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
  40 #include <sys/param.h>
  41 #include <sys/kernel.h>
  42 #include <sys/malloc.h>
  43 #include <sys/mbuf.h>
  44 #include <sys/proc.h>           /* for proc0 declaration */
  45 #include <sys/protosw.h>
  46 #include <sys/signalvar.h>
  47 #include <sys/socket.h>
  48 #include <sys/socketvar.h>
  49 #include <sys/sysctl.h>
  50 #include <sys/syslog.h>
  51 #include <sys/systm.h>
  52
  53 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  54
  55 #include <vm/uma.h>
  56
  57 #include <net/if.h>
  58 #include <net/route.h>
  59
  60 #include <netinet/in.h>
  61 #include <netinet/in_pcb.h>
  62 #include <netinet/in_systm.h>
  63 #include <netinet/in_var.h>
  64 #include <netinet/ip.h>
  65 #include <netinet/ip_icmp.h>    /* required for icmp_var.h */
  66 #include <netinet/icmp_var.h>   /* for ICMP_BANDLIM */
  67 #include <netinet/ip_var.h>
  68 #include <netinet/ip_options.h>
  69 #include <netinet/ip6.h>
  70 #include <netinet/icmp6.h>
  71 #include <netinet6/in6_pcb.h>
  72 #include <netinet6/ip6_var.h>
  73 #include <netinet6/nd6.h>
  74 #include <netinet/tcp.h>
  75 #include <netinet/tcp_fsm.h>
  76 #include <netinet/tcp_seq.h>
  77 #include <netinet/tcp_timer.h>
  78 #include <netinet/tcp_var.h>
  79 #include <netinet6/tcp6_var.h>
  80 #include <netinet/tcpip.h>
  81 #ifdef TCPDEBUG
  82 #include <netinet/tcp_debug.h>
  83 #endif /* TCPDEBUG */
  84
  85 #ifdef FAST_IPSEC
  86 #include <netipsec/ipsec.h>
  87 #include <netipsec/ipsec6.h>
  88 #endif /*FAST_IPSEC*/
  89
  90 #ifdef IPSEC
  91 #include <netinet6/ipsec.h>
  92 #include <netinet6/ipsec6.h>
  93 #include <netkey/key.h>
  94 #endif /*IPSEC*/
  95
  96 #include <machine/in_cksum.h>
  97
  98 #include <security/mac/mac_framework.h>
  99
 100 static const int tcprexmtthresh = 3;
 101
 102 struct  tcpstat tcpstat;
 103 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
 104     &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
 105
 106 static int tcp_log_in_vain = 0;
 107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
 108     &tcp_log_in_vain, 0, "Log all incoming TCP segments to closed ports");
 109
 110 static int blackhole = 0;
 111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
 112     &blackhole, 0, "Do not send RST on segments to closed ports");
 113
 114 int tcp_delack_enabled = 1;
 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
 116     &tcp_delack_enabled, 0,
 117     "Delay ACK to try and piggyback it onto a data packet");
 118
 119 static int drop_synfin = 0;
 120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
 121     &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
 122
 123 static int tcp_do_rfc3042 = 1;
 124 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
 125     &tcp_do_rfc3042, 0, "Enable RFC 3042 (Limited Transmit)");
 126
 127 static int tcp_do_rfc3390 = 1;
 128 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
 129     &tcp_do_rfc3390, 0,
 130     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 131
 132 static int tcp_insecure_rst = 0;
 133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
 134     &tcp_insecure_rst, 0,
 135     "Follow the old (insecure) criteria for accepting RST packets");
 136
 137 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
 138     "TCP Segment Reassembly Queue");
 139
 140 static int tcp_reass_maxseg = 0;
 141 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RDTUN,
 142     &tcp_reass_maxseg, 0,
 143     "Global maximum number of TCP Segments in Reassembly Queue");
 144
 145 int tcp_reass_qsize = 0;
 146 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD,
 147     &tcp_reass_qsize, 0,
 148     "Global number of TCP Segments currently in Reassembly Queue");
 149
 150 static int tcp_reass_maxqlen = 48;
 151 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxqlen, CTLFLAG_RW,
 152     &tcp_reass_maxqlen, 0,
 153     "Maximum number of TCP Segments per individual Reassembly Queue");
 154
 155 static int tcp_reass_overflows = 0;
 156 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD,
 157     &tcp_reass_overflows, 0,
 158     "Global number of TCP Segment Reassembly Queue Overflows");
 159
 160 int     tcp_do_autorcvbuf = 1;
 161 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
 162     &tcp_do_autorcvbuf, 0, "Enable automatic receive buffer sizing");
 163
 164 int     tcp_autorcvbuf_inc = 16*1024;
 165 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
 166     &tcp_autorcvbuf_inc, 0,
 167     "Incrementor step size of automatic receive buffer");
 168
 169 int     tcp_autorcvbuf_max = 256*1024;
 170 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
 171     &tcp_autorcvbuf_max, 0, "Max size of automatic receive buffer");
 172
 173 struct inpcbhead tcb;
 174 #define tcb6    tcb  /* for KAME src sync over BSD*'s */
 175 struct inpcbinfo tcbinfo;
 176
 177 static void      tcp_dooptions(struct tcpopt *, u_char *, int, int);
 178 static void      tcp_do_segment(struct mbuf *, struct tcphdr *,
 179                      struct socket *, struct tcpcb *, int, int);
 180 static void      tcp_dropwithreset(struct mbuf *, struct tcphdr *,
 181                      struct tcpcb *, int, int);
 182 static void      tcp_pulloutofband(struct socket *,
 183                      struct tcphdr *, struct mbuf *, int);
 184 static int       tcp_reass(struct tcpcb *, struct tcphdr *, int *,
 185                      struct mbuf *);
 186 static void      tcp_xmit_timer(struct tcpcb *, int);
 187 static void      tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
 188 static int       tcp_timewait(struct inpcb *, struct tcpopt *,
 189                      struct tcphdr *, struct mbuf *, int);
 190
 191 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
 192 #ifdef INET6
 193 #define ND6_HINT(tp) \
 194 do { \
 195         if ((tp) && (tp)->t_inpcb && \
 196             ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
 197                 nd6_nud_hint(NULL, NULL, 0); \
 198 } while (0)
 199 #else
 200 #define ND6_HINT(tp)
 201 #endif
 202
 203 /*
 204  * Indicate whether this ack should be delayed.  We can delay the ack if
 205  *      - there is no delayed ack timer in progress and
 206  *      - our last ack wasn't a 0-sized window.  We never want to delay
 207  *        the ack that opens up a 0-sized window and
 208  *              - delayed acks are enabled or
 209  *              - this is a half-synchronized T/TCP connection.
 210  */
 211 #define DELAY_ACK(tp)                                                   \
 212         ((!tcp_timer_active(tp, TT_DELACK) &&                           \
 213             (tp->t_flags & TF_RXWIN0SENT) == 0) &&                      \
 214             (tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
 215
 216 /* Initialize TCP reassembly queue */
 217 static void
 218 tcp_reass_zone_change(void *tag)
 219 {
 220
 221         tcp_reass_maxseg = nmbclusters / 16;
 222         uma_zone_set_max(tcp_reass_zone, tcp_reass_maxseg);
 223 }
 224
 225 uma_zone_t      tcp_reass_zone;
 226 void
 227 tcp_reass_init()
 228 {
 229         tcp_reass_maxseg = nmbclusters / 16;
 230         TUNABLE_INT_FETCH("net.inet.tcp.reass.maxsegments",
 231             &tcp_reass_maxseg);
 232         tcp_reass_zone = uma_zcreate("tcpreass", sizeof (struct tseg_qent),
 233             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
 234         uma_zone_set_max(tcp_reass_zone, tcp_reass_maxseg);
 235         EVENTHANDLER_REGISTER(nmbclusters_change,
 236             tcp_reass_zone_change, NULL, EVENTHANDLER_PRI_ANY);
 237 }
 238
 239 static int
 240 tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
 241 {
 242         struct tseg_qent *q;
 243         struct tseg_qent *p = NULL;
 244         struct tseg_qent *nq;
 245         struct tseg_qent *te = NULL;
 246         struct socket *so = tp->t_inpcb->inp_socket;
 247         int flags;
 248
 249         INP_LOCK_ASSERT(tp->t_inpcb);
 250
 251         /*
 252          * XXX: tcp_reass() is rather inefficient with its data structures
 253          * and should be rewritten (see NetBSD for optimizations).  While
 254          * doing that it should move to its own file tcp_reass.c.
 255          */
 256
 257         /*
 258          * Call with th==NULL after become established to
 259          * force pre-ESTABLISHED data up to user socket.
 260          */
 261         if (th == NULL)
 262                 goto present;
 263
 264         /*
 265          * Limit the number of segments in the reassembly queue to prevent
 266          * holding on to too many segments (and thus running out of mbufs).
 267          * Make sure to let the missing segment through which caused this
 268          * queue.  Always keep one global queue entry spare to be able to
 269          * process the missing segment.
 270          */
 271         if (th->th_seq != tp->rcv_nxt &&
 272             (tcp_reass_qsize + 1 >= tcp_reass_maxseg ||
 273              tp->t_segqlen >= tcp_reass_maxqlen)) {
 274                 tcp_reass_overflows++;
 275                 tcpstat.tcps_rcvmemdrop++;
 276                 m_freem(m);
 277                 *tlenp = 0;
 278                 return (0);
 279         }
 280
 281         /*
 282          * Allocate a new queue entry. If we can't, or hit the zone limit
 283          * just drop the pkt.
 284          */
 285         te = uma_zalloc(tcp_reass_zone, M_NOWAIT);
 286         if (te == NULL) {
 287                 tcpstat.tcps_rcvmemdrop++;
 288                 m_freem(m);
 289                 *tlenp = 0;
 290                 return (0);
 291         }
 292         tp->t_segqlen++;
 293         tcp_reass_qsize++;
 294
 295         /*
 296          * Find a segment which begins after this one does.
 297          */
 298         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
 299                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
 300                         break;
 301                 p = q;
 302         }
 303
 304         /*
 305          * If there is a preceding segment, it may provide some of
 306          * our data already.  If so, drop the data from the incoming
 307          * segment.  If it provides all of our data, drop us.
 308          */
 309         if (p != NULL) {
 310                 int i;
 311                 /* conversion to int (in i) handles seq wraparound */
 312                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
 313                 if (i > 0) {
 314                         if (i >= *tlenp) {
 315                                 tcpstat.tcps_rcvduppack++;
 316                                 tcpstat.tcps_rcvdupbyte += *tlenp;
 317                                 m_freem(m);
 318                                 uma_zfree(tcp_reass_zone, te);
 319                                 tp->t_segqlen--;
 320                                 tcp_reass_qsize--;
 321                                 /*
 322                                  * Try to present any queued data
 323                                  * at the left window edge to the user.
 324                                  * This is needed after the 3-WHS
 325                                  * completes.
 326                                  */
 327                                 goto present;   /* ??? */
 328                         }
 329                         m_adj(m, i);
 330                         *tlenp -= i;
 331                         th->th_seq += i;
 332                 }
 333         }
 334         tcpstat.tcps_rcvoopack++;
 335         tcpstat.tcps_rcvoobyte += *tlenp;
 336
 337         /*
 338          * While we overlap succeeding segments trim them or,
 339          * if they are completely covered, dequeue them.
 340          */
 341         while (q) {
 342                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
 343                 if (i <= 0)
 344                         break;
 345                 if (i < q->tqe_len) {
 346                         q->tqe_th->th_seq += i;
 347                         q->tqe_len -= i;
 348                         m_adj(q->tqe_m, i);
 349                         break;
 350                 }
 351
 352                 nq = LIST_NEXT(q, tqe_q);
 353                 LIST_REMOVE(q, tqe_q);
 354                 m_freem(q->tqe_m);
 355                 uma_zfree(tcp_reass_zone, q);
 356                 tp->t_segqlen--;
 357                 tcp_reass_qsize--;
 358                 q = nq;
 359         }
 360
 361         /* Insert the new segment queue entry into place. */
 362         te->tqe_m = m;
 363         te->tqe_th = th;
 364         te->tqe_len = *tlenp;
 365
 366         if (p == NULL) {
 367                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 368         } else {
 369                 LIST_INSERT_AFTER(p, te, tqe_q);
 370         }
 371
 372 present:
 373         /*
 374          * Present data to user, advancing rcv_nxt through
 375          * completed sequence space.
 376          */
 377         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 378                 return (0);
 379         q = LIST_FIRST(&tp->t_segq);
 380         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
 381                 return (0);
 382         SOCKBUF_LOCK(&so->so_rcv);
 383         do {
 384                 tp->rcv_nxt += q->tqe_len;
 385                 flags = q->tqe_th->th_flags & TH_FIN;
 386                 nq = LIST_NEXT(q, tqe_q);
 387                 LIST_REMOVE(q, tqe_q);
 388                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
 389                         m_freem(q->tqe_m);
 390                 else
 391                         sbappendstream_locked(&so->so_rcv, q->tqe_m);
 392                 uma_zfree(tcp_reass_zone, q);
 393                 tp->t_segqlen--;
 394                 tcp_reass_qsize--;
 395                 q = nq;
 396         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
 397         ND6_HINT(tp);
 398         sorwakeup_locked(so);
 399         return (flags);
 400 }
 401
 402 /*
 403  * TCP input routine, follows pages 65-76 of the
 404  * protocol specification dated September, 1981 very closely.
 405  */
 406 #ifdef INET6
 407 int
 408 tcp6_input(struct mbuf **mp, int *offp, int proto)
 409 {
 410         struct mbuf *m = *mp;
 411         struct in6_ifaddr *ia6;
 412
 413         IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
 414
 415         /*
 416          * draft-itojun-ipv6-tcp-to-anycast
 417          * better place to put this in?
 418          */
 419         ia6 = ip6_getdstifaddr(m);
 420         if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
 421                 struct ip6_hdr *ip6;
 422
 423                 ip6 = mtod(m, struct ip6_hdr *);
 424                 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
 425                             (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
 426                 return IPPROTO_DONE;
 427         }
 428
 429         tcp_input(m, *offp);
 430         return IPPROTO_DONE;
 431 }
 432 #endif
 433
 434 void
 435 tcp_input(struct mbuf *m, int off0)
 436 {
 437         struct tcphdr *th;
 438         struct ip *ip = NULL;
 439         struct ipovly *ipov;
 440         struct inpcb *inp = NULL;
 441         struct tcpcb *tp = NULL;
 442         struct socket *so = NULL;
 443         u_char *optp = NULL;
 444         int optlen = 0;
 445         int len, tlen, off;
 446         int drop_hdrlen;
 447         int thflags;
 448         int rstreason = 0;      /* For badport_bandlim accounting purposes */
 449 #ifdef IPFIREWALL_FORWARD
 450         struct m_tag *fwd_tag;
 451 #endif
 452 #ifdef INET6
 453         struct ip6_hdr *ip6 = NULL;
 454         int isipv6;
 455         char ip6buf[INET6_ADDRSTRLEN];
 456 #else
 457         const int isipv6 = 0;
 458 #endif
 459         struct tcpopt to;               /* options in this segment */
 460
 461 #ifdef TCPDEBUG
 462         /*
 463          * The size of tcp_saveipgen must be the size of the max ip header,
 464          * now IPv6.
 465          */
 466         u_char tcp_saveipgen[IP6_HDR_LEN];
 467         struct tcphdr tcp_savetcp;
 468         short ostate = 0;
 469 #endif
 470
 471 #ifdef INET6
 472         isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
 473 #endif
 474
 475         to.to_flags = 0;
 476         tcpstat.tcps_rcvtotal++;
 477
 478         if (isipv6) {
 479 #ifdef INET6
 480                 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
 481                 ip6 = mtod(m, struct ip6_hdr *);
 482                 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
 483                 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
 484                         tcpstat.tcps_rcvbadsum++;
 485                         goto drop;
 486                 }
 487                 th = (struct tcphdr *)((caddr_t)ip6 + off0);
 488
 489                 /*
 490                  * Be proactive about unspecified IPv6 address in source.
 491                  * As we use all-zero to indicate unbounded/unconnected pcb,
 492                  * unspecified IPv6 address can be used to confuse us.
 493                  *
 494                  * Note that packets with unspecified IPv6 destination is
 495                  * already dropped in ip6_input.
 496                  */
 497                 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 498                         /* XXX stat */
 499                         goto drop;
 500                 }
 501 #else
 502                 th = NULL;              /* XXX: avoid compiler warning */
 503 #endif
 504         } else {
 505                 /*
 506                  * Get IP and TCP header together in first mbuf.
 507                  * Note: IP leaves IP header in first mbuf.
 508                  */
 509                 if (off0 > sizeof (struct ip)) {
 510                         ip_stripoptions(m, (struct mbuf *)0);
 511                         off0 = sizeof(struct ip);
 512                 }
 513                 if (m->m_len < sizeof (struct tcpiphdr)) {
 514                         if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
 515                             == NULL) {
 516                                 tcpstat.tcps_rcvshort++;
 517                                 return;
 518                         }
 519                 }
 520                 ip = mtod(m, struct ip *);
 521                 ipov = (struct ipovly *)ip;
 522                 th = (struct tcphdr *)((caddr_t)ip + off0);
 523                 tlen = ip->ip_len;
 524
 525                 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
 526                         if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 527                                 th->th_sum = m->m_pkthdr.csum_data;
 528                         else
 529                                 th->th_sum = in_pseudo(ip->ip_src.s_addr,
 530                                                 ip->ip_dst.s_addr,
 531                                                 htonl(m->m_pkthdr.csum_data +
 532                                                         ip->ip_len +
 533                                                         IPPROTO_TCP));
 534                         th->th_sum ^= 0xffff;
 535 #ifdef TCPDEBUG
 536                         ipov->ih_len = (u_short)tlen;
 537                         ipov->ih_len = htons(ipov->ih_len);
 538 #endif
 539                 } else {
 540                         /*
 541                          * Checksum extended TCP header and data.
 542                          */
 543                         len = sizeof (struct ip) + tlen;
 544                         bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
 545                         ipov->ih_len = (u_short)tlen;
 546                         ipov->ih_len = htons(ipov->ih_len);
 547                         th->th_sum = in_cksum(m, len);
 548                 }
 549                 if (th->th_sum) {
 550                         tcpstat.tcps_rcvbadsum++;
 551                         goto drop;
 552                 }
 553                 /* Re-initialization for later version check */
 554                 ip->ip_v = IPVERSION;
 555         }
 556
 557         /*
 558          * Check that TCP offset makes sense,
 559          * pull out TCP options and adjust length.              XXX
 560          */
 561         off = th->th_off << 2;
 562         if (off < sizeof (struct tcphdr) || off > tlen) {
 563                 tcpstat.tcps_rcvbadoff++;
 564                 goto drop;
 565         }
 566         tlen -= off;    /* tlen is used instead of ti->ti_len */
 567         if (off > sizeof (struct tcphdr)) {
 568                 if (isipv6) {
 569 #ifdef INET6
 570                         IP6_EXTHDR_CHECK(m, off0, off, );
 571                         ip6 = mtod(m, struct ip6_hdr *);
 572                         th = (struct tcphdr *)((caddr_t)ip6 + off0);
 573 #endif
 574                 } else {
 575                         if (m->m_len < sizeof(struct ip) + off) {
 576                                 if ((m = m_pullup(m, sizeof (struct ip) + off))
 577                                     == NULL) {
 578                                         tcpstat.tcps_rcvshort++;
 579                                         return;
 580                                 }
 581                                 ip = mtod(m, struct ip *);
 582                                 ipov = (struct ipovly *)ip;
 583                                 th = (struct tcphdr *)((caddr_t)ip + off0);
 584                         }
 585                 }
 586                 optlen = off - sizeof (struct tcphdr);
 587                 optp = (u_char *)(th + 1);
 588         }
 589         thflags = th->th_flags;
 590
 591         /*
 592          * If the drop_synfin option is enabled, drop all packets with
 593          * both the SYN and FIN bits set. This prevents e.g. nmap from
 594          * identifying the TCP/IP stack.
 595          *
 596          * This is a violation of the TCP specification.
 597          */
 598         if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
 599                 goto drop;
 600
 601         /*
 602          * Convert TCP protocol specific fields to host format.
 603          */
 604         th->th_seq = ntohl(th->th_seq);
 605         th->th_ack = ntohl(th->th_ack);
 606         th->th_win = ntohs(th->th_win);
 607         th->th_urp = ntohs(th->th_urp);
 608
 609         /*
 610          * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
 611          */
 612         drop_hdrlen = off0 + off;
 613
 614         /*
 615          * Locate pcb for segment.
 616          */
 617         INP_INFO_WLOCK(&tcbinfo);
 618 findpcb:
 619         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 620 #ifdef IPFIREWALL_FORWARD
 621         /* Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain. */
 622         fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
 623
 624         if (fwd_tag != NULL && isipv6 == 0) {   /* IPv6 support is not yet */
 625                 struct sockaddr_in *next_hop;
 626
 627                 next_hop = (struct sockaddr_in *)(fwd_tag+1);
 628                 /*
 629                  * Transparently forwarded. Pretend to be the destination.
 630                  * already got one like this?
 631                  */
 632                 inp = in_pcblookup_hash(&tcbinfo,
 633                                         ip->ip_src, th->th_sport,
 634                                         ip->ip_dst, th->th_dport,
 635                                         0, m->m_pkthdr.rcvif);
 636                 if (!inp) {
 637                         /* It's new.  Try to find the ambushing socket. */
 638                         inp = in_pcblookup_hash(&tcbinfo,
 639                                                 ip->ip_src, th->th_sport,
 640                                                 next_hop->sin_addr,
 641                                                 next_hop->sin_port ?
 642                                                     ntohs(next_hop->sin_port) :
 643                                                     th->th_dport,
 644                                                 INPLOOKUP_WILDCARD,
 645                                                 m->m_pkthdr.rcvif);
 646                 }
 647                 /* Remove the tag from the packet.  We don't need it anymore. */
 648                 m_tag_delete(m, fwd_tag);
 649         } else
 650 #endif /* IPFIREWALL_FORWARD */
 651         {
 652                 if (isipv6) {
 653 #ifdef INET6
 654                         inp = in6_pcblookup_hash(&tcbinfo,
 655                                                  &ip6->ip6_src, th->th_sport,
 656                                                  &ip6->ip6_dst, th->th_dport,
 657                                                  INPLOOKUP_WILDCARD,
 658                                                  m->m_pkthdr.rcvif);
 659 #endif
 660                 } else
 661                         inp = in_pcblookup_hash(&tcbinfo,
 662                                                 ip->ip_src, th->th_sport,
 663                                                 ip->ip_dst, th->th_dport,
 664                                                 INPLOOKUP_WILDCARD,
 665                                                 m->m_pkthdr.rcvif);
 666         }
 667
 668 #if defined(IPSEC) || defined(FAST_IPSEC)
 669 #ifdef INET6
 670         if (isipv6 && inp != NULL && ipsec6_in_reject(m, inp)) {
 671 #ifdef IPSEC
 672                 ipsec6stat.in_polvio++;
 673 #endif
 674                 goto dropunlock;
 675         } else
 676 #endif /* INET6 */
 677         if (inp != NULL && ipsec4_in_reject(m, inp)) {
 678 #ifdef IPSEC
 679                 ipsecstat.in_polvio++;
 680 #endif
 681                 goto dropunlock;
 682         }
 683 #endif /*IPSEC || FAST_IPSEC*/
 684
 685         /*
 686          * If the INPCB does not exist then all data in the incoming
 687          * segment is discarded and an appropriate RST is sent back.
 688          */
 689         if (inp == NULL) {
 690                 /*
 691                  * Log communication attempts to ports that are not
 692                  * in use.
 693                  */
 694                 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
 695                     tcp_log_in_vain == 2) {
 696 #ifndef INET6
 697                         char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
 698 #else
 699                         char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
 700                         if (isipv6) {
 701                                 strcpy(dbuf, "[");
 702                                 strcat(dbuf,
 703                                     ip6_sprintf(ip6buf, &ip6->ip6_dst));
 704                                 strcat(dbuf, "]");
 705                                 strcpy(sbuf, "[");
 706                                 strcat(sbuf,
 707                                     ip6_sprintf(ip6buf, &ip6->ip6_src));
 708                                 strcat(sbuf, "]");
 709                         } else
 710 #endif /* INET6 */
 711                         {
 712                                 strcpy(dbuf, inet_ntoa(ip->ip_dst));
 713                                 strcpy(sbuf, inet_ntoa(ip->ip_src));
 714                         }
 715                         log(LOG_INFO,
 716                             "Connection attempt to TCP %s:%d "
 717                             "from %s:%d flags:0x%02x\n",
 718                             dbuf, ntohs(th->th_dport), sbuf,
 719                             ntohs(th->th_sport), thflags);
 720                 }
 721                 /*
 722                  * When blackholing do not respond with a RST but
 723                  * completely ignore the segment and drop it.
 724                  */
 725                 if ((blackhole == 1 && (thflags & TH_SYN)) ||
 726                     blackhole == 2)
 727                         goto dropunlock;
 728
 729                 rstreason = BANDLIM_RST_CLOSEDPORT;
 730                 goto dropwithreset;
 731         }
 732         INP_LOCK(inp);
 733
 734         /* Check the minimum TTL for socket. */
 735         if (inp->inp_ip_minttl != 0) {
 736 #ifdef INET6
 737                 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
 738                         goto dropunlock;
 739                 else
 740 #endif
 741                 if (inp->inp_ip_minttl > ip->ip_ttl)
 742                         goto dropunlock;
 743         }
 744
 745         /*
 746          * A previous connection in TIMEWAIT state is supposed to catch
 747          * stray or duplicate segments arriving late.  If this segment
 748          * was a legitimate new connection attempt the old INPCB gets
 749          * removed and we can try again to find a listening socket.
 750          */
 751         if (inp->inp_vflag & INP_TIMEWAIT) {
 752                 if (thflags & TH_SYN)
 753                         tcp_dooptions(&to, optp, optlen, TO_SYN);
 754                 /* NB: tcp_timewait unlocks the INP and frees the mbuf. */
 755                 if (tcp_timewait(inp, &to, th, m, tlen))
 756                         goto findpcb;
 757                 INP_INFO_WUNLOCK(&tcbinfo);
 758                 return;
 759         }
 760         /*
 761          * The TCPCB may no longer exist if the connection is winding
 762          * down or it is in the CLOSED state.  Either way we drop the
 763          * segment and send an appropriate response.
 764          */
 765         tp = intotcpcb(inp);
 766         if (tp == NULL) {
 767                 rstreason = BANDLIM_RST_CLOSEDPORT;
 768                 goto dropwithreset;
 769         }
 770         if (tp->t_state == TCPS_CLOSED)
 771                 goto dropunlock;        /* XXX: dropwithreset??? */
 772
 773 #ifdef MAC
 774         INP_LOCK_ASSERT(inp);
 775         if (mac_check_inpcb_deliver(inp, m))
 776                 goto dropunlock;
 777 #endif
 778         so = inp->inp_socket;
 779         KASSERT(so != NULL, ("%s: so == NULL", __func__));
 780 #ifdef TCPDEBUG
 781         if (so->so_options & SO_DEBUG) {
 782                 ostate = tp->t_state;
 783                 if (isipv6)
 784                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 785                 else
 786                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 787                 tcp_savetcp = *th;
 788         }
 789 #endif
 790         /*
 791          * When the socket is accepting connections (the INPCB is in LISTEN
 792          * state) we look into the SYN cache if this is a new connection
 793          * attempt or the completion of a previous one.
 794          */
 795         if (so->so_options & SO_ACCEPTCONN) {
 796                 struct in_conninfo inc;
 797
 798                 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
 799                     "tp not listening", __func__));
 800
 801                 bzero(&inc, sizeof(inc));
 802                 inc.inc_isipv6 = isipv6;
 803 #ifdef INET6
 804                 if (isipv6) {
 805                         inc.inc6_faddr = ip6->ip6_src;
 806                         inc.inc6_laddr = ip6->ip6_dst;
 807                 } else
 808 #endif
 809                 {
 810                         inc.inc_faddr = ip->ip_src;
 811                         inc.inc_laddr = ip->ip_dst;
 812                 }
 813                 inc.inc_fport = th->th_sport;
 814                 inc.inc_lport = th->th_dport;
 815
 816                 /*
 817                  * If the state is LISTEN then ignore segment if it contains
 818                  * a RST.  If the segment contains an ACK then it is bad and
 819                  * send a RST.  If it does not contain a SYN then it is not
 820                  * interesting; drop it.
 821                  *
 822                  * If the state is SYN_RECEIVED (syncache) and seg contains
 823                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 824                  * contains a RST, check the sequence number to see if it
 825                  * is a valid reset segment.
 826                  */
 827                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 828                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 829                                 /*
 830                                  * Parse the TCP options here because
 831                                  * syncookies need access to the reflected
 832                                  * timestamp.
 833                                  */
 834                                 tcp_dooptions(&to, optp, optlen, 0);
 835                                 /*
 836                                  * NB: syncache_expand() doesn't unlock
 837                                  * inp and tcpinfo locks.
 838                                  */
 839                                 if (!syncache_expand(&inc, &to, th, &so, m)) {
 840                                         /*
 841                                          * No syncache entry or ACK was not
 842                                          * for our SYN/ACK.  Send a RST.
 843                                          */
 844                                         rstreason = BANDLIM_RST_OPENPORT;
 845                                         goto dropwithreset;
 846                                 }
 847                                 if (so == NULL) {
 848                                         /*
 849                                          * We completed the 3-way handshake
 850                                          * but could not allocate a socket
 851                                          * either due to memory shortage,
 852                                          * listen queue length limits or
 853                                          * global socket limits.
 854                                          */
 855                                         rstreason = BANDLIM_UNLIMITED;
 856                                         goto dropwithreset;
 857                                 }
 858                                 /*
 859                                  * Socket is created in state SYN_RECEIVED.
 860                                  * Continue processing segment.
 861                                  */
 862                                 INP_UNLOCK(inp);        /* listen socket */
 863                                 inp = sotoinpcb(so);
 864                                 INP_LOCK(inp);          /* new connection */
 865                                 tp = intotcpcb(inp);
 866                                 /*
 867                                  * Process the segment and the data it
 868                                  * contains.  tcp_do_segment() consumes
 869                                  * the mbuf chain and unlocks the inpcb.
 870                                  */
 871                                 tcp_do_segment(m, th, so, tp, drop_hdrlen,
 872                                                 tlen);
 873                                 INP_INFO_UNLOCK_ASSERT(&tcbinfo);
 874                                 return;
 875                         }
 876                         if (thflags & TH_RST) {
 877                                 syncache_chkrst(&inc, th);
 878                                 goto dropunlock;
 879                         }
 880                         if (thflags & TH_ACK) {
 881                                 syncache_badack(&inc);
 882                                 tcpstat.tcps_badsyn++;
 883                                 rstreason = BANDLIM_RST_OPENPORT;
 884                                 goto dropwithreset;
 885                         }
 886                         goto dropunlock;
 887                 }
 888
 889                 /*
 890                  * Segment's flags are (SYN) or (SYN|FIN).
 891                  */
 892 #ifdef INET6
 893                 /*
 894                  * If deprecated address is forbidden,
 895                  * we do not accept SYN to deprecated interface
 896                  * address to prevent any new inbound connection from
 897                  * getting established.
 898                  * When we do not accept SYN, we send a TCP RST,
 899                  * with deprecated source address (instead of dropping
 900                  * it).  We compromise it as it is much better for peer
 901                  * to send a RST, and RST will be the final packet
 902                  * for the exchange.
 903                  *
 904                  * If we do not forbid deprecated addresses, we accept
 905                  * the SYN packet.  RFC2462 does not suggest dropping
 906                  * SYN in this case.
 907                  * If we decipher RFC2462 5.5.4, it says like this:
 908                  * 1. use of deprecated addr with existing
 909                  *    communication is okay - "SHOULD continue to be
 910                  *    used"
 911                  * 2. use of it with new communication:
 912                  *   (2a) "SHOULD NOT be used if alternate address
 913                  *        with sufficient scope is available"
 914                  *   (2b) nothing mentioned otherwise.
 915                  * Here we fall into (2b) case as we have no choice in
 916                  * our source address selection - we must obey the peer.
 917                  *
 918                  * The wording in RFC2462 is confusing, and there are
 919                  * multiple description text for deprecated address
 920                  * handling - worse, they are not exactly the same.
 921                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 922                  */
 923                 if (isipv6 && !ip6_use_deprecated) {
 924                         struct in6_ifaddr *ia6;
 925
 926                         if ((ia6 = ip6_getdstifaddr(m)) &&
 927                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 928                                 rstreason = BANDLIM_RST_OPENPORT;
 929                                 goto dropwithreset;
 930                         }
 931                 }
 932 #endif
 933                 /*
 934                  * Basic sanity checks on incoming SYN requests:
 935                  *
 936                  * Don't bother responding if the destination was a
 937                  * broadcast according to RFC1122 4.2.3.10, p. 104.
 938                  *
 939                  * If it is from this socket, drop it, it must be forged.
 940                  *
 941                  * Note that it is quite possible to receive unicast
 942                  * link-layer packets with a broadcast IP address. Use
 943                  * in_broadcast() to find them.
 944                  */
 945                 if (m->m_flags & (M_BCAST|M_MCAST))
 946                         goto dropunlock;
 947                 if (isipv6) {
 948 #ifdef INET6
 949                         if (th->th_dport == th->th_sport &&
 950                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src))
 951                                 goto dropunlock;
 952                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 953                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 954                                 goto dropunlock;
 955 #endif
 956                 } else {
 957                         if (th->th_dport == th->th_sport &&
 958                             ip->ip_dst.s_addr == ip->ip_src.s_addr)
 959                                 goto dropunlock;
 960                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 961                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 962                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 963                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 964                                 goto dropunlock;
 965                 }
 966                 /*
 967                  * SYN appears to be valid.  Create compressed TCP state
 968                  * for syncache.
 969                  */
 970 #ifdef TCPDEBUG
 971                 if (so->so_options & SO_DEBUG)
 972                         tcp_trace(TA_INPUT, ostate, tp,
 973                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
 974 #endif
 975                 tcp_dooptions(&to, optp, optlen, TO_SYN);
 976                 syncache_add(&inc, &to, th, inp, &so, m);
 977                 /*
 978                  * Entry added to syncache and mbuf consumed.
 979                  * Everything unlocked already by syncache_add().
 980                  */
 981                 return;
 982         }
 983
 984         /*
 985          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or late
 986          * state.  tcp_do_segment() always consumes the mbuf chain, unlocks the
 987          * inpcb, and unlocks the pcbinfo.
 988          */
 989         tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen);
 990         INP_INFO_UNLOCK_ASSERT(&tcbinfo);
 991         return;
 992
 993 dropwithreset:
 994         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 995         tcp_dropwithreset(m, th, tp, tlen, rstreason);
 996         m = NULL;       /* mbuf chain got consumed. */
 997 dropunlock:
 998         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 999         if (inp != NULL)
1000                 INP_UNLOCK(inp);
1001         INP_INFO_WUNLOCK(&tcbinfo);
1002 drop:
1003         INP_INFO_UNLOCK_ASSERT(&tcbinfo);
1004         if (m != NULL)
1005                 m_freem(m);
1006         return;
1007 }
1008
1009 static void
1010 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1011     struct tcpcb *tp, int drop_hdrlen, int tlen)
1012 {
1013         int thflags, acked, ourfinisacked, needoutput = 0;
1014         int headlocked = 1;
1015         int rstreason, todrop, win;
1016         u_long tiwin;
1017         struct tcpopt to;
1018
1019 #ifdef TCPDEBUG
1020         /*
1021          * The size of tcp_saveipgen must be the size of the max ip header,
1022          * now IPv6.
1023          */
1024         u_char tcp_saveipgen[IP6_HDR_LEN];
1025         struct tcphdr tcp_savetcp;
1026         short ostate = 0;
1027 #endif
1028         thflags = th->th_flags;
1029
1030         INP_INFO_WLOCK_ASSERT(&tcbinfo);
1031         INP_LOCK_ASSERT(tp->t_inpcb);
1032         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
1033             __func__));
1034         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
1035             __func__));
1036
1037         /*
1038          * Segment received on connection.
1039          * Reset idle time and keep-alive timer.
1040          */
1041         tp->t_rcvtime = ticks;
1042         if (TCPS_HAVEESTABLISHED(tp->t_state))
1043                 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
1044
1045         /*
1046          * Unscale the window into a 32-bit value.
1047          * This value is bogus for the TCPS_SYN_SENT state
1048          * and is overwritten later.
1049          */
1050         tiwin = th->th_win << tp->snd_scale;
1051
1052         /*
1053          * Parse options on any incoming segment.
1054          */
1055         tcp_dooptions(&to, (u_char *)(th + 1),
1056             (th->th_off << 2) - sizeof(struct tcphdr),
1057             (thflags & TH_SYN) ? TO_SYN : 0);
1058
1059         /*
1060          * If echoed timestamp is later than the current time,
1061          * fall back to non RFC1323 RTT calculation.  Normalize
1062          * timestamp if syncookies were used when this connection
1063          * was established.
1064          */
1065         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1066                 to.to_tsecr -= tp->ts_offset;
1067                 if (TSTMP_GT(to.to_tsecr, ticks))
1068                         to.to_tsecr = 0;
1069         }
1070
1071         /*
1072          * Process options only when we get SYN/ACK back. The SYN case
1073          * for incoming connections is handled in tcp_syncache.
1074          * XXX this is traditional behavior, may need to be cleaned up.
1075          */
1076         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1077                 if ((to.to_flags & TOF_SCALE) &&
1078                     (tp->t_flags & TF_REQ_SCALE)) {
1079                         tp->t_flags |= TF_RCVD_SCALE;
1080                         tp->snd_scale = to.to_wscale;
1081                         tp->snd_wnd = th->th_win << tp->snd_scale;
1082                         tiwin = tp->snd_wnd;
1083                 }
1084                 if (to.to_flags & TOF_TS) {
1085                         tp->t_flags |= TF_RCVD_TSTMP;
1086                         tp->ts_recent = to.to_tsval;
1087                         tp->ts_recent_age = ticks;
1088                 }
1089                 /* Initial send window, already scaled. */
1090                 tp->snd_wnd = th->th_win;
1091                 if (to.to_flags & TOF_MSS)
1092                         tcp_mss(tp, to.to_mss);
1093                 if (tp->sack_enable) {
1094                         if (!(to.to_flags & TOF_SACKPERM))
1095                                 tp->sack_enable = 0;
1096                         else
1097                                 tp->t_flags |= TF_SACK_PERMIT;
1098                 }
1099
1100         }
1101
1102         /*
1103          * Header prediction: check for the two common cases
1104          * of a uni-directional data xfer.  If the packet has
1105          * no control flags, is in-sequence, the window didn't
1106          * change and we're not retransmitting, it's a
1107          * candidate.  If the length is zero and the ack moved
1108          * forward, we're the sender side of the xfer.  Just
1109          * free the data acked & wake any higher level process
1110          * that was blocked waiting for space.  If the length
1111          * is non-zero and the ack didn't move, we're the
1112          * receiver side.  If we're getting packets in-order
1113          * (the reassembly queue is empty), add the data to
1114          * the socket buffer and note that we need a delayed ack.
1115          * Make sure that the hidden state-flags are also off.
1116          * Since we check for TCPS_ESTABLISHED above, it can only
1117          * be TH_NEEDSYN.
1118          */
1119         if (tp->t_state == TCPS_ESTABLISHED &&
1120             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1121             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1122             ((to.to_flags & TOF_TS) == 0 ||
1123              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
1124              th->th_seq == tp->rcv_nxt && tiwin && tiwin == tp->snd_wnd &&
1125              tp->snd_nxt == tp->snd_max) {
1126
1127                 /*
1128                  * If last ACK falls within this segment's sequence numbers,
1129                  * record the timestamp.
1130                  * NOTE that the test is modified according to the latest
1131                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1132                  */
1133                 if ((to.to_flags & TOF_TS) != 0 &&
1134                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1135                         tp->ts_recent_age = ticks;
1136                         tp->ts_recent = to.to_tsval;
1137                 }
1138
1139                 if (tlen == 0) {
1140                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1141                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1142                             tp->snd_cwnd >= tp->snd_wnd &&
1143                             ((!tcp_do_newreno && !tp->sack_enable &&
1144                               tp->t_dupacks < tcprexmtthresh) ||
1145                              ((tcp_do_newreno || tp->sack_enable) &&
1146                               !IN_FASTRECOVERY(tp) &&
1147                               (to.to_flags & TOF_SACK) == 0 &&
1148                               TAILQ_EMPTY(&tp->snd_holes)))) {
1149                                 KASSERT(headlocked,
1150                                     ("%s: headlocked", __func__));
1151                                 INP_INFO_WUNLOCK(&tcbinfo);
1152                                 headlocked = 0;
1153                                 /*
1154                                  * this is a pure ack for outstanding data.
1155                                  */
1156                                 ++tcpstat.tcps_predack;
1157                                 /*
1158                                  * "bad retransmit" recovery
1159                                  */
1160                                 if (tp->t_rxtshift == 1 &&
1161                                     ticks < tp->t_badrxtwin) {
1162                                         ++tcpstat.tcps_sndrexmitbad;
1163                                         tp->snd_cwnd = tp->snd_cwnd_prev;
1164                                         tp->snd_ssthresh =
1165                                             tp->snd_ssthresh_prev;
1166                                         tp->snd_recover = tp->snd_recover_prev;
1167                                         if (tp->t_flags & TF_WASFRECOVERY)
1168                                             ENTER_FASTRECOVERY(tp);
1169                                         tp->snd_nxt = tp->snd_max;
1170                                         tp->t_badrxtwin = 0;
1171                                 }
1172
1173                                 /*
1174                                  * Recalculate the transmit timer / rtt.
1175                                  *
1176                                  * Some boxes send broken timestamp replies
1177                                  * during the SYN+ACK phase, ignore
1178                                  * timestamps of 0 or we could calculate a
1179                                  * huge RTT and blow up the retransmit timer.
1180                                  */
1181                                 if ((to.to_flags & TOF_TS) != 0 &&
1182                                     to.to_tsecr) {
1183                                         if (!tp->t_rttlow ||
1184                                             tp->t_rttlow > ticks - to.to_tsecr)
1185                                                 tp->t_rttlow = ticks - to.to_tsecr;
1186                                         tcp_xmit_timer(tp,
1187                                             ticks - to.to_tsecr + 1);
1188                                 } else if (tp->t_rtttime &&
1189                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
1190                                         if (!tp->t_rttlow ||
1191                                             tp->t_rttlow > ticks - tp->t_rtttime)
1192                                                 tp->t_rttlow = ticks - tp->t_rtttime;
1193                                         tcp_xmit_timer(tp,
1194                                                         ticks - tp->t_rtttime);
1195                                 }
1196                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1197                                 acked = th->th_ack - tp->snd_una;
1198                                 tcpstat.tcps_rcvackpack++;
1199                                 tcpstat.tcps_rcvackbyte += acked;
1200                                 sbdrop(&so->so_snd, acked);
1201                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1202                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1203                                         tp->snd_recover = th->th_ack - 1;
1204                                 tp->snd_una = th->th_ack;
1205                                 /*
1206                                  * pull snd_wl2 up to prevent seq wrap relative
1207                                  * to th_ack.
1208                                  */
1209                                 tp->snd_wl2 = th->th_ack;
1210                                 tp->t_dupacks = 0;
1211                                 m_freem(m);
1212                                 ND6_HINT(tp); /* some progress has been done */
1213
1214                                 /*
1215                                  * If all outstanding data are acked, stop
1216                                  * retransmit timer, otherwise restart timer
1217                                  * using current (possibly backed-off) value.
1218                                  * If process is waiting for space,
1219                                  * wakeup/selwakeup/signal.  If data
1220                                  * are ready to send, let tcp_output
1221                                  * decide between more output or persist.
1222
1223 #ifdef TCPDEBUG
1224                                 if (so->so_options & SO_DEBUG)
1225                                         tcp_trace(TA_INPUT, ostate, tp,
1226                                             (void *)tcp_saveipgen,
1227                                             &tcp_savetcp, 0);
1228 #endif
1229                                  */
1230                                 if (tp->snd_una == tp->snd_max)
1231                                         tcp_timer_activate(tp, TT_REXMT, 0);
1232                                 else if (!tcp_timer_active(tp, TT_PERSIST))
1233                                         tcp_timer_activate(tp, TT_REXMT,
1234                                                       tp->t_rxtcur);
1235
1236                                 sowwakeup(so);
1237                                 if (so->so_snd.sb_cc)
1238                                         (void) tcp_output(tp);
1239                                 goto check_delack;
1240                         }
1241                 } else if (th->th_ack == tp->snd_una &&
1242                     LIST_EMPTY(&tp->t_segq) &&
1243                     tlen <= sbspace(&so->so_rcv)) {
1244                         int newsize = 0;        /* automatic sockbuf scaling */
1245
1246                         KASSERT(headlocked, ("%s: headlocked", __func__));
1247                         INP_INFO_WUNLOCK(&tcbinfo);
1248                         headlocked = 0;
1249                         /*
1250                          * this is a pure, in-sequence data packet
1251                          * with nothing on the reassembly queue and
1252                          * we have enough buffer space to take it.
1253                          */
1254                         /* Clean receiver SACK report if present */
1255                         if (tp->sack_enable && tp->rcv_numsacks)
1256                                 tcp_clean_sackreport(tp);
1257                         ++tcpstat.tcps_preddat;
1258                         tp->rcv_nxt += tlen;
1259                         /*
1260                          * Pull snd_wl1 up to prevent seq wrap relative to
1261                          * th_seq.
1262                          */
1263                         tp->snd_wl1 = th->th_seq;
1264                         /*
1265                          * Pull rcv_up up to prevent seq wrap relative to
1266                          * rcv_nxt.
1267                          */
1268                         tp->rcv_up = tp->rcv_nxt;
1269                         tcpstat.tcps_rcvpack++;
1270                         tcpstat.tcps_rcvbyte += tlen;
1271                         ND6_HINT(tp);   /* some progress has been done */
1272 #ifdef TCPDEBUG
1273                         if (so->so_options & SO_DEBUG)
1274                                 tcp_trace(TA_INPUT, ostate, tp,
1275                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
1276 #endif
1277                 /*
1278                  * Automatic sizing of receive socket buffer.  Often the send
1279                  * buffer size is not optimally adjusted to the actual network
1280                  * conditions at hand (delay bandwidth product).  Setting the
1281                  * buffer size too small limits throughput on links with high
1282                  * bandwidth and high delay (eg. trans-continental/oceanic links).
1283                  *
1284                  * On the receive side the socket buffer memory is only rarely
1285                  * used to any significant extent.  This allows us to be much
1286                  * more aggressive in scaling the receive socket buffer.  For
1287                  * the case that the buffer space is actually used to a large
1288                  * extent and we run out of kernel memory we can simply drop
1289                  * the new segments; TCP on the sender will just retransmit it
1290                  * later.  Setting the buffer size too big may only consume too
1291                  * much kernel memory if the application doesn't read() from
1292                  * the socket or packet loss or reordering makes use of the
1293                  * reassembly queue.
1294                  *
1295                  * The criteria to step up the receive buffer one notch are:
1296                  *  1. the number of bytes received during the time it takes
1297                  *     one timestamp to be reflected back to us (the RTT);
1298                  *  2. received bytes per RTT is within seven eighth of the
1299                  *     current socket buffer size;
1300                  *  3. receive buffer size has not hit maximal automatic size;
1301                  *
1302                  * This algorithm does one step per RTT at most and only if
1303                  * we receive a bulk stream w/o packet losses or reorderings.
1304                  * Shrinking the buffer during idle times is not necessary as
1305                  * it doesn't consume any memory when idle.
1306                  *
1307                  * TODO: Only step up if the application is actually serving
1308                  * the buffer to better manage the socket buffer resources.
1309                  */
1310                         if (tcp_do_autorcvbuf &&
1311                             to.to_tsecr &&
1312                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1313                                 if (to.to_tsecr > tp->rfbuf_ts &&
1314                                     to.to_tsecr - tp->rfbuf_ts < hz) {
1315                                         if (tp->rfbuf_cnt >
1316                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
1317                                             so->so_rcv.sb_hiwat <
1318                                             tcp_autorcvbuf_max) {
1319                                                 newsize =
1320                                                     min(so->so_rcv.sb_hiwat +
1321                                                     tcp_autorcvbuf_inc,
1322                                                     tcp_autorcvbuf_max);
1323                                         }
1324                                         /* Start over with next RTT. */
1325                                         tp->rfbuf_ts = 0;
1326                                         tp->rfbuf_cnt = 0;
1327                                 } else
1328                                         tp->rfbuf_cnt += tlen;  /* add up */
1329                         }
1330
1331                         /* Add data to socket buffer. */
1332                         SOCKBUF_LOCK(&so->so_rcv);
1333                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1334                                 m_freem(m);
1335                         } else {
1336                                 /*
1337                                  * Set new socket buffer size.
1338                                  * Give up when limit is reached.
1339                                  */
1340                                 if (newsize)
1341                                         if (!sbreserve_locked(&so->so_rcv,
1342                                             newsize, so, curthread))
1343                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1344                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1345                                 sbappendstream_locked(&so->so_rcv, m);
1346                         }
1347                         sorwakeup_locked(so);
1348                         if (DELAY_ACK(tp)) {
1349                                 tp->t_flags |= TF_DELACK;
1350                         } else {
1351                                 tp->t_flags |= TF_ACKNOW;
1352                                 tcp_output(tp);
1353                         }
1354                         goto check_delack;
1355                 }
1356         }
1357
1358         /*
1359          * Calculate amount of space in receive window,
1360          * and then do TCP input processing.
1361          * Receive window is amount of space in rcv queue,
1362          * but not less than advertised window.
1363          */
1364         win = sbspace(&so->so_rcv);
1365         if (win < 0)
1366                 win = 0;
1367         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1368
1369         /* Reset receive buffer auto scaling when not in bulk receive mode. */
1370         tp->rfbuf_ts = 0;
1371         tp->rfbuf_cnt = 0;
1372
1373         switch (tp->t_state) {
1374
1375         /*
1376          * If the state is SYN_RECEIVED:
1377          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1378          */
1379         case TCPS_SYN_RECEIVED:
1380                 if ((thflags & TH_ACK) &&
1381                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1382                      SEQ_GT(th->th_ack, tp->snd_max))) {
1383                                 rstreason = BANDLIM_RST_OPENPORT;
1384                                 goto dropwithreset;
1385                 }
1386                 break;
1387
1388         /*
1389          * If the state is SYN_SENT:
1390          *      if seg contains an ACK, but not for our SYN, drop the input.
1391          *      if seg contains a RST, then drop the connection.
1392          *      if seg does not contain SYN, then drop it.
1393          * Otherwise this is an acceptable SYN segment
1394          *      initialize tp->rcv_nxt and tp->irs
1395          *      if seg contains ack then advance tp->snd_una
1396          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1397          *      arrange for segment to be acked (eventually)
1398          *      continue processing rest of data/controls, beginning with URG
1399          */
1400         case TCPS_SYN_SENT:
1401                 if ((thflags & TH_ACK) &&
1402                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1403                      SEQ_GT(th->th_ack, tp->snd_max))) {
1404                         rstreason = BANDLIM_UNLIMITED;
1405                         goto dropwithreset;
1406                 }
1407                 if (thflags & TH_RST) {
1408                         if (thflags & TH_ACK) {
1409                                 KASSERT(headlocked, ("%s: after_listen: "
1410                                     "tcp_drop.2: head not locked", __func__));
1411                                 tp = tcp_drop(tp, ECONNREFUSED);
1412                         }
1413                         goto drop;
1414                 }
1415                 if ((thflags & TH_SYN) == 0)
1416                         goto drop;
1417
1418                 tp->irs = th->th_seq;
1419                 tcp_rcvseqinit(tp);
1420                 if (thflags & TH_ACK) {
1421                         tcpstat.tcps_connects++;
1422                         soisconnected(so);
1423 #ifdef MAC
1424                         SOCK_LOCK(so);
1425                         mac_set_socket_peer_from_mbuf(m, so);
1426                         SOCK_UNLOCK(so);
1427 #endif
1428                         /* Do window scaling on this connection? */
1429                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1430                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1431                                 tp->rcv_scale = tp->request_r_scale;
1432                         }
1433                         tp->rcv_adv += tp->rcv_wnd;
1434                         tp->snd_una++;          /* SYN is acked */
1435                         /*
1436                          * If there's data, delay ACK; if there's also a FIN
1437                          * ACKNOW will be turned on later.
1438                          */
1439                         if (DELAY_ACK(tp) && tlen != 0)
1440                                 tcp_timer_activate(tp, TT_DELACK,
1441                                     tcp_delacktime);
1442                         else
1443                                 tp->t_flags |= TF_ACKNOW;
1444                         /*
1445                          * Received <SYN,ACK> in SYN_SENT[*] state.
1446                          * Transitions:
1447                          *      SYN_SENT  --> ESTABLISHED
1448                          *      SYN_SENT* --> FIN_WAIT_1
1449                          */
1450                         tp->t_starttime = ticks;
1451                         if (tp->t_flags & TF_NEEDFIN) {
1452                                 tp->t_state = TCPS_FIN_WAIT_1;
1453                                 tp->t_flags &= ~TF_NEEDFIN;
1454                                 thflags &= ~TH_SYN;
1455                         } else {
1456                                 tp->t_state = TCPS_ESTABLISHED;
1457                                 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
1458                         }
1459                 } else {
1460                         /*
1461                          * Received initial SYN in SYN-SENT[*] state =>
1462                          * simultaneous open.  If segment contains CC option
1463                          * and there is a cached CC, apply TAO test.
1464                          * If it succeeds, connection is * half-synchronized.
1465                          * Otherwise, do 3-way handshake:
1466                          *        SYN-SENT -> SYN-RECEIVED
1467                          *        SYN-SENT* -> SYN-RECEIVED*
1468                          * If there was no CC option, clear cached CC value.
1469                          */
1470                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
1471                         tcp_timer_activate(tp, TT_REXMT, 0);
1472                         tp->t_state = TCPS_SYN_RECEIVED;
1473                 }
1474
1475                 KASSERT(headlocked, ("%s: trimthenstep6: head not locked",
1476                     __func__));
1477                 INP_LOCK_ASSERT(tp->t_inpcb);
1478
1479                 /*
1480                  * Advance th->th_seq to correspond to first data byte.
1481                  * If data, trim to stay within window,
1482                  * dropping FIN if necessary.
1483                  */
1484                 th->th_seq++;
1485                 if (tlen > tp->rcv_wnd) {
1486                         todrop = tlen - tp->rcv_wnd;
1487                         m_adj(m, -todrop);
1488                         tlen = tp->rcv_wnd;
1489                         thflags &= ~TH_FIN;
1490                         tcpstat.tcps_rcvpackafterwin++;
1491                         tcpstat.tcps_rcvbyteafterwin += todrop;
1492                 }
1493                 tp->snd_wl1 = th->th_seq - 1;
1494                 tp->rcv_up = th->th_seq;
1495                 /*
1496                  * Client side of transaction: already sent SYN and data.
1497                  * If the remote host used T/TCP to validate the SYN,
1498                  * our data will be ACK'd; if so, enter normal data segment
1499                  * processing in the middle of step 5, ack processing.
1500                  * Otherwise, goto step 6.
1501                  */
1502                 if (thflags & TH_ACK)
1503                         goto process_ACK;
1504
1505                 goto step6;
1506
1507         /*
1508          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1509          *      do normal processing.
1510          *
1511          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
1512          */
1513         case TCPS_LAST_ACK:
1514         case TCPS_CLOSING:
1515                 break;  /* continue normal processing */
1516         }
1517
1518         /*
1519          * States other than LISTEN or SYN_SENT.
1520          * First check the RST flag and sequence number since reset segments
1521          * are exempt from the timestamp and connection count tests.  This
1522          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1523          * below which allowed reset segments in half the sequence space
1524          * to fall though and be processed (which gives forged reset
1525          * segments with a random sequence number a 50 percent chance of
1526          * killing a connection).
1527          * Then check timestamp, if present.
1528          * Then check the connection count, if present.
1529          * Then check that at least some bytes of segment are within
1530          * receive window.  If segment begins before rcv_nxt,
1531          * drop leading data (and SYN); if nothing left, just ack.
1532          *
1533          *
1534          * If the RST bit is set, check the sequence number to see
1535          * if this is a valid reset segment.
1536          * RFC 793 page 37:
1537          *   In all states except SYN-SENT, all reset (RST) segments
1538          *   are validated by checking their SEQ-fields.  A reset is
1539          *   valid if its sequence number is in the window.
1540          * Note: this does not take into account delayed ACKs, so
1541          *   we should test against last_ack_sent instead of rcv_nxt.
1542          *   The sequence number in the reset segment is normally an
1543          *   echo of our outgoing acknowlegement numbers, but some hosts
1544          *   send a reset with the sequence number at the rightmost edge
1545          *   of our receive window, and we have to handle this case.
1546          * Note 2: Paul Watson's paper "Slipping in the Window" has shown
1547          *   that brute force RST attacks are possible.  To combat this,
1548          *   we use a much stricter check while in the ESTABLISHED state,
1549          *   only accepting RSTs where the sequence number is equal to
1550          *   last_ack_sent.  In all other states (the states in which a
1551          *   RST is more likely), the more permissive check is used.
1552          * If we have multiple segments in flight, the intial reset
1553          * segment sequence numbers will be to the left of last_ack_sent,
1554          * but they will eventually catch up.
1555          * In any case, it never made sense to trim reset segments to
1556          * fit the receive window since RFC 1122 says:
1557          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1558          *
1559          *    A TCP SHOULD allow a received RST segment to include data.
1560          *
1561          *    DISCUSSION
1562          *         It has been suggested that a RST segment could contain
1563          *         ASCII text that encoded and explained the cause of the
1564          *         RST.  No standard has yet been established for such
1565          *         data.
1566          *
1567          * If the reset segment passes the sequence number test examine
1568          * the state:
1569          *    SYN_RECEIVED STATE:
1570          *      If passive open, return to LISTEN state.
1571          *      If active open, inform user that connection was refused.
1572          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1573          *      Inform user that connection was reset, and close tcb.
1574          *    CLOSING, LAST_ACK STATES:
1575          *      Close the tcb.
1576          *    TIME_WAIT STATE:
1577          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1578          *      RFC 1337.
1579          */
1580         if (thflags & TH_RST) {
1581                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1582                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1583                         switch (tp->t_state) {
1584
1585                         case TCPS_SYN_RECEIVED:
1586                                 so->so_error = ECONNREFUSED;
1587                                 goto close;
1588
1589                         case TCPS_ESTABLISHED:
1590                                 if (tcp_insecure_rst == 0 &&
1591                                     !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
1592                                     SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
1593                                     !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1594                                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
1595                                         tcpstat.tcps_badrst++;
1596                                         goto drop;
1597                                 }
1598                         case TCPS_FIN_WAIT_1:
1599                         case TCPS_FIN_WAIT_2:
1600                         case TCPS_CLOSE_WAIT:
1601                                 so->so_error = ECONNRESET;
1602                         close:
1603                                 tp->t_state = TCPS_CLOSED;
1604                                 tcpstat.tcps_drops++;
1605                                 KASSERT(headlocked, ("%s: trimthenstep6: "
1606                                     "tcp_close: head not locked", __func__));
1607                                 tp = tcp_close(tp);
1608                                 break;
1609
1610                         case TCPS_CLOSING:
1611                         case TCPS_LAST_ACK:
1612                                 KASSERT(headlocked, ("%s: trimthenstep6: "
1613                                     "tcp_close.2: head not locked", __func__));
1614                                 tp = tcp_close(tp);
1615                                 break;
1616                         }
1617                 }
1618                 goto drop;
1619         }
1620
1621         /*
1622          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1623          * and it's less than ts_recent, drop it.
1624          */
1625         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1626             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1627
1628                 /* Check to see if ts_recent is over 24 days old.  */
1629                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1630                         /*
1631                          * Invalidate ts_recent.  If this segment updates
1632                          * ts_recent, the age will be reset later and ts_recent
1633                          * will get a valid value.  If it does not, setting
1634                          * ts_recent to zero will at least satisfy the
1635                          * requirement that zero be placed in the timestamp
1636                          * echo reply when ts_recent isn't valid.  The
1637                          * age isn't reset until we get a valid ts_recent
1638                          * because we don't want out-of-order segments to be
1639                          * dropped when ts_recent is old.
1640                          */
1641                         tp->ts_recent = 0;
1642                 } else {
1643                         tcpstat.tcps_rcvduppack++;
1644                         tcpstat.tcps_rcvdupbyte += tlen;
1645                         tcpstat.tcps_pawsdrop++;
1646                         if (tlen)
1647                                 goto dropafterack;
1648                         goto drop;
1649                 }
1650         }
1651
1652         /*
1653          * In the SYN-RECEIVED state, validate that the packet belongs to
1654          * this connection before trimming the data to fit the receive
1655          * window.  Check the sequence number versus IRS since we know
1656          * the sequence numbers haven't wrapped.  This is a partial fix
1657          * for the "LAND" DoS attack.
1658          */
1659         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1660                 rstreason = BANDLIM_RST_OPENPORT;
1661                 goto dropwithreset;
1662         }
1663
1664         todrop = tp->rcv_nxt - th->th_seq;
1665         if (todrop > 0) {
1666                 if (thflags & TH_SYN) {
1667                         thflags &= ~TH_SYN;
1668                         th->th_seq++;
1669                         if (th->th_urp > 1)
1670                                 th->th_urp--;
1671                         else
1672                                 thflags &= ~TH_URG;
1673                         todrop--;
1674                 }
1675                 /*
1676                  * Following if statement from Stevens, vol. 2, p. 960.
1677                  */
1678                 if (todrop > tlen
1679                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1680                         /*
1681                          * Any valid FIN must be to the left of the window.
1682                          * At this point the FIN must be a duplicate or out
1683                          * of sequence; drop it.
1684                          */
1685                         thflags &= ~TH_FIN;
1686
1687                         /*
1688                          * Send an ACK to resynchronize and drop any data.
1689                          * But keep on processing for RST or ACK.
1690                          */
1691                         tp->t_flags |= TF_ACKNOW;
1692                         todrop = tlen;
1693                         tcpstat.tcps_rcvduppack++;
1694                         tcpstat.tcps_rcvdupbyte += todrop;
1695                 } else {
1696                         tcpstat.tcps_rcvpartduppack++;
1697                         tcpstat.tcps_rcvpartdupbyte += todrop;
1698                 }
1699                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1700                 th->th_seq += todrop;
1701                 tlen -= todrop;
1702                 if (th->th_urp > todrop)
1703                         th->th_urp -= todrop;
1704                 else {
1705                         thflags &= ~TH_URG;
1706                         th->th_urp = 0;
1707                 }
1708         }
1709
1710         /*
1711          * If new data are received on a connection after the
1712          * user processes are gone, then RST the other end.
1713          */
1714         if ((so->so_state & SS_NOFDREF) &&
1715             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1716                 KASSERT(headlocked, ("%s: trimthenstep6: tcp_close.3: head "
1717                     "not locked", __func__));
1718                 tp = tcp_close(tp);
1719                 tcpstat.tcps_rcvafterclose++;
1720                 rstreason = BANDLIM_UNLIMITED;
1721                 goto dropwithreset;
1722         }
1723
1724         /*
1725          * If segment ends after window, drop trailing data
1726          * (and PUSH and FIN); if nothing left, just ACK.
1727          */
1728         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1729         if (todrop > 0) {
1730                 tcpstat.tcps_rcvpackafterwin++;
1731                 if (todrop >= tlen) {
1732                         tcpstat.tcps_rcvbyteafterwin += tlen;
1733                         /*
1734                          * If window is closed can only take segments at
1735                          * window edge, and have to drop data and PUSH from
1736                          * incoming segments.  Continue processing, but
1737                          * remember to ack.  Otherwise, drop segment
1738                          * and ack.
1739                          */
1740                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1741                                 tp->t_flags |= TF_ACKNOW;
1742                                 tcpstat.tcps_rcvwinprobe++;
1743                         } else
1744                                 goto dropafterack;
1745                 } else
1746                         tcpstat.tcps_rcvbyteafterwin += todrop;
1747                 m_adj(m, -todrop);
1748                 tlen -= todrop;
1749                 thflags &= ~(TH_PUSH|TH_FIN);
1750         }
1751
1752         /*
1753          * If last ACK falls within this segment's sequence numbers,
1754          * record its timestamp.
1755          * NOTE:
1756          * 1) That the test incorporates suggestions from the latest
1757          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
1758          * 2) That updating only on newer timestamps interferes with
1759          *    our earlier PAWS tests, so this check should be solely
1760          *    predicated on the sequence space of this segment.
1761          * 3) That we modify the segment boundary check to be
1762          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
1763          *    instead of RFC1323's
1764          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
1765          *    This modified check allows us to overcome RFC1323's
1766          *    limitations as described in Stevens TCP/IP Illustrated
1767          *    Vol. 2 p.869. In such cases, we can still calculate the
1768          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
1769          */
1770         if ((to.to_flags & TOF_TS) != 0 &&
1771             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
1772             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
1773                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
1774                 tp->ts_recent_age = ticks;
1775                 tp->ts_recent = to.to_tsval;
1776         }
1777
1778         /*
1779          * If a SYN is in the window, then this is an
1780          * error and we send an RST and drop the connection.
1781          */
1782         if (thflags & TH_SYN) {
1783                 KASSERT(headlocked, ("%s: tcp_drop: trimthenstep6: "
1784                     "head not locked", __func__));
1785                 tp = tcp_drop(tp, ECONNRESET);
1786                 rstreason = BANDLIM_UNLIMITED;
1787                 goto drop;
1788         }
1789
1790         /*
1791          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1792          * flag is on (half-synchronized state), then queue data for
1793          * later processing; else drop segment and return.
1794          */
1795         if ((thflags & TH_ACK) == 0) {
1796                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1797                     (tp->t_flags & TF_NEEDSYN))
1798                         goto step6;
1799                 else if (tp->t_flags & TF_ACKNOW)
1800                         goto dropafterack;
1801                 else
1802                         goto drop;
1803         }
1804
1805         /*
1806          * Ack processing.
1807          */
1808         switch (tp->t_state) {
1809
1810         /*
1811          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1812          * ESTABLISHED state and continue processing.
1813          * The ACK was checked above.
1814          */
1815         case TCPS_SYN_RECEIVED:
1816
1817                 tcpstat.tcps_connects++;
1818                 soisconnected(so);
1819                 /* Do window scaling? */
1820                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1821                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1822                         tp->rcv_scale = tp->request_r_scale;
1823                         tp->snd_wnd = tiwin;
1824                 }
1825                 /*
1826                  * Make transitions:
1827                  *      SYN-RECEIVED  -> ESTABLISHED
1828                  *      SYN-RECEIVED* -> FIN-WAIT-1
1829                  */
1830                 tp->t_starttime = ticks;
1831                 if (tp->t_flags & TF_NEEDFIN) {
1832                         tp->t_state = TCPS_FIN_WAIT_1;
1833                         tp->t_flags &= ~TF_NEEDFIN;
1834                 } else {
1835                         tp->t_state = TCPS_ESTABLISHED;
1836                         tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
1837                 }
1838                 /*
1839                  * If segment contains data or ACK, will call tcp_reass()
1840                  * later; if not, do so now to pass queued data to user.
1841                  */
1842                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1843                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1844                             (struct mbuf *)0);
1845                 tp->snd_wl1 = th->th_seq - 1;
1846                 /* FALLTHROUGH */
1847
1848         /*
1849          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1850          * ACKs.  If the ack is in the range
1851          *      tp->snd_una < th->th_ack <= tp->snd_max
1852          * then advance tp->snd_una to th->th_ack and drop
1853          * data from the retransmission queue.  If this ACK reflects
1854          * more up to date window information we update our window information.
1855          */
1856         case TCPS_ESTABLISHED:
1857         case TCPS_FIN_WAIT_1:
1858         case TCPS_FIN_WAIT_2:
1859         case TCPS_CLOSE_WAIT:
1860         case TCPS_CLOSING:
1861         case TCPS_LAST_ACK:
1862                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1863                         tcpstat.tcps_rcvacktoomuch++;
1864                         goto dropafterack;
1865                 }
1866                 if (tp->sack_enable &&
1867                     ((to.to_flags & TOF_SACK) ||
1868                      !TAILQ_EMPTY(&tp->snd_holes)))
1869                         tcp_sack_doack(tp, &to, th->th_ack);
1870                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1871                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1872                                 tcpstat.tcps_rcvdupack++;
1873                                 /*
1874                                  * If we have outstanding data (other than
1875                                  * a window probe), this is a completely
1876                                  * duplicate ack (ie, window info didn't
1877                                  * change), the ack is the biggest we've
1878                                  * seen and we've seen exactly our rexmt
1879                                  * threshhold of them, assume a packet
1880                                  * has been dropped and retransmit it.
1881                                  * Kludge snd_nxt & the congestion
1882                                  * window so we send only this one
1883                                  * packet.
1884                                  *
1885                                  * We know we're losing at the current
1886                                  * window size so do congestion avoidance
1887                                  * (set ssthresh to half the current window
1888                                  * and pull our congestion window back to
1889                                  * the new ssthresh).
1890                                  *
1891                                  * Dup acks mean that packets have left the
1892                                  * network (they're now cached at the receiver)
1893                                  * so bump cwnd by the amount in the receiver
1894                                  * to keep a constant cwnd packets in the
1895                                  * network.
1896                                  */
1897                                 if (!tcp_timer_active(tp, TT_REXMT) ||
1898                                     th->th_ack != tp->snd_una)
1899                                         tp->t_dupacks = 0;
1900                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1901                                     ((tcp_do_newreno || tp->sack_enable) &&
1902                                      IN_FASTRECOVERY(tp))) {
1903                                         if (tp->sack_enable && IN_FASTRECOVERY(tp)) {
1904                                                 int awnd;
1905
1906                                                 /*
1907                                                  * Compute the amount of data in flight first.
1908                                                  * We can inject new data into the pipe iff
1909                                                  * we have less than 1/2 the original window's
1910                                                  * worth of data in flight.
1911                                                  */
1912                                                 awnd = (tp->snd_nxt - tp->snd_fack) +
1913                                                         tp->sackhint.sack_bytes_rexmit;
1914                                                 if (awnd < tp->snd_ssthresh) {
1915                                                         tp->snd_cwnd += tp->t_maxseg;
1916                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
1917                                                                 tp->snd_cwnd = tp->snd_ssthresh;
1918                                                 }
1919                                         } else
1920                                                 tp->snd_cwnd += tp->t_maxseg;
1921                                         (void) tcp_output(tp);
1922                                         goto drop;
1923                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1924                                         tcp_seq onxt = tp->snd_nxt;
1925                                         u_int win;
1926
1927                                         /*
1928                                          * If we're doing sack, check to
1929                                          * see if we're already in sack
1930                                          * recovery. If we're not doing sack,
1931                                          * check to see if we're in newreno
1932                                          * recovery.
1933                                          */
1934                                         if (tp->sack_enable) {
1935                                                 if (IN_FASTRECOVERY(tp)) {
1936                                                         tp->t_dupacks = 0;
1937                                                         break;
1938                                                 }
1939                                         } else if (tcp_do_newreno) {
1940                                                 if (SEQ_LEQ(th->th_ack,
1941                                                     tp->snd_recover)) {
1942                                                         tp->t_dupacks = 0;
1943                                                         break;
1944                                                 }
1945                                         }
1946                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1947                                             2 / tp->t_maxseg;
1948                                         if (win < 2)
1949                                                 win = 2;
1950                                         tp->snd_ssthresh = win * tp->t_maxseg;
1951                                         ENTER_FASTRECOVERY(tp);
1952                                         tp->snd_recover = tp->snd_max;
1953                                         tcp_timer_activate(tp, TT_REXMT, 0);
1954                                         tp->t_rtttime = 0;
1955                                         if (tp->sack_enable) {
1956                                                 tcpstat.tcps_sack_recovery_episode++;
1957                                                 tp->sack_newdata = tp->snd_nxt;
1958                                                 tp->snd_cwnd = tp->t_maxseg;
1959                                                 (void) tcp_output(tp);
1960                                                 goto drop;
1961                                         }
1962                                         tp->snd_nxt = th->th_ack;
1963                                         tp->snd_cwnd = tp->t_maxseg;
1964                                         (void) tcp_output(tp);
1965                                         KASSERT(tp->snd_limited <= 2,
1966                                             ("%s: tp->snd_limited too big",
1967                                             __func__));
1968                                         tp->snd_cwnd = tp->snd_ssthresh +
1969                                              tp->t_maxseg *
1970                                              (tp->t_dupacks - tp->snd_limited);
1971                                         if (SEQ_GT(onxt, tp->snd_nxt))
1972                                                 tp->snd_nxt = onxt;
1973                                         goto drop;
1974                                 } else if (tcp_do_rfc3042) {
1975                                         u_long oldcwnd = tp->snd_cwnd;
1976                                         tcp_seq oldsndmax = tp->snd_max;
1977                                         u_int sent;
1978
1979                                         KASSERT(tp->t_dupacks == 1 ||
1980                                             tp->t_dupacks == 2,
1981                                             ("%s: dupacks not 1 or 2",
1982                                             __func__));
1983                                         if (tp->t_dupacks == 1)
1984                                                 tp->snd_limited = 0;
1985                                         tp->snd_cwnd =
1986                                             (tp->snd_nxt - tp->snd_una) +
1987                                             (tp->t_dupacks - tp->snd_limited) *
1988                                             tp->t_maxseg;
1989                                         (void) tcp_output(tp);
1990                                         sent = tp->snd_max - oldsndmax;
1991                                         if (sent > tp->t_maxseg) {
1992                                                 KASSERT((tp->t_dupacks == 2 &&
1993                                                     tp->snd_limited == 0) ||
1994                                                    (sent == tp->t_maxseg + 1 &&
1995                                                     tp->t_flags & TF_SENTFIN),
1996                                                     ("%s: sent too much",
1997                                                     __func__));
1998                                                 tp->snd_limited = 2;
1999                                         } else if (sent > 0)
2000                                                 ++tp->snd_limited;
2001                                         tp->snd_cwnd = oldcwnd;
2002                                         goto drop;
2003                                 }
2004                         } else
2005                                 tp->t_dupacks = 0;
2006                         break;
2007                 }
2008
2009                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2010                     ("%s: th_ack <= snd_una", __func__));
2011
2012                 /*
2013                  * If the congestion window was inflated to account
2014                  * for the other side's cached packets, retract it.
2015                  */
2016                 if (tcp_do_newreno || tp->sack_enable) {
2017                         if (IN_FASTRECOVERY(tp)) {
2018                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2019                                         if (tp->sack_enable)
2020                                                 tcp_sack_partialack(tp, th);
2021                                         else
2022                                                 tcp_newreno_partial_ack(tp, th);
2023                                 } else {
2024                                         /*
2025                                          * Out of fast recovery.
2026                                          * Window inflation should have left us
2027                                          * with approximately snd_ssthresh
2028                                          * outstanding data.
2029                                          * But in case we would be inclined to
2030                                          * send a burst, better to do it via
2031                                          * the slow start mechanism.
2032                                          */
2033                                         if (SEQ_GT(th->th_ack +
2034                                                         tp->snd_ssthresh,
2035                                                    tp->snd_max))
2036                                                 tp->snd_cwnd = tp->snd_max -
2037                                                                 th->th_ack +
2038                                                                 tp->t_maxseg;
2039                                         else
2040                                                 tp->snd_cwnd = tp->snd_ssthresh;
2041                                 }
2042                         }
2043                 } else {
2044                         if (tp->t_dupacks >= tcprexmtthresh &&
2045                             tp->snd_cwnd > tp->snd_ssthresh)
2046                                 tp->snd_cwnd = tp->snd_ssthresh;
2047                 }
2048                 tp->t_dupacks = 0;
2049                 /*
2050                  * If we reach this point, ACK is not a duplicate,
2051                  *     i.e., it ACKs something we sent.
2052                  */
2053                 if (tp->t_flags & TF_NEEDSYN) {
2054                         /*
2055                          * T/TCP: Connection was half-synchronized, and our
2056                          * SYN has been ACK'd (so connection is now fully
2057                          * synchronized).  Go to non-starred state,
2058                          * increment snd_una for ACK of SYN, and check if
2059                          * we can do window scaling.
2060                          */
2061                         tp->t_flags &= ~TF_NEEDSYN;
2062                         tp->snd_una++;
2063                         /* Do window scaling? */
2064                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2065                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
2066                                 tp->rcv_scale = tp->request_r_scale;
2067                                 /* Send window already scaled. */
2068                         }
2069                 }
2070
2071 process_ACK:
2072                 KASSERT(headlocked, ("%s: process_ACK: head not locked",
2073                     __func__));
2074                 INP_LOCK_ASSERT(tp->t_inpcb);
2075
2076                 acked = th->th_ack - tp->snd_una;
2077                 tcpstat.tcps_rcvackpack++;
2078                 tcpstat.tcps_rcvackbyte += acked;
2079
2080                 /*
2081                  * If we just performed our first retransmit, and the ACK
2082                  * arrives within our recovery window, then it was a mistake
2083                  * to do the retransmit in the first place.  Recover our
2084                  * original cwnd and ssthresh, and proceed to transmit where
2085                  * we left off.
2086                  */
2087                 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
2088                         ++tcpstat.tcps_sndrexmitbad;
2089                         tp->snd_cwnd = tp->snd_cwnd_prev;
2090                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
2091                         tp->snd_recover = tp->snd_recover_prev;
2092                         if (tp->t_flags & TF_WASFRECOVERY)
2093                                 ENTER_FASTRECOVERY(tp);
2094                         tp->snd_nxt = tp->snd_max;
2095                         tp->t_badrxtwin = 0;    /* XXX probably not required */
2096                 }
2097
2098                 /*
2099                  * If we have a timestamp reply, update smoothed
2100                  * round trip time.  If no timestamp is present but
2101                  * transmit timer is running and timed sequence
2102                  * number was acked, update smoothed round trip time.
2103                  * Since we now have an rtt measurement, cancel the
2104                  * timer backoff (cf., Phil Karn's retransmit alg.).
2105                  * Recompute the initial retransmit timer.
2106                  *
2107                  * Some boxes send broken timestamp replies
2108                  * during the SYN+ACK phase, ignore
2109                  * timestamps of 0 or we could calculate a
2110                  * huge RTT and blow up the retransmit timer.
2111                  */
2112                 if ((to.to_flags & TOF_TS) != 0 &&
2113                     to.to_tsecr) {
2114                         if (!tp->t_rttlow || tp->t_rttlow > ticks - to.to_tsecr)
2115                                 tp->t_rttlow = ticks - to.to_tsecr;
2116                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
2117                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2118                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2119                                 tp->t_rttlow = ticks - tp->t_rtttime;
2120                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2121                 }
2122                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
2123
2124                 /*
2125                  * If all outstanding data is acked, stop retransmit
2126                  * timer and remember to restart (more output or persist).
2127                  * If there is more data to be acked, restart retransmit
2128                  * timer, using current (possibly backed-off) value.
2129                  */
2130                 if (th->th_ack == tp->snd_max) {
2131                         tcp_timer_activate(tp, TT_REXMT, 0);
2132                         needoutput = 1;
2133                 } else if (!tcp_timer_active(tp, TT_PERSIST))
2134                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2135
2136                 /*
2137                  * If no data (only SYN) was ACK'd,
2138                  *    skip rest of ACK processing.
2139                  */
2140                 if (acked == 0)
2141                         goto step6;
2142
2143                 /*
2144                  * When new data is acked, open the congestion window.
2145                  * If the window gives us less than ssthresh packets
2146                  * in flight, open exponentially (maxseg per packet).
2147                  * Otherwise open linearly: maxseg per window
2148                  * (maxseg^2 / cwnd per packet).
2149                  */
2150                 if ((!tcp_do_newreno && !tp->sack_enable) ||
2151                     !IN_FASTRECOVERY(tp)) {
2152                         u_int cw = tp->snd_cwnd;
2153                         u_int incr = tp->t_maxseg;
2154                         if (cw > tp->snd_ssthresh)
2155                                 incr = incr * incr / cw;
2156                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
2157                 }
2158                 SOCKBUF_LOCK(&so->so_snd);
2159                 if (acked > so->so_snd.sb_cc) {
2160                         tp->snd_wnd -= so->so_snd.sb_cc;
2161                         sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
2162                         ourfinisacked = 1;
2163                 } else {
2164                         sbdrop_locked(&so->so_snd, acked);
2165                         tp->snd_wnd -= acked;
2166                         ourfinisacked = 0;
2167                 }
2168                 sowwakeup_locked(so);
2169                 /* detect una wraparound */
2170                 if ((tcp_do_newreno || tp->sack_enable) &&
2171                     !IN_FASTRECOVERY(tp) &&
2172                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
2173                     SEQ_LEQ(th->th_ack, tp->snd_recover))
2174                         tp->snd_recover = th->th_ack - 1;
2175                 if ((tcp_do_newreno || tp->sack_enable) &&
2176                     IN_FASTRECOVERY(tp) &&
2177                     SEQ_GEQ(th->th_ack, tp->snd_recover))
2178                         EXIT_FASTRECOVERY(tp);
2179                 tp->snd_una = th->th_ack;
2180                 if (tp->sack_enable) {
2181                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
2182                                 tp->snd_recover = tp->snd_una;
2183                 }
2184                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2185                         tp->snd_nxt = tp->snd_una;
2186
2187                 switch (tp->t_state) {
2188
2189                 /*
2190                  * In FIN_WAIT_1 STATE in addition to the processing
2191                  * for the ESTABLISHED state if our FIN is now acknowledged
2192                  * then enter FIN_WAIT_2.
2193                  */
2194                 case TCPS_FIN_WAIT_1:
2195                         if (ourfinisacked) {
2196                                 /*
2197                                  * If we can't receive any more
2198                                  * data, then closing user can proceed.
2199                                  * Starting the timer is contrary to the
2200                                  * specification, but if we don't get a FIN
2201                                  * we'll hang forever.
2202                                  */
2203                 /* XXXjl
2204                  * we should release the tp also, and use a
2205                  * compressed state.
2206                  */
2207                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2208                                         int timeout;
2209
2210                                         soisdisconnected(so);
2211                                         timeout = (tcp_fast_finwait2_recycle) ?
2212                                                 tcp_finwait2_timeout : tcp_maxidle;
2213                                         tcp_timer_activate(tp, TT_2MSL, timeout);
2214                                 }
2215                                 tp->t_state = TCPS_FIN_WAIT_2;
2216                         }
2217                         break;
2218
2219                 /*
2220                  * In CLOSING STATE in addition to the processing for
2221                  * the ESTABLISHED state if the ACK acknowledges our FIN
2222                  * then enter the TIME-WAIT state, otherwise ignore
2223                  * the segment.
2224                  */
2225                 case TCPS_CLOSING:
2226                         if (ourfinisacked) {
2227                                 KASSERT(headlocked, ("%s: process_ACK: "
2228                                     "head not locked", __func__));
2229                                 tcp_twstart(tp);
2230                                 INP_INFO_WUNLOCK(&tcbinfo);
2231                                 headlocked = 0;
2232                                 m_freem(m);
2233                                 return;
2234                         }
2235                         break;
2236
2237                 /*
2238                  * In LAST_ACK, we may still be waiting for data to drain
2239                  * and/or to be acked, as well as for the ack of our FIN.
2240                  * If our FIN is now acknowledged, delete the TCB,
2241                  * enter the closed state and return.
2242                  */
2243                 case TCPS_LAST_ACK:
2244                         if (ourfinisacked) {
2245                                 KASSERT(headlocked, ("%s: process_ACK: "
2246                                     "tcp_close: head not locked", __func__));
2247                                 tp = tcp_close(tp);
2248                                 goto drop;
2249                         }
2250                         break;
2251                 }
2252         }
2253
2254 step6:
2255         KASSERT(headlocked, ("%s: step6: head not locked", __func__));
2256         INP_LOCK_ASSERT(tp->t_inpcb);
2257
2258         /*
2259          * Update window information.
2260          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2261          */
2262         if ((thflags & TH_ACK) &&
2263             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2264             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2265              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2266                 /* keep track of pure window updates */
2267                 if (tlen == 0 &&
2268                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2269                         tcpstat.tcps_rcvwinupd++;
2270                 tp->snd_wnd = tiwin;
2271                 tp->snd_wl1 = th->th_seq;
2272                 tp->snd_wl2 = th->th_ack;
2273                 if (tp->snd_wnd > tp->max_sndwnd)
2274                         tp->max_sndwnd = tp->snd_wnd;
2275                 needoutput = 1;
2276         }
2277
2278         /*
2279          * Process segments with URG.
2280          */
2281         if ((thflags & TH_URG) && th->th_urp &&
2282             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2283                 /*
2284                  * This is a kludge, but if we receive and accept
2285                  * random urgent pointers, we'll crash in
2286                  * soreceive.  It's hard to imagine someone
2287                  * actually wanting to send this much urgent data.
2288                  */
2289                 SOCKBUF_LOCK(&so->so_rcv);
2290                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2291                         th->th_urp = 0;                 /* XXX */
2292                         thflags &= ~TH_URG;             /* XXX */
2293                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
2294                         goto dodata;                    /* XXX */
2295                 }
2296                 /*
2297                  * If this segment advances the known urgent pointer,
2298                  * then mark the data stream.  This should not happen
2299                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2300                  * a FIN has been received from the remote side.
2301                  * In these states we ignore the URG.
2302                  *
2303                  * According to RFC961 (Assigned Protocols),
2304                  * the urgent pointer points to the last octet
2305                  * of urgent data.  We continue, however,
2306                  * to consider it to indicate the first octet
2307                  * of data past the urgent section as the original
2308                  * spec states (in one of two places).
2309                  */
2310                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2311                         tp->rcv_up = th->th_seq + th->th_urp;
2312                         so->so_oobmark = so->so_rcv.sb_cc +
2313                             (tp->rcv_up - tp->rcv_nxt) - 1;
2314                         if (so->so_oobmark == 0)
2315                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
2316                         sohasoutofband(so);
2317                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2318                 }
2319                 SOCKBUF_UNLOCK(&so->so_rcv);
2320                 /*
2321                  * Remove out of band data so doesn't get presented to user.
2322                  * This can happen independent of advancing the URG pointer,
2323                  * but if two URG's are pending at once, some out-of-band
2324                  * data may creep in... ick.
2325                  */
2326                 if (th->th_urp <= (u_long)tlen &&
2327                     !(so->so_options & SO_OOBINLINE)) {
2328                         /* hdr drop is delayed */
2329                         tcp_pulloutofband(so, th, m, drop_hdrlen);
2330                 }
2331         } else {
2332                 /*
2333                  * If no out of band data is expected,
2334                  * pull receive urgent pointer along
2335                  * with the receive window.
2336                  */
2337                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2338                         tp->rcv_up = tp->rcv_nxt;
2339         }
2340 dodata:                                                 /* XXX */
2341         KASSERT(headlocked, ("%s: dodata: head not locked", __func__));
2342         INP_LOCK_ASSERT(tp->t_inpcb);
2343
2344         /*
2345          * Process the segment text, merging it into the TCP sequencing queue,
2346          * and arranging for acknowledgment of receipt if necessary.
2347          * This process logically involves adjusting tp->rcv_wnd as data
2348          * is presented to the user (this happens in tcp_usrreq.c,
2349          * case PRU_RCVD).  If a FIN has already been received on this
2350          * connection then we just ignore the text.
2351          */
2352         if ((tlen || (thflags & TH_FIN)) &&
2353             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2354                 tcp_seq save_start = th->th_seq;
2355                 tcp_seq save_end = th->th_seq + tlen;
2356                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2357                 /*
2358                  * Insert segment which includes th into TCP reassembly queue
2359                  * with control block tp.  Set thflags to whether reassembly now
2360                  * includes a segment with FIN.  This handles the common case
2361                  * inline (segment is the next to be received on an established
2362                  * connection, and the queue is empty), avoiding linkage into
2363                  * and removal from the queue and repetition of various
2364                  * conversions.
2365                  * Set DELACK for segments received in order, but ack
2366                  * immediately when segments are out of order (so
2367                  * fast retransmit can work).
2368                  */
2369                 if (th->th_seq == tp->rcv_nxt &&
2370                     LIST_EMPTY(&tp->t_segq) &&
2371                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2372                         if (DELAY_ACK(tp))
2373                                 tp->t_flags |= TF_DELACK;
2374                         else
2375                                 tp->t_flags |= TF_ACKNOW;
2376                         tp->rcv_nxt += tlen;
2377                         thflags = th->th_flags & TH_FIN;
2378                         tcpstat.tcps_rcvpack++;
2379                         tcpstat.tcps_rcvbyte += tlen;
2380                         ND6_HINT(tp);
2381                         SOCKBUF_LOCK(&so->so_rcv);
2382                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
2383                                 m_freem(m);
2384                         else
2385                                 sbappendstream_locked(&so->so_rcv, m);
2386                         sorwakeup_locked(so);
2387                 } else {
2388                         thflags = tcp_reass(tp, th, &tlen, m);
2389                         tp->t_flags |= TF_ACKNOW;
2390                 }
2391                 if (tlen > 0 && tp->sack_enable)
2392                         tcp_update_sack_list(tp, save_start, save_end);
2393 #if 0
2394                 /*
2395                  * Note the amount of data that peer has sent into
2396                  * our window, in order to estimate the sender's
2397                  * buffer size.
2398                  * XXX: Unused.
2399                  */
2400                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2401 #endif
2402         } else {
2403                 m_freem(m);
2404                 thflags &= ~TH_FIN;
2405         }
2406
2407         /*
2408          * If FIN is received ACK the FIN and let the user know
2409          * that the connection is closing.
2410          */
2411         if (thflags & TH_FIN) {
2412                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2413                         socantrcvmore(so);
2414                         /*
2415                          * If connection is half-synchronized
2416                          * (ie NEEDSYN flag on) then delay ACK,
2417                          * so it may be piggybacked when SYN is sent.
2418                          * Otherwise, since we received a FIN then no
2419                          * more input can be expected, send ACK now.
2420                          */
2421                         if (tp->t_flags & TF_NEEDSYN)
2422                                 tp->t_flags |= TF_DELACK;
2423                         else
2424                                 tp->t_flags |= TF_ACKNOW;
2425                         tp->rcv_nxt++;
2426                 }
2427                 switch (tp->t_state) {
2428
2429                 /*
2430                  * In SYN_RECEIVED and ESTABLISHED STATES
2431                  * enter the CLOSE_WAIT state.
2432                  */
2433                 case TCPS_SYN_RECEIVED:
2434                         tp->t_starttime = ticks;
2435                         /*FALLTHROUGH*/
2436                 case TCPS_ESTABLISHED:
2437                         tp->t_state = TCPS_CLOSE_WAIT;
2438                         break;
2439
2440                 /*
2441                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2442                  * enter the CLOSING state.
2443                  */
2444                 case TCPS_FIN_WAIT_1:
2445                         tp->t_state = TCPS_CLOSING;
2446                         break;
2447
2448                 /*
2449                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2450                  * starting the time-wait timer, turning off the other
2451                  * standard timers.
2452                  */
2453                 case TCPS_FIN_WAIT_2:
2454                         KASSERT(headlocked == 1, ("%s: dodata: "
2455                             "TCP_FIN_WAIT_2: head not locked", __func__));
2456                         tcp_twstart(tp);
2457                         INP_INFO_WUNLOCK(&tcbinfo);
2458                         return;
2459                 }
2460         }
2461         INP_INFO_WUNLOCK(&tcbinfo);
2462         headlocked = 0;
2463 #ifdef TCPDEBUG
2464         if (so->so_options & SO_DEBUG)
2465                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2466                           &tcp_savetcp, 0);
2467 #endif
2468
2469         /*
2470          * Return any desired output.
2471          */
2472         if (needoutput || (tp->t_flags & TF_ACKNOW))
2473                 (void) tcp_output(tp);
2474
2475 check_delack:
2476         KASSERT(headlocked == 0, ("%s: check_delack: head locked",
2477             __func__));
2478         INP_INFO_UNLOCK_ASSERT(&tcbinfo);
2479         INP_LOCK_ASSERT(tp->t_inpcb);
2480         if (tp->t_flags & TF_DELACK) {
2481                 tp->t_flags &= ~TF_DELACK;
2482                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
2483         }
2484         INP_UNLOCK(tp->t_inpcb);
2485         return;
2486
2487 dropafterack:
2488         KASSERT(headlocked, ("%s: dropafterack: head not locked", __func__));
2489         /*
2490          * Generate an ACK dropping incoming segment if it occupies
2491          * sequence space, where the ACK reflects our state.
2492          *
2493          * We can now skip the test for the RST flag since all
2494          * paths to this code happen after packets containing
2495          * RST have been dropped.
2496          *
2497          * In the SYN-RECEIVED state, don't send an ACK unless the
2498          * segment we received passes the SYN-RECEIVED ACK test.
2499          * If it fails send a RST.  This breaks the loop in the
2500          * "LAND" DoS attack, and also prevents an ACK storm
2501          * between two listening ports that have been sent forged
2502          * SYN segments, each with the source address of the other.
2503          */
2504         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2505             (SEQ_GT(tp->snd_una, th->th_ack) ||
2506              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2507                 rstreason = BANDLIM_RST_OPENPORT;
2508                 goto dropwithreset;
2509         }
2510 #ifdef TCPDEBUG
2511         if (so->so_options & SO_DEBUG)
2512                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2513                           &tcp_savetcp, 0);
2514 #endif
2515         KASSERT(headlocked, ("%s: headlocked should be 1", __func__));
2516         INP_INFO_WUNLOCK(&tcbinfo);
2517         tp->t_flags |= TF_ACKNOW;
2518         (void) tcp_output(tp);
2519         INP_UNLOCK(tp->t_inpcb);
2520         m_freem(m);
2521         return;
2522
2523 dropwithreset:
2524         KASSERT(headlocked, ("%s: dropwithreset: head not locked", __func__));
2525
2526         tcp_dropwithreset(m, th, tp, tlen, rstreason);
2527
2528         if (tp != NULL)
2529                 INP_UNLOCK(tp->t_inpcb);
2530         if (headlocked)
2531                 INP_INFO_WUNLOCK(&tcbinfo);
2532         return;
2533
2534 drop:
2535         /*
2536          * Drop space held by incoming segment and return.
2537          */
2538 #ifdef TCPDEBUG
2539         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2540                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2541                           &tcp_savetcp, 0);
2542 #endif
2543         if (tp != NULL)
2544                 INP_UNLOCK(tp->t_inpcb);
2545         if (headlocked)
2546                 INP_INFO_WUNLOCK(&tcbinfo);
2547         m_freem(m);
2548         return;
2549 }
2550
2551
2552 /*
2553  * Issue RST on TCP segment.  The mbuf must still include the original
2554  * packet header.
2555  */
2556 static void
2557 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
2558     int tlen, int rstreason)
2559 {
2560         struct ip *ip;
2561 #ifdef INET6
2562         struct ip6_hdr *ip6;
2563 #endif
2564         /*
2565          * Generate a RST, dropping incoming segment.
2566          * Make ACK acceptable to originator of segment.
2567          * Don't bother to respond if destination was broadcast/multicast.
2568          * tp may be NULL.
2569          */
2570         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2571                 goto drop;
2572 #ifdef INET6
2573         if (mtod(m, struct ip *)->ip_v == 6) {
2574                 ip6 = mtod(m, struct ip6_hdr *);
2575                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2576                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2577                         goto drop;
2578                 /* IPv6 anycast check is done at tcp6_input() */
2579         } else
2580 #endif
2581         {
2582                 ip = mtod(m, struct ip *);
2583                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2584                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2585                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2586                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2587                         goto drop;
2588         }
2589
2590         /* Perform bandwidth limiting. */
2591         if (badport_bandlim(rstreason) < 0)
2592                 goto drop;
2593
2594         /* tcp_respond consumes the mbuf chain. */
2595         if (th->th_flags & TH_ACK) {
2596                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
2597                     th->th_ack, TH_RST);
2598         } else {
2599                 if (th->th_flags & TH_SYN)
2600                         tlen++;
2601                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2602                     (tcp_seq)0, TH_RST|TH_ACK);
2603         }
2604         return;
2605 drop:
2606         m_freem(m);
2607         return;
2608 }
2609
2610 /*
2611  * Parse TCP options and place in tcpopt.
2612  */
2613 static void
2614 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
2615 {
2616         int opt, optlen;
2617
2618         to->to_flags = 0;
2619         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2620                 opt = cp[0];
2621                 if (opt == TCPOPT_EOL)
2622                         break;
2623                 if (opt == TCPOPT_NOP)
2624                         optlen = 1;
2625                 else {
2626                         if (cnt < 2)
2627                                 break;
2628                         optlen = cp[1];
2629                         if (optlen < 2 || optlen > cnt)
2630                                 break;
2631                 }
2632                 switch (opt) {
2633                 case TCPOPT_MAXSEG:
2634                         if (optlen != TCPOLEN_MAXSEG)
2635                                 continue;
2636                         if (!(flags & TO_SYN))
2637                                 continue;
2638                         to->to_flags |= TOF_MSS;
2639                         bcopy((char *)cp + 2,
2640                             (char *)&to->to_mss, sizeof(to->to_mss));
2641                         to->to_mss = ntohs(to->to_mss);
2642                         break;
2643                 case TCPOPT_WINDOW:
2644                         if (optlen != TCPOLEN_WINDOW)
2645                                 continue;
2646                         if (!(flags & TO_SYN))
2647                                 continue;
2648                         to->to_flags |= TOF_SCALE;
2649                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
2650                         break;
2651                 case TCPOPT_TIMESTAMP:
2652                         if (optlen != TCPOLEN_TIMESTAMP)
2653                                 continue;
2654                         to->to_flags |= TOF_TS;
2655                         bcopy((char *)cp + 2,
2656                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2657                         to->to_tsval = ntohl(to->to_tsval);
2658                         bcopy((char *)cp + 6,
2659                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2660                         to->to_tsecr = ntohl(to->to_tsecr);
2661                         break;
2662 #ifdef TCP_SIGNATURE
2663                 /*
2664                  * XXX In order to reply to a host which has set the
2665                  * TCP_SIGNATURE option in its initial SYN, we have to
2666                  * record the fact that the option was observed here
2667                  * for the syncache code to perform the correct response.
2668                  */
2669                 case TCPOPT_SIGNATURE:
2670                         if (optlen != TCPOLEN_SIGNATURE)
2671                                 continue;
2672                         to->to_flags |= TOF_SIGNATURE;
2673                         to->to_signature = cp + 2;
2674                         break;
2675 #endif
2676                 case TCPOPT_SACK_PERMITTED:
2677                         if (optlen != TCPOLEN_SACK_PERMITTED)
2678                                 continue;
2679                         if (!(flags & TO_SYN))
2680                                 continue;
2681                         if (!tcp_do_sack)
2682                                 continue;
2683                         to->to_flags |= TOF_SACKPERM;
2684                         break;
2685                 case TCPOPT_SACK:
2686                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
2687                                 continue;
2688                         if (flags & TO_SYN)
2689                                 continue;
2690                         to->to_flags |= TOF_SACK;
2691                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
2692                         to->to_sacks = cp + 2;
2693                         tcpstat.tcps_sack_rcv_blocks++;
2694                         break;
2695                 default:
2696                         continue;
2697                 }
2698         }
2699 }
2700
2701 /*
2702  * Pull out of band byte out of a segment so
2703  * it doesn't appear in the user's data queue.
2704  * It is still reflected in the segment length for
2705  * sequencing purposes.
2706  */
2707 static void
2708 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
2709     int off)
2710 {
2711         int cnt = off + th->th_urp - 1;
2712
2713         while (cnt >= 0) {
2714                 if (m->m_len > cnt) {
2715                         char *cp = mtod(m, caddr_t) + cnt;
2716                         struct tcpcb *tp = sototcpcb(so);
2717
2718                         tp->t_iobc = *cp;
2719                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2720                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2721                         m->m_len--;
2722                         if (m->m_flags & M_PKTHDR)
2723                                 m->m_pkthdr.len--;
2724                         return;
2725                 }
2726                 cnt -= m->m_len;
2727                 m = m->m_next;
2728                 if (m == NULL)
2729                         break;
2730         }
2731         panic("tcp_pulloutofband");
2732 }
2733
2734 /*
2735  * Collect new round-trip time estimate
2736  * and update averages and current timeout.
2737  */
2738 static void
2739 tcp_xmit_timer(struct tcpcb *tp, int rtt)
2740 {
2741         int delta;
2742
2743         INP_LOCK_ASSERT(tp->t_inpcb);
2744
2745         tcpstat.tcps_rttupdated++;
2746         tp->t_rttupdated++;
2747         if (tp->t_srtt != 0) {
2748                 /*
2749                  * srtt is stored as fixed point with 5 bits after the
2750                  * binary point (i.e., scaled by 8).  The following magic
2751                  * is equivalent to the smoothing algorithm in rfc793 with
2752                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2753                  * point).  Adjust rtt to origin 0.
2754                  */
2755                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2756                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2757
2758                 if ((tp->t_srtt += delta) <= 0)
2759                         tp->t_srtt = 1;
2760
2761                 /*
2762                  * We accumulate a smoothed rtt variance (actually, a
2763                  * smoothed mean difference), then set the retransmit
2764                  * timer to smoothed rtt + 4 times the smoothed variance.
2765                  * rttvar is stored as fixed point with 4 bits after the
2766                  * binary point (scaled by 16).  The following is
2767                  * equivalent to rfc793 smoothing with an alpha of .75
2768                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2769                  * rfc793's wired-in beta.
2770                  */
2771                 if (delta < 0)
2772                         delta = -delta;
2773                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2774                 if ((tp->t_rttvar += delta) <= 0)
2775                         tp->t_rttvar = 1;
2776                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2777                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2778         } else {
2779                 /*
2780                  * No rtt measurement yet - use the unsmoothed rtt.
2781                  * Set the variance to half the rtt (so our first
2782                  * retransmit happens at 3*rtt).
2783                  */
2784                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2785                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2786                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2787         }
2788         tp->t_rtttime = 0;
2789         tp->t_rxtshift = 0;
2790
2791         /*
2792          * the retransmit should happen at rtt + 4 * rttvar.
2793          * Because of the way we do the smoothing, srtt and rttvar
2794          * will each average +1/2 tick of bias.  When we compute
2795          * the retransmit timer, we want 1/2 tick of rounding and
2796          * 1 extra tick because of +-1/2 tick uncertainty in the
2797          * firing of the timer.  The bias will give us exactly the
2798          * 1.5 tick we need.  But, because the bias is
2799          * statistical, we have to test that we don't drop below
2800          * the minimum feasible timer (which is 2 ticks).
2801          */
2802         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2803                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2804
2805         /*
2806          * We received an ack for a packet that wasn't retransmitted;
2807          * it is probably safe to discard any error indications we've
2808          * received recently.  This isn't quite right, but close enough
2809          * for now (a route might have failed after we sent a segment,
2810          * and the return path might not be symmetrical).
2811          */
2812         tp->t_softerror = 0;
2813 }
2814
2815 /*
2816  * Determine a reasonable value for maxseg size.
2817  * If the route is known, check route for mtu.
2818  * If none, use an mss that can be handled on the outgoing
2819  * interface without forcing IP to fragment; if bigger than
2820  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2821  * to utilize large mbufs.  If no route is found, route has no mtu,
2822  * or the destination isn't local, use a default, hopefully conservative
2823  * size (usually 512 or the default IP max size, but no more than the mtu
2824  * of the interface), as we can't discover anything about intervening
2825  * gateways or networks.  We also initialize the congestion/slow start
2826  * window to be a single segment if the destination isn't local.
2827  * While looking at the routing entry, we also initialize other path-dependent
2828  * parameters from pre-set or cached values in the routing entry.
2829  *
2830  * Also take into account the space needed for options that we
2831  * send regularly.  Make maxseg shorter by that amount to assure
2832  * that we can send maxseg amount of data even when the options
2833  * are present.  Store the upper limit of the length of options plus
2834  * data in maxopd.
2835  *
2836  *
2837  * In case of T/TCP, we call this routine during implicit connection
2838  * setup as well (offer = -1), to initialize maxseg from the cached
2839  * MSS of our peer.
2840  *
2841  * NOTE that this routine is only called when we process an incoming
2842  * segment. Outgoing SYN/ACK MSS settings are handled in tcp_mssopt().
2843  */
2844 void
2845 tcp_mss(struct tcpcb *tp, int offer)
2846 {
2847         int rtt, mss;
2848         u_long bufsize;
2849         u_long maxmtu;
2850         struct inpcb *inp = tp->t_inpcb;
2851         struct socket *so;
2852         struct hc_metrics_lite metrics;
2853         int origoffer = offer;
2854         int mtuflags = 0;
2855 #ifdef INET6
2856         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2857         size_t min_protoh = isipv6 ?
2858                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
2859                             sizeof (struct tcpiphdr);
2860 #else
2861         const size_t min_protoh = sizeof(struct tcpiphdr);
2862 #endif
2863
2864         /* initialize */
2865 #ifdef INET6
2866         if (isipv6) {
2867                 maxmtu = tcp_maxmtu6(&inp->inp_inc, &mtuflags);
2868                 tp->t_maxopd = tp->t_maxseg = tcp_v6mssdflt;
2869         } else
2870 #endif
2871         {
2872                 maxmtu = tcp_maxmtu(&inp->inp_inc, &mtuflags);
2873                 tp->t_maxopd = tp->t_maxseg = tcp_mssdflt;
2874         }
2875         so = inp->inp_socket;
2876
2877         /*
2878          * no route to sender, stay with default mss and return
2879          */
2880         if (maxmtu == 0)
2881                 return;
2882
2883         /* what have we got? */
2884         switch (offer) {
2885                 case 0:
2886                         /*
2887                          * Offer == 0 means that there was no MSS on the SYN
2888                          * segment, in this case we use tcp_mssdflt.
2889                          */
2890                         offer =
2891 #ifdef INET6
2892                                 isipv6 ? tcp_v6mssdflt :
2893 #endif
2894                                 tcp_mssdflt;
2895                         break;
2896
2897                 case -1:
2898                         /*
2899                          * Offer == -1 means that we didn't receive SYN yet.
2900                          */
2901                         /* FALLTHROUGH */
2902
2903                 default:
2904                         /*
2905                          * Prevent DoS attack with too small MSS. Round up
2906                          * to at least minmss.
2907                          */
2908                         offer = max(offer, tcp_minmss);
2909                         /*
2910                          * Sanity check: make sure that maxopd will be large
2911                          * enough to allow some data on segments even if the
2912                          * all the option space is used (40bytes).  Otherwise
2913                          * funny things may happen in tcp_output.
2914                          */
2915                         offer = max(offer, 64);
2916         }
2917
2918         /*
2919          * rmx information is now retrieved from tcp_hostcache
2920          */
2921         tcp_hc_get(&inp->inp_inc, &metrics);
2922
2923         /*
2924          * if there's a discovered mtu int tcp hostcache, use it
2925          * else, use the link mtu.
2926          */
2927         if (metrics.rmx_mtu)
2928                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
2929         else {
2930 #ifdef INET6
2931                 if (isipv6) {
2932                         mss = maxmtu - min_protoh;
2933                         if (!path_mtu_discovery &&
2934                             !in6_localaddr(&inp->in6p_faddr))
2935                                 mss = min(mss, tcp_v6mssdflt);
2936                 } else
2937 #endif
2938                 {
2939                         mss = maxmtu - min_protoh;
2940                         if (!path_mtu_discovery &&
2941                             !in_localaddr(inp->inp_faddr))
2942                                 mss = min(mss, tcp_mssdflt);
2943                 }
2944         }
2945         mss = min(mss, offer);
2946
2947         /*
2948          * maxopd stores the maximum length of data AND options
2949          * in a segment; maxseg is the amount of data in a normal
2950          * segment.  We need to store this value (maxopd) apart
2951          * from maxseg, because now every segment carries options
2952          * and thus we normally have somewhat less data in segments.
2953          */
2954         tp->t_maxopd = mss;
2955
2956         /*
2957          * origoffer==-1 indicates, that no segments were received yet.
2958          * In this case we just guess.
2959          */
2960         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2961             (origoffer == -1 ||
2962              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2963                 mss -= TCPOLEN_TSTAMP_APPA;
2964         tp->t_maxseg = mss;
2965
2966 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
2967                 if (mss > MCLBYTES)
2968                         mss &= ~(MCLBYTES-1);
2969 #else
2970                 if (mss > MCLBYTES)
2971                         mss = mss / MCLBYTES * MCLBYTES;
2972 #endif
2973         tp->t_maxseg = mss;
2974
2975         /*
2976          * If there's a pipesize, change the socket buffer to that size,
2977          * don't change if sb_hiwat is different than default (then it
2978          * has been changed on purpose with setsockopt).
2979          * Make the socket buffers an integral number of mss units;
2980          * if the mss is larger than the socket buffer, decrease the mss.
2981          */
2982         SOCKBUF_LOCK(&so->so_snd);
2983         if ((so->so_snd.sb_hiwat == tcp_sendspace) && metrics.rmx_sendpipe)
2984                 bufsize = metrics.rmx_sendpipe;
2985         else
2986                 bufsize = so->so_snd.sb_hiwat;
2987         if (bufsize < mss)
2988                 mss = bufsize;
2989         else {
2990                 bufsize = roundup(bufsize, mss);
2991                 if (bufsize > sb_max)
2992                         bufsize = sb_max;
2993                 if (bufsize > so->so_snd.sb_hiwat)
2994                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
2995         }
2996         SOCKBUF_UNLOCK(&so->so_snd);
2997         tp->t_maxseg = mss;
2998
2999         SOCKBUF_LOCK(&so->so_rcv);
3000         if ((so->so_rcv.sb_hiwat == tcp_recvspace) && metrics.rmx_recvpipe)
3001                 bufsize = metrics.rmx_recvpipe;
3002         else
3003                 bufsize = so->so_rcv.sb_hiwat;
3004         if (bufsize > mss) {
3005                 bufsize = roundup(bufsize, mss);
3006                 if (bufsize > sb_max)
3007                         bufsize = sb_max;
3008                 if (bufsize > so->so_rcv.sb_hiwat)
3009                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3010         }
3011         SOCKBUF_UNLOCK(&so->so_rcv);
3012         /*
3013          * While we're here, check the others too
3014          */
3015         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
3016                 tp->t_srtt = rtt;
3017                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
3018                 tcpstat.tcps_usedrtt++;
3019                 if (metrics.rmx_rttvar) {
3020                         tp->t_rttvar = metrics.rmx_rttvar;
3021                         tcpstat.tcps_usedrttvar++;
3022                 } else {
3023                         /* default variation is +- 1 rtt */
3024                         tp->t_rttvar =
3025                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
3026                 }
3027                 TCPT_RANGESET(tp->t_rxtcur,
3028                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
3029                               tp->t_rttmin, TCPTV_REXMTMAX);
3030         }
3031         if (metrics.rmx_ssthresh) {
3032                 /*
3033                  * There's some sort of gateway or interface
3034                  * buffer limit on the path.  Use this to set
3035                  * the slow start threshhold, but set the
3036                  * threshold to no less than 2*mss.
3037                  */
3038                 tp->snd_ssthresh = max(2 * mss, metrics.rmx_ssthresh);
3039                 tcpstat.tcps_usedssthresh++;
3040         }
3041         if (metrics.rmx_bandwidth)
3042                 tp->snd_bandwidth = metrics.rmx_bandwidth;
3043
3044         /*
3045          * Set the slow-start flight size depending on whether this
3046          * is a local network or not.
3047          *
3048          * Extend this so we cache the cwnd too and retrieve it here.
3049          * Make cwnd even bigger than RFC3390 suggests but only if we
3050          * have previous experience with the remote host. Be careful
3051          * not make cwnd bigger than remote receive window or our own
3052          * send socket buffer. Maybe put some additional upper bound
3053          * on the retrieved cwnd. Should do incremental updates to
3054          * hostcache when cwnd collapses so next connection doesn't
3055          * overloads the path again.
3056          *
3057          * RFC3390 says only do this if SYN or SYN/ACK didn't got lost.
3058          * We currently check only in syncache_socket for that.
3059          */
3060 #define TCP_METRICS_CWND
3061 #ifdef TCP_METRICS_CWND
3062         if (metrics.rmx_cwnd)
3063                 tp->snd_cwnd = max(mss,
3064                                 min(metrics.rmx_cwnd / 2,
3065                                  min(tp->snd_wnd, so->so_snd.sb_hiwat)));
3066         else
3067 #endif
3068         if (tcp_do_rfc3390)
3069                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
3070 #ifdef INET6
3071         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
3072                  (!isipv6 && in_localaddr(inp->inp_faddr)))
3073 #else
3074         else if (in_localaddr(inp->inp_faddr))
3075 #endif
3076                 tp->snd_cwnd = mss * ss_fltsz_local;
3077         else
3078                 tp->snd_cwnd = mss * ss_fltsz;
3079
3080         /* Check the interface for TSO capabilities. */
3081         if (mtuflags & CSUM_TSO)
3082                 tp->t_flags |= TF_TSO;
3083 }
3084
3085 /*
3086  * Determine the MSS option to send on an outgoing SYN.
3087  */
3088 int
3089 tcp_mssopt(struct in_conninfo *inc)
3090 {
3091         int mss = 0;
3092         u_long maxmtu = 0;
3093         u_long thcmtu = 0;
3094         size_t min_protoh;
3095 #ifdef INET6
3096         int isipv6 = inc->inc_isipv6 ? 1 : 0;
3097 #endif
3098
3099         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3100
3101 #ifdef INET6
3102         if (isipv6) {
3103                 mss = tcp_v6mssdflt;
3104                 maxmtu = tcp_maxmtu6(inc, NULL);
3105                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3106                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3107         } else
3108 #endif
3109         {
3110                 mss = tcp_mssdflt;
3111                 maxmtu = tcp_maxmtu(inc, NULL);
3112                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3113                 min_protoh = sizeof(struct tcpiphdr);
3114         }
3115         if (maxmtu && thcmtu)
3116                 mss = min(maxmtu, thcmtu) - min_protoh;
3117         else if (maxmtu || thcmtu)
3118                 mss = max(maxmtu, thcmtu) - min_protoh;
3119
3120         return (mss);
3121 }
3122
3123
3124 /*
3125  * On a partial ack arrives, force the retransmission of the
3126  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3127  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3128  * be started again.
3129  */
3130 static void
3131 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3132 {
3133         tcp_seq onxt = tp->snd_nxt;
3134         u_long  ocwnd = tp->snd_cwnd;
3135
3136         tcp_timer_activate(tp, TT_REXMT, 0);
3137         tp->t_rtttime = 0;
3138         tp->snd_nxt = th->th_ack;
3139         /*
3140          * Set snd_cwnd to one segment beyond acknowledged offset.
3141          * (tp->snd_una has not yet been updated when this function is called.)
3142          */
3143         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
3144         tp->t_flags |= TF_ACKNOW;
3145         (void) tcp_output(tp);
3146         tp->snd_cwnd = ocwnd;
3147         if (SEQ_GT(onxt, tp->snd_nxt))
3148                 tp->snd_nxt = onxt;
3149         /*
3150          * Partial window deflation.  Relies on fact that tp->snd_una
3151          * not updated yet.
3152          */
3153         if (tp->snd_cwnd > th->th_ack - tp->snd_una)
3154                 tp->snd_cwnd -= th->th_ack - tp->snd_una;
3155         else
3156                 tp->snd_cwnd = 0;
3157         tp->snd_cwnd += tp->t_maxseg;
3158 }
3159
3160 /*
3161  * Returns 1 if the TIME_WAIT state was killed and we should start over,
3162  * looking for a pcb in the listen state.  Returns 0 otherwise.
3163  */
3164 static int
3165 tcp_timewait(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th,
3166     struct mbuf *m, int tlen)
3167 {
3168         struct tcptw *tw;
3169         int thflags;
3170         tcp_seq seq;
3171 #ifdef INET6
3172         int isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
3173 #else
3174         const int isipv6 = 0;
3175 #endif
3176
3177         /* tcbinfo lock required for tcp_twclose(), tcp_timer_2msl_reset(). */
3178         INP_INFO_WLOCK_ASSERT(&tcbinfo);
3179         INP_LOCK_ASSERT(inp);
3180
3181         /*
3182          * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
3183          * still present.  This is undesirable, but temporarily necessary
3184          * until we work out how to handle inpcb's who's timewait state has
3185          * been removed.
3186          */
3187         tw = intotw(inp);
3188         if (tw == NULL)
3189                 goto drop;
3190
3191         thflags = th->th_flags;
3192
3193         /*
3194          * NOTE: for FIN_WAIT_2 (to be added later),
3195          * must validate sequence number before accepting RST
3196          */
3197
3198         /*
3199          * If the segment contains RST:
3200          *      Drop the segment - see Stevens, vol. 2, p. 964 and
3201          *      RFC 1337.
3202          */
3203         if (thflags & TH_RST)
3204                 goto drop;
3205
3206 #if 0
3207 /* PAWS not needed at the moment */
3208         /*
3209          * RFC 1323 PAWS: If we have a timestamp reply on this segment
3210          * and it's less than ts_recent, drop it.
3211          */
3212         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
3213             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
3214                 if ((thflags & TH_ACK) == 0)
3215                         goto drop;
3216                 goto ack;
3217         }
3218         /*
3219          * ts_recent is never updated because we never accept new segments.
3220          */
3221 #endif
3222
3223         /*
3224          * If a new connection request is received
3225          * while in TIME_WAIT, drop the old connection
3226          * and start over if the sequence numbers
3227          * are above the previous ones.
3228          */
3229         if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
3230                 tcp_twclose(tw, 0);
3231                 return (1);
3232         }
3233
3234         /*
3235          * Drop the the segment if it does not contain an ACK.
3236          */
3237         if ((thflags & TH_ACK) == 0)
3238                 goto drop;
3239
3240         /*
3241          * Reset the 2MSL timer if this is a duplicate FIN.
3242          */
3243         if (thflags & TH_FIN) {
3244                 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
3245                 if (seq + 1 == tw->rcv_nxt)
3246                         tcp_timer_2msl_reset(tw, 1);
3247         }
3248
3249         /*
3250          * Acknowledge the segment if it has data or is not a duplicate ACK.
3251          */
3252         if (thflags != TH_ACK || tlen != 0 ||
3253             th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
3254                 tcp_twrespond(tw, TH_ACK);
3255         goto drop;
3256
3257         /*
3258          * Generate a RST, dropping incoming segment.
3259          * Make ACK acceptable to originator of segment.
3260          * Don't bother to respond if destination was broadcast/multicast.
3261          */
3262         if (m->m_flags & (M_BCAST|M_MCAST))
3263                 goto drop;
3264         if (isipv6) {
3265                 struct ip6_hdr *ip6;
3266
3267                 /* IPv6 anycast check is done at tcp6_input() */
3268                 ip6 = mtod(m, struct ip6_hdr *);
3269                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3270                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3271                         goto drop;
3272         } else {
3273                 struct ip *ip;
3274
3275                 ip = mtod(m, struct ip *);
3276                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3277                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3278                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3279                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3280                         goto drop;
3281         }
3282         if (thflags & TH_ACK) {
3283                 tcp_respond(NULL,
3284                     mtod(m, void *), th, m, 0, th->th_ack, TH_RST);
3285         } else {
3286                 seq = th->th_seq + (thflags & TH_SYN ? 1 : 0);
3287                 tcp_respond(NULL,
3288                     mtod(m, void *), th, m, seq, 0, TH_RST|TH_ACK);
3289         }
3290         INP_UNLOCK(inp);
3291         return (0);
3292
3293 drop:
3294         INP_UNLOCK(inp);
3295         m_freem(m);
3296         return (0);
3297 }