sys/netinet/tcp_input.c

   1 /*-
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 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 int       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                 if (tcp_timewait(inp, &to, th, m, tlen))
 755                         goto findpcb;
 756                 /* tcp_timewait unlocks inp. */
 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                 INP_UNLOCK(inp);
 768                 rstreason = BANDLIM_RST_CLOSEDPORT;
 769                 goto dropwithreset;
 770         }
 771         if (tp->t_state == TCPS_CLOSED)
 772                 goto dropunlock;        /* XXX: dropwithreset??? */
 773
 774 #ifdef MAC
 775         INP_LOCK_ASSERT(inp);
 776         if (mac_check_inpcb_deliver(inp, m))
 777                 goto dropunlock;
 778 #endif
 779         so = inp->inp_socket;
 780         KASSERT(so != NULL, ("%s: so == NULL", __func__));
 781 #ifdef TCPDEBUG
 782         if (so->so_options & SO_DEBUG) {
 783                 ostate = tp->t_state;
 784                 if (isipv6)
 785                         bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
 786                 else
 787                         bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
 788                 tcp_savetcp = *th;
 789         }
 790 #endif
 791         /*
 792          * When the socket is accepting connections (the INPCB is in LISTEN
 793          * state) we look into the SYN cache if this is a new connection
 794          * attempt or the completion of a previous one.
 795          */
 796         if (so->so_options & SO_ACCEPTCONN) {
 797                 struct in_conninfo inc;
 798
 799                 bzero(&inc, sizeof(inc));
 800                 inc.inc_isipv6 = isipv6;
 801 #ifdef INET6
 802                 if (isipv6) {
 803                         inc.inc6_faddr = ip6->ip6_src;
 804                         inc.inc6_laddr = ip6->ip6_dst;
 805                 } else
 806 #endif
 807                 {
 808                         inc.inc_faddr = ip->ip_src;
 809                         inc.inc_laddr = ip->ip_dst;
 810                 }
 811                 inc.inc_fport = th->th_sport;
 812                 inc.inc_lport = th->th_dport;
 813
 814                 /*
 815                  * If the state is LISTEN then ignore segment if it contains
 816                  * a RST.  If the segment contains an ACK then it is bad and
 817                  * send a RST.  If it does not contain a SYN then it is not
 818                  * interesting; drop it.
 819                  *
 820                  * If the state is SYN_RECEIVED (syncache) and seg contains
 821                  * an ACK, but not for our SYN/ACK, send a RST.  If the seg
 822                  * contains a RST, check the sequence number to see if it
 823                  * is a valid reset segment.
 824                  */
 825                 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
 826                         if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
 827                                 /*
 828                                  * Parse the TCP options here because
 829                                  * syncookies need access to the reflected
 830                                  * timestamp.
 831                                  */
 832                                 tcp_dooptions(&to, optp, optlen, 0);
 833                                 if (!syncache_expand(&inc, &to, th, &so, m)) {
 834                                         /*
 835                                          * No syncache entry or ACK was not
 836                                          * for our SYN/ACK.  Send a RST.
 837                                          */
 838                                         rstreason = BANDLIM_RST_OPENPORT;
 839                                         goto dropwithreset;
 840                                 }
 841                                 if (so == NULL) {
 842                                         /*
 843                                          * We completed the 3-way handshake
 844                                          * but could not allocate a socket
 845                                          * either due to memory shortage,
 846                                          * listen queue length limits or
 847                                          * global socket limits.
 848                                          */
 849                                         rstreason = BANDLIM_UNLIMITED;
 850                                         goto dropwithreset;
 851                                 }
 852                                 /*
 853                                  * Socket is created in state SYN_RECEIVED.
 854                                  * Continue processing segment.
 855                                  */
 856                                 INP_UNLOCK(inp);        /* listen socket */
 857                                 inp = sotoinpcb(so);
 858                                 INP_LOCK(inp);          /* new connection */
 859                                 tp = intotcpcb(inp);
 860                                 /*
 861                                  * Process the segment and the data it
 862                                  * contains.  tcp_do_segment() consumes
 863                                  * the mbuf chain and unlocks the inpcb.
 864                                  * XXX: The potential return value of
 865                                  * TIME_WAIT nuked is supposed to be
 866                                  * handled above.
 867                                  */
 868                                 if (tcp_do_segment(m, th, so, tp,
 869                                                    drop_hdrlen, tlen))
 870                                         goto findpcb;   /* TIME_WAIT nuked */
 871                                 return;
 872                         }
 873                         if (thflags & TH_RST) {
 874                                 syncache_chkrst(&inc, th);
 875                                 goto dropunlock;
 876                         }
 877                         if (thflags & TH_ACK) {
 878                                 syncache_badack(&inc);
 879                                 tcpstat.tcps_badsyn++;
 880                                 rstreason = BANDLIM_RST_OPENPORT;
 881                                 goto dropwithreset;
 882                         }
 883                         goto dropunlock;
 884                 }
 885
 886                 /*
 887                  * Segment's flags are (SYN) or (SYN|FIN).
 888                  */
 889 #ifdef INET6
 890                 /*
 891                  * If deprecated address is forbidden,
 892                  * we do not accept SYN to deprecated interface
 893                  * address to prevent any new inbound connection from
 894                  * getting established.
 895                  * When we do not accept SYN, we send a TCP RST,
 896                  * with deprecated source address (instead of dropping
 897                  * it).  We compromise it as it is much better for peer
 898                  * to send a RST, and RST will be the final packet
 899                  * for the exchange.
 900                  *
 901                  * If we do not forbid deprecated addresses, we accept
 902                  * the SYN packet.  RFC2462 does not suggest dropping
 903                  * SYN in this case.
 904                  * If we decipher RFC2462 5.5.4, it says like this:
 905                  * 1. use of deprecated addr with existing
 906                  *    communication is okay - "SHOULD continue to be
 907                  *    used"
 908                  * 2. use of it with new communication:
 909                  *   (2a) "SHOULD NOT be used if alternate address
 910                  *        with sufficient scope is available"
 911                  *   (2b) nothing mentioned otherwise.
 912                  * Here we fall into (2b) case as we have no choice in
 913                  * our source address selection - we must obey the peer.
 914                  *
 915                  * The wording in RFC2462 is confusing, and there are
 916                  * multiple description text for deprecated address
 917                  * handling - worse, they are not exactly the same.
 918                  * I believe 5.5.4 is the best one, so we follow 5.5.4.
 919                  */
 920                 if (isipv6 && !ip6_use_deprecated) {
 921                         struct in6_ifaddr *ia6;
 922
 923                         if ((ia6 = ip6_getdstifaddr(m)) &&
 924                             (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
 925                                 INP_UNLOCK(inp);
 926                                 tp = NULL;
 927                                 rstreason = BANDLIM_RST_OPENPORT;
 928                                 goto dropwithreset;
 929                         }
 930                 }
 931 #endif
 932                 /*
 933                  * Basic sanity checks on incoming SYN requests:
 934                  *
 935                  * Don't bother responding if the destination was a
 936                  * broadcast according to RFC1122 4.2.3.10, p. 104.
 937                  *
 938                  * If it is from this socket, drop it, it must be forged.
 939                  *
 940                  * Note that it is quite possible to receive unicast
 941                  * link-layer packets with a broadcast IP address. Use
 942                  * in_broadcast() to find them.
 943                  */
 944                 if (m->m_flags & (M_BCAST|M_MCAST))
 945                         goto dropunlock;
 946                 if (isipv6) {
 947 #ifdef INET6
 948                         if (th->th_dport == th->th_sport &&
 949                             IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src))
 950                                 goto dropunlock;
 951                         if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 952                             IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
 953                                 goto dropunlock;
 954 #endif
 955                 } else {
 956                         if (th->th_dport == th->th_sport &&
 957                             ip->ip_dst.s_addr == ip->ip_src.s_addr)
 958                                 goto dropunlock;
 959                         if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 960                             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 961                             ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
 962                             in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
 963                                 goto dropunlock;
 964                 }
 965                 /*
 966                  * SYN appears to be valid.  Create compressed TCP state
 967                  * for syncache.
 968                  */
 969 #ifdef TCPDEBUG
 970                 if (so->so_options & SO_DEBUG)
 971                         tcp_trace(TA_INPUT, ostate, tp,
 972                             (void *)tcp_saveipgen, &tcp_savetcp, 0);
 973 #endif
 974                 tcp_dooptions(&to, optp, optlen, TO_SYN);
 975                 syncache_add(&inc, &to, th, inp, &so, m);
 976                 /*
 977                  * Entry added to syncache and mbuf consumed.
 978                  * Everything unlocked already by syncache_add().
 979                  */
 980                 return;
 981         }
 982
 983         /*
 984          * Segment belongs to a connection in SYN_SENT, ESTABLISHED or
 985          * later state.  tcp_do_segment() always consumes the mbuf chain
 986          * and unlocks the inpcb.
 987          */
 988         if (tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen))
 989                 goto findpcb;   /* XXX: TIME_WAIT was nuked. */
 990         return;
 991
 992 dropwithreset:
 993         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 994         tcp_dropwithreset(m, th, tp, tlen, rstreason);
 995         m = NULL;       /* mbuf chain got consumed. */
 996 dropunlock:
 997         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 998         if (tp != NULL)
 999                 INP_UNLOCK(inp);
1000         INP_INFO_WUNLOCK(&tcbinfo);
1001 drop:
1002         INP_INFO_UNLOCK_ASSERT(&tcbinfo);
1003         if (m != NULL)
1004                 m_freem(m);
1005         return;
1006 }
1007
1008 static int
1009 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1010     struct tcpcb *tp, int drop_hdrlen, int tlen)
1011 {
1012         int thflags, acked, ourfinisacked, needoutput = 0;
1013         int headlocked = 1;
1014         int rstreason, todrop, win;
1015         u_long tiwin;
1016         struct tcpopt to;
1017
1018 #ifdef TCPDEBUG
1019         /*
1020          * The size of tcp_saveipgen must be the size of the max ip header,
1021          * now IPv6.
1022          */
1023         u_char tcp_saveipgen[IP6_HDR_LEN];
1024         struct tcphdr tcp_savetcp;
1025         short ostate = 0;
1026 #endif
1027         thflags = th->th_flags;
1028
1029         INP_INFO_WLOCK_ASSERT(&tcbinfo);
1030         INP_LOCK_ASSERT(tp->t_inpcb);
1031         KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN", __func__));
1032
1033         /*
1034          * Segment received on connection.
1035          * Reset idle time and keep-alive timer.
1036          */
1037         tp->t_rcvtime = ticks;
1038         if (TCPS_HAVEESTABLISHED(tp->t_state))
1039                 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
1040
1041         /*
1042          * Unscale the window into a 32-bit value.
1043          * This value is bogus for the TCPS_SYN_SENT state
1044          * and is overwritten later.
1045          */
1046         tiwin = th->th_win << tp->snd_scale;
1047
1048         /*
1049          * Parse options on any incoming segment.
1050          */
1051         tcp_dooptions(&to, (u_char *)(th + 1),
1052             (th->th_off << 2) - sizeof(struct tcphdr),
1053             (thflags & TH_SYN) ? TO_SYN : 0);
1054
1055         /*
1056          * If echoed timestamp is later than the current time,
1057          * fall back to non RFC1323 RTT calculation.  Normalize
1058          * timestamp if syncookies were used when this connection
1059          * was established.
1060          */
1061         if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1062                 to.to_tsecr -= tp->ts_offset;
1063                 if (TSTMP_GT(to.to_tsecr, ticks))
1064                         to.to_tsecr = 0;
1065         }
1066
1067         /*
1068          * Process options only when we get SYN/ACK back. The SYN case
1069          * for incoming connections is handled in tcp_syncache.
1070          * XXX this is traditional behavior, may need to be cleaned up.
1071          */
1072         if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1073                 if ((to.to_flags & TOF_SCALE) &&
1074                     (tp->t_flags & TF_REQ_SCALE)) {
1075                         tp->t_flags |= TF_RCVD_SCALE;
1076                         tp->snd_scale = to.to_wscale;
1077                         tp->snd_wnd = th->th_win << tp->snd_scale;
1078                         tiwin = tp->snd_wnd;
1079                 }
1080                 if (to.to_flags & TOF_TS) {
1081                         tp->t_flags |= TF_RCVD_TSTMP;
1082                         tp->ts_recent = to.to_tsval;
1083                         tp->ts_recent_age = ticks;
1084                 }
1085                 /* Initial send window, already scaled. */
1086                 tp->snd_wnd = th->th_win;
1087                 if (to.to_flags & TOF_MSS)
1088                         tcp_mss(tp, to.to_mss);
1089                 if (tp->sack_enable) {
1090                         if (!(to.to_flags & TOF_SACKPERM))
1091                                 tp->sack_enable = 0;
1092                         else
1093                                 tp->t_flags |= TF_SACK_PERMIT;
1094                 }
1095
1096         }
1097
1098         /*
1099          * Header prediction: check for the two common cases
1100          * of a uni-directional data xfer.  If the packet has
1101          * no control flags, is in-sequence, the window didn't
1102          * change and we're not retransmitting, it's a
1103          * candidate.  If the length is zero and the ack moved
1104          * forward, we're the sender side of the xfer.  Just
1105          * free the data acked & wake any higher level process
1106          * that was blocked waiting for space.  If the length
1107          * is non-zero and the ack didn't move, we're the
1108          * receiver side.  If we're getting packets in-order
1109          * (the reassembly queue is empty), add the data to
1110          * the socket buffer and note that we need a delayed ack.
1111          * Make sure that the hidden state-flags are also off.
1112          * Since we check for TCPS_ESTABLISHED above, it can only
1113          * be TH_NEEDSYN.
1114          */
1115         if (tp->t_state == TCPS_ESTABLISHED &&
1116             (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1117             ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1118             ((to.to_flags & TOF_TS) == 0 ||
1119              TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
1120              th->th_seq == tp->rcv_nxt && tiwin && tiwin == tp->snd_wnd &&
1121              tp->snd_nxt == tp->snd_max) {
1122
1123                 /*
1124                  * If last ACK falls within this segment's sequence numbers,
1125                  * record the timestamp.
1126                  * NOTE that the test is modified according to the latest
1127                  * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1128                  */
1129                 if ((to.to_flags & TOF_TS) != 0 &&
1130                     SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1131                         tp->ts_recent_age = ticks;
1132                         tp->ts_recent = to.to_tsval;
1133                 }
1134
1135                 if (tlen == 0) {
1136                         if (SEQ_GT(th->th_ack, tp->snd_una) &&
1137                             SEQ_LEQ(th->th_ack, tp->snd_max) &&
1138                             tp->snd_cwnd >= tp->snd_wnd &&
1139                             ((!tcp_do_newreno && !tp->sack_enable &&
1140                               tp->t_dupacks < tcprexmtthresh) ||
1141                              ((tcp_do_newreno || tp->sack_enable) &&
1142                               !IN_FASTRECOVERY(tp) &&
1143                               (to.to_flags & TOF_SACK) == 0 &&
1144                               TAILQ_EMPTY(&tp->snd_holes)))) {
1145                                 KASSERT(headlocked,
1146                                     ("%s: headlocked", __func__));
1147                                 INP_INFO_WUNLOCK(&tcbinfo);
1148                                 headlocked = 0;
1149                                 /*
1150                                  * this is a pure ack for outstanding data.
1151                                  */
1152                                 ++tcpstat.tcps_predack;
1153                                 /*
1154                                  * "bad retransmit" recovery
1155                                  */
1156                                 if (tp->t_rxtshift == 1 &&
1157                                     ticks < tp->t_badrxtwin) {
1158                                         ++tcpstat.tcps_sndrexmitbad;
1159                                         tp->snd_cwnd = tp->snd_cwnd_prev;
1160                                         tp->snd_ssthresh =
1161                                             tp->snd_ssthresh_prev;
1162                                         tp->snd_recover = tp->snd_recover_prev;
1163                                         if (tp->t_flags & TF_WASFRECOVERY)
1164                                             ENTER_FASTRECOVERY(tp);
1165                                         tp->snd_nxt = tp->snd_max;
1166                                         tp->t_badrxtwin = 0;
1167                                 }
1168
1169                                 /*
1170                                  * Recalculate the transmit timer / rtt.
1171                                  *
1172                                  * Some boxes send broken timestamp replies
1173                                  * during the SYN+ACK phase, ignore
1174                                  * timestamps of 0 or we could calculate a
1175                                  * huge RTT and blow up the retransmit timer.
1176                                  */
1177                                 if ((to.to_flags & TOF_TS) != 0 &&
1178                                     to.to_tsecr) {
1179                                         if (!tp->t_rttlow ||
1180                                             tp->t_rttlow > ticks - to.to_tsecr)
1181                                                 tp->t_rttlow = ticks - to.to_tsecr;
1182                                         tcp_xmit_timer(tp,
1183                                             ticks - to.to_tsecr + 1);
1184                                 } else if (tp->t_rtttime &&
1185                                     SEQ_GT(th->th_ack, tp->t_rtseq)) {
1186                                         if (!tp->t_rttlow ||
1187                                             tp->t_rttlow > ticks - tp->t_rtttime)
1188                                                 tp->t_rttlow = ticks - tp->t_rtttime;
1189                                         tcp_xmit_timer(tp,
1190                                                         ticks - tp->t_rtttime);
1191                                 }
1192                                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1193                                 acked = th->th_ack - tp->snd_una;
1194                                 tcpstat.tcps_rcvackpack++;
1195                                 tcpstat.tcps_rcvackbyte += acked;
1196                                 sbdrop(&so->so_snd, acked);
1197                                 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1198                                     SEQ_LEQ(th->th_ack, tp->snd_recover))
1199                                         tp->snd_recover = th->th_ack - 1;
1200                                 tp->snd_una = th->th_ack;
1201                                 /*
1202                                  * pull snd_wl2 up to prevent seq wrap relative
1203                                  * to th_ack.
1204                                  */
1205                                 tp->snd_wl2 = th->th_ack;
1206                                 tp->t_dupacks = 0;
1207                                 m_freem(m);
1208                                 ND6_HINT(tp); /* some progress has been done */
1209
1210                                 /*
1211                                  * If all outstanding data are acked, stop
1212                                  * retransmit timer, otherwise restart timer
1213                                  * using current (possibly backed-off) value.
1214                                  * If process is waiting for space,
1215                                  * wakeup/selwakeup/signal.  If data
1216                                  * are ready to send, let tcp_output
1217                                  * decide between more output or persist.
1218
1219 #ifdef TCPDEBUG
1220                                 if (so->so_options & SO_DEBUG)
1221                                         tcp_trace(TA_INPUT, ostate, tp,
1222                                             (void *)tcp_saveipgen,
1223                                             &tcp_savetcp, 0);
1224 #endif
1225                                  */
1226                                 if (tp->snd_una == tp->snd_max)
1227                                         tcp_timer_activate(tp, TT_REXMT, 0);
1228                                 else if (!tcp_timer_active(tp, TT_PERSIST))
1229                                         tcp_timer_activate(tp, TT_REXMT,
1230                                                       tp->t_rxtcur);
1231
1232                                 sowwakeup(so);
1233                                 if (so->so_snd.sb_cc)
1234                                         (void) tcp_output(tp);
1235                                 goto check_delack;
1236                         }
1237                 } else if (th->th_ack == tp->snd_una &&
1238                     LIST_EMPTY(&tp->t_segq) &&
1239                     tlen <= sbspace(&so->so_rcv)) {
1240                         int newsize = 0;        /* automatic sockbuf scaling */
1241
1242                         KASSERT(headlocked, ("%s: headlocked", __func__));
1243                         INP_INFO_WUNLOCK(&tcbinfo);
1244                         headlocked = 0;
1245                         /*
1246                          * this is a pure, in-sequence data packet
1247                          * with nothing on the reassembly queue and
1248                          * we have enough buffer space to take it.
1249                          */
1250                         /* Clean receiver SACK report if present */
1251                         if (tp->sack_enable && tp->rcv_numsacks)
1252                                 tcp_clean_sackreport(tp);
1253                         ++tcpstat.tcps_preddat;
1254                         tp->rcv_nxt += tlen;
1255                         /*
1256                          * Pull snd_wl1 up to prevent seq wrap relative to
1257                          * th_seq.
1258                          */
1259                         tp->snd_wl1 = th->th_seq;
1260                         /*
1261                          * Pull rcv_up up to prevent seq wrap relative to
1262                          * rcv_nxt.
1263                          */
1264                         tp->rcv_up = tp->rcv_nxt;
1265                         tcpstat.tcps_rcvpack++;
1266                         tcpstat.tcps_rcvbyte += tlen;
1267                         ND6_HINT(tp);   /* some progress has been done */
1268 #ifdef TCPDEBUG
1269                         if (so->so_options & SO_DEBUG)
1270                                 tcp_trace(TA_INPUT, ostate, tp,
1271                                     (void *)tcp_saveipgen, &tcp_savetcp, 0);
1272 #endif
1273                 /*
1274                  * Automatic sizing of receive socket buffer.  Often the send
1275                  * buffer size is not optimally adjusted to the actual network
1276                  * conditions at hand (delay bandwidth product).  Setting the
1277                  * buffer size too small limits throughput on links with high
1278                  * bandwidth and high delay (eg. trans-continental/oceanic links).
1279                  *
1280                  * On the receive side the socket buffer memory is only rarely
1281                  * used to any significant extent.  This allows us to be much
1282                  * more aggressive in scaling the receive socket buffer.  For
1283                  * the case that the buffer space is actually used to a large
1284                  * extent and we run out of kernel memory we can simply drop
1285                  * the new segments; TCP on the sender will just retransmit it
1286                  * later.  Setting the buffer size too big may only consume too
1287                  * much kernel memory if the application doesn't read() from
1288                  * the socket or packet loss or reordering makes use of the
1289                  * reassembly queue.
1290                  *
1291                  * The criteria to step up the receive buffer one notch are:
1292                  *  1. the number of bytes received during the time it takes
1293                  *     one timestamp to be reflected back to us (the RTT);
1294                  *  2. received bytes per RTT is within seven eighth of the
1295                  *     current socket buffer size;
1296                  *  3. receive buffer size has not hit maximal automatic size;
1297                  *
1298                  * This algorithm does one step per RTT at most and only if
1299                  * we receive a bulk stream w/o packet losses or reorderings.
1300                  * Shrinking the buffer during idle times is not necessary as
1301                  * it doesn't consume any memory when idle.
1302                  *
1303                  * TODO: Only step up if the application is actually serving
1304                  * the buffer to better manage the socket buffer resources.
1305                  */
1306                         if (tcp_do_autorcvbuf &&
1307                             to.to_tsecr &&
1308                             (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1309                                 if (to.to_tsecr > tp->rfbuf_ts &&
1310                                     to.to_tsecr - tp->rfbuf_ts < hz) {
1311                                         if (tp->rfbuf_cnt >
1312                                             (so->so_rcv.sb_hiwat / 8 * 7) &&
1313                                             so->so_rcv.sb_hiwat <
1314                                             tcp_autorcvbuf_max) {
1315                                                 newsize =
1316                                                     min(so->so_rcv.sb_hiwat +
1317                                                     tcp_autorcvbuf_inc,
1318                                                     tcp_autorcvbuf_max);
1319                                         }
1320                                         /* Start over with next RTT. */
1321                                         tp->rfbuf_ts = 0;
1322                                         tp->rfbuf_cnt = 0;
1323                                 } else
1324                                         tp->rfbuf_cnt += tlen;  /* add up */
1325                         }
1326
1327                         /* Add data to socket buffer. */
1328                         SOCKBUF_LOCK(&so->so_rcv);
1329                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1330                                 m_freem(m);
1331                         } else {
1332                                 /*
1333                                  * Set new socket buffer size.
1334                                  * Give up when limit is reached.
1335                                  */
1336                                 if (newsize)
1337                                         if (!sbreserve_locked(&so->so_rcv,
1338                                             newsize, so, curthread))
1339                                                 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1340                                 m_adj(m, drop_hdrlen);  /* delayed header drop */
1341                                 sbappendstream_locked(&so->so_rcv, m);
1342                         }
1343                         sorwakeup_locked(so);
1344                         if (DELAY_ACK(tp)) {
1345                                 tp->t_flags |= TF_DELACK;
1346                         } else {
1347                                 tp->t_flags |= TF_ACKNOW;
1348                                 tcp_output(tp);
1349                         }
1350                         goto check_delack;
1351                 }
1352         }
1353
1354         /*
1355          * Calculate amount of space in receive window,
1356          * and then do TCP input processing.
1357          * Receive window is amount of space in rcv queue,
1358          * but not less than advertised window.
1359          */
1360         win = sbspace(&so->so_rcv);
1361         if (win < 0)
1362                 win = 0;
1363         tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1364
1365         /* Reset receive buffer auto scaling when not in bulk receive mode. */
1366         tp->rfbuf_ts = 0;
1367         tp->rfbuf_cnt = 0;
1368
1369         switch (tp->t_state) {
1370
1371         /*
1372          * If the state is SYN_RECEIVED:
1373          *      if seg contains an ACK, but not for our SYN/ACK, send a RST.
1374          */
1375         case TCPS_SYN_RECEIVED:
1376                 if ((thflags & TH_ACK) &&
1377                     (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1378                      SEQ_GT(th->th_ack, tp->snd_max))) {
1379                                 rstreason = BANDLIM_RST_OPENPORT;
1380                                 goto dropwithreset;
1381                 }
1382                 break;
1383
1384         /*
1385          * If the state is SYN_SENT:
1386          *      if seg contains an ACK, but not for our SYN, drop the input.
1387          *      if seg contains a RST, then drop the connection.
1388          *      if seg does not contain SYN, then drop it.
1389          * Otherwise this is an acceptable SYN segment
1390          *      initialize tp->rcv_nxt and tp->irs
1391          *      if seg contains ack then advance tp->snd_una
1392          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1393          *      arrange for segment to be acked (eventually)
1394          *      continue processing rest of data/controls, beginning with URG
1395          */
1396         case TCPS_SYN_SENT:
1397                 if ((thflags & TH_ACK) &&
1398                     (SEQ_LEQ(th->th_ack, tp->iss) ||
1399                      SEQ_GT(th->th_ack, tp->snd_max))) {
1400                         rstreason = BANDLIM_UNLIMITED;
1401                         goto dropwithreset;
1402                 }
1403                 if (thflags & TH_RST) {
1404                         if (thflags & TH_ACK) {
1405                                 KASSERT(headlocked, ("%s: after_listen: "
1406                                     "tcp_drop.2: head not locked", __func__));
1407                                 tp = tcp_drop(tp, ECONNREFUSED);
1408                         }
1409                         goto drop;
1410                 }
1411                 if ((thflags & TH_SYN) == 0)
1412                         goto drop;
1413
1414                 tp->irs = th->th_seq;
1415                 tcp_rcvseqinit(tp);
1416                 if (thflags & TH_ACK) {
1417                         tcpstat.tcps_connects++;
1418                         soisconnected(so);
1419 #ifdef MAC
1420                         SOCK_LOCK(so);
1421                         mac_set_socket_peer_from_mbuf(m, so);
1422                         SOCK_UNLOCK(so);
1423 #endif
1424                         /* Do window scaling on this connection? */
1425                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1426                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1427                                 tp->rcv_scale = tp->request_r_scale;
1428                         }
1429                         tp->rcv_adv += tp->rcv_wnd;
1430                         tp->snd_una++;          /* SYN is acked */
1431                         /*
1432                          * If there's data, delay ACK; if there's also a FIN
1433                          * ACKNOW will be turned on later.
1434                          */
1435                         if (DELAY_ACK(tp) && tlen != 0)
1436                                 tcp_timer_activate(tp, TT_DELACK,
1437                                     tcp_delacktime);
1438                         else
1439                                 tp->t_flags |= TF_ACKNOW;
1440                         /*
1441                          * Received <SYN,ACK> in SYN_SENT[*] state.
1442                          * Transitions:
1443                          *      SYN_SENT  --> ESTABLISHED
1444                          *      SYN_SENT* --> FIN_WAIT_1
1445                          */
1446                         tp->t_starttime = ticks;
1447                         if (tp->t_flags & TF_NEEDFIN) {
1448                                 tp->t_state = TCPS_FIN_WAIT_1;
1449                                 tp->t_flags &= ~TF_NEEDFIN;
1450                                 thflags &= ~TH_SYN;
1451                         } else {
1452                                 tp->t_state = TCPS_ESTABLISHED;
1453                                 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
1454                         }
1455                 } else {
1456                         /*
1457                          * Received initial SYN in SYN-SENT[*] state =>
1458                          * simultaneous open.  If segment contains CC option
1459                          * and there is a cached CC, apply TAO test.
1460                          * If it succeeds, connection is * half-synchronized.
1461                          * Otherwise, do 3-way handshake:
1462                          *        SYN-SENT -> SYN-RECEIVED
1463                          *        SYN-SENT* -> SYN-RECEIVED*
1464                          * If there was no CC option, clear cached CC value.
1465                          */
1466                         tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
1467                         tcp_timer_activate(tp, TT_REXMT, 0);
1468                         tp->t_state = TCPS_SYN_RECEIVED;
1469                 }
1470
1471                 KASSERT(headlocked, ("%s: trimthenstep6: head not locked",
1472                     __func__));
1473                 INP_LOCK_ASSERT(tp->t_inpcb);
1474
1475                 /*
1476                  * Advance th->th_seq to correspond to first data byte.
1477                  * If data, trim to stay within window,
1478                  * dropping FIN if necessary.
1479                  */
1480                 th->th_seq++;
1481                 if (tlen > tp->rcv_wnd) {
1482                         todrop = tlen - tp->rcv_wnd;
1483                         m_adj(m, -todrop);
1484                         tlen = tp->rcv_wnd;
1485                         thflags &= ~TH_FIN;
1486                         tcpstat.tcps_rcvpackafterwin++;
1487                         tcpstat.tcps_rcvbyteafterwin += todrop;
1488                 }
1489                 tp->snd_wl1 = th->th_seq - 1;
1490                 tp->rcv_up = th->th_seq;
1491                 /*
1492                  * Client side of transaction: already sent SYN and data.
1493                  * If the remote host used T/TCP to validate the SYN,
1494                  * our data will be ACK'd; if so, enter normal data segment
1495                  * processing in the middle of step 5, ack processing.
1496                  * Otherwise, goto step 6.
1497                  */
1498                 if (thflags & TH_ACK)
1499                         goto process_ACK;
1500
1501                 goto step6;
1502
1503         /*
1504          * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1505          *      do normal processing.
1506          *
1507          * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
1508          */
1509         case TCPS_LAST_ACK:
1510         case TCPS_CLOSING:
1511         case TCPS_TIME_WAIT:
1512                 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: timewait",
1513                     __func__));
1514                 break;  /* continue normal processing */
1515         }
1516
1517         /*
1518          * States other than LISTEN or SYN_SENT.
1519          * First check the RST flag and sequence number since reset segments
1520          * are exempt from the timestamp and connection count tests.  This
1521          * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1522          * below which allowed reset segments in half the sequence space
1523          * to fall though and be processed (which gives forged reset
1524          * segments with a random sequence number a 50 percent chance of
1525          * killing a connection).
1526          * Then check timestamp, if present.
1527          * Then check the connection count, if present.
1528          * Then check that at least some bytes of segment are within
1529          * receive window.  If segment begins before rcv_nxt,
1530          * drop leading data (and SYN); if nothing left, just ack.
1531          *
1532          *
1533          * If the RST bit is set, check the sequence number to see
1534          * if this is a valid reset segment.
1535          * RFC 793 page 37:
1536          *   In all states except SYN-SENT, all reset (RST) segments
1537          *   are validated by checking their SEQ-fields.  A reset is
1538          *   valid if its sequence number is in the window.
1539          * Note: this does not take into account delayed ACKs, so
1540          *   we should test against last_ack_sent instead of rcv_nxt.
1541          *   The sequence number in the reset segment is normally an
1542          *   echo of our outgoing acknowlegement numbers, but some hosts
1543          *   send a reset with the sequence number at the rightmost edge
1544          *   of our receive window, and we have to handle this case.
1545          * Note 2: Paul Watson's paper "Slipping in the Window" has shown
1546          *   that brute force RST attacks are possible.  To combat this,
1547          *   we use a much stricter check while in the ESTABLISHED state,
1548          *   only accepting RSTs where the sequence number is equal to
1549          *   last_ack_sent.  In all other states (the states in which a
1550          *   RST is more likely), the more permissive check is used.
1551          * If we have multiple segments in flight, the intial reset
1552          * segment sequence numbers will be to the left of last_ack_sent,
1553          * but they will eventually catch up.
1554          * In any case, it never made sense to trim reset segments to
1555          * fit the receive window since RFC 1122 says:
1556          *   4.2.2.12  RST Segment: RFC-793 Section 3.4
1557          *
1558          *    A TCP SHOULD allow a received RST segment to include data.
1559          *
1560          *    DISCUSSION
1561          *         It has been suggested that a RST segment could contain
1562          *         ASCII text that encoded and explained the cause of the
1563          *         RST.  No standard has yet been established for such
1564          *         data.
1565          *
1566          * If the reset segment passes the sequence number test examine
1567          * the state:
1568          *    SYN_RECEIVED STATE:
1569          *      If passive open, return to LISTEN state.
1570          *      If active open, inform user that connection was refused.
1571          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1572          *      Inform user that connection was reset, and close tcb.
1573          *    CLOSING, LAST_ACK STATES:
1574          *      Close the tcb.
1575          *    TIME_WAIT STATE:
1576          *      Drop the segment - see Stevens, vol. 2, p. 964 and
1577          *      RFC 1337.
1578          */
1579         if (thflags & TH_RST) {
1580                 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1581                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1582                         switch (tp->t_state) {
1583
1584                         case TCPS_SYN_RECEIVED:
1585                                 so->so_error = ECONNREFUSED;
1586                                 goto close;
1587
1588                         case TCPS_ESTABLISHED:
1589                                 if (tcp_insecure_rst == 0 &&
1590                                     !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
1591                                     SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
1592                                     !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1593                                     SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
1594                                         tcpstat.tcps_badrst++;
1595                                         goto drop;
1596                                 }
1597                         case TCPS_FIN_WAIT_1:
1598                         case TCPS_FIN_WAIT_2:
1599                         case TCPS_CLOSE_WAIT:
1600                                 so->so_error = ECONNRESET;
1601                         close:
1602                                 tp->t_state = TCPS_CLOSED;
1603                                 tcpstat.tcps_drops++;
1604                                 KASSERT(headlocked, ("%s: trimthenstep6: "
1605                                     "tcp_close: head not locked", __func__));
1606                                 tp = tcp_close(tp);
1607                                 break;
1608
1609                         case TCPS_CLOSING:
1610                         case TCPS_LAST_ACK:
1611                                 KASSERT(headlocked, ("%s: trimthenstep6: "
1612                                     "tcp_close.2: head not locked", __func__));
1613                                 tp = tcp_close(tp);
1614                                 break;
1615
1616                         case TCPS_TIME_WAIT:
1617                                 KASSERT(tp->t_state != TCPS_TIME_WAIT,
1618                                     ("%s: timewait", __func__));
1619                                 break;
1620                         }
1621                 }
1622                 goto drop;
1623         }
1624
1625         /*
1626          * RFC 1323 PAWS: If we have a timestamp reply on this segment
1627          * and it's less than ts_recent, drop it.
1628          */
1629         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1630             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1631
1632                 /* Check to see if ts_recent is over 24 days old.  */
1633                 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1634                         /*
1635                          * Invalidate ts_recent.  If this segment updates
1636                          * ts_recent, the age will be reset later and ts_recent
1637                          * will get a valid value.  If it does not, setting
1638                          * ts_recent to zero will at least satisfy the
1639                          * requirement that zero be placed in the timestamp
1640                          * echo reply when ts_recent isn't valid.  The
1641                          * age isn't reset until we get a valid ts_recent
1642                          * because we don't want out-of-order segments to be
1643                          * dropped when ts_recent is old.
1644                          */
1645                         tp->ts_recent = 0;
1646                 } else {
1647                         tcpstat.tcps_rcvduppack++;
1648                         tcpstat.tcps_rcvdupbyte += tlen;
1649                         tcpstat.tcps_pawsdrop++;
1650                         if (tlen)
1651                                 goto dropafterack;
1652                         goto drop;
1653                 }
1654         }
1655
1656         /*
1657          * In the SYN-RECEIVED state, validate that the packet belongs to
1658          * this connection before trimming the data to fit the receive
1659          * window.  Check the sequence number versus IRS since we know
1660          * the sequence numbers haven't wrapped.  This is a partial fix
1661          * for the "LAND" DoS attack.
1662          */
1663         if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1664                 rstreason = BANDLIM_RST_OPENPORT;
1665                 goto dropwithreset;
1666         }
1667
1668         todrop = tp->rcv_nxt - th->th_seq;
1669         if (todrop > 0) {
1670                 if (thflags & TH_SYN) {
1671                         thflags &= ~TH_SYN;
1672                         th->th_seq++;
1673                         if (th->th_urp > 1)
1674                                 th->th_urp--;
1675                         else
1676                                 thflags &= ~TH_URG;
1677                         todrop--;
1678                 }
1679                 /*
1680                  * Following if statement from Stevens, vol. 2, p. 960.
1681                  */
1682                 if (todrop > tlen
1683                     || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1684                         /*
1685                          * Any valid FIN must be to the left of the window.
1686                          * At this point the FIN must be a duplicate or out
1687                          * of sequence; drop it.
1688                          */
1689                         thflags &= ~TH_FIN;
1690
1691                         /*
1692                          * Send an ACK to resynchronize and drop any data.
1693                          * But keep on processing for RST or ACK.
1694                          */
1695                         tp->t_flags |= TF_ACKNOW;
1696                         todrop = tlen;
1697                         tcpstat.tcps_rcvduppack++;
1698                         tcpstat.tcps_rcvdupbyte += todrop;
1699                 } else {
1700                         tcpstat.tcps_rcvpartduppack++;
1701                         tcpstat.tcps_rcvpartdupbyte += todrop;
1702                 }
1703                 drop_hdrlen += todrop;  /* drop from the top afterwards */
1704                 th->th_seq += todrop;
1705                 tlen -= todrop;
1706                 if (th->th_urp > todrop)
1707                         th->th_urp -= todrop;
1708                 else {
1709                         thflags &= ~TH_URG;
1710                         th->th_urp = 0;
1711                 }
1712         }
1713
1714         /*
1715          * If new data are received on a connection after the
1716          * user processes are gone, then RST the other end.
1717          */
1718         if ((so->so_state & SS_NOFDREF) &&
1719             tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1720                 KASSERT(headlocked, ("%s: trimthenstep6: tcp_close.3: head "
1721                     "not locked", __func__));
1722                 tp = tcp_close(tp);
1723                 tcpstat.tcps_rcvafterclose++;
1724                 rstreason = BANDLIM_UNLIMITED;
1725                 goto dropwithreset;
1726         }
1727
1728         /*
1729          * If segment ends after window, drop trailing data
1730          * (and PUSH and FIN); if nothing left, just ACK.
1731          */
1732         todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
1733         if (todrop > 0) {
1734                 tcpstat.tcps_rcvpackafterwin++;
1735                 if (todrop >= tlen) {
1736                         tcpstat.tcps_rcvbyteafterwin += tlen;
1737                         /*
1738                          * If a new connection request is received
1739                          * while in TIME_WAIT, drop the old connection
1740                          * and start over if the sequence numbers
1741                          * are above the previous ones.
1742                          */
1743                         KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: timewait",
1744                             __func__));
1745                         if (thflags & TH_SYN &&
1746                             tp->t_state == TCPS_TIME_WAIT &&
1747                             SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1748                                 KASSERT(headlocked, ("%s: trimthenstep6: "
1749                                     "tcp_close.4: head not locked", __func__));
1750                                 tp = tcp_close(tp);
1751                                 /* XXX: Shouldn't be possible. */
1752                                 return (1);
1753                         }
1754                         /*
1755                          * If window is closed can only take segments at
1756                          * window edge, and have to drop data and PUSH from
1757                          * incoming segments.  Continue processing, but
1758                          * remember to ack.  Otherwise, drop segment
1759                          * and ack.
1760                          */
1761                         if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1762                                 tp->t_flags |= TF_ACKNOW;
1763                                 tcpstat.tcps_rcvwinprobe++;
1764                         } else
1765                                 goto dropafterack;
1766                 } else
1767                         tcpstat.tcps_rcvbyteafterwin += todrop;
1768                 m_adj(m, -todrop);
1769                 tlen -= todrop;
1770                 thflags &= ~(TH_PUSH|TH_FIN);
1771         }
1772
1773         /*
1774          * If last ACK falls within this segment's sequence numbers,
1775          * record its timestamp.
1776          * NOTE:
1777          * 1) That the test incorporates suggestions from the latest
1778          *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
1779          * 2) That updating only on newer timestamps interferes with
1780          *    our earlier PAWS tests, so this check should be solely
1781          *    predicated on the sequence space of this segment.
1782          * 3) That we modify the segment boundary check to be
1783          *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
1784          *    instead of RFC1323's
1785          *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
1786          *    This modified check allows us to overcome RFC1323's
1787          *    limitations as described in Stevens TCP/IP Illustrated
1788          *    Vol. 2 p.869. In such cases, we can still calculate the
1789          *    RTT correctly when RCV.NXT == Last.ACK.Sent.
1790          */
1791         if ((to.to_flags & TOF_TS) != 0 &&
1792             SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
1793             SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
1794                 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
1795                 tp->ts_recent_age = ticks;
1796                 tp->ts_recent = to.to_tsval;
1797         }
1798
1799         /*
1800          * If a SYN is in the window, then this is an
1801          * error and we send an RST and drop the connection.
1802          */
1803         if (thflags & TH_SYN) {
1804                 KASSERT(headlocked, ("%s: tcp_drop: trimthenstep6: "
1805                     "head not locked", __func__));
1806                 tp = tcp_drop(tp, ECONNRESET);
1807                 rstreason = BANDLIM_UNLIMITED;
1808                 goto drop;
1809         }
1810
1811         /*
1812          * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
1813          * flag is on (half-synchronized state), then queue data for
1814          * later processing; else drop segment and return.
1815          */
1816         if ((thflags & TH_ACK) == 0) {
1817                 if (tp->t_state == TCPS_SYN_RECEIVED ||
1818                     (tp->t_flags & TF_NEEDSYN))
1819                         goto step6;
1820                 else if (tp->t_flags & TF_ACKNOW)
1821                         goto dropafterack;
1822                 else
1823                         goto drop;
1824         }
1825
1826         /*
1827          * Ack processing.
1828          */
1829         switch (tp->t_state) {
1830
1831         /*
1832          * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1833          * ESTABLISHED state and continue processing.
1834          * The ACK was checked above.
1835          */
1836         case TCPS_SYN_RECEIVED:
1837
1838                 tcpstat.tcps_connects++;
1839                 soisconnected(so);
1840                 /* Do window scaling? */
1841                 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1842                         (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1843                         tp->rcv_scale = tp->request_r_scale;
1844                         tp->snd_wnd = tiwin;
1845                 }
1846                 /*
1847                  * Make transitions:
1848                  *      SYN-RECEIVED  -> ESTABLISHED
1849                  *      SYN-RECEIVED* -> FIN-WAIT-1
1850                  */
1851                 tp->t_starttime = ticks;
1852                 if (tp->t_flags & TF_NEEDFIN) {
1853                         tp->t_state = TCPS_FIN_WAIT_1;
1854                         tp->t_flags &= ~TF_NEEDFIN;
1855                 } else {
1856                         tp->t_state = TCPS_ESTABLISHED;
1857                         tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
1858                 }
1859                 /*
1860                  * If segment contains data or ACK, will call tcp_reass()
1861                  * later; if not, do so now to pass queued data to user.
1862                  */
1863                 if (tlen == 0 && (thflags & TH_FIN) == 0)
1864                         (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1865                             (struct mbuf *)0);
1866                 tp->snd_wl1 = th->th_seq - 1;
1867                 /* FALLTHROUGH */
1868
1869         /*
1870          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1871          * ACKs.  If the ack is in the range
1872          *      tp->snd_una < th->th_ack <= tp->snd_max
1873          * then advance tp->snd_una to th->th_ack and drop
1874          * data from the retransmission queue.  If this ACK reflects
1875          * more up to date window information we update our window information.
1876          */
1877         case TCPS_ESTABLISHED:
1878         case TCPS_FIN_WAIT_1:
1879         case TCPS_FIN_WAIT_2:
1880         case TCPS_CLOSE_WAIT:
1881         case TCPS_CLOSING:
1882         case TCPS_LAST_ACK:
1883         case TCPS_TIME_WAIT:
1884                 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: timewait",
1885                     __func__));
1886                 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1887                         tcpstat.tcps_rcvacktoomuch++;
1888                         goto dropafterack;
1889                 }
1890                 if (tp->sack_enable &&
1891                     ((to.to_flags & TOF_SACK) ||
1892                      !TAILQ_EMPTY(&tp->snd_holes)))
1893                         tcp_sack_doack(tp, &to, th->th_ack);
1894                 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1895                         if (tlen == 0 && tiwin == tp->snd_wnd) {
1896                                 tcpstat.tcps_rcvdupack++;
1897                                 /*
1898                                  * If we have outstanding data (other than
1899                                  * a window probe), this is a completely
1900                                  * duplicate ack (ie, window info didn't
1901                                  * change), the ack is the biggest we've
1902                                  * seen and we've seen exactly our rexmt
1903                                  * threshhold of them, assume a packet
1904                                  * has been dropped and retransmit it.
1905                                  * Kludge snd_nxt & the congestion
1906                                  * window so we send only this one
1907                                  * packet.
1908                                  *
1909                                  * We know we're losing at the current
1910                                  * window size so do congestion avoidance
1911                                  * (set ssthresh to half the current window
1912                                  * and pull our congestion window back to
1913                                  * the new ssthresh).
1914                                  *
1915                                  * Dup acks mean that packets have left the
1916                                  * network (they're now cached at the receiver)
1917                                  * so bump cwnd by the amount in the receiver
1918                                  * to keep a constant cwnd packets in the
1919                                  * network.
1920                                  */
1921                                 if (!tcp_timer_active(tp, TT_REXMT) ||
1922                                     th->th_ack != tp->snd_una)
1923                                         tp->t_dupacks = 0;
1924                                 else if (++tp->t_dupacks > tcprexmtthresh ||
1925                                     ((tcp_do_newreno || tp->sack_enable) &&
1926                                      IN_FASTRECOVERY(tp))) {
1927                                         if (tp->sack_enable && IN_FASTRECOVERY(tp)) {
1928                                                 int awnd;
1929
1930                                                 /*
1931                                                  * Compute the amount of data in flight first.
1932                                                  * We can inject new data into the pipe iff
1933                                                  * we have less than 1/2 the original window's
1934                                                  * worth of data in flight.
1935                                                  */
1936                                                 awnd = (tp->snd_nxt - tp->snd_fack) +
1937                                                         tp->sackhint.sack_bytes_rexmit;
1938                                                 if (awnd < tp->snd_ssthresh) {
1939                                                         tp->snd_cwnd += tp->t_maxseg;
1940                                                         if (tp->snd_cwnd > tp->snd_ssthresh)
1941                                                                 tp->snd_cwnd = tp->snd_ssthresh;
1942                                                 }
1943                                         } else
1944                                                 tp->snd_cwnd += tp->t_maxseg;
1945                                         (void) tcp_output(tp);
1946                                         goto drop;
1947                                 } else if (tp->t_dupacks == tcprexmtthresh) {
1948                                         tcp_seq onxt = tp->snd_nxt;
1949                                         u_int win;
1950
1951                                         /*
1952                                          * If we're doing sack, check to
1953                                          * see if we're already in sack
1954                                          * recovery. If we're not doing sack,
1955                                          * check to see if we're in newreno
1956                                          * recovery.
1957                                          */
1958                                         if (tp->sack_enable) {
1959                                                 if (IN_FASTRECOVERY(tp)) {
1960                                                         tp->t_dupacks = 0;
1961                                                         break;
1962                                                 }
1963                                         } else if (tcp_do_newreno) {
1964                                                 if (SEQ_LEQ(th->th_ack,
1965                                                     tp->snd_recover)) {
1966                                                         tp->t_dupacks = 0;
1967                                                         break;
1968                                                 }
1969                                         }
1970                                         win = min(tp->snd_wnd, tp->snd_cwnd) /
1971                                             2 / tp->t_maxseg;
1972                                         if (win < 2)
1973                                                 win = 2;
1974                                         tp->snd_ssthresh = win * tp->t_maxseg;
1975                                         ENTER_FASTRECOVERY(tp);
1976                                         tp->snd_recover = tp->snd_max;
1977                                         tcp_timer_activate(tp, TT_REXMT, 0);
1978                                         tp->t_rtttime = 0;
1979                                         if (tp->sack_enable) {
1980                                                 tcpstat.tcps_sack_recovery_episode++;
1981                                                 tp->sack_newdata = tp->snd_nxt;
1982                                                 tp->snd_cwnd = tp->t_maxseg;
1983                                                 (void) tcp_output(tp);
1984                                                 goto drop;
1985                                         }
1986                                         tp->snd_nxt = th->th_ack;
1987                                         tp->snd_cwnd = tp->t_maxseg;
1988                                         (void) tcp_output(tp);
1989                                         KASSERT(tp->snd_limited <= 2,
1990                                             ("%s: tp->snd_limited too big",
1991                                             __func__));
1992                                         tp->snd_cwnd = tp->snd_ssthresh +
1993                                              tp->t_maxseg *
1994                                              (tp->t_dupacks - tp->snd_limited);
1995                                         if (SEQ_GT(onxt, tp->snd_nxt))
1996                                                 tp->snd_nxt = onxt;
1997                                         goto drop;
1998                                 } else if (tcp_do_rfc3042) {
1999                                         u_long oldcwnd = tp->snd_cwnd;
2000                                         tcp_seq oldsndmax = tp->snd_max;
2001                                         u_int sent;
2002
2003                                         KASSERT(tp->t_dupacks == 1 ||
2004                                             tp->t_dupacks == 2,
2005                                             ("%s: dupacks not 1 or 2",
2006                                             __func__));
2007                                         if (tp->t_dupacks == 1)
2008                                                 tp->snd_limited = 0;
2009                                         tp->snd_cwnd =
2010                                             (tp->snd_nxt - tp->snd_una) +
2011                                             (tp->t_dupacks - tp->snd_limited) *
2012                                             tp->t_maxseg;
2013                                         (void) tcp_output(tp);
2014                                         sent = tp->snd_max - oldsndmax;
2015                                         if (sent > tp->t_maxseg) {
2016                                                 KASSERT((tp->t_dupacks == 2 &&
2017                                                     tp->snd_limited == 0) ||
2018                                                    (sent == tp->t_maxseg + 1 &&
2019                                                     tp->t_flags & TF_SENTFIN),
2020                                                     ("%s: sent too much",
2021                                                     __func__));
2022                                                 tp->snd_limited = 2;
2023                                         } else if (sent > 0)
2024                                                 ++tp->snd_limited;
2025                                         tp->snd_cwnd = oldcwnd;
2026                                         goto drop;
2027                                 }
2028                         } else
2029                                 tp->t_dupacks = 0;
2030                         break;
2031                 }
2032
2033                 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2034                     ("%s: th_ack <= snd_una", __func__));
2035
2036                 /*
2037                  * If the congestion window was inflated to account
2038                  * for the other side's cached packets, retract it.
2039                  */
2040                 if (tcp_do_newreno || tp->sack_enable) {
2041                         if (IN_FASTRECOVERY(tp)) {
2042                                 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2043                                         if (tp->sack_enable)
2044                                                 tcp_sack_partialack(tp, th);
2045                                         else
2046                                                 tcp_newreno_partial_ack(tp, th);
2047                                 } else {
2048                                         /*
2049                                          * Out of fast recovery.
2050                                          * Window inflation should have left us
2051                                          * with approximately snd_ssthresh
2052                                          * outstanding data.
2053                                          * But in case we would be inclined to
2054                                          * send a burst, better to do it via
2055                                          * the slow start mechanism.
2056                                          */
2057                                         if (SEQ_GT(th->th_ack +
2058                                                         tp->snd_ssthresh,
2059                                                    tp->snd_max))
2060                                                 tp->snd_cwnd = tp->snd_max -
2061                                                                 th->th_ack +
2062                                                                 tp->t_maxseg;
2063                                         else
2064                                                 tp->snd_cwnd = tp->snd_ssthresh;
2065                                 }
2066                         }
2067                 } else {
2068                         if (tp->t_dupacks >= tcprexmtthresh &&
2069                             tp->snd_cwnd > tp->snd_ssthresh)
2070                                 tp->snd_cwnd = tp->snd_ssthresh;
2071                 }
2072                 tp->t_dupacks = 0;
2073                 /*
2074                  * If we reach this point, ACK is not a duplicate,
2075                  *     i.e., it ACKs something we sent.
2076                  */
2077                 if (tp->t_flags & TF_NEEDSYN) {
2078                         /*
2079                          * T/TCP: Connection was half-synchronized, and our
2080                          * SYN has been ACK'd (so connection is now fully
2081                          * synchronized).  Go to non-starred state,
2082                          * increment snd_una for ACK of SYN, and check if
2083                          * we can do window scaling.
2084                          */
2085                         tp->t_flags &= ~TF_NEEDSYN;
2086                         tp->snd_una++;
2087                         /* Do window scaling? */
2088                         if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2089                                 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
2090                                 tp->rcv_scale = tp->request_r_scale;
2091                                 /* Send window already scaled. */
2092                         }
2093                 }
2094
2095 process_ACK:
2096                 KASSERT(headlocked, ("%s: process_ACK: head not locked",
2097                     __func__));
2098                 INP_LOCK_ASSERT(tp->t_inpcb);
2099
2100                 acked = th->th_ack - tp->snd_una;
2101                 tcpstat.tcps_rcvackpack++;
2102                 tcpstat.tcps_rcvackbyte += acked;
2103
2104                 /*
2105                  * If we just performed our first retransmit, and the ACK
2106                  * arrives within our recovery window, then it was a mistake
2107                  * to do the retransmit in the first place.  Recover our
2108                  * original cwnd and ssthresh, and proceed to transmit where
2109                  * we left off.
2110                  */
2111                 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
2112                         ++tcpstat.tcps_sndrexmitbad;
2113                         tp->snd_cwnd = tp->snd_cwnd_prev;
2114                         tp->snd_ssthresh = tp->snd_ssthresh_prev;
2115                         tp->snd_recover = tp->snd_recover_prev;
2116                         if (tp->t_flags & TF_WASFRECOVERY)
2117                                 ENTER_FASTRECOVERY(tp);
2118                         tp->snd_nxt = tp->snd_max;
2119                         tp->t_badrxtwin = 0;    /* XXX probably not required */
2120                 }
2121
2122                 /*
2123                  * If we have a timestamp reply, update smoothed
2124                  * round trip time.  If no timestamp is present but
2125                  * transmit timer is running and timed sequence
2126                  * number was acked, update smoothed round trip time.
2127                  * Since we now have an rtt measurement, cancel the
2128                  * timer backoff (cf., Phil Karn's retransmit alg.).
2129                  * Recompute the initial retransmit timer.
2130                  *
2131                  * Some boxes send broken timestamp replies
2132                  * during the SYN+ACK phase, ignore
2133                  * timestamps of 0 or we could calculate a
2134                  * huge RTT and blow up the retransmit timer.
2135                  */
2136                 if ((to.to_flags & TOF_TS) != 0 &&
2137                     to.to_tsecr) {
2138                         if (!tp->t_rttlow || tp->t_rttlow > ticks - to.to_tsecr)
2139                                 tp->t_rttlow = ticks - to.to_tsecr;
2140                         tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
2141                 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2142                         if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2143                                 tp->t_rttlow = ticks - tp->t_rtttime;
2144                         tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2145                 }
2146                 tcp_xmit_bandwidth_limit(tp, th->th_ack);
2147
2148                 /*
2149                  * If all outstanding data is acked, stop retransmit
2150                  * timer and remember to restart (more output or persist).
2151                  * If there is more data to be acked, restart retransmit
2152                  * timer, using current (possibly backed-off) value.
2153                  */
2154                 if (th->th_ack == tp->snd_max) {
2155                         tcp_timer_activate(tp, TT_REXMT, 0);
2156                         needoutput = 1;
2157                 } else if (!tcp_timer_active(tp, TT_PERSIST))
2158                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2159
2160                 /*
2161                  * If no data (only SYN) was ACK'd,
2162                  *    skip rest of ACK processing.
2163                  */
2164                 if (acked == 0)
2165                         goto step6;
2166
2167                 /*
2168                  * When new data is acked, open the congestion window.
2169                  * If the window gives us less than ssthresh packets
2170                  * in flight, open exponentially (maxseg per packet).
2171                  * Otherwise open linearly: maxseg per window
2172                  * (maxseg^2 / cwnd per packet).
2173                  */
2174                 if ((!tcp_do_newreno && !tp->sack_enable) ||
2175                     !IN_FASTRECOVERY(tp)) {
2176                         u_int cw = tp->snd_cwnd;
2177                         u_int incr = tp->t_maxseg;
2178                         if (cw > tp->snd_ssthresh)
2179                                 incr = incr * incr / cw;
2180                         tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
2181                 }
2182                 SOCKBUF_LOCK(&so->so_snd);
2183                 if (acked > so->so_snd.sb_cc) {
2184                         tp->snd_wnd -= so->so_snd.sb_cc;
2185                         sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
2186                         ourfinisacked = 1;
2187                 } else {
2188                         sbdrop_locked(&so->so_snd, acked);
2189                         tp->snd_wnd -= acked;
2190                         ourfinisacked = 0;
2191                 }
2192                 sowwakeup_locked(so);
2193                 /* detect una wraparound */
2194                 if ((tcp_do_newreno || tp->sack_enable) &&
2195                     !IN_FASTRECOVERY(tp) &&
2196                     SEQ_GT(tp->snd_una, tp->snd_recover) &&
2197                     SEQ_LEQ(th->th_ack, tp->snd_recover))
2198                         tp->snd_recover = th->th_ack - 1;
2199                 if ((tcp_do_newreno || tp->sack_enable) &&
2200                     IN_FASTRECOVERY(tp) &&
2201                     SEQ_GEQ(th->th_ack, tp->snd_recover))
2202                         EXIT_FASTRECOVERY(tp);
2203                 tp->snd_una = th->th_ack;
2204                 if (tp->sack_enable) {
2205                         if (SEQ_GT(tp->snd_una, tp->snd_recover))
2206                                 tp->snd_recover = tp->snd_una;
2207                 }
2208                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2209                         tp->snd_nxt = tp->snd_una;
2210
2211                 switch (tp->t_state) {
2212
2213                 /*
2214                  * In FIN_WAIT_1 STATE in addition to the processing
2215                  * for the ESTABLISHED state if our FIN is now acknowledged
2216                  * then enter FIN_WAIT_2.
2217                  */
2218                 case TCPS_FIN_WAIT_1:
2219                         if (ourfinisacked) {
2220                                 /*
2221                                  * If we can't receive any more
2222                                  * data, then closing user can proceed.
2223                                  * Starting the timer is contrary to the
2224                                  * specification, but if we don't get a FIN
2225                                  * we'll hang forever.
2226                                  */
2227                 /* XXXjl
2228                  * we should release the tp also, and use a
2229                  * compressed state.
2230                  */
2231                                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2232                                         int timeout;
2233
2234                                         soisdisconnected(so);
2235                                         timeout = (tcp_fast_finwait2_recycle) ?
2236                                                 tcp_finwait2_timeout : tcp_maxidle;
2237                                         tcp_timer_activate(tp, TT_2MSL, timeout);
2238                                 }
2239                                 tp->t_state = TCPS_FIN_WAIT_2;
2240                         }
2241                         break;
2242
2243                 /*
2244                  * In CLOSING STATE in addition to the processing for
2245                  * the ESTABLISHED state if the ACK acknowledges our FIN
2246                  * then enter the TIME-WAIT state, otherwise ignore
2247                  * the segment.
2248                  */
2249                 case TCPS_CLOSING:
2250                         if (ourfinisacked) {
2251                                 KASSERT(headlocked, ("%s: process_ACK: "
2252                                     "head not locked", __func__));
2253                                 tcp_twstart(tp);
2254                                 INP_INFO_WUNLOCK(&tcbinfo);
2255                                 headlocked = 0;
2256                                 m_freem(m);
2257                                 return (0);
2258                         }
2259                         break;
2260
2261                 /*
2262                  * In LAST_ACK, we may still be waiting for data to drain
2263                  * and/or to be acked, as well as for the ack of our FIN.
2264                  * If our FIN is now acknowledged, delete the TCB,
2265                  * enter the closed state and return.
2266                  */
2267                 case TCPS_LAST_ACK:
2268                         if (ourfinisacked) {
2269                                 KASSERT(headlocked, ("%s: process_ACK: "
2270                                     "tcp_close: head not locked", __func__));
2271                                 tp = tcp_close(tp);
2272                                 goto drop;
2273                         }
2274                         break;
2275
2276                 /*
2277                  * In TIME_WAIT state the only thing that should arrive
2278                  * is a retransmission of the remote FIN.  Acknowledge
2279                  * it and restart the finack timer.
2280                  */
2281                 case TCPS_TIME_WAIT:
2282                         KASSERT(tp->t_state != TCPS_TIME_WAIT,
2283                             ("%s: timewait", __func__));
2284                         tcp_timer_activate(tp, TT_2MSL, 2 * tcp_msl);
2285                         goto dropafterack;
2286                 }
2287         }
2288
2289 step6:
2290         KASSERT(headlocked, ("%s: step6: head not locked", __func__));
2291         INP_LOCK_ASSERT(tp->t_inpcb);
2292
2293         /*
2294          * Update window information.
2295          * Don't look at window if no ACK: TAC's send garbage on first SYN.
2296          */
2297         if ((thflags & TH_ACK) &&
2298             (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2299             (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2300              (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2301                 /* keep track of pure window updates */
2302                 if (tlen == 0 &&
2303                     tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2304                         tcpstat.tcps_rcvwinupd++;
2305                 tp->snd_wnd = tiwin;
2306                 tp->snd_wl1 = th->th_seq;
2307                 tp->snd_wl2 = th->th_ack;
2308                 if (tp->snd_wnd > tp->max_sndwnd)
2309                         tp->max_sndwnd = tp->snd_wnd;
2310                 needoutput = 1;
2311         }
2312
2313         /*
2314          * Process segments with URG.
2315          */
2316         if ((thflags & TH_URG) && th->th_urp &&
2317             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2318                 /*
2319                  * This is a kludge, but if we receive and accept
2320                  * random urgent pointers, we'll crash in
2321                  * soreceive.  It's hard to imagine someone
2322                  * actually wanting to send this much urgent data.
2323                  */
2324                 SOCKBUF_LOCK(&so->so_rcv);
2325                 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2326                         th->th_urp = 0;                 /* XXX */
2327                         thflags &= ~TH_URG;             /* XXX */
2328                         SOCKBUF_UNLOCK(&so->so_rcv);    /* XXX */
2329                         goto dodata;                    /* XXX */
2330                 }
2331                 /*
2332                  * If this segment advances the known urgent pointer,
2333                  * then mark the data stream.  This should not happen
2334                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2335                  * a FIN has been received from the remote side.
2336                  * In these states we ignore the URG.
2337                  *
2338                  * According to RFC961 (Assigned Protocols),
2339                  * the urgent pointer points to the last octet
2340                  * of urgent data.  We continue, however,
2341                  * to consider it to indicate the first octet
2342                  * of data past the urgent section as the original
2343                  * spec states (in one of two places).
2344                  */
2345                 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2346                         tp->rcv_up = th->th_seq + th->th_urp;
2347                         so->so_oobmark = so->so_rcv.sb_cc +
2348                             (tp->rcv_up - tp->rcv_nxt) - 1;
2349                         if (so->so_oobmark == 0)
2350                                 so->so_rcv.sb_state |= SBS_RCVATMARK;
2351                         sohasoutofband(so);
2352                         tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2353                 }
2354                 SOCKBUF_UNLOCK(&so->so_rcv);
2355                 /*
2356                  * Remove out of band data so doesn't get presented to user.
2357                  * This can happen independent of advancing the URG pointer,
2358                  * but if two URG's are pending at once, some out-of-band
2359                  * data may creep in... ick.
2360                  */
2361                 if (th->th_urp <= (u_long)tlen &&
2362                     !(so->so_options & SO_OOBINLINE)) {
2363                         /* hdr drop is delayed */
2364                         tcp_pulloutofband(so, th, m, drop_hdrlen);
2365                 }
2366         } else {
2367                 /*
2368                  * If no out of band data is expected,
2369                  * pull receive urgent pointer along
2370                  * with the receive window.
2371                  */
2372                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2373                         tp->rcv_up = tp->rcv_nxt;
2374         }
2375 dodata:                                                 /* XXX */
2376         KASSERT(headlocked, ("%s: dodata: head not locked", __func__));
2377         INP_LOCK_ASSERT(tp->t_inpcb);
2378
2379         /*
2380          * Process the segment text, merging it into the TCP sequencing queue,
2381          * and arranging for acknowledgment of receipt if necessary.
2382          * This process logically involves adjusting tp->rcv_wnd as data
2383          * is presented to the user (this happens in tcp_usrreq.c,
2384          * case PRU_RCVD).  If a FIN has already been received on this
2385          * connection then we just ignore the text.
2386          */
2387         if ((tlen || (thflags & TH_FIN)) &&
2388             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2389                 tcp_seq save_start = th->th_seq;
2390                 tcp_seq save_end = th->th_seq + tlen;
2391                 m_adj(m, drop_hdrlen);  /* delayed header drop */
2392                 /*
2393                  * Insert segment which includes th into TCP reassembly queue
2394                  * with control block tp.  Set thflags to whether reassembly now
2395                  * includes a segment with FIN.  This handles the common case
2396                  * inline (segment is the next to be received on an established
2397                  * connection, and the queue is empty), avoiding linkage into
2398                  * and removal from the queue and repetition of various
2399                  * conversions.
2400                  * Set DELACK for segments received in order, but ack
2401                  * immediately when segments are out of order (so
2402                  * fast retransmit can work).
2403                  */
2404                 if (th->th_seq == tp->rcv_nxt &&
2405                     LIST_EMPTY(&tp->t_segq) &&
2406                     TCPS_HAVEESTABLISHED(tp->t_state)) {
2407                         if (DELAY_ACK(tp))
2408                                 tp->t_flags |= TF_DELACK;
2409                         else
2410                                 tp->t_flags |= TF_ACKNOW;
2411                         tp->rcv_nxt += tlen;
2412                         thflags = th->th_flags & TH_FIN;
2413                         tcpstat.tcps_rcvpack++;
2414                         tcpstat.tcps_rcvbyte += tlen;
2415                         ND6_HINT(tp);
2416                         SOCKBUF_LOCK(&so->so_rcv);
2417                         if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
2418                                 m_freem(m);
2419                         else
2420                                 sbappendstream_locked(&so->so_rcv, m);
2421                         sorwakeup_locked(so);
2422                 } else {
2423                         thflags = tcp_reass(tp, th, &tlen, m);
2424                         tp->t_flags |= TF_ACKNOW;
2425                 }
2426                 if (tlen > 0 && tp->sack_enable)
2427                         tcp_update_sack_list(tp, save_start, save_end);
2428 #if 0
2429                 /*
2430                  * Note the amount of data that peer has sent into
2431                  * our window, in order to estimate the sender's
2432                  * buffer size.
2433                  * XXX: Unused.
2434                  */
2435                 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2436 #endif
2437         } else {
2438                 m_freem(m);
2439                 thflags &= ~TH_FIN;
2440         }
2441
2442         /*
2443          * If FIN is received ACK the FIN and let the user know
2444          * that the connection is closing.
2445          */
2446         if (thflags & TH_FIN) {
2447                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2448                         socantrcvmore(so);
2449                         /*
2450                          * If connection is half-synchronized
2451                          * (ie NEEDSYN flag on) then delay ACK,
2452                          * so it may be piggybacked when SYN is sent.
2453                          * Otherwise, since we received a FIN then no
2454                          * more input can be expected, send ACK now.
2455                          */
2456                         if (tp->t_flags & TF_NEEDSYN)
2457                                 tp->t_flags |= TF_DELACK;
2458                         else
2459                                 tp->t_flags |= TF_ACKNOW;
2460                         tp->rcv_nxt++;
2461                 }
2462                 switch (tp->t_state) {
2463
2464                 /*
2465                  * In SYN_RECEIVED and ESTABLISHED STATES
2466                  * enter the CLOSE_WAIT state.
2467                  */
2468                 case TCPS_SYN_RECEIVED:
2469                         tp->t_starttime = ticks;
2470                         /*FALLTHROUGH*/
2471                 case TCPS_ESTABLISHED:
2472                         tp->t_state = TCPS_CLOSE_WAIT;
2473                         break;
2474
2475                 /*
2476                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
2477                  * enter the CLOSING state.
2478                  */
2479                 case TCPS_FIN_WAIT_1:
2480                         tp->t_state = TCPS_CLOSING;
2481                         break;
2482
2483                 /*
2484                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
2485                  * starting the time-wait timer, turning off the other
2486                  * standard timers.
2487                  */
2488                 case TCPS_FIN_WAIT_2:
2489                         KASSERT(headlocked == 1, ("%s: dodata: "
2490                             "TCP_FIN_WAIT_2: head not locked", __func__));
2491                         tcp_twstart(tp);
2492                         INP_INFO_WUNLOCK(&tcbinfo);
2493                         return (0);
2494
2495                 /*
2496                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
2497                  */
2498                 case TCPS_TIME_WAIT:
2499                         KASSERT(tp->t_state != TCPS_TIME_WAIT,
2500                             ("%s: timewait", __func__));
2501                         tcp_timer_activate(tp, TT_2MSL, 2 * tcp_msl);
2502                         break;
2503                 }
2504         }
2505         INP_INFO_WUNLOCK(&tcbinfo);
2506         headlocked = 0;
2507 #ifdef TCPDEBUG
2508         if (so->so_options & SO_DEBUG)
2509                 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2510                           &tcp_savetcp, 0);
2511 #endif
2512
2513         /*
2514          * Return any desired output.
2515          */
2516         if (needoutput || (tp->t_flags & TF_ACKNOW))
2517                 (void) tcp_output(tp);
2518
2519 check_delack:
2520         KASSERT(headlocked == 0, ("%s: check_delack: head locked",
2521             __func__));
2522         INP_LOCK_ASSERT(tp->t_inpcb);
2523         if (tp->t_flags & TF_DELACK) {
2524                 tp->t_flags &= ~TF_DELACK;
2525                 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
2526         }
2527         INP_UNLOCK(tp->t_inpcb);
2528         return (0);
2529
2530 dropafterack:
2531         KASSERT(headlocked, ("%s: dropafterack: head not locked", __func__));
2532         /*
2533          * Generate an ACK dropping incoming segment if it occupies
2534          * sequence space, where the ACK reflects our state.
2535          *
2536          * We can now skip the test for the RST flag since all
2537          * paths to this code happen after packets containing
2538          * RST have been dropped.
2539          *
2540          * In the SYN-RECEIVED state, don't send an ACK unless the
2541          * segment we received passes the SYN-RECEIVED ACK test.
2542          * If it fails send a RST.  This breaks the loop in the
2543          * "LAND" DoS attack, and also prevents an ACK storm
2544          * between two listening ports that have been sent forged
2545          * SYN segments, each with the source address of the other.
2546          */
2547         if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2548             (SEQ_GT(tp->snd_una, th->th_ack) ||
2549              SEQ_GT(th->th_ack, tp->snd_max)) ) {
2550                 rstreason = BANDLIM_RST_OPENPORT;
2551                 goto dropwithreset;
2552         }
2553 #ifdef TCPDEBUG
2554         if (so->so_options & SO_DEBUG)
2555                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2556                           &tcp_savetcp, 0);
2557 #endif
2558         KASSERT(headlocked, ("%s: headlocked should be 1", __func__));
2559         INP_INFO_WUNLOCK(&tcbinfo);
2560         tp->t_flags |= TF_ACKNOW;
2561         (void) tcp_output(tp);
2562         INP_UNLOCK(tp->t_inpcb);
2563         m_freem(m);
2564         return (0);
2565
2566 dropwithreset:
2567         KASSERT(headlocked, ("%s: dropwithreset: head not locked", __func__));
2568
2569         tcp_dropwithreset(m, th, tp, tlen, rstreason);
2570
2571         if (tp != NULL)
2572                 INP_UNLOCK(tp->t_inpcb);
2573         if (headlocked)
2574                 INP_INFO_WUNLOCK(&tcbinfo);
2575         return (0);
2576
2577 drop:
2578         /*
2579          * Drop space held by incoming segment and return.
2580          */
2581 #ifdef TCPDEBUG
2582         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2583                 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2584                           &tcp_savetcp, 0);
2585 #endif
2586         if (tp != NULL)
2587                 INP_UNLOCK(tp->t_inpcb);
2588         if (headlocked)
2589                 INP_INFO_WUNLOCK(&tcbinfo);
2590         m_freem(m);
2591         return (0);
2592 }
2593
2594
2595 /*
2596  * Issue RST on TCP segment.  The mbuf must still include the original
2597  * packet header.
2598  */
2599 static void
2600 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
2601     int tlen, int rstreason)
2602 {
2603         struct ip *ip;
2604 #ifdef INET6
2605         struct ip6_hdr *ip6;
2606 #endif
2607         /*
2608          * Generate a RST, dropping incoming segment.
2609          * Make ACK acceptable to originator of segment.
2610          * Don't bother to respond if destination was broadcast/multicast.
2611          * tp may be NULL.
2612          */
2613         if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2614                 goto drop;
2615 #ifdef INET6
2616         if (mtod(m, struct ip *)->ip_v == 6) {
2617                 ip6 = mtod(m, struct ip6_hdr *);
2618                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2619                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2620                         goto drop;
2621                 /* IPv6 anycast check is done at tcp6_input() */
2622         } else
2623 #endif
2624         {
2625                 ip = mtod(m, struct ip *);
2626                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2627                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2628                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2629                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2630                         goto drop;
2631         }
2632
2633         /* Perform bandwidth limiting. */
2634         if (badport_bandlim(rstreason) < 0)
2635                 goto drop;
2636
2637         /* tcp_respond consumes the mbuf chain. */
2638         if (th->th_flags & TH_ACK) {
2639                 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
2640                     th->th_ack, TH_RST);
2641         } else {
2642                 if (th->th_flags & TH_SYN)
2643                         tlen++;
2644                 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2645                     (tcp_seq)0, TH_RST|TH_ACK);
2646         }
2647         return;
2648 drop:
2649         m_freem(m);
2650         return;
2651 }
2652
2653 /*
2654  * Parse TCP options and place in tcpopt.
2655  */
2656 static void
2657 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
2658 {
2659         int opt, optlen;
2660
2661         to->to_flags = 0;
2662         for (; cnt > 0; cnt -= optlen, cp += optlen) {
2663                 opt = cp[0];
2664                 if (opt == TCPOPT_EOL)
2665                         break;
2666                 if (opt == TCPOPT_NOP)
2667                         optlen = 1;
2668                 else {
2669                         if (cnt < 2)
2670                                 break;
2671                         optlen = cp[1];
2672                         if (optlen < 2 || optlen > cnt)
2673                                 break;
2674                 }
2675                 switch (opt) {
2676                 case TCPOPT_MAXSEG:
2677                         if (optlen != TCPOLEN_MAXSEG)
2678                                 continue;
2679                         if (!(flags & TO_SYN))
2680                                 continue;
2681                         to->to_flags |= TOF_MSS;
2682                         bcopy((char *)cp + 2,
2683                             (char *)&to->to_mss, sizeof(to->to_mss));
2684                         to->to_mss = ntohs(to->to_mss);
2685                         break;
2686                 case TCPOPT_WINDOW:
2687                         if (optlen != TCPOLEN_WINDOW)
2688                                 continue;
2689                         if (!(flags & TO_SYN))
2690                                 continue;
2691                         to->to_flags |= TOF_SCALE;
2692                         to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
2693                         break;
2694                 case TCPOPT_TIMESTAMP:
2695                         if (optlen != TCPOLEN_TIMESTAMP)
2696                                 continue;
2697                         to->to_flags |= TOF_TS;
2698                         bcopy((char *)cp + 2,
2699                             (char *)&to->to_tsval, sizeof(to->to_tsval));
2700                         to->to_tsval = ntohl(to->to_tsval);
2701                         bcopy((char *)cp + 6,
2702                             (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2703                         to->to_tsecr = ntohl(to->to_tsecr);
2704                         break;
2705 #ifdef TCP_SIGNATURE
2706                 /*
2707                  * XXX In order to reply to a host which has set the
2708                  * TCP_SIGNATURE option in its initial SYN, we have to
2709                  * record the fact that the option was observed here
2710                  * for the syncache code to perform the correct response.
2711                  */
2712                 case TCPOPT_SIGNATURE:
2713                         if (optlen != TCPOLEN_SIGNATURE)
2714                                 continue;
2715                         to->to_flags |= (TOF_SIGNATURE | TOF_SIGLEN);
2716                         break;
2717 #endif
2718                 case TCPOPT_SACK_PERMITTED:
2719                         if (optlen != TCPOLEN_SACK_PERMITTED)
2720                                 continue;
2721                         if (!(flags & TO_SYN))
2722                                 continue;
2723                         if (!tcp_do_sack)
2724                                 continue;
2725                         to->to_flags |= TOF_SACKPERM;
2726                         break;
2727                 case TCPOPT_SACK:
2728                         if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
2729                                 continue;
2730                         if (flags & TO_SYN)
2731                                 continue;
2732                         to->to_flags |= TOF_SACK;
2733                         to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
2734                         to->to_sacks = cp + 2;
2735                         tcpstat.tcps_sack_rcv_blocks++;
2736                         break;
2737                 default:
2738                         continue;
2739                 }
2740         }
2741 }
2742
2743 /*
2744  * Pull out of band byte out of a segment so
2745  * it doesn't appear in the user's data queue.
2746  * It is still reflected in the segment length for
2747  * sequencing purposes.
2748  */
2749 static void
2750 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
2751     int off)
2752 {
2753         int cnt = off + th->th_urp - 1;
2754
2755         while (cnt >= 0) {
2756                 if (m->m_len > cnt) {
2757                         char *cp = mtod(m, caddr_t) + cnt;
2758                         struct tcpcb *tp = sototcpcb(so);
2759
2760                         tp->t_iobc = *cp;
2761                         tp->t_oobflags |= TCPOOB_HAVEDATA;
2762                         bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2763                         m->m_len--;
2764                         if (m->m_flags & M_PKTHDR)
2765                                 m->m_pkthdr.len--;
2766                         return;
2767                 }
2768                 cnt -= m->m_len;
2769                 m = m->m_next;
2770                 if (m == NULL)
2771                         break;
2772         }
2773         panic("tcp_pulloutofband");
2774 }
2775
2776 /*
2777  * Collect new round-trip time estimate
2778  * and update averages and current timeout.
2779  */
2780 static void
2781 tcp_xmit_timer(struct tcpcb *tp, int rtt)
2782 {
2783         int delta;
2784
2785         INP_LOCK_ASSERT(tp->t_inpcb);
2786
2787         tcpstat.tcps_rttupdated++;
2788         tp->t_rttupdated++;
2789         if (tp->t_srtt != 0) {
2790                 /*
2791                  * srtt is stored as fixed point with 5 bits after the
2792                  * binary point (i.e., scaled by 8).  The following magic
2793                  * is equivalent to the smoothing algorithm in rfc793 with
2794                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2795                  * point).  Adjust rtt to origin 0.
2796                  */
2797                 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2798                         - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2799
2800                 if ((tp->t_srtt += delta) <= 0)
2801                         tp->t_srtt = 1;
2802
2803                 /*
2804                  * We accumulate a smoothed rtt variance (actually, a
2805                  * smoothed mean difference), then set the retransmit
2806                  * timer to smoothed rtt + 4 times the smoothed variance.
2807                  * rttvar is stored as fixed point with 4 bits after the
2808                  * binary point (scaled by 16).  The following is
2809                  * equivalent to rfc793 smoothing with an alpha of .75
2810                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
2811                  * rfc793's wired-in beta.
2812                  */
2813                 if (delta < 0)
2814                         delta = -delta;
2815                 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2816                 if ((tp->t_rttvar += delta) <= 0)
2817                         tp->t_rttvar = 1;
2818                 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2819                     tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2820         } else {
2821                 /*
2822                  * No rtt measurement yet - use the unsmoothed rtt.
2823                  * Set the variance to half the rtt (so our first
2824                  * retransmit happens at 3*rtt).
2825                  */
2826                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2827                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2828                 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2829         }
2830         tp->t_rtttime = 0;
2831         tp->t_rxtshift = 0;
2832
2833         /*
2834          * the retransmit should happen at rtt + 4 * rttvar.
2835          * Because of the way we do the smoothing, srtt and rttvar
2836          * will each average +1/2 tick of bias.  When we compute
2837          * the retransmit timer, we want 1/2 tick of rounding and
2838          * 1 extra tick because of +-1/2 tick uncertainty in the
2839          * firing of the timer.  The bias will give us exactly the
2840          * 1.5 tick we need.  But, because the bias is
2841          * statistical, we have to test that we don't drop below
2842          * the minimum feasible timer (which is 2 ticks).
2843          */
2844         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2845                       max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2846
2847         /*
2848          * We received an ack for a packet that wasn't retransmitted;
2849          * it is probably safe to discard any error indications we've
2850          * received recently.  This isn't quite right, but close enough
2851          * for now (a route might have failed after we sent a segment,
2852          * and the return path might not be symmetrical).
2853          */
2854         tp->t_softerror = 0;
2855 }
2856
2857 /*
2858  * Determine a reasonable value for maxseg size.
2859  * If the route is known, check route for mtu.
2860  * If none, use an mss that can be handled on the outgoing
2861  * interface without forcing IP to fragment; if bigger than
2862  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2863  * to utilize large mbufs.  If no route is found, route has no mtu,
2864  * or the destination isn't local, use a default, hopefully conservative
2865  * size (usually 512 or the default IP max size, but no more than the mtu
2866  * of the interface), as we can't discover anything about intervening
2867  * gateways or networks.  We also initialize the congestion/slow start
2868  * window to be a single segment if the destination isn't local.
2869  * While looking at the routing entry, we also initialize other path-dependent
2870  * parameters from pre-set or cached values in the routing entry.
2871  *
2872  * Also take into account the space needed for options that we
2873  * send regularly.  Make maxseg shorter by that amount to assure
2874  * that we can send maxseg amount of data even when the options
2875  * are present.  Store the upper limit of the length of options plus
2876  * data in maxopd.
2877  *
2878  *
2879  * In case of T/TCP, we call this routine during implicit connection
2880  * setup as well (offer = -1), to initialize maxseg from the cached
2881  * MSS of our peer.
2882  *
2883  * NOTE that this routine is only called when we process an incoming
2884  * segment. Outgoing SYN/ACK MSS settings are handled in tcp_mssopt().
2885  */
2886 void
2887 tcp_mss(struct tcpcb *tp, int offer)
2888 {
2889         int rtt, mss;
2890         u_long bufsize;
2891         u_long maxmtu;
2892         struct inpcb *inp = tp->t_inpcb;
2893         struct socket *so;
2894         struct hc_metrics_lite metrics;
2895         int origoffer = offer;
2896         int mtuflags = 0;
2897 #ifdef INET6
2898         int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2899         size_t min_protoh = isipv6 ?
2900                             sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
2901                             sizeof (struct tcpiphdr);
2902 #else
2903         const size_t min_protoh = sizeof(struct tcpiphdr);
2904 #endif
2905
2906         /* initialize */
2907 #ifdef INET6
2908         if (isipv6) {
2909                 maxmtu = tcp_maxmtu6(&inp->inp_inc, &mtuflags);
2910                 tp->t_maxopd = tp->t_maxseg = tcp_v6mssdflt;
2911         } else
2912 #endif
2913         {
2914                 maxmtu = tcp_maxmtu(&inp->inp_inc, &mtuflags);
2915                 tp->t_maxopd = tp->t_maxseg = tcp_mssdflt;
2916         }
2917         so = inp->inp_socket;
2918
2919         /*
2920          * no route to sender, stay with default mss and return
2921          */
2922         if (maxmtu == 0)
2923                 return;
2924
2925         /* what have we got? */
2926         switch (offer) {
2927                 case 0:
2928                         /*
2929                          * Offer == 0 means that there was no MSS on the SYN
2930                          * segment, in this case we use tcp_mssdflt.
2931                          */
2932                         offer =
2933 #ifdef INET6
2934                                 isipv6 ? tcp_v6mssdflt :
2935 #endif
2936                                 tcp_mssdflt;
2937                         break;
2938
2939                 case -1:
2940                         /*
2941                          * Offer == -1 means that we didn't receive SYN yet.
2942                          */
2943                         /* FALLTHROUGH */
2944
2945                 default:
2946                         /*
2947                          * Prevent DoS attack with too small MSS. Round up
2948                          * to at least minmss.
2949                          */
2950                         offer = max(offer, tcp_minmss);
2951                         /*
2952                          * Sanity check: make sure that maxopd will be large
2953                          * enough to allow some data on segments even if the
2954                          * all the option space is used (40bytes).  Otherwise
2955                          * funny things may happen in tcp_output.
2956                          */
2957                         offer = max(offer, 64);
2958         }
2959
2960         /*
2961          * rmx information is now retrieved from tcp_hostcache
2962          */
2963         tcp_hc_get(&inp->inp_inc, &metrics);
2964
2965         /*
2966          * if there's a discovered mtu int tcp hostcache, use it
2967          * else, use the link mtu.
2968          */
2969         if (metrics.rmx_mtu)
2970                 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
2971         else {
2972 #ifdef INET6
2973                 if (isipv6) {
2974                         mss = maxmtu - min_protoh;
2975                         if (!path_mtu_discovery &&
2976                             !in6_localaddr(&inp->in6p_faddr))
2977                                 mss = min(mss, tcp_v6mssdflt);
2978                 } else
2979 #endif
2980                 {
2981                         mss = maxmtu - min_protoh;
2982                         if (!path_mtu_discovery &&
2983                             !in_localaddr(inp->inp_faddr))
2984                                 mss = min(mss, tcp_mssdflt);
2985                 }
2986         }
2987         mss = min(mss, offer);
2988
2989         /*
2990          * maxopd stores the maximum length of data AND options
2991          * in a segment; maxseg is the amount of data in a normal
2992          * segment.  We need to store this value (maxopd) apart
2993          * from maxseg, because now every segment carries options
2994          * and thus we normally have somewhat less data in segments.
2995          */
2996         tp->t_maxopd = mss;
2997
2998         /*
2999          * origoffer==-1 indicates, that no segments were received yet.
3000          * In this case we just guess.
3001          */
3002         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
3003             (origoffer == -1 ||
3004              (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
3005                 mss -= TCPOLEN_TSTAMP_APPA;
3006         tp->t_maxseg = mss;
3007
3008 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
3009                 if (mss > MCLBYTES)
3010                         mss &= ~(MCLBYTES-1);
3011 #else
3012                 if (mss > MCLBYTES)
3013                         mss = mss / MCLBYTES * MCLBYTES;
3014 #endif
3015         tp->t_maxseg = mss;
3016
3017         /*
3018          * If there's a pipesize, change the socket buffer to that size,
3019          * don't change if sb_hiwat is different than default (then it
3020          * has been changed on purpose with setsockopt).
3021          * Make the socket buffers an integral number of mss units;
3022          * if the mss is larger than the socket buffer, decrease the mss.
3023          */
3024         SOCKBUF_LOCK(&so->so_snd);
3025         if ((so->so_snd.sb_hiwat == tcp_sendspace) && metrics.rmx_sendpipe)
3026                 bufsize = metrics.rmx_sendpipe;
3027         else
3028                 bufsize = so->so_snd.sb_hiwat;
3029         if (bufsize < mss)
3030                 mss = bufsize;
3031         else {
3032                 bufsize = roundup(bufsize, mss);
3033                 if (bufsize > sb_max)
3034                         bufsize = sb_max;
3035                 if (bufsize > so->so_snd.sb_hiwat)
3036                         (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3037         }
3038         SOCKBUF_UNLOCK(&so->so_snd);
3039         tp->t_maxseg = mss;
3040
3041         SOCKBUF_LOCK(&so->so_rcv);
3042         if ((so->so_rcv.sb_hiwat == tcp_recvspace) && metrics.rmx_recvpipe)
3043                 bufsize = metrics.rmx_recvpipe;
3044         else
3045                 bufsize = so->so_rcv.sb_hiwat;
3046         if (bufsize > mss) {
3047                 bufsize = roundup(bufsize, mss);
3048                 if (bufsize > sb_max)
3049                         bufsize = sb_max;
3050                 if (bufsize > so->so_rcv.sb_hiwat)
3051                         (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3052         }
3053         SOCKBUF_UNLOCK(&so->so_rcv);
3054         /*
3055          * While we're here, check the others too
3056          */
3057         if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
3058                 tp->t_srtt = rtt;
3059                 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
3060                 tcpstat.tcps_usedrtt++;
3061                 if (metrics.rmx_rttvar) {
3062                         tp->t_rttvar = metrics.rmx_rttvar;
3063                         tcpstat.tcps_usedrttvar++;
3064                 } else {
3065                         /* default variation is +- 1 rtt */
3066                         tp->t_rttvar =
3067                             tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
3068                 }
3069                 TCPT_RANGESET(tp->t_rxtcur,
3070                               ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
3071                               tp->t_rttmin, TCPTV_REXMTMAX);
3072         }
3073         if (metrics.rmx_ssthresh) {
3074                 /*
3075                  * There's some sort of gateway or interface
3076                  * buffer limit on the path.  Use this to set
3077                  * the slow start threshhold, but set the
3078                  * threshold to no less than 2*mss.
3079                  */
3080                 tp->snd_ssthresh = max(2 * mss, metrics.rmx_ssthresh);
3081                 tcpstat.tcps_usedssthresh++;
3082         }
3083         if (metrics.rmx_bandwidth)
3084                 tp->snd_bandwidth = metrics.rmx_bandwidth;
3085
3086         /*
3087          * Set the slow-start flight size depending on whether this
3088          * is a local network or not.
3089          *
3090          * Extend this so we cache the cwnd too and retrieve it here.
3091          * Make cwnd even bigger than RFC3390 suggests but only if we
3092          * have previous experience with the remote host. Be careful
3093          * not make cwnd bigger than remote receive window or our own
3094          * send socket buffer. Maybe put some additional upper bound
3095          * on the retrieved cwnd. Should do incremental updates to
3096          * hostcache when cwnd collapses so next connection doesn't
3097          * overloads the path again.
3098          *
3099          * RFC3390 says only do this if SYN or SYN/ACK didn't got lost.
3100          * We currently check only in syncache_socket for that.
3101          */
3102 #define TCP_METRICS_CWND
3103 #ifdef TCP_METRICS_CWND
3104         if (metrics.rmx_cwnd)
3105                 tp->snd_cwnd = max(mss,
3106                                 min(metrics.rmx_cwnd / 2,
3107                                  min(tp->snd_wnd, so->so_snd.sb_hiwat)));
3108         else
3109 #endif
3110         if (tcp_do_rfc3390)
3111                 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
3112 #ifdef INET6
3113         else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
3114                  (!isipv6 && in_localaddr(inp->inp_faddr)))
3115 #else
3116         else if (in_localaddr(inp->inp_faddr))
3117 #endif
3118                 tp->snd_cwnd = mss * ss_fltsz_local;
3119         else
3120                 tp->snd_cwnd = mss * ss_fltsz;
3121
3122         /* Check the interface for TSO capabilities. */
3123         if (mtuflags & CSUM_TSO)
3124                 tp->t_flags |= TF_TSO;
3125 }
3126
3127 /*
3128  * Determine the MSS option to send on an outgoing SYN.
3129  */
3130 int
3131 tcp_mssopt(struct in_conninfo *inc)
3132 {
3133         int mss = 0;
3134         u_long maxmtu = 0;
3135         u_long thcmtu = 0;
3136         size_t min_protoh;
3137 #ifdef INET6
3138         int isipv6 = inc->inc_isipv6 ? 1 : 0;
3139 #endif
3140
3141         KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3142
3143 #ifdef INET6
3144         if (isipv6) {
3145                 mss = tcp_v6mssdflt;
3146                 maxmtu = tcp_maxmtu6(inc, NULL);
3147                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3148                 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3149         } else
3150 #endif
3151         {
3152                 mss = tcp_mssdflt;
3153                 maxmtu = tcp_maxmtu(inc, NULL);
3154                 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3155                 min_protoh = sizeof(struct tcpiphdr);
3156         }
3157         if (maxmtu && thcmtu)
3158                 mss = min(maxmtu, thcmtu) - min_protoh;
3159         else if (maxmtu || thcmtu)
3160                 mss = max(maxmtu, thcmtu) - min_protoh;
3161
3162         return (mss);
3163 }
3164
3165
3166 /*
3167  * On a partial ack arrives, force the retransmission of the
3168  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3169  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3170  * be started again.
3171  */
3172 static void
3173 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3174 {
3175         tcp_seq onxt = tp->snd_nxt;
3176         u_long  ocwnd = tp->snd_cwnd;
3177
3178         tcp_timer_activate(tp, TT_REXMT, 0);
3179         tp->t_rtttime = 0;
3180         tp->snd_nxt = th->th_ack;
3181         /*
3182          * Set snd_cwnd to one segment beyond acknowledged offset.
3183          * (tp->snd_una has not yet been updated when this function is called.)
3184          */
3185         tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
3186         tp->t_flags |= TF_ACKNOW;
3187         (void) tcp_output(tp);
3188         tp->snd_cwnd = ocwnd;
3189         if (SEQ_GT(onxt, tp->snd_nxt))
3190                 tp->snd_nxt = onxt;
3191         /*
3192          * Partial window deflation.  Relies on fact that tp->snd_una
3193          * not updated yet.
3194          */
3195         if (tp->snd_cwnd > th->th_ack - tp->snd_una)
3196                 tp->snd_cwnd -= th->th_ack - tp->snd_una;
3197         else
3198                 tp->snd_cwnd = 0;
3199         tp->snd_cwnd += tp->t_maxseg;
3200 }
3201
3202 /*
3203  * Returns 1 if the TIME_WAIT state was killed and we should start over,
3204  * looking for a pcb in the listen state.  Returns 0 otherwise.
3205  */
3206 static int
3207 tcp_timewait(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th,
3208     struct mbuf *m, int tlen)
3209 {
3210         struct tcptw *tw;
3211         int thflags;
3212         tcp_seq seq;
3213 #ifdef INET6
3214         int isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
3215 #else
3216         const int isipv6 = 0;
3217 #endif
3218
3219         /* tcbinfo lock required for tcp_twclose(), tcp_timer_2msl_reset(). */
3220         INP_INFO_WLOCK_ASSERT(&tcbinfo);
3221         INP_LOCK_ASSERT(inp);
3222
3223         /*
3224          * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
3225          * still present.  This is undesirable, but temporarily necessary
3226          * until we work out how to handle inpcb's who's timewait state has
3227          * been removed.
3228          */
3229         tw = intotw(inp);
3230         if (tw == NULL)
3231                 goto drop;
3232
3233         thflags = th->th_flags;
3234
3235         /*
3236          * NOTE: for FIN_WAIT_2 (to be added later),
3237          * must validate sequence number before accepting RST
3238          */
3239
3240         /*
3241          * If the segment contains RST:
3242          *      Drop the segment - see Stevens, vol. 2, p. 964 and
3243          *      RFC 1337.
3244          */
3245         if (thflags & TH_RST)
3246                 goto drop;
3247
3248 #if 0
3249 /* PAWS not needed at the moment */
3250         /*
3251          * RFC 1323 PAWS: If we have a timestamp reply on this segment
3252          * and it's less than ts_recent, drop it.
3253          */
3254         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
3255             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
3256                 if ((thflags & TH_ACK) == 0)
3257                         goto drop;
3258                 goto ack;
3259         }
3260         /*
3261          * ts_recent is never updated because we never accept new segments.
3262          */
3263 #endif
3264
3265         /*
3266          * If a new connection request is received
3267          * while in TIME_WAIT, drop the old connection
3268          * and start over if the sequence numbers
3269          * are above the previous ones.
3270          */
3271         if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
3272                 tcp_twclose(tw, 0);
3273                 return (1);
3274         }
3275
3276         /*
3277          * Drop the the segment if it does not contain an ACK.
3278          */
3279         if ((thflags & TH_ACK) == 0)
3280                 goto drop;
3281
3282         /*
3283          * Reset the 2MSL timer if this is a duplicate FIN.
3284          */
3285         if (thflags & TH_FIN) {
3286                 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
3287                 if (seq + 1 == tw->rcv_nxt)
3288                         tcp_timer_2msl_reset(tw, 1);
3289         }
3290
3291         /*
3292          * Acknowledge the segment if it has data or is not a duplicate ACK.
3293          */
3294         if (thflags != TH_ACK || tlen != 0 ||
3295             th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
3296                 tcp_twrespond(tw, TH_ACK);
3297         goto drop;
3298
3299         /*
3300          * Generate a RST, dropping incoming segment.
3301          * Make ACK acceptable to originator of segment.
3302          * Don't bother to respond if destination was broadcast/multicast.
3303          */
3304         if (m->m_flags & (M_BCAST|M_MCAST))
3305                 goto drop;
3306         if (isipv6) {
3307                 struct ip6_hdr *ip6;
3308
3309                 /* IPv6 anycast check is done at tcp6_input() */
3310                 ip6 = mtod(m, struct ip6_hdr *);
3311                 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3312                     IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3313                         goto drop;
3314         } else {
3315                 struct ip *ip;
3316
3317                 ip = mtod(m, struct ip *);
3318                 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3319                     IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3320                     ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3321                     in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3322                         goto drop;
3323         }
3324         if (thflags & TH_ACK) {
3325                 tcp_respond(NULL,
3326                     mtod(m, void *), th, m, 0, th->th_ack, TH_RST);
3327         } else {
3328                 seq = th->th_seq + (thflags & TH_SYN ? 1 : 0);
3329                 tcp_respond(NULL,
3330                     mtod(m, void *), th, m, seq, 0, TH_RST|TH_ACK);
3331         }
3332         INP_UNLOCK(inp);
3333         return (0);
3334
3335 drop:
3336         INP_UNLOCK(inp);
3337         m_freem(m);
3338         return (0);
3339 }