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

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    1 /*-
    2  * Copyright (c) 2001 McAfee, Inc.
    3  * Copyright (c) 2006 Andre Oppermann, Internet Business Solutions AG
    4  * All rights reserved.
    5  *
    6  * This software was developed for the FreeBSD Project by Jonathan Lemon
    7  * and McAfee Research, the Security Research Division of McAfee, Inc. under
    8  * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
    9  * DARPA CHATS research program.
   10  *
   11  * Redistribution and use in source and binary forms, with or without
   12  * modification, are permitted provided that the following conditions
   13  * are met:
   14  * 1. Redistributions of source code must retain the above copyright
   15  *    notice, this list of conditions and the following disclaimer.
   16  * 2. Redistributions in binary form must reproduce the above copyright
   17  *    notice, this list of conditions and the following disclaimer in the
   18  *    documentation and/or other materials provided with the distribution.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   30  * SUCH DAMAGE.
   31  */
   32 
   33 #include <sys/cdefs.h>
   34 __FBSDID("$FreeBSD: releng/9.2/sys/netinet/tcp_syncache.c 252790 2013-07-05 15:18:54Z andre $");
   35 
   36 #include "opt_inet.h"
   37 #include "opt_inet6.h"
   38 #include "opt_ipsec.h"
   39 #include "opt_pcbgroup.h"
   40 
   41 #include <sys/param.h>
   42 #include <sys/systm.h>
   43 #include <sys/kernel.h>
   44 #include <sys/sysctl.h>
   45 #include <sys/limits.h>
   46 #include <sys/lock.h>
   47 #include <sys/mutex.h>
   48 #include <sys/malloc.h>
   49 #include <sys/mbuf.h>
   50 #include <sys/md5.h>
   51 #include <sys/proc.h>           /* for proc0 declaration */
   52 #include <sys/random.h>
   53 #include <sys/socket.h>
   54 #include <sys/socketvar.h>
   55 #include <sys/syslog.h>
   56 #include <sys/ucred.h>
   57 
   58 #include <vm/uma.h>
   59 
   60 #include <net/if.h>
   61 #include <net/route.h>
   62 #include <net/vnet.h>
   63 
   64 #include <netinet/in.h>
   65 #include <netinet/in_systm.h>
   66 #include <netinet/ip.h>
   67 #include <netinet/in_var.h>
   68 #include <netinet/in_pcb.h>
   69 #include <netinet/ip_var.h>
   70 #include <netinet/ip_options.h>
   71 #ifdef INET6
   72 #include <netinet/ip6.h>
   73 #include <netinet/icmp6.h>
   74 #include <netinet6/nd6.h>
   75 #include <netinet6/ip6_var.h>
   76 #include <netinet6/in6_pcb.h>
   77 #endif
   78 #include <netinet/tcp.h>
   79 #include <netinet/tcp_fsm.h>
   80 #include <netinet/tcp_seq.h>
   81 #include <netinet/tcp_timer.h>
   82 #include <netinet/tcp_var.h>
   83 #include <netinet/tcp_syncache.h>
   84 #ifdef INET6
   85 #include <netinet6/tcp6_var.h>
   86 #endif
   87 #ifdef TCP_OFFLOAD
   88 #include <netinet/toecore.h>
   89 #endif
   90 
   91 #ifdef IPSEC
   92 #include <netipsec/ipsec.h>
   93 #ifdef INET6
   94 #include <netipsec/ipsec6.h>
   95 #endif
   96 #include <netipsec/key.h>
   97 #endif /*IPSEC*/
   98 
   99 #include <machine/in_cksum.h>
  100 
  101 #include <security/mac/mac_framework.h>
  102 
  103 static VNET_DEFINE(int, tcp_syncookies) = 1;
  104 #define V_tcp_syncookies                VNET(tcp_syncookies)
  105 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
  106     &VNET_NAME(tcp_syncookies), 0,
  107     "Use TCP SYN cookies if the syncache overflows");
  108 
  109 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
  110 #define V_tcp_syncookiesonly            VNET(tcp_syncookiesonly)
  111 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
  112     &VNET_NAME(tcp_syncookiesonly), 0,
  113     "Use only TCP SYN cookies");
  114 
  115 #ifdef TCP_OFFLOAD
  116 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
  117 #endif
  118 
  119 static void      syncache_drop(struct syncache *, struct syncache_head *);
  120 static void      syncache_free(struct syncache *);
  121 static void      syncache_insert(struct syncache *, struct syncache_head *);
  122 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
  123 static int       syncache_respond(struct syncache *);
  124 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  125                     struct mbuf *m);
  126 static int       syncache_sysctl_count(SYSCTL_HANDLER_ARGS);
  127 static void      syncache_timeout(struct syncache *sc, struct syncache_head *sch,
  128                     int docallout);
  129 static void      syncache_timer(void *);
  130 static void      syncookie_generate(struct syncache_head *, struct syncache *,
  131                     u_int32_t *);
  132 static struct syncache
  133                 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
  134                     struct syncache *, struct tcpopt *, struct tcphdr *,
  135                     struct socket *);
  136 
  137 /*
  138  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  139  * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
  140  * the odds are that the user has given up attempting to connect by then.
  141  */
  142 #define SYNCACHE_MAXREXMTS              3
  143 
  144 /* Arbitrary values */
  145 #define TCP_SYNCACHE_HASHSIZE           512
  146 #define TCP_SYNCACHE_BUCKETLIMIT        30
  147 
  148 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
  149 #define V_tcp_syncache                  VNET(tcp_syncache)
  150 
  151 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
  152     "TCP SYN cache");
  153 
  154 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
  155     &VNET_NAME(tcp_syncache.bucket_limit), 0,
  156     "Per-bucket hash limit for syncache");
  157 
  158 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
  159     &VNET_NAME(tcp_syncache.cache_limit), 0,
  160     "Overall entry limit for syncache");
  161 
  162 SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD),
  163     NULL, 0, &syncache_sysctl_count, "IU",
  164     "Current number of entries in syncache");
  165 
  166 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
  167     &VNET_NAME(tcp_syncache.hashsize), 0,
  168     "Size of TCP syncache hashtable");
  169 
  170 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
  171     &VNET_NAME(tcp_syncache.rexmt_limit), 0,
  172     "Limit on SYN/ACK retransmissions");
  173 
  174 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
  175 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
  176     CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
  177     "Send reset on socket allocation failure");
  178 
  179 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  180 
  181 #define SYNCACHE_HASH(inc, mask)                                        \
  182         ((V_tcp_syncache.hash_secret ^                                  \
  183           (inc)->inc_faddr.s_addr ^                                     \
  184           ((inc)->inc_faddr.s_addr >> 16) ^                             \
  185           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  186 
  187 #define SYNCACHE_HASH6(inc, mask)                                       \
  188         ((V_tcp_syncache.hash_secret ^                                  \
  189           (inc)->inc6_faddr.s6_addr32[0] ^                              \
  190           (inc)->inc6_faddr.s6_addr32[3] ^                              \
  191           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  192 
  193 #define ENDPTS_EQ(a, b) (                                               \
  194         (a)->ie_fport == (b)->ie_fport &&                               \
  195         (a)->ie_lport == (b)->ie_lport &&                               \
  196         (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr &&                 \
  197         (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr                    \
  198 )
  199 
  200 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
  201 
  202 #define SCH_LOCK(sch)           mtx_lock(&(sch)->sch_mtx)
  203 #define SCH_UNLOCK(sch)         mtx_unlock(&(sch)->sch_mtx)
  204 #define SCH_LOCK_ASSERT(sch)    mtx_assert(&(sch)->sch_mtx, MA_OWNED)
  205 
  206 /*
  207  * Requires the syncache entry to be already removed from the bucket list.
  208  */
  209 static void
  210 syncache_free(struct syncache *sc)
  211 {
  212 
  213         if (sc->sc_ipopts)
  214                 (void) m_free(sc->sc_ipopts);
  215         if (sc->sc_cred)
  216                 crfree(sc->sc_cred);
  217 #ifdef MAC
  218         mac_syncache_destroy(&sc->sc_label);
  219 #endif
  220 
  221         uma_zfree(V_tcp_syncache.zone, sc);
  222 }
  223 
  224 void
  225 syncache_init(void)
  226 {
  227         int i;
  228 
  229         V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  230         V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  231         V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  232         V_tcp_syncache.hash_secret = arc4random();
  233 
  234         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  235             &V_tcp_syncache.hashsize);
  236         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  237             &V_tcp_syncache.bucket_limit);
  238         if (!powerof2(V_tcp_syncache.hashsize) ||
  239             V_tcp_syncache.hashsize == 0) {
  240                 printf("WARNING: syncache hash size is not a power of 2.\n");
  241                 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  242         }
  243         V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
  244 
  245         /* Set limits. */
  246         V_tcp_syncache.cache_limit =
  247             V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
  248         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  249             &V_tcp_syncache.cache_limit);
  250 
  251         /* Allocate the hash table. */
  252         V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
  253             sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
  254 
  255         /* Initialize the hash buckets. */
  256         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  257 #ifdef VIMAGE
  258                 V_tcp_syncache.hashbase[i].sch_vnet = curvnet;
  259 #endif
  260                 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
  261                 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
  262                          NULL, MTX_DEF);
  263                 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
  264                          &V_tcp_syncache.hashbase[i].sch_mtx, 0);
  265                 V_tcp_syncache.hashbase[i].sch_length = 0;
  266         }
  267 
  268         /* Create the syncache entry zone. */
  269         V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  270             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  271         V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
  272             V_tcp_syncache.cache_limit);
  273 }
  274 
  275 #ifdef VIMAGE
  276 void
  277 syncache_destroy(void)
  278 {
  279         struct syncache_head *sch;
  280         struct syncache *sc, *nsc;
  281         int i;
  282 
  283         /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
  284         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  285 
  286                 sch = &V_tcp_syncache.hashbase[i];
  287                 callout_drain(&sch->sch_timer);
  288 
  289                 SCH_LOCK(sch);
  290                 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
  291                         syncache_drop(sc, sch);
  292                 SCH_UNLOCK(sch);
  293                 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
  294                     ("%s: sch->sch_bucket not empty", __func__));
  295                 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
  296                     __func__, sch->sch_length));
  297                 mtx_destroy(&sch->sch_mtx);
  298         }
  299 
  300         KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
  301             ("%s: cache_count not 0", __func__));
  302 
  303         /* Free the allocated global resources. */
  304         uma_zdestroy(V_tcp_syncache.zone);
  305         free(V_tcp_syncache.hashbase, M_SYNCACHE);
  306 }
  307 #endif
  308 
  309 static int
  310 syncache_sysctl_count(SYSCTL_HANDLER_ARGS)
  311 {
  312         int count;
  313 
  314         count = uma_zone_get_cur(V_tcp_syncache.zone);
  315         return (sysctl_handle_int(oidp, &count, 0, req));
  316 }
  317 
  318 /*
  319  * Inserts a syncache entry into the specified bucket row.
  320  * Locks and unlocks the syncache_head autonomously.
  321  */
  322 static void
  323 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  324 {
  325         struct syncache *sc2;
  326 
  327         SCH_LOCK(sch);
  328 
  329         /*
  330          * Make sure that we don't overflow the per-bucket limit.
  331          * If the bucket is full, toss the oldest element.
  332          */
  333         if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
  334                 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
  335                         ("sch->sch_length incorrect"));
  336                 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
  337                 syncache_drop(sc2, sch);
  338                 TCPSTAT_INC(tcps_sc_bucketoverflow);
  339         }
  340 
  341         /* Put it into the bucket. */
  342         TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
  343         sch->sch_length++;
  344 
  345 #ifdef TCP_OFFLOAD
  346         if (ADDED_BY_TOE(sc)) {
  347                 struct toedev *tod = sc->sc_tod;
  348 
  349                 tod->tod_syncache_added(tod, sc->sc_todctx);
  350         }
  351 #endif
  352 
  353         /* Reinitialize the bucket row's timer. */
  354         if (sch->sch_length == 1)
  355                 sch->sch_nextc = ticks + INT_MAX;
  356         syncache_timeout(sc, sch, 1);
  357 
  358         SCH_UNLOCK(sch);
  359 
  360         TCPSTAT_INC(tcps_sc_added);
  361 }
  362 
  363 /*
  364  * Remove and free entry from syncache bucket row.
  365  * Expects locked syncache head.
  366  */
  367 static void
  368 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  369 {
  370 
  371         SCH_LOCK_ASSERT(sch);
  372 
  373         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  374         sch->sch_length--;
  375 
  376 #ifdef TCP_OFFLOAD
  377         if (ADDED_BY_TOE(sc)) {
  378                 struct toedev *tod = sc->sc_tod;
  379 
  380                 tod->tod_syncache_removed(tod, sc->sc_todctx);
  381         }
  382 #endif
  383 
  384         syncache_free(sc);
  385 }
  386 
  387 /*
  388  * Engage/reengage time on bucket row.
  389  */
  390 static void
  391 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
  392 {
  393         sc->sc_rxttime = ticks +
  394                 TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]);
  395         sc->sc_rxmits++;
  396         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
  397                 sch->sch_nextc = sc->sc_rxttime;
  398                 if (docallout)
  399                         callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
  400                             syncache_timer, (void *)sch);
  401         }
  402 }
  403 
  404 /*
  405  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  406  * If we have retransmitted an entry the maximum number of times, expire it.
  407  * One separate timer for each bucket row.
  408  */
  409 static void
  410 syncache_timer(void *xsch)
  411 {
  412         struct syncache_head *sch = (struct syncache_head *)xsch;
  413         struct syncache *sc, *nsc;
  414         int tick = ticks;
  415         char *s;
  416 
  417         CURVNET_SET(sch->sch_vnet);
  418 
  419         /* NB: syncache_head has already been locked by the callout. */
  420         SCH_LOCK_ASSERT(sch);
  421 
  422         /*
  423          * In the following cycle we may remove some entries and/or
  424          * advance some timeouts, so re-initialize the bucket timer.
  425          */
  426         sch->sch_nextc = tick + INT_MAX;
  427 
  428         TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
  429                 /*
  430                  * We do not check if the listen socket still exists
  431                  * and accept the case where the listen socket may be
  432                  * gone by the time we resend the SYN/ACK.  We do
  433                  * not expect this to happens often. If it does,
  434                  * then the RST will be sent by the time the remote
  435                  * host does the SYN/ACK->ACK.
  436                  */
  437                 if (TSTMP_GT(sc->sc_rxttime, tick)) {
  438                         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
  439                                 sch->sch_nextc = sc->sc_rxttime;
  440                         continue;
  441                 }
  442                 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
  443                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  444                                 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
  445                                     "giving up and removing syncache entry\n",
  446                                     s, __func__);
  447                                 free(s, M_TCPLOG);
  448                         }
  449                         syncache_drop(sc, sch);
  450                         TCPSTAT_INC(tcps_sc_stale);
  451                         continue;
  452                 }
  453                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  454                         log(LOG_DEBUG, "%s; %s: Response timeout, "
  455                             "retransmitting (%u) SYN|ACK\n",
  456                             s, __func__, sc->sc_rxmits);
  457                         free(s, M_TCPLOG);
  458                 }
  459 
  460                 (void) syncache_respond(sc);
  461                 TCPSTAT_INC(tcps_sc_retransmitted);
  462                 syncache_timeout(sc, sch, 0);
  463         }
  464         if (!TAILQ_EMPTY(&(sch)->sch_bucket))
  465                 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
  466                         syncache_timer, (void *)(sch));
  467         CURVNET_RESTORE();
  468 }
  469 
  470 /*
  471  * Find an entry in the syncache.
  472  * Returns always with locked syncache_head plus a matching entry or NULL.
  473  */
  474 struct syncache *
  475 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  476 {
  477         struct syncache *sc;
  478         struct syncache_head *sch;
  479 
  480 #ifdef INET6
  481         if (inc->inc_flags & INC_ISIPV6) {
  482                 sch = &V_tcp_syncache.hashbase[
  483                     SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)];
  484                 *schp = sch;
  485 
  486                 SCH_LOCK(sch);
  487 
  488                 /* Circle through bucket row to find matching entry. */
  489                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  490                         if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  491                                 return (sc);
  492                 }
  493         } else
  494 #endif
  495         {
  496                 sch = &V_tcp_syncache.hashbase[
  497                     SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)];
  498                 *schp = sch;
  499 
  500                 SCH_LOCK(sch);
  501 
  502                 /* Circle through bucket row to find matching entry. */
  503                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  504 #ifdef INET6
  505                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
  506                                 continue;
  507 #endif
  508                         if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  509                                 return (sc);
  510                 }
  511         }
  512         SCH_LOCK_ASSERT(*schp);
  513         return (NULL);                  /* always returns with locked sch */
  514 }
  515 
  516 /*
  517  * This function is called when we get a RST for a
  518  * non-existent connection, so that we can see if the
  519  * connection is in the syn cache.  If it is, zap it.
  520  */
  521 void
  522 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
  523 {
  524         struct syncache *sc;
  525         struct syncache_head *sch;
  526         char *s = NULL;
  527 
  528         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  529         SCH_LOCK_ASSERT(sch);
  530 
  531         /*
  532          * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
  533          * See RFC 793 page 65, section SEGMENT ARRIVES.
  534          */
  535         if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
  536                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  537                         log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
  538                             "FIN flag set, segment ignored\n", s, __func__);
  539                 TCPSTAT_INC(tcps_badrst);
  540                 goto done;
  541         }
  542 
  543         /*
  544          * No corresponding connection was found in syncache.
  545          * If syncookies are enabled and possibly exclusively
  546          * used, or we are under memory pressure, a valid RST
  547          * may not find a syncache entry.  In that case we're
  548          * done and no SYN|ACK retransmissions will happen.
  549          * Otherwise the RST was misdirected or spoofed.
  550          */
  551         if (sc == NULL) {
  552                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  553                         log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
  554                             "syncache entry (possibly syncookie only), "
  555                             "segment ignored\n", s, __func__);
  556                 TCPSTAT_INC(tcps_badrst);
  557                 goto done;
  558         }
  559 
  560         /*
  561          * If the RST bit is set, check the sequence number to see
  562          * if this is a valid reset segment.
  563          * RFC 793 page 37:
  564          *   In all states except SYN-SENT, all reset (RST) segments
  565          *   are validated by checking their SEQ-fields.  A reset is
  566          *   valid if its sequence number is in the window.
  567          *
  568          *   The sequence number in the reset segment is normally an
  569          *   echo of our outgoing acknowlegement numbers, but some hosts
  570          *   send a reset with the sequence number at the rightmost edge
  571          *   of our receive window, and we have to handle this case.
  572          */
  573         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  574             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  575                 syncache_drop(sc, sch);
  576                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  577                         log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
  578                             "connection attempt aborted by remote endpoint\n",
  579                             s, __func__);
  580                 TCPSTAT_INC(tcps_sc_reset);
  581         } else {
  582                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  583                         log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
  584                             "IRS %u (+WND %u), segment ignored\n",
  585                             s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
  586                 TCPSTAT_INC(tcps_badrst);
  587         }
  588 
  589 done:
  590         if (s != NULL)
  591                 free(s, M_TCPLOG);
  592         SCH_UNLOCK(sch);
  593 }
  594 
  595 void
  596 syncache_badack(struct in_conninfo *inc)
  597 {
  598         struct syncache *sc;
  599         struct syncache_head *sch;
  600 
  601         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  602         SCH_LOCK_ASSERT(sch);
  603         if (sc != NULL) {
  604                 syncache_drop(sc, sch);
  605                 TCPSTAT_INC(tcps_sc_badack);
  606         }
  607         SCH_UNLOCK(sch);
  608 }
  609 
  610 void
  611 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
  612 {
  613         struct syncache *sc;
  614         struct syncache_head *sch;
  615 
  616         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  617         SCH_LOCK_ASSERT(sch);
  618         if (sc == NULL)
  619                 goto done;
  620 
  621         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  622         if (ntohl(th->th_seq) != sc->sc_iss)
  623                 goto done;
  624 
  625         /*
  626          * If we've rertransmitted 3 times and this is our second error,
  627          * we remove the entry.  Otherwise, we allow it to continue on.
  628          * This prevents us from incorrectly nuking an entry during a
  629          * spurious network outage.
  630          *
  631          * See tcp_notify().
  632          */
  633         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
  634                 sc->sc_flags |= SCF_UNREACH;
  635                 goto done;
  636         }
  637         syncache_drop(sc, sch);
  638         TCPSTAT_INC(tcps_sc_unreach);
  639 done:
  640         SCH_UNLOCK(sch);
  641 }
  642 
  643 /*
  644  * Build a new TCP socket structure from a syncache entry.
  645  */
  646 static struct socket *
  647 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  648 {
  649         struct inpcb *inp = NULL;
  650         struct socket *so;
  651         struct tcpcb *tp;
  652         int error;
  653         char *s;
  654 
  655         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  656 
  657         /*
  658          * Ok, create the full blown connection, and set things up
  659          * as they would have been set up if we had created the
  660          * connection when the SYN arrived.  If we can't create
  661          * the connection, abort it.
  662          */
  663         so = sonewconn(lso, SS_ISCONNECTED);
  664         if (so == NULL) {
  665                 /*
  666                  * Drop the connection; we will either send a RST or
  667                  * have the peer retransmit its SYN again after its
  668                  * RTO and try again.
  669                  */
  670                 TCPSTAT_INC(tcps_listendrop);
  671                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  672                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  673                             "due to limits or memory shortage\n",
  674                             s, __func__);
  675                         free(s, M_TCPLOG);
  676                 }
  677                 goto abort2;
  678         }
  679 #ifdef MAC
  680         mac_socketpeer_set_from_mbuf(m, so);
  681 #endif
  682 
  683         inp = sotoinpcb(so);
  684         inp->inp_inc.inc_fibnum = so->so_fibnum;
  685         INP_WLOCK(inp);
  686         INP_HASH_WLOCK(&V_tcbinfo);
  687 
  688         /* Insert new socket into PCB hash list. */
  689         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  690 #ifdef INET6
  691         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  692                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  693         } else {
  694                 inp->inp_vflag &= ~INP_IPV6;
  695                 inp->inp_vflag |= INP_IPV4;
  696 #endif
  697                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  698 #ifdef INET6
  699         }
  700 #endif
  701 
  702         /*
  703          * Install in the reservation hash table for now, but don't yet
  704          * install a connection group since the full 4-tuple isn't yet
  705          * configured.
  706          */
  707         inp->inp_lport = sc->sc_inc.inc_lport;
  708         if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
  709                 /*
  710                  * Undo the assignments above if we failed to
  711                  * put the PCB on the hash lists.
  712                  */
  713 #ifdef INET6
  714                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  715                         inp->in6p_laddr = in6addr_any;
  716                 else
  717 #endif
  718                         inp->inp_laddr.s_addr = INADDR_ANY;
  719                 inp->inp_lport = 0;
  720                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  721                         log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
  722                             "with error %i\n",
  723                             s, __func__, error);
  724                         free(s, M_TCPLOG);
  725                 }
  726                 INP_HASH_WUNLOCK(&V_tcbinfo);
  727                 goto abort;
  728         }
  729 #ifdef IPSEC
  730         /* Copy old policy into new socket's. */
  731         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  732                 printf("syncache_socket: could not copy policy\n");
  733 #endif
  734 #ifdef INET6
  735         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  736                 struct inpcb *oinp = sotoinpcb(lso);
  737                 struct in6_addr laddr6;
  738                 struct sockaddr_in6 sin6;
  739                 /*
  740                  * Inherit socket options from the listening socket.
  741                  * Note that in6p_inputopts are not (and should not be)
  742                  * copied, since it stores previously received options and is
  743                  * used to detect if each new option is different than the
  744                  * previous one and hence should be passed to a user.
  745                  * If we copied in6p_inputopts, a user would not be able to
  746                  * receive options just after calling the accept system call.
  747                  */
  748                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  749                 if (oinp->in6p_outputopts)
  750                         inp->in6p_outputopts =
  751                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  752 
  753                 sin6.sin6_family = AF_INET6;
  754                 sin6.sin6_len = sizeof(sin6);
  755                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  756                 sin6.sin6_port = sc->sc_inc.inc_fport;
  757                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  758                 laddr6 = inp->in6p_laddr;
  759                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  760                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  761                 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
  762                     thread0.td_ucred, m)) != 0) {
  763                         inp->in6p_laddr = laddr6;
  764                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  765                                 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
  766                                     "with error %i\n",
  767                                     s, __func__, error);
  768                                 free(s, M_TCPLOG);
  769                         }
  770                         INP_HASH_WUNLOCK(&V_tcbinfo);
  771                         goto abort;
  772                 }
  773                 /* Override flowlabel from in6_pcbconnect. */
  774                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  775                 inp->inp_flow |= sc->sc_flowlabel;
  776         }
  777 #endif /* INET6 */
  778 #if defined(INET) && defined(INET6)
  779         else
  780 #endif
  781 #ifdef INET
  782         {
  783                 struct in_addr laddr;
  784                 struct sockaddr_in sin;
  785 
  786                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  787                 
  788                 if (inp->inp_options == NULL) {
  789                         inp->inp_options = sc->sc_ipopts;
  790                         sc->sc_ipopts = NULL;
  791                 }
  792 
  793                 sin.sin_family = AF_INET;
  794                 sin.sin_len = sizeof(sin);
  795                 sin.sin_addr = sc->sc_inc.inc_faddr;
  796                 sin.sin_port = sc->sc_inc.inc_fport;
  797                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  798                 laddr = inp->inp_laddr;
  799                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  800                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  801                 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
  802                     thread0.td_ucred, m)) != 0) {
  803                         inp->inp_laddr = laddr;
  804                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  805                                 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
  806                                     "with error %i\n",
  807                                     s, __func__, error);
  808                                 free(s, M_TCPLOG);
  809                         }
  810                         INP_HASH_WUNLOCK(&V_tcbinfo);
  811                         goto abort;
  812                 }
  813         }
  814 #endif /* INET */
  815         INP_HASH_WUNLOCK(&V_tcbinfo);
  816         tp = intotcpcb(inp);
  817         tp->t_state = TCPS_SYN_RECEIVED;
  818         tp->iss = sc->sc_iss;
  819         tp->irs = sc->sc_irs;
  820         tcp_rcvseqinit(tp);
  821         tcp_sendseqinit(tp);
  822         tp->snd_wl1 = sc->sc_irs;
  823         tp->snd_max = tp->iss + 1;
  824         tp->snd_nxt = tp->iss + 1;
  825         tp->rcv_up = sc->sc_irs + 1;
  826         tp->rcv_wnd = sc->sc_wnd;
  827         tp->rcv_adv += tp->rcv_wnd;
  828         tp->last_ack_sent = tp->rcv_nxt;
  829 
  830         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  831         if (sc->sc_flags & SCF_NOOPT)
  832                 tp->t_flags |= TF_NOOPT;
  833         else {
  834                 if (sc->sc_flags & SCF_WINSCALE) {
  835                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  836                         tp->snd_scale = sc->sc_requested_s_scale;
  837                         tp->request_r_scale = sc->sc_requested_r_scale;
  838                 }
  839                 if (sc->sc_flags & SCF_TIMESTAMP) {
  840                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  841                         tp->ts_recent = sc->sc_tsreflect;
  842                         tp->ts_recent_age = tcp_ts_getticks();
  843                         tp->ts_offset = sc->sc_tsoff;
  844                 }
  845 #ifdef TCP_SIGNATURE
  846                 if (sc->sc_flags & SCF_SIGNATURE)
  847                         tp->t_flags |= TF_SIGNATURE;
  848 #endif
  849                 if (sc->sc_flags & SCF_SACK)
  850                         tp->t_flags |= TF_SACK_PERMIT;
  851         }
  852 
  853         if (sc->sc_flags & SCF_ECN)
  854                 tp->t_flags |= TF_ECN_PERMIT;
  855 
  856         /*
  857          * Set up MSS and get cached values from tcp_hostcache.
  858          * This might overwrite some of the defaults we just set.
  859          */
  860         tcp_mss(tp, sc->sc_peer_mss);
  861 
  862         /*
  863          * If the SYN,ACK was retransmitted, indicate that CWND to be
  864          * limited to one segment in cc_conn_init().
  865          * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
  866          */
  867         if (sc->sc_rxmits > 1)
  868                 tp->snd_cwnd = 1;
  869 
  870 #ifdef TCP_OFFLOAD
  871         /*
  872          * Allow a TOE driver to install its hooks.  Note that we hold the
  873          * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
  874          * new connection before the TOE driver has done its thing.
  875          */
  876         if (ADDED_BY_TOE(sc)) {
  877                 struct toedev *tod = sc->sc_tod;
  878 
  879                 tod->tod_offload_socket(tod, sc->sc_todctx, so);
  880         }
  881 #endif
  882         /*
  883          * Copy and activate timers.
  884          */
  885         tp->t_keepinit = sototcpcb(lso)->t_keepinit;
  886         tp->t_keepidle = sototcpcb(lso)->t_keepidle;
  887         tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
  888         tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
  889         tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
  890 
  891         INP_WUNLOCK(inp);
  892 
  893         TCPSTAT_INC(tcps_accepts);
  894         return (so);
  895 
  896 abort:
  897         INP_WUNLOCK(inp);
  898 abort2:
  899         if (so != NULL)
  900                 soabort(so);
  901         return (NULL);
  902 }
  903 
  904 /*
  905  * This function gets called when we receive an ACK for a
  906  * socket in the LISTEN state.  We look up the connection
  907  * in the syncache, and if its there, we pull it out of
  908  * the cache and turn it into a full-blown connection in
  909  * the SYN-RECEIVED state.
  910  */
  911 int
  912 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  913     struct socket **lsop, struct mbuf *m)
  914 {
  915         struct syncache *sc;
  916         struct syncache_head *sch;
  917         struct syncache scs;
  918         char *s;
  919 
  920         /*
  921          * Global TCP locks are held because we manipulate the PCB lists
  922          * and create a new socket.
  923          */
  924         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  925         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  926             ("%s: can handle only ACK", __func__));
  927 
  928         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  929         SCH_LOCK_ASSERT(sch);
  930         if (sc == NULL) {
  931                 /*
  932                  * There is no syncache entry, so see if this ACK is
  933                  * a returning syncookie.  To do this, first:
  934                  *  A. See if this socket has had a syncache entry dropped in
  935                  *     the past.  We don't want to accept a bogus syncookie
  936                  *     if we've never received a SYN.
  937                  *  B. check that the syncookie is valid.  If it is, then
  938                  *     cobble up a fake syncache entry, and return.
  939                  */
  940                 if (!V_tcp_syncookies) {
  941                         SCH_UNLOCK(sch);
  942                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  943                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  944                                     "segment rejected (syncookies disabled)\n",
  945                                     s, __func__);
  946                         goto failed;
  947                 }
  948                 bzero(&scs, sizeof(scs));
  949                 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop);
  950                 SCH_UNLOCK(sch);
  951                 if (sc == NULL) {
  952                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  953                                 log(LOG_DEBUG, "%s; %s: Segment failed "
  954                                     "SYNCOOKIE authentication, segment rejected "
  955                                     "(probably spoofed)\n", s, __func__);
  956                         goto failed;
  957                 }
  958         } else {
  959                 /* Pull out the entry to unlock the bucket row. */
  960                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  961                 sch->sch_length--;
  962 #ifdef TCP_OFFLOAD
  963                 if (ADDED_BY_TOE(sc)) {
  964                         struct toedev *tod = sc->sc_tod;
  965 
  966                         tod->tod_syncache_removed(tod, sc->sc_todctx);
  967                 }
  968 #endif
  969                 SCH_UNLOCK(sch);
  970         }
  971 
  972         /*
  973          * Segment validation:
  974          * ACK must match our initial sequence number + 1 (the SYN|ACK).
  975          */
  976         if (th->th_ack != sc->sc_iss + 1) {
  977                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  978                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
  979                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
  980                 goto failed;
  981         }
  982 
  983         /*
  984          * The SEQ must fall in the window starting at the received
  985          * initial receive sequence number + 1 (the SYN).
  986          */
  987         if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
  988             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  989                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  990                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
  991                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
  992                 goto failed;
  993         }
  994 
  995         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
  996                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  997                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
  998                             "segment rejected\n", s, __func__);
  999                 goto failed;
 1000         }
 1001         /*
 1002          * If timestamps were negotiated the reflected timestamp
 1003          * must be equal to what we actually sent in the SYN|ACK.
 1004          */
 1005         if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
 1006                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1007                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
 1008                             "segment rejected\n",
 1009                             s, __func__, to->to_tsecr, sc->sc_ts);
 1010                 goto failed;
 1011         }
 1012 
 1013         *lsop = syncache_socket(sc, *lsop, m);
 1014 
 1015         if (*lsop == NULL)
 1016                 TCPSTAT_INC(tcps_sc_aborted);
 1017         else
 1018                 TCPSTAT_INC(tcps_sc_completed);
 1019 
 1020 /* how do we find the inp for the new socket? */
 1021         if (sc != &scs)
 1022                 syncache_free(sc);
 1023         return (1);
 1024 failed:
 1025         if (sc != NULL && sc != &scs)
 1026                 syncache_free(sc);
 1027         if (s != NULL)
 1028                 free(s, M_TCPLOG);
 1029         *lsop = NULL;
 1030         return (0);
 1031 }
 1032 
 1033 /*
 1034  * Given a LISTEN socket and an inbound SYN request, add
 1035  * this to the syn cache, and send back a segment:
 1036  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 1037  * to the source.
 1038  *
 1039  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
 1040  * Doing so would require that we hold onto the data and deliver it
 1041  * to the application.  However, if we are the target of a SYN-flood
 1042  * DoS attack, an attacker could send data which would eventually
 1043  * consume all available buffer space if it were ACKed.  By not ACKing
 1044  * the data, we avoid this DoS scenario.
 1045  */
 1046 static void
 1047 _syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1048     struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
 1049     void *todctx)
 1050 {
 1051         struct tcpcb *tp;
 1052         struct socket *so;
 1053         struct syncache *sc = NULL;
 1054         struct syncache_head *sch;
 1055         struct mbuf *ipopts = NULL;
 1056         u_int32_t flowtmp;
 1057         u_int ltflags;
 1058         int win, sb_hiwat, ip_ttl, ip_tos;
 1059         char *s;
 1060 #ifdef INET6
 1061         int autoflowlabel = 0;
 1062 #endif
 1063 #ifdef MAC
 1064         struct label *maclabel;
 1065 #endif
 1066         struct syncache scs;
 1067         struct ucred *cred;
 1068 
 1069         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1070         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1071         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1072             ("%s: unexpected tcp flags", __func__));
 1073 
 1074         /*
 1075          * Combine all so/tp operations very early to drop the INP lock as
 1076          * soon as possible.
 1077          */
 1078         so = *lsop;
 1079         tp = sototcpcb(so);
 1080         cred = crhold(so->so_cred);
 1081 
 1082 #ifdef INET6
 1083         if ((inc->inc_flags & INC_ISIPV6) &&
 1084             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1085                 autoflowlabel = 1;
 1086 #endif
 1087         ip_ttl = inp->inp_ip_ttl;
 1088         ip_tos = inp->inp_ip_tos;
 1089         win = sbspace(&so->so_rcv);
 1090         sb_hiwat = so->so_rcv.sb_hiwat;
 1091         ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
 1092 
 1093         /* By the time we drop the lock these should no longer be used. */
 1094         so = NULL;
 1095         tp = NULL;
 1096 
 1097 #ifdef MAC
 1098         if (mac_syncache_init(&maclabel) != 0) {
 1099                 INP_WUNLOCK(inp);
 1100                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1101                 goto done;
 1102         } else
 1103                 mac_syncache_create(maclabel, inp);
 1104 #endif
 1105         INP_WUNLOCK(inp);
 1106         INP_INFO_WUNLOCK(&V_tcbinfo);
 1107 
 1108         /*
 1109          * Remember the IP options, if any.
 1110          */
 1111 #ifdef INET6
 1112         if (!(inc->inc_flags & INC_ISIPV6))
 1113 #endif
 1114 #ifdef INET
 1115                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1116 #else
 1117                 ipopts = NULL;
 1118 #endif
 1119 
 1120         /*
 1121          * See if we already have an entry for this connection.
 1122          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1123          *
 1124          * XXX: should the syncache be re-initialized with the contents
 1125          * of the new SYN here (which may have different options?)
 1126          *
 1127          * XXX: We do not check the sequence number to see if this is a
 1128          * real retransmit or a new connection attempt.  The question is
 1129          * how to handle such a case; either ignore it as spoofed, or
 1130          * drop the current entry and create a new one?
 1131          */
 1132         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1133         SCH_LOCK_ASSERT(sch);
 1134         if (sc != NULL) {
 1135                 TCPSTAT_INC(tcps_sc_dupsyn);
 1136                 if (ipopts) {
 1137                         /*
 1138                          * If we were remembering a previous source route,
 1139                          * forget it and use the new one we've been given.
 1140                          */
 1141                         if (sc->sc_ipopts)
 1142                                 (void) m_free(sc->sc_ipopts);
 1143                         sc->sc_ipopts = ipopts;
 1144                 }
 1145                 /*
 1146                  * Update timestamp if present.
 1147                  */
 1148                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1149                         sc->sc_tsreflect = to->to_tsval;
 1150                 else
 1151                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1152 #ifdef MAC
 1153                 /*
 1154                  * Since we have already unconditionally allocated label
 1155                  * storage, free it up.  The syncache entry will already
 1156                  * have an initialized label we can use.
 1157                  */
 1158                 mac_syncache_destroy(&maclabel);
 1159 #endif
 1160                 /* Retransmit SYN|ACK and reset retransmit count. */
 1161                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1162                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1163                             "resetting timer and retransmitting SYN|ACK\n",
 1164                             s, __func__);
 1165                         free(s, M_TCPLOG);
 1166                 }
 1167                 if (syncache_respond(sc) == 0) {
 1168                         sc->sc_rxmits = 0;
 1169                         syncache_timeout(sc, sch, 1);
 1170                         TCPSTAT_INC(tcps_sndacks);
 1171                         TCPSTAT_INC(tcps_sndtotal);
 1172                 }
 1173                 SCH_UNLOCK(sch);
 1174                 goto done;
 1175         }
 1176 
 1177         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1178         if (sc == NULL) {
 1179                 /*
 1180                  * The zone allocator couldn't provide more entries.
 1181                  * Treat this as if the cache was full; drop the oldest
 1182                  * entry and insert the new one.
 1183                  */
 1184                 TCPSTAT_INC(tcps_sc_zonefail);
 1185                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
 1186                         syncache_drop(sc, sch);
 1187                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1188                 if (sc == NULL) {
 1189                         if (V_tcp_syncookies) {
 1190                                 bzero(&scs, sizeof(scs));
 1191                                 sc = &scs;
 1192                         } else {
 1193                                 SCH_UNLOCK(sch);
 1194                                 if (ipopts)
 1195                                         (void) m_free(ipopts);
 1196                                 goto done;
 1197                         }
 1198                 }
 1199         }
 1200         
 1201         /*
 1202          * Fill in the syncache values.
 1203          */
 1204 #ifdef MAC
 1205         sc->sc_label = maclabel;
 1206 #endif
 1207         sc->sc_cred = cred;
 1208         cred = NULL;
 1209         sc->sc_ipopts = ipopts;
 1210         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1211 #ifdef INET6
 1212         if (!(inc->inc_flags & INC_ISIPV6))
 1213 #endif
 1214         {
 1215                 sc->sc_ip_tos = ip_tos;
 1216                 sc->sc_ip_ttl = ip_ttl;
 1217         }
 1218 #ifdef TCP_OFFLOAD
 1219         sc->sc_tod = tod;
 1220         sc->sc_todctx = todctx;
 1221 #endif
 1222         sc->sc_irs = th->th_seq;
 1223         sc->sc_iss = arc4random();
 1224         sc->sc_flags = 0;
 1225         sc->sc_flowlabel = 0;
 1226 
 1227         /*
 1228          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1229          * win was derived from socket earlier in the function.
 1230          */
 1231         win = imax(win, 0);
 1232         win = imin(win, TCP_MAXWIN);
 1233         sc->sc_wnd = win;
 1234 
 1235         if (V_tcp_do_rfc1323) {
 1236                 /*
 1237                  * A timestamp received in a SYN makes
 1238                  * it ok to send timestamp requests and replies.
 1239                  */
 1240                 if (to->to_flags & TOF_TS) {
 1241                         sc->sc_tsreflect = to->to_tsval;
 1242                         sc->sc_ts = tcp_ts_getticks();
 1243                         sc->sc_flags |= SCF_TIMESTAMP;
 1244                 }
 1245                 if (to->to_flags & TOF_SCALE) {
 1246                         int wscale = 0;
 1247 
 1248                         /*
 1249                          * Pick the smallest possible scaling factor that
 1250                          * will still allow us to scale up to sb_max, aka
 1251                          * kern.ipc.maxsockbuf.
 1252                          *
 1253                          * We do this because there are broken firewalls that
 1254                          * will corrupt the window scale option, leading to
 1255                          * the other endpoint believing that our advertised
 1256                          * window is unscaled.  At scale factors larger than
 1257                          * 5 the unscaled window will drop below 1500 bytes,
 1258                          * leading to serious problems when traversing these
 1259                          * broken firewalls.
 1260                          *
 1261                          * With the default maxsockbuf of 256K, a scale factor
 1262                          * of 3 will be chosen by this algorithm.  Those who
 1263                          * choose a larger maxsockbuf should watch out
 1264                          * for the compatiblity problems mentioned above.
 1265                          *
 1266                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1267                          * or <SYN,ACK>) segment itself is never scaled.
 1268                          */
 1269                         while (wscale < TCP_MAX_WINSHIFT &&
 1270                             (TCP_MAXWIN << wscale) < sb_max)
 1271                                 wscale++;
 1272                         sc->sc_requested_r_scale = wscale;
 1273                         sc->sc_requested_s_scale = to->to_wscale;
 1274                         sc->sc_flags |= SCF_WINSCALE;
 1275                 }
 1276         }
 1277 #ifdef TCP_SIGNATURE
 1278         /*
 1279          * If listening socket requested TCP digests, and received SYN
 1280          * contains the option, flag this in the syncache so that
 1281          * syncache_respond() will do the right thing with the SYN+ACK.
 1282          * XXX: Currently we always record the option by default and will
 1283          * attempt to use it in syncache_respond().
 1284          */
 1285         if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
 1286                 sc->sc_flags |= SCF_SIGNATURE;
 1287 #endif
 1288         if (to->to_flags & TOF_SACKPERM)
 1289                 sc->sc_flags |= SCF_SACK;
 1290         if (to->to_flags & TOF_MSS)
 1291                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1292         if (ltflags & TF_NOOPT)
 1293                 sc->sc_flags |= SCF_NOOPT;
 1294         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1295                 sc->sc_flags |= SCF_ECN;
 1296 
 1297         if (V_tcp_syncookies) {
 1298                 syncookie_generate(sch, sc, &flowtmp);
 1299 #ifdef INET6
 1300                 if (autoflowlabel)
 1301                         sc->sc_flowlabel = flowtmp;
 1302 #endif
 1303         } else {
 1304 #ifdef INET6
 1305                 if (autoflowlabel)
 1306                         sc->sc_flowlabel =
 1307                             (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
 1308 #endif
 1309         }
 1310         SCH_UNLOCK(sch);
 1311 
 1312         /*
 1313          * Do a standard 3-way handshake.
 1314          */
 1315         if (syncache_respond(sc) == 0) {
 1316                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1317                         syncache_free(sc);
 1318                 else if (sc != &scs)
 1319                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1320                 TCPSTAT_INC(tcps_sndacks);
 1321                 TCPSTAT_INC(tcps_sndtotal);
 1322         } else {
 1323                 if (sc != &scs)
 1324                         syncache_free(sc);
 1325                 TCPSTAT_INC(tcps_sc_dropped);
 1326         }
 1327 
 1328 done:
 1329         if (cred != NULL)
 1330                 crfree(cred);
 1331 #ifdef MAC
 1332         if (sc == &scs)
 1333                 mac_syncache_destroy(&maclabel);
 1334 #endif
 1335         if (m) {
 1336                 
 1337                 *lsop = NULL;
 1338                 m_freem(m);
 1339         }
 1340 }
 1341 
 1342 static int
 1343 syncache_respond(struct syncache *sc)
 1344 {
 1345         struct ip *ip = NULL;
 1346         struct mbuf *m;
 1347         struct tcphdr *th = NULL;
 1348         int optlen, error = 0;  /* Make compiler happy */
 1349         u_int16_t hlen, tlen, mssopt;
 1350         struct tcpopt to;
 1351 #ifdef INET6
 1352         struct ip6_hdr *ip6 = NULL;
 1353 #endif
 1354 
 1355         hlen =
 1356 #ifdef INET6
 1357                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1358 #endif
 1359                 sizeof(struct ip);
 1360         tlen = hlen + sizeof(struct tcphdr);
 1361 
 1362         /* Determine MSS we advertize to other end of connection. */
 1363         mssopt = tcp_mssopt(&sc->sc_inc);
 1364         if (sc->sc_peer_mss)
 1365                 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
 1366 
 1367         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1368         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1369             ("syncache: mbuf too small"));
 1370 
 1371         /* Create the IP+TCP header from scratch. */
 1372         m = m_gethdr(M_DONTWAIT, MT_DATA);
 1373         if (m == NULL)
 1374                 return (ENOBUFS);
 1375 #ifdef MAC
 1376         mac_syncache_create_mbuf(sc->sc_label, m);
 1377 #endif
 1378         m->m_data += max_linkhdr;
 1379         m->m_len = tlen;
 1380         m->m_pkthdr.len = tlen;
 1381         m->m_pkthdr.rcvif = NULL;
 1382 
 1383 #ifdef INET6
 1384         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1385                 ip6 = mtod(m, struct ip6_hdr *);
 1386                 ip6->ip6_vfc = IPV6_VERSION;
 1387                 ip6->ip6_nxt = IPPROTO_TCP;
 1388                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1389                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1390                 ip6->ip6_plen = htons(tlen - hlen);
 1391                 /* ip6_hlim is set after checksum */
 1392                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1393                 ip6->ip6_flow |= sc->sc_flowlabel;
 1394 
 1395                 th = (struct tcphdr *)(ip6 + 1);
 1396         }
 1397 #endif
 1398 #if defined(INET6) && defined(INET)
 1399         else
 1400 #endif
 1401 #ifdef INET
 1402         {
 1403                 ip = mtod(m, struct ip *);
 1404                 ip->ip_v = IPVERSION;
 1405                 ip->ip_hl = sizeof(struct ip) >> 2;
 1406                 ip->ip_len = tlen;
 1407                 ip->ip_id = 0;
 1408                 ip->ip_off = 0;
 1409                 ip->ip_sum = 0;
 1410                 ip->ip_p = IPPROTO_TCP;
 1411                 ip->ip_src = sc->sc_inc.inc_laddr;
 1412                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1413                 ip->ip_ttl = sc->sc_ip_ttl;
 1414                 ip->ip_tos = sc->sc_ip_tos;
 1415 
 1416                 /*
 1417                  * See if we should do MTU discovery.  Route lookups are
 1418                  * expensive, so we will only unset the DF bit if:
 1419                  *
 1420                  *      1) path_mtu_discovery is disabled
 1421                  *      2) the SCF_UNREACH flag has been set
 1422                  */
 1423                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1424                        ip->ip_off |= IP_DF;
 1425 
 1426                 th = (struct tcphdr *)(ip + 1);
 1427         }
 1428 #endif /* INET */
 1429         th->th_sport = sc->sc_inc.inc_lport;
 1430         th->th_dport = sc->sc_inc.inc_fport;
 1431 
 1432         th->th_seq = htonl(sc->sc_iss);
 1433         th->th_ack = htonl(sc->sc_irs + 1);
 1434         th->th_off = sizeof(struct tcphdr) >> 2;
 1435         th->th_x2 = 0;
 1436         th->th_flags = TH_SYN|TH_ACK;
 1437         th->th_win = htons(sc->sc_wnd);
 1438         th->th_urp = 0;
 1439 
 1440         if (sc->sc_flags & SCF_ECN) {
 1441                 th->th_flags |= TH_ECE;
 1442                 TCPSTAT_INC(tcps_ecn_shs);
 1443         }
 1444 
 1445         /* Tack on the TCP options. */
 1446         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1447                 to.to_flags = 0;
 1448 
 1449                 to.to_mss = mssopt;
 1450                 to.to_flags = TOF_MSS;
 1451                 if (sc->sc_flags & SCF_WINSCALE) {
 1452                         to.to_wscale = sc->sc_requested_r_scale;
 1453                         to.to_flags |= TOF_SCALE;
 1454                 }
 1455                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1456                         /* Virgin timestamp or TCP cookie enhanced one. */
 1457                         to.to_tsval = sc->sc_ts;
 1458                         to.to_tsecr = sc->sc_tsreflect;
 1459                         to.to_flags |= TOF_TS;
 1460                 }
 1461                 if (sc->sc_flags & SCF_SACK)
 1462                         to.to_flags |= TOF_SACKPERM;
 1463 #ifdef TCP_SIGNATURE
 1464                 if (sc->sc_flags & SCF_SIGNATURE)
 1465                         to.to_flags |= TOF_SIGNATURE;
 1466 #endif
 1467                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1468 
 1469                 /* Adjust headers by option size. */
 1470                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1471                 m->m_len += optlen;
 1472                 m->m_pkthdr.len += optlen;
 1473 
 1474 #ifdef TCP_SIGNATURE
 1475                 if (sc->sc_flags & SCF_SIGNATURE)
 1476                         tcp_signature_compute(m, 0, 0, optlen,
 1477                             to.to_signature, IPSEC_DIR_OUTBOUND);
 1478 #endif
 1479 #ifdef INET6
 1480                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1481                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1482                 else
 1483 #endif
 1484                         ip->ip_len += optlen;
 1485         } else
 1486                 optlen = 0;
 1487 
 1488         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1489         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1490 #ifdef INET6
 1491         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1492                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 1493                 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
 1494                     IPPROTO_TCP, 0);
 1495                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1496 #ifdef TCP_OFFLOAD
 1497                 if (ADDED_BY_TOE(sc)) {
 1498                         struct toedev *tod = sc->sc_tod;
 1499 
 1500                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1501 
 1502                         return (error);
 1503                 }
 1504 #endif
 1505                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1506         }
 1507 #endif
 1508 #if defined(INET6) && defined(INET)
 1509         else
 1510 #endif
 1511 #ifdef INET
 1512         {
 1513                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1514                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1515                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1516 #ifdef TCP_OFFLOAD
 1517                 if (ADDED_BY_TOE(sc)) {
 1518                         struct toedev *tod = sc->sc_tod;
 1519 
 1520                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1521 
 1522                         return (error);
 1523                 }
 1524 #endif
 1525                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1526         }
 1527 #endif
 1528         return (error);
 1529 }
 1530 
 1531 void
 1532 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1533     struct inpcb *inp, struct socket **lsop, struct mbuf *m)
 1534 {
 1535         _syncache_add(inc, to, th, inp, lsop, m, NULL, NULL);
 1536 }
 1537 
 1538 void
 1539 tcp_offload_syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1540     struct inpcb *inp, struct socket **lsop, void *tod, void *todctx)
 1541 {
 1542 
 1543         _syncache_add(inc, to, th, inp, lsop, NULL, tod, todctx);
 1544 }
 1545 /*
 1546  * The purpose of SYN cookies is to avoid keeping track of all SYN's we
 1547  * receive and to be able to handle SYN floods from bogus source addresses
 1548  * (where we will never receive any reply).  SYN floods try to exhaust all
 1549  * our memory and available slots in the SYN cache table to cause a denial
 1550  * of service to legitimate users of the local host.
 1551  *
 1552  * The idea of SYN cookies is to encode and include all necessary information
 1553  * about the connection setup state within the SYN-ACK we send back and thus
 1554  * to get along without keeping any local state until the ACK to the SYN-ACK
 1555  * arrives (if ever).  Everything we need to know should be available from
 1556  * the information we encoded in the SYN-ACK.
 1557  *
 1558  * More information about the theory behind SYN cookies and its first
 1559  * discussion and specification can be found at:
 1560  *  http://cr.yp.to/syncookies.html    (overview)
 1561  *  http://cr.yp.to/syncookies/archive (gory details)
 1562  *
 1563  * This implementation extends the orginal idea and first implementation
 1564  * of FreeBSD by using not only the initial sequence number field to store
 1565  * information but also the timestamp field if present.  This way we can
 1566  * keep track of the entire state we need to know to recreate the session in
 1567  * its original form.  Almost all TCP speakers implement RFC1323 timestamps
 1568  * these days.  For those that do not we still have to live with the known
 1569  * shortcomings of the ISN only SYN cookies.
 1570  *
 1571  * Cookie layers:
 1572  *
 1573  * Initial sequence number we send:
 1574  * 31|................................|0
 1575  *    DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP
 1576  *    D = MD5 Digest (first dword)
 1577  *    M = MSS index
 1578  *    R = Rotation of secret
 1579  *    P = Odd or Even secret
 1580  *
 1581  * The MD5 Digest is computed with over following parameters:
 1582  *  a) randomly rotated secret
 1583  *  b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6)
 1584  *  c) the received initial sequence number from remote host
 1585  *  d) the rotation offset and odd/even bit
 1586  *
 1587  * Timestamp we send:
 1588  * 31|................................|0
 1589  *    DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5
 1590  *    D = MD5 Digest (third dword) (only as filler)
 1591  *    S = Requested send window scale
 1592  *    R = Requested receive window scale
 1593  *    A = SACK allowed
 1594  *    5 = TCP-MD5 enabled (not implemented yet)
 1595  *    XORed with MD5 Digest (forth dword)
 1596  *
 1597  * The timestamp isn't cryptographically secure and doesn't need to be.
 1598  * The double use of the MD5 digest dwords ties it to a specific remote/
 1599  * local host/port, remote initial sequence number and our local time
 1600  * limited secret.  A received timestamp is reverted (XORed) and then
 1601  * the contained MD5 dword is compared to the computed one to ensure the
 1602  * timestamp belongs to the SYN-ACK we sent.  The other parameters may
 1603  * have been tampered with but this isn't different from supplying bogus
 1604  * values in the SYN in the first place.
 1605  *
 1606  * Some problems with SYN cookies remain however:
 1607  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1608  * original SYN was accepted, the connection is established.  The second
 1609  * SYN is inflight, and if it arrives with an ISN that falls within the
 1610  * receive window, the connection is killed.
 1611  *
 1612  * Notes:
 1613  * A heuristic to determine when to accept syn cookies is not necessary.
 1614  * An ACK flood would cause the syncookie verification to be attempted,
 1615  * but a SYN flood causes syncookies to be generated.  Both are of equal
 1616  * cost, so there's no point in trying to optimize the ACK flood case.
 1617  * Also, if you don't process certain ACKs for some reason, then all someone
 1618  * would have to do is launch a SYN and ACK flood at the same time, which
 1619  * would stop cookie verification and defeat the entire purpose of syncookies.
 1620  */
 1621 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 };
 1622 
 1623 static void
 1624 syncookie_generate(struct syncache_head *sch, struct syncache *sc,
 1625     u_int32_t *flowlabel)
 1626 {
 1627         MD5_CTX ctx;
 1628         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1629         u_int32_t data;
 1630         u_int32_t *secbits;
 1631         u_int off, pmss, mss;
 1632         int i;
 1633 
 1634         SCH_LOCK_ASSERT(sch);
 1635 
 1636         /* Which of the two secrets to use. */
 1637         secbits = sch->sch_oddeven ?
 1638                         sch->sch_secbits_odd : sch->sch_secbits_even;
 1639 
 1640         /* Reseed secret if too old. */
 1641         if (sch->sch_reseed < time_uptime) {
 1642                 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1;    /* toggle */
 1643                 secbits = sch->sch_oddeven ?
 1644                                 sch->sch_secbits_odd : sch->sch_secbits_even;
 1645                 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++)
 1646                         secbits[i] = arc4random();
 1647                 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME;
 1648         }
 1649 
 1650         /* Secret rotation offset. */
 1651         off = sc->sc_iss & 0x7;                 /* iss was randomized before */
 1652 
 1653         /* Maximum segment size calculation. */
 1654         pmss =
 1655             max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), V_tcp_minmss);
 1656         for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--)
 1657                 if (tcp_sc_msstab[mss] <= pmss)
 1658                         break;
 1659 
 1660         /* Fold parameters and MD5 digest into the ISN we will send. */
 1661         data = sch->sch_oddeven;/* odd or even secret, 1 bit */
 1662         data |= off << 1;       /* secret offset, derived from iss, 3 bits */
 1663         data |= mss << 4;       /* mss, 3 bits */
 1664 
 1665         MD5Init(&ctx);
 1666         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1667             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1668         MD5Update(&ctx, secbits, off);
 1669         MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc));
 1670         MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs));
 1671         MD5Update(&ctx, &data, sizeof(data));
 1672         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1673 
 1674         data |= (md5_buffer[0] << 7);
 1675         sc->sc_iss = data;
 1676 
 1677 #ifdef INET6
 1678         *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1679 #endif
 1680 
 1681         /* Additional parameters are stored in the timestamp if present. */
 1682         if (sc->sc_flags & SCF_TIMESTAMP) {
 1683                 data =  ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */
 1684                 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */
 1685                 data |= sc->sc_requested_s_scale << 2;  /* SWIN scale, 4 bits */
 1686                 data |= sc->sc_requested_r_scale << 6;  /* RWIN scale, 4 bits */
 1687                 data |= md5_buffer[2] << 10;            /* more digest bits */
 1688                 data ^= md5_buffer[3];
 1689                 sc->sc_ts = data;
 1690                 sc->sc_tsoff = data - tcp_ts_getticks();        /* after XOR */
 1691         }
 1692 
 1693         TCPSTAT_INC(tcps_sc_sendcookie);
 1694 }
 1695 
 1696 static struct syncache *
 1697 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 1698     struct syncache *sc, struct tcpopt *to, struct tcphdr *th,
 1699     struct socket *so)
 1700 {
 1701         MD5_CTX ctx;
 1702         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1703         u_int32_t data = 0;
 1704         u_int32_t *secbits;
 1705         tcp_seq ack, seq;
 1706         int off, mss, wnd, flags;
 1707 
 1708         SCH_LOCK_ASSERT(sch);
 1709 
 1710         /*
 1711          * Pull information out of SYN-ACK/ACK and
 1712          * revert sequence number advances.
 1713          */
 1714         ack = th->th_ack - 1;
 1715         seq = th->th_seq - 1;
 1716         off = (ack >> 1) & 0x7;
 1717         mss = (ack >> 4) & 0x7;
 1718         flags = ack & 0x7f;
 1719 
 1720         /* Which of the two secrets to use. */
 1721         secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even;
 1722 
 1723         /*
 1724          * The secret wasn't updated for the lifetime of a syncookie,
 1725          * so this SYN-ACK/ACK is either too old (replay) or totally bogus.
 1726          */
 1727         if (sch->sch_reseed + SYNCOOKIE_LIFETIME < time_uptime) {
 1728                 return (NULL);
 1729         }
 1730 
 1731         /* Recompute the digest so we can compare it. */
 1732         MD5Init(&ctx);
 1733         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1734             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1735         MD5Update(&ctx, secbits, off);
 1736         MD5Update(&ctx, inc, sizeof(*inc));
 1737         MD5Update(&ctx, &seq, sizeof(seq));
 1738         MD5Update(&ctx, &flags, sizeof(flags));
 1739         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1740 
 1741         /* Does the digest part of or ACK'ed ISS match? */
 1742         if ((ack & (~0x7f)) != (md5_buffer[0] << 7))
 1743                 return (NULL);
 1744 
 1745         /* Does the digest part of our reflected timestamp match? */
 1746         if (to->to_flags & TOF_TS) {
 1747                 data = md5_buffer[3] ^ to->to_tsecr;
 1748                 if ((data & (~0x3ff)) != (md5_buffer[2] << 10))
 1749                         return (NULL);
 1750         }
 1751 
 1752         /* Fill in the syncache values. */
 1753         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1754         sc->sc_ipopts = NULL;
 1755         
 1756         sc->sc_irs = seq;
 1757         sc->sc_iss = ack;
 1758 
 1759 #ifdef INET6
 1760         if (inc->inc_flags & INC_ISIPV6) {
 1761                 if (sotoinpcb(so)->inp_flags & IN6P_AUTOFLOWLABEL)
 1762                         sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1763         } else
 1764 #endif
 1765         {
 1766                 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl;
 1767                 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos;
 1768         }
 1769 
 1770         /* Additional parameters that were encoded in the timestamp. */
 1771         if (data) {
 1772                 sc->sc_flags |= SCF_TIMESTAMP;
 1773                 sc->sc_tsreflect = to->to_tsval;
 1774                 sc->sc_ts = to->to_tsecr;
 1775                 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
 1776                 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0;
 1777                 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0;
 1778                 sc->sc_requested_s_scale = min((data >> 2) & 0xf,
 1779                     TCP_MAX_WINSHIFT);
 1780                 sc->sc_requested_r_scale = min((data >> 6) & 0xf,
 1781                     TCP_MAX_WINSHIFT);
 1782                 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale)
 1783                         sc->sc_flags |= SCF_WINSCALE;
 1784         } else
 1785                 sc->sc_flags |= SCF_NOOPT;
 1786 
 1787         wnd = sbspace(&so->so_rcv);
 1788         wnd = imax(wnd, 0);
 1789         wnd = imin(wnd, TCP_MAXWIN);
 1790         sc->sc_wnd = wnd;
 1791 
 1792         sc->sc_rxmits = 0;
 1793         sc->sc_peer_mss = tcp_sc_msstab[mss];
 1794 
 1795         TCPSTAT_INC(tcps_sc_recvcookie);
 1796         return (sc);
 1797 }
 1798 
 1799 /*
 1800  * Returns the current number of syncache entries.  This number
 1801  * will probably change before you get around to calling 
 1802  * syncache_pcblist.
 1803  */
 1804 
 1805 int
 1806 syncache_pcbcount(void)
 1807 {
 1808         struct syncache_head *sch;
 1809         int count, i;
 1810 
 1811         for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 1812                 /* No need to lock for a read. */
 1813                 sch = &V_tcp_syncache.hashbase[i];
 1814                 count += sch->sch_length;
 1815         }
 1816         return count;
 1817 }
 1818 
 1819 /*
 1820  * Exports the syncache entries to userland so that netstat can display
 1821  * them alongside the other sockets.  This function is intended to be
 1822  * called only from tcp_pcblist.
 1823  *
 1824  * Due to concurrency on an active system, the number of pcbs exported
 1825  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 1826  * amount of space the caller allocated for this function to use.
 1827  */
 1828 int
 1829 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 1830 {
 1831         struct xtcpcb xt;
 1832         struct syncache *sc;
 1833         struct syncache_head *sch;
 1834         int count, error, i;
 1835 
 1836         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 1837                 sch = &V_tcp_syncache.hashbase[i];
 1838                 SCH_LOCK(sch);
 1839                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 1840                         if (count >= max_pcbs) {
 1841                                 SCH_UNLOCK(sch);
 1842                                 goto exit;
 1843                         }
 1844                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 1845                                 continue;
 1846                         bzero(&xt, sizeof(xt));
 1847                         xt.xt_len = sizeof(xt);
 1848                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1849                                 xt.xt_inp.inp_vflag = INP_IPV6;
 1850                         else
 1851                                 xt.xt_inp.inp_vflag = INP_IPV4;
 1852                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 1853                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 1854                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 1855                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 1856                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 1857                         xt.xt_socket.so_type = SOCK_STREAM;
 1858                         xt.xt_socket.so_state = SS_ISCONNECTING;
 1859                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 1860                         if (error) {
 1861                                 SCH_UNLOCK(sch);
 1862                                 goto exit;
 1863                         }
 1864                         count++;
 1865                 }
 1866                 SCH_UNLOCK(sch);
 1867         }
 1868 exit:
 1869         *pcbs_exported = count;
 1870         return error;
 1871 }

Cache object: 9bc1edea909814b7b4c83169b8c0ab18


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