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/11.1/sys/netinet/tcp_syncache.c 319654 2017-06-07 12:50:54Z tuexen $");
   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 #include <netipsec/ipsec_support.h>
  100 
  101 #include <machine/in_cksum.h>
  102 
  103 #include <security/mac/mac_framework.h>
  104 
  105 static VNET_DEFINE(int, tcp_syncookies) = 1;
  106 #define V_tcp_syncookies                VNET(tcp_syncookies)
  107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
  108     &VNET_NAME(tcp_syncookies), 0,
  109     "Use TCP SYN cookies if the syncache overflows");
  110 
  111 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
  112 #define V_tcp_syncookiesonly            VNET(tcp_syncookiesonly)
  113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
  114     &VNET_NAME(tcp_syncookiesonly), 0,
  115     "Use only TCP SYN cookies");
  116 
  117 #ifdef TCP_OFFLOAD
  118 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
  119 #endif
  120 
  121 static void      syncache_drop(struct syncache *, struct syncache_head *);
  122 static void      syncache_free(struct syncache *);
  123 static void      syncache_insert(struct syncache *, struct syncache_head *);
  124 static int       syncache_respond(struct syncache *, struct syncache_head *, int,
  125                     const struct mbuf *);
  126 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  127                     struct mbuf *m);
  128 static void      syncache_timeout(struct syncache *sc, struct syncache_head *sch,
  129                     int docallout);
  130 static void      syncache_timer(void *);
  131 
  132 static uint32_t  syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
  133                     uint8_t *, uintptr_t);
  134 static tcp_seq   syncookie_generate(struct syncache_head *, struct syncache *);
  135 static struct syncache
  136                 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
  137                     struct syncache *, struct tcphdr *, struct tcpopt *,
  138                     struct socket *);
  139 static void      syncookie_reseed(void *);
  140 #ifdef INVARIANTS
  141 static int       syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
  142                     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
  143                     struct socket *lso);
  144 #endif
  145 
  146 /*
  147  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  148  * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
  149  * the odds are that the user has given up attempting to connect by then.
  150  */
  151 #define SYNCACHE_MAXREXMTS              3
  152 
  153 /* Arbitrary values */
  154 #define TCP_SYNCACHE_HASHSIZE           512
  155 #define TCP_SYNCACHE_BUCKETLIMIT        30
  156 
  157 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
  158 #define V_tcp_syncache                  VNET(tcp_syncache)
  159 
  160 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
  161     "TCP SYN cache");
  162 
  163 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
  164     &VNET_NAME(tcp_syncache.bucket_limit), 0,
  165     "Per-bucket hash limit for syncache");
  166 
  167 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
  168     &VNET_NAME(tcp_syncache.cache_limit), 0,
  169     "Overall entry limit for syncache");
  170 
  171 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
  172     &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
  173 
  174 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
  175     &VNET_NAME(tcp_syncache.hashsize), 0,
  176     "Size of TCP syncache hashtable");
  177 
  178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW,
  179     &VNET_NAME(tcp_syncache.rexmt_limit), 0,
  180     "Limit on SYN/ACK retransmissions");
  181 
  182 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
  183 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
  184     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
  185     "Send reset on socket allocation failure");
  186 
  187 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  188 
  189 #define SCH_LOCK(sch)           mtx_lock(&(sch)->sch_mtx)
  190 #define SCH_UNLOCK(sch)         mtx_unlock(&(sch)->sch_mtx)
  191 #define SCH_LOCK_ASSERT(sch)    mtx_assert(&(sch)->sch_mtx, MA_OWNED)
  192 
  193 /*
  194  * Requires the syncache entry to be already removed from the bucket list.
  195  */
  196 static void
  197 syncache_free(struct syncache *sc)
  198 {
  199 
  200         if (sc->sc_ipopts)
  201                 (void) m_free(sc->sc_ipopts);
  202         if (sc->sc_cred)
  203                 crfree(sc->sc_cred);
  204 #ifdef MAC
  205         mac_syncache_destroy(&sc->sc_label);
  206 #endif
  207 
  208         uma_zfree(V_tcp_syncache.zone, sc);
  209 }
  210 
  211 void
  212 syncache_init(void)
  213 {
  214         int i;
  215 
  216         V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  217         V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  218         V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  219         V_tcp_syncache.hash_secret = arc4random();
  220 
  221         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  222             &V_tcp_syncache.hashsize);
  223         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  224             &V_tcp_syncache.bucket_limit);
  225         if (!powerof2(V_tcp_syncache.hashsize) ||
  226             V_tcp_syncache.hashsize == 0) {
  227                 printf("WARNING: syncache hash size is not a power of 2.\n");
  228                 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  229         }
  230         V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
  231 
  232         /* Set limits. */
  233         V_tcp_syncache.cache_limit =
  234             V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
  235         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  236             &V_tcp_syncache.cache_limit);
  237 
  238         /* Allocate the hash table. */
  239         V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
  240             sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
  241 
  242 #ifdef VIMAGE
  243         V_tcp_syncache.vnet = curvnet;
  244 #endif
  245 
  246         /* Initialize the hash buckets. */
  247         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  248                 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
  249                 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
  250                          NULL, MTX_DEF);
  251                 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
  252                          &V_tcp_syncache.hashbase[i].sch_mtx, 0);
  253                 V_tcp_syncache.hashbase[i].sch_length = 0;
  254                 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
  255                 V_tcp_syncache.hashbase[i].sch_last_overflow =
  256                     -(SYNCOOKIE_LIFETIME + 1);
  257         }
  258 
  259         /* Create the syncache entry zone. */
  260         V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  261             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  262         V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
  263             V_tcp_syncache.cache_limit);
  264 
  265         /* Start the SYN cookie reseeder callout. */
  266         callout_init(&V_tcp_syncache.secret.reseed, 1);
  267         arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
  268         arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
  269         callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
  270             syncookie_reseed, &V_tcp_syncache);
  271 }
  272 
  273 #ifdef VIMAGE
  274 void
  275 syncache_destroy(void)
  276 {
  277         struct syncache_head *sch;
  278         struct syncache *sc, *nsc;
  279         int i;
  280 
  281         /*
  282          * Stop the re-seed timer before freeing resources.  No need to
  283          * possibly schedule it another time.
  284          */
  285         callout_drain(&V_tcp_syncache.secret.reseed);
  286 
  287         /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
  288         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  289 
  290                 sch = &V_tcp_syncache.hashbase[i];
  291                 callout_drain(&sch->sch_timer);
  292 
  293                 SCH_LOCK(sch);
  294                 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
  295                         syncache_drop(sc, sch);
  296                 SCH_UNLOCK(sch);
  297                 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
  298                     ("%s: sch->sch_bucket not empty", __func__));
  299                 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
  300                     __func__, sch->sch_length));
  301                 mtx_destroy(&sch->sch_mtx);
  302         }
  303 
  304         KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
  305             ("%s: cache_count not 0", __func__));
  306 
  307         /* Free the allocated global resources. */
  308         uma_zdestroy(V_tcp_syncache.zone);
  309         free(V_tcp_syncache.hashbase, M_SYNCACHE);
  310 }
  311 #endif
  312 
  313 /*
  314  * Inserts a syncache entry into the specified bucket row.
  315  * Locks and unlocks the syncache_head autonomously.
  316  */
  317 static void
  318 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  319 {
  320         struct syncache *sc2;
  321 
  322         SCH_LOCK(sch);
  323 
  324         /*
  325          * Make sure that we don't overflow the per-bucket limit.
  326          * If the bucket is full, toss the oldest element.
  327          */
  328         if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
  329                 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
  330                         ("sch->sch_length incorrect"));
  331                 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
  332                 sch->sch_last_overflow = time_uptime;
  333                 syncache_drop(sc2, sch);
  334                 TCPSTAT_INC(tcps_sc_bucketoverflow);
  335         }
  336 
  337         /* Put it into the bucket. */
  338         TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
  339         sch->sch_length++;
  340 
  341 #ifdef TCP_OFFLOAD
  342         if (ADDED_BY_TOE(sc)) {
  343                 struct toedev *tod = sc->sc_tod;
  344 
  345                 tod->tod_syncache_added(tod, sc->sc_todctx);
  346         }
  347 #endif
  348 
  349         /* Reinitialize the bucket row's timer. */
  350         if (sch->sch_length == 1)
  351                 sch->sch_nextc = ticks + INT_MAX;
  352         syncache_timeout(sc, sch, 1);
  353 
  354         SCH_UNLOCK(sch);
  355 
  356         TCPSTATES_INC(TCPS_SYN_RECEIVED);
  357         TCPSTAT_INC(tcps_sc_added);
  358 }
  359 
  360 /*
  361  * Remove and free entry from syncache bucket row.
  362  * Expects locked syncache head.
  363  */
  364 static void
  365 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  366 {
  367 
  368         SCH_LOCK_ASSERT(sch);
  369 
  370         TCPSTATES_DEC(TCPS_SYN_RECEIVED);
  371         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  372         sch->sch_length--;
  373 
  374 #ifdef TCP_OFFLOAD
  375         if (ADDED_BY_TOE(sc)) {
  376                 struct toedev *tod = sc->sc_tod;
  377 
  378                 tod->tod_syncache_removed(tod, sc->sc_todctx);
  379         }
  380 #endif
  381 
  382         syncache_free(sc);
  383 }
  384 
  385 /*
  386  * Engage/reengage time on bucket row.
  387  */
  388 static void
  389 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
  390 {
  391         sc->sc_rxttime = ticks +
  392                 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
  393         sc->sc_rxmits++;
  394         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
  395                 sch->sch_nextc = sc->sc_rxttime;
  396                 if (docallout)
  397                         callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
  398                             syncache_timer, (void *)sch);
  399         }
  400 }
  401 
  402 /*
  403  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  404  * If we have retransmitted an entry the maximum number of times, expire it.
  405  * One separate timer for each bucket row.
  406  */
  407 static void
  408 syncache_timer(void *xsch)
  409 {
  410         struct syncache_head *sch = (struct syncache_head *)xsch;
  411         struct syncache *sc, *nsc;
  412         int tick = ticks;
  413         char *s;
  414 
  415         CURVNET_SET(sch->sch_sc->vnet);
  416 
  417         /* NB: syncache_head has already been locked by the callout. */
  418         SCH_LOCK_ASSERT(sch);
  419 
  420         /*
  421          * In the following cycle we may remove some entries and/or
  422          * advance some timeouts, so re-initialize the bucket timer.
  423          */
  424         sch->sch_nextc = tick + INT_MAX;
  425 
  426         TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
  427                 /*
  428                  * We do not check if the listen socket still exists
  429                  * and accept the case where the listen socket may be
  430                  * gone by the time we resend the SYN/ACK.  We do
  431                  * not expect this to happens often. If it does,
  432                  * then the RST will be sent by the time the remote
  433                  * host does the SYN/ACK->ACK.
  434                  */
  435                 if (TSTMP_GT(sc->sc_rxttime, tick)) {
  436                         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
  437                                 sch->sch_nextc = sc->sc_rxttime;
  438                         continue;
  439                 }
  440                 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
  441                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  442                                 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
  443                                     "giving up and removing syncache entry\n",
  444                                     s, __func__);
  445                                 free(s, M_TCPLOG);
  446                         }
  447                         syncache_drop(sc, sch);
  448                         TCPSTAT_INC(tcps_sc_stale);
  449                         continue;
  450                 }
  451                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  452                         log(LOG_DEBUG, "%s; %s: Response timeout, "
  453                             "retransmitting (%u) SYN|ACK\n",
  454                             s, __func__, sc->sc_rxmits);
  455                         free(s, M_TCPLOG);
  456                 }
  457 
  458                 syncache_respond(sc, sch, 1, NULL);
  459                 TCPSTAT_INC(tcps_sc_retransmitted);
  460                 syncache_timeout(sc, sch, 0);
  461         }
  462         if (!TAILQ_EMPTY(&(sch)->sch_bucket))
  463                 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
  464                         syncache_timer, (void *)(sch));
  465         CURVNET_RESTORE();
  466 }
  467 
  468 /*
  469  * Find an entry in the syncache.
  470  * Returns always with locked syncache_head plus a matching entry or NULL.
  471  */
  472 static struct syncache *
  473 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  474 {
  475         struct syncache *sc;
  476         struct syncache_head *sch;
  477         uint32_t hash;
  478 
  479         /*
  480          * The hash is built on foreign port + local port + foreign address.
  481          * We rely on the fact that struct in_conninfo starts with 16 bits
  482          * of foreign port, then 16 bits of local port then followed by 128
  483          * bits of foreign address.  In case of IPv4 address, the first 3
  484          * 32-bit words of the address always are zeroes.
  485          */
  486         hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
  487             V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
  488 
  489         sch = &V_tcp_syncache.hashbase[hash];
  490         *schp = sch;
  491         SCH_LOCK(sch);
  492 
  493         /* Circle through bucket row to find matching entry. */
  494         TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
  495                 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
  496                     sizeof(struct in_endpoints)) == 0)
  497                         break;
  498 
  499         return (sc);    /* Always returns with locked sch. */
  500 }
  501 
  502 /*
  503  * This function is called when we get a RST for a
  504  * non-existent connection, so that we can see if the
  505  * connection is in the syn cache.  If it is, zap it.
  506  */
  507 void
  508 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
  509 {
  510         struct syncache *sc;
  511         struct syncache_head *sch;
  512         char *s = NULL;
  513 
  514         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  515         SCH_LOCK_ASSERT(sch);
  516 
  517         /*
  518          * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
  519          * See RFC 793 page 65, section SEGMENT ARRIVES.
  520          */
  521         if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
  522                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  523                         log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
  524                             "FIN flag set, segment ignored\n", s, __func__);
  525                 TCPSTAT_INC(tcps_badrst);
  526                 goto done;
  527         }
  528 
  529         /*
  530          * No corresponding connection was found in syncache.
  531          * If syncookies are enabled and possibly exclusively
  532          * used, or we are under memory pressure, a valid RST
  533          * may not find a syncache entry.  In that case we're
  534          * done and no SYN|ACK retransmissions will happen.
  535          * Otherwise the RST was misdirected or spoofed.
  536          */
  537         if (sc == NULL) {
  538                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  539                         log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
  540                             "syncache entry (possibly syncookie only), "
  541                             "segment ignored\n", s, __func__);
  542                 TCPSTAT_INC(tcps_badrst);
  543                 goto done;
  544         }
  545 
  546         /*
  547          * If the RST bit is set, check the sequence number to see
  548          * if this is a valid reset segment.
  549          * RFC 793 page 37:
  550          *   In all states except SYN-SENT, all reset (RST) segments
  551          *   are validated by checking their SEQ-fields.  A reset is
  552          *   valid if its sequence number is in the window.
  553          *
  554          *   The sequence number in the reset segment is normally an
  555          *   echo of our outgoing acknowlegement numbers, but some hosts
  556          *   send a reset with the sequence number at the rightmost edge
  557          *   of our receive window, and we have to handle this case.
  558          */
  559         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  560             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  561                 syncache_drop(sc, sch);
  562                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  563                         log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
  564                             "connection attempt aborted by remote endpoint\n",
  565                             s, __func__);
  566                 TCPSTAT_INC(tcps_sc_reset);
  567         } else {
  568                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  569                         log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
  570                             "IRS %u (+WND %u), segment ignored\n",
  571                             s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
  572                 TCPSTAT_INC(tcps_badrst);
  573         }
  574 
  575 done:
  576         if (s != NULL)
  577                 free(s, M_TCPLOG);
  578         SCH_UNLOCK(sch);
  579 }
  580 
  581 void
  582 syncache_badack(struct in_conninfo *inc)
  583 {
  584         struct syncache *sc;
  585         struct syncache_head *sch;
  586 
  587         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  588         SCH_LOCK_ASSERT(sch);
  589         if (sc != NULL) {
  590                 syncache_drop(sc, sch);
  591                 TCPSTAT_INC(tcps_sc_badack);
  592         }
  593         SCH_UNLOCK(sch);
  594 }
  595 
  596 void
  597 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq)
  598 {
  599         struct syncache *sc;
  600         struct syncache_head *sch;
  601 
  602         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  603         SCH_LOCK_ASSERT(sch);
  604         if (sc == NULL)
  605                 goto done;
  606 
  607         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  608         if (ntohl(th_seq) != sc->sc_iss)
  609                 goto done;
  610 
  611         /*
  612          * If we've rertransmitted 3 times and this is our second error,
  613          * we remove the entry.  Otherwise, we allow it to continue on.
  614          * This prevents us from incorrectly nuking an entry during a
  615          * spurious network outage.
  616          *
  617          * See tcp_notify().
  618          */
  619         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
  620                 sc->sc_flags |= SCF_UNREACH;
  621                 goto done;
  622         }
  623         syncache_drop(sc, sch);
  624         TCPSTAT_INC(tcps_sc_unreach);
  625 done:
  626         SCH_UNLOCK(sch);
  627 }
  628 
  629 /*
  630  * Build a new TCP socket structure from a syncache entry.
  631  *
  632  * On success return the newly created socket with its underlying inp locked.
  633  */
  634 static struct socket *
  635 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  636 {
  637         struct tcp_function_block *blk;
  638         struct inpcb *inp = NULL;
  639         struct socket *so;
  640         struct tcpcb *tp;
  641         int error;
  642         char *s;
  643 
  644         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  645 
  646         /*
  647          * Ok, create the full blown connection, and set things up
  648          * as they would have been set up if we had created the
  649          * connection when the SYN arrived.  If we can't create
  650          * the connection, abort it.
  651          */
  652         so = sonewconn(lso, 0);
  653         if (so == NULL) {
  654                 /*
  655                  * Drop the connection; we will either send a RST or
  656                  * have the peer retransmit its SYN again after its
  657                  * RTO and try again.
  658                  */
  659                 TCPSTAT_INC(tcps_listendrop);
  660                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  661                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  662                             "due to limits or memory shortage\n",
  663                             s, __func__);
  664                         free(s, M_TCPLOG);
  665                 }
  666                 goto abort2;
  667         }
  668 #ifdef MAC
  669         mac_socketpeer_set_from_mbuf(m, so);
  670 #endif
  671 
  672         inp = sotoinpcb(so);
  673         inp->inp_inc.inc_fibnum = so->so_fibnum;
  674         INP_WLOCK(inp);
  675         /*
  676          * Exclusive pcbinfo lock is not required in syncache socket case even
  677          * if two inpcb locks can be acquired simultaneously:
  678          *  - the inpcb in LISTEN state,
  679          *  - the newly created inp.
  680          *
  681          * In this case, an inp cannot be at same time in LISTEN state and
  682          * just created by an accept() call.
  683          */
  684         INP_HASH_WLOCK(&V_tcbinfo);
  685 
  686         /* Insert new socket into PCB hash list. */
  687         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  688 #ifdef INET6
  689         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  690                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  691         } else {
  692                 inp->inp_vflag &= ~INP_IPV6;
  693                 inp->inp_vflag |= INP_IPV4;
  694 #endif
  695                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  696 #ifdef INET6
  697         }
  698 #endif
  699 
  700         /*
  701          * If there's an mbuf and it has a flowid, then let's initialise the
  702          * inp with that particular flowid.
  703          */
  704         if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
  705                 inp->inp_flowid = m->m_pkthdr.flowid;
  706                 inp->inp_flowtype = M_HASHTYPE_GET(m);
  707         }
  708 
  709         /*
  710          * Install in the reservation hash table for now, but don't yet
  711          * install a connection group since the full 4-tuple isn't yet
  712          * configured.
  713          */
  714         inp->inp_lport = sc->sc_inc.inc_lport;
  715         if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
  716                 /*
  717                  * Undo the assignments above if we failed to
  718                  * put the PCB on the hash lists.
  719                  */
  720 #ifdef INET6
  721                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  722                         inp->in6p_laddr = in6addr_any;
  723                 else
  724 #endif
  725                         inp->inp_laddr.s_addr = INADDR_ANY;
  726                 inp->inp_lport = 0;
  727                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  728                         log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
  729                             "with error %i\n",
  730                             s, __func__, error);
  731                         free(s, M_TCPLOG);
  732                 }
  733                 INP_HASH_WUNLOCK(&V_tcbinfo);
  734                 goto abort;
  735         }
  736 #ifdef INET6
  737         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  738                 struct inpcb *oinp = sotoinpcb(lso);
  739                 struct in6_addr laddr6;
  740                 struct sockaddr_in6 sin6;
  741                 /*
  742                  * Inherit socket options from the listening socket.
  743                  * Note that in6p_inputopts are not (and should not be)
  744                  * copied, since it stores previously received options and is
  745                  * used to detect if each new option is different than the
  746                  * previous one and hence should be passed to a user.
  747                  * If we copied in6p_inputopts, a user would not be able to
  748                  * receive options just after calling the accept system call.
  749                  */
  750                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  751                 if (oinp->in6p_outputopts)
  752                         inp->in6p_outputopts =
  753                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  754 
  755                 sin6.sin6_family = AF_INET6;
  756                 sin6.sin6_len = sizeof(sin6);
  757                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  758                 sin6.sin6_port = sc->sc_inc.inc_fport;
  759                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  760                 laddr6 = inp->in6p_laddr;
  761                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  762                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  763                 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
  764                     thread0.td_ucred, m)) != 0) {
  765                         inp->in6p_laddr = laddr6;
  766                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  767                                 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
  768                                     "with error %i\n",
  769                                     s, __func__, error);
  770                                 free(s, M_TCPLOG);
  771                         }
  772                         INP_HASH_WUNLOCK(&V_tcbinfo);
  773                         goto abort;
  774                 }
  775                 /* Override flowlabel from in6_pcbconnect. */
  776                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  777                 inp->inp_flow |= sc->sc_flowlabel;
  778         }
  779 #endif /* INET6 */
  780 #if defined(INET) && defined(INET6)
  781         else
  782 #endif
  783 #ifdef INET
  784         {
  785                 struct in_addr laddr;
  786                 struct sockaddr_in sin;
  787 
  788                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  789                 
  790                 if (inp->inp_options == NULL) {
  791                         inp->inp_options = sc->sc_ipopts;
  792                         sc->sc_ipopts = NULL;
  793                 }
  794 
  795                 sin.sin_family = AF_INET;
  796                 sin.sin_len = sizeof(sin);
  797                 sin.sin_addr = sc->sc_inc.inc_faddr;
  798                 sin.sin_port = sc->sc_inc.inc_fport;
  799                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  800                 laddr = inp->inp_laddr;
  801                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  802                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  803                 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
  804                     thread0.td_ucred, m)) != 0) {
  805                         inp->inp_laddr = laddr;
  806                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  807                                 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
  808                                     "with error %i\n",
  809                                     s, __func__, error);
  810                                 free(s, M_TCPLOG);
  811                         }
  812                         INP_HASH_WUNLOCK(&V_tcbinfo);
  813                         goto abort;
  814                 }
  815         }
  816 #endif /* INET */
  817 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
  818         /* Copy old policy into new socket's. */
  819         if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
  820                 printf("syncache_socket: could not copy policy\n");
  821 #endif
  822         INP_HASH_WUNLOCK(&V_tcbinfo);
  823         tp = intotcpcb(inp);
  824         tcp_state_change(tp, TCPS_SYN_RECEIVED);
  825         tp->iss = sc->sc_iss;
  826         tp->irs = sc->sc_irs;
  827         tcp_rcvseqinit(tp);
  828         tcp_sendseqinit(tp);
  829         blk = sototcpcb(lso)->t_fb;
  830         if (blk != tp->t_fb) {
  831                 /*
  832                  * Our parents t_fb was not the default,
  833                  * we need to release our ref on tp->t_fb and 
  834                  * pickup one on the new entry.
  835                  */
  836                 struct tcp_function_block *rblk;
  837                 
  838                 rblk = find_and_ref_tcp_fb(blk);
  839                 KASSERT(rblk != NULL,
  840                     ("cannot find blk %p out of syncache?", blk));
  841                 if (tp->t_fb->tfb_tcp_fb_fini)
  842                         (*tp->t_fb->tfb_tcp_fb_fini)(tp);
  843                 refcount_release(&tp->t_fb->tfb_refcnt);
  844                 tp->t_fb = rblk;
  845                 if (tp->t_fb->tfb_tcp_fb_init) {
  846                         (*tp->t_fb->tfb_tcp_fb_init)(tp);
  847                 }
  848         }               
  849         tp->snd_wl1 = sc->sc_irs;
  850         tp->snd_max = tp->iss + 1;
  851         tp->snd_nxt = tp->iss + 1;
  852         tp->rcv_up = sc->sc_irs + 1;
  853         tp->rcv_wnd = sc->sc_wnd;
  854         tp->rcv_adv += tp->rcv_wnd;
  855         tp->last_ack_sent = tp->rcv_nxt;
  856 
  857         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  858         if (sc->sc_flags & SCF_NOOPT)
  859                 tp->t_flags |= TF_NOOPT;
  860         else {
  861                 if (sc->sc_flags & SCF_WINSCALE) {
  862                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  863                         tp->snd_scale = sc->sc_requested_s_scale;
  864                         tp->request_r_scale = sc->sc_requested_r_scale;
  865                 }
  866                 if (sc->sc_flags & SCF_TIMESTAMP) {
  867                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  868                         tp->ts_recent = sc->sc_tsreflect;
  869                         tp->ts_recent_age = tcp_ts_getticks();
  870                         tp->ts_offset = sc->sc_tsoff;
  871                 }
  872 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
  873                 if (sc->sc_flags & SCF_SIGNATURE)
  874                         tp->t_flags |= TF_SIGNATURE;
  875 #endif
  876                 if (sc->sc_flags & SCF_SACK)
  877                         tp->t_flags |= TF_SACK_PERMIT;
  878         }
  879 
  880         if (sc->sc_flags & SCF_ECN)
  881                 tp->t_flags |= TF_ECN_PERMIT;
  882 
  883         /*
  884          * Set up MSS and get cached values from tcp_hostcache.
  885          * This might overwrite some of the defaults we just set.
  886          */
  887         tcp_mss(tp, sc->sc_peer_mss);
  888 
  889         /*
  890          * If the SYN,ACK was retransmitted, indicate that CWND to be
  891          * limited to one segment in cc_conn_init().
  892          * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
  893          */
  894         if (sc->sc_rxmits > 1)
  895                 tp->snd_cwnd = 1;
  896 
  897 #ifdef TCP_OFFLOAD
  898         /*
  899          * Allow a TOE driver to install its hooks.  Note that we hold the
  900          * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
  901          * new connection before the TOE driver has done its thing.
  902          */
  903         if (ADDED_BY_TOE(sc)) {
  904                 struct toedev *tod = sc->sc_tod;
  905 
  906                 tod->tod_offload_socket(tod, sc->sc_todctx, so);
  907         }
  908 #endif
  909         /*
  910          * Copy and activate timers.
  911          */
  912         tp->t_keepinit = sototcpcb(lso)->t_keepinit;
  913         tp->t_keepidle = sototcpcb(lso)->t_keepidle;
  914         tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
  915         tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
  916         tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
  917 
  918         TCPSTAT_INC(tcps_accepts);
  919         return (so);
  920 
  921 abort:
  922         INP_WUNLOCK(inp);
  923 abort2:
  924         if (so != NULL)
  925                 soabort(so);
  926         return (NULL);
  927 }
  928 
  929 /*
  930  * This function gets called when we receive an ACK for a
  931  * socket in the LISTEN state.  We look up the connection
  932  * in the syncache, and if its there, we pull it out of
  933  * the cache and turn it into a full-blown connection in
  934  * the SYN-RECEIVED state.
  935  *
  936  * On syncache_socket() success the newly created socket
  937  * has its underlying inp locked.
  938  */
  939 int
  940 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  941     struct socket **lsop, struct mbuf *m)
  942 {
  943         struct syncache *sc;
  944         struct syncache_head *sch;
  945         struct syncache scs;
  946         char *s;
  947 
  948         /*
  949          * Global TCP locks are held because we manipulate the PCB lists
  950          * and create a new socket.
  951          */
  952         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  953         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  954             ("%s: can handle only ACK", __func__));
  955 
  956         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  957         SCH_LOCK_ASSERT(sch);
  958 
  959 #ifdef INVARIANTS
  960         /*
  961          * Test code for syncookies comparing the syncache stored
  962          * values with the reconstructed values from the cookie.
  963          */
  964         if (sc != NULL)
  965                 syncookie_cmp(inc, sch, sc, th, to, *lsop);
  966 #endif
  967 
  968         if (sc == NULL) {
  969                 /*
  970                  * There is no syncache entry, so see if this ACK is
  971                  * a returning syncookie.  To do this, first:
  972                  *  A. Check if syncookies are used in case of syncache
  973                  *     overflows
  974                  *  B. See if this socket has had a syncache entry dropped in
  975                  *     the recent past. We don't want to accept a bogus
  976                  *     syncookie if we've never received a SYN or accept it
  977                  *     twice.
  978                  *  C. check that the syncookie is valid.  If it is, then
  979                  *     cobble up a fake syncache entry, and return.
  980                  */
  981                 if (!V_tcp_syncookies) {
  982                         SCH_UNLOCK(sch);
  983                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  984                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  985                                     "segment rejected (syncookies disabled)\n",
  986                                     s, __func__);
  987                         goto failed;
  988                 }
  989                 if (!V_tcp_syncookiesonly &&
  990                     sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
  991                         SCH_UNLOCK(sch);
  992                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  993                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  994                                     "segment rejected (no syncache entry)\n",
  995                                     s, __func__);
  996                         goto failed;
  997                 }
  998                 bzero(&scs, sizeof(scs));
  999                 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
 1000                 SCH_UNLOCK(sch);
 1001                 if (sc == NULL) {
 1002                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1003                                 log(LOG_DEBUG, "%s; %s: Segment failed "
 1004                                     "SYNCOOKIE authentication, segment rejected "
 1005                                     "(probably spoofed)\n", s, __func__);
 1006                         goto failed;
 1007                 }
 1008 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1009                 /* If received ACK has MD5 signature, check it. */
 1010                 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
 1011                     (!TCPMD5_ENABLED() ||
 1012                     TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
 1013                         /* Drop the ACK. */
 1014                         if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1015                                 log(LOG_DEBUG, "%s; %s: Segment rejected, "
 1016                                     "MD5 signature doesn't match.\n",
 1017                                     s, __func__);
 1018                                 free(s, M_TCPLOG);
 1019                         }
 1020                         TCPSTAT_INC(tcps_sig_err_sigopt);
 1021                         return (-1); /* Do not send RST */
 1022                 }
 1023 #endif /* TCP_SIGNATURE */
 1024         } else {
 1025 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1026                 /*
 1027                  * If listening socket requested TCP digests, check that
 1028                  * received ACK has signature and it is correct.
 1029                  * If not, drop the ACK and leave sc entry in th cache,
 1030                  * because SYN was received with correct signature.
 1031                  */
 1032                 if (sc->sc_flags & SCF_SIGNATURE) {
 1033                         if ((to->to_flags & TOF_SIGNATURE) == 0) {
 1034                                 /* No signature */
 1035                                 TCPSTAT_INC(tcps_sig_err_nosigopt);
 1036                                 SCH_UNLOCK(sch);
 1037                                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1038                                         log(LOG_DEBUG, "%s; %s: Segment "
 1039                                             "rejected, MD5 signature wasn't "
 1040                                             "provided.\n", s, __func__);
 1041                                         free(s, M_TCPLOG);
 1042                                 }
 1043                                 return (-1); /* Do not send RST */
 1044                         }
 1045                         if (!TCPMD5_ENABLED() ||
 1046                             TCPMD5_INPUT(m, th, to->to_signature) != 0) {
 1047                                 /* Doesn't match or no SA */
 1048                                 SCH_UNLOCK(sch);
 1049                                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1050                                         log(LOG_DEBUG, "%s; %s: Segment "
 1051                                             "rejected, MD5 signature doesn't "
 1052                                             "match.\n", s, __func__);
 1053                                         free(s, M_TCPLOG);
 1054                                 }
 1055                                 return (-1); /* Do not send RST */
 1056                         }
 1057                 }
 1058 #endif /* TCP_SIGNATURE */
 1059                 /*
 1060                  * Pull out the entry to unlock the bucket row.
 1061                  * 
 1062                  * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
 1063                  * tcp_state_change().  The tcpcb is not existent at this
 1064                  * moment.  A new one will be allocated via syncache_socket->
 1065                  * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
 1066                  * syncache_socket() will change it to TCPS_SYN_RECEIVED.
 1067                  */
 1068                 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
 1069                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
 1070                 sch->sch_length--;
 1071 #ifdef TCP_OFFLOAD
 1072                 if (ADDED_BY_TOE(sc)) {
 1073                         struct toedev *tod = sc->sc_tod;
 1074 
 1075                         tod->tod_syncache_removed(tod, sc->sc_todctx);
 1076                 }
 1077 #endif
 1078                 SCH_UNLOCK(sch);
 1079         }
 1080 
 1081         /*
 1082          * Segment validation:
 1083          * ACK must match our initial sequence number + 1 (the SYN|ACK).
 1084          */
 1085         if (th->th_ack != sc->sc_iss + 1) {
 1086                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1087                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
 1088                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
 1089                 goto failed;
 1090         }
 1091 
 1092         /*
 1093          * The SEQ must fall in the window starting at the received
 1094          * initial receive sequence number + 1 (the SYN).
 1095          */
 1096         if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
 1097             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
 1098                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1099                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
 1100                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
 1101                 goto failed;
 1102         }
 1103 
 1104         /*
 1105          * If timestamps were not negotiated during SYN/ACK they
 1106          * must not appear on any segment during this session.
 1107          */
 1108         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
 1109                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1110                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1111                             "segment rejected\n", s, __func__);
 1112                 goto failed;
 1113         }
 1114 
 1115         /*
 1116          * If timestamps were negotiated during SYN/ACK they should
 1117          * appear on every segment during this session.
 1118          * XXXAO: This is only informal as there have been unverified
 1119          * reports of non-compliants stacks.
 1120          */
 1121         if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
 1122                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1123                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1124                             "no action\n", s, __func__);
 1125                         free(s, M_TCPLOG);
 1126                         s = NULL;
 1127                 }
 1128         }
 1129 
 1130         /*
 1131          * If timestamps were negotiated, the reflected timestamp
 1132          * must be equal to what we actually sent in the SYN|ACK
 1133          * except in the case of 0. Some boxes are known for sending
 1134          * broken timestamp replies during the 3whs (and potentially
 1135          * during the connection also).
 1136          *
 1137          * Accept the final ACK of 3whs with reflected timestamp of 0
 1138          * instead of sending a RST and deleting the syncache entry.
 1139          */
 1140         if ((to->to_flags & TOF_TS) && to->to_tsecr &&
 1141             to->to_tsecr != sc->sc_ts) {
 1142                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1143                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
 1144                             "segment rejected\n",
 1145                             s, __func__, to->to_tsecr, sc->sc_ts);
 1146                 goto failed;
 1147         }
 1148 
 1149         *lsop = syncache_socket(sc, *lsop, m);
 1150 
 1151         if (*lsop == NULL)
 1152                 TCPSTAT_INC(tcps_sc_aborted);
 1153         else
 1154                 TCPSTAT_INC(tcps_sc_completed);
 1155 
 1156 /* how do we find the inp for the new socket? */
 1157         if (sc != &scs)
 1158                 syncache_free(sc);
 1159         return (1);
 1160 failed:
 1161         if (sc != NULL && sc != &scs)
 1162                 syncache_free(sc);
 1163         if (s != NULL)
 1164                 free(s, M_TCPLOG);
 1165         *lsop = NULL;
 1166         return (0);
 1167 }
 1168 
 1169 #ifdef TCP_RFC7413
 1170 static void
 1171 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
 1172     uint64_t response_cookie)
 1173 {
 1174         struct inpcb *inp;
 1175         struct tcpcb *tp;
 1176         unsigned int *pending_counter;
 1177 
 1178         /*
 1179          * Global TCP locks are held because we manipulate the PCB lists
 1180          * and create a new socket.
 1181          */
 1182         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1183 
 1184         pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
 1185         *lsop = syncache_socket(sc, *lsop, m);
 1186         if (*lsop == NULL) {
 1187                 TCPSTAT_INC(tcps_sc_aborted);
 1188                 atomic_subtract_int(pending_counter, 1);
 1189         } else {
 1190                 inp = sotoinpcb(*lsop);
 1191                 tp = intotcpcb(inp);
 1192                 tp->t_flags |= TF_FASTOPEN;
 1193                 tp->t_tfo_cookie = response_cookie;
 1194                 tp->snd_max = tp->iss;
 1195                 tp->snd_nxt = tp->iss;
 1196                 tp->t_tfo_pending = pending_counter;
 1197                 TCPSTAT_INC(tcps_sc_completed);
 1198         }
 1199 }
 1200 #endif /* TCP_RFC7413 */
 1201 
 1202 /*
 1203  * Given a LISTEN socket and an inbound SYN request, add
 1204  * this to the syn cache, and send back a segment:
 1205  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 1206  * to the source.
 1207  *
 1208  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
 1209  * Doing so would require that we hold onto the data and deliver it
 1210  * to the application.  However, if we are the target of a SYN-flood
 1211  * DoS attack, an attacker could send data which would eventually
 1212  * consume all available buffer space if it were ACKed.  By not ACKing
 1213  * the data, we avoid this DoS scenario.
 1214  *
 1215  * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
 1216  * cookie is processed, V_tcp_fastopen_enabled set to true, and the
 1217  * TCP_FASTOPEN socket option is set.  In this case, a new socket is created
 1218  * and returned via lsop, the mbuf is not freed so that tcp_input() can
 1219  * queue its data to the socket, and 1 is returned to indicate the
 1220  * TFO-socket-creation path was taken.
 1221  */
 1222 int
 1223 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1224     struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
 1225     void *todctx)
 1226 {
 1227         struct tcpcb *tp;
 1228         struct socket *so;
 1229         struct syncache *sc = NULL;
 1230         struct syncache_head *sch;
 1231         struct mbuf *ipopts = NULL;
 1232         u_int ltflags;
 1233         int win, sb_hiwat, ip_ttl, ip_tos;
 1234         char *s;
 1235         int rv = 0;
 1236 #ifdef INET6
 1237         int autoflowlabel = 0;
 1238 #endif
 1239 #ifdef MAC
 1240         struct label *maclabel;
 1241 #endif
 1242         struct syncache scs;
 1243         struct ucred *cred;
 1244 #ifdef TCP_RFC7413
 1245         uint64_t tfo_response_cookie;
 1246         int tfo_cookie_valid = 0;
 1247         int tfo_response_cookie_valid = 0;
 1248 #endif
 1249 
 1250         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1251         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1252             ("%s: unexpected tcp flags", __func__));
 1253 
 1254         /*
 1255          * Combine all so/tp operations very early to drop the INP lock as
 1256          * soon as possible.
 1257          */
 1258         so = *lsop;
 1259         tp = sototcpcb(so);
 1260         cred = crhold(so->so_cred);
 1261 
 1262 #ifdef INET6
 1263         if ((inc->inc_flags & INC_ISIPV6) &&
 1264             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1265                 autoflowlabel = 1;
 1266 #endif
 1267         ip_ttl = inp->inp_ip_ttl;
 1268         ip_tos = inp->inp_ip_tos;
 1269         win = sbspace(&so->so_rcv);
 1270         sb_hiwat = so->so_rcv.sb_hiwat;
 1271         ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
 1272 
 1273 #ifdef TCP_RFC7413
 1274         if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
 1275             (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
 1276                 /*
 1277                  * Limit the number of pending TFO connections to
 1278                  * approximately half of the queue limit.  This prevents TFO
 1279                  * SYN floods from starving the service by filling the
 1280                  * listen queue with bogus TFO connections.
 1281                  */
 1282                 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
 1283                     (so->so_qlimit / 2)) {
 1284                         int result;
 1285 
 1286                         result = tcp_fastopen_check_cookie(inc,
 1287                             to->to_tfo_cookie, to->to_tfo_len,
 1288                             &tfo_response_cookie);
 1289                         tfo_cookie_valid = (result > 0);
 1290                         tfo_response_cookie_valid = (result >= 0);
 1291                 } else
 1292                         atomic_subtract_int(tp->t_tfo_pending, 1);
 1293         }
 1294 #endif
 1295 
 1296         /* By the time we drop the lock these should no longer be used. */
 1297         so = NULL;
 1298         tp = NULL;
 1299 
 1300 #ifdef MAC
 1301         if (mac_syncache_init(&maclabel) != 0) {
 1302                 INP_WUNLOCK(inp);
 1303                 goto done;
 1304         } else
 1305                 mac_syncache_create(maclabel, inp);
 1306 #endif
 1307 #ifdef TCP_RFC7413
 1308         if (!tfo_cookie_valid)
 1309 #endif
 1310                 INP_WUNLOCK(inp);
 1311 
 1312         /*
 1313          * Remember the IP options, if any.
 1314          */
 1315 #ifdef INET6
 1316         if (!(inc->inc_flags & INC_ISIPV6))
 1317 #endif
 1318 #ifdef INET
 1319                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1320 #else
 1321                 ipopts = NULL;
 1322 #endif
 1323 
 1324 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1325         /*
 1326          * If listening socket requested TCP digests, check that received
 1327          * SYN has signature and it is correct. If signature doesn't match
 1328          * or TCP_SIGNATURE support isn't enabled, drop the packet.
 1329          */
 1330         if (ltflags & TF_SIGNATURE) {
 1331                 if ((to->to_flags & TOF_SIGNATURE) == 0) {
 1332                         TCPSTAT_INC(tcps_sig_err_nosigopt);
 1333                         goto done;
 1334                 }
 1335                 if (!TCPMD5_ENABLED() ||
 1336                     TCPMD5_INPUT(m, th, to->to_signature) != 0)
 1337                         goto done;
 1338         }
 1339 #endif  /* TCP_SIGNATURE */
 1340         /*
 1341          * See if we already have an entry for this connection.
 1342          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1343          *
 1344          * XXX: should the syncache be re-initialized with the contents
 1345          * of the new SYN here (which may have different options?)
 1346          *
 1347          * XXX: We do not check the sequence number to see if this is a
 1348          * real retransmit or a new connection attempt.  The question is
 1349          * how to handle such a case; either ignore it as spoofed, or
 1350          * drop the current entry and create a new one?
 1351          */
 1352         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1353         SCH_LOCK_ASSERT(sch);
 1354         if (sc != NULL) {
 1355 #ifdef TCP_RFC7413
 1356                 if (tfo_cookie_valid)
 1357                         INP_WUNLOCK(inp);
 1358 #endif
 1359                 TCPSTAT_INC(tcps_sc_dupsyn);
 1360                 if (ipopts) {
 1361                         /*
 1362                          * If we were remembering a previous source route,
 1363                          * forget it and use the new one we've been given.
 1364                          */
 1365                         if (sc->sc_ipopts)
 1366                                 (void) m_free(sc->sc_ipopts);
 1367                         sc->sc_ipopts = ipopts;
 1368                 }
 1369                 /*
 1370                  * Update timestamp if present.
 1371                  */
 1372                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1373                         sc->sc_tsreflect = to->to_tsval;
 1374                 else
 1375                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1376 #ifdef MAC
 1377                 /*
 1378                  * Since we have already unconditionally allocated label
 1379                  * storage, free it up.  The syncache entry will already
 1380                  * have an initialized label we can use.
 1381                  */
 1382                 mac_syncache_destroy(&maclabel);
 1383 #endif
 1384                 /* Retransmit SYN|ACK and reset retransmit count. */
 1385                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1386                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1387                             "resetting timer and retransmitting SYN|ACK\n",
 1388                             s, __func__);
 1389                         free(s, M_TCPLOG);
 1390                 }
 1391                 if (syncache_respond(sc, sch, 1, m) == 0) {
 1392                         sc->sc_rxmits = 0;
 1393                         syncache_timeout(sc, sch, 1);
 1394                         TCPSTAT_INC(tcps_sndacks);
 1395                         TCPSTAT_INC(tcps_sndtotal);
 1396                 }
 1397                 SCH_UNLOCK(sch);
 1398                 goto done;
 1399         }
 1400 
 1401 #ifdef TCP_RFC7413
 1402         if (tfo_cookie_valid) {
 1403                 bzero(&scs, sizeof(scs));
 1404                 sc = &scs;
 1405                 goto skip_alloc;
 1406         }
 1407 #endif
 1408 
 1409         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1410         if (sc == NULL) {
 1411                 /*
 1412                  * The zone allocator couldn't provide more entries.
 1413                  * Treat this as if the cache was full; drop the oldest
 1414                  * entry and insert the new one.
 1415                  */
 1416                 TCPSTAT_INC(tcps_sc_zonefail);
 1417                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) {
 1418                         sch->sch_last_overflow = time_uptime;
 1419                         syncache_drop(sc, sch);
 1420                 }
 1421                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1422                 if (sc == NULL) {
 1423                         if (V_tcp_syncookies) {
 1424                                 bzero(&scs, sizeof(scs));
 1425                                 sc = &scs;
 1426                         } else {
 1427                                 SCH_UNLOCK(sch);
 1428                                 if (ipopts)
 1429                                         (void) m_free(ipopts);
 1430                                 goto done;
 1431                         }
 1432                 }
 1433         }
 1434 
 1435 #ifdef TCP_RFC7413
 1436 skip_alloc:
 1437         if (!tfo_cookie_valid && tfo_response_cookie_valid)
 1438                 sc->sc_tfo_cookie = &tfo_response_cookie;
 1439 #endif
 1440 
 1441         /*
 1442          * Fill in the syncache values.
 1443          */
 1444 #ifdef MAC
 1445         sc->sc_label = maclabel;
 1446 #endif
 1447         sc->sc_cred = cred;
 1448         cred = NULL;
 1449         sc->sc_ipopts = ipopts;
 1450         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1451 #ifdef INET6
 1452         if (!(inc->inc_flags & INC_ISIPV6))
 1453 #endif
 1454         {
 1455                 sc->sc_ip_tos = ip_tos;
 1456                 sc->sc_ip_ttl = ip_ttl;
 1457         }
 1458 #ifdef TCP_OFFLOAD
 1459         sc->sc_tod = tod;
 1460         sc->sc_todctx = todctx;
 1461 #endif
 1462         sc->sc_irs = th->th_seq;
 1463         sc->sc_iss = arc4random();
 1464         sc->sc_flags = 0;
 1465         sc->sc_flowlabel = 0;
 1466 
 1467         /*
 1468          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1469          * win was derived from socket earlier in the function.
 1470          */
 1471         win = imax(win, 0);
 1472         win = imin(win, TCP_MAXWIN);
 1473         sc->sc_wnd = win;
 1474 
 1475         if (V_tcp_do_rfc1323) {
 1476                 /*
 1477                  * A timestamp received in a SYN makes
 1478                  * it ok to send timestamp requests and replies.
 1479                  */
 1480                 if (to->to_flags & TOF_TS) {
 1481                         sc->sc_tsreflect = to->to_tsval;
 1482                         sc->sc_ts = tcp_ts_getticks();
 1483                         sc->sc_flags |= SCF_TIMESTAMP;
 1484                 }
 1485                 if (to->to_flags & TOF_SCALE) {
 1486                         int wscale = 0;
 1487 
 1488                         /*
 1489                          * Pick the smallest possible scaling factor that
 1490                          * will still allow us to scale up to sb_max, aka
 1491                          * kern.ipc.maxsockbuf.
 1492                          *
 1493                          * We do this because there are broken firewalls that
 1494                          * will corrupt the window scale option, leading to
 1495                          * the other endpoint believing that our advertised
 1496                          * window is unscaled.  At scale factors larger than
 1497                          * 5 the unscaled window will drop below 1500 bytes,
 1498                          * leading to serious problems when traversing these
 1499                          * broken firewalls.
 1500                          *
 1501                          * With the default maxsockbuf of 256K, a scale factor
 1502                          * of 3 will be chosen by this algorithm.  Those who
 1503                          * choose a larger maxsockbuf should watch out
 1504                          * for the compatibility problems mentioned above.
 1505                          *
 1506                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1507                          * or <SYN,ACK>) segment itself is never scaled.
 1508                          */
 1509                         while (wscale < TCP_MAX_WINSHIFT &&
 1510                             (TCP_MAXWIN << wscale) < sb_max)
 1511                                 wscale++;
 1512                         sc->sc_requested_r_scale = wscale;
 1513                         sc->sc_requested_s_scale = to->to_wscale;
 1514                         sc->sc_flags |= SCF_WINSCALE;
 1515                 }
 1516         }
 1517 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1518         /*
 1519          * If listening socket requested TCP digests, flag this in the
 1520          * syncache so that syncache_respond() will do the right thing
 1521          * with the SYN+ACK.
 1522          */
 1523         if (ltflags & TF_SIGNATURE)
 1524                 sc->sc_flags |= SCF_SIGNATURE;
 1525 #endif  /* TCP_SIGNATURE */
 1526         if (to->to_flags & TOF_SACKPERM)
 1527                 sc->sc_flags |= SCF_SACK;
 1528         if (to->to_flags & TOF_MSS)
 1529                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1530         if (ltflags & TF_NOOPT)
 1531                 sc->sc_flags |= SCF_NOOPT;
 1532         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1533                 sc->sc_flags |= SCF_ECN;
 1534 
 1535         if (V_tcp_syncookies)
 1536                 sc->sc_iss = syncookie_generate(sch, sc);
 1537 #ifdef INET6
 1538         if (autoflowlabel) {
 1539                 if (V_tcp_syncookies)
 1540                         sc->sc_flowlabel = sc->sc_iss;
 1541                 else
 1542                         sc->sc_flowlabel = ip6_randomflowlabel();
 1543                 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
 1544         }
 1545 #endif
 1546         SCH_UNLOCK(sch);
 1547 
 1548 #ifdef TCP_RFC7413
 1549         if (tfo_cookie_valid) {
 1550                 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
 1551                 /* INP_WUNLOCK(inp) will be performed by the called */
 1552                 rv = 1;
 1553                 goto tfo_done;
 1554         }
 1555 #endif
 1556 
 1557         /*
 1558          * Do a standard 3-way handshake.
 1559          */
 1560         if (syncache_respond(sc, sch, 0, m) == 0) {
 1561                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1562                         syncache_free(sc);
 1563                 else if (sc != &scs)
 1564                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1565                 TCPSTAT_INC(tcps_sndacks);
 1566                 TCPSTAT_INC(tcps_sndtotal);
 1567         } else {
 1568                 if (sc != &scs)
 1569                         syncache_free(sc);
 1570                 TCPSTAT_INC(tcps_sc_dropped);
 1571         }
 1572 
 1573 done:
 1574         if (m) {
 1575                 *lsop = NULL;
 1576                 m_freem(m);
 1577         }
 1578 #ifdef TCP_RFC7413
 1579 tfo_done:
 1580 #endif
 1581         if (cred != NULL)
 1582                 crfree(cred);
 1583 #ifdef MAC
 1584         if (sc == &scs)
 1585                 mac_syncache_destroy(&maclabel);
 1586 #endif
 1587         return (rv);
 1588 }
 1589 
 1590 /*
 1591  * Send SYN|ACK to the peer.  Either in response to the peer's SYN,
 1592  * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
 1593  */
 1594 static int
 1595 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked,
 1596     const struct mbuf *m0)
 1597 {
 1598         struct ip *ip = NULL;
 1599         struct mbuf *m;
 1600         struct tcphdr *th = NULL;
 1601         int optlen, error = 0;  /* Make compiler happy */
 1602         u_int16_t hlen, tlen, mssopt;
 1603         struct tcpopt to;
 1604 #ifdef INET6
 1605         struct ip6_hdr *ip6 = NULL;
 1606 #endif
 1607         hlen =
 1608 #ifdef INET6
 1609                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1610 #endif
 1611                 sizeof(struct ip);
 1612         tlen = hlen + sizeof(struct tcphdr);
 1613 
 1614         /* Determine MSS we advertize to other end of connection. */
 1615         mssopt = tcp_mssopt(&sc->sc_inc);
 1616         if (sc->sc_peer_mss)
 1617                 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
 1618 
 1619         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1620         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1621             ("syncache: mbuf too small"));
 1622 
 1623         /* Create the IP+TCP header from scratch. */
 1624         m = m_gethdr(M_NOWAIT, MT_DATA);
 1625         if (m == NULL)
 1626                 return (ENOBUFS);
 1627 #ifdef MAC
 1628         mac_syncache_create_mbuf(sc->sc_label, m);
 1629 #endif
 1630         m->m_data += max_linkhdr;
 1631         m->m_len = tlen;
 1632         m->m_pkthdr.len = tlen;
 1633         m->m_pkthdr.rcvif = NULL;
 1634 
 1635 #ifdef INET6
 1636         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1637                 ip6 = mtod(m, struct ip6_hdr *);
 1638                 ip6->ip6_vfc = IPV6_VERSION;
 1639                 ip6->ip6_nxt = IPPROTO_TCP;
 1640                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1641                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1642                 ip6->ip6_plen = htons(tlen - hlen);
 1643                 /* ip6_hlim is set after checksum */
 1644                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1645                 ip6->ip6_flow |= sc->sc_flowlabel;
 1646 
 1647                 th = (struct tcphdr *)(ip6 + 1);
 1648         }
 1649 #endif
 1650 #if defined(INET6) && defined(INET)
 1651         else
 1652 #endif
 1653 #ifdef INET
 1654         {
 1655                 ip = mtod(m, struct ip *);
 1656                 ip->ip_v = IPVERSION;
 1657                 ip->ip_hl = sizeof(struct ip) >> 2;
 1658                 ip->ip_len = htons(tlen);
 1659                 ip->ip_id = 0;
 1660                 ip->ip_off = 0;
 1661                 ip->ip_sum = 0;
 1662                 ip->ip_p = IPPROTO_TCP;
 1663                 ip->ip_src = sc->sc_inc.inc_laddr;
 1664                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1665                 ip->ip_ttl = sc->sc_ip_ttl;
 1666                 ip->ip_tos = sc->sc_ip_tos;
 1667 
 1668                 /*
 1669                  * See if we should do MTU discovery.  Route lookups are
 1670                  * expensive, so we will only unset the DF bit if:
 1671                  *
 1672                  *      1) path_mtu_discovery is disabled
 1673                  *      2) the SCF_UNREACH flag has been set
 1674                  */
 1675                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1676                        ip->ip_off |= htons(IP_DF);
 1677 
 1678                 th = (struct tcphdr *)(ip + 1);
 1679         }
 1680 #endif /* INET */
 1681         th->th_sport = sc->sc_inc.inc_lport;
 1682         th->th_dport = sc->sc_inc.inc_fport;
 1683 
 1684         th->th_seq = htonl(sc->sc_iss);
 1685         th->th_ack = htonl(sc->sc_irs + 1);
 1686         th->th_off = sizeof(struct tcphdr) >> 2;
 1687         th->th_x2 = 0;
 1688         th->th_flags = TH_SYN|TH_ACK;
 1689         th->th_win = htons(sc->sc_wnd);
 1690         th->th_urp = 0;
 1691 
 1692         if (sc->sc_flags & SCF_ECN) {
 1693                 th->th_flags |= TH_ECE;
 1694                 TCPSTAT_INC(tcps_ecn_shs);
 1695         }
 1696 
 1697         /* Tack on the TCP options. */
 1698         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1699                 to.to_flags = 0;
 1700 
 1701                 to.to_mss = mssopt;
 1702                 to.to_flags = TOF_MSS;
 1703                 if (sc->sc_flags & SCF_WINSCALE) {
 1704                         to.to_wscale = sc->sc_requested_r_scale;
 1705                         to.to_flags |= TOF_SCALE;
 1706                 }
 1707                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1708                         /* Virgin timestamp or TCP cookie enhanced one. */
 1709                         to.to_tsval = sc->sc_ts;
 1710                         to.to_tsecr = sc->sc_tsreflect;
 1711                         to.to_flags |= TOF_TS;
 1712                 }
 1713                 if (sc->sc_flags & SCF_SACK)
 1714                         to.to_flags |= TOF_SACKPERM;
 1715 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1716                 if (sc->sc_flags & SCF_SIGNATURE)
 1717                         to.to_flags |= TOF_SIGNATURE;
 1718 #endif
 1719 #ifdef TCP_RFC7413
 1720                 if (sc->sc_tfo_cookie) {
 1721                         to.to_flags |= TOF_FASTOPEN;
 1722                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 1723                         to.to_tfo_cookie = sc->sc_tfo_cookie;
 1724                         /* don't send cookie again when retransmitting response */
 1725                         sc->sc_tfo_cookie = NULL;
 1726                 }
 1727 #endif
 1728                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1729 
 1730                 /* Adjust headers by option size. */
 1731                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1732                 m->m_len += optlen;
 1733                 m->m_pkthdr.len += optlen;
 1734 #ifdef INET6
 1735                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1736                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1737                 else
 1738 #endif
 1739                         ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
 1740 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1741                 if (sc->sc_flags & SCF_SIGNATURE) {
 1742                         KASSERT(to.to_flags & TOF_SIGNATURE,
 1743                             ("tcp_addoptions() didn't set tcp_signature"));
 1744 
 1745                         /* NOTE: to.to_signature is inside of mbuf */
 1746                         if (!TCPMD5_ENABLED() ||
 1747                             TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
 1748                                 m_freem(m);
 1749                                 return (EACCES);
 1750                         }
 1751                 }
 1752 #endif
 1753         } else
 1754                 optlen = 0;
 1755 
 1756         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1757         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1758         /*
 1759          * If we have peer's SYN and it has a flowid, then let's assign it to
 1760          * our SYN|ACK.  ip6_output() and ip_output() will not assign flowid
 1761          * to SYN|ACK due to lack of inp here.
 1762          */
 1763         if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
 1764                 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
 1765                 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
 1766         }
 1767 #ifdef INET6
 1768         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1769                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 1770                 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
 1771                     IPPROTO_TCP, 0);
 1772                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1773 #ifdef TCP_OFFLOAD
 1774                 if (ADDED_BY_TOE(sc)) {
 1775                         struct toedev *tod = sc->sc_tod;
 1776 
 1777                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1778 
 1779                         return (error);
 1780                 }
 1781 #endif
 1782                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1783         }
 1784 #endif
 1785 #if defined(INET6) && defined(INET)
 1786         else
 1787 #endif
 1788 #ifdef INET
 1789         {
 1790                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1791                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1792                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1793 #ifdef TCP_OFFLOAD
 1794                 if (ADDED_BY_TOE(sc)) {
 1795                         struct toedev *tod = sc->sc_tod;
 1796 
 1797                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1798 
 1799                         return (error);
 1800                 }
 1801 #endif
 1802                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1803         }
 1804 #endif
 1805         return (error);
 1806 }
 1807 
 1808 /*
 1809  * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
 1810  * that exceed the capacity of the syncache by avoiding the storage of any
 1811  * of the SYNs we receive.  Syncookies defend against blind SYN flooding
 1812  * attacks where the attacker does not have access to our responses.
 1813  *
 1814  * Syncookies encode and include all necessary information about the
 1815  * connection setup within the SYN|ACK that we send back.  That way we
 1816  * can avoid keeping any local state until the ACK to our SYN|ACK returns
 1817  * (if ever).  Normally the syncache and syncookies are running in parallel
 1818  * with the latter taking over when the former is exhausted.  When matching
 1819  * syncache entry is found the syncookie is ignored.
 1820  *
 1821  * The only reliable information persisting the 3WHS is our initial sequence
 1822  * number ISS of 32 bits.  Syncookies embed a cryptographically sufficient
 1823  * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
 1824  * of our SYN|ACK.  The MAC can be recomputed when the ACK to our SYN|ACK
 1825  * returns and signifies a legitimate connection if it matches the ACK.
 1826  *
 1827  * The available space of 32 bits to store the hash and to encode the SYN
 1828  * option information is very tight and we should have at least 24 bits for
 1829  * the MAC to keep the number of guesses by blind spoofing reasonably high.
 1830  *
 1831  * SYN option information we have to encode to fully restore a connection:
 1832  * MSS: is imporant to chose an optimal segment size to avoid IP level
 1833  *   fragmentation along the path.  The common MSS values can be encoded
 1834  *   in a 3-bit table.  Uncommon values are captured by the next lower value
 1835  *   in the table leading to a slight increase in packetization overhead.
 1836  * WSCALE: is necessary to allow large windows to be used for high delay-
 1837  *   bandwidth product links.  Not scaling the window when it was initially
 1838  *   negotiated is bad for performance as lack of scaling further decreases
 1839  *   the apparent available send window.  We only need to encode the WSCALE
 1840  *   we received from the remote end.  Our end can be recalculated at any
 1841  *   time.  The common WSCALE values can be encoded in a 3-bit table.
 1842  *   Uncommon values are captured by the next lower value in the table
 1843  *   making us under-estimate the available window size halving our
 1844  *   theoretically possible maximum throughput for that connection.
 1845  * SACK: Greatly assists in packet loss recovery and requires 1 bit.
 1846  * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
 1847  *   that are included in all segments on a connection.  We enable them when
 1848  *   the ACK has them.
 1849  *
 1850  * Security of syncookies and attack vectors:
 1851  *
 1852  * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
 1853  * together with the gloabl secret to make it unique per connection attempt.
 1854  * Thus any change of any of those parameters results in a different MAC output
 1855  * in an unpredictable way unless a collision is encountered.  24 bits of the
 1856  * MAC are embedded into the ISS.
 1857  *
 1858  * To prevent replay attacks two rotating global secrets are updated with a
 1859  * new random value every 15 seconds.  The life-time of a syncookie is thus
 1860  * 15-30 seconds.
 1861  *
 1862  * Vector 1: Attacking the secret.  This requires finding a weakness in the
 1863  * MAC itself or the way it is used here.  The attacker can do a chosen plain
 1864  * text attack by varying and testing the all parameters under his control.
 1865  * The strength depends on the size and randomness of the secret, and the
 1866  * cryptographic security of the MAC function.  Due to the constant updating
 1867  * of the secret the attacker has at most 29.999 seconds to find the secret
 1868  * and launch spoofed connections.  After that he has to start all over again.
 1869  *
 1870  * Vector 2: Collision attack on the MAC of a single ACK.  With a 24 bit MAC
 1871  * size an average of 4,823 attempts are required for a 50% chance of success
 1872  * to spoof a single syncookie (birthday collision paradox).  However the
 1873  * attacker is blind and doesn't know if one of his attempts succeeded unless
 1874  * he has a side channel to interfere success from.  A single connection setup
 1875  * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
 1876  * This many attempts are required for each one blind spoofed connection.  For
 1877  * every additional spoofed connection he has to launch another N attempts.
 1878  * Thus for a sustained rate 100 spoofed connections per second approximately
 1879  * 1,800,000 packets per second would have to be sent.
 1880  *
 1881  * NB: The MAC function should be fast so that it doesn't become a CPU
 1882  * exhaustion attack vector itself.
 1883  *
 1884  * References:
 1885  *  RFC4987 TCP SYN Flooding Attacks and Common Mitigations
 1886  *  SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
 1887  *   http://cr.yp.to/syncookies.html    (overview)
 1888  *   http://cr.yp.to/syncookies/archive (details)
 1889  *
 1890  *
 1891  * Schematic construction of a syncookie enabled Initial Sequence Number:
 1892  *  0        1         2         3
 1893  *  12345678901234567890123456789012
 1894  * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
 1895  *
 1896  *  x 24 MAC (truncated)
 1897  *  W  3 Send Window Scale index
 1898  *  M  3 MSS index
 1899  *  S  1 SACK permitted
 1900  *  P  1 Odd/even secret
 1901  */
 1902 
 1903 /*
 1904  * Distribution and probability of certain MSS values.  Those in between are
 1905  * rounded down to the next lower one.
 1906  * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
 1907  *                            .2%  .3%   5%    7%    7%    20%   15%   45%
 1908  */
 1909 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
 1910 
 1911 /*
 1912  * Distribution and probability of certain WSCALE values.  We have to map the
 1913  * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
 1914  * bits based on prevalence of certain values.  Where we don't have an exact
 1915  * match for are rounded down to the next lower one letting us under-estimate
 1916  * the true available window.  At the moment this would happen only for the
 1917  * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
 1918  * and window size).  The absence of the WSCALE option (no scaling in either
 1919  * direction) is encoded with index zero.
 1920  * [WSCALE values histograms, Allman, 2012]
 1921  *                            X 10 10 35  5  6 14 10%   by host
 1922  *                            X 11  4  5  5 18 49  3%   by connections
 1923  */
 1924 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
 1925 
 1926 /*
 1927  * Compute the MAC for the SYN cookie.  SIPHASH-2-4 is chosen for its speed
 1928  * and good cryptographic properties.
 1929  */
 1930 static uint32_t
 1931 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
 1932     uint8_t *secbits, uintptr_t secmod)
 1933 {
 1934         SIPHASH_CTX ctx;
 1935         uint32_t siphash[2];
 1936 
 1937         SipHash24_Init(&ctx);
 1938         SipHash_SetKey(&ctx, secbits);
 1939         switch (inc->inc_flags & INC_ISIPV6) {
 1940 #ifdef INET
 1941         case 0:
 1942                 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
 1943                 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
 1944                 break;
 1945 #endif
 1946 #ifdef INET6
 1947         case INC_ISIPV6:
 1948                 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
 1949                 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
 1950                 break;
 1951 #endif
 1952         }
 1953         SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
 1954         SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
 1955         SipHash_Update(&ctx, &irs, sizeof(irs));
 1956         SipHash_Update(&ctx, &flags, sizeof(flags));
 1957         SipHash_Update(&ctx, &secmod, sizeof(secmod));
 1958         SipHash_Final((u_int8_t *)&siphash, &ctx);
 1959 
 1960         return (siphash[0] ^ siphash[1]);
 1961 }
 1962 
 1963 static tcp_seq
 1964 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
 1965 {
 1966         u_int i, mss, secbit, wscale;
 1967         uint32_t iss, hash;
 1968         uint8_t *secbits;
 1969         union syncookie cookie;
 1970 
 1971         SCH_LOCK_ASSERT(sch);
 1972 
 1973         cookie.cookie = 0;
 1974 
 1975         /* Map our computed MSS into the 3-bit index. */
 1976         mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
 1977         for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0;
 1978              i--)
 1979                 ;
 1980         cookie.flags.mss_idx = i;
 1981 
 1982         /*
 1983          * Map the send window scale into the 3-bit index but only if
 1984          * the wscale option was received.
 1985          */
 1986         if (sc->sc_flags & SCF_WINSCALE) {
 1987                 wscale = sc->sc_requested_s_scale;
 1988                 for (i = nitems(tcp_sc_wstab) - 1;
 1989                     tcp_sc_wstab[i] > wscale && i > 0;
 1990                      i--)
 1991                         ;
 1992                 cookie.flags.wscale_idx = i;
 1993         }
 1994 
 1995         /* Can we do SACK? */
 1996         if (sc->sc_flags & SCF_SACK)
 1997                 cookie.flags.sack_ok = 1;
 1998 
 1999         /* Which of the two secrets to use. */
 2000         secbit = sch->sch_sc->secret.oddeven & 0x1;
 2001         cookie.flags.odd_even = secbit;
 2002 
 2003         secbits = sch->sch_sc->secret.key[secbit];
 2004         hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
 2005             (uintptr_t)sch);
 2006 
 2007         /*
 2008          * Put the flags into the hash and XOR them to get better ISS number
 2009          * variance.  This doesn't enhance the cryptographic strength and is
 2010          * done to prevent the 8 cookie bits from showing up directly on the
 2011          * wire.
 2012          */
 2013         iss = hash & ~0xff;
 2014         iss |= cookie.cookie ^ (hash >> 24);
 2015 
 2016         /* Randomize the timestamp. */
 2017         if (sc->sc_flags & SCF_TIMESTAMP) {
 2018                 sc->sc_ts = arc4random();
 2019                 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
 2020         }
 2021 
 2022         TCPSTAT_INC(tcps_sc_sendcookie);
 2023         return (iss);
 2024 }
 2025 
 2026 static struct syncache *
 2027 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 2028     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2029     struct socket *lso)
 2030 {
 2031         uint32_t hash;
 2032         uint8_t *secbits;
 2033         tcp_seq ack, seq;
 2034         int wnd, wscale = 0;
 2035         union syncookie cookie;
 2036 
 2037         SCH_LOCK_ASSERT(sch);
 2038 
 2039         /*
 2040          * Pull information out of SYN-ACK/ACK and revert sequence number
 2041          * advances.
 2042          */
 2043         ack = th->th_ack - 1;
 2044         seq = th->th_seq - 1;
 2045 
 2046         /*
 2047          * Unpack the flags containing enough information to restore the
 2048          * connection.
 2049          */
 2050         cookie.cookie = (ack & 0xff) ^ (ack >> 24);
 2051 
 2052         /* Which of the two secrets to use. */
 2053         secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
 2054 
 2055         hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
 2056 
 2057         /* The recomputed hash matches the ACK if this was a genuine cookie. */
 2058         if ((ack & ~0xff) != (hash & ~0xff))
 2059                 return (NULL);
 2060 
 2061         /* Fill in the syncache values. */
 2062         sc->sc_flags = 0;
 2063         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 2064         sc->sc_ipopts = NULL;
 2065         
 2066         sc->sc_irs = seq;
 2067         sc->sc_iss = ack;
 2068 
 2069         switch (inc->inc_flags & INC_ISIPV6) {
 2070 #ifdef INET
 2071         case 0:
 2072                 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
 2073                 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
 2074                 break;
 2075 #endif
 2076 #ifdef INET6
 2077         case INC_ISIPV6:
 2078                 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
 2079                         sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
 2080                 break;
 2081 #endif
 2082         }
 2083 
 2084         sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
 2085 
 2086         /* We can simply recompute receive window scale we sent earlier. */
 2087         while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
 2088                 wscale++;
 2089 
 2090         /* Only use wscale if it was enabled in the orignal SYN. */
 2091         if (cookie.flags.wscale_idx > 0) {
 2092                 sc->sc_requested_r_scale = wscale;
 2093                 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
 2094                 sc->sc_flags |= SCF_WINSCALE;
 2095         }
 2096 
 2097         wnd = sbspace(&lso->so_rcv);
 2098         wnd = imax(wnd, 0);
 2099         wnd = imin(wnd, TCP_MAXWIN);
 2100         sc->sc_wnd = wnd;
 2101 
 2102         if (cookie.flags.sack_ok)
 2103                 sc->sc_flags |= SCF_SACK;
 2104 
 2105         if (to->to_flags & TOF_TS) {
 2106                 sc->sc_flags |= SCF_TIMESTAMP;
 2107                 sc->sc_tsreflect = to->to_tsval;
 2108                 sc->sc_ts = to->to_tsecr;
 2109                 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
 2110         }
 2111 
 2112         if (to->to_flags & TOF_SIGNATURE)
 2113                 sc->sc_flags |= SCF_SIGNATURE;
 2114 
 2115         sc->sc_rxmits = 0;
 2116 
 2117         TCPSTAT_INC(tcps_sc_recvcookie);
 2118         return (sc);
 2119 }
 2120 
 2121 #ifdef INVARIANTS
 2122 static int
 2123 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
 2124     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2125     struct socket *lso)
 2126 {
 2127         struct syncache scs, *scx;
 2128         char *s;
 2129 
 2130         bzero(&scs, sizeof(scs));
 2131         scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
 2132 
 2133         if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
 2134                 return (0);
 2135 
 2136         if (scx != NULL) {
 2137                 if (sc->sc_peer_mss != scx->sc_peer_mss)
 2138                         log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
 2139                             s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
 2140 
 2141                 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
 2142                         log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
 2143                             s, __func__, sc->sc_requested_r_scale,
 2144                             scx->sc_requested_r_scale);
 2145 
 2146                 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
 2147                         log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
 2148                             s, __func__, sc->sc_requested_s_scale,
 2149                             scx->sc_requested_s_scale);
 2150 
 2151                 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
 2152                         log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
 2153         }
 2154 
 2155         if (s != NULL)
 2156                 free(s, M_TCPLOG);
 2157         return (0);
 2158 }
 2159 #endif /* INVARIANTS */
 2160 
 2161 static void
 2162 syncookie_reseed(void *arg)
 2163 {
 2164         struct tcp_syncache *sc = arg;
 2165         uint8_t *secbits;
 2166         int secbit;
 2167 
 2168         /*
 2169          * Reseeding the secret doesn't have to be protected by a lock.
 2170          * It only must be ensured that the new random values are visible
 2171          * to all CPUs in a SMP environment.  The atomic with release
 2172          * semantics ensures that.
 2173          */
 2174         secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
 2175         secbits = sc->secret.key[secbit];
 2176         arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
 2177         atomic_add_rel_int(&sc->secret.oddeven, 1);
 2178 
 2179         /* Reschedule ourself. */
 2180         callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
 2181 }
 2182 
 2183 /*
 2184  * Exports the syncache entries to userland so that netstat can display
 2185  * them alongside the other sockets.  This function is intended to be
 2186  * called only from tcp_pcblist.
 2187  *
 2188  * Due to concurrency on an active system, the number of pcbs exported
 2189  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 2190  * amount of space the caller allocated for this function to use.
 2191  */
 2192 int
 2193 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 2194 {
 2195         struct xtcpcb xt;
 2196         struct syncache *sc;
 2197         struct syncache_head *sch;
 2198         int count, error, i;
 2199 
 2200         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 2201                 sch = &V_tcp_syncache.hashbase[i];
 2202                 SCH_LOCK(sch);
 2203                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 2204                         if (count >= max_pcbs) {
 2205                                 SCH_UNLOCK(sch);
 2206                                 goto exit;
 2207                         }
 2208                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 2209                                 continue;
 2210                         bzero(&xt, sizeof(xt));
 2211                         xt.xt_len = sizeof(xt);
 2212                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 2213                                 xt.xt_inp.inp_vflag = INP_IPV6;
 2214                         else
 2215                                 xt.xt_inp.inp_vflag = INP_IPV4;
 2216                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 2217                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 2218                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 2219                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 2220                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 2221                         xt.xt_socket.so_type = SOCK_STREAM;
 2222                         xt.xt_socket.so_state = SS_ISCONNECTING;
 2223                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 2224                         if (error) {
 2225                                 SCH_UNLOCK(sch);
 2226                                 goto exit;
 2227                         }
 2228                         count++;
 2229                 }
 2230                 SCH_UNLOCK(sch);
 2231         }
 2232 exit:
 2233         *pcbs_exported = count;
 2234         return error;
 2235 }

Cache object: 4cc887cd9b71f42403ade666c76e365f


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