The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]

FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_syncache.c

Version: -  FREEBSD  -  FREEBSD-12-STABLE  -  FREEBSD-12-0  -  FREEBSD-11-STABLE  -  FREEBSD-11-2  -  FREEBSD-11-1  -  FREEBSD-11-0  -  FREEBSD-10-STABLE  -  FREEBSD-10-4  -  FREEBSD-10-3  -  FREEBSD-10-2  -  FREEBSD-10-1  -  FREEBSD-10-0  -  FREEBSD-9-STABLE  -  FREEBSD-9-3  -  FREEBSD-9-2  -  FREEBSD-9-1  -  FREEBSD-9-0  -  FREEBSD-8-STABLE  -  FREEBSD-8-4  -  FREEBSD-8-3  -  FREEBSD-8-2  -  FREEBSD-8-1  -  FREEBSD-8-0  -  FREEBSD-7-STABLE  -  FREEBSD-7-4  -  FREEBSD-7-3  -  FREEBSD-7-2  -  FREEBSD-7-1  -  FREEBSD-7-0  -  FREEBSD-6-STABLE  -  FREEBSD-6-4  -  FREEBSD-6-3  -  FREEBSD-6-2  -  FREEBSD-6-1  -  FREEBSD-6-0  -  FREEBSD-5-STABLE  -  FREEBSD-5-5  -  FREEBSD-5-4  -  FREEBSD-5-3  -  FREEBSD-5-2  -  FREEBSD-5-1  -  FREEBSD-5-0  -  FREEBSD-4-STABLE  -  FREEBSD-3-STABLE  -  FREEBSD22  -  linux-2.6  -  linux-2.4.22  -  MK83  -  MK84  -  PLAN9  -  DFBSD  -  NETBSD  -  NETBSD5  -  NETBSD4  -  NETBSD3  -  NETBSD20  -  OPENBSD  -  xnu-517  -  xnu-792  -  xnu-792.6.70  -  xnu-1228  -  xnu-1456.1.26  -  xnu-1699.24.8  -  xnu-2050.18.24  -  OPENSOLARIS  -  minix-3-1-1 
SearchContext: -  none  -  3  -  10 

    1 /*-
    2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (c) 2001 McAfee, Inc.
    5  * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
    6  * All rights reserved.
    7  *
    8  * This software was developed for the FreeBSD Project by Jonathan Lemon
    9  * and McAfee Research, the Security Research Division of McAfee, Inc. under
   10  * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
   11  * DARPA CHATS research program. [2001 McAfee, Inc.]
   12  *
   13  * Redistribution and use in source and binary forms, with or without
   14  * modification, are permitted provided that the following conditions
   15  * are met:
   16  * 1. Redistributions of source code must retain the above copyright
   17  *    notice, this list of conditions and the following disclaimer.
   18  * 2. Redistributions in binary form must reproduce the above copyright
   19  *    notice, this list of conditions and the following disclaimer in the
   20  *    documentation and/or other materials provided with the distribution.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  */
   34 
   35 #include <sys/cdefs.h>
   36 __FBSDID("$FreeBSD: releng/12.0/sys/netinet/tcp_syncache.c 339430 2018-10-18 19:21:18Z tuexen $");
   37 
   38 #include "opt_inet.h"
   39 #include "opt_inet6.h"
   40 #include "opt_ipsec.h"
   41 #include "opt_pcbgroup.h"
   42 
   43 #include <sys/param.h>
   44 #include <sys/systm.h>
   45 #include <sys/hash.h>
   46 #include <sys/refcount.h>
   47 #include <sys/kernel.h>
   48 #include <sys/sysctl.h>
   49 #include <sys/limits.h>
   50 #include <sys/lock.h>
   51 #include <sys/mutex.h>
   52 #include <sys/malloc.h>
   53 #include <sys/mbuf.h>
   54 #include <sys/proc.h>           /* for proc0 declaration */
   55 #include <sys/random.h>
   56 #include <sys/socket.h>
   57 #include <sys/socketvar.h>
   58 #include <sys/syslog.h>
   59 #include <sys/ucred.h>
   60 
   61 #include <sys/md5.h>
   62 #include <crypto/siphash/siphash.h>
   63 
   64 #include <vm/uma.h>
   65 
   66 #include <net/if.h>
   67 #include <net/if_var.h>
   68 #include <net/route.h>
   69 #include <net/vnet.h>
   70 
   71 #include <netinet/in.h>
   72 #include <netinet/in_kdtrace.h>
   73 #include <netinet/in_systm.h>
   74 #include <netinet/ip.h>
   75 #include <netinet/in_var.h>
   76 #include <netinet/in_pcb.h>
   77 #include <netinet/ip_var.h>
   78 #include <netinet/ip_options.h>
   79 #ifdef INET6
   80 #include <netinet/ip6.h>
   81 #include <netinet/icmp6.h>
   82 #include <netinet6/nd6.h>
   83 #include <netinet6/ip6_var.h>
   84 #include <netinet6/in6_pcb.h>
   85 #endif
   86 #include <netinet/tcp.h>
   87 #include <netinet/tcp_fastopen.h>
   88 #include <netinet/tcp_fsm.h>
   89 #include <netinet/tcp_seq.h>
   90 #include <netinet/tcp_timer.h>
   91 #include <netinet/tcp_var.h>
   92 #include <netinet/tcp_syncache.h>
   93 #ifdef INET6
   94 #include <netinet6/tcp6_var.h>
   95 #endif
   96 #ifdef TCP_OFFLOAD
   97 #include <netinet/toecore.h>
   98 #endif
   99 
  100 #include <netipsec/ipsec_support.h>
  101 
  102 #include <machine/in_cksum.h>
  103 
  104 #include <security/mac/mac_framework.h>
  105 
  106 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1;
  107 #define V_tcp_syncookies                VNET(tcp_syncookies)
  108 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
  109     &VNET_NAME(tcp_syncookies), 0,
  110     "Use TCP SYN cookies if the syncache overflows");
  111 
  112 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0;
  113 #define V_tcp_syncookiesonly            VNET(tcp_syncookiesonly)
  114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
  115     &VNET_NAME(tcp_syncookiesonly), 0,
  116     "Use only TCP SYN cookies");
  117 
  118 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1;
  119 #define V_functions_inherit_listen_socket_stack \
  120     VNET(functions_inherit_listen_socket_stack)
  121 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack,
  122     CTLFLAG_VNET | CTLFLAG_RW,
  123     &VNET_NAME(functions_inherit_listen_socket_stack), 0,
  124     "Inherit listen socket's stack");
  125 
  126 #ifdef TCP_OFFLOAD
  127 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
  128 #endif
  129 
  130 static void      syncache_drop(struct syncache *, struct syncache_head *);
  131 static void      syncache_free(struct syncache *);
  132 static void      syncache_insert(struct syncache *, struct syncache_head *);
  133 static int       syncache_respond(struct syncache *, struct syncache_head *,
  134                     const struct mbuf *, int);
  135 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  136                     struct mbuf *m);
  137 static void      syncache_timeout(struct syncache *sc, struct syncache_head *sch,
  138                     int docallout);
  139 static void      syncache_timer(void *);
  140 
  141 static uint32_t  syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
  142                     uint8_t *, uintptr_t);
  143 static tcp_seq   syncookie_generate(struct syncache_head *, struct syncache *);
  144 static struct syncache
  145                 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
  146                     struct syncache *, struct tcphdr *, struct tcpopt *,
  147                     struct socket *);
  148 static void      syncookie_reseed(void *);
  149 #ifdef INVARIANTS
  150 static int       syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
  151                     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
  152                     struct socket *lso);
  153 #endif
  154 
  155 /*
  156  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  157  * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
  158  * the odds are that the user has given up attempting to connect by then.
  159  */
  160 #define SYNCACHE_MAXREXMTS              3
  161 
  162 /* Arbitrary values */
  163 #define TCP_SYNCACHE_HASHSIZE           512
  164 #define TCP_SYNCACHE_BUCKETLIMIT        30
  165 
  166 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
  167 #define V_tcp_syncache                  VNET(tcp_syncache)
  168 
  169 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
  170     "TCP SYN cache");
  171 
  172 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
  173     &VNET_NAME(tcp_syncache.bucket_limit), 0,
  174     "Per-bucket hash limit for syncache");
  175 
  176 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
  177     &VNET_NAME(tcp_syncache.cache_limit), 0,
  178     "Overall entry limit for syncache");
  179 
  180 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
  181     &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
  182 
  183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
  184     &VNET_NAME(tcp_syncache.hashsize), 0,
  185     "Size of TCP syncache hashtable");
  186 
  187 static int
  188 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
  189 {
  190         int error;
  191         u_int new;
  192 
  193         new = V_tcp_syncache.rexmt_limit;
  194         error = sysctl_handle_int(oidp, &new, 0, req);
  195         if ((error == 0) && (req->newptr != NULL)) {
  196                 if (new > TCP_MAXRXTSHIFT)
  197                         error = EINVAL;
  198                 else
  199                         V_tcp_syncache.rexmt_limit = new;
  200         }
  201         return (error);
  202 }
  203 
  204 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
  205     CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW,
  206     &VNET_NAME(tcp_syncache.rexmt_limit), 0,
  207     sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI",
  208     "Limit on SYN/ACK retransmissions");
  209 
  210 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
  211 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
  212     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
  213     "Send reset on socket allocation failure");
  214 
  215 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  216 
  217 #define SCH_LOCK(sch)           mtx_lock(&(sch)->sch_mtx)
  218 #define SCH_UNLOCK(sch)         mtx_unlock(&(sch)->sch_mtx)
  219 #define SCH_LOCK_ASSERT(sch)    mtx_assert(&(sch)->sch_mtx, MA_OWNED)
  220 
  221 /*
  222  * Requires the syncache entry to be already removed from the bucket list.
  223  */
  224 static void
  225 syncache_free(struct syncache *sc)
  226 {
  227 
  228         if (sc->sc_ipopts)
  229                 (void) m_free(sc->sc_ipopts);
  230         if (sc->sc_cred)
  231                 crfree(sc->sc_cred);
  232 #ifdef MAC
  233         mac_syncache_destroy(&sc->sc_label);
  234 #endif
  235 
  236         uma_zfree(V_tcp_syncache.zone, sc);
  237 }
  238 
  239 void
  240 syncache_init(void)
  241 {
  242         int i;
  243 
  244         V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  245         V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  246         V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  247         V_tcp_syncache.hash_secret = arc4random();
  248 
  249         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  250             &V_tcp_syncache.hashsize);
  251         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  252             &V_tcp_syncache.bucket_limit);
  253         if (!powerof2(V_tcp_syncache.hashsize) ||
  254             V_tcp_syncache.hashsize == 0) {
  255                 printf("WARNING: syncache hash size is not a power of 2.\n");
  256                 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  257         }
  258         V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
  259 
  260         /* Set limits. */
  261         V_tcp_syncache.cache_limit =
  262             V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
  263         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  264             &V_tcp_syncache.cache_limit);
  265 
  266         /* Allocate the hash table. */
  267         V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
  268             sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
  269 
  270 #ifdef VIMAGE
  271         V_tcp_syncache.vnet = curvnet;
  272 #endif
  273 
  274         /* Initialize the hash buckets. */
  275         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  276                 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
  277                 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
  278                          NULL, MTX_DEF);
  279                 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
  280                          &V_tcp_syncache.hashbase[i].sch_mtx, 0);
  281                 V_tcp_syncache.hashbase[i].sch_length = 0;
  282                 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
  283                 V_tcp_syncache.hashbase[i].sch_last_overflow =
  284                     -(SYNCOOKIE_LIFETIME + 1);
  285         }
  286 
  287         /* Create the syncache entry zone. */
  288         V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  289             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  290         V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
  291             V_tcp_syncache.cache_limit);
  292 
  293         /* Start the SYN cookie reseeder callout. */
  294         callout_init(&V_tcp_syncache.secret.reseed, 1);
  295         arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
  296         arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
  297         callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
  298             syncookie_reseed, &V_tcp_syncache);
  299 }
  300 
  301 #ifdef VIMAGE
  302 void
  303 syncache_destroy(void)
  304 {
  305         struct syncache_head *sch;
  306         struct syncache *sc, *nsc;
  307         int i;
  308 
  309         /*
  310          * Stop the re-seed timer before freeing resources.  No need to
  311          * possibly schedule it another time.
  312          */
  313         callout_drain(&V_tcp_syncache.secret.reseed);
  314 
  315         /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
  316         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  317 
  318                 sch = &V_tcp_syncache.hashbase[i];
  319                 callout_drain(&sch->sch_timer);
  320 
  321                 SCH_LOCK(sch);
  322                 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
  323                         syncache_drop(sc, sch);
  324                 SCH_UNLOCK(sch);
  325                 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
  326                     ("%s: sch->sch_bucket not empty", __func__));
  327                 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
  328                     __func__, sch->sch_length));
  329                 mtx_destroy(&sch->sch_mtx);
  330         }
  331 
  332         KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
  333             ("%s: cache_count not 0", __func__));
  334 
  335         /* Free the allocated global resources. */
  336         uma_zdestroy(V_tcp_syncache.zone);
  337         free(V_tcp_syncache.hashbase, M_SYNCACHE);
  338 }
  339 #endif
  340 
  341 /*
  342  * Inserts a syncache entry into the specified bucket row.
  343  * Locks and unlocks the syncache_head autonomously.
  344  */
  345 static void
  346 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  347 {
  348         struct syncache *sc2;
  349 
  350         SCH_LOCK(sch);
  351 
  352         /*
  353          * Make sure that we don't overflow the per-bucket limit.
  354          * If the bucket is full, toss the oldest element.
  355          */
  356         if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
  357                 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
  358                         ("sch->sch_length incorrect"));
  359                 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
  360                 sch->sch_last_overflow = time_uptime;
  361                 syncache_drop(sc2, sch);
  362                 TCPSTAT_INC(tcps_sc_bucketoverflow);
  363         }
  364 
  365         /* Put it into the bucket. */
  366         TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
  367         sch->sch_length++;
  368 
  369 #ifdef TCP_OFFLOAD
  370         if (ADDED_BY_TOE(sc)) {
  371                 struct toedev *tod = sc->sc_tod;
  372 
  373                 tod->tod_syncache_added(tod, sc->sc_todctx);
  374         }
  375 #endif
  376 
  377         /* Reinitialize the bucket row's timer. */
  378         if (sch->sch_length == 1)
  379                 sch->sch_nextc = ticks + INT_MAX;
  380         syncache_timeout(sc, sch, 1);
  381 
  382         SCH_UNLOCK(sch);
  383 
  384         TCPSTATES_INC(TCPS_SYN_RECEIVED);
  385         TCPSTAT_INC(tcps_sc_added);
  386 }
  387 
  388 /*
  389  * Remove and free entry from syncache bucket row.
  390  * Expects locked syncache head.
  391  */
  392 static void
  393 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  394 {
  395 
  396         SCH_LOCK_ASSERT(sch);
  397 
  398         TCPSTATES_DEC(TCPS_SYN_RECEIVED);
  399         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  400         sch->sch_length--;
  401 
  402 #ifdef TCP_OFFLOAD
  403         if (ADDED_BY_TOE(sc)) {
  404                 struct toedev *tod = sc->sc_tod;
  405 
  406                 tod->tod_syncache_removed(tod, sc->sc_todctx);
  407         }
  408 #endif
  409 
  410         syncache_free(sc);
  411 }
  412 
  413 /*
  414  * Engage/reengage time on bucket row.
  415  */
  416 static void
  417 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
  418 {
  419         int rexmt;
  420 
  421         if (sc->sc_rxmits == 0)
  422                 rexmt = TCPTV_RTOBASE;
  423         else
  424                 TCPT_RANGESET(rexmt, TCPTV_RTOBASE * tcp_syn_backoff[sc->sc_rxmits],
  425                     tcp_rexmit_min, TCPTV_REXMTMAX);
  426         sc->sc_rxttime = ticks + rexmt;
  427         sc->sc_rxmits++;
  428         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
  429                 sch->sch_nextc = sc->sc_rxttime;
  430                 if (docallout)
  431                         callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
  432                             syncache_timer, (void *)sch);
  433         }
  434 }
  435 
  436 /*
  437  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  438  * If we have retransmitted an entry the maximum number of times, expire it.
  439  * One separate timer for each bucket row.
  440  */
  441 static void
  442 syncache_timer(void *xsch)
  443 {
  444         struct syncache_head *sch = (struct syncache_head *)xsch;
  445         struct syncache *sc, *nsc;
  446         int tick = ticks;
  447         char *s;
  448 
  449         CURVNET_SET(sch->sch_sc->vnet);
  450 
  451         /* NB: syncache_head has already been locked by the callout. */
  452         SCH_LOCK_ASSERT(sch);
  453 
  454         /*
  455          * In the following cycle we may remove some entries and/or
  456          * advance some timeouts, so re-initialize the bucket timer.
  457          */
  458         sch->sch_nextc = tick + INT_MAX;
  459 
  460         TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
  461                 /*
  462                  * We do not check if the listen socket still exists
  463                  * and accept the case where the listen socket may be
  464                  * gone by the time we resend the SYN/ACK.  We do
  465                  * not expect this to happens often. If it does,
  466                  * then the RST will be sent by the time the remote
  467                  * host does the SYN/ACK->ACK.
  468                  */
  469                 if (TSTMP_GT(sc->sc_rxttime, tick)) {
  470                         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
  471                                 sch->sch_nextc = sc->sc_rxttime;
  472                         continue;
  473                 }
  474                 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
  475                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  476                                 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
  477                                     "giving up and removing syncache entry\n",
  478                                     s, __func__);
  479                                 free(s, M_TCPLOG);
  480                         }
  481                         syncache_drop(sc, sch);
  482                         TCPSTAT_INC(tcps_sc_stale);
  483                         continue;
  484                 }
  485                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  486                         log(LOG_DEBUG, "%s; %s: Response timeout, "
  487                             "retransmitting (%u) SYN|ACK\n",
  488                             s, __func__, sc->sc_rxmits);
  489                         free(s, M_TCPLOG);
  490                 }
  491 
  492                 syncache_respond(sc, sch, NULL, TH_SYN|TH_ACK);
  493                 TCPSTAT_INC(tcps_sc_retransmitted);
  494                 syncache_timeout(sc, sch, 0);
  495         }
  496         if (!TAILQ_EMPTY(&(sch)->sch_bucket))
  497                 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
  498                         syncache_timer, (void *)(sch));
  499         CURVNET_RESTORE();
  500 }
  501 
  502 /*
  503  * Find an entry in the syncache.
  504  * Returns always with locked syncache_head plus a matching entry or NULL.
  505  */
  506 static struct syncache *
  507 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  508 {
  509         struct syncache *sc;
  510         struct syncache_head *sch;
  511         uint32_t hash;
  512 
  513         /*
  514          * The hash is built on foreign port + local port + foreign address.
  515          * We rely on the fact that struct in_conninfo starts with 16 bits
  516          * of foreign port, then 16 bits of local port then followed by 128
  517          * bits of foreign address.  In case of IPv4 address, the first 3
  518          * 32-bit words of the address always are zeroes.
  519          */
  520         hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
  521             V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
  522 
  523         sch = &V_tcp_syncache.hashbase[hash];
  524         *schp = sch;
  525         SCH_LOCK(sch);
  526 
  527         /* Circle through bucket row to find matching entry. */
  528         TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
  529                 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
  530                     sizeof(struct in_endpoints)) == 0)
  531                         break;
  532 
  533         return (sc);    /* Always returns with locked sch. */
  534 }
  535 
  536 /*
  537  * This function is called when we get a RST for a
  538  * non-existent connection, so that we can see if the
  539  * connection is in the syn cache.  If it is, zap it.
  540  * If required send a challenge ACK.
  541  */
  542 void
  543 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m)
  544 {
  545         struct syncache *sc;
  546         struct syncache_head *sch;
  547         char *s = NULL;
  548 
  549         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  550         SCH_LOCK_ASSERT(sch);
  551 
  552         /*
  553          * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
  554          * See RFC 793 page 65, section SEGMENT ARRIVES.
  555          */
  556         if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
  557                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  558                         log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
  559                             "FIN flag set, segment ignored\n", s, __func__);
  560                 TCPSTAT_INC(tcps_badrst);
  561                 goto done;
  562         }
  563 
  564         /*
  565          * No corresponding connection was found in syncache.
  566          * If syncookies are enabled and possibly exclusively
  567          * used, or we are under memory pressure, a valid RST
  568          * may not find a syncache entry.  In that case we're
  569          * done and no SYN|ACK retransmissions will happen.
  570          * Otherwise the RST was misdirected or spoofed.
  571          */
  572         if (sc == NULL) {
  573                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  574                         log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
  575                             "syncache entry (possibly syncookie only), "
  576                             "segment ignored\n", s, __func__);
  577                 TCPSTAT_INC(tcps_badrst);
  578                 goto done;
  579         }
  580 
  581         /*
  582          * If the RST bit is set, check the sequence number to see
  583          * if this is a valid reset segment.
  584          * RFC 793 page 37:
  585          *   In all states except SYN-SENT, all reset (RST) segments
  586          *   are validated by checking their SEQ-fields.  A reset is
  587          *   valid if its sequence number is in the window.
  588          *
  589          *   The sequence number in the reset segment is normally an
  590          *   echo of our outgoing acknowlegement numbers, but some hosts
  591          *   send a reset with the sequence number at the rightmost edge
  592          *   of our receive window, and we have to handle this case.
  593          */
  594         if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
  595             SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
  596             (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
  597                 if (V_tcp_insecure_rst ||
  598                     th->th_seq == sc->sc_irs + 1) {
  599                         syncache_drop(sc, sch);
  600                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  601                                 log(LOG_DEBUG,
  602                                     "%s; %s: Our SYN|ACK was rejected, "
  603                                     "connection attempt aborted by remote "
  604                                     "endpoint\n",
  605                                     s, __func__);
  606                         TCPSTAT_INC(tcps_sc_reset);
  607                 } else {
  608                         TCPSTAT_INC(tcps_badrst);
  609                         /* Send challenge ACK. */
  610                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  611                                 log(LOG_DEBUG, "%s; %s: RST with invalid "
  612                                     " SEQ %u != NXT %u (+WND %u), "
  613                                     "sending challenge ACK\n",
  614                                     s, __func__,
  615                                     th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
  616                         syncache_respond(sc, sch, m, TH_ACK);
  617                 }
  618         } else {
  619                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  620                         log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
  621                             "NXT %u (+WND %u), segment ignored\n",
  622                             s, __func__,
  623                             th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
  624                 TCPSTAT_INC(tcps_badrst);
  625         }
  626 
  627 done:
  628         if (s != NULL)
  629                 free(s, M_TCPLOG);
  630         SCH_UNLOCK(sch);
  631 }
  632 
  633 void
  634 syncache_badack(struct in_conninfo *inc)
  635 {
  636         struct syncache *sc;
  637         struct syncache_head *sch;
  638 
  639         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  640         SCH_LOCK_ASSERT(sch);
  641         if (sc != NULL) {
  642                 syncache_drop(sc, sch);
  643                 TCPSTAT_INC(tcps_sc_badack);
  644         }
  645         SCH_UNLOCK(sch);
  646 }
  647 
  648 void
  649 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq)
  650 {
  651         struct syncache *sc;
  652         struct syncache_head *sch;
  653 
  654         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  655         SCH_LOCK_ASSERT(sch);
  656         if (sc == NULL)
  657                 goto done;
  658 
  659         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  660         if (ntohl(th_seq) != sc->sc_iss)
  661                 goto done;
  662 
  663         /*
  664          * If we've rertransmitted 3 times and this is our second error,
  665          * we remove the entry.  Otherwise, we allow it to continue on.
  666          * This prevents us from incorrectly nuking an entry during a
  667          * spurious network outage.
  668          *
  669          * See tcp_notify().
  670          */
  671         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
  672                 sc->sc_flags |= SCF_UNREACH;
  673                 goto done;
  674         }
  675         syncache_drop(sc, sch);
  676         TCPSTAT_INC(tcps_sc_unreach);
  677 done:
  678         SCH_UNLOCK(sch);
  679 }
  680 
  681 /*
  682  * Build a new TCP socket structure from a syncache entry.
  683  *
  684  * On success return the newly created socket with its underlying inp locked.
  685  */
  686 static struct socket *
  687 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  688 {
  689         struct tcp_function_block *blk;
  690         struct inpcb *inp = NULL;
  691         struct socket *so;
  692         struct tcpcb *tp;
  693         int error;
  694         char *s;
  695 
  696         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
  697 
  698         /*
  699          * Ok, create the full blown connection, and set things up
  700          * as they would have been set up if we had created the
  701          * connection when the SYN arrived.  If we can't create
  702          * the connection, abort it.
  703          */
  704         so = sonewconn(lso, 0);
  705         if (so == NULL) {
  706                 /*
  707                  * Drop the connection; we will either send a RST or
  708                  * have the peer retransmit its SYN again after its
  709                  * RTO and try again.
  710                  */
  711                 TCPSTAT_INC(tcps_listendrop);
  712                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  713                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  714                             "due to limits or memory shortage\n",
  715                             s, __func__);
  716                         free(s, M_TCPLOG);
  717                 }
  718                 goto abort2;
  719         }
  720 #ifdef MAC
  721         mac_socketpeer_set_from_mbuf(m, so);
  722 #endif
  723 
  724         inp = sotoinpcb(so);
  725         inp->inp_inc.inc_fibnum = so->so_fibnum;
  726         INP_WLOCK(inp);
  727         /*
  728          * Exclusive pcbinfo lock is not required in syncache socket case even
  729          * if two inpcb locks can be acquired simultaneously:
  730          *  - the inpcb in LISTEN state,
  731          *  - the newly created inp.
  732          *
  733          * In this case, an inp cannot be at same time in LISTEN state and
  734          * just created by an accept() call.
  735          */
  736         INP_HASH_WLOCK(&V_tcbinfo);
  737 
  738         /* Insert new socket into PCB hash list. */
  739         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  740 #ifdef INET6
  741         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  742                 inp->inp_vflag &= ~INP_IPV4;
  743                 inp->inp_vflag |= INP_IPV6;
  744                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  745         } else {
  746                 inp->inp_vflag &= ~INP_IPV6;
  747                 inp->inp_vflag |= INP_IPV4;
  748 #endif
  749                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  750 #ifdef INET6
  751         }
  752 #endif
  753 
  754         /*
  755          * If there's an mbuf and it has a flowid, then let's initialise the
  756          * inp with that particular flowid.
  757          */
  758         if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
  759                 inp->inp_flowid = m->m_pkthdr.flowid;
  760                 inp->inp_flowtype = M_HASHTYPE_GET(m);
  761         }
  762 
  763         /*
  764          * Install in the reservation hash table for now, but don't yet
  765          * install a connection group since the full 4-tuple isn't yet
  766          * configured.
  767          */
  768         inp->inp_lport = sc->sc_inc.inc_lport;
  769         if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
  770                 /*
  771                  * Undo the assignments above if we failed to
  772                  * put the PCB on the hash lists.
  773                  */
  774 #ifdef INET6
  775                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  776                         inp->in6p_laddr = in6addr_any;
  777                 else
  778 #endif
  779                         inp->inp_laddr.s_addr = INADDR_ANY;
  780                 inp->inp_lport = 0;
  781                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  782                         log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
  783                             "with error %i\n",
  784                             s, __func__, error);
  785                         free(s, M_TCPLOG);
  786                 }
  787                 INP_HASH_WUNLOCK(&V_tcbinfo);
  788                 goto abort;
  789         }
  790 #ifdef INET6
  791         if (inp->inp_vflag & INP_IPV6PROTO) {
  792                 struct inpcb *oinp = sotoinpcb(lso);
  793 
  794                 /*
  795                  * Inherit socket options from the listening socket.
  796                  * Note that in6p_inputopts are not (and should not be)
  797                  * copied, since it stores previously received options and is
  798                  * used to detect if each new option is different than the
  799                  * previous one and hence should be passed to a user.
  800                  * If we copied in6p_inputopts, a user would not be able to
  801                  * receive options just after calling the accept system call.
  802                  */
  803                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  804                 if (oinp->in6p_outputopts)
  805                         inp->in6p_outputopts =
  806                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  807         }
  808 
  809         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  810                 struct in6_addr laddr6;
  811                 struct sockaddr_in6 sin6;
  812 
  813                 sin6.sin6_family = AF_INET6;
  814                 sin6.sin6_len = sizeof(sin6);
  815                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  816                 sin6.sin6_port = sc->sc_inc.inc_fport;
  817                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  818                 laddr6 = inp->in6p_laddr;
  819                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  820                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  821                 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
  822                     thread0.td_ucred, m)) != 0) {
  823                         inp->in6p_laddr = laddr6;
  824                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  825                                 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
  826                                     "with error %i\n",
  827                                     s, __func__, error);
  828                                 free(s, M_TCPLOG);
  829                         }
  830                         INP_HASH_WUNLOCK(&V_tcbinfo);
  831                         goto abort;
  832                 }
  833                 /* Override flowlabel from in6_pcbconnect. */
  834                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  835                 inp->inp_flow |= sc->sc_flowlabel;
  836         }
  837 #endif /* INET6 */
  838 #if defined(INET) && defined(INET6)
  839         else
  840 #endif
  841 #ifdef INET
  842         {
  843                 struct in_addr laddr;
  844                 struct sockaddr_in sin;
  845 
  846                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  847                 
  848                 if (inp->inp_options == NULL) {
  849                         inp->inp_options = sc->sc_ipopts;
  850                         sc->sc_ipopts = NULL;
  851                 }
  852 
  853                 sin.sin_family = AF_INET;
  854                 sin.sin_len = sizeof(sin);
  855                 sin.sin_addr = sc->sc_inc.inc_faddr;
  856                 sin.sin_port = sc->sc_inc.inc_fport;
  857                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  858                 laddr = inp->inp_laddr;
  859                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  860                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  861                 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
  862                     thread0.td_ucred, m)) != 0) {
  863                         inp->inp_laddr = laddr;
  864                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  865                                 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
  866                                     "with error %i\n",
  867                                     s, __func__, error);
  868                                 free(s, M_TCPLOG);
  869                         }
  870                         INP_HASH_WUNLOCK(&V_tcbinfo);
  871                         goto abort;
  872                 }
  873         }
  874 #endif /* INET */
  875 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
  876         /* Copy old policy into new socket's. */
  877         if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
  878                 printf("syncache_socket: could not copy policy\n");
  879 #endif
  880         INP_HASH_WUNLOCK(&V_tcbinfo);
  881         tp = intotcpcb(inp);
  882         tcp_state_change(tp, TCPS_SYN_RECEIVED);
  883         tp->iss = sc->sc_iss;
  884         tp->irs = sc->sc_irs;
  885         tcp_rcvseqinit(tp);
  886         tcp_sendseqinit(tp);
  887         blk = sototcpcb(lso)->t_fb;
  888         if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) {
  889                 /*
  890                  * Our parents t_fb was not the default,
  891                  * we need to release our ref on tp->t_fb and 
  892                  * pickup one on the new entry.
  893                  */
  894                 struct tcp_function_block *rblk;
  895                 
  896                 rblk = find_and_ref_tcp_fb(blk);
  897                 KASSERT(rblk != NULL,
  898                     ("cannot find blk %p out of syncache?", blk));
  899                 if (tp->t_fb->tfb_tcp_fb_fini)
  900                         (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
  901                 refcount_release(&tp->t_fb->tfb_refcnt);
  902                 tp->t_fb = rblk;
  903                 /*
  904                  * XXXrrs this is quite dangerous, it is possible
  905                  * for the new function to fail to init. We also
  906                  * are not asking if the handoff_is_ok though at
  907                  * the very start thats probalbly ok.
  908                  */
  909                 if (tp->t_fb->tfb_tcp_fb_init) {
  910                         (*tp->t_fb->tfb_tcp_fb_init)(tp);
  911                 }
  912         }               
  913         tp->snd_wl1 = sc->sc_irs;
  914         tp->snd_max = tp->iss + 1;
  915         tp->snd_nxt = tp->iss + 1;
  916         tp->rcv_up = sc->sc_irs + 1;
  917         tp->rcv_wnd = sc->sc_wnd;
  918         tp->rcv_adv += tp->rcv_wnd;
  919         tp->last_ack_sent = tp->rcv_nxt;
  920 
  921         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  922         if (sc->sc_flags & SCF_NOOPT)
  923                 tp->t_flags |= TF_NOOPT;
  924         else {
  925                 if (sc->sc_flags & SCF_WINSCALE) {
  926                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  927                         tp->snd_scale = sc->sc_requested_s_scale;
  928                         tp->request_r_scale = sc->sc_requested_r_scale;
  929                 }
  930                 if (sc->sc_flags & SCF_TIMESTAMP) {
  931                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  932                         tp->ts_recent = sc->sc_tsreflect;
  933                         tp->ts_recent_age = tcp_ts_getticks();
  934                         tp->ts_offset = sc->sc_tsoff;
  935                 }
  936 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
  937                 if (sc->sc_flags & SCF_SIGNATURE)
  938                         tp->t_flags |= TF_SIGNATURE;
  939 #endif
  940                 if (sc->sc_flags & SCF_SACK)
  941                         tp->t_flags |= TF_SACK_PERMIT;
  942         }
  943 
  944         if (sc->sc_flags & SCF_ECN)
  945                 tp->t_flags |= TF_ECN_PERMIT;
  946 
  947         /*
  948          * Set up MSS and get cached values from tcp_hostcache.
  949          * This might overwrite some of the defaults we just set.
  950          */
  951         tcp_mss(tp, sc->sc_peer_mss);
  952 
  953         /*
  954          * If the SYN,ACK was retransmitted, indicate that CWND to be
  955          * limited to one segment in cc_conn_init().
  956          * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
  957          */
  958         if (sc->sc_rxmits > 1)
  959                 tp->snd_cwnd = 1;
  960 
  961 #ifdef TCP_OFFLOAD
  962         /*
  963          * Allow a TOE driver to install its hooks.  Note that we hold the
  964          * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
  965          * new connection before the TOE driver has done its thing.
  966          */
  967         if (ADDED_BY_TOE(sc)) {
  968                 struct toedev *tod = sc->sc_tod;
  969 
  970                 tod->tod_offload_socket(tod, sc->sc_todctx, so);
  971         }
  972 #endif
  973         /*
  974          * Copy and activate timers.
  975          */
  976         tp->t_keepinit = sototcpcb(lso)->t_keepinit;
  977         tp->t_keepidle = sototcpcb(lso)->t_keepidle;
  978         tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
  979         tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
  980         tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
  981 
  982         TCPSTAT_INC(tcps_accepts);
  983         return (so);
  984 
  985 abort:
  986         INP_WUNLOCK(inp);
  987 abort2:
  988         if (so != NULL)
  989                 soabort(so);
  990         return (NULL);
  991 }
  992 
  993 /*
  994  * This function gets called when we receive an ACK for a
  995  * socket in the LISTEN state.  We look up the connection
  996  * in the syncache, and if its there, we pull it out of
  997  * the cache and turn it into a full-blown connection in
  998  * the SYN-RECEIVED state.
  999  *
 1000  * On syncache_socket() success the newly created socket
 1001  * has its underlying inp locked.
 1002  */
 1003 int
 1004 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1005     struct socket **lsop, struct mbuf *m)
 1006 {
 1007         struct syncache *sc;
 1008         struct syncache_head *sch;
 1009         struct syncache scs;
 1010         char *s;
 1011 
 1012         /*
 1013          * Global TCP locks are held because we manipulate the PCB lists
 1014          * and create a new socket.
 1015          */
 1016         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1017         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
 1018             ("%s: can handle only ACK", __func__));
 1019 
 1020         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
 1021         SCH_LOCK_ASSERT(sch);
 1022 
 1023 #ifdef INVARIANTS
 1024         /*
 1025          * Test code for syncookies comparing the syncache stored
 1026          * values with the reconstructed values from the cookie.
 1027          */
 1028         if (sc != NULL)
 1029                 syncookie_cmp(inc, sch, sc, th, to, *lsop);
 1030 #endif
 1031 
 1032         if (sc == NULL) {
 1033                 /*
 1034                  * There is no syncache entry, so see if this ACK is
 1035                  * a returning syncookie.  To do this, first:
 1036                  *  A. Check if syncookies are used in case of syncache
 1037                  *     overflows
 1038                  *  B. See if this socket has had a syncache entry dropped in
 1039                  *     the recent past. We don't want to accept a bogus
 1040                  *     syncookie if we've never received a SYN or accept it
 1041                  *     twice.
 1042                  *  C. check that the syncookie is valid.  If it is, then
 1043                  *     cobble up a fake syncache entry, and return.
 1044                  */
 1045                 if (!V_tcp_syncookies) {
 1046                         SCH_UNLOCK(sch);
 1047                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1048                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
 1049                                     "segment rejected (syncookies disabled)\n",
 1050                                     s, __func__);
 1051                         goto failed;
 1052                 }
 1053                 if (!V_tcp_syncookiesonly &&
 1054                     sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) {
 1055                         SCH_UNLOCK(sch);
 1056                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1057                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
 1058                                     "segment rejected (no syncache entry)\n",
 1059                                     s, __func__);
 1060                         goto failed;
 1061                 }
 1062                 bzero(&scs, sizeof(scs));
 1063                 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
 1064                 SCH_UNLOCK(sch);
 1065                 if (sc == NULL) {
 1066                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1067                                 log(LOG_DEBUG, "%s; %s: Segment failed "
 1068                                     "SYNCOOKIE authentication, segment rejected "
 1069                                     "(probably spoofed)\n", s, __func__);
 1070                         goto failed;
 1071                 }
 1072 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1073                 /* If received ACK has MD5 signature, check it. */
 1074                 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
 1075                     (!TCPMD5_ENABLED() ||
 1076                     TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
 1077                         /* Drop the ACK. */
 1078                         if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1079                                 log(LOG_DEBUG, "%s; %s: Segment rejected, "
 1080                                     "MD5 signature doesn't match.\n",
 1081                                     s, __func__);
 1082                                 free(s, M_TCPLOG);
 1083                         }
 1084                         TCPSTAT_INC(tcps_sig_err_sigopt);
 1085                         return (-1); /* Do not send RST */
 1086                 }
 1087 #endif /* TCP_SIGNATURE */
 1088         } else {
 1089 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1090                 /*
 1091                  * If listening socket requested TCP digests, check that
 1092                  * received ACK has signature and it is correct.
 1093                  * If not, drop the ACK and leave sc entry in th cache,
 1094                  * because SYN was received with correct signature.
 1095                  */
 1096                 if (sc->sc_flags & SCF_SIGNATURE) {
 1097                         if ((to->to_flags & TOF_SIGNATURE) == 0) {
 1098                                 /* No signature */
 1099                                 TCPSTAT_INC(tcps_sig_err_nosigopt);
 1100                                 SCH_UNLOCK(sch);
 1101                                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1102                                         log(LOG_DEBUG, "%s; %s: Segment "
 1103                                             "rejected, MD5 signature wasn't "
 1104                                             "provided.\n", s, __func__);
 1105                                         free(s, M_TCPLOG);
 1106                                 }
 1107                                 return (-1); /* Do not send RST */
 1108                         }
 1109                         if (!TCPMD5_ENABLED() ||
 1110                             TCPMD5_INPUT(m, th, to->to_signature) != 0) {
 1111                                 /* Doesn't match or no SA */
 1112                                 SCH_UNLOCK(sch);
 1113                                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1114                                         log(LOG_DEBUG, "%s; %s: Segment "
 1115                                             "rejected, MD5 signature doesn't "
 1116                                             "match.\n", s, __func__);
 1117                                         free(s, M_TCPLOG);
 1118                                 }
 1119                                 return (-1); /* Do not send RST */
 1120                         }
 1121                 }
 1122 #endif /* TCP_SIGNATURE */
 1123                 /*
 1124                  * Pull out the entry to unlock the bucket row.
 1125                  * 
 1126                  * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
 1127                  * tcp_state_change().  The tcpcb is not existent at this
 1128                  * moment.  A new one will be allocated via syncache_socket->
 1129                  * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
 1130                  * syncache_socket() will change it to TCPS_SYN_RECEIVED.
 1131                  */
 1132                 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
 1133                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
 1134                 sch->sch_length--;
 1135 #ifdef TCP_OFFLOAD
 1136                 if (ADDED_BY_TOE(sc)) {
 1137                         struct toedev *tod = sc->sc_tod;
 1138 
 1139                         tod->tod_syncache_removed(tod, sc->sc_todctx);
 1140                 }
 1141 #endif
 1142                 SCH_UNLOCK(sch);
 1143         }
 1144 
 1145         /*
 1146          * Segment validation:
 1147          * ACK must match our initial sequence number + 1 (the SYN|ACK).
 1148          */
 1149         if (th->th_ack != sc->sc_iss + 1) {
 1150                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1151                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
 1152                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
 1153                 goto failed;
 1154         }
 1155 
 1156         /*
 1157          * The SEQ must fall in the window starting at the received
 1158          * initial receive sequence number + 1 (the SYN).
 1159          */
 1160         if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
 1161             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
 1162                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1163                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
 1164                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
 1165                 goto failed;
 1166         }
 1167 
 1168         /*
 1169          * If timestamps were not negotiated during SYN/ACK they
 1170          * must not appear on any segment during this session.
 1171          */
 1172         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
 1173                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
 1174                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
 1175                             "segment rejected\n", s, __func__);
 1176                 goto failed;
 1177         }
 1178 
 1179         /*
 1180          * If timestamps were negotiated during SYN/ACK they should
 1181          * appear on every segment during this session.
 1182          * XXXAO: This is only informal as there have been unverified
 1183          * reports of non-compliants stacks.
 1184          */
 1185         if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
 1186                 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 1187                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
 1188                             "no action\n", s, __func__);
 1189                         free(s, M_TCPLOG);
 1190                         s = NULL;
 1191                 }
 1192         }
 1193 
 1194         *lsop = syncache_socket(sc, *lsop, m);
 1195 
 1196         if (*lsop == NULL)
 1197                 TCPSTAT_INC(tcps_sc_aborted);
 1198         else
 1199                 TCPSTAT_INC(tcps_sc_completed);
 1200 
 1201 /* how do we find the inp for the new socket? */
 1202         if (sc != &scs)
 1203                 syncache_free(sc);
 1204         return (1);
 1205 failed:
 1206         if (sc != NULL && sc != &scs)
 1207                 syncache_free(sc);
 1208         if (s != NULL)
 1209                 free(s, M_TCPLOG);
 1210         *lsop = NULL;
 1211         return (0);
 1212 }
 1213 
 1214 static void
 1215 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
 1216     uint64_t response_cookie)
 1217 {
 1218         struct inpcb *inp;
 1219         struct tcpcb *tp;
 1220         unsigned int *pending_counter;
 1221 
 1222         /*
 1223          * Global TCP locks are held because we manipulate the PCB lists
 1224          * and create a new socket.
 1225          */
 1226         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 1227 
 1228         pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
 1229         *lsop = syncache_socket(sc, *lsop, m);
 1230         if (*lsop == NULL) {
 1231                 TCPSTAT_INC(tcps_sc_aborted);
 1232                 atomic_subtract_int(pending_counter, 1);
 1233         } else {
 1234                 soisconnected(*lsop);
 1235                 inp = sotoinpcb(*lsop);
 1236                 tp = intotcpcb(inp);
 1237                 tp->t_flags |= TF_FASTOPEN;
 1238                 tp->t_tfo_cookie.server = response_cookie;
 1239                 tp->snd_max = tp->iss;
 1240                 tp->snd_nxt = tp->iss;
 1241                 tp->t_tfo_pending = pending_counter;
 1242                 TCPSTAT_INC(tcps_sc_completed);
 1243         }
 1244 }
 1245 
 1246 /*
 1247  * Given a LISTEN socket and an inbound SYN request, add
 1248  * this to the syn cache, and send back a segment:
 1249  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 1250  * to the source.
 1251  *
 1252  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
 1253  * Doing so would require that we hold onto the data and deliver it
 1254  * to the application.  However, if we are the target of a SYN-flood
 1255  * DoS attack, an attacker could send data which would eventually
 1256  * consume all available buffer space if it were ACKed.  By not ACKing
 1257  * the data, we avoid this DoS scenario.
 1258  *
 1259  * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
 1260  * cookie is processed and a new socket is created.  In this case, any data
 1261  * accompanying the SYN will be queued to the socket by tcp_input() and will
 1262  * be ACKed either when the application sends response data or the delayed
 1263  * ACK timer expires, whichever comes first.
 1264  */
 1265 int
 1266 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1267     struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
 1268     void *todctx)
 1269 {
 1270         struct tcpcb *tp;
 1271         struct socket *so;
 1272         struct syncache *sc = NULL;
 1273         struct syncache_head *sch;
 1274         struct mbuf *ipopts = NULL;
 1275         u_int ltflags;
 1276         int win, ip_ttl, ip_tos;
 1277         char *s;
 1278         int rv = 0;
 1279 #ifdef INET6
 1280         int autoflowlabel = 0;
 1281 #endif
 1282 #ifdef MAC
 1283         struct label *maclabel;
 1284 #endif
 1285         struct syncache scs;
 1286         struct ucred *cred;
 1287         uint64_t tfo_response_cookie;
 1288         unsigned int *tfo_pending = NULL;
 1289         int tfo_cookie_valid = 0;
 1290         int tfo_response_cookie_valid = 0;
 1291 
 1292         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1293         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1294             ("%s: unexpected tcp flags", __func__));
 1295 
 1296         /*
 1297          * Combine all so/tp operations very early to drop the INP lock as
 1298          * soon as possible.
 1299          */
 1300         so = *lsop;
 1301         KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
 1302         tp = sototcpcb(so);
 1303         cred = crhold(so->so_cred);
 1304 
 1305 #ifdef INET6
 1306         if ((inc->inc_flags & INC_ISIPV6) &&
 1307             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1308                 autoflowlabel = 1;
 1309 #endif
 1310         ip_ttl = inp->inp_ip_ttl;
 1311         ip_tos = inp->inp_ip_tos;
 1312         win = so->sol_sbrcv_hiwat;
 1313         ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
 1314 
 1315         if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) &&
 1316             (tp->t_tfo_pending != NULL) &&
 1317             (to->to_flags & TOF_FASTOPEN)) {
 1318                 /*
 1319                  * Limit the number of pending TFO connections to
 1320                  * approximately half of the queue limit.  This prevents TFO
 1321                  * SYN floods from starving the service by filling the
 1322                  * listen queue with bogus TFO connections.
 1323                  */
 1324                 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
 1325                     (so->sol_qlimit / 2)) {
 1326                         int result;
 1327 
 1328                         result = tcp_fastopen_check_cookie(inc,
 1329                             to->to_tfo_cookie, to->to_tfo_len,
 1330                             &tfo_response_cookie);
 1331                         tfo_cookie_valid = (result > 0);
 1332                         tfo_response_cookie_valid = (result >= 0);
 1333                 }
 1334 
 1335                 /*
 1336                  * Remember the TFO pending counter as it will have to be
 1337                  * decremented below if we don't make it to syncache_tfo_expand().
 1338                  */
 1339                 tfo_pending = tp->t_tfo_pending;
 1340         }
 1341 
 1342         /* By the time we drop the lock these should no longer be used. */
 1343         so = NULL;
 1344         tp = NULL;
 1345 
 1346 #ifdef MAC
 1347         if (mac_syncache_init(&maclabel) != 0) {
 1348                 INP_WUNLOCK(inp);
 1349                 goto done;
 1350         } else
 1351                 mac_syncache_create(maclabel, inp);
 1352 #endif
 1353         if (!tfo_cookie_valid)
 1354                 INP_WUNLOCK(inp);
 1355 
 1356         /*
 1357          * Remember the IP options, if any.
 1358          */
 1359 #ifdef INET6
 1360         if (!(inc->inc_flags & INC_ISIPV6))
 1361 #endif
 1362 #ifdef INET
 1363                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1364 #else
 1365                 ipopts = NULL;
 1366 #endif
 1367 
 1368 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1369         /*
 1370          * If listening socket requested TCP digests, check that received
 1371          * SYN has signature and it is correct. If signature doesn't match
 1372          * or TCP_SIGNATURE support isn't enabled, drop the packet.
 1373          */
 1374         if (ltflags & TF_SIGNATURE) {
 1375                 if ((to->to_flags & TOF_SIGNATURE) == 0) {
 1376                         TCPSTAT_INC(tcps_sig_err_nosigopt);
 1377                         goto done;
 1378                 }
 1379                 if (!TCPMD5_ENABLED() ||
 1380                     TCPMD5_INPUT(m, th, to->to_signature) != 0)
 1381                         goto done;
 1382         }
 1383 #endif  /* TCP_SIGNATURE */
 1384         /*
 1385          * See if we already have an entry for this connection.
 1386          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1387          *
 1388          * XXX: should the syncache be re-initialized with the contents
 1389          * of the new SYN here (which may have different options?)
 1390          *
 1391          * XXX: We do not check the sequence number to see if this is a
 1392          * real retransmit or a new connection attempt.  The question is
 1393          * how to handle such a case; either ignore it as spoofed, or
 1394          * drop the current entry and create a new one?
 1395          */
 1396         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1397         SCH_LOCK_ASSERT(sch);
 1398         if (sc != NULL) {
 1399                 if (tfo_cookie_valid)
 1400                         INP_WUNLOCK(inp);
 1401                 TCPSTAT_INC(tcps_sc_dupsyn);
 1402                 if (ipopts) {
 1403                         /*
 1404                          * If we were remembering a previous source route,
 1405                          * forget it and use the new one we've been given.
 1406                          */
 1407                         if (sc->sc_ipopts)
 1408                                 (void) m_free(sc->sc_ipopts);
 1409                         sc->sc_ipopts = ipopts;
 1410                 }
 1411                 /*
 1412                  * Update timestamp if present.
 1413                  */
 1414                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1415                         sc->sc_tsreflect = to->to_tsval;
 1416                 else
 1417                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1418 #ifdef MAC
 1419                 /*
 1420                  * Since we have already unconditionally allocated label
 1421                  * storage, free it up.  The syncache entry will already
 1422                  * have an initialized label we can use.
 1423                  */
 1424                 mac_syncache_destroy(&maclabel);
 1425 #endif
 1426                 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
 1427                 /* Retransmit SYN|ACK and reset retransmit count. */
 1428                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1429                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1430                             "resetting timer and retransmitting SYN|ACK\n",
 1431                             s, __func__);
 1432                         free(s, M_TCPLOG);
 1433                 }
 1434                 if (syncache_respond(sc, sch, m, TH_SYN|TH_ACK) == 0) {
 1435                         sc->sc_rxmits = 0;
 1436                         syncache_timeout(sc, sch, 1);
 1437                         TCPSTAT_INC(tcps_sndacks);
 1438                         TCPSTAT_INC(tcps_sndtotal);
 1439                 }
 1440                 SCH_UNLOCK(sch);
 1441                 goto donenoprobe;
 1442         }
 1443 
 1444         if (tfo_cookie_valid) {
 1445                 bzero(&scs, sizeof(scs));
 1446                 sc = &scs;
 1447                 goto skip_alloc;
 1448         }
 1449 
 1450         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1451         if (sc == NULL) {
 1452                 /*
 1453                  * The zone allocator couldn't provide more entries.
 1454                  * Treat this as if the cache was full; drop the oldest
 1455                  * entry and insert the new one.
 1456                  */
 1457                 TCPSTAT_INC(tcps_sc_zonefail);
 1458                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) {
 1459                         sch->sch_last_overflow = time_uptime;
 1460                         syncache_drop(sc, sch);
 1461                 }
 1462                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1463                 if (sc == NULL) {
 1464                         if (V_tcp_syncookies) {
 1465                                 bzero(&scs, sizeof(scs));
 1466                                 sc = &scs;
 1467                         } else {
 1468                                 SCH_UNLOCK(sch);
 1469                                 if (ipopts)
 1470                                         (void) m_free(ipopts);
 1471                                 goto done;
 1472                         }
 1473                 }
 1474         }
 1475 
 1476 skip_alloc:
 1477         if (!tfo_cookie_valid && tfo_response_cookie_valid)
 1478                 sc->sc_tfo_cookie = &tfo_response_cookie;
 1479 
 1480         /*
 1481          * Fill in the syncache values.
 1482          */
 1483 #ifdef MAC
 1484         sc->sc_label = maclabel;
 1485 #endif
 1486         sc->sc_cred = cred;
 1487         cred = NULL;
 1488         sc->sc_ipopts = ipopts;
 1489         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1490 #ifdef INET6
 1491         if (!(inc->inc_flags & INC_ISIPV6))
 1492 #endif
 1493         {
 1494                 sc->sc_ip_tos = ip_tos;
 1495                 sc->sc_ip_ttl = ip_ttl;
 1496         }
 1497 #ifdef TCP_OFFLOAD
 1498         sc->sc_tod = tod;
 1499         sc->sc_todctx = todctx;
 1500 #endif
 1501         sc->sc_irs = th->th_seq;
 1502         sc->sc_iss = arc4random();
 1503         sc->sc_flags = 0;
 1504         sc->sc_flowlabel = 0;
 1505 
 1506         /*
 1507          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1508          * win was derived from socket earlier in the function.
 1509          */
 1510         win = imax(win, 0);
 1511         win = imin(win, TCP_MAXWIN);
 1512         sc->sc_wnd = win;
 1513 
 1514         if (V_tcp_do_rfc1323) {
 1515                 /*
 1516                  * A timestamp received in a SYN makes
 1517                  * it ok to send timestamp requests and replies.
 1518                  */
 1519                 if (to->to_flags & TOF_TS) {
 1520                         sc->sc_tsreflect = to->to_tsval;
 1521                         sc->sc_flags |= SCF_TIMESTAMP;
 1522                         sc->sc_tsoff = tcp_new_ts_offset(inc);
 1523                 }
 1524                 if (to->to_flags & TOF_SCALE) {
 1525                         int wscale = 0;
 1526 
 1527                         /*
 1528                          * Pick the smallest possible scaling factor that
 1529                          * will still allow us to scale up to sb_max, aka
 1530                          * kern.ipc.maxsockbuf.
 1531                          *
 1532                          * We do this because there are broken firewalls that
 1533                          * will corrupt the window scale option, leading to
 1534                          * the other endpoint believing that our advertised
 1535                          * window is unscaled.  At scale factors larger than
 1536                          * 5 the unscaled window will drop below 1500 bytes,
 1537                          * leading to serious problems when traversing these
 1538                          * broken firewalls.
 1539                          *
 1540                          * With the default maxsockbuf of 256K, a scale factor
 1541                          * of 3 will be chosen by this algorithm.  Those who
 1542                          * choose a larger maxsockbuf should watch out
 1543                          * for the compatibility problems mentioned above.
 1544                          *
 1545                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1546                          * or <SYN,ACK>) segment itself is never scaled.
 1547                          */
 1548                         while (wscale < TCP_MAX_WINSHIFT &&
 1549                             (TCP_MAXWIN << wscale) < sb_max)
 1550                                 wscale++;
 1551                         sc->sc_requested_r_scale = wscale;
 1552                         sc->sc_requested_s_scale = to->to_wscale;
 1553                         sc->sc_flags |= SCF_WINSCALE;
 1554                 }
 1555         }
 1556 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1557         /*
 1558          * If listening socket requested TCP digests, flag this in the
 1559          * syncache so that syncache_respond() will do the right thing
 1560          * with the SYN+ACK.
 1561          */
 1562         if (ltflags & TF_SIGNATURE)
 1563                 sc->sc_flags |= SCF_SIGNATURE;
 1564 #endif  /* TCP_SIGNATURE */
 1565         if (to->to_flags & TOF_SACKPERM)
 1566                 sc->sc_flags |= SCF_SACK;
 1567         if (to->to_flags & TOF_MSS)
 1568                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1569         if (ltflags & TF_NOOPT)
 1570                 sc->sc_flags |= SCF_NOOPT;
 1571         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1572                 sc->sc_flags |= SCF_ECN;
 1573 
 1574         if (V_tcp_syncookies)
 1575                 sc->sc_iss = syncookie_generate(sch, sc);
 1576 #ifdef INET6
 1577         if (autoflowlabel) {
 1578                 if (V_tcp_syncookies)
 1579                         sc->sc_flowlabel = sc->sc_iss;
 1580                 else
 1581                         sc->sc_flowlabel = ip6_randomflowlabel();
 1582                 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
 1583         }
 1584 #endif
 1585         SCH_UNLOCK(sch);
 1586 
 1587         if (tfo_cookie_valid) {
 1588                 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
 1589                 /* INP_WUNLOCK(inp) will be performed by the caller */
 1590                 rv = 1;
 1591                 goto tfo_expanded;
 1592         }
 1593 
 1594         TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
 1595         /*
 1596          * Do a standard 3-way handshake.
 1597          */
 1598         if (syncache_respond(sc, sch, m, TH_SYN|TH_ACK) == 0) {
 1599                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1600                         syncache_free(sc);
 1601                 else if (sc != &scs)
 1602                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1603                 TCPSTAT_INC(tcps_sndacks);
 1604                 TCPSTAT_INC(tcps_sndtotal);
 1605         } else {
 1606                 if (sc != &scs)
 1607                         syncache_free(sc);
 1608                 TCPSTAT_INC(tcps_sc_dropped);
 1609         }
 1610         goto donenoprobe;
 1611 
 1612 done:
 1613         TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
 1614 donenoprobe:
 1615         if (m) {
 1616                 *lsop = NULL;
 1617                 m_freem(m);
 1618         }
 1619         /*
 1620          * If tfo_pending is not NULL here, then a TFO SYN that did not
 1621          * result in a new socket was processed and the associated pending
 1622          * counter has not yet been decremented.  All such TFO processing paths
 1623          * transit this point.
 1624          */
 1625         if (tfo_pending != NULL)
 1626                 tcp_fastopen_decrement_counter(tfo_pending);
 1627 
 1628 tfo_expanded:
 1629         if (cred != NULL)
 1630                 crfree(cred);
 1631 #ifdef MAC
 1632         if (sc == &scs)
 1633                 mac_syncache_destroy(&maclabel);
 1634 #endif
 1635         return (rv);
 1636 }
 1637 
 1638 /*
 1639  * Send SYN|ACK or ACK to the peer.  Either in response to a peer's segment,
 1640  * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
 1641  */
 1642 static int
 1643 syncache_respond(struct syncache *sc, struct syncache_head *sch,
 1644     const struct mbuf *m0, int flags)
 1645 {
 1646         struct ip *ip = NULL;
 1647         struct mbuf *m;
 1648         struct tcphdr *th = NULL;
 1649         int optlen, error = 0;  /* Make compiler happy */
 1650         u_int16_t hlen, tlen, mssopt;
 1651         struct tcpopt to;
 1652 #ifdef INET6
 1653         struct ip6_hdr *ip6 = NULL;
 1654 #endif
 1655         hlen =
 1656 #ifdef INET6
 1657                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1658 #endif
 1659                 sizeof(struct ip);
 1660         tlen = hlen + sizeof(struct tcphdr);
 1661 
 1662         /* Determine MSS we advertize to other end of connection. */
 1663         mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss);
 1664 
 1665         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1666         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1667             ("syncache: mbuf too small"));
 1668 
 1669         /* Create the IP+TCP header from scratch. */
 1670         m = m_gethdr(M_NOWAIT, MT_DATA);
 1671         if (m == NULL)
 1672                 return (ENOBUFS);
 1673 #ifdef MAC
 1674         mac_syncache_create_mbuf(sc->sc_label, m);
 1675 #endif
 1676         m->m_data += max_linkhdr;
 1677         m->m_len = tlen;
 1678         m->m_pkthdr.len = tlen;
 1679         m->m_pkthdr.rcvif = NULL;
 1680 
 1681 #ifdef INET6
 1682         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1683                 ip6 = mtod(m, struct ip6_hdr *);
 1684                 ip6->ip6_vfc = IPV6_VERSION;
 1685                 ip6->ip6_nxt = IPPROTO_TCP;
 1686                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1687                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1688                 ip6->ip6_plen = htons(tlen - hlen);
 1689                 /* ip6_hlim is set after checksum */
 1690                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1691                 ip6->ip6_flow |= sc->sc_flowlabel;
 1692 
 1693                 th = (struct tcphdr *)(ip6 + 1);
 1694         }
 1695 #endif
 1696 #if defined(INET6) && defined(INET)
 1697         else
 1698 #endif
 1699 #ifdef INET
 1700         {
 1701                 ip = mtod(m, struct ip *);
 1702                 ip->ip_v = IPVERSION;
 1703                 ip->ip_hl = sizeof(struct ip) >> 2;
 1704                 ip->ip_len = htons(tlen);
 1705                 ip->ip_id = 0;
 1706                 ip->ip_off = 0;
 1707                 ip->ip_sum = 0;
 1708                 ip->ip_p = IPPROTO_TCP;
 1709                 ip->ip_src = sc->sc_inc.inc_laddr;
 1710                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1711                 ip->ip_ttl = sc->sc_ip_ttl;
 1712                 ip->ip_tos = sc->sc_ip_tos;
 1713 
 1714                 /*
 1715                  * See if we should do MTU discovery.  Route lookups are
 1716                  * expensive, so we will only unset the DF bit if:
 1717                  *
 1718                  *      1) path_mtu_discovery is disabled
 1719                  *      2) the SCF_UNREACH flag has been set
 1720                  */
 1721                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1722                        ip->ip_off |= htons(IP_DF);
 1723 
 1724                 th = (struct tcphdr *)(ip + 1);
 1725         }
 1726 #endif /* INET */
 1727         th->th_sport = sc->sc_inc.inc_lport;
 1728         th->th_dport = sc->sc_inc.inc_fport;
 1729 
 1730         if (flags & TH_SYN)
 1731                 th->th_seq = htonl(sc->sc_iss);
 1732         else
 1733                 th->th_seq = htonl(sc->sc_iss + 1);
 1734         th->th_ack = htonl(sc->sc_irs + 1);
 1735         th->th_off = sizeof(struct tcphdr) >> 2;
 1736         th->th_x2 = 0;
 1737         th->th_flags = flags;
 1738         th->th_win = htons(sc->sc_wnd);
 1739         th->th_urp = 0;
 1740 
 1741         if ((flags & TH_SYN) && (sc->sc_flags & SCF_ECN)) {
 1742                 th->th_flags |= TH_ECE;
 1743                 TCPSTAT_INC(tcps_ecn_shs);
 1744         }
 1745 
 1746         /* Tack on the TCP options. */
 1747         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1748                 to.to_flags = 0;
 1749 
 1750                 if (flags & TH_SYN) {
 1751                         to.to_mss = mssopt;
 1752                         to.to_flags = TOF_MSS;
 1753                         if (sc->sc_flags & SCF_WINSCALE) {
 1754                                 to.to_wscale = sc->sc_requested_r_scale;
 1755                                 to.to_flags |= TOF_SCALE;
 1756                         }
 1757                         if (sc->sc_flags & SCF_SACK)
 1758                                 to.to_flags |= TOF_SACKPERM;
 1759 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1760                         if (sc->sc_flags & SCF_SIGNATURE)
 1761                                 to.to_flags |= TOF_SIGNATURE;
 1762 #endif
 1763                         if (sc->sc_tfo_cookie) {
 1764                                 to.to_flags |= TOF_FASTOPEN;
 1765                                 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 1766                                 to.to_tfo_cookie = sc->sc_tfo_cookie;
 1767                                 /* don't send cookie again when retransmitting response */
 1768                                 sc->sc_tfo_cookie = NULL;
 1769                         }
 1770                 }
 1771                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1772                         to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
 1773                         to.to_tsecr = sc->sc_tsreflect;
 1774                         to.to_flags |= TOF_TS;
 1775                 }
 1776                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1777 
 1778                 /* Adjust headers by option size. */
 1779                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1780                 m->m_len += optlen;
 1781                 m->m_pkthdr.len += optlen;
 1782 #ifdef INET6
 1783                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1784                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1785                 else
 1786 #endif
 1787                         ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
 1788 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 1789                 if (sc->sc_flags & SCF_SIGNATURE) {
 1790                         KASSERT(to.to_flags & TOF_SIGNATURE,
 1791                             ("tcp_addoptions() didn't set tcp_signature"));
 1792 
 1793                         /* NOTE: to.to_signature is inside of mbuf */
 1794                         if (!TCPMD5_ENABLED() ||
 1795                             TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
 1796                                 m_freem(m);
 1797                                 return (EACCES);
 1798                         }
 1799                 }
 1800 #endif
 1801         } else
 1802                 optlen = 0;
 1803 
 1804         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1805         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1806         /*
 1807          * If we have peer's SYN and it has a flowid, then let's assign it to
 1808          * our SYN|ACK.  ip6_output() and ip_output() will not assign flowid
 1809          * to SYN|ACK due to lack of inp here.
 1810          */
 1811         if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
 1812                 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
 1813                 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
 1814         }
 1815 #ifdef INET6
 1816         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1817                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 1818                 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
 1819                     IPPROTO_TCP, 0);
 1820                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1821 #ifdef TCP_OFFLOAD
 1822                 if (ADDED_BY_TOE(sc)) {
 1823                         struct toedev *tod = sc->sc_tod;
 1824 
 1825                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1826 
 1827                         return (error);
 1828                 }
 1829 #endif
 1830                 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
 1831                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1832         }
 1833 #endif
 1834 #if defined(INET6) && defined(INET)
 1835         else
 1836 #endif
 1837 #ifdef INET
 1838         {
 1839                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1840                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1841                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1842 #ifdef TCP_OFFLOAD
 1843                 if (ADDED_BY_TOE(sc)) {
 1844                         struct toedev *tod = sc->sc_tod;
 1845 
 1846                         error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
 1847 
 1848                         return (error);
 1849                 }
 1850 #endif
 1851                 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
 1852                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1853         }
 1854 #endif
 1855         return (error);
 1856 }
 1857 
 1858 /*
 1859  * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
 1860  * that exceed the capacity of the syncache by avoiding the storage of any
 1861  * of the SYNs we receive.  Syncookies defend against blind SYN flooding
 1862  * attacks where the attacker does not have access to our responses.
 1863  *
 1864  * Syncookies encode and include all necessary information about the
 1865  * connection setup within the SYN|ACK that we send back.  That way we
 1866  * can avoid keeping any local state until the ACK to our SYN|ACK returns
 1867  * (if ever).  Normally the syncache and syncookies are running in parallel
 1868  * with the latter taking over when the former is exhausted.  When matching
 1869  * syncache entry is found the syncookie is ignored.
 1870  *
 1871  * The only reliable information persisting the 3WHS is our initial sequence
 1872  * number ISS of 32 bits.  Syncookies embed a cryptographically sufficient
 1873  * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
 1874  * of our SYN|ACK.  The MAC can be recomputed when the ACK to our SYN|ACK
 1875  * returns and signifies a legitimate connection if it matches the ACK.
 1876  *
 1877  * The available space of 32 bits to store the hash and to encode the SYN
 1878  * option information is very tight and we should have at least 24 bits for
 1879  * the MAC to keep the number of guesses by blind spoofing reasonably high.
 1880  *
 1881  * SYN option information we have to encode to fully restore a connection:
 1882  * MSS: is imporant to chose an optimal segment size to avoid IP level
 1883  *   fragmentation along the path.  The common MSS values can be encoded
 1884  *   in a 3-bit table.  Uncommon values are captured by the next lower value
 1885  *   in the table leading to a slight increase in packetization overhead.
 1886  * WSCALE: is necessary to allow large windows to be used for high delay-
 1887  *   bandwidth product links.  Not scaling the window when it was initially
 1888  *   negotiated is bad for performance as lack of scaling further decreases
 1889  *   the apparent available send window.  We only need to encode the WSCALE
 1890  *   we received from the remote end.  Our end can be recalculated at any
 1891  *   time.  The common WSCALE values can be encoded in a 3-bit table.
 1892  *   Uncommon values are captured by the next lower value in the table
 1893  *   making us under-estimate the available window size halving our
 1894  *   theoretically possible maximum throughput for that connection.
 1895  * SACK: Greatly assists in packet loss recovery and requires 1 bit.
 1896  * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
 1897  *   that are included in all segments on a connection.  We enable them when
 1898  *   the ACK has them.
 1899  *
 1900  * Security of syncookies and attack vectors:
 1901  *
 1902  * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
 1903  * together with the gloabl secret to make it unique per connection attempt.
 1904  * Thus any change of any of those parameters results in a different MAC output
 1905  * in an unpredictable way unless a collision is encountered.  24 bits of the
 1906  * MAC are embedded into the ISS.
 1907  *
 1908  * To prevent replay attacks two rotating global secrets are updated with a
 1909  * new random value every 15 seconds.  The life-time of a syncookie is thus
 1910  * 15-30 seconds.
 1911  *
 1912  * Vector 1: Attacking the secret.  This requires finding a weakness in the
 1913  * MAC itself or the way it is used here.  The attacker can do a chosen plain
 1914  * text attack by varying and testing the all parameters under his control.
 1915  * The strength depends on the size and randomness of the secret, and the
 1916  * cryptographic security of the MAC function.  Due to the constant updating
 1917  * of the secret the attacker has at most 29.999 seconds to find the secret
 1918  * and launch spoofed connections.  After that he has to start all over again.
 1919  *
 1920  * Vector 2: Collision attack on the MAC of a single ACK.  With a 24 bit MAC
 1921  * size an average of 4,823 attempts are required for a 50% chance of success
 1922  * to spoof a single syncookie (birthday collision paradox).  However the
 1923  * attacker is blind and doesn't know if one of his attempts succeeded unless
 1924  * he has a side channel to interfere success from.  A single connection setup
 1925  * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
 1926  * This many attempts are required for each one blind spoofed connection.  For
 1927  * every additional spoofed connection he has to launch another N attempts.
 1928  * Thus for a sustained rate 100 spoofed connections per second approximately
 1929  * 1,800,000 packets per second would have to be sent.
 1930  *
 1931  * NB: The MAC function should be fast so that it doesn't become a CPU
 1932  * exhaustion attack vector itself.
 1933  *
 1934  * References:
 1935  *  RFC4987 TCP SYN Flooding Attacks and Common Mitigations
 1936  *  SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
 1937  *   http://cr.yp.to/syncookies.html    (overview)
 1938  *   http://cr.yp.to/syncookies/archive (details)
 1939  *
 1940  *
 1941  * Schematic construction of a syncookie enabled Initial Sequence Number:
 1942  *  0        1         2         3
 1943  *  12345678901234567890123456789012
 1944  * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
 1945  *
 1946  *  x 24 MAC (truncated)
 1947  *  W  3 Send Window Scale index
 1948  *  M  3 MSS index
 1949  *  S  1 SACK permitted
 1950  *  P  1 Odd/even secret
 1951  */
 1952 
 1953 /*
 1954  * Distribution and probability of certain MSS values.  Those in between are
 1955  * rounded down to the next lower one.
 1956  * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
 1957  *                            .2%  .3%   5%    7%    7%    20%   15%   45%
 1958  */
 1959 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
 1960 
 1961 /*
 1962  * Distribution and probability of certain WSCALE values.  We have to map the
 1963  * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
 1964  * bits based on prevalence of certain values.  Where we don't have an exact
 1965  * match for are rounded down to the next lower one letting us under-estimate
 1966  * the true available window.  At the moment this would happen only for the
 1967  * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
 1968  * and window size).  The absence of the WSCALE option (no scaling in either
 1969  * direction) is encoded with index zero.
 1970  * [WSCALE values histograms, Allman, 2012]
 1971  *                            X 10 10 35  5  6 14 10%   by host
 1972  *                            X 11  4  5  5 18 49  3%   by connections
 1973  */
 1974 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
 1975 
 1976 /*
 1977  * Compute the MAC for the SYN cookie.  SIPHASH-2-4 is chosen for its speed
 1978  * and good cryptographic properties.
 1979  */
 1980 static uint32_t
 1981 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
 1982     uint8_t *secbits, uintptr_t secmod)
 1983 {
 1984         SIPHASH_CTX ctx;
 1985         uint32_t siphash[2];
 1986 
 1987         SipHash24_Init(&ctx);
 1988         SipHash_SetKey(&ctx, secbits);
 1989         switch (inc->inc_flags & INC_ISIPV6) {
 1990 #ifdef INET
 1991         case 0:
 1992                 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
 1993                 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
 1994                 break;
 1995 #endif
 1996 #ifdef INET6
 1997         case INC_ISIPV6:
 1998                 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
 1999                 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
 2000                 break;
 2001 #endif
 2002         }
 2003         SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
 2004         SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
 2005         SipHash_Update(&ctx, &irs, sizeof(irs));
 2006         SipHash_Update(&ctx, &flags, sizeof(flags));
 2007         SipHash_Update(&ctx, &secmod, sizeof(secmod));
 2008         SipHash_Final((u_int8_t *)&siphash, &ctx);
 2009 
 2010         return (siphash[0] ^ siphash[1]);
 2011 }
 2012 
 2013 static tcp_seq
 2014 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
 2015 {
 2016         u_int i, secbit, wscale;
 2017         uint32_t iss, hash;
 2018         uint8_t *secbits;
 2019         union syncookie cookie;
 2020 
 2021         SCH_LOCK_ASSERT(sch);
 2022 
 2023         cookie.cookie = 0;
 2024 
 2025         /* Map our computed MSS into the 3-bit index. */
 2026         for (i = nitems(tcp_sc_msstab) - 1;
 2027              tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
 2028              i--)
 2029                 ;
 2030         cookie.flags.mss_idx = i;
 2031 
 2032         /*
 2033          * Map the send window scale into the 3-bit index but only if
 2034          * the wscale option was received.
 2035          */
 2036         if (sc->sc_flags & SCF_WINSCALE) {
 2037                 wscale = sc->sc_requested_s_scale;
 2038                 for (i = nitems(tcp_sc_wstab) - 1;
 2039                     tcp_sc_wstab[i] > wscale && i > 0;
 2040                      i--)
 2041                         ;
 2042                 cookie.flags.wscale_idx = i;
 2043         }
 2044 
 2045         /* Can we do SACK? */
 2046         if (sc->sc_flags & SCF_SACK)
 2047                 cookie.flags.sack_ok = 1;
 2048 
 2049         /* Which of the two secrets to use. */
 2050         secbit = sch->sch_sc->secret.oddeven & 0x1;
 2051         cookie.flags.odd_even = secbit;
 2052 
 2053         secbits = sch->sch_sc->secret.key[secbit];
 2054         hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
 2055             (uintptr_t)sch);
 2056 
 2057         /*
 2058          * Put the flags into the hash and XOR them to get better ISS number
 2059          * variance.  This doesn't enhance the cryptographic strength and is
 2060          * done to prevent the 8 cookie bits from showing up directly on the
 2061          * wire.
 2062          */
 2063         iss = hash & ~0xff;
 2064         iss |= cookie.cookie ^ (hash >> 24);
 2065 
 2066         TCPSTAT_INC(tcps_sc_sendcookie);
 2067         return (iss);
 2068 }
 2069 
 2070 static struct syncache *
 2071 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 2072     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2073     struct socket *lso)
 2074 {
 2075         uint32_t hash;
 2076         uint8_t *secbits;
 2077         tcp_seq ack, seq;
 2078         int wnd, wscale = 0;
 2079         union syncookie cookie;
 2080 
 2081         SCH_LOCK_ASSERT(sch);
 2082 
 2083         /*
 2084          * Pull information out of SYN-ACK/ACK and revert sequence number
 2085          * advances.
 2086          */
 2087         ack = th->th_ack - 1;
 2088         seq = th->th_seq - 1;
 2089 
 2090         /*
 2091          * Unpack the flags containing enough information to restore the
 2092          * connection.
 2093          */
 2094         cookie.cookie = (ack & 0xff) ^ (ack >> 24);
 2095 
 2096         /* Which of the two secrets to use. */
 2097         secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
 2098 
 2099         hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
 2100 
 2101         /* The recomputed hash matches the ACK if this was a genuine cookie. */
 2102         if ((ack & ~0xff) != (hash & ~0xff))
 2103                 return (NULL);
 2104 
 2105         /* Fill in the syncache values. */
 2106         sc->sc_flags = 0;
 2107         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 2108         sc->sc_ipopts = NULL;
 2109         
 2110         sc->sc_irs = seq;
 2111         sc->sc_iss = ack;
 2112 
 2113         switch (inc->inc_flags & INC_ISIPV6) {
 2114 #ifdef INET
 2115         case 0:
 2116                 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
 2117                 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
 2118                 break;
 2119 #endif
 2120 #ifdef INET6
 2121         case INC_ISIPV6:
 2122                 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
 2123                         sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
 2124                 break;
 2125 #endif
 2126         }
 2127 
 2128         sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
 2129 
 2130         /* We can simply recompute receive window scale we sent earlier. */
 2131         while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
 2132                 wscale++;
 2133 
 2134         /* Only use wscale if it was enabled in the orignal SYN. */
 2135         if (cookie.flags.wscale_idx > 0) {
 2136                 sc->sc_requested_r_scale = wscale;
 2137                 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
 2138                 sc->sc_flags |= SCF_WINSCALE;
 2139         }
 2140 
 2141         wnd = lso->sol_sbrcv_hiwat;
 2142         wnd = imax(wnd, 0);
 2143         wnd = imin(wnd, TCP_MAXWIN);
 2144         sc->sc_wnd = wnd;
 2145 
 2146         if (cookie.flags.sack_ok)
 2147                 sc->sc_flags |= SCF_SACK;
 2148 
 2149         if (to->to_flags & TOF_TS) {
 2150                 sc->sc_flags |= SCF_TIMESTAMP;
 2151                 sc->sc_tsreflect = to->to_tsval;
 2152                 sc->sc_tsoff = tcp_new_ts_offset(inc);
 2153         }
 2154 
 2155         if (to->to_flags & TOF_SIGNATURE)
 2156                 sc->sc_flags |= SCF_SIGNATURE;
 2157 
 2158         sc->sc_rxmits = 0;
 2159 
 2160         TCPSTAT_INC(tcps_sc_recvcookie);
 2161         return (sc);
 2162 }
 2163 
 2164 #ifdef INVARIANTS
 2165 static int
 2166 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
 2167     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
 2168     struct socket *lso)
 2169 {
 2170         struct syncache scs, *scx;
 2171         char *s;
 2172 
 2173         bzero(&scs, sizeof(scs));
 2174         scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
 2175 
 2176         if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
 2177                 return (0);
 2178 
 2179         if (scx != NULL) {
 2180                 if (sc->sc_peer_mss != scx->sc_peer_mss)
 2181                         log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
 2182                             s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
 2183 
 2184                 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
 2185                         log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
 2186                             s, __func__, sc->sc_requested_r_scale,
 2187                             scx->sc_requested_r_scale);
 2188 
 2189                 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
 2190                         log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
 2191                             s, __func__, sc->sc_requested_s_scale,
 2192                             scx->sc_requested_s_scale);
 2193 
 2194                 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
 2195                         log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
 2196         }
 2197 
 2198         if (s != NULL)
 2199                 free(s, M_TCPLOG);
 2200         return (0);
 2201 }
 2202 #endif /* INVARIANTS */
 2203 
 2204 static void
 2205 syncookie_reseed(void *arg)
 2206 {
 2207         struct tcp_syncache *sc = arg;
 2208         uint8_t *secbits;
 2209         int secbit;
 2210 
 2211         /*
 2212          * Reseeding the secret doesn't have to be protected by a lock.
 2213          * It only must be ensured that the new random values are visible
 2214          * to all CPUs in a SMP environment.  The atomic with release
 2215          * semantics ensures that.
 2216          */
 2217         secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
 2218         secbits = sc->secret.key[secbit];
 2219         arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
 2220         atomic_add_rel_int(&sc->secret.oddeven, 1);
 2221 
 2222         /* Reschedule ourself. */
 2223         callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
 2224 }
 2225 
 2226 /*
 2227  * Exports the syncache entries to userland so that netstat can display
 2228  * them alongside the other sockets.  This function is intended to be
 2229  * called only from tcp_pcblist.
 2230  *
 2231  * Due to concurrency on an active system, the number of pcbs exported
 2232  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 2233  * amount of space the caller allocated for this function to use.
 2234  */
 2235 int
 2236 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 2237 {
 2238         struct xtcpcb xt;
 2239         struct syncache *sc;
 2240         struct syncache_head *sch;
 2241         int count, error, i;
 2242 
 2243         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 2244                 sch = &V_tcp_syncache.hashbase[i];
 2245                 SCH_LOCK(sch);
 2246                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 2247                         if (count >= max_pcbs) {
 2248                                 SCH_UNLOCK(sch);
 2249                                 goto exit;
 2250                         }
 2251                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 2252                                 continue;
 2253                         bzero(&xt, sizeof(xt));
 2254                         xt.xt_len = sizeof(xt);
 2255                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 2256                                 xt.xt_inp.inp_vflag = INP_IPV6;
 2257                         else
 2258                                 xt.xt_inp.inp_vflag = INP_IPV4;
 2259                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
 2260                             sizeof (struct in_conninfo));
 2261                         xt.t_state = TCPS_SYN_RECEIVED;
 2262                         xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
 2263                         xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
 2264                         xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
 2265                         xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
 2266                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 2267                         if (error) {
 2268                                 SCH_UNLOCK(sch);
 2269                                 goto exit;
 2270                         }
 2271                         count++;
 2272                 }
 2273                 SCH_UNLOCK(sch);
 2274         }
 2275 exit:
 2276         *pcbs_exported = count;
 2277         return error;
 2278 }

Cache object: 67035c94c8a328adcf36c5cf0b42bdeb


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]


This page is part of the FreeBSD/Linux Linux Kernel Cross-Reference, and was automatically generated using a modified version of the LXR engine.