The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_reass.c

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    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  */
   31 
   32 #include <sys/cdefs.h>
   33 __FBSDID("$FreeBSD: releng/9.0/sys/netinet/tcp_reass.c 228059 2011-11-28 11:14:32Z lstewart $");
   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/kernel.h>
   41 #include <sys/malloc.h>
   42 #include <sys/mbuf.h>
   43 #include <sys/socket.h>
   44 #include <sys/socketvar.h>
   45 #include <sys/sysctl.h>
   46 #include <sys/syslog.h>
   47 #include <sys/systm.h>
   48 
   49 #include <vm/uma.h>
   50 
   51 #include <net/if.h>
   52 #include <net/route.h>
   53 #include <net/vnet.h>
   54 
   55 #include <netinet/in.h>
   56 #include <netinet/in_pcb.h>
   57 #include <netinet/in_systm.h>
   58 #include <netinet/in_var.h>
   59 #include <netinet/ip.h>
   60 #include <netinet/ip_var.h>
   61 #include <netinet/ip_options.h>
   62 #include <netinet/ip6.h>
   63 #include <netinet6/in6_pcb.h>
   64 #include <netinet6/ip6_var.h>
   65 #include <netinet6/nd6.h>
   66 #include <netinet/tcp.h>
   67 #include <netinet/tcp_fsm.h>
   68 #include <netinet/tcp_seq.h>
   69 #include <netinet/tcp_timer.h>
   70 #include <netinet/tcp_var.h>
   71 #include <netinet6/tcp6_var.h>
   72 #include <netinet/tcpip.h>
   73 #ifdef TCPDEBUG
   74 #include <netinet/tcp_debug.h>
   75 #endif /* TCPDEBUG */
   76 
   77 static int tcp_reass_sysctl_maxseg(SYSCTL_HANDLER_ARGS);
   78 static int tcp_reass_sysctl_qsize(SYSCTL_HANDLER_ARGS);
   79 
   80 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
   81     "TCP Segment Reassembly Queue");
   82 
   83 static VNET_DEFINE(int, tcp_reass_maxseg) = 0;
   84 #define V_tcp_reass_maxseg              VNET(tcp_reass_maxseg)
   85 SYSCTL_VNET_PROC(_net_inet_tcp_reass, OID_AUTO, maxsegments,
   86     CTLTYPE_INT | CTLFLAG_RDTUN,
   87     &VNET_NAME(tcp_reass_maxseg), 0, &tcp_reass_sysctl_maxseg, "I",
   88     "Global maximum number of TCP Segments in Reassembly Queue");
   89 
   90 static VNET_DEFINE(int, tcp_reass_qsize) = 0;
   91 #define V_tcp_reass_qsize               VNET(tcp_reass_qsize)
   92 SYSCTL_VNET_PROC(_net_inet_tcp_reass, OID_AUTO, cursegments,
   93     CTLTYPE_INT | CTLFLAG_RD,
   94     &VNET_NAME(tcp_reass_qsize), 0, &tcp_reass_sysctl_qsize, "I",
   95     "Global number of TCP Segments currently in Reassembly Queue");
   96 
   97 static VNET_DEFINE(int, tcp_reass_overflows) = 0;
   98 #define V_tcp_reass_overflows           VNET(tcp_reass_overflows)
   99 SYSCTL_VNET_INT(_net_inet_tcp_reass, OID_AUTO, overflows,
  100     CTLTYPE_INT | CTLFLAG_RD,
  101     &VNET_NAME(tcp_reass_overflows), 0,
  102     "Global number of TCP Segment Reassembly Queue Overflows");
  103 
  104 static VNET_DEFINE(uma_zone_t, tcp_reass_zone);
  105 #define V_tcp_reass_zone                VNET(tcp_reass_zone)
  106 
  107 /* Initialize TCP reassembly queue */
  108 static void
  109 tcp_reass_zone_change(void *tag)
  110 {
  111 
  112         V_tcp_reass_maxseg = nmbclusters / 16;
  113         uma_zone_set_max(V_tcp_reass_zone, V_tcp_reass_maxseg);
  114 }
  115 
  116 void
  117 tcp_reass_init(void)
  118 {
  119 
  120         V_tcp_reass_maxseg = nmbclusters / 16;
  121         TUNABLE_INT_FETCH("net.inet.tcp.reass.maxsegments",
  122             &V_tcp_reass_maxseg);
  123         V_tcp_reass_zone = uma_zcreate("tcpreass", sizeof (struct tseg_qent),
  124             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
  125         uma_zone_set_max(V_tcp_reass_zone, V_tcp_reass_maxseg);
  126         EVENTHANDLER_REGISTER(nmbclusters_change,
  127             tcp_reass_zone_change, NULL, EVENTHANDLER_PRI_ANY);
  128 }
  129 
  130 #ifdef VIMAGE
  131 void
  132 tcp_reass_destroy(void)
  133 {
  134 
  135         uma_zdestroy(V_tcp_reass_zone);
  136 }
  137 #endif
  138 
  139 void
  140 tcp_reass_flush(struct tcpcb *tp)
  141 {
  142         struct tseg_qent *qe;
  143 
  144         INP_WLOCK_ASSERT(tp->t_inpcb);
  145 
  146         while ((qe = LIST_FIRST(&tp->t_segq)) != NULL) {
  147                 LIST_REMOVE(qe, tqe_q);
  148                 m_freem(qe->tqe_m);
  149                 uma_zfree(V_tcp_reass_zone, qe);
  150                 tp->t_segqlen--;
  151         }
  152 
  153         KASSERT((tp->t_segqlen == 0),
  154             ("TCP reass queue %p segment count is %d instead of 0 after flush.",
  155             tp, tp->t_segqlen));
  156 }
  157 
  158 static int
  159 tcp_reass_sysctl_maxseg(SYSCTL_HANDLER_ARGS)
  160 {
  161         V_tcp_reass_maxseg = uma_zone_get_max(V_tcp_reass_zone);
  162         return (sysctl_handle_int(oidp, arg1, arg2, req));
  163 }
  164 
  165 static int
  166 tcp_reass_sysctl_qsize(SYSCTL_HANDLER_ARGS)
  167 {
  168         V_tcp_reass_qsize = uma_zone_get_cur(V_tcp_reass_zone);
  169         return (sysctl_handle_int(oidp, arg1, arg2, req));
  170 }
  171 
  172 int
  173 tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
  174 {
  175         struct tseg_qent *q;
  176         struct tseg_qent *p = NULL;
  177         struct tseg_qent *nq;
  178         struct tseg_qent *te = NULL;
  179         struct socket *so = tp->t_inpcb->inp_socket;
  180         char *s = NULL;
  181         int flags;
  182         struct tseg_qent tqs;
  183 
  184         INP_WLOCK_ASSERT(tp->t_inpcb);
  185 
  186         /*
  187          * XXX: tcp_reass() is rather inefficient with its data structures
  188          * and should be rewritten (see NetBSD for optimizations).
  189          */
  190 
  191         /*
  192          * Call with th==NULL after become established to
  193          * force pre-ESTABLISHED data up to user socket.
  194          */
  195         if (th == NULL)
  196                 goto present;
  197 
  198         /*
  199          * Limit the number of segments that can be queued to reduce the
  200          * potential for mbuf exhaustion. For best performance, we want to be
  201          * able to queue a full window's worth of segments. The size of the
  202          * socket receive buffer determines our advertised window and grows
  203          * automatically when socket buffer autotuning is enabled. Use it as the
  204          * basis for our queue limit.
  205          * Always let the missing segment through which caused this queue.
  206          * NB: Access to the socket buffer is left intentionally unlocked as we
  207          * can tolerate stale information here.
  208          *
  209          * XXXLAS: Using sbspace(so->so_rcv) instead of so->so_rcv.sb_hiwat
  210          * should work but causes packets to be dropped when they shouldn't.
  211          * Investigate why and re-evaluate the below limit after the behaviour
  212          * is understood.
  213          */
  214         if (th->th_seq != tp->rcv_nxt &&
  215             tp->t_segqlen >= (so->so_rcv.sb_hiwat / tp->t_maxseg) + 1) {
  216                 V_tcp_reass_overflows++;
  217                 TCPSTAT_INC(tcps_rcvmemdrop);
  218                 m_freem(m);
  219                 *tlenp = 0;
  220                 if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
  221                         log(LOG_DEBUG, "%s; %s: queue limit reached, "
  222                             "segment dropped\n", s, __func__);
  223                         free(s, M_TCPLOG);
  224                 }
  225                 return (0);
  226         }
  227 
  228         /*
  229          * Allocate a new queue entry. If we can't, or hit the zone limit
  230          * just drop the pkt.
  231          *
  232          * Use a temporary structure on the stack for the missing segment
  233          * when the zone is exhausted. Otherwise we may get stuck.
  234          */
  235         te = uma_zalloc(V_tcp_reass_zone, M_NOWAIT);
  236         if (te == NULL) {
  237                 if (th->th_seq != tp->rcv_nxt) {
  238                         TCPSTAT_INC(tcps_rcvmemdrop);
  239                         m_freem(m);
  240                         *tlenp = 0;
  241                         if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
  242                             NULL))) {
  243                                 log(LOG_DEBUG, "%s; %s: global zone limit "
  244                                     "reached, segment dropped\n", s, __func__);
  245                                 free(s, M_TCPLOG);
  246                         }
  247                         return (0);
  248                 } else {
  249                         bzero(&tqs, sizeof(struct tseg_qent));
  250                         te = &tqs;
  251                         if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
  252                             NULL))) {
  253                                 log(LOG_DEBUG,
  254                                     "%s; %s: global zone limit reached, using "
  255                                     "stack for missing segment\n", s, __func__);
  256                                 free(s, M_TCPLOG);
  257                         }
  258                 }
  259         }
  260         tp->t_segqlen++;
  261 
  262         /*
  263          * Find a segment which begins after this one does.
  264          */
  265         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
  266                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
  267                         break;
  268                 p = q;
  269         }
  270 
  271         /*
  272          * If there is a preceding segment, it may provide some of
  273          * our data already.  If so, drop the data from the incoming
  274          * segment.  If it provides all of our data, drop us.
  275          */
  276         if (p != NULL) {
  277                 int i;
  278                 /* conversion to int (in i) handles seq wraparound */
  279                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
  280                 if (i > 0) {
  281                         if (i >= *tlenp) {
  282                                 TCPSTAT_INC(tcps_rcvduppack);
  283                                 TCPSTAT_ADD(tcps_rcvdupbyte, *tlenp);
  284                                 m_freem(m);
  285                                 uma_zfree(V_tcp_reass_zone, te);
  286                                 tp->t_segqlen--;
  287                                 /*
  288                                  * Try to present any queued data
  289                                  * at the left window edge to the user.
  290                                  * This is needed after the 3-WHS
  291                                  * completes.
  292                                  */
  293                                 goto present;   /* ??? */
  294                         }
  295                         m_adj(m, i);
  296                         *tlenp -= i;
  297                         th->th_seq += i;
  298                 }
  299         }
  300         tp->t_rcvoopack++;
  301         TCPSTAT_INC(tcps_rcvoopack);
  302         TCPSTAT_ADD(tcps_rcvoobyte, *tlenp);
  303 
  304         /*
  305          * While we overlap succeeding segments trim them or,
  306          * if they are completely covered, dequeue them.
  307          */
  308         while (q) {
  309                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
  310                 if (i <= 0)
  311                         break;
  312                 if (i < q->tqe_len) {
  313                         q->tqe_th->th_seq += i;
  314                         q->tqe_len -= i;
  315                         m_adj(q->tqe_m, i);
  316                         break;
  317                 }
  318 
  319                 nq = LIST_NEXT(q, tqe_q);
  320                 LIST_REMOVE(q, tqe_q);
  321                 m_freem(q->tqe_m);
  322                 uma_zfree(V_tcp_reass_zone, q);
  323                 tp->t_segqlen--;
  324                 q = nq;
  325         }
  326 
  327         /* Insert the new segment queue entry into place. */
  328         te->tqe_m = m;
  329         te->tqe_th = th;
  330         te->tqe_len = *tlenp;
  331 
  332         if (p == NULL) {
  333                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
  334         } else {
  335                 KASSERT(te != &tqs, ("%s: temporary stack based entry not "
  336                     "first element in queue", __func__));
  337                 LIST_INSERT_AFTER(p, te, tqe_q);
  338         }
  339 
  340 present:
  341         /*
  342          * Present data to user, advancing rcv_nxt through
  343          * completed sequence space.
  344          */
  345         if (!TCPS_HAVEESTABLISHED(tp->t_state))
  346                 return (0);
  347         q = LIST_FIRST(&tp->t_segq);
  348         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
  349                 return (0);
  350         SOCKBUF_LOCK(&so->so_rcv);
  351         do {
  352                 tp->rcv_nxt += q->tqe_len;
  353                 flags = q->tqe_th->th_flags & TH_FIN;
  354                 nq = LIST_NEXT(q, tqe_q);
  355                 LIST_REMOVE(q, tqe_q);
  356                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
  357                         m_freem(q->tqe_m);
  358                 else
  359                         sbappendstream_locked(&so->so_rcv, q->tqe_m);
  360                 if (q != &tqs)
  361                         uma_zfree(V_tcp_reass_zone, q);
  362                 tp->t_segqlen--;
  363                 q = nq;
  364         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
  365         ND6_HINT(tp);
  366         sorwakeup_locked(so);
  367         return (flags);
  368 }

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