The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_syncache.c

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    1 /*-
    2  * Copyright (c) 2001 McAfee, Inc.
    3  * Copyright (c) 2006 Andre Oppermann, Internet Business Solutions AG
    4  * All rights reserved.
    5  *
    6  * This software was developed for the FreeBSD Project by Jonathan Lemon
    7  * and McAfee Research, the Security Research Division of McAfee, Inc. under
    8  * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
    9  * DARPA CHATS research program.
   10  *
   11  * Redistribution and use in source and binary forms, with or without
   12  * modification, are permitted provided that the following conditions
   13  * are met:
   14  * 1. Redistributions of source code must retain the above copyright
   15  *    notice, this list of conditions and the following disclaimer.
   16  * 2. Redistributions in binary form must reproduce the above copyright
   17  *    notice, this list of conditions and the following disclaimer in the
   18  *    documentation and/or other materials provided with the distribution.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   30  * SUCH DAMAGE.
   31  */
   32 
   33 #include <sys/cdefs.h>
   34 __FBSDID("$FreeBSD: releng/7.3/sys/netinet/tcp_syncache.c 196010 2009-08-01 07:09:50Z julian $");
   35 
   36 #include "opt_inet.h"
   37 #include "opt_inet6.h"
   38 #include "opt_ipsec.h"
   39 #include "opt_mac.h"
   40 
   41 #include <sys/param.h>
   42 #include <sys/systm.h>
   43 #include <sys/kernel.h>
   44 #include <sys/sysctl.h>
   45 #include <sys/limits.h>
   46 #include <sys/lock.h>
   47 #include <sys/mutex.h>
   48 #include <sys/malloc.h>
   49 #include <sys/mbuf.h>
   50 #include <sys/md5.h>
   51 #include <sys/proc.h>           /* for proc0 declaration */
   52 #include <sys/random.h>
   53 #include <sys/socket.h>
   54 #include <sys/socketvar.h>
   55 #include <sys/syslog.h>
   56 #include <sys/ucred.h>
   57 
   58 #include <vm/uma.h>
   59 
   60 #include <net/if.h>
   61 #include <net/route.h>
   62 
   63 #include <netinet/in.h>
   64 #include <netinet/in_systm.h>
   65 #include <netinet/ip.h>
   66 #include <netinet/in_var.h>
   67 #include <netinet/in_pcb.h>
   68 #include <netinet/ip_var.h>
   69 #include <netinet/ip_options.h>
   70 #ifdef INET6
   71 #include <netinet/ip6.h>
   72 #include <netinet/icmp6.h>
   73 #include <netinet6/nd6.h>
   74 #include <netinet6/ip6_var.h>
   75 #include <netinet6/in6_pcb.h>
   76 #endif
   77 #include <netinet/tcp.h>
   78 #include <netinet/tcp_fsm.h>
   79 #include <netinet/tcp_seq.h>
   80 #include <netinet/tcp_timer.h>
   81 #include <netinet/tcp_var.h>
   82 #include <netinet/tcp_syncache.h>
   83 #include <netinet/tcp_offload.h>
   84 #ifdef INET6
   85 #include <netinet6/tcp6_var.h>
   86 #endif
   87 
   88 #ifdef IPSEC
   89 #include <netipsec/ipsec.h>
   90 #ifdef INET6
   91 #include <netipsec/ipsec6.h>
   92 #endif
   93 #include <netipsec/key.h>
   94 #endif /*IPSEC*/
   95 
   96 #include <machine/in_cksum.h>
   97 
   98 #include <security/mac/mac_framework.h>
   99 
  100 static int tcp_syncookies = 1;
  101 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
  102     &tcp_syncookies, 0,
  103     "Use TCP SYN cookies if the syncache overflows");
  104 
  105 static int tcp_syncookiesonly = 0;
  106 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
  107     &tcp_syncookiesonly, 0,
  108     "Use only TCP SYN cookies");
  109 
  110 #define SYNCOOKIE_SECRET_SIZE   8       /* dwords */
  111 #define SYNCOOKIE_LIFETIME      16      /* seconds */
  112 
  113 struct syncache {
  114         TAILQ_ENTRY(syncache)   sc_hash;
  115         struct          in_conninfo sc_inc;     /* addresses */
  116         int             sc_rxttime;             /* retransmit time */
  117         u_int16_t       sc_rxmits;              /* retransmit counter */
  118         u_int32_t       sc_tsreflect;           /* timestamp to reflect */
  119         u_int32_t       sc_ts;                  /* our timestamp to send */
  120         u_int32_t       sc_tsoff;               /* ts offset w/ syncookies */
  121         u_int32_t       sc_flowlabel;           /* IPv6 flowlabel */
  122         tcp_seq         sc_irs;                 /* seq from peer */
  123         tcp_seq         sc_iss;                 /* our ISS */
  124         struct          mbuf *sc_ipopts;        /* source route */
  125         u_int16_t       sc_peer_mss;            /* peer's MSS */
  126         u_int16_t       sc_wnd;                 /* advertised window */
  127         u_int8_t        sc_ip_ttl;              /* IPv4 TTL */
  128         u_int8_t        sc_ip_tos;              /* IPv4 TOS */
  129         u_int8_t        sc_requested_s_scale:4,
  130                         sc_requested_r_scale:4;
  131         u_int8_t        sc_flags;
  132 #ifndef TCP_OFFLOAD_DISABLE
  133         struct toe_usrreqs *sc_tu;              /* TOE operations */
  134         void            *sc_toepcb;             /* TOE protocol block */
  135 #endif                  
  136 #ifdef MAC
  137         struct label    *sc_label;              /* MAC label reference */
  138 #endif
  139         struct ucred    *sc_cred;               /* cred cache for jail checks */
  140 };
  141 
  142 /*
  143  * Flags for the sc_flags field.
  144  */
  145 #define SCF_NOOPT       0x01                    /* no TCP options */
  146 #define SCF_WINSCALE    0x02                    /* negotiated window scaling */
  147 #define SCF_TIMESTAMP   0x04                    /* negotiated timestamps */
  148                                                 /* MSS is implicit */
  149 #define SCF_UNREACH     0x10                    /* icmp unreachable received */
  150 #define SCF_SIGNATURE   0x20                    /* send MD5 digests */
  151 #define SCF_SACK        0x80                    /* send SACK option */
  152 
  153 #ifdef TCP_OFFLOAD_DISABLE
  154 #define TOEPCB_ISSET(sc) (0)
  155 #else
  156 #define TOEPCB_ISSET(sc) ((sc)->sc_toepcb != NULL)
  157 #endif
  158 
  159 
  160 struct syncache_head {
  161         struct mtx      sch_mtx;
  162         TAILQ_HEAD(sch_head, syncache)  sch_bucket;
  163         struct callout  sch_timer;
  164         int             sch_nextc;
  165         u_int           sch_length;
  166         u_int           sch_oddeven;
  167         u_int32_t       sch_secbits_odd[SYNCOOKIE_SECRET_SIZE];
  168         u_int32_t       sch_secbits_even[SYNCOOKIE_SECRET_SIZE];
  169         u_int           sch_reseed;             /* time_uptime, seconds */
  170 };
  171 
  172 static void      syncache_drop(struct syncache *, struct syncache_head *);
  173 static void      syncache_free(struct syncache *);
  174 static void      syncache_insert(struct syncache *, struct syncache_head *);
  175 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
  176 static int       syncache_respond(struct syncache *);
  177 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  178                     struct mbuf *m);
  179 static void      syncache_timeout(struct syncache *sc, struct syncache_head *sch,
  180                     int docallout);
  181 static void      syncache_timer(void *);
  182 static void      syncookie_generate(struct syncache_head *, struct syncache *,
  183                     u_int32_t *);
  184 static struct syncache
  185                 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
  186                     struct syncache *, struct tcpopt *, struct tcphdr *,
  187                     struct socket *);
  188 
  189 /*
  190  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  191  * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
  192  * the odds are that the user has given up attempting to connect by then.
  193  */
  194 #define SYNCACHE_MAXREXMTS              3
  195 
  196 /* Arbitrary values */
  197 #define TCP_SYNCACHE_HASHSIZE           512
  198 #define TCP_SYNCACHE_BUCKETLIMIT        30
  199 
  200 struct tcp_syncache {
  201         struct  syncache_head *hashbase;
  202         uma_zone_t zone;
  203         u_int   hashsize;
  204         u_int   hashmask;
  205         u_int   bucket_limit;
  206         u_int   cache_count;            /* XXX: unprotected */
  207         u_int   cache_limit;
  208         u_int   rexmt_limit;
  209         u_int   hash_secret;
  210 };
  211 static struct tcp_syncache tcp_syncache;
  212 
  213 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
  214 
  215 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
  216      &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
  217 
  218 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
  219      &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
  220 
  221 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
  222      &tcp_syncache.cache_count, 0, "Current number of entries in syncache");
  223 
  224 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
  225      &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
  226 
  227 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
  228      &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
  229 
  230 int     tcp_sc_rst_sock_fail = 1;
  231 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, CTLFLAG_RW,
  232      &tcp_sc_rst_sock_fail, 0, "Send reset on socket allocation failure");
  233 
  234 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  235 
  236 #define SYNCACHE_HASH(inc, mask)                                        \
  237         ((tcp_syncache.hash_secret ^                                    \
  238           (inc)->inc_faddr.s_addr ^                                     \
  239           ((inc)->inc_faddr.s_addr >> 16) ^                             \
  240           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  241 
  242 #define SYNCACHE_HASH6(inc, mask)                                       \
  243         ((tcp_syncache.hash_secret ^                                    \
  244           (inc)->inc6_faddr.s6_addr32[0] ^                              \
  245           (inc)->inc6_faddr.s6_addr32[3] ^                              \
  246           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  247 
  248 #define ENDPTS_EQ(a, b) (                                               \
  249         (a)->ie_fport == (b)->ie_fport &&                               \
  250         (a)->ie_lport == (b)->ie_lport &&                               \
  251         (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr &&                 \
  252         (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr                    \
  253 )
  254 
  255 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
  256 
  257 #define SCH_LOCK(sch)           mtx_lock(&(sch)->sch_mtx)
  258 #define SCH_UNLOCK(sch)         mtx_unlock(&(sch)->sch_mtx)
  259 #define SCH_LOCK_ASSERT(sch)    mtx_assert(&(sch)->sch_mtx, MA_OWNED)
  260 
  261 /*
  262  * Requires the syncache entry to be already removed from the bucket list.
  263  */
  264 static void
  265 syncache_free(struct syncache *sc)
  266 {
  267         if (sc->sc_ipopts)
  268                 (void) m_free(sc->sc_ipopts);
  269         if (sc->sc_cred)
  270                 crfree(sc->sc_cred);
  271 #ifdef MAC
  272         mac_destroy_syncache(&sc->sc_label);
  273 #endif
  274 
  275         uma_zfree(tcp_syncache.zone, sc);
  276 }
  277 
  278 void
  279 syncache_init(void)
  280 {
  281         int i;
  282 
  283         tcp_syncache.cache_count = 0;
  284         tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  285         tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  286         tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  287         tcp_syncache.hash_secret = arc4random();
  288 
  289         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  290             &tcp_syncache.hashsize);
  291         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  292             &tcp_syncache.bucket_limit);
  293         if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) {
  294                 printf("WARNING: syncache hash size is not a power of 2.\n");
  295                 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  296         }
  297         tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
  298 
  299         /* Set limits. */
  300         tcp_syncache.cache_limit =
  301             tcp_syncache.hashsize * tcp_syncache.bucket_limit;
  302         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  303             &tcp_syncache.cache_limit);
  304 
  305         /* Allocate the hash table. */
  306         MALLOC(tcp_syncache.hashbase, struct syncache_head *,
  307             tcp_syncache.hashsize * sizeof(struct syncache_head),
  308             M_SYNCACHE, M_WAITOK | M_ZERO);
  309 
  310         /* Initialize the hash buckets. */
  311         for (i = 0; i < tcp_syncache.hashsize; i++) {
  312                 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket);
  313                 mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
  314                          NULL, MTX_DEF);
  315                 callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer,
  316                          &tcp_syncache.hashbase[i].sch_mtx, 0);
  317                 tcp_syncache.hashbase[i].sch_length = 0;
  318         }
  319 
  320         /* Create the syncache entry zone. */
  321         tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  322             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  323         uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit);
  324 }
  325 
  326 /*
  327  * Inserts a syncache entry into the specified bucket row.
  328  * Locks and unlocks the syncache_head autonomously.
  329  */
  330 static void
  331 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  332 {
  333         struct syncache *sc2;
  334 
  335         SCH_LOCK(sch);
  336 
  337         /*
  338          * Make sure that we don't overflow the per-bucket limit.
  339          * If the bucket is full, toss the oldest element.
  340          */
  341         if (sch->sch_length >= tcp_syncache.bucket_limit) {
  342                 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
  343                         ("sch->sch_length incorrect"));
  344                 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
  345                 syncache_drop(sc2, sch);
  346                 tcpstat.tcps_sc_bucketoverflow++;
  347         }
  348 
  349         /* Put it into the bucket. */
  350         TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
  351         sch->sch_length++;
  352 
  353         /* Reinitialize the bucket row's timer. */
  354         if (sch->sch_length == 1)
  355                 sch->sch_nextc = ticks + INT_MAX;
  356         syncache_timeout(sc, sch, 1);
  357 
  358         SCH_UNLOCK(sch);
  359 
  360         tcp_syncache.cache_count++;
  361         tcpstat.tcps_sc_added++;
  362 }
  363 
  364 /*
  365  * Remove and free entry from syncache bucket row.
  366  * Expects locked syncache head.
  367  */
  368 static void
  369 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  370 {
  371 
  372         SCH_LOCK_ASSERT(sch);
  373 
  374         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  375         sch->sch_length--;
  376 
  377 #ifndef TCP_OFFLOAD_DISABLE
  378         if (sc->sc_tu)
  379                 sc->sc_tu->tu_syncache_event(TOE_SC_DROP, sc->sc_toepcb);
  380 #endif              
  381         syncache_free(sc);
  382         tcp_syncache.cache_count--;
  383 }
  384 
  385 /*
  386  * Engage/reengage time on bucket row.
  387  */
  388 static void
  389 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
  390 {
  391         sc->sc_rxttime = ticks +
  392                 TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]);
  393         sc->sc_rxmits++;
  394         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
  395                 sch->sch_nextc = sc->sc_rxttime;
  396                 if (docallout)
  397                         callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
  398                             syncache_timer, (void *)sch);
  399         }
  400 }
  401 
  402 /*
  403  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  404  * If we have retransmitted an entry the maximum number of times, expire it.
  405  * One separate timer for each bucket row.
  406  */
  407 static void
  408 syncache_timer(void *xsch)
  409 {
  410         struct syncache_head *sch = (struct syncache_head *)xsch;
  411         struct syncache *sc, *nsc;
  412         int tick = ticks;
  413         char *s;
  414 
  415         /* NB: syncache_head has already been locked by the callout. */
  416         SCH_LOCK_ASSERT(sch);
  417 
  418         /*
  419          * In the following cycle we may remove some entries and/or
  420          * advance some timeouts, so re-initialize the bucket timer.
  421          */
  422         sch->sch_nextc = tick + INT_MAX;
  423 
  424         TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
  425                 /*
  426                  * We do not check if the listen socket still exists
  427                  * and accept the case where the listen socket may be
  428                  * gone by the time we resend the SYN/ACK.  We do
  429                  * not expect this to happens often. If it does,
  430                  * then the RST will be sent by the time the remote
  431                  * host does the SYN/ACK->ACK.
  432                  */
  433                 if (TSTMP_GT(sc->sc_rxttime, tick)) {
  434                         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
  435                                 sch->sch_nextc = sc->sc_rxttime;
  436                         continue;
  437                 }
  438 
  439                 if (sc->sc_rxmits > tcp_syncache.rexmt_limit) {
  440                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  441                                 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
  442                                     "giving up and removing syncache entry\n",
  443                                     s, __func__);
  444                                 free(s, M_TCPLOG);
  445                         }
  446                         syncache_drop(sc, sch);
  447                         tcpstat.tcps_sc_stale++;
  448                         continue;
  449                 }
  450                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  451                         log(LOG_DEBUG, "%s; %s: Response timeout, "
  452                             "retransmitting (%u) SYN|ACK\n",
  453                             s, __func__, sc->sc_rxmits);
  454                         free(s, M_TCPLOG);
  455                 }
  456 
  457                 (void) syncache_respond(sc);
  458                 tcpstat.tcps_sc_retransmitted++;
  459                 syncache_timeout(sc, sch, 0);
  460         }
  461         if (!TAILQ_EMPTY(&(sch)->sch_bucket))
  462                 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
  463                         syncache_timer, (void *)(sch));
  464 }
  465 
  466 /*
  467  * Find an entry in the syncache.
  468  * Returns always with locked syncache_head plus a matching entry or NULL.
  469  */
  470 struct syncache *
  471 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  472 {
  473         struct syncache *sc;
  474         struct syncache_head *sch;
  475 
  476 #ifdef INET6
  477         if (inc->inc_flags & INC_ISIPV6) {
  478                 sch = &tcp_syncache.hashbase[
  479                     SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
  480                 *schp = sch;
  481 
  482                 SCH_LOCK(sch);
  483 
  484                 /* Circle through bucket row to find matching entry. */
  485                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  486                         if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  487                                 return (sc);
  488                 }
  489         } else
  490 #endif
  491         {
  492                 sch = &tcp_syncache.hashbase[
  493                     SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
  494                 *schp = sch;
  495 
  496                 SCH_LOCK(sch);
  497 
  498                 /* Circle through bucket row to find matching entry. */
  499                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  500 #ifdef INET6
  501                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
  502                                 continue;
  503 #endif
  504                         if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  505                                 return (sc);
  506                 }
  507         }
  508         SCH_LOCK_ASSERT(*schp);
  509         return (NULL);                  /* always returns with locked sch */
  510 }
  511 
  512 /*
  513  * This function is called when we get a RST for a
  514  * non-existent connection, so that we can see if the
  515  * connection is in the syn cache.  If it is, zap it.
  516  */
  517 void
  518 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
  519 {
  520         struct syncache *sc;
  521         struct syncache_head *sch;
  522         char *s = NULL;
  523 
  524         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  525         SCH_LOCK_ASSERT(sch);
  526 
  527         /*
  528          * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
  529          * See RFC 793 page 65, section SEGMENT ARRIVES.
  530          */
  531         if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
  532                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  533                         log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
  534                             "FIN flag set, segment ignored\n", s, __func__);
  535                 tcpstat.tcps_badrst++;
  536                 goto done;
  537         }
  538 
  539         /*
  540          * No corresponding connection was found in syncache.
  541          * If syncookies are enabled and possibly exclusively
  542          * used, or we are under memory pressure, a valid RST
  543          * may not find a syncache entry.  In that case we're
  544          * done and no SYN|ACK retransmissions will happen.
  545          * Otherwise the the RST was misdirected or spoofed.
  546          */
  547         if (sc == NULL) {
  548                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  549                         log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
  550                             "syncache entry (possibly syncookie only), "
  551                             "segment ignored\n", s, __func__);
  552                 tcpstat.tcps_badrst++;
  553                 goto done;
  554         }
  555 
  556         /*
  557          * If the RST bit is set, check the sequence number to see
  558          * if this is a valid reset segment.
  559          * RFC 793 page 37:
  560          *   In all states except SYN-SENT, all reset (RST) segments
  561          *   are validated by checking their SEQ-fields.  A reset is
  562          *   valid if its sequence number is in the window.
  563          *
  564          *   The sequence number in the reset segment is normally an
  565          *   echo of our outgoing acknowlegement numbers, but some hosts
  566          *   send a reset with the sequence number at the rightmost edge
  567          *   of our receive window, and we have to handle this case.
  568          */
  569         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  570             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  571                 syncache_drop(sc, sch);
  572                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  573                         log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
  574                             "connection attempt aborted by remote endpoint\n",
  575                             s, __func__);
  576                 tcpstat.tcps_sc_reset++;
  577         } else {
  578                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  579                         log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
  580                             "IRS %u (+WND %u), segment ignored\n",
  581                             s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
  582                 tcpstat.tcps_badrst++;
  583         }
  584 
  585 done:
  586         if (s != NULL)
  587                 free(s, M_TCPLOG);
  588         SCH_UNLOCK(sch);
  589 }
  590 
  591 void
  592 syncache_badack(struct in_conninfo *inc)
  593 {
  594         struct syncache *sc;
  595         struct syncache_head *sch;
  596 
  597         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  598         SCH_LOCK_ASSERT(sch);
  599         if (sc != NULL) {
  600                 syncache_drop(sc, sch);
  601                 tcpstat.tcps_sc_badack++;
  602         }
  603         SCH_UNLOCK(sch);
  604 }
  605 
  606 void
  607 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
  608 {
  609         struct syncache *sc;
  610         struct syncache_head *sch;
  611 
  612         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  613         SCH_LOCK_ASSERT(sch);
  614         if (sc == NULL)
  615                 goto done;
  616 
  617         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  618         if (ntohl(th->th_seq) != sc->sc_iss)
  619                 goto done;
  620 
  621         /*
  622          * If we've rertransmitted 3 times and this is our second error,
  623          * we remove the entry.  Otherwise, we allow it to continue on.
  624          * This prevents us from incorrectly nuking an entry during a
  625          * spurious network outage.
  626          *
  627          * See tcp_notify().
  628          */
  629         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
  630                 sc->sc_flags |= SCF_UNREACH;
  631                 goto done;
  632         }
  633         syncache_drop(sc, sch);
  634         tcpstat.tcps_sc_unreach++;
  635 done:
  636         SCH_UNLOCK(sch);
  637 }
  638 
  639 /*
  640  * Build a new TCP socket structure from a syncache entry.
  641  */
  642 static struct socket *
  643 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  644 {
  645         struct inpcb *inp = NULL;
  646         struct socket *so;
  647         struct tcpcb *tp;
  648         char *s;
  649 
  650         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  651 
  652         /*
  653          * Ok, create the full blown connection, and set things up
  654          * as they would have been set up if we had created the
  655          * connection when the SYN arrived.  If we can't create
  656          * the connection, abort it.
  657          */
  658         so = sonewconn(lso, SS_ISCONNECTED);
  659         if (so == NULL) {
  660                 /*
  661                  * Drop the connection; we will either send a RST or
  662                  * have the peer retransmit its SYN again after its
  663                  * RTO and try again.
  664                  */
  665                 tcpstat.tcps_listendrop++;
  666                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  667                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  668                             "due to limits or memory shortage\n",
  669                             s, __func__);
  670                         free(s, M_TCPLOG);
  671                 }
  672                 goto abort2;
  673         }
  674 #ifdef MAC
  675         SOCK_LOCK(so);
  676         mac_set_socket_peer_from_mbuf(m, so);
  677         SOCK_UNLOCK(so);
  678 #endif
  679 
  680         inp = sotoinpcb(so);
  681         inp->inp_inc.inc_fibnum = so->so_fibnum;
  682         INP_WLOCK(inp);
  683 
  684         /* Insert new socket into PCB hash list. */
  685         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  686 #ifdef INET6
  687         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  688                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  689         } else {
  690                 inp->inp_vflag &= ~INP_IPV6;
  691                 inp->inp_vflag |= INP_IPV4;
  692 #endif
  693                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  694 #ifdef INET6
  695         }
  696 #endif
  697         inp->inp_lport = sc->sc_inc.inc_lport;
  698         if (in_pcbinshash(inp) != 0) {
  699                 /*
  700                  * Undo the assignments above if we failed to
  701                  * put the PCB on the hash lists.
  702                  */
  703 #ifdef INET6
  704                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  705                         inp->in6p_laddr = in6addr_any;
  706                 else
  707 #endif
  708                         inp->inp_laddr.s_addr = INADDR_ANY;
  709                 inp->inp_lport = 0;
  710                 goto abort;
  711         }
  712 #ifdef IPSEC
  713         /* Copy old policy into new socket's. */
  714         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  715                 printf("syncache_socket: could not copy policy\n");
  716 #endif
  717 #ifdef INET6
  718         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  719                 struct inpcb *oinp = sotoinpcb(lso);
  720                 struct in6_addr laddr6;
  721                 struct sockaddr_in6 sin6;
  722                 /*
  723                  * Inherit socket options from the listening socket.
  724                  * Note that in6p_inputopts are not (and should not be)
  725                  * copied, since it stores previously received options and is
  726                  * used to detect if each new option is different than the
  727                  * previous one and hence should be passed to a user.
  728                  * If we copied in6p_inputopts, a user would not be able to
  729                  * receive options just after calling the accept system call.
  730                  */
  731                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  732                 if (oinp->in6p_outputopts)
  733                         inp->in6p_outputopts =
  734                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  735 
  736                 sin6.sin6_family = AF_INET6;
  737                 sin6.sin6_len = sizeof(sin6);
  738                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  739                 sin6.sin6_port = sc->sc_inc.inc_fport;
  740                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  741                 laddr6 = inp->in6p_laddr;
  742                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  743                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  744                 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6,
  745                     thread0.td_ucred)) {
  746                         inp->in6p_laddr = laddr6;
  747                         goto abort;
  748                 }
  749                 /* Override flowlabel from in6_pcbconnect. */
  750                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  751                 inp->inp_flow |= sc->sc_flowlabel;
  752         } else
  753 #endif
  754         {
  755                 struct in_addr laddr;
  756                 struct sockaddr_in sin;
  757 
  758                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  759                 
  760                 if (inp->inp_options == NULL) {
  761                         inp->inp_options = sc->sc_ipopts;
  762                         sc->sc_ipopts = NULL;
  763                 }
  764 
  765                 sin.sin_family = AF_INET;
  766                 sin.sin_len = sizeof(sin);
  767                 sin.sin_addr = sc->sc_inc.inc_faddr;
  768                 sin.sin_port = sc->sc_inc.inc_fport;
  769                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  770                 laddr = inp->inp_laddr;
  771                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  772                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  773                 if (in_pcbconnect(inp, (struct sockaddr *)&sin,
  774                     thread0.td_ucred)) {
  775                         inp->inp_laddr = laddr;
  776                         goto abort;
  777                 }
  778         }
  779         tp = intotcpcb(inp);
  780         tp->t_state = TCPS_SYN_RECEIVED;
  781         tp->iss = sc->sc_iss;
  782         tp->irs = sc->sc_irs;
  783         tcp_rcvseqinit(tp);
  784         tcp_sendseqinit(tp);
  785         tp->snd_wl1 = sc->sc_irs;
  786         tp->snd_max = tp->iss + 1;
  787         tp->snd_nxt = tp->iss + 1;
  788         tp->rcv_up = sc->sc_irs + 1;
  789         tp->rcv_wnd = sc->sc_wnd;
  790         tp->rcv_adv += tp->rcv_wnd;
  791         tp->last_ack_sent = tp->rcv_nxt;
  792 
  793         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  794         if (sc->sc_flags & SCF_NOOPT)
  795                 tp->t_flags |= TF_NOOPT;
  796         else {
  797                 if (sc->sc_flags & SCF_WINSCALE) {
  798                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  799                         tp->snd_scale = sc->sc_requested_s_scale;
  800                         tp->request_r_scale = sc->sc_requested_r_scale;
  801                 }
  802                 if (sc->sc_flags & SCF_TIMESTAMP) {
  803                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  804                         tp->ts_recent = sc->sc_tsreflect;
  805                         tp->ts_recent_age = ticks;
  806                         tp->ts_offset = sc->sc_tsoff;
  807                 }
  808 #ifdef TCP_SIGNATURE
  809                 if (sc->sc_flags & SCF_SIGNATURE)
  810                         tp->t_flags |= TF_SIGNATURE;
  811 #endif
  812                 if (sc->sc_flags & SCF_SACK)
  813                         tp->t_flags |= TF_SACK_PERMIT;
  814         }
  815 
  816         /*
  817          * Set up MSS and get cached values from tcp_hostcache.
  818          * This might overwrite some of the defaults we just set.
  819          */
  820         tcp_mss(tp, sc->sc_peer_mss);
  821 
  822         /*
  823          * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
  824          */
  825         if (sc->sc_rxmits)
  826                 tp->snd_cwnd = tp->t_maxseg;
  827         tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
  828 
  829         INP_WUNLOCK(inp);
  830 
  831         tcpstat.tcps_accepts++;
  832         return (so);
  833 
  834 abort:
  835         INP_WUNLOCK(inp);
  836 abort2:
  837         if (so != NULL)
  838                 soabort(so);
  839         return (NULL);
  840 }
  841 
  842 /*
  843  * This function gets called when we receive an ACK for a
  844  * socket in the LISTEN state.  We look up the connection
  845  * in the syncache, and if its there, we pull it out of
  846  * the cache and turn it into a full-blown connection in
  847  * the SYN-RECEIVED state.
  848  */
  849 int
  850 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  851     struct socket **lsop, struct mbuf *m)
  852 {
  853         struct syncache *sc;
  854         struct syncache_head *sch;
  855         struct syncache scs;
  856         char *s;
  857 
  858         /*
  859          * Global TCP locks are held because we manipulate the PCB lists
  860          * and create a new socket.
  861          */
  862         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  863         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  864             ("%s: can handle only ACK", __func__));
  865 
  866         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  867         SCH_LOCK_ASSERT(sch);
  868         if (sc == NULL) {
  869                 /*
  870                  * There is no syncache entry, so see if this ACK is
  871                  * a returning syncookie.  To do this, first:
  872                  *  A. See if this socket has had a syncache entry dropped in
  873                  *     the past.  We don't want to accept a bogus syncookie
  874                  *     if we've never received a SYN.
  875                  *  B. check that the syncookie is valid.  If it is, then
  876                  *     cobble up a fake syncache entry, and return.
  877                  */
  878                 if (!tcp_syncookies) {
  879                         SCH_UNLOCK(sch);
  880                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  881                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  882                                     "segment rejected (syncookies disabled)\n",
  883                                     s, __func__);
  884                         goto failed;
  885                 }
  886                 bzero(&scs, sizeof(scs));
  887                 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop);
  888                 SCH_UNLOCK(sch);
  889                 if (sc == NULL) {
  890                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  891                                 log(LOG_DEBUG, "%s; %s: Segment failed "
  892                                     "SYNCOOKIE authentication, segment rejected "
  893                                     "(probably spoofed)\n", s, __func__);
  894                         goto failed;
  895                 }
  896         } else {
  897                 /* Pull out the entry to unlock the bucket row. */
  898                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  899                 sch->sch_length--;
  900                 tcp_syncache.cache_count--;
  901                 SCH_UNLOCK(sch);
  902         }
  903 
  904         /*
  905          * Segment validation:
  906          * ACK must match our initial sequence number + 1 (the SYN|ACK).
  907          */
  908         if (th->th_ack != sc->sc_iss + 1 && !TOEPCB_ISSET(sc)) {
  909                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  910                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
  911                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
  912                 goto failed;
  913         }
  914 
  915         /*
  916          * The SEQ must fall in the window starting at the received
  917          * initial receive sequence number + 1 (the SYN).
  918          */
  919         if ((SEQ_LEQ(th->th_seq, sc->sc_irs) ||
  920             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) &&
  921             !TOEPCB_ISSET(sc)) {
  922                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  923                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
  924                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
  925                 goto failed;
  926         }
  927 #if 0
  928         /*
  929          * If timestamps were present in the SYN and we accepted
  930          * them in our SYN|ACK we require them to be present from
  931          * now on.  And vice versa.
  932          *
  933          * Unfortunately, during testing of 7.0 some users found
  934          * network devices that violate this constraint, so it must
  935          * be disabled.
  936          */
  937         if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
  938                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  939                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
  940                             "segment rejected\n", s, __func__);
  941                 goto failed;
  942         }
  943 #endif
  944         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
  945                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  946                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
  947                             "segment rejected\n", s, __func__);
  948                 goto failed;
  949         }
  950         /*
  951          * If timestamps were negotiated the reflected timestamp
  952          * must be equal to what we actually sent in the SYN|ACK.
  953          */
  954         if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts &&
  955             !TOEPCB_ISSET(sc)) {
  956                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  957                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
  958                             "segment rejected\n",
  959                             s, __func__, to->to_tsecr, sc->sc_ts);
  960                 goto failed;
  961         }
  962 
  963         *lsop = syncache_socket(sc, *lsop, m);
  964 
  965         if (*lsop == NULL)
  966                 tcpstat.tcps_sc_aborted++;
  967         else
  968                 tcpstat.tcps_sc_completed++;
  969 
  970 /* how do we find the inp for the new socket? */
  971         if (sc != &scs)
  972                 syncache_free(sc);
  973         return (1);
  974 failed:
  975         if (sc != NULL && sc != &scs)
  976                 syncache_free(sc);
  977         if (s != NULL)
  978                 free(s, M_TCPLOG);
  979         *lsop = NULL;
  980         return (0);
  981 }
  982 
  983 int
  984 tcp_offload_syncache_expand(struct in_conninfo *inc, struct tcpopt *to,
  985     struct tcphdr *th, struct socket **lsop, struct mbuf *m)
  986 {
  987         int rc;
  988         
  989         INP_INFO_WLOCK(&tcbinfo);
  990         rc = syncache_expand(inc, to, th, lsop, m);
  991         INP_INFO_WUNLOCK(&tcbinfo);
  992 
  993         return (rc);
  994 }
  995 
  996 /*
  997  * Given a LISTEN socket and an inbound SYN request, add
  998  * this to the syn cache, and send back a segment:
  999  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 1000  * to the source.
 1001  *
 1002  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
 1003  * Doing so would require that we hold onto the data and deliver it
 1004  * to the application.  However, if we are the target of a SYN-flood
 1005  * DoS attack, an attacker could send data which would eventually
 1006  * consume all available buffer space if it were ACKed.  By not ACKing
 1007  * the data, we avoid this DoS scenario.
 1008  */
 1009 static void
 1010 _syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1011     struct inpcb *inp, struct socket **lsop, struct mbuf *m,
 1012     struct toe_usrreqs *tu, void *toepcb)
 1013 {
 1014         struct tcpcb *tp;
 1015         struct socket *so;
 1016         struct syncache *sc = NULL;
 1017         struct syncache_head *sch;
 1018         struct mbuf *ipopts = NULL;
 1019         u_int32_t flowtmp;
 1020         int win, sb_hiwat, ip_ttl, ip_tos, noopt;
 1021         char *s;
 1022 #ifdef INET6
 1023         int autoflowlabel = 0;
 1024 #endif
 1025 #ifdef MAC
 1026         struct label *maclabel;
 1027 #endif
 1028         struct syncache scs;
 1029         struct ucred *cred;
 1030 
 1031         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 1032         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1033         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1034             ("%s: unexpected tcp flags", __func__));
 1035 
 1036         /*
 1037          * Combine all so/tp operations very early to drop the INP lock as
 1038          * soon as possible.
 1039          */
 1040         so = *lsop;
 1041         tp = sototcpcb(so);
 1042         cred = crhold(so->so_cred);
 1043 
 1044 #ifdef INET6
 1045         if ((inc->inc_flags & INC_ISIPV6) &&
 1046             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1047                 autoflowlabel = 1;
 1048 #endif
 1049         ip_ttl = inp->inp_ip_ttl;
 1050         ip_tos = inp->inp_ip_tos;
 1051         win = sbspace(&so->so_rcv);
 1052         sb_hiwat = so->so_rcv.sb_hiwat;
 1053         noopt = (tp->t_flags & TF_NOOPT);
 1054 
 1055         /* By the time we drop the lock these should no longer be used. */
 1056         so = NULL;
 1057         tp = NULL;
 1058 
 1059 #ifdef MAC
 1060         if (mac_init_syncache(&maclabel) != 0) {
 1061                 INP_WUNLOCK(inp);
 1062                 INP_INFO_WUNLOCK(&tcbinfo);
 1063                 goto done;
 1064         } else
 1065                 mac_init_syncache_from_inpcb(maclabel, inp);
 1066 #endif
 1067         INP_WUNLOCK(inp);
 1068         INP_INFO_WUNLOCK(&tcbinfo);
 1069 
 1070         /*
 1071          * Remember the IP options, if any.
 1072          */
 1073 #ifdef INET6
 1074         if (!(inc->inc_flags & INC_ISIPV6))
 1075 #endif
 1076                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1077 
 1078         /*
 1079          * See if we already have an entry for this connection.
 1080          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1081          *
 1082          * XXX: should the syncache be re-initialized with the contents
 1083          * of the new SYN here (which may have different options?)
 1084          *
 1085          * XXX: We do not check the sequence number to see if this is a
 1086          * real retransmit or a new connection attempt.  The question is
 1087          * how to handle such a case; either ignore it as spoofed, or
 1088          * drop the current entry and create a new one?
 1089          */
 1090         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1091         SCH_LOCK_ASSERT(sch);
 1092         if (sc != NULL) {
 1093 #ifndef TCP_OFFLOAD_DISABLE
 1094                 if (sc->sc_tu)
 1095                         sc->sc_tu->tu_syncache_event(TOE_SC_ENTRY_PRESENT,
 1096                             sc->sc_toepcb);
 1097 #endif              
 1098                 tcpstat.tcps_sc_dupsyn++;
 1099                 if (ipopts) {
 1100                         /*
 1101                          * If we were remembering a previous source route,
 1102                          * forget it and use the new one we've been given.
 1103                          */
 1104                         if (sc->sc_ipopts)
 1105                                 (void) m_free(sc->sc_ipopts);
 1106                         sc->sc_ipopts = ipopts;
 1107                 }
 1108                 /*
 1109                  * Update timestamp if present.
 1110                  */
 1111                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1112                         sc->sc_tsreflect = to->to_tsval;
 1113                 else
 1114                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1115 #ifdef MAC
 1116                 /*
 1117                  * Since we have already unconditionally allocated label
 1118                  * storage, free it up.  The syncache entry will already
 1119                  * have an initialized label we can use.
 1120                  */
 1121                 mac_destroy_syncache(&maclabel);
 1122                 KASSERT(sc->sc_label != NULL,
 1123                     ("%s: label not initialized", __func__));
 1124 #endif
 1125                 /* Retransmit SYN|ACK and reset retransmit count. */
 1126                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1127                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1128                             "resetting timer and retransmitting SYN|ACK\n",
 1129                             s, __func__);
 1130                         free(s, M_TCPLOG);
 1131                 }
 1132                 if (!TOEPCB_ISSET(sc) && syncache_respond(sc) == 0) {
 1133                         sc->sc_rxmits = 0;
 1134                         syncache_timeout(sc, sch, 1);
 1135                         tcpstat.tcps_sndacks++;
 1136                         tcpstat.tcps_sndtotal++;
 1137                 }
 1138                 SCH_UNLOCK(sch);
 1139                 goto done;
 1140         }
 1141 
 1142         sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1143         if (sc == NULL) {
 1144                 /*
 1145                  * The zone allocator couldn't provide more entries.
 1146                  * Treat this as if the cache was full; drop the oldest
 1147                  * entry and insert the new one.
 1148                  */
 1149                 tcpstat.tcps_sc_zonefail++;
 1150                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
 1151                         syncache_drop(sc, sch);
 1152                 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1153                 if (sc == NULL) {
 1154                         if (tcp_syncookies) {
 1155                                 bzero(&scs, sizeof(scs));
 1156                                 sc = &scs;
 1157                         } else {
 1158                                 SCH_UNLOCK(sch);
 1159                                 if (ipopts)
 1160                                         (void) m_free(ipopts);
 1161                                 goto done;
 1162                         }
 1163                 }
 1164         }
 1165 
 1166         /*
 1167          * Fill in the syncache values.
 1168          */
 1169 #ifdef MAC
 1170         sc->sc_label = maclabel;
 1171 #endif
 1172         sc->sc_cred = cred;
 1173         cred = NULL;
 1174         sc->sc_ipopts = ipopts;
 1175         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1176 #ifdef INET6
 1177         if (!(inc->inc_flags & INC_ISIPV6))
 1178 #endif
 1179         {
 1180                 sc->sc_ip_tos = ip_tos;
 1181                 sc->sc_ip_ttl = ip_ttl;
 1182         }
 1183 #ifndef TCP_OFFLOAD_DISABLE     
 1184         sc->sc_tu = tu;
 1185         sc->sc_toepcb = toepcb;
 1186 #endif
 1187         sc->sc_irs = th->th_seq;
 1188         sc->sc_iss = arc4random();
 1189         sc->sc_flags = 0;
 1190         sc->sc_flowlabel = 0;
 1191 
 1192         /*
 1193          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1194          * win was derived from socket earlier in the function.
 1195          */
 1196         win = imax(win, 0);
 1197         win = imin(win, TCP_MAXWIN);
 1198         sc->sc_wnd = win;
 1199 
 1200         if (tcp_do_rfc1323) {
 1201                 /*
 1202                  * A timestamp received in a SYN makes
 1203                  * it ok to send timestamp requests and replies.
 1204                  */
 1205                 if (to->to_flags & TOF_TS) {
 1206                         sc->sc_tsreflect = to->to_tsval;
 1207                         sc->sc_ts = ticks;
 1208                         sc->sc_flags |= SCF_TIMESTAMP;
 1209                 }
 1210                 if (to->to_flags & TOF_SCALE) {
 1211                         int wscale = 0;
 1212 
 1213                         /*
 1214                          * Pick the smallest possible scaling factor that
 1215                          * will still allow us to scale up to sb_max, aka
 1216                          * kern.ipc.maxsockbuf.
 1217                          *
 1218                          * We do this because there are broken firewalls that
 1219                          * will corrupt the window scale option, leading to
 1220                          * the other endpoint believing that our advertised
 1221                          * window is unscaled.  At scale factors larger than
 1222                          * 5 the unscaled window will drop below 1500 bytes,
 1223                          * leading to serious problems when traversing these
 1224                          * broken firewalls.
 1225                          *
 1226                          * With the default maxsockbuf of 256K, a scale factor
 1227                          * of 3 will be chosen by this algorithm.  Those who
 1228                          * choose a larger maxsockbuf should watch out
 1229                          * for the compatiblity problems mentioned above.
 1230                          *
 1231                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1232                          * or <SYN,ACK>) segment itself is never scaled.
 1233                          */
 1234                         while (wscale < TCP_MAX_WINSHIFT &&
 1235                             (TCP_MAXWIN << wscale) < sb_max)
 1236                                 wscale++;
 1237                         sc->sc_requested_r_scale = wscale;
 1238                         sc->sc_requested_s_scale = to->to_wscale;
 1239                         sc->sc_flags |= SCF_WINSCALE;
 1240                 }
 1241         }
 1242 #ifdef TCP_SIGNATURE
 1243         /*
 1244          * If listening socket requested TCP digests, and received SYN
 1245          * contains the option, flag this in the syncache so that
 1246          * syncache_respond() will do the right thing with the SYN+ACK.
 1247          * XXX: Currently we always record the option by default and will
 1248          * attempt to use it in syncache_respond().
 1249          */
 1250         if (to->to_flags & TOF_SIGNATURE)
 1251                 sc->sc_flags |= SCF_SIGNATURE;
 1252 #endif
 1253         if (to->to_flags & TOF_SACKPERM)
 1254                 sc->sc_flags |= SCF_SACK;
 1255         if (to->to_flags & TOF_MSS)
 1256                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1257         if (noopt)
 1258                 sc->sc_flags |= SCF_NOOPT;
 1259 
 1260         if (tcp_syncookies) {
 1261                 syncookie_generate(sch, sc, &flowtmp);
 1262 #ifdef INET6
 1263                 if (autoflowlabel)
 1264                         sc->sc_flowlabel = flowtmp;
 1265 #endif
 1266         } else {
 1267 #ifdef INET6
 1268                 if (autoflowlabel)
 1269                         sc->sc_flowlabel =
 1270                             (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
 1271 #endif
 1272         }
 1273         SCH_UNLOCK(sch);
 1274 
 1275         /*
 1276          * Do a standard 3-way handshake.
 1277          */
 1278         if (TOEPCB_ISSET(sc) || syncache_respond(sc) == 0) {
 1279                 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs)
 1280                         syncache_free(sc);
 1281                 else if (sc != &scs)
 1282                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1283                 tcpstat.tcps_sndacks++;
 1284                 tcpstat.tcps_sndtotal++;
 1285         } else {
 1286                 if (sc != &scs)
 1287                         syncache_free(sc);
 1288                 tcpstat.tcps_sc_dropped++;
 1289         }
 1290 
 1291 done:
 1292         if (cred != NULL)
 1293                 crfree(cred);
 1294 #ifdef MAC
 1295         if (sc == &scs)
 1296                 mac_destroy_syncache(&maclabel);
 1297 #endif
 1298         *lsop = NULL;
 1299         m_freem(m);
 1300 }
 1301 
 1302 static int
 1303 syncache_respond(struct syncache *sc)
 1304 {
 1305         struct ip *ip = NULL;
 1306         struct mbuf *m;
 1307         struct tcphdr *th;
 1308         int optlen, error;
 1309         u_int16_t hlen, tlen, mssopt;
 1310         struct tcpopt to;
 1311 #ifdef INET6
 1312         struct ip6_hdr *ip6 = NULL;
 1313 #endif
 1314 
 1315         hlen =
 1316 #ifdef INET6
 1317                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1318 #endif
 1319                 sizeof(struct ip);
 1320         tlen = hlen + sizeof(struct tcphdr);
 1321 
 1322         /* Determine MSS we advertize to other end of connection. */
 1323         mssopt = tcp_mssopt(&sc->sc_inc);
 1324         if (sc->sc_peer_mss)
 1325                 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss);
 1326 
 1327         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1328         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1329             ("syncache: mbuf too small"));
 1330 
 1331         /* Create the IP+TCP header from scratch. */
 1332         m = m_gethdr(M_DONTWAIT, MT_DATA);
 1333         if (m == NULL)
 1334                 return (ENOBUFS);
 1335 #ifdef MAC
 1336         mac_create_mbuf_from_syncache(sc->sc_label, m);
 1337 #endif
 1338         m->m_data += max_linkhdr;
 1339         m->m_len = tlen;
 1340         m->m_pkthdr.len = tlen;
 1341         m->m_pkthdr.rcvif = NULL;
 1342 
 1343 #ifdef INET6
 1344         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1345                 ip6 = mtod(m, struct ip6_hdr *);
 1346                 ip6->ip6_vfc = IPV6_VERSION;
 1347                 ip6->ip6_nxt = IPPROTO_TCP;
 1348                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1349                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1350                 ip6->ip6_plen = htons(tlen - hlen);
 1351                 /* ip6_hlim is set after checksum */
 1352                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1353                 ip6->ip6_flow |= sc->sc_flowlabel;
 1354 
 1355                 th = (struct tcphdr *)(ip6 + 1);
 1356         } else
 1357 #endif
 1358         {
 1359                 ip = mtod(m, struct ip *);
 1360                 ip->ip_v = IPVERSION;
 1361                 ip->ip_hl = sizeof(struct ip) >> 2;
 1362                 ip->ip_len = tlen;
 1363                 ip->ip_id = 0;
 1364                 ip->ip_off = 0;
 1365                 ip->ip_sum = 0;
 1366                 ip->ip_p = IPPROTO_TCP;
 1367                 ip->ip_src = sc->sc_inc.inc_laddr;
 1368                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1369                 ip->ip_ttl = sc->sc_ip_ttl;
 1370                 ip->ip_tos = sc->sc_ip_tos;
 1371 
 1372                 /*
 1373                  * See if we should do MTU discovery.  Route lookups are
 1374                  * expensive, so we will only unset the DF bit if:
 1375                  *
 1376                  *      1) path_mtu_discovery is disabled
 1377                  *      2) the SCF_UNREACH flag has been set
 1378                  */
 1379                 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1380                        ip->ip_off |= IP_DF;
 1381 
 1382                 th = (struct tcphdr *)(ip + 1);
 1383         }
 1384         th->th_sport = sc->sc_inc.inc_lport;
 1385         th->th_dport = sc->sc_inc.inc_fport;
 1386 
 1387         th->th_seq = htonl(sc->sc_iss);
 1388         th->th_ack = htonl(sc->sc_irs + 1);
 1389         th->th_off = sizeof(struct tcphdr) >> 2;
 1390         th->th_x2 = 0;
 1391         th->th_flags = TH_SYN|TH_ACK;
 1392         th->th_win = htons(sc->sc_wnd);
 1393         th->th_urp = 0;
 1394 
 1395         /* Tack on the TCP options. */
 1396         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1397                 to.to_flags = 0;
 1398 
 1399                 to.to_mss = mssopt;
 1400                 to.to_flags = TOF_MSS;
 1401                 if (sc->sc_flags & SCF_WINSCALE) {
 1402                         to.to_wscale = sc->sc_requested_r_scale;
 1403                         to.to_flags |= TOF_SCALE;
 1404                 }
 1405                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1406                         /* Virgin timestamp or TCP cookie enhanced one. */
 1407                         to.to_tsval = sc->sc_ts;
 1408                         to.to_tsecr = sc->sc_tsreflect;
 1409                         to.to_flags |= TOF_TS;
 1410                 }
 1411                 if (sc->sc_flags & SCF_SACK)
 1412                         to.to_flags |= TOF_SACKPERM;
 1413 #ifdef TCP_SIGNATURE
 1414                 if (sc->sc_flags & SCF_SIGNATURE)
 1415                         to.to_flags |= TOF_SIGNATURE;
 1416 #endif
 1417                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1418 
 1419                 /* Adjust headers by option size. */
 1420                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1421                 m->m_len += optlen;
 1422                 m->m_pkthdr.len += optlen;
 1423 
 1424 #ifdef TCP_SIGNATURE
 1425                 if (sc->sc_flags & SCF_SIGNATURE)
 1426                         tcp_signature_compute(m, 0, 0, optlen,
 1427                             to.to_signature, IPSEC_DIR_OUTBOUND);
 1428 #endif
 1429 #ifdef INET6
 1430                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1431                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1432                 else
 1433 #endif
 1434                         ip->ip_len += optlen;
 1435         } else
 1436                 optlen = 0;
 1437 
 1438         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1439 #ifdef INET6
 1440         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1441                 th->th_sum = 0;
 1442                 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen,
 1443                                        tlen + optlen - hlen);
 1444                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1445                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1446         } else
 1447 #endif
 1448         {
 1449                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1450                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1451                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1452                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1453                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1454         }
 1455         return (error);
 1456 }
 1457 
 1458 void
 1459 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1460     struct inpcb *inp, struct socket **lsop, struct mbuf *m)
 1461 {
 1462 
 1463         _syncache_add(inc, to, th, inp, lsop, m, NULL, NULL);
 1464 }
 1465 
 1466 void
 1467 tcp_offload_syncache_add(struct in_conninfo *inc, struct tcpopt *to,
 1468     struct tcphdr *th, struct inpcb *inp, struct socket **lsop,
 1469     struct toe_usrreqs *tu, void *toepcb)
 1470 {
 1471 
 1472 
 1473         INP_INFO_WLOCK(&tcbinfo);
 1474         INP_WLOCK(inp);
 1475         _syncache_add(inc, to, th, inp, lsop, NULL, tu, toepcb);
 1476         
 1477 }
 1478 
 1479 /*
 1480  * The purpose of SYN cookies is to avoid keeping track of all SYN's we
 1481  * receive and to be able to handle SYN floods from bogus source addresses
 1482  * (where we will never receive any reply).  SYN floods try to exhaust all
 1483  * our memory and available slots in the SYN cache table to cause a denial
 1484  * of service to legitimate users of the local host.
 1485  *
 1486  * The idea of SYN cookies is to encode and include all necessary information
 1487  * about the connection setup state within the SYN-ACK we send back and thus
 1488  * to get along without keeping any local state until the ACK to the SYN-ACK
 1489  * arrives (if ever).  Everything we need to know should be available from
 1490  * the information we encoded in the SYN-ACK.
 1491  *
 1492  * More information about the theory behind SYN cookies and its first
 1493  * discussion and specification can be found at:
 1494  *  http://cr.yp.to/syncookies.html    (overview)
 1495  *  http://cr.yp.to/syncookies/archive (gory details)
 1496  *
 1497  * This implementation extends the orginal idea and first implementation
 1498  * of FreeBSD by using not only the initial sequence number field to store
 1499  * information but also the timestamp field if present.  This way we can
 1500  * keep track of the entire state we need to know to recreate the session in
 1501  * its original form.  Almost all TCP speakers implement RFC1323 timestamps
 1502  * these days.  For those that do not we still have to live with the known
 1503  * shortcomings of the ISN only SYN cookies.
 1504  *
 1505  * Cookie layers:
 1506  *
 1507  * Initial sequence number we send:
 1508  * 31|................................|0
 1509  *    DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP
 1510  *    D = MD5 Digest (first dword)
 1511  *    M = MSS index
 1512  *    R = Rotation of secret
 1513  *    P = Odd or Even secret
 1514  *
 1515  * The MD5 Digest is computed with over following parameters:
 1516  *  a) randomly rotated secret
 1517  *  b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6)
 1518  *  c) the received initial sequence number from remote host
 1519  *  d) the rotation offset and odd/even bit
 1520  *
 1521  * Timestamp we send:
 1522  * 31|................................|0
 1523  *    DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5
 1524  *    D = MD5 Digest (third dword) (only as filler)
 1525  *    S = Requested send window scale
 1526  *    R = Requested receive window scale
 1527  *    A = SACK allowed
 1528  *    5 = TCP-MD5 enabled (not implemented yet)
 1529  *    XORed with MD5 Digest (forth dword)
 1530  *
 1531  * The timestamp isn't cryptographically secure and doesn't need to be.
 1532  * The double use of the MD5 digest dwords ties it to a specific remote/
 1533  * local host/port, remote initial sequence number and our local time
 1534  * limited secret.  A received timestamp is reverted (XORed) and then
 1535  * the contained MD5 dword is compared to the computed one to ensure the
 1536  * timestamp belongs to the SYN-ACK we sent.  The other parameters may
 1537  * have been tampered with but this isn't different from supplying bogus
 1538  * values in the SYN in the first place.
 1539  *
 1540  * Some problems with SYN cookies remain however:
 1541  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1542  * original SYN was accepted, the connection is established.  The second
 1543  * SYN is inflight, and if it arrives with an ISN that falls within the
 1544  * receive window, the connection is killed.
 1545  *
 1546  * Notes:
 1547  * A heuristic to determine when to accept syn cookies is not necessary.
 1548  * An ACK flood would cause the syncookie verification to be attempted,
 1549  * but a SYN flood causes syncookies to be generated.  Both are of equal
 1550  * cost, so there's no point in trying to optimize the ACK flood case.
 1551  * Also, if you don't process certain ACKs for some reason, then all someone
 1552  * would have to do is launch a SYN and ACK flood at the same time, which
 1553  * would stop cookie verification and defeat the entire purpose of syncookies.
 1554  */
 1555 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 };
 1556 
 1557 static void
 1558 syncookie_generate(struct syncache_head *sch, struct syncache *sc,
 1559     u_int32_t *flowlabel)
 1560 {
 1561         MD5_CTX ctx;
 1562         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1563         u_int32_t data;
 1564         u_int32_t *secbits;
 1565         u_int off, pmss, mss;
 1566         int i;
 1567 
 1568         SCH_LOCK_ASSERT(sch);
 1569 
 1570         /* Which of the two secrets to use. */
 1571         secbits = sch->sch_oddeven ?
 1572                         sch->sch_secbits_odd : sch->sch_secbits_even;
 1573 
 1574         /* Reseed secret if too old. */
 1575         if (sch->sch_reseed < time_uptime) {
 1576                 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1;    /* toggle */
 1577                 secbits = sch->sch_oddeven ?
 1578                                 sch->sch_secbits_odd : sch->sch_secbits_even;
 1579                 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++)
 1580                         secbits[i] = arc4random();
 1581                 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME;
 1582         }
 1583 
 1584         /* Secret rotation offset. */
 1585         off = sc->sc_iss & 0x7;                 /* iss was randomized before */
 1586 
 1587         /* Maximum segment size calculation. */
 1588         pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss);
 1589         for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--)
 1590                 if (tcp_sc_msstab[mss] <= pmss)
 1591                         break;
 1592 
 1593         /* Fold parameters and MD5 digest into the ISN we will send. */
 1594         data = sch->sch_oddeven;/* odd or even secret, 1 bit */
 1595         data |= off << 1;       /* secret offset, derived from iss, 3 bits */
 1596         data |= mss << 4;       /* mss, 3 bits */
 1597 
 1598         MD5Init(&ctx);
 1599         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1600             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1601         MD5Update(&ctx, secbits, off);
 1602         MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc));
 1603         MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs));
 1604         MD5Update(&ctx, &data, sizeof(data));
 1605         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1606 
 1607         data |= (md5_buffer[0] << 7);
 1608         sc->sc_iss = data;
 1609 
 1610 #ifdef INET6
 1611         *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1612 #endif
 1613 
 1614         /* Additional parameters are stored in the timestamp if present. */
 1615         if (sc->sc_flags & SCF_TIMESTAMP) {
 1616                 data =  ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */
 1617                 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */
 1618                 data |= sc->sc_requested_s_scale << 2;  /* SWIN scale, 4 bits */
 1619                 data |= sc->sc_requested_r_scale << 6;  /* RWIN scale, 4 bits */
 1620                 data |= md5_buffer[2] << 10;            /* more digest bits */
 1621                 data ^= md5_buffer[3];
 1622                 sc->sc_ts = data;
 1623                 sc->sc_tsoff = data - ticks;            /* after XOR */
 1624         }
 1625 
 1626         tcpstat.tcps_sc_sendcookie++;
 1627 }
 1628 
 1629 static struct syncache *
 1630 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 1631     struct syncache *sc, struct tcpopt *to, struct tcphdr *th,
 1632     struct socket *so)
 1633 {
 1634         MD5_CTX ctx;
 1635         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1636         u_int32_t data = 0;
 1637         u_int32_t *secbits;
 1638         tcp_seq ack, seq;
 1639         int off, mss, wnd, flags;
 1640 
 1641         SCH_LOCK_ASSERT(sch);
 1642 
 1643         /*
 1644          * Pull information out of SYN-ACK/ACK and
 1645          * revert sequence number advances.
 1646          */
 1647         ack = th->th_ack - 1;
 1648         seq = th->th_seq - 1;
 1649         off = (ack >> 1) & 0x7;
 1650         mss = (ack >> 4) & 0x7;
 1651         flags = ack & 0x7f;
 1652 
 1653         /* Which of the two secrets to use. */
 1654         secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even;
 1655 
 1656         /*
 1657          * The secret wasn't updated for the lifetime of a syncookie,
 1658          * so this SYN-ACK/ACK is either too old (replay) or totally bogus.
 1659          */
 1660         if (sch->sch_reseed + SYNCOOKIE_LIFETIME < time_uptime) {
 1661                 return (NULL);
 1662         }
 1663 
 1664         /* Recompute the digest so we can compare it. */
 1665         MD5Init(&ctx);
 1666         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1667             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1668         MD5Update(&ctx, secbits, off);
 1669         MD5Update(&ctx, inc, sizeof(*inc));
 1670         MD5Update(&ctx, &seq, sizeof(seq));
 1671         MD5Update(&ctx, &flags, sizeof(flags));
 1672         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1673 
 1674         /* Does the digest part of or ACK'ed ISS match? */
 1675         if ((ack & (~0x7f)) != (md5_buffer[0] << 7))
 1676                 return (NULL);
 1677 
 1678         /* Does the digest part of our reflected timestamp match? */
 1679         if (to->to_flags & TOF_TS) {
 1680                 data = md5_buffer[3] ^ to->to_tsecr;
 1681                 if ((data & (~0x3ff)) != (md5_buffer[2] << 10))
 1682                         return (NULL);
 1683         }
 1684 
 1685         /* Fill in the syncache values. */
 1686         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1687         sc->sc_ipopts = NULL;
 1688         
 1689         sc->sc_irs = seq;
 1690         sc->sc_iss = ack;
 1691 
 1692 #ifdef INET6
 1693         if (inc->inc_flags & INC_ISIPV6) {
 1694                 if (sotoinpcb(so)->inp_flags & IN6P_AUTOFLOWLABEL)
 1695                         sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1696         } else
 1697 #endif
 1698         {
 1699                 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl;
 1700                 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos;
 1701         }
 1702 
 1703         /* Additional parameters that were encoded in the timestamp. */
 1704         if (data) {
 1705                 sc->sc_flags |= SCF_TIMESTAMP;
 1706                 sc->sc_tsreflect = to->to_tsval;
 1707                 sc->sc_ts = to->to_tsecr;
 1708                 sc->sc_tsoff = to->to_tsecr - ticks;
 1709                 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0;
 1710                 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0;
 1711                 sc->sc_requested_s_scale = min((data >> 2) & 0xf,
 1712                     TCP_MAX_WINSHIFT);
 1713                 sc->sc_requested_r_scale = min((data >> 6) & 0xf,
 1714                     TCP_MAX_WINSHIFT);
 1715                 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale)
 1716                         sc->sc_flags |= SCF_WINSCALE;
 1717         } else
 1718                 sc->sc_flags |= SCF_NOOPT;
 1719 
 1720         wnd = sbspace(&so->so_rcv);
 1721         wnd = imax(wnd, 0);
 1722         wnd = imin(wnd, TCP_MAXWIN);
 1723         sc->sc_wnd = wnd;
 1724 
 1725         sc->sc_rxmits = 0;
 1726         sc->sc_peer_mss = tcp_sc_msstab[mss];
 1727 
 1728         tcpstat.tcps_sc_recvcookie++;
 1729         return (sc);
 1730 }
 1731 
 1732 /*
 1733  * Returns the current number of syncache entries.  This number
 1734  * will probably change before you get around to calling 
 1735  * syncache_pcblist.
 1736  */
 1737 
 1738 int
 1739 syncache_pcbcount(void)
 1740 {
 1741         struct syncache_head *sch;
 1742         int count, i;
 1743 
 1744         for (count = 0, i = 0; i < tcp_syncache.hashsize; i++) {
 1745                 /* No need to lock for a read. */
 1746                 sch = &tcp_syncache.hashbase[i];
 1747                 count += sch->sch_length;
 1748         }
 1749         return count;
 1750 }
 1751 
 1752 /*
 1753  * Exports the syncache entries to userland so that netstat can display
 1754  * them alongside the other sockets.  This function is intended to be
 1755  * called only from tcp_pcblist.
 1756  *
 1757  * Due to concurrency on an active system, the number of pcbs exported
 1758  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 1759  * amount of space the caller allocated for this function to use.
 1760  */
 1761 int
 1762 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 1763 {
 1764         struct xtcpcb xt;
 1765         struct syncache *sc;
 1766         struct syncache_head *sch;
 1767         int count, error, i;
 1768 
 1769         for (count = 0, error = 0, i = 0; i < tcp_syncache.hashsize; i++) {
 1770                 sch = &tcp_syncache.hashbase[i];
 1771                 SCH_LOCK(sch);
 1772                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 1773                         if (count >= max_pcbs) {
 1774                                 SCH_UNLOCK(sch);
 1775                                 goto exit;
 1776                         }
 1777                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 1778                                 continue;
 1779                         bzero(&xt, sizeof(xt));
 1780                         xt.xt_len = sizeof(xt);
 1781                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1782                                 xt.xt_inp.inp_vflag = INP_IPV6;
 1783                         else
 1784                                 xt.xt_inp.inp_vflag = INP_IPV4;
 1785                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 1786                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 1787                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 1788                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 1789                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 1790                         xt.xt_socket.so_type = SOCK_STREAM;
 1791                         xt.xt_socket.so_state = SS_ISCONNECTING;
 1792                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 1793                         if (error) {
 1794                                 SCH_UNLOCK(sch);
 1795                                 goto exit;
 1796                         }
 1797                         count++;
 1798                 }
 1799                 SCH_UNLOCK(sch);
 1800         }
 1801 exit:
 1802         *pcbs_exported = count;
 1803         return error;
 1804 }
 1805 

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