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) 2006,2013 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. [2001 McAfee, Inc.]
   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/10.3/sys/netinet/tcp_syncache.c 293402 2016-01-08 00:46:28Z stas $");
   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/proc.h>           /* for proc0 declaration */
   51 #include <sys/random.h>
   52 #include <sys/socket.h>
   53 #include <sys/socketvar.h>
   54 #include <sys/syslog.h>
   55 #include <sys/ucred.h>
   56 
   57 #include <sys/md5.h>
   58 #include <crypto/siphash/siphash.h>
   59 
   60 #include <vm/uma.h>
   61 
   62 #include <net/if.h>
   63 #include <net/route.h>
   64 #include <net/vnet.h>
   65 
   66 #include <netinet/in.h>
   67 #include <netinet/in_systm.h>
   68 #include <netinet/ip.h>
   69 #include <netinet/in_var.h>
   70 #include <netinet/in_pcb.h>
   71 #include <netinet/ip_var.h>
   72 #include <netinet/ip_options.h>
   73 #ifdef INET6
   74 #include <netinet/ip6.h>
   75 #include <netinet/icmp6.h>
   76 #include <netinet6/nd6.h>
   77 #include <netinet6/ip6_var.h>
   78 #include <netinet6/in6_pcb.h>
   79 #endif
   80 #include <netinet/tcp.h>
   81 #ifdef TCP_RFC7413
   82 #include <netinet/tcp_fastopen.h>
   83 #endif
   84 #include <netinet/tcp_fsm.h>
   85 #include <netinet/tcp_seq.h>
   86 #include <netinet/tcp_timer.h>
   87 #include <netinet/tcp_var.h>
   88 #include <netinet/tcp_syncache.h>
   89 #ifdef INET6
   90 #include <netinet6/tcp6_var.h>
   91 #endif
   92 #ifdef TCP_OFFLOAD
   93 #include <netinet/toecore.h>
   94 #endif
   95 
   96 #ifdef IPSEC
   97 #include <netipsec/ipsec.h>
   98 #ifdef INET6
   99 #include <netipsec/ipsec6.h>
  100 #endif
  101 #include <netipsec/key.h>
  102 #endif /*IPSEC*/
  103 
  104 #include <machine/in_cksum.h>
  105 
  106 #include <security/mac/mac_framework.h>
  107 
  108 static VNET_DEFINE(int, tcp_syncookies) = 1;
  109 #define V_tcp_syncookies                VNET(tcp_syncookies)
  110 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
  111     &VNET_NAME(tcp_syncookies), 0,
  112     "Use TCP SYN cookies if the syncache overflows");
  113 
  114 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
  115 #define V_tcp_syncookiesonly            VNET(tcp_syncookiesonly)
  116 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
  117     &VNET_NAME(tcp_syncookiesonly), 0,
  118     "Use only TCP SYN cookies");
  119 
  120 #ifdef TCP_OFFLOAD
  121 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
  122 #endif
  123 
  124 static void      syncache_drop(struct syncache *, struct syncache_head *);
  125 static void      syncache_free(struct syncache *);
  126 static void      syncache_insert(struct syncache *, struct syncache_head *);
  127 static int       syncache_respond(struct syncache *);
  128 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  129                     struct mbuf *m);
  130 static int       syncache_sysctl_count(SYSCTL_HANDLER_ARGS);
  131 static void      syncache_timeout(struct syncache *sc, struct syncache_head *sch,
  132                     int docallout);
  133 static void      syncache_timer(void *);
  134 
  135 static uint32_t  syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
  136                     uint8_t *, uintptr_t);
  137 static tcp_seq   syncookie_generate(struct syncache_head *, struct syncache *);
  138 static struct syncache
  139                 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
  140                     struct syncache *, struct tcphdr *, struct tcpopt *,
  141                     struct socket *);
  142 static void      syncookie_reseed(void *);
  143 #ifdef INVARIANTS
  144 static int       syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
  145                     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
  146                     struct socket *lso);
  147 #endif
  148 
  149 /*
  150  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  151  * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
  152  * the odds are that the user has given up attempting to connect by then.
  153  */
  154 #define SYNCACHE_MAXREXMTS              3
  155 
  156 /* Arbitrary values */
  157 #define TCP_SYNCACHE_HASHSIZE           512
  158 #define TCP_SYNCACHE_BUCKETLIMIT        30
  159 
  160 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
  161 #define V_tcp_syncache                  VNET(tcp_syncache)
  162 
  163 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
  164     "TCP SYN cache");
  165 
  166 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
  167     &VNET_NAME(tcp_syncache.bucket_limit), 0,
  168     "Per-bucket hash limit for syncache");
  169 
  170 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
  171     &VNET_NAME(tcp_syncache.cache_limit), 0,
  172     "Overall entry limit for syncache");
  173 
  174 SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD),
  175     NULL, 0, &syncache_sysctl_count, "IU",
  176     "Current number of entries in syncache");
  177 
  178 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
  179     &VNET_NAME(tcp_syncache.hashsize), 0,
  180     "Size of TCP syncache hashtable");
  181 
  182 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
  183     &VNET_NAME(tcp_syncache.rexmt_limit), 0,
  184     "Limit on SYN/ACK retransmissions");
  185 
  186 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
  187 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
  188     CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
  189     "Send reset on socket allocation failure");
  190 
  191 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  192 
  193 #define SYNCACHE_HASH(inc, mask)                                        \
  194         ((V_tcp_syncache.hash_secret ^                                  \
  195           (inc)->inc_faddr.s_addr ^                                     \
  196           ((inc)->inc_faddr.s_addr >> 16) ^                             \
  197           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  198 
  199 #define SYNCACHE_HASH6(inc, mask)                                       \
  200         ((V_tcp_syncache.hash_secret ^                                  \
  201           (inc)->inc6_faddr.s6_addr32[0] ^                              \
  202           (inc)->inc6_faddr.s6_addr32[3] ^                              \
  203           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  204 
  205 #define ENDPTS_EQ(a, b) (                                               \
  206         (a)->ie_fport == (b)->ie_fport &&                               \
  207         (a)->ie_lport == (b)->ie_lport &&                               \
  208         (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr &&                 \
  209         (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr                    \
  210 )
  211 
  212 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
  213 
  214 #define SCH_LOCK(sch)           mtx_lock(&(sch)->sch_mtx)
  215 #define SCH_UNLOCK(sch)         mtx_unlock(&(sch)->sch_mtx)
  216 #define SCH_LOCK_ASSERT(sch)    mtx_assert(&(sch)->sch_mtx, MA_OWNED)
  217 
  218 /*
  219  * Requires the syncache entry to be already removed from the bucket list.
  220  */
  221 static void
  222 syncache_free(struct syncache *sc)
  223 {
  224 
  225         if (sc->sc_ipopts)
  226                 (void) m_free(sc->sc_ipopts);
  227         if (sc->sc_cred)
  228                 crfree(sc->sc_cred);
  229 #ifdef MAC
  230         mac_syncache_destroy(&sc->sc_label);
  231 #endif
  232 
  233         uma_zfree(V_tcp_syncache.zone, sc);
  234 }
  235 
  236 void
  237 syncache_init(void)
  238 {
  239         int i;
  240 
  241         V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  242         V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  243         V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  244         V_tcp_syncache.hash_secret = arc4random();
  245 
  246         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  247             &V_tcp_syncache.hashsize);
  248         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  249             &V_tcp_syncache.bucket_limit);
  250         if (!powerof2(V_tcp_syncache.hashsize) ||
  251             V_tcp_syncache.hashsize == 0) {
  252                 printf("WARNING: syncache hash size is not a power of 2.\n");
  253                 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  254         }
  255         V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
  256 
  257         /* Set limits. */
  258         V_tcp_syncache.cache_limit =
  259             V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
  260         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  261             &V_tcp_syncache.cache_limit);
  262 
  263         /* Allocate the hash table. */
  264         V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
  265             sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
  266 
  267 #ifdef VIMAGE
  268         V_tcp_syncache.vnet = curvnet;
  269 #endif
  270 
  271         /* Initialize the hash buckets. */
  272         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  273                 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
  274                 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
  275                          NULL, MTX_DEF);
  276                 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
  277                          &V_tcp_syncache.hashbase[i].sch_mtx, 0);
  278                 V_tcp_syncache.hashbase[i].sch_length = 0;
  279                 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
  280         }
  281 
  282         /* Create the syncache entry zone. */
  283         V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  284             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  285         V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
  286             V_tcp_syncache.cache_limit);
  287 
  288         /* Start the SYN cookie reseeder callout. */
  289         callout_init(&V_tcp_syncache.secret.reseed, 1);
  290         arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
  291         arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
  292         callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
  293             syncookie_reseed, &V_tcp_syncache);
  294 }
  295 
  296 #ifdef VIMAGE
  297 void
  298 syncache_destroy(void)
  299 {
  300         struct syncache_head *sch;
  301         struct syncache *sc, *nsc;
  302         int i;
  303 
  304         /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
  305         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  306 
  307                 sch = &V_tcp_syncache.hashbase[i];
  308                 callout_drain(&sch->sch_timer);
  309 
  310                 SCH_LOCK(sch);
  311                 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
  312                         syncache_drop(sc, sch);
  313                 SCH_UNLOCK(sch);
  314                 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
  315                     ("%s: sch->sch_bucket not empty", __func__));
  316                 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
  317                     __func__, sch->sch_length));
  318                 mtx_destroy(&sch->sch_mtx);
  319         }
  320 
  321         KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
  322             ("%s: cache_count not 0", __func__));
  323 
  324         /* Free the allocated global resources. */
  325         uma_zdestroy(V_tcp_syncache.zone);
  326         free(V_tcp_syncache.hashbase, M_SYNCACHE);
  327 
  328         callout_drain(&V_tcp_syncache.secret.reseed);
  329 }
  330 #endif
  331 
  332 static int
  333 syncache_sysctl_count(SYSCTL_HANDLER_ARGS)
  334 {
  335         int count;
  336 
  337         count = uma_zone_get_cur(V_tcp_syncache.zone);
  338         return (sysctl_handle_int(oidp, &count, 0, req));
  339 }
  340 
  341 /*
  342  * Inserts a syncache entry into the specified bucket row.
  343  * Locks and unlocks the syncache_head autonomously.
  344  */
  345 static void
  346 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  347 {
  348         struct syncache *sc2;
  349 
  350         SCH_LOCK(sch);
  351 
  352         /*
  353          * Make sure that we don't overflow the per-bucket limit.
  354          * If the bucket is full, toss the oldest element.
  355          */
  356         if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
  357                 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
  358                         ("sch->sch_length incorrect"));
  359                 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
  360                 syncache_drop(sc2, sch);
  361                 TCPSTAT_INC(tcps_sc_bucketoverflow);
  362         }
  363 
  364         /* Put it into the bucket. */
  365         TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
  366         sch->sch_length++;
  367 
  368 #ifdef TCP_OFFLOAD
  369         if (ADDED_BY_TOE(sc)) {
  370                 struct toedev *tod = sc->sc_tod;
  371 
  372                 tod->tod_syncache_added(tod, sc->sc_todctx);
  373         }
  374 #endif
  375 
  376         /* Reinitialize the bucket row's timer. */
  377         if (sch->sch_length == 1)
  378                 sch->sch_nextc = ticks + INT_MAX;
  379         syncache_timeout(sc, sch, 1);
  380 
  381         SCH_UNLOCK(sch);
  382 
  383         TCPSTAT_INC(tcps_sc_added);
  384 }
  385 
  386 /*
  387  * Remove and free entry from syncache bucket row.
  388  * Expects locked syncache head.
  389  */
  390 static void
  391 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  392 {
  393 
  394         SCH_LOCK_ASSERT(sch);
  395 
  396         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  397         sch->sch_length--;
  398 
  399 #ifdef TCP_OFFLOAD
  400         if (ADDED_BY_TOE(sc)) {
  401                 struct toedev *tod = sc->sc_tod;
  402 
  403                 tod->tod_syncache_removed(tod, sc->sc_todctx);
  404         }
  405 #endif
  406 
  407         syncache_free(sc);
  408 }
  409 
  410 /*
  411  * Engage/reengage time on bucket row.
  412  */
  413 static void
  414 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
  415 {
  416         sc->sc_rxttime = ticks +
  417                 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
  418         sc->sc_rxmits++;
  419         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
  420                 sch->sch_nextc = sc->sc_rxttime;
  421                 if (docallout)
  422                         callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
  423                             syncache_timer, (void *)sch);
  424         }
  425 }
  426 
  427 /*
  428  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  429  * If we have retransmitted an entry the maximum number of times, expire it.
  430  * One separate timer for each bucket row.
  431  */
  432 static void
  433 syncache_timer(void *xsch)
  434 {
  435         struct syncache_head *sch = (struct syncache_head *)xsch;
  436         struct syncache *sc, *nsc;
  437         int tick = ticks;
  438         char *s;
  439 
  440         CURVNET_SET(sch->sch_sc->vnet);
  441 
  442         /* NB: syncache_head has already been locked by the callout. */
  443         SCH_LOCK_ASSERT(sch);
  444 
  445         /*
  446          * In the following cycle we may remove some entries and/or
  447          * advance some timeouts, so re-initialize the bucket timer.
  448          */
  449         sch->sch_nextc = tick + INT_MAX;
  450 
  451         TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
  452                 /*
  453                  * We do not check if the listen socket still exists
  454                  * and accept the case where the listen socket may be
  455                  * gone by the time we resend the SYN/ACK.  We do
  456                  * not expect this to happens often. If it does,
  457                  * then the RST will be sent by the time the remote
  458                  * host does the SYN/ACK->ACK.
  459                  */
  460                 if (TSTMP_GT(sc->sc_rxttime, tick)) {
  461                         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
  462                                 sch->sch_nextc = sc->sc_rxttime;
  463                         continue;
  464                 }
  465                 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
  466                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  467                                 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
  468                                     "giving up and removing syncache entry\n",
  469                                     s, __func__);
  470                                 free(s, M_TCPLOG);
  471                         }
  472                         syncache_drop(sc, sch);
  473                         TCPSTAT_INC(tcps_sc_stale);
  474                         continue;
  475                 }
  476                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  477                         log(LOG_DEBUG, "%s; %s: Response timeout, "
  478                             "retransmitting (%u) SYN|ACK\n",
  479                             s, __func__, sc->sc_rxmits);
  480                         free(s, M_TCPLOG);
  481                 }
  482 
  483                 (void) syncache_respond(sc);
  484                 TCPSTAT_INC(tcps_sc_retransmitted);
  485                 syncache_timeout(sc, sch, 0);
  486         }
  487         if (!TAILQ_EMPTY(&(sch)->sch_bucket))
  488                 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
  489                         syncache_timer, (void *)(sch));
  490         CURVNET_RESTORE();
  491 }
  492 
  493 /*
  494  * Find an entry in the syncache.
  495  * Returns always with locked syncache_head plus a matching entry or NULL.
  496  */
  497 static struct syncache *
  498 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  499 {
  500         struct syncache *sc;
  501         struct syncache_head *sch;
  502 
  503 #ifdef INET6
  504         if (inc->inc_flags & INC_ISIPV6) {
  505                 sch = &V_tcp_syncache.hashbase[
  506                     SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)];
  507                 *schp = sch;
  508 
  509                 SCH_LOCK(sch);
  510 
  511                 /* Circle through bucket row to find matching entry. */
  512                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  513                         if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  514                                 return (sc);
  515                 }
  516         } else
  517 #endif
  518         {
  519                 sch = &V_tcp_syncache.hashbase[
  520                     SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)];
  521                 *schp = sch;
  522 
  523                 SCH_LOCK(sch);
  524 
  525                 /* Circle through bucket row to find matching entry. */
  526                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  527 #ifdef INET6
  528                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
  529                                 continue;
  530 #endif
  531                         if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  532                                 return (sc);
  533                 }
  534         }
  535         SCH_LOCK_ASSERT(*schp);
  536         return (NULL);                  /* always returns with locked sch */
  537 }
  538 
  539 /*
  540  * This function is called when we get a RST for a
  541  * non-existent connection, so that we can see if the
  542  * connection is in the syn cache.  If it is, zap it.
  543  */
  544 void
  545 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
  546 {
  547         struct syncache *sc;
  548         struct syncache_head *sch;
  549         char *s = NULL;
  550 
  551         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  552         SCH_LOCK_ASSERT(sch);
  553 
  554         /*
  555          * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
  556          * See RFC 793 page 65, section SEGMENT ARRIVES.
  557          */
  558         if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
  559                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  560                         log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
  561                             "FIN flag set, segment ignored\n", s, __func__);
  562                 TCPSTAT_INC(tcps_badrst);
  563                 goto done;
  564         }
  565 
  566         /*
  567          * No corresponding connection was found in syncache.
  568          * If syncookies are enabled and possibly exclusively
  569          * used, or we are under memory pressure, a valid RST
  570          * may not find a syncache entry.  In that case we're
  571          * done and no SYN|ACK retransmissions will happen.
  572          * Otherwise the RST was misdirected or spoofed.
  573          */
  574         if (sc == NULL) {
  575                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  576                         log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
  577                             "syncache entry (possibly syncookie only), "
  578                             "segment ignored\n", s, __func__);
  579                 TCPSTAT_INC(tcps_badrst);
  580                 goto done;
  581         }
  582 
  583         /*
  584          * If the RST bit is set, check the sequence number to see
  585          * if this is a valid reset segment.
  586          * RFC 793 page 37:
  587          *   In all states except SYN-SENT, all reset (RST) segments
  588          *   are validated by checking their SEQ-fields.  A reset is
  589          *   valid if its sequence number is in the window.
  590          *
  591          *   The sequence number in the reset segment is normally an
  592          *   echo of our outgoing acknowlegement numbers, but some hosts
  593          *   send a reset with the sequence number at the rightmost edge
  594          *   of our receive window, and we have to handle this case.
  595          */
  596         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  597             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  598                 syncache_drop(sc, sch);
  599                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  600                         log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
  601                             "connection attempt aborted by remote endpoint\n",
  602                             s, __func__);
  603                 TCPSTAT_INC(tcps_sc_reset);
  604         } else {
  605                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  606                         log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
  607                             "IRS %u (+WND %u), segment ignored\n",
  608                             s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
  609                 TCPSTAT_INC(tcps_badrst);
  610         }
  611 
  612 done:
  613         if (s != NULL)
  614                 free(s, M_TCPLOG);
  615         SCH_UNLOCK(sch);
  616 }
  617 
  618 void
  619 syncache_badack(struct in_conninfo *inc)
  620 {
  621         struct syncache *sc;
  622         struct syncache_head *sch;
  623 
  624         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  625         SCH_LOCK_ASSERT(sch);
  626         if (sc != NULL) {
  627                 syncache_drop(sc, sch);
  628                 TCPSTAT_INC(tcps_sc_badack);
  629         }
  630         SCH_UNLOCK(sch);
  631 }
  632 
  633 void
  634 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
  635 {
  636         struct syncache *sc;
  637         struct syncache_head *sch;
  638 
  639         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  640         SCH_LOCK_ASSERT(sch);
  641         if (sc == NULL)
  642                 goto done;
  643 
  644         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  645         if (ntohl(th->th_seq) != sc->sc_iss)
  646                 goto done;
  647 
  648         /*
  649          * If we've rertransmitted 3 times and this is our second error,
  650          * we remove the entry.  Otherwise, we allow it to continue on.
  651          * This prevents us from incorrectly nuking an entry during a
  652          * spurious network outage.
  653          *
  654          * See tcp_notify().
  655          */
  656         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
  657                 sc->sc_flags |= SCF_UNREACH;
  658                 goto done;
  659         }
  660         syncache_drop(sc, sch);
  661         TCPSTAT_INC(tcps_sc_unreach);
  662 done:
  663         SCH_UNLOCK(sch);
  664 }
  665 
  666 /*
  667  * Build a new TCP socket structure from a syncache entry.
  668  */
  669 static struct socket *
  670 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  671 {
  672         struct inpcb *inp = NULL;
  673         struct socket *so;
  674         struct tcpcb *tp;
  675         int error;
  676         char *s;
  677 
  678         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  679 
  680         /*
  681          * Ok, create the full blown connection, and set things up
  682          * as they would have been set up if we had created the
  683          * connection when the SYN arrived.  If we can't create
  684          * the connection, abort it.
  685          */
  686         so = sonewconn(lso, SS_ISCONNECTED);
  687         if (so == NULL) {
  688                 /*
  689                  * Drop the connection; we will either send a RST or
  690                  * have the peer retransmit its SYN again after its
  691                  * RTO and try again.
  692                  */
  693                 TCPSTAT_INC(tcps_listendrop);
  694                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  695                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  696                             "due to limits or memory shortage\n",
  697                             s, __func__);
  698                         free(s, M_TCPLOG);
  699                 }
  700                 goto abort2;
  701         }
  702 #ifdef MAC
  703         mac_socketpeer_set_from_mbuf(m, so);
  704 #endif
  705 
  706         inp = sotoinpcb(so);
  707         inp->inp_inc.inc_fibnum = so->so_fibnum;
  708         INP_WLOCK(inp);
  709         INP_HASH_WLOCK(&V_tcbinfo);
  710 
  711         /* Insert new socket into PCB hash list. */
  712         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  713 #ifdef INET6
  714         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  715                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  716         } else {
  717                 inp->inp_vflag &= ~INP_IPV6;
  718                 inp->inp_vflag |= INP_IPV4;
  719 #endif
  720                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  721 #ifdef INET6
  722         }
  723 #endif
  724 
  725         /*
  726          * If there's an mbuf and it has a flowid, then let's initialise the
  727          * inp with that particular flowid.
  728          */
  729         if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
  730                 inp->inp_flowid = m->m_pkthdr.flowid;
  731                 inp->inp_flowtype = M_HASHTYPE_GET(m);
  732         }
  733 
  734         /*
  735          * Install in the reservation hash table for now, but don't yet
  736          * install a connection group since the full 4-tuple isn't yet
  737          * configured.
  738          */
  739         inp->inp_lport = sc->sc_inc.inc_lport;
  740         if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
  741                 /*
  742                  * Undo the assignments above if we failed to
  743                  * put the PCB on the hash lists.
  744                  */
  745 #ifdef INET6
  746                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  747                         inp->in6p_laddr = in6addr_any;
  748                 else
  749 #endif
  750                         inp->inp_laddr.s_addr = INADDR_ANY;
  751                 inp->inp_lport = 0;
  752                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  753                         log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
  754                             "with error %i\n",
  755                             s, __func__, error);
  756                         free(s, M_TCPLOG);
  757                 }
  758                 INP_HASH_WUNLOCK(&V_tcbinfo);
  759                 goto abort;
  760         }
  761 #ifdef IPSEC
  762         /* Copy old policy into new socket's. */
  763         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  764                 printf("syncache_socket: could not copy policy\n");
  765 #endif
  766 #ifdef INET6
  767         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  768                 struct inpcb *oinp = sotoinpcb(lso);
  769                 struct in6_addr laddr6;
  770                 struct sockaddr_in6 sin6;
  771                 /*
  772                  * Inherit socket options from the listening socket.
  773                  * Note that in6p_inputopts are not (and should not be)
  774                  * copied, since it stores previously received options and is
  775                  * used to detect if each new option is different than the
  776                  * previous one and hence should be passed to a user.
  777                  * If we copied in6p_inputopts, a user would not be able to
  778                  * receive options just after calling the accept system call.
  779                  */
  780                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  781                 if (oinp->in6p_outputopts)
  782                         inp->in6p_outputopts =
  783                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  784 
  785                 sin6.sin6_family = AF_INET6;
  786                 sin6.sin6_len = sizeof(sin6);
  787                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  788                 sin6.sin6_port = sc->sc_inc.inc_fport;
  789                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  790                 laddr6 = inp->in6p_laddr;
  791                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  792                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  793                 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
  794                     thread0.td_ucred, m)) != 0) {
  795                         inp->in6p_laddr = laddr6;
  796                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  797                                 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
  798                                     "with error %i\n",
  799                                     s, __func__, error);
  800                                 free(s, M_TCPLOG);
  801                         }
  802                         INP_HASH_WUNLOCK(&V_tcbinfo);
  803                         goto abort;
  804                 }
  805                 /* Override flowlabel from in6_pcbconnect. */
  806                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  807                 inp->inp_flow |= sc->sc_flowlabel;
  808         }
  809 #endif /* INET6 */
  810 #if defined(INET) && defined(INET6)
  811         else
  812 #endif
  813 #ifdef INET
  814         {
  815                 struct in_addr laddr;
  816                 struct sockaddr_in sin;
  817 
  818                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  819                 
  820                 if (inp->inp_options == NULL) {
  821                         inp->inp_options = sc->sc_ipopts;
  822                         sc->sc_ipopts = NULL;
  823                 }
  824 
  825                 sin.sin_family = AF_INET;
  826                 sin.sin_len = sizeof(sin);
  827                 sin.sin_addr = sc->sc_inc.inc_faddr;
  828                 sin.sin_port = sc->sc_inc.inc_fport;
  829                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  830                 laddr = inp->inp_laddr;
  831                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  832                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  833                 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
  834                     thread0.td_ucred, m)) != 0) {
  835                         inp->inp_laddr = laddr;
  836                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  837                                 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
  838                                     "with error %i\n",
  839                                     s, __func__, error);
  840                                 free(s, M_TCPLOG);
  841                         }
  842                         INP_HASH_WUNLOCK(&V_tcbinfo);
  843                         goto abort;
  844                 }
  845         }
  846 #endif /* INET */
  847         INP_HASH_WUNLOCK(&V_tcbinfo);
  848         tp = intotcpcb(inp);
  849         tcp_state_change(tp, TCPS_SYN_RECEIVED);
  850         tp->iss = sc->sc_iss;
  851         tp->irs = sc->sc_irs;
  852         tcp_rcvseqinit(tp);
  853         tcp_sendseqinit(tp);
  854         tp->snd_wl1 = sc->sc_irs;
  855         tp->snd_max = tp->iss + 1;
  856         tp->snd_nxt = tp->iss + 1;
  857         tp->rcv_up = sc->sc_irs + 1;
  858         tp->rcv_wnd = sc->sc_wnd;
  859         tp->rcv_adv += tp->rcv_wnd;
  860         tp->last_ack_sent = tp->rcv_nxt;
  861 
  862         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  863         if (sc->sc_flags & SCF_NOOPT)
  864                 tp->t_flags |= TF_NOOPT;
  865         else {
  866                 if (sc->sc_flags & SCF_WINSCALE) {
  867                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  868                         tp->snd_scale = sc->sc_requested_s_scale;
  869                         tp->request_r_scale = sc->sc_requested_r_scale;
  870                 }
  871                 if (sc->sc_flags & SCF_TIMESTAMP) {
  872                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  873                         tp->ts_recent = sc->sc_tsreflect;
  874                         tp->ts_recent_age = tcp_ts_getticks();
  875                         tp->ts_offset = sc->sc_tsoff;
  876                 }
  877 #ifdef TCP_SIGNATURE
  878                 if (sc->sc_flags & SCF_SIGNATURE)
  879                         tp->t_flags |= TF_SIGNATURE;
  880 #endif
  881                 if (sc->sc_flags & SCF_SACK)
  882                         tp->t_flags |= TF_SACK_PERMIT;
  883         }
  884 
  885         if (sc->sc_flags & SCF_ECN)
  886                 tp->t_flags |= TF_ECN_PERMIT;
  887 
  888         /*
  889          * Set up MSS and get cached values from tcp_hostcache.
  890          * This might overwrite some of the defaults we just set.
  891          */
  892         tcp_mss(tp, sc->sc_peer_mss);
  893 
  894         /*
  895          * If the SYN,ACK was retransmitted, indicate that CWND to be
  896          * limited to one segment in cc_conn_init().
  897          * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
  898          */
  899         if (sc->sc_rxmits > 1)
  900                 tp->snd_cwnd = 1;
  901 
  902 #ifdef TCP_OFFLOAD
  903         /*
  904          * Allow a TOE driver to install its hooks.  Note that we hold the
  905          * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
  906          * new connection before the TOE driver has done its thing.
  907          */
  908         if (ADDED_BY_TOE(sc)) {
  909                 struct toedev *tod = sc->sc_tod;
  910 
  911                 tod->tod_offload_socket(tod, sc->sc_todctx, so);
  912         }
  913 #endif
  914         /*
  915          * Copy and activate timers.
  916          */
  917         tp->t_keepinit = sototcpcb(lso)->t_keepinit;
  918         tp->t_keepidle = sototcpcb(lso)->t_keepidle;
  919         tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
  920         tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
  921         tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
  922 
  923         INP_WUNLOCK(inp);
  924 
  925         TCPSTAT_INC(tcps_accepts);
  926         return (so);
  927 
  928 abort:
  929         INP_WUNLOCK(inp);
  930 abort2:
  931         if (so != NULL)
  932                 soabort(so);
  933         return (NULL);
  934 }
  935 
  936 /*
  937  * This function gets called when we receive an ACK for a
  938  * socket in the LISTEN state.  We look up the connection
  939  * in the syncache, and if its there, we pull it out of
  940  * the cache and turn it into a full-blown connection in
  941  * the SYN-RECEIVED state.
  942  */
  943 int
  944 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  945     struct socket **lsop, struct mbuf *m)
  946 {
  947         struct syncache *sc;
  948         struct syncache_head *sch;
  949         struct syncache scs;
  950         char *s;
  951 
  952         /*
  953          * Global TCP locks are held because we manipulate the PCB lists
  954          * and create a new socket.
  955          */
  956         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  957         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  958             ("%s: can handle only ACK", __func__));
  959 
  960         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  961         SCH_LOCK_ASSERT(sch);
  962 
  963 #ifdef INVARIANTS
  964         /*
  965          * Test code for syncookies comparing the syncache stored
  966          * values with the reconstructed values from the cookie.
  967          */
  968         if (sc != NULL)
  969                 syncookie_cmp(inc, sch, sc, th, to, *lsop);
  970 #endif
  971 
  972         if (sc == NULL) {
  973                 /*
  974                  * There is no syncache entry, so see if this ACK is
  975                  * a returning syncookie.  To do this, first:
  976                  *  A. See if this socket has had a syncache entry dropped in
  977                  *     the past.  We don't want to accept a bogus syncookie
  978                  *     if we've never received a SYN.
  979                  *  B. check that the syncookie is valid.  If it is, then
  980                  *     cobble up a fake syncache entry, and return.
  981                  */
  982                 if (!V_tcp_syncookies) {
  983                         SCH_UNLOCK(sch);
  984                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  985                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  986                                     "segment rejected (syncookies disabled)\n",
  987                                     s, __func__);
  988                         goto failed;
  989                 }
  990                 bzero(&scs, sizeof(scs));
  991                 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
  992                 SCH_UNLOCK(sch);
  993                 if (sc == NULL) {
  994                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  995                                 log(LOG_DEBUG, "%s; %s: Segment failed "
  996                                     "SYNCOOKIE authentication, segment rejected "
  997                                     "(probably spoofed)\n", s, __func__);
  998                         goto failed;
  999                 }
 1000         } else {
 1001                 /* Pull out the entry to unlock the bucket row. */
 1002                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
 1003                 sch->sch_length--;
 1004 #ifdef TCP_OFFLOAD
 1005                 if (ADDED_BY_TOE(sc)) {
 1006                         struct toedev *tod = sc->sc_tod;
 1007 
 1008                         tod->tod_syncache_removed(tod, sc->sc_todctx);
 1009                 }
 1010 #endif
 1011                 SCH_UNLOCK(sch);
 1012         }
 1013 
 1014         /*
 1015          * Segment validation:
 1016          * ACK must match our initial sequence number + 1 (the SYN|ACK).
 1017          */
 1018         if (th->th_ack != sc->sc_iss + 1) {
 1019                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1020                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
 1021                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
 1022                 goto failed;
 1023         }
 1024 
 1025         /*
 1026          * The SEQ must fall in the window starting at the received
 1027          * initial receive sequence number + 1 (the SYN).
 1028          */
 1029         if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
 1030             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
 1031                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1032                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
 1033                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
 1034                 goto failed;
 1035         }
 1036 
 1037         /*
 1038          * If timestamps were not negotiated during SYN/ACK they
 1039          * must not appear on any segment during this session.
 1040          */
 1041         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
 1042                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1043                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1044                             "segment rejected\n", s, __func__);
 1045                 goto failed;
 1046         }
 1047 
 1048         /*
 1049          * If timestamps were negotiated during SYN/ACK they should
 1050          * appear on every segment during this session.
 1051          * XXXAO: This is only informal as there have been unverified
 1052          * reports of non-compliants stacks.
 1053          */
 1054         if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
 1055                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1056                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1057                             "no action\n", s, __func__);
 1058                         free(s, M_TCPLOG);
 1059                         s = NULL;
 1060                 }
 1061         }
 1062 
 1063         /*
 1064          * If timestamps were negotiated the reflected timestamp
 1065          * must be equal to what we actually sent in the SYN|ACK.
 1066          */
 1067         if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
 1068                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1069                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
 1070                             "segment rejected\n",
 1071                             s, __func__, to->to_tsecr, sc->sc_ts);
 1072                 goto failed;
 1073         }
 1074 
 1075         *lsop = syncache_socket(sc, *lsop, m);
 1076 
 1077         if (*lsop == NULL)
 1078                 TCPSTAT_INC(tcps_sc_aborted);
 1079         else
 1080                 TCPSTAT_INC(tcps_sc_completed);
 1081 
 1082 /* how do we find the inp for the new socket? */
 1083         if (sc != &scs)
 1084                 syncache_free(sc);
 1085         return (1);
 1086 failed:
 1087         if (sc != NULL && sc != &scs)
 1088                 syncache_free(sc);
 1089         if (s != NULL)
 1090                 free(s, M_TCPLOG);
 1091         *lsop = NULL;
 1092         return (0);
 1093 }
 1094 
 1095 #ifdef TCP_RFC7413
 1096 static void
 1097 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
 1098     uint64_t response_cookie)
 1099 {
 1100         struct inpcb *inp;
 1101         struct tcpcb *tp;
 1102         unsigned int *pending_counter;
 1103 
 1104         /*
 1105          * Global TCP locks are held because we manipulate the PCB lists
 1106          * and create a new socket.
 1107          */
 1108         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1109 
 1110         pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
 1111         *lsop = syncache_socket(sc, *lsop, m);
 1112         if (*lsop == NULL) {
 1113                 TCPSTAT_INC(tcps_sc_aborted);
 1114                 atomic_subtract_int(pending_counter, 1);
 1115         } else {
 1116                 inp = sotoinpcb(*lsop);
 1117                 tp = intotcpcb(inp);
 1118                 tp->t_flags |= TF_FASTOPEN;
 1119                 tp->t_tfo_cookie = response_cookie;
 1120                 tp->snd_max = tp->iss;
 1121                 tp->snd_nxt = tp->iss;
 1122                 tp->t_tfo_pending = pending_counter;
 1123                 TCPSTAT_INC(tcps_sc_completed);
 1124         }
 1125 }
 1126 #endif /* TCP_RFC7413 */
 1127 
 1128 /*
 1129  * Given a LISTEN socket and an inbound SYN request, add
 1130  * this to the syn cache, and send back a segment:
 1131  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 1132  * to the source.
 1133  *
 1134  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
 1135  * Doing so would require that we hold onto the data and deliver it
 1136  * to the application.  However, if we are the target of a SYN-flood
 1137  * DoS attack, an attacker could send data which would eventually
 1138  * consume all available buffer space if it were ACKed.  By not ACKing
 1139  * the data, we avoid this DoS scenario.
 1140  *
 1141  * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
 1142  * cookie is processed, V_tcp_fastopen_enabled set to true, and the
 1143  * TCP_FASTOPEN socket option is set.  In this case, a new socket is created
 1144  * and returned via lsop, the mbuf is not freed so that tcp_input() can
 1145  * queue its data to the socket, and 1 is returned to indicate the
 1146  * TFO-socket-creation path was taken.
 1147  */
 1148 int
 1149 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1150     struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
 1151     void *todctx)
 1152 {
 1153         struct tcpcb *tp;
 1154         struct socket *so;
 1155         struct syncache *sc = NULL;
 1156         struct syncache_head *sch;
 1157         struct mbuf *ipopts = NULL;
 1158         u_int ltflags;
 1159         int win, sb_hiwat, ip_ttl, ip_tos;
 1160         char *s;
 1161         int rv = 0;
 1162 #ifdef INET6
 1163         int autoflowlabel = 0;
 1164 #endif
 1165 #ifdef MAC
 1166         struct label *maclabel;
 1167 #endif
 1168         struct syncache scs;
 1169         struct ucred *cred;
 1170 #ifdef TCP_RFC7413
 1171         uint64_t tfo_response_cookie;
 1172         int tfo_cookie_valid = 0;
 1173         int tfo_response_cookie_valid = 0;
 1174 #endif
 1175 
 1176         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1177         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1178         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1179             ("%s: unexpected tcp flags", __func__));
 1180 
 1181         /*
 1182          * Combine all so/tp operations very early to drop the INP lock as
 1183          * soon as possible.
 1184          */
 1185         so = *lsop;
 1186         tp = sototcpcb(so);
 1187         cred = crhold(so->so_cred);
 1188 
 1189 #ifdef INET6
 1190         if ((inc->inc_flags & INC_ISIPV6) &&
 1191             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1192                 autoflowlabel = 1;
 1193 #endif
 1194         ip_ttl = inp->inp_ip_ttl;
 1195         ip_tos = inp->inp_ip_tos;
 1196         win = sbspace(&so->so_rcv);
 1197         sb_hiwat = so->so_rcv.sb_hiwat;
 1198         ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
 1199 
 1200 #ifdef TCP_RFC7413
 1201         if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
 1202             (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
 1203                 /*
 1204                  * Limit the number of pending TFO connections to
 1205                  * approximately half of the queue limit.  This prevents TFO
 1206                  * SYN floods from starving the service by filling the
 1207                  * listen queue with bogus TFO connections.
 1208                  */
 1209                 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
 1210                     (so->so_qlimit / 2)) {
 1211                         int result;
 1212 
 1213                         result = tcp_fastopen_check_cookie(inc,
 1214                             to->to_tfo_cookie, to->to_tfo_len,
 1215                             &tfo_response_cookie);
 1216                         tfo_cookie_valid = (result > 0);
 1217                         tfo_response_cookie_valid = (result >= 0);
 1218                 } else
 1219                         atomic_subtract_int(tp->t_tfo_pending, 1);
 1220         }
 1221 #endif
 1222 
 1223         /* By the time we drop the lock these should no longer be used. */
 1224         so = NULL;
 1225         tp = NULL;
 1226 
 1227 #ifdef MAC
 1228         if (mac_syncache_init(&maclabel) != 0) {
 1229                 INP_WUNLOCK(inp);
 1230                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1231                 goto done;
 1232         } else
 1233                 mac_syncache_create(maclabel, inp);
 1234 #endif
 1235 #ifdef TCP_RFC7413
 1236         if (!tfo_cookie_valid) {
 1237                 INP_WUNLOCK(inp);
 1238                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1239         }
 1240 #else
 1241         INP_WUNLOCK(inp);
 1242         INP_INFO_WUNLOCK(&V_tcbinfo);
 1243 #endif
 1244         
 1245         /*
 1246          * Remember the IP options, if any.
 1247          */
 1248 #ifdef INET6
 1249         if (!(inc->inc_flags & INC_ISIPV6))
 1250 #endif
 1251 #ifdef INET
 1252                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1253 #else
 1254                 ipopts = NULL;
 1255 #endif
 1256 
 1257         /*
 1258          * See if we already have an entry for this connection.
 1259          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1260          *
 1261          * XXX: should the syncache be re-initialized with the contents
 1262          * of the new SYN here (which may have different options?)
 1263          *
 1264          * XXX: We do not check the sequence number to see if this is a
 1265          * real retransmit or a new connection attempt.  The question is
 1266          * how to handle such a case; either ignore it as spoofed, or
 1267          * drop the current entry and create a new one?
 1268          */
 1269         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1270         SCH_LOCK_ASSERT(sch);
 1271         if (sc != NULL) {
 1272 #ifdef TCP_RFC7413
 1273                 if (tfo_cookie_valid) {
 1274                         INP_WUNLOCK(inp);
 1275                         INP_INFO_WUNLOCK(&V_tcbinfo);
 1276                 }
 1277 #endif
 1278                 TCPSTAT_INC(tcps_sc_dupsyn);
 1279                 if (ipopts) {
 1280                         /*
 1281                          * If we were remembering a previous source route,
 1282                          * forget it and use the new one we've been given.
 1283                          */
 1284                         if (sc->sc_ipopts)
 1285                                 (void) m_free(sc->sc_ipopts);
 1286                         sc->sc_ipopts = ipopts;
 1287                 }
 1288                 /*
 1289                  * Update timestamp if present.
 1290                  */
 1291                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1292                         sc->sc_tsreflect = to->to_tsval;
 1293                 else
 1294                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1295 #ifdef MAC
 1296                 /*
 1297                  * Since we have already unconditionally allocated label
 1298                  * storage, free it up.  The syncache entry will already
 1299                  * have an initialized label we can use.
 1300                  */
 1301                 mac_syncache_destroy(&maclabel);
 1302 #endif
 1303                 /* Retransmit SYN|ACK and reset retransmit count. */
 1304                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1305                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1306                             "resetting timer and retransmitting SYN|ACK\n",
 1307                             s, __func__);
 1308                         free(s, M_TCPLOG);
 1309                 }
 1310                 if (syncache_respond(sc) == 0) {
 1311                         sc->sc_rxmits = 0;
 1312                         syncache_timeout(sc, sch, 1);
 1313                         TCPSTAT_INC(tcps_sndacks);
 1314                         TCPSTAT_INC(tcps_sndtotal);
 1315                 }
 1316                 SCH_UNLOCK(sch);
 1317                 goto done;
 1318         }
 1319 
 1320 #ifdef TCP_RFC7413
 1321         if (tfo_cookie_valid) {
 1322                 bzero(&scs, sizeof(scs));
 1323                 sc = &scs;
 1324                 goto skip_alloc;
 1325         }
 1326 #endif
 1327 
 1328         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1329         if (sc == NULL) {
 1330                 /*
 1331                  * The zone allocator couldn't provide more entries.
 1332                  * Treat this as if the cache was full; drop the oldest
 1333                  * entry and insert the new one.
 1334                  */
 1335                 TCPSTAT_INC(tcps_sc_zonefail);
 1336                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
 1337                         syncache_drop(sc, sch);
 1338                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1339                 if (sc == NULL) {
 1340                         if (V_tcp_syncookies) {
 1341                                 bzero(&scs, sizeof(scs));
 1342                                 sc = &scs;
 1343                         } else {
 1344                                 SCH_UNLOCK(sch);
 1345                                 if (ipopts)
 1346                                         (void) m_free(ipopts);
 1347                                 goto done;
 1348                         }
 1349                 }
 1350         }
 1351 
 1352 #ifdef TCP_RFC7413
 1353 skip_alloc:
 1354         if (!tfo_cookie_valid && tfo_response_cookie_valid)
 1355                 sc->sc_tfo_cookie = &tfo_response_cookie;
 1356 #endif
 1357 
 1358         /*
 1359          * Fill in the syncache values.
 1360          */
 1361 #ifdef MAC
 1362         sc->sc_label = maclabel;
 1363 #endif
 1364         sc->sc_cred = cred;
 1365         cred = NULL;
 1366         sc->sc_ipopts = ipopts;
 1367         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1368 #ifdef INET6
 1369         if (!(inc->inc_flags & INC_ISIPV6))
 1370 #endif
 1371         {
 1372                 sc->sc_ip_tos = ip_tos;
 1373                 sc->sc_ip_ttl = ip_ttl;
 1374         }
 1375 #ifdef TCP_OFFLOAD
 1376         sc->sc_tod = tod;
 1377         sc->sc_todctx = todctx;
 1378 #endif
 1379         sc->sc_irs = th->th_seq;
 1380         sc->sc_iss = arc4random();
 1381         sc->sc_flags = 0;
 1382         sc->sc_flowlabel = 0;
 1383 
 1384         /*
 1385          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1386          * win was derived from socket earlier in the function.
 1387          */
 1388         win = imax(win, 0);
 1389         win = imin(win, TCP_MAXWIN);
 1390         sc->sc_wnd = win;
 1391 
 1392         if (V_tcp_do_rfc1323) {
 1393                 /*
 1394                  * A timestamp received in a SYN makes
 1395                  * it ok to send timestamp requests and replies.
 1396                  */
 1397                 if (to->to_flags & TOF_TS) {
 1398                         sc->sc_tsreflect = to->to_tsval;
 1399                         sc->sc_ts = tcp_ts_getticks();
 1400                         sc->sc_flags |= SCF_TIMESTAMP;
 1401                 }
 1402                 if (to->to_flags & TOF_SCALE) {
 1403                         int wscale = 0;
 1404 
 1405                         /*
 1406                          * Pick the smallest possible scaling factor that
 1407                          * will still allow us to scale up to sb_max, aka
 1408                          * kern.ipc.maxsockbuf.
 1409                          *
 1410                          * We do this because there are broken firewalls that
 1411                          * will corrupt the window scale option, leading to
 1412                          * the other endpoint believing that our advertised
 1413                          * window is unscaled.  At scale factors larger than
 1414                          * 5 the unscaled window will drop below 1500 bytes,
 1415                          * leading to serious problems when traversing these
 1416                          * broken firewalls.
 1417                          *
 1418                          * With the default maxsockbuf of 256K, a scale factor
 1419                          * of 3 will be chosen by this algorithm.  Those who
 1420                          * choose a larger maxsockbuf should watch out
 1421                          * for the compatiblity problems mentioned above.
 1422                          *
 1423                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1424                          * or <SYN,ACK>) segment itself is never scaled.
 1425                          */
 1426                         while (wscale < TCP_MAX_WINSHIFT &&
 1427                             (TCP_MAXWIN << wscale) < sb_max)
 1428                                 wscale++;
 1429                         sc->sc_requested_r_scale = wscale;
 1430                         sc->sc_requested_s_scale = to->to_wscale;
 1431                         sc->sc_flags |= SCF_WINSCALE;
 1432                 }
 1433         }
 1434 #ifdef TCP_SIGNATURE
 1435         /*
 1436          * If listening socket requested TCP digests, and received SYN
 1437          * contains the option, flag this in the syncache so that
 1438          * syncache_respond() will do the right thing with the SYN+ACK.
 1439          * XXX: Currently we always record the option by default and will
 1440          * attempt to use it in syncache_respond().
 1441          */
 1442         if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
 1443                 sc->sc_flags |= SCF_SIGNATURE;
 1444 #endif
 1445         if (to->to_flags & TOF_SACKPERM)
 1446                 sc->sc_flags |= SCF_SACK;
 1447         if (to->to_flags & TOF_MSS)
 1448                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1449         if (ltflags & TF_NOOPT)
 1450                 sc->sc_flags |= SCF_NOOPT;
 1451         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1452                 sc->sc_flags |= SCF_ECN;
 1453 
 1454         if (V_tcp_syncookies)
 1455                 sc->sc_iss = syncookie_generate(sch, sc);
 1456 #ifdef INET6
 1457         if (autoflowlabel) {
 1458                 if (V_tcp_syncookies)
 1459                         sc->sc_flowlabel = sc->sc_iss;
 1460                 else
 1461                         sc->sc_flowlabel = ip6_randomflowlabel();
 1462                 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
 1463         }
 1464 #endif
 1465         SCH_UNLOCK(sch);
 1466 
 1467 #ifdef TCP_RFC7413
 1468         if (tfo_cookie_valid) {
 1469                 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
 1470                 /* INP_WUNLOCK(inp) will be performed by the called */
 1471                 rv = 1;
 1472                 goto tfo_done;
 1473         }
 1474 #endif
 1475 
 1476         /*
 1477          * Do a standard 3-way handshake.
 1478          */
 1479         if (syncache_respond(sc) == 0) {
 1480                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1481                         syncache_free(sc);
 1482                 else if (sc != &scs)
 1483                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1484                 TCPSTAT_INC(tcps_sndacks);
 1485                 TCPSTAT_INC(tcps_sndtotal);
 1486         } else {
 1487                 if (sc != &scs)
 1488                         syncache_free(sc);
 1489                 TCPSTAT_INC(tcps_sc_dropped);
 1490         }
 1491 
 1492 done:
 1493         if (m) {
 1494                 *lsop = NULL;
 1495                 m_freem(m);
 1496         }
 1497 #ifdef TCP_RFC7413
 1498 tfo_done:
 1499 #endif
 1500         if (cred != NULL)
 1501                 crfree(cred);
 1502 #ifdef MAC
 1503         if (sc == &scs)
 1504                 mac_syncache_destroy(&maclabel);
 1505 #endif
 1506         return (rv);
 1507 }
 1508 
 1509 static int
 1510 syncache_respond(struct syncache *sc)
 1511 {
 1512         struct ip *ip = NULL;
 1513         struct mbuf *m;
 1514         struct tcphdr *th = NULL;
 1515         int optlen, error = 0;  /* Make compiler happy */
 1516         u_int16_t hlen, tlen, mssopt;
 1517         struct tcpopt to;
 1518 #ifdef INET6
 1519         struct ip6_hdr *ip6 = NULL;
 1520 #endif
 1521 
 1522         hlen =
 1523 #ifdef INET6
 1524                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1525 #endif
 1526                 sizeof(struct ip);
 1527         tlen = hlen + sizeof(struct tcphdr);
 1528 
 1529         /* Determine MSS we advertize to other end of connection. */
 1530         mssopt = tcp_mssopt(&sc->sc_inc);
 1531         if (sc->sc_peer_mss)
 1532                 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
 1533 
 1534         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1535         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1536             ("syncache: mbuf too small"));
 1537 
 1538         /* Create the IP+TCP header from scratch. */
 1539         m = m_gethdr(M_NOWAIT, MT_DATA);
 1540         if (m == NULL)
 1541                 return (ENOBUFS);
 1542 #ifdef MAC
 1543         mac_syncache_create_mbuf(sc->sc_label, m);
 1544 #endif
 1545         m->m_data += max_linkhdr;
 1546         m->m_len = tlen;
 1547         m->m_pkthdr.len = tlen;
 1548         m->m_pkthdr.rcvif = NULL;
 1549 
 1550 #ifdef INET6
 1551         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1552                 ip6 = mtod(m, struct ip6_hdr *);
 1553                 ip6->ip6_vfc = IPV6_VERSION;
 1554                 ip6->ip6_nxt = IPPROTO_TCP;
 1555                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1556                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1557                 ip6->ip6_plen = htons(tlen - hlen);
 1558                 /* ip6_hlim is set after checksum */
 1559                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1560                 ip6->ip6_flow |= sc->sc_flowlabel;
 1561 
 1562                 th = (struct tcphdr *)(ip6 + 1);
 1563         }
 1564 #endif
 1565 #if defined(INET6) && defined(INET)
 1566         else
 1567 #endif
 1568 #ifdef INET
 1569         {
 1570                 ip = mtod(m, struct ip *);
 1571                 ip->ip_v = IPVERSION;
 1572                 ip->ip_hl = sizeof(struct ip) >> 2;
 1573                 ip->ip_len = htons(tlen);
 1574                 ip->ip_id = 0;
 1575                 ip->ip_off = 0;
 1576                 ip->ip_sum = 0;
 1577                 ip->ip_p = IPPROTO_TCP;
 1578                 ip->ip_src = sc->sc_inc.inc_laddr;
 1579                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1580                 ip->ip_ttl = sc->sc_ip_ttl;
 1581                 ip->ip_tos = sc->sc_ip_tos;
 1582 
 1583                 /*
 1584                  * See if we should do MTU discovery.  Route lookups are
 1585                  * expensive, so we will only unset the DF bit if:
 1586                  *
 1587                  *      1) path_mtu_discovery is disabled
 1588                  *      2) the SCF_UNREACH flag has been set
 1589                  */
 1590                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1591                        ip->ip_off |= htons(IP_DF);
 1592 
 1593                 th = (struct tcphdr *)(ip + 1);
 1594         }
 1595 #endif /* INET */
 1596         th->th_sport = sc->sc_inc.inc_lport;
 1597         th->th_dport = sc->sc_inc.inc_fport;
 1598 
 1599         th->th_seq = htonl(sc->sc_iss);
 1600         th->th_ack = htonl(sc->sc_irs + 1);
 1601         th->th_off = sizeof(struct tcphdr) >> 2;
 1602         th->th_x2 = 0;
 1603         th->th_flags = TH_SYN|TH_ACK;
 1604         th->th_win = htons(sc->sc_wnd);
 1605         th->th_urp = 0;
 1606 
 1607         if (sc->sc_flags & SCF_ECN) {
 1608                 th->th_flags |= TH_ECE;
 1609                 TCPSTAT_INC(tcps_ecn_shs);
 1610         }
 1611 
 1612         /* Tack on the TCP options. */
 1613         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1614                 to.to_flags = 0;
 1615 
 1616                 to.to_mss = mssopt;
 1617                 to.to_flags = TOF_MSS;
 1618                 if (sc->sc_flags & SCF_WINSCALE) {
 1619                         to.to_wscale = sc->sc_requested_r_scale;
 1620                         to.to_flags |= TOF_SCALE;
 1621                 }
 1622                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1623                         /* Virgin timestamp or TCP cookie enhanced one. */
 1624                         to.to_tsval = sc->sc_ts;
 1625                         to.to_tsecr = sc->sc_tsreflect;
 1626                         to.to_flags |= TOF_TS;
 1627                 }
 1628                 if (sc->sc_flags & SCF_SACK)
 1629                         to.to_flags |= TOF_SACKPERM;
 1630 #ifdef TCP_SIGNATURE
 1631                 if (sc->sc_flags & SCF_SIGNATURE)
 1632                         to.to_flags |= TOF_SIGNATURE;
 1633 #endif
 1634 
 1635 #ifdef TCP_RFC7413
 1636                 if (sc->sc_tfo_cookie) {
 1637                         to.to_flags |= TOF_FASTOPEN;
 1638                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 1639                         to.to_tfo_cookie = sc->sc_tfo_cookie;
 1640                         /* don't send cookie again when retransmitting response */
 1641                         sc->sc_tfo_cookie = NULL;
 1642                 }
 1643 #endif
 1644                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1645 
 1646                 /* Adjust headers by option size. */
 1647                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1648                 m->m_len += optlen;
 1649                 m->m_pkthdr.len += optlen;
 1650 
 1651 #ifdef TCP_SIGNATURE
 1652                 if (sc->sc_flags & SCF_SIGNATURE)
 1653                         tcp_signature_compute(m, 0, 0, optlen,
 1654                             to.to_signature, IPSEC_DIR_OUTBOUND);
 1655 #endif
 1656 #ifdef INET6
 1657                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1658                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1659                 else
 1660 #endif
 1661                         ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
 1662         } else
 1663                 optlen = 0;
 1664 
 1665         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1666         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1667 #ifdef INET6
 1668         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1669                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 1670                 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
 1671                     IPPROTO_TCP, 0);
 1672                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1673 #ifdef TCP_OFFLOAD
 1674                 if (ADDED_BY_TOE(sc)) {
 1675                         struct toedev *tod = sc->sc_tod;
 1676 
 1677                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1678 
 1679                         return (error);
 1680                 }
 1681 #endif
 1682                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1683         }
 1684 #endif
 1685 #if defined(INET6) && defined(INET)
 1686         else
 1687 #endif
 1688 #ifdef INET
 1689         {
 1690                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1691                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1692                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1693 #ifdef TCP_OFFLOAD
 1694                 if (ADDED_BY_TOE(sc)) {
 1695                         struct toedev *tod = sc->sc_tod;
 1696 
 1697                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1698 
 1699                         return (error);
 1700                 }
 1701 #endif
 1702                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1703         }
 1704 #endif
 1705         return (error);
 1706 }
 1707 
 1708 /*
 1709  * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
 1710  * that exceed the capacity of the syncache by avoiding the storage of any
 1711  * of the SYNs we receive.  Syncookies defend against blind SYN flooding
 1712  * attacks where the attacker does not have access to our responses.
 1713  *
 1714  * Syncookies encode and include all necessary information about the
 1715  * connection setup within the SYN|ACK that we send back.  That way we
 1716  * can avoid keeping any local state until the ACK to our SYN|ACK returns
 1717  * (if ever).  Normally the syncache and syncookies are running in parallel
 1718  * with the latter taking over when the former is exhausted.  When matching
 1719  * syncache entry is found the syncookie is ignored.
 1720  *
 1721  * The only reliable information persisting the 3WHS is our inital sequence
 1722  * number ISS of 32 bits.  Syncookies embed a cryptographically sufficient
 1723  * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
 1724  * of our SYN|ACK.  The MAC can be recomputed when the ACK to our SYN|ACK
 1725  * returns and signifies a legitimate connection if it matches the ACK.
 1726  *
 1727  * The available space of 32 bits to store the hash and to encode the SYN
 1728  * option information is very tight and we should have at least 24 bits for
 1729  * the MAC to keep the number of guesses by blind spoofing reasonably high.
 1730  *
 1731  * SYN option information we have to encode to fully restore a connection:
 1732  * MSS: is imporant to chose an optimal segment size to avoid IP level
 1733  *   fragmentation along the path.  The common MSS values can be encoded
 1734  *   in a 3-bit table.  Uncommon values are captured by the next lower value
 1735  *   in the table leading to a slight increase in packetization overhead.
 1736  * WSCALE: is necessary to allow large windows to be used for high delay-
 1737  *   bandwidth product links.  Not scaling the window when it was initially
 1738  *   negotiated is bad for performance as lack of scaling further decreases
 1739  *   the apparent available send window.  We only need to encode the WSCALE
 1740  *   we received from the remote end.  Our end can be recalculated at any
 1741  *   time.  The common WSCALE values can be encoded in a 3-bit table.
 1742  *   Uncommon values are captured by the next lower value in the table
 1743  *   making us under-estimate the available window size halving our
 1744  *   theoretically possible maximum throughput for that connection.
 1745  * SACK: Greatly assists in packet loss recovery and requires 1 bit.
 1746  * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
 1747  *   that are included in all segments on a connection.  We enable them when
 1748  *   the ACK has them.
 1749  *
 1750  * Security of syncookies and attack vectors:
 1751  *
 1752  * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
 1753  * together with the gloabl secret to make it unique per connection attempt.
 1754  * Thus any change of any of those parameters results in a different MAC output
 1755  * in an unpredictable way unless a collision is encountered.  24 bits of the
 1756  * MAC are embedded into the ISS.
 1757  *
 1758  * To prevent replay attacks two rotating global secrets are updated with a
 1759  * new random value every 15 seconds.  The life-time of a syncookie is thus
 1760  * 15-30 seconds.
 1761  *
 1762  * Vector 1: Attacking the secret.  This requires finding a weakness in the
 1763  * MAC itself or the way it is used here.  The attacker can do a chosen plain
 1764  * text attack by varying and testing the all parameters under his control.
 1765  * The strength depends on the size and randomness of the secret, and the
 1766  * cryptographic security of the MAC function.  Due to the constant updating
 1767  * of the secret the attacker has at most 29.999 seconds to find the secret
 1768  * and launch spoofed connections.  After that he has to start all over again.
 1769  *
 1770  * Vector 2: Collision attack on the MAC of a single ACK.  With a 24 bit MAC
 1771  * size an average of 4,823 attempts are required for a 50% chance of success
 1772  * to spoof a single syncookie (birthday collision paradox).  However the
 1773  * attacker is blind and doesn't know if one of his attempts succeeded unless
 1774  * he has a side channel to interfere success from.  A single connection setup
 1775  * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
 1776  * This many attempts are required for each one blind spoofed connection.  For
 1777  * every additional spoofed connection he has to launch another N attempts.
 1778  * Thus for a sustained rate 100 spoofed connections per second approximately
 1779  * 1,800,000 packets per second would have to be sent.
 1780  *
 1781  * NB: The MAC function should be fast so that it doesn't become a CPU
 1782  * exhaustion attack vector itself.
 1783  *
 1784  * References:
 1785  *  RFC4987 TCP SYN Flooding Attacks and Common Mitigations
 1786  *  SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
 1787  *   http://cr.yp.to/syncookies.html    (overview)
 1788  *   http://cr.yp.to/syncookies/archive (details)
 1789  *
 1790  *
 1791  * Schematic construction of a syncookie enabled Initial Sequence Number:
 1792  *  0        1         2         3
 1793  *  12345678901234567890123456789012
 1794  * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
 1795  *
 1796  *  x 24 MAC (truncated)
 1797  *  W  3 Send Window Scale index
 1798  *  M  3 MSS index
 1799  *  S  1 SACK permitted
 1800  *  P  1 Odd/even secret
 1801  */
 1802 
 1803 /*
 1804  * Distribution and probability of certain MSS values.  Those in between are
 1805  * rounded down to the next lower one.
 1806  * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
 1807  *                            .2%  .3%   5%    7%    7%    20%   15%   45%
 1808  */
 1809 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
 1810 
 1811 /*
 1812  * Distribution and probability of certain WSCALE values.  We have to map the
 1813  * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
 1814  * bits based on prevalence of certain values.  Where we don't have an exact
 1815  * match for are rounded down to the next lower one letting us under-estimate
 1816  * the true available window.  At the moment this would happen only for the
 1817  * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
 1818  * and window size).  The absence of the WSCALE option (no scaling in either
 1819  * direction) is encoded with index zero.
 1820  * [WSCALE values histograms, Allman, 2012]
 1821  *                            X 10 10 35  5  6 14 10%   by host
 1822  *                            X 11  4  5  5 18 49  3%   by connections
 1823  */
 1824 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
 1825 
 1826 /*
 1827  * Compute the MAC for the SYN cookie.  SIPHASH-2-4 is chosen for its speed
 1828  * and good cryptographic properties.
 1829  */
 1830 static uint32_t
 1831 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
 1832     uint8_t *secbits, uintptr_t secmod)
 1833 {
 1834         SIPHASH_CTX ctx;
 1835         uint32_t siphash[2];
 1836 
 1837         SipHash24_Init(&ctx);
 1838         SipHash_SetKey(&ctx, secbits);
 1839         switch (inc->inc_flags & INC_ISIPV6) {
 1840 #ifdef INET
 1841         case 0:
 1842                 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
 1843                 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
 1844                 break;
 1845 #endif
 1846 #ifdef INET6
 1847         case INC_ISIPV6:
 1848                 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
 1849                 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
 1850                 break;
 1851 #endif
 1852         }
 1853         SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
 1854         SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
 1855         SipHash_Update(&ctx, &irs, sizeof(irs));
 1856         SipHash_Update(&ctx, &flags, sizeof(flags));
 1857         SipHash_Update(&ctx, &secmod, sizeof(secmod));
 1858         SipHash_Final((u_int8_t *)&siphash, &ctx);
 1859 
 1860         return (siphash[0] ^ siphash[1]);
 1861 }
 1862 
 1863 static tcp_seq
 1864 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
 1865 {
 1866         u_int i, mss, secbit, wscale;
 1867         uint32_t iss, hash;
 1868         uint8_t *secbits;
 1869         union syncookie cookie;
 1870 
 1871         SCH_LOCK_ASSERT(sch);
 1872 
 1873         cookie.cookie = 0;
 1874 
 1875         /* Map our computed MSS into the 3-bit index. */
 1876         mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
 1877         for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1;
 1878              tcp_sc_msstab[i] > mss && i > 0;
 1879              i--)
 1880                 ;
 1881         cookie.flags.mss_idx = i;
 1882 
 1883         /*
 1884          * Map the send window scale into the 3-bit index but only if
 1885          * the wscale option was received.
 1886          */
 1887         if (sc->sc_flags & SCF_WINSCALE) {
 1888                 wscale = sc->sc_requested_s_scale;
 1889                 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1;
 1890                      tcp_sc_wstab[i] > wscale && i > 0;
 1891                      i--)
 1892                         ;
 1893                 cookie.flags.wscale_idx = i;
 1894         }
 1895 
 1896         /* Can we do SACK? */
 1897         if (sc->sc_flags & SCF_SACK)
 1898                 cookie.flags.sack_ok = 1;
 1899 
 1900         /* Which of the two secrets to use. */
 1901         secbit = sch->sch_sc->secret.oddeven & 0x1;
 1902         cookie.flags.odd_even = secbit;
 1903 
 1904         secbits = sch->sch_sc->secret.key[secbit];
 1905         hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
 1906             (uintptr_t)sch);
 1907 
 1908         /*
 1909          * Put the flags into the hash and XOR them to get better ISS number
 1910          * variance.  This doesn't enhance the cryptographic strength and is
 1911          * done to prevent the 8 cookie bits from showing up directly on the
 1912          * wire.
 1913          */
 1914         iss = hash & ~0xff;
 1915         iss |= cookie.cookie ^ (hash >> 24);
 1916 
 1917         /* Randomize the timestamp. */
 1918         if (sc->sc_flags & SCF_TIMESTAMP) {
 1919                 sc->sc_ts = arc4random();
 1920                 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
 1921         }
 1922 
 1923         TCPSTAT_INC(tcps_sc_sendcookie);
 1924         return (iss);
 1925 }
 1926 
 1927 static struct syncache *
 1928 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 1929     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 1930     struct socket *lso)
 1931 {
 1932         uint32_t hash;
 1933         uint8_t *secbits;
 1934         tcp_seq ack, seq;
 1935         int wnd, wscale = 0;
 1936         union syncookie cookie;
 1937 
 1938         SCH_LOCK_ASSERT(sch);
 1939 
 1940         /*
 1941          * Pull information out of SYN-ACK/ACK and revert sequence number
 1942          * advances.
 1943          */
 1944         ack = th->th_ack - 1;
 1945         seq = th->th_seq - 1;
 1946 
 1947         /*
 1948          * Unpack the flags containing enough information to restore the
 1949          * connection.
 1950          */
 1951         cookie.cookie = (ack & 0xff) ^ (ack >> 24);
 1952 
 1953         /* Which of the two secrets to use. */
 1954         secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
 1955 
 1956         hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
 1957 
 1958         /* The recomputed hash matches the ACK if this was a genuine cookie. */
 1959         if ((ack & ~0xff) != (hash & ~0xff))
 1960                 return (NULL);
 1961 
 1962         /* Fill in the syncache values. */
 1963         sc->sc_flags = 0;
 1964         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1965         sc->sc_ipopts = NULL;
 1966         
 1967         sc->sc_irs = seq;
 1968         sc->sc_iss = ack;
 1969 
 1970         switch (inc->inc_flags & INC_ISIPV6) {
 1971 #ifdef INET
 1972         case 0:
 1973                 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
 1974                 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
 1975                 break;
 1976 #endif
 1977 #ifdef INET6
 1978         case INC_ISIPV6:
 1979                 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
 1980                         sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
 1981                 break;
 1982 #endif
 1983         }
 1984 
 1985         sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
 1986 
 1987         /* We can simply recompute receive window scale we sent earlier. */
 1988         while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
 1989                 wscale++;
 1990 
 1991         /* Only use wscale if it was enabled in the orignal SYN. */
 1992         if (cookie.flags.wscale_idx > 0) {
 1993                 sc->sc_requested_r_scale = wscale;
 1994                 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
 1995                 sc->sc_flags |= SCF_WINSCALE;
 1996         }
 1997 
 1998         wnd = sbspace(&lso->so_rcv);
 1999         wnd = imax(wnd, 0);
 2000         wnd = imin(wnd, TCP_MAXWIN);
 2001         sc->sc_wnd = wnd;
 2002 
 2003         if (cookie.flags.sack_ok)
 2004                 sc->sc_flags |= SCF_SACK;
 2005 
 2006         if (to->to_flags & TOF_TS) {
 2007                 sc->sc_flags |= SCF_TIMESTAMP;
 2008                 sc->sc_tsreflect = to->to_tsval;
 2009                 sc->sc_ts = to->to_tsecr;
 2010                 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
 2011         }
 2012 
 2013         if (to->to_flags & TOF_SIGNATURE)
 2014                 sc->sc_flags |= SCF_SIGNATURE;
 2015 
 2016         sc->sc_rxmits = 0;
 2017 
 2018         TCPSTAT_INC(tcps_sc_recvcookie);
 2019         return (sc);
 2020 }
 2021 
 2022 #ifdef INVARIANTS
 2023 static int
 2024 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
 2025     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2026     struct socket *lso)
 2027 {
 2028         struct syncache scs, *scx;
 2029         char *s;
 2030 
 2031         bzero(&scs, sizeof(scs));
 2032         scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
 2033 
 2034         if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
 2035                 return (0);
 2036 
 2037         if (scx != NULL) {
 2038                 if (sc->sc_peer_mss != scx->sc_peer_mss)
 2039                         log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
 2040                             s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
 2041 
 2042                 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
 2043                         log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
 2044                             s, __func__, sc->sc_requested_r_scale,
 2045                             scx->sc_requested_r_scale);
 2046 
 2047                 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
 2048                         log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
 2049                             s, __func__, sc->sc_requested_s_scale,
 2050                             scx->sc_requested_s_scale);
 2051 
 2052                 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
 2053                         log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
 2054         }
 2055 
 2056         if (s != NULL)
 2057                 free(s, M_TCPLOG);
 2058         return (0);
 2059 }
 2060 #endif /* INVARIANTS */
 2061 
 2062 static void
 2063 syncookie_reseed(void *arg)
 2064 {
 2065         struct tcp_syncache *sc = arg;
 2066         uint8_t *secbits;
 2067         int secbit;
 2068 
 2069         /*
 2070          * Reseeding the secret doesn't have to be protected by a lock.
 2071          * It only must be ensured that the new random values are visible
 2072          * to all CPUs in a SMP environment.  The atomic with release
 2073          * semantics ensures that.
 2074          */
 2075         secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
 2076         secbits = sc->secret.key[secbit];
 2077         arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
 2078         atomic_add_rel_int(&sc->secret.oddeven, 1);
 2079 
 2080         /* Reschedule ourself. */
 2081         callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
 2082 }
 2083 
 2084 /*
 2085  * Returns the current number of syncache entries.  This number
 2086  * will probably change before you get around to calling 
 2087  * syncache_pcblist.
 2088  */
 2089 int
 2090 syncache_pcbcount(void)
 2091 {
 2092         struct syncache_head *sch;
 2093         int count, i;
 2094 
 2095         for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 2096                 /* No need to lock for a read. */
 2097                 sch = &V_tcp_syncache.hashbase[i];
 2098                 count += sch->sch_length;
 2099         }
 2100         return count;
 2101 }
 2102 
 2103 /*
 2104  * Exports the syncache entries to userland so that netstat can display
 2105  * them alongside the other sockets.  This function is intended to be
 2106  * called only from tcp_pcblist.
 2107  *
 2108  * Due to concurrency on an active system, the number of pcbs exported
 2109  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 2110  * amount of space the caller allocated for this function to use.
 2111  */
 2112 int
 2113 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 2114 {
 2115         struct xtcpcb xt;
 2116         struct syncache *sc;
 2117         struct syncache_head *sch;
 2118         int count, error, i;
 2119 
 2120         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 2121                 sch = &V_tcp_syncache.hashbase[i];
 2122                 SCH_LOCK(sch);
 2123                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 2124                         if (count >= max_pcbs) {
 2125                                 SCH_UNLOCK(sch);
 2126                                 goto exit;
 2127                         }
 2128                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 2129                                 continue;
 2130                         bzero(&xt, sizeof(xt));
 2131                         xt.xt_len = sizeof(xt);
 2132                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 2133                                 xt.xt_inp.inp_vflag = INP_IPV6;
 2134                         else
 2135                                 xt.xt_inp.inp_vflag = INP_IPV4;
 2136                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 2137                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 2138                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 2139                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 2140                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 2141                         xt.xt_socket.so_type = SOCK_STREAM;
 2142                         xt.xt_socket.so_state = SS_ISCONNECTING;
 2143                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 2144                         if (error) {
 2145                                 SCH_UNLOCK(sch);
 2146                                 goto exit;
 2147                         }
 2148                         count++;
 2149                 }
 2150                 SCH_UNLOCK(sch);
 2151         }
 2152 exit:
 2153         *pcbs_exported = count;
 2154         return error;
 2155 }

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