrives within our recovery window, then it was a mistake
1931                  * to do the retransmit in the first place.  Recover our
1932                  * original cwnd and ssthresh, and proceed to transmit where
1933                  * we left off.
1934                  */
1935                 if (tcp_do_eifel_detect && acked &&
1936                     (to.to_flags & TOF_TS) && (to.to_tsecr != 0) &&
1937                     (tp->t_flags & TF_FIRSTACCACK)) {
1938                         /* Eifel detection applicable. */
1939                         if (to.to_tsecr < tp->t_rexmtTS) {
1940                                 ++tcpstat.tcps_eifeldetected;
1941                                 tcp_revert_congestion_state(tp);
1942                                 if (tp->t_rxtshift == 1 &&
1943                                     ticks >= tp->t_badrxtwin)
1944                                         ++tcpstat.tcps_rttcantdetect;
1945                         }
1946                 } else if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1947                         tcp_revert_congestion_state(tp);
1948                         ++tcpstat.tcps_rttdetected;
1949                 }
1950
1951                 /*
1952                  * If we have a timestamp reply, update smoothed
1953                  * round trip time.  If no timestamp is present but
1954                  * transmit timer is running and timed sequence
1955                  * number was acked, update smoothed round trip time.
1956                  * Since we now have an rtt measurement, cancel the
1957                  * timer backoff (cf., Phil Karn's retransmit alg.).
1958                  * Recompute the initial retransmit timer.
1959                  *
1960                  * Some machines (certain windows boxes) send broken
1961                  * timestamp replies during the SYN+ACK phase, ignore
1962                  * timestamps of 0.
1963                  */
1964                 if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0))
1965                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1966                 else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq))
1967                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1968                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1969
1970                 /*
1971                  * If all outstanding data is acked, stop retransmit
1972                  * timer and remember to restart (more output or persist).
1973                  * If there is more data to be acked, restart retransmit
1974                  * timer, using current (possibly backed-off) value.
1975                  */
1976                 if (th->th_ack == tp->snd_max) {
1977                         callout_stop(tp->tt_rexmt);
1978                         needoutput = 1;
1979                 } else if (!callout_active(tp->tt_persist))
1980                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1981                                       tcp_timer_rexmt, tp);
1982
1983                 /*
1984                  * If no data (only SYN) was ACK'd,
1985                  *    skip rest of ACK processing.
1986                  */
1987                 if (acked == 0)
1988                         goto step6;
1989
1990                 /* Stop looking for an acceptable ACK since one was received. */
1991                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT | TF_EARLYREXMT);
1992
1993                 /*
1994                  * When new data is acked, open the congestion window.
1995                  * If the window gives us less than ssthresh packets
1996                  * in flight, open exponentially (maxseg per packet).
1997                  * Otherwise open linearly: maxseg per window
1998                  * (maxseg^2 / cwnd per packet).
1999                  */
2000                 if (!IN_FASTRECOVERY(tp)) {
2001                         u_int cw = tp->snd_cwnd;
2002                         u_int incr = tp->t_maxseg;
2003
2004                         if (cw > tp->snd_ssthresh)
2005                                 incr = incr * incr / cw;
2006                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
2007                 }
2008                 if (acked > so->so_snd.sb_cc) {
2009                         tp->snd_wnd -= so->so_snd.sb_cc;
2010                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
2011                         ourfinisacked = 1;
2012                 } else {
2013                         sbdrop(&so->so_snd, acked);
2014                         tp->snd_wnd -= acked;
2015                         ourfinisacked = 0;
2016                 }
2017                 sowwakeup(so);
2018                 if (IN_FASTRECOVERY(tp)) {
2019                         if (SEQ_GEQ(th->th_ack, tp->snd_recover))
2020                                 EXIT_FASTRECOVERY(tp);
2021                 } else {
2022                         tp->snd_recover = th->th_ack - 1;
2023                 }
2024                 tp->snd_una = th->th_ack;
2025                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2026                         tp->snd_nxt = tp->snd_una;
2027
2028                 switch (tp->t_state) {
2029
2030                 /*
2031                  * In FIN_WAIT_1 STATE in addition to the processing
2032                  * for the ESTABLISHED state if our FIN is now acknowledged
2033                  * then enter FIN_WAIT_2.
2034                  */
2035                 case TCPS_FIN_WAIT_1:
2036                         if (ourfinisacked) {
2037                                 /*
2038                                  * If we can't receive any more
2039                                  * data, then closing user can proceed.
2040                                  * Starting the timer is contrary to the
2041                                  * specification, but if we don't get a FIN
2042                                  * we'll hang forever.
2043                                  */
2044                                 if (so->so_state & SS_CANTRCVMORE) {
2045                                         soisdisconnected(so);
2046                                         callout_reset(tp->tt_2msl, tcp_maxidle,
2047                                                       tcp_timer_2msl, tp);
2048                                 }
2049                                 tp->t_state = TCPS_FIN_WAIT_2;
2050                         }
2051                         break;
2052
2053                 /*
2054                  * In CLOSING STATE in addition to the processing for
2055                  * the ESTABLISHED state if the ACK acknowledges our FIN
2056                  * then enter the TIME-WAIT state, otherwise ignore
2057                  * the segment.
2058                  */
2059                 case TCPS_CLOSING:
2060                         if (ourfinisacked) {
2061                                 tp->t_state = TCPS_TIME_WAIT;
2062                                 tcp_canceltimers(tp);
2063                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
2064                                 if (tp->cc_recv != 0 &&
2065                                     (ticks - tp->t_starttime) < tcp_msl)
2066                                         callout_reset(tp->tt_2msl,
2067                                                       tp->t_rxtcur *
2068                                                       TCPTV_TWTRUNC,
2069                                                       tcp_timer_2msl, tp);
2070                                 else
2071                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2072                                                       tcp_timer_2msl, tp);
2073                                 soisdisconnected(so);
2074                         }
2075                         break;
2076
2077                 /*
2078                  * In LAST_ACK, we may still be waiting for data to drain
2079                  * and/or to be acked, as well as for the ack of our FIN.
2080                  * If our FIN is now acknowledged, delete the TCB,
2081                  * enter the closed state and return.
2082                  */
2083                 case TCPS_LAST_ACK:
2084                         if (ourfinisacked) {
2085                                 tp = tcp_close(tp);
2086                                 goto drop;
2087                         }
2088                         break;
2089
2090                 /*
2091                  * In TIME_WAIT state the only thing that should arrive
2092                  * is a retransmission of the remote FIN.  Acknowledge
2093                  * it and restart the finack timer.
2094                  */
2095                 case TCPS_TIME_WAIT:
2096                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2097                                       tcp_timer_2msl, tp);
2098                         goto dropafterack;
2099                 }
2100         }
2101
2102 step6:
2103         /*
2104          * Update window information.
2105          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2106          */
2107         if ((thflags & TH_ACK) &&
2108             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2109             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2110              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2111                 /* keep track of pure window updates */
2112                 if (tlen == 0 &&
2113                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2114                         tcpstat.tcps_rcvwinupd++;
2115                 tp->snd_wnd = tiwin;
2116                 tp->snd_wl1 = th->th_seq;
2117                 tp->snd_wl2 = th->th_ack;
2118                 if (tp->snd_wnd > tp->max_sndwnd)
2119                         tp->max_sndwnd = tp->snd_wnd;
2120                 needoutput = 1;
2121         }
2122
2123         /*
2124          * Process segments with URG.
2125          */
2126         if ((thflags & TH_URG) && th->th_urp &&
2127             !TCPS_HAVERCVDFIN(tp->t_state)) {
2128                 /*
2129                  * This is a kludge, but if we receive and accept
2130                  * random urgent pointers, we'll crash in
2131                  * soreceive.  It's hard to imagine someone
2132                  * actually wanting to send this much urgent data.
2133                  */
2134                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2135                         th->th_urp = 0;                 /* XXX */
2136                         thflags &= ~TH_URG;             /* XXX */
2137                         goto dodata;                    /* XXX */
2138                 }
2139                 /*
2140                  * If this segment advances the known urgent pointer,
2141                  * then mark the data stream.  This should not happen
2142                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2143                  * a FIN has been received from the remote side.
2144                  * In these states we ignore the URG.
2145                  *
2146                  * According to RFC961 (Assigned Protocols),
2147                  * the urgent pointer points to the last octet
2148                  * of urgent data.  We continue, however,
2149                  * to consider it to indicate the first octet
2150                  * of data past the urgent section as the original
2151                  * spec states (in one of two places).
2152                  */
2153                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2154                         tp->rcv_up = th->th_seq + th->th_urp;
2155                         so->so_oobmark = so->so_rcv.sb_cc +
2156                             (tp->rcv_up - tp->rcv_nxt) - 1;
2157                         if (so->so_oobmark == 0)
2158                                 so->so_state |= SS_RCVATMARK;
2159                         sohasoutofband(so);
2160                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2161                 }
2162                 /*
2163                  * Remove out of band data so doesn't get presented to user.
2164                  * This can happen independent of advancing the URG pointer,
2165                  * but if two URG's are pending at once, some out-of-band
2166                  * data may creep in... ick.
2167                  */
2168                 if (th->th_urp <= (u_long)tlen
2169 #ifdef SO_OOBINLINE
2170                      && (so->so_options & SO_OOBINLINE) == 0
2171 #endif
2172                      )
2173                         tcp_pulloutofband(so, th, m,
2174                                 drop_hdrlen);   /* hdr drop is delayed */
2175         } else {
2176                 /*
2177                  * If no out of band data is expected,
2178                  * pull receive urgent pointer along
2179                  * with the receive window.
2180                  */
2181                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2182                         tp->rcv_up = tp->rcv_nxt;
2183         }
2184 dodata:                                                 /* XXX */
2185
2186         /*
2187          * Process the segment text, merging it into the TCP sequencing queue,
2188          * and arranging for acknowledgment of receipt if necessary.
2189          * This process logically involves adjusting tp->rcv_wnd as data
2190          * is presented to the user (this happens in tcp_usrreq.c,
2191          * case PRU_RCVD).  If a FIN has already been received on this
2192          * connection then we just ignore the text.
2193          */
2194         if ((tlen || (thflags & TH_FIN)) && !TCPS_HAVERCVDFIN(tp->t_state)) {
2195                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2196                 /*
2197                  * Insert segment which includes th into TCP reassembly queue
2198                  * with control block tp.  Set thflags to whether reassembly now
2199                  * includes a segment with FIN.  This handles the common case
2200                  * inline (segment is the next to be received on an established
2201                  * connection, and the queue is empty), avoiding linkage into
2202                  * and removal from the queue and repetition of various
2203                  * conversions.
2204                  * Set DELACK for segments received in order, but ack
2205                  * immediately when segments are out of order (so
2206                  * fast retransmit can work).
2207                  */
2208                 if (th->th_seq == tp->rcv_nxt &&
2209                     LIST_EMPTY(&tp->t_segq) &&
2210                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2211                         if (DELAY_ACK(tp))
2212                                 callout_reset(tp->tt_delack, tcp_delacktime,
2213                                               tcp_timer_delack, tp);
2214                         else
2215                                 tp->t_flags |= TF_ACKNOW;
2216                         tp->rcv_nxt += tlen;
2217                         thflags = th->th_flags & TH_FIN;
2218                         tcpstat.tcps_rcvpack++;
2219                         tcpstat.tcps_rcvbyte += tlen;
2220                         ND6_HINT(tp);
2221                         if (so->so_state & SS_CANTRCVMORE)
2222                                 m_freem(m);
2223                         else
2224                                 sbappend(&so->so_rcv, m);
2225                         sorwakeup(so);
2226                 } else {
2227                         thflags = tcp_reass(tp, th, &tlen, m);
2228                         tp->t_flags |= TF_ACKNOW;
2229                 }
2230
2231                 /*
2232                  * Note the amount of data that peer has sent into
2233                  * our window, in order to estimate the sender's
2234                  * buffer size.
2235                  */
2236                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2237         } else {
2238                 m_freem(m);
2239                 thflags &= ~TH_FIN;
2240         }
2241
2242         /*
2243          * If FIN is received ACK the FIN and let the user know
2244          * that the connection is closing.
2245          */
2246         if (thflags & TH_FIN) {
2247                 if (!TCPS_HAVERCVDFIN(tp->t_state)) {
2248                         socantrcvmore(so);
2249                         /*
2250                          * If connection is half-synchronized
2251                          * (ie NEEDSYN flag on) then delay ACK,
2252                          * so it may be piggybacked when SYN is sent.
2253                          * Otherwise, since we received a FIN then no
2254                          * more input can be expected, send ACK now.
2255                          */
2256                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2257                                 callout_reset(tp->tt_delack, tcp_delacktime,
2258                                     tcp_timer_delack, tp);
2259                         else
2260                                 tp->t_flags |= TF_ACKNOW;
2261                         tp->rcv_nxt++;
2262                 }
2263                 switch (tp->t_state) {
2264
2265                 /*
2266                  * In SYN_RECEIVED and ESTABLISHED STATES
2267                  * enter the CLOSE_WAIT state.
2268                  */
2269                 case TCPS_SYN_RECEIVED:
2270                         tp->t_starttime = ticks;
2271                         /*FALLTHROUGH*/
2272                 case TCPS_ESTABLISHED:
2273                         tp->t_state = TCPS_CLOSE_WAIT;
2274                         break;
2275
2276                 /*
2277                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2278                  * enter the CLOSING state.
2279                  */
2280                 case TCPS_FIN_WAIT_1:
2281                         tp->t_state = TCPS_CLOSING;
2282                         break;
2283
2284                 /*
2285                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2286                  * starting the time-wait timer, turning off the other
2287                  * standard timers.
2288                  */
2289                 case TCPS_FIN_WAIT_2:
2290                         tp->t_state = TCPS_TIME_WAIT;
2291                         tcp_canceltimers(tp);
2292                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2293                         if (tp->cc_recv != 0 &&
2294                             (ticks - tp->t_starttime) < tcp_msl) {
2295                                 callout_reset(tp->tt_2msl,
2296                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2297                                               tcp_timer_2msl, tp);
2298                                 /* For transaction client, force ACK now. */
2299                                 tp->t_flags |= TF_ACKNOW;
2300                         }
2301                         else
2302                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2303                                               tcp_timer_2msl, tp);
2304                         soisdisconnected(so);
2305                         break;
2306
2307                 /*
2308                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2309                  */
2310                 case TCPS_TIME_WAIT:
2311                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2312                                       tcp_timer_2msl, tp);
2313                         break;
2314                 }
2315         }
2316 #ifdef TCPDEBUG
2317         if (so->so_options & SO_DEBUG)
2318                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2319                           &tcp_savetcp, 0);
2320 #endif
2321
2322         /*
2323          * Return any desired output.
2324          */
2325         if (needoutput || (tp->t_flags & TF_ACKNOW))
2326                 (void) tcp_output(tp);
2327         return;
2328
2329 dropafterack:
2330         /*
2331          * Generate an ACK dropping incoming segment if it occupies
2332          * sequence space, where the ACK reflects our state.
2333          *
2334          * We can now skip the test for the RST flag since all
2335          * paths to this code happen after packets containing
2336          * RST have been dropped.
2337          *
2338          * In the SYN-RECEIVED state, don't send an ACK unless the
2339          * segment we received passes the SYN-RECEIVED ACK test.
2340          * If it fails send a RST.  This breaks the loop in the
2341          * "LAND" DoS attack, and also prevents an ACK storm
2342          * between two listening ports that have been sent forged
2343          * SYN segments, each with the source address of the other.
2344          */
2345         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2346             (SEQ_GT(tp->snd_una, th->th_ack) ||
2347              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2348                 rstreason = BANDLIM_RST_OPENPORT;
2349                 goto dropwithreset;
2350         }
2351 #ifdef TCPDEBUG
2352         if (so->so_options & SO_DEBUG)
2353                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2354                           &tcp_savetcp, 0);
2355 #endif
2356         m_freem(m);
2357         tp->t_flags |= TF_ACKNOW;
2358         (void) tcp_output(tp);
2359         return;
2360
2361 dropwithreset:
2362         /*
2363          * Generate a RST, dropping incoming segment.
2364          * Make ACK acceptable to originator of segment.
2365          * Don't bother to respond if destination was broadcast/multicast.
2366          */
2367         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2368                 goto drop;
2369         if (isipv6) {
2370                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2371                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2372                         goto drop;
2373         } else {
2374                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2375                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2376                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2377                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2378                         goto drop;
2379         }
2380         /* IPv6 anycast check is done at tcp6_input() */
2381
2382         /*
2383          * Perform bandwidth limiting.
2384          */
2385 #ifdef ICMP_BANDLIM
2386         if (badport_bandlim(rstreason) < 0)
2387                 goto drop;
2388 #endif
2389
2390 #ifdef TCPDEBUG
2391         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2392                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2393                           &tcp_savetcp, 0);
2394 #endif
2395         if (thflags & TH_ACK)
2396                 /* mtod() below is safe as long as hdr dropping is delayed */
2397                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2398                             TH_RST);
2399         else {
2400                 if (thflags & TH_SYN)
2401                         tlen++;
2402                 /* mtod() below is safe as long as hdr dropping is delayed */
2403                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2404                             (tcp_seq)0, TH_RST|TH_ACK);
2405         }
2406         return;
2407
2408 drop:
2409         /*
2410          * Drop space held by incoming segment and return.
2411          */
2412 #ifdef TCPDEBUG
2413         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2414                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2415                           &tcp_savetcp, 0);
2416 #endif
2417         m_freem(m);
2418         return;
2419 }
2420
2421 /*
2422  * Parse TCP options and place in tcpopt.
2423  */
2424 static void
2425 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, boolean_t is_syn)
2426 {
2427         int opt, optlen;
2428
2429         to->to_flags = 0;
2430         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2431                 opt = cp[0];
2432                 if (opt == TCPOPT_EOL)
2433                         break;
2434                 if (opt == TCPOPT_NOP)
2435                         optlen = 1;
2436                 else {
2437                         if (cnt < 2)
2438                                 break;
2439                         optlen = cp[1];
2440                         if (optlen < 2 || optlen > cnt)
2441                                 break;
2442                 }
2443                 switch (opt) {
2444                 case TCPOPT_MAXSEG:
2445                         if (optlen != TCPOLEN_MAXSEG)
2446                                 continue;
2447                         if (!is_syn)
2448                                 continue;
2449                         to->to_flags |= TOF_MSS;
2450                         bcopy(cp + 2, &to->to_mss, sizeof(to->to_mss));
2451                         to->to_mss = ntohs(to->to_mss);
2452                         break;
2453                 case TCPOPT_WINDOW:
2454                         if (optlen != TCPOLEN_WINDOW)
2455                                 continue;
2456                         if (!is_syn)
2457                                 continue;
2458                         to->to_flags |= TOF_SCALE;
2459                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2460                         break;
2461                 case TCPOPT_TIMESTAMP:
2462                         if (optlen != TCPOLEN_TIMESTAMP)
2463                                 continue;
2464                         to->to_flags |= TOF_TS;
2465                         bcopy(cp + 2, &to->to_tsval, sizeof(to->to_tsval));
2466                         to->to_tsval = ntohl(to->to_tsval);
2467                         bcopy(cp + 6, &to->to_tsecr, sizeof(to->to_tsecr));
2468                         to->to_tsecr = ntohl(to->to_tsecr);
2469                         break;
2470                 case TCPOPT_CC:
2471                         if (optlen != TCPOLEN_CC)
2472                                 continue;
2473                         to->to_flags |= TOF_CC;
2474                         bcopy(cp + 2, &to->to_cc, sizeof(to->to_cc));
2475                         to->to_cc = ntohl(to->to_cc);
2476                         break;
2477                 case TCPOPT_CCNEW:
2478                         if (optlen != TCPOLEN_CC)
2479                                 continue;
2480                         if (!is_syn)
2481                                 continue;
2482                         to->to_flags |= TOF_CCNEW;
2483                         bcopy(cp + 2, &to->to_cc, sizeof(to->to_cc));
2484                         to->to_cc = ntohl(to->to_cc);
2485                         break;
2486                 case TCPOPT_CCECHO:
2487                         if (optlen != TCPOLEN_CC)
2488                                 continue;
2489                         if (!is_syn)
2490                                 continue;
2491                         to->to_flags |= TOF_CCECHO;
2492                         bcopy(cp + 2, &to->to_ccecho, sizeof(to->to_ccecho));
2493                         to->to_ccecho = ntohl(to->to_ccecho);
2494                         break;
2495                 default:
2496                         continue;
2497                 }
2498         }
2499 }
2500
2501 /*
2502  * Pull out of band byte out of a segment so
2503  * it doesn't appear in the user's data queue.
2504  * It is still reflected in the segment length for
2505  * sequencing purposes.
2506  * "off" is the delayed to be dropped hdrlen.
2507  */
2508 static void
2509 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m, int off)
2510 {
2511         int cnt = off + th->th_urp - 1;
2512
2513         while (cnt >= 0) {
2514                 if (m->m_len > cnt) {
2515                         char *cp = mtod(m, caddr_t) + cnt;
2516                         struct tcpcb *tp = sototcpcb(so);
2517
2518                         tp->t_iobc = *cp;
2519                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2520                         bcopy(cp + 1, cp, m->m_len - cnt - 1);
2521                         m->m_len--;
2522                         if (m->m_flags & M_PKTHDR)
2523                                 m->m_pkthdr.len--;
2524                         return;
2525                 }
2526                 cnt -= m->m_len;
2527                 m = m->m_next;
2528                 if (m == 0)
2529                         break;
2530         }
2531         panic("tcp_pulloutofband");
2532 }
2533
2534 /*
2535  * Collect new round-trip time estimate
2536  * and update averages and current timeout.
2537  */
2538 static void
2539 tcp_xmit_timer(struct tcpcb *tp, int rtt)
2540 {
2541         int delta;
2542
2543         tcpstat.tcps_rttupdated++;
2544         tp->t_rttupdated++;
2545         if (tp->t_srtt != 0) {
2546                 /*
2547                  * srtt is stored as fixed point with 5 bits after the
2548                  * binary point (i.e., scaled by 8).  The following magic
2549                  * is equivalent to the smoothing algorithm in rfc793 with
2550                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2551                  * point).  Adjust rtt to origin 0.
2552                  */
2553                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2554                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2555
2556                 if ((tp->t_srtt += delta) <= 0)
2557                         tp->t_srtt = 1;
2558
2559                 /*
2560                  * We accumulate a smoothed rtt variance (actually, a
2561                  * smoothed mean difference), then set the retransmit
2562                  * timer to smoothed rtt + 4 times the smoothed variance.
2563                  * rttvar is stored as fixed point with 4 bits after the
2564                  * binary point (scaled by 16).  The following is
2565                  * equivalent to rfc793 smoothing with an alpha of .75
2566                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2567                  * rfc793's wired-in beta.
2568                  */
2569                 if (delta < 0)
2570                         delta = -delta;
2571                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2572                 if ((tp->t_rttvar += delta) <= 0)
2573                         tp->t_rttvar = 1;
2574                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2575                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2576         } else {
2577                 /*
2578                  * No rtt measurement yet - use the unsmoothed rtt.
2579                  * Set the variance to half the rtt (so our first
2580                  * retransmit happens at 3*rtt).
2581                  */
2582                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2583                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2584                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2585         }
2586         tp->t_rtttime = 0;
2587         tp->t_rxtshift = 0;
2588
2589         /*
2590          * the retransmit should happen at rtt + 4 * rttvar.
2591          * Because of the way we do the smoothing, srtt and rttvar
2592          * will each average +1/2 tick of bias.  When we compute
2593          * the retransmit timer, we want 1/2 tick of rounding and
2594          * 1 extra tick because of +-1/2 tick uncertainty in the
2595          * firing of the timer.  The bias will give us exactly the
2596          * 1.5 tick we need.  But, because the bias is
2597          * statistical, we have to test that we don't drop below
2598          * the minimum feasible timer (which is 2 ticks).
2599          */
2600         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2601                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2602
2603         /*
2604          * We received an ack for a packet that wasn't retransmitted;
2605          * it is probably safe to discard any error indications we've
2606          * received recently.  This isn't quite right, but close enough
2607          * for now (a route might have failed after we sent a segment,
2608          * and the return path might not be symmetrical).
2609          */
2610         tp->t_softerror = 0;
2611 }
2612
2613 /*
2614  * Determine a reasonable value for maxseg size.
2615  * If the route is known, check route for mtu.
2616  * If none, use an mss that can be handled on the outgoing
2617  * interface without forcing IP to fragment; if bigger than
2618  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2619  * to utilize large mbufs.  If no route is found, route has no mtu,
2620  * or the destination isn't local, use a default, hopefully conservative
2621  * size (usually 512 or the default IP max size, but no more than the mtu
2622  * of the interface), as we can't discover anything about intervening
2623  * gateways or networks.  We also initialize the congestion/slow start
2624  * window to be a single segment if the destination isn't local.
2625  * While looking at the routing entry, we also initialize other path-dependent
2626  * parameters from pre-set or cached values in the routing entry.
2627  *
2628  * Also take into account the space needed for options that we
2629  * send regularly.  Make maxseg shorter by that amount to assure
2630  * that we can send maxseg amount of data even when the options
2631  * are present.  Store the upper limit of the length of options plus
2632  * data in maxopd.
2633  *
2634  * NOTE that this routine is only called when we process an incoming
2635  * segment, for outgoing segments only tcp_mssopt is called.
2636  *
2637  * In case of T/TCP, we call this routine during implicit connection
2638  * setup as well (offer = -1), to initialize maxseg from the cached
2639  * MSS of our peer.
2640  */
2641 void
2642 tcp_mss(struct tcpcb *tp, int offer)
2643 {
2644         struct rtentry *rt;
2645         struct ifnet *ifp;
2646         int rtt, mss;
2647         u_long bufsize;
2648         struct inpcb *inp = tp->t_inpcb;
2649         struct socket *so;
2650         struct rmxp_tao *taop;
2651         int origoffer = offer;
2652 #ifdef INET6
2653         boolean_t isipv6 = ((inp->inp_vflag & INP_IPV6) ? TRUE : FALSE);
2654         size_t min_protoh = isipv6 ?
2655                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2656                             sizeof(struct tcpiphdr);
2657 #else
2658         const boolean_t isipv6 = FALSE;
2659         const size_t min_protoh = sizeof(struct tcpiphdr);
2660 #endif
2661
2662         if (isipv6)
2663                 rt = tcp_rtlookup6(&inp->inp_inc);
2664         else
2665                 rt = tcp_rtlookup(&inp->inp_inc);
2666         if (rt == NULL) {
2667                 tp->t_maxopd = tp->t_maxseg =
2668                     (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2669                 return;
2670         }
2671         ifp = rt->rt_ifp;
2672         so = inp->inp_socket;
2673
2674         taop = rmx_taop(rt->rt_rmx);
2675         /*
2676          * Offer == -1 means that we didn't receive SYN yet,
2677          * use cached value in that case;
2678          */
2679         if (offer == -1)
2680                 offer = taop->tao_mssopt;
2681         /*
2682          * Offer == 0 means that there was no MSS on the SYN segment,
2683          * in this case we use tcp_mssdflt.
2684          */
2685         if (offer == 0)
2686                 offer = (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2687         else
2688                 /*
2689                  * Sanity check: make sure that maxopd will be large
2690                  * enough to allow some data on segments even is the
2691                  * all the option space is used (40bytes).  Otherwise
2692                  * funny things may happen in tcp_output.
2693                  */
2694                 offer = max(offer, 64);
2695         taop->tao_mssopt = offer;
2696
2697         /*
2698          * While we're here, check if there's an initial rtt
2699          * or rttvar.  Convert from the route-table units
2700          * to scaled multiples of the slow timeout timer.
2701          */
2702         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2703                 /*
2704                  * XXX the lock bit for RTT indicates that the value
2705                  * is also a minimum value; this is subject to time.
2706                  */
2707                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2708                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2709                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2710                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2711                 tcpstat.tcps_usedrtt++;
2712                 if (rt->rt_rmx.rmx_rttvar) {
2713                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2714                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2715                         tcpstat.tcps_usedrttvar++;
2716                 } else {
2717                         /* default variation is +- 1 rtt */
2718                         tp->t_rttvar =
2719                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2720                 }
2721                 TCPT_RANGESET(tp->t_rxtcur,
2722                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2723                               tp->t_rttmin, TCPTV_REXMTMAX);
2724         }
2725         /*
2726          * if there's an mtu associated with the route, use it
2727          * else, use the link mtu.
2728          */
2729         if (rt->rt_rmx.rmx_mtu)
2730                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2731         else {
2732                 if (isipv6) {
2733                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2734                                 min_protoh;
2735                         if (!in6_localaddr(&inp->in6p_faddr))
2736                                 mss = min(mss, tcp_v6mssdflt);
2737                 } else {
2738                         mss = ifp->if_mtu - min_protoh;
2739                         if (!in_localaddr(inp->inp_faddr))
2740                                 mss = min(mss, tcp_mssdflt);
2741                 }
2742         }
2743         mss = min(mss, offer);
2744         /*
2745          * maxopd stores the maximum length of data AND options
2746          * in a segment; maxseg is the amount of data in a normal
2747          * segment.  We need to store this value (maxopd) apart
2748          * from maxseg, because now every segment carries options
2749          * and thus we normally have somewhat less data in segments.
2750          */
2751         tp->t_maxopd = mss;
2752
2753         /*
2754          * In case of T/TCP, origoffer==-1 indicates, that no segments
2755          * were received yet.  In this case we just guess, otherwise
2756          * we do the same as before T/TCP.
2757          */
2758         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2759             (origoffer == -1 ||
2760              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2761                 mss -= TCPOLEN_TSTAMP_APPA;
2762         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2763             (origoffer == -1 ||
2764              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2765                 mss -= TCPOLEN_CC_APPA;
2766
2767 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2768                 if (mss > MCLBYTES)
2769                         mss &= ~(MCLBYTES-1);
2770 #else
2771                 if (mss > MCLBYTES)
2772                         mss = mss / MCLBYTES * MCLBYTES;
2773 #endif
2774         /*
2775          * If there's a pipesize, change the socket buffer
2776          * to that size.  Make the socket buffers an integral
2777          * number of mss units; if the mss is larger than
2778          * the socket buffer, decrease the mss.
2779          */
2780 #ifdef RTV_SPIPE
2781         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2782 #endif
2783                 bufsize = so->so_snd.sb_hiwat;
2784         if (bufsize < mss)
2785                 mss = bufsize;
2786         else {
2787                 bufsize = roundup(bufsize, mss);
2788                 if (bufsize > sb_max)
2789                         bufsize = sb_max;
2790                 if (bufsize > so->so_snd.sb_hiwat)
2791                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2792         }
2793         tp->t_maxseg = mss;
2794
2795 #ifdef RTV_RPIPE
2796         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2797 #endif
2798                 bufsize = so->so_rcv.sb_hiwat;
2799         if (bufsize > mss) {
2800                 bufsize = roundup(bufsize, mss);
2801                 if (bufsize > sb_max)
2802                         bufsize = sb_max;
2803                 if (bufsize > so->so_rcv.sb_hiwat)
2804                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2805         }
2806
2807         /*
2808          * Set the slow-start flight size depending on whether this
2809          * is a local network or not.
2810          */
2811         if (tcp_do_rfc3390)
2812                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2813         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2814                  (!isipv6 && in_localaddr(inp->inp_faddr)))
2815                 tp->snd_cwnd = mss * ss_fltsz_local;
2816         else
2817                 tp->snd_cwnd = mss * ss_fltsz;
2818
2819         if (rt->rt_rmx.rmx_ssthresh) {
2820                 /*
2821                  * There's some sort of gateway or interface
2822                  * buffer limit on the path.  Use this to set
2823                  * the slow start threshhold, but set the
2824                  * threshold to no less than 2*mss.
2825                  */
2826                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2827                 tcpstat.tcps_usedssthresh++;
2828         }
2829 }
2830
2831 /*
2832  * Determine the MSS option to send on an outgoing SYN.
2833  */
2834 int
2835 tcp_mssopt(struct tcpcb *tp)
2836 {
2837         struct rtentry *rt;
2838 #ifdef INET6
2839         boolean_t isipv6 =
2840             ((tp->t_inpcb->inp_vflag & INP_IPV6) ? TRUE : FALSE);
2841         int min_protoh = isipv6 ?
2842                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2843                              sizeof(struct tcpiphdr);
2844 #else
2845         const boolean_t isipv6 = FALSE;
2846         const size_t min_protoh = sizeof(struct tcpiphdr);
2847 #endif
2848
2849         if (isipv6)
2850                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2851         else
2852                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2853         if (rt == NULL)
2854                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2855
2856         return (rt->rt_ifp->if_mtu - min_protoh);
2857 }
2858
2859
2860 /*
2861  * When a partial ack arrives, force the retransmission of the
2862  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2863  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2864  * be started again.
2865  */
2866 static void
2867 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
2868 {
2869         tcp_seq onxt = tp->snd_nxt;
2870         u_long  ocwnd = tp->snd_cwnd;
2871
2872         callout_stop(tp->tt_rexmt);
2873         tp->t_rtttime = 0;
2874         tp->snd_nxt = th->th_ack;
2875         /*
2876          * Set snd_cwnd to one segment beyond acknowledged offset
2877          * (tp->snd_una has not yet been updated when this function is called.)
2878          */
2879         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2880         tp->t_flags |= TF_ACKNOW;
2881         (void) tcp_output(tp);
2882         tp->snd_cwnd = ocwnd;
2883         if (SEQ_GT(onxt, tp->snd_nxt))
2884                 tp->snd_nxt = onxt;
2885         /*
2886          * Partial window deflation.  Relies on fact that tp->snd_una
2887          * not updated yet.
2888          */
2889         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2890 }