sys/netinet/tcp_timewait.c

   1 /*-
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 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_subr.c  8.2 (Berkeley) 5/24/95
  30  */
  31
  32 #include <sys/cdefs.h>
  33 __FBSDID("$FreeBSD$");
  34
  35 #include "opt_inet.h"
  36 #include "opt_inet6.h"
  37 #include "opt_tcpdebug.h"
  38
  39 #include <sys/param.h>
  40 #include <sys/systm.h>
  41 #include <sys/callout.h>
  42 #include <sys/kernel.h>
  43 #include <sys/sysctl.h>
  44 #include <sys/malloc.h>
  45 #include <sys/mbuf.h>
  46 #include <sys/priv.h>
  47 #include <sys/proc.h>
  48 #include <sys/socket.h>
  49 #include <sys/socketvar.h>
  50 #include <sys/protosw.h>
  51 #include <sys/random.h>
  52
  53 #include <vm/uma.h>
  54
  55 #include <net/route.h>
  56 #include <net/if.h>
  57 #include <net/if_var.h>
  58 #include <net/vnet.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>
  66 #include <netinet/ip_var.h>
  67 #ifdef INET6
  68 #include <netinet/ip6.h>
  69 #include <netinet6/in6_pcb.h>
  70 #include <netinet6/ip6_var.h>
  71 #include <netinet6/scope6_var.h>
  72 #include <netinet6/nd6.h>
  73 #endif
  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 #ifdef INET6
  80 #include <netinet6/tcp6_var.h>
  81 #endif
  82 #include <netinet/tcpip.h>
  83 #ifdef TCPDEBUG
  84 #include <netinet/tcp_debug.h>
  85 #endif
  86 #ifdef INET6
  87 #include <netinet6/ip6protosw.h>
  88 #endif
  89
  90 #include <machine/in_cksum.h>
  91
  92 #include <security/mac/mac_framework.h>
  93
  94 static VNET_DEFINE(uma_zone_t, tcptw_zone);
  95 #define V_tcptw_zone            VNET(tcptw_zone)
  96 static int      maxtcptw;
  97
  98 /*
  99  * The timed wait queue contains references to each of the TCP sessions
 100  * currently in the TIME_WAIT state.  The queue pointers, including the
 101  * queue pointers in each tcptw structure, are protected using the global
 102  * timewait lock, which must be held over queue iteration and modification.
 103  *
 104  * Rules on tcptw usage:
 105  *  - a inpcb is always freed _after_ its tcptw
 106  *  - a tcptw relies on its inpcb reference counting for memory stability
 107  *  - a tcptw is dereferenceable only while its inpcb is locked
 108  */
 109 static VNET_DEFINE(TAILQ_HEAD(, tcptw), twq_2msl);
 110 #define V_twq_2msl              VNET(twq_2msl)
 111
 112 /* Global timewait lock */
 113 static VNET_DEFINE(struct rwlock, tw_lock);
 114 #define V_tw_lock               VNET(tw_lock)
 115
 116 #define TW_LOCK_INIT(tw, d)     rw_init_flags(&(tw), (d), 0)
 117 #define TW_LOCK_DESTROY(tw)     rw_destroy(&(tw))
 118 #define TW_RLOCK(tw)            rw_rlock(&(tw))
 119 #define TW_WLOCK(tw)            rw_wlock(&(tw))
 120 #define TW_RUNLOCK(tw)          rw_runlock(&(tw))
 121 #define TW_WUNLOCK(tw)          rw_wunlock(&(tw))
 122 #define TW_LOCK_ASSERT(tw)      rw_assert(&(tw), RA_LOCKED)
 123 #define TW_RLOCK_ASSERT(tw)     rw_assert(&(tw), RA_RLOCKED)
 124 #define TW_WLOCK_ASSERT(tw)     rw_assert(&(tw), RA_WLOCKED)
 125 #define TW_UNLOCK_ASSERT(tw)    rw_assert(&(tw), RA_UNLOCKED)
 126
 127 static void     tcp_tw_2msl_reset(struct tcptw *, int);
 128 static void     tcp_tw_2msl_stop(struct tcptw *, int);
 129 static int      tcp_twrespond(struct tcptw *, int);
 130
 131 static int
 132 tcptw_auto_size(void)
 133 {
 134         int halfrange;
 135
 136         /*
 137          * Max out at half the ephemeral port range so that TIME_WAIT
 138          * sockets don't tie up too many ephemeral ports.
 139          */
 140         if (V_ipport_lastauto > V_ipport_firstauto)
 141                 halfrange = (V_ipport_lastauto - V_ipport_firstauto) / 2;
 142         else
 143                 halfrange = (V_ipport_firstauto - V_ipport_lastauto) / 2;
 144         /* Protect against goofy port ranges smaller than 32. */
 145         return (imin(imax(halfrange, 32), maxsockets / 5));
 146 }
 147
 148 static int
 149 sysctl_maxtcptw(SYSCTL_HANDLER_ARGS)
 150 {
 151         int error, new;
 152
 153         if (maxtcptw == 0)
 154                 new = tcptw_auto_size();
 155         else
 156                 new = maxtcptw;
 157         error = sysctl_handle_int(oidp, &new, 0, req);
 158         if (error == 0 && req->newptr)
 159                 if (new >= 32) {
 160                         maxtcptw = new;
 161                         uma_zone_set_max(V_tcptw_zone, maxtcptw);
 162                 }
 163         return (error);
 164 }
 165
 166 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxtcptw, CTLTYPE_INT|CTLFLAG_RW,
 167     &maxtcptw, 0, sysctl_maxtcptw, "IU",
 168     "Maximum number of compressed TCP TIME_WAIT entries");
 169
 170 VNET_DEFINE(int, nolocaltimewait) = 0;
 171 #define V_nolocaltimewait       VNET(nolocaltimewait)
 172 SYSCTL_INT(_net_inet_tcp, OID_AUTO, nolocaltimewait, CTLFLAG_VNET | CTLFLAG_RW,
 173     &VNET_NAME(nolocaltimewait), 0,
 174     "Do not create compressed TCP TIME_WAIT entries for local connections");
 175
 176 void
 177 tcp_tw_zone_change(void)
 178 {
 179
 180         if (maxtcptw == 0)
 181                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
 182 }
 183
 184 void
 185 tcp_tw_init(void)
 186 {
 187
 188         V_tcptw_zone = uma_zcreate("tcptw", sizeof(struct tcptw),
 189             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
 190         TUNABLE_INT_FETCH("net.inet.tcp.maxtcptw", &maxtcptw);
 191         if (maxtcptw == 0)
 192                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
 193         else
 194                 uma_zone_set_max(V_tcptw_zone, maxtcptw);
 195         TAILQ_INIT(&V_twq_2msl);
 196         TW_LOCK_INIT(V_tw_lock, "tcptw");
 197 }
 198
 199 #ifdef VIMAGE
 200 void
 201 tcp_tw_destroy(void)
 202 {
 203         struct tcptw *tw;
 204
 205         INP_INFO_WLOCK(&V_tcbinfo);
 206         while ((tw = TAILQ_FIRST(&V_twq_2msl)) != NULL)
 207                 tcp_twclose(tw, 0);
 208         INP_INFO_WUNLOCK(&V_tcbinfo);
 209
 210         TW_LOCK_DESTROY(V_tw_lock);
 211         uma_zdestroy(V_tcptw_zone);
 212 }
 213 #endif
 214
 215 /*
 216  * Move a TCP connection into TIME_WAIT state.
 217  *    tcbinfo is locked.
 218  *    inp is locked, and is unlocked before returning.
 219  */
 220 void
 221 tcp_twstart(struct tcpcb *tp)
 222 {
 223         struct tcptw *tw;
 224         struct inpcb *inp = tp->t_inpcb;
 225         int acknow;
 226         struct socket *so;
 227 #ifdef INET6
 228         int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
 229 #endif
 230
 231         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 232         INP_WLOCK_ASSERT(inp);
 233
 234         if (V_nolocaltimewait) {
 235                 int error = 0;
 236 #ifdef INET6
 237                 if (isipv6)
 238                         error = in6_localaddr(&inp->in6p_faddr);
 239 #endif
 240 #if defined(INET6) && defined(INET)
 241                 else
 242 #endif
 243 #ifdef INET
 244                         error = in_localip(inp->inp_faddr);
 245 #endif
 246                 if (error) {
 247                         tp = tcp_close(tp);
 248                         if (tp != NULL)
 249                                 INP_WUNLOCK(inp);
 250                         return;
 251                 }
 252         }
 253
 254         tw = uma_zalloc(V_tcptw_zone, M_NOWAIT);
 255         if (tw == NULL) {
 256                 /*
 257                  * Reached limit on total number of TIMEWAIT connections
 258                  * allowed. Remove a connection from TIMEWAIT queue in LRU
 259                  * fashion to make room for this connection.
 260                  *
 261                  * pcbinfo lock is needed here to prevent deadlock as
 262                  * two inpcb locks can be acquired simultaneously.
 263                  */
 264                 tw = tcp_tw_2msl_scan(1);
 265                 if (tw == NULL) {
 266                         tp = tcp_close(tp);
 267                         if (tp != NULL)
 268                                 INP_WUNLOCK(inp);
 269                         return;
 270                 }
 271         }
 272         /*
 273          * The tcptw will hold a reference on its inpcb until tcp_twclose
 274          * is called
 275          */
 276         tw->tw_inpcb = inp;
 277         in_pcbref(inp); /* Reference from tw */
 278
 279         /*
 280          * Recover last window size sent.
 281          */
 282         if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
 283                 tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale;
 284         else
 285                 tw->last_win = 0;
 286
 287         /*
 288          * Set t_recent if timestamps are used on the connection.
 289          */
 290         if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) ==
 291             (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
 292                 tw->t_recent = tp->ts_recent;
 293                 tw->ts_offset = tp->ts_offset;
 294         } else {
 295                 tw->t_recent = 0;
 296                 tw->ts_offset = 0;
 297         }
 298
 299         tw->snd_nxt = tp->snd_nxt;
 300         tw->rcv_nxt = tp->rcv_nxt;
 301         tw->iss     = tp->iss;
 302         tw->irs     = tp->irs;
 303         tw->t_starttime = tp->t_starttime;
 304         tw->tw_time = 0;
 305
 306 /* XXX
 307  * If this code will
 308  * be used for fin-wait-2 state also, then we may need
 309  * a ts_recent from the last segment.
 310  */
 311         acknow = tp->t_flags & TF_ACKNOW;
 312
 313         /*
 314          * First, discard tcpcb state, which includes stopping its timers and
 315          * freeing it.  tcp_discardcb() used to also release the inpcb, but
 316          * that work is now done in the caller.
 317          *
 318          * Note: soisdisconnected() call used to be made in tcp_discardcb(),
 319          * and might not be needed here any longer.
 320          */
 321         tcp_discardcb(tp);
 322         so = inp->inp_socket;
 323         soisdisconnected(so);
 324         tw->tw_cred = crhold(so->so_cred);
 325         SOCK_LOCK(so);
 326         tw->tw_so_options = so->so_options;
 327         SOCK_UNLOCK(so);
 328         if (acknow)
 329                 tcp_twrespond(tw, TH_ACK);
 330         inp->inp_ppcb = tw;
 331         inp->inp_flags |= INP_TIMEWAIT;
 332         tcp_tw_2msl_reset(tw, 0);
 333
 334         /*
 335          * If the inpcb owns the sole reference to the socket, then we can
 336          * detach and free the socket as it is not needed in time wait.
 337          */
 338         if (inp->inp_flags & INP_SOCKREF) {
 339                 KASSERT(so->so_state & SS_PROTOREF,
 340                     ("tcp_twstart: !SS_PROTOREF"));
 341                 inp->inp_flags &= ~INP_SOCKREF;
 342                 INP_WUNLOCK(inp);
 343                 ACCEPT_LOCK();
 344                 SOCK_LOCK(so);
 345                 so->so_state &= ~SS_PROTOREF;
 346                 sofree(so);
 347         } else
 348                 INP_WUNLOCK(inp);
 349 }
 350
 351 /*
 352  * Returns 1 if the TIME_WAIT state was killed and we should start over,
 353  * looking for a pcb in the listen state.  Returns 0 otherwise.
 354  */
 355 int
 356 tcp_twcheck(struct inpcb *inp, struct tcpopt *to __unused, struct tcphdr *th,
 357     struct mbuf *m, int tlen)
 358 {
 359         struct tcptw *tw;
 360         int thflags;
 361         tcp_seq seq;
 362
 363         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 364         INP_WLOCK_ASSERT(inp);
 365
 366         /*
 367          * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
 368          * still present.  This is undesirable, but temporarily necessary
 369          * until we work out how to handle inpcb's who's timewait state has
 370          * been removed.
 371          */
 372         tw = intotw(inp);
 373         if (tw == NULL)
 374                 goto drop;
 375
 376         thflags = th->th_flags;
 377
 378         /*
 379          * NOTE: for FIN_WAIT_2 (to be added later),
 380          * must validate sequence number before accepting RST
 381          */
 382
 383         /*
 384          * If the segment contains RST:
 385          *      Drop the segment - see Stevens, vol. 2, p. 964 and
 386          *      RFC 1337.
 387          */
 388         if (thflags & TH_RST)
 389                 goto drop;
 390
 391 #if 0
 392 /* PAWS not needed at the moment */
 393         /*
 394          * RFC 1323 PAWS: If we have a timestamp reply on this segment
 395          * and it's less than ts_recent, drop it.
 396          */
 397         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
 398             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
 399                 if ((thflags & TH_ACK) == 0)
 400                         goto drop;
 401                 goto ack;
 402         }
 403         /*
 404          * ts_recent is never updated because we never accept new segments.
 405          */
 406 #endif
 407
 408         /*
 409          * If a new connection request is received
 410          * while in TIME_WAIT, drop the old connection
 411          * and start over if the sequence numbers
 412          * are above the previous ones.
 413          */
 414         if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
 415                 tcp_twclose(tw, 0);
 416                 return (1);
 417         }
 418
 419         /*
 420          * Drop the segment if it does not contain an ACK.
 421          */
 422         if ((thflags & TH_ACK) == 0)
 423                 goto drop;
 424
 425         /*
 426          * Reset the 2MSL timer if this is a duplicate FIN.
 427          */
 428         if (thflags & TH_FIN) {
 429                 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
 430                 if (seq + 1 == tw->rcv_nxt)
 431                         tcp_tw_2msl_reset(tw, 1);
 432         }
 433
 434         /*
 435          * Acknowledge the segment if it has data or is not a duplicate ACK.
 436          */
 437         if (thflags != TH_ACK || tlen != 0 ||
 438             th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
 439                 tcp_twrespond(tw, TH_ACK);
 440 drop:
 441         INP_WUNLOCK(inp);
 442         m_freem(m);
 443         return (0);
 444 }
 445
 446 void
 447 tcp_twclose(struct tcptw *tw, int reuse)
 448 {
 449         struct socket *so;
 450         struct inpcb *inp;
 451
 452         /*
 453          * At this point, we are in one of two situations:
 454          *
 455          * (1) We have no socket, just an inpcb<->twtcp pair.  We can free
 456          *     all state.
 457          *
 458          * (2) We have a socket -- if we own a reference, release it and
 459          *     notify the socket layer.
 460          */
 461         inp = tw->tw_inpcb;
 462         KASSERT((inp->inp_flags & INP_TIMEWAIT), ("tcp_twclose: !timewait"));
 463         KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw"));
 464         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);      /* in_pcbfree() */
 465         INP_WLOCK_ASSERT(inp);
 466
 467         tcp_tw_2msl_stop(tw, reuse);
 468         inp->inp_ppcb = NULL;
 469         in_pcbdrop(inp);
 470
 471         so = inp->inp_socket;
 472         if (so != NULL) {
 473                 /*
 474                  * If there's a socket, handle two cases: first, we own a
 475                  * strong reference, which we will now release, or we don't
 476                  * in which case another reference exists (XXXRW: think
 477                  * about this more), and we don't need to take action.
 478                  */
 479                 if (inp->inp_flags & INP_SOCKREF) {
 480                         inp->inp_flags &= ~INP_SOCKREF;
 481                         INP_WUNLOCK(inp);
 482                         ACCEPT_LOCK();
 483                         SOCK_LOCK(so);
 484                         KASSERT(so->so_state & SS_PROTOREF,
 485                             ("tcp_twclose: INP_SOCKREF && !SS_PROTOREF"));
 486                         so->so_state &= ~SS_PROTOREF;
 487                         sofree(so);
 488                 } else {
 489                         /*
 490                          * If we don't own the only reference, the socket and
 491                          * inpcb need to be left around to be handled by
 492                          * tcp_usr_detach() later.
 493                          */
 494                         INP_WUNLOCK(inp);
 495                 }
 496         } else {
 497                 /*
 498                  * The socket has been already cleaned-up for us, only free the
 499                  * inpcb.
 500                  */
 501                 in_pcbfree(inp);
 502         }
 503         TCPSTAT_INC(tcps_closed);
 504 }
 505
 506 static int
 507 tcp_twrespond(struct tcptw *tw, int flags)
 508 {
 509         struct inpcb *inp = tw->tw_inpcb;
 510 #if defined(INET6) || defined(INET)
 511         struct tcphdr *th = NULL;
 512 #endif
 513         struct mbuf *m;
 514 #ifdef INET
 515         struct ip *ip = NULL;
 516 #endif
 517         u_int hdrlen, optlen;
 518         int error = 0;                  /* Keep compiler happy */
 519         struct tcpopt to;
 520 #ifdef INET6
 521         struct ip6_hdr *ip6 = NULL;
 522         int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
 523 #endif
 524         hdrlen = 0;                     /* Keep compiler happy */
 525
 526         INP_WLOCK_ASSERT(inp);
 527
 528         m = m_gethdr(M_NOWAIT, MT_DATA);
 529         if (m == NULL)
 530                 return (ENOBUFS);
 531         m->m_data += max_linkhdr;
 532
 533 #ifdef MAC
 534         mac_inpcb_create_mbuf(inp, m);
 535 #endif
 536
 537 #ifdef INET6
 538         if (isipv6) {
 539                 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
 540                 ip6 = mtod(m, struct ip6_hdr *);
 541                 th = (struct tcphdr *)(ip6 + 1);
 542                 tcpip_fillheaders(inp, ip6, th);
 543         }
 544 #endif
 545 #if defined(INET6) && defined(INET)
 546         else
 547 #endif
 548 #ifdef INET
 549         {
 550                 hdrlen = sizeof(struct tcpiphdr);
 551                 ip = mtod(m, struct ip *);
 552                 th = (struct tcphdr *)(ip + 1);
 553                 tcpip_fillheaders(inp, ip, th);
 554         }
 555 #endif
 556         to.to_flags = 0;
 557
 558         /*
 559          * Send a timestamp and echo-reply if both our side and our peer
 560          * have sent timestamps in our SYN's and this is not a RST.
 561          */
 562         if (tw->t_recent && flags == TH_ACK) {
 563                 to.to_flags |= TOF_TS;
 564                 to.to_tsval = tcp_ts_getticks() + tw->ts_offset;
 565                 to.to_tsecr = tw->t_recent;
 566         }
 567         optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 568
 569         m->m_len = hdrlen + optlen;
 570         m->m_pkthdr.len = m->m_len;
 571
 572         KASSERT(max_linkhdr + m->m_len <= MHLEN, ("tcptw: mbuf too small"));
 573
 574         th->th_seq = htonl(tw->snd_nxt);
 575         th->th_ack = htonl(tw->rcv_nxt);
 576         th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 577         th->th_flags = flags;
 578         th->th_win = htons(tw->last_win);
 579
 580         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 581 #ifdef INET6
 582         if (isipv6) {
 583                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 584                 th->th_sum = in6_cksum_pseudo(ip6,
 585                     sizeof(struct tcphdr) + optlen, IPPROTO_TCP, 0);
 586                 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
 587                 error = ip6_output(m, inp->in6p_outputopts, NULL,
 588                     (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp);
 589         }
 590 #endif
 591 #if defined(INET6) && defined(INET)
 592         else
 593 #endif
 594 #ifdef INET
 595         {
 596                 m->m_pkthdr.csum_flags = CSUM_TCP;
 597                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 598                     htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP));
 599                 ip->ip_len = htons(m->m_pkthdr.len);
 600                 if (V_path_mtu_discovery)
 601                         ip->ip_off |= htons(IP_DF);
 602                 error = ip_output(m, inp->inp_options, NULL,
 603                     ((tw->tw_so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
 604                     NULL, inp);
 605         }
 606 #endif
 607         if (flags & TH_ACK)
 608                 TCPSTAT_INC(tcps_sndacks);
 609         else
 610                 TCPSTAT_INC(tcps_sndctrl);
 611         TCPSTAT_INC(tcps_sndtotal);
 612         return (error);
 613 }
 614
 615 static void
 616 tcp_tw_2msl_reset(struct tcptw *tw, int rearm)
 617 {
 618
 619         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 620         INP_WLOCK_ASSERT(tw->tw_inpcb);
 621
 622         TW_WLOCK(V_tw_lock);
 623         if (rearm)
 624                 TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
 625         tw->tw_time = ticks + 2 * tcp_msl;
 626         TAILQ_INSERT_TAIL(&V_twq_2msl, tw, tw_2msl);
 627         TW_WUNLOCK(V_tw_lock);
 628 }
 629
 630 static void
 631 tcp_tw_2msl_stop(struct tcptw *tw, int reuse)
 632 {
 633         struct ucred *cred;
 634         struct inpcb *inp;
 635         int released;
 636
 637         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 638
 639         TW_WLOCK(V_tw_lock);
 640         inp = tw->tw_inpcb;
 641         tw->tw_inpcb = NULL;
 642
 643         TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
 644         cred = tw->tw_cred;
 645         tw->tw_cred = NULL;
 646         TW_WUNLOCK(V_tw_lock);
 647
 648         if (cred != NULL)
 649                 crfree(cred);
 650
 651         released = in_pcbrele_wlocked(inp);
 652         KASSERT(!released, ("%s: inp should not be released here", __func__));
 653
 654         if (!reuse)
 655                 uma_zfree(V_tcptw_zone, tw);
 656 }
 657
 658 struct tcptw *
 659 tcp_tw_2msl_scan(int reuse)
 660 {
 661         struct tcptw *tw;
 662         struct inpcb *inp;
 663
 664 #ifdef INVARIANTS
 665         if (reuse) {
 666                 /*
 667                  * pcbinfo lock is needed in reuse case to prevent deadlock
 668                  * as two inpcb locks can be acquired simultaneously:
 669                  *  - the inpcb transitioning to TIME_WAIT state in
 670                  *    tcp_tw_start(),
 671                  *  - the inpcb closed by tcp_twclose().
 672                  */
 673                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 674         }
 675 #endif
 676
 677         for (;;) {
 678                 TW_RLOCK(V_tw_lock);
 679                 tw = TAILQ_FIRST(&V_twq_2msl);
 680                 if (tw == NULL || (!reuse && (tw->tw_time - ticks) > 0)) {
 681                         TW_RUNLOCK(V_tw_lock);
 682                         break;
 683                 }
 684                 KASSERT(tw->tw_inpcb != NULL, ("%s: tw->tw_inpcb == NULL",
 685                     __func__));
 686
 687                 inp = tw->tw_inpcb;
 688                 in_pcbref(inp);
 689                 TW_RUNLOCK(V_tw_lock);
 690
 691                 if (INP_INFO_TRY_WLOCK(&V_tcbinfo)) {
 692
 693                         INP_WLOCK(inp);
 694                         tw = intotw(inp);
 695                         if (in_pcbrele_wlocked(inp)) {
 696                                 KASSERT(tw == NULL, ("%s: held last inp "
 697                                     "reference but tw not NULL", __func__));
 698                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 699                                 continue;
 700                         }
 701
 702                         if (tw == NULL) {
 703                                 /* tcp_twclose() has already been called */
 704                                 INP_WUNLOCK(inp);
 705                                 INP_INFO_WUNLOCK(&V_tcbinfo);
 706                                 continue;
 707                         }
 708
 709                         tcp_twclose(tw, reuse);
 710                         INP_INFO_WUNLOCK(&V_tcbinfo);
 711                         if (reuse)
 712                             return tw;
 713                 } else {
 714                         /* INP_INFO lock is busy, continue later. */
 715                         INP_WLOCK(inp);
 716                         if (!in_pcbrele_wlocked(inp))
 717                                 INP_WUNLOCK(inp);
 718                         break;
 719                 }
 720         }
 721
 722         return NULL;
 723 }