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/11.0/sys/netinet/tcp_syncache.c 299315 2016-05-10 04:59:04Z sephe $");
   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/hash.h>
   44 #include <sys/refcount.h>
   45 #include <sys/kernel.h>
   46 #include <sys/sysctl.h>
   47 #include <sys/limits.h>
   48 #include <sys/lock.h>
   49 #include <sys/mutex.h>
   50 #include <sys/malloc.h>
   51 #include <sys/mbuf.h>
   52 #include <sys/proc.h>           /* for proc0 declaration */
   53 #include <sys/random.h>
   54 #include <sys/socket.h>
   55 #include <sys/socketvar.h>
   56 #include <sys/syslog.h>
   57 #include <sys/ucred.h>
   58 
   59 #include <sys/md5.h>
   60 #include <crypto/siphash/siphash.h>
   61 
   62 #include <vm/uma.h>
   63 
   64 #include <net/if.h>
   65 #include <net/if_var.h>
   66 #include <net/route.h>
   67 #include <net/vnet.h>
   68 
   69 #include <netinet/in.h>
   70 #include <netinet/in_systm.h>
   71 #include <netinet/ip.h>
   72 #include <netinet/in_var.h>
   73 #include <netinet/in_pcb.h>
   74 #include <netinet/ip_var.h>
   75 #include <netinet/ip_options.h>
   76 #ifdef INET6
   77 #include <netinet/ip6.h>
   78 #include <netinet/icmp6.h>
   79 #include <netinet6/nd6.h>
   80 #include <netinet6/ip6_var.h>
   81 #include <netinet6/in6_pcb.h>
   82 #endif
   83 #include <netinet/tcp.h>
   84 #ifdef TCP_RFC7413
   85 #include <netinet/tcp_fastopen.h>
   86 #endif
   87 #include <netinet/tcp_fsm.h>
   88 #include <netinet/tcp_seq.h>
   89 #include <netinet/tcp_timer.h>
   90 #include <netinet/tcp_var.h>
   91 #include <netinet/tcp_syncache.h>
   92 #ifdef INET6
   93 #include <netinet6/tcp6_var.h>
   94 #endif
   95 #ifdef TCP_OFFLOAD
   96 #include <netinet/toecore.h>
   97 #endif
   98 
   99 #ifdef IPSEC
  100 #include <netipsec/ipsec.h>
  101 #ifdef INET6
  102 #include <netipsec/ipsec6.h>
  103 #endif
  104 #include <netipsec/key.h>
  105 #endif /*IPSEC*/
  106 
  107 #include <machine/in_cksum.h>
  108 
  109 #include <security/mac/mac_framework.h>
  110 
  111 static VNET_DEFINE(int, tcp_syncookies) = 1;
  112 #define V_tcp_syncookies                VNET(tcp_syncookies)
  113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
  114     &VNET_NAME(tcp_syncookies), 0,
  115     "Use TCP SYN cookies if the syncache overflows");
  116 
  117 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
  118 #define V_tcp_syncookiesonly            VNET(tcp_syncookiesonly)
  119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
  120     &VNET_NAME(tcp_syncookiesonly), 0,
  121     "Use only TCP SYN cookies");
  122 
  123 #ifdef TCP_OFFLOAD
  124 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
  125 #endif
  126 
  127 static void      syncache_drop(struct syncache *, struct syncache_head *);
  128 static void      syncache_free(struct syncache *);
  129 static void      syncache_insert(struct syncache *, struct syncache_head *);
  130 static int       syncache_respond(struct syncache *, struct syncache_head *, int,
  131                     const struct mbuf *);
  132 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  133                     struct mbuf *m);
  134 static void      syncache_timeout(struct syncache *sc, struct syncache_head *sch,
  135                     int docallout);
  136 static void      syncache_timer(void *);
  137 
  138 static uint32_t  syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
  139                     uint8_t *, uintptr_t);
  140 static tcp_seq   syncookie_generate(struct syncache_head *, struct syncache *);
  141 static struct syncache
  142                 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
  143                     struct syncache *, struct tcphdr *, struct tcpopt *,
  144                     struct socket *);
  145 static void      syncookie_reseed(void *);
  146 #ifdef INVARIANTS
  147 static int       syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
  148                     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
  149                     struct socket *lso);
  150 #endif
  151 
  152 /*
  153  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  154  * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
  155  * the odds are that the user has given up attempting to connect by then.
  156  */
  157 #define SYNCACHE_MAXREXMTS              3
  158 
  159 /* Arbitrary values */
  160 #define TCP_SYNCACHE_HASHSIZE           512
  161 #define TCP_SYNCACHE_BUCKETLIMIT        30
  162 
  163 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
  164 #define V_tcp_syncache                  VNET(tcp_syncache)
  165 
  166 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
  167     "TCP SYN cache");
  168 
  169 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
  170     &VNET_NAME(tcp_syncache.bucket_limit), 0,
  171     "Per-bucket hash limit for syncache");
  172 
  173 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
  174     &VNET_NAME(tcp_syncache.cache_limit), 0,
  175     "Overall entry limit for syncache");
  176 
  177 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
  178     &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
  179 
  180 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
  181     &VNET_NAME(tcp_syncache.hashsize), 0,
  182     "Size of TCP syncache hashtable");
  183 
  184 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW,
  185     &VNET_NAME(tcp_syncache.rexmt_limit), 0,
  186     "Limit on SYN/ACK retransmissions");
  187 
  188 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
  189 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
  190     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
  191     "Send reset on socket allocation failure");
  192 
  193 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  194 
  195 #define SCH_LOCK(sch)           mtx_lock(&(sch)->sch_mtx)
  196 #define SCH_UNLOCK(sch)         mtx_unlock(&(sch)->sch_mtx)
  197 #define SCH_LOCK_ASSERT(sch)    mtx_assert(&(sch)->sch_mtx, MA_OWNED)
  198 
  199 /*
  200  * Requires the syncache entry to be already removed from the bucket list.
  201  */
  202 static void
  203 syncache_free(struct syncache *sc)
  204 {
  205 
  206         if (sc->sc_ipopts)
  207                 (void) m_free(sc->sc_ipopts);
  208         if (sc->sc_cred)
  209                 crfree(sc->sc_cred);
  210 #ifdef MAC
  211         mac_syncache_destroy(&sc->sc_label);
  212 #endif
  213 
  214         uma_zfree(V_tcp_syncache.zone, sc);
  215 }
  216 
  217 void
  218 syncache_init(void)
  219 {
  220         int i;
  221 
  222         V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  223         V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  224         V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  225         V_tcp_syncache.hash_secret = arc4random();
  226 
  227         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  228             &V_tcp_syncache.hashsize);
  229         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  230             &V_tcp_syncache.bucket_limit);
  231         if (!powerof2(V_tcp_syncache.hashsize) ||
  232             V_tcp_syncache.hashsize == 0) {
  233                 printf("WARNING: syncache hash size is not a power of 2.\n");
  234                 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  235         }
  236         V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
  237 
  238         /* Set limits. */
  239         V_tcp_syncache.cache_limit =
  240             V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
  241         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  242             &V_tcp_syncache.cache_limit);
  243 
  244         /* Allocate the hash table. */
  245         V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
  246             sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
  247 
  248 #ifdef VIMAGE
  249         V_tcp_syncache.vnet = curvnet;
  250 #endif
  251 
  252         /* Initialize the hash buckets. */
  253         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  254                 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
  255                 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
  256                          NULL, MTX_DEF);
  257                 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
  258                          &V_tcp_syncache.hashbase[i].sch_mtx, 0);
  259                 V_tcp_syncache.hashbase[i].sch_length = 0;
  260                 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
  261         }
  262 
  263         /* Create the syncache entry zone. */
  264         V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  265             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  266         V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
  267             V_tcp_syncache.cache_limit);
  268 
  269         /* Start the SYN cookie reseeder callout. */
  270         callout_init(&V_tcp_syncache.secret.reseed, 1);
  271         arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
  272         arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
  273         callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
  274             syncookie_reseed, &V_tcp_syncache);
  275 }
  276 
  277 #ifdef VIMAGE
  278 void
  279 syncache_destroy(void)
  280 {
  281         struct syncache_head *sch;
  282         struct syncache *sc, *nsc;
  283         int i;
  284 
  285         /*
  286          * Stop the re-seed timer before freeing resources.  No need to
  287          * possibly schedule it another time.
  288          */
  289         callout_drain(&V_tcp_syncache.secret.reseed);
  290 
  291         /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
  292         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  293 
  294                 sch = &V_tcp_syncache.hashbase[i];
  295                 callout_drain(&sch->sch_timer);
  296 
  297                 SCH_LOCK(sch);
  298                 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
  299                         syncache_drop(sc, sch);
  300                 SCH_UNLOCK(sch);
  301                 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
  302                     ("%s: sch->sch_bucket not empty", __func__));
  303                 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
  304                     __func__, sch->sch_length));
  305                 mtx_destroy(&sch->sch_mtx);
  306         }
  307 
  308         KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
  309             ("%s: cache_count not 0", __func__));
  310 
  311         /* Free the allocated global resources. */
  312         uma_zdestroy(V_tcp_syncache.zone);
  313         free(V_tcp_syncache.hashbase, M_SYNCACHE);
  314 }
  315 #endif
  316 
  317 /*
  318  * Inserts a syncache entry into the specified bucket row.
  319  * Locks and unlocks the syncache_head autonomously.
  320  */
  321 static void
  322 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  323 {
  324         struct syncache *sc2;
  325 
  326         SCH_LOCK(sch);
  327 
  328         /*
  329          * Make sure that we don't overflow the per-bucket limit.
  330          * If the bucket is full, toss the oldest element.
  331          */
  332         if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
  333                 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
  334                         ("sch->sch_length incorrect"));
  335                 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
  336                 syncache_drop(sc2, sch);
  337                 TCPSTAT_INC(tcps_sc_bucketoverflow);
  338         }
  339 
  340         /* Put it into the bucket. */
  341         TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
  342         sch->sch_length++;
  343 
  344 #ifdef TCP_OFFLOAD
  345         if (ADDED_BY_TOE(sc)) {
  346                 struct toedev *tod = sc->sc_tod;
  347 
  348                 tod->tod_syncache_added(tod, sc->sc_todctx);
  349         }
  350 #endif
  351 
  352         /* Reinitialize the bucket row's timer. */
  353         if (sch->sch_length == 1)
  354                 sch->sch_nextc = ticks + INT_MAX;
  355         syncache_timeout(sc, sch, 1);
  356 
  357         SCH_UNLOCK(sch);
  358 
  359         TCPSTATES_INC(TCPS_SYN_RECEIVED);
  360         TCPSTAT_INC(tcps_sc_added);
  361 }
  362 
  363 /*
  364  * Remove and free entry from syncache bucket row.
  365  * Expects locked syncache head.
  366  */
  367 static void
  368 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  369 {
  370 
  371         SCH_LOCK_ASSERT(sch);
  372 
  373         TCPSTATES_DEC(TCPS_SYN_RECEIVED);
  374         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  375         sch->sch_length--;
  376 
  377 #ifdef TCP_OFFLOAD
  378         if (ADDED_BY_TOE(sc)) {
  379                 struct toedev *tod = sc->sc_tod;
  380 
  381                 tod->tod_syncache_removed(tod, sc->sc_todctx);
  382         }
  383 #endif
  384 
  385         syncache_free(sc);
  386 }
  387 
  388 /*
  389  * Engage/reengage time on bucket row.
  390  */
  391 static void
  392 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
  393 {
  394         sc->sc_rxttime = ticks +
  395                 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
  396         sc->sc_rxmits++;
  397         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
  398                 sch->sch_nextc = sc->sc_rxttime;
  399                 if (docallout)
  400                         callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
  401                             syncache_timer, (void *)sch);
  402         }
  403 }
  404 
  405 /*
  406  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  407  * If we have retransmitted an entry the maximum number of times, expire it.
  408  * One separate timer for each bucket row.
  409  */
  410 static void
  411 syncache_timer(void *xsch)
  412 {
  413         struct syncache_head *sch = (struct syncache_head *)xsch;
  414         struct syncache *sc, *nsc;
  415         int tick = ticks;
  416         char *s;
  417 
  418         CURVNET_SET(sch->sch_sc->vnet);
  419 
  420         /* NB: syncache_head has already been locked by the callout. */
  421         SCH_LOCK_ASSERT(sch);
  422 
  423         /*
  424          * In the following cycle we may remove some entries and/or
  425          * advance some timeouts, so re-initialize the bucket timer.
  426          */
  427         sch->sch_nextc = tick + INT_MAX;
  428 
  429         TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
  430                 /*
  431                  * We do not check if the listen socket still exists
  432                  * and accept the case where the listen socket may be
  433                  * gone by the time we resend the SYN/ACK.  We do
  434                  * not expect this to happens often. If it does,
  435                  * then the RST will be sent by the time the remote
  436                  * host does the SYN/ACK->ACK.
  437                  */
  438                 if (TSTMP_GT(sc->sc_rxttime, tick)) {
  439                         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
  440                                 sch->sch_nextc = sc->sc_rxttime;
  441                         continue;
  442                 }
  443                 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
  444                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  445                                 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
  446                                     "giving up and removing syncache entry\n",
  447                                     s, __func__);
  448                                 free(s, M_TCPLOG);
  449                         }
  450                         syncache_drop(sc, sch);
  451                         TCPSTAT_INC(tcps_sc_stale);
  452                         continue;
  453                 }
  454                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  455                         log(LOG_DEBUG, "%s; %s: Response timeout, "
  456                             "retransmitting (%u) SYN|ACK\n",
  457                             s, __func__, sc->sc_rxmits);
  458                         free(s, M_TCPLOG);
  459                 }
  460 
  461                 syncache_respond(sc, sch, 1, NULL);
  462                 TCPSTAT_INC(tcps_sc_retransmitted);
  463                 syncache_timeout(sc, sch, 0);
  464         }
  465         if (!TAILQ_EMPTY(&(sch)->sch_bucket))
  466                 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
  467                         syncache_timer, (void *)(sch));
  468         CURVNET_RESTORE();
  469 }
  470 
  471 /*
  472  * Find an entry in the syncache.
  473  * Returns always with locked syncache_head plus a matching entry or NULL.
  474  */
  475 static struct syncache *
  476 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  477 {
  478         struct syncache *sc;
  479         struct syncache_head *sch;
  480         uint32_t hash;
  481 
  482         /*
  483          * The hash is built on foreign port + local port + foreign address.
  484          * We rely on the fact that struct in_conninfo starts with 16 bits
  485          * of foreign port, then 16 bits of local port then followed by 128
  486          * bits of foreign address.  In case of IPv4 address, the first 3
  487          * 32-bit words of the address always are zeroes.
  488          */
  489         hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
  490             V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
  491 
  492         sch = &V_tcp_syncache.hashbase[hash];
  493         *schp = sch;
  494         SCH_LOCK(sch);
  495 
  496         /* Circle through bucket row to find matching entry. */
  497         TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
  498                 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
  499                     sizeof(struct in_endpoints)) == 0)
  500                         break;
  501 
  502         return (sc);    /* Always returns with locked sch. */
  503 }
  504 
  505 /*
  506  * This function is called when we get a RST for a
  507  * non-existent connection, so that we can see if the
  508  * connection is in the syn cache.  If it is, zap it.
  509  */
  510 void
  511 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
  512 {
  513         struct syncache *sc;
  514         struct syncache_head *sch;
  515         char *s = NULL;
  516 
  517         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  518         SCH_LOCK_ASSERT(sch);
  519 
  520         /*
  521          * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
  522          * See RFC 793 page 65, section SEGMENT ARRIVES.
  523          */
  524         if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
  525                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  526                         log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
  527                             "FIN flag set, segment ignored\n", s, __func__);
  528                 TCPSTAT_INC(tcps_badrst);
  529                 goto done;
  530         }
  531 
  532         /*
  533          * No corresponding connection was found in syncache.
  534          * If syncookies are enabled and possibly exclusively
  535          * used, or we are under memory pressure, a valid RST
  536          * may not find a syncache entry.  In that case we're
  537          * done and no SYN|ACK retransmissions will happen.
  538          * Otherwise the RST was misdirected or spoofed.
  539          */
  540         if (sc == NULL) {
  541                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  542                         log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
  543                             "syncache entry (possibly syncookie only), "
  544                             "segment ignored\n", s, __func__);
  545                 TCPSTAT_INC(tcps_badrst);
  546                 goto done;
  547         }
  548 
  549         /*
  550          * If the RST bit is set, check the sequence number to see
  551          * if this is a valid reset segment.
  552          * RFC 793 page 37:
  553          *   In all states except SYN-SENT, all reset (RST) segments
  554          *   are validated by checking their SEQ-fields.  A reset is
  555          *   valid if its sequence number is in the window.
  556          *
  557          *   The sequence number in the reset segment is normally an
  558          *   echo of our outgoing acknowlegement numbers, but some hosts
  559          *   send a reset with the sequence number at the rightmost edge
  560          *   of our receive window, and we have to handle this case.
  561          */
  562         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  563             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  564                 syncache_drop(sc, sch);
  565                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  566                         log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
  567                             "connection attempt aborted by remote endpoint\n",
  568                             s, __func__);
  569                 TCPSTAT_INC(tcps_sc_reset);
  570         } else {
  571                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  572                         log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
  573                             "IRS %u (+WND %u), segment ignored\n",
  574                             s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
  575                 TCPSTAT_INC(tcps_badrst);
  576         }
  577 
  578 done:
  579         if (s != NULL)
  580                 free(s, M_TCPLOG);
  581         SCH_UNLOCK(sch);
  582 }
  583 
  584 void
  585 syncache_badack(struct in_conninfo *inc)
  586 {
  587         struct syncache *sc;
  588         struct syncache_head *sch;
  589 
  590         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  591         SCH_LOCK_ASSERT(sch);
  592         if (sc != NULL) {
  593                 syncache_drop(sc, sch);
  594                 TCPSTAT_INC(tcps_sc_badack);
  595         }
  596         SCH_UNLOCK(sch);
  597 }
  598 
  599 void
  600 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
  601 {
  602         struct syncache *sc;
  603         struct syncache_head *sch;
  604 
  605         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  606         SCH_LOCK_ASSERT(sch);
  607         if (sc == NULL)
  608                 goto done;
  609 
  610         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  611         if (ntohl(th->th_seq) != sc->sc_iss)
  612                 goto done;
  613 
  614         /*
  615          * If we've rertransmitted 3 times and this is our second error,
  616          * we remove the entry.  Otherwise, we allow it to continue on.
  617          * This prevents us from incorrectly nuking an entry during a
  618          * spurious network outage.
  619          *
  620          * See tcp_notify().
  621          */
  622         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
  623                 sc->sc_flags |= SCF_UNREACH;
  624                 goto done;
  625         }
  626         syncache_drop(sc, sch);
  627         TCPSTAT_INC(tcps_sc_unreach);
  628 done:
  629         SCH_UNLOCK(sch);
  630 }
  631 
  632 /*
  633  * Build a new TCP socket structure from a syncache entry.
  634  *
  635  * On success return the newly created socket with its underlying inp locked.
  636  */
  637 static struct socket *
  638 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  639 {
  640         struct tcp_function_block *blk;
  641         struct inpcb *inp = NULL;
  642         struct socket *so;
  643         struct tcpcb *tp;
  644         int error;
  645         char *s;
  646 
  647         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  648 
  649         /*
  650          * Ok, create the full blown connection, and set things up
  651          * as they would have been set up if we had created the
  652          * connection when the SYN arrived.  If we can't create
  653          * the connection, abort it.
  654          */
  655         so = sonewconn(lso, 0);
  656         if (so == NULL) {
  657                 /*
  658                  * Drop the connection; we will either send a RST or
  659                  * have the peer retransmit its SYN again after its
  660                  * RTO and try again.
  661                  */
  662                 TCPSTAT_INC(tcps_listendrop);
  663                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  664                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  665                             "due to limits or memory shortage\n",
  666                             s, __func__);
  667                         free(s, M_TCPLOG);
  668                 }
  669                 goto abort2;
  670         }
  671 #ifdef MAC
  672         mac_socketpeer_set_from_mbuf(m, so);
  673 #endif
  674 
  675         inp = sotoinpcb(so);
  676         inp->inp_inc.inc_fibnum = so->so_fibnum;
  677         INP_WLOCK(inp);
  678         /*
  679          * Exclusive pcbinfo lock is not required in syncache socket case even
  680          * if two inpcb locks can be acquired simultaneously:
  681          *  - the inpcb in LISTEN state,
  682          *  - the newly created inp.
  683          *
  684          * In this case, an inp cannot be at same time in LISTEN state and
  685          * just created by an accept() call.
  686          */
  687         INP_HASH_WLOCK(&V_tcbinfo);
  688 
  689         /* Insert new socket into PCB hash list. */
  690         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  691 #ifdef INET6
  692         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  693                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  694         } else {
  695                 inp->inp_vflag &= ~INP_IPV6;
  696                 inp->inp_vflag |= INP_IPV4;
  697 #endif
  698                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  699 #ifdef INET6
  700         }
  701 #endif
  702 
  703         /*
  704          * If there's an mbuf and it has a flowid, then let's initialise the
  705          * inp with that particular flowid.
  706          */
  707         if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
  708                 inp->inp_flowid = m->m_pkthdr.flowid;
  709                 inp->inp_flowtype = M_HASHTYPE_GET(m);
  710         }
  711 
  712         /*
  713          * Install in the reservation hash table for now, but don't yet
  714          * install a connection group since the full 4-tuple isn't yet
  715          * configured.
  716          */
  717         inp->inp_lport = sc->sc_inc.inc_lport;
  718         if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
  719                 /*
  720                  * Undo the assignments above if we failed to
  721                  * put the PCB on the hash lists.
  722                  */
  723 #ifdef INET6
  724                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  725                         inp->in6p_laddr = in6addr_any;
  726                 else
  727 #endif
  728                         inp->inp_laddr.s_addr = INADDR_ANY;
  729                 inp->inp_lport = 0;
  730                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  731                         log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
  732                             "with error %i\n",
  733                             s, __func__, error);
  734                         free(s, M_TCPLOG);
  735                 }
  736                 INP_HASH_WUNLOCK(&V_tcbinfo);
  737                 goto abort;
  738         }
  739 #ifdef IPSEC
  740         /* Copy old policy into new socket's. */
  741         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  742                 printf("syncache_socket: could not copy policy\n");
  743 #endif
  744 #ifdef INET6
  745         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  746                 struct inpcb *oinp = sotoinpcb(lso);
  747                 struct in6_addr laddr6;
  748                 struct sockaddr_in6 sin6;
  749                 /*
  750                  * Inherit socket options from the listening socket.
  751                  * Note that in6p_inputopts are not (and should not be)
  752                  * copied, since it stores previously received options and is
  753                  * used to detect if each new option is different than the
  754                  * previous one and hence should be passed to a user.
  755                  * If we copied in6p_inputopts, a user would not be able to
  756                  * receive options just after calling the accept system call.
  757                  */
  758                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  759                 if (oinp->in6p_outputopts)
  760                         inp->in6p_outputopts =
  761                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  762 
  763                 sin6.sin6_family = AF_INET6;
  764                 sin6.sin6_len = sizeof(sin6);
  765                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  766                 sin6.sin6_port = sc->sc_inc.inc_fport;
  767                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  768                 laddr6 = inp->in6p_laddr;
  769                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  770                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  771                 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
  772                     thread0.td_ucred, m)) != 0) {
  773                         inp->in6p_laddr = laddr6;
  774                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  775                                 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
  776                                     "with error %i\n",
  777                                     s, __func__, error);
  778                                 free(s, M_TCPLOG);
  779                         }
  780                         INP_HASH_WUNLOCK(&V_tcbinfo);
  781                         goto abort;
  782                 }
  783                 /* Override flowlabel from in6_pcbconnect. */
  784                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  785                 inp->inp_flow |= sc->sc_flowlabel;
  786         }
  787 #endif /* INET6 */
  788 #if defined(INET) && defined(INET6)
  789         else
  790 #endif
  791 #ifdef INET
  792         {
  793                 struct in_addr laddr;
  794                 struct sockaddr_in sin;
  795 
  796                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  797                 
  798                 if (inp->inp_options == NULL) {
  799                         inp->inp_options = sc->sc_ipopts;
  800                         sc->sc_ipopts = NULL;
  801                 }
  802 
  803                 sin.sin_family = AF_INET;
  804                 sin.sin_len = sizeof(sin);
  805                 sin.sin_addr = sc->sc_inc.inc_faddr;
  806                 sin.sin_port = sc->sc_inc.inc_fport;
  807                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  808                 laddr = inp->inp_laddr;
  809                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  810                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  811                 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
  812                     thread0.td_ucred, m)) != 0) {
  813                         inp->inp_laddr = laddr;
  814                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  815                                 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
  816                                     "with error %i\n",
  817                                     s, __func__, error);
  818                                 free(s, M_TCPLOG);
  819                         }
  820                         INP_HASH_WUNLOCK(&V_tcbinfo);
  821                         goto abort;
  822                 }
  823         }
  824 #endif /* INET */
  825         INP_HASH_WUNLOCK(&V_tcbinfo);
  826         tp = intotcpcb(inp);
  827         tcp_state_change(tp, TCPS_SYN_RECEIVED);
  828         tp->iss = sc->sc_iss;
  829         tp->irs = sc->sc_irs;
  830         tcp_rcvseqinit(tp);
  831         tcp_sendseqinit(tp);
  832         blk = sototcpcb(lso)->t_fb;
  833         if (blk != tp->t_fb) {
  834                 /*
  835                  * Our parents t_fb was not the default,
  836                  * we need to release our ref on tp->t_fb and 
  837                  * pickup one on the new entry.
  838                  */
  839                 struct tcp_function_block *rblk;
  840                 
  841                 rblk = find_and_ref_tcp_fb(blk);
  842                 KASSERT(rblk != NULL,
  843                     ("cannot find blk %p out of syncache?", blk));
  844                 if (tp->t_fb->tfb_tcp_fb_fini)
  845                         (*tp->t_fb->tfb_tcp_fb_fini)(tp);
  846                 refcount_release(&tp->t_fb->tfb_refcnt);
  847                 tp->t_fb = rblk;
  848                 if (tp->t_fb->tfb_tcp_fb_init) {
  849                         (*tp->t_fb->tfb_tcp_fb_init)(tp);
  850                 }
  851         }               
  852         tp->snd_wl1 = sc->sc_irs;
  853         tp->snd_max = tp->iss + 1;
  854         tp->snd_nxt = tp->iss + 1;
  855         tp->rcv_up = sc->sc_irs + 1;
  856         tp->rcv_wnd = sc->sc_wnd;
  857         tp->rcv_adv += tp->rcv_wnd;
  858         tp->last_ack_sent = tp->rcv_nxt;
  859 
  860         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  861         if (sc->sc_flags & SCF_NOOPT)
  862                 tp->t_flags |= TF_NOOPT;
  863         else {
  864                 if (sc->sc_flags & SCF_WINSCALE) {
  865                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  866                         tp->snd_scale = sc->sc_requested_s_scale;
  867                         tp->request_r_scale = sc->sc_requested_r_scale;
  868                 }
  869                 if (sc->sc_flags & SCF_TIMESTAMP) {
  870                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  871                         tp->ts_recent = sc->sc_tsreflect;
  872                         tp->ts_recent_age = tcp_ts_getticks();
  873                         tp->ts_offset = sc->sc_tsoff;
  874                 }
  875 #ifdef TCP_SIGNATURE
  876                 if (sc->sc_flags & SCF_SIGNATURE)
  877                         tp->t_flags |= TF_SIGNATURE;
  878 #endif
  879                 if (sc->sc_flags & SCF_SACK)
  880                         tp->t_flags |= TF_SACK_PERMIT;
  881         }
  882 
  883         if (sc->sc_flags & SCF_ECN)
  884                 tp->t_flags |= TF_ECN_PERMIT;
  885 
  886         /*
  887          * Set up MSS and get cached values from tcp_hostcache.
  888          * This might overwrite some of the defaults we just set.
  889          */
  890         tcp_mss(tp, sc->sc_peer_mss);
  891 
  892         /*
  893          * If the SYN,ACK was retransmitted, indicate that CWND to be
  894          * limited to one segment in cc_conn_init().
  895          * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
  896          */
  897         if (sc->sc_rxmits > 1)
  898                 tp->snd_cwnd = 1;
  899 
  900 #ifdef TCP_OFFLOAD
  901         /*
  902          * Allow a TOE driver to install its hooks.  Note that we hold the
  903          * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
  904          * new connection before the TOE driver has done its thing.
  905          */
  906         if (ADDED_BY_TOE(sc)) {
  907                 struct toedev *tod = sc->sc_tod;
  908 
  909                 tod->tod_offload_socket(tod, sc->sc_todctx, so);
  910         }
  911 #endif
  912         /*
  913          * Copy and activate timers.
  914          */
  915         tp->t_keepinit = sototcpcb(lso)->t_keepinit;
  916         tp->t_keepidle = sototcpcb(lso)->t_keepidle;
  917         tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
  918         tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
  919         tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
  920 
  921         soisconnected(so);
  922 
  923         TCPSTAT_INC(tcps_accepts);
  924         return (so);
  925 
  926 abort:
  927         INP_WUNLOCK(inp);
  928 abort2:
  929         if (so != NULL)
  930                 soabort(so);
  931         return (NULL);
  932 }
  933 
  934 /*
  935  * This function gets called when we receive an ACK for a
  936  * socket in the LISTEN state.  We look up the connection
  937  * in the syncache, and if its there, we pull it out of
  938  * the cache and turn it into a full-blown connection in
  939  * the SYN-RECEIVED state.
  940  *
  941  * On syncache_socket() success the newly created socket
  942  * has its underlying inp locked.
  943  */
  944 int
  945 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  946     struct socket **lsop, struct mbuf *m)
  947 {
  948         struct syncache *sc;
  949         struct syncache_head *sch;
  950         struct syncache scs;
  951         char *s;
  952 
  953         /*
  954          * Global TCP locks are held because we manipulate the PCB lists
  955          * and create a new socket.
  956          */
  957         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  958         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  959             ("%s: can handle only ACK", __func__));
  960 
  961         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  962         SCH_LOCK_ASSERT(sch);
  963 
  964 #ifdef INVARIANTS
  965         /*
  966          * Test code for syncookies comparing the syncache stored
  967          * values with the reconstructed values from the cookie.
  968          */
  969         if (sc != NULL)
  970                 syncookie_cmp(inc, sch, sc, th, to, *lsop);
  971 #endif
  972 
  973         if (sc == NULL) {
  974                 /*
  975                  * There is no syncache entry, so see if this ACK is
  976                  * a returning syncookie.  To do this, first:
  977                  *  A. See if this socket has had a syncache entry dropped in
  978                  *     the past.  We don't want to accept a bogus syncookie
  979                  *     if we've never received a SYN.
  980                  *  B. check that the syncookie is valid.  If it is, then
  981                  *     cobble up a fake syncache entry, and return.
  982                  */
  983                 if (!V_tcp_syncookies) {
  984                         SCH_UNLOCK(sch);
  985                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  986                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  987                                     "segment rejected (syncookies disabled)\n",
  988                                     s, __func__);
  989                         goto failed;
  990                 }
  991                 bzero(&scs, sizeof(scs));
  992                 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
  993                 SCH_UNLOCK(sch);
  994                 if (sc == NULL) {
  995                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  996                                 log(LOG_DEBUG, "%s; %s: Segment failed "
  997                                     "SYNCOOKIE authentication, segment rejected "
  998                                     "(probably spoofed)\n", s, __func__);
  999                         goto failed;
 1000                 }
 1001         } else {
 1002                 /*
 1003                  * Pull out the entry to unlock the bucket row.
 1004                  * 
 1005                  * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
 1006                  * tcp_state_change().  The tcpcb is not existent at this
 1007                  * moment.  A new one will be allocated via syncache_socket->
 1008                  * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
 1009                  * syncache_socket() will change it to TCPS_SYN_RECEIVED.
 1010                  */
 1011                 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
 1012                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
 1013                 sch->sch_length--;
 1014 #ifdef TCP_OFFLOAD
 1015                 if (ADDED_BY_TOE(sc)) {
 1016                         struct toedev *tod = sc->sc_tod;
 1017 
 1018                         tod->tod_syncache_removed(tod, sc->sc_todctx);
 1019                 }
 1020 #endif
 1021                 SCH_UNLOCK(sch);
 1022         }
 1023 
 1024         /*
 1025          * Segment validation:
 1026          * ACK must match our initial sequence number + 1 (the SYN|ACK).
 1027          */
 1028         if (th->th_ack != sc->sc_iss + 1) {
 1029                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1030                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
 1031                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
 1032                 goto failed;
 1033         }
 1034 
 1035         /*
 1036          * The SEQ must fall in the window starting at the received
 1037          * initial receive sequence number + 1 (the SYN).
 1038          */
 1039         if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
 1040             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
 1041                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1042                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
 1043                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
 1044                 goto failed;
 1045         }
 1046 
 1047         /*
 1048          * If timestamps were not negotiated during SYN/ACK they
 1049          * must not appear on any segment during this session.
 1050          */
 1051         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
 1052                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1053                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1054                             "segment rejected\n", s, __func__);
 1055                 goto failed;
 1056         }
 1057 
 1058         /*
 1059          * If timestamps were negotiated during SYN/ACK they should
 1060          * appear on every segment during this session.
 1061          * XXXAO: This is only informal as there have been unverified
 1062          * reports of non-compliants stacks.
 1063          */
 1064         if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
 1065                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1066                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1067                             "no action\n", s, __func__);
 1068                         free(s, M_TCPLOG);
 1069                         s = NULL;
 1070                 }
 1071         }
 1072 
 1073         /*
 1074          * If timestamps were negotiated the reflected timestamp
 1075          * must be equal to what we actually sent in the SYN|ACK.
 1076          */
 1077         if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
 1078                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1079                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
 1080                             "segment rejected\n",
 1081                             s, __func__, to->to_tsecr, sc->sc_ts);
 1082                 goto failed;
 1083         }
 1084 
 1085         *lsop = syncache_socket(sc, *lsop, m);
 1086 
 1087         if (*lsop == NULL)
 1088                 TCPSTAT_INC(tcps_sc_aborted);
 1089         else
 1090                 TCPSTAT_INC(tcps_sc_completed);
 1091 
 1092 /* how do we find the inp for the new socket? */
 1093         if (sc != &scs)
 1094                 syncache_free(sc);
 1095         return (1);
 1096 failed:
 1097         if (sc != NULL && sc != &scs)
 1098                 syncache_free(sc);
 1099         if (s != NULL)
 1100                 free(s, M_TCPLOG);
 1101         *lsop = NULL;
 1102         return (0);
 1103 }
 1104 
 1105 #ifdef TCP_RFC7413
 1106 static void
 1107 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
 1108     uint64_t response_cookie)
 1109 {
 1110         struct inpcb *inp;
 1111         struct tcpcb *tp;
 1112         unsigned int *pending_counter;
 1113 
 1114         /*
 1115          * Global TCP locks are held because we manipulate the PCB lists
 1116          * and create a new socket.
 1117          */
 1118         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1119 
 1120         pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
 1121         *lsop = syncache_socket(sc, *lsop, m);
 1122         if (*lsop == NULL) {
 1123                 TCPSTAT_INC(tcps_sc_aborted);
 1124                 atomic_subtract_int(pending_counter, 1);
 1125         } else {
 1126                 inp = sotoinpcb(*lsop);
 1127                 tp = intotcpcb(inp);
 1128                 tp->t_flags |= TF_FASTOPEN;
 1129                 tp->t_tfo_cookie = response_cookie;
 1130                 tp->snd_max = tp->iss;
 1131                 tp->snd_nxt = tp->iss;
 1132                 tp->t_tfo_pending = pending_counter;
 1133                 TCPSTAT_INC(tcps_sc_completed);
 1134         }
 1135 }
 1136 #endif /* TCP_RFC7413 */
 1137 
 1138 /*
 1139  * Given a LISTEN socket and an inbound SYN request, add
 1140  * this to the syn cache, and send back a segment:
 1141  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 1142  * to the source.
 1143  *
 1144  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
 1145  * Doing so would require that we hold onto the data and deliver it
 1146  * to the application.  However, if we are the target of a SYN-flood
 1147  * DoS attack, an attacker could send data which would eventually
 1148  * consume all available buffer space if it were ACKed.  By not ACKing
 1149  * the data, we avoid this DoS scenario.
 1150  *
 1151  * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
 1152  * cookie is processed, V_tcp_fastopen_enabled set to true, and the
 1153  * TCP_FASTOPEN socket option is set.  In this case, a new socket is created
 1154  * and returned via lsop, the mbuf is not freed so that tcp_input() can
 1155  * queue its data to the socket, and 1 is returned to indicate the
 1156  * TFO-socket-creation path was taken.
 1157  */
 1158 int
 1159 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1160     struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
 1161     void *todctx)
 1162 {
 1163         struct tcpcb *tp;
 1164         struct socket *so;
 1165         struct syncache *sc = NULL;
 1166         struct syncache_head *sch;
 1167         struct mbuf *ipopts = NULL;
 1168         u_int ltflags;
 1169         int win, sb_hiwat, ip_ttl, ip_tos;
 1170         char *s;
 1171         int rv = 0;
 1172 #ifdef INET6
 1173         int autoflowlabel = 0;
 1174 #endif
 1175 #ifdef MAC
 1176         struct label *maclabel;
 1177 #endif
 1178         struct syncache scs;
 1179         struct ucred *cred;
 1180 #ifdef TCP_RFC7413
 1181         uint64_t tfo_response_cookie;
 1182         int tfo_cookie_valid = 0;
 1183         int tfo_response_cookie_valid = 0;
 1184 #endif
 1185 
 1186         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1187         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1188             ("%s: unexpected tcp flags", __func__));
 1189 
 1190         /*
 1191          * Combine all so/tp operations very early to drop the INP lock as
 1192          * soon as possible.
 1193          */
 1194         so = *lsop;
 1195         tp = sototcpcb(so);
 1196         cred = crhold(so->so_cred);
 1197 
 1198 #ifdef INET6
 1199         if ((inc->inc_flags & INC_ISIPV6) &&
 1200             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1201                 autoflowlabel = 1;
 1202 #endif
 1203         ip_ttl = inp->inp_ip_ttl;
 1204         ip_tos = inp->inp_ip_tos;
 1205         win = sbspace(&so->so_rcv);
 1206         sb_hiwat = so->so_rcv.sb_hiwat;
 1207         ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
 1208 
 1209 #ifdef TCP_RFC7413
 1210         if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
 1211             (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
 1212                 /*
 1213                  * Limit the number of pending TFO connections to
 1214                  * approximately half of the queue limit.  This prevents TFO
 1215                  * SYN floods from starving the service by filling the
 1216                  * listen queue with bogus TFO connections.
 1217                  */
 1218                 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
 1219                     (so->so_qlimit / 2)) {
 1220                         int result;
 1221 
 1222                         result = tcp_fastopen_check_cookie(inc,
 1223                             to->to_tfo_cookie, to->to_tfo_len,
 1224                             &tfo_response_cookie);
 1225                         tfo_cookie_valid = (result > 0);
 1226                         tfo_response_cookie_valid = (result >= 0);
 1227                 } else
 1228                         atomic_subtract_int(tp->t_tfo_pending, 1);
 1229         }
 1230 #endif
 1231 
 1232         /* By the time we drop the lock these should no longer be used. */
 1233         so = NULL;
 1234         tp = NULL;
 1235 
 1236 #ifdef MAC
 1237         if (mac_syncache_init(&maclabel) != 0) {
 1238                 INP_WUNLOCK(inp);
 1239                 goto done;
 1240         } else
 1241                 mac_syncache_create(maclabel, inp);
 1242 #endif
 1243 #ifdef TCP_RFC7413
 1244         if (!tfo_cookie_valid)
 1245 #endif
 1246                 INP_WUNLOCK(inp);
 1247 
 1248         /*
 1249          * Remember the IP options, if any.
 1250          */
 1251 #ifdef INET6
 1252         if (!(inc->inc_flags & INC_ISIPV6))
 1253 #endif
 1254 #ifdef INET
 1255                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1256 #else
 1257                 ipopts = NULL;
 1258 #endif
 1259 
 1260         /*
 1261          * See if we already have an entry for this connection.
 1262          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1263          *
 1264          * XXX: should the syncache be re-initialized with the contents
 1265          * of the new SYN here (which may have different options?)
 1266          *
 1267          * XXX: We do not check the sequence number to see if this is a
 1268          * real retransmit or a new connection attempt.  The question is
 1269          * how to handle such a case; either ignore it as spoofed, or
 1270          * drop the current entry and create a new one?
 1271          */
 1272         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1273         SCH_LOCK_ASSERT(sch);
 1274         if (sc != NULL) {
 1275 #ifdef TCP_RFC7413
 1276                 if (tfo_cookie_valid)
 1277                         INP_WUNLOCK(inp);
 1278 #endif
 1279                 TCPSTAT_INC(tcps_sc_dupsyn);
 1280                 if (ipopts) {
 1281                         /*
 1282                          * If we were remembering a previous source route,
 1283                          * forget it and use the new one we've been given.
 1284                          */
 1285                         if (sc->sc_ipopts)
 1286                                 (void) m_free(sc->sc_ipopts);
 1287                         sc->sc_ipopts = ipopts;
 1288                 }
 1289                 /*
 1290                  * Update timestamp if present.
 1291                  */
 1292                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1293                         sc->sc_tsreflect = to->to_tsval;
 1294                 else
 1295                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1296 #ifdef MAC
 1297                 /*
 1298                  * Since we have already unconditionally allocated label
 1299                  * storage, free it up.  The syncache entry will already
 1300                  * have an initialized label we can use.
 1301                  */
 1302                 mac_syncache_destroy(&maclabel);
 1303 #endif
 1304                 /* Retransmit SYN|ACK and reset retransmit count. */
 1305                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1306                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1307                             "resetting timer and retransmitting SYN|ACK\n",
 1308                             s, __func__);
 1309                         free(s, M_TCPLOG);
 1310                 }
 1311                 if (syncache_respond(sc, sch, 1, m) == 0) {
 1312                         sc->sc_rxmits = 0;
 1313                         syncache_timeout(sc, sch, 1);
 1314                         TCPSTAT_INC(tcps_sndacks);
 1315                         TCPSTAT_INC(tcps_sndtotal);
 1316                 }
 1317                 SCH_UNLOCK(sch);
 1318                 goto done;
 1319         }
 1320 
 1321 #ifdef TCP_RFC7413
 1322         if (tfo_cookie_valid) {
 1323                 bzero(&scs, sizeof(scs));
 1324                 sc = &scs;
 1325                 goto skip_alloc;
 1326         }
 1327 #endif
 1328 
 1329         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1330         if (sc == NULL) {
 1331                 /*
 1332                  * The zone allocator couldn't provide more entries.
 1333                  * Treat this as if the cache was full; drop the oldest
 1334                  * entry and insert the new one.
 1335                  */
 1336                 TCPSTAT_INC(tcps_sc_zonefail);
 1337                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
 1338                         syncache_drop(sc, sch);
 1339                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1340                 if (sc == NULL) {
 1341                         if (V_tcp_syncookies) {
 1342                                 bzero(&scs, sizeof(scs));
 1343                                 sc = &scs;
 1344                         } else {
 1345                                 SCH_UNLOCK(sch);
 1346                                 if (ipopts)
 1347                                         (void) m_free(ipopts);
 1348                                 goto done;
 1349                         }
 1350                 }
 1351         }
 1352 
 1353 #ifdef TCP_RFC7413
 1354 skip_alloc:
 1355         if (!tfo_cookie_valid && tfo_response_cookie_valid)
 1356                 sc->sc_tfo_cookie = &tfo_response_cookie;
 1357 #endif
 1358 
 1359         /*
 1360          * Fill in the syncache values.
 1361          */
 1362 #ifdef MAC
 1363         sc->sc_label = maclabel;
 1364 #endif
 1365         sc->sc_cred = cred;
 1366         cred = NULL;
 1367         sc->sc_ipopts = ipopts;
 1368         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1369 #ifdef INET6
 1370         if (!(inc->inc_flags & INC_ISIPV6))
 1371 #endif
 1372         {
 1373                 sc->sc_ip_tos = ip_tos;
 1374                 sc->sc_ip_ttl = ip_ttl;
 1375         }
 1376 #ifdef TCP_OFFLOAD
 1377         sc->sc_tod = tod;
 1378         sc->sc_todctx = todctx;
 1379 #endif
 1380         sc->sc_irs = th->th_seq;
 1381         sc->sc_iss = arc4random();
 1382         sc->sc_flags = 0;
 1383         sc->sc_flowlabel = 0;
 1384 
 1385         /*
 1386          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1387          * win was derived from socket earlier in the function.
 1388          */
 1389         win = imax(win, 0);
 1390         win = imin(win, TCP_MAXWIN);
 1391         sc->sc_wnd = win;
 1392 
 1393         if (V_tcp_do_rfc1323) {
 1394                 /*
 1395                  * A timestamp received in a SYN makes
 1396                  * it ok to send timestamp requests and replies.
 1397                  */
 1398                 if (to->to_flags & TOF_TS) {
 1399                         sc->sc_tsreflect = to->to_tsval;
 1400                         sc->sc_ts = tcp_ts_getticks();
 1401                         sc->sc_flags |= SCF_TIMESTAMP;
 1402                 }
 1403                 if (to->to_flags & TOF_SCALE) {
 1404                         int wscale = 0;
 1405 
 1406                         /*
 1407                          * Pick the smallest possible scaling factor that
 1408                          * will still allow us to scale up to sb_max, aka
 1409                          * kern.ipc.maxsockbuf.
 1410                          *
 1411                          * We do this because there are broken firewalls that
 1412                          * will corrupt the window scale option, leading to
 1413                          * the other endpoint believing that our advertised
 1414                          * window is unscaled.  At scale factors larger than
 1415                          * 5 the unscaled window will drop below 1500 bytes,
 1416                          * leading to serious problems when traversing these
 1417                          * broken firewalls.
 1418                          *
 1419                          * With the default maxsockbuf of 256K, a scale factor
 1420                          * of 3 will be chosen by this algorithm.  Those who
 1421                          * choose a larger maxsockbuf should watch out
 1422                          * for the compatibility problems mentioned above.
 1423                          *
 1424                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1425                          * or <SYN,ACK>) segment itself is never scaled.
 1426                          */
 1427                         while (wscale < TCP_MAX_WINSHIFT &&
 1428                             (TCP_MAXWIN << wscale) < sb_max)
 1429                                 wscale++;
 1430                         sc->sc_requested_r_scale = wscale;
 1431                         sc->sc_requested_s_scale = to->to_wscale;
 1432                         sc->sc_flags |= SCF_WINSCALE;
 1433                 }
 1434         }
 1435 #ifdef TCP_SIGNATURE
 1436         /*
 1437          * If listening socket requested TCP digests, OR received SYN
 1438          * contains the option, flag this in the syncache so that
 1439          * syncache_respond() will do the right thing with the SYN+ACK.
 1440          */
 1441         if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
 1442                 sc->sc_flags |= SCF_SIGNATURE;
 1443 #endif
 1444         if (to->to_flags & TOF_SACKPERM)
 1445                 sc->sc_flags |= SCF_SACK;
 1446         if (to->to_flags & TOF_MSS)
 1447                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1448         if (ltflags & TF_NOOPT)
 1449                 sc->sc_flags |= SCF_NOOPT;
 1450         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1451                 sc->sc_flags |= SCF_ECN;
 1452 
 1453         if (V_tcp_syncookies)
 1454                 sc->sc_iss = syncookie_generate(sch, sc);
 1455 #ifdef INET6
 1456         if (autoflowlabel) {
 1457                 if (V_tcp_syncookies)
 1458                         sc->sc_flowlabel = sc->sc_iss;
 1459                 else
 1460                         sc->sc_flowlabel = ip6_randomflowlabel();
 1461                 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
 1462         }
 1463 #endif
 1464         SCH_UNLOCK(sch);
 1465 
 1466 #ifdef TCP_RFC7413
 1467         if (tfo_cookie_valid) {
 1468                 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
 1469                 /* INP_WUNLOCK(inp) will be performed by the called */
 1470                 rv = 1;
 1471                 goto tfo_done;
 1472         }
 1473 #endif
 1474 
 1475         /*
 1476          * Do a standard 3-way handshake.
 1477          */
 1478         if (syncache_respond(sc, sch, 0, m) == 0) {
 1479                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1480                         syncache_free(sc);
 1481                 else if (sc != &scs)
 1482                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1483                 TCPSTAT_INC(tcps_sndacks);
 1484                 TCPSTAT_INC(tcps_sndtotal);
 1485         } else {
 1486                 if (sc != &scs)
 1487                         syncache_free(sc);
 1488                 TCPSTAT_INC(tcps_sc_dropped);
 1489         }
 1490 
 1491 done:
 1492         if (m) {
 1493                 *lsop = NULL;
 1494                 m_freem(m);
 1495         }
 1496 #ifdef TCP_RFC7413
 1497 tfo_done:
 1498 #endif
 1499         if (cred != NULL)
 1500                 crfree(cred);
 1501 #ifdef MAC
 1502         if (sc == &scs)
 1503                 mac_syncache_destroy(&maclabel);
 1504 #endif
 1505         return (rv);
 1506 }
 1507 
 1508 /*
 1509  * Send SYN|ACK to the peer.  Either in response to the peer's SYN,
 1510  * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
 1511  */
 1512 static int
 1513 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked,
 1514     const struct mbuf *m0)
 1515 {
 1516         struct ip *ip = NULL;
 1517         struct mbuf *m;
 1518         struct tcphdr *th = NULL;
 1519         int optlen, error = 0;  /* Make compiler happy */
 1520         u_int16_t hlen, tlen, mssopt;
 1521         struct tcpopt to;
 1522 #ifdef INET6
 1523         struct ip6_hdr *ip6 = NULL;
 1524 #endif
 1525 #ifdef TCP_SIGNATURE
 1526         struct secasvar *sav;
 1527 #endif
 1528 
 1529         hlen =
 1530 #ifdef INET6
 1531                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1532 #endif
 1533                 sizeof(struct ip);
 1534         tlen = hlen + sizeof(struct tcphdr);
 1535 
 1536         /* Determine MSS we advertize to other end of connection. */
 1537         mssopt = tcp_mssopt(&sc->sc_inc);
 1538         if (sc->sc_peer_mss)
 1539                 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
 1540 
 1541         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1542         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1543             ("syncache: mbuf too small"));
 1544 
 1545         /* Create the IP+TCP header from scratch. */
 1546         m = m_gethdr(M_NOWAIT, MT_DATA);
 1547         if (m == NULL)
 1548                 return (ENOBUFS);
 1549 #ifdef MAC
 1550         mac_syncache_create_mbuf(sc->sc_label, m);
 1551 #endif
 1552         m->m_data += max_linkhdr;
 1553         m->m_len = tlen;
 1554         m->m_pkthdr.len = tlen;
 1555         m->m_pkthdr.rcvif = NULL;
 1556 
 1557 #ifdef INET6
 1558         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1559                 ip6 = mtod(m, struct ip6_hdr *);
 1560                 ip6->ip6_vfc = IPV6_VERSION;
 1561                 ip6->ip6_nxt = IPPROTO_TCP;
 1562                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1563                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1564                 ip6->ip6_plen = htons(tlen - hlen);
 1565                 /* ip6_hlim is set after checksum */
 1566                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1567                 ip6->ip6_flow |= sc->sc_flowlabel;
 1568 
 1569                 th = (struct tcphdr *)(ip6 + 1);
 1570         }
 1571 #endif
 1572 #if defined(INET6) && defined(INET)
 1573         else
 1574 #endif
 1575 #ifdef INET
 1576         {
 1577                 ip = mtod(m, struct ip *);
 1578                 ip->ip_v = IPVERSION;
 1579                 ip->ip_hl = sizeof(struct ip) >> 2;
 1580                 ip->ip_len = htons(tlen);
 1581                 ip->ip_id = 0;
 1582                 ip->ip_off = 0;
 1583                 ip->ip_sum = 0;
 1584                 ip->ip_p = IPPROTO_TCP;
 1585                 ip->ip_src = sc->sc_inc.inc_laddr;
 1586                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1587                 ip->ip_ttl = sc->sc_ip_ttl;
 1588                 ip->ip_tos = sc->sc_ip_tos;
 1589 
 1590                 /*
 1591                  * See if we should do MTU discovery.  Route lookups are
 1592                  * expensive, so we will only unset the DF bit if:
 1593                  *
 1594                  *      1) path_mtu_discovery is disabled
 1595                  *      2) the SCF_UNREACH flag has been set
 1596                  */
 1597                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1598                        ip->ip_off |= htons(IP_DF);
 1599 
 1600                 th = (struct tcphdr *)(ip + 1);
 1601         }
 1602 #endif /* INET */
 1603         th->th_sport = sc->sc_inc.inc_lport;
 1604         th->th_dport = sc->sc_inc.inc_fport;
 1605 
 1606         th->th_seq = htonl(sc->sc_iss);
 1607         th->th_ack = htonl(sc->sc_irs + 1);
 1608         th->th_off = sizeof(struct tcphdr) >> 2;
 1609         th->th_x2 = 0;
 1610         th->th_flags = TH_SYN|TH_ACK;
 1611         th->th_win = htons(sc->sc_wnd);
 1612         th->th_urp = 0;
 1613 
 1614         if (sc->sc_flags & SCF_ECN) {
 1615                 th->th_flags |= TH_ECE;
 1616                 TCPSTAT_INC(tcps_ecn_shs);
 1617         }
 1618 
 1619         /* Tack on the TCP options. */
 1620         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1621                 to.to_flags = 0;
 1622 
 1623                 to.to_mss = mssopt;
 1624                 to.to_flags = TOF_MSS;
 1625                 if (sc->sc_flags & SCF_WINSCALE) {
 1626                         to.to_wscale = sc->sc_requested_r_scale;
 1627                         to.to_flags |= TOF_SCALE;
 1628                 }
 1629                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1630                         /* Virgin timestamp or TCP cookie enhanced one. */
 1631                         to.to_tsval = sc->sc_ts;
 1632                         to.to_tsecr = sc->sc_tsreflect;
 1633                         to.to_flags |= TOF_TS;
 1634                 }
 1635                 if (sc->sc_flags & SCF_SACK)
 1636                         to.to_flags |= TOF_SACKPERM;
 1637 #ifdef TCP_SIGNATURE
 1638                 sav = NULL;
 1639                 if (sc->sc_flags & SCF_SIGNATURE) {
 1640                         sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND);
 1641                         if (sav != NULL)
 1642                                 to.to_flags |= TOF_SIGNATURE;
 1643                         else {
 1644 
 1645                                 /*
 1646                                  * We've got SCF_SIGNATURE flag
 1647                                  * inherited from listening socket,
 1648                                  * but no SADB key for given source
 1649                                  * address. Assume signature is not
 1650                                  * required and remove signature flag
 1651                                  * instead of silently dropping
 1652                                  * connection.
 1653                                  */
 1654                                 if (locked == 0)
 1655                                         SCH_LOCK(sch);
 1656                                 sc->sc_flags &= ~SCF_SIGNATURE;
 1657                                 if (locked == 0)
 1658                                         SCH_UNLOCK(sch);
 1659                         }
 1660                 }
 1661 #endif
 1662 
 1663 #ifdef TCP_RFC7413
 1664                 if (sc->sc_tfo_cookie) {
 1665                         to.to_flags |= TOF_FASTOPEN;
 1666                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 1667                         to.to_tfo_cookie = sc->sc_tfo_cookie;
 1668                         /* don't send cookie again when retransmitting response */
 1669                         sc->sc_tfo_cookie = NULL;
 1670                 }
 1671 #endif
 1672                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1673 
 1674                 /* Adjust headers by option size. */
 1675                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1676                 m->m_len += optlen;
 1677                 m->m_pkthdr.len += optlen;
 1678 
 1679 #ifdef TCP_SIGNATURE
 1680                 if (sc->sc_flags & SCF_SIGNATURE)
 1681                         tcp_signature_do_compute(m, 0, optlen,
 1682                             to.to_signature, sav);
 1683 #endif
 1684 #ifdef INET6
 1685                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1686                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1687                 else
 1688 #endif
 1689                         ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
 1690         } else
 1691                 optlen = 0;
 1692 
 1693         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1694         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1695         /*
 1696          * If we have peer's SYN and it has a flowid, then let's assign it to
 1697          * our SYN|ACK.  ip6_output() and ip_output() will not assign flowid
 1698          * to SYN|ACK due to lack of inp here.
 1699          */
 1700         if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
 1701                 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
 1702                 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
 1703         }
 1704 #ifdef INET6
 1705         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1706                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 1707                 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
 1708                     IPPROTO_TCP, 0);
 1709                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1710 #ifdef TCP_OFFLOAD
 1711                 if (ADDED_BY_TOE(sc)) {
 1712                         struct toedev *tod = sc->sc_tod;
 1713 
 1714                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1715 
 1716                         return (error);
 1717                 }
 1718 #endif
 1719                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1720         }
 1721 #endif
 1722 #if defined(INET6) && defined(INET)
 1723         else
 1724 #endif
 1725 #ifdef INET
 1726         {
 1727                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1728                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1729                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1730 #ifdef TCP_OFFLOAD
 1731                 if (ADDED_BY_TOE(sc)) {
 1732                         struct toedev *tod = sc->sc_tod;
 1733 
 1734                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1735 
 1736                         return (error);
 1737                 }
 1738 #endif
 1739                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1740         }
 1741 #endif
 1742         return (error);
 1743 }
 1744 
 1745 /*
 1746  * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
 1747  * that exceed the capacity of the syncache by avoiding the storage of any
 1748  * of the SYNs we receive.  Syncookies defend against blind SYN flooding
 1749  * attacks where the attacker does not have access to our responses.
 1750  *
 1751  * Syncookies encode and include all necessary information about the
 1752  * connection setup within the SYN|ACK that we send back.  That way we
 1753  * can avoid keeping any local state until the ACK to our SYN|ACK returns
 1754  * (if ever).  Normally the syncache and syncookies are running in parallel
 1755  * with the latter taking over when the former is exhausted.  When matching
 1756  * syncache entry is found the syncookie is ignored.
 1757  *
 1758  * The only reliable information persisting the 3WHS is our initial sequence
 1759  * number ISS of 32 bits.  Syncookies embed a cryptographically sufficient
 1760  * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
 1761  * of our SYN|ACK.  The MAC can be recomputed when the ACK to our SYN|ACK
 1762  * returns and signifies a legitimate connection if it matches the ACK.
 1763  *
 1764  * The available space of 32 bits to store the hash and to encode the SYN
 1765  * option information is very tight and we should have at least 24 bits for
 1766  * the MAC to keep the number of guesses by blind spoofing reasonably high.
 1767  *
 1768  * SYN option information we have to encode to fully restore a connection:
 1769  * MSS: is imporant to chose an optimal segment size to avoid IP level
 1770  *   fragmentation along the path.  The common MSS values can be encoded
 1771  *   in a 3-bit table.  Uncommon values are captured by the next lower value
 1772  *   in the table leading to a slight increase in packetization overhead.
 1773  * WSCALE: is necessary to allow large windows to be used for high delay-
 1774  *   bandwidth product links.  Not scaling the window when it was initially
 1775  *   negotiated is bad for performance as lack of scaling further decreases
 1776  *   the apparent available send window.  We only need to encode the WSCALE
 1777  *   we received from the remote end.  Our end can be recalculated at any
 1778  *   time.  The common WSCALE values can be encoded in a 3-bit table.
 1779  *   Uncommon values are captured by the next lower value in the table
 1780  *   making us under-estimate the available window size halving our
 1781  *   theoretically possible maximum throughput for that connection.
 1782  * SACK: Greatly assists in packet loss recovery and requires 1 bit.
 1783  * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
 1784  *   that are included in all segments on a connection.  We enable them when
 1785  *   the ACK has them.
 1786  *
 1787  * Security of syncookies and attack vectors:
 1788  *
 1789  * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
 1790  * together with the gloabl secret to make it unique per connection attempt.
 1791  * Thus any change of any of those parameters results in a different MAC output
 1792  * in an unpredictable way unless a collision is encountered.  24 bits of the
 1793  * MAC are embedded into the ISS.
 1794  *
 1795  * To prevent replay attacks two rotating global secrets are updated with a
 1796  * new random value every 15 seconds.  The life-time of a syncookie is thus
 1797  * 15-30 seconds.
 1798  *
 1799  * Vector 1: Attacking the secret.  This requires finding a weakness in the
 1800  * MAC itself or the way it is used here.  The attacker can do a chosen plain
 1801  * text attack by varying and testing the all parameters under his control.
 1802  * The strength depends on the size and randomness of the secret, and the
 1803  * cryptographic security of the MAC function.  Due to the constant updating
 1804  * of the secret the attacker has at most 29.999 seconds to find the secret
 1805  * and launch spoofed connections.  After that he has to start all over again.
 1806  *
 1807  * Vector 2: Collision attack on the MAC of a single ACK.  With a 24 bit MAC
 1808  * size an average of 4,823 attempts are required for a 50% chance of success
 1809  * to spoof a single syncookie (birthday collision paradox).  However the
 1810  * attacker is blind and doesn't know if one of his attempts succeeded unless
 1811  * he has a side channel to interfere success from.  A single connection setup
 1812  * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
 1813  * This many attempts are required for each one blind spoofed connection.  For
 1814  * every additional spoofed connection he has to launch another N attempts.
 1815  * Thus for a sustained rate 100 spoofed connections per second approximately
 1816  * 1,800,000 packets per second would have to be sent.
 1817  *
 1818  * NB: The MAC function should be fast so that it doesn't become a CPU
 1819  * exhaustion attack vector itself.
 1820  *
 1821  * References:
 1822  *  RFC4987 TCP SYN Flooding Attacks and Common Mitigations
 1823  *  SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
 1824  *   http://cr.yp.to/syncookies.html    (overview)
 1825  *   http://cr.yp.to/syncookies/archive (details)
 1826  *
 1827  *
 1828  * Schematic construction of a syncookie enabled Initial Sequence Number:
 1829  *  0        1         2         3
 1830  *  12345678901234567890123456789012
 1831  * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
 1832  *
 1833  *  x 24 MAC (truncated)
 1834  *  W  3 Send Window Scale index
 1835  *  M  3 MSS index
 1836  *  S  1 SACK permitted
 1837  *  P  1 Odd/even secret
 1838  */
 1839 
 1840 /*
 1841  * Distribution and probability of certain MSS values.  Those in between are
 1842  * rounded down to the next lower one.
 1843  * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
 1844  *                            .2%  .3%   5%    7%    7%    20%   15%   45%
 1845  */
 1846 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
 1847 
 1848 /*
 1849  * Distribution and probability of certain WSCALE values.  We have to map the
 1850  * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
 1851  * bits based on prevalence of certain values.  Where we don't have an exact
 1852  * match for are rounded down to the next lower one letting us under-estimate
 1853  * the true available window.  At the moment this would happen only for the
 1854  * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
 1855  * and window size).  The absence of the WSCALE option (no scaling in either
 1856  * direction) is encoded with index zero.
 1857  * [WSCALE values histograms, Allman, 2012]
 1858  *                            X 10 10 35  5  6 14 10%   by host
 1859  *                            X 11  4  5  5 18 49  3%   by connections
 1860  */
 1861 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
 1862 
 1863 /*
 1864  * Compute the MAC for the SYN cookie.  SIPHASH-2-4 is chosen for its speed
 1865  * and good cryptographic properties.
 1866  */
 1867 static uint32_t
 1868 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
 1869     uint8_t *secbits, uintptr_t secmod)
 1870 {
 1871         SIPHASH_CTX ctx;
 1872         uint32_t siphash[2];
 1873 
 1874         SipHash24_Init(&ctx);
 1875         SipHash_SetKey(&ctx, secbits);
 1876         switch (inc->inc_flags & INC_ISIPV6) {
 1877 #ifdef INET
 1878         case 0:
 1879                 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
 1880                 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
 1881                 break;
 1882 #endif
 1883 #ifdef INET6
 1884         case INC_ISIPV6:
 1885                 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
 1886                 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
 1887                 break;
 1888 #endif
 1889         }
 1890         SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
 1891         SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
 1892         SipHash_Update(&ctx, &irs, sizeof(irs));
 1893         SipHash_Update(&ctx, &flags, sizeof(flags));
 1894         SipHash_Update(&ctx, &secmod, sizeof(secmod));
 1895         SipHash_Final((u_int8_t *)&siphash, &ctx);
 1896 
 1897         return (siphash[0] ^ siphash[1]);
 1898 }
 1899 
 1900 static tcp_seq
 1901 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
 1902 {
 1903         u_int i, mss, secbit, wscale;
 1904         uint32_t iss, hash;
 1905         uint8_t *secbits;
 1906         union syncookie cookie;
 1907 
 1908         SCH_LOCK_ASSERT(sch);
 1909 
 1910         cookie.cookie = 0;
 1911 
 1912         /* Map our computed MSS into the 3-bit index. */
 1913         mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
 1914         for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0;
 1915              i--)
 1916                 ;
 1917         cookie.flags.mss_idx = i;
 1918 
 1919         /*
 1920          * Map the send window scale into the 3-bit index but only if
 1921          * the wscale option was received.
 1922          */
 1923         if (sc->sc_flags & SCF_WINSCALE) {
 1924                 wscale = sc->sc_requested_s_scale;
 1925                 for (i = nitems(tcp_sc_wstab) - 1;
 1926                     tcp_sc_wstab[i] > wscale && i > 0;
 1927                      i--)
 1928                         ;
 1929                 cookie.flags.wscale_idx = i;
 1930         }
 1931 
 1932         /* Can we do SACK? */
 1933         if (sc->sc_flags & SCF_SACK)
 1934                 cookie.flags.sack_ok = 1;
 1935 
 1936         /* Which of the two secrets to use. */
 1937         secbit = sch->sch_sc->secret.oddeven & 0x1;
 1938         cookie.flags.odd_even = secbit;
 1939 
 1940         secbits = sch->sch_sc->secret.key[secbit];
 1941         hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
 1942             (uintptr_t)sch);
 1943 
 1944         /*
 1945          * Put the flags into the hash and XOR them to get better ISS number
 1946          * variance.  This doesn't enhance the cryptographic strength and is
 1947          * done to prevent the 8 cookie bits from showing up directly on the
 1948          * wire.
 1949          */
 1950         iss = hash & ~0xff;
 1951         iss |= cookie.cookie ^ (hash >> 24);
 1952 
 1953         /* Randomize the timestamp. */
 1954         if (sc->sc_flags & SCF_TIMESTAMP) {
 1955                 sc->sc_ts = arc4random();
 1956                 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
 1957         }
 1958 
 1959         TCPSTAT_INC(tcps_sc_sendcookie);
 1960         return (iss);
 1961 }
 1962 
 1963 static struct syncache *
 1964 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 1965     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 1966     struct socket *lso)
 1967 {
 1968         uint32_t hash;
 1969         uint8_t *secbits;
 1970         tcp_seq ack, seq;
 1971         int wnd, wscale = 0;
 1972         union syncookie cookie;
 1973 
 1974         SCH_LOCK_ASSERT(sch);
 1975 
 1976         /*
 1977          * Pull information out of SYN-ACK/ACK and revert sequence number
 1978          * advances.
 1979          */
 1980         ack = th->th_ack - 1;
 1981         seq = th->th_seq - 1;
 1982 
 1983         /*
 1984          * Unpack the flags containing enough information to restore the
 1985          * connection.
 1986          */
 1987         cookie.cookie = (ack & 0xff) ^ (ack >> 24);
 1988 
 1989         /* Which of the two secrets to use. */
 1990         secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
 1991 
 1992         hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
 1993 
 1994         /* The recomputed hash matches the ACK if this was a genuine cookie. */
 1995         if ((ack & ~0xff) != (hash & ~0xff))
 1996                 return (NULL);
 1997 
 1998         /* Fill in the syncache values. */
 1999         sc->sc_flags = 0;
 2000         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 2001         sc->sc_ipopts = NULL;
 2002         
 2003         sc->sc_irs = seq;
 2004         sc->sc_iss = ack;
 2005 
 2006         switch (inc->inc_flags & INC_ISIPV6) {
 2007 #ifdef INET
 2008         case 0:
 2009                 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
 2010                 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
 2011                 break;
 2012 #endif
 2013 #ifdef INET6
 2014         case INC_ISIPV6:
 2015                 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
 2016                         sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
 2017                 break;
 2018 #endif
 2019         }
 2020 
 2021         sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
 2022 
 2023         /* We can simply recompute receive window scale we sent earlier. */
 2024         while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
 2025                 wscale++;
 2026 
 2027         /* Only use wscale if it was enabled in the orignal SYN. */
 2028         if (cookie.flags.wscale_idx > 0) {
 2029                 sc->sc_requested_r_scale = wscale;
 2030                 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
 2031                 sc->sc_flags |= SCF_WINSCALE;
 2032         }
 2033 
 2034         wnd = sbspace(&lso->so_rcv);
 2035         wnd = imax(wnd, 0);
 2036         wnd = imin(wnd, TCP_MAXWIN);
 2037         sc->sc_wnd = wnd;
 2038 
 2039         if (cookie.flags.sack_ok)
 2040                 sc->sc_flags |= SCF_SACK;
 2041 
 2042         if (to->to_flags & TOF_TS) {
 2043                 sc->sc_flags |= SCF_TIMESTAMP;
 2044                 sc->sc_tsreflect = to->to_tsval;
 2045                 sc->sc_ts = to->to_tsecr;
 2046                 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
 2047         }
 2048 
 2049         if (to->to_flags & TOF_SIGNATURE)
 2050                 sc->sc_flags |= SCF_SIGNATURE;
 2051 
 2052         sc->sc_rxmits = 0;
 2053 
 2054         TCPSTAT_INC(tcps_sc_recvcookie);
 2055         return (sc);
 2056 }
 2057 
 2058 #ifdef INVARIANTS
 2059 static int
 2060 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
 2061     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2062     struct socket *lso)
 2063 {
 2064         struct syncache scs, *scx;
 2065         char *s;
 2066 
 2067         bzero(&scs, sizeof(scs));
 2068         scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
 2069 
 2070         if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
 2071                 return (0);
 2072 
 2073         if (scx != NULL) {
 2074                 if (sc->sc_peer_mss != scx->sc_peer_mss)
 2075                         log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
 2076                             s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
 2077 
 2078                 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
 2079                         log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
 2080                             s, __func__, sc->sc_requested_r_scale,
 2081                             scx->sc_requested_r_scale);
 2082 
 2083                 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
 2084                         log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
 2085                             s, __func__, sc->sc_requested_s_scale,
 2086                             scx->sc_requested_s_scale);
 2087 
 2088                 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
 2089                         log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
 2090         }
 2091 
 2092         if (s != NULL)
 2093                 free(s, M_TCPLOG);
 2094         return (0);
 2095 }
 2096 #endif /* INVARIANTS */
 2097 
 2098 static void
 2099 syncookie_reseed(void *arg)
 2100 {
 2101         struct tcp_syncache *sc = arg;
 2102         uint8_t *secbits;
 2103         int secbit;
 2104 
 2105         /*
 2106          * Reseeding the secret doesn't have to be protected by a lock.
 2107          * It only must be ensured that the new random values are visible
 2108          * to all CPUs in a SMP environment.  The atomic with release
 2109          * semantics ensures that.
 2110          */
 2111         secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
 2112         secbits = sc->secret.key[secbit];
 2113         arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
 2114         atomic_add_rel_int(&sc->secret.oddeven, 1);
 2115 
 2116         /* Reschedule ourself. */
 2117         callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
 2118 }
 2119 
 2120 /*
 2121  * Exports the syncache entries to userland so that netstat can display
 2122  * them alongside the other sockets.  This function is intended to be
 2123  * called only from tcp_pcblist.
 2124  *
 2125  * Due to concurrency on an active system, the number of pcbs exported
 2126  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 2127  * amount of space the caller allocated for this function to use.
 2128  */
 2129 int
 2130 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 2131 {
 2132         struct xtcpcb xt;
 2133         struct syncache *sc;
 2134         struct syncache_head *sch;
 2135         int count, error, i;
 2136 
 2137         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 2138                 sch = &V_tcp_syncache.hashbase[i];
 2139                 SCH_LOCK(sch);
 2140                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 2141                         if (count >= max_pcbs) {
 2142                                 SCH_UNLOCK(sch);
 2143                                 goto exit;
 2144                         }
 2145                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 2146                                 continue;
 2147                         bzero(&xt, sizeof(xt));
 2148                         xt.xt_len = sizeof(xt);
 2149                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 2150                                 xt.xt_inp.inp_vflag = INP_IPV6;
 2151                         else
 2152                                 xt.xt_inp.inp_vflag = INP_IPV4;
 2153                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 2154                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 2155                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 2156                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 2157                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 2158                         xt.xt_socket.so_type = SOCK_STREAM;
 2159                         xt.xt_socket.so_state = SS_ISCONNECTING;
 2160                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 2161                         if (error) {
 2162                                 SCH_UNLOCK(sch);
 2163                                 goto exit;
 2164                         }
 2165                         count++;
 2166                 }
 2167                 SCH_UNLOCK(sch);
 2168         }
 2169 exit:
 2170         *pcbs_exported = count;
 2171         return error;
 2172 }

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