sys/netinet/tcp_input.c

   1 /*
   2  * Copyright (c) 2002-2003 Jeffrey Hsu
   3  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   4  *      The Regents of the University of California.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 3. All advertising materials mentioning features or use of this software
  15  *    must display the following acknowledgement:
  16  *      This product includes software developed by the University of
  17  *      California, Berkeley and its contributors.
  18  * 4. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  35  * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
  36  * $DragonFly: src/sys/netinet/tcp_input.c,v 1.12 2003/10/19 05:19:21 hsu Exp $
  37  */
  38
  39 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  40 #include "opt_inet6.h"
  41 #include "opt_ipsec.h"
  42 #include "opt_tcpdebug.h"
  43 #include "opt_tcp_input.h"
  44
  45 #include <sys/param.h>
  46 #include <sys/systm.h>
  47 #include <sys/kernel.h>
  48 #include <sys/sysctl.h>
  49 #include <sys/malloc.h>
  50 #include <sys/mbuf.h>
  51 #include <sys/proc.h>           /* for proc0 declaration */
  52 #include <sys/protosw.h>
  53 #include <sys/socket.h>
  54 #include <sys/socketvar.h>
  55 #include <sys/syslog.h>
  56
  57 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  58
  59 #include <net/if.h>
  60 #include <net/route.h>
  61
  62 #include <netinet/in.h>
  63 #include <netinet/in_systm.h>
  64 #include <netinet/ip.h>
  65 #include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM             */
  66 #include <netinet/in_var.h>
  67 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM             */
  68 #include <netinet/in_pcb.h>
  69 #include <netinet/ip_var.h>
  70 #include <netinet/ip6.h>
  71 #include <netinet/icmp6.h>
  72 #include <netinet6/nd6.h>
  73 #include <netinet6/ip6_var.h>
  74 #include <netinet6/in6_pcb.h>
  75 #include <netinet/tcp.h>
  76 #include <netinet/tcp_fsm.h>
  77 #include <netinet/tcp_seq.h>
  78 #include <netinet/tcp_timer.h>
  79 #include <netinet/tcp_var.h>
  80 #include <netinet6/tcp6_var.h>
  81 #include <netinet/tcpip.h>
  82 #ifdef TCPDEBUG
  83 #include <netinet/tcp_debug.h>
  84
  85 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
  86 struct tcphdr tcp_savetcp;
  87 #endif /* TCPDEBUG */
  88
  89 #ifdef FAST_IPSEC
  90 #include <netipsec/ipsec.h>
  91 #include <netipsec/ipsec6.h>
  92 #endif
  93
  94 #ifdef IPSEC
  95 #include <netinet6/ipsec.h>
  96 #include <netinet6/ipsec6.h>
  97 #include <netproto/key/key.h>
  98 #endif /*IPSEC*/
  99
 100 #include <machine/in_cksum.h>
 101
 102 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
 103
 104 static const int tcprexmtthresh = 3;
 105 tcp_cc  tcp_ccgen;
 106
 107 struct  tcpstat tcpstat;
 108 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 109     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 110
 111 static int log_in_vain = 0;
 112 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 113     &log_in_vain, 0, "Log all incoming TCP connections");
 114
 115 static int blackhole = 0;
 116 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 117     &blackhole, 0, "Do not send RST when dropping refused connections");
 118
 119 int tcp_delack_enabled = 1;
 120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 121     &tcp_delack_enabled, 0,
 122     "Delay ACK to try and piggyback it onto a data packet");
 123
 124 #ifdef TCP_DROP_SYNFIN
 125 static int drop_synfin = 0;
 126 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 127     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 128 #endif
 129
 130 static int tcp_do_limitedtransmit = 1;
 131 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
 132     &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
 133
 134 static int tcp_do_rfc3390 = 1;
 135 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 136     &tcp_do_rfc3390, 0,
 137     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 138
 139 static int tcp_do_eifel_detect = 1;
 140 SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel, CTLFLAG_RW,
 141     &tcp_do_eifel_detect, 0, "Eifel detection algorithm (RFC 3522)");
 142
 143 struct inpcbhead tcb;
 144 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 145 struct inpcbinfo tcbinfo;
 146
 147 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 148 static void      tcp_pulloutofband(struct socket *,
 149                      struct tcphdr *, struct mbuf *, int);
 150 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 151                      struct mbuf *);
 152 static void      tcp_xmit_timer(struct tcpcb *, int);
 153 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 154
 155 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 156 #ifdef INET6
 157 #define ND6_HINT(tp) \
 158 do { \
 159         if ((tp) && (tp)->t_inpcb && \
 160             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
 161             (tp)->t_inpcb->in6p_route.ro_rt) \
 162                 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
 163 } while (0)
 164 #else
 165 #define ND6_HINT(tp)
 166 #endif
 167
 168 /*
 169  * Indicate whether this ack should be delayed.  We can delay the ack if
 170  *      - delayed acks are enabled and
 171  *      - there is no delayed ack timer in progress and
 172  *      - our last ack wasn't a 0-sized window.  We never want to delay
 173  *        the ack that opens up a 0-sized window.
 174  */
 175 #define DELAY_ACK(tp) \
 176         (tcp_delack_enabled && !callout_pending(tp->tt_delack) && \
 177         (tp->t_flags & TF_RXWIN0SENT) == 0)
 178
 179 static int
 180 tcp_reass(tp, th, tlenp, m)
 181         struct tcpcb *tp;
 182         struct tcphdr *th;
 183         int *tlenp;
 184         struct mbuf *m;
 185 {
 186         struct tseg_qent *q;
 187         struct tseg_qent *p = NULL;
 188         struct tseg_qent *nq;
 189         struct tseg_qent *te;
 190         struct socket *so = tp->t_inpcb->inp_socket;
 191         int flags;
 192
 193         /*
 194          * Call with th==0 after become established to
 195          * force pre-ESTABLISHED data up to user socket.
 196          */
 197         if (th == 0)
 198                 goto present;
 199
 200         /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
 201         MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
 202                M_NOWAIT);
 203         if (te == NULL) {
 204                 tcpstat.tcps_rcvmemdrop++;
 205                 m_freem(m);
 206                 return (0);
 207         }
 208
 209         /*
 210          * Find a segment which begins after this one does.
 211          */
 212         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 213                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 214                         break;
 215                 p = q;
 216         }
 217
 218         /*
 219          * If there is a preceding segment, it may provide some of
 220          * our data already.  If so, drop the data from the incoming
 221          * segment.  If it provides all of our data, drop us.
 222          */
 223         if (p != NULL) {
 224                 int i;
 225                 /* conversion to int (in i) handles seq wraparound */
 226                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 227                 if (i > 0) {
 228                         if (i >= *tlenp) {
 229                                 tcpstat.tcps_rcvduppack++;
 230                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 231                                 m_freem(m);
 232                                 free(te, M_TSEGQ);
 233                                 /*
 234                                  * Try to present any queued data
 235                                  * at the left window edge to the user.
 236                                  * This is needed after the 3-WHS
 237                                  * completes.
 238                                  */
 239                                 goto present;   /* ??? */
 240                         }
 241                         m_adj(m, i);
 242                         *tlenp -= i;
 243                         th->th_seq += i;
 244                 }
 245         }
 246         tcpstat.tcps_rcvoopack++;
 247         tcpstat.tcps_rcvoobyte += *tlenp;
 248
 249         /*
 250          * While we overlap succeeding segments trim them or,
 251          * if they are completely covered, dequeue them.
 252          */
 253         while (q) {
 254                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 255                 if (i <= 0)
 256                         break;
 257                 if (i < q->tqe_len) {
 258                         q->tqe_th->th_seq += i;
 259                         q->tqe_len -= i;
 260                         m_adj(q->tqe_m, i);
 261                         break;
 262                 }
 263
 264                 nq = LIST_NEXT(q, tqe_q);
 265                 LIST_REMOVE(q, tqe_q);
 266                 m_freem(q->tqe_m);
 267                 free(q, M_TSEGQ);
 268                 q = nq;
 269         }
 270
 271         /* Insert the new segment queue entry into place. */
 272         te->tqe_m = m;
 273         te->tqe_th = th;
 274         te->tqe_len = *tlenp;
 275
 276         if (p == NULL) {
 277                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 278         } else {
 279                 LIST_INSERT_AFTER(p, te, tqe_q);
 280         }
 281
 282 present:
 283         /*
 284          * Present data to user, advancing rcv_nxt through
 285          * completed sequence space.
 286          */
 287         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 288                 return (0);
 289         q = LIST_FIRST(&tp->t_segq);
 290         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 291                 return (0);
 292         do {
 293                 tp->rcv_nxt += q->tqe_len;
 294                 flags = q->tqe_th->th_flags & TH_FIN;
 295                 nq = LIST_NEXT(q, tqe_q);
 296                 LIST_REMOVE(q, tqe_q);
 297                 if (so->so_state & SS_CANTRCVMORE)
 298                         m_freem(q->tqe_m);
 299                 else
 300                         sbappend(&so->so_rcv, q->tqe_m);
 301                 free(q, M_TSEGQ);
 302                 q = nq;
 303         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 304         ND6_HINT(tp);
 305         sorwakeup(so);
 306         return (flags);
 307 }
 308
 309 /*
 310  * TCP input routine, follows pages 65-76 of the
 311  * protocol specification dated September, 1981 very closely.
 312  */
 313 #ifdef INET6
 314 int
 315 tcp6_input(mp, offp, proto)
 316         struct mbuf **mp;
 317         int *offp, proto;
 318 {
 319         struct mbuf *m = *mp;
 320         struct in6_ifaddr *ia6;
 321
 322         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 323
 324         /*
 325          * draft-itojun-ipv6-tcp-to-anycast
 326          * better place to put this in?
 327          */
 328         ia6 = ip6_getdstifaddr(m);
 329         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 330                 struct ip6_hdr *ip6;
 331
 332                 ip6 = mtod(m, struct ip6_hdr *);
 333                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 334                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 335                 return IPPROTO_DONE;
 336         }
 337
 338         tcp_input(m, *offp, proto);
 339         return IPPROTO_DONE;
 340 }
 341 #endif
 342
 343 void
 344 tcp_input(m, off0, proto)
 345         struct mbuf *m;
 346         int off0, proto;
 347 {
 348         struct tcphdr *th;
 349         struct ip *ip = NULL;
 350         struct ipovly *ipov;
 351         struct inpcb *inp = NULL;
 352         u_char *optp = NULL;
 353         int optlen = 0;
 354         int len, tlen, off;
 355         int drop_hdrlen;
 356         struct tcpcb *tp = NULL;
 357         int thflags;
 358         struct socket *so = 0;
 359         int todrop, acked, ourfinisacked, needoutput = 0;
 360         u_long tiwin;
 361         struct tcpopt to;               /* options in this segment */
 362         struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
 363         struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
 364         struct sockaddr_in *next_hop = NULL;
 365         int rstreason; /* For badport_bandlim accounting purposes */
 366         struct ip6_hdr *ip6 = NULL;
 367 #ifdef INET6
 368         int isipv6;
 369 #else
 370         const int isipv6 = 0;
 371 #endif
 372 #ifdef TCPDEBUG
 373         short ostate = 0;
 374 #endif
 375
 376         /* Grab info from MT_TAG mbufs prepended to the chain. */
 377         for (;m && m->m_type == MT_TAG; m = m->m_next) {
 378                 if (m->_m_tag_id == PACKET_TAG_IPFORWARD)
 379                         next_hop = (struct sockaddr_in *)m->m_hdr.mh_data;
 380         }
 381 #ifdef INET6
 382         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 383 #endif
 384         bzero((char *)&to, sizeof(to));
 385
 386         tcpstat.tcps_rcvtotal++;
 387
 388         if (isipv6) {
 389                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 390                 ip6 = mtod(m, struct ip6_hdr *);
 391                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 392                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 393                         tcpstat.tcps_rcvbadsum++;
 394                         goto drop;
 395                 }
 396                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 397
 398                 /*
 399                  * Be proactive about unspecified IPv6 address in source.
 400                  * As we use all-zero to indicate unbounded/unconnected pcb,
 401                  * unspecified IPv6 address can be used to confuse us.
 402                  *
 403                  * Note that packets with unspecified IPv6 destination is
 404                  * already dropped in ip6_input.
 405                  */
 406                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 407                         /* XXX stat */
 408                         goto drop;
 409                 }
 410         } else {
 411                 /*
 412                  * Get IP and TCP header together in first mbuf.
 413                  * Note: IP leaves IP header in first mbuf.
 414                  */
 415                 if (off0 > sizeof(struct ip)) {
 416                         ip_stripoptions(m, (struct mbuf *)0);
 417                         off0 = sizeof(struct ip);
 418                 }
 419                 if (m->m_len < sizeof(struct tcpiphdr)) {
 420                         if ((m = m_pullup(m, sizeof(struct tcpiphdr))) == 0) {
 421                                 tcpstat.tcps_rcvshort++;
 422                                 return;
 423                         }
 424                 }
 425                 ip = mtod(m, struct ip *);
 426                 ipov = (struct ipovly *)ip;
 427                 th = (struct tcphdr *)((caddr_t)ip + off0);
 428                 tlen = ip->ip_len;
 429
 430                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 431                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 432                                 th->th_sum = m->m_pkthdr.csum_data;
 433                         else
 434                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 435                                                 ip->ip_dst.s_addr,
 436                                                 htonl(m->m_pkthdr.csum_data +
 437                                                         ip->ip_len +
 438                                                         IPPROTO_TCP));
 439                         th->th_sum ^= 0xffff;
 440                 } else {
 441                         /*
 442                          * Checksum extended TCP header and data.
 443                          */
 444                         len = sizeof(struct ip) + tlen;
 445                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 446                         ipov->ih_len = (u_short)tlen;
 447                         ipov->ih_len = htons(ipov->ih_len);
 448                         th->th_sum = in_cksum(m, len);
 449                 }
 450                 if (th->th_sum) {
 451                         tcpstat.tcps_rcvbadsum++;
 452                         goto drop;
 453                 }
 454 #ifdef INET6
 455                 /* Re-initialization for later version check */
 456                 ip->ip_v = IPVERSION;
 457 #endif
 458         }
 459
 460         /*
 461          * Check that TCP offset makes sense,
 462          * pull out TCP options and adjust length.              XXX
 463          */
 464         off = th->th_off << 2;
 465         if (off < sizeof(struct tcphdr) || off > tlen) {
 466                 tcpstat.tcps_rcvbadoff++;
 467                 goto drop;
 468         }
 469         tlen -= off;    /* tlen is used instead of ti->ti_len */
 470         if (off > sizeof(struct tcphdr)) {
 471                 if (isipv6) {
 472                         IP6_EXTHDR_CHECK(m, off0, off, );
 473                         ip6 = mtod(m, struct ip6_hdr *);
 474                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 475                 } else {
 476                         if (m->m_len < sizeof(struct ip) + off) {
 477                                 if ((m = m_pullup(m, sizeof(struct ip) + off))
 478                                                 == 0) {
 479                                         tcpstat.tcps_rcvshort++;
 480                                         return;
 481                                 }
 482                                 ip = mtod(m, struct ip *);
 483                                 ipov = (struct ipovly *)ip;
 484                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 485                         }
 486                 }
 487                 optlen = off - sizeof(struct tcphdr);
 488                 optp = (u_char *)(th + 1);
 489         }
 490         thflags = th->th_flags;
 491
 492 #ifdef TCP_DROP_SYNFIN
 493         /*
 494          * If the drop_synfin option is enabled, drop all packets with
 495          * both the SYN and FIN bits set. This prevents e.g. nmap from
 496          * identifying the TCP/IP stack.
 497          *
 498          * This is a violation of the TCP specification.
 499          */
 500         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 501                 goto drop;
 502 #endif
 503
 504         /*
 505          * Convert TCP protocol specific fields to host format.
 506          */
 507         th->th_seq = ntohl(th->th_seq);
 508         th->th_ack = ntohl(th->th_ack);
 509         th->th_win = ntohs(th->th_win);
 510         th->th_urp = ntohs(th->th_urp);
 511
 512         /*
 513          * Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
 514          * until after ip6_savecontrol() is called and before other functions
 515          * which don't want those proto headers.
 516          * Because ip6_savecontrol() is going to parse the mbuf to
 517          * search for data to be passed up to user-land, it wants mbuf
 518          * parameters to be unchanged.
 519          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 520          * latest version of the advanced API (20020110).
 521          */
 522         drop_hdrlen = off0 + off;
 523
 524         /*
 525          * Locate pcb for segment.
 526          */
 527 findpcb:
 528         /* IPFIREWALL_FORWARD section */
 529         if (next_hop != NULL && isipv6 == 0) {  /* IPv6 support is not yet */
 530                 /*
 531                  * Transparently forwarded. Pretend to be the destination.
 532                  * already got one like this?
 533                  */
 534                 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
 535                                         ip->ip_dst, th->th_dport,
 536                                         0, m->m_pkthdr.rcvif);
 537                 if (!inp) {
 538                         /* It's new.  Try find the ambushing socket. */
 539                         inp = in_pcblookup_hash(&tcbinfo,
 540                                                 ip->ip_src, th->th_sport,
 541                                                 next_hop->sin_addr,
 542                                                 next_hop->sin_port ?
 543                                                     ntohs(next_hop->sin_port) :
 544                                                     th->th_dport,
 545                                                 1, m->m_pkthdr.rcvif);
 546                 }
 547         } else {
 548                 if (isipv6)
 549                         inp = in6_pcblookup_hash(&tcbinfo,
 550                                                  &ip6->ip6_src, th->th_sport,
 551                                                  &ip6->ip6_dst, th->th_dport,
 552                                                  1, m->m_pkthdr.rcvif);
 553                 else
 554                         inp = in_pcblookup_hash(&tcbinfo,
 555                                                 ip->ip_src, th->th_sport,
 556                                                 ip->ip_dst, th->th_dport,
 557                                                 1, m->m_pkthdr.rcvif);
 558       }
 559
 560 #ifdef IPSEC
 561         if (isipv6) {
 562                 if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
 563                         ipsec6stat.in_polvio++;
 564                         goto drop;
 565                 }
 566         } else {
 567                 if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
 568                         ipsecstat.in_polvio++;
 569                         goto drop;
 570                 }
 571         }
 572 #endif
 573 #ifdef FAST_IPSEC
 574         if (isipv6) {
 575                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 576                         goto drop;
 577                 }
 578         } else {
 579                 if (inp != NULL && ipsec4_in_reject(m, inp)) {
 580                         goto drop;
 581                 }
 582         }
 583 #endif
 584
 585         /*
 586          * If the state is CLOSED (i.e., TCB does not exist) then
 587          * all data in the incoming segment is discarded.
 588          * If the TCB exists but is in CLOSED state, it is embryonic,
 589          * but should either do a listen or a connect soon.
 590          */
 591         if (inp == NULL) {
 592                 if (log_in_vain) {
 593 #ifdef INET6
 594                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 595 #else
 596                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 597 #endif
 598                         if (isipv6) {
 599                                 strcpy(dbuf, "[");
 600                                 strcpy(sbuf, "[");
 601                                 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
 602                                 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
 603                                 strcat(dbuf, "]");
 604                                 strcat(sbuf, "]");
 605                         } else {
 606                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 607                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 608                         }
 609                         switch (log_in_vain) {
 610                         case 1:
 611                                 if ((thflags & TH_SYN) == 0)
 612                                         break;
 613                         case 2:
 614                                 log(LOG_INFO,
 615                                     "Connection attempt to TCP %s:%d "
 616                                     "from %s:%d flags:0x%02x\n",
 617                                     dbuf, ntohs(th->th_dport), sbuf,
 618                                     ntohs(th->th_sport), thflags);
 619                                 break;
 620                         default:
 621                                 break;
 622                         }
 623                 }
 624                 if (blackhole) {
 625                         switch (blackhole) {
 626                         case 1:
 627                                 if (thflags & TH_SYN)
 628                                         goto drop;
 629                                 break;
 630                         case 2:
 631                                 goto drop;
 632                         default:
 633                                 goto drop;
 634                         }
 635                 }
 636                 rstreason = BANDLIM_RST_CLOSEDPORT;
 637                 goto dropwithreset;
 638         }
 639         tp = intotcpcb(inp);
 640         if (tp == NULL) {
 641                 rstreason = BANDLIM_RST_CLOSEDPORT;
 642                 goto dropwithreset;
 643         }
 644         if (tp->t_state == TCPS_CLOSED)
 645                 goto drop;
 646
 647         /* Unscale the window into a 32-bit value. */
 648         if ((thflags & TH_SYN) == 0)
 649                 tiwin = th->th_win << tp->snd_scale;
 650         else
 651                 tiwin = th->th_win;
 652
 653         so = inp->inp_socket;
 654
 655 #ifdef TCPDEBUG
 656         if (so->so_options & SO_DEBUG) {
 657                 ostate = tp->t_state;
 658                 if (isipv6)
 659                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 660                 else
 661                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 662                 tcp_savetcp = *th;
 663         }
 664 #endif
 665
 666         if (so->so_options & SO_ACCEPTCONN) {
 667                 struct in_conninfo inc;
 668
 669 #ifdef INET6
 670                 inc.inc_isipv6 = isipv6;
 671 #endif
 672                 if (isipv6) {
 673                         inc.inc6_faddr = ip6->ip6_src;
 674                         inc.inc6_laddr = ip6->ip6_dst;
 675                         inc.inc6_route.ro_rt = NULL;            /* XXX */
 676                 } else {
 677                         inc.inc_faddr = ip->ip_src;
 678                         inc.inc_laddr = ip->ip_dst;
 679                         inc.inc_route.ro_rt = NULL;             /* XXX */
 680                 }
 681                 inc.inc_fport = th->th_sport;
 682                 inc.inc_lport = th->th_dport;
 683
 684                 /*
 685                  * If the state is LISTEN then ignore segment if it contains
 686                  * a RST.  If the segment contains an ACK then it is bad and
 687                  * send a RST.  If it does not contain a SYN then it is not
 688                  * interesting; drop it.
 689                  *
 690                  * If the state is SYN_RECEIVED (syncache) and seg contains
 691                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 692                  * contains a RST, check the sequence number to see if it
 693                  * is a valid reset segment.
 694                  */
 695                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 696                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 697                                 if (!syncache_expand(&inc, th, &so, m)) {
 698                                         /*
 699                                          * No syncache entry, or ACK was not
 700                                          * for our SYN/ACK.  Send a RST.
 701                                          */
 702                                         tcpstat.tcps_badsyn++;
 703                                         rstreason = BANDLIM_RST_OPENPORT;
 704                                         goto dropwithreset;
 705                                 }
 706                                 if (so == NULL)
 707                                         /*
 708                                          * Could not complete 3-way handshake,
 709                                          * connection is being closed down, and
 710                                          * syncache will free mbuf.
 711                                          */
 712                                         return;
 713                                 /*
 714                                  * Socket is created in state SYN_RECEIVED.
 715                                  * Continue processing segment.
 716                                  */
 717                                 inp = sotoinpcb(so);
 718                                 tp = intotcpcb(inp);
 719                                 /*
 720                                  * This is what would have happened in
 721                                  * tcp_output() when the SYN,ACK was sent.
 722                                  */
 723                                 tp->snd_up = tp->snd_una;
 724                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 725                                 tp->last_ack_sent = tp->rcv_nxt;
 726 /*
 727  * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
 728  * until the _second_ ACK is received:
 729  *    rcv SYN (set wscale opts)  --> send SYN/ACK, set snd_wnd = window.
 730  *    rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
 731  *        move to ESTAB, set snd_wnd to tiwin.
 732  */
 733                                 tp->snd_wnd = tiwin;    /* unscaled */
 734                                 goto after_listen;
 735                         }
 736                         if (thflags & TH_RST) {
 737                                 syncache_chkrst(&inc, th);
 738                                 goto drop;
 739                         }
 740                         if (thflags & TH_ACK) {
 741                                 syncache_badack(&inc);
 742                                 tcpstat.tcps_badsyn++;
 743                                 rstreason = BANDLIM_RST_OPENPORT;
 744                                 goto dropwithreset;
 745                         }
 746                         goto drop;
 747                 }
 748
 749                 /*
 750                  * Segment's flags are (SYN) or (SYN|FIN).
 751                  */
 752 #ifdef INET6
 753                 /*
 754                  * If deprecated address is forbidden,
 755                  * we do not accept SYN to deprecated interface
 756                  * address to prevent any new inbound connection from
 757                  * getting established.
 758                  * When we do not accept SYN, we send a TCP RST,
 759                  * with deprecated source address (instead of dropping
 760                  * it).  We compromise it as it is much better for peer
 761                  * to send a RST, and RST will be the final packet
 762                  * for the exchange.
 763                  *
 764                  * If we do not forbid deprecated addresses, we accept
 765                  * the SYN packet.  RFC2462 does not suggest dropping
 766                  * SYN in this case.
 767                  * If we decipher RFC2462 5.5.4, it says like this:
 768                  * 1. use of deprecated addr with existing
 769                  *    communication is okay - "SHOULD continue to be
 770                  *    used"
 771                  * 2. use of it with new communication:
 772                  *   (2a) "SHOULD NOT be used if alternate address
 773                  *        with sufficient scope is available"
 774                  *   (2b) nothing mentioned otherwise.
 775                  * Here we fall into (2b) case as we have no choice in
 776                  * our source address selection - we must obey the peer.
 777                  *
 778                  * The wording in RFC2462 is confusing, and there are
 779                  * multiple description text for deprecated address
 780                  * handling - worse, they are not exactly the same.
 781                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 782                  */
 783                 if (isipv6 && !ip6_use_deprecated) {
 784                         struct in6_ifaddr *ia6;
 785
 786                         if ((ia6 = ip6_getdstifaddr(m)) &&
 787                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 788                                 tp = NULL;
 789                                 rstreason = BANDLIM_RST_OPENPORT;
 790                                 goto dropwithreset;
 791                         }
 792                 }
 793 #endif
 794                 /*
 795                  * If it is from this socket, drop it, it must be forged.
 796                  * Don't bother responding if the destination was a broadcast.
 797                  */
 798                 if (th->th_dport == th->th_sport) {
 799                         if (isipv6) {
 800                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 801                                                        &ip6->ip6_src))
 802                                         goto drop;
 803                         } else {
 804                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 805                                         goto drop;
 806                         }
 807                 }
 808                 /*
 809                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 810                  *
 811                  * Note that it is quite possible to receive unicast
 812                  * link-layer packets with a broadcast IP address. Use
 813                  * in_broadcast() to find them.
 814                  */
 815                 if (m->m_flags & (M_BCAST|M_MCAST))
 816                         goto drop;
 817                 if (isipv6) {
 818                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 819                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 820                                 goto drop;
 821                 } else {
 822                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 823                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 824                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 825                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 826                                 goto drop;
 827                 }
 828                 /*
 829                  * SYN appears to be valid; create compressed TCP state
 830                  * for syncache, or perform t/tcp connection.
 831                  */
 832                 if (so->so_qlen <= so->so_qlimit) {
 833                         tcp_dooptions(&to, optp, optlen, 1);
 834                         if (!syncache_add(&inc, &to, th, &so, m))
 835                                 goto drop;
 836                         if (so == NULL)
 837                                 /*
 838                                  * Entry added to syncache, mbuf used to
 839                                  * send SYN,ACK packet.
 840                                  */
 841                                 return;
 842                         /*
 843                          * Segment passed TAO tests.
 844                          */
 845                         inp = sotoinpcb(so);
 846                         tp = intotcpcb(inp);
 847                         tp->snd_wnd = tiwin;
 848                         tp->t_starttime = ticks;
 849                         tp->t_state = TCPS_ESTABLISHED;
 850
 851                         /*
 852                          * If there is a FIN, or if there is data and the
 853                          * connection is local, then delay SYN,ACK(SYN) in
 854                          * the hope of piggy-backing it on a response
 855                          * segment.  Otherwise must send ACK now in case
 856                          * the other side is slow starting.
 857                          */
 858                         if (DELAY_ACK(tp) &&
 859                             ((thflags & TH_FIN) ||
 860                              (tlen != 0 &&
 861                               ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
 862                                (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
 863                                 callout_reset(tp->tt_delack, tcp_delacktime,
 864                                                 tcp_timer_delack, tp);
 865                                 tp->t_flags |= TF_NEEDSYN;
 866                         } else
 867                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
 868
 869                         tcpstat.tcps_connects++;
 870                         soisconnected(so);
 871                         goto trimthenstep6;
 872                 }
 873                 goto drop;
 874         }
 875 after_listen:
 876
 877 /* XXX temp debugging */
 878         /* should not happen - syncache should pick up these connections */
 879         if (tp->t_state == TCPS_LISTEN)
 880                 panic("tcp_input: TCPS_LISTEN");
 881
 882         /*
 883          * Segment received on connection.
 884          * Reset idle time and keep-alive timer.
 885          */
 886         tp->t_rcvtime = ticks;
 887         if (TCPS_HAVEESTABLISHED(tp->t_state))
 888                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 889
 890         /*
 891          * Process options.
 892          * XXX this is tradtitional behavior, may need to be cleaned up.
 893          */
 894         tcp_dooptions(&to, optp, optlen, thflags & TH_SYN);
 895         if (thflags & TH_SYN) {
 896                 if (to.to_flags & TOF_SCALE) {
 897                         tp->t_flags |= TF_RCVD_SCALE;
 898                         tp->requested_s_scale = to.to_requested_s_scale;
 899                 }
 900                 if (to.to_flags & TOF_TS) {
 901                         tp->t_flags |= TF_RCVD_TSTMP;
 902                         tp->ts_recent = to.to_tsval;
 903                         tp->ts_recent_age = ticks;
 904                 }
 905                 if (to.to_flags & (TOF_CC|TOF_CCNEW))
 906                         tp->t_flags |= TF_RCVD_CC;
 907                 if (to.to_flags & TOF_MSS)
 908                         tcp_mss(tp, to.to_mss);
 909         }
 910
 911         /*
 912          * Header prediction: check for the two common cases
 913          * of a uni-directional data xfer.  If the packet has
 914          * no control flags, is in-sequence, the window didn't
 915          * change and we're not retransmitting, it's a
 916          * candidate.  If the length is zero and the ack moved
 917          * forward, we're the sender side of the xfer.  Just
 918          * free the data acked & wake any higher level process
 919          * that was blocked waiting for space.  If the length
 920          * is non-zero and the ack didn't move, we're the
 921          * receiver side.  If we're getting packets in-order
 922          * (the reassembly queue is empty), add the data to
 923          * the socket buffer and note that we need a delayed ack.
 924          * Make sure that the hidden state-flags are also off.
 925          * Since we check for TCPS_ESTABLISHED above, it can only
 926          * be TH_NEEDSYN.
 927          */
 928         if (tp->t_state == TCPS_ESTABLISHED &&
 929             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 930             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
 931             ((to.to_flags & TOF_TS) == 0 ||
 932              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
 933             /*
 934              * Using the CC option is compulsory if once started:
 935              *   the segment is OK if no T/TCP was negotiated or
 936              *   if the segment has a CC option equal to CCrecv
 937              */
 938             ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
 939              ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
 940             th->th_seq == tp->rcv_nxt &&
 941             tiwin && tiwin == tp->snd_wnd &&
 942             tp->snd_nxt == tp->snd_max) {
 943
 944                 /*
 945                  * If last ACK falls within this segment's sequence numbers,
 946                  * record the timestamp.
 947                  * NOTE that the test is modified according to the latest
 948                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
 949                  */
 950                 if ((to.to_flags & TOF_TS) != 0 &&
 951                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
 952                         tp->ts_recent_age = ticks;
 953                         tp->ts_recent = to.to_tsval;
 954                 }
 955
 956                 if (tlen == 0) {
 957                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
 958                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
 959                             tp->snd_cwnd >= tp->snd_wnd &&
 960                             ((!tcp_do_newreno &&
 961                               tp->t_dupacks < tcprexmtthresh) ||
 962                              (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) {
 963                                 /*
 964                                  * this is a pure ack for outstanding data.
 965                                  */
 966                                 ++tcpstat.tcps_predack;
 967                                 /*
 968                                  * "bad retransmit" recovery
 969                                  *
 970                                  * If Eifel detection applies, then
 971                                  * it is deterministic, so use it
 972                                  * unconditionally over the old heuristic.
 973                                  * Otherwise, fall back to the old heuristic.
 974                                  */
 975                                 if (tcp_do_eifel_detect &&
 976                                     (to.to_flags & TOF_TS) && to.to_tsecr &&
 977                                     (tp->t_flags & TF_FIRSTACCACK)) {
 978                                         /* Eifel detection applicable. */
 979                                         if (to.to_tsecr < tp->t_rexmtTS) {
 980                                                 tcp_revert_congestion_state(tp);
 981                                                 ++tcpstat.tcps_eifeldetected;
 982                                         }
 983                                 } else if (tp->t_rxtshift == 1 &&
 984                                            ticks < tp->t_badrxtwin) {
 985                                         tcp_revert_congestion_state(tp);
 986                                         ++tcpstat.tcps_rttdetected;
 987                                 }
 988                                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT);
 989                                 /*
 990                                  * Recalculate the retransmit timer / rtt.
 991                                  *
 992                                  * Some machines (certain windows boxes)
 993                                  * send broken timestamp replies during the
 994                                  * SYN+ACK phase, ignore timestamps of 0.
 995                                  */
 996                                 if ((to.to_flags & TOF_TS) != 0 &&
 997                                     to.to_tsecr) {
 998                                         tcp_xmit_timer(tp,
 999                                             ticks - to.to_tsecr + 1);
1000                                 } else if (tp->t_rtttime &&
1001                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
1002                                         tcp_xmit_timer(tp,
1003                                                        ticks - tp->t_rtttime);
1004                                 }
1005                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1006                                 acked = th->th_ack - tp->snd_una;
1007                                 tcpstat.tcps_rcvackpack++;
1008                                 tcpstat.tcps_rcvackbyte += acked;
1009                                 sbdrop(&so->so_snd, acked);
1010                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1011                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1012                                         tp->snd_recover = th->th_ack - 1;
1013                                 tp->snd_una = th->th_ack;
1014                                 tp->t_dupacks = 0;
1015                                 m_freem(m);
1016                                 ND6_HINT(tp); /* some progress has been done */
1017
1018                                 /*
1019                                  * If all outstanding data are acked, stop
1020                                  * retransmit timer, otherwise restart timer
1021                                  * using current (possibly backed-off) value.
1022                                  * If process is waiting for space,
1023                                  * wakeup/selwakeup/signal.  If data
1024                                  * are ready to send, let tcp_output
1025                                  * decide between more output or persist.
1026                                  */
1027                                 if (tp->snd_una == tp->snd_max)
1028                                         callout_stop(tp->tt_rexmt);
1029                                 else if (!callout_active(tp->tt_persist))
1030                                         callout_reset(tp->tt_rexmt,
1031                                                       tp->t_rxtcur,
1032                                                       tcp_timer_rexmt, tp);
1033
1034                                 sowwakeup(so);
1035                                 if (so->so_snd.sb_cc)
1036                                         (void) tcp_output(tp);
1037                                 return;
1038                         }
1039                 } else if (th->th_ack == tp->snd_una &&
1040                     LIST_EMPTY(&tp->t_segq) &&
1041                     tlen <= sbspace(&so->so_rcv)) {
1042                         /*
1043                          * this is a pure, in-sequence data packet
1044                          * with nothing on the reassembly queue and
1045                          * we have enough buffer space to take it.
1046                          */
1047                         ++tcpstat.tcps_preddat;
1048                         tp->rcv_nxt += tlen;
1049                         tcpstat.tcps_rcvpack++;
1050                         tcpstat.tcps_rcvbyte += tlen;
1051                         ND6_HINT(tp);   /* some progress has been done */
1052                         /*
1053                          * Add data to socket buffer.
1054                          */
1055                         if (so->so_state & SS_CANTRCVMORE) {
1056                                 m_freem(m);
1057                         } else {
1058                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1059                                 sbappend(&so->so_rcv, m);
1060                         }
1061                         sorwakeup(so);
1062                         if (DELAY_ACK(tp)) {
1063                                 callout_reset(tp->tt_delack, tcp_delacktime,
1064                                     tcp_timer_delack, tp);
1065                         } else {
1066                                 tp->t_flags |= TF_ACKNOW;
1067                                 tcp_output(tp);
1068                         }
1069                         return;
1070                 }
1071         }
1072
1073         /*
1074          * Calculate amount of space in receive window,
1075          * and then do TCP input processing.
1076          * Receive window is amount of space in rcv queue,
1077          * but not less than advertised window.
1078          */
1079         { int win;
1080
1081         win = sbspace(&so->so_rcv);
1082         if (win < 0)
1083                 win = 0;
1084         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1085         }
1086
1087         switch (tp->t_state) {
1088
1089         /*
1090          * If the state is SYN_RECEIVED:
1091          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1092          */
1093         case TCPS_SYN_RECEIVED:
1094                 if ((thflags & TH_ACK) &&
1095                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1096                      SEQ_GT(th->th_ack, tp->snd_max))) {
1097                                 rstreason = BANDLIM_RST_OPENPORT;
1098                                 goto dropwithreset;
1099                 }
1100                 break;
1101
1102         /*
1103          * If the state is SYN_SENT:
1104          *      if seg contains an ACK, but not for our SYN, drop the input.
1105          *      if seg contains a RST, then drop the connection.
1106          *      if seg does not contain SYN, then drop it.
1107          * Otherwise this is an acceptable SYN segment
1108          *      initialize tp->rcv_nxt and tp->irs
1109          *      if seg contains ack then advance tp->snd_una
1110          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1111          *      arrange for segment to be acked (eventually)
1112          *      continue processing rest of data/controls, beginning with URG
1113          */
1114         case TCPS_SYN_SENT:
1115                 if ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL) {
1116                         taop = &tao_noncached;
1117                         bzero(taop, sizeof(*taop));
1118                 }
1119
1120                 if ((thflags & TH_ACK) &&
1121                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1122                      SEQ_GT(th->th_ack, tp->snd_max))) {
1123                         /*
1124                          * If we have a cached CCsent for the remote host,
1125                          * hence we haven't just crashed and restarted,
1126                          * do not send a RST.  This may be a retransmission
1127                          * from the other side after our earlier ACK was lost.
1128                          * Our new SYN, when it arrives, will serve as the
1129                          * needed ACK.
1130                          */
1131                         if (taop->tao_ccsent != 0)
1132                                 goto drop;
1133                         else {
1134                                 rstreason = BANDLIM_UNLIMITED;
1135                                 goto dropwithreset;
1136                         }
1137                 }
1138                 if (thflags & TH_RST) {
1139                         if (thflags & TH_ACK)
1140                                 tp = tcp_drop(tp, ECONNREFUSED);
1141                         goto drop;
1142                 }
1143                 if ((thflags & TH_SYN) == 0)
1144                         goto drop;
1145                 tp->snd_wnd = th->th_win;       /* initial send window */
1146                 tp->cc_recv = to.to_cc;         /* foreign CC */
1147
1148                 tp->irs = th->th_seq;
1149                 tcp_rcvseqinit(tp);
1150                 if (thflags & TH_ACK) {
1151                         /*
1152                          * Our SYN was acked.  If segment contains CC.ECHO
1153                          * option, check it to make sure this segment really
1154                          * matches our SYN.  If not, just drop it as old
1155                          * duplicate, but send an RST if we're still playing
1156                          * by the old rules.  If no CC.ECHO option, make sure
1157                          * we don't get fooled into using T/TCP.
1158                          */
1159                         if (to.to_flags & TOF_CCECHO) {
1160                                 if (tp->cc_send != to.to_ccecho) {
1161                                         if (taop->tao_ccsent != 0)
1162                                                 goto drop;
1163                                         else {
1164                                                 rstreason = BANDLIM_UNLIMITED;
1165                                                 goto dropwithreset;
1166                                         }
1167                                 }
1168                         } else
1169                                 tp->t_flags &= ~TF_RCVD_CC;
1170                         tcpstat.tcps_connects++;
1171                         soisconnected(so);
1172                         /* Do window scaling on this connection? */
1173                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1174                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1175                                 tp->snd_scale = tp->requested_s_scale;
1176                                 tp->rcv_scale = tp->request_r_scale;
1177                         }
1178                         /* Segment is acceptable, update cache if undefined. */
1179                         if (taop->tao_ccsent == 0)
1180                                 taop->tao_ccsent = to.to_ccecho;
1181
1182                         tp->rcv_adv += tp->rcv_wnd;
1183                         tp->snd_una++;          /* SYN is acked */
1184                         /*
1185                          * If there's data, delay ACK; if there's also a FIN
1186                          * ACKNOW will be turned on later.
1187                          */
1188                         if (DELAY_ACK(tp) && tlen != 0)
1189                                 callout_reset(tp->tt_delack, tcp_delacktime,
1190                                     tcp_timer_delack, tp);
1191                         else
1192                                 tp->t_flags |= TF_ACKNOW;
1193                         /*
1194                          * Received <SYN,ACK> in SYN_SENT[*] state.
1195                          * Transitions:
1196                          *      SYN_SENT  --> ESTABLISHED
1197                          *      SYN_SENT* --> FIN_WAIT_1
1198                          */
1199                         tp->t_starttime = ticks;
1200                         if (tp->t_flags & TF_NEEDFIN) {
1201                                 tp->t_state = TCPS_FIN_WAIT_1;
1202                                 tp->t_flags &= ~TF_NEEDFIN;
1203                                 thflags &= ~TH_SYN;
1204                         } else {
1205                                 tp->t_state = TCPS_ESTABLISHED;
1206                                 callout_reset(tp->tt_keep, tcp_keepidle,
1207                                               tcp_timer_keep, tp);
1208                         }
1209                 } else {
1210                         /*
1211                          * Received initial SYN in SYN-SENT[*] state =>
1212                          * simultaneous open.  If segment contains CC option
1213                          * and there is a cached CC, apply TAO test.
1214                          * If it succeeds, connection is * half-synchronized.
1215                          * Otherwise, do 3-way handshake:
1216                          *        SYN-SENT -> SYN-RECEIVED
1217                          *        SYN-SENT* -> SYN-RECEIVED*
1218                          * If there was no CC option, clear cached CC value.
1219                          */
1220                         tp->t_flags |= TF_ACKNOW;
1221                         callout_stop(tp->tt_rexmt);
1222                         if (to.to_flags & TOF_CC) {
1223                                 if (taop->tao_cc != 0 &&
1224                                     CC_GT(to.to_cc, taop->tao_cc)) {
1225                                         /*
1226                                          * update cache and make transition:
1227                                          *        SYN-SENT -> ESTABLISHED*
1228                                          *        SYN-SENT* -> FIN-WAIT-1*
1229                                          */
1230                                         taop->tao_cc = to.to_cc;
1231                                         tp->t_starttime = ticks;
1232                                         if (tp->t_flags & TF_NEEDFIN) {
1233                                                 tp->t_state = TCPS_FIN_WAIT_1;
1234                                                 tp->t_flags &= ~TF_NEEDFIN;
1235                                         } else {
1236                                                 tp->t_state = TCPS_ESTABLISHED;
1237                                                 callout_reset(tp->tt_keep,
1238                                                               tcp_keepidle,
1239                                                               tcp_timer_keep,
1240                                                               tp);
1241                                         }
1242                                         tp->t_flags |= TF_NEEDSYN;
1243                                 } else
1244                                         tp->t_state = TCPS_SYN_RECEIVED;
1245                         } else {
1246                                 /* CC.NEW or no option => invalidate cache */
1247                                 taop->tao_cc = 0;
1248                                 tp->t_state = TCPS_SYN_RECEIVED;
1249                         }
1250                 }
1251
1252 trimthenstep6:
1253                 /*
1254                  * Advance th->th_seq to correspond to first data byte.
1255                  * If data, trim to stay within window,
1256                  * dropping FIN if necessary.
1257                  */
1258                 th->th_seq++;
1259                 if (tlen > tp->rcv_wnd) {
1260                         todrop = tlen - tp->rcv_wnd;
1261                         m_adj(m, -todrop);
1262                         tlen = tp->rcv_wnd;
1263                         thflags &= ~TH_FIN;
1264                         tcpstat.tcps_rcvpackafterwin++;
1265                         tcpstat.tcps_rcvbyteafterwin += todrop;
1266                 }
1267                 tp->snd_wl1 = th->th_seq - 1;
1268                 tp->rcv_up = th->th_seq;
1269                 /*
1270                  * Client side of transaction: already sent SYN and data.
1271                  * If the remote host used T/TCP to validate the SYN,
1272                  * our data will be ACK'd; if so, enter normal data segment
1273                  * processing in the middle of step 5, ack processing.
1274                  * Otherwise, goto step 6.
1275                  */
1276                 if (thflags & TH_ACK)
1277                         goto process_ACK;
1278
1279                 goto step6;
1280
1281         /*
1282          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1283          *      if segment contains a SYN and CC [not CC.NEW] option:
1284          *              if state == TIME_WAIT and connection duration > MSL,
1285          *                  drop packet and send RST;
1286          *
1287          *              if SEG.CC > CCrecv then is new SYN, and can implicitly
1288          *                  ack the FIN (and data) in retransmission queue.
1289          *                  Complete close and delete TCPCB.  Then reprocess
1290          *                  segment, hoping to find new TCPCB in LISTEN state;
1291          *
1292          *              else must be old SYN; drop it.
1293          *      else do normal processing.
1294          */
1295         case TCPS_LAST_ACK:
1296         case TCPS_CLOSING:
1297         case TCPS_TIME_WAIT:
1298                 if ((thflags & TH_SYN) &&
1299                     (to.to_flags & TOF_CC) && tp->cc_recv != 0) {
1300                         if (tp->t_state == TCPS_TIME_WAIT &&
1301                                         (ticks - tp->t_starttime) > tcp_msl) {
1302                                 rstreason = BANDLIM_UNLIMITED;
1303                                 goto dropwithreset;
1304                         }
1305                         if (CC_GT(to.to_cc, tp->cc_recv)) {
1306                                 tp = tcp_close(tp);
1307                                 goto findpcb;
1308                         }
1309                         else
1310                                 goto drop;
1311                 }
1312                 break;  /* continue normal processing */
1313         }
1314
1315         /*
1316          * States other than LISTEN or SYN_SENT.
1317          * First check the RST flag and sequence number since reset segments
1318          * are exempt from the timestamp and connection count tests.  This
1319          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1320          * below which allowed reset segments in half the sequence space
1321          * to fall though and be processed (which gives forged reset
1322          * segments with a random sequence number a 50 percent chance of
1323          * killing a connection).
1324          * Then check timestamp, if present.
1325          * Then check the connection count, if present.
1326          * Then check that at least some bytes of segment are within
1327          * receive window.  If segment begins before rcv_nxt,
1328          * drop leading data (and SYN); if nothing left, just ack.
1329          *
1330          *
1331          * If the RST bit is set, check the sequence number to see
1332          * if this is a valid reset segment.
1333          * RFC 793 page 37:
1334          *   In all states except SYN-SENT, all reset (RST) segments
1335          *   are validated by checking their SEQ-fields.  A reset is
1336          *   valid if its sequence number is in the window.
1337          * Note: this does not take into account delayed ACKs, so
1338          *   we should test against last_ack_sent instead of rcv_nxt.
1339          *   The sequence number in the reset segment is normally an
1340          *   echo of our outgoing acknowlegement numbers, but some hosts
1341          *   send a reset with the sequence number at the rightmost edge
1342          *   of our receive window, and we have to handle this case.
1343          * If we have multiple segments in flight, the intial reset
1344          * segment sequence numbers will be to the left of last_ack_sent,
1345          * but they will eventually catch up.
1346          * In any case, it never made sense to trim reset segments to
1347          * fit the receive window since RFC 1122 says:
1348          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1349          *
1350          *    A TCP SHOULD allow a received RST segment to include data.
1351          *
1352          *    DISCUSSION
1353          *         It has been suggested that a RST segment could contain
1354          *         ASCII text that encoded and explained the cause of the
1355          *         RST.  No standard has yet been established for such
1356          *         data.
1357          *
1358          * If the reset segment passes the sequence number test examine
1359          * the state:
1360          *    SYN_RECEIVED STATE:
1361          *      If passive open, return to LISTEN state.
1362          *      If active open, inform user that connection was refused.
1363          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1364          *      Inform user that connection was reset, and close tcb.
1365          *    CLOSING, LAST_ACK STATES:
1366          *      Close the tcb.
1367          *    TIME_WAIT STATE:
1368          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1369          *      RFC 1337.
1370          */
1371         if (thflags & TH_RST) {
1372                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1373                     SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1374                         switch (tp->t_state) {
1375
1376                         case TCPS_SYN_RECEIVED:
1377                                 so->so_error = ECONNREFUSED;
1378                                 goto close;
1379
1380                         case TCPS_ESTABLISHED:
1381                         case TCPS_FIN_WAIT_1:
1382                         case TCPS_FIN_WAIT_2:
1383                         case TCPS_CLOSE_WAIT:
1384                                 so->so_error = ECONNRESET;
1385                         close:
1386                                 tp->t_state = TCPS_CLOSED;
1387                                 tcpstat.tcps_drops++;
1388                                 tp = tcp_close(tp);
1389                                 break;
1390
1391                         case TCPS_CLOSING:
1392                         case TCPS_LAST_ACK:
1393                                 tp = tcp_close(tp);
1394                                 break;
1395
1396                         case TCPS_TIME_WAIT:
1397                                 break;
1398                         }
1399                 }
1400                 goto drop;
1401         }
1402
1403         /*
1404          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1405          * and it's less than ts_recent, drop it.
1406          */
1407         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1408             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1409
1410                 /* Check to see if ts_recent is over 24 days old.  */
1411                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1412                         /*
1413                          * Invalidate ts_recent.  If this segment updates
1414                          * ts_recent, the age will be reset later and ts_recent
1415                          * will get a valid value.  If it does not, setting
1416                          * ts_recent to zero will at least satisfy the
1417                          * requirement that zero be placed in the timestamp
1418                          * echo reply when ts_recent isn't valid.  The
1419                          * age isn't reset until we get a valid ts_recent
1420                          * because we don't want out-of-order segments to be
1421                          * dropped when ts_recent is old.
1422                          */
1423                         tp->ts_recent = 0;
1424                 } else {
1425                         tcpstat.tcps_rcvduppack++;
1426                         tcpstat.tcps_rcvdupbyte += tlen;
1427                         tcpstat.tcps_pawsdrop++;
1428                         if (tlen)
1429                                 goto dropafterack;
1430                         goto drop;
1431                 }
1432         }
1433
1434         /*
1435          * T/TCP mechanism
1436          *   If T/TCP was negotiated and the segment doesn't have CC,
1437          *   or if its CC is wrong then drop the segment.
1438          *   RST segments do not have to comply with this.
1439          */
1440         if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
1441             ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
1442                 goto dropafterack;
1443
1444         /*
1445          * In the SYN-RECEIVED state, validate that the packet belongs to
1446          * this connection before trimming the data to fit the receive
1447          * window.  Check the sequence number versus IRS since we know
1448          * the sequence numbers haven't wrapped.  This is a partial fix
1449          * for the "LAND" DoS attack.
1450          */
1451         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1452                 rstreason = BANDLIM_RST_OPENPORT;
1453                 goto dropwithreset;
1454         }
1455
1456         todrop = tp->rcv_nxt - th->th_seq;
1457         if (todrop > 0) {
1458                 if (thflags & TH_SYN) {
1459                         thflags &= ~TH_SYN;
1460                         th->th_seq++;
1461                         if (th->th_urp > 1)
1462                                 th->th_urp--;
1463                         else
1464                                 thflags &= ~TH_URG;
1465                         todrop--;
1466                 }
1467                 /*
1468                  * Following if statement from Stevens, vol. 2, p. 960.
1469                  */
1470                 if (todrop > tlen
1471                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1472                         /*
1473                          * Any valid FIN must be to the left of the window.
1474                          * At this point the FIN must be a duplicate or out
1475                          * of sequence; drop it.
1476                          */
1477                         thflags &= ~TH_FIN;
1478
1479                         /*
1480                          * Send an ACK to resynchronize and drop any data.
1481                          * But keep on processing for RST or ACK.
1482                          */
1483                         tp->t_flags |= TF_ACKNOW;
1484                         todrop = tlen;
1485                         tcpstat.tcps_rcvduppack++;
1486                         tcpstat.tcps_rcvdupbyte += todrop;
1487                 } else {
1488                         tcpstat.tcps_rcvpartduppack++;
1489                         tcpstat.tcps_rcvpartdupbyte += todrop;
1490                 }
1491                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1492                 th->th_seq += todrop;
1493                 tlen -= todrop;
1494                 if (th->th_urp > todrop)
1495                         th->th_urp -= todrop;
1496                 else {
1497                         thflags &= ~TH_URG;
1498                         th->th_urp = 0;
1499                 }
1500         }
1501
1502         /*
1503          * If new data are received on a connection after the
1504          * user processes are gone, then RST the other end.
1505          */
1506         if ((so->so_state & SS_NOFDREF) &&
1507             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1508                 tp = tcp_close(tp);
1509                 tcpstat.tcps_rcvafterclose++;
1510                 rstreason = BANDLIM_UNLIMITED;
1511                 goto dropwithreset;
1512         }
1513
1514         /*
1515          * If segment ends after window, drop trailing data
1516          * (and PUSH and FIN); if nothing left, just ACK.
1517          */
1518         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1519         if (todrop > 0) {
1520                 tcpstat.tcps_rcvpackafterwin++;
1521                 if (todrop >= tlen) {
1522                         tcpstat.tcps_rcvbyteafterwin += tlen;
1523                         /*
1524                          * If a new connection request is received
1525                          * while in TIME_WAIT, drop the old connection
1526                          * and start over if the sequence numbers
1527                          * are above the previous ones.
1528                          */
1529                         if (thflags & TH_SYN &&
1530                             tp->t_state == TCPS_TIME_WAIT &&
1531                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1532                                 tp = tcp_close(tp);
1533                                 goto findpcb;
1534                         }
1535                         /*
1536                          * If window is closed can only take segments at
1537                          * window edge, and have to drop data and PUSH from
1538                          * incoming segments.  Continue processing, but
1539                          * remember to ack.  Otherwise, drop segment
1540                          * and ack.
1541                          */
1542                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1543                                 tp->t_flags |= TF_ACKNOW;
1544                                 tcpstat.tcps_rcvwinprobe++;
1545                         } else
1546                                 goto dropafterack;
1547                 } else
1548                         tcpstat.tcps_rcvbyteafterwin += todrop;
1549                 m_adj(m, -todrop);
1550                 tlen -= todrop;
1551                 thflags &= ~(TH_PUSH|TH_FIN);
1552         }
1553
1554         /*
1555          * If last ACK falls within this segment's sequence numbers,
1556          * record its timestamp.
1557          * NOTE that the test is modified according to the latest
1558          * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1559          */
1560         if ((to.to_flags & TOF_TS) != 0 &&
1561             SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1562                 tp->ts_recent_age = ticks;
1563                 tp->ts_recent = to.to_tsval;
1564         }
1565
1566         /*
1567          * If a SYN is in the window, then this is an
1568          * error and we send an RST and drop the connection.
1569          */
1570         if (thflags & TH_SYN) {
1571                 tp = tcp_drop(tp, ECONNRESET);
1572                 rstreason = BANDLIM_UNLIMITED;
1573                 goto dropwithreset;
1574         }
1575
1576         /*
1577          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1578          * flag is on (half-synchronized state), then queue data for
1579          * later processing; else drop segment and return.
1580          */
1581         if ((thflags & TH_ACK) == 0) {
1582                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1583                     (tp->t_flags & TF_NEEDSYN))
1584                         goto step6;
1585                 else
1586                         goto drop;
1587         }
1588
1589         /*
1590          * Ack processing.
1591          */
1592         switch (tp->t_state) {
1593
1594         /*
1595          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1596          * ESTABLISHED state and continue processing.
1597          * The ACK was checked above.
1598          */
1599         case TCPS_SYN_RECEIVED:
1600
1601                 tcpstat.tcps_connects++;
1602                 soisconnected(so);
1603                 /* Do window scaling? */
1604                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1605                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1606                         tp->snd_scale = tp->requested_s_scale;
1607                         tp->rcv_scale = tp->request_r_scale;
1608                 }
1609                 /*
1610                  * Upon successful completion of 3-way handshake,
1611                  * update cache.CC if it was undefined, pass any queued
1612                  * data to the user, and advance state appropriately.
1613                  */
1614                 if ((taop = tcp_gettaocache(&inp->inp_inc)) != NULL &&
1615                     taop->tao_cc == 0)
1616                         taop->tao_cc = tp->cc_recv;
1617
1618                 /*
1619                  * Make transitions:
1620                  *      SYN-RECEIVED  -> ESTABLISHED
1621                  *      SYN-RECEIVED* -> FIN-WAIT-1
1622                  */
1623                 tp->t_starttime = ticks;
1624                 if (tp->t_flags & TF_NEEDFIN) {
1625                         tp->t_state = TCPS_FIN_WAIT_1;
1626                         tp->t_flags &= ~TF_NEEDFIN;
1627                 } else {
1628                         tp->t_state = TCPS_ESTABLISHED;
1629                         callout_reset(tp->tt_keep, tcp_keepidle,
1630                                       tcp_timer_keep, tp);
1631                 }
1632                 /*
1633                  * If segment contains data or ACK, will call tcp_reass()
1634                  * later; if not, do so now to pass queued data to user.
1635                  */
1636                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1637                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1638                             (struct mbuf *)0);
1639                 tp->snd_wl1 = th->th_seq - 1;
1640                 /* fall into ... */
1641
1642         /*
1643          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1644          * ACKs.  If the ack is in the range
1645          *      tp->snd_una < th->th_ack <= tp->snd_max
1646          * then advance tp->snd_una to th->th_ack and drop
1647          * data from the retransmission queue.  If this ACK reflects
1648          * more up to date window information we update our window information.
1649          */
1650         case TCPS_ESTABLISHED:
1651         case TCPS_FIN_WAIT_1:
1652         case TCPS_FIN_WAIT_2:
1653         case TCPS_CLOSE_WAIT:
1654         case TCPS_CLOSING:
1655         case TCPS_LAST_ACK:
1656         case TCPS_TIME_WAIT:
1657
1658                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1659                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1660                                 tcpstat.tcps_rcvdupack++;
1661                                 /*
1662                                  * If we have outstanding data (other than
1663                                  * a window probe), this is a completely
1664                                  * duplicate ack (ie, window info didn't
1665                                  * change), the ack is the biggest we've
1666                                  * seen and we've seen exactly our rexmt
1667                                  * threshhold of them, assume a packet
1668                                  * has been dropped and retransmit it.
1669                                  * Kludge snd_nxt & the congestion
1670                                  * window so we send only this one
1671                                  * packet.
1672                                  *
1673                                  * We know we're losing at the current
1674                                  * window size so do congestion avoidance
1675                                  * (set ssthresh to half the current window
1676                                  * and pull our congestion window back to
1677                                  * the new ssthresh).
1678                                  *
1679                                  * Dup acks mean that packets have left the
1680                                  * network (they're now cached at the receiver)
1681                                  * so bump cwnd by the amount in the receiver
1682                                  * to keep a constant cwnd packets in the
1683                                  * network.
1684                                  */
1685                                 if (!callout_active(tp->tt_rexmt) ||
1686                                     th->th_ack != tp->snd_una)
1687                                         tp->t_dupacks = 0;
1688                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1689                                          (tcp_do_newreno &&
1690                                           IN_FASTRECOVERY(tp))) {
1691                                         tp->snd_cwnd += tp->t_maxseg;
1692                                         (void) tcp_output(tp);
1693                                         goto drop;
1694                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1695                                         tcp_seq onxt = tp->snd_nxt;
1696                                         u_int win;
1697                                         if (tcp_do_newreno &&
1698                                             SEQ_LEQ(th->th_ack,
1699                                                     tp->snd_recover)) {
1700                                                 tp->t_dupacks = 0;
1701                                                 break;
1702                                         }
1703                                         if (tcp_do_eifel_detect &&
1704                                             (tp->t_flags & TF_RCVD_TSTMP)) {
1705                                                 tcp_save_congestion_state(tp);
1706                                                 tp->t_flags |= TF_FASTREXMT;
1707                                         }
1708                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1709                                             2 / tp->t_maxseg;
1710                                         if (win < 2)
1711                                                 win = 2;
1712                                         tp->snd_ssthresh = win * tp->t_maxseg;
1713                                         ENTER_FASTRECOVERY(tp);
1714                                         tp->snd_recover = tp->snd_max;
1715                                         callout_stop(tp->tt_rexmt);
1716                                         tp->t_rtttime = 0;
1717                                         tp->snd_nxt = th->th_ack;
1718                                         tp->snd_cwnd = tp->t_maxseg;
1719                                         (void) tcp_output(tp);
1720                                         KASSERT(tp->snd_limited <= 2,
1721                                             ("tp->snd_limited too big"));
1722                                         tp->snd_cwnd = tp->snd_ssthresh +
1723                                             (tp->t_maxseg *
1724                                              (tp->t_dupacks - tp->snd_limited));
1725                                         if (SEQ_GT(onxt, tp->snd_nxt))
1726                                                 tp->snd_nxt = onxt;
1727                                         goto drop;
1728                                 } else if (tcp_do_limitedtransmit) {
1729                                         u_long oldcwnd = tp->snd_cwnd;
1730                                         tcp_seq oldsndmax = tp->snd_max;
1731                                         u_int sent;
1732                                         KASSERT(tp->t_dupacks == 1 ||
1733                                             tp->t_dupacks == 2,
1734                                             ("dupacks not 1 or 2"));
1735                                         if (tp->t_dupacks == 1)
1736                                                 tp->snd_limited = 0;
1737                                         tp->snd_cwnd =
1738                                             (tp->snd_nxt - tp->snd_una) +
1739                                             (tp->t_dupacks - tp->snd_limited) *
1740                                             tp->t_maxseg;
1741                                         (void) tcp_output(tp);
1742                                         sent = tp->snd_max - oldsndmax;
1743                                         if (sent > tp->t_maxseg) {
1744                                                 KASSERT(tp->snd_limited == 0 &&
1745                                                     tp->t_dupacks == 2,
1746                                                     ("sent too much"));
1747                                                 tp->snd_limited = 2;
1748                                         } else if (sent > 0)
1749                                                 ++tp->snd_limited;
1750                                         tp->snd_cwnd = oldcwnd;
1751                                         goto drop;
1752                                 }
1753                         } else
1754                                 tp->t_dupacks = 0;
1755                         break;
1756                 }
1757
1758                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
1759
1760                 /*
1761                  * If the congestion window was inflated to account
1762                  * for the other side's cached packets, retract it.
1763                  */
1764                 if (tcp_do_newreno) {
1765                         if (IN_FASTRECOVERY(tp)) {
1766                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1767                                         tcp_newreno_partial_ack(tp, th);
1768                                 } else {
1769                                         /*
1770                                          * Window inflation should have left us
1771                                          * with approximately snd_ssthresh
1772                                          * outstanding data.
1773                                          * But in case we would be inclined to
1774                                          * send a burst, better to do it via
1775                                          * the slow start mechanism.
1776                                          */
1777                                         if (SEQ_GT(th->th_ack +
1778                                                         tp->snd_ssthresh,
1779                                                    tp->snd_max))
1780                                                 tp->snd_cwnd = tp->snd_max -
1781                                                                 th->th_ack +
1782                                                                 tp->t_maxseg;
1783                                         else
1784                                                 tp->snd_cwnd = tp->snd_ssthresh;
1785                                 }
1786                         }
1787                 } else {
1788                         if (tp->t_dupacks >= tcprexmtthresh &&
1789                             tp->snd_cwnd > tp->snd_ssthresh)
1790                                 tp->snd_cwnd = tp->snd_ssthresh;
1791                 }
1792                 tp->t_dupacks = 0;
1793                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1794                         tcpstat.tcps_rcvacktoomuch++;
1795                         goto dropafterack;
1796                 }
1797                 /*
1798                  * If we reach this point, ACK is not a duplicate,
1799                  *     i.e., it ACKs something we sent.
1800                  */
1801                 if (tp->t_flags & TF_NEEDSYN) {
1802                         /*
1803                          * T/TCP: Connection was half-synchronized, and our
1804                          * SYN has been ACK'd (so connection is now fully
1805                          * synchronized).  Go to non-starred state,
1806                          * increment snd_una for ACK of SYN, and check if
1807                          * we can do window scaling.
1808                          */
1809                         tp->t_flags &= ~TF_NEEDSYN;
1810                         tp->snd_una++;
1811                         /* Do window scaling? */
1812                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1813                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1814                                 tp->snd_scale = tp->requested_s_scale;
1815                                 tp->rcv_scale = tp->request_r_scale;
1816                         }
1817                 }
1818
1819 process_ACK:
1820                 acked = th->th_ack - tp->snd_una;
1821                 tcpstat.tcps_rcvackpack++;
1822                 tcpstat.tcps_rcvackbyte += acked;
1823
1824                 /*
1825                  * If we just performed our first retransmit, and the ACK
1826                  * arrives within our recovery window, then it was a mistake
1827                  * to do the retransmit in the first place.  Recover our
1828                  * original cwnd and ssthresh, and proceed to transmit where
1829                  * we left off.
1830                  */
1831                 if (tcp_do_eifel_detect && acked &&
1832                     (to.to_flags & TOF_TS) && to.to_tsecr &&
1833                     (tp->t_flags & TF_FIRSTACCACK)) {
1834                         /* Eifel detection applicable. */
1835                         if (to.to_tsecr < tp->t_rexmtTS) {
1836                                 tcp_revert_congestion_state(tp);
1837                                 ++tcpstat.tcps_eifeldetected;
1838                         }
1839                 } else if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1840                         tcp_revert_congestion_state(tp);
1841                         ++tcpstat.tcps_rttdetected;
1842                 }
1843
1844                 /*
1845                  * If we have a timestamp reply, update smoothed
1846                  * round trip time.  If no timestamp is present but
1847                  * transmit timer is running and timed sequence
1848                  * number was acked, update smoothed round trip time.
1849                  * Since we now have an rtt measurement, cancel the
1850                  * timer backoff (cf., Phil Karn's retransmit alg.).
1851                  * Recompute the initial retransmit timer.
1852                  *
1853                  * Some machines (certain windows boxes) send broken
1854                  * timestamp replies during the SYN+ACK phase, ignore
1855                  * timestamps of 0.
1856                  */
1857                 if ((to.to_flags & TOF_TS) != 0 &&
1858                     to.to_tsecr) {
1859                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1860                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1861                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1862                 }
1863                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1864
1865                 /*
1866                  * If all outstanding data is acked, stop retransmit
1867                  * timer and remember to restart (more output or persist).
1868                  * If there is more data to be acked, restart retransmit
1869                  * timer, using current (possibly backed-off) value.
1870                  */
1871                 if (th->th_ack == tp->snd_max) {
1872                         callout_stop(tp->tt_rexmt);
1873                         needoutput = 1;
1874                 } else if (!callout_active(tp->tt_persist))
1875                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1876                                       tcp_timer_rexmt, tp);
1877
1878                 /*
1879                  * If no data (only SYN) was ACK'd,
1880                  *    skip rest of ACK processing.
1881                  */
1882                 if (acked == 0)
1883                         goto step6;
1884
1885                 /* Stop looking for an acceptable ACK since one was received. */
1886                 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT);
1887
1888                 /*
1889                  * When new data is acked, open the congestion window.
1890                  * If the window gives us less than ssthresh packets
1891                  * in flight, open exponentially (maxseg per packet).
1892                  * Otherwise open linearly: maxseg per window
1893                  * (maxseg^2 / cwnd per packet).
1894                  */
1895                 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) {
1896                         u_int cw = tp->snd_cwnd;
1897                         u_int incr = tp->t_maxseg;
1898                         if (cw > tp->snd_ssthresh)
1899                                 incr = incr * incr / cw;
1900                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
1901                 }
1902                 if (acked > so->so_snd.sb_cc) {
1903                         tp->snd_wnd -= so->so_snd.sb_cc;
1904                         sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
1905                         ourfinisacked = 1;
1906                 } else {
1907                         sbdrop(&so->so_snd, acked);
1908                         tp->snd_wnd -= acked;
1909                         ourfinisacked = 0;
1910                 }
1911                 sowwakeup(so);
1912                 /* detect una wraparound */
1913                 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) &&
1914                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
1915                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1916                         tp->snd_recover = th->th_ack - 1;
1917                 if (tcp_do_newreno && IN_FASTRECOVERY(tp) &&
1918                     SEQ_GEQ(th->th_ack, tp->snd_recover))
1919                         EXIT_FASTRECOVERY(tp);
1920                 tp->snd_una = th->th_ack;
1921                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1922                         tp->snd_nxt = tp->snd_una;
1923
1924                 switch (tp->t_state) {
1925
1926                 /*
1927                  * In FIN_WAIT_1 STATE in addition to the processing
1928                  * for the ESTABLISHED state if our FIN is now acknowledged
1929                  * then enter FIN_WAIT_2.
1930                  */
1931                 case TCPS_FIN_WAIT_1:
1932                         if (ourfinisacked) {
1933                                 /*
1934                                  * If we can't receive any more
1935                                  * data, then closing user can proceed.
1936                                  * Starting the timer is contrary to the
1937                                  * specification, but if we don't get a FIN
1938                                  * we'll hang forever.
1939                                  */
1940                                 if (so->so_state & SS_CANTRCVMORE) {
1941                                         soisdisconnected(so);
1942                                         callout_reset(tp->tt_2msl, tcp_maxidle,
1943                                                       tcp_timer_2msl, tp);
1944                                 }
1945                                 tp->t_state = TCPS_FIN_WAIT_2;
1946                         }
1947                         break;
1948
1949                 /*
1950                  * In CLOSING STATE in addition to the processing for
1951                  * the ESTABLISHED state if the ACK acknowledges our FIN
1952                  * then enter the TIME-WAIT state, otherwise ignore
1953                  * the segment.
1954                  */
1955                 case TCPS_CLOSING:
1956                         if (ourfinisacked) {
1957                                 tp->t_state = TCPS_TIME_WAIT;
1958                                 tcp_canceltimers(tp);
1959                                 /* Shorten TIME_WAIT [RFC-1644, p.28] */
1960                                 if (tp->cc_recv != 0 &&
1961                                     (ticks - tp->t_starttime) < tcp_msl)
1962                                         callout_reset(tp->tt_2msl,
1963                                                       tp->t_rxtcur *
1964                                                       TCPTV_TWTRUNC,
1965                                                       tcp_timer_2msl, tp);
1966                                 else
1967                                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1968                                                       tcp_timer_2msl, tp);
1969                                 soisdisconnected(so);
1970                         }
1971                         break;
1972
1973                 /*
1974                  * In LAST_ACK, we may still be waiting for data to drain
1975                  * and/or to be acked, as well as for the ack of our FIN.
1976                  * If our FIN is now acknowledged, delete the TCB,
1977                  * enter the closed state and return.
1978                  */
1979                 case TCPS_LAST_ACK:
1980                         if (ourfinisacked) {
1981                                 tp = tcp_close(tp);
1982                                 goto drop;
1983                         }
1984                         break;
1985
1986                 /*
1987                  * In TIME_WAIT state the only thing that should arrive
1988                  * is a retransmission of the remote FIN.  Acknowledge
1989                  * it and restart the finack timer.
1990                  */
1991                 case TCPS_TIME_WAIT:
1992                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
1993                                       tcp_timer_2msl, tp);
1994                         goto dropafterack;
1995                 }
1996         }
1997
1998 step6:
1999         /*
2000          * Update window information.
2001          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2002          */
2003         if ((thflags & TH_ACK) &&
2004             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2005             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2006              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2007                 /* keep track of pure window updates */
2008                 if (tlen == 0 &&
2009                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2010                         tcpstat.tcps_rcvwinupd++;
2011                 tp->snd_wnd = tiwin;
2012                 tp->snd_wl1 = th->th_seq;
2013                 tp->snd_wl2 = th->th_ack;
2014                 if (tp->snd_wnd > tp->max_sndwnd)
2015                         tp->max_sndwnd = tp->snd_wnd;
2016                 needoutput = 1;
2017         }
2018
2019         /*
2020          * Process segments with URG.
2021          */
2022         if ((thflags & TH_URG) && th->th_urp &&
2023             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2024                 /*
2025                  * This is a kludge, but if we receive and accept
2026                  * random urgent pointers, we'll crash in
2027                  * soreceive.  It's hard to imagine someone
2028                  * actually wanting to send this much urgent data.
2029                  */
2030                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2031                         th->th_urp = 0;                 /* XXX */
2032                         thflags &= ~TH_URG;             /* XXX */
2033                         goto dodata;                    /* XXX */
2034                 }
2035                 /*
2036                  * If this segment advances the known urgent pointer,
2037                  * then mark the data stream.  This should not happen
2038                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2039                  * a FIN has been received from the remote side.
2040                  * In these states we ignore the URG.
2041                  *
2042                  * According to RFC961 (Assigned Protocols),
2043                  * the urgent pointer points to the last octet
2044                  * of urgent data.  We continue, however,
2045                  * to consider it to indicate the first octet
2046                  * of data past the urgent section as the original
2047                  * spec states (in one of two places).
2048                  */
2049                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2050                         tp->rcv_up = th->th_seq + th->th_urp;
2051                         so->so_oobmark = so->so_rcv.sb_cc +
2052                             (tp->rcv_up - tp->rcv_nxt) - 1;
2053                         if (so->so_oobmark == 0)
2054                                 so->so_state |= SS_RCVATMARK;
2055                         sohasoutofband(so);
2056                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2057                 }
2058                 /*
2059                  * Remove out of band data so doesn't get presented to user.
2060                  * This can happen independent of advancing the URG pointer,
2061                  * but if two URG's are pending at once, some out-of-band
2062                  * data may creep in... ick.
2063                  */
2064                 if (th->th_urp <= (u_long)tlen
2065 #ifdef SO_OOBINLINE
2066                      && (so->so_options & SO_OOBINLINE) == 0
2067 #endif
2068                      )
2069                         tcp_pulloutofband(so, th, m,
2070                                 drop_hdrlen);   /* hdr drop is delayed */
2071         } else {
2072                 /*
2073                  * If no out of band data is expected,
2074                  * pull receive urgent pointer along
2075                  * with the receive window.
2076                  */
2077                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2078                         tp->rcv_up = tp->rcv_nxt;
2079         }
2080 dodata:                                                 /* XXX */
2081
2082         /*
2083          * Process the segment text, merging it into the TCP sequencing queue,
2084          * and arranging for acknowledgment of receipt if necessary.
2085          * This process logically involves adjusting tp->rcv_wnd as data
2086          * is presented to the user (this happens in tcp_usrreq.c,
2087          * case PRU_RCVD).  If a FIN has already been received on this
2088          * connection then we just ignore the text.
2089          */
2090         if ((tlen || (thflags & TH_FIN)) &&
2091             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2092                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2093                 /*
2094                  * Insert segment which includes th into TCP reassembly queue
2095                  * with control block tp.  Set thflags to whether reassembly now
2096                  * includes a segment with FIN.  This handles the common case
2097                  * inline (segment is the next to be received on an established
2098                  * connection, and the queue is empty), avoiding linkage into
2099                  * and removal from the queue and repetition of various
2100                  * conversions.
2101                  * Set DELACK for segments received in order, but ack
2102                  * immediately when segments are out of order (so
2103                  * fast retransmit can work).
2104                  */
2105                 if (th->th_seq == tp->rcv_nxt &&
2106                     LIST_EMPTY(&tp->t_segq) &&
2107                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2108                         if (DELAY_ACK(tp))
2109                                 callout_reset(tp->tt_delack, tcp_delacktime,
2110                                               tcp_timer_delack, tp);
2111                         else
2112                                 tp->t_flags |= TF_ACKNOW;
2113                         tp->rcv_nxt += tlen;
2114                         thflags = th->th_flags & TH_FIN;
2115                         tcpstat.tcps_rcvpack++;
2116                         tcpstat.tcps_rcvbyte += tlen;
2117                         ND6_HINT(tp);
2118                         if (so->so_state & SS_CANTRCVMORE)
2119                                 m_freem(m);
2120                         else
2121                                 sbappend(&so->so_rcv, m);
2122                         sorwakeup(so);
2123                 } else {
2124                         thflags = tcp_reass(tp, th, &tlen, m);
2125                         tp->t_flags |= TF_ACKNOW;
2126                 }
2127
2128                 /*
2129                  * Note the amount of data that peer has sent into
2130                  * our window, in order to estimate the sender's
2131                  * buffer size.
2132                  */
2133                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2134         } else {
2135                 m_freem(m);
2136                 thflags &= ~TH_FIN;
2137         }
2138
2139         /*
2140          * If FIN is received ACK the FIN and let the user know
2141          * that the connection is closing.
2142          */
2143         if (thflags & TH_FIN) {
2144                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2145                         socantrcvmore(so);
2146                         /*
2147                          * If connection is half-synchronized
2148                          * (ie NEEDSYN flag on) then delay ACK,
2149                          * so it may be piggybacked when SYN is sent.
2150                          * Otherwise, since we received a FIN then no
2151                          * more input can be expected, send ACK now.
2152                          */
2153                         if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN))
2154                                 callout_reset(tp->tt_delack, tcp_delacktime,
2155                                     tcp_timer_delack, tp);
2156                         else
2157                                 tp->t_flags |= TF_ACKNOW;
2158                         tp->rcv_nxt++;
2159                 }
2160                 switch (tp->t_state) {
2161
2162                 /*
2163                  * In SYN_RECEIVED and ESTABLISHED STATES
2164                  * enter the CLOSE_WAIT state.
2165                  */
2166                 case TCPS_SYN_RECEIVED:
2167                         tp->t_starttime = ticks;
2168                         /*FALLTHROUGH*/
2169                 case TCPS_ESTABLISHED:
2170                         tp->t_state = TCPS_CLOSE_WAIT;
2171                         break;
2172
2173                 /*
2174                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2175                  * enter the CLOSING state.
2176                  */
2177                 case TCPS_FIN_WAIT_1:
2178                         tp->t_state = TCPS_CLOSING;
2179                         break;
2180
2181                 /*
2182                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2183                  * starting the time-wait timer, turning off the other
2184                  * standard timers.
2185                  */
2186                 case TCPS_FIN_WAIT_2:
2187                         tp->t_state = TCPS_TIME_WAIT;
2188                         tcp_canceltimers(tp);
2189                         /* Shorten TIME_WAIT [RFC-1644, p.28] */
2190                         if (tp->cc_recv != 0 &&
2191                             (ticks - tp->t_starttime) < tcp_msl) {
2192                                 callout_reset(tp->tt_2msl,
2193                                               tp->t_rxtcur * TCPTV_TWTRUNC,
2194                                               tcp_timer_2msl, tp);
2195                                 /* For transaction client, force ACK now. */
2196                                 tp->t_flags |= TF_ACKNOW;
2197                         }
2198                         else
2199                                 callout_reset(tp->tt_2msl, 2 * tcp_msl,
2200                                               tcp_timer_2msl, tp);
2201                         soisdisconnected(so);
2202                         break;
2203
2204                 /*
2205                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2206                  */
2207                 case TCPS_TIME_WAIT:
2208                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2209                                       tcp_timer_2msl, tp);
2210                         break;
2211                 }
2212         }
2213 #ifdef TCPDEBUG
2214         if (so->so_options & SO_DEBUG)
2215                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2216                           &tcp_savetcp, 0);
2217 #endif
2218
2219         /*
2220          * Return any desired output.
2221          */
2222         if (needoutput || (tp->t_flags & TF_ACKNOW))
2223                 (void) tcp_output(tp);
2224         return;
2225
2226 dropafterack:
2227         /*
2228          * Generate an ACK dropping incoming segment if it occupies
2229          * sequence space, where the ACK reflects our state.
2230          *
2231          * We can now skip the test for the RST flag since all
2232          * paths to this code happen after packets containing
2233          * RST have been dropped.
2234          *
2235          * In the SYN-RECEIVED state, don't send an ACK unless the
2236          * segment we received passes the SYN-RECEIVED ACK test.
2237          * If it fails send a RST.  This breaks the loop in the
2238          * "LAND" DoS attack, and also prevents an ACK storm
2239          * between two listening ports that have been sent forged
2240          * SYN segments, each with the source address of the other.
2241          */
2242         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2243             (SEQ_GT(tp->snd_una, th->th_ack) ||
2244              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2245                 rstreason = BANDLIM_RST_OPENPORT;
2246                 goto dropwithreset;
2247         }
2248 #ifdef TCPDEBUG
2249         if (so->so_options & SO_DEBUG)
2250                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2251                           &tcp_savetcp, 0);
2252 #endif
2253         m_freem(m);
2254         tp->t_flags |= TF_ACKNOW;
2255         (void) tcp_output(tp);
2256         return;
2257
2258 dropwithreset:
2259         /*
2260          * Generate a RST, dropping incoming segment.
2261          * Make ACK acceptable to originator of segment.
2262          * Don't bother to respond if destination was broadcast/multicast.
2263          */
2264         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2265                 goto drop;
2266         if (isipv6) {
2267                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2268                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2269                         goto drop;
2270         } else {
2271                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2272                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2273                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2274                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2275                         goto drop;
2276         }
2277         /* IPv6 anycast check is done at tcp6_input() */
2278
2279         /*
2280          * Perform bandwidth limiting.
2281          */
2282 #ifdef ICMP_BANDLIM
2283         if (badport_bandlim(rstreason) < 0)
2284                 goto drop;
2285 #endif
2286
2287 #ifdef TCPDEBUG
2288         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2289                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2290                           &tcp_savetcp, 0);
2291 #endif
2292         if (thflags & TH_ACK)
2293                 /* mtod() below is safe as long as hdr dropping is delayed */
2294                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2295                             TH_RST);
2296         else {
2297                 if (thflags & TH_SYN)
2298                         tlen++;
2299                 /* mtod() below is safe as long as hdr dropping is delayed */
2300                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2301                             (tcp_seq)0, TH_RST|TH_ACK);
2302         }
2303         return;
2304
2305 drop:
2306         /*
2307          * Drop space held by incoming segment and return.
2308          */
2309 #ifdef TCPDEBUG
2310         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2311                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2312                           &tcp_savetcp, 0);
2313 #endif
2314         m_freem(m);
2315         return;
2316 }
2317
2318 /*
2319  * Parse TCP options and place in tcpopt.
2320  */
2321 static void
2322 tcp_dooptions(to, cp, cnt, is_syn)
2323         struct tcpopt *to;
2324         u_char *cp;
2325         int cnt;
2326 {
2327         int opt, optlen;
2328
2329         to->to_flags = 0;
2330         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2331                 opt = cp[0];
2332                 if (opt == TCPOPT_EOL)
2333                         break;
2334                 if (opt == TCPOPT_NOP)
2335                         optlen = 1;
2336                 else {
2337                         if (cnt < 2)
2338                                 break;
2339                         optlen = cp[1];
2340                         if (optlen < 2 || optlen > cnt)
2341                                 break;
2342                 }
2343                 switch (opt) {
2344                 case TCPOPT_MAXSEG:
2345                         if (optlen != TCPOLEN_MAXSEG)
2346                                 continue;
2347                         if (!is_syn)
2348                                 continue;
2349                         to->to_flags |= TOF_MSS;
2350                         bcopy((char *)cp + 2,
2351                             (char *)&to->to_mss, sizeof(to->to_mss));
2352                         to->to_mss = ntohs(to->to_mss);
2353                         break;
2354                 case TCPOPT_WINDOW:
2355                         if (optlen != TCPOLEN_WINDOW)
2356                                 continue;
2357                         if (! is_syn)
2358                                 continue;
2359                         to->to_flags |= TOF_SCALE;
2360                         to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2361                         break;
2362                 case TCPOPT_TIMESTAMP:
2363                         if (optlen != TCPOLEN_TIMESTAMP)
2364                                 continue;
2365                         to->to_flags |= TOF_TS;
2366                         bcopy((char *)cp + 2,
2367                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2368                         to->to_tsval = ntohl(to->to_tsval);
2369                         bcopy((char *)cp + 6,
2370                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2371                         to->to_tsecr = ntohl(to->to_tsecr);
2372                         break;
2373                 case TCPOPT_CC:
2374                         if (optlen != TCPOLEN_CC)
2375                                 continue;
2376                         to->to_flags |= TOF_CC;
2377                         bcopy((char *)cp + 2,
2378                             (char *)&to->to_cc, sizeof(to->to_cc));
2379                         to->to_cc = ntohl(to->to_cc);
2380                         break;
2381                 case TCPOPT_CCNEW:
2382                         if (optlen != TCPOLEN_CC)
2383                                 continue;
2384                         if (!is_syn)
2385                                 continue;
2386                         to->to_flags |= TOF_CCNEW;
2387                         bcopy((char *)cp + 2,
2388                             (char *)&to->to_cc, sizeof(to->to_cc));
2389                         to->to_cc = ntohl(to->to_cc);
2390                         break;
2391                 case TCPOPT_CCECHO:
2392                         if (optlen != TCPOLEN_CC)
2393                                 continue;
2394                         if (!is_syn)
2395                                 continue;
2396                         to->to_flags |= TOF_CCECHO;
2397                         bcopy((char *)cp + 2,
2398                             (char *)&to->to_ccecho, sizeof(to->to_ccecho));
2399                         to->to_ccecho = ntohl(to->to_ccecho);
2400                         break;
2401                 default:
2402                         continue;
2403                 }
2404         }
2405 }
2406
2407 /*
2408  * Pull out of band byte out of a segment so
2409  * it doesn't appear in the user's data queue.
2410  * It is still reflected in the segment length for
2411  * sequencing purposes.
2412  */
2413 static void
2414 tcp_pulloutofband(so, th, m, off)
2415         struct socket *so;
2416         struct tcphdr *th;
2417         struct mbuf *m;
2418         int off;                /* delayed to be droped hdrlen */
2419 {
2420         int cnt = off + th->th_urp - 1;
2421
2422         while (cnt >= 0) {
2423                 if (m->m_len > cnt) {
2424                         char *cp = mtod(m, caddr_t) + cnt;
2425                         struct tcpcb *tp = sototcpcb(so);
2426
2427                         tp->t_iobc = *cp;
2428                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2429                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2430                         m->m_len--;
2431                         if (m->m_flags & M_PKTHDR)
2432                                 m->m_pkthdr.len--;
2433                         return;
2434                 }
2435                 cnt -= m->m_len;
2436                 m = m->m_next;
2437                 if (m == 0)
2438                         break;
2439         }
2440         panic("tcp_pulloutofband");
2441 }
2442
2443 /*
2444  * Collect new round-trip time estimate
2445  * and update averages and current timeout.
2446  */
2447 static void
2448 tcp_xmit_timer(tp, rtt)
2449         struct tcpcb *tp;
2450         int rtt;
2451 {
2452         int delta;
2453
2454         tcpstat.tcps_rttupdated++;
2455         tp->t_rttupdated++;
2456         if (tp->t_srtt != 0) {
2457                 /*
2458                  * srtt is stored as fixed point with 5 bits after the
2459                  * binary point (i.e., scaled by 8).  The following magic
2460                  * is equivalent to the smoothing algorithm in rfc793 with
2461                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2462                  * point).  Adjust rtt to origin 0.
2463                  */
2464                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2465                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2466
2467                 if ((tp->t_srtt += delta) <= 0)
2468                         tp->t_srtt = 1;
2469
2470                 /*
2471                  * We accumulate a smoothed rtt variance (actually, a
2472                  * smoothed mean difference), then set the retransmit
2473                  * timer to smoothed rtt + 4 times the smoothed variance.
2474                  * rttvar is stored as fixed point with 4 bits after the
2475                  * binary point (scaled by 16).  The following is
2476                  * equivalent to rfc793 smoothing with an alpha of .75
2477                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2478                  * rfc793's wired-in beta.
2479                  */
2480                 if (delta < 0)
2481                         delta = -delta;
2482                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2483                 if ((tp->t_rttvar += delta) <= 0)
2484                         tp->t_rttvar = 1;
2485                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2486                         tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2487         } else {
2488                 /*
2489                  * No rtt measurement yet - use the unsmoothed rtt.
2490                  * Set the variance to half the rtt (so our first
2491                  * retransmit happens at 3*rtt).
2492                  */
2493                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2494                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2495                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2496         }
2497         tp->t_rtttime = 0;
2498         tp->t_rxtshift = 0;
2499
2500         /*
2501          * the retransmit should happen at rtt + 4 * rttvar.
2502          * Because of the way we do the smoothing, srtt and rttvar
2503          * will each average +1/2 tick of bias.  When we compute
2504          * the retransmit timer, we want 1/2 tick of rounding and
2505          * 1 extra tick because of +-1/2 tick uncertainty in the
2506          * firing of the timer.  The bias will give us exactly the
2507          * 1.5 tick we need.  But, because the bias is
2508          * statistical, we have to test that we don't drop below
2509          * the minimum feasible timer (which is 2 ticks).
2510          */
2511         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2512                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2513
2514         /*
2515          * We received an ack for a packet that wasn't retransmitted;
2516          * it is probably safe to discard any error indications we've
2517          * received recently.  This isn't quite right, but close enough
2518          * for now (a route might have failed after we sent a segment,
2519          * and the return path might not be symmetrical).
2520          */
2521         tp->t_softerror = 0;
2522 }
2523
2524 /*
2525  * Determine a reasonable value for maxseg size.
2526  * If the route is known, check route for mtu.
2527  * If none, use an mss that can be handled on the outgoing
2528  * interface without forcing IP to fragment; if bigger than
2529  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2530  * to utilize large mbufs.  If no route is found, route has no mtu,
2531  * or the destination isn't local, use a default, hopefully conservative
2532  * size (usually 512 or the default IP max size, but no more than the mtu
2533  * of the interface), as we can't discover anything about intervening
2534  * gateways or networks.  We also initialize the congestion/slow start
2535  * window to be a single segment if the destination isn't local.
2536  * While looking at the routing entry, we also initialize other path-dependent
2537  * parameters from pre-set or cached values in the routing entry.
2538  *
2539  * Also take into account the space needed for options that we
2540  * send regularly.  Make maxseg shorter by that amount to assure
2541  * that we can send maxseg amount of data even when the options
2542  * are present.  Store the upper limit of the length of options plus
2543  * data in maxopd.
2544  *
2545  * NOTE that this routine is only called when we process an incoming
2546  * segment, for outgoing segments only tcp_mssopt is called.
2547  *
2548  * In case of T/TCP, we call this routine during implicit connection
2549  * setup as well (offer = -1), to initialize maxseg from the cached
2550  * MSS of our peer.
2551  */
2552 void
2553 tcp_mss(tp, offer)
2554         struct tcpcb *tp;
2555         int offer;
2556 {
2557         struct rtentry *rt;
2558         struct ifnet *ifp;
2559         int rtt, mss;
2560         u_long bufsize;
2561         struct inpcb *inp = tp->t_inpcb;
2562         struct socket *so;
2563         struct rmxp_tao *taop;
2564         int origoffer = offer;
2565 #ifdef INET6
2566         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2567         size_t min_protoh = isipv6 ?
2568                             sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2569                             sizeof(struct tcpiphdr);
2570 #else
2571         const int isipv6 = 0;
2572         const size_t min_protoh = sizeof(struct tcpiphdr);
2573 #endif
2574
2575         if (isipv6)
2576                 rt = tcp_rtlookup6(&inp->inp_inc);
2577         else
2578                 rt = tcp_rtlookup(&inp->inp_inc);
2579         if (rt == NULL) {
2580                 tp->t_maxopd = tp->t_maxseg =
2581                                 isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2582                 return;
2583         }
2584         ifp = rt->rt_ifp;
2585         so = inp->inp_socket;
2586
2587         taop = rmx_taop(rt->rt_rmx);
2588         /*
2589          * Offer == -1 means that we didn't receive SYN yet,
2590          * use cached value in that case;
2591          */
2592         if (offer == -1)
2593                 offer = taop->tao_mssopt;
2594         /*
2595          * Offer == 0 means that there was no MSS on the SYN segment,
2596          * in this case we use tcp_mssdflt.
2597          */
2598         if (offer == 0)
2599                 offer = isipv6 ? tcp_v6mssdflt : tcp_mssdflt;
2600         else
2601                 /*
2602                  * Sanity check: make sure that maxopd will be large
2603                  * enough to allow some data on segments even is the
2604                  * all the option space is used (40bytes).  Otherwise
2605                  * funny things may happen in tcp_output.
2606                  */
2607                 offer = max(offer, 64);
2608         taop->tao_mssopt = offer;
2609
2610         /*
2611          * While we're here, check if there's an initial rtt
2612          * or rttvar.  Convert from the route-table units
2613          * to scaled multiples of the slow timeout timer.
2614          */
2615         if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2616                 /*
2617                  * XXX the lock bit for RTT indicates that the value
2618                  * is also a minimum value; this is subject to time.
2619                  */
2620                 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2621                         tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2622                 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2623                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2624                 tcpstat.tcps_usedrtt++;
2625                 if (rt->rt_rmx.rmx_rttvar) {
2626                         tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2627                             (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2628                         tcpstat.tcps_usedrttvar++;
2629                 } else {
2630                         /* default variation is +- 1 rtt */
2631                         tp->t_rttvar =
2632                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2633                 }
2634                 TCPT_RANGESET(tp->t_rxtcur,
2635                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2636                               tp->t_rttmin, TCPTV_REXMTMAX);
2637         }
2638         /*
2639          * if there's an mtu associated with the route, use it
2640          * else, use the link mtu.
2641          */
2642         if (rt->rt_rmx.rmx_mtu)
2643                 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2644         else {
2645                 if (isipv6) {
2646                         mss = nd_ifinfo[rt->rt_ifp->if_index].linkmtu -
2647                                 min_protoh;
2648                         if (!in6_localaddr(&inp->in6p_faddr))
2649                                 mss = min(mss, tcp_v6mssdflt);
2650                 } else {
2651                         mss = ifp->if_mtu - min_protoh;
2652                         if (!in_localaddr(inp->inp_faddr))
2653                                 mss = min(mss, tcp_mssdflt);
2654                 }
2655         }
2656         mss = min(mss, offer);
2657         /*
2658          * maxopd stores the maximum length of data AND options
2659          * in a segment; maxseg is the amount of data in a normal
2660          * segment.  We need to store this value (maxopd) apart
2661          * from maxseg, because now every segment carries options
2662          * and thus we normally have somewhat less data in segments.
2663          */
2664         tp->t_maxopd = mss;
2665
2666         /*
2667          * In case of T/TCP, origoffer==-1 indicates, that no segments
2668          * were received yet.  In this case we just guess, otherwise
2669          * we do the same as before T/TCP.
2670          */
2671         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2672             (origoffer == -1 ||
2673              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2674                 mss -= TCPOLEN_TSTAMP_APPA;
2675         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
2676             (origoffer == -1 ||
2677              (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
2678                 mss -= TCPOLEN_CC_APPA;
2679
2680 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2681                 if (mss > MCLBYTES)
2682                         mss &= ~(MCLBYTES-1);
2683 #else
2684                 if (mss > MCLBYTES)
2685                         mss = mss / MCLBYTES * MCLBYTES;
2686 #endif
2687         /*
2688          * If there's a pipesize, change the socket buffer
2689          * to that size.  Make the socket buffers an integral
2690          * number of mss units; if the mss is larger than
2691          * the socket buffer, decrease the mss.
2692          */
2693 #ifdef RTV_SPIPE
2694         if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2695 #endif
2696                 bufsize = so->so_snd.sb_hiwat;
2697         if (bufsize < mss)
2698                 mss = bufsize;
2699         else {
2700                 bufsize = roundup(bufsize, mss);
2701                 if (bufsize > sb_max)
2702                         bufsize = sb_max;
2703                 if (bufsize > so->so_snd.sb_hiwat)
2704                         (void)sbreserve(&so->so_snd, bufsize, so, NULL);
2705         }
2706         tp->t_maxseg = mss;
2707
2708 #ifdef RTV_RPIPE
2709         if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
2710 #endif
2711                 bufsize = so->so_rcv.sb_hiwat;
2712         if (bufsize > mss) {
2713                 bufsize = roundup(bufsize, mss);
2714                 if (bufsize > sb_max)
2715                         bufsize = sb_max;
2716                 if (bufsize > so->so_rcv.sb_hiwat)
2717                         (void)sbreserve(&so->so_rcv, bufsize, so, NULL);
2718         }
2719
2720         /*
2721          * Set the slow-start flight size depending on whether this
2722          * is a local network or not.
2723          */
2724         if (tcp_do_rfc3390)
2725                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2726         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2727                  (!isipv6 && in_localaddr(inp->inp_faddr)))
2728                 tp->snd_cwnd = mss * ss_fltsz_local;
2729         else
2730                 tp->snd_cwnd = mss * ss_fltsz;
2731
2732         if (rt->rt_rmx.rmx_ssthresh) {
2733                 /*
2734                  * There's some sort of gateway or interface
2735                  * buffer limit on the path.  Use this to set
2736                  * the slow start threshhold, but set the
2737                  * threshold to no less than 2*mss.
2738                  */
2739                 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
2740                 tcpstat.tcps_usedssthresh++;
2741         }
2742 }
2743
2744 /*
2745  * Determine the MSS option to send on an outgoing SYN.
2746  */
2747 int
2748 tcp_mssopt(tp)
2749         struct tcpcb *tp;
2750 {
2751         struct rtentry *rt;
2752 #ifdef INET6
2753         int isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2754         int min_protoh = isipv6 ?
2755                              sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2756                              sizeof(struct tcpiphdr);
2757 #else
2758         const int isipv6 = 0;
2759         const size_t min_protoh = sizeof(struct tcpiphdr);
2760 #endif
2761
2762         if (isipv6)
2763                 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
2764         else
2765                 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
2766         if (rt == NULL)
2767                 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2768
2769         return (rt->rt_ifp->if_mtu - min_protoh);
2770 }
2771
2772
2773 /*
2774  * When a partial ack arrives, force the retransmission of the
2775  * next unacknowledged segment.  Do not clear tp->t_dupacks.
2776  * By setting snd_nxt to ti_ack, this forces retransmission timer to
2777  * be started again.
2778  */
2779 static void
2780 tcp_newreno_partial_ack(tp, th)
2781         struct tcpcb *tp;
2782         struct tcphdr *th;
2783 {
2784         tcp_seq onxt = tp->snd_nxt;
2785         u_long  ocwnd = tp->snd_cwnd;
2786
2787         callout_stop(tp->tt_rexmt);
2788         tp->t_rtttime = 0;
2789         tp->snd_nxt = th->th_ack;
2790         /*
2791          * Set snd_cwnd to one segment beyond acknowledged offset
2792          * (tp->snd_una has not yet been updated when this function is called.)
2793          */
2794         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
2795         tp->t_flags |= TF_ACKNOW;
2796         (void) tcp_output(tp);
2797         tp->snd_cwnd = ocwnd;
2798         if (SEQ_GT(onxt, tp->snd_nxt))
2799                 tp->snd_nxt = onxt;
2800         /*
2801          * Partial window deflation.  Relies on fact that tp->snd_una
2802          * not updated yet.
2803          */
2804         tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
2805 }