sys/netinet/tcp_input.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  34  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
  35  * $DragonFly: src/sys/netinet/tcp_input.c,v 1.5 2003/07/24 23:33:33 hsu Exp $
  36  */
  37
  38 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  39 #include "opt_inet6.h"
  40 #include "opt_ipsec.h"
  41 #include "opt_tcpdebug.h"
  42 #include "opt_tcp_input.h"
  43
  44 #include <sys/param.h>
  45 #include <sys/systm.h>
  46 #include <sys/kernel.h>
  47 #include <sys/sysctl.h>
  48 #include <sys/malloc.h>
  49 #include <sys/mbuf.h>
  50 #include <sys/proc.h>           /* for proc0 declaration */
  51 #include <sys/protosw.h>
  52 #include <sys/socket.h>
  53 #include <sys/socketvar.h>
  54 #include <sys/syslog.h>
  55
  56 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  57
  58 #include <net/if.h>
  59 #include <net/route.h>
  60
  61 #include <netinet/in.h>
  62 #include <netinet/in_systm.h>
  63 #include <netinet/ip.h>
  64 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
  65 #include <netinet/in_var.h>
  66 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
  67 #include <netinet/in_pcb.h>
  68 #include <netinet/ip_var.h>
  69 #include <netinet/ip6.h>
  70 #include <netinet/icmp6.h>
  71 #include <netinet6/nd6.h>
  72 #include <netinet6/ip6_var.h>
  73 #include <netinet6/in6_pcb.h>
  74 #include <netinet/tcp.h>
  75 #include <netinet/tcp_fsm.h>
  76 #include <netinet/tcp_seq.h>
  77 #include <netinet/tcp_timer.h>
  78 #include <netinet/tcp_var.h>
  79 #include <netinet6/tcp6_var.h>
  80 #include <netinet/tcpip.h>
  81 #ifdef TCPDEBUG
  82 #include <netinet/tcp_debug.h>
  83
  84 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
  85 struct tcphdr tcp_savetcp;
  86 #endif /* TCPDEBUG */
  87
  88 #ifdef FAST_IPSEC
  89 #include <netipsec/ipsec.h>
  90 #include <netipsec/ipsec6.h>
  91 #endif
  92
  93 #ifdef IPSEC
  94 #include <netinet6/ipsec.h>
  95 #include <netinet6/ipsec6.h>
  96 #include <netkey/key.h>
  97 #endif /*IPSEC*/
  98
  99 #include <machine/in_cksum.h>
 100
 101 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
 102
 103 static const int tcprexmtthresh = 3;
 104 tcp_cc  tcp_ccgen;
 105
 106 struct  tcpstat tcpstat;
 107 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 108     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 109
 110 static int log_in_vain = 0;
 111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 112     &log_in_vain, 0, "Log all incoming TCP connections");
 113
 114 static int blackhole = 0;
 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 116     &blackhole, 0, "Do not send RST when dropping refused connections");
 117
 118 int tcp_delack_enabled = 1;
 119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 120     &tcp_delack_enabled, 0,
 121     "Delay ACK to try and piggyback it onto a data packet");
 122
 123 #ifdef TCP_DROP_SYNFIN
 124 static int drop_synfin = 0;
 125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 126     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 127 #endif
 128
 129 static int tcp_do_limitedtransmit = 1;
 130 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
 131     &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
 132
 133 static int tcp_do_rfc3390 = 1;
 134 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 135     &tcp_do_rfc3390, 0,
 136     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 137
 138 struct inpcbhead tcb;
 139 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 140 struct inpcbinfo tcbinfo;
 141
 142 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 143 static void      tcp_pulloutofband(struct socket *,
 144                      struct tcphdr *, struct mbuf *, int);
 145 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 146                      struct mbuf *);
 147 static void      tcp_xmit_timer(struct tcpcb *, int);
 148 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 149
 150 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 151 #ifdef INET6
 152 #define ND6_HINT(tp) \
 153 do { \
 154         if ((tp) && (tp)->t_inpcb && \
 155             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 156             (tp)->t_inpcb->in6p_route.ro_rt) \
 157                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 158 } while (0)
 159 #else
 160 #define ND6_HINT(tp)
 161 #endif
 162
 163 /*
 164  * Indicate whether this ack should be delayed.  We can delay the ack if
 165  *      - delayed acks are enabled and
 166  *      - there is no delayed ack timer in progress and
 167  *      - our last ack wasn't a 0-sized window.  We never want to delay
 168  *        the ack that opens up a 0-sized window.
 169  */
 170 #define DELAY_ACK(tp) \
 171         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
 172         (tp->t_flags & TF_RXWIN0SENT) == 0)
 173
 174 static int
 175 tcp_reass(tp, th, tlenp, m)
 176         register struct tcpcb *tp;
 177         register struct tcphdr *th;
 178         int *tlenp;
 179         struct mbuf *m;
 180 {
 181         struct tseg_qent *q;
 182         struct tseg_qent *p = NULL;
 183         struct tseg_qent *nq;
 184         struct tseg_qent *te;
 185         struct socket *so = tp->t_inpcb->inp_socket;
 186         int flags;
 187
 188         /*
 189          * Call with th==0 after become established to
 190          * force pre-ESTABLISHED data up to user socket.
 191          */
 192         if (th == 0)
 193                 goto present;
 194
 195         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
 196         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
 197                M_NOWAIT);
 198         if (te == NULL) {
 199                 tcpstat.tcps_rcvmemdrop++;
 200                 m_freem(m);
 201                 return (0);
 202         }
 203
 204         /*
 205          * Find a segment which begins after this one does.
 206          */
 207         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 208                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 209                         break;
 210                 p = q;
 211         }
 212
 213         /*
 214          * If there is a preceding segment, it may provide some of
 215          * our data already.  If so, drop the data from the incoming
 216          * segment.  If it provides all of our data, drop us.
 217          */
 218         if (p != NULL) {
 219                 register int i;
 220                 /* conversion to int (in i) handles seq wraparound */
 221                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 222                 if (i > 0) {
 223                         if (i >= *tlenp) {
 224                                 tcpstat.tcps_rcvduppack++;
 225                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 226                                 m_freem(m);
 227                                 free(te, M_TSEGQ);
 228                                 /*
 229                                  * Try to present any queued data
 230                                  * at the left window edge to the user.
 231                                  * This is needed after the 3-WHS
 232                                  * completes.
 233                                  */
 234                                 goto present;   /* ??? */
 235                         }
 236                         m_adj(m, i);
 237                         *tlenp -= i;
 238                         th->th_seq += i;
 239                 }
 240         }
 241         tcpstat.tcps_rcvoopack++;
 242         tcpstat.tcps_rcvoobyte += *tlenp;
 243
 244         /*
 245          * While we overlap succeeding segments trim them or,
 246          * if they are completely covered, dequeue them.
 247          */
 248         while (q) {
 249                 register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 250                 if (i <= 0)
 251                         break;
 252                 if (i < q->tqe_len) {
 253                         q->tqe_th->th_seq += i;
 254                         q->tqe_len -= i;
 255                         m_adj(q->tqe_m, i);
 256                         break;
 257                 }
 258
 259                 nq = LIST_NEXT(q, tqe_q);
 260                 LIST_REMOVE(q, tqe_q);
 261                 m_freem(q->tqe_m);
 262                 free(q, M_TSEGQ);
 263                 q = nq;
 264         }
 265
 266         /* Insert the new segment queue entry into place. */
 267         te->tqe_m = m;
 268         te->tqe_th = th;
 269         te->tqe_len = *tlenp;
 270
 271         if (p == NULL) {
 272                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 273         } else {
 274                 LIST_INSERT_AFTER(p, te, tqe_q);
 275         }
 276
 277 present:
 278         /*
 279          * Present data to user, advancing rcv_nxt through
 280          * completed sequence space.
 281          */
 282         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 283                 return (0);
 284         q = LIST_FIRST(&tp->t_segq);
 285         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 286                 return (0);
 287         do {
 288                 tp->rcv_nxt += q->tqe_len;
 289                 flags = q->tqe_th->th_flags & TH_FIN;
 290                 nq = LIST_NEXT(q, tqe_q);
 291                 LIST_REMOVE(q, tqe_q);
 292                 if (so->so_state & SS_CANTRCVMORE)
 293                         m_freem(q->tqe_m);
 294                 else
 295                         sbappend(&so->so_rcv, q->tqe_m);
 296                 free(q, M_TSEGQ);
 297                 q = nq;
 298         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 299         ND6_HINT(tp);
 300         sorwakeup(so);
 301         return (flags);
 302 }
 303
 304 /*
 305  * TCP input routine, follows pages 65-76 of the
 306  * protocol specification dated September, 1981 very closely.
 307  */
 308 #ifdef INET6
 309 int
 310 tcp6_input(mp, offp, proto)
 311         struct mbuf **mp;
 312         int *offp, proto;
 313 {
 314         register struct mbuf *m = *mp;
 315         struct in6_ifaddr *ia6;
 316
 317         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 318
 319         /*
 320          * draft-itojun-ipv6-tcp-to-anycast
 321          * better place to put this in?
 322          */
 323         ia6 = ip6_getdstifaddr(m);
 324         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 325                 struct ip6_hdr *ip6;
 326
 327                 ip6 = mtod(m, struct ip6_hdr *);
 328                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 329                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 330                 return IPPROTO_DONE;
 331         }
 332
 333         tcp_input(m, *offp, proto);
 334         return IPPROTO_DONE;
 335 }
 336 #endif
 337
 338 void
 339 tcp_input(m, off0, proto)
 340         register struct mbuf *m;
 341         int off0, proto;
 342 {
 343         register struct tcphdr *th;
 344         register struct ip *ip = NULL;
 345         register struct ipovly *ipov;
 346         register struct inpcb *inp = NULL;
 347         u_char *optp = NULL;
 348         int optlen = 0;
 349         int len, tlen, off;
 350         int drop_hdrlen;
 351         register struct tcpcb *tp = NULL;
 352         register int thflags;
 353         struct socket *so = 0;
 354         int todrop, acked, ourfinisacked, needoutput = 0;
 355         u_long tiwin;
 356         struct tcpopt to;               /* options in this segment */
 357         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 358         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 359         struct sockaddr_in *next_hop = NULL;
 360         int rstreason; /* For badport_bandlim accounting purposes */
 361         struct ip6_hdr *ip6 = NULL;
 362 #ifdef INET6
 363         int isipv6;
 364 #else
 365         const int isipv6 = 0;
 366 #endif
 367 #ifdef TCPDEBUG
 368         short ostate = 0;
 369 #endif
 370
 371         /* Grab info from MT_TAG mbufs prepended to the chain. */
 372         for (;m && m->m_type == MT_TAG; m = m->m_next) {
 373                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 374                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 375         }
 376 #ifdef INET6
 377         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 378 #endif
 379         bzero((char *)&to, sizeof(to));
 380
 381         tcpstat.tcps_rcvtotal++;
 382
 383         if (isipv6) {
 384                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 385                 ip6 = mtod(m, struct ip6_hdr *);
 386                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 387                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 388                         tcpstat.tcps_rcvbadsum++;
 389                         goto drop;
 390                 }
 391                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 392
 393                 /*
 394                  * Be proactive about unspecified IPv6 address in source.
 395                  * As we use all-zero to indicate unbounded/unconnected pcb,
 396                  * unspecified IPv6 address can be used to confuse us.
 397                  *
 398                  * Note that packets with unspecified IPv6 destination is
 399                  * already dropped in ip6_input.
 400                  */
 401                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 402                         /* XXX stat */
 403                         goto drop;
 404                 }
 405         } else {
 406                 /*
 407                  * Get IP and TCP header together in first mbuf.
 408                  * Note: IP leaves IP header in first mbuf.
 409                  */
 410                 if (off0 > sizeof(struct ip)) {
 411                         ip_stripoptions(m, (struct mbuf *)0);
 412                         off0 = sizeof(struct ip);
 413                 }
 414                 if (m->m_len < sizeof(struct tcpiphdr)) {
 415                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
 416                                 tcpstat.tcps_rcvshort++;
 417                                 return;
 418                         }
 419                 }
 420                 ip = mtod(m, struct ip *);
 421                 ipov = (struct ipovly *)ip;
 422                 th = (struct tcphdr *)((caddr_t)ip + off0);
 423                 tlen = ip->ip_len;
 424
 425                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 426                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 427                                 th->th_sum = m->m_pkthdr.csum_data;
 428                         else
 429                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 430                                                 ip->ip_dst.s_addr,
 431                                                 htonl(m->m_pkthdr.csum_data +
 432                                                         ip->ip_len +
 433                                                         IPPROTO_TCP));
 434                         th->th_sum ^= 0xffff;
 435                 } else {
 436                         /*
 437                          * Checksum extended TCP header and data.
 438                          */
 439                         len = sizeof(struct ip) + tlen;
 440                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 441                         ipov->ih_len = (u_short)tlen;
 442                         ipov->ih_len = htons(ipov->ih_len);
 443                         th->th_sum = in_cksum(m, len);
 444                 }
 445                 if (th->th_sum) {
 446                         tcpstat.tcps_rcvbadsum++;
 447                         goto drop;
 448                 }
 449 #ifdef INET6
 450                 /* Re-initialization for later version check */
 451                 ip->ip_v = IPVERSION;
 452 #endif
 453         }
 454
 455         /*
 456          * Check that TCP offset makes sense,
 457          * pull out TCP options and adjust length.              XXX
 458          */
 459         off = th->th_off << 2;
 460         if (off < sizeof(struct tcphdr) || off > tlen) {
 461                 tcpstat.tcps_rcvbadoff++;
 462                 goto drop;
 463         }
 464         tlen -= off;    /* tlen is used instead of ti->ti_len */
 465         if (off > sizeof(struct tcphdr)) {
 466                 if (isipv6) {
 467                         IP6_EXTHDR_CHECK(m, off0, off, );
 468                         ip6 = mtod(m, struct ip6_hdr *);
 469                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 470                 } else {
 471                         if (m->m_len < sizeof(struct ip) + off) {
 472                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
 473                                                 == 0) {
 474                                         tcpstat.tcps_rcvshort++;
 475                                         return;
 476                                 }
 477                                 ip = mtod(m, struct ip *);
 478                                 ipov = (struct ipovly *)ip;
 479                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 480                         }
 481                 }
 482                 optlen = off - sizeof(struct tcphdr);
 483                 optp = (u_char *)(th + 1);
 484         }
 485         thflags = th->th_flags;
 486
 487 #ifdef TCP_DROP_SYNFIN
 488         /*
 489          * If the drop_synfin option is enabled, drop all packets with
 490          * both the SYN and FIN bits set. This prevents e.g. nmap from
 491          * identifying the TCP/IP stack.
 492          *
 493          * This is a violation of the TCP specification.
 494          */
 495         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 496                 goto drop;
 497 #endif
 498
 499         /*
 500          * Convert TCP protocol specific fields to host format.
 501          */
 502         th->th_seq = ntohl(th->th_seq);
 503         th->th_ack = ntohl(th->th_ack);
 504         th->th_win = ntohs(th->th_win);
 505         th->th_urp = ntohs(th->th_urp);
 506
 507         /*
 508          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
 509          * until after ip6_savecontrol() is called and before other functions
 510          * which don't want those proto headers.
 511          * Because ip6_savecontrol() is going to parse the mbuf to
 512          * search for data to be passed up to user-land, it wants mbuf
 513          * parameters to be unchanged.
 514          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 515          * latest version of the advanced API (20020110).
 516          */
 517         drop_hdrlen = off0 + off;
 518
 519         /*
 520          * Locate pcb for segment.
 521          */
 522 findpcb:
 523         /* IPFIREWALL_FORWARD section */
 524         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
 525                 /*
 526                  * Transparently forwarded. Pretend to be the destination.
 527                  * already got one like this?
 528                  */
 529                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
 530                                         ip->ip_dst, th->th_dport,
 531                                         0, m->m_pkthdr.rcvif);
 532                 if (!inp) {
 533                         /* It's new.  Try find the ambushing socket. */
 534                         inp = in_pcblookup_hash(&tcbinfo,
 535                                                 ip->ip_src, th->th_sport,
 536                                                 next_hop->sin_addr,
 537                                                 next_hop->sin_port ?
 538                                                     ntohs(next_hop->sin_port) :
 539                                                     th->th_dport,
 540                                                 1, m->m_pkthdr.rcvif);
 541                 }
 542         } else {
 543                 if (isipv6)
 544                         inp = in6_pcblookup_hash(&tcbinfo,
 545                                                  &ip6->ip6_src, th->th_sport,
 546                                                  &ip6->ip6_dst, th->th_dport,
 547                                                  1, m->m_pkthdr.rcvif);
 548                 else
 549                         inp = in_pcblookup_hash(&tcbinfo,
 550                                                 ip->ip_src, th->th_sport,
 551                                                 ip->ip_dst, th->th_dport,
 552                                                 1, m->m_pkthdr.rcvif);
 553       }
 554
 555 #ifdef IPSEC
 556         if (isipv6) {
 557                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 558                         ipsec6stat.in_polvio++;
 559                         goto drop;
 560                 }
 561         } else {
 562                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 563                         ipsecstat.in_polvio++;
 564                         goto drop;
 565                 }
 566         }
 567 #endif
 568 #ifdef FAST_IPSEC
 569         if (isipv6) {
 570                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 571                         goto drop;
 572                 }
 573         } else {
 574                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 575                         goto drop;
 576                 }
 577         }
 578 #endif
 579
 580         /*
 581          * If the state is CLOSED (i.e., TCB does not exist) then
 582          * all data in the incoming segment is discarded.
 583          * If the TCB exists but is in CLOSED state, it is embryonic,
 584          * but should either do a listen or a connect soon.
 585          */
 586         if (inp == NULL) {
 587                 if (log_in_vain) {
 588 #ifdef INET6
 589                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 590 #else
 591                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 592 #endif
 593                         if (isipv6) {
 594                                 strcpy(dbuf, "[");
 595                                 strcpy(sbuf, "[");
 596                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 597                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 598                                 strcat(dbuf, "]");
 599                                 strcat(sbuf, "]");
 600                         } else {
 601                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 602                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 603                         }
 604                         switch (log_in_vain) {
 605                         case 1:
 606                                 if ((thflags & TH_SYN) == 0)
 607                                         break;
 608                         case 2:
 609                                 log(LOG_INFO,
 610                                     "Connection attempt to TCP %s:%d "
 611                                     "from %s:%d flags:0x%02x\n",
 612                                     dbuf, ntohs(th->th_dport), sbuf,
 613                                     ntohs(th->th_sport), thflags);
 614                                 break;
 615                         default:
 616                                 break;
 617                         }
 618                 }
 619                 if (blackhole) {
 620                         switch (blackhole) {
 621                         case 1:
 622                                 if (thflags & TH_SYN)
 623                                         goto drop;
 624                                 break;
 625                         case 2:
 626                                 goto drop;
 627                         default:
 628                                 goto drop;
 629                         }
 630                 }
 631                 rstreason = BANDLIM_RST_CLOSEDPORT;
 632                 goto dropwithreset;
 633         }
 634         tp = intotcpcb(inp);
 635         if (tp == NULL) {
 636                 rstreason = BANDLIM_RST_CLOSEDPORT;
 637                 goto dropwithreset;
 638         }
 639         if (tp->t_state == TCPS_CLOSED)
 640                 goto drop;
 641
 642         /* Unscale the window into a 32-bit value. */
 643         if ((thflags & TH_SYN) == 0)
 644                 tiwin = th->th_win << tp->snd_scale;
 645         else
 646                 tiwin = th->th_win;
 647
 648         so = inp->inp_socket;
 649         if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
 650                 struct in_conninfo inc;
 651 #ifdef TCPDEBUG
 652                 if (so->so_options & SO_DEBUG) {
 653                         ostate = tp->t_state;
 654                         if (isipv6)
 655                                 bcopy((char *)ip6, (char *)tcp_saveipgen,
 656                                     sizeof(*ip6));
 657                         else
 658                                 bcopy((char *)ip, (char *)tcp_saveipgen,
 659                                     sizeof(*ip));
 660                         tcp_savetcp = *th;
 661                 }
 662 #endif
 663                 /* skip if this isn't a listen socket */
 664                 if ((so->so_options & SO_ACCEPTCONN) == 0)
 665                         goto after_listen;
 666 #ifdef INET6
 667                 inc.inc_isipv6 = isipv6;
 668 #endif
 669                 if (isipv6) {
 670                         inc.inc6_faddr = ip6->ip6_src;
 671                         inc.inc6_laddr = ip6->ip6_dst;
 672                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 673                 } else {
 674                         inc.inc_faddr = ip->ip_src;
 675                         inc.inc_laddr = ip->ip_dst;
 676                         inc.inc_route.ro_rt = NULL;             /* XXX */
 677                 }
 678                 inc.inc_fport = th->th_sport;
 679                 inc.inc_lport = th->th_dport;
 680
 681                 /*
 682                  * If the state is LISTEN then ignore segment if it contains
 683                  * a RST.  If the segment contains an ACK then it is bad and
 684                  * send a RST.  If it does not contain a SYN then it is not
 685                  * interesting; drop it.
 686                  *
 687                  * If the state is SYN_RECEIVED (syncache) and seg contains
 688                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 689                  * contains a RST, check the sequence number to see if it
 690                  * is a valid reset segment.
 691                  */
 692                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 693                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 694                                 if (!syncache_expand(&inc, th, &so, m)) {
 695                                         /*
 696                                          * No syncache entry, or ACK was not
 697                                          * for our SYN/ACK.  Send a RST.
 698                                          */
 699                                         tcpstat.tcps_badsyn++;
 700                                         rstreason = BANDLIM_RST_OPENPORT;
 701                                         goto dropwithreset;
 702                                 }
 703                                 if (so == NULL)
 704                                         /*
 705                                          * Could not complete 3-way handshake,
 706                                          * connection is being closed down, and
 707                                          * syncache will free mbuf.
 708                                          */
 709                                         return;
 710                                 /*
 711                                  * Socket is created in state SYN_RECEIVED.
 712                                  * Continue processing segment.
 713                                  */
 714                                 inp = sotoinpcb(so);
 715                                 tp = intotcpcb(inp);
 716                                 /*
 717                                  * This is what would have happened in
 718                                  * tcp_output() when the SYN,ACK was sent.
 719                                  */
 720                                 tp->snd_up = tp->snd_una;
 721                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 722                                 tp->last_ack_sent = tp->rcv_nxt;
 723 /*
 724  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 725  * until the _second_ ACK is received:
 726  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 727  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 728  *        move to ESTAB, set snd_wnd to tiwin.
 729  */
 730                                 tp->snd_wnd = tiwin;    /* unscaled */
 731                                 goto after_listen;
 732                         }
 733                         if (thflags & TH_RST) {
 734                                 syncache_chkrst(&inc, th);
 735                                 goto drop;
 736                         }
 737                         if (thflags & TH_ACK) {
 738                                 syncache_badack(&inc);
 739                                 tcpstat.tcps_badsyn++;
 740                                 rstreason = BANDLIM_RST_OPENPORT;
 741                                 goto dropwithreset;
 742                         }
 743                         goto drop;
 744                 }
 745
 746                 /*
 747                  * Segment's flags are (SYN) or (SYN|FIN).
 748                  */
 749 #ifdef INET6
 750                 /*
 751                  * If deprecated address is forbidden,
 752                  * we do not accept SYN to deprecated interface
 753                  * address to prevent any new inbound connection from
 754                  * getting established.
 755                  * When we do not accept SYN, we send a TCP RST,
 756                  * with deprecated source address (instead of dropping
 757                  * it).  We compromise it as it is much better for peer
 758                  * to send a RST, and RST will be the final packet
 759                  * for the exchange.
 760                  *
 761                  * If we do not forbid deprecated addresses, we accept
 762                  * the SYN packet.  RFC2462 does not suggest dropping
 763                  * SYN in this case.
 764                  * If we decipher RFC2462 5.5.4, it says like this:
 765                  * 1. use of deprecated addr with existing
 766                  *    communication is okay - "SHOULD continue to be
 767                  *    used"
 768                  * 2. use of it with new communication:
 769                  *   (2a) "SHOULD NOT be used if alternate address
 770                  *        with sufficient scope is available"
 771                  *   (2b) nothing mentioned otherwise.
 772                  * Here we fall into (2b) case as we have no choice in
 773                  * our source address selection - we must obey the peer.
 774                  *
 775                  * The wording in RFC2462 is confusing, and there are
 776                  * multiple description text for deprecated address
 777                  * handling - worse, they are not exactly the same.
 778                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 779                  */
 780                 if (isipv6 && !ip6_use_deprecated) {
 781                         struct in6_ifaddr *ia6;
 782
 783                         if ((ia6 = ip6_getdstifaddr(m)) &&
 784                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 785                                 tp = NULL;
 786                                 rstreason = BANDLIM_RST_OPENPORT;
 787                                 goto dropwithreset;
 788                         }
 789                 }
 790 #endif
 791                 /*
 792                  * If it is from this socket, drop it, it must be forged.
 793                  * Don't bother responding if the destination was a broadcast.
 794                  */
 795                 if (th->th_dport == th->th_sport) {
 796                         if (isipv6) {
 797                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 798                                                        &ip6->ip6_src))
 799                                         goto drop;
 800                         } else {
 801                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 802                                         goto drop;
 803                         }
 804                 }
 805                 /*
 806                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 807                  *
 808                  * Note that it is quite possible to receive unicast
 809                  * link-layer packets with a broadcast IP address. Use
 810                  * in_broadcast() to find them.
 811                  */
 812                 if (m->m_flags & (M_BCAST|M_MCAST))
 813                         goto drop;
 814                 if (isipv6) {
 815                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 816                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 817                                 goto drop;
 818                 } else {
 819                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 820                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 821                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 822                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 823                                 goto drop;
 824                 }
 825                 /*
 826                  * SYN appears to be valid; create compressed TCP state
 827                  * for syncache, or perform t/tcp connection.
 828                  */
 829                 if (so->so_qlen <= so->so_qlimit) {
 830                         tcp_dooptions(&to, optp, optlen, 1);
 831                         if (!syncache_add(&inc, &to, th, &so, m))
 832                                 goto drop;
 833                         if (so == NULL)
 834                                 /*
 835                                  * Entry added to syncache, mbuf used to
 836                                  * send SYN,ACK packet.
 837                                  */
 838                                 return;
 839                         /*
 840                          * Segment passed TAO tests.
 841                          */
 842                         inp = sotoinpcb(so);
 843                         tp = intotcpcb(inp);
 844                         tp->snd_wnd = tiwin;
 845                         tp->t_starttime = ticks;
 846                         tp->t_state = TCPS_ESTABLISHED;
 847
 848                         /*
 849                          * If there is a FIN, or if there is data and the
 850                          * connection is local, then delay SYN,ACK(SYN) in
 851                          * the hope of piggy-backing it on a response
 852                          * segment.  Otherwise must send ACK now in case
 853                          * the other side is slow starting.
 854                          */
 855                         if (DELAY_ACK(tp) &&
 856                             ((thflags & TH_FIN) ||
 857                              (tlen != 0 &&
 858                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 859                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 860                                 callout_reset(tp->tt_delack, tcp_delacktime,
 861                                                 tcp_timer_delack, tp);
 862                                 tp->t_flags |= TF_NEEDSYN;
 863                         } else
 864                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 865
 866                         tcpstat.tcps_connects++;
 867                         soisconnected(so);
 868                         goto trimthenstep6;
 869                 }
 870                 goto drop;
 871         }
 872 after_listen:
 873
 874 /* XXX temp debugging */
 875         /* should not happen - syncache should pick up these connections */
 876         if (tp->t_state == TCPS_LISTEN)
 877                 panic("tcp_input: TCPS_LISTEN");
 878
 879         /*
 880          * Segment received on connection.
 881          * Reset idle time and keep-alive timer.
 882          */
 883         tp->t_rcvtime = ticks;
 884         if (TCPS_HAVEESTABLISHED(tp->t_state))
 885                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 886
 887         /*
 888          * Process options.
 889          * XXX this is tradtitional behavior, may need to be cleaned up.
 890          */
 891         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
 892         if (thflags & TH_SYN) {
 893                 if (to.to_flags & TOF_SCALE) {
 894                         tp->t_flags |= TF_RCVD_SCALE;
 895                         tp->requested_s_scale = to.to_requested_s_scale;
 896                 }
 897                 if (to.to_flags & TOF_TS) {
 898                         tp->t_flags |= TF_RCVD_TSTMP;
 899                         tp->ts_recent = to.to_tsval;
 900                         tp->ts_recent_age = ticks;
 901                 }
 902                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 903                         tp->t_flags |= TF_RCVD_CC;
 904                 if (to.to_flags & TOF_MSS)
 905                         tcp_mss(tp, to.to_mss);
 906         }
 907
 908         /*
 909          * Header prediction: check for the two common cases
 910          * of a uni-directional data xfer.  If the packet has
 911          * no control flags, is in-sequence, the window didn't
 912          * change and we're not retransmitting, it's a
 913          * candidate.  If the length is zero and the ack moved
 914          * forward, we're the sender side of the xfer.  Just
 915          * free the data acked & wake any higher level process
 916          * that was blocked waiting for space.  If the length
 917          * is non-zero and the ack didn't move, we're the
 918          * receiver side.  If we're getting packets in-order
 919          * (the reassembly queue is empty), add the data to
 920          * the socket buffer and note that we need a delayed ack.
 921          * Make sure that the hidden state-flags are also off.
 922          * Since we check for TCPS_ESTABLISHED above, it can only
 923          * be TH_NEEDSYN.
 924          */
 925         if (tp->t_state == TCPS_ESTABLISHED &&
 926             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 927             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 928             ((to.to_flags & TOF_TS) == 0 ||
 929              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 930             /*
 931              * Using the CC option is compulsory if once started:
 932              *   the segment is OK if no T/TCP was negotiated or
 933              *   if the segment has a CC option equal to CCrecv
 934              */
 935             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 936              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 937             th->th_seq == tp->rcv_nxt &&
 938             tiwin && tiwin == tp->snd_wnd &&
 939             tp->snd_nxt == tp->snd_max) {
 940
 941                 /*
 942                  * If last ACK falls within this segment's sequence numbers,
 943                  * record the timestamp.
 944                  * NOTE that the test is modified according to the latest
 945                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 946                  */
 947                 if ((to.to_flags & TOF_TS) != 0 &&
 948                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 949                         tp->ts_recent_age = ticks;
 950                         tp->ts_recent = to.to_tsval;
 951                 }
 952
 953                 if (tlen == 0) {
 954                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 955                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 956                             tp->snd_cwnd >= tp->snd_wnd &&
 957                             ((!tcp_do_newreno &&
 958                               tp->t_dupacks < tcprexmtthresh) ||
 959                              (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) {
 960                                 /*
 961                                  * this is a pure ack for outstanding data.
 962                                  */
 963                                 ++tcpstat.tcps_predack;
 964                                 /*
 965                                  * "bad retransmit" recovery
 966                                  */
 967                                 if (tp->t_rxtshift == 1 &&
 968                                     ticks < tp->t_badrxtwin) {
 969                                         tp->snd_cwnd = tp->snd_cwnd_prev;
 970                                         tp->snd_ssthresh =
 971                                             tp->snd_ssthresh_prev;
 972                                         tp->snd_recover = tp->snd_recover_prev;
 973                                         if (tp->t_flags & TF_WASFRECOVERY)
 974                                             ENTER_FASTRECOVERY(tp);
 975                                         tp->snd_nxt = tp->snd_max;
 976                                         tp->t_badrxtwin = 0;
 977                                 }
 978                                 /*
 979                                  * Recalculate the retransmit timer / rtt.
 980                                  *
 981                                  * Some machines (certain windows boxes)
 982                                  * send broken timestamp replies during the
 983                                  * SYN+ACK phase, ignore timestamps of 0.
 984                                  */
 985                                 if ((to.to_flags & TOF_TS) != 0 &&
 986                                     to.to_tsecr) {
 987                                         tcp_xmit_timer(tp,
 988                                             ticks - to.to_tsecr + 1);
 989                                 } else if (tp->t_rtttime &&
 990                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
 991                                         tcp_xmit_timer(tp,
 992                                                        ticks - tp->t_rtttime);
 993                                 }
 994                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
 995                                 acked = th->th_ack - tp->snd_una;
 996                                 tcpstat.tcps_rcvackpack++;
 997                                 tcpstat.tcps_rcvackbyte += acked;
 998                                 sbdrop(&so->so_snd, acked);
 999                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1000                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1001                                         tp->snd_recover = th->th_ack - 1;
1002                                 tp->snd_una = th->th_ack;
1003                                 tp->t_dupacks = 0;
1004                                 m_freem(m);
1005                                 ND6_HINT(tp); /* some progress has been done */
1006
1007                                 /*
1008                                  * If all outstanding data are acked, stop
1009                                  * retransmit timer, otherwise restart timer
1010                                  * using current (possibly backed-off) value.
1011                                  * If process is waiting for space,
1012                                  * wakeup/selwakeup/signal.  If data
1013                                  * are ready to send, let tcp_output
1014                                  * decide between more output or persist.
1015                                  */
1016                                 if (tp->snd_una == tp->snd_max)
1017                                         callout_stop(tp->tt_rexmt);
1018                                 else if (!callout_active(tp->tt_persist))
1019                                         callout_reset(tp->tt_rexmt,
1020                                                       tp->t_rxtcur,
1021                                                       tcp_timer_rexmt, tp);
1022
1023                                 sowwakeup(so);
1024                                 if (so->so_snd.sb_cc)
1025                                         (void) tcp_output(tp);
1026                                 return;
1027                         }
1028                 } else if (th->th_ack == tp->snd_una &&
1029                     LIST_EMPTY(&tp->t_segq) &&
1030                     tlen <= sbspace(&so->so_rcv)) {
1031                         /*
1032                          * this is a pure, in-sequence data packet
1033                          * with nothing on the reassembly queue and
1034                          * we have enough buffer space to take it.
1035                          */
1036                         ++tcpstat.tcps_preddat;
1037                         tp->rcv_nxt += tlen;
1038                         tcpstat.tcps_rcvpack++;
1039                         tcpstat.tcps_rcvbyte += tlen;
1040                         ND6_HINT(tp);   /* some progress has been done */
1041                         /*
1042                          * Add data to socket buffer.
1043                          */
1044                         if (so->so_state & SS_CANTRCVMORE) {
1045                                 m_freem(m);
1046                         } else {
1047                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1048                                 sbappend(&so->so_rcv, m);
1049                         }
1050                         sorwakeup(so);
1051                         if (DELAY_ACK(tp)) {
1052                                 callout_reset(tp->tt_delack, tcp_delacktime,
1053                                     tcp_timer_delack, tp);
1054                         } else {
1055                                 tp->t_flags |= TF_ACKNOW;
1056                                 tcp_output(tp);
1057                         }
1058                         return;
1059                 }
1060         }
1061
1062         /*
1063          * Calculate amount of space in receive window,
1064          * and then do TCP input processing.
1065          * Receive window is amount of space in rcv queue,
1066          * but not less than advertised window.
1067          */
1068         { int win;
1069
1070         win = sbspace(&so->so_rcv);
1071         if (win < 0)
1072                 win = 0;
1073         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1074         }
1075
1076         switch (tp->t_state) {
1077
1078         /*
1079          * If the state is SYN_RECEIVED:
1080          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1081          */
1082         case TCPS_SYN_RECEIVED:
1083                 if ((thflags & TH_ACK) &&
1084                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1085                      SEQ_GT(th->th_ack, tp->snd_max))) {
1086                                 rstreason = BANDLIM_RST_OPENPORT;
1087                                 goto dropwithreset;
1088                 }
1089                 break;
1090
1091         /*
1092          * If the state is SYN_SENT:
1093          *      if seg contains an ACK, but not for our SYN, drop the input.
1094          *      if seg contains a RST, then drop the connection.
1095          *      if seg does not contain SYN, then drop it.
1096          * Otherwise this is an acceptable SYN segment
1097          *      initialize tp->rcv_nxt and tp->irs
1098          *      if seg contains ack then advance tp->snd_una
1099          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1100          *      arrange for segment to be acked (eventually)
1101          *      continue processing rest of data/controls, beginning with URG
1102          */
1103         case TCPS_SYN_SENT:
1104                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1105                         taop = &tao_noncached;
1106                         bzero(taop, sizeof(*taop));
1107                 }
1108
1109                 if ((thflags & TH_ACK) &&
1110                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1111                      SEQ_GT(th->th_ack, tp->snd_max))) {
1112                         /*
1113                          * If we have a cached CCsent for the remote host,
1114                          * hence we haven't just crashed and restarted,
1115                          * do not send a RST.  This may be a retransmission
1116                          * from the other side after our earlier ACK was lost.
1117                          * Our new SYN, when it arrives, will serve as the
1118                          * needed ACK.
1119                          */
1120                         if (taop->tao_ccsent != 0)
1121                                 goto drop;
1122                         else {
1123                                 rstreason = BANDLIM_UNLIMITED;
1124                                 goto dropwithreset;
1125                         }
1126                 }
1127                 if (thflags & TH_RST) {
1128                         if (thflags & TH_ACK)
1129                                 tp = tcp_drop(tp, ECONNREFUSED);
1130                         goto drop;
1131                 }
1132                 if ((thflags & TH_SYN) == 0)
1133                         goto drop;
1134                 tp->snd_wnd = th->th_win;       /* initial send window */
1135                 tp->cc_recv = to.to_cc;         /* foreign CC */
1136
1137                 tp->irs = th->th_seq;
1138                 tcp_rcvseqinit(tp);
1139                 if (thflags & TH_ACK) {
1140                         /*
1141                          * Our SYN was acked.  If segment contains CC.ECHO
1142                          * option, check it to make sure this segment really
1143                          * matches our SYN.  If not, just drop it as old
1144                          * duplicate, but send an RST if we're still playing
1145                          * by the old rules.  If no CC.ECHO option, make sure
1146                          * we don't get fooled into using T/TCP.
1147                          */
1148                         if (to.to_flags & TOF_CCECHO) {
1149                                 if (tp->cc_send != to.to_ccecho) {
1150                                         if (taop->tao_ccsent != 0)
1151                                                 goto drop;
1152                                         else {
1153                                                 rstreason = BANDLIM_UNLIMITED;
1154                                                 goto dropwithreset;
1155                                         }
1156                                 }
1157                         } else
1158                                 tp->t_flags &= ~TF_RCVD_CC;
1159                         tcpstat.tcps_connects++;
1160                         soisconnected(so);
1161                         /* Do window scaling on this connection? */
1162                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1163                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1164                                 tp->snd_scale = tp->requested_s_scale;
1165                                 tp->rcv_scale = tp->request_r_scale;
1166                         }
1167                         /* Segment is acceptable, update cache if undefined. */
1168                         if (taop->tao_ccsent == 0)
1169                                 taop->tao_ccsent = to.to_ccecho;
1170
1171                         tp->rcv_adv += tp->rcv_wnd;
1172                         tp->snd_una++;          /* SYN is acked */
1173                         /*
1174                          * If there's data, delay ACK; if there's also a FIN
1175                          * ACKNOW will be turned on later.
1176                          */
1177                         if (DELAY_ACK(tp) && tlen != 0)
1178                                 callout_reset(tp->tt_delack, tcp_delacktime,
1179                                     tcp_timer_delack, tp);
1180                         else
1181                                 tp->t_flags |= TF_ACKNOW;
1182                         /*
1183                          * Received <SYN,ACK> in SYN_SENT[*] state.
1184                          * Transitions:
1185                          *      SYN_SENT  --> ESTABLISHED
1186                          *      SYN_SENT* --> FIN_WAIT_1
1187                          */
1188                         tp->t_starttime = ticks;
1189                         if (tp->t_flags & TF_NEEDFIN) {
1190                                 tp->t_state = TCPS_FIN_WAIT_1;
1191                                 tp->t_flags &= ~TF_NEEDFIN;
1192                                 thflags &= ~TH_SYN;
1193                         } else {
1194                                 tp->t_state = TCPS_ESTABLISHED;
1195                                 callout_reset(tp->tt_keep, tcp_keepidle,
1196                                               tcp_timer_keep, tp);
1197                         }
1198                 } else {
1199                         /*
1200                          * Received initial SYN in SYN-SENT[*] state =>
1201                          * simultaneous open.  If segment contains CC option
1202                          * and there is a cached CC, apply TAO test.
1203                          * If it succeeds, connection is * half-synchronized.
1204                          * Otherwise, do 3-way handshake:
1205                          *        SYN-SENT -> SYN-RECEIVED
1206                          *        SYN-SENT* -> SYN-RECEIVED*
1207                          * If there was no CC option, clear cached CC value.
1208                          */
1209                         tp->t_flags |= TF_ACKNOW;
1210                         callout_stop(tp->tt_rexmt);
1211                         if (to.to_flags & TOF_CC) {
1212                                 if (taop->tao_cc != 0 &&
1213                                     CC_GT(to.to_cc, taop->tao_cc)) {
1214                                         /*
1215                                          * update cache and make transition:
1216                                          *        SYN-SENT -> ESTABLISHED*
1217                                          *        SYN-SENT* -> FIN-WAIT-1*
1218                                          */
1219                                         taop->tao_cc = to.to_cc;
1220                                         tp->t_starttime = ticks;
1221                                         if (tp->t_flags & TF_NEEDFIN) {
1222                                                 tp->t_state = TCPS_FIN_WAIT_1;
1223                                                 tp->t_flags &= ~TF_NEEDFIN;
1224                                         } else {
1225                                                 tp->t_state = TCPS_ESTABLISHED;
1226                                                 callout_reset(tp->tt_keep,
1227                                                               tcp_keepidle,
1228                                                               tcp_timer_keep,
1229                                                               tp);
1230                                         }
1231                                         tp->t_flags |= TF_NEEDSYN;
1232                                 } else
1233                                         tp->t_state = TCPS_SYN_RECEIVED;
1234                         } else {
1235                                 /* CC.NEW or no option => invalidate cache */
1236                                 taop->tao_cc = 0;
1237                                 tp->t_state = TCPS_SYN_RECEIVED;
1238                         }
1239                 }
1240
1241 trimthenstep6:
1242                 /*
1243                  * Advance th->th_seq to correspond to first data byte.
1244                  * If data, trim to stay within window,
1245                  * dropping FIN if necessary.
1246                  */
1247                 th->th_seq++;
1248                 if (tlen > tp->rcv_wnd) {
1249                         todrop = tlen - tp->rcv_wnd;
1250                         m_adj(m, -todrop);
1251                         tlen = tp->rcv_wnd;
1252                         thflags &= ~TH_FIN;
1253                         tcpstat.tcps_rcvpackafterwin++;
1254                         tcpstat.tcps_rcvbyteafterwin += todrop;
1255                 }
1256                 tp->snd_wl1 = th->th_seq - 1;
1257                 tp->rcv_up = th->th_seq;
1258                 /*
1259                  * Client side of transaction: already sent SYN and data.
1260                  * If the remote host used T/TCP to validate the SYN,
1261                  * our data will be ACK'd; if so, enter normal data segment
1262                  * processing in the middle of step 5, ack processing.
1263                  * Otherwise, goto step 6.
1264                  */
1265                 if (thflags & TH_ACK)
1266                         goto process_ACK;
1267
1268                 goto step6;
1269
1270         /*
1271          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1272          *      if segment contains a SYN and CC [not CC.NEW] option:
1273          *              if state == TIME_WAIT and connection duration > MSL,
1274          *                  drop packet and send RST;
1275          *
1276          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1277          *                  ack the FIN (and data) in retransmission queue.
1278          *                  Complete close and delete TCPCB.  Then reprocess
1279          *                  segment, hoping to find new TCPCB in LISTEN state;
1280          *
1281          *              else must be old SYN; drop it.
1282          *      else do normal processing.
1283          */
1284         case TCPS_LAST_ACK:
1285         case TCPS_CLOSING:
1286         case TCPS_TIME_WAIT:
1287                 if ((thflags & TH_SYN) &&
1288                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1289                         if (tp->t_state == TCPS_TIME_WAIT &&
1290                                         (ticks - tp->t_starttime) > tcp_msl) {
1291                                 rstreason = BANDLIM_UNLIMITED;
1292                                 goto dropwithreset;
1293                         }
1294                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1295                                 tp = tcp_close(tp);
1296                                 goto findpcb;
1297                         }
1298                         else
1299                                 goto drop;
1300                 }
1301                 break;  /* continue normal processing */
1302         }
1303
1304         /*
1305          * States other than LISTEN or SYN_SENT.
1306          * First check the RST flag and sequence number since reset segments
1307          * are exempt from the timestamp and connection count tests.  This
1308          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1309          * below which allowed reset segments in half the sequence space
1310          * to fall though and be processed (which gives forged reset
1311          * segments with a random sequence number a 50 percent chance of
1312          * killing a connection).
1313          * Then check timestamp, if present.
1314          * Then check the connection count, if present.
1315          * Then check that at least some bytes of segment are within
1316          * receive window.  If segment begins before rcv_nxt,
1317          * drop leading data (and SYN); if nothing left, just ack.
1318          *
1319          *
1320          * If the RST bit is set, check the sequence number to see
1321          * if this is a valid reset segment.
1322          * RFC 793 page 37:
1323          *   In all states except SYN-SENT, all reset (RST) segments
1324          *   are validated by checking their SEQ-fields.  A reset is
1325          *   valid if its sequence number is in the window.
1326          * Note: this does not take into account delayed ACKs, so
1327          *   we should test against last_ack_sent instead of rcv_nxt.
1328          *   The sequence number in the reset segment is normally an
1329          *   echo of our outgoing acknowlegement numbers, but some hosts
1330          *   send a reset with the sequence number at the rightmost edge
1331          *   of our receive window, and we have to handle this case.
1332          * If we have multiple segments in flight, the intial reset
1333          * segment sequence numbers will be to the left of last_ack_sent,
1334          * but they will eventually catch up.
1335          * In any case, it never made sense to trim reset segments to
1336          * fit the receive window since RFC 1122 says:
1337          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1338          *
1339          *    A TCP SHOULD allow a received RST segment to include data.
1340          *
1341          *    DISCUSSION
1342          *         It has been suggested that a RST segment could contain
1343          *         ASCII text that encoded and explained the cause of the
1344          *         RST.  No standard has yet been established for such
1345          *         data.
1346          *
1347          * If the reset segment passes the sequence number test examine
1348          * the state:
1349          *    SYN_RECEIVED STATE:
1350          *      If passive open, return to LISTEN state.
1351          *      If active open, inform user that connection was refused.
1352          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1353          *      Inform user that connection was reset, and close tcb.
1354          *    CLOSING, LAST_ACK STATES:
1355          *      Close the tcb.
1356          *    TIME_WAIT STATE:
1357          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1358          *      RFC 1337.
1359          */
1360         if (thflags & TH_RST) {
1361                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1362                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1363                         switch (tp->t_state) {
1364
1365                         case TCPS_SYN_RECEIVED:
1366                                 so->so_error = ECONNREFUSED;
1367                                 goto close;
1368
1369                         case TCPS_ESTABLISHED:
1370                         case TCPS_FIN_WAIT_1:
1371                         case TCPS_FIN_WAIT_2:
1372                         case TCPS_CLOSE_WAIT:
1373                                 so->so_error = ECONNRESET;
1374                         close:
1375                                 tp->t_state = TCPS_CLOSED;
1376                                 tcpstat.tcps_drops++;
1377                                 tp = tcp_close(tp);
1378                                 break;
1379
1380                         case TCPS_CLOSING:
1381                         case TCPS_LAST_ACK:
1382                                 tp = tcp_close(tp);
1383                                 break;
1384
1385                         case TCPS_TIME_WAIT:
1386                                 break;
1387                         }
1388                 }
1389                 goto drop;
1390         }
1391
1392         /*
1393          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1394          * and it's less than ts_recent, drop it.
1395          */
1396         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1397             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1398
1399                 /* Check to see if ts_recent is over 24 days old.  */
1400                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1401                         /*
1402                          * Invalidate ts_recent.  If this segment updates
1403                          * ts_recent, the age will be reset later and ts_recent
1404                          * will get a valid value.  If it does not, setting
1405                          * ts_recent to zero will at least satisfy the
1406                          * requirement that zero be placed in the timestamp
1407                          * echo reply when ts_recent isn't valid.  The
1408                          * age isn't reset until we get a valid ts_recent
1409                          * because we don't want out-of-order segments to be
1410                          * dropped when ts_recent is old.
1411                          */
1412                         tp->ts_recent = 0;
1413                 } else {
1414                         tcpstat.tcps_rcvduppack++;
1415                         tcpstat.tcps_rcvdupbyte += tlen;
1416                         tcpstat.tcps_pawsdrop++;
1417                         if (tlen)
1418                                 goto dropafterack;
1419                         goto drop;
1420                 }
1421         }
1422
1423         /*
1424          * T/TCP mechanism
1425          *   If T/TCP was negotiated and the segment doesn't have CC,
1426          *   or if its CC is wrong then drop the segment.
1427          *   RST segments do not have to comply with this.
1428          */
1429         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1430             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1431                 goto dropafterack;
1432
1433         /*
1434          * In the SYN-RECEIVED state, validate that the packet belongs to
1435          * this connection before trimming the data to fit the receive
1436          * window.  Check the sequence number versus IRS since we know
1437          * the sequence numbers haven't wrapped.  This is a partial fix
1438          * for the "LAND" DoS attack.
1439          */
1440         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1441                 rstreason = BANDLIM_RST_OPENPORT;
1442                 goto dropwithreset;
1443         }
1444
1445         todrop = tp->rcv_nxt - th->th_seq;
1446         if (todrop > 0) {
1447                 if (thflags & TH_SYN) {
1448                         thflags &= ~TH_SYN;
1449                         th->th_seq++;
1450                         if (th->th_urp > 1)
1451                                 th->th_urp--;
1452                         else
1453                                 thflags &= ~TH_URG;
1454                         todrop--;
1455                 }
1456                 /*
1457                  * Following if statement from Stevens, vol. 2, p. 960.
1458                  */
1459                 if (todrop > tlen
1460                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1461                         /*
1462                          * Any valid FIN must be to the left of the window.
1463                          * At this point the FIN must be a duplicate or out
1464                          * of sequence; drop it.
1465                          */
1466                         thflags &= ~TH_FIN;
1467
1468                         /*
1469                          * Send an ACK to resynchronize and drop any data.
1470                          * But keep on processing for RST or ACK.
1471                          */
1472                         tp->t_flags |= TF_ACKNOW;
1473                         todrop = tlen;
1474                         tcpstat.tcps_rcvduppack++;
1475                         tcpstat.tcps_rcvdupbyte += todrop;
1476                 } else {
1477                         tcpstat.tcps_rcvpartduppack++;
1478                         tcpstat.tcps_rcvpartdupbyte += todrop;
1479                 }
1480                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1481                 th->th_seq += todrop;
1482                 tlen -= todrop;
1483                 if (th->th_urp > todrop)
1484                         th->th_urp -= todrop;
1485                 else {
1486                         thflags &= ~TH_URG;
1487                         th->th_urp = 0;
1488                 }
1489         }
1490
1491         /*
1492          * If new data are received on a connection after the
1493          * user processes are gone, then RST the other end.
1494          */
1495         if ((so->so_state & SS_NOFDREF) &&
1496             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1497                 tp = tcp_close(tp);
1498                 tcpstat.tcps_rcvafterclose++;
1499                 rstreason = BANDLIM_UNLIMITED;
1500                 goto dropwithreset;
1501         }
1502
1503         /*
1504          * If segment ends after window, drop trailing data
1505          * (and PUSH and FIN); if nothing left, just ACK.
1506          */
1507         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1508         if (todrop > 0) {
1509                 tcpstat.tcps_rcvpackafterwin++;
1510                 if (todrop >= tlen) {
1511                         tcpstat.tcps_rcvbyteafterwin += tlen;
1512                         /*
1513                          * If a new connection request is received
1514                          * while in TIME_WAIT, drop the old connection
1515                          * and start over if the sequence numbers
1516                          * are above the previous ones.
1517                          */
1518                         if (thflags & TH_SYN &&
1519                             tp->t_state == TCPS_TIME_WAIT &&
1520                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1521                                 tp = tcp_close(tp);
1522                                 goto findpcb;
1523                         }
1524                         /*
1525                          * If window is closed can only take segments at
1526                          * window edge, and have to drop data and PUSH from
1527                          * incoming segments.  Continue processing, but
1528                          * remember to ack.  Otherwise, drop segment
1529                          * and ack.
1530                          */
1531                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1532                                 tp->t_flags |= TF_ACKNOW;
1533                                 tcpstat.tcps_rcvwinprobe++;
1534                         } else
1535                                 goto dropafterack;
1536                 } else
1537                         tcpstat.tcps_rcvbyteafterwin += todrop;
1538                 m_adj(m, -todrop);
1539                 tlen -= todrop;
1540                 thflags &= ~(TH_PUSH|TH_FIN);
1541         }
1542
1543         /*
1544          * If last ACK falls within this segment's sequence numbers,
1545          * record its timestamp.
1546          * NOTE that the test is modified according to the latest
1547          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1548          */
1549         if ((to.to_flags & TOF_TS) != 0 &&
1550             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1551                 tp->ts_recent_age = ticks;
1552                 tp->ts_recent = to.to_tsval;
1553         }
1554
1555         /*
1556          * If a SYN is in the window, then this is an
1557          * error and we send an RST and drop the connection.
1558          */
1559         if (thflags & TH_SYN) {
1560                 tp = tcp_drop(tp, ECONNRESET);
1561                 rstreason = BANDLIM_UNLIMITED;
1562                 goto dropwithreset;
1563         }
1564
1565         /*
1566          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1567          * flag is on (half-synchronized state), then queue data for
1568          * later processing; else drop segment and return.
1569          */
1570         if ((thflags & TH_ACK) == 0) {
1571                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1572                     (tp->t_flags & TF_NEEDSYN))
1573                         goto step6;
1574                 else
1575                         goto drop;
1576         }
1577
1578         /*
1579          * Ack processing.
1580          */
1581         switch (tp->t_state) {
1582
1583         /*
1584          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1585          * ESTABLISHED state and continue processing.
1586          * The ACK was checked above.
1587          */
1588         case TCPS_SYN_RECEIVED:
1589
1590                 tcpstat.tcps_connects++;
1591                 soisconnected(so);
1592                 /* Do window scaling? */
1593                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1594                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1595                         tp->snd_scale = tp->requested_s_scale;
1596                         tp->rcv_scale = tp->request_r_scale;
1597                 }
1598                 /*
1599                  * Upon successful completion of 3-way handshake,
1600                  * update cache.CC if it was undefined, pass any queued
1601                  * data to the user, and advance state appropriately.
1602                  */
1603                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1604                     taop->tao_cc == 0)
1605                         taop->tao_cc = tp->cc_recv;
1606
1607                 /*
1608                  * Make transitions:
1609                  *      SYN-RECEIVED  -> ESTABLISHED
1610                  *      SYN-RECEIVED* -> FIN-WAIT-1
1611                  */
1612                 tp->t_starttime = ticks;
1613                 if (tp->t_flags & TF_NEEDFIN) {
1614                         tp->t_state = TCPS_FIN_WAIT_1;
1615                         tp->t_flags &= ~TF_NEEDFIN;
1616                 } else {
1617                         tp->t_state = TCPS_ESTABLISHED;
1618                         callout_reset(tp->tt_keep, tcp_keepidle,
1619                                       tcp_timer_keep, tp);
1620                 }
1621                 /*
1622                  * If segment contains data or ACK, will call tcp_reass()
1623                  * later; if not, do so now to pass queued data to user.
1624                  */
1625                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1626                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1627                             (struct mbuf *)0);
1628                 tp->snd_wl1 = th->th_seq - 1;
1629                 /* fall into ... */
1630
1631         /*
1632          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1633          * ACKs.  If the ack is in the range
1634          *      tp->snd_una < th->th_ack <= tp->snd_max
1635          * then advance tp->snd_una to th->th_ack and drop
1636          * data from the retransmission queue.  If this ACK reflects
1637          * more up to date window information we update our window information.
1638          */
1639         case TCPS_ESTABLISHED:
1640         case TCPS_FIN_WAIT_1:
1641         case TCPS_FIN_WAIT_2:
1642         case TCPS_CLOSE_WAIT:
1643         case TCPS_CLOSING:
1644         case TCPS_LAST_ACK:
1645         case TCPS_TIME_WAIT:
1646
1647                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1648                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1649                                 tcpstat.tcps_rcvdupack++;
1650                                 /*
1651                                  * If we have outstanding data (other than
1652                                  * a window probe), this is a completely
1653                                  * duplicate ack (ie, window info didn't
1654                                  * change), the ack is the biggest we've
1655                                  * seen and we've seen exactly our rexmt
1656                                  * threshhold of them, assume a packet
1657                                  * has been dropped and retransmit it.
1658                                  * Kludge snd_nxt & the congestion
1659                                  * window so we send only this one
1660                                  * packet.
1661                                  *
1662                                  * We know we're losing at the current
1663                                  * window size so do congestion avoidance
1664                                  * (set ssthresh to half the current window
1665                                  * and pull our congestion window back to
1666                                  * the new ssthresh).
1667                                  *
1668                                  * Dup acks mean that packets have left the
1669                                  * network (they're now cached at the receiver)
1670                                  * so bump cwnd by the amount in the receiver
1671                                  * to keep a constant cwnd packets in the
1672                                  * network.
1673                                  */
1674                                 if (!callout_active(tp->tt_rexmt) ||
1675                                     th->th_ack != tp->snd_una)
1676                                         tp->t_dupacks = 0;
1677                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1678                                          (tcp_do_newreno &&
1679                                           IN_FASTRECOVERY(tp))) {
1680                                         tp->snd_cwnd += tp->t_maxseg;
1681                                         (void) tcp_output(tp);
1682                                         goto drop;
1683                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1684                                         tcp_seq onxt = tp->snd_nxt;
1685                                         u_int win;
1686                                         if (tcp_do_newreno &&
1687                                             SEQ_LEQ(th->th_ack,
1688                                                     tp->snd_recover)) {
1689                                                 tp->t_dupacks = 0;
1690                                                 break;
1691                                         }
1692                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1693                                             2 / tp->t_maxseg;
1694                                         if (win < 2)
1695                                                 win = 2;
1696                                         tp->snd_ssthresh = win * tp->t_maxseg;
1697                                         ENTER_FASTRECOVERY(tp);
1698                                         tp->snd_recover = tp->snd_max;
1699                                         callout_stop(tp->tt_rexmt);
1700                                         tp->t_rtttime = 0;
1701                                         tp->snd_nxt = th->th_ack;
1702                                         tp->snd_cwnd = tp->t_maxseg;
1703                                         (void) tcp_output(tp);
1704                                         KASSERT(tp->snd_limited <= 2,
1705                                             ("tp->snd_limited too big"));
1706                                         tp->snd_cwnd = tp->snd_ssthresh +
1707                                             (tp->t_maxseg *
1708                                              (tp->t_dupacks - tp->snd_limited));
1709                                         if (SEQ_GT(onxt, tp->snd_nxt))
1710                                                 tp->snd_nxt = onxt;
1711                                         goto drop;
1712                                 } else if (tcp_do_limitedtransmit) {
1713                                         u_long oldcwnd = tp->snd_cwnd;
1714                                         tcp_seq oldsndmax = tp->snd_max;
1715                                         u_int sent;
1716                                         KASSERT(tp->t_dupacks == 1 ||
1717                                             tp->t_dupacks == 2,
1718                                             ("dupacks not 1 or 2"));
1719                                         if (tp->t_dupacks == 1) {
1720                                                 tp->snd_limited = 0;
1721                                                 tp->snd_cwnd += tp->t_maxseg;
1722                                         } else {
1723                                                 tp->snd_cwnd +=
1724                                                     tp->t_maxseg * 2;
1725                                         }
1726                                         (void) tcp_output(tp);
1727                                         sent = tp->snd_max - oldsndmax;
1728                                         if (sent > tp->t_maxseg) {
1729                                                 KASSERT(tp->snd_limited == 0 &&
1730                                                     tp->t_dupacks == 2,
1731                                                     ("sent too much"));
1732                                                 tp->snd_limited = 2;
1733                                         } else if (sent > 0)
1734                                                 ++tp->snd_limited;
1735                                         tp->snd_cwnd = oldcwnd;
1736                                         goto drop;
1737                                 }
1738                         } else
1739                                 tp->t_dupacks = 0;
1740                         break;
1741                 }
1742
1743                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1744
1745                 /*
1746                  * If the congestion window was inflated to account
1747                  * for the other side's cached packets, retract it.
1748                  */
1749                 if (tcp_do_newreno) {
1750                         if (IN_FASTRECOVERY(tp)) {
1751                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1752                                         tcp_newreno_partial_ack(tp, th);
1753                                 } else {
1754                                         /*
1755                                          * Window inflation should have left us
1756                                          * with approximately snd_ssthresh
1757                                          * outstanding data.
1758                                          * But in case we would be inclined to
1759                                          * send a burst, better to do it via
1760                                          * the slow start mechanism.
1761                                          */
1762                                         if (SEQ_GT(th->th_ack +
1763                                                         tp->snd_ssthresh,
1764                                                    tp->snd_max))
1765                                                 tp->snd_cwnd = tp->snd_max -
1766                                                                 th->th_ack +
1767                                                                 tp->t_maxseg;
1768                                         else
1769                                                 tp->snd_cwnd = tp->snd_ssthresh;
1770                                 }
1771                         }
1772                 } else {
1773                         if (tp->t_dupacks >= tcprexmtthresh &&
1774                             tp->snd_cwnd > tp->snd_ssthresh)
1775                                 tp->snd_cwnd = tp->snd_ssthresh;
1776                 }
1777                 tp->t_dupacks = 0;
1778                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1779                         tcpstat.tcps_rcvacktoomuch++;
1780                         goto dropafterack;
1781                 }
1782                 /*
1783                  * If we reach this point, ACK is not a duplicate,
1784                  *     i.e., it ACKs something we sent.
1785                  */
1786                 if (tp->t_flags & TF_NEEDSYN) {
1787                         /*
1788                          * T/TCP: Connection was half-synchronized, and our
1789                          * SYN has been ACK'd (so connection is now fully
1790                          * synchronized).  Go to non-starred state,
1791                          * increment snd_una for ACK of SYN, and check if
1792                          * we can do window scaling.
1793                          */
1794                         tp->t_flags &= ~TF_NEEDSYN;
1795                         tp->snd_una++;
1796                         /* Do window scaling? */
1797                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1798                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1799                                 tp->snd_scale = tp->requested_s_scale;
1800                                 tp->rcv_scale = tp->request_r_scale;
1801                         }
1802                 }
1803
1804 process_ACK:
1805                 acked = th->th_ack - tp->snd_una;
1806                 tcpstat.tcps_rcvackpack++;
1807                 tcpstat.tcps_rcvackbyte += acked;
1808
1809                 /*
1810                  * If we just performed our first retransmit, and the ACK
1811                  * arrives within our recovery window, then it was a mistake
1812                  * to do the retransmit in the first place.  Recover our
1813                  * original cwnd and ssthresh, and proceed to transmit where
1814                  * we left off.
1815                  */
1816                 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1817                         tp->snd_cwnd = tp->snd_cwnd_prev;
1818                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
1819                         tp->snd_recover = tp->snd_recover_prev;
1820                         if (tp->t_flags & TF_WASFRECOVERY)
1821                                 ENTER_FASTRECOVERY(tp);
1822                         tp->snd_nxt = tp->snd_max;
1823                         tp->t_badrxtwin = 0;    /* XXX probably not required */
1824                 }
1825
1826                 /*
1827                  * If we have a timestamp reply, update smoothed
1828                  * round trip time.  If no timestamp is present but
1829                  * transmit timer is running and timed sequence
1830                  * number was acked, update smoothed round trip time.
1831                  * Since we now have an rtt measurement, cancel the
1832                  * timer backoff (cf., Phil Karn's retransmit alg.).
1833                  * Recompute the initial retransmit timer.
1834                  *
1835                  * Some machines (certain windows boxes) send broken
1836                  * timestamp replies during the SYN+ACK phase, ignore
1837                  * timestamps of 0.
1838                  */
1839                 if ((to.to_flags & TOF_TS) != 0 &&
1840                     to.to_tsecr) {
1841                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1842                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1843                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1844                 }
1845                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1846
1847                 /*
1848                  * If all outstanding data is acked, stop retransmit
1849                  * timer and remember to restart (more output or persist).
1850                  * If there is more data to be acked, restart retransmit
1851                  * timer, using current (possibly backed-off) value.
1852                  */
1853                 if (th->th_ack == tp->snd_max) {
1854                         callout_stop(tp->tt_rexmt);
1855                         needoutput = 1;
1856                 } else if (!callout_active(tp->tt_persist))
1857                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1858                                       tcp_timer_rexmt, tp);
1859
1860                 /*
1861                  * If no data (only SYN) was ACK'd,
1862                  *    skip rest of ACK processing.
1863                  */
1864                 if (acked == 0)
1865                         goto step6;
1866
1867                 /*
1868                  * When new data is acked, open the congestion window.
1869                  * If the window gives us less than ssthresh packets
1870                  * in flight, open exponentially (maxseg per packet).
1871                  * Otherwise open linearly: maxseg per window
1872                  * (maxseg^2 / cwnd per packet).
1873                  */
1874                 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) {
1875                         register u_int cw = tp->snd_cwnd;
1876                         register u_int incr = tp->t_maxseg;
1877                         if (cw > tp->snd_ssthresh)
1878                                 incr = incr * incr / cw;
1879                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1880                 }
1881                 if (acked > so->so_snd.sb_cc) {
1882                         tp->snd_wnd -= so->so_snd.sb_cc;
1883                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1884                         ourfinisacked = 1;
1885                 } else {
1886                         sbdrop(&so->so_snd, acked);
1887                         tp->snd_wnd -= acked;
1888                         ourfinisacked = 0;
1889                 }
1890                 sowwakeup(so);
1891                 /* detect una wraparound */
1892                 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) &&
1893                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
1894                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1895                         tp->snd_recover = th->th_ack - 1;
1896                 if (tcp_do_newreno && IN_FASTRECOVERY(tp) &&
1897                     SEQ_GEQ(th->th_ack, tp->snd_recover))
1898                         EXIT_FASTRECOVERY(tp);
1899                 tp->snd_una = th->th_ack;
1900                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1901                         tp->snd_nxt = tp->snd_una;
1902
1903                 switch (tp->t_state) {
1904
1905                 /*
1906                  * In FIN_WAIT_1 STATE in addition to the processing
1907                  * for the ESTABLISHED state if our FIN is now acknowledged
1908                  * then enter FIN_WAIT_2.
1909                  */
1910                 case TCPS_FIN_WAIT_1:
1911                         if (ourfinisacked) {
1912                                 /*
1913                                  * If we can't receive any more
1914                                  * data, then closing user can proceed.
1915                                  * Starting the timer is contrary to the
1916                                  * specification, but if we don't get a FIN
1917                                  * we'll hang forever.
1918                                  */
1919                                 if (so->so_state & SS_CANTRCVMORE) {
1920                                         soisdisconnected(so);
1921                                         callout_reset(tp->tt_2msl, tcp_maxidle,
1922                                                       tcp_timer_2msl, tp);
1923                                 }
1924                                 tp->t_state = TCPS_FIN_WAIT_2;
1925                         }
1926                         break;
1927
1928                 /*
1929                  * In CLOSING STATE in addition to the processing for
1930                  * the ESTABLISHED state if the ACK acknowledges our FIN
1931                  * then enter the TIME-WAIT state, otherwise ignore
1932                  * the segment.
1933                  */
1934                 case TCPS_CLOSING:
1935                         if (ourfinisacked) {
1936                                 tp->t_state = TCPS_TIME_WAIT;
1937                                 tcp_canceltimers(tp);
1938                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
1939                                 if (tp->cc_recv != 0 &&
1940                                     (ticks - tp->t_starttime) < tcp_msl)
1941                                         callout_reset(tp->tt_2msl,
1942                                                       tp->t_rxtcur *
1943                                                       TCPTV_TWTRUNC,
1944                                                       tcp_timer_2msl, tp);
1945                                 else
1946                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1947                                                       tcp_timer_2msl, tp);
1948                                 soisdisconnected(so);
1949                         }
1950                         break;
1951
1952                 /*
1953                  * In LAST_ACK, we may still be waiting for data to drain
1954                  * and/or to be acked, as well as for the ack of our FIN.
1955                  * If our FIN is now acknowledged, delete the TCB,
1956                  * enter the closed state and return.
1957                  */
1958                 case TCPS_LAST_ACK:
1959                         if (ourfinisacked) {
1960                                 tp = tcp_close(tp);
1961                                 goto drop;
1962                         }
1963                         break;
1964
1965                 /*
1966                  * In TIME_WAIT state the only thing that should arrive
1967                  * is a retransmission of the remote FIN.  Acknowledge
1968                  * it and restart the finack timer.
1969                  */
1970                 case TCPS_TIME_WAIT:
1971                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1972                                       tcp_timer_2msl, tp);
1973                         goto dropafterack;
1974                 }
1975         }
1976
1977 step6:
1978         /*
1979          * Update window information.
1980          * Don't look at window if no ACK: TAC's send garbage on first SYN.
1981          */
1982         if ((thflags & TH_ACK) &&
1983             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
1984             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
1985              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
1986                 /* keep track of pure window updates */
1987                 if (tlen == 0 &&
1988                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
1989                         tcpstat.tcps_rcvwinupd++;
1990                 tp->snd_wnd = tiwin;
1991                 tp->snd_wl1 = th->th_seq;
1992                 tp->snd_wl2 = th->th_ack;
1993                 if (tp->snd_wnd > tp->max_sndwnd)
1994                         tp->max_sndwnd = tp->snd_wnd;
1995                 needoutput = 1;
1996         }
1997
1998         /*
1999          * Process segments with URG.
2000          */
2001         if ((thflags & TH_URG) && th->th_urp &&
2002             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2003                 /*
2004                  * This is a kludge, but if we receive and accept
2005                  * random urgent pointers, we'll crash in
2006                  * soreceive.  It's hard to imagine someone
2007                  * actually wanting to send this much urgent data.
2008                  */
2009                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2010                         th->th_urp = 0;                 /* XXX */
2011                         thflags &= ~TH_URG;             /* XXX */
2012                         goto dodata;                    /* XXX */
2013                 }
2014                 /*
2015                  * If this segment advances the known urgent pointer,
2016                  * then mark the data stream.  This should not happen
2017                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2018                  * a FIN has been received from the remote side.
2019                  * In these states we ignore the URG.
2020                  *
2021                  * According to RFC961 (Assigned Protocols),
2022                  * the urgent pointer points to the last octet
2023                  * of urgent data.  We continue, however,
2024                  * to consider it to indicate the first octet
2025                  * of data past the urgent section as the original
2026                  * spec states (in one of two places).
2027                  */
2028                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2029                         tp->rcv_up = th->th_seq + th->th_urp;
2030                         so->so_oobmark = so->so_rcv.sb_cc +
2031                             (tp->rcv_up - tp->rcv_nxt) - 1;
2032                         if (so->so_oobmark == 0)
2033                                 so->so_state |= SS_RCVATMARK;
2034                         sohasoutofband(so);
2035                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2036                 }
2037                 /*
2038                  * Remove out of band data so doesn't get presented to user.
2039                  * This can happen independent of advancing the URG pointer,
2040                  * but if two URG's are pending at once, some out-of-band
2041                  * data may creep in... ick.
2042                  */
2043                 if (th->th_urp <= (u_long)tlen
2044 #ifdef SO_OOBINLINE
2045                      && (so->so_options & SO_OOBINLINE) == 0
2046 #endif
2047                      )
2048                         tcp_pulloutofband(so, th, m,
2049                                 drop_hdrlen);   /* hdr drop is delayed */
2050         } else {
2051                 /*
2052                  * If no out of band data is expected,
2053                  * pull receive urgent pointer along
2054                  * with the receive window.
2055                  */
2056                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2057                         tp->rcv_up = tp->rcv_nxt;
2058         }
2059 dodata:                                                 /* XXX */
2060
2061         /*
2062          * Process the segment text, merging it into the TCP sequencing queue,
2063          * and arranging for acknowledgment of receipt if necessary.
2064          * This process logically involves adjusting tp->rcv_wnd as data
2065          * is presented to the user (this happens in tcp_usrreq.c,
2066          * case PRU_RCVD).  If a FIN has already been received on this
2067          * connection then we just ignore the text.
2068          */
2069         if ((tlen || (thflags & TH_FIN)) &&
2070             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2071                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2072                 /*
2073                  * Insert segment which includes th into TCP reassembly queue
2074                  * with control block tp.  Set thflags to whether reassembly now
2075                  * includes a segment with FIN.  This handles the common case
2076                  * inline (segment is the next to be received on an established
2077                  * connection, and the queue is empty), avoiding linkage into
2078                  * and removal from the queue and repetition of various
2079                  * conversions.
2080                  * Set DELACK for segments received in order, but ack
2081                  * immediately when segments are out of order (so
2082                  * fast retransmit can work).
2083                  */
2084                 if (th->th_seq == tp->rcv_nxt &&
2085                     LIST_EMPTY(&tp->t_segq) &&
2086                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2087                         if (DELAY_ACK(tp))
2088                                 callout_reset(tp->tt_delack, tcp_delacktime,
2089                                               tcp_timer_delack, tp);
2090                         else
2091                                 tp->t_flags |= TF_ACKNOW;
2092                         tp->rcv_nxt += tlen;
2093                         thflags = th->th_flags & TH_FIN;
2094                         tcpstat.tcps_rcvpack++;
2095                         tcpstat.tcps_rcvbyte += tlen;
2096                         ND6_HINT(tp);
2097                         if (so->so_state & SS_CANTRCVMORE)
2098                                 m_freem(m);
2099                         else
2100                                 sbappend(&so->so_rcv, m);
2101                         sorwakeup(so);
2102                 } else {
2103                         thflags = tcp_reass(tp, th, &tlen, m);
2104                         tp->t_flags |= TF_ACKNOW;
2105                 }
2106
2107                 /*
2108                  * Note the amount of data that peer has sent into
2109                  * our window, in order to estimate the sender's
2110                  * buffer size.
2111                  */
2112                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2113         } else {
2114                 m_freem(m);
2115                 thflags &= ~TH_FIN;
2116         }
2117
2118         /*
2119          * If FIN is received ACK the FIN and let the user know
2120          * that the connection is closing.
2121          */
2122         if (thflags & TH_FIN) {
2123                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2124                         socantrcvmore(so);
2125                         /*
2126                          * If connection is half-synchronized
2127                          * (ie NEEDSYN flag on) then delay ACK,
2128                          * so it may be piggybacked when SYN is sent.
2129                          * Otherwise, since we received a FIN then no
2130                          * more input can be expected, send ACK now.
2131                          */
2132                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2133                                 callout_reset(tp->tt_delack, tcp_delacktime,
2134                                     tcp_timer_delack, tp);
2135                         else
2136                                 tp->t_flags |= TF_ACKNOW;
2137                         tp->rcv_nxt++;
2138                 }
2139                 switch (tp->t_state) {
2140
2141                 /*
2142                  * In SYN_RECEIVED and ESTABLISHED STATES
2143                  * enter the CLOSE_WAIT state.
2144                  */
2145                 case TCPS_SYN_RECEIVED:
2146                         tp->t_starttime = ticks;
2147                         /*FALLTHROUGH*/
2148                 case TCPS_ESTABLISHED:
2149                         tp->t_state = TCPS_CLOSE_WAIT;
2150                         break;
2151
2152                 /*
2153                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2154                  * enter the CLOSING state.
2155                  */
2156                 case TCPS_FIN_WAIT_1:
2157                         tp->t_state = TCPS_CLOSING;
2158                         break;
2159
2160                 /*
2161                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2162                  * starting the time-wait timer, turning off the other
2163                  * standard timers.
2164                  */
2165                 case TCPS_FIN_WAIT_2:
2166                         tp->t_state = TCPS_TIME_WAIT;
2167                         tcp_canceltimers(tp);
2168                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2169                         if (tp->cc_recv != 0 &&
2170                             (ticks - tp->t_starttime) < tcp_msl) {
2171                                 callout_reset(tp->tt_2msl,
2172                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2173                                               tcp_timer_2msl, tp);
2174                                 /* For transaction client, force ACK now. */
2175                                 tp->t_flags |= TF_ACKNOW;
2176                         }
2177                         else
2178                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2179                                               tcp_timer_2msl, tp);
2180                         soisdisconnected(so);
2181                         break;
2182
2183                 /*
2184                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2185                  */
2186                 case TCPS_TIME_WAIT:
2187                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2188                                       tcp_timer_2msl, tp);
2189                         break;
2190                 }
2191         }
2192 #ifdef TCPDEBUG
2193         if (so->so_options & SO_DEBUG)
2194                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2195                           &tcp_savetcp, 0);
2196 #endif
2197
2198         /*
2199          * Return any desired output.
2200          */
2201         if (needoutput || (tp->t_flags & TF_ACKNOW))
2202                 (void) tcp_output(tp);
2203         return;
2204
2205 dropafterack:
2206         /*
2207          * Generate an ACK dropping incoming segment if it occupies
2208          * sequence space, where the ACK reflects our state.
2209          *
2210          * We can now skip the test for the RST flag since all
2211          * paths to this code happen after packets containing
2212          * RST have been dropped.
2213          *
2214          * In the SYN-RECEIVED state, don't send an ACK unless the
2215          * segment we received passes the SYN-RECEIVED ACK test.
2216          * If it fails send a RST.  This breaks the loop in the
2217          * "LAND" DoS attack, and also prevents an ACK storm
2218          * between two listening ports that have been sent forged
2219          * SYN segments, each with the source address of the other.
2220          */
2221         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2222             (SEQ_GT(tp->snd_una, th->th_ack) ||
2223              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2224                 rstreason = BANDLIM_RST_OPENPORT;
2225                 goto dropwithreset;
2226         }
2227 #ifdef TCPDEBUG
2228         if (so->so_options & SO_DEBUG)
2229                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2230                           &tcp_savetcp, 0);
2231 #endif
2232         m_freem(m);
2233         tp->t_flags |= TF_ACKNOW;
2234         (void) tcp_output(tp);
2235         return;
2236
2237 dropwithreset:
2238         /*
2239          * Generate a RST, dropping incoming segment.
2240          * Make ACK acceptable to originator of segment.
2241          * Don't bother to respond if destination was broadcast/multicast.
2242          */
2243         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2244                 goto drop;
2245         if (isipv6) {
2246                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2247                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2248                         goto drop;
2249         } else {
2250                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2251                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2252                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2253                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2254                         goto drop;
2255         }
2256         /* IPv6 anycast check is done at tcp6_input() */
2257
2258         /*
2259          * Perform bandwidth limiting.
2260          */
2261 #ifdef ICMP_BANDLIM
2262         if (badport_bandlim(rstreason) < 0)
2263                 goto drop;
2264 #endif
2265
2266 #ifdef TCPDEBUG
2267         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2268                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2269                           &tcp_savetcp, 0);
2270 #endif
2271         if (thflags & TH_ACK)
2272                 /* mtod() below is safe as long as hdr dropping is delayed */
2273                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2274                             TH_RST);
2275         else {
2276                 if (thflags & TH_SYN)
2277                         tlen++;
2278                 /* mtod() below is safe as long as hdr dropping is delayed */
2279                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2280                             (tcp_seq)0, TH_RST|TH_ACK);
2281         }
2282         return;
2283
2284 drop:
2285         /*
2286          * Drop space held by incoming segment and return.
2287          */
2288 #ifdef TCPDEBUG
2289         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2290                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2291                           &tcp_savetcp, 0);
2292 #endif
2293         m_freem(m);
2294         return;
2295 }
2296
2297 /*
2298  * Parse TCP options and place in tcpopt.
2299  */
2300 static void
2301 tcp_dooptions(to, cp, cnt, is_syn)
2302         struct tcpopt *to;
2303         u_char *cp;
2304         int cnt;
2305 {
2306         int opt, optlen;
2307
2308         to->to_flags = 0;
2309         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2310                 opt = cp[0];
2311                 if (opt == TCPOPT_EOL)
2312                         break;
2313                 if (opt == TCPOPT_NOP)
2314                         optlen = 1;
2315                 else {
2316                         if (cnt < 2)
2317                                 break;
2318                         optlen = cp[1];
2319                         if (optlen < 2 || optlen > cnt)
2320                                 break;
2321                 }
2322                 switch (opt) {
2323                 case TCPOPT_MAXSEG:
2324                         if (optlen != TCPOLEN_MAXSEG)
2325                                 continue;
2326                         if (!is_syn)
2327                                 continue;
2328                         to->to_flags |= TOF_MSS;
2329                         bcopy((char *)cp + 2,
2330                             (char *)&to->to_mss, sizeof(to->to_mss));
2331                         to->to_mss = ntohs(to->to_mss);
2332                         break;
2333                 case TCPOPT_WINDOW:
2334                         if (optlen != TCPOLEN_WINDOW)
2335                                 continue;
2336                         if (! is_syn)
2337                                 continue;
2338                         to->to_flags |= TOF_SCALE;
2339                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2340                         break;
2341                 case TCPOPT_TIMESTAMP:
2342                         if (optlen != TCPOLEN_TIMESTAMP)
2343                                 continue;
2344                         to->to_flags |= TOF_TS;
2345                         bcopy((char *)cp + 2,
2346                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2347                         to->to_tsval = ntohl(to->to_tsval);
2348                         bcopy((char *)cp + 6,
2349                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2350                         to->to_tsecr = ntohl(to->to_tsecr);
2351                         break;
2352                 case TCPOPT_CC:
2353                         if (optlen != TCPOLEN_CC)
2354                                 continue;
2355                         to->to_flags |= TOF_CC;
2356                         bcopy((char *)cp + 2,
2357                             (char *)&to->to_cc, sizeof(to->to_cc));
2358                         to->to_cc = ntohl(to->to_cc);
2359                         break;
2360                 case TCPOPT_CCNEW:
2361                         if (optlen != TCPOLEN_CC)
2362                                 continue;
2363                         if (!is_syn)
2364                                 continue;
2365                         to->to_flags |= TOF_CCNEW;
2366                         bcopy((char *)cp + 2,
2367                             (char *)&to->to_cc, sizeof(to->to_cc));
2368                         to->to_cc = ntohl(to->to_cc);
2369                         break;
2370                 case TCPOPT_CCECHO:
2371                         if (optlen != TCPOLEN_CC)
2372                                 continue;
2373                         if (!is_syn)
2374                                 continue;
2375                         to->to_flags |= TOF_CCECHO;
2376                         bcopy((char *)cp + 2,
2377                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2378                         to->to_ccecho = ntohl(to->to_ccecho);
2379                         break;
2380                 default:
2381                         continue;
2382                 }
2383         }
2384 }
2385
2386 /*
2387  * Pull out of band byte out of a segment so
2388  * it doesn't appear in the user's data queue.
2389  * It is still reflected in the segment length for
2390  * sequencing purposes.
2391  */
2392 static void
2393 tcp_pulloutofband(so, th, m, off)
2394         struct socket *so;
2395         struct tcphdr *th;
2396         register struct mbuf *m;
2397         int off;                /* delayed to be droped hdrlen */
2398 {
2399         int cnt = off + th->th_urp - 1;
2400
2401         while (cnt >= 0) {
2402                 if (m->m_len > cnt) {
2403                         char *cp = mtod(m, caddr_t) + cnt;
2404                         struct tcpcb *tp = sototcpcb(so);
2405
2406                         tp->t_iobc = *cp;
2407                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2408                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2409                         m->m_len--;
2410                         if (m->m_flags & M_PKTHDR)
2411                                 m->m_pkthdr.len--;
2412                         return;
2413                 }
2414                 cnt -= m->m_len;
2415                 m = m->m_next;
2416                 if (m == 0)
2417                         break;
2418         }
2419         panic("tcp_pulloutofband");
2420 }
2421
2422 /*
2423  * Collect new round-trip time estimate
2424  * and update averages and current timeout.
2425  */
2426 static void
2427 tcp_xmit_timer(tp, rtt)
2428         register struct tcpcb *tp;
2429         int rtt;
2430 {
2431         register int delta;
2432
2433         tcpstat.tcps_rttupdated++;
2434         tp->t_rttupdated++;
2435         if (tp->t_srtt != 0) {
2436                 /*
2437                  * srtt is stored as fixed point with 5 bits after the
2438                  * binary point (i.e., scaled by 8).  The following magic
2439                  * is equivalent to the smoothing algorithm in rfc793 with
2440                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2441                  * point).  Adjust rtt to origin 0.
2442                  */
2443                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2444                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2445
2446                 if ((tp->t_srtt += delta) <= 0)
2447                         tp->t_srtt = 1;
2448
2449                 /*
2450                  * We accumulate a smoothed rtt variance (actually, a
2451                  * smoothed mean difference), then set the retransmit
2452                  * timer to smoothed rtt + 4 times the smoothed variance.
2453                  * rttvar is stored as fixed point with 4 bits after the
2454                  * binary point (scaled by 16).  The following is
2455                  * equivalent to rfc793 smoothing with an alpha of .75
2456                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2457                  * rfc793's wired-in beta.
2458                  */
2459                 if (delta < 0)
2460                         delta = -delta;
2461                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2462                 if ((tp->t_rttvar += delta) <= 0)
2463                         tp->t_rttvar = 1;
2464                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2465                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2466         } else {
2467                 /*
2468                  * No rtt measurement yet - use the unsmoothed rtt.
2469                  * Set the variance to half the rtt (so our first
2470                  * retransmit happens at 3*rtt).
2471                  */
2472                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2473                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2474                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2475         }
2476         tp->t_rtttime = 0;
2477         tp->t_rxtshift = 0;
2478
2479         /*
2480          * the retransmit should happen at rtt + 4 * rttvar.
2481          * Because of the way we do the smoothing, srtt and rttvar
2482          * will each average +1/2 tick of bias.  When we compute
2483          * the retransmit timer, we want 1/2 tick of rounding and
2484          * 1 extra tick because of +-1/2 tick uncertainty in the
2485          * firing of the timer.  The bias will give us exactly the
2486          * 1.5 tick we need.  But, because the bias is
2487          * statistical, we have to test that we don't drop below
2488          * the minimum feasible timer (which is 2 ticks).
2489          */
2490         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2491                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2492
2493         /*
2494          * We received an ack for a packet that wasn't retransmitted;
2495          * it is probably safe to discard any error indications we've
2496          * received recently.  This isn't quite right, but close enough
2497          * for now (a route might have failed after we sent a segment,
2498          * and the return path might not be symmetrical).
2499          */
2500         tp->t_softerror = 0;
2501 }
2502
2503 /*
2504  * Determine a reasonable value for maxseg size.
2505  * If the route is known, check route for mtu.
2506  * If none, use an mss that can be handled on the outgoing
2507  * interface without forcing IP to fragment; if bigger than
2508  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2509  * to utilize large mbufs.  If no route is found, route has no mtu,
2510  * or the destination isn't local, use a default, hopefully conservative
2511  * size (usually 512 or the default IP max size, but no more than the mtu
2512  * of the interface), as we can't discover anything about intervening
2513  * gateways or networks.  We also initialize the congestion/slow start
2514  * window to be a single segment if the destination isn't local.
2515  * While looking at the routing entry, we also initialize other path-dependent
2516  * parameters from pre-set or cached values in the routing entry.
2517  *
2518  * Also take into account the space needed for options that we
2519  * send regularly.  Make maxseg shorter by that amount to assure
2520  * that we can send maxseg amount of data even when the options
2521  * are present.  Store the upper limit of the length of options plus
2522  * data in maxopd.
2523  *
2524  * NOTE that this routine is only called when we process an incoming
2525  * segment, for outgoing segments only tcp_mssopt is called.
2526  *
2527  * In case of T/TCP, we call this routine during implicit connection
2528  * setup as well (offer = -1), to initialize maxseg from the cached
2529  * MSS of our peer.
2530  */
2531 void
2532 tcp_mss(tp, offer)
2533         struct tcpcb *tp;
2534         int offer;
2535 {
2536         register struct rtentry *rt;
2537         struct ifnet *ifp;
2538         register int rtt, mss;
2539         u_long bufsize;
2540         struct inpcb *inp = tp->t_inpcb;
2541         struct socket *so;
2542         struct rmxp_tao *taop;
2543         int origoffer = offer;
2544 #ifdef INET6
2545         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2546         size_t min_protoh = isipv6 ?
2547                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2548                             sizeof(struct tcpiphdr);
2549 #else
2550         const int isipv6 = 0;
2551         const size_t min_protoh = sizeof(struct tcpiphdr);
2552 #endif
2553
2554         if (isipv6)
2555                 rt = tcp_rtlookup6(&inp->inp_inc);
2556         else
2557                 rt = tcp_rtlookup(&inp->inp_inc);
2558         if (rt == NULL) {
2559                 tp->t_maxopd = tp->t_maxseg =
2560                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2561                 return;
2562         }
2563         ifp = rt->rt_ifp;
2564         so = inp->inp_socket;
2565
2566         taop = rmx_taop(rt->rt_rmx);
2567         /*
2568          * Offer == -1 means that we didn't receive SYN yet,
2569          * use cached value in that case;
2570          */
2571         if (offer == -1)
2572                 offer = taop->tao_mssopt;
2573         /*
2574          * Offer == 0 means that there was no MSS on the SYN segment,
2575          * in this case we use tcp_mssdflt.
2576          */
2577         if (offer == 0)
2578                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2579         else
2580                 /*
2581                  * Sanity check: make sure that maxopd will be large
2582                  * enough to allow some data on segments even is the
2583                  * all the option space is used (40bytes).  Otherwise
2584                  * funny things may happen in tcp_output.
2585                  */
2586                 offer = max(offer, 64);
2587         taop->tao_mssopt = offer;
2588
2589         /*
2590          * While we're here, check if there's an initial rtt
2591          * or rttvar.  Convert from the route-table units
2592          * to scaled multiples of the slow timeout timer.
2593          */
2594         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2595                 /*
2596                  * XXX the lock bit for RTT indicates that the value
2597                  * is also a minimum value; this is subject to time.
2598                  */
2599                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2600                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2601                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2602                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2603                 tcpstat.tcps_usedrtt++;
2604                 if (rt->rt_rmx.rmx_rttvar) {
2605                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2606                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2607                         tcpstat.tcps_usedrttvar++;
2608                 } else {
2609                         /* default variation is +- 1 rtt */
2610                         tp->t_rttvar =
2611                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2612                 }
2613                 TCPT_RANGESET(tp->t_rxtcur,
2614                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2615                               tp->t_rttmin, TCPTV_REXMTMAX);
2616         }
2617         /*
2618          * if there's an mtu associated with the route, use it
2619          * else, use the link mtu.
2620          */
2621         if (rt->rt_rmx.rmx_mtu)
2622                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2623         else {
2624                 if (isipv6) {
2625                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2626                                 min_protoh;
2627                         if (!in6_localaddr(&inp->in6p_faddr))
2628                                 mss = min(mss, tcp_v6mssdflt);
2629                 } else {
2630                         mss = ifp->if_mtu - min_protoh;
2631                         if (!in_localaddr(inp->inp_faddr))
2632                                 mss = min(mss, tcp_mssdflt);
2633                 }
2634         }
2635         mss = min(mss, offer);
2636         /*
2637          * maxopd stores the maximum length of data AND options
2638          * in a segment; maxseg is the amount of data in a normal
2639          * segment.  We need to store this value (maxopd) apart
2640          * from maxseg, because now every segment carries options
2641          * and thus we normally have somewhat less data in segments.
2642          */
2643         tp->t_maxopd = mss;
2644
2645         /*
2646          * In case of T/TCP, origoffer==-1 indicates, that no segments
2647          * were received yet.  In this case we just guess, otherwise
2648          * we do the same as before T/TCP.
2649          */
2650         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2651             (origoffer == -1 ||
2652              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2653                 mss -= TCPOLEN_TSTAMP_APPA;
2654         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2655             (origoffer == -1 ||
2656              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2657                 mss -= TCPOLEN_CC_APPA;
2658
2659 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2660                 if (mss > MCLBYTES)
2661                         mss &= ~(MCLBYTES-1);
2662 #else
2663                 if (mss > MCLBYTES)
2664                         mss = mss / MCLBYTES * MCLBYTES;
2665 #endif
2666         /*
2667          * If there's a pipesize, change the socket buffer
2668          * to that size.  Make the socket buffers an integral
2669          * number of mss units; if the mss is larger than
2670          * the socket buffer, decrease the mss.
2671          */
2672 #ifdef RTV_SPIPE
2673         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2674 #endif
2675                 bufsize = so->so_snd.sb_hiwat;
2676         if (bufsize < mss)
2677                 mss = bufsize;
2678         else {
2679                 bufsize = roundup(bufsize, mss);
2680                 if (bufsize > sb_max)
2681                         bufsize = sb_max;
2682                 if (bufsize > so->so_snd.sb_hiwat)
2683                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2684         }
2685         tp->t_maxseg = mss;
2686
2687 #ifdef RTV_RPIPE
2688         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2689 #endif
2690                 bufsize = so->so_rcv.sb_hiwat;
2691         if (bufsize > mss) {
2692                 bufsize = roundup(bufsize, mss);
2693                 if (bufsize > sb_max)
2694                         bufsize = sb_max;
2695                 if (bufsize > so->so_rcv.sb_hiwat)
2696                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2697         }
2698
2699         /*
2700          * Set the slow-start flight size depending on whether this
2701          * is a local network or not.
2702          */
2703         if (tcp_do_rfc3390)
2704                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2705         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2706                  (!isipv6 && in_localaddr(inp->inp_faddr)))
2707                 tp->snd_cwnd = mss * ss_fltsz_local;
2708         else
2709                 tp->snd_cwnd = mss * ss_fltsz;
2710
2711         if (rt->rt_rmx.rmx_ssthresh) {
2712                 /*
2713                  * There's some sort of gateway or interface
2714                  * buffer limit on the path.  Use this to set
2715                  * the slow start threshhold, but set the
2716                  * threshold to no less than 2*mss.
2717                  */
2718                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2719                 tcpstat.tcps_usedssthresh++;
2720         }
2721 }
2722
2723 /*
2724  * Determine the MSS option to send on an outgoing SYN.
2725  */
2726 int
2727 tcp_mssopt(tp)
2728         struct tcpcb *tp;
2729 {
2730         struct rtentry *rt;
2731 #ifdef INET6
2732         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2733         int min_protoh = isipv6 ?
2734                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2735                              sizeof(struct tcpiphdr);
2736 #else
2737         const int isipv6 = 0;
2738         const size_t min_protoh = sizeof(struct tcpiphdr);
2739 #endif
2740
2741         if (isipv6)
2742                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2743         else
2744                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2745         if (rt == NULL)
2746                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2747
2748         return (rt->rt_ifp->if_mtu - min_protoh);
2749 }
2750
2751
2752 /*
2753  * When a partial ack arrives, force the retransmission of the
2754  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2755  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2756  * be started again.
2757  */
2758 static void
2759 tcp_newreno_partial_ack(tp, th)
2760         struct tcpcb *tp;
2761         struct tcphdr *th;
2762 {
2763         tcp_seq onxt = tp->snd_nxt;
2764         u_long  ocwnd = tp->snd_cwnd;
2765
2766         callout_stop(tp->tt_rexmt);
2767         tp->t_rtttime = 0;
2768         tp->snd_nxt = th->th_ack;
2769         /*
2770          * Set snd_cwnd to one segment beyond acknowledged offset
2771          * (tp->snd_una has not yet been updated when this function is called.)
2772          */
2773         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2774         tp->t_flags |= TF_ACKNOW;
2775         (void) tcp_output(tp);
2776         tp->snd_cwnd = ocwnd;
2777         if (SEQ_GT(onxt, tp->snd_nxt))
2778                 tp->snd_nxt = onxt;
2779         /*
2780          * Partial window deflation.  Relies on fact that tp->snd_una
2781          * not updated yet.
2782          */
2783         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2784 }