sys/netinet/tcp_reass.c

   1 /*-
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 4. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
  30  * $FreeBSD$
  31  */
  32
  33 #include "opt_ipfw.h"           /* for ipfw_fwd         */
  34 #include "opt_inet.h"
  35 #include "opt_inet6.h"
  36 #include "opt_ipsec.h"
  37 #include "opt_mac.h"
  38 #include "opt_tcpdebug.h"
  39 #include "opt_tcp_input.h"
  40 #include "opt_tcp_sack.h"
  41
  42 #include <sys/param.h>
  43 #include <sys/kernel.h>
  44 #include <sys/malloc.h>
  45 #include <sys/mbuf.h>
  46 #include <sys/proc.h>           /* for proc0 declaration */
  47 #include <sys/protosw.h>
  48 #include <sys/signalvar.h>
  49 #include <sys/socket.h>
  50 #include <sys/socketvar.h>
  51 #include <sys/sysctl.h>
  52 #include <sys/syslog.h>
  53 #include <sys/systm.h>
  54
  55 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  56
  57 #include <vm/uma.h>
  58
  59 #include <net/if.h>
  60 #include <net/route.h>
  61
  62 #include <netinet/in.h>
  63 #include <netinet/in_pcb.h>
  64 #include <netinet/in_systm.h>
  65 #include <netinet/in_var.h>
  66 #include <netinet/ip.h>
  67 #include <netinet/ip_icmp.h>    /* required for icmp_var.h */
  68 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
  69 #include <netinet/ip_var.h>
  70 #include <netinet/ip_options.h>
  71 #include <netinet/ip6.h>
  72 #include <netinet/icmp6.h>
  73 #include <netinet6/in6_pcb.h>
  74 #include <netinet6/ip6_var.h>
  75 #include <netinet6/nd6.h>
  76 #include <netinet/tcp.h>
  77 #include <netinet/tcp_fsm.h>
  78 #include <netinet/tcp_seq.h>
  79 #include <netinet/tcp_timer.h>
  80 #include <netinet/tcp_var.h>
  81 #include <netinet6/tcp6_var.h>
  82 #include <netinet/tcpip.h>
  83 #ifdef TCPDEBUG
  84 #include <netinet/tcp_debug.h>
  85 #endif /* TCPDEBUG */
  86
  87 #ifdef FAST_IPSEC
  88 #include <netipsec/ipsec.h>
  89 #include <netipsec/ipsec6.h>
  90 #endif /*FAST_IPSEC*/
  91
  92 #ifdef IPSEC
  93 #include <netinet6/ipsec.h>
  94 #include <netinet6/ipsec6.h>
  95 #include <netkey/key.h>
  96 #endif /*IPSEC*/
  97
  98 #include <machine/in_cksum.h>
  99
 100 #include <security/mac/mac_framework.h>
 101
 102 static const int tcprexmtthresh = 3;
 103
 104 struct  tcpstat tcpstat;
 105 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 106     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 107
 108 static int tcp_log_in_vain = 0;
 109 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 110     &tcp_log_in_vain, 0, "Log all incoming TCP connections");
 111
 112 static int blackhole = 0;
 113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 114     &blackhole, 0, "Do not send RST when dropping refused connections");
 115
 116 int tcp_delack_enabled = 1;
 117 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 118     &tcp_delack_enabled, 0,
 119     "Delay ACK to try and piggyback it onto a data packet");
 120
 121 #ifdef TCP_DROP_SYNFIN
 122 static int drop_synfin = 0;
 123 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 124     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 125 #endif
 126
 127 static int tcp_do_rfc3042 = 1;
 128 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
 129     &tcp_do_rfc3042, 0, "Enable RFC 3042 (Limited Transmit)");
 130
 131 static int tcp_do_rfc3390 = 1;
 132 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 133     &tcp_do_rfc3390, 0,
 134     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 135
 136 static int tcp_insecure_rst = 0;
 137 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
 138     &tcp_insecure_rst, 0,
 139     "Follow the old (insecure) criteria for accepting RST packets");
 140
 141 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
 142     "TCP Segment Reassembly Queue");
 143
 144 static int tcp_reass_maxseg = 0;
 145 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RDTUN,
 146     &tcp_reass_maxseg, 0,
 147     "Global maximum number of TCP Segments in Reassembly Queue");
 148
 149 int tcp_reass_qsize = 0;
 150 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD,
 151     &tcp_reass_qsize, 0,
 152     "Global number of TCP Segments currently in Reassembly Queue");
 153
 154 static int tcp_reass_maxqlen = 48;
 155 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxqlen, CTLFLAG_RW,
 156     &tcp_reass_maxqlen, 0,
 157     "Maximum number of TCP Segments per individual Reassembly Queue");
 158
 159 static int tcp_reass_overflows = 0;
 160 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD,
 161     &tcp_reass_overflows, 0,
 162     "Global number of TCP Segment Reassembly Queue Overflows");
 163
 164 int     tcp_do_autorcvbuf = 1;
 165 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
 166     &tcp_do_autorcvbuf, 0, "Enable automatic receive buffer sizing");
 167
 168 int     tcp_autorcvbuf_inc = 16*1024;
 169 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
 170     &tcp_autorcvbuf_inc, 0,
 171     "Incrementor step size of automatic receive buffer");
 172
 173 int     tcp_autorcvbuf_max = 256*1024;
 174 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
 175     &tcp_autorcvbuf_max, 0, "Max size of automatic receive buffer");
 176
 177 struct inpcbhead tcb;
 178 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 179 struct inpcbinfo tcbinfo;
 180 struct mtx      *tcbinfo_mtx;
 181
 182 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 183
 184 static void      tcp_pulloutofband(struct socket *,
 185                      struct tcphdr *, struct mbuf *, int);
 186 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 187                      struct mbuf *);
 188 static void      tcp_xmit_timer(struct tcpcb *, int);
 189 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 190 static int       tcp_timewait(struct inpcb *, struct tcpopt *,
 191                      struct tcphdr *, struct mbuf *, int);
 192
 193 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 194 #ifdef INET6
 195 #define ND6_HINT(tp) \
 196 do { \
 197         if ((tp) && (tp)->t_inpcb && \
 198             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
 199                 nd6_nud_hint(NULL, NULL, 0); \
 200 } while (0)
 201 #else
 202 #define ND6_HINT(tp)
 203 #endif
 204
 205 /*
 206  * Indicate whether this ack should be delayed.  We can delay the ack if
 207  *      - there is no delayed ack timer in progress and
 208  *      - our last ack wasn't a 0-sized window.  We never want to delay
 209  *        the ack that opens up a 0-sized window and
 210  *              - delayed acks are enabled or
 211  *              - this is a half-synchronized T/TCP connection.
 212  */
 213 #define DELAY_ACK(tp)                                                   \
 214         ((!callout_active(tp->tt_delack) &&                             \
 215             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
 216             (tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
 217
 218 /* Initialize TCP reassembly queue */
 219 static void
 220 tcp_reass_zone_change(void *tag)
 221 {
 222
 223         tcp_reass_maxseg = nmbclusters / 16;
 224         uma_zone_set_max(tcp_reass_zone, tcp_reass_maxseg);
 225 }
 226
 227 uma_zone_t      tcp_reass_zone;
 228 void
 229 tcp_reass_init()
 230 {
 231         tcp_reass_maxseg = nmbclusters / 16;
 232         TUNABLE_INT_FETCH("net.inet.tcp.reass.maxsegments",
 233             &tcp_reass_maxseg);
 234         tcp_reass_zone = uma_zcreate("tcpreass", sizeof (struct tseg_qent),
 235             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
 236         uma_zone_set_max(tcp_reass_zone, tcp_reass_maxseg);
 237         EVENTHANDLER_REGISTER(nmbclusters_change,
 238             tcp_reass_zone_change, NULL, EVENTHANDLER_PRI_ANY);
 239 }
 240
 241 static int
 242 tcp_reass(tp, th, tlenp, m)
 243         register struct tcpcb *tp;
 244         register struct tcphdr *th;
 245         int *tlenp;
 246         struct mbuf *m;
 247 {
 248         struct tseg_qent *q;
 249         struct tseg_qent *p = NULL;
 250         struct tseg_qent *nq;
 251         struct tseg_qent *te = NULL;
 252         struct socket *so = tp->t_inpcb->inp_socket;
 253         int flags;
 254
 255         INP_LOCK_ASSERT(tp->t_inpcb);
 256
 257         /*
 258          * XXX: tcp_reass() is rather inefficient with its data structures
 259          * and should be rewritten (see NetBSD for optimizations).  While
 260          * doing that it should move to its own file tcp_reass.c.
 261          */
 262
 263         /*
 264          * Call with th==NULL after become established to
 265          * force pre-ESTABLISHED data up to user socket.
 266          */
 267         if (th == NULL)
 268                 goto present;
 269
 270         /*
 271          * Limit the number of segments in the reassembly queue to prevent
 272          * holding on to too many segments (and thus running out of mbufs).
 273          * Make sure to let the missing segment through which caused this
 274          * queue.  Always keep one global queue entry spare to be able to
 275          * process the missing segment.
 276          */
 277         if (th->th_seq != tp->rcv_nxt &&
 278             (tcp_reass_qsize + 1 >= tcp_reass_maxseg ||
 279              tp->t_segqlen >= tcp_reass_maxqlen)) {
 280                 tcp_reass_overflows++;
 281                 tcpstat.tcps_rcvmemdrop++;
 282                 m_freem(m);
 283                 *tlenp = 0;
 284                 return (0);
 285         }
 286
 287         /*
 288          * Allocate a new queue entry. If we can't, or hit the zone limit
 289          * just drop the pkt.
 290          */
 291         te = uma_zalloc(tcp_reass_zone, M_NOWAIT);
 292         if (te == NULL) {
 293                 tcpstat.tcps_rcvmemdrop++;
 294                 m_freem(m);
 295                 *tlenp = 0;
 296                 return (0);
 297         }
 298         tp->t_segqlen++;
 299         tcp_reass_qsize++;
 300
 301         /*
 302          * Find a segment which begins after this one does.
 303          */
 304         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 305                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 306                         break;
 307                 p = q;
 308         }
 309
 310         /*
 311          * If there is a preceding segment, it may provide some of
 312          * our data already.  If so, drop the data from the incoming
 313          * segment.  If it provides all of our data, drop us.
 314          */
 315         if (p != NULL) {
 316                 register int i;
 317                 /* conversion to int (in i) handles seq wraparound */
 318                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 319                 if (i > 0) {
 320                         if (i >= *tlenp) {
 321                                 tcpstat.tcps_rcvduppack++;
 322                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 323                                 m_freem(m);
 324                                 uma_zfree(tcp_reass_zone, te);
 325                                 tp->t_segqlen--;
 326                                 tcp_reass_qsize--;
 327                                 /*
 328                                  * Try to present any queued data
 329                                  * at the left window edge to the user.
 330                                  * This is needed after the 3-WHS
 331                                  * completes.
 332                                  */
 333                                 goto present;   /* ??? */
 334                         }
 335                         m_adj(m, i);
 336                         *tlenp -= i;
 337                         th->th_seq += i;
 338                 }
 339         }
 340         tcpstat.tcps_rcvoopack++;
 341         tcpstat.tcps_rcvoobyte += *tlenp;
 342
 343         /*
 344          * While we overlap succeeding segments trim them or,
 345          * if they are completely covered, dequeue them.
 346          */
 347         while (q) {
 348                 register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 349                 if (i <= 0)
 350                         break;
 351                 if (i < q->tqe_len) {
 352                         q->tqe_th->th_seq += i;
 353                         q->tqe_len -= i;
 354                         m_adj(q->tqe_m, i);
 355                         break;
 356                 }
 357
 358                 nq = LIST_NEXT(q, tqe_q);
 359                 LIST_REMOVE(q, tqe_q);
 360                 m_freem(q->tqe_m);
 361                 uma_zfree(tcp_reass_zone, q);
 362                 tp->t_segqlen--;
 363                 tcp_reass_qsize--;
 364                 q = nq;
 365         }
 366
 367         /* Insert the new segment queue entry into place. */
 368         te->tqe_m = m;
 369         te->tqe_th = th;
 370         te->tqe_len = *tlenp;
 371
 372         if (p == NULL) {
 373                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 374         } else {
 375                 LIST_INSERT_AFTER(p, te, tqe_q);
 376         }
 377
 378 present:
 379         /*
 380          * Present data to user, advancing rcv_nxt through
 381          * completed sequence space.
 382          */
 383         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 384                 return (0);
 385         q = LIST_FIRST(&tp->t_segq);
 386         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 387                 return (0);
 388         SOCKBUF_LOCK(&so->so_rcv);
 389         do {
 390                 tp->rcv_nxt += q->tqe_len;
 391                 flags = q->tqe_th->th_flags & TH_FIN;
 392                 nq = LIST_NEXT(q, tqe_q);
 393                 LIST_REMOVE(q, tqe_q);
 394                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
 395                         m_freem(q->tqe_m);
 396                 else
 397                         sbappendstream_locked(&so->so_rcv, q->tqe_m);
 398                 uma_zfree(tcp_reass_zone, q);
 399                 tp->t_segqlen--;
 400                 tcp_reass_qsize--;
 401                 q = nq;
 402         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 403         ND6_HINT(tp);
 404         sorwakeup_locked(so);
 405         return (flags);
 406 }
 407
 408 /*
 409  * TCP input routine, follows pages 65-76 of the
 410  * protocol specification dated September, 1981 very closely.
 411  */
 412 #ifdef INET6
 413 int
 414 tcp6_input(mp, offp, proto)
 415         struct mbuf **mp;
 416         int *offp, proto;
 417 {
 418         register struct mbuf *m = *mp;
 419         struct in6_ifaddr *ia6;
 420
 421         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 422
 423         /*
 424          * draft-itojun-ipv6-tcp-to-anycast
 425          * better place to put this in?
 426          */
 427         ia6 = ip6_getdstifaddr(m);
 428         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 429                 struct ip6_hdr *ip6;
 430
 431                 ip6 = mtod(m, struct ip6_hdr *);
 432                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 433                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 434                 return IPPROTO_DONE;
 435         }
 436
 437         tcp_input(m, *offp);
 438         return IPPROTO_DONE;
 439 }
 440 #endif
 441
 442 void
 443 tcp_input(m, off0)
 444         register struct mbuf *m;
 445         int off0;
 446 {
 447         register struct tcphdr *th;
 448         register struct ip *ip = NULL;
 449         register struct ipovly *ipov;
 450         register struct inpcb *inp = NULL;
 451         u_char *optp = NULL;
 452         int optlen = 0;
 453         int len, tlen, off;
 454         int drop_hdrlen;
 455         register struct tcpcb *tp = 0;
 456         register int thflags;
 457         struct socket *so = 0;
 458         int todrop, acked, ourfinisacked, needoutput = 0;
 459         u_long tiwin;
 460         struct tcpopt to;               /* options in this segment */
 461         int headlocked = 0;
 462 #ifdef IPFIREWALL_FORWARD
 463         struct m_tag *fwd_tag;
 464 #endif
 465         int rstreason; /* For badport_bandlim accounting purposes */
 466
 467         struct ip6_hdr *ip6 = NULL;
 468 #ifdef INET6
 469         int isipv6;
 470         char ip6buf[INET6_ADDRSTRLEN];
 471 #else
 472         const int isipv6 = 0;
 473 #endif
 474
 475 #ifdef TCPDEBUG
 476         /*
 477          * The size of tcp_saveipgen must be the size of the max ip header,
 478          * now IPv6.
 479          */
 480         u_char tcp_saveipgen[40];
 481         struct tcphdr tcp_savetcp;
 482         short ostate = 0;
 483 #endif
 484
 485 #ifdef INET6
 486         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 487 #endif
 488         bzero((char *)&to, sizeof(to));
 489
 490         tcpstat.tcps_rcvtotal++;
 491
 492         if (isipv6) {
 493 #ifdef INET6
 494                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 495                 ip6 = mtod(m, struct ip6_hdr *);
 496                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 497                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 498                         tcpstat.tcps_rcvbadsum++;
 499                         goto drop;
 500                 }
 501                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 502
 503                 /*
 504                  * Be proactive about unspecified IPv6 address in source.
 505                  * As we use all-zero to indicate unbounded/unconnected pcb,
 506                  * unspecified IPv6 address can be used to confuse us.
 507                  *
 508                  * Note that packets with unspecified IPv6 destination is
 509                  * already dropped in ip6_input.
 510                  */
 511                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 512                         /* XXX stat */
 513                         goto drop;
 514                 }
 515 #else
 516                 th = NULL;              /* XXX: avoid compiler warning */
 517 #endif
 518         } else {
 519                 /*
 520                  * Get IP and TCP header together in first mbuf.
 521                  * Note: IP leaves IP header in first mbuf.
 522                  */
 523                 if (off0 > sizeof (struct ip)) {
 524                         ip_stripoptions(m, (struct mbuf *)0);
 525                         off0 = sizeof(struct ip);
 526                 }
 527                 if (m->m_len < sizeof (struct tcpiphdr)) {
 528                         if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) {
 529                                 tcpstat.tcps_rcvshort++;
 530                                 return;
 531                         }
 532                 }
 533                 ip = mtod(m, struct ip *);
 534                 ipov = (struct ipovly *)ip;
 535                 th = (struct tcphdr *)((caddr_t)ip + off0);
 536                 tlen = ip->ip_len;
 537
 538                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 539                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 540                                 th->th_sum = m->m_pkthdr.csum_data;
 541                         else
 542                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 543                                                 ip->ip_dst.s_addr,
 544                                                 htonl(m->m_pkthdr.csum_data +
 545                                                         ip->ip_len +
 546                                                         IPPROTO_TCP));
 547                         th->th_sum ^= 0xffff;
 548 #ifdef TCPDEBUG
 549                         ipov->ih_len = (u_short)tlen;
 550                         ipov->ih_len = htons(ipov->ih_len);
 551 #endif
 552                 } else {
 553                         /*
 554                          * Checksum extended TCP header and data.
 555                          */
 556                         len = sizeof (struct ip) + tlen;
 557                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 558                         ipov->ih_len = (u_short)tlen;
 559                         ipov->ih_len = htons(ipov->ih_len);
 560                         th->th_sum = in_cksum(m, len);
 561                 }
 562                 if (th->th_sum) {
 563                         tcpstat.tcps_rcvbadsum++;
 564                         goto drop;
 565                 }
 566                 /* Re-initialization for later version check */
 567                 ip->ip_v = IPVERSION;
 568         }
 569
 570         /*
 571          * Check that TCP offset makes sense,
 572          * pull out TCP options and adjust length.              XXX
 573          */
 574         off = th->th_off << 2;
 575         if (off < sizeof (struct tcphdr) || off > tlen) {
 576                 tcpstat.tcps_rcvbadoff++;
 577                 goto drop;
 578         }
 579         tlen -= off;    /* tlen is used instead of ti->ti_len */
 580         if (off > sizeof (struct tcphdr)) {
 581                 if (isipv6) {
 582 #ifdef INET6
 583                         IP6_EXTHDR_CHECK(m, off0, off, );
 584                         ip6 = mtod(m, struct ip6_hdr *);
 585                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 586 #endif
 587                 } else {
 588                         if (m->m_len < sizeof(struct ip) + off) {
 589                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
 590                                                 == 0) {
 591                                         tcpstat.tcps_rcvshort++;
 592                                         return;
 593                                 }
 594                                 ip = mtod(m, struct ip *);
 595                                 ipov = (struct ipovly *)ip;
 596                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 597                         }
 598                 }
 599                 optlen = off - sizeof (struct tcphdr);
 600                 optp = (u_char *)(th + 1);
 601         }
 602         thflags = th->th_flags;
 603
 604 #ifdef TCP_DROP_SYNFIN
 605         /*
 606          * If the drop_synfin option is enabled, drop all packets with
 607          * both the SYN and FIN bits set. This prevents e.g. nmap from
 608          * identifying the TCP/IP stack.
 609          *
 610          * This is a violation of the TCP specification.
 611          */
 612         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 613                 goto drop;
 614 #endif
 615
 616         /*
 617          * Convert TCP protocol specific fields to host format.
 618          */
 619         th->th_seq = ntohl(th->th_seq);
 620         th->th_ack = ntohl(th->th_ack);
 621         th->th_win = ntohs(th->th_win);
 622         th->th_urp = ntohs(th->th_urp);
 623
 624         /*
 625          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options,
 626          * until after ip6_savecontrol() is called and before other functions
 627          * which don't want those proto headers.
 628          * Because ip6_savecontrol() is going to parse the mbuf to
 629          * search for data to be passed up to user-land, it wants mbuf
 630          * parameters to be unchanged.
 631          * XXX: the call of ip6_savecontrol() has been obsoleted based on
 632          * latest version of the advanced API (20020110).
 633          */
 634         drop_hdrlen = off0 + off;
 635
 636         /*
 637          * Locate pcb for segment.
 638          */
 639         INP_INFO_WLOCK(&tcbinfo);
 640         headlocked = 1;
 641 findpcb:
 642         KASSERT(headlocked, ("tcp_input: findpcb: head not locked"));
 643 #ifdef IPFIREWALL_FORWARD
 644         /* Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain. */
 645         fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
 646
 647         if (fwd_tag != NULL && isipv6 == 0) {   /* IPv6 support is not yet */
 648                 struct sockaddr_in *next_hop;
 649
 650                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
 651                 /*
 652                  * Transparently forwarded. Pretend to be the destination.
 653                  * already got one like this?
 654                  */
 655                 inp = in_pcblookup_hash(&tcbinfo,
 656                                         ip->ip_src, th->th_sport,
 657                                         ip->ip_dst, th->th_dport,
 658                                         0, m->m_pkthdr.rcvif);
 659                 if (!inp) {
 660                         /* It's new.  Try to find the ambushing socket. */
 661                         inp = in_pcblookup_hash(&tcbinfo,
 662                                                 ip->ip_src, th->th_sport,
 663                                                 next_hop->sin_addr,
 664                                                 next_hop->sin_port ?
 665                                                     ntohs(next_hop->sin_port) :
 666                                                     th->th_dport,
 667                                                 INPLOOKUP_WILDCARD,
 668                                                 m->m_pkthdr.rcvif);
 669                 }
 670                 /* Remove the tag from the packet.  We don't need it anymore. */
 671                 m_tag_delete(m, fwd_tag);
 672         } else {
 673 #endif /* IPFIREWALL_FORWARD */
 674                 if (isipv6) {
 675 #ifdef INET6
 676                         inp = in6_pcblookup_hash(&tcbinfo,
 677                                                  &ip6->ip6_src, th->th_sport,
 678                                                  &ip6->ip6_dst, th->th_dport,
 679                                                  INPLOOKUP_WILDCARD,
 680                                                  m->m_pkthdr.rcvif);
 681 #endif
 682                 } else
 683                         inp = in_pcblookup_hash(&tcbinfo,
 684                                                 ip->ip_src, th->th_sport,
 685                                                 ip->ip_dst, th->th_dport,
 686                                                 INPLOOKUP_WILDCARD,
 687                                                 m->m_pkthdr.rcvif);
 688 #ifdef IPFIREWALL_FORWARD
 689         }
 690 #endif /* IPFIREWALL_FORWARD */
 691
 692 #if defined(IPSEC) || defined(FAST_IPSEC)
 693 #ifdef INET6
 694         if (isipv6) {
 695                 if (inp != NULL && ipsec6_in_reject(m, inp)) {
 696 #ifdef IPSEC
 697                         ipsec6stat.in_polvio++;
 698 #endif
 699                         goto drop;
 700                 }
 701         } else
 702 #endif /* INET6 */
 703         if (inp != NULL && ipsec4_in_reject(m, inp)) {
 704 #ifdef IPSEC
 705                 ipsecstat.in_polvio++;
 706 #endif
 707                 goto drop;
 708         }
 709 #endif /*IPSEC || FAST_IPSEC*/
 710
 711         /*
 712          * If the state is CLOSED (i.e., TCB does not exist) then
 713          * all data in the incoming segment is discarded.
 714          * If the TCB exists but is in CLOSED state, it is embryonic,
 715          * but should either do a listen or a connect soon.
 716          */
 717         if (inp == NULL) {
 718                 if (tcp_log_in_vain) {
 719 #ifdef INET6
 720                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 721 #else
 722                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 723 #endif
 724
 725                         if (isipv6) {
 726 #ifdef INET6
 727                                 strcpy(dbuf, "[");
 728                                 strcpy(sbuf, "[");
 729                                 strcat(dbuf,
 730                                     ip6_sprintf(ip6buf, &ip6->ip6_dst));
 731                                 strcat(sbuf,
 732                                     ip6_sprintf(ip6buf, &ip6->ip6_src));
 733                                 strcat(dbuf, "]");
 734                                 strcat(sbuf, "]");
 735 #endif
 736                         } else {
 737                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 738                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 739                         }
 740                         switch (tcp_log_in_vain) {
 741                         case 1:
 742                                 if ((thflags & TH_SYN) == 0)
 743                                         break;
 744                                 /* FALLTHROUGH */
 745                         case 2:
 746                                 log(LOG_INFO,
 747                                     "Connection attempt to TCP %s:%d "
 748                                     "from %s:%d flags:0x%02x\n",
 749                                     dbuf, ntohs(th->th_dport), sbuf,
 750                                     ntohs(th->th_sport), thflags);
 751                                 break;
 752                         default:
 753                                 break;
 754                         }
 755                 }
 756                 if (blackhole) {
 757                         switch (blackhole) {
 758                         case 1:
 759                                 if (thflags & TH_SYN)
 760                                         goto drop;
 761                                 break;
 762                         case 2:
 763                                 goto drop;
 764                         default:
 765                                 goto drop;
 766                         }
 767                 }
 768                 rstreason = BANDLIM_RST_CLOSEDPORT;
 769                 goto dropwithreset;
 770         }
 771         INP_LOCK(inp);
 772
 773         /* Check the minimum TTL for socket. */
 774         if (inp->inp_ip_minttl != 0) {
 775 #ifdef INET6
 776                 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
 777                         goto drop;
 778                 else
 779 #endif
 780                 if (inp->inp_ip_minttl > ip->ip_ttl)
 781                         goto drop;
 782         }
 783
 784         if (inp->inp_vflag & INP_TIMEWAIT) {
 785                 /*
 786                  * The only option of relevance is TOF_CC, and only if
 787                  * present in a SYN segment.  See tcp_timewait().
 788                  */
 789                 if (thflags & TH_SYN)
 790                         tcp_dooptions(&to, optp, optlen, TO_SYN);
 791                 if (tcp_timewait(inp, &to, th, m, tlen))
 792                         goto findpcb;
 793                 /*
 794                  * tcp_timewait unlocks inp.
 795                  */
 796                 INP_INFO_WUNLOCK(&tcbinfo);
 797                 return;
 798         }
 799         tp = intotcpcb(inp);
 800         if (tp == 0) {
 801                 INP_UNLOCK(inp);
 802                 rstreason = BANDLIM_RST_CLOSEDPORT;
 803                 goto dropwithreset;
 804         }
 805         if (tp->t_state == TCPS_CLOSED)
 806                 goto drop;
 807
 808 #ifdef MAC
 809         INP_LOCK_ASSERT(inp);
 810         if (mac_check_inpcb_deliver(inp, m))
 811                 goto drop;
 812 #endif
 813         so = inp->inp_socket;
 814         KASSERT(so != NULL, ("tcp_input: so == NULL"));
 815 #ifdef TCPDEBUG
 816         if (so->so_options & SO_DEBUG) {
 817                 ostate = tp->t_state;
 818                 if (isipv6)
 819                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 820                 else
 821                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 822                 tcp_savetcp = *th;
 823         }
 824 #endif
 825         if (so->so_options & SO_ACCEPTCONN) {
 826                 struct in_conninfo inc;
 827
 828                 bzero(&inc, sizeof(inc));
 829 #ifdef INET6
 830                 inc.inc_isipv6 = isipv6;
 831 #endif
 832                 if (isipv6) {
 833                         inc.inc6_faddr = ip6->ip6_src;
 834                         inc.inc6_laddr = ip6->ip6_dst;
 835                 } else {
 836                         inc.inc_faddr = ip->ip_src;
 837                         inc.inc_laddr = ip->ip_dst;
 838                 }
 839                 inc.inc_fport = th->th_sport;
 840                 inc.inc_lport = th->th_dport;
 841
 842                 /*
 843                  * If the state is LISTEN then ignore segment if it contains
 844                  * a RST.  If the segment contains an ACK then it is bad and
 845                  * send a RST.  If it does not contain a SYN then it is not
 846                  * interesting; drop it.
 847                  *
 848                  * If the state is SYN_RECEIVED (syncache) and seg contains
 849                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 850                  * contains a RST, check the sequence number to see if it
 851                  * is a valid reset segment.
 852                  */
 853                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 854                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 855                                 /*
 856                                  * Parse the TCP options here because
 857                                  * syncookies need access to the reflected
 858                                  * timestamp.
 859                                  */
 860                                 tcp_dooptions(&to, optp, optlen, 0);
 861                                 if (!syncache_expand(&inc, &to, th, &so, m)) {
 862                                         /*
 863                                          * No syncache entry, or ACK was not
 864                                          * for our SYN/ACK.  Send a RST.
 865                                          */
 866                                         tcpstat.tcps_badsyn++;
 867                                         rstreason = BANDLIM_RST_OPENPORT;
 868                                         goto dropwithreset;
 869                                 }
 870                                 if (so == NULL) {
 871                                         /*
 872                                          * Could not complete 3-way handshake,
 873                                          * connection is being closed down, and
 874                                          * syncache has free'd mbuf.
 875                                          */
 876                                         INP_UNLOCK(inp);
 877                                         INP_INFO_WUNLOCK(&tcbinfo);
 878                                         return;
 879                                 }
 880                                 /*
 881                                  * Socket is created in state SYN_RECEIVED.
 882                                  * Continue processing segment.
 883                                  */
 884                                 INP_UNLOCK(inp);
 885                                 inp = sotoinpcb(so);
 886                                 INP_LOCK(inp);
 887                                 tp = intotcpcb(inp);
 888                                 /*
 889                                  * This is what would have happened in
 890                                  * tcp_output() when the SYN,ACK was sent.
 891                                  */
 892                                 tp->snd_up = tp->snd_una;
 893                                 tp->snd_max = tp->snd_nxt = tp->iss + 1;
 894                                 tp->last_ack_sent = tp->rcv_nxt;
 895                                 goto after_listen;
 896                         }
 897                         if (thflags & TH_RST) {
 898                                 syncache_chkrst(&inc, th);
 899                                 goto drop;
 900                         }
 901                         if (thflags & TH_ACK) {
 902                                 syncache_badack(&inc);
 903                                 tcpstat.tcps_badsyn++;
 904                                 rstreason = BANDLIM_RST_OPENPORT;
 905                                 goto dropwithreset;
 906                         }
 907                         goto drop;
 908                 }
 909
 910                 /*
 911                  * Segment's flags are (SYN) or (SYN|FIN).
 912                  */
 913 #ifdef INET6
 914                 /*
 915                  * If deprecated address is forbidden,
 916                  * we do not accept SYN to deprecated interface
 917                  * address to prevent any new inbound connection from
 918                  * getting established.
 919                  * When we do not accept SYN, we send a TCP RST,
 920                  * with deprecated source address (instead of dropping
 921                  * it).  We compromise it as it is much better for peer
 922                  * to send a RST, and RST will be the final packet
 923                  * for the exchange.
 924                  *
 925                  * If we do not forbid deprecated addresses, we accept
 926                  * the SYN packet.  RFC2462 does not suggest dropping
 927                  * SYN in this case.
 928                  * If we decipher RFC2462 5.5.4, it says like this:
 929                  * 1. use of deprecated addr with existing
 930                  *    communication is okay - "SHOULD continue to be
 931                  *    used"
 932                  * 2. use of it with new communication:
 933                  *   (2a) "SHOULD NOT be used if alternate address
 934                  *        with sufficient scope is available"
 935                  *   (2b) nothing mentioned otherwise.
 936                  * Here we fall into (2b) case as we have no choice in
 937                  * our source address selection - we must obey the peer.
 938                  *
 939                  * The wording in RFC2462 is confusing, and there are
 940                  * multiple description text for deprecated address
 941                  * handling - worse, they are not exactly the same.
 942                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 943                  */
 944                 if (isipv6 && !ip6_use_deprecated) {
 945                         struct in6_ifaddr *ia6;
 946
 947                         if ((ia6 = ip6_getdstifaddr(m)) &&
 948                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 949                                 INP_UNLOCK(inp);
 950                                 tp = NULL;
 951                                 rstreason = BANDLIM_RST_OPENPORT;
 952                                 goto dropwithreset;
 953                         }
 954                 }
 955 #endif
 956                 /*
 957                  * If it is from this socket, drop it, it must be forged.
 958                  * Don't bother responding if the destination was a broadcast.
 959                  */
 960                 if (th->th_dport == th->th_sport) {
 961                         if (isipv6) {
 962                                 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
 963                                                        &ip6->ip6_src))
 964                                         goto drop;
 965                         } else {
 966                                 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
 967                                         goto drop;
 968                         }
 969                 }
 970                 /*
 971                  * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
 972                  *
 973                  * Note that it is quite possible to receive unicast
 974                  * link-layer packets with a broadcast IP address. Use
 975                  * in_broadcast() to find them.
 976                  */
 977                 if (m->m_flags & (M_BCAST|M_MCAST))
 978                         goto drop;
 979                 if (isipv6) {
 980                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 981                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 982                                 goto drop;
 983                 } else {
 984                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 985                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 986                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 987                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 988                                 goto drop;
 989                 }
 990                 /*
 991                  * SYN appears to be valid; create compressed TCP state
 992                  * for syncache, or perform t/tcp connection.
 993                  */
 994                 if (so->so_qlen <= so->so_qlimit) {
 995 #ifdef TCPDEBUG
 996                         if (so->so_options & SO_DEBUG)
 997                                 tcp_trace(TA_INPUT, ostate, tp,
 998                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
 999 #endif
1000                         tcp_dooptions(&to, optp, optlen, TO_SYN);
1001                         if (!syncache_add(&inc, &to, th, inp, &so, m))
1002                                 goto drop;      /* XXX: does not happen */
1003                         if (so == NULL) {
1004                                 /*
1005                                  * Entry added to syncache, mbuf used to
1006                                  * send SYN,ACK packet.  Everything unlocked
1007                                  * already.
1008                                  */
1009                                 return;
1010                         }
1011                         panic("T/TCP not supported at the moment");
1012 #if 0 /* T/TCP */
1013                         /*
1014                          * Segment passed TAO tests.
1015                          * XXX: Can't happen at the moment.
1016                          */
1017                         INP_UNLOCK(inp);
1018                         inp = sotoinpcb(so);
1019                         INP_LOCK(inp);
1020                         tp = intotcpcb(inp);
1021                         tp->t_starttime = ticks;
1022                         tp->t_state = TCPS_ESTABLISHED;
1023
1024                         /*
1025                          * T/TCP logic:
1026                          * If there is a FIN or if there is data, then
1027                          * delay SYN,ACK(SYN) in the hope of piggy-backing
1028                          * it on a response segment.  Otherwise must send
1029                          * ACK now in case the other side is slow starting.
1030                          */
1031                         if (thflags & TH_FIN || tlen != 0)
1032                                 tp->t_flags |= (TF_DELACK | TF_NEEDSYN);
1033                         else
1034                                 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
1035                         tiwin = th->th_win << tp->snd_scale;
1036                         tcpstat.tcps_connects++;
1037                         soisconnected(so);
1038                         goto trimthenstep6;
1039 #endif  /* T/TCP */
1040                 }
1041                 goto drop;
1042         }
1043 after_listen:
1044         KASSERT(headlocked, ("tcp_input: after_listen: head not locked"));
1045         INP_LOCK_ASSERT(inp);
1046
1047         /* Syncache takes care of sockets in the listen state. */
1048         KASSERT(tp->t_state != TCPS_LISTEN, ("tcp_input: TCPS_LISTEN"));
1049
1050         /*
1051          * This is the second part of the MSS DoS prevention code (after
1052          * minmss on the sending side) and it deals with too many too small
1053          * tcp packets in a too short timeframe (1 second).
1054          *
1055          * For every full second we count the number of received packets
1056          * and bytes. If we get a lot of packets per second for this connection
1057          * (tcp_minmssoverload) we take a closer look at it and compute the
1058          * average packet size for the past second. If that is less than
1059          * tcp_minmss we get too many packets with very small payload which
1060          * is not good and burdens our system (and every packet generates
1061          * a wakeup to the process connected to our socket). We can reasonable
1062          * expect this to be small packet DoS attack to exhaust our CPU
1063          * cycles.
1064          *
1065          * Care has to be taken for the minimum packet overload value. This
1066          * value defines the minimum number of packets per second before we
1067          * start to worry. This must not be too low to avoid killing for
1068          * example interactive connections with many small packets like
1069          * telnet or SSH.
1070          *
1071          * Setting either tcp_minmssoverload or tcp_minmss to "0" disables
1072          * this check.
1073          *
1074          * Account for packet if payload packet, skip over ACK, etc.
1075          */
1076         if (tcp_minmss && tcp_minmssoverload &&
1077             tp->t_state == TCPS_ESTABLISHED && tlen > 0) {
1078                 if ((unsigned int)(tp->rcv_second - ticks) < hz) {
1079                         tp->rcv_pps++;
1080                         tp->rcv_byps += tlen + off;
1081                         if (tp->rcv_pps > tcp_minmssoverload) {
1082                                 if ((tp->rcv_byps / tp->rcv_pps) < tcp_minmss) {
1083                                         printf("too many small tcp packets from "
1084                                                "%s:%u, av. %lubyte/packet, "
1085                                                "dropping connection\n",
1086 #ifdef INET6
1087                                                 isipv6 ?
1088                                                 ip6_sprintf(ip6buf,
1089                                                     &inp->inp_inc.inc6_faddr) :
1090 #endif
1091                                                 inet_ntoa(inp->inp_inc.inc_faddr),
1092                                                 inp->inp_inc.inc_fport,
1093                                                 tp->rcv_byps / tp->rcv_pps);
1094                                         KASSERT(headlocked, ("tcp_input: "
1095                                             "after_listen: tcp_drop: head "
1096                                             "not locked"));
1097                                         tp = tcp_drop(tp, ECONNRESET);
1098                                         tcpstat.tcps_minmssdrops++;
1099                                         goto drop;
1100                                 }
1101                         }
1102                 } else {
1103                         tp->rcv_second = ticks + hz;
1104                         tp->rcv_pps = 1;
1105                         tp->rcv_byps = tlen + off;
1106                 }
1107         }
1108
1109         /*
1110          * Segment received on connection.
1111          * Reset idle time and keep-alive timer.
1112          */
1113         tp->t_rcvtime = ticks;
1114         if (TCPS_HAVEESTABLISHED(tp->t_state))
1115                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
1116
1117         /*
1118          * Unscale the window into a 32-bit value.
1119          * This value is bogus for the TCPS_SYN_SENT state
1120          * and is overwritten later.
1121          */
1122         tiwin = th->th_win << tp->snd_scale;
1123
1124         /*
1125          * Parse options on any incoming segment.
1126          */
1127         tcp_dooptions(&to, optp, optlen, (thflags & TH_SYN) ? TO_SYN : 0);
1128
1129         /*
1130          * If echoed timestamp is later than the current time,
1131          * fall back to non RFC1323 RTT calculation.  Normalize
1132          * timestamp if syncookies were used when this connection
1133          * was established.
1134          */
1135         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1136                 to.to_tsecr -= tp->ts_offset;
1137                 if (TSTMP_GT(to.to_tsecr, ticks))
1138                         to.to_tsecr = 0;
1139         }
1140
1141         /*
1142          * Process options only when we get SYN/ACK back. The SYN case
1143          * for incoming connections is handled in tcp_syncache.
1144          * XXX this is traditional behavior, may need to be cleaned up.
1145          */
1146         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1147                 if ((to.to_flags & TOF_SCALE) &&
1148                     (tp->t_flags & TF_REQ_SCALE)) {
1149                         tp->t_flags |= TF_RCVD_SCALE;
1150                         tp->snd_scale = to.to_wscale;
1151                         tp->snd_wnd = th->th_win << tp->snd_scale;
1152                         tiwin = tp->snd_wnd;
1153                 }
1154                 if (to.to_flags & TOF_TS) {
1155                         tp->t_flags |= TF_RCVD_TSTMP;
1156                         tp->ts_recent = to.to_tsval;
1157                         tp->ts_recent_age = ticks;
1158                 }
1159                 /* Initial send window, already scaled. */
1160                 tp->snd_wnd = th->th_win;
1161                 if (to.to_flags & TOF_MSS)
1162                         tcp_mss(tp, to.to_mss);
1163                 if (tp->sack_enable) {
1164                         if (!(to.to_flags & TOF_SACK))
1165                                 tp->sack_enable = 0;
1166                         else
1167                                 tp->t_flags |= TF_SACK_PERMIT;
1168                 }
1169
1170         }
1171
1172         /*
1173          * Header prediction: check for the two common cases
1174          * of a uni-directional data xfer.  If the packet has
1175          * no control flags, is in-sequence, the window didn't
1176          * change and we're not retransmitting, it's a
1177          * candidate.  If the length is zero and the ack moved
1178          * forward, we're the sender side of the xfer.  Just
1179          * free the data acked & wake any higher level process
1180          * that was blocked waiting for space.  If the length
1181          * is non-zero and the ack didn't move, we're the
1182          * receiver side.  If we're getting packets in-order
1183          * (the reassembly queue is empty), add the data to
1184          * the socket buffer and note that we need a delayed ack.
1185          * Make sure that the hidden state-flags are also off.
1186          * Since we check for TCPS_ESTABLISHED above, it can only
1187          * be TH_NEEDSYN.
1188          */
1189         if (tp->t_state == TCPS_ESTABLISHED &&
1190             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1191             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1192             ((to.to_flags & TOF_TS) == 0 ||
1193              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
1194              th->th_seq == tp->rcv_nxt && tiwin && tiwin == tp->snd_wnd &&
1195              tp->snd_nxt == tp->snd_max) {
1196
1197                 /*
1198                  * If last ACK falls within this segment's sequence numbers,
1199                  * record the timestamp.
1200                  * NOTE that the test is modified according to the latest
1201                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1202                  */
1203                 if ((to.to_flags & TOF_TS) != 0 &&
1204                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1205                         tp->ts_recent_age = ticks;
1206                         tp->ts_recent = to.to_tsval;
1207                 }
1208
1209                 if (tlen == 0) {
1210                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1211                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1212                             tp->snd_cwnd >= tp->snd_wnd &&
1213                             ((!tcp_do_newreno && !tp->sack_enable &&
1214                               tp->t_dupacks < tcprexmtthresh) ||
1215                              ((tcp_do_newreno || tp->sack_enable) &&
1216                               !IN_FASTRECOVERY(tp) && to.to_nsacks == 0 &&
1217                               TAILQ_EMPTY(&tp->snd_holes)))) {
1218                                 KASSERT(headlocked, ("headlocked"));
1219                                 INP_INFO_WUNLOCK(&tcbinfo);
1220                                 headlocked = 0;
1221                                 /*
1222                                  * this is a pure ack for outstanding data.
1223                                  */
1224                                 ++tcpstat.tcps_predack;
1225                                 /*
1226                                  * "bad retransmit" recovery
1227                                  */
1228                                 if (tp->t_rxtshift == 1 &&
1229                                     ticks < tp->t_badrxtwin) {
1230                                         ++tcpstat.tcps_sndrexmitbad;
1231                                         tp->snd_cwnd = tp->snd_cwnd_prev;
1232                                         tp->snd_ssthresh =
1233                                             tp->snd_ssthresh_prev;
1234                                         tp->snd_recover = tp->snd_recover_prev;
1235                                         if (tp->t_flags & TF_WASFRECOVERY)
1236                                             ENTER_FASTRECOVERY(tp);
1237                                         tp->snd_nxt = tp->snd_max;
1238                                         tp->t_badrxtwin = 0;
1239                                 }
1240
1241                                 /*
1242                                  * Recalculate the transmit timer / rtt.
1243                                  *
1244                                  * Some boxes send broken timestamp replies
1245                                  * during the SYN+ACK phase, ignore
1246                                  * timestamps of 0 or we could calculate a
1247                                  * huge RTT and blow up the retransmit timer.
1248                                  */
1249                                 if ((to.to_flags & TOF_TS) != 0 &&
1250                                     to.to_tsecr) {
1251                                         if (!tp->t_rttlow ||
1252                                             tp->t_rttlow > ticks - to.to_tsecr)
1253                                                 tp->t_rttlow = ticks - to.to_tsecr;
1254                                         tcp_xmit_timer(tp,
1255                                             ticks - to.to_tsecr + 1);
1256                                 } else if (tp->t_rtttime &&
1257                                             SEQ_GT(th->th_ack, tp->t_rtseq)) {
1258                                         if (!tp->t_rttlow ||
1259                                             tp->t_rttlow > ticks - tp->t_rtttime)
1260                                                 tp->t_rttlow = ticks - tp->t_rtttime;
1261                                         tcp_xmit_timer(tp,
1262                                                         ticks - tp->t_rtttime);
1263                                 }
1264                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1265                                 acked = th->th_ack - tp->snd_una;
1266                                 tcpstat.tcps_rcvackpack++;
1267                                 tcpstat.tcps_rcvackbyte += acked;
1268                                 sbdrop(&so->so_snd, acked);
1269                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1270                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1271                                         tp->snd_recover = th->th_ack - 1;
1272                                 tp->snd_una = th->th_ack;
1273                                 /*
1274                                  * pull snd_wl2 up to prevent seq wrap relative
1275                                  * to th_ack.
1276                                  */
1277                                 tp->snd_wl2 = th->th_ack;
1278                                 tp->t_dupacks = 0;
1279                                 m_freem(m);
1280                                 ND6_HINT(tp); /* some progress has been done */
1281
1282                                 /*
1283                                  * If all outstanding data are acked, stop
1284                                  * retransmit timer, otherwise restart timer
1285                                  * using current (possibly backed-off) value.
1286                                  * If process is waiting for space,
1287                                  * wakeup/selwakeup/signal.  If data
1288                                  * are ready to send, let tcp_output
1289                                  * decide between more output or persist.
1290
1291 #ifdef TCPDEBUG
1292                                 if (so->so_options & SO_DEBUG)
1293                                         tcp_trace(TA_INPUT, ostate, tp,
1294                                             (void *)tcp_saveipgen,
1295                                             &tcp_savetcp, 0);
1296 #endif
1297                                  */
1298                                 if (tp->snd_una == tp->snd_max)
1299                                         callout_stop(tp->tt_rexmt);
1300                                 else if (!callout_active(tp->tt_persist))
1301                                         callout_reset(tp->tt_rexmt,
1302                                                       tp->t_rxtcur,
1303                                                       tcp_timer_rexmt, tp);
1304
1305                                 sowwakeup(so);
1306                                 if (so->so_snd.sb_cc)
1307                                         (void) tcp_output(tp);
1308                                 goto check_delack;
1309                         }
1310                 } else if (th->th_ack == tp->snd_una &&
1311                     LIST_EMPTY(&tp->t_segq) &&
1312                     tlen <= sbspace(&so->so_rcv)) {
1313                         int newsize = 0;        /* automatic sockbuf scaling */
1314
1315                         KASSERT(headlocked, ("headlocked"));
1316                         INP_INFO_WUNLOCK(&tcbinfo);
1317                         headlocked = 0;
1318                         /*
1319                          * this is a pure, in-sequence data packet
1320                          * with nothing on the reassembly queue and
1321                          * we have enough buffer space to take it.
1322                          */
1323                         /* Clean receiver SACK report if present */
1324                         if (tp->sack_enable && tp->rcv_numsacks)
1325                                 tcp_clean_sackreport(tp);
1326                         ++tcpstat.tcps_preddat;
1327                         tp->rcv_nxt += tlen;
1328                         /*
1329                          * Pull snd_wl1 up to prevent seq wrap relative to
1330                          * th_seq.
1331                          */
1332                         tp->snd_wl1 = th->th_seq;
1333                         /*
1334                          * Pull rcv_up up to prevent seq wrap relative to
1335                          * rcv_nxt.
1336                          */
1337                         tp->rcv_up = tp->rcv_nxt;
1338                         tcpstat.tcps_rcvpack++;
1339                         tcpstat.tcps_rcvbyte += tlen;
1340                         ND6_HINT(tp);   /* some progress has been done */
1341 #ifdef TCPDEBUG
1342                         if (so->so_options & SO_DEBUG)
1343                                 tcp_trace(TA_INPUT, ostate, tp,
1344                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
1345 #endif
1346                 /*
1347                  * Automatic sizing of receive socket buffer.  Often the send
1348                  * buffer size is not optimally adjusted to the actual network
1349                  * conditions at hand (delay bandwidth product).  Setting the
1350                  * buffer size too small limits throughput on links with high
1351                  * bandwidth and high delay (eg. trans-continental/oceanic links).
1352                  *
1353                  * On the receive side the socket buffer memory is only rarely
1354                  * used to any significant extent.  This allows us to be much
1355                  * more aggressive in scaling the receive socket buffer.  For
1356                  * the case that the buffer space is actually used to a large
1357                  * extent and we run out of kernel memory we can simply drop
1358                  * the new segments; TCP on the sender will just retransmit it
1359                  * later.  Setting the buffer size too big may only consume too
1360                  * much kernel memory if the application doesn't read() from
1361                  * the socket or packet loss or reordering makes use of the
1362                  * reassembly queue.
1363                  *
1364                  * The criteria to step up the receive buffer one notch are:
1365                  *  1. the number of bytes received during the time it takes
1366                  *     one timestamp to be reflected back to us (the RTT);
1367                  *  2. received bytes per RTT is within seven eighth of the
1368                  *     current socket buffer size;
1369                  *  3. receive buffer size has not hit maximal automatic size;
1370                  *
1371                  * This algorithm does one step per RTT at most and only if
1372                  * we receive a bulk stream w/o packet losses or reorderings.
1373                  * Shrinking the buffer during idle times is not necessary as
1374                  * it doesn't consume any memory when idle.
1375                  *
1376                  * TODO: Only step up if the application is actually serving
1377                  * the buffer to better manage the socket buffer resources.
1378                  */
1379                         if (tcp_do_autorcvbuf &&
1380                             to.to_tsecr &&
1381                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1382                                 if (to.to_tsecr > tp->rfbuf_ts &&
1383                                     to.to_tsecr - tp->rfbuf_ts < hz) {
1384                                         if (tp->rfbuf_cnt >
1385                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
1386                                             so->so_rcv.sb_hiwat <
1387                                             tcp_autorcvbuf_max) {
1388                                                 newsize =
1389                                                     min(so->so_rcv.sb_hiwat +
1390                                                     tcp_autorcvbuf_inc,
1391                                                     tcp_autorcvbuf_max);
1392                                         }
1393                                         /* Start over with next RTT. */
1394                                         tp->rfbuf_ts = 0;
1395                                         tp->rfbuf_cnt = 0;
1396                                 } else
1397                                         tp->rfbuf_cnt += tlen;  /* add up */
1398                         }
1399
1400                         /* Add data to socket buffer. */
1401                         SOCKBUF_LOCK(&so->so_rcv);
1402                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1403                                 m_freem(m);
1404                         } else {
1405                                 /*
1406                                  * Set new socket buffer size.
1407                                  * Give up when limit is reached.
1408                                  */
1409                                 if (newsize)
1410                                         if (!sbreserve_locked(&so->so_rcv,
1411                                             newsize, so, curthread))
1412                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1413                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1414                                 sbappendstream_locked(&so->so_rcv, m);
1415                         }
1416                         sorwakeup_locked(so);
1417                         if (DELAY_ACK(tp)) {
1418                                 tp->t_flags |= TF_DELACK;
1419                         } else {
1420                                 tp->t_flags |= TF_ACKNOW;
1421                                 tcp_output(tp);
1422                         }
1423                         goto check_delack;
1424                 }
1425         }
1426
1427         /*
1428          * Calculate amount of space in receive window,
1429          * and then do TCP input processing.
1430          * Receive window is amount of space in rcv queue,
1431          * but not less than advertised window.
1432          */
1433         { int win;
1434
1435         win = sbspace(&so->so_rcv);
1436         if (win < 0)
1437                 win = 0;
1438         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1439         }
1440
1441         /* Reset receive buffer auto scaling when not in bulk receive mode. */
1442         tp->rfbuf_ts = 0;
1443         tp->rfbuf_cnt = 0;
1444
1445         switch (tp->t_state) {
1446
1447         /*
1448          * If the state is SYN_RECEIVED:
1449          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1450          */
1451         case TCPS_SYN_RECEIVED:
1452                 if ((thflags & TH_ACK) &&
1453                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1454                      SEQ_GT(th->th_ack, tp->snd_max))) {
1455                                 rstreason = BANDLIM_RST_OPENPORT;
1456                                 goto dropwithreset;
1457                 }
1458                 break;
1459
1460         /*
1461          * If the state is SYN_SENT:
1462          *      if seg contains an ACK, but not for our SYN, drop the input.
1463          *      if seg contains a RST, then drop the connection.
1464          *      if seg does not contain SYN, then drop it.
1465          * Otherwise this is an acceptable SYN segment
1466          *      initialize tp->rcv_nxt and tp->irs
1467          *      if seg contains ack then advance tp->snd_una
1468          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1469          *      arrange for segment to be acked (eventually)
1470          *      continue processing rest of data/controls, beginning with URG
1471          */
1472         case TCPS_SYN_SENT:
1473                 if ((thflags & TH_ACK) &&
1474                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1475                      SEQ_GT(th->th_ack, tp->snd_max))) {
1476                         rstreason = BANDLIM_UNLIMITED;
1477                         goto dropwithreset;
1478                 }
1479                 if (thflags & TH_RST) {
1480                         if (thflags & TH_ACK) {
1481                                 KASSERT(headlocked, ("tcp_input: after_listen"
1482                                     ": tcp_drop.2: head not locked"));
1483                                 tp = tcp_drop(tp, ECONNREFUSED);
1484                         }
1485                         goto drop;
1486                 }
1487                 if ((thflags & TH_SYN) == 0)
1488                         goto drop;
1489
1490                 tp->irs = th->th_seq;
1491                 tcp_rcvseqinit(tp);
1492                 if (thflags & TH_ACK) {
1493                         tcpstat.tcps_connects++;
1494                         soisconnected(so);
1495 #ifdef MAC
1496                         SOCK_LOCK(so);
1497                         mac_set_socket_peer_from_mbuf(m, so);
1498                         SOCK_UNLOCK(so);
1499 #endif
1500                         /* Do window scaling on this connection? */
1501                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1502                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1503                                 tp->rcv_scale = tp->request_r_scale;
1504                         }
1505                         tp->rcv_adv += tp->rcv_wnd;
1506                         tp->snd_una++;          /* SYN is acked */
1507                         /*
1508                          * If there's data, delay ACK; if there's also a FIN
1509                          * ACKNOW will be turned on later.
1510                          */
1511                         if (DELAY_ACK(tp) && tlen != 0)
1512                                 callout_reset(tp->tt_delack, tcp_delacktime,
1513                                     tcp_timer_delack, tp);
1514                         else
1515                                 tp->t_flags |= TF_ACKNOW;
1516                         /*
1517                          * Received <SYN,ACK> in SYN_SENT[*] state.
1518                          * Transitions:
1519                          *      SYN_SENT  --> ESTABLISHED
1520                          *      SYN_SENT* --> FIN_WAIT_1
1521                          */
1522                         tp->t_starttime = ticks;
1523                         if (tp->t_flags & TF_NEEDFIN) {
1524                                 tp->t_state = TCPS_FIN_WAIT_1;
1525                                 tp->t_flags &= ~TF_NEEDFIN;
1526                                 thflags &= ~TH_SYN;
1527                         } else {
1528                                 tp->t_state = TCPS_ESTABLISHED;
1529                                 callout_reset(tp->tt_keep, tcp_keepidle,
1530                                               tcp_timer_keep, tp);
1531                         }
1532                 } else {
1533                         /*
1534                          * Received initial SYN in SYN-SENT[*] state =>
1535                          * simultaneous open.  If segment contains CC option
1536                          * and there is a cached CC, apply TAO test.
1537                          * If it succeeds, connection is * half-synchronized.
1538                          * Otherwise, do 3-way handshake:
1539                          *        SYN-SENT -> SYN-RECEIVED
1540                          *        SYN-SENT* -> SYN-RECEIVED*
1541                          * If there was no CC option, clear cached CC value.
1542                          */
1543                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
1544                         callout_stop(tp->tt_rexmt);
1545                         tp->t_state = TCPS_SYN_RECEIVED;
1546                 }
1547
1548 #if 0 /* T/TCP */
1549 trimthenstep6:
1550 #endif
1551                 KASSERT(headlocked, ("tcp_input: trimthenstep6: head not "
1552                     "locked"));
1553                 INP_LOCK_ASSERT(inp);
1554
1555                 /*
1556                  * Advance th->th_seq to correspond to first data byte.
1557                  * If data, trim to stay within window,
1558                  * dropping FIN if necessary.
1559                  */
1560                 th->th_seq++;
1561                 if (tlen > tp->rcv_wnd) {
1562                         todrop = tlen - tp->rcv_wnd;
1563                         m_adj(m, -todrop);
1564                         tlen = tp->rcv_wnd;
1565                         thflags &= ~TH_FIN;
1566                         tcpstat.tcps_rcvpackafterwin++;
1567                         tcpstat.tcps_rcvbyteafterwin += todrop;
1568                 }
1569                 tp->snd_wl1 = th->th_seq - 1;
1570                 tp->rcv_up = th->th_seq;
1571                 /*
1572                  * Client side of transaction: already sent SYN and data.
1573                  * If the remote host used T/TCP to validate the SYN,
1574                  * our data will be ACK'd; if so, enter normal data segment
1575                  * processing in the middle of step 5, ack processing.
1576                  * Otherwise, goto step 6.
1577                  */
1578                 if (thflags & TH_ACK)
1579                         goto process_ACK;
1580
1581                 goto step6;
1582
1583         /*
1584          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1585          *      do normal processing.
1586          *
1587          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
1588          */
1589         case TCPS_LAST_ACK:
1590         case TCPS_CLOSING:
1591         case TCPS_TIME_WAIT:
1592                 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait"));
1593                 break;  /* continue normal processing */
1594         }
1595
1596         /*
1597          * States other than LISTEN or SYN_SENT.
1598          * First check the RST flag and sequence number since reset segments
1599          * are exempt from the timestamp and connection count tests.  This
1600          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1601          * below which allowed reset segments in half the sequence space
1602          * to fall though and be processed (which gives forged reset
1603          * segments with a random sequence number a 50 percent chance of
1604          * killing a connection).
1605          * Then check timestamp, if present.
1606          * Then check the connection count, if present.
1607          * Then check that at least some bytes of segment are within
1608          * receive window.  If segment begins before rcv_nxt,
1609          * drop leading data (and SYN); if nothing left, just ack.
1610          *
1611          *
1612          * If the RST bit is set, check the sequence number to see
1613          * if this is a valid reset segment.
1614          * RFC 793 page 37:
1615          *   In all states except SYN-SENT, all reset (RST) segments
1616          *   are validated by checking their SEQ-fields.  A reset is
1617          *   valid if its sequence number is in the window.
1618          * Note: this does not take into account delayed ACKs, so
1619          *   we should test against last_ack_sent instead of rcv_nxt.
1620          *   The sequence number in the reset segment is normally an
1621          *   echo of our outgoing acknowlegement numbers, but some hosts
1622          *   send a reset with the sequence number at the rightmost edge
1623          *   of our receive window, and we have to handle this case.
1624          * Note 2: Paul Watson's paper "Slipping in the Window" has shown
1625          *   that brute force RST attacks are possible.  To combat this,
1626          *   we use a much stricter check while in the ESTABLISHED state,
1627          *   only accepting RSTs where the sequence number is equal to
1628          *   last_ack_sent.  In all other states (the states in which a
1629          *   RST is more likely), the more permissive check is used.
1630          * If we have multiple segments in flight, the intial reset
1631          * segment sequence numbers will be to the left of last_ack_sent,
1632          * but they will eventually catch up.
1633          * In any case, it never made sense to trim reset segments to
1634          * fit the receive window since RFC 1122 says:
1635          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1636          *
1637          *    A TCP SHOULD allow a received RST segment to include data.
1638          *
1639          *    DISCUSSION
1640          *         It has been suggested that a RST segment could contain
1641          *         ASCII text that encoded and explained the cause of the
1642          *         RST.  No standard has yet been established for such
1643          *         data.
1644          *
1645          * If the reset segment passes the sequence number test examine
1646          * the state:
1647          *    SYN_RECEIVED STATE:
1648          *      If passive open, return to LISTEN state.
1649          *      If active open, inform user that connection was refused.
1650          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1651          *      Inform user that connection was reset, and close tcb.
1652          *    CLOSING, LAST_ACK STATES:
1653          *      Close the tcb.
1654          *    TIME_WAIT STATE:
1655          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1656          *      RFC 1337.
1657          */
1658         if (thflags & TH_RST) {
1659                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1660                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1661                         switch (tp->t_state) {
1662
1663                         case TCPS_SYN_RECEIVED:
1664                                 so->so_error = ECONNREFUSED;
1665                                 goto close;
1666
1667                         case TCPS_ESTABLISHED:
1668                                 if (tcp_insecure_rst == 0 &&
1669                                     !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
1670                                     SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
1671                                     !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1672                                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
1673                                         tcpstat.tcps_badrst++;
1674                                         goto drop;
1675                                 }
1676                         case TCPS_FIN_WAIT_1:
1677                         case TCPS_FIN_WAIT_2:
1678                         case TCPS_CLOSE_WAIT:
1679                                 so->so_error = ECONNRESET;
1680                         close:
1681                                 tp->t_state = TCPS_CLOSED;
1682                                 tcpstat.tcps_drops++;
1683                                 KASSERT(headlocked, ("tcp_input: "
1684                                     "trimthenstep6: tcp_close: head not "
1685                                     "locked"));
1686                                 tp = tcp_close(tp);
1687                                 break;
1688
1689                         case TCPS_CLOSING:
1690                         case TCPS_LAST_ACK:
1691                                 KASSERT(headlocked, ("trimthenstep6: "
1692                                     "tcp_close.2: head not locked"));
1693                                 tp = tcp_close(tp);
1694                                 break;
1695
1696                         case TCPS_TIME_WAIT:
1697                                 KASSERT(tp->t_state != TCPS_TIME_WAIT,
1698                                     ("timewait"));
1699                                 break;
1700                         }
1701                 }
1702                 goto drop;
1703         }
1704
1705         /*
1706          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1707          * and it's less than ts_recent, drop it.
1708          */
1709         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1710             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1711
1712                 /* Check to see if ts_recent is over 24 days old.  */
1713                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1714                         /*
1715                          * Invalidate ts_recent.  If this segment updates
1716                          * ts_recent, the age will be reset later and ts_recent
1717                          * will get a valid value.  If it does not, setting
1718                          * ts_recent to zero will at least satisfy the
1719                          * requirement that zero be placed in the timestamp
1720                          * echo reply when ts_recent isn't valid.  The
1721                          * age isn't reset until we get a valid ts_recent
1722                          * because we don't want out-of-order segments to be
1723                          * dropped when ts_recent is old.
1724                          */
1725                         tp->ts_recent = 0;
1726                 } else {
1727                         tcpstat.tcps_rcvduppack++;
1728                         tcpstat.tcps_rcvdupbyte += tlen;
1729                         tcpstat.tcps_pawsdrop++;
1730                         if (tlen)
1731                                 goto dropafterack;
1732                         goto drop;
1733                 }
1734         }
1735
1736         /*
1737          * In the SYN-RECEIVED state, validate that the packet belongs to
1738          * this connection before trimming the data to fit the receive
1739          * window.  Check the sequence number versus IRS since we know
1740          * the sequence numbers haven't wrapped.  This is a partial fix
1741          * for the "LAND" DoS attack.
1742          */
1743         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1744                 rstreason = BANDLIM_RST_OPENPORT;
1745                 goto dropwithreset;
1746         }
1747
1748         todrop = tp->rcv_nxt - th->th_seq;
1749         if (todrop > 0) {
1750                 if (thflags & TH_SYN) {
1751                         thflags &= ~TH_SYN;
1752                         th->th_seq++;
1753                         if (th->th_urp > 1)
1754                                 th->th_urp--;
1755                         else
1756                                 thflags &= ~TH_URG;
1757                         todrop--;
1758                 }
1759                 /*
1760                  * Following if statement from Stevens, vol. 2, p. 960.
1761                  */
1762                 if (todrop > tlen
1763                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1764                         /*
1765                          * Any valid FIN must be to the left of the window.
1766                          * At this point the FIN must be a duplicate or out
1767                          * of sequence; drop it.
1768                          */
1769                         thflags &= ~TH_FIN;
1770
1771                         /*
1772                          * Send an ACK to resynchronize and drop any data.
1773                          * But keep on processing for RST or ACK.
1774                          */
1775                         tp->t_flags |= TF_ACKNOW;
1776                         todrop = tlen;
1777                         tcpstat.tcps_rcvduppack++;
1778                         tcpstat.tcps_rcvdupbyte += todrop;
1779                 } else {
1780                         tcpstat.tcps_rcvpartduppack++;
1781                         tcpstat.tcps_rcvpartdupbyte += todrop;
1782                 }
1783                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1784                 th->th_seq += todrop;
1785                 tlen -= todrop;
1786                 if (th->th_urp > todrop)
1787                         th->th_urp -= todrop;
1788                 else {
1789                         thflags &= ~TH_URG;
1790                         th->th_urp = 0;
1791                 }
1792         }
1793
1794         /*
1795          * If new data are received on a connection after the
1796          * user processes are gone, then RST the other end.
1797          */
1798         if ((so->so_state & SS_NOFDREF) &&
1799             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1800                 KASSERT(headlocked, ("trimthenstep6: tcp_close.3: head not "
1801                     "locked"));
1802                 tp = tcp_close(tp);
1803                 tcpstat.tcps_rcvafterclose++;
1804                 rstreason = BANDLIM_UNLIMITED;
1805                 goto dropwithreset;
1806         }
1807
1808         /*
1809          * If segment ends after window, drop trailing data
1810          * (and PUSH and FIN); if nothing left, just ACK.
1811          */
1812         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1813         if (todrop > 0) {
1814                 tcpstat.tcps_rcvpackafterwin++;
1815                 if (todrop >= tlen) {
1816                         tcpstat.tcps_rcvbyteafterwin += tlen;
1817                         /*
1818                          * If a new connection request is received
1819                          * while in TIME_WAIT, drop the old connection
1820                          * and start over if the sequence numbers
1821                          * are above the previous ones.
1822                          */
1823                         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait"));
1824                         if (thflags & TH_SYN &&
1825                             tp->t_state == TCPS_TIME_WAIT &&
1826                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1827                                 KASSERT(headlocked, ("trimthenstep6: "
1828                                     "tcp_close.4: head not locked"));
1829                                 tp = tcp_close(tp);
1830                                 goto findpcb;
1831                         }
1832                         /*
1833                          * If window is closed can only take segments at
1834                          * window edge, and have to drop data and PUSH from
1835                          * incoming segments.  Continue processing, but
1836                          * remember to ack.  Otherwise, drop segment
1837                          * and ack.
1838                          */
1839                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1840                                 tp->t_flags |= TF_ACKNOW;
1841                                 tcpstat.tcps_rcvwinprobe++;
1842                         } else
1843                                 goto dropafterack;
1844                 } else
1845                         tcpstat.tcps_rcvbyteafterwin += todrop;
1846                 m_adj(m, -todrop);
1847                 tlen -= todrop;
1848                 thflags &= ~(TH_PUSH|TH_FIN);
1849         }
1850
1851         /*
1852          * If last ACK falls within this segment's sequence numbers,
1853          * record its timestamp.
1854          * NOTE:
1855          * 1) That the test incorporates suggestions from the latest
1856          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
1857          * 2) That updating only on newer timestamps interferes with
1858          *    our earlier PAWS tests, so this check should be solely
1859          *    predicated on the sequence space of this segment.
1860          * 3) That we modify the segment boundary check to be
1861          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
1862          *    instead of RFC1323's
1863          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
1864          *    This modified check allows us to overcome RFC1323's
1865          *    limitations as described in Stevens TCP/IP Illustrated
1866          *    Vol. 2 p.869. In such cases, we can still calculate the
1867          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
1868          */
1869         if ((to.to_flags & TOF_TS) != 0 &&
1870             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
1871             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
1872                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
1873                 tp->ts_recent_age = ticks;
1874                 tp->ts_recent = to.to_tsval;
1875         }
1876
1877         /*
1878          * If a SYN is in the window, then this is an
1879          * error and we send an RST and drop the connection.
1880          */
1881         if (thflags & TH_SYN) {
1882                 KASSERT(headlocked, ("tcp_input: tcp_drop: trimthenstep6: "
1883                     "head not locked"));
1884                 tp = tcp_drop(tp, ECONNRESET);
1885                 rstreason = BANDLIM_UNLIMITED;
1886                 goto drop;
1887         }
1888
1889         /*
1890          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1891          * flag is on (half-synchronized state), then queue data for
1892          * later processing; else drop segment and return.
1893          */
1894         if ((thflags & TH_ACK) == 0) {
1895                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1896                     (tp->t_flags & TF_NEEDSYN))
1897                         goto step6;
1898                 else if (tp->t_flags & TF_ACKNOW)
1899                         goto dropafterack;
1900                 else
1901                         goto drop;
1902         }
1903
1904         /*
1905          * Ack processing.
1906          */
1907         switch (tp->t_state) {
1908
1909         /*
1910          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1911          * ESTABLISHED state and continue processing.
1912          * The ACK was checked above.
1913          */
1914         case TCPS_SYN_RECEIVED:
1915
1916                 tcpstat.tcps_connects++;
1917                 soisconnected(so);
1918                 /* Do window scaling? */
1919                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1920                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1921                         tp->rcv_scale = tp->request_r_scale;
1922                         tp->snd_wnd = tiwin;
1923                 }
1924                 /*
1925                  * Make transitions:
1926                  *      SYN-RECEIVED  -> ESTABLISHED
1927                  *      SYN-RECEIVED* -> FIN-WAIT-1
1928                  */
1929                 tp->t_starttime = ticks;
1930                 if (tp->t_flags & TF_NEEDFIN) {
1931                         tp->t_state = TCPS_FIN_WAIT_1;
1932                         tp->t_flags &= ~TF_NEEDFIN;
1933                 } else {
1934                         tp->t_state = TCPS_ESTABLISHED;
1935                         callout_reset(tp->tt_keep, tcp_keepidle,
1936                                       tcp_timer_keep, tp);
1937                 }
1938                 /*
1939                  * If segment contains data or ACK, will call tcp_reass()
1940                  * later; if not, do so now to pass queued data to user.
1941                  */
1942                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1943                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1944                             (struct mbuf *)0);
1945                 tp->snd_wl1 = th->th_seq - 1;
1946                 /* FALLTHROUGH */
1947
1948         /*
1949          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1950          * ACKs.  If the ack is in the range
1951          *      tp->snd_una < th->th_ack <= tp->snd_max
1952          * then advance tp->snd_una to th->th_ack and drop
1953          * data from the retransmission queue.  If this ACK reflects
1954          * more up to date window information we update our window information.
1955          */
1956         case TCPS_ESTABLISHED:
1957         case TCPS_FIN_WAIT_1:
1958         case TCPS_FIN_WAIT_2:
1959         case TCPS_CLOSE_WAIT:
1960         case TCPS_CLOSING:
1961         case TCPS_LAST_ACK:
1962         case TCPS_TIME_WAIT:
1963                 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait"));
1964                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1965                         tcpstat.tcps_rcvacktoomuch++;
1966                         goto dropafterack;
1967                 }
1968                 if (tp->sack_enable &&
1969                     (to.to_nsacks > 0 || !TAILQ_EMPTY(&tp->snd_holes)))
1970                         tcp_sack_doack(tp, &to, th->th_ack);
1971                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1972                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1973                                 tcpstat.tcps_rcvdupack++;
1974                                 /*
1975                                  * If we have outstanding data (other than
1976                                  * a window probe), this is a completely
1977                                  * duplicate ack (ie, window info didn't
1978                                  * change), the ack is the biggest we've
1979                                  * seen and we've seen exactly our rexmt
1980                                  * threshhold of them, assume a packet
1981                                  * has been dropped and retransmit it.
1982                                  * Kludge snd_nxt & the congestion
1983                                  * window so we send only this one
1984                                  * packet.
1985                                  *
1986                                  * We know we're losing at the current
1987                                  * window size so do congestion avoidance
1988                                  * (set ssthresh to half the current window
1989                                  * and pull our congestion window back to
1990                                  * the new ssthresh).
1991                                  *
1992                                  * Dup acks mean that packets have left the
1993                                  * network (they're now cached at the receiver)
1994                                  * so bump cwnd by the amount in the receiver
1995                                  * to keep a constant cwnd packets in the
1996                                  * network.
1997                                  */
1998                                 if (!callout_active(tp->tt_rexmt) ||
1999                                     th->th_ack != tp->snd_una)
2000                                         tp->t_dupacks = 0;
2001                                 else if (++tp->t_dupacks > tcprexmtthresh ||
2002                                          ((tcp_do_newreno || tp->sack_enable) &&
2003                                           IN_FASTRECOVERY(tp))) {
2004                                         if (tp->sack_enable && IN_FASTRECOVERY(tp)) {
2005                                                 int awnd;
2006
2007                                                 /*
2008                                                  * Compute the amount of data in flight first.
2009                                                  * We can inject new data into the pipe iff
2010                                                  * we have less than 1/2 the original window's
2011                                                  * worth of data in flight.
2012                                                  */
2013                                                 awnd = (tp->snd_nxt - tp->snd_fack) +
2014                                                         tp->sackhint.sack_bytes_rexmit;
2015                                                 if (awnd < tp->snd_ssthresh) {
2016                                                         tp->snd_cwnd += tp->t_maxseg;
2017                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
2018                                                                 tp->snd_cwnd = tp->snd_ssthresh;
2019                                                 }
2020                                         } else
2021                                                 tp->snd_cwnd += tp->t_maxseg;
2022                                         (void) tcp_output(tp);
2023                                         goto drop;
2024                                 } else if (tp->t_dupacks == tcprexmtthresh) {
2025                                         tcp_seq onxt = tp->snd_nxt;
2026                                         u_int win;
2027
2028                                         /*
2029                                          * If we're doing sack, check to
2030                                          * see if we're already in sack
2031                                          * recovery. If we're not doing sack,
2032                                          * check to see if we're in newreno
2033                                          * recovery.
2034                                          */
2035                                         if (tp->sack_enable) {
2036                                                 if (IN_FASTRECOVERY(tp)) {
2037                                                         tp->t_dupacks = 0;
2038                                                         break;
2039                                                 }
2040                                         } else if (tcp_do_newreno) {
2041                                                 if (SEQ_LEQ(th->th_ack,
2042                                                     tp->snd_recover)) {
2043                                                         tp->t_dupacks = 0;
2044                                                         break;
2045                                                 }
2046                                         }
2047                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
2048                                             2 / tp->t_maxseg;
2049                                         if (win < 2)
2050                                                 win = 2;
2051                                         tp->snd_ssthresh = win * tp->t_maxseg;
2052                                         ENTER_FASTRECOVERY(tp);
2053                                         tp->snd_recover = tp->snd_max;
2054                                         callout_stop(tp->tt_rexmt);
2055                                         tp->t_rtttime = 0;
2056                                         if (tp->sack_enable) {
2057                                                 tcpstat.tcps_sack_recovery_episode++;
2058                                                 tp->sack_newdata = tp->snd_nxt;
2059                                                 tp->snd_cwnd = tp->t_maxseg;
2060                                                 (void) tcp_output(tp);
2061                                                 goto drop;
2062                                         }
2063                                         tp->snd_nxt = th->th_ack;
2064                                         tp->snd_cwnd = tp->t_maxseg;
2065                                         (void) tcp_output(tp);
2066                                         KASSERT(tp->snd_limited <= 2,
2067                                             ("tp->snd_limited too big"));
2068                                         tp->snd_cwnd = tp->snd_ssthresh +
2069                                              tp->t_maxseg *
2070                                              (tp->t_dupacks - tp->snd_limited);
2071                                         if (SEQ_GT(onxt, tp->snd_nxt))
2072                                                 tp->snd_nxt = onxt;
2073                                         goto drop;
2074                                 } else if (tcp_do_rfc3042) {
2075                                         u_long oldcwnd = tp->snd_cwnd;
2076                                         tcp_seq oldsndmax = tp->snd_max;
2077                                         u_int sent;
2078
2079                                         KASSERT(tp->t_dupacks == 1 ||
2080                                             tp->t_dupacks == 2,
2081                                             ("dupacks not 1 or 2"));
2082                                         if (tp->t_dupacks == 1)
2083                                                 tp->snd_limited = 0;
2084                                         tp->snd_cwnd =
2085                                             (tp->snd_nxt - tp->snd_una) +
2086                                             (tp->t_dupacks - tp->snd_limited) *
2087                                             tp->t_maxseg;
2088                                         (void) tcp_output(tp);
2089                                         sent = tp->snd_max - oldsndmax;
2090                                         if (sent > tp->t_maxseg) {
2091                                                 KASSERT((tp->t_dupacks == 2 &&
2092                                                     tp->snd_limited == 0) ||
2093                                                    (sent == tp->t_maxseg + 1 &&
2094                                                     tp->t_flags & TF_SENTFIN),
2095                                                     ("sent too much"));
2096                                                 tp->snd_limited = 2;
2097                                         } else if (sent > 0)
2098                                                 ++tp->snd_limited;
2099                                         tp->snd_cwnd = oldcwnd;
2100                                         goto drop;
2101                                 }
2102                         } else
2103                                 tp->t_dupacks = 0;
2104                         break;
2105                 }
2106
2107                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
2108
2109                 /*
2110                  * If the congestion window was inflated to account
2111                  * for the other side's cached packets, retract it.
2112                  */
2113                 if (tcp_do_newreno || tp->sack_enable) {
2114                         if (IN_FASTRECOVERY(tp)) {
2115                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2116                                         if (tp->sack_enable)
2117                                                 tcp_sack_partialack(tp, th);
2118                                         else
2119                                                 tcp_newreno_partial_ack(tp, th);
2120                                 } else {
2121                                         /*
2122                                          * Out of fast recovery.
2123                                          * Window inflation should have left us
2124                                          * with approximately snd_ssthresh
2125                                          * outstanding data.
2126                                          * But in case we would be inclined to
2127                                          * send a burst, better to do it via
2128                                          * the slow start mechanism.
2129                                          */
2130                                         if (SEQ_GT(th->th_ack +
2131                                                         tp->snd_ssthresh,
2132                                                    tp->snd_max))
2133                                                 tp->snd_cwnd = tp->snd_max -
2134                                                                 th->th_ack +
2135                                                                 tp->t_maxseg;
2136                                         else
2137                                                 tp->snd_cwnd = tp->snd_ssthresh;
2138                                 }
2139                         }
2140                 } else {
2141                         if (tp->t_dupacks >= tcprexmtthresh &&
2142                             tp->snd_cwnd > tp->snd_ssthresh)
2143                                 tp->snd_cwnd = tp->snd_ssthresh;
2144                 }
2145                 tp->t_dupacks = 0;
2146                 /*
2147                  * If we reach this point, ACK is not a duplicate,
2148                  *     i.e., it ACKs something we sent.
2149                  */
2150                 if (tp->t_flags & TF_NEEDSYN) {
2151                         /*
2152                          * T/TCP: Connection was half-synchronized, and our
2153                          * SYN has been ACK'd (so connection is now fully
2154                          * synchronized).  Go to non-starred state,
2155                          * increment snd_una for ACK of SYN, and check if
2156                          * we can do window scaling.
2157                          */
2158                         tp->t_flags &= ~TF_NEEDSYN;
2159                         tp->snd_una++;
2160                         /* Do window scaling? */
2161                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2162                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
2163                                 tp->rcv_scale = tp->request_r_scale;
2164                                 /* Send window already scaled. */
2165                         }
2166                 }
2167
2168 process_ACK:
2169                 KASSERT(headlocked, ("tcp_input: process_ACK: head not "
2170                     "locked"));
2171                 INP_LOCK_ASSERT(inp);
2172
2173                 acked = th->th_ack - tp->snd_una;
2174                 tcpstat.tcps_rcvackpack++;
2175                 tcpstat.tcps_rcvackbyte += acked;
2176
2177                 /*
2178                  * If we just performed our first retransmit, and the ACK
2179                  * arrives within our recovery window, then it was a mistake
2180                  * to do the retransmit in the first place.  Recover our
2181                  * original cwnd and ssthresh, and proceed to transmit where
2182                  * we left off.
2183                  */
2184                 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
2185                         ++tcpstat.tcps_sndrexmitbad;
2186                         tp->snd_cwnd = tp->snd_cwnd_prev;
2187                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
2188                         tp->snd_recover = tp->snd_recover_prev;
2189                         if (tp->t_flags & TF_WASFRECOVERY)
2190                                 ENTER_FASTRECOVERY(tp);
2191                         tp->snd_nxt = tp->snd_max;
2192                         tp->t_badrxtwin = 0;    /* XXX probably not required */
2193                 }
2194
2195                 /*
2196                  * If we have a timestamp reply, update smoothed
2197                  * round trip time.  If no timestamp is present but
2198                  * transmit timer is running and timed sequence
2199                  * number was acked, update smoothed round trip time.
2200                  * Since we now have an rtt measurement, cancel the
2201                  * timer backoff (cf., Phil Karn's retransmit alg.).
2202                  * Recompute the initial retransmit timer.
2203                  *
2204                  * Some boxes send broken timestamp replies
2205                  * during the SYN+ACK phase, ignore
2206                  * timestamps of 0 or we could calculate a
2207                  * huge RTT and blow up the retransmit timer.
2208                  */
2209                 if ((to.to_flags & TOF_TS) != 0 &&
2210                     to.to_tsecr) {
2211                         if (!tp->t_rttlow || tp->t_rttlow > ticks - to.to_tsecr)
2212                                 tp->t_rttlow = ticks - to.to_tsecr;
2213                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
2214                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2215                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2216                                 tp->t_rttlow = ticks - tp->t_rtttime;
2217                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2218                 }
2219                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
2220
2221                 /*
2222                  * If all outstanding data is acked, stop retransmit
2223                  * timer and remember to restart (more output or persist).
2224                  * If there is more data to be acked, restart retransmit
2225                  * timer, using current (possibly backed-off) value.
2226                  */
2227                 if (th->th_ack == tp->snd_max) {
2228                         callout_stop(tp->tt_rexmt);
2229                         needoutput = 1;
2230                 } else if (!callout_active(tp->tt_persist))
2231                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
2232                                       tcp_timer_rexmt, tp);
2233
2234                 /*
2235                  * If no data (only SYN) was ACK'd,
2236                  *    skip rest of ACK processing.
2237                  */
2238                 if (acked == 0)
2239                         goto step6;
2240
2241                 /*
2242                  * When new data is acked, open the congestion window.
2243                  * If the window gives us less than ssthresh packets
2244                  * in flight, open exponentially (maxseg per packet).
2245                  * Otherwise open linearly: maxseg per window
2246                  * (maxseg^2 / cwnd per packet).
2247                  */
2248                 if ((!tcp_do_newreno && !tp->sack_enable) ||
2249                     !IN_FASTRECOVERY(tp)) {
2250                         register u_int cw = tp->snd_cwnd;
2251                         register u_int incr = tp->t_maxseg;
2252                         if (cw > tp->snd_ssthresh)
2253                                 incr = incr * incr / cw;
2254                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
2255                 }
2256                 SOCKBUF_LOCK(&so->so_snd);
2257                 if (acked > so->so_snd.sb_cc) {
2258                         tp->snd_wnd -= so->so_snd.sb_cc;
2259                         sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
2260                         ourfinisacked = 1;
2261                 } else {
2262                         sbdrop_locked(&so->so_snd, acked);
2263                         tp->snd_wnd -= acked;
2264                         ourfinisacked = 0;
2265                 }
2266                 sowwakeup_locked(so);
2267                 /* detect una wraparound */
2268                 if ((tcp_do_newreno || tp->sack_enable) &&
2269                     !IN_FASTRECOVERY(tp) &&
2270                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
2271                     SEQ_LEQ(th->th_ack, tp->snd_recover))
2272                         tp->snd_recover = th->th_ack - 1;
2273                 if ((tcp_do_newreno || tp->sack_enable) &&
2274                     IN_FASTRECOVERY(tp) &&
2275                     SEQ_GEQ(th->th_ack, tp->snd_recover))
2276                         EXIT_FASTRECOVERY(tp);
2277                 tp->snd_una = th->th_ack;
2278                 if (tp->sack_enable) {
2279                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
2280                                 tp->snd_recover = tp->snd_una;
2281                 }
2282                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2283                         tp->snd_nxt = tp->snd_una;
2284
2285                 switch (tp->t_state) {
2286
2287                 /*
2288                  * In FIN_WAIT_1 STATE in addition to the processing
2289                  * for the ESTABLISHED state if our FIN is now acknowledged
2290                  * then enter FIN_WAIT_2.
2291                  */
2292                 case TCPS_FIN_WAIT_1:
2293                         if (ourfinisacked) {
2294                                 /*
2295                                  * If we can't receive any more
2296                                  * data, then closing user can proceed.
2297                                  * Starting the timer is contrary to the
2298                                  * specification, but if we don't get a FIN
2299                                  * we'll hang forever.
2300                                  */
2301                 /* XXXjl
2302                  * we should release the tp also, and use a
2303                  * compressed state.
2304                  */
2305                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2306                                         int timeout;
2307
2308                                         soisdisconnected(so);
2309                                         timeout = (tcp_fast_finwait2_recycle) ?
2310                                                 tcp_finwait2_timeout : tcp_maxidle;
2311                                         callout_reset(tp->tt_2msl, timeout,
2312                                                       tcp_timer_2msl, tp);
2313                                 }
2314                                 tp->t_state = TCPS_FIN_WAIT_2;
2315                         }
2316                         break;
2317
2318                 /*
2319                  * In CLOSING STATE in addition to the processing for
2320                  * the ESTABLISHED state if the ACK acknowledges our FIN
2321                  * then enter the TIME-WAIT state, otherwise ignore
2322                  * the segment.
2323                  */
2324                 case TCPS_CLOSING:
2325                         if (ourfinisacked) {
2326                                 KASSERT(headlocked, ("tcp_input: process_ACK: "
2327                                     "head not locked"));
2328                                 tcp_twstart(tp);
2329                                 INP_INFO_WUNLOCK(&tcbinfo);
2330                                 m_freem(m);
2331                                 return;
2332                         }
2333                         break;
2334
2335                 /*
2336                  * In LAST_ACK, we may still be waiting for data to drain
2337                  * and/or to be acked, as well as for the ack of our FIN.
2338                  * If our FIN is now acknowledged, delete the TCB,
2339                  * enter the closed state and return.
2340                  */
2341                 case TCPS_LAST_ACK:
2342                         if (ourfinisacked) {
2343                                 KASSERT(headlocked, ("tcp_input: process_ACK:"
2344                                     " tcp_close: head not locked"));
2345                                 tp = tcp_close(tp);
2346                                 goto drop;
2347                         }
2348                         break;
2349
2350                 /*
2351                  * In TIME_WAIT state the only thing that should arrive
2352                  * is a retransmission of the remote FIN.  Acknowledge
2353                  * it and restart the finack timer.
2354                  */
2355                 case TCPS_TIME_WAIT:
2356                         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait"));
2357                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2358                                       tcp_timer_2msl, tp);
2359                         goto dropafterack;
2360                 }
2361         }
2362
2363 step6:
2364         KASSERT(headlocked, ("tcp_input: step6: head not locked"));
2365         INP_LOCK_ASSERT(inp);
2366
2367         /*
2368          * Update window information.
2369          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2370          */
2371         if ((thflags & TH_ACK) &&
2372             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2373             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2374              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2375                 /* keep track of pure window updates */
2376                 if (tlen == 0 &&
2377                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2378                         tcpstat.tcps_rcvwinupd++;
2379                 tp->snd_wnd = tiwin;
2380                 tp->snd_wl1 = th->th_seq;
2381                 tp->snd_wl2 = th->th_ack;
2382                 if (tp->snd_wnd > tp->max_sndwnd)
2383                         tp->max_sndwnd = tp->snd_wnd;
2384                 needoutput = 1;
2385         }
2386
2387         /*
2388          * Process segments with URG.
2389          */
2390         if ((thflags & TH_URG) && th->th_urp &&
2391             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2392                 /*
2393                  * This is a kludge, but if we receive and accept
2394                  * random urgent pointers, we'll crash in
2395                  * soreceive.  It's hard to imagine someone
2396                  * actually wanting to send this much urgent data.
2397                  */
2398                 SOCKBUF_LOCK(&so->so_rcv);
2399                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2400                         th->th_urp = 0;                 /* XXX */
2401                         thflags &= ~TH_URG;             /* XXX */
2402                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
2403                         goto dodata;                    /* XXX */
2404                 }
2405                 /*
2406                  * If this segment advances the known urgent pointer,
2407                  * then mark the data stream.  This should not happen
2408                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2409                  * a FIN has been received from the remote side.
2410                  * In these states we ignore the URG.
2411                  *
2412                  * According to RFC961 (Assigned Protocols),
2413                  * the urgent pointer points to the last octet
2414                  * of urgent data.  We continue, however,
2415                  * to consider it to indicate the first octet
2416                  * of data past the urgent section as the original
2417                  * spec states (in one of two places).
2418                  */
2419                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2420                         tp->rcv_up = th->th_seq + th->th_urp;
2421                         so->so_oobmark = so->so_rcv.sb_cc +
2422                             (tp->rcv_up - tp->rcv_nxt) - 1;
2423                         if (so->so_oobmark == 0)
2424                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
2425                         sohasoutofband(so);
2426                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2427                 }
2428                 SOCKBUF_UNLOCK(&so->so_rcv);
2429                 /*
2430                  * Remove out of band data so doesn't get presented to user.
2431                  * This can happen independent of advancing the URG pointer,
2432                  * but if two URG's are pending at once, some out-of-band
2433                  * data may creep in... ick.
2434                  */
2435                 if (th->th_urp <= (u_long)tlen &&
2436                     !(so->so_options & SO_OOBINLINE)) {
2437                         /* hdr drop is delayed */
2438                         tcp_pulloutofband(so, th, m, drop_hdrlen);
2439                 }
2440         } else {
2441                 /*
2442                  * If no out of band data is expected,
2443                  * pull receive urgent pointer along
2444                  * with the receive window.
2445                  */
2446                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2447                         tp->rcv_up = tp->rcv_nxt;
2448         }
2449 dodata:                                                 /* XXX */
2450         KASSERT(headlocked, ("tcp_input: dodata: head not locked"));
2451         INP_LOCK_ASSERT(inp);
2452
2453         /*
2454          * Process the segment text, merging it into the TCP sequencing queue,
2455          * and arranging for acknowledgment of receipt if necessary.
2456          * This process logically involves adjusting tp->rcv_wnd as data
2457          * is presented to the user (this happens in tcp_usrreq.c,
2458          * case PRU_RCVD).  If a FIN has already been received on this
2459          * connection then we just ignore the text.
2460          */
2461         if ((tlen || (thflags & TH_FIN)) &&
2462             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2463                 tcp_seq save_start = th->th_seq;
2464                 tcp_seq save_end = th->th_seq + tlen;
2465                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2466                 /*
2467                  * Insert segment which includes th into TCP reassembly queue
2468                  * with control block tp.  Set thflags to whether reassembly now
2469                  * includes a segment with FIN.  This handles the common case
2470                  * inline (segment is the next to be received on an established
2471                  * connection, and the queue is empty), avoiding linkage into
2472                  * and removal from the queue and repetition of various
2473                  * conversions.
2474                  * Set DELACK for segments received in order, but ack
2475                  * immediately when segments are out of order (so
2476                  * fast retransmit can work).
2477                  */
2478                 if (th->th_seq == tp->rcv_nxt &&
2479                     LIST_EMPTY(&tp->t_segq) &&
2480                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2481                         if (DELAY_ACK(tp))
2482                                 tp->t_flags |= TF_DELACK;
2483                         else
2484                                 tp->t_flags |= TF_ACKNOW;
2485                         tp->rcv_nxt += tlen;
2486                         thflags = th->th_flags & TH_FIN;
2487                         tcpstat.tcps_rcvpack++;
2488                         tcpstat.tcps_rcvbyte += tlen;
2489                         ND6_HINT(tp);
2490                         SOCKBUF_LOCK(&so->so_rcv);
2491                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
2492                                 m_freem(m);
2493                         else
2494                                 sbappendstream_locked(&so->so_rcv, m);
2495                         sorwakeup_locked(so);
2496                 } else {
2497                         thflags = tcp_reass(tp, th, &tlen, m);
2498                         tp->t_flags |= TF_ACKNOW;
2499                 }
2500                 if (tlen > 0 && tp->sack_enable)
2501                         tcp_update_sack_list(tp, save_start, save_end);
2502                 /*
2503                  * Note the amount of data that peer has sent into
2504                  * our window, in order to estimate the sender's
2505                  * buffer size.
2506                  */
2507                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2508         } else {
2509                 m_freem(m);
2510                 thflags &= ~TH_FIN;
2511         }
2512
2513         /*
2514          * If FIN is received ACK the FIN and let the user know
2515          * that the connection is closing.
2516          */
2517         if (thflags & TH_FIN) {
2518                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2519                         socantrcvmore(so);
2520                         /*
2521                          * If connection is half-synchronized
2522                          * (ie NEEDSYN flag on) then delay ACK,
2523                          * so it may be piggybacked when SYN is sent.
2524                          * Otherwise, since we received a FIN then no
2525                          * more input can be expected, send ACK now.
2526                          */
2527                         if (tp->t_flags & TF_NEEDSYN)
2528                                 tp->t_flags |= TF_DELACK;
2529                         else
2530                                 tp->t_flags |= TF_ACKNOW;
2531                         tp->rcv_nxt++;
2532                 }
2533                 switch (tp->t_state) {
2534
2535                 /*
2536                  * In SYN_RECEIVED and ESTABLISHED STATES
2537                  * enter the CLOSE_WAIT state.
2538                  */
2539                 case TCPS_SYN_RECEIVED:
2540                         tp->t_starttime = ticks;
2541                         /*FALLTHROUGH*/
2542                 case TCPS_ESTABLISHED:
2543                         tp->t_state = TCPS_CLOSE_WAIT;
2544                         break;
2545
2546                 /*
2547                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2548                  * enter the CLOSING state.
2549                  */
2550                 case TCPS_FIN_WAIT_1:
2551                         tp->t_state = TCPS_CLOSING;
2552                         break;
2553
2554                 /*
2555                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2556                  * starting the time-wait timer, turning off the other
2557                  * standard timers.
2558                  */
2559                 case TCPS_FIN_WAIT_2:
2560                         KASSERT(headlocked == 1, ("tcp_input: dodata: "
2561                             "TCP_FIN_WAIT_2: head not locked"));
2562                         tcp_twstart(tp);
2563                         INP_INFO_WUNLOCK(&tcbinfo);
2564                         return;
2565
2566                 /*
2567                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2568                  */
2569                 case TCPS_TIME_WAIT:
2570                         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait"));
2571                         callout_reset(tp->tt_2msl, 2 * tcp_msl,
2572                                       tcp_timer_2msl, tp);
2573                         break;
2574                 }
2575         }
2576         INP_INFO_WUNLOCK(&tcbinfo);
2577         headlocked = 0;
2578 #ifdef TCPDEBUG
2579         if (so->so_options & SO_DEBUG)
2580                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2581                           &tcp_savetcp, 0);
2582 #endif
2583
2584         /*
2585          * Return any desired output.
2586          */
2587         if (needoutput || (tp->t_flags & TF_ACKNOW))
2588                 (void) tcp_output(tp);
2589
2590 check_delack:
2591         KASSERT(headlocked == 0, ("tcp_input: check_delack: head locked"));
2592         INP_LOCK_ASSERT(inp);
2593         if (tp->t_flags & TF_DELACK) {
2594                 tp->t_flags &= ~TF_DELACK;
2595                 callout_reset(tp->tt_delack, tcp_delacktime,
2596                     tcp_timer_delack, tp);
2597         }
2598         INP_UNLOCK(inp);
2599         return;
2600
2601 dropafterack:
2602         KASSERT(headlocked, ("tcp_input: dropafterack: head not locked"));
2603         /*
2604          * Generate an ACK dropping incoming segment if it occupies
2605          * sequence space, where the ACK reflects our state.
2606          *
2607          * We can now skip the test for the RST flag since all
2608          * paths to this code happen after packets containing
2609          * RST have been dropped.
2610          *
2611          * In the SYN-RECEIVED state, don't send an ACK unless the
2612          * segment we received passes the SYN-RECEIVED ACK test.
2613          * If it fails send a RST.  This breaks the loop in the
2614          * "LAND" DoS attack, and also prevents an ACK storm
2615          * between two listening ports that have been sent forged
2616          * SYN segments, each with the source address of the other.
2617          */
2618         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2619             (SEQ_GT(tp->snd_una, th->th_ack) ||
2620              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2621                 rstreason = BANDLIM_RST_OPENPORT;
2622                 goto dropwithreset;
2623         }
2624 #ifdef TCPDEBUG
2625         if (so->so_options & SO_DEBUG)
2626                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2627                           &tcp_savetcp, 0);
2628 #endif
2629         KASSERT(headlocked, ("headlocked should be 1"));
2630         INP_INFO_WUNLOCK(&tcbinfo);
2631         tp->t_flags |= TF_ACKNOW;
2632         (void) tcp_output(tp);
2633         INP_UNLOCK(inp);
2634         m_freem(m);
2635         return;
2636
2637 dropwithreset:
2638         KASSERT(headlocked, ("tcp_input: dropwithreset: head not locked"));
2639         /*
2640          * Generate a RST, dropping incoming segment.
2641          * Make ACK acceptable to originator of segment.
2642          * Don't bother to respond if destination was broadcast/multicast.
2643          */
2644         if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2645                 goto drop;
2646         if (isipv6) {
2647                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2648                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2649                         goto drop;
2650         } else {
2651                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2652                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2653                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2654                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2655                         goto drop;
2656         }
2657         /* IPv6 anycast check is done at tcp6_input() */
2658
2659         /*
2660          * Perform bandwidth limiting.
2661          */
2662         if (badport_bandlim(rstreason) < 0)
2663                 goto drop;
2664
2665 #ifdef TCPDEBUG
2666         if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2667                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2668                           &tcp_savetcp, 0);
2669 #endif
2670
2671         if (thflags & TH_ACK)
2672                 /* mtod() below is safe as long as hdr dropping is delayed */
2673                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2674                             TH_RST);
2675         else {
2676                 if (thflags & TH_SYN)
2677                         tlen++;
2678                 /* mtod() below is safe as long as hdr dropping is delayed */
2679                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2680                             (tcp_seq)0, TH_RST|TH_ACK);
2681         }
2682
2683         if (tp != NULL)
2684                 INP_UNLOCK(inp);
2685         if (headlocked)
2686                 INP_INFO_WUNLOCK(&tcbinfo);
2687         return;
2688
2689 drop:
2690         /*
2691          * Drop space held by incoming segment and return.
2692          */
2693 #ifdef TCPDEBUG
2694         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2695                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2696                           &tcp_savetcp, 0);
2697 #endif
2698         if (tp != NULL)
2699                 INP_UNLOCK(inp);
2700         if (headlocked)
2701                 INP_INFO_WUNLOCK(&tcbinfo);
2702         m_freem(m);
2703         return;
2704 }
2705
2706 /*
2707  * Parse TCP options and place in tcpopt.
2708  */
2709 static void
2710 tcp_dooptions(to, cp, cnt, flags)
2711         struct tcpopt *to;
2712         u_char *cp;
2713         int cnt;
2714         int flags;
2715 {
2716         int opt, optlen;
2717
2718         to->to_flags = 0;
2719         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2720                 opt = cp[0];
2721                 if (opt == TCPOPT_EOL)
2722                         break;
2723                 if (opt == TCPOPT_NOP)
2724                         optlen = 1;
2725                 else {
2726                         if (cnt < 2)
2727                                 break;
2728                         optlen = cp[1];
2729                         if (optlen < 2 || optlen > cnt)
2730                                 break;
2731                 }
2732                 switch (opt) {
2733                 case TCPOPT_MAXSEG:
2734                         if (optlen != TCPOLEN_MAXSEG)
2735                                 continue;
2736                         if (!(flags & TO_SYN))
2737                                 continue;
2738                         to->to_flags |= TOF_MSS;
2739                         bcopy((char *)cp + 2,
2740                             (char *)&to->to_mss, sizeof(to->to_mss));
2741                         to->to_mss = ntohs(to->to_mss);
2742                         break;
2743                 case TCPOPT_WINDOW:
2744                         if (optlen != TCPOLEN_WINDOW)
2745                                 continue;
2746                         if (!(flags & TO_SYN))
2747                                 continue;
2748                         to->to_flags |= TOF_SCALE;
2749                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
2750                         break;
2751                 case TCPOPT_TIMESTAMP:
2752                         if (optlen != TCPOLEN_TIMESTAMP)
2753                                 continue;
2754                         to->to_flags |= TOF_TS;
2755                         bcopy((char *)cp + 2,
2756                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2757                         to->to_tsval = ntohl(to->to_tsval);
2758                         bcopy((char *)cp + 6,
2759                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2760                         to->to_tsecr = ntohl(to->to_tsecr);
2761                         break;
2762 #ifdef TCP_SIGNATURE
2763                 /*
2764                  * XXX In order to reply to a host which has set the
2765                  * TCP_SIGNATURE option in its initial SYN, we have to
2766                  * record the fact that the option was observed here
2767                  * for the syncache code to perform the correct response.
2768                  */
2769                 case TCPOPT_SIGNATURE:
2770                         if (optlen != TCPOLEN_SIGNATURE)
2771                                 continue;
2772                         to->to_flags |= (TOF_SIGNATURE | TOF_SIGLEN);
2773                         break;
2774 #endif
2775                 case TCPOPT_SACK_PERMITTED:
2776                         if (optlen != TCPOLEN_SACK_PERMITTED)
2777                                 continue;
2778                         if (!(flags & TO_SYN))
2779                                 continue;
2780                         if (!tcp_do_sack)
2781                                 continue;
2782                         to->to_flags |= TOF_SACK;
2783                         break;
2784                 case TCPOPT_SACK:
2785                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
2786                                 continue;
2787                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
2788                         to->to_sacks = cp + 2;
2789                         tcpstat.tcps_sack_rcv_blocks++;
2790                         break;
2791                 default:
2792                         continue;
2793                 }
2794         }
2795 }
2796
2797 /*
2798  * Pull out of band byte out of a segment so
2799  * it doesn't appear in the user's data queue.
2800  * It is still reflected in the segment length for
2801  * sequencing purposes.
2802  */
2803 static void
2804 tcp_pulloutofband(so, th, m, off)
2805         struct socket *so;
2806         struct tcphdr *th;
2807         register struct mbuf *m;
2808         int off;                /* delayed to be droped hdrlen */
2809 {
2810         int cnt = off + th->th_urp - 1;
2811
2812         while (cnt >= 0) {
2813                 if (m->m_len > cnt) {
2814                         char *cp = mtod(m, caddr_t) + cnt;
2815                         struct tcpcb *tp = sototcpcb(so);
2816
2817                         tp->t_iobc = *cp;
2818                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2819                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2820                         m->m_len--;
2821                         if (m->m_flags & M_PKTHDR)
2822                                 m->m_pkthdr.len--;
2823                         return;
2824                 }
2825                 cnt -= m->m_len;
2826                 m = m->m_next;
2827                 if (m == 0)
2828                         break;
2829         }
2830         panic("tcp_pulloutofband");
2831 }
2832
2833 /*
2834  * Collect new round-trip time estimate
2835  * and update averages and current timeout.
2836  */
2837 static void
2838 tcp_xmit_timer(tp, rtt)
2839         register struct tcpcb *tp;
2840         int rtt;
2841 {
2842         register int delta;
2843
2844         INP_LOCK_ASSERT(tp->t_inpcb);
2845
2846         tcpstat.tcps_rttupdated++;
2847         tp->t_rttupdated++;
2848         if (tp->t_srtt != 0) {
2849                 /*
2850                  * srtt is stored as fixed point with 5 bits after the
2851                  * binary point (i.e., scaled by 8).  The following magic
2852                  * is equivalent to the smoothing algorithm in rfc793 with
2853                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2854                  * point).  Adjust rtt to origin 0.
2855                  */
2856                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2857                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2858
2859                 if ((tp->t_srtt += delta) <= 0)
2860                         tp->t_srtt = 1;
2861
2862                 /*
2863                  * We accumulate a smoothed rtt variance (actually, a
2864                  * smoothed mean difference), then set the retransmit
2865                  * timer to smoothed rtt + 4 times the smoothed variance.
2866                  * rttvar is stored as fixed point with 4 bits after the
2867                  * binary point (scaled by 16).  The following is
2868                  * equivalent to rfc793 smoothing with an alpha of .75
2869                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2870                  * rfc793's wired-in beta.
2871                  */
2872                 if (delta < 0)
2873                         delta = -delta;
2874                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2875                 if ((tp->t_rttvar += delta) <= 0)
2876                         tp->t_rttvar = 1;
2877                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2878                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2879         } else {
2880                 /*
2881                  * No rtt measurement yet - use the unsmoothed rtt.
2882                  * Set the variance to half the rtt (so our first
2883                  * retransmit happens at 3*rtt).
2884                  */
2885                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2886                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2887                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2888         }
2889         tp->t_rtttime = 0;
2890         tp->t_rxtshift = 0;
2891
2892         /*
2893          * the retransmit should happen at rtt + 4 * rttvar.
2894          * Because of the way we do the smoothing, srtt and rttvar
2895          * will each average +1/2 tick of bias.  When we compute
2896          * the retransmit timer, we want 1/2 tick of rounding and
2897          * 1 extra tick because of +-1/2 tick uncertainty in the
2898          * firing of the timer.  The bias will give us exactly the
2899          * 1.5 tick we need.  But, because the bias is
2900          * statistical, we have to test that we don't drop below
2901          * the minimum feasible timer (which is 2 ticks).
2902          */
2903         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2904                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2905
2906         /*
2907          * We received an ack for a packet that wasn't retransmitted;
2908          * it is probably safe to discard any error indications we've
2909          * received recently.  This isn't quite right, but close enough
2910          * for now (a route might have failed after we sent a segment,
2911          * and the return path might not be symmetrical).
2912          */
2913         tp->t_softerror = 0;
2914 }
2915
2916 /*
2917  * Determine a reasonable value for maxseg size.
2918  * If the route is known, check route for mtu.
2919  * If none, use an mss that can be handled on the outgoing
2920  * interface without forcing IP to fragment; if bigger than
2921  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2922  * to utilize large mbufs.  If no route is found, route has no mtu,
2923  * or the destination isn't local, use a default, hopefully conservative
2924  * size (usually 512 or the default IP max size, but no more than the mtu
2925  * of the interface), as we can't discover anything about intervening
2926  * gateways or networks.  We also initialize the congestion/slow start
2927  * window to be a single segment if the destination isn't local.
2928  * While looking at the routing entry, we also initialize other path-dependent
2929  * parameters from pre-set or cached values in the routing entry.
2930  *
2931  * Also take into account the space needed for options that we
2932  * send regularly.  Make maxseg shorter by that amount to assure
2933  * that we can send maxseg amount of data even when the options
2934  * are present.  Store the upper limit of the length of options plus
2935  * data in maxopd.
2936  *
2937  *
2938  * In case of T/TCP, we call this routine during implicit connection
2939  * setup as well (offer = -1), to initialize maxseg from the cached
2940  * MSS of our peer.
2941  *
2942  * NOTE that this routine is only called when we process an incoming
2943  * segment. Outgoing SYN/ACK MSS settings are handled in tcp_mssopt().
2944  */
2945 void
2946 tcp_mss(tp, offer)
2947         struct tcpcb *tp;
2948         int offer;
2949 {
2950         int rtt, mss;
2951         u_long bufsize;
2952         u_long maxmtu;
2953         struct inpcb *inp = tp->t_inpcb;
2954         struct socket *so;
2955         struct hc_metrics_lite metrics;
2956         int origoffer = offer;
2957         int mtuflags = 0;
2958 #ifdef INET6
2959         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2960         size_t min_protoh = isipv6 ?
2961                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
2962                             sizeof (struct tcpiphdr);
2963 #else
2964         const size_t min_protoh = sizeof(struct tcpiphdr);
2965 #endif
2966
2967         /* initialize */
2968 #ifdef INET6
2969         if (isipv6) {
2970                 maxmtu = tcp_maxmtu6(&inp->inp_inc, &mtuflags);
2971                 tp->t_maxopd = tp->t_maxseg = tcp_v6mssdflt;
2972         } else
2973 #endif
2974         {
2975                 maxmtu = tcp_maxmtu(&inp->inp_inc, &mtuflags);
2976                 tp->t_maxopd = tp->t_maxseg = tcp_mssdflt;
2977         }
2978         so = inp->inp_socket;
2979
2980         /*
2981          * no route to sender, stay with default mss and return
2982          */
2983         if (maxmtu == 0)
2984                 return;
2985
2986         /* what have we got? */
2987         switch (offer) {
2988                 case 0:
2989                         /*
2990                          * Offer == 0 means that there was no MSS on the SYN
2991                          * segment, in this case we use tcp_mssdflt.
2992                          */
2993                         offer =
2994 #ifdef INET6
2995                                 isipv6 ? tcp_v6mssdflt :
2996 #endif
2997                                 tcp_mssdflt;
2998                         break;
2999
3000                 case -1:
3001                         /*
3002                          * Offer == -1 means that we didn't receive SYN yet.
3003                          */
3004                         /* FALLTHROUGH */
3005
3006                 default:
3007                         /*
3008                          * Prevent DoS attack with too small MSS. Round up
3009                          * to at least minmss.
3010                          */
3011                         offer = max(offer, tcp_minmss);
3012                         /*
3013                          * Sanity check: make sure that maxopd will be large
3014                          * enough to allow some data on segments even if the
3015                          * all the option space is used (40bytes).  Otherwise
3016                          * funny things may happen in tcp_output.
3017                          */
3018                         offer = max(offer, 64);
3019         }
3020
3021         /*
3022          * rmx information is now retrieved from tcp_hostcache
3023          */
3024         tcp_hc_get(&inp->inp_inc, &metrics);
3025
3026         /*
3027          * if there's a discovered mtu int tcp hostcache, use it
3028          * else, use the link mtu.
3029          */
3030         if (metrics.rmx_mtu)
3031                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
3032         else {
3033 #ifdef INET6
3034                 if (isipv6) {
3035                         mss = maxmtu - min_protoh;
3036                         if (!path_mtu_discovery &&
3037                             !in6_localaddr(&inp->in6p_faddr))
3038                                 mss = min(mss, tcp_v6mssdflt);
3039                 } else
3040 #endif
3041                 {
3042                         mss = maxmtu - min_protoh;
3043                         if (!path_mtu_discovery &&
3044                             !in_localaddr(inp->inp_faddr))
3045                                 mss = min(mss, tcp_mssdflt);
3046                 }
3047         }
3048         mss = min(mss, offer);
3049
3050         /*
3051          * maxopd stores the maximum length of data AND options
3052          * in a segment; maxseg is the amount of data in a normal
3053          * segment.  We need to store this value (maxopd) apart
3054          * from maxseg, because now every segment carries options
3055          * and thus we normally have somewhat less data in segments.
3056          */
3057         tp->t_maxopd = mss;
3058
3059         /*
3060          * origoffer==-1 indicates, that no segments were received yet.
3061          * In this case we just guess.
3062          */
3063         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
3064             (origoffer == -1 ||
3065              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
3066                 mss -= TCPOLEN_TSTAMP_APPA;
3067         tp->t_maxseg = mss;
3068
3069 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
3070                 if (mss > MCLBYTES)
3071                         mss &= ~(MCLBYTES-1);
3072 #else
3073                 if (mss > MCLBYTES)
3074                         mss = mss / MCLBYTES * MCLBYTES;
3075 #endif
3076         tp->t_maxseg = mss;
3077
3078         /*
3079          * If there's a pipesize, change the socket buffer to that size,
3080          * don't change if sb_hiwat is different than default (then it
3081          * has been changed on purpose with setsockopt).
3082          * Make the socket buffers an integral number of mss units;
3083          * if the mss is larger than the socket buffer, decrease the mss.
3084          */
3085         SOCKBUF_LOCK(&so->so_snd);
3086         if ((so->so_snd.sb_hiwat == tcp_sendspace) && metrics.rmx_sendpipe)
3087                 bufsize = metrics.rmx_sendpipe;
3088         else
3089                 bufsize = so->so_snd.sb_hiwat;
3090         if (bufsize < mss)
3091                 mss = bufsize;
3092         else {
3093                 bufsize = roundup(bufsize, mss);
3094                 if (bufsize > sb_max)
3095                         bufsize = sb_max;
3096                 if (bufsize > so->so_snd.sb_hiwat)
3097                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3098         }
3099         SOCKBUF_UNLOCK(&so->so_snd);
3100         tp->t_maxseg = mss;
3101
3102         SOCKBUF_LOCK(&so->so_rcv);
3103         if ((so->so_rcv.sb_hiwat == tcp_recvspace) && metrics.rmx_recvpipe)
3104                 bufsize = metrics.rmx_recvpipe;
3105         else
3106                 bufsize = so->so_rcv.sb_hiwat;
3107         if (bufsize > mss) {
3108                 bufsize = roundup(bufsize, mss);
3109                 if (bufsize > sb_max)
3110                         bufsize = sb_max;
3111                 if (bufsize > so->so_rcv.sb_hiwat)
3112                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3113         }
3114         SOCKBUF_UNLOCK(&so->so_rcv);
3115         /*
3116          * While we're here, check the others too
3117          */
3118         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
3119                 tp->t_srtt = rtt;
3120                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
3121                 tcpstat.tcps_usedrtt++;
3122                 if (metrics.rmx_rttvar) {
3123                         tp->t_rttvar = metrics.rmx_rttvar;
3124                         tcpstat.tcps_usedrttvar++;
3125                 } else {
3126                         /* default variation is +- 1 rtt */
3127                         tp->t_rttvar =
3128                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
3129                 }
3130                 TCPT_RANGESET(tp->t_rxtcur,
3131                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
3132                               tp->t_rttmin, TCPTV_REXMTMAX);
3133         }
3134         if (metrics.rmx_ssthresh) {
3135                 /*
3136                  * There's some sort of gateway or interface
3137                  * buffer limit on the path.  Use this to set
3138                  * the slow start threshhold, but set the
3139                  * threshold to no less than 2*mss.
3140                  */
3141                 tp->snd_ssthresh = max(2 * mss, metrics.rmx_ssthresh);
3142                 tcpstat.tcps_usedssthresh++;
3143         }
3144         if (metrics.rmx_bandwidth)
3145                 tp->snd_bandwidth = metrics.rmx_bandwidth;
3146
3147         /*
3148          * Set the slow-start flight size depending on whether this
3149          * is a local network or not.
3150          *
3151          * Extend this so we cache the cwnd too and retrieve it here.
3152          * Make cwnd even bigger than RFC3390 suggests but only if we
3153          * have previous experience with the remote host. Be careful
3154          * not make cwnd bigger than remote receive window or our own
3155          * send socket buffer. Maybe put some additional upper bound
3156          * on the retrieved cwnd. Should do incremental updates to
3157          * hostcache when cwnd collapses so next connection doesn't
3158          * overloads the path again.
3159          *
3160          * RFC3390 says only do this if SYN or SYN/ACK didn't got lost.
3161          * We currently check only in syncache_socket for that.
3162          */
3163 #define TCP_METRICS_CWND
3164 #ifdef TCP_METRICS_CWND
3165         if (metrics.rmx_cwnd)
3166                 tp->snd_cwnd = max(mss,
3167                                 min(metrics.rmx_cwnd / 2,
3168                                  min(tp->snd_wnd, so->so_snd.sb_hiwat)));
3169         else
3170 #endif
3171         if (tcp_do_rfc3390)
3172                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
3173 #ifdef INET6
3174         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
3175                  (!isipv6 && in_localaddr(inp->inp_faddr)))
3176 #else
3177         else if (in_localaddr(inp->inp_faddr))
3178 #endif
3179                 tp->snd_cwnd = mss * ss_fltsz_local;
3180         else
3181                 tp->snd_cwnd = mss * ss_fltsz;
3182
3183         /* Check the interface for TSO capabilities. */
3184         if (mtuflags & CSUM_TSO)
3185                 tp->t_flags |= TF_TSO;
3186 }
3187
3188 /*
3189  * Determine the MSS option to send on an outgoing SYN.
3190  */
3191 int
3192 tcp_mssopt(inc)
3193         struct in_conninfo *inc;
3194 {
3195         int mss = 0;
3196         u_long maxmtu = 0;
3197         u_long thcmtu = 0;
3198         size_t min_protoh;
3199 #ifdef INET6
3200         int isipv6 = inc->inc_isipv6 ? 1 : 0;
3201 #endif
3202
3203         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3204
3205 #ifdef INET6
3206         if (isipv6) {
3207                 mss = tcp_v6mssdflt;
3208                 maxmtu = tcp_maxmtu6(inc, NULL);
3209                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3210                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3211         } else
3212 #endif
3213         {
3214                 mss = tcp_mssdflt;
3215                 maxmtu = tcp_maxmtu(inc, NULL);
3216                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3217                 min_protoh = sizeof(struct tcpiphdr);
3218         }
3219         if (maxmtu && thcmtu)
3220                 mss = min(maxmtu, thcmtu) - min_protoh;
3221         else if (maxmtu || thcmtu)
3222                 mss = max(maxmtu, thcmtu) - min_protoh;
3223
3224         return (mss);
3225 }
3226
3227
3228 /*
3229  * On a partial ack arrives, force the retransmission of the
3230  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3231  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3232  * be started again.
3233  */
3234 static void
3235 tcp_newreno_partial_ack(tp, th)
3236         struct tcpcb *tp;
3237         struct tcphdr *th;
3238 {
3239         tcp_seq onxt = tp->snd_nxt;
3240         u_long  ocwnd = tp->snd_cwnd;
3241
3242         callout_stop(tp->tt_rexmt);
3243         tp->t_rtttime = 0;
3244         tp->snd_nxt = th->th_ack;
3245         /*
3246          * Set snd_cwnd to one segment beyond acknowledged offset.
3247          * (tp->snd_una has not yet been updated when this function is called.)
3248          */
3249         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
3250         tp->t_flags |= TF_ACKNOW;
3251         (void) tcp_output(tp);
3252         tp->snd_cwnd = ocwnd;
3253         if (SEQ_GT(onxt, tp->snd_nxt))
3254                 tp->snd_nxt = onxt;
3255         /*
3256          * Partial window deflation.  Relies on fact that tp->snd_una
3257          * not updated yet.
3258          */
3259         if (tp->snd_cwnd > th->th_ack - tp->snd_una)
3260                 tp->snd_cwnd -= th->th_ack - tp->snd_una;
3261         else
3262                 tp->snd_cwnd = 0;
3263         tp->snd_cwnd += tp->t_maxseg;
3264 }
3265
3266 /*
3267  * Returns 1 if the TIME_WAIT state was killed and we should start over,
3268  * looking for a pcb in the listen state.  Returns 0 otherwise.
3269  */
3270 static int
3271 tcp_timewait(inp, to, th, m, tlen)
3272         struct inpcb *inp;
3273         struct tcpopt *to;
3274         struct tcphdr *th;
3275         struct mbuf *m;
3276         int tlen;
3277 {
3278         struct tcptw *tw;
3279         int thflags;
3280         tcp_seq seq;
3281 #ifdef INET6
3282         int isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
3283 #else
3284         const int isipv6 = 0;
3285 #endif
3286
3287         /* tcbinfo lock required for tcp_twclose(), tcp_timer_2msl_reset(). */
3288         INP_INFO_WLOCK_ASSERT(&tcbinfo);
3289         INP_LOCK_ASSERT(inp);
3290
3291         /*
3292          * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
3293          * still present.  This is undesirable, but temporarily necessary
3294          * until we work out how to handle inpcb's who's timewait state has
3295          * been removed.
3296          */
3297         tw = intotw(inp);
3298         if (tw == NULL)
3299                 goto drop;
3300
3301         thflags = th->th_flags;
3302
3303         /*
3304          * NOTE: for FIN_WAIT_2 (to be added later),
3305          * must validate sequence number before accepting RST
3306          */
3307
3308         /*
3309          * If the segment contains RST:
3310          *      Drop the segment - see Stevens, vol. 2, p. 964 and
3311          *      RFC 1337.
3312          */
3313         if (thflags & TH_RST)
3314                 goto drop;
3315
3316 #if 0
3317 /* PAWS not needed at the moment */
3318         /*
3319          * RFC 1323 PAWS: If we have a timestamp reply on this segment
3320          * and it's less than ts_recent, drop it.
3321          */
3322         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
3323             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
3324                 if ((thflags & TH_ACK) == 0)
3325                         goto drop;
3326                 goto ack;
3327         }
3328         /*
3329          * ts_recent is never updated because we never accept new segments.
3330          */
3331 #endif
3332
3333         /*
3334          * If a new connection request is received
3335          * while in TIME_WAIT, drop the old connection
3336          * and start over if the sequence numbers
3337          * are above the previous ones.
3338          */
3339         if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
3340                 tcp_twclose(tw, 0);
3341                 return (1);
3342         }
3343
3344         /*
3345          * Drop the the segment if it does not contain an ACK.
3346          */
3347         if ((thflags & TH_ACK) == 0)
3348                 goto drop;
3349
3350         /*
3351          * Reset the 2MSL timer if this is a duplicate FIN.
3352          */
3353         if (thflags & TH_FIN) {
3354                 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
3355                 if (seq + 1 == tw->rcv_nxt)
3356                         tcp_timer_2msl_reset(tw, 1);
3357         }
3358
3359         /*
3360          * Acknowledge the segment if it has data or is not a duplicate ACK.
3361          */
3362         if (thflags != TH_ACK || tlen != 0 ||
3363             th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
3364                 tcp_twrespond(tw, TH_ACK);
3365         goto drop;
3366
3367         /*
3368          * Generate a RST, dropping incoming segment.
3369          * Make ACK acceptable to originator of segment.
3370          * Don't bother to respond if destination was broadcast/multicast.
3371          */
3372         if (m->m_flags & (M_BCAST|M_MCAST))
3373                 goto drop;
3374         if (isipv6) {
3375                 struct ip6_hdr *ip6;
3376
3377                 /* IPv6 anycast check is done at tcp6_input() */
3378                 ip6 = mtod(m, struct ip6_hdr *);
3379                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3380                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3381                         goto drop;
3382         } else {
3383                 struct ip *ip;
3384
3385                 ip = mtod(m, struct ip *);
3386                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3387                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3388                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3389                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3390                         goto drop;
3391         }
3392         if (thflags & TH_ACK) {
3393                 tcp_respond(NULL,
3394                     mtod(m, void *), th, m, 0, th->th_ack, TH_RST);
3395         } else {
3396                 seq = th->th_seq + (thflags & TH_SYN ? 1 : 0);
3397                 tcp_respond(NULL,
3398                     mtod(m, void *), th, m, seq, 0, TH_RST|TH_ACK);
3399         }
3400         INP_UNLOCK(inp);
3401         return (0);
3402
3403 drop:
3404         INP_UNLOCK(inp);
3405         m_freem(m);
3406         return (0);
3407 }