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/11.2/sys/netinet/tcp_syncache.c 334740 2018-06-06 22:02:44Z 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 static int
  179 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
  180 {
  181         int error;
  182         u_int new;
  183 
  184         new = V_tcp_syncache.rexmt_limit;
  185         error = sysctl_handle_int(oidp, &new, 0, req);
  186         if ((error == 0) && (req->newptr != NULL)) {
  187                 if (new > TCP_MAXRXTSHIFT)
  188                         error = EINVAL;
  189                 else
  190                         V_tcp_syncache.rexmt_limit = new;
  191         }
  192         return (error);
  193 }
  194 
  195 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
  196     CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW,
  197     &VNET_NAME(tcp_syncache.rexmt_limit), 0,
  198     sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI",
  199     "Limit on SYN/ACK retransmissions");
  200 
  201 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
  202 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
  203     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
  204     "Send reset on socket allocation failure");
  205 
  206 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  207 
  208 #define SCH_LOCK(sch)           mtx_lock(&(sch)->sch_mtx)
  209 #define SCH_UNLOCK(sch)         mtx_unlock(&(sch)->sch_mtx)
  210 #define SCH_LOCK_ASSERT(sch)    mtx_assert(&(sch)->sch_mtx, MA_OWNED)
  211 
  212 /*
  213  * Requires the syncache entry to be already removed from the bucket list.
  214  */
  215 static void
  216 syncache_free(struct syncache *sc)
  217 {
  218 
  219         if (sc->sc_ipopts)
  220                 (void) m_free(sc->sc_ipopts);
  221         if (sc->sc_cred)
  222                 crfree(sc->sc_cred);
  223 #ifdef MAC
  224         mac_syncache_destroy(&sc->sc_label);
  225 #endif
  226 
  227         uma_zfree(V_tcp_syncache.zone, sc);
  228 }
  229 
  230 void
  231 syncache_init(void)
  232 {
  233         int i;
  234 
  235         V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  236         V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  237         V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  238         V_tcp_syncache.hash_secret = arc4random();
  239 
  240         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  241             &V_tcp_syncache.hashsize);
  242         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  243             &V_tcp_syncache.bucket_limit);
  244         if (!powerof2(V_tcp_syncache.hashsize) ||
  245             V_tcp_syncache.hashsize == 0) {
  246                 printf("WARNING: syncache hash size is not a power of 2.\n");
  247                 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  248         }
  249         V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
  250 
  251         /* Set limits. */
  252         V_tcp_syncache.cache_limit =
  253             V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
  254         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  255             &V_tcp_syncache.cache_limit);
  256 
  257         /* Allocate the hash table. */
  258         V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
  259             sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
  260 
  261 #ifdef VIMAGE
  262         V_tcp_syncache.vnet = curvnet;
  263 #endif
  264 
  265         /* Initialize the hash buckets. */
  266         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  267                 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
  268                 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
  269                          NULL, MTX_DEF);
  270                 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
  271                          &V_tcp_syncache.hashbase[i].sch_mtx, 0);
  272                 V_tcp_syncache.hashbase[i].sch_length = 0;
  273                 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
  274                 V_tcp_syncache.hashbase[i].sch_last_overflow =
  275                     -(SYNCOOKIE_LIFETIME + 1);
  276         }
  277 
  278         /* Create the syncache entry zone. */
  279         V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  280             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  281         V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
  282             V_tcp_syncache.cache_limit);
  283 
  284         /* Start the SYN cookie reseeder callout. */
  285         callout_init(&V_tcp_syncache.secret.reseed, 1);
  286         arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
  287         arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
  288         callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
  289             syncookie_reseed, &V_tcp_syncache);
  290 }
  291 
  292 #ifdef VIMAGE
  293 void
  294 syncache_destroy(void)
  295 {
  296         struct syncache_head *sch;
  297         struct syncache *sc, *nsc;
  298         int i;
  299 
  300         /*
  301          * Stop the re-seed timer before freeing resources.  No need to
  302          * possibly schedule it another time.
  303          */
  304         callout_drain(&V_tcp_syncache.secret.reseed);
  305 
  306         /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
  307         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  308 
  309                 sch = &V_tcp_syncache.hashbase[i];
  310                 callout_drain(&sch->sch_timer);
  311 
  312                 SCH_LOCK(sch);
  313                 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
  314                         syncache_drop(sc, sch);
  315                 SCH_UNLOCK(sch);
  316                 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
  317                     ("%s: sch->sch_bucket not empty", __func__));
  318                 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
  319                     __func__, sch->sch_length));
  320                 mtx_destroy(&sch->sch_mtx);
  321         }
  322 
  323         KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
  324             ("%s: cache_count not 0", __func__));
  325 
  326         /* Free the allocated global resources. */
  327         uma_zdestroy(V_tcp_syncache.zone);
  328         free(V_tcp_syncache.hashbase, M_SYNCACHE);
  329 }
  330 #endif
  331 
  332 /*
  333  * Inserts a syncache entry into the specified bucket row.
  334  * Locks and unlocks the syncache_head autonomously.
  335  */
  336 static void
  337 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  338 {
  339         struct syncache *sc2;
  340 
  341         SCH_LOCK(sch);
  342 
  343         /*
  344          * Make sure that we don't overflow the per-bucket limit.
  345          * If the bucket is full, toss the oldest element.
  346          */
  347         if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
  348                 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
  349                         ("sch->sch_length incorrect"));
  350                 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
  351                 sch->sch_last_overflow = time_uptime;
  352                 syncache_drop(sc2, sch);
  353                 TCPSTAT_INC(tcps_sc_bucketoverflow);
  354         }
  355 
  356         /* Put it into the bucket. */
  357         TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
  358         sch->sch_length++;
  359 
  360 #ifdef TCP_OFFLOAD
  361         if (ADDED_BY_TOE(sc)) {
  362                 struct toedev *tod = sc->sc_tod;
  363 
  364                 tod->tod_syncache_added(tod, sc->sc_todctx);
  365         }
  366 #endif
  367 
  368         /* Reinitialize the bucket row's timer. */
  369         if (sch->sch_length == 1)
  370                 sch->sch_nextc = ticks + INT_MAX;
  371         syncache_timeout(sc, sch, 1);
  372 
  373         SCH_UNLOCK(sch);
  374 
  375         TCPSTATES_INC(TCPS_SYN_RECEIVED);
  376         TCPSTAT_INC(tcps_sc_added);
  377 }
  378 
  379 /*
  380  * Remove and free entry from syncache bucket row.
  381  * Expects locked syncache head.
  382  */
  383 static void
  384 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  385 {
  386 
  387         SCH_LOCK_ASSERT(sch);
  388 
  389         TCPSTATES_DEC(TCPS_SYN_RECEIVED);
  390         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  391         sch->sch_length--;
  392 
  393 #ifdef TCP_OFFLOAD
  394         if (ADDED_BY_TOE(sc)) {
  395                 struct toedev *tod = sc->sc_tod;
  396 
  397                 tod->tod_syncache_removed(tod, sc->sc_todctx);
  398         }
  399 #endif
  400 
  401         syncache_free(sc);
  402 }
  403 
  404 /*
  405  * Engage/reengage time on bucket row.
  406  */
  407 static void
  408 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
  409 {
  410         int rexmt;
  411 
  412         if (sc->sc_rxmits == 0)
  413                 rexmt = TCPTV_RTOBASE;
  414         else
  415                 TCPT_RANGESET(rexmt, TCPTV_RTOBASE * tcp_syn_backoff[sc->sc_rxmits],
  416                     tcp_rexmit_min, TCPTV_REXMTMAX);
  417         sc->sc_rxttime = ticks + rexmt;
  418         sc->sc_rxmits++;
  419         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
  420                 sch->sch_nextc = sc->sc_rxttime;
  421                 if (docallout)
  422                         callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
  423                             syncache_timer, (void *)sch);
  424         }
  425 }
  426 
  427 /*
  428  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  429  * If we have retransmitted an entry the maximum number of times, expire it.
  430  * One separate timer for each bucket row.
  431  */
  432 static void
  433 syncache_timer(void *xsch)
  434 {
  435         struct syncache_head *sch = (struct syncache_head *)xsch;
  436         struct syncache *sc, *nsc;
  437         int tick = ticks;
  438         char *s;
  439 
  440         CURVNET_SET(sch->sch_sc->vnet);
  441 
  442         /* NB: syncache_head has already been locked by the callout. */
  443         SCH_LOCK_ASSERT(sch);
  444 
  445         /*
  446          * In the following cycle we may remove some entries and/or
  447          * advance some timeouts, so re-initialize the bucket timer.
  448          */
  449         sch->sch_nextc = tick + INT_MAX;
  450 
  451         TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
  452                 /*
  453                  * We do not check if the listen socket still exists
  454                  * and accept the case where the listen socket may be
  455                  * gone by the time we resend the SYN/ACK.  We do
  456                  * not expect this to happens often. If it does,
  457                  * then the RST will be sent by the time the remote
  458                  * host does the SYN/ACK->ACK.
  459                  */
  460                 if (TSTMP_GT(sc->sc_rxttime, tick)) {
  461                         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
  462                                 sch->sch_nextc = sc->sc_rxttime;
  463                         continue;
  464                 }
  465                 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
  466                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  467                                 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
  468                                     "giving up and removing syncache entry\n",
  469                                     s, __func__);
  470                                 free(s, M_TCPLOG);
  471                         }
  472                         syncache_drop(sc, sch);
  473                         TCPSTAT_INC(tcps_sc_stale);
  474                         continue;
  475                 }
  476                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  477                         log(LOG_DEBUG, "%s; %s: Response timeout, "
  478                             "retransmitting (%u) SYN|ACK\n",
  479                             s, __func__, sc->sc_rxmits);
  480                         free(s, M_TCPLOG);
  481                 }
  482 
  483                 syncache_respond(sc, sch, 1, NULL);
  484                 TCPSTAT_INC(tcps_sc_retransmitted);
  485                 syncache_timeout(sc, sch, 0);
  486         }
  487         if (!TAILQ_EMPTY(&(sch)->sch_bucket))
  488                 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
  489                         syncache_timer, (void *)(sch));
  490         CURVNET_RESTORE();
  491 }
  492 
  493 /*
  494  * Find an entry in the syncache.
  495  * Returns always with locked syncache_head plus a matching entry or NULL.
  496  */
  497 static struct syncache *
  498 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  499 {
  500         struct syncache *sc;
  501         struct syncache_head *sch;
  502         uint32_t hash;
  503 
  504         /*
  505          * The hash is built on foreign port + local port + foreign address.
  506          * We rely on the fact that struct in_conninfo starts with 16 bits
  507          * of foreign port, then 16 bits of local port then followed by 128
  508          * bits of foreign address.  In case of IPv4 address, the first 3
  509          * 32-bit words of the address always are zeroes.
  510          */
  511         hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
  512             V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
  513 
  514         sch = &V_tcp_syncache.hashbase[hash];
  515         *schp = sch;
  516         SCH_LOCK(sch);
  517 
  518         /* Circle through bucket row to find matching entry. */
  519         TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
  520                 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
  521                     sizeof(struct in_endpoints)) == 0)
  522                         break;
  523 
  524         return (sc);    /* Always returns with locked sch. */
  525 }
  526 
  527 /*
  528  * This function is called when we get a RST for a
  529  * non-existent connection, so that we can see if the
  530  * connection is in the syn cache.  If it is, zap it.
  531  */
  532 void
  533 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
  534 {
  535         struct syncache *sc;
  536         struct syncache_head *sch;
  537         char *s = NULL;
  538 
  539         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  540         SCH_LOCK_ASSERT(sch);
  541 
  542         /*
  543          * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
  544          * See RFC 793 page 65, section SEGMENT ARRIVES.
  545          */
  546         if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
  547                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  548                         log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
  549                             "FIN flag set, segment ignored\n", s, __func__);
  550                 TCPSTAT_INC(tcps_badrst);
  551                 goto done;
  552         }
  553 
  554         /*
  555          * No corresponding connection was found in syncache.
  556          * If syncookies are enabled and possibly exclusively
  557          * used, or we are under memory pressure, a valid RST
  558          * may not find a syncache entry.  In that case we're
  559          * done and no SYN|ACK retransmissions will happen.
  560          * Otherwise the RST was misdirected or spoofed.
  561          */
  562         if (sc == NULL) {
  563                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  564                         log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
  565                             "syncache entry (possibly syncookie only), "
  566                             "segment ignored\n", s, __func__);
  567                 TCPSTAT_INC(tcps_badrst);
  568                 goto done;
  569         }
  570 
  571         /*
  572          * If the RST bit is set, check the sequence number to see
  573          * if this is a valid reset segment.
  574          * RFC 793 page 37:
  575          *   In all states except SYN-SENT, all reset (RST) segments
  576          *   are validated by checking their SEQ-fields.  A reset is
  577          *   valid if its sequence number is in the window.
  578          *
  579          *   The sequence number in the reset segment is normally an
  580          *   echo of our outgoing acknowlegement numbers, but some hosts
  581          *   send a reset with the sequence number at the rightmost edge
  582          *   of our receive window, and we have to handle this case.
  583          */
  584         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  585             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  586                 syncache_drop(sc, sch);
  587                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  588                         log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
  589                             "connection attempt aborted by remote endpoint\n",
  590                             s, __func__);
  591                 TCPSTAT_INC(tcps_sc_reset);
  592         } else {
  593                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  594                         log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
  595                             "IRS %u (+WND %u), segment ignored\n",
  596                             s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
  597                 TCPSTAT_INC(tcps_badrst);
  598         }
  599 
  600 done:
  601         if (s != NULL)
  602                 free(s, M_TCPLOG);
  603         SCH_UNLOCK(sch);
  604 }
  605 
  606 void
  607 syncache_badack(struct in_conninfo *inc)
  608 {
  609         struct syncache *sc;
  610         struct syncache_head *sch;
  611 
  612         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  613         SCH_LOCK_ASSERT(sch);
  614         if (sc != NULL) {
  615                 syncache_drop(sc, sch);
  616                 TCPSTAT_INC(tcps_sc_badack);
  617         }
  618         SCH_UNLOCK(sch);
  619 }
  620 
  621 void
  622 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq)
  623 {
  624         struct syncache *sc;
  625         struct syncache_head *sch;
  626 
  627         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  628         SCH_LOCK_ASSERT(sch);
  629         if (sc == NULL)
  630                 goto done;
  631 
  632         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  633         if (ntohl(th_seq) != sc->sc_iss)
  634                 goto done;
  635 
  636         /*
  637          * If we've rertransmitted 3 times and this is our second error,
  638          * we remove the entry.  Otherwise, we allow it to continue on.
  639          * This prevents us from incorrectly nuking an entry during a
  640          * spurious network outage.
  641          *
  642          * See tcp_notify().
  643          */
  644         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
  645                 sc->sc_flags |= SCF_UNREACH;
  646                 goto done;
  647         }
  648         syncache_drop(sc, sch);
  649         TCPSTAT_INC(tcps_sc_unreach);
  650 done:
  651         SCH_UNLOCK(sch);
  652 }
  653 
  654 /*
  655  * Build a new TCP socket structure from a syncache entry.
  656  *
  657  * On success return the newly created socket with its underlying inp locked.
  658  */
  659 static struct socket *
  660 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  661 {
  662         struct tcp_function_block *blk;
  663         struct inpcb *inp = NULL;
  664         struct socket *so;
  665         struct tcpcb *tp;
  666         int error;
  667         char *s;
  668 
  669         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  670 
  671         /*
  672          * Ok, create the full blown connection, and set things up
  673          * as they would have been set up if we had created the
  674          * connection when the SYN arrived.  If we can't create
  675          * the connection, abort it.
  676          */
  677         so = sonewconn(lso, 0);
  678         if (so == NULL) {
  679                 /*
  680                  * Drop the connection; we will either send a RST or
  681                  * have the peer retransmit its SYN again after its
  682                  * RTO and try again.
  683                  */
  684                 TCPSTAT_INC(tcps_listendrop);
  685                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  686                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  687                             "due to limits or memory shortage\n",
  688                             s, __func__);
  689                         free(s, M_TCPLOG);
  690                 }
  691                 goto abort2;
  692         }
  693 #ifdef MAC
  694         mac_socketpeer_set_from_mbuf(m, so);
  695 #endif
  696 
  697         inp = sotoinpcb(so);
  698         inp->inp_inc.inc_fibnum = so->so_fibnum;
  699         INP_WLOCK(inp);
  700         /*
  701          * Exclusive pcbinfo lock is not required in syncache socket case even
  702          * if two inpcb locks can be acquired simultaneously:
  703          *  - the inpcb in LISTEN state,
  704          *  - the newly created inp.
  705          *
  706          * In this case, an inp cannot be at same time in LISTEN state and
  707          * just created by an accept() call.
  708          */
  709         INP_HASH_WLOCK(&V_tcbinfo);
  710 
  711         /* Insert new socket into PCB hash list. */
  712         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  713 #ifdef INET6
  714         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  715                 inp->inp_vflag &= ~INP_IPV4;
  716                 inp->inp_vflag |= INP_IPV6;
  717                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  718         } else {
  719                 inp->inp_vflag &= ~INP_IPV6;
  720                 inp->inp_vflag |= INP_IPV4;
  721 #endif
  722                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  723 #ifdef INET6
  724         }
  725 #endif
  726 
  727         /*
  728          * If there's an mbuf and it has a flowid, then let's initialise the
  729          * inp with that particular flowid.
  730          */
  731         if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
  732                 inp->inp_flowid = m->m_pkthdr.flowid;
  733                 inp->inp_flowtype = M_HASHTYPE_GET(m);
  734         }
  735 
  736         /*
  737          * Install in the reservation hash table for now, but don't yet
  738          * install a connection group since the full 4-tuple isn't yet
  739          * configured.
  740          */
  741         inp->inp_lport = sc->sc_inc.inc_lport;
  742         if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
  743                 /*
  744                  * Undo the assignments above if we failed to
  745                  * put the PCB on the hash lists.
  746                  */
  747 #ifdef INET6
  748                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  749                         inp->in6p_laddr = in6addr_any;
  750                 else
  751 #endif
  752                         inp->inp_laddr.s_addr = INADDR_ANY;
  753                 inp->inp_lport = 0;
  754                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  755                         log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
  756                             "with error %i\n",
  757                             s, __func__, error);
  758                         free(s, M_TCPLOG);
  759                 }
  760                 INP_HASH_WUNLOCK(&V_tcbinfo);
  761                 goto abort;
  762         }
  763 #ifdef INET6
  764         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  765                 struct inpcb *oinp = sotoinpcb(lso);
  766                 struct in6_addr laddr6;
  767                 struct sockaddr_in6 sin6;
  768                 /*
  769                  * Inherit socket options from the listening socket.
  770                  * Note that in6p_inputopts are not (and should not be)
  771                  * copied, since it stores previously received options and is
  772                  * used to detect if each new option is different than the
  773                  * previous one and hence should be passed to a user.
  774                  * If we copied in6p_inputopts, a user would not be able to
  775                  * receive options just after calling the accept system call.
  776                  */
  777                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  778                 if (oinp->in6p_outputopts)
  779                         inp->in6p_outputopts =
  780                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  781 
  782                 sin6.sin6_family = AF_INET6;
  783                 sin6.sin6_len = sizeof(sin6);
  784                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  785                 sin6.sin6_port = sc->sc_inc.inc_fport;
  786                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  787                 laddr6 = inp->in6p_laddr;
  788                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  789                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  790                 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
  791                     thread0.td_ucred, m)) != 0) {
  792                         inp->in6p_laddr = laddr6;
  793                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  794                                 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
  795                                     "with error %i\n",
  796                                     s, __func__, error);
  797                                 free(s, M_TCPLOG);
  798                         }
  799                         INP_HASH_WUNLOCK(&V_tcbinfo);
  800                         goto abort;
  801                 }
  802                 /* Override flowlabel from in6_pcbconnect. */
  803                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  804                 inp->inp_flow |= sc->sc_flowlabel;
  805         }
  806 #endif /* INET6 */
  807 #if defined(INET) && defined(INET6)
  808         else
  809 #endif
  810 #ifdef INET
  811         {
  812                 struct in_addr laddr;
  813                 struct sockaddr_in sin;
  814 
  815                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  816                 
  817                 if (inp->inp_options == NULL) {
  818                         inp->inp_options = sc->sc_ipopts;
  819                         sc->sc_ipopts = NULL;
  820                 }
  821 
  822                 sin.sin_family = AF_INET;
  823                 sin.sin_len = sizeof(sin);
  824                 sin.sin_addr = sc->sc_inc.inc_faddr;
  825                 sin.sin_port = sc->sc_inc.inc_fport;
  826                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  827                 laddr = inp->inp_laddr;
  828                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  829                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  830                 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
  831                     thread0.td_ucred, m)) != 0) {
  832                         inp->inp_laddr = laddr;
  833                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  834                                 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
  835                                     "with error %i\n",
  836                                     s, __func__, error);
  837                                 free(s, M_TCPLOG);
  838                         }
  839                         INP_HASH_WUNLOCK(&V_tcbinfo);
  840                         goto abort;
  841                 }
  842         }
  843 #endif /* INET */
  844 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
  845         /* Copy old policy into new socket's. */
  846         if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
  847                 printf("syncache_socket: could not copy policy\n");
  848 #endif
  849         INP_HASH_WUNLOCK(&V_tcbinfo);
  850         tp = intotcpcb(inp);
  851         tcp_state_change(tp, TCPS_SYN_RECEIVED);
  852         tp->iss = sc->sc_iss;
  853         tp->irs = sc->sc_irs;
  854         tcp_rcvseqinit(tp);
  855         tcp_sendseqinit(tp);
  856         blk = sototcpcb(lso)->t_fb;
  857         if (blk != tp->t_fb) {
  858                 /*
  859                  * Our parents t_fb was not the default,
  860                  * we need to release our ref on tp->t_fb and 
  861                  * pickup one on the new entry.
  862                  */
  863                 struct tcp_function_block *rblk;
  864                 
  865                 rblk = find_and_ref_tcp_fb(blk);
  866                 KASSERT(rblk != NULL,
  867                     ("cannot find blk %p out of syncache?", blk));
  868                 if (tp->t_fb->tfb_tcp_fb_fini)
  869                         (*tp->t_fb->tfb_tcp_fb_fini)(tp);
  870                 refcount_release(&tp->t_fb->tfb_refcnt);
  871                 tp->t_fb = rblk;
  872                 if (tp->t_fb->tfb_tcp_fb_init) {
  873                         (*tp->t_fb->tfb_tcp_fb_init)(tp);
  874                 }
  875         }               
  876         tp->snd_wl1 = sc->sc_irs;
  877         tp->snd_max = tp->iss + 1;
  878         tp->snd_nxt = tp->iss + 1;
  879         tp->rcv_up = sc->sc_irs + 1;
  880         tp->rcv_wnd = sc->sc_wnd;
  881         tp->rcv_adv += tp->rcv_wnd;
  882         tp->last_ack_sent = tp->rcv_nxt;
  883 
  884         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  885         if (sc->sc_flags & SCF_NOOPT)
  886                 tp->t_flags |= TF_NOOPT;
  887         else {
  888                 if (sc->sc_flags & SCF_WINSCALE) {
  889                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  890                         tp->snd_scale = sc->sc_requested_s_scale;
  891                         tp->request_r_scale = sc->sc_requested_r_scale;
  892                 }
  893                 if (sc->sc_flags & SCF_TIMESTAMP) {
  894                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  895                         tp->ts_recent = sc->sc_tsreflect;
  896                         tp->ts_recent_age = tcp_ts_getticks();
  897                         tp->ts_offset = sc->sc_tsoff;
  898                 }
  899 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
  900                 if (sc->sc_flags & SCF_SIGNATURE)
  901                         tp->t_flags |= TF_SIGNATURE;
  902 #endif
  903                 if (sc->sc_flags & SCF_SACK)
  904                         tp->t_flags |= TF_SACK_PERMIT;
  905         }
  906 
  907         if (sc->sc_flags & SCF_ECN)
  908                 tp->t_flags |= TF_ECN_PERMIT;
  909 
  910         /*
  911          * Set up MSS and get cached values from tcp_hostcache.
  912          * This might overwrite some of the defaults we just set.
  913          */
  914         tcp_mss(tp, sc->sc_peer_mss);
  915 
  916         /*
  917          * If the SYN,ACK was retransmitted, indicate that CWND to be
  918          * limited to one segment in cc_conn_init().
  919          * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
  920          */
  921         if (sc->sc_rxmits > 1)
  922                 tp->snd_cwnd = 1;
  923 
  924 #ifdef TCP_OFFLOAD
  925         /*
  926          * Allow a TOE driver to install its hooks.  Note that we hold the
  927          * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
  928          * new connection before the TOE driver has done its thing.
  929          */
  930         if (ADDED_BY_TOE(sc)) {
  931                 struct toedev *tod = sc->sc_tod;
  932 
  933                 tod->tod_offload_socket(tod, sc->sc_todctx, so);
  934         }
  935 #endif
  936         /*
  937          * Copy and activate timers.
  938          */
  939         tp->t_keepinit = sototcpcb(lso)->t_keepinit;
  940         tp->t_keepidle = sototcpcb(lso)->t_keepidle;
  941         tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
  942         tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
  943         tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
  944 
  945         TCPSTAT_INC(tcps_accepts);
  946         return (so);
  947 
  948 abort:
  949         INP_WUNLOCK(inp);
  950 abort2:
  951         if (so != NULL)
  952                 soabort(so);
  953         return (NULL);
  954 }
  955 
  956 /*
  957  * This function gets called when we receive an ACK for a
  958  * socket in the LISTEN state.  We look up the connection
  959  * in the syncache, and if its there, we pull it out of
  960  * the cache and turn it into a full-blown connection in
  961  * the SYN-RECEIVED state.
  962  *
  963  * On syncache_socket() success the newly created socket
  964  * has its underlying inp locked.
  965  */
  966 int
  967 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  968     struct socket **lsop, struct mbuf *m)
  969 {
  970         struct syncache *sc;
  971         struct syncache_head *sch;
  972         struct syncache scs;
  973         char *s;
  974 
  975         /*
  976          * Global TCP locks are held because we manipulate the PCB lists
  977          * and create a new socket.
  978          */
  979         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  980         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  981             ("%s: can handle only ACK", __func__));
  982 
  983         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  984         SCH_LOCK_ASSERT(sch);
  985 
  986 #ifdef INVARIANTS
  987         /*
  988          * Test code for syncookies comparing the syncache stored
  989          * values with the reconstructed values from the cookie.
  990          */
  991         if (sc != NULL)
  992                 syncookie_cmp(inc, sch, sc, th, to, *lsop);
  993 #endif
  994 
  995         if (sc == NULL) {
  996                 /*
  997                  * There is no syncache entry, so see if this ACK is
  998                  * a returning syncookie.  To do this, first:
  999                  *  A. Check if syncookies are used in case of syncache
 1000                  *     overflows
 1001                  *  B. See if this socket has had a syncache entry dropped in
 1002                  *     the recent past. We don't want to accept a bogus
 1003                  *     syncookie if we've never received a SYN or accept it
 1004                  *     twice.
 1005                  *  C. check that the syncookie is valid.  If it is, then
 1006                  *     cobble up a fake syncache entry, and return.
 1007                  */
 1008                 if (!V_tcp_syncookies) {
 1009                         SCH_UNLOCK(sch);
 1010                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1011                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
 1012                                     "segment rejected (syncookies disabled)\n",
 1013                                     s, __func__);
 1014                         goto failed;
 1015                 }
 1016                 if (!V_tcp_syncookiesonly &&
 1017                     sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
 1018                         SCH_UNLOCK(sch);
 1019                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1020                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
 1021                                     "segment rejected (no syncache entry)\n",
 1022                                     s, __func__);
 1023                         goto failed;
 1024                 }
 1025                 bzero(&scs, sizeof(scs));
 1026                 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
 1027                 SCH_UNLOCK(sch);
 1028                 if (sc == NULL) {
 1029                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1030                                 log(LOG_DEBUG, "%s; %s: Segment failed "
 1031                                     "SYNCOOKIE authentication, segment rejected "
 1032                                     "(probably spoofed)\n", s, __func__);
 1033                         goto failed;
 1034                 }
 1035 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1036                 /* If received ACK has MD5 signature, check it. */
 1037                 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
 1038                     (!TCPMD5_ENABLED() ||
 1039                     TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
 1040                         /* Drop the ACK. */
 1041                         if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1042                                 log(LOG_DEBUG, "%s; %s: Segment rejected, "
 1043                                     "MD5 signature doesn't match.\n",
 1044                                     s, __func__);
 1045                                 free(s, M_TCPLOG);
 1046                         }
 1047                         TCPSTAT_INC(tcps_sig_err_sigopt);
 1048                         return (-1); /* Do not send RST */
 1049                 }
 1050 #endif /* TCP_SIGNATURE */
 1051         } else {
 1052 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1053                 /*
 1054                  * If listening socket requested TCP digests, check that
 1055                  * received ACK has signature and it is correct.
 1056                  * If not, drop the ACK and leave sc entry in th cache,
 1057                  * because SYN was received with correct signature.
 1058                  */
 1059                 if (sc->sc_flags & SCF_SIGNATURE) {
 1060                         if ((to->to_flags & TOF_SIGNATURE) == 0) {
 1061                                 /* No signature */
 1062                                 TCPSTAT_INC(tcps_sig_err_nosigopt);
 1063                                 SCH_UNLOCK(sch);
 1064                                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1065                                         log(LOG_DEBUG, "%s; %s: Segment "
 1066                                             "rejected, MD5 signature wasn't "
 1067                                             "provided.\n", s, __func__);
 1068                                         free(s, M_TCPLOG);
 1069                                 }
 1070                                 return (-1); /* Do not send RST */
 1071                         }
 1072                         if (!TCPMD5_ENABLED() ||
 1073                             TCPMD5_INPUT(m, th, to->to_signature) != 0) {
 1074                                 /* Doesn't match or no SA */
 1075                                 SCH_UNLOCK(sch);
 1076                                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1077                                         log(LOG_DEBUG, "%s; %s: Segment "
 1078                                             "rejected, MD5 signature doesn't "
 1079                                             "match.\n", s, __func__);
 1080                                         free(s, M_TCPLOG);
 1081                                 }
 1082                                 return (-1); /* Do not send RST */
 1083                         }
 1084                 }
 1085 #endif /* TCP_SIGNATURE */
 1086                 /*
 1087                  * Pull out the entry to unlock the bucket row.
 1088                  * 
 1089                  * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
 1090                  * tcp_state_change().  The tcpcb is not existent at this
 1091                  * moment.  A new one will be allocated via syncache_socket->
 1092                  * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
 1093                  * syncache_socket() will change it to TCPS_SYN_RECEIVED.
 1094                  */
 1095                 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
 1096                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
 1097                 sch->sch_length--;
 1098 #ifdef TCP_OFFLOAD
 1099                 if (ADDED_BY_TOE(sc)) {
 1100                         struct toedev *tod = sc->sc_tod;
 1101 
 1102                         tod->tod_syncache_removed(tod, sc->sc_todctx);
 1103                 }
 1104 #endif
 1105                 SCH_UNLOCK(sch);
 1106         }
 1107 
 1108         /*
 1109          * Segment validation:
 1110          * ACK must match our initial sequence number + 1 (the SYN|ACK).
 1111          */
 1112         if (th->th_ack != sc->sc_iss + 1) {
 1113                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1114                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
 1115                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
 1116                 goto failed;
 1117         }
 1118 
 1119         /*
 1120          * The SEQ must fall in the window starting at the received
 1121          * initial receive sequence number + 1 (the SYN).
 1122          */
 1123         if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
 1124             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
 1125                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1126                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
 1127                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
 1128                 goto failed;
 1129         }
 1130 
 1131         /*
 1132          * If timestamps were not negotiated during SYN/ACK they
 1133          * must not appear on any segment during this session.
 1134          */
 1135         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
 1136                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1137                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1138                             "segment rejected\n", s, __func__);
 1139                 goto failed;
 1140         }
 1141 
 1142         /*
 1143          * If timestamps were negotiated during SYN/ACK they should
 1144          * appear on every segment during this session.
 1145          * XXXAO: This is only informal as there have been unverified
 1146          * reports of non-compliants stacks.
 1147          */
 1148         if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
 1149                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1150                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1151                             "no action\n", s, __func__);
 1152                         free(s, M_TCPLOG);
 1153                         s = NULL;
 1154                 }
 1155         }
 1156 
 1157         /*
 1158          * If timestamps were negotiated, the reflected timestamp
 1159          * must be equal to what we actually sent in the SYN|ACK
 1160          * except in the case of 0. Some boxes are known for sending
 1161          * broken timestamp replies during the 3whs (and potentially
 1162          * during the connection also).
 1163          *
 1164          * Accept the final ACK of 3whs with reflected timestamp of 0
 1165          * instead of sending a RST and deleting the syncache entry.
 1166          */
 1167         if ((to->to_flags & TOF_TS) && to->to_tsecr &&
 1168             to->to_tsecr != sc->sc_ts) {
 1169                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1170                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
 1171                             "segment rejected\n",
 1172                             s, __func__, to->to_tsecr, sc->sc_ts);
 1173                 goto failed;
 1174         }
 1175 
 1176         *lsop = syncache_socket(sc, *lsop, m);
 1177 
 1178         if (*lsop == NULL)
 1179                 TCPSTAT_INC(tcps_sc_aborted);
 1180         else
 1181                 TCPSTAT_INC(tcps_sc_completed);
 1182 
 1183 /* how do we find the inp for the new socket? */
 1184         if (sc != &scs)
 1185                 syncache_free(sc);
 1186         return (1);
 1187 failed:
 1188         if (sc != NULL && sc != &scs)
 1189                 syncache_free(sc);
 1190         if (s != NULL)
 1191                 free(s, M_TCPLOG);
 1192         *lsop = NULL;
 1193         return (0);
 1194 }
 1195 
 1196 #ifdef TCP_RFC7413
 1197 static void
 1198 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
 1199     uint64_t response_cookie)
 1200 {
 1201         struct inpcb *inp;
 1202         struct tcpcb *tp;
 1203         unsigned int *pending_counter;
 1204 
 1205         /*
 1206          * Global TCP locks are held because we manipulate the PCB lists
 1207          * and create a new socket.
 1208          */
 1209         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1210 
 1211         pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
 1212         *lsop = syncache_socket(sc, *lsop, m);
 1213         if (*lsop == NULL) {
 1214                 TCPSTAT_INC(tcps_sc_aborted);
 1215                 atomic_subtract_int(pending_counter, 1);
 1216         } else {
 1217                 inp = sotoinpcb(*lsop);
 1218                 tp = intotcpcb(inp);
 1219                 tp->t_flags |= TF_FASTOPEN;
 1220                 tp->t_tfo_cookie = response_cookie;
 1221                 tp->snd_max = tp->iss;
 1222                 tp->snd_nxt = tp->iss;
 1223                 tp->t_tfo_pending = pending_counter;
 1224                 TCPSTAT_INC(tcps_sc_completed);
 1225         }
 1226 }
 1227 #endif /* TCP_RFC7413 */
 1228 
 1229 /*
 1230  * Given a LISTEN socket and an inbound SYN request, add
 1231  * this to the syn cache, and send back a segment:
 1232  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 1233  * to the source.
 1234  *
 1235  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
 1236  * Doing so would require that we hold onto the data and deliver it
 1237  * to the application.  However, if we are the target of a SYN-flood
 1238  * DoS attack, an attacker could send data which would eventually
 1239  * consume all available buffer space if it were ACKed.  By not ACKing
 1240  * the data, we avoid this DoS scenario.
 1241  *
 1242  * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
 1243  * cookie is processed, V_tcp_fastopen_enabled set to true, and the
 1244  * TCP_FASTOPEN socket option is set.  In this case, a new socket is created
 1245  * and returned via lsop, the mbuf is not freed so that tcp_input() can
 1246  * queue its data to the socket, and 1 is returned to indicate the
 1247  * TFO-socket-creation path was taken.
 1248  */
 1249 int
 1250 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1251     struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
 1252     void *todctx)
 1253 {
 1254         struct tcpcb *tp;
 1255         struct socket *so;
 1256         struct syncache *sc = NULL;
 1257         struct syncache_head *sch;
 1258         struct mbuf *ipopts = NULL;
 1259         u_int ltflags;
 1260         int win, sb_hiwat, ip_ttl, ip_tos;
 1261         char *s;
 1262         int rv = 0;
 1263 #ifdef INET6
 1264         int autoflowlabel = 0;
 1265 #endif
 1266 #ifdef MAC
 1267         struct label *maclabel;
 1268 #endif
 1269         struct syncache scs;
 1270         struct ucred *cred;
 1271 #ifdef TCP_RFC7413
 1272         uint64_t tfo_response_cookie;
 1273         int tfo_cookie_valid = 0;
 1274         int tfo_response_cookie_valid = 0;
 1275 #endif
 1276 
 1277         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1278         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1279             ("%s: unexpected tcp flags", __func__));
 1280 
 1281         /*
 1282          * Combine all so/tp operations very early to drop the INP lock as
 1283          * soon as possible.
 1284          */
 1285         so = *lsop;
 1286         tp = sototcpcb(so);
 1287         cred = crhold(so->so_cred);
 1288 
 1289 #ifdef INET6
 1290         if ((inc->inc_flags & INC_ISIPV6) &&
 1291             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1292                 autoflowlabel = 1;
 1293 #endif
 1294         ip_ttl = inp->inp_ip_ttl;
 1295         ip_tos = inp->inp_ip_tos;
 1296         win = sbspace(&so->so_rcv);
 1297         sb_hiwat = so->so_rcv.sb_hiwat;
 1298         ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
 1299 
 1300 #ifdef TCP_RFC7413
 1301         if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
 1302             (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
 1303                 /*
 1304                  * Limit the number of pending TFO connections to
 1305                  * approximately half of the queue limit.  This prevents TFO
 1306                  * SYN floods from starving the service by filling the
 1307                  * listen queue with bogus TFO connections.
 1308                  */
 1309                 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
 1310                     (so->so_qlimit / 2)) {
 1311                         int result;
 1312 
 1313                         result = tcp_fastopen_check_cookie(inc,
 1314                             to->to_tfo_cookie, to->to_tfo_len,
 1315                             &tfo_response_cookie);
 1316                         tfo_cookie_valid = (result > 0);
 1317                         tfo_response_cookie_valid = (result >= 0);
 1318                 } else
 1319                         atomic_subtract_int(tp->t_tfo_pending, 1);
 1320         }
 1321 #endif
 1322 
 1323         /* By the time we drop the lock these should no longer be used. */
 1324         so = NULL;
 1325         tp = NULL;
 1326 
 1327 #ifdef MAC
 1328         if (mac_syncache_init(&maclabel) != 0) {
 1329                 INP_WUNLOCK(inp);
 1330                 goto done;
 1331         } else
 1332                 mac_syncache_create(maclabel, inp);
 1333 #endif
 1334 #ifdef TCP_RFC7413
 1335         if (!tfo_cookie_valid)
 1336 #endif
 1337                 INP_WUNLOCK(inp);
 1338 
 1339         /*
 1340          * Remember the IP options, if any.
 1341          */
 1342 #ifdef INET6
 1343         if (!(inc->inc_flags & INC_ISIPV6))
 1344 #endif
 1345 #ifdef INET
 1346                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1347 #else
 1348                 ipopts = NULL;
 1349 #endif
 1350 
 1351 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1352         /*
 1353          * If listening socket requested TCP digests, check that received
 1354          * SYN has signature and it is correct. If signature doesn't match
 1355          * or TCP_SIGNATURE support isn't enabled, drop the packet.
 1356          */
 1357         if (ltflags & TF_SIGNATURE) {
 1358                 if ((to->to_flags & TOF_SIGNATURE) == 0) {
 1359                         TCPSTAT_INC(tcps_sig_err_nosigopt);
 1360                         goto done;
 1361                 }
 1362                 if (!TCPMD5_ENABLED() ||
 1363                     TCPMD5_INPUT(m, th, to->to_signature) != 0)
 1364                         goto done;
 1365         }
 1366 #endif  /* TCP_SIGNATURE */
 1367         /*
 1368          * See if we already have an entry for this connection.
 1369          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1370          *
 1371          * XXX: should the syncache be re-initialized with the contents
 1372          * of the new SYN here (which may have different options?)
 1373          *
 1374          * XXX: We do not check the sequence number to see if this is a
 1375          * real retransmit or a new connection attempt.  The question is
 1376          * how to handle such a case; either ignore it as spoofed, or
 1377          * drop the current entry and create a new one?
 1378          */
 1379         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1380         SCH_LOCK_ASSERT(sch);
 1381         if (sc != NULL) {
 1382 #ifdef TCP_RFC7413
 1383                 if (tfo_cookie_valid)
 1384                         INP_WUNLOCK(inp);
 1385 #endif
 1386                 TCPSTAT_INC(tcps_sc_dupsyn);
 1387                 if (ipopts) {
 1388                         /*
 1389                          * If we were remembering a previous source route,
 1390                          * forget it and use the new one we've been given.
 1391                          */
 1392                         if (sc->sc_ipopts)
 1393                                 (void) m_free(sc->sc_ipopts);
 1394                         sc->sc_ipopts = ipopts;
 1395                 }
 1396                 /*
 1397                  * Update timestamp if present.
 1398                  */
 1399                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1400                         sc->sc_tsreflect = to->to_tsval;
 1401                 else
 1402                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1403 #ifdef MAC
 1404                 /*
 1405                  * Since we have already unconditionally allocated label
 1406                  * storage, free it up.  The syncache entry will already
 1407                  * have an initialized label we can use.
 1408                  */
 1409                 mac_syncache_destroy(&maclabel);
 1410 #endif
 1411                 /* Retransmit SYN|ACK and reset retransmit count. */
 1412                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1413                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1414                             "resetting timer and retransmitting SYN|ACK\n",
 1415                             s, __func__);
 1416                         free(s, M_TCPLOG);
 1417                 }
 1418                 if (syncache_respond(sc, sch, 1, m) == 0) {
 1419                         sc->sc_rxmits = 0;
 1420                         syncache_timeout(sc, sch, 1);
 1421                         TCPSTAT_INC(tcps_sndacks);
 1422                         TCPSTAT_INC(tcps_sndtotal);
 1423                 }
 1424                 SCH_UNLOCK(sch);
 1425                 goto done;
 1426         }
 1427 
 1428 #ifdef TCP_RFC7413
 1429         if (tfo_cookie_valid) {
 1430                 bzero(&scs, sizeof(scs));
 1431                 sc = &scs;
 1432                 goto skip_alloc;
 1433         }
 1434 #endif
 1435 
 1436         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1437         if (sc == NULL) {
 1438                 /*
 1439                  * The zone allocator couldn't provide more entries.
 1440                  * Treat this as if the cache was full; drop the oldest
 1441                  * entry and insert the new one.
 1442                  */
 1443                 TCPSTAT_INC(tcps_sc_zonefail);
 1444                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) {
 1445                         sch->sch_last_overflow = time_uptime;
 1446                         syncache_drop(sc, sch);
 1447                 }
 1448                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1449                 if (sc == NULL) {
 1450                         if (V_tcp_syncookies) {
 1451                                 bzero(&scs, sizeof(scs));
 1452                                 sc = &scs;
 1453                         } else {
 1454                                 SCH_UNLOCK(sch);
 1455                                 if (ipopts)
 1456                                         (void) m_free(ipopts);
 1457                                 goto done;
 1458                         }
 1459                 }
 1460         }
 1461 
 1462 #ifdef TCP_RFC7413
 1463 skip_alloc:
 1464         if (!tfo_cookie_valid && tfo_response_cookie_valid)
 1465                 sc->sc_tfo_cookie = &tfo_response_cookie;
 1466 #endif
 1467 
 1468         /*
 1469          * Fill in the syncache values.
 1470          */
 1471 #ifdef MAC
 1472         sc->sc_label = maclabel;
 1473 #endif
 1474         sc->sc_cred = cred;
 1475         cred = NULL;
 1476         sc->sc_ipopts = ipopts;
 1477         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1478 #ifdef INET6
 1479         if (!(inc->inc_flags & INC_ISIPV6))
 1480 #endif
 1481         {
 1482                 sc->sc_ip_tos = ip_tos;
 1483                 sc->sc_ip_ttl = ip_ttl;
 1484         }
 1485 #ifdef TCP_OFFLOAD
 1486         sc->sc_tod = tod;
 1487         sc->sc_todctx = todctx;
 1488 #endif
 1489         sc->sc_irs = th->th_seq;
 1490         sc->sc_iss = arc4random();
 1491         sc->sc_flags = 0;
 1492         sc->sc_flowlabel = 0;
 1493 
 1494         /*
 1495          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1496          * win was derived from socket earlier in the function.
 1497          */
 1498         win = imax(win, 0);
 1499         win = imin(win, TCP_MAXWIN);
 1500         sc->sc_wnd = win;
 1501 
 1502         if (V_tcp_do_rfc1323) {
 1503                 /*
 1504                  * A timestamp received in a SYN makes
 1505                  * it ok to send timestamp requests and replies.
 1506                  */
 1507                 if (to->to_flags & TOF_TS) {
 1508                         sc->sc_tsreflect = to->to_tsval;
 1509                         sc->sc_ts = tcp_ts_getticks();
 1510                         sc->sc_flags |= SCF_TIMESTAMP;
 1511                 }
 1512                 if (to->to_flags & TOF_SCALE) {
 1513                         int wscale = 0;
 1514 
 1515                         /*
 1516                          * Pick the smallest possible scaling factor that
 1517                          * will still allow us to scale up to sb_max, aka
 1518                          * kern.ipc.maxsockbuf.
 1519                          *
 1520                          * We do this because there are broken firewalls that
 1521                          * will corrupt the window scale option, leading to
 1522                          * the other endpoint believing that our advertised
 1523                          * window is unscaled.  At scale factors larger than
 1524                          * 5 the unscaled window will drop below 1500 bytes,
 1525                          * leading to serious problems when traversing these
 1526                          * broken firewalls.
 1527                          *
 1528                          * With the default maxsockbuf of 256K, a scale factor
 1529                          * of 3 will be chosen by this algorithm.  Those who
 1530                          * choose a larger maxsockbuf should watch out
 1531                          * for the compatibility problems mentioned above.
 1532                          *
 1533                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1534                          * or <SYN,ACK>) segment itself is never scaled.
 1535                          */
 1536                         while (wscale < TCP_MAX_WINSHIFT &&
 1537                             (TCP_MAXWIN << wscale) < sb_max)
 1538                                 wscale++;
 1539                         sc->sc_requested_r_scale = wscale;
 1540                         sc->sc_requested_s_scale = to->to_wscale;
 1541                         sc->sc_flags |= SCF_WINSCALE;
 1542                 }
 1543         }
 1544 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1545         /*
 1546          * If listening socket requested TCP digests, flag this in the
 1547          * syncache so that syncache_respond() will do the right thing
 1548          * with the SYN+ACK.
 1549          */
 1550         if (ltflags & TF_SIGNATURE)
 1551                 sc->sc_flags |= SCF_SIGNATURE;
 1552 #endif  /* TCP_SIGNATURE */
 1553         if (to->to_flags & TOF_SACKPERM)
 1554                 sc->sc_flags |= SCF_SACK;
 1555         if (to->to_flags & TOF_MSS)
 1556                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1557         if (ltflags & TF_NOOPT)
 1558                 sc->sc_flags |= SCF_NOOPT;
 1559         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1560                 sc->sc_flags |= SCF_ECN;
 1561 
 1562         if (V_tcp_syncookies)
 1563                 sc->sc_iss = syncookie_generate(sch, sc);
 1564 #ifdef INET6
 1565         if (autoflowlabel) {
 1566                 if (V_tcp_syncookies)
 1567                         sc->sc_flowlabel = sc->sc_iss;
 1568                 else
 1569                         sc->sc_flowlabel = ip6_randomflowlabel();
 1570                 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
 1571         }
 1572 #endif
 1573         SCH_UNLOCK(sch);
 1574 
 1575 #ifdef TCP_RFC7413
 1576         if (tfo_cookie_valid) {
 1577                 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
 1578                 /* INP_WUNLOCK(inp) will be performed by the called */
 1579                 rv = 1;
 1580                 goto tfo_done;
 1581         }
 1582 #endif
 1583 
 1584         /*
 1585          * Do a standard 3-way handshake.
 1586          */
 1587         if (syncache_respond(sc, sch, 0, m) == 0) {
 1588                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1589                         syncache_free(sc);
 1590                 else if (sc != &scs)
 1591                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1592                 TCPSTAT_INC(tcps_sndacks);
 1593                 TCPSTAT_INC(tcps_sndtotal);
 1594         } else {
 1595                 if (sc != &scs)
 1596                         syncache_free(sc);
 1597                 TCPSTAT_INC(tcps_sc_dropped);
 1598         }
 1599 
 1600 done:
 1601         if (m) {
 1602                 *lsop = NULL;
 1603                 m_freem(m);
 1604         }
 1605 #ifdef TCP_RFC7413
 1606 tfo_done:
 1607 #endif
 1608         if (cred != NULL)
 1609                 crfree(cred);
 1610 #ifdef MAC
 1611         if (sc == &scs)
 1612                 mac_syncache_destroy(&maclabel);
 1613 #endif
 1614         return (rv);
 1615 }
 1616 
 1617 /*
 1618  * Send SYN|ACK to the peer.  Either in response to the peer's SYN,
 1619  * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
 1620  */
 1621 static int
 1622 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked,
 1623     const struct mbuf *m0)
 1624 {
 1625         struct ip *ip = NULL;
 1626         struct mbuf *m;
 1627         struct tcphdr *th = NULL;
 1628         int optlen, error = 0;  /* Make compiler happy */
 1629         u_int16_t hlen, tlen, mssopt;
 1630         struct tcpopt to;
 1631 #ifdef INET6
 1632         struct ip6_hdr *ip6 = NULL;
 1633 #endif
 1634         hlen =
 1635 #ifdef INET6
 1636                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1637 #endif
 1638                 sizeof(struct ip);
 1639         tlen = hlen + sizeof(struct tcphdr);
 1640 
 1641         /* Determine MSS we advertize to other end of connection. */
 1642         mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss);
 1643 
 1644         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1645         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1646             ("syncache: mbuf too small"));
 1647 
 1648         /* Create the IP+TCP header from scratch. */
 1649         m = m_gethdr(M_NOWAIT, MT_DATA);
 1650         if (m == NULL)
 1651                 return (ENOBUFS);
 1652 #ifdef MAC
 1653         mac_syncache_create_mbuf(sc->sc_label, m);
 1654 #endif
 1655         m->m_data += max_linkhdr;
 1656         m->m_len = tlen;
 1657         m->m_pkthdr.len = tlen;
 1658         m->m_pkthdr.rcvif = NULL;
 1659 
 1660 #ifdef INET6
 1661         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1662                 ip6 = mtod(m, struct ip6_hdr *);
 1663                 ip6->ip6_vfc = IPV6_VERSION;
 1664                 ip6->ip6_nxt = IPPROTO_TCP;
 1665                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1666                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1667                 ip6->ip6_plen = htons(tlen - hlen);
 1668                 /* ip6_hlim is set after checksum */
 1669                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1670                 ip6->ip6_flow |= sc->sc_flowlabel;
 1671 
 1672                 th = (struct tcphdr *)(ip6 + 1);
 1673         }
 1674 #endif
 1675 #if defined(INET6) && defined(INET)
 1676         else
 1677 #endif
 1678 #ifdef INET
 1679         {
 1680                 ip = mtod(m, struct ip *);
 1681                 ip->ip_v = IPVERSION;
 1682                 ip->ip_hl = sizeof(struct ip) >> 2;
 1683                 ip->ip_len = htons(tlen);
 1684                 ip->ip_id = 0;
 1685                 ip->ip_off = 0;
 1686                 ip->ip_sum = 0;
 1687                 ip->ip_p = IPPROTO_TCP;
 1688                 ip->ip_src = sc->sc_inc.inc_laddr;
 1689                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1690                 ip->ip_ttl = sc->sc_ip_ttl;
 1691                 ip->ip_tos = sc->sc_ip_tos;
 1692 
 1693                 /*
 1694                  * See if we should do MTU discovery.  Route lookups are
 1695                  * expensive, so we will only unset the DF bit if:
 1696                  *
 1697                  *      1) path_mtu_discovery is disabled
 1698                  *      2) the SCF_UNREACH flag has been set
 1699                  */
 1700                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1701                        ip->ip_off |= htons(IP_DF);
 1702 
 1703                 th = (struct tcphdr *)(ip + 1);
 1704         }
 1705 #endif /* INET */
 1706         th->th_sport = sc->sc_inc.inc_lport;
 1707         th->th_dport = sc->sc_inc.inc_fport;
 1708 
 1709         th->th_seq = htonl(sc->sc_iss);
 1710         th->th_ack = htonl(sc->sc_irs + 1);
 1711         th->th_off = sizeof(struct tcphdr) >> 2;
 1712         th->th_x2 = 0;
 1713         th->th_flags = TH_SYN|TH_ACK;
 1714         th->th_win = htons(sc->sc_wnd);
 1715         th->th_urp = 0;
 1716 
 1717         if (sc->sc_flags & SCF_ECN) {
 1718                 th->th_flags |= TH_ECE;
 1719                 TCPSTAT_INC(tcps_ecn_shs);
 1720         }
 1721 
 1722         /* Tack on the TCP options. */
 1723         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1724                 to.to_flags = 0;
 1725 
 1726                 to.to_mss = mssopt;
 1727                 to.to_flags = TOF_MSS;
 1728                 if (sc->sc_flags & SCF_WINSCALE) {
 1729                         to.to_wscale = sc->sc_requested_r_scale;
 1730                         to.to_flags |= TOF_SCALE;
 1731                 }
 1732                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1733                         /* Virgin timestamp or TCP cookie enhanced one. */
 1734                         to.to_tsval = sc->sc_ts;
 1735                         to.to_tsecr = sc->sc_tsreflect;
 1736                         to.to_flags |= TOF_TS;
 1737                 }
 1738                 if (sc->sc_flags & SCF_SACK)
 1739                         to.to_flags |= TOF_SACKPERM;
 1740 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1741                 if (sc->sc_flags & SCF_SIGNATURE)
 1742                         to.to_flags |= TOF_SIGNATURE;
 1743 #endif
 1744 #ifdef TCP_RFC7413
 1745                 if (sc->sc_tfo_cookie) {
 1746                         to.to_flags |= TOF_FASTOPEN;
 1747                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 1748                         to.to_tfo_cookie = sc->sc_tfo_cookie;
 1749                         /* don't send cookie again when retransmitting response */
 1750                         sc->sc_tfo_cookie = NULL;
 1751                 }
 1752 #endif
 1753                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1754 
 1755                 /* Adjust headers by option size. */
 1756                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1757                 m->m_len += optlen;
 1758                 m->m_pkthdr.len += optlen;
 1759 #ifdef INET6
 1760                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1761                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1762                 else
 1763 #endif
 1764                         ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
 1765 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1766                 if (sc->sc_flags & SCF_SIGNATURE) {
 1767                         KASSERT(to.to_flags & TOF_SIGNATURE,
 1768                             ("tcp_addoptions() didn't set tcp_signature"));
 1769 
 1770                         /* NOTE: to.to_signature is inside of mbuf */
 1771                         if (!TCPMD5_ENABLED() ||
 1772                             TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
 1773                                 m_freem(m);
 1774                                 return (EACCES);
 1775                         }
 1776                 }
 1777 #endif
 1778         } else
 1779                 optlen = 0;
 1780 
 1781         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1782         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1783         /*
 1784          * If we have peer's SYN and it has a flowid, then let's assign it to
 1785          * our SYN|ACK.  ip6_output() and ip_output() will not assign flowid
 1786          * to SYN|ACK due to lack of inp here.
 1787          */
 1788         if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
 1789                 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
 1790                 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
 1791         }
 1792 #ifdef INET6
 1793         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1794                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 1795                 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
 1796                     IPPROTO_TCP, 0);
 1797                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1798 #ifdef TCP_OFFLOAD
 1799                 if (ADDED_BY_TOE(sc)) {
 1800                         struct toedev *tod = sc->sc_tod;
 1801 
 1802                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1803 
 1804                         return (error);
 1805                 }
 1806 #endif
 1807                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1808         }
 1809 #endif
 1810 #if defined(INET6) && defined(INET)
 1811         else
 1812 #endif
 1813 #ifdef INET
 1814         {
 1815                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1816                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1817                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1818 #ifdef TCP_OFFLOAD
 1819                 if (ADDED_BY_TOE(sc)) {
 1820                         struct toedev *tod = sc->sc_tod;
 1821 
 1822                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1823 
 1824                         return (error);
 1825                 }
 1826 #endif
 1827                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1828         }
 1829 #endif
 1830         return (error);
 1831 }
 1832 
 1833 /*
 1834  * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
 1835  * that exceed the capacity of the syncache by avoiding the storage of any
 1836  * of the SYNs we receive.  Syncookies defend against blind SYN flooding
 1837  * attacks where the attacker does not have access to our responses.
 1838  *
 1839  * Syncookies encode and include all necessary information about the
 1840  * connection setup within the SYN|ACK that we send back.  That way we
 1841  * can avoid keeping any local state until the ACK to our SYN|ACK returns
 1842  * (if ever).  Normally the syncache and syncookies are running in parallel
 1843  * with the latter taking over when the former is exhausted.  When matching
 1844  * syncache entry is found the syncookie is ignored.
 1845  *
 1846  * The only reliable information persisting the 3WHS is our initial sequence
 1847  * number ISS of 32 bits.  Syncookies embed a cryptographically sufficient
 1848  * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
 1849  * of our SYN|ACK.  The MAC can be recomputed when the ACK to our SYN|ACK
 1850  * returns and signifies a legitimate connection if it matches the ACK.
 1851  *
 1852  * The available space of 32 bits to store the hash and to encode the SYN
 1853  * option information is very tight and we should have at least 24 bits for
 1854  * the MAC to keep the number of guesses by blind spoofing reasonably high.
 1855  *
 1856  * SYN option information we have to encode to fully restore a connection:
 1857  * MSS: is imporant to chose an optimal segment size to avoid IP level
 1858  *   fragmentation along the path.  The common MSS values can be encoded
 1859  *   in a 3-bit table.  Uncommon values are captured by the next lower value
 1860  *   in the table leading to a slight increase in packetization overhead.
 1861  * WSCALE: is necessary to allow large windows to be used for high delay-
 1862  *   bandwidth product links.  Not scaling the window when it was initially
 1863  *   negotiated is bad for performance as lack of scaling further decreases
 1864  *   the apparent available send window.  We only need to encode the WSCALE
 1865  *   we received from the remote end.  Our end can be recalculated at any
 1866  *   time.  The common WSCALE values can be encoded in a 3-bit table.
 1867  *   Uncommon values are captured by the next lower value in the table
 1868  *   making us under-estimate the available window size halving our
 1869  *   theoretically possible maximum throughput for that connection.
 1870  * SACK: Greatly assists in packet loss recovery and requires 1 bit.
 1871  * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
 1872  *   that are included in all segments on a connection.  We enable them when
 1873  *   the ACK has them.
 1874  *
 1875  * Security of syncookies and attack vectors:
 1876  *
 1877  * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
 1878  * together with the gloabl secret to make it unique per connection attempt.
 1879  * Thus any change of any of those parameters results in a different MAC output
 1880  * in an unpredictable way unless a collision is encountered.  24 bits of the
 1881  * MAC are embedded into the ISS.
 1882  *
 1883  * To prevent replay attacks two rotating global secrets are updated with a
 1884  * new random value every 15 seconds.  The life-time of a syncookie is thus
 1885  * 15-30 seconds.
 1886  *
 1887  * Vector 1: Attacking the secret.  This requires finding a weakness in the
 1888  * MAC itself or the way it is used here.  The attacker can do a chosen plain
 1889  * text attack by varying and testing the all parameters under his control.
 1890  * The strength depends on the size and randomness of the secret, and the
 1891  * cryptographic security of the MAC function.  Due to the constant updating
 1892  * of the secret the attacker has at most 29.999 seconds to find the secret
 1893  * and launch spoofed connections.  After that he has to start all over again.
 1894  *
 1895  * Vector 2: Collision attack on the MAC of a single ACK.  With a 24 bit MAC
 1896  * size an average of 4,823 attempts are required for a 50% chance of success
 1897  * to spoof a single syncookie (birthday collision paradox).  However the
 1898  * attacker is blind and doesn't know if one of his attempts succeeded unless
 1899  * he has a side channel to interfere success from.  A single connection setup
 1900  * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
 1901  * This many attempts are required for each one blind spoofed connection.  For
 1902  * every additional spoofed connection he has to launch another N attempts.
 1903  * Thus for a sustained rate 100 spoofed connections per second approximately
 1904  * 1,800,000 packets per second would have to be sent.
 1905  *
 1906  * NB: The MAC function should be fast so that it doesn't become a CPU
 1907  * exhaustion attack vector itself.
 1908  *
 1909  * References:
 1910  *  RFC4987 TCP SYN Flooding Attacks and Common Mitigations
 1911  *  SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
 1912  *   http://cr.yp.to/syncookies.html    (overview)
 1913  *   http://cr.yp.to/syncookies/archive (details)
 1914  *
 1915  *
 1916  * Schematic construction of a syncookie enabled Initial Sequence Number:
 1917  *  0        1         2         3
 1918  *  12345678901234567890123456789012
 1919  * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
 1920  *
 1921  *  x 24 MAC (truncated)
 1922  *  W  3 Send Window Scale index
 1923  *  M  3 MSS index
 1924  *  S  1 SACK permitted
 1925  *  P  1 Odd/even secret
 1926  */
 1927 
 1928 /*
 1929  * Distribution and probability of certain MSS values.  Those in between are
 1930  * rounded down to the next lower one.
 1931  * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
 1932  *                            .2%  .3%   5%    7%    7%    20%   15%   45%
 1933  */
 1934 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
 1935 
 1936 /*
 1937  * Distribution and probability of certain WSCALE values.  We have to map the
 1938  * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
 1939  * bits based on prevalence of certain values.  Where we don't have an exact
 1940  * match for are rounded down to the next lower one letting us under-estimate
 1941  * the true available window.  At the moment this would happen only for the
 1942  * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
 1943  * and window size).  The absence of the WSCALE option (no scaling in either
 1944  * direction) is encoded with index zero.
 1945  * [WSCALE values histograms, Allman, 2012]
 1946  *                            X 10 10 35  5  6 14 10%   by host
 1947  *                            X 11  4  5  5 18 49  3%   by connections
 1948  */
 1949 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
 1950 
 1951 /*
 1952  * Compute the MAC for the SYN cookie.  SIPHASH-2-4 is chosen for its speed
 1953  * and good cryptographic properties.
 1954  */
 1955 static uint32_t
 1956 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
 1957     uint8_t *secbits, uintptr_t secmod)
 1958 {
 1959         SIPHASH_CTX ctx;
 1960         uint32_t siphash[2];
 1961 
 1962         SipHash24_Init(&ctx);
 1963         SipHash_SetKey(&ctx, secbits);
 1964         switch (inc->inc_flags & INC_ISIPV6) {
 1965 #ifdef INET
 1966         case 0:
 1967                 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
 1968                 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
 1969                 break;
 1970 #endif
 1971 #ifdef INET6
 1972         case INC_ISIPV6:
 1973                 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
 1974                 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
 1975                 break;
 1976 #endif
 1977         }
 1978         SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
 1979         SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
 1980         SipHash_Update(&ctx, &irs, sizeof(irs));
 1981         SipHash_Update(&ctx, &flags, sizeof(flags));
 1982         SipHash_Update(&ctx, &secmod, sizeof(secmod));
 1983         SipHash_Final((u_int8_t *)&siphash, &ctx);
 1984 
 1985         return (siphash[0] ^ siphash[1]);
 1986 }
 1987 
 1988 static tcp_seq
 1989 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
 1990 {
 1991         u_int i, secbit, wscale;
 1992         uint32_t iss, hash;
 1993         uint8_t *secbits;
 1994         union syncookie cookie;
 1995 
 1996         SCH_LOCK_ASSERT(sch);
 1997 
 1998         cookie.cookie = 0;
 1999 
 2000         /* Map our computed MSS into the 3-bit index. */
 2001         for (i = nitems(tcp_sc_msstab) - 1;
 2002              tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
 2003              i--)
 2004                 ;
 2005         cookie.flags.mss_idx = i;
 2006 
 2007         /*
 2008          * Map the send window scale into the 3-bit index but only if
 2009          * the wscale option was received.
 2010          */
 2011         if (sc->sc_flags & SCF_WINSCALE) {
 2012                 wscale = sc->sc_requested_s_scale;
 2013                 for (i = nitems(tcp_sc_wstab) - 1;
 2014                     tcp_sc_wstab[i] > wscale && i > 0;
 2015                      i--)
 2016                         ;
 2017                 cookie.flags.wscale_idx = i;
 2018         }
 2019 
 2020         /* Can we do SACK? */
 2021         if (sc->sc_flags & SCF_SACK)
 2022                 cookie.flags.sack_ok = 1;
 2023 
 2024         /* Which of the two secrets to use. */
 2025         secbit = sch->sch_sc->secret.oddeven & 0x1;
 2026         cookie.flags.odd_even = secbit;
 2027 
 2028         secbits = sch->sch_sc->secret.key[secbit];
 2029         hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
 2030             (uintptr_t)sch);
 2031 
 2032         /*
 2033          * Put the flags into the hash and XOR them to get better ISS number
 2034          * variance.  This doesn't enhance the cryptographic strength and is
 2035          * done to prevent the 8 cookie bits from showing up directly on the
 2036          * wire.
 2037          */
 2038         iss = hash & ~0xff;
 2039         iss |= cookie.cookie ^ (hash >> 24);
 2040 
 2041         /* Randomize the timestamp. */
 2042         if (sc->sc_flags & SCF_TIMESTAMP) {
 2043                 sc->sc_ts = arc4random();
 2044                 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
 2045         }
 2046 
 2047         TCPSTAT_INC(tcps_sc_sendcookie);
 2048         return (iss);
 2049 }
 2050 
 2051 static struct syncache *
 2052 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 2053     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2054     struct socket *lso)
 2055 {
 2056         uint32_t hash;
 2057         uint8_t *secbits;
 2058         tcp_seq ack, seq;
 2059         int wnd, wscale = 0;
 2060         union syncookie cookie;
 2061 
 2062         SCH_LOCK_ASSERT(sch);
 2063 
 2064         /*
 2065          * Pull information out of SYN-ACK/ACK and revert sequence number
 2066          * advances.
 2067          */
 2068         ack = th->th_ack - 1;
 2069         seq = th->th_seq - 1;
 2070 
 2071         /*
 2072          * Unpack the flags containing enough information to restore the
 2073          * connection.
 2074          */
 2075         cookie.cookie = (ack & 0xff) ^ (ack >> 24);
 2076 
 2077         /* Which of the two secrets to use. */
 2078         secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
 2079 
 2080         hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
 2081 
 2082         /* The recomputed hash matches the ACK if this was a genuine cookie. */
 2083         if ((ack & ~0xff) != (hash & ~0xff))
 2084                 return (NULL);
 2085 
 2086         /* Fill in the syncache values. */
 2087         sc->sc_flags = 0;
 2088         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 2089         sc->sc_ipopts = NULL;
 2090         
 2091         sc->sc_irs = seq;
 2092         sc->sc_iss = ack;
 2093 
 2094         switch (inc->inc_flags & INC_ISIPV6) {
 2095 #ifdef INET
 2096         case 0:
 2097                 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
 2098                 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
 2099                 break;
 2100 #endif
 2101 #ifdef INET6
 2102         case INC_ISIPV6:
 2103                 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
 2104                         sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
 2105                 break;
 2106 #endif
 2107         }
 2108 
 2109         sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
 2110 
 2111         /* We can simply recompute receive window scale we sent earlier. */
 2112         while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
 2113                 wscale++;
 2114 
 2115         /* Only use wscale if it was enabled in the orignal SYN. */
 2116         if (cookie.flags.wscale_idx > 0) {
 2117                 sc->sc_requested_r_scale = wscale;
 2118                 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
 2119                 sc->sc_flags |= SCF_WINSCALE;
 2120         }
 2121 
 2122         wnd = sbspace(&lso->so_rcv);
 2123         wnd = imax(wnd, 0);
 2124         wnd = imin(wnd, TCP_MAXWIN);
 2125         sc->sc_wnd = wnd;
 2126 
 2127         if (cookie.flags.sack_ok)
 2128                 sc->sc_flags |= SCF_SACK;
 2129 
 2130         if (to->to_flags & TOF_TS) {
 2131                 sc->sc_flags |= SCF_TIMESTAMP;
 2132                 sc->sc_tsreflect = to->to_tsval;
 2133                 sc->sc_ts = to->to_tsecr;
 2134                 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
 2135         }
 2136 
 2137         if (to->to_flags & TOF_SIGNATURE)
 2138                 sc->sc_flags |= SCF_SIGNATURE;
 2139 
 2140         sc->sc_rxmits = 0;
 2141 
 2142         TCPSTAT_INC(tcps_sc_recvcookie);
 2143         return (sc);
 2144 }
 2145 
 2146 #ifdef INVARIANTS
 2147 static int
 2148 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
 2149     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2150     struct socket *lso)
 2151 {
 2152         struct syncache scs, *scx;
 2153         char *s;
 2154 
 2155         bzero(&scs, sizeof(scs));
 2156         scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
 2157 
 2158         if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
 2159                 return (0);
 2160 
 2161         if (scx != NULL) {
 2162                 if (sc->sc_peer_mss != scx->sc_peer_mss)
 2163                         log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
 2164                             s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
 2165 
 2166                 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
 2167                         log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
 2168                             s, __func__, sc->sc_requested_r_scale,
 2169                             scx->sc_requested_r_scale);
 2170 
 2171                 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
 2172                         log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
 2173                             s, __func__, sc->sc_requested_s_scale,
 2174                             scx->sc_requested_s_scale);
 2175 
 2176                 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
 2177                         log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
 2178         }
 2179 
 2180         if (s != NULL)
 2181                 free(s, M_TCPLOG);
 2182         return (0);
 2183 }
 2184 #endif /* INVARIANTS */
 2185 
 2186 static void
 2187 syncookie_reseed(void *arg)
 2188 {
 2189         struct tcp_syncache *sc = arg;
 2190         uint8_t *secbits;
 2191         int secbit;
 2192 
 2193         /*
 2194          * Reseeding the secret doesn't have to be protected by a lock.
 2195          * It only must be ensured that the new random values are visible
 2196          * to all CPUs in a SMP environment.  The atomic with release
 2197          * semantics ensures that.
 2198          */
 2199         secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
 2200         secbits = sc->secret.key[secbit];
 2201         arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
 2202         atomic_add_rel_int(&sc->secret.oddeven, 1);
 2203 
 2204         /* Reschedule ourself. */
 2205         callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
 2206 }
 2207 
 2208 /*
 2209  * Exports the syncache entries to userland so that netstat can display
 2210  * them alongside the other sockets.  This function is intended to be
 2211  * called only from tcp_pcblist.
 2212  *
 2213  * Due to concurrency on an active system, the number of pcbs exported
 2214  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 2215  * amount of space the caller allocated for this function to use.
 2216  */
 2217 int
 2218 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 2219 {
 2220         struct xtcpcb xt;
 2221         struct syncache *sc;
 2222         struct syncache_head *sch;
 2223         int count, error, i;
 2224 
 2225         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 2226                 sch = &V_tcp_syncache.hashbase[i];
 2227                 SCH_LOCK(sch);
 2228                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 2229                         if (count >= max_pcbs) {
 2230                                 SCH_UNLOCK(sch);
 2231                                 goto exit;
 2232                         }
 2233                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 2234                                 continue;
 2235                         bzero(&xt, sizeof(xt));
 2236                         xt.xt_len = sizeof(xt);
 2237                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 2238                                 xt.xt_inp.inp_vflag = INP_IPV6;
 2239                         else
 2240                                 xt.xt_inp.inp_vflag = INP_IPV4;
 2241                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 2242                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 2243                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 2244                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 2245                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 2246                         xt.xt_socket.so_type = SOCK_STREAM;
 2247                         xt.xt_socket.so_state = SS_ISCONNECTING;
 2248                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 2249                         if (error) {
 2250                                 SCH_UNLOCK(sch);
 2251                                 goto exit;
 2252                         }
 2253                         count++;
 2254                 }
 2255                 SCH_UNLOCK(sch);
 2256         }
 2257 exit:
 2258         *pcbs_exported = count;
 2259         return error;
 2260 }

Cache object: 4892341395ba470649a7abe454e27abb


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