The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_timewait.c

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    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: releng/10.3/sys/netinet/tcp_timewait.c 282826 2015-05-13 00:28:36Z gnn $");
   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/vnet.h>
   58 
   59 #include <netinet/in.h>
   60 #include <netinet/in_pcb.h>
   61 #include <netinet/in_systm.h>
   62 #include <netinet/in_var.h>
   63 #include <netinet/ip.h>
   64 #include <netinet/ip_icmp.h>
   65 #include <netinet/ip_var.h>
   66 #ifdef INET6
   67 #include <netinet/ip6.h>
   68 #include <netinet6/in6_pcb.h>
   69 #include <netinet6/ip6_var.h>
   70 #include <netinet6/scope6_var.h>
   71 #include <netinet6/nd6.h>
   72 #endif
   73 #include <netinet/tcp.h>
   74 #include <netinet/tcp_fsm.h>
   75 #include <netinet/tcp_seq.h>
   76 #include <netinet/tcp_timer.h>
   77 #include <netinet/tcp_var.h>
   78 #ifdef INET6
   79 #include <netinet6/tcp6_var.h>
   80 #endif
   81 #include <netinet/tcpip.h>
   82 #ifdef TCPDEBUG
   83 #include <netinet/tcp_debug.h>
   84 #endif
   85 #ifdef INET6
   86 #include <netinet6/ip6protosw.h>
   87 #endif
   88 
   89 #include <machine/in_cksum.h>
   90 
   91 #include <security/mac/mac_framework.h>
   92 
   93 static VNET_DEFINE(uma_zone_t, tcptw_zone);
   94 #define V_tcptw_zone            VNET(tcptw_zone)
   95 static int      maxtcptw;
   96 
   97 /*
   98  * The timed wait queue contains references to each of the TCP sessions
   99  * currently in the TIME_WAIT state.  The queue pointers, including the
  100  * queue pointers in each tcptw structure, are protected using the global
  101  * timewait lock, which must be held over queue iteration and modification.
  102  *
  103  * Rules on tcptw usage:
  104  *  - a inpcb is always freed _after_ its tcptw
  105  *  - a tcptw relies on its inpcb reference counting for memory stability
  106  *  - a tcptw is dereferenceable only while its inpcb is locked
  107  */
  108 static VNET_DEFINE(TAILQ_HEAD(, tcptw), twq_2msl);
  109 #define V_twq_2msl              VNET(twq_2msl)
  110 
  111 /* Global timewait lock */
  112 static VNET_DEFINE(struct rwlock, tw_lock);
  113 #define V_tw_lock               VNET(tw_lock)
  114 
  115 #define TW_LOCK_INIT(tw, d)     rw_init_flags(&(tw), (d), 0)
  116 #define TW_LOCK_DESTROY(tw)     rw_destroy(&(tw))
  117 #define TW_RLOCK(tw)            rw_rlock(&(tw))
  118 #define TW_WLOCK(tw)            rw_wlock(&(tw))
  119 #define TW_RUNLOCK(tw)          rw_runlock(&(tw))
  120 #define TW_WUNLOCK(tw)          rw_wunlock(&(tw))
  121 #define TW_LOCK_ASSERT(tw)      rw_assert(&(tw), RA_LOCKED)
  122 #define TW_RLOCK_ASSERT(tw)     rw_assert(&(tw), RA_RLOCKED)
  123 #define TW_WLOCK_ASSERT(tw)     rw_assert(&(tw), RA_WLOCKED)
  124 #define TW_UNLOCK_ASSERT(tw)    rw_assert(&(tw), RA_UNLOCKED)
  125 
  126 static void     tcp_tw_2msl_reset(struct tcptw *, int);
  127 static void     tcp_tw_2msl_stop(struct tcptw *, int);
  128 static int      tcp_twrespond(struct tcptw *, int);
  129 
  130 static int
  131 tcptw_auto_size(void)
  132 {
  133         int halfrange;
  134 
  135         /*
  136          * Max out at half the ephemeral port range so that TIME_WAIT
  137          * sockets don't tie up too many ephemeral ports.
  138          */
  139         if (V_ipport_lastauto > V_ipport_firstauto)
  140                 halfrange = (V_ipport_lastauto - V_ipport_firstauto) / 2;
  141         else
  142                 halfrange = (V_ipport_firstauto - V_ipport_lastauto) / 2;
  143         /* Protect against goofy port ranges smaller than 32. */
  144         return (imin(imax(halfrange, 32), maxsockets / 5));
  145 }
  146 
  147 static int
  148 sysctl_maxtcptw(SYSCTL_HANDLER_ARGS)
  149 {
  150         int error, new;
  151 
  152         if (maxtcptw == 0)
  153                 new = tcptw_auto_size();
  154         else
  155                 new = maxtcptw;
  156         error = sysctl_handle_int(oidp, &new, 0, req);
  157         if (error == 0 && req->newptr)
  158                 if (new >= 32) {
  159                         maxtcptw = new;
  160                         uma_zone_set_max(V_tcptw_zone, maxtcptw);
  161                 }
  162         return (error);
  163 }
  164 
  165 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxtcptw, CTLTYPE_INT|CTLFLAG_RW,
  166     &maxtcptw, 0, sysctl_maxtcptw, "IU",
  167     "Maximum number of compressed TCP TIME_WAIT entries");
  168 
  169 VNET_DEFINE(int, nolocaltimewait) = 0;
  170 #define V_nolocaltimewait       VNET(nolocaltimewait)
  171 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, nolocaltimewait, CTLFLAG_RW,
  172     &VNET_NAME(nolocaltimewait), 0,
  173     "Do not create compressed TCP TIME_WAIT entries for local connections");
  174 
  175 void
  176 tcp_tw_zone_change(void)
  177 {
  178 
  179         if (maxtcptw == 0)
  180                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
  181 }
  182 
  183 void
  184 tcp_tw_init(void)
  185 {
  186 
  187         V_tcptw_zone = uma_zcreate("tcptw", sizeof(struct tcptw),
  188             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
  189         TUNABLE_INT_FETCH("net.inet.tcp.maxtcptw", &maxtcptw);
  190         if (maxtcptw == 0)
  191                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
  192         else
  193                 uma_zone_set_max(V_tcptw_zone, maxtcptw);
  194         TAILQ_INIT(&V_twq_2msl);
  195         TW_LOCK_INIT(V_tw_lock, "tcptw");
  196 }
  197 
  198 #ifdef VIMAGE
  199 void
  200 tcp_tw_destroy(void)
  201 {
  202         struct tcptw *tw;
  203 
  204         INP_INFO_WLOCK(&V_tcbinfo);
  205         while ((tw = TAILQ_FIRST(&V_twq_2msl)) != NULL)
  206                 tcp_twclose(tw, 0);
  207         INP_INFO_WUNLOCK(&V_tcbinfo);
  208 
  209         TW_LOCK_DESTROY(V_tw_lock);
  210         uma_zdestroy(V_tcptw_zone);
  211 }
  212 #endif
  213 
  214 /*
  215  * Move a TCP connection into TIME_WAIT state.
  216  *    tcbinfo is locked.
  217  *    inp is locked, and is unlocked before returning.
  218  */
  219 void
  220 tcp_twstart(struct tcpcb *tp)
  221 {
  222         struct tcptw *tw;
  223         struct inpcb *inp = tp->t_inpcb;
  224         int acknow;
  225         struct socket *so;
  226 #ifdef INET6
  227         int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
  228 #endif
  229 
  230         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  231         INP_WLOCK_ASSERT(inp);
  232 
  233         if (V_nolocaltimewait) {
  234                 int error = 0;
  235 #ifdef INET6
  236                 if (isipv6)
  237                         error = in6_localaddr(&inp->in6p_faddr);
  238 #endif
  239 #if defined(INET6) && defined(INET)
  240                 else
  241 #endif
  242 #ifdef INET
  243                         error = in_localip(inp->inp_faddr);
  244 #endif
  245                 if (error) {
  246                         tp = tcp_close(tp);
  247                         if (tp != NULL)
  248                                 INP_WUNLOCK(inp);
  249                         return;
  250                 }
  251         }
  252 
  253 
  254         /*
  255          * For use only by DTrace.  We do not reference the state
  256          * after this point so modifying it in place is not a problem.
  257          */
  258         tcp_state_change(tp, TCPS_TIME_WAIT);
  259 
  260         tw = uma_zalloc(V_tcptw_zone, M_NOWAIT);
  261         if (tw == NULL) {
  262                 /*
  263                  * Reached limit on total number of TIMEWAIT connections
  264                  * allowed. Remove a connection from TIMEWAIT queue in LRU
  265                  * fashion to make room for this connection.
  266                  *
  267                  * pcbinfo lock is needed here to prevent deadlock as
  268                  * two inpcb locks can be acquired simultaneously.
  269                  */
  270                 tw = tcp_tw_2msl_scan(1);
  271                 if (tw == NULL) {
  272                         tp = tcp_close(tp);
  273                         if (tp != NULL)
  274                                 INP_WUNLOCK(inp);
  275                         return;
  276                 }
  277         }
  278         /*
  279          * The tcptw will hold a reference on its inpcb until tcp_twclose
  280          * is called
  281          */
  282         tw->tw_inpcb = inp;
  283         in_pcbref(inp); /* Reference from tw */
  284 
  285         /*
  286          * Recover last window size sent.
  287          */
  288         if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
  289                 tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale;
  290         else
  291                 tw->last_win = 0;
  292 
  293         /*
  294          * Set t_recent if timestamps are used on the connection.
  295          */
  296         if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) ==
  297             (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
  298                 tw->t_recent = tp->ts_recent;
  299                 tw->ts_offset = tp->ts_offset;
  300         } else {
  301                 tw->t_recent = 0;
  302                 tw->ts_offset = 0;
  303         }
  304 
  305         tw->snd_nxt = tp->snd_nxt;
  306         tw->rcv_nxt = tp->rcv_nxt;
  307         tw->iss     = tp->iss;
  308         tw->irs     = tp->irs;
  309         tw->t_starttime = tp->t_starttime;
  310         tw->tw_time = 0;
  311 
  312 /* XXX
  313  * If this code will
  314  * be used for fin-wait-2 state also, then we may need
  315  * a ts_recent from the last segment.
  316  */
  317         acknow = tp->t_flags & TF_ACKNOW;
  318 
  319         /*
  320          * First, discard tcpcb state, which includes stopping its timers and
  321          * freeing it.  tcp_discardcb() used to also release the inpcb, but
  322          * that work is now done in the caller.
  323          *
  324          * Note: soisdisconnected() call used to be made in tcp_discardcb(),
  325          * and might not be needed here any longer.
  326          */
  327         tcp_discardcb(tp);
  328         so = inp->inp_socket;
  329         soisdisconnected(so);
  330         tw->tw_cred = crhold(so->so_cred);
  331         SOCK_LOCK(so);
  332         tw->tw_so_options = so->so_options;
  333         SOCK_UNLOCK(so);
  334         if (acknow)
  335                 tcp_twrespond(tw, TH_ACK);
  336         inp->inp_ppcb = tw;
  337         inp->inp_flags |= INP_TIMEWAIT;
  338         tcp_tw_2msl_reset(tw, 0);
  339 
  340         /*
  341          * If the inpcb owns the sole reference to the socket, then we can
  342          * detach and free the socket as it is not needed in time wait.
  343          */
  344         if (inp->inp_flags & INP_SOCKREF) {
  345                 KASSERT(so->so_state & SS_PROTOREF,
  346                     ("tcp_twstart: !SS_PROTOREF"));
  347                 inp->inp_flags &= ~INP_SOCKREF;
  348                 INP_WUNLOCK(inp);
  349                 ACCEPT_LOCK();
  350                 SOCK_LOCK(so);
  351                 so->so_state &= ~SS_PROTOREF;
  352                 sofree(so);
  353         } else
  354                 INP_WUNLOCK(inp);
  355 }
  356 
  357 #if 0
  358 /*
  359  * The appromixate rate of ISN increase of Microsoft TCP stacks;
  360  * the actual rate is slightly higher due to the addition of
  361  * random positive increments.
  362  *
  363  * Most other new OSes use semi-randomized ISN values, so we
  364  * do not need to worry about them.
  365  */
  366 #define MS_ISN_BYTES_PER_SECOND         250000
  367 
  368 /*
  369  * Determine if the ISN we will generate has advanced beyond the last
  370  * sequence number used by the previous connection.  If so, indicate
  371  * that it is safe to recycle this tw socket by returning 1.
  372  */
  373 int
  374 tcp_twrecycleable(struct tcptw *tw)
  375 {
  376         tcp_seq new_iss = tw->iss;
  377         tcp_seq new_irs = tw->irs;
  378 
  379         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  380         new_iss += (ticks - tw->t_starttime) * (ISN_BYTES_PER_SECOND / hz);
  381         new_irs += (ticks - tw->t_starttime) * (MS_ISN_BYTES_PER_SECOND / hz);
  382 
  383         if (SEQ_GT(new_iss, tw->snd_nxt) && SEQ_GT(new_irs, tw->rcv_nxt))
  384                 return (1);
  385         else
  386                 return (0);
  387 }
  388 #endif
  389 
  390 /*
  391  * Returns 1 if the TIME_WAIT state was killed and we should start over,
  392  * looking for a pcb in the listen state.  Returns 0 otherwise.
  393  */
  394 int
  395 tcp_twcheck(struct inpcb *inp, struct tcpopt *to __unused, struct tcphdr *th,
  396     struct mbuf *m, int tlen)
  397 {
  398         struct tcptw *tw;
  399         int thflags;
  400         tcp_seq seq;
  401 
  402         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  403         INP_WLOCK_ASSERT(inp);
  404 
  405         /*
  406          * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
  407          * still present.  This is undesirable, but temporarily necessary
  408          * until we work out how to handle inpcb's who's timewait state has
  409          * been removed.
  410          */
  411         tw = intotw(inp);
  412         if (tw == NULL)
  413                 goto drop;
  414 
  415         thflags = th->th_flags;
  416 
  417         /*
  418          * NOTE: for FIN_WAIT_2 (to be added later),
  419          * must validate sequence number before accepting RST
  420          */
  421 
  422         /*
  423          * If the segment contains RST:
  424          *      Drop the segment - see Stevens, vol. 2, p. 964 and
  425          *      RFC 1337.
  426          */
  427         if (thflags & TH_RST)
  428                 goto drop;
  429 
  430 #if 0
  431 /* PAWS not needed at the moment */
  432         /*
  433          * RFC 1323 PAWS: If we have a timestamp reply on this segment
  434          * and it's less than ts_recent, drop it.
  435          */
  436         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
  437             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
  438                 if ((thflags & TH_ACK) == 0)
  439                         goto drop;
  440                 goto ack;
  441         }
  442         /*
  443          * ts_recent is never updated because we never accept new segments.
  444          */
  445 #endif
  446 
  447         /*
  448          * If a new connection request is received
  449          * while in TIME_WAIT, drop the old connection
  450          * and start over if the sequence numbers
  451          * are above the previous ones.
  452          */
  453         if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
  454                 tcp_twclose(tw, 0);
  455                 return (1);
  456         }
  457 
  458         /*
  459          * Drop the segment if it does not contain an ACK.
  460          */
  461         if ((thflags & TH_ACK) == 0)
  462                 goto drop;
  463 
  464         /*
  465          * Reset the 2MSL timer if this is a duplicate FIN.
  466          */
  467         if (thflags & TH_FIN) {
  468                 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
  469                 if (seq + 1 == tw->rcv_nxt)
  470                         tcp_tw_2msl_reset(tw, 1);
  471         }
  472 
  473         /*
  474          * Acknowledge the segment if it has data or is not a duplicate ACK.
  475          */
  476         if (thflags != TH_ACK || tlen != 0 ||
  477             th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
  478                 tcp_twrespond(tw, TH_ACK);
  479 drop:
  480         INP_WUNLOCK(inp);
  481         m_freem(m);
  482         return (0);
  483 }
  484 
  485 void
  486 tcp_twclose(struct tcptw *tw, int reuse)
  487 {
  488         struct socket *so;
  489         struct inpcb *inp;
  490 
  491         /*
  492          * At this point, we are in one of two situations:
  493          *
  494          * (1) We have no socket, just an inpcb<->twtcp pair.  We can free
  495          *     all state.
  496          *
  497          * (2) We have a socket -- if we own a reference, release it and
  498          *     notify the socket layer.
  499          */
  500         inp = tw->tw_inpcb;
  501         KASSERT((inp->inp_flags & INP_TIMEWAIT), ("tcp_twclose: !timewait"));
  502         KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw"));
  503         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);      /* in_pcbfree() */
  504         INP_WLOCK_ASSERT(inp);
  505 
  506         tcp_tw_2msl_stop(tw, reuse);
  507         inp->inp_ppcb = NULL;
  508         in_pcbdrop(inp);
  509 
  510         so = inp->inp_socket;
  511         if (so != NULL) {
  512                 /*
  513                  * If there's a socket, handle two cases: first, we own a
  514                  * strong reference, which we will now release, or we don't
  515                  * in which case another reference exists (XXXRW: think
  516                  * about this more), and we don't need to take action.
  517                  */
  518                 if (inp->inp_flags & INP_SOCKREF) {
  519                         inp->inp_flags &= ~INP_SOCKREF;
  520                         INP_WUNLOCK(inp);
  521                         ACCEPT_LOCK();
  522                         SOCK_LOCK(so);
  523                         KASSERT(so->so_state & SS_PROTOREF,
  524                             ("tcp_twclose: INP_SOCKREF && !SS_PROTOREF"));
  525                         so->so_state &= ~SS_PROTOREF;
  526                         sofree(so);
  527                 } else {
  528                         /*
  529                          * If we don't own the only reference, the socket and
  530                          * inpcb need to be left around to be handled by
  531                          * tcp_usr_detach() later.
  532                          */
  533                         INP_WUNLOCK(inp);
  534                 }
  535         } else {
  536                 /*
  537                  * The socket has been already cleaned-up for us, only free the
  538                  * inpcb.
  539                  */
  540                 in_pcbfree(inp);
  541         }
  542         TCPSTAT_INC(tcps_closed);
  543 }
  544 
  545 static int
  546 tcp_twrespond(struct tcptw *tw, int flags)
  547 {
  548         struct inpcb *inp = tw->tw_inpcb;
  549 #if defined(INET6) || defined(INET)
  550         struct tcphdr *th = NULL;
  551 #endif
  552         struct mbuf *m;
  553 #ifdef INET
  554         struct ip *ip = NULL;
  555 #endif
  556         u_int hdrlen, optlen;
  557         int error = 0;                  /* Keep compiler happy */
  558         struct tcpopt to;
  559 #ifdef INET6
  560         struct ip6_hdr *ip6 = NULL;
  561         int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
  562 #endif
  563         hdrlen = 0;                     /* Keep compiler happy */
  564 
  565         INP_WLOCK_ASSERT(inp);
  566 
  567         m = m_gethdr(M_NOWAIT, MT_DATA);
  568         if (m == NULL)
  569                 return (ENOBUFS);
  570         m->m_data += max_linkhdr;
  571 
  572 #ifdef MAC
  573         mac_inpcb_create_mbuf(inp, m);
  574 #endif
  575 
  576 #ifdef INET6
  577         if (isipv6) {
  578                 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
  579                 ip6 = mtod(m, struct ip6_hdr *);
  580                 th = (struct tcphdr *)(ip6 + 1);
  581                 tcpip_fillheaders(inp, ip6, th);
  582         }
  583 #endif
  584 #if defined(INET6) && defined(INET)
  585         else
  586 #endif
  587 #ifdef INET
  588         {
  589                 hdrlen = sizeof(struct tcpiphdr);
  590                 ip = mtod(m, struct ip *);
  591                 th = (struct tcphdr *)(ip + 1);
  592                 tcpip_fillheaders(inp, ip, th);
  593         }
  594 #endif
  595         to.to_flags = 0;
  596 
  597         /*
  598          * Send a timestamp and echo-reply if both our side and our peer
  599          * have sent timestamps in our SYN's and this is not a RST.
  600          */
  601         if (tw->t_recent && flags == TH_ACK) {
  602                 to.to_flags |= TOF_TS;
  603                 to.to_tsval = tcp_ts_getticks() + tw->ts_offset;
  604                 to.to_tsecr = tw->t_recent;
  605         }
  606         optlen = tcp_addoptions(&to, (u_char *)(th + 1));
  607 
  608         m->m_len = hdrlen + optlen;
  609         m->m_pkthdr.len = m->m_len;
  610 
  611         KASSERT(max_linkhdr + m->m_len <= MHLEN, ("tcptw: mbuf too small"));
  612 
  613         th->th_seq = htonl(tw->snd_nxt);
  614         th->th_ack = htonl(tw->rcv_nxt);
  615         th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
  616         th->th_flags = flags;
  617         th->th_win = htons(tw->last_win);
  618 
  619         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
  620 #ifdef INET6
  621         if (isipv6) {
  622                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
  623                 th->th_sum = in6_cksum_pseudo(ip6,
  624                     sizeof(struct tcphdr) + optlen, IPPROTO_TCP, 0);
  625                 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
  626                 error = ip6_output(m, inp->in6p_outputopts, NULL,
  627                     (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp);
  628         }
  629 #endif
  630 #if defined(INET6) && defined(INET)
  631         else
  632 #endif
  633 #ifdef INET
  634         {
  635                 m->m_pkthdr.csum_flags = CSUM_TCP;
  636                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
  637                     htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP));
  638                 ip->ip_len = htons(m->m_pkthdr.len);
  639                 if (V_path_mtu_discovery)
  640                         ip->ip_off |= htons(IP_DF);
  641                 error = ip_output(m, inp->inp_options, NULL,
  642                     ((tw->tw_so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
  643                     NULL, inp);
  644         }
  645 #endif
  646         if (flags & TH_ACK)
  647                 TCPSTAT_INC(tcps_sndacks);
  648         else
  649                 TCPSTAT_INC(tcps_sndctrl);
  650         TCPSTAT_INC(tcps_sndtotal);
  651         return (error);
  652 }
  653 
  654 static void
  655 tcp_tw_2msl_reset(struct tcptw *tw, int rearm)
  656 {
  657 
  658         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  659         INP_WLOCK_ASSERT(tw->tw_inpcb);
  660 
  661         TW_WLOCK(V_tw_lock);
  662         if (rearm)
  663                 TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
  664         tw->tw_time = ticks + 2 * tcp_msl;
  665         TAILQ_INSERT_TAIL(&V_twq_2msl, tw, tw_2msl);
  666         TW_WUNLOCK(V_tw_lock);
  667 }
  668 
  669 static void
  670 tcp_tw_2msl_stop(struct tcptw *tw, int reuse)
  671 {
  672         struct ucred *cred;
  673         struct inpcb *inp;
  674         int released;
  675 
  676         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  677 
  678         TW_WLOCK(V_tw_lock);
  679         inp = tw->tw_inpcb;
  680         tw->tw_inpcb = NULL;
  681 
  682         TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
  683         cred = tw->tw_cred;
  684         tw->tw_cred = NULL;
  685         TW_WUNLOCK(V_tw_lock);
  686 
  687         if (cred != NULL)
  688                 crfree(cred);
  689 
  690         released = in_pcbrele_wlocked(inp);
  691         KASSERT(!released, ("%s: inp should not be released here", __func__));
  692 
  693         if (!reuse)
  694                 uma_zfree(V_tcptw_zone, tw);
  695 }
  696 
  697 struct tcptw *
  698 tcp_tw_2msl_scan(int reuse)
  699 {
  700         struct tcptw *tw;
  701         struct inpcb *inp;
  702 
  703 #ifdef INVARIANTS
  704         if (reuse) {
  705                 /*
  706                  * pcbinfo lock is needed in reuse case to prevent deadlock
  707                  * as two inpcb locks can be acquired simultaneously:
  708                  *  - the inpcb transitioning to TIME_WAIT state in
  709                  *    tcp_tw_start(),
  710                  *  - the inpcb closed by tcp_twclose().
  711                  */
  712                 INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  713         }
  714 #endif
  715 
  716         for (;;) {
  717                 TW_RLOCK(V_tw_lock);
  718                 tw = TAILQ_FIRST(&V_twq_2msl);
  719                 if (tw == NULL || (!reuse && (tw->tw_time - ticks) > 0)) {
  720                         TW_RUNLOCK(V_tw_lock);
  721                         break;
  722                 }
  723                 KASSERT(tw->tw_inpcb != NULL, ("%s: tw->tw_inpcb == NULL",
  724                     __func__));
  725 
  726                 inp = tw->tw_inpcb;
  727                 in_pcbref(inp);
  728                 TW_RUNLOCK(V_tw_lock);
  729 
  730                 if (INP_INFO_TRY_WLOCK(&V_tcbinfo)) {
  731 
  732                         INP_WLOCK(inp);
  733                         tw = intotw(inp);
  734                         if (in_pcbrele_wlocked(inp)) {
  735                                 KASSERT(tw == NULL, ("%s: held last inp "
  736                                     "reference but tw not NULL", __func__));
  737                                 INP_INFO_WUNLOCK(&V_tcbinfo);
  738                                 continue;
  739                         }
  740 
  741                         if (tw == NULL) {
  742                                 /* tcp_twclose() has already been called */
  743                                 INP_WUNLOCK(inp);
  744                                 INP_INFO_WUNLOCK(&V_tcbinfo);
  745                                 continue;
  746                         }
  747 
  748                         tcp_twclose(tw, reuse);
  749                         INP_INFO_WUNLOCK(&V_tcbinfo);
  750                         if (reuse)
  751                             return tw;
  752                 } else {
  753                         /* INP_INFO lock is busy, continue later. */
  754                         INP_WLOCK(inp);
  755                         if (!in_pcbrele_wlocked(inp))
  756                                 INP_WUNLOCK(inp);
  757                         break;
  758                 }
  759         }
  760 
  761         return NULL;
  762 }

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