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: stable/11/sys/netinet/tcp_syncache.c 343431 2019-01-25 15:21:42Z 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 (inp->inp_vflag & INP_IPV6PROTO) {
  765                 struct inpcb *oinp = sotoinpcb(lso);
  766 
  767                 /*
  768                  * Inherit socket options from the listening socket.
  769                  * Note that in6p_inputopts are not (and should not be)
  770                  * copied, since it stores previously received options and is
  771                  * used to detect if each new option is different than the
  772                  * previous one and hence should be passed to a user.
  773                  * If we copied in6p_inputopts, a user would not be able to
  774                  * receive options just after calling the accept system call.
  775                  */
  776                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  777                 if (oinp->in6p_outputopts)
  778                         inp->in6p_outputopts =
  779                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  780         }
  781 
  782         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  783                 struct in6_addr laddr6;
  784                 struct sockaddr_in6 sin6;
  785 
  786                 sin6.sin6_family = AF_INET6;
  787                 sin6.sin6_len = sizeof(sin6);
  788                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  789                 sin6.sin6_port = sc->sc_inc.inc_fport;
  790                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  791                 laddr6 = inp->in6p_laddr;
  792                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  793                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  794                 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
  795                     thread0.td_ucred, m)) != 0) {
  796                         inp->in6p_laddr = laddr6;
  797                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  798                                 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
  799                                     "with error %i\n",
  800                                     s, __func__, error);
  801                                 free(s, M_TCPLOG);
  802                         }
  803                         INP_HASH_WUNLOCK(&V_tcbinfo);
  804                         goto abort;
  805                 }
  806                 /* Override flowlabel from in6_pcbconnect. */
  807                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  808                 inp->inp_flow |= sc->sc_flowlabel;
  809         }
  810 #endif /* INET6 */
  811 #if defined(INET) && defined(INET6)
  812         else
  813 #endif
  814 #ifdef INET
  815         {
  816                 struct in_addr laddr;
  817                 struct sockaddr_in sin;
  818 
  819                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  820                 
  821                 if (inp->inp_options == NULL) {
  822                         inp->inp_options = sc->sc_ipopts;
  823                         sc->sc_ipopts = NULL;
  824                 }
  825 
  826                 sin.sin_family = AF_INET;
  827                 sin.sin_len = sizeof(sin);
  828                 sin.sin_addr = sc->sc_inc.inc_faddr;
  829                 sin.sin_port = sc->sc_inc.inc_fport;
  830                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  831                 laddr = inp->inp_laddr;
  832                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  833                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  834                 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
  835                     thread0.td_ucred, m)) != 0) {
  836                         inp->inp_laddr = laddr;
  837                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  838                                 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
  839                                     "with error %i\n",
  840                                     s, __func__, error);
  841                                 free(s, M_TCPLOG);
  842                         }
  843                         INP_HASH_WUNLOCK(&V_tcbinfo);
  844                         goto abort;
  845                 }
  846         }
  847 #endif /* INET */
  848 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
  849         /* Copy old policy into new socket's. */
  850         if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
  851                 printf("syncache_socket: could not copy policy\n");
  852 #endif
  853         INP_HASH_WUNLOCK(&V_tcbinfo);
  854         tp = intotcpcb(inp);
  855         tcp_state_change(tp, TCPS_SYN_RECEIVED);
  856         tp->iss = sc->sc_iss;
  857         tp->irs = sc->sc_irs;
  858         tcp_rcvseqinit(tp);
  859         tcp_sendseqinit(tp);
  860         blk = sototcpcb(lso)->t_fb;
  861         if (blk != tp->t_fb) {
  862                 /*
  863                  * Our parents t_fb was not the default,
  864                  * we need to release our ref on tp->t_fb and 
  865                  * pickup one on the new entry.
  866                  */
  867                 struct tcp_function_block *rblk;
  868                 
  869                 rblk = find_and_ref_tcp_fb(blk);
  870                 KASSERT(rblk != NULL,
  871                     ("cannot find blk %p out of syncache?", blk));
  872                 if (tp->t_fb->tfb_tcp_fb_fini)
  873                         (*tp->t_fb->tfb_tcp_fb_fini)(tp);
  874                 refcount_release(&tp->t_fb->tfb_refcnt);
  875                 tp->t_fb = rblk;
  876                 if (tp->t_fb->tfb_tcp_fb_init) {
  877                         (*tp->t_fb->tfb_tcp_fb_init)(tp);
  878                 }
  879         }               
  880         tp->snd_wl1 = sc->sc_irs;
  881         tp->snd_max = tp->iss + 1;
  882         tp->snd_nxt = tp->iss + 1;
  883         tp->rcv_up = sc->sc_irs + 1;
  884         tp->rcv_wnd = sc->sc_wnd;
  885         tp->rcv_adv += tp->rcv_wnd;
  886         tp->last_ack_sent = tp->rcv_nxt;
  887 
  888         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  889         if (sc->sc_flags & SCF_NOOPT)
  890                 tp->t_flags |= TF_NOOPT;
  891         else {
  892                 if (sc->sc_flags & SCF_WINSCALE) {
  893                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  894                         tp->snd_scale = sc->sc_requested_s_scale;
  895                         tp->request_r_scale = sc->sc_requested_r_scale;
  896                 }
  897                 if (sc->sc_flags & SCF_TIMESTAMP) {
  898                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  899                         tp->ts_recent = sc->sc_tsreflect;
  900                         tp->ts_recent_age = tcp_ts_getticks();
  901                         tp->ts_offset = sc->sc_tsoff;
  902                 }
  903 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
  904                 if (sc->sc_flags & SCF_SIGNATURE)
  905                         tp->t_flags |= TF_SIGNATURE;
  906 #endif
  907                 if (sc->sc_flags & SCF_SACK)
  908                         tp->t_flags |= TF_SACK_PERMIT;
  909         }
  910 
  911         if (sc->sc_flags & SCF_ECN)
  912                 tp->t_flags |= TF_ECN_PERMIT;
  913 
  914         /*
  915          * Set up MSS and get cached values from tcp_hostcache.
  916          * This might overwrite some of the defaults we just set.
  917          */
  918         tcp_mss(tp, sc->sc_peer_mss);
  919 
  920         /*
  921          * If the SYN,ACK was retransmitted, indicate that CWND to be
  922          * limited to one segment in cc_conn_init().
  923          * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
  924          */
  925         if (sc->sc_rxmits > 1)
  926                 tp->snd_cwnd = 1;
  927 
  928 #ifdef TCP_OFFLOAD
  929         /*
  930          * Allow a TOE driver to install its hooks.  Note that we hold the
  931          * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
  932          * new connection before the TOE driver has done its thing.
  933          */
  934         if (ADDED_BY_TOE(sc)) {
  935                 struct toedev *tod = sc->sc_tod;
  936 
  937                 tod->tod_offload_socket(tod, sc->sc_todctx, so);
  938         }
  939 #endif
  940         /*
  941          * Copy and activate timers.
  942          */
  943         tp->t_keepinit = sototcpcb(lso)->t_keepinit;
  944         tp->t_keepidle = sototcpcb(lso)->t_keepidle;
  945         tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
  946         tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
  947         tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
  948 
  949         TCPSTAT_INC(tcps_accepts);
  950         return (so);
  951 
  952 abort:
  953         INP_WUNLOCK(inp);
  954 abort2:
  955         if (so != NULL)
  956                 soabort(so);
  957         return (NULL);
  958 }
  959 
  960 /*
  961  * This function gets called when we receive an ACK for a
  962  * socket in the LISTEN state.  We look up the connection
  963  * in the syncache, and if its there, we pull it out of
  964  * the cache and turn it into a full-blown connection in
  965  * the SYN-RECEIVED state.
  966  *
  967  * On syncache_socket() success the newly created socket
  968  * has its underlying inp locked.
  969  */
  970 int
  971 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  972     struct socket **lsop, struct mbuf *m)
  973 {
  974         struct syncache *sc;
  975         struct syncache_head *sch;
  976         struct syncache scs;
  977         char *s;
  978 
  979         /*
  980          * Global TCP locks are held because we manipulate the PCB lists
  981          * and create a new socket.
  982          */
  983         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  984         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  985             ("%s: can handle only ACK", __func__));
  986 
  987         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  988         SCH_LOCK_ASSERT(sch);
  989 
  990 #ifdef INVARIANTS
  991         /*
  992          * Test code for syncookies comparing the syncache stored
  993          * values with the reconstructed values from the cookie.
  994          */
  995         if (sc != NULL)
  996                 syncookie_cmp(inc, sch, sc, th, to, *lsop);
  997 #endif
  998 
  999         if (sc == NULL) {
 1000                 /*
 1001                  * There is no syncache entry, so see if this ACK is
 1002                  * a returning syncookie.  To do this, first:
 1003                  *  A. Check if syncookies are used in case of syncache
 1004                  *     overflows
 1005                  *  B. See if this socket has had a syncache entry dropped in
 1006                  *     the recent past. We don't want to accept a bogus
 1007                  *     syncookie if we've never received a SYN or accept it
 1008                  *     twice.
 1009                  *  C. check that the syncookie is valid.  If it is, then
 1010                  *     cobble up a fake syncache entry, and return.
 1011                  */
 1012                 if (!V_tcp_syncookies) {
 1013                         SCH_UNLOCK(sch);
 1014                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1015                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
 1016                                     "segment rejected (syncookies disabled)\n",
 1017                                     s, __func__);
 1018                         goto failed;
 1019                 }
 1020                 if (!V_tcp_syncookiesonly &&
 1021                     sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
 1022                         SCH_UNLOCK(sch);
 1023                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1024                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
 1025                                     "segment rejected (no syncache entry)\n",
 1026                                     s, __func__);
 1027                         goto failed;
 1028                 }
 1029                 bzero(&scs, sizeof(scs));
 1030                 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
 1031                 SCH_UNLOCK(sch);
 1032                 if (sc == NULL) {
 1033                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1034                                 log(LOG_DEBUG, "%s; %s: Segment failed "
 1035                                     "SYNCOOKIE authentication, segment rejected "
 1036                                     "(probably spoofed)\n", s, __func__);
 1037                         goto failed;
 1038                 }
 1039 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1040                 /* If received ACK has MD5 signature, check it. */
 1041                 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
 1042                     (!TCPMD5_ENABLED() ||
 1043                     TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
 1044                         /* Drop the ACK. */
 1045                         if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1046                                 log(LOG_DEBUG, "%s; %s: Segment rejected, "
 1047                                     "MD5 signature doesn't match.\n",
 1048                                     s, __func__);
 1049                                 free(s, M_TCPLOG);
 1050                         }
 1051                         TCPSTAT_INC(tcps_sig_err_sigopt);
 1052                         return (-1); /* Do not send RST */
 1053                 }
 1054 #endif /* TCP_SIGNATURE */
 1055         } else {
 1056 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1057                 /*
 1058                  * If listening socket requested TCP digests, check that
 1059                  * received ACK has signature and it is correct.
 1060                  * If not, drop the ACK and leave sc entry in th cache,
 1061                  * because SYN was received with correct signature.
 1062                  */
 1063                 if (sc->sc_flags & SCF_SIGNATURE) {
 1064                         if ((to->to_flags & TOF_SIGNATURE) == 0) {
 1065                                 /* No signature */
 1066                                 TCPSTAT_INC(tcps_sig_err_nosigopt);
 1067                                 SCH_UNLOCK(sch);
 1068                                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1069                                         log(LOG_DEBUG, "%s; %s: Segment "
 1070                                             "rejected, MD5 signature wasn't "
 1071                                             "provided.\n", s, __func__);
 1072                                         free(s, M_TCPLOG);
 1073                                 }
 1074                                 return (-1); /* Do not send RST */
 1075                         }
 1076                         if (!TCPMD5_ENABLED() ||
 1077                             TCPMD5_INPUT(m, th, to->to_signature) != 0) {
 1078                                 /* Doesn't match or no SA */
 1079                                 SCH_UNLOCK(sch);
 1080                                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1081                                         log(LOG_DEBUG, "%s; %s: Segment "
 1082                                             "rejected, MD5 signature doesn't "
 1083                                             "match.\n", s, __func__);
 1084                                         free(s, M_TCPLOG);
 1085                                 }
 1086                                 return (-1); /* Do not send RST */
 1087                         }
 1088                 }
 1089 #endif /* TCP_SIGNATURE */
 1090                 /*
 1091                  * Pull out the entry to unlock the bucket row.
 1092                  * 
 1093                  * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
 1094                  * tcp_state_change().  The tcpcb is not existent at this
 1095                  * moment.  A new one will be allocated via syncache_socket->
 1096                  * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
 1097                  * syncache_socket() will change it to TCPS_SYN_RECEIVED.
 1098                  */
 1099                 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
 1100                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
 1101                 sch->sch_length--;
 1102 #ifdef TCP_OFFLOAD
 1103                 if (ADDED_BY_TOE(sc)) {
 1104                         struct toedev *tod = sc->sc_tod;
 1105 
 1106                         tod->tod_syncache_removed(tod, sc->sc_todctx);
 1107                 }
 1108 #endif
 1109                 SCH_UNLOCK(sch);
 1110         }
 1111 
 1112         /*
 1113          * Segment validation:
 1114          * ACK must match our initial sequence number + 1 (the SYN|ACK).
 1115          */
 1116         if (th->th_ack != sc->sc_iss + 1) {
 1117                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1118                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
 1119                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
 1120                 goto failed;
 1121         }
 1122 
 1123         /*
 1124          * The SEQ must fall in the window starting at the received
 1125          * initial receive sequence number + 1 (the SYN).
 1126          */
 1127         if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
 1128             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
 1129                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1130                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
 1131                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
 1132                 goto failed;
 1133         }
 1134 
 1135         /*
 1136          * If timestamps were not negotiated during SYN/ACK they
 1137          * must not appear on any segment during this session.
 1138          */
 1139         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
 1140                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1141                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1142                             "segment rejected\n", s, __func__);
 1143                 goto failed;
 1144         }
 1145 
 1146         /*
 1147          * If timestamps were negotiated during SYN/ACK they should
 1148          * appear on every segment during this session.
 1149          * XXXAO: This is only informal as there have been unverified
 1150          * reports of non-compliants stacks.
 1151          */
 1152         if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
 1153                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1154                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1155                             "no action\n", s, __func__);
 1156                         free(s, M_TCPLOG);
 1157                         s = NULL;
 1158                 }
 1159         }
 1160 
 1161         /*
 1162          * If timestamps were negotiated, the reflected timestamp
 1163          * must be equal to what we actually sent in the SYN|ACK
 1164          * except in the case of 0. Some boxes are known for sending
 1165          * broken timestamp replies during the 3whs (and potentially
 1166          * during the connection also).
 1167          *
 1168          * Accept the final ACK of 3whs with reflected timestamp of 0
 1169          * instead of sending a RST and deleting the syncache entry.
 1170          */
 1171         if ((to->to_flags & TOF_TS) && to->to_tsecr &&
 1172             to->to_tsecr != sc->sc_ts) {
 1173                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1174                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
 1175                             "segment rejected\n",
 1176                             s, __func__, to->to_tsecr, sc->sc_ts);
 1177                 goto failed;
 1178         }
 1179 
 1180         *lsop = syncache_socket(sc, *lsop, m);
 1181 
 1182         if (*lsop == NULL)
 1183                 TCPSTAT_INC(tcps_sc_aborted);
 1184         else
 1185                 TCPSTAT_INC(tcps_sc_completed);
 1186 
 1187 /* how do we find the inp for the new socket? */
 1188         if (sc != &scs)
 1189                 syncache_free(sc);
 1190         return (1);
 1191 failed:
 1192         if (sc != NULL && sc != &scs)
 1193                 syncache_free(sc);
 1194         if (s != NULL)
 1195                 free(s, M_TCPLOG);
 1196         *lsop = NULL;
 1197         return (0);
 1198 }
 1199 
 1200 #ifdef TCP_RFC7413
 1201 static void
 1202 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
 1203     uint64_t response_cookie)
 1204 {
 1205         struct inpcb *inp;
 1206         struct tcpcb *tp;
 1207         unsigned int *pending_counter;
 1208 
 1209         /*
 1210          * Global TCP locks are held because we manipulate the PCB lists
 1211          * and create a new socket.
 1212          */
 1213         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1214 
 1215         pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
 1216         *lsop = syncache_socket(sc, *lsop, m);
 1217         if (*lsop == NULL) {
 1218                 TCPSTAT_INC(tcps_sc_aborted);
 1219                 atomic_subtract_int(pending_counter, 1);
 1220         } else {
 1221                 inp = sotoinpcb(*lsop);
 1222                 tp = intotcpcb(inp);
 1223                 tp->t_flags |= TF_FASTOPEN;
 1224                 tp->t_tfo_cookie = response_cookie;
 1225                 tp->snd_max = tp->iss;
 1226                 tp->snd_nxt = tp->iss;
 1227                 tp->t_tfo_pending = pending_counter;
 1228                 TCPSTAT_INC(tcps_sc_completed);
 1229         }
 1230 }
 1231 #endif /* TCP_RFC7413 */
 1232 
 1233 /*
 1234  * Given a LISTEN socket and an inbound SYN request, add
 1235  * this to the syn cache, and send back a segment:
 1236  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 1237  * to the source.
 1238  *
 1239  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
 1240  * Doing so would require that we hold onto the data and deliver it
 1241  * to the application.  However, if we are the target of a SYN-flood
 1242  * DoS attack, an attacker could send data which would eventually
 1243  * consume all available buffer space if it were ACKed.  By not ACKing
 1244  * the data, we avoid this DoS scenario.
 1245  *
 1246  * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
 1247  * cookie is processed, V_tcp_fastopen_enabled set to true, and the
 1248  * TCP_FASTOPEN socket option is set.  In this case, a new socket is created
 1249  * and returned via lsop, the mbuf is not freed so that tcp_input() can
 1250  * queue its data to the socket, and 1 is returned to indicate the
 1251  * TFO-socket-creation path was taken.
 1252  */
 1253 int
 1254 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1255     struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
 1256     void *todctx)
 1257 {
 1258         struct tcpcb *tp;
 1259         struct socket *so;
 1260         struct syncache *sc = NULL;
 1261         struct syncache_head *sch;
 1262         struct mbuf *ipopts = NULL;
 1263         u_int ltflags;
 1264         int win, sb_hiwat, ip_ttl, ip_tos;
 1265         char *s;
 1266         int rv = 0;
 1267 #ifdef INET6
 1268         int autoflowlabel = 0;
 1269 #endif
 1270 #ifdef MAC
 1271         struct label *maclabel;
 1272 #endif
 1273         struct syncache scs;
 1274         struct ucred *cred;
 1275 #ifdef TCP_RFC7413
 1276         uint64_t tfo_response_cookie;
 1277         int tfo_cookie_valid = 0;
 1278         int tfo_response_cookie_valid = 0;
 1279 #endif
 1280 
 1281         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1282         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1283             ("%s: unexpected tcp flags", __func__));
 1284 
 1285         /*
 1286          * Combine all so/tp operations very early to drop the INP lock as
 1287          * soon as possible.
 1288          */
 1289         so = *lsop;
 1290         tp = sototcpcb(so);
 1291         cred = crhold(so->so_cred);
 1292 
 1293 #ifdef INET6
 1294         if ((inc->inc_flags & INC_ISIPV6) &&
 1295             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1296                 autoflowlabel = 1;
 1297 #endif
 1298         ip_ttl = inp->inp_ip_ttl;
 1299         ip_tos = inp->inp_ip_tos;
 1300         win = sbspace(&so->so_rcv);
 1301         sb_hiwat = so->so_rcv.sb_hiwat;
 1302         ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
 1303 
 1304 #ifdef TCP_RFC7413
 1305         if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
 1306             (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
 1307                 /*
 1308                  * Limit the number of pending TFO connections to
 1309                  * approximately half of the queue limit.  This prevents TFO
 1310                  * SYN floods from starving the service by filling the
 1311                  * listen queue with bogus TFO connections.
 1312                  */
 1313                 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
 1314                     (so->so_qlimit / 2)) {
 1315                         int result;
 1316 
 1317                         result = tcp_fastopen_check_cookie(inc,
 1318                             to->to_tfo_cookie, to->to_tfo_len,
 1319                             &tfo_response_cookie);
 1320                         tfo_cookie_valid = (result > 0);
 1321                         tfo_response_cookie_valid = (result >= 0);
 1322                 } else
 1323                         atomic_subtract_int(tp->t_tfo_pending, 1);
 1324         }
 1325 #endif
 1326 
 1327         /* By the time we drop the lock these should no longer be used. */
 1328         so = NULL;
 1329         tp = NULL;
 1330 
 1331 #ifdef MAC
 1332         if (mac_syncache_init(&maclabel) != 0) {
 1333                 INP_WUNLOCK(inp);
 1334                 goto done;
 1335         } else
 1336                 mac_syncache_create(maclabel, inp);
 1337 #endif
 1338 #ifdef TCP_RFC7413
 1339         if (!tfo_cookie_valid)
 1340 #endif
 1341                 INP_WUNLOCK(inp);
 1342 
 1343         /*
 1344          * Remember the IP options, if any.
 1345          */
 1346 #ifdef INET6
 1347         if (!(inc->inc_flags & INC_ISIPV6))
 1348 #endif
 1349 #ifdef INET
 1350                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1351 #else
 1352                 ipopts = NULL;
 1353 #endif
 1354 
 1355 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1356         /*
 1357          * If listening socket requested TCP digests, check that received
 1358          * SYN has signature and it is correct. If signature doesn't match
 1359          * or TCP_SIGNATURE support isn't enabled, drop the packet.
 1360          */
 1361         if (ltflags & TF_SIGNATURE) {
 1362                 if ((to->to_flags & TOF_SIGNATURE) == 0) {
 1363                         TCPSTAT_INC(tcps_sig_err_nosigopt);
 1364                         goto done;
 1365                 }
 1366                 if (!TCPMD5_ENABLED() ||
 1367                     TCPMD5_INPUT(m, th, to->to_signature) != 0)
 1368                         goto done;
 1369         }
 1370 #endif  /* TCP_SIGNATURE */
 1371         /*
 1372          * See if we already have an entry for this connection.
 1373          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1374          *
 1375          * XXX: should the syncache be re-initialized with the contents
 1376          * of the new SYN here (which may have different options?)
 1377          *
 1378          * XXX: We do not check the sequence number to see if this is a
 1379          * real retransmit or a new connection attempt.  The question is
 1380          * how to handle such a case; either ignore it as spoofed, or
 1381          * drop the current entry and create a new one?
 1382          */
 1383         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1384         SCH_LOCK_ASSERT(sch);
 1385         if (sc != NULL) {
 1386 #ifdef TCP_RFC7413
 1387                 if (tfo_cookie_valid)
 1388                         INP_WUNLOCK(inp);
 1389 #endif
 1390                 TCPSTAT_INC(tcps_sc_dupsyn);
 1391                 if (ipopts) {
 1392                         /*
 1393                          * If we were remembering a previous source route,
 1394                          * forget it and use the new one we've been given.
 1395                          */
 1396                         if (sc->sc_ipopts)
 1397                                 (void) m_free(sc->sc_ipopts);
 1398                         sc->sc_ipopts = ipopts;
 1399                 }
 1400                 /*
 1401                  * Update timestamp if present.
 1402                  */
 1403                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1404                         sc->sc_tsreflect = to->to_tsval;
 1405                 else
 1406                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1407 #ifdef MAC
 1408                 /*
 1409                  * Since we have already unconditionally allocated label
 1410                  * storage, free it up.  The syncache entry will already
 1411                  * have an initialized label we can use.
 1412                  */
 1413                 mac_syncache_destroy(&maclabel);
 1414 #endif
 1415                 /* Retransmit SYN|ACK and reset retransmit count. */
 1416                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1417                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1418                             "resetting timer and retransmitting SYN|ACK\n",
 1419                             s, __func__);
 1420                         free(s, M_TCPLOG);
 1421                 }
 1422                 if (syncache_respond(sc, sch, 1, m) == 0) {
 1423                         sc->sc_rxmits = 0;
 1424                         syncache_timeout(sc, sch, 1);
 1425                         TCPSTAT_INC(tcps_sndacks);
 1426                         TCPSTAT_INC(tcps_sndtotal);
 1427                 }
 1428                 SCH_UNLOCK(sch);
 1429                 goto done;
 1430         }
 1431 
 1432 #ifdef TCP_RFC7413
 1433         if (tfo_cookie_valid) {
 1434                 bzero(&scs, sizeof(scs));
 1435                 sc = &scs;
 1436                 goto skip_alloc;
 1437         }
 1438 #endif
 1439 
 1440         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1441         if (sc == NULL) {
 1442                 /*
 1443                  * The zone allocator couldn't provide more entries.
 1444                  * Treat this as if the cache was full; drop the oldest
 1445                  * entry and insert the new one.
 1446                  */
 1447                 TCPSTAT_INC(tcps_sc_zonefail);
 1448                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) {
 1449                         sch->sch_last_overflow = time_uptime;
 1450                         syncache_drop(sc, sch);
 1451                 }
 1452                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1453                 if (sc == NULL) {
 1454                         if (V_tcp_syncookies) {
 1455                                 bzero(&scs, sizeof(scs));
 1456                                 sc = &scs;
 1457                         } else {
 1458                                 SCH_UNLOCK(sch);
 1459                                 if (ipopts)
 1460                                         (void) m_free(ipopts);
 1461                                 goto done;
 1462                         }
 1463                 }
 1464         }
 1465 
 1466 #ifdef TCP_RFC7413
 1467 skip_alloc:
 1468         if (!tfo_cookie_valid && tfo_response_cookie_valid)
 1469                 sc->sc_tfo_cookie = &tfo_response_cookie;
 1470 #endif
 1471 
 1472         /*
 1473          * Fill in the syncache values.
 1474          */
 1475 #ifdef MAC
 1476         sc->sc_label = maclabel;
 1477 #endif
 1478         sc->sc_cred = cred;
 1479         cred = NULL;
 1480         sc->sc_ipopts = ipopts;
 1481         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1482 #ifdef INET6
 1483         if (!(inc->inc_flags & INC_ISIPV6))
 1484 #endif
 1485         {
 1486                 sc->sc_ip_tos = ip_tos;
 1487                 sc->sc_ip_ttl = ip_ttl;
 1488         }
 1489 #ifdef TCP_OFFLOAD
 1490         sc->sc_tod = tod;
 1491         sc->sc_todctx = todctx;
 1492 #endif
 1493         sc->sc_irs = th->th_seq;
 1494         sc->sc_iss = arc4random();
 1495         sc->sc_flags = 0;
 1496         sc->sc_flowlabel = 0;
 1497 
 1498         /*
 1499          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1500          * win was derived from socket earlier in the function.
 1501          */
 1502         win = imax(win, 0);
 1503         win = imin(win, TCP_MAXWIN);
 1504         sc->sc_wnd = win;
 1505 
 1506         if (V_tcp_do_rfc1323) {
 1507                 /*
 1508                  * A timestamp received in a SYN makes
 1509                  * it ok to send timestamp requests and replies.
 1510                  */
 1511                 if (to->to_flags & TOF_TS) {
 1512                         sc->sc_tsreflect = to->to_tsval;
 1513                         sc->sc_ts = tcp_ts_getticks();
 1514                         sc->sc_flags |= SCF_TIMESTAMP;
 1515                 }
 1516                 if (to->to_flags & TOF_SCALE) {
 1517                         int wscale = 0;
 1518 
 1519                         /*
 1520                          * Pick the smallest possible scaling factor that
 1521                          * will still allow us to scale up to sb_max, aka
 1522                          * kern.ipc.maxsockbuf.
 1523                          *
 1524                          * We do this because there are broken firewalls that
 1525                          * will corrupt the window scale option, leading to
 1526                          * the other endpoint believing that our advertised
 1527                          * window is unscaled.  At scale factors larger than
 1528                          * 5 the unscaled window will drop below 1500 bytes,
 1529                          * leading to serious problems when traversing these
 1530                          * broken firewalls.
 1531                          *
 1532                          * With the default maxsockbuf of 256K, a scale factor
 1533                          * of 3 will be chosen by this algorithm.  Those who
 1534                          * choose a larger maxsockbuf should watch out
 1535                          * for the compatibility problems mentioned above.
 1536                          *
 1537                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1538                          * or <SYN,ACK>) segment itself is never scaled.
 1539                          */
 1540                         while (wscale < TCP_MAX_WINSHIFT &&
 1541                             (TCP_MAXWIN << wscale) < sb_max)
 1542                                 wscale++;
 1543                         sc->sc_requested_r_scale = wscale;
 1544                         sc->sc_requested_s_scale = to->to_wscale;
 1545                         sc->sc_flags |= SCF_WINSCALE;
 1546                 }
 1547         }
 1548 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1549         /*
 1550          * If listening socket requested TCP digests, flag this in the
 1551          * syncache so that syncache_respond() will do the right thing
 1552          * with the SYN+ACK.
 1553          */
 1554         if (ltflags & TF_SIGNATURE)
 1555                 sc->sc_flags |= SCF_SIGNATURE;
 1556 #endif  /* TCP_SIGNATURE */
 1557         if (to->to_flags & TOF_SACKPERM)
 1558                 sc->sc_flags |= SCF_SACK;
 1559         if (to->to_flags & TOF_MSS)
 1560                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1561         if (ltflags & TF_NOOPT)
 1562                 sc->sc_flags |= SCF_NOOPT;
 1563         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1564                 sc->sc_flags |= SCF_ECN;
 1565 
 1566         if (V_tcp_syncookies)
 1567                 sc->sc_iss = syncookie_generate(sch, sc);
 1568 #ifdef INET6
 1569         if (autoflowlabel) {
 1570                 if (V_tcp_syncookies)
 1571                         sc->sc_flowlabel = sc->sc_iss;
 1572                 else
 1573                         sc->sc_flowlabel = ip6_randomflowlabel();
 1574                 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
 1575         }
 1576 #endif
 1577         SCH_UNLOCK(sch);
 1578 
 1579 #ifdef TCP_RFC7413
 1580         if (tfo_cookie_valid) {
 1581                 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
 1582                 /* INP_WUNLOCK(inp) will be performed by the called */
 1583                 rv = 1;
 1584                 goto tfo_done;
 1585         }
 1586 #endif
 1587 
 1588         /*
 1589          * Do a standard 3-way handshake.
 1590          */
 1591         if (syncache_respond(sc, sch, 0, m) == 0) {
 1592                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1593                         syncache_free(sc);
 1594                 else if (sc != &scs)
 1595                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1596                 TCPSTAT_INC(tcps_sndacks);
 1597                 TCPSTAT_INC(tcps_sndtotal);
 1598         } else {
 1599                 if (sc != &scs)
 1600                         syncache_free(sc);
 1601                 TCPSTAT_INC(tcps_sc_dropped);
 1602         }
 1603 
 1604 done:
 1605         if (m) {
 1606                 *lsop = NULL;
 1607                 m_freem(m);
 1608         }
 1609 #ifdef TCP_RFC7413
 1610 tfo_done:
 1611 #endif
 1612         if (cred != NULL)
 1613                 crfree(cred);
 1614 #ifdef MAC
 1615         if (sc == &scs)
 1616                 mac_syncache_destroy(&maclabel);
 1617 #endif
 1618         return (rv);
 1619 }
 1620 
 1621 /*
 1622  * Send SYN|ACK to the peer.  Either in response to the peer's SYN,
 1623  * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
 1624  */
 1625 static int
 1626 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked,
 1627     const struct mbuf *m0)
 1628 {
 1629         struct ip *ip = NULL;
 1630         struct mbuf *m;
 1631         struct tcphdr *th = NULL;
 1632         int optlen, error = 0;  /* Make compiler happy */
 1633         u_int16_t hlen, tlen, mssopt;
 1634         struct tcpopt to;
 1635 #ifdef INET6
 1636         struct ip6_hdr *ip6 = NULL;
 1637 #endif
 1638         hlen =
 1639 #ifdef INET6
 1640                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1641 #endif
 1642                 sizeof(struct ip);
 1643         tlen = hlen + sizeof(struct tcphdr);
 1644 
 1645         /* Determine MSS we advertize to other end of connection. */
 1646         mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss);
 1647 
 1648         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1649         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1650             ("syncache: mbuf too small"));
 1651 
 1652         /* Create the IP+TCP header from scratch. */
 1653         m = m_gethdr(M_NOWAIT, MT_DATA);
 1654         if (m == NULL)
 1655                 return (ENOBUFS);
 1656 #ifdef MAC
 1657         mac_syncache_create_mbuf(sc->sc_label, m);
 1658 #endif
 1659         m->m_data += max_linkhdr;
 1660         m->m_len = tlen;
 1661         m->m_pkthdr.len = tlen;
 1662         m->m_pkthdr.rcvif = NULL;
 1663 
 1664 #ifdef INET6
 1665         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1666                 ip6 = mtod(m, struct ip6_hdr *);
 1667                 ip6->ip6_vfc = IPV6_VERSION;
 1668                 ip6->ip6_nxt = IPPROTO_TCP;
 1669                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1670                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1671                 ip6->ip6_plen = htons(tlen - hlen);
 1672                 /* ip6_hlim is set after checksum */
 1673                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1674                 ip6->ip6_flow |= sc->sc_flowlabel;
 1675 
 1676                 th = (struct tcphdr *)(ip6 + 1);
 1677         }
 1678 #endif
 1679 #if defined(INET6) && defined(INET)
 1680         else
 1681 #endif
 1682 #ifdef INET
 1683         {
 1684                 ip = mtod(m, struct ip *);
 1685                 ip->ip_v = IPVERSION;
 1686                 ip->ip_hl = sizeof(struct ip) >> 2;
 1687                 ip->ip_len = htons(tlen);
 1688                 ip->ip_id = 0;
 1689                 ip->ip_off = 0;
 1690                 ip->ip_sum = 0;
 1691                 ip->ip_p = IPPROTO_TCP;
 1692                 ip->ip_src = sc->sc_inc.inc_laddr;
 1693                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1694                 ip->ip_ttl = sc->sc_ip_ttl;
 1695                 ip->ip_tos = sc->sc_ip_tos;
 1696 
 1697                 /*
 1698                  * See if we should do MTU discovery.  Route lookups are
 1699                  * expensive, so we will only unset the DF bit if:
 1700                  *
 1701                  *      1) path_mtu_discovery is disabled
 1702                  *      2) the SCF_UNREACH flag has been set
 1703                  */
 1704                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1705                        ip->ip_off |= htons(IP_DF);
 1706 
 1707                 th = (struct tcphdr *)(ip + 1);
 1708         }
 1709 #endif /* INET */
 1710         th->th_sport = sc->sc_inc.inc_lport;
 1711         th->th_dport = sc->sc_inc.inc_fport;
 1712 
 1713         th->th_seq = htonl(sc->sc_iss);
 1714         th->th_ack = htonl(sc->sc_irs + 1);
 1715         th->th_off = sizeof(struct tcphdr) >> 2;
 1716         th->th_x2 = 0;
 1717         th->th_flags = TH_SYN|TH_ACK;
 1718         th->th_win = htons(sc->sc_wnd);
 1719         th->th_urp = 0;
 1720 
 1721         if (sc->sc_flags & SCF_ECN) {
 1722                 th->th_flags |= TH_ECE;
 1723                 TCPSTAT_INC(tcps_ecn_shs);
 1724         }
 1725 
 1726         /* Tack on the TCP options. */
 1727         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1728                 to.to_flags = 0;
 1729 
 1730                 to.to_mss = mssopt;
 1731                 to.to_flags = TOF_MSS;
 1732                 if (sc->sc_flags & SCF_WINSCALE) {
 1733                         to.to_wscale = sc->sc_requested_r_scale;
 1734                         to.to_flags |= TOF_SCALE;
 1735                 }
 1736                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1737                         /* Virgin timestamp or TCP cookie enhanced one. */
 1738                         to.to_tsval = sc->sc_ts;
 1739                         to.to_tsecr = sc->sc_tsreflect;
 1740                         to.to_flags |= TOF_TS;
 1741                 }
 1742                 if (sc->sc_flags & SCF_SACK)
 1743                         to.to_flags |= TOF_SACKPERM;
 1744 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1745                 if (sc->sc_flags & SCF_SIGNATURE)
 1746                         to.to_flags |= TOF_SIGNATURE;
 1747 #endif
 1748 #ifdef TCP_RFC7413
 1749                 if (sc->sc_tfo_cookie) {
 1750                         to.to_flags |= TOF_FASTOPEN;
 1751                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 1752                         to.to_tfo_cookie = sc->sc_tfo_cookie;
 1753                         /* don't send cookie again when retransmitting response */
 1754                         sc->sc_tfo_cookie = NULL;
 1755                 }
 1756 #endif
 1757                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1758 
 1759                 /* Adjust headers by option size. */
 1760                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1761                 m->m_len += optlen;
 1762                 m->m_pkthdr.len += optlen;
 1763 #ifdef INET6
 1764                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1765                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1766                 else
 1767 #endif
 1768                         ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
 1769 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1770                 if (sc->sc_flags & SCF_SIGNATURE) {
 1771                         KASSERT(to.to_flags & TOF_SIGNATURE,
 1772                             ("tcp_addoptions() didn't set tcp_signature"));
 1773 
 1774                         /* NOTE: to.to_signature is inside of mbuf */
 1775                         if (!TCPMD5_ENABLED() ||
 1776                             TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
 1777                                 m_freem(m);
 1778                                 return (EACCES);
 1779                         }
 1780                 }
 1781 #endif
 1782         } else
 1783                 optlen = 0;
 1784 
 1785         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1786         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1787         /*
 1788          * If we have peer's SYN and it has a flowid, then let's assign it to
 1789          * our SYN|ACK.  ip6_output() and ip_output() will not assign flowid
 1790          * to SYN|ACK due to lack of inp here.
 1791          */
 1792         if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
 1793                 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
 1794                 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
 1795         }
 1796 #ifdef INET6
 1797         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1798                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 1799                 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
 1800                     IPPROTO_TCP, 0);
 1801                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1802 #ifdef TCP_OFFLOAD
 1803                 if (ADDED_BY_TOE(sc)) {
 1804                         struct toedev *tod = sc->sc_tod;
 1805 
 1806                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1807 
 1808                         return (error);
 1809                 }
 1810 #endif
 1811                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1812         }
 1813 #endif
 1814 #if defined(INET6) && defined(INET)
 1815         else
 1816 #endif
 1817 #ifdef INET
 1818         {
 1819                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1820                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1821                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1822 #ifdef TCP_OFFLOAD
 1823                 if (ADDED_BY_TOE(sc)) {
 1824                         struct toedev *tod = sc->sc_tod;
 1825 
 1826                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1827 
 1828                         return (error);
 1829                 }
 1830 #endif
 1831                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1832         }
 1833 #endif
 1834         return (error);
 1835 }
 1836 
 1837 /*
 1838  * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
 1839  * that exceed the capacity of the syncache by avoiding the storage of any
 1840  * of the SYNs we receive.  Syncookies defend against blind SYN flooding
 1841  * attacks where the attacker does not have access to our responses.
 1842  *
 1843  * Syncookies encode and include all necessary information about the
 1844  * connection setup within the SYN|ACK that we send back.  That way we
 1845  * can avoid keeping any local state until the ACK to our SYN|ACK returns
 1846  * (if ever).  Normally the syncache and syncookies are running in parallel
 1847  * with the latter taking over when the former is exhausted.  When matching
 1848  * syncache entry is found the syncookie is ignored.
 1849  *
 1850  * The only reliable information persisting the 3WHS is our initial sequence
 1851  * number ISS of 32 bits.  Syncookies embed a cryptographically sufficient
 1852  * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
 1853  * of our SYN|ACK.  The MAC can be recomputed when the ACK to our SYN|ACK
 1854  * returns and signifies a legitimate connection if it matches the ACK.
 1855  *
 1856  * The available space of 32 bits to store the hash and to encode the SYN
 1857  * option information is very tight and we should have at least 24 bits for
 1858  * the MAC to keep the number of guesses by blind spoofing reasonably high.
 1859  *
 1860  * SYN option information we have to encode to fully restore a connection:
 1861  * MSS: is imporant to chose an optimal segment size to avoid IP level
 1862  *   fragmentation along the path.  The common MSS values can be encoded
 1863  *   in a 3-bit table.  Uncommon values are captured by the next lower value
 1864  *   in the table leading to a slight increase in packetization overhead.
 1865  * WSCALE: is necessary to allow large windows to be used for high delay-
 1866  *   bandwidth product links.  Not scaling the window when it was initially
 1867  *   negotiated is bad for performance as lack of scaling further decreases
 1868  *   the apparent available send window.  We only need to encode the WSCALE
 1869  *   we received from the remote end.  Our end can be recalculated at any
 1870  *   time.  The common WSCALE values can be encoded in a 3-bit table.
 1871  *   Uncommon values are captured by the next lower value in the table
 1872  *   making us under-estimate the available window size halving our
 1873  *   theoretically possible maximum throughput for that connection.
 1874  * SACK: Greatly assists in packet loss recovery and requires 1 bit.
 1875  * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
 1876  *   that are included in all segments on a connection.  We enable them when
 1877  *   the ACK has them.
 1878  *
 1879  * Security of syncookies and attack vectors:
 1880  *
 1881  * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
 1882  * together with the gloabl secret to make it unique per connection attempt.
 1883  * Thus any change of any of those parameters results in a different MAC output
 1884  * in an unpredictable way unless a collision is encountered.  24 bits of the
 1885  * MAC are embedded into the ISS.
 1886  *
 1887  * To prevent replay attacks two rotating global secrets are updated with a
 1888  * new random value every 15 seconds.  The life-time of a syncookie is thus
 1889  * 15-30 seconds.
 1890  *
 1891  * Vector 1: Attacking the secret.  This requires finding a weakness in the
 1892  * MAC itself or the way it is used here.  The attacker can do a chosen plain
 1893  * text attack by varying and testing the all parameters under his control.
 1894  * The strength depends on the size and randomness of the secret, and the
 1895  * cryptographic security of the MAC function.  Due to the constant updating
 1896  * of the secret the attacker has at most 29.999 seconds to find the secret
 1897  * and launch spoofed connections.  After that he has to start all over again.
 1898  *
 1899  * Vector 2: Collision attack on the MAC of a single ACK.  With a 24 bit MAC
 1900  * size an average of 4,823 attempts are required for a 50% chance of success
 1901  * to spoof a single syncookie (birthday collision paradox).  However the
 1902  * attacker is blind and doesn't know if one of his attempts succeeded unless
 1903  * he has a side channel to interfere success from.  A single connection setup
 1904  * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
 1905  * This many attempts are required for each one blind spoofed connection.  For
 1906  * every additional spoofed connection he has to launch another N attempts.
 1907  * Thus for a sustained rate 100 spoofed connections per second approximately
 1908  * 1,800,000 packets per second would have to be sent.
 1909  *
 1910  * NB: The MAC function should be fast so that it doesn't become a CPU
 1911  * exhaustion attack vector itself.
 1912  *
 1913  * References:
 1914  *  RFC4987 TCP SYN Flooding Attacks and Common Mitigations
 1915  *  SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
 1916  *   http://cr.yp.to/syncookies.html    (overview)
 1917  *   http://cr.yp.to/syncookies/archive (details)
 1918  *
 1919  *
 1920  * Schematic construction of a syncookie enabled Initial Sequence Number:
 1921  *  0        1         2         3
 1922  *  12345678901234567890123456789012
 1923  * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
 1924  *
 1925  *  x 24 MAC (truncated)
 1926  *  W  3 Send Window Scale index
 1927  *  M  3 MSS index
 1928  *  S  1 SACK permitted
 1929  *  P  1 Odd/even secret
 1930  */
 1931 
 1932 /*
 1933  * Distribution and probability of certain MSS values.  Those in between are
 1934  * rounded down to the next lower one.
 1935  * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
 1936  *                            .2%  .3%   5%    7%    7%    20%   15%   45%
 1937  */
 1938 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
 1939 
 1940 /*
 1941  * Distribution and probability of certain WSCALE values.  We have to map the
 1942  * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
 1943  * bits based on prevalence of certain values.  Where we don't have an exact
 1944  * match for are rounded down to the next lower one letting us under-estimate
 1945  * the true available window.  At the moment this would happen only for the
 1946  * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
 1947  * and window size).  The absence of the WSCALE option (no scaling in either
 1948  * direction) is encoded with index zero.
 1949  * [WSCALE values histograms, Allman, 2012]
 1950  *                            X 10 10 35  5  6 14 10%   by host
 1951  *                            X 11  4  5  5 18 49  3%   by connections
 1952  */
 1953 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
 1954 
 1955 /*
 1956  * Compute the MAC for the SYN cookie.  SIPHASH-2-4 is chosen for its speed
 1957  * and good cryptographic properties.
 1958  */
 1959 static uint32_t
 1960 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
 1961     uint8_t *secbits, uintptr_t secmod)
 1962 {
 1963         SIPHASH_CTX ctx;
 1964         uint32_t siphash[2];
 1965 
 1966         SipHash24_Init(&ctx);
 1967         SipHash_SetKey(&ctx, secbits);
 1968         switch (inc->inc_flags & INC_ISIPV6) {
 1969 #ifdef INET
 1970         case 0:
 1971                 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
 1972                 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
 1973                 break;
 1974 #endif
 1975 #ifdef INET6
 1976         case INC_ISIPV6:
 1977                 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
 1978                 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
 1979                 break;
 1980 #endif
 1981         }
 1982         SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
 1983         SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
 1984         SipHash_Update(&ctx, &irs, sizeof(irs));
 1985         SipHash_Update(&ctx, &flags, sizeof(flags));
 1986         SipHash_Update(&ctx, &secmod, sizeof(secmod));
 1987         SipHash_Final((u_int8_t *)&siphash, &ctx);
 1988 
 1989         return (siphash[0] ^ siphash[1]);
 1990 }
 1991 
 1992 static tcp_seq
 1993 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
 1994 {
 1995         u_int i, secbit, wscale;
 1996         uint32_t iss, hash;
 1997         uint8_t *secbits;
 1998         union syncookie cookie;
 1999 
 2000         SCH_LOCK_ASSERT(sch);
 2001 
 2002         cookie.cookie = 0;
 2003 
 2004         /* Map our computed MSS into the 3-bit index. */
 2005         for (i = nitems(tcp_sc_msstab) - 1;
 2006              tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
 2007              i--)
 2008                 ;
 2009         cookie.flags.mss_idx = i;
 2010 
 2011         /*
 2012          * Map the send window scale into the 3-bit index but only if
 2013          * the wscale option was received.
 2014          */
 2015         if (sc->sc_flags & SCF_WINSCALE) {
 2016                 wscale = sc->sc_requested_s_scale;
 2017                 for (i = nitems(tcp_sc_wstab) - 1;
 2018                     tcp_sc_wstab[i] > wscale && i > 0;
 2019                      i--)
 2020                         ;
 2021                 cookie.flags.wscale_idx = i;
 2022         }
 2023 
 2024         /* Can we do SACK? */
 2025         if (sc->sc_flags & SCF_SACK)
 2026                 cookie.flags.sack_ok = 1;
 2027 
 2028         /* Which of the two secrets to use. */
 2029         secbit = sch->sch_sc->secret.oddeven & 0x1;
 2030         cookie.flags.odd_even = secbit;
 2031 
 2032         secbits = sch->sch_sc->secret.key[secbit];
 2033         hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
 2034             (uintptr_t)sch);
 2035 
 2036         /*
 2037          * Put the flags into the hash and XOR them to get better ISS number
 2038          * variance.  This doesn't enhance the cryptographic strength and is
 2039          * done to prevent the 8 cookie bits from showing up directly on the
 2040          * wire.
 2041          */
 2042         iss = hash & ~0xff;
 2043         iss |= cookie.cookie ^ (hash >> 24);
 2044 
 2045         /* Randomize the timestamp. */
 2046         if (sc->sc_flags & SCF_TIMESTAMP) {
 2047                 sc->sc_ts = arc4random();
 2048                 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
 2049         }
 2050 
 2051         TCPSTAT_INC(tcps_sc_sendcookie);
 2052         return (iss);
 2053 }
 2054 
 2055 static struct syncache *
 2056 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 2057     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2058     struct socket *lso)
 2059 {
 2060         uint32_t hash;
 2061         uint8_t *secbits;
 2062         tcp_seq ack, seq;
 2063         int wnd, wscale = 0;
 2064         union syncookie cookie;
 2065 
 2066         SCH_LOCK_ASSERT(sch);
 2067 
 2068         /*
 2069          * Pull information out of SYN-ACK/ACK and revert sequence number
 2070          * advances.
 2071          */
 2072         ack = th->th_ack - 1;
 2073         seq = th->th_seq - 1;
 2074 
 2075         /*
 2076          * Unpack the flags containing enough information to restore the
 2077          * connection.
 2078          */
 2079         cookie.cookie = (ack & 0xff) ^ (ack >> 24);
 2080 
 2081         /* Which of the two secrets to use. */
 2082         secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
 2083 
 2084         hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
 2085 
 2086         /* The recomputed hash matches the ACK if this was a genuine cookie. */
 2087         if ((ack & ~0xff) != (hash & ~0xff))
 2088                 return (NULL);
 2089 
 2090         /* Fill in the syncache values. */
 2091         sc->sc_flags = 0;
 2092         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 2093         sc->sc_ipopts = NULL;
 2094         
 2095         sc->sc_irs = seq;
 2096         sc->sc_iss = ack;
 2097 
 2098         switch (inc->inc_flags & INC_ISIPV6) {
 2099 #ifdef INET
 2100         case 0:
 2101                 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
 2102                 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
 2103                 break;
 2104 #endif
 2105 #ifdef INET6
 2106         case INC_ISIPV6:
 2107                 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
 2108                         sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
 2109                 break;
 2110 #endif
 2111         }
 2112 
 2113         sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
 2114 
 2115         /* We can simply recompute receive window scale we sent earlier. */
 2116         while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
 2117                 wscale++;
 2118 
 2119         /* Only use wscale if it was enabled in the orignal SYN. */
 2120         if (cookie.flags.wscale_idx > 0) {
 2121                 sc->sc_requested_r_scale = wscale;
 2122                 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
 2123                 sc->sc_flags |= SCF_WINSCALE;
 2124         }
 2125 
 2126         wnd = sbspace(&lso->so_rcv);
 2127         wnd = imax(wnd, 0);
 2128         wnd = imin(wnd, TCP_MAXWIN);
 2129         sc->sc_wnd = wnd;
 2130 
 2131         if (cookie.flags.sack_ok)
 2132                 sc->sc_flags |= SCF_SACK;
 2133 
 2134         if (to->to_flags & TOF_TS) {
 2135                 sc->sc_flags |= SCF_TIMESTAMP;
 2136                 sc->sc_tsreflect = to->to_tsval;
 2137                 sc->sc_ts = to->to_tsecr;
 2138                 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
 2139         }
 2140 
 2141         if (to->to_flags & TOF_SIGNATURE)
 2142                 sc->sc_flags |= SCF_SIGNATURE;
 2143 
 2144         sc->sc_rxmits = 0;
 2145 
 2146         TCPSTAT_INC(tcps_sc_recvcookie);
 2147         return (sc);
 2148 }
 2149 
 2150 #ifdef INVARIANTS
 2151 static int
 2152 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
 2153     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2154     struct socket *lso)
 2155 {
 2156         struct syncache scs, *scx;
 2157         char *s;
 2158 
 2159         bzero(&scs, sizeof(scs));
 2160         scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
 2161 
 2162         if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
 2163                 return (0);
 2164 
 2165         if (scx != NULL) {
 2166                 if (sc->sc_peer_mss != scx->sc_peer_mss)
 2167                         log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
 2168                             s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
 2169 
 2170                 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
 2171                         log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
 2172                             s, __func__, sc->sc_requested_r_scale,
 2173                             scx->sc_requested_r_scale);
 2174 
 2175                 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
 2176                         log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
 2177                             s, __func__, sc->sc_requested_s_scale,
 2178                             scx->sc_requested_s_scale);
 2179 
 2180                 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
 2181                         log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
 2182         }
 2183 
 2184         if (s != NULL)
 2185                 free(s, M_TCPLOG);
 2186         return (0);
 2187 }
 2188 #endif /* INVARIANTS */
 2189 
 2190 static void
 2191 syncookie_reseed(void *arg)
 2192 {
 2193         struct tcp_syncache *sc = arg;
 2194         uint8_t *secbits;
 2195         int secbit;
 2196 
 2197         /*
 2198          * Reseeding the secret doesn't have to be protected by a lock.
 2199          * It only must be ensured that the new random values are visible
 2200          * to all CPUs in a SMP environment.  The atomic with release
 2201          * semantics ensures that.
 2202          */
 2203         secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
 2204         secbits = sc->secret.key[secbit];
 2205         arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
 2206         atomic_add_rel_int(&sc->secret.oddeven, 1);
 2207 
 2208         /* Reschedule ourself. */
 2209         callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
 2210 }
 2211 
 2212 /*
 2213  * Exports the syncache entries to userland so that netstat can display
 2214  * them alongside the other sockets.  This function is intended to be
 2215  * called only from tcp_pcblist.
 2216  *
 2217  * Due to concurrency on an active system, the number of pcbs exported
 2218  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 2219  * amount of space the caller allocated for this function to use.
 2220  */
 2221 int
 2222 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 2223 {
 2224         struct xtcpcb xt;
 2225         struct syncache *sc;
 2226         struct syncache_head *sch;
 2227         int count, error, i;
 2228 
 2229         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 2230                 sch = &V_tcp_syncache.hashbase[i];
 2231                 SCH_LOCK(sch);
 2232                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 2233                         if (count >= max_pcbs) {
 2234                                 SCH_UNLOCK(sch);
 2235                                 goto exit;
 2236                         }
 2237                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 2238                                 continue;
 2239                         bzero(&xt, sizeof(xt));
 2240                         xt.xt_len = sizeof(xt);
 2241                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 2242                                 xt.xt_inp.inp_vflag = INP_IPV6;
 2243                         else
 2244                                 xt.xt_inp.inp_vflag = INP_IPV4;
 2245                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 2246                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 2247                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 2248                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 2249                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 2250                         xt.xt_socket.so_type = SOCK_STREAM;
 2251                         xt.xt_socket.so_state = SS_ISCONNECTING;
 2252                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 2253                         if (error) {
 2254                                 SCH_UNLOCK(sch);
 2255                                 goto exit;
 2256                         }
 2257                         count++;
 2258                 }
 2259                 SCH_UNLOCK(sch);
 2260         }
 2261 exit:
 2262         *pcbs_exported = count;
 2263         return error;
 2264 }

Cache object: 6895f90818cbe2771a5458cfcc463978


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