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("$FreeBSD$");
   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_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_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 = sc->sc_inc.inc_fibnum;
  682         so->so_fibnum = sc->sc_inc.inc_fibnum;
  683         INP_WLOCK(inp);
  684 
  685         /* Insert new socket into PCB hash list. */
  686         inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
  687 #ifdef INET6
  688         if (sc->sc_inc.inc_isipv6) {
  689                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  690         } else {
  691                 inp->inp_vflag &= ~INP_IPV6;
  692                 inp->inp_vflag |= INP_IPV4;
  693 #endif
  694                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  695 #ifdef INET6
  696         }
  697 #endif
  698         inp->inp_lport = sc->sc_inc.inc_lport;
  699         if (in_pcbinshash(inp) != 0) {
  700                 /*
  701                  * Undo the assignments above if we failed to
  702                  * put the PCB on the hash lists.
  703                  */
  704 #ifdef INET6
  705                 if (sc->sc_inc.inc_isipv6)
  706                         inp->in6p_laddr = in6addr_any;
  707                 else
  708 #endif
  709                         inp->inp_laddr.s_addr = INADDR_ANY;
  710                 inp->inp_lport = 0;
  711                 goto abort;
  712         }
  713 #ifdef IPSEC
  714         /* Copy old policy into new socket's. */
  715         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  716                 printf("syncache_socket: could not copy policy\n");
  717 #endif
  718 #ifdef INET6
  719         if (sc->sc_inc.inc_isipv6) {
  720                 struct inpcb *oinp = sotoinpcb(lso);
  721                 struct in6_addr laddr6;
  722                 struct sockaddr_in6 sin6;
  723                 /*
  724                  * Inherit socket options from the listening socket.
  725                  * Note that in6p_inputopts are not (and should not be)
  726                  * copied, since it stores previously received options and is
  727                  * used to detect if each new option is different than the
  728                  * previous one and hence should be passed to a user.
  729                  * If we copied in6p_inputopts, a user would not be able to
  730                  * receive options just after calling the accept system call.
  731                  */
  732                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  733                 if (oinp->in6p_outputopts)
  734                         inp->in6p_outputopts =
  735                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  736 
  737                 sin6.sin6_family = AF_INET6;
  738                 sin6.sin6_len = sizeof(sin6);
  739                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  740                 sin6.sin6_port = sc->sc_inc.inc_fport;
  741                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  742                 laddr6 = inp->in6p_laddr;
  743                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  744                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  745                 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6,
  746                     thread0.td_ucred)) {
  747                         inp->in6p_laddr = laddr6;
  748                         goto abort;
  749                 }
  750                 /* Override flowlabel from in6_pcbconnect. */
  751                 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK;
  752                 inp->in6p_flowinfo |= sc->sc_flowlabel;
  753         } else
  754 #endif
  755         {
  756                 struct in_addr laddr;
  757                 struct sockaddr_in sin;
  758 
  759                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  760                 
  761                 if (inp->inp_options == NULL) {
  762                         inp->inp_options = sc->sc_ipopts;
  763                         sc->sc_ipopts = NULL;
  764                 }
  765 
  766                 sin.sin_family = AF_INET;
  767                 sin.sin_len = sizeof(sin);
  768                 sin.sin_addr = sc->sc_inc.inc_faddr;
  769                 sin.sin_port = sc->sc_inc.inc_fport;
  770                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  771                 laddr = inp->inp_laddr;
  772                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  773                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  774                 if (in_pcbconnect(inp, (struct sockaddr *)&sin,
  775                     thread0.td_ucred)) {
  776                         inp->inp_laddr = laddr;
  777                         goto abort;
  778                 }
  779         }
  780         tp = intotcpcb(inp);
  781         tp->t_state = TCPS_SYN_RECEIVED;
  782         tp->iss = sc->sc_iss;
  783         tp->irs = sc->sc_irs;
  784         tcp_rcvseqinit(tp);
  785         tcp_sendseqinit(tp);
  786         tp->snd_wl1 = sc->sc_irs;
  787         tp->snd_max = tp->iss + 1;
  788         tp->snd_nxt = tp->iss + 1;
  789         tp->rcv_up = sc->sc_irs + 1;
  790         tp->rcv_wnd = sc->sc_wnd;
  791         tp->rcv_adv += tp->rcv_wnd;
  792         tp->last_ack_sent = tp->rcv_nxt;
  793 
  794         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  795         if (sc->sc_flags & SCF_NOOPT)
  796                 tp->t_flags |= TF_NOOPT;
  797         else {
  798                 if (sc->sc_flags & SCF_WINSCALE) {
  799                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  800                         tp->snd_scale = sc->sc_requested_s_scale;
  801                         tp->request_r_scale = sc->sc_requested_r_scale;
  802                 }
  803                 if (sc->sc_flags & SCF_TIMESTAMP) {
  804                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  805                         tp->ts_recent = sc->sc_tsreflect;
  806                         tp->ts_recent_age = ticks;
  807                         tp->ts_offset = sc->sc_tsoff;
  808                 }
  809 #ifdef TCP_SIGNATURE
  810                 if (sc->sc_flags & SCF_SIGNATURE)
  811                         tp->t_flags |= TF_SIGNATURE;
  812 #endif
  813                 if (sc->sc_flags & SCF_SACK)
  814                         tp->t_flags |= TF_SACK_PERMIT;
  815         }
  816 
  817         /*
  818          * Set up MSS and get cached values from tcp_hostcache.
  819          * This might overwrite some of the defaults we just set.
  820          */
  821         tcp_mss(tp, sc->sc_peer_mss);
  822 
  823         /*
  824          * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
  825          */
  826         if (sc->sc_rxmits)
  827                 tp->snd_cwnd = tp->t_maxseg;
  828         tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
  829 
  830         INP_WUNLOCK(inp);
  831 
  832         tcpstat.tcps_accepts++;
  833         return (so);
  834 
  835 abort:
  836         INP_WUNLOCK(inp);
  837 abort2:
  838         if (so != NULL)
  839                 soabort(so);
  840         return (NULL);
  841 }
  842 
  843 /*
  844  * This function gets called when we receive an ACK for a
  845  * socket in the LISTEN state.  We look up the connection
  846  * in the syncache, and if its there, we pull it out of
  847  * the cache and turn it into a full-blown connection in
  848  * the SYN-RECEIVED state.
  849  */
  850 int
  851 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  852     struct socket **lsop, struct mbuf *m)
  853 {
  854         struct syncache *sc;
  855         struct syncache_head *sch;
  856         struct syncache scs;
  857         char *s;
  858 
  859         /*
  860          * Global TCP locks are held because we manipulate the PCB lists
  861          * and create a new socket.
  862          */
  863         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  864         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  865             ("%s: can handle only ACK", __func__));
  866 
  867         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  868         SCH_LOCK_ASSERT(sch);
  869         if (sc == NULL) {
  870                 /*
  871                  * There is no syncache entry, so see if this ACK is
  872                  * a returning syncookie.  To do this, first:
  873                  *  A. See if this socket has had a syncache entry dropped in
  874                  *     the past.  We don't want to accept a bogus syncookie
  875                  *     if we've never received a SYN.
  876                  *  B. check that the syncookie is valid.  If it is, then
  877                  *     cobble up a fake syncache entry, and return.
  878                  */
  879                 if (!tcp_syncookies) {
  880                         SCH_UNLOCK(sch);
  881                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  882                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  883                                     "segment rejected (syncookies disabled)\n",
  884                                     s, __func__);
  885                         goto failed;
  886                 }
  887                 bzero(&scs, sizeof(scs));
  888                 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop);
  889                 SCH_UNLOCK(sch);
  890                 if (sc == NULL) {
  891                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  892                                 log(LOG_DEBUG, "%s; %s: Segment failed "
  893                                     "SYNCOOKIE authentication, segment rejected "
  894                                     "(probably spoofed)\n", s, __func__);
  895                         goto failed;
  896                 }
  897         } else {
  898                 /* Pull out the entry to unlock the bucket row. */
  899                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  900                 sch->sch_length--;
  901                 tcp_syncache.cache_count--;
  902                 SCH_UNLOCK(sch);
  903         }
  904 
  905         /*
  906          * Segment validation:
  907          * ACK must match our initial sequence number + 1 (the SYN|ACK).
  908          */
  909         if (th->th_ack != sc->sc_iss + 1 && !TOEPCB_ISSET(sc)) {
  910                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  911                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
  912                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
  913                 goto failed;
  914         }
  915 
  916         /*
  917          * The SEQ must fall in the window starting at the received
  918          * initial receive sequence number + 1 (the SYN).
  919          */
  920         if ((SEQ_LEQ(th->th_seq, sc->sc_irs) ||
  921             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) &&
  922             !TOEPCB_ISSET(sc)) {
  923                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  924                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
  925                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
  926                 goto failed;
  927         }
  928 #if 0
  929         /*
  930          * If timestamps were present in the SYN and we accepted
  931          * them in our SYN|ACK we require them to be present from
  932          * now on.  And vice versa.
  933          *
  934          * Unfortunately, during testing of 7.0 some users found
  935          * network devices that violate this constraint, so it must
  936          * be disabled.
  937          */
  938         if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
  939                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  940                         log(LOG_DEBUG, "%s; %s: Timestamp missing, "
  941                             "segment rejected\n", s, __func__);
  942                 goto failed;
  943         }
  944 #endif
  945         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
  946                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  947                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
  948                             "segment rejected\n", s, __func__);
  949                 goto failed;
  950         }
  951         /*
  952          * If timestamps were negotiated the reflected timestamp
  953          * must be equal to what we actually sent in the SYN|ACK.
  954          */
  955         if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts &&
  956             !TOEPCB_ISSET(sc)) {
  957                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  958                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
  959                             "segment rejected\n",
  960                             s, __func__, to->to_tsecr, sc->sc_ts);
  961                 goto failed;
  962         }
  963 
  964         *lsop = syncache_socket(sc, *lsop, m);
  965 
  966         if (*lsop == NULL)
  967                 tcpstat.tcps_sc_aborted++;
  968         else
  969                 tcpstat.tcps_sc_completed++;
  970 
  971 /* how do we find the inp for the new socket? */
  972         if (sc != &scs)
  973                 syncache_free(sc);
  974         return (1);
  975 failed:
  976         if (sc != NULL && sc != &scs)
  977                 syncache_free(sc);
  978         if (s != NULL)
  979                 free(s, M_TCPLOG);
  980         *lsop = NULL;
  981         return (0);
  982 }
  983 
  984 int
  985 tcp_offload_syncache_expand(struct in_conninfo *inc, struct tcpopt *to,
  986     struct tcphdr *th, struct socket **lsop, struct mbuf *m)
  987 {
  988         int rc;
  989         
  990         INP_INFO_WLOCK(&tcbinfo);
  991         rc = syncache_expand(inc, to, th, lsop, m);
  992         INP_INFO_WUNLOCK(&tcbinfo);
  993 
  994         return (rc);
  995 }
  996 
  997 /*
  998  * Given a LISTEN socket and an inbound SYN request, add
  999  * this to the syn cache, and send back a segment:
 1000  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 1001  * to the source.
 1002  *
 1003  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
 1004  * Doing so would require that we hold onto the data and deliver it
 1005  * to the application.  However, if we are the target of a SYN-flood
 1006  * DoS attack, an attacker could send data which would eventually
 1007  * consume all available buffer space if it were ACKed.  By not ACKing
 1008  * the data, we avoid this DoS scenario.
 1009  */
 1010 static void
 1011 _syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1012     struct inpcb *inp, struct socket **lsop, struct mbuf *m,
 1013     struct toe_usrreqs *tu, void *toepcb)
 1014 {
 1015         struct tcpcb *tp;
 1016         struct socket *so;
 1017         struct syncache *sc = NULL;
 1018         struct syncache_head *sch;
 1019         struct mbuf *ipopts = NULL;
 1020         u_int32_t flowtmp;
 1021         int win, sb_hiwat, ip_ttl, ip_tos, noopt;
 1022         char *s;
 1023 #ifdef INET6
 1024         int autoflowlabel = 0;
 1025 #endif
 1026 #ifdef MAC
 1027         struct label *maclabel;
 1028 #endif
 1029         struct syncache scs;
 1030         struct ucred *cred;
 1031 
 1032         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 1033         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1034         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1035             ("%s: unexpected tcp flags", __func__));
 1036 
 1037         /*
 1038          * Combine all so/tp operations very early to drop the INP lock as
 1039          * soon as possible.
 1040          */
 1041         so = *lsop;
 1042         tp = sototcpcb(so);
 1043         cred = crhold(so->so_cred);
 1044 
 1045 #ifdef INET6
 1046         if (inc->inc_isipv6 &&
 1047             (inp->in6p_flags & IN6P_AUTOFLOWLABEL))
 1048                 autoflowlabel = 1;
 1049 #endif
 1050         ip_ttl = inp->inp_ip_ttl;
 1051         ip_tos = inp->inp_ip_tos;
 1052         win = sbspace(&so->so_rcv);
 1053         sb_hiwat = so->so_rcv.sb_hiwat;
 1054         noopt = (tp->t_flags & TF_NOOPT);
 1055 
 1056         /* By the time we drop the lock these should no longer be used. */
 1057         so = NULL;
 1058         tp = NULL;
 1059 
 1060 #ifdef MAC
 1061         if (mac_init_syncache(&maclabel) != 0) {
 1062                 INP_WUNLOCK(inp);
 1063                 INP_INFO_WUNLOCK(&tcbinfo);
 1064                 goto done;
 1065         } else
 1066                 mac_init_syncache_from_inpcb(maclabel, inp);
 1067 #endif
 1068         INP_WUNLOCK(inp);
 1069         INP_INFO_WUNLOCK(&tcbinfo);
 1070 
 1071         /*
 1072          * Remember the IP options, if any.
 1073          */
 1074 #ifdef INET6
 1075         if (!inc->inc_isipv6)
 1076 #endif
 1077                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1078 
 1079         /*
 1080          * See if we already have an entry for this connection.
 1081          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1082          *
 1083          * XXX: should the syncache be re-initialized with the contents
 1084          * of the new SYN here (which may have different options?)
 1085          *
 1086          * XXX: We do not check the sequence number to see if this is a
 1087          * real retransmit or a new connection attempt.  The question is
 1088          * how to handle such a case; either ignore it as spoofed, or
 1089          * drop the current entry and create a new one?
 1090          */
 1091         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1092         SCH_LOCK_ASSERT(sch);
 1093         if (sc != NULL) {
 1094 #ifndef TCP_OFFLOAD_DISABLE
 1095                 if (sc->sc_tu)
 1096                         sc->sc_tu->tu_syncache_event(TOE_SC_ENTRY_PRESENT,
 1097                             sc->sc_toepcb);
 1098 #endif              
 1099                 tcpstat.tcps_sc_dupsyn++;
 1100                 if (ipopts) {
 1101                         /*
 1102                          * If we were remembering a previous source route,
 1103                          * forget it and use the new one we've been given.
 1104                          */
 1105                         if (sc->sc_ipopts)
 1106                                 (void) m_free(sc->sc_ipopts);
 1107                         sc->sc_ipopts = ipopts;
 1108                 }
 1109                 /*
 1110                  * Update timestamp if present.
 1111                  */
 1112                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1113                         sc->sc_tsreflect = to->to_tsval;
 1114                 else
 1115                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1116 #ifdef MAC
 1117                 /*
 1118                  * Since we have already unconditionally allocated label
 1119                  * storage, free it up.  The syncache entry will already
 1120                  * have an initialized label we can use.
 1121                  */
 1122                 mac_destroy_syncache(&maclabel);
 1123                 KASSERT(sc->sc_label != NULL,
 1124                     ("%s: label not initialized", __func__));
 1125 #endif
 1126                 /* Retransmit SYN|ACK and reset retransmit count. */
 1127                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1128                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1129                             "resetting timer and retransmitting SYN|ACK\n",
 1130                             s, __func__);
 1131                         free(s, M_TCPLOG);
 1132                 }
 1133                 if (!TOEPCB_ISSET(sc) && syncache_respond(sc) == 0) {
 1134                         sc->sc_rxmits = 0;
 1135                         syncache_timeout(sc, sch, 1);
 1136                         tcpstat.tcps_sndacks++;
 1137                         tcpstat.tcps_sndtotal++;
 1138                 }
 1139                 SCH_UNLOCK(sch);
 1140                 goto done;
 1141         }
 1142 
 1143         sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1144         if (sc == NULL) {
 1145                 /*
 1146                  * The zone allocator couldn't provide more entries.
 1147                  * Treat this as if the cache was full; drop the oldest
 1148                  * entry and insert the new one.
 1149                  */
 1150                 tcpstat.tcps_sc_zonefail++;
 1151                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
 1152                         syncache_drop(sc, sch);
 1153                 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1154                 if (sc == NULL) {
 1155                         if (tcp_syncookies) {
 1156                                 bzero(&scs, sizeof(scs));
 1157                                 sc = &scs;
 1158                         } else {
 1159                                 SCH_UNLOCK(sch);
 1160                                 if (ipopts)
 1161                                         (void) m_free(ipopts);
 1162                                 goto done;
 1163                         }
 1164                 }
 1165         }
 1166 
 1167         /*
 1168          * Fill in the syncache values.
 1169          */
 1170 #ifdef MAC
 1171         sc->sc_label = maclabel;
 1172 #endif
 1173         sc->sc_cred = cred;
 1174         cred = NULL;
 1175         sc->sc_ipopts = ipopts;
 1176         sc->sc_inc.inc_fibnum = inp->inp_inc.inc_fibnum;
 1177         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1178 #ifdef INET6
 1179         if (!inc->inc_isipv6)
 1180 #endif
 1181         {
 1182                 sc->sc_ip_tos = ip_tos;
 1183                 sc->sc_ip_ttl = ip_ttl;
 1184         }
 1185 #ifndef TCP_OFFLOAD_DISABLE     
 1186         sc->sc_tu = tu;
 1187         sc->sc_toepcb = toepcb;
 1188 #endif
 1189         sc->sc_irs = th->th_seq;
 1190         sc->sc_iss = arc4random();
 1191         sc->sc_flags = 0;
 1192         sc->sc_flowlabel = 0;
 1193 
 1194         /*
 1195          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1196          * win was derived from socket earlier in the function.
 1197          */
 1198         win = imax(win, 0);
 1199         win = imin(win, TCP_MAXWIN);
 1200         sc->sc_wnd = win;
 1201 
 1202         if (tcp_do_rfc1323) {
 1203                 /*
 1204                  * A timestamp received in a SYN makes
 1205                  * it ok to send timestamp requests and replies.
 1206                  */
 1207                 if (to->to_flags & TOF_TS) {
 1208                         sc->sc_tsreflect = to->to_tsval;
 1209                         sc->sc_ts = ticks;
 1210                         sc->sc_flags |= SCF_TIMESTAMP;
 1211                 }
 1212                 if (to->to_flags & TOF_SCALE) {
 1213                         int wscale = 0;
 1214 
 1215                         /*
 1216                          * Pick the smallest possible scaling factor that
 1217                          * will still allow us to scale up to sb_max, aka
 1218                          * kern.ipc.maxsockbuf.
 1219                          *
 1220                          * We do this because there are broken firewalls that
 1221                          * will corrupt the window scale option, leading to
 1222                          * the other endpoint believing that our advertised
 1223                          * window is unscaled.  At scale factors larger than
 1224                          * 5 the unscaled window will drop below 1500 bytes,
 1225                          * leading to serious problems when traversing these
 1226                          * broken firewalls.
 1227                          *
 1228                          * With the default maxsockbuf of 256K, a scale factor
 1229                          * of 3 will be chosen by this algorithm.  Those who
 1230                          * choose a larger maxsockbuf should watch out
 1231                          * for the compatiblity problems mentioned above.
 1232                          *
 1233                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1234                          * or <SYN,ACK>) segment itself is never scaled.
 1235                          */
 1236                         while (wscale < TCP_MAX_WINSHIFT &&
 1237                             (TCP_MAXWIN << wscale) < sb_max)
 1238                                 wscale++;
 1239                         sc->sc_requested_r_scale = wscale;
 1240                         sc->sc_requested_s_scale = to->to_wscale;
 1241                         sc->sc_flags |= SCF_WINSCALE;
 1242                 }
 1243         }
 1244 #ifdef TCP_SIGNATURE
 1245         /*
 1246          * If listening socket requested TCP digests, and received SYN
 1247          * contains the option, flag this in the syncache so that
 1248          * syncache_respond() will do the right thing with the SYN+ACK.
 1249          * XXX: Currently we always record the option by default and will
 1250          * attempt to use it in syncache_respond().
 1251          */
 1252         if (to->to_flags & TOF_SIGNATURE)
 1253                 sc->sc_flags |= SCF_SIGNATURE;
 1254 #endif
 1255         if (to->to_flags & TOF_SACKPERM)
 1256                 sc->sc_flags |= SCF_SACK;
 1257         if (to->to_flags & TOF_MSS)
 1258                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1259         if (noopt)
 1260                 sc->sc_flags |= SCF_NOOPT;
 1261 
 1262         if (tcp_syncookies) {
 1263                 syncookie_generate(sch, sc, &flowtmp);
 1264 #ifdef INET6
 1265                 if (autoflowlabel)
 1266                         sc->sc_flowlabel = flowtmp;
 1267 #endif
 1268         } else {
 1269 #ifdef INET6
 1270                 if (autoflowlabel)
 1271                         sc->sc_flowlabel =
 1272                             (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
 1273 #endif
 1274         }
 1275         SCH_UNLOCK(sch);
 1276 
 1277         /*
 1278          * Do a standard 3-way handshake.
 1279          */
 1280         if (TOEPCB_ISSET(sc) || syncache_respond(sc) == 0) {
 1281                 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs)
 1282                         syncache_free(sc);
 1283                 else if (sc != &scs)
 1284                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1285                 tcpstat.tcps_sndacks++;
 1286                 tcpstat.tcps_sndtotal++;
 1287         } else {
 1288                 if (sc != &scs)
 1289                         syncache_free(sc);
 1290                 tcpstat.tcps_sc_dropped++;
 1291         }
 1292 
 1293 done:
 1294         if (cred != NULL)
 1295                 crfree(cred);
 1296 #ifdef MAC
 1297         if (sc == &scs)
 1298                 mac_destroy_syncache(&maclabel);
 1299 #endif
 1300         *lsop = NULL;
 1301         m_freem(m);
 1302 }
 1303 
 1304 static int
 1305 syncache_respond(struct syncache *sc)
 1306 {
 1307         struct ip *ip = NULL;
 1308         struct mbuf *m;
 1309         struct tcphdr *th;
 1310         int optlen, error;
 1311         u_int16_t hlen, tlen, mssopt;
 1312         struct tcpopt to;
 1313 #ifdef INET6
 1314         struct ip6_hdr *ip6 = NULL;
 1315 #endif
 1316 
 1317         hlen =
 1318 #ifdef INET6
 1319                (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) :
 1320 #endif
 1321                 sizeof(struct ip);
 1322         tlen = hlen + sizeof(struct tcphdr);
 1323 
 1324         /* Determine MSS we advertize to other end of connection. */
 1325         mssopt = tcp_mssopt(&sc->sc_inc);
 1326         if (sc->sc_peer_mss)
 1327                 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss);
 1328 
 1329         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1330         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1331             ("syncache: mbuf too small"));
 1332 
 1333         /* Create the IP+TCP header from scratch. */
 1334         m = m_gethdr(M_DONTWAIT, MT_DATA);
 1335         if (m == NULL)
 1336                 return (ENOBUFS);
 1337 #ifdef MAC
 1338         mac_create_mbuf_from_syncache(sc->sc_label, m);
 1339 #endif
 1340         m->m_data += max_linkhdr;
 1341         m->m_len = tlen;
 1342         m->m_pkthdr.len = tlen;
 1343         m->m_pkthdr.rcvif = NULL;
 1344 
 1345 #ifdef INET6
 1346         if (sc->sc_inc.inc_isipv6) {
 1347                 ip6 = mtod(m, struct ip6_hdr *);
 1348                 ip6->ip6_vfc = IPV6_VERSION;
 1349                 ip6->ip6_nxt = IPPROTO_TCP;
 1350                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1351                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1352                 ip6->ip6_plen = htons(tlen - hlen);
 1353                 /* ip6_hlim is set after checksum */
 1354                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1355                 ip6->ip6_flow |= sc->sc_flowlabel;
 1356 
 1357                 th = (struct tcphdr *)(ip6 + 1);
 1358         } else
 1359 #endif
 1360         {
 1361                 ip = mtod(m, struct ip *);
 1362                 ip->ip_v = IPVERSION;
 1363                 ip->ip_hl = sizeof(struct ip) >> 2;
 1364                 ip->ip_len = tlen;
 1365                 ip->ip_id = 0;
 1366                 ip->ip_off = 0;
 1367                 ip->ip_sum = 0;
 1368                 ip->ip_p = IPPROTO_TCP;
 1369                 ip->ip_src = sc->sc_inc.inc_laddr;
 1370                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1371                 ip->ip_ttl = sc->sc_ip_ttl;
 1372                 ip->ip_tos = sc->sc_ip_tos;
 1373 
 1374                 /*
 1375                  * See if we should do MTU discovery.  Route lookups are
 1376                  * expensive, so we will only unset the DF bit if:
 1377                  *
 1378                  *      1) path_mtu_discovery is disabled
 1379                  *      2) the SCF_UNREACH flag has been set
 1380                  */
 1381                 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1382                        ip->ip_off |= IP_DF;
 1383 
 1384                 th = (struct tcphdr *)(ip + 1);
 1385         }
 1386         th->th_sport = sc->sc_inc.inc_lport;
 1387         th->th_dport = sc->sc_inc.inc_fport;
 1388 
 1389         th->th_seq = htonl(sc->sc_iss);
 1390         th->th_ack = htonl(sc->sc_irs + 1);
 1391         th->th_off = sizeof(struct tcphdr) >> 2;
 1392         th->th_x2 = 0;
 1393         th->th_flags = TH_SYN|TH_ACK;
 1394         th->th_win = htons(sc->sc_wnd);
 1395         th->th_urp = 0;
 1396 
 1397         /* Tack on the TCP options. */
 1398         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1399                 to.to_flags = 0;
 1400 
 1401                 to.to_mss = mssopt;
 1402                 to.to_flags = TOF_MSS;
 1403                 if (sc->sc_flags & SCF_WINSCALE) {
 1404                         to.to_wscale = sc->sc_requested_r_scale;
 1405                         to.to_flags |= TOF_SCALE;
 1406                 }
 1407                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1408                         /* Virgin timestamp or TCP cookie enhanced one. */
 1409                         to.to_tsval = sc->sc_ts;
 1410                         to.to_tsecr = sc->sc_tsreflect;
 1411                         to.to_flags |= TOF_TS;
 1412                 }
 1413                 if (sc->sc_flags & SCF_SACK)
 1414                         to.to_flags |= TOF_SACKPERM;
 1415 #ifdef TCP_SIGNATURE
 1416                 if (sc->sc_flags & SCF_SIGNATURE)
 1417                         to.to_flags |= TOF_SIGNATURE;
 1418 #endif
 1419                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1420 
 1421                 /* Adjust headers by option size. */
 1422                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1423                 m->m_len += optlen;
 1424                 m->m_pkthdr.len += optlen;
 1425 
 1426 #ifdef TCP_SIGNATURE
 1427                 if (sc->sc_flags & SCF_SIGNATURE)
 1428                         tcp_signature_compute(m, sizeof(struct ip), 0, optlen,
 1429                             to.to_signature, IPSEC_DIR_OUTBOUND);
 1430 #endif
 1431 #ifdef INET6
 1432                 if (sc->sc_inc.inc_isipv6)
 1433                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1434                 else
 1435 #endif
 1436                         ip->ip_len += optlen;
 1437         } else
 1438                 optlen = 0;
 1439 
 1440 #ifdef INET6
 1441         if (sc->sc_inc.inc_isipv6) {
 1442                 th->th_sum = 0;
 1443                 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen,
 1444                                        tlen + optlen - hlen);
 1445                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1446                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1447         } else
 1448 #endif
 1449         {
 1450                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1451                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1452                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1453                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1454                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1455         }
 1456         return (error);
 1457 }
 1458 
 1459 void
 1460 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1461     struct inpcb *inp, struct socket **lsop, struct mbuf *m)
 1462 {
 1463 
 1464         _syncache_add(inc, to, th, inp, lsop, m, NULL, NULL);
 1465 }
 1466 
 1467 void
 1468 tcp_offload_syncache_add(struct in_conninfo *inc, struct tcpopt *to,
 1469     struct tcphdr *th, struct inpcb *inp, struct socket **lsop,
 1470     struct toe_usrreqs *tu, void *toepcb)
 1471 {
 1472 
 1473 
 1474         INP_INFO_WLOCK(&tcbinfo);
 1475         INP_WLOCK(inp);
 1476         _syncache_add(inc, to, th, inp, lsop, NULL, tu, toepcb);
 1477         
 1478 }
 1479 
 1480 /*
 1481  * The purpose of SYN cookies is to avoid keeping track of all SYN's we
 1482  * receive and to be able to handle SYN floods from bogus source addresses
 1483  * (where we will never receive any reply).  SYN floods try to exhaust all
 1484  * our memory and available slots in the SYN cache table to cause a denial
 1485  * of service to legitimate users of the local host.
 1486  *
 1487  * The idea of SYN cookies is to encode and include all necessary information
 1488  * about the connection setup state within the SYN-ACK we send back and thus
 1489  * to get along without keeping any local state until the ACK to the SYN-ACK
 1490  * arrives (if ever).  Everything we need to know should be available from
 1491  * the information we encoded in the SYN-ACK.
 1492  *
 1493  * More information about the theory behind SYN cookies and its first
 1494  * discussion and specification can be found at:
 1495  *  http://cr.yp.to/syncookies.html    (overview)
 1496  *  http://cr.yp.to/syncookies/archive (gory details)
 1497  *
 1498  * This implementation extends the orginal idea and first implementation
 1499  * of FreeBSD by using not only the initial sequence number field to store
 1500  * information but also the timestamp field if present.  This way we can
 1501  * keep track of the entire state we need to know to recreate the session in
 1502  * its original form.  Almost all TCP speakers implement RFC1323 timestamps
 1503  * these days.  For those that do not we still have to live with the known
 1504  * shortcomings of the ISN only SYN cookies.
 1505  *
 1506  * Cookie layers:
 1507  *
 1508  * Initial sequence number we send:
 1509  * 31|................................|0
 1510  *    DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP
 1511  *    D = MD5 Digest (first dword)
 1512  *    M = MSS index
 1513  *    R = Rotation of secret
 1514  *    P = Odd or Even secret
 1515  *
 1516  * The MD5 Digest is computed with over following parameters:
 1517  *  a) randomly rotated secret
 1518  *  b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6)
 1519  *  c) the received initial sequence number from remote host
 1520  *  d) the rotation offset and odd/even bit
 1521  *
 1522  * Timestamp we send:
 1523  * 31|................................|0
 1524  *    DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5
 1525  *    D = MD5 Digest (third dword) (only as filler)
 1526  *    S = Requested send window scale
 1527  *    R = Requested receive window scale
 1528  *    A = SACK allowed
 1529  *    5 = TCP-MD5 enabled (not implemented yet)
 1530  *    XORed with MD5 Digest (forth dword)
 1531  *
 1532  * The timestamp isn't cryptographically secure and doesn't need to be.
 1533  * The double use of the MD5 digest dwords ties it to a specific remote/
 1534  * local host/port, remote initial sequence number and our local time
 1535  * limited secret.  A received timestamp is reverted (XORed) and then
 1536  * the contained MD5 dword is compared to the computed one to ensure the
 1537  * timestamp belongs to the SYN-ACK we sent.  The other parameters may
 1538  * have been tampered with but this isn't different from supplying bogus
 1539  * values in the SYN in the first place.
 1540  *
 1541  * Some problems with SYN cookies remain however:
 1542  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1543  * original SYN was accepted, the connection is established.  The second
 1544  * SYN is inflight, and if it arrives with an ISN that falls within the
 1545  * receive window, the connection is killed.
 1546  *
 1547  * Notes:
 1548  * A heuristic to determine when to accept syn cookies is not necessary.
 1549  * An ACK flood would cause the syncookie verification to be attempted,
 1550  * but a SYN flood causes syncookies to be generated.  Both are of equal
 1551  * cost, so there's no point in trying to optimize the ACK flood case.
 1552  * Also, if you don't process certain ACKs for some reason, then all someone
 1553  * would have to do is launch a SYN and ACK flood at the same time, which
 1554  * would stop cookie verification and defeat the entire purpose of syncookies.
 1555  */
 1556 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 };
 1557 
 1558 static void
 1559 syncookie_generate(struct syncache_head *sch, struct syncache *sc,
 1560     u_int32_t *flowlabel)
 1561 {
 1562         MD5_CTX ctx;
 1563         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1564         u_int32_t data;
 1565         u_int32_t *secbits;
 1566         u_int off, pmss, mss;
 1567         int i;
 1568 
 1569         SCH_LOCK_ASSERT(sch);
 1570 
 1571         /* Which of the two secrets to use. */
 1572         secbits = sch->sch_oddeven ?
 1573                         sch->sch_secbits_odd : sch->sch_secbits_even;
 1574 
 1575         /* Reseed secret if too old. */
 1576         if (sch->sch_reseed < time_uptime) {
 1577                 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1;    /* toggle */
 1578                 secbits = sch->sch_oddeven ?
 1579                                 sch->sch_secbits_odd : sch->sch_secbits_even;
 1580                 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++)
 1581                         secbits[i] = arc4random();
 1582                 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME;
 1583         }
 1584 
 1585         /* Secret rotation offset. */
 1586         off = sc->sc_iss & 0x7;                 /* iss was randomized before */
 1587 
 1588         /* Maximum segment size calculation. */
 1589         pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss);
 1590         for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--)
 1591                 if (tcp_sc_msstab[mss] <= pmss)
 1592                         break;
 1593 
 1594         /* Fold parameters and MD5 digest into the ISN we will send. */
 1595         data = sch->sch_oddeven;/* odd or even secret, 1 bit */
 1596         data |= off << 1;       /* secret offset, derived from iss, 3 bits */
 1597         data |= mss << 4;       /* mss, 3 bits */
 1598 
 1599         MD5Init(&ctx);
 1600         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1601             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1602         MD5Update(&ctx, secbits, off);
 1603         MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc));
 1604         MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs));
 1605         MD5Update(&ctx, &data, sizeof(data));
 1606         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1607 
 1608         data |= (md5_buffer[0] << 7);
 1609         sc->sc_iss = data;
 1610 
 1611 #ifdef INET6
 1612         *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1613 #endif
 1614 
 1615         /* Additional parameters are stored in the timestamp if present. */
 1616         if (sc->sc_flags & SCF_TIMESTAMP) {
 1617                 data =  ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */
 1618                 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */
 1619                 data |= sc->sc_requested_s_scale << 2;  /* SWIN scale, 4 bits */
 1620                 data |= sc->sc_requested_r_scale << 6;  /* RWIN scale, 4 bits */
 1621                 data |= md5_buffer[2] << 10;            /* more digest bits */
 1622                 data ^= md5_buffer[3];
 1623                 sc->sc_ts = data;
 1624                 sc->sc_tsoff = data - ticks;            /* after XOR */
 1625         }
 1626 
 1627         tcpstat.tcps_sc_sendcookie++;
 1628 }
 1629 
 1630 static struct syncache *
 1631 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 1632     struct syncache *sc, struct tcpopt *to, struct tcphdr *th,
 1633     struct socket *so)
 1634 {
 1635         MD5_CTX ctx;
 1636         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1637         u_int32_t data = 0;
 1638         u_int32_t *secbits;
 1639         tcp_seq ack, seq;
 1640         int off, mss, wnd, flags;
 1641 
 1642         SCH_LOCK_ASSERT(sch);
 1643 
 1644         /*
 1645          * Pull information out of SYN-ACK/ACK and
 1646          * revert sequence number advances.
 1647          */
 1648         ack = th->th_ack - 1;
 1649         seq = th->th_seq - 1;
 1650         off = (ack >> 1) & 0x7;
 1651         mss = (ack >> 4) & 0x7;
 1652         flags = ack & 0x7f;
 1653 
 1654         /* Which of the two secrets to use. */
 1655         secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even;
 1656 
 1657         /*
 1658          * The secret wasn't updated for the lifetime of a syncookie,
 1659          * so this SYN-ACK/ACK is either too old (replay) or totally bogus.
 1660          */
 1661         if (sch->sch_reseed + SYNCOOKIE_LIFETIME < time_uptime) {
 1662                 return (NULL);
 1663         }
 1664 
 1665         /* Recompute the digest so we can compare it. */
 1666         MD5Init(&ctx);
 1667         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1668             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1669         MD5Update(&ctx, secbits, off);
 1670         MD5Update(&ctx, inc, sizeof(*inc));
 1671         MD5Update(&ctx, &seq, sizeof(seq));
 1672         MD5Update(&ctx, &flags, sizeof(flags));
 1673         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1674 
 1675         /* Does the digest part of or ACK'ed ISS match? */
 1676         if ((ack & (~0x7f)) != (md5_buffer[0] << 7))
 1677                 return (NULL);
 1678 
 1679         /* Does the digest part of our reflected timestamp match? */
 1680         if (to->to_flags & TOF_TS) {
 1681                 data = md5_buffer[3] ^ to->to_tsecr;
 1682                 if ((data & (~0x3ff)) != (md5_buffer[2] << 10))
 1683                         return (NULL);
 1684         }
 1685 
 1686         /* Fill in the syncache values. */
 1687         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1688         sc->sc_ipopts = NULL;
 1689         
 1690         sc->sc_irs = seq;
 1691         sc->sc_iss = ack;
 1692 
 1693 #ifdef INET6
 1694         if (inc->inc_isipv6) {
 1695                 if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL)
 1696                         sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1697         } else
 1698 #endif
 1699         {
 1700                 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl;
 1701                 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos;
 1702         }
 1703 
 1704         /* Additional parameters that were encoded in the timestamp. */
 1705         if (data) {
 1706                 sc->sc_flags |= SCF_TIMESTAMP;
 1707                 sc->sc_tsreflect = to->to_tsval;
 1708                 sc->sc_ts = to->to_tsecr;
 1709                 sc->sc_tsoff = to->to_tsecr - ticks;
 1710                 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0;
 1711                 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0;
 1712                 sc->sc_requested_s_scale = min((data >> 2) & 0xf,
 1713                     TCP_MAX_WINSHIFT);
 1714                 sc->sc_requested_r_scale = min((data >> 6) & 0xf,
 1715                     TCP_MAX_WINSHIFT);
 1716                 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale)
 1717                         sc->sc_flags |= SCF_WINSCALE;
 1718         } else
 1719                 sc->sc_flags |= SCF_NOOPT;
 1720 
 1721         wnd = sbspace(&so->so_rcv);
 1722         wnd = imax(wnd, 0);
 1723         wnd = imin(wnd, TCP_MAXWIN);
 1724         sc->sc_wnd = wnd;
 1725 
 1726         sc->sc_rxmits = 0;
 1727         sc->sc_peer_mss = tcp_sc_msstab[mss];
 1728 
 1729         tcpstat.tcps_sc_recvcookie++;
 1730         return (sc);
 1731 }
 1732 
 1733 /*
 1734  * Returns the current number of syncache entries.  This number
 1735  * will probably change before you get around to calling 
 1736  * syncache_pcblist.
 1737  */
 1738 
 1739 int
 1740 syncache_pcbcount(void)
 1741 {
 1742         struct syncache_head *sch;
 1743         int count, i;
 1744 
 1745         for (count = 0, i = 0; i < tcp_syncache.hashsize; i++) {
 1746                 /* No need to lock for a read. */
 1747                 sch = &tcp_syncache.hashbase[i];
 1748                 count += sch->sch_length;
 1749         }
 1750         return count;
 1751 }
 1752 
 1753 /*
 1754  * Exports the syncache entries to userland so that netstat can display
 1755  * them alongside the other sockets.  This function is intended to be
 1756  * called only from tcp_pcblist.
 1757  *
 1758  * Due to concurrency on an active system, the number of pcbs exported
 1759  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 1760  * amount of space the caller allocated for this function to use.
 1761  */
 1762 int
 1763 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 1764 {
 1765         struct xtcpcb xt;
 1766         struct syncache *sc;
 1767         struct syncache_head *sch;
 1768         int count, error, i;
 1769 
 1770         for (count = 0, error = 0, i = 0; i < tcp_syncache.hashsize; i++) {
 1771                 sch = &tcp_syncache.hashbase[i];
 1772                 SCH_LOCK(sch);
 1773                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 1774                         if (count >= max_pcbs) {
 1775                                 SCH_UNLOCK(sch);
 1776                                 goto exit;
 1777                         }
 1778                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 1779                                 continue;
 1780                         bzero(&xt, sizeof(xt));
 1781                         xt.xt_len = sizeof(xt);
 1782                         if (sc->sc_inc.inc_isipv6)
 1783                                 xt.xt_inp.inp_vflag = INP_IPV6;
 1784                         else
 1785                                 xt.xt_inp.inp_vflag = INP_IPV4;
 1786                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 1787                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 1788                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 1789                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 1790                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 1791                         xt.xt_socket.so_type = SOCK_STREAM;
 1792                         xt.xt_socket.so_state = SS_ISCONNECTING;
 1793                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 1794                         if (error) {
 1795                                 SCH_UNLOCK(sch);
 1796                                 goto exit;
 1797                         }
 1798                         count++;
 1799                 }
 1800                 SCH_UNLOCK(sch);
 1801         }
 1802 exit:
 1803         *pcbs_exported = count;
 1804         return error;
 1805 }
 1806 

Cache object: e6c602a03d2fb80015d23d19418ebc6e


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