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 57 #include <vm/uma.h> 58 59 #include <net/if.h> 60 #include <net/route.h> 61 62 #include <netinet/in.h> 63 #include <netinet/in_systm.h> 64 #include <netinet/ip.h> 65 #include <netinet/in_var.h> 66 #include <netinet/in_pcb.h> 67 #include <netinet/ip_var.h> 68 #include <netinet/ip_options.h> 69 #ifdef INET6 70 #include <netinet/ip6.h> 71 #include <netinet/icmp6.h> 72 #include <netinet6/nd6.h> 73 #include <netinet6/ip6_var.h> 74 #include <netinet6/in6_pcb.h> 75 #endif 76 #include <netinet/tcp.h> 77 #include <netinet/tcp_fsm.h> 78 #include <netinet/tcp_seq.h> 79 #include <netinet/tcp_timer.h> 80 #include <netinet/tcp_var.h> 81 #include <netinet/tcp_syncache.h> 82 #include <netinet/tcp_offload.h> 83 #ifdef INET6 84 #include <netinet6/tcp6_var.h> 85 #endif 86 87 #ifdef IPSEC 88 #include <netipsec/ipsec.h> 89 #ifdef INET6 90 #include <netipsec/ipsec6.h> 91 #endif 92 #include <netipsec/key.h> 93 #endif /*IPSEC*/ 94 95 #include <machine/in_cksum.h> 96 97 #include <security/mac/mac_framework.h> 98 99 static int tcp_syncookies = 1; 100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 101 &tcp_syncookies, 0, 102 "Use TCP SYN cookies if the syncache overflows"); 103 104 static int tcp_syncookiesonly = 0; 105 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 106 &tcp_syncookiesonly, 0, 107 "Use only TCP SYN cookies"); 108 109 #define SYNCOOKIE_SECRET_SIZE 8 /* dwords */ 110 #define SYNCOOKIE_LIFETIME 16 /* seconds */ 111 112 struct syncache { 113 TAILQ_ENTRY(syncache) sc_hash; 114 struct in_conninfo sc_inc; /* addresses */ 115 int sc_rxttime; /* retransmit time */ 116 u_int16_t sc_rxmits; /* retransmit counter */ 117 118 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 */ 125 126 u_int16_t sc_peer_mss; /* peer's MSS */ 127 u_int16_t sc_wnd; /* advertised window */ 128 u_int8_t sc_ip_ttl; /* IPv4 TTL */ 129 u_int8_t sc_ip_tos; /* IPv4 TOS */ 130 u_int8_t sc_requested_s_scale:4, 131 sc_requested_r_scale:4; 132 u_int8_t sc_flags; 133 #define SCF_NOOPT 0x01 /* no TCP options */ 134 #define SCF_WINSCALE 0x02 /* negotiated window scaling */ 135 #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */ 136 /* MSS is implicit */ 137 #define SCF_UNREACH 0x10 /* icmp unreachable received */ 138 #define SCF_SIGNATURE 0x20 /* send MD5 digests */ 139 #define SCF_SACK 0x80 /* send SACK option */ 140 #ifndef TCP_OFFLOAD_DISABLE 141 struct toe_usrreqs *sc_tu; /* TOE operations */ 142 void *sc_toepcb; /* TOE protocol block */ 143 #endif 144 #ifdef MAC 145 struct label *sc_label; /* MAC label reference */ 146 #endif 147 }; 148 149 #ifdef TCP_OFFLOAD_DISABLE 150 #define TOEPCB_ISSET(sc) (0) 151 #else 152 #define TOEPCB_ISSET(sc) ((sc)->sc_toepcb != NULL) 153 #endif 154 155 156 struct syncache_head { 157 struct mtx sch_mtx; 158 TAILQ_HEAD(sch_head, syncache) sch_bucket; 159 struct callout sch_timer; 160 int sch_nextc; 161 u_int sch_length; 162 u_int sch_oddeven; 163 u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE]; 164 u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE]; 165 u_int sch_reseed; /* time_uptime, seconds */ 166 }; 167 168 static void syncache_drop(struct syncache *, struct syncache_head *); 169 static void syncache_free(struct syncache *); 170 static void syncache_insert(struct syncache *, struct syncache_head *); 171 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 172 static int syncache_respond(struct syncache *); 173 static struct socket *syncache_socket(struct syncache *, struct socket *, 174 struct mbuf *m); 175 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 176 int docallout); 177 static void syncache_timer(void *); 178 static void syncookie_generate(struct syncache_head *, struct syncache *, 179 u_int32_t *); 180 static struct syncache 181 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 182 struct syncache *, struct tcpopt *, struct tcphdr *, 183 struct socket *); 184 185 /* 186 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 187 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 188 * the odds are that the user has given up attempting to connect by then. 189 */ 190 #define SYNCACHE_MAXREXMTS 3 191 192 /* Arbitrary values */ 193 #define TCP_SYNCACHE_HASHSIZE 512 194 #define TCP_SYNCACHE_BUCKETLIMIT 30 195 196 struct tcp_syncache { 197 struct syncache_head *hashbase; 198 uma_zone_t zone; 199 u_int hashsize; 200 u_int hashmask; 201 u_int bucket_limit; 202 u_int cache_count; /* XXX: unprotected */ 203 u_int cache_limit; 204 u_int rexmt_limit; 205 u_int hash_secret; 206 }; 207 static struct tcp_syncache tcp_syncache; 208 209 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 210 211 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 212 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 213 214 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 215 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 216 217 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 218 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 219 220 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 221 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 222 223 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 224 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 225 226 int tcp_sc_rst_sock_fail = 1; 227 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, CTLFLAG_RW, 228 &tcp_sc_rst_sock_fail, 0, "Send reset on socket allocation failure"); 229 230 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 231 232 #define SYNCACHE_HASH(inc, mask) \ 233 ((tcp_syncache.hash_secret ^ \ 234 (inc)->inc_faddr.s_addr ^ \ 235 ((inc)->inc_faddr.s_addr >> 16) ^ \ 236 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 237 238 #define SYNCACHE_HASH6(inc, mask) \ 239 ((tcp_syncache.hash_secret ^ \ 240 (inc)->inc6_faddr.s6_addr32[0] ^ \ 241 (inc)->inc6_faddr.s6_addr32[3] ^ \ 242 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 243 244 #define ENDPTS_EQ(a, b) ( \ 245 (a)->ie_fport == (b)->ie_fport && \ 246 (a)->ie_lport == (b)->ie_lport && \ 247 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 248 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 249 ) 250 251 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 252 253 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 254 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 255 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 256 257 /* 258 * Requires the syncache entry to be already removed from the bucket list. 259 */ 260 static void 261 syncache_free(struct syncache *sc) 262 { 263 if (sc->sc_ipopts) 264 (void) m_free(sc->sc_ipopts); 265 #ifdef MAC 266 mac_syncache_destroy(&sc->sc_label); 267 #endif 268 269 uma_zfree(tcp_syncache.zone, sc); 270 } 271 272 void 273 syncache_init(void) 274 { 275 int i; 276 277 tcp_syncache.cache_count = 0; 278 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 279 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 280 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 281 tcp_syncache.hash_secret = arc4random(); 282 283 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 284 &tcp_syncache.hashsize); 285 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 286 &tcp_syncache.bucket_limit); 287 if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) { 288 printf("WARNING: syncache hash size is not a power of 2.\n"); 289 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 290 } 291 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 292 293 /* Set limits. */ 294 tcp_syncache.cache_limit = 295 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 296 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 297 &tcp_syncache.cache_limit); 298 299 /* Allocate the hash table. */ 300 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 301 tcp_syncache.hashsize * sizeof(struct syncache_head), 302 M_SYNCACHE, M_WAITOK | M_ZERO); 303 304 /* Initialize the hash buckets. */ 305 for (i = 0; i < tcp_syncache.hashsize; i++) { 306 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 307 mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 308 NULL, MTX_DEF); 309 callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer, 310 &tcp_syncache.hashbase[i].sch_mtx, 0); 311 tcp_syncache.hashbase[i].sch_length = 0; 312 } 313 314 /* Create the syncache entry zone. */ 315 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 316 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 317 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); 318 } 319 320 /* 321 * Inserts a syncache entry into the specified bucket row. 322 * Locks and unlocks the syncache_head autonomously. 323 */ 324 static void 325 syncache_insert(struct syncache *sc, struct syncache_head *sch) 326 { 327 struct syncache *sc2; 328 329 SCH_LOCK(sch); 330 331 /* 332 * Make sure that we don't overflow the per-bucket limit. 333 * If the bucket is full, toss the oldest element. 334 */ 335 if (sch->sch_length >= tcp_syncache.bucket_limit) { 336 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 337 ("sch->sch_length incorrect")); 338 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 339 syncache_drop(sc2, sch); 340 tcpstat.tcps_sc_bucketoverflow++; 341 } 342 343 /* Put it into the bucket. */ 344 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 345 sch->sch_length++; 346 347 /* Reinitialize the bucket row's timer. */ 348 if (sch->sch_length == 1) 349 sch->sch_nextc = ticks + INT_MAX; 350 syncache_timeout(sc, sch, 1); 351 352 SCH_UNLOCK(sch); 353 354 tcp_syncache.cache_count++; 355 tcpstat.tcps_sc_added++; 356 } 357 358 /* 359 * Remove and free entry from syncache bucket row. 360 * Expects locked syncache head. 361 */ 362 static void 363 syncache_drop(struct syncache *sc, struct syncache_head *sch) 364 { 365 366 SCH_LOCK_ASSERT(sch); 367 368 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 369 sch->sch_length--; 370 371 #ifndef TCP_OFFLOAD_DISABLE 372 if (sc->sc_tu) 373 sc->sc_tu->tu_syncache_event(TOE_SC_DROP, sc->sc_toepcb); 374 #endif 375 syncache_free(sc); 376 tcp_syncache.cache_count--; 377 } 378 379 /* 380 * Engage/reengage time on bucket row. 381 */ 382 static void 383 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 384 { 385 sc->sc_rxttime = ticks + 386 TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]); 387 sc->sc_rxmits++; 388 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 389 sch->sch_nextc = sc->sc_rxttime; 390 if (docallout) 391 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 392 syncache_timer, (void *)sch); 393 } 394 } 395 396 /* 397 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 398 * If we have retransmitted an entry the maximum number of times, expire it. 399 * One separate timer for each bucket row. 400 */ 401 static void 402 syncache_timer(void *xsch) 403 { 404 struct syncache_head *sch = (struct syncache_head *)xsch; 405 struct syncache *sc, *nsc; 406 int tick = ticks; 407 char *s; 408 409 /* NB: syncache_head has already been locked by the callout. */ 410 SCH_LOCK_ASSERT(sch); 411 412 /* 413 * In the following cycle we may remove some entries and/or 414 * advance some timeouts, so re-initialize the bucket timer. 415 */ 416 sch->sch_nextc = tick + INT_MAX; 417 418 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 419 /* 420 * We do not check if the listen socket still exists 421 * and accept the case where the listen socket may be 422 * gone by the time we resend the SYN/ACK. We do 423 * not expect this to happens often. If it does, 424 * then the RST will be sent by the time the remote 425 * host does the SYN/ACK->ACK. 426 */ 427 if (TSTMP_GT(sc->sc_rxttime, tick)) { 428 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 429 sch->sch_nextc = sc->sc_rxttime; 430 continue; 431 } 432 if (sc->sc_rxmits > tcp_syncache.rexmt_limit) { 433 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 434 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 435 "giving up and removing syncache entry\n", 436 s, __func__); 437 free(s, M_TCPLOG); 438 } 439 syncache_drop(sc, sch); 440 tcpstat.tcps_sc_stale++; 441 continue; 442 } 443 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 444 log(LOG_DEBUG, "%s; %s: Response timeout, " 445 "retransmitting (%u) SYN|ACK\n", 446 s, __func__, sc->sc_rxmits); 447 free(s, M_TCPLOG); 448 } 449 450 (void) syncache_respond(sc); 451 tcpstat.tcps_sc_retransmitted++; 452 syncache_timeout(sc, sch, 0); 453 } 454 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 455 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 456 syncache_timer, (void *)(sch)); 457 } 458 459 /* 460 * Find an entry in the syncache. 461 * Returns always with locked syncache_head plus a matching entry or NULL. 462 */ 463 struct syncache * 464 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 465 { 466 struct syncache *sc; 467 struct syncache_head *sch; 468 469 #ifdef INET6 470 if (inc->inc_isipv6) { 471 sch = &tcp_syncache.hashbase[ 472 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 473 *schp = sch; 474 475 SCH_LOCK(sch); 476 477 /* Circle through bucket row to find matching entry. */ 478 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 479 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 480 return (sc); 481 } 482 } else 483 #endif 484 { 485 sch = &tcp_syncache.hashbase[ 486 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 487 *schp = sch; 488 489 SCH_LOCK(sch); 490 491 /* Circle through bucket row to find matching entry. */ 492 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 493 #ifdef INET6 494 if (sc->sc_inc.inc_isipv6) 495 continue; 496 #endif 497 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 498 return (sc); 499 } 500 } 501 SCH_LOCK_ASSERT(*schp); 502 return (NULL); /* always returns with locked sch */ 503 } 504 505 /* 506 * This function is called when we get a RST for a 507 * non-existent connection, so that we can see if the 508 * connection is in the syn cache. If it is, zap it. 509 */ 510 void 511 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 512 { 513 struct syncache *sc; 514 struct syncache_head *sch; 515 char *s = NULL; 516 517 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 518 SCH_LOCK_ASSERT(sch); 519 520 /* 521 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 522 * See RFC 793 page 65, section SEGMENT ARRIVES. 523 */ 524 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 525 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 526 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 527 "FIN flag set, segment ignored\n", s, __func__); 528 tcpstat.tcps_badrst++; 529 goto done; 530 } 531 532 /* 533 * No corresponding connection was found in syncache. 534 * If syncookies are enabled and possibly exclusively 535 * used, or we are under memory pressure, a valid RST 536 * may not find a syncache entry. In that case we're 537 * done and no SYN|ACK retransmissions will happen. 538 * Otherwise the the RST was misdirected or spoofed. 539 */ 540 if (sc == NULL) { 541 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 542 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 543 "syncache entry (possibly syncookie only), " 544 "segment ignored\n", s, __func__); 545 tcpstat.tcps_badrst++; 546 goto done; 547 } 548 549 /* 550 * If the RST bit is set, check the sequence number to see 551 * if this is a valid reset segment. 552 * RFC 793 page 37: 553 * In all states except SYN-SENT, all reset (RST) segments 554 * are validated by checking their SEQ-fields. A reset is 555 * valid if its sequence number is in the window. 556 * 557 * The sequence number in the reset segment is normally an 558 * echo of our outgoing acknowlegement numbers, but some hosts 559 * send a reset with the sequence number at the rightmost edge 560 * of our receive window, and we have to handle this case. 561 */ 562 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 563 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 564 syncache_drop(sc, sch); 565 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 566 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 567 "connection attempt aborted by remote endpoint\n", 568 s, __func__); 569 tcpstat.tcps_sc_reset++; 570 } else if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 571 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != IRS %u " 572 "(+WND %u), segment ignored\n", 573 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 574 tcpstat.tcps_badrst++; 575 } 576 577 done: 578 if (s != NULL) 579 free(s, M_TCPLOG); 580 SCH_UNLOCK(sch); 581 } 582 583 void 584 syncache_badack(struct in_conninfo *inc) 585 { 586 struct syncache *sc; 587 struct syncache_head *sch; 588 589 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 590 SCH_LOCK_ASSERT(sch); 591 if (sc != NULL) { 592 syncache_drop(sc, sch); 593 tcpstat.tcps_sc_badack++; 594 } 595 SCH_UNLOCK(sch); 596 } 597 598 void 599 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 600 { 601 struct syncache *sc; 602 struct syncache_head *sch; 603 604 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 605 SCH_LOCK_ASSERT(sch); 606 if (sc == NULL) 607 goto done; 608 609 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 610 if (ntohl(th->th_seq) != sc->sc_iss) 611 goto done; 612 613 /* 614 * If we've rertransmitted 3 times and this is our second error, 615 * we remove the entry. Otherwise, we allow it to continue on. 616 * This prevents us from incorrectly nuking an entry during a 617 * spurious network outage. 618 * 619 * See tcp_notify(). 620 */ 621 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 622 sc->sc_flags |= SCF_UNREACH; 623 goto done; 624 } 625 syncache_drop(sc, sch); 626 tcpstat.tcps_sc_unreach++; 627 done: 628 SCH_UNLOCK(sch); 629 } 630 631 /* 632 * Build a new TCP socket structure from a syncache entry. 633 */ 634 static struct socket * 635 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 636 { 637 struct inpcb *inp = NULL; 638 struct socket *so; 639 struct tcpcb *tp; 640 char *s; 641 642 INP_INFO_WLOCK_ASSERT(&tcbinfo); 643 644 /* 645 * Ok, create the full blown connection, and set things up 646 * as they would have been set up if we had created the 647 * connection when the SYN arrived. If we can't create 648 * the connection, abort it. 649 */ 650 so = sonewconn(lso, SS_ISCONNECTED); 651 if (so == NULL) { 652 /* 653 * Drop the connection; we will either send a RST or 654 * have the peer retransmit its SYN again after its 655 * RTO and try again. 656 */ 657 tcpstat.tcps_listendrop++; 658 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 659 log(LOG_DEBUG, "%s; %s: Socket create failed " 660 "due to limits or memory shortage\n", 661 s, __func__); 662 free(s, M_TCPLOG); 663 } 664 goto abort2; 665 } 666 #ifdef MAC 667 SOCK_LOCK(so); 668 mac_socketpeer_set_from_mbuf(m, so); 669 SOCK_UNLOCK(so); 670 #endif 671 672 inp = sotoinpcb(so); 673 INP_LOCK(inp); 674 675 /* Insert new socket into PCB hash list. */ 676 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 677 #ifdef INET6 678 if (sc->sc_inc.inc_isipv6) { 679 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 680 } else { 681 inp->inp_vflag &= ~INP_IPV6; 682 inp->inp_vflag |= INP_IPV4; 683 #endif 684 inp->inp_laddr = sc->sc_inc.inc_laddr; 685 #ifdef INET6 686 } 687 #endif 688 inp->inp_lport = sc->sc_inc.inc_lport; 689 if (in_pcbinshash(inp) != 0) { 690 /* 691 * Undo the assignments above if we failed to 692 * put the PCB on the hash lists. 693 */ 694 #ifdef INET6 695 if (sc->sc_inc.inc_isipv6) 696 inp->in6p_laddr = in6addr_any; 697 else 698 #endif 699 inp->inp_laddr.s_addr = INADDR_ANY; 700 inp->inp_lport = 0; 701 goto abort; 702 } 703 #ifdef IPSEC 704 /* Copy old policy into new socket's. */ 705 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 706 printf("syncache_socket: could not copy policy\n"); 707 #endif 708 #ifdef INET6 709 if (sc->sc_inc.inc_isipv6) { 710 struct inpcb *oinp = sotoinpcb(lso); 711 struct in6_addr laddr6; 712 struct sockaddr_in6 sin6; 713 /* 714 * Inherit socket options from the listening socket. 715 * Note that in6p_inputopts are not (and should not be) 716 * copied, since it stores previously received options and is 717 * used to detect if each new option is different than the 718 * previous one and hence should be passed to a user. 719 * If we copied in6p_inputopts, a user would not be able to 720 * receive options just after calling the accept system call. 721 */ 722 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 723 if (oinp->in6p_outputopts) 724 inp->in6p_outputopts = 725 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 726 727 sin6.sin6_family = AF_INET6; 728 sin6.sin6_len = sizeof(sin6); 729 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 730 sin6.sin6_port = sc->sc_inc.inc_fport; 731 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 732 laddr6 = inp->in6p_laddr; 733 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 734 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 735 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6, 736 thread0.td_ucred)) { 737 inp->in6p_laddr = laddr6; 738 goto abort; 739 } 740 /* Override flowlabel from in6_pcbconnect. */ 741 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK; 742 inp->in6p_flowinfo |= sc->sc_flowlabel; 743 } else 744 #endif 745 { 746 struct in_addr laddr; 747 struct sockaddr_in sin; 748 749 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 750 751 if (inp->inp_options == NULL) { 752 inp->inp_options = sc->sc_ipopts; 753 sc->sc_ipopts = NULL; 754 } 755 756 sin.sin_family = AF_INET; 757 sin.sin_len = sizeof(sin); 758 sin.sin_addr = sc->sc_inc.inc_faddr; 759 sin.sin_port = sc->sc_inc.inc_fport; 760 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 761 laddr = inp->inp_laddr; 762 if (inp->inp_laddr.s_addr == INADDR_ANY) 763 inp->inp_laddr = sc->sc_inc.inc_laddr; 764 if (in_pcbconnect(inp, (struct sockaddr *)&sin, 765 thread0.td_ucred)) { 766 inp->inp_laddr = laddr; 767 goto abort; 768 } 769 } 770 tp = intotcpcb(inp); 771 tp->t_state = TCPS_SYN_RECEIVED; 772 tp->iss = sc->sc_iss; 773 tp->irs = sc->sc_irs; 774 tcp_rcvseqinit(tp); 775 tcp_sendseqinit(tp); 776 tp->snd_wl1 = sc->sc_irs; 777 tp->snd_max = tp->iss + 1; 778 tp->snd_nxt = tp->iss + 1; 779 tp->rcv_up = sc->sc_irs + 1; 780 tp->rcv_wnd = sc->sc_wnd; 781 tp->rcv_adv += tp->rcv_wnd; 782 tp->last_ack_sent = tp->rcv_nxt; 783 784 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 785 if (sc->sc_flags & SCF_NOOPT) 786 tp->t_flags |= TF_NOOPT; 787 else { 788 if (sc->sc_flags & SCF_WINSCALE) { 789 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 790 tp->snd_scale = sc->sc_requested_s_scale; 791 tp->request_r_scale = sc->sc_requested_r_scale; 792 } 793 if (sc->sc_flags & SCF_TIMESTAMP) { 794 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 795 tp->ts_recent = sc->sc_tsreflect; 796 tp->ts_recent_age = ticks; 797 tp->ts_offset = sc->sc_tsoff; 798 } 799 #ifdef TCP_SIGNATURE 800 if (sc->sc_flags & SCF_SIGNATURE) 801 tp->t_flags |= TF_SIGNATURE; 802 #endif 803 if (sc->sc_flags & SCF_SACK) 804 tp->t_flags |= TF_SACK_PERMIT; 805 } 806 807 /* 808 * Set up MSS and get cached values from tcp_hostcache. 809 * This might overwrite some of the defaults we just set. 810 */ 811 tcp_mss(tp, sc->sc_peer_mss); 812 813 /* 814 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 815 */ 816 if (sc->sc_rxmits) 817 tp->snd_cwnd = tp->t_maxseg; 818 tcp_timer_activate(tp, TT_KEEP, tcp_keepinit); 819 820 INP_UNLOCK(inp); 821 822 tcpstat.tcps_accepts++; 823 return (so); 824 825 abort: 826 INP_UNLOCK(inp); 827 abort2: 828 if (so != NULL) 829 soabort(so); 830 return (NULL); 831 } 832 833 /* 834 * This function gets called when we receive an ACK for a 835 * socket in the LISTEN state. We look up the connection 836 * in the syncache, and if its there, we pull it out of 837 * the cache and turn it into a full-blown connection in 838 * the SYN-RECEIVED state. 839 */ 840 int 841 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 842 struct socket **lsop, struct mbuf *m) 843 { 844 struct syncache *sc; 845 struct syncache_head *sch; 846 struct syncache scs; 847 char *s; 848 849 /* 850 * Global TCP locks are held because we manipulate the PCB lists 851 * and create a new socket. 852 */ 853 INP_INFO_WLOCK_ASSERT(&tcbinfo); 854 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 855 ("%s: can handle only ACK", __func__)); 856 857 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 858 SCH_LOCK_ASSERT(sch); 859 if (sc == NULL) { 860 /* 861 * There is no syncache entry, so see if this ACK is 862 * a returning syncookie. To do this, first: 863 * A. See if this socket has had a syncache entry dropped in 864 * the past. We don't want to accept a bogus syncookie 865 * if we've never received a SYN. 866 * B. check that the syncookie is valid. If it is, then 867 * cobble up a fake syncache entry, and return. 868 */ 869 if (!tcp_syncookies) { 870 SCH_UNLOCK(sch); 871 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 872 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 873 "segment rejected (syncookies disabled)\n", 874 s, __func__); 875 goto failed; 876 } 877 bzero(&scs, sizeof(scs)); 878 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop); 879 SCH_UNLOCK(sch); 880 if (sc == NULL) { 881 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 882 log(LOG_DEBUG, "%s; %s: Segment failed " 883 "SYNCOOKIE authentication, segment rejected " 884 "(probably spoofed)\n", s, __func__); 885 goto failed; 886 } 887 } else { 888 /* Pull out the entry to unlock the bucket row. */ 889 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 890 sch->sch_length--; 891 tcp_syncache.cache_count--; 892 SCH_UNLOCK(sch); 893 } 894 895 /* 896 * Segment validation: 897 * ACK must match our initial sequence number + 1 (the SYN|ACK). 898 */ 899 if (th->th_ack != sc->sc_iss + 1 && !TOEPCB_ISSET(sc)) { 900 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 901 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 902 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 903 goto failed; 904 } 905 /* 906 * The SEQ must match the received initial receive sequence 907 * number + 1 (the SYN) because we didn't ACK any data that 908 * may have come with the SYN. 909 */ 910 if (th->th_seq != sc->sc_irs + 1 && !TOEPCB_ISSET(sc)) { 911 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 912 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 913 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 914 goto failed; 915 } 916 917 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 918 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 919 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 920 "segment rejected\n", s, __func__); 921 goto failed; 922 } 923 /* 924 * If timestamps were negotiated the reflected timestamp 925 * must be equal to what we actually sent in the SYN|ACK. 926 */ 927 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts && 928 !TOEPCB_ISSET(sc)) { 929 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 930 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 931 "segment rejected\n", 932 s, __func__, to->to_tsecr, sc->sc_ts); 933 goto failed; 934 } 935 936 *lsop = syncache_socket(sc, *lsop, m); 937 938 if (*lsop == NULL) 939 tcpstat.tcps_sc_aborted++; 940 else 941 tcpstat.tcps_sc_completed++; 942 943 if (sc != &scs) 944 syncache_free(sc); 945 return (1); 946 failed: 947 if (sc != NULL && sc != &scs) 948 syncache_free(sc); 949 if (s != NULL) 950 free(s, M_TCPLOG); 951 *lsop = NULL; 952 return (0); 953 } 954 955 /* 956 * Given a LISTEN socket and an inbound SYN request, add 957 * this to the syn cache, and send back a segment: 958 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 959 * to the source. 960 * 961 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 962 * Doing so would require that we hold onto the data and deliver it 963 * to the application. However, if we are the target of a SYN-flood 964 * DoS attack, an attacker could send data which would eventually 965 * consume all available buffer space if it were ACKed. By not ACKing 966 * the data, we avoid this DoS scenario. 967 */ 968 static void 969 _syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 970 struct inpcb *inp, struct socket **lsop, struct mbuf *m, 971 struct toe_usrreqs *tu, void *toepcb) 972 { 973 struct tcpcb *tp; 974 struct socket *so; 975 struct syncache *sc = NULL; 976 struct syncache_head *sch; 977 struct mbuf *ipopts = NULL; 978 u_int32_t flowtmp; 979 int win, sb_hiwat, ip_ttl, ip_tos, noopt; 980 char *s; 981 #ifdef INET6 982 int autoflowlabel = 0; 983 #endif 984 #ifdef MAC 985 struct label *maclabel; 986 #endif 987 struct syncache scs; 988 989 INP_INFO_WLOCK_ASSERT(&tcbinfo); 990 INP_LOCK_ASSERT(inp); /* listen socket */ 991 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 992 ("%s: unexpected tcp flags", __func__)); 993 994 /* 995 * Combine all so/tp operations very early to drop the INP lock as 996 * soon as possible. 997 */ 998 so = *lsop; 999 tp = sototcpcb(so); 1000 1001 #ifdef INET6 1002 if (inc->inc_isipv6 && 1003 (inp->in6p_flags & IN6P_AUTOFLOWLABEL)) 1004 autoflowlabel = 1; 1005 #endif 1006 ip_ttl = inp->inp_ip_ttl; 1007 ip_tos = inp->inp_ip_tos; 1008 win = sbspace(&so->so_rcv); 1009 sb_hiwat = so->so_rcv.sb_hiwat; 1010 noopt = (tp->t_flags & TF_NOOPT); 1011 1012 so = NULL; 1013 tp = NULL; 1014 1015 #ifdef MAC 1016 if (mac_syncache_init(&maclabel) != 0) { 1017 INP_UNLOCK(inp); 1018 INP_INFO_WUNLOCK(&tcbinfo); 1019 goto done; 1020 } else 1021 mac_syncache_create(maclabel, inp); 1022 #endif 1023 INP_UNLOCK(inp); 1024 INP_INFO_WUNLOCK(&tcbinfo); 1025 1026 /* 1027 * Remember the IP options, if any. 1028 */ 1029 #ifdef INET6 1030 if (!inc->inc_isipv6) 1031 #endif 1032 ipopts = (m) ? ip_srcroute(m) : NULL; 1033 1034 /* 1035 * See if we already have an entry for this connection. 1036 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1037 * 1038 * XXX: should the syncache be re-initialized with the contents 1039 * of the new SYN here (which may have different options?) 1040 * 1041 * XXX: We do not check the sequence number to see if this is a 1042 * real retransmit or a new connection attempt. The question is 1043 * how to handle such a case; either ignore it as spoofed, or 1044 * drop the current entry and create a new one? 1045 */ 1046 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1047 SCH_LOCK_ASSERT(sch); 1048 if (sc != NULL) { 1049 #ifndef TCP_OFFLOAD_DISABLE 1050 if (sc->sc_tu) 1051 sc->sc_tu->tu_syncache_event(TOE_SC_ENTRY_PRESENT, 1052 sc->sc_toepcb); 1053 #endif 1054 tcpstat.tcps_sc_dupsyn++; 1055 if (ipopts) { 1056 /* 1057 * If we were remembering a previous source route, 1058 * forget it and use the new one we've been given. 1059 */ 1060 if (sc->sc_ipopts) 1061 (void) m_free(sc->sc_ipopts); 1062 sc->sc_ipopts = ipopts; 1063 } 1064 /* 1065 * Update timestamp if present. 1066 */ 1067 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1068 sc->sc_tsreflect = to->to_tsval; 1069 else 1070 sc->sc_flags &= ~SCF_TIMESTAMP; 1071 #ifdef MAC 1072 /* 1073 * Since we have already unconditionally allocated label 1074 * storage, free it up. The syncache entry will already 1075 * have an initialized label we can use. 1076 */ 1077 mac_syncache_destroy(&maclabel); 1078 KASSERT(sc->sc_label != NULL, 1079 ("%s: label not initialized", __func__)); 1080 #endif 1081 /* Retransmit SYN|ACK and reset retransmit count. */ 1082 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1083 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1084 "resetting timer and retransmitting SYN|ACK\n", 1085 s, __func__); 1086 free(s, M_TCPLOG); 1087 } 1088 if (!TOEPCB_ISSET(sc) && syncache_respond(sc) == 0) { 1089 sc->sc_rxmits = 0; 1090 syncache_timeout(sc, sch, 1); 1091 tcpstat.tcps_sndacks++; 1092 tcpstat.tcps_sndtotal++; 1093 } 1094 SCH_UNLOCK(sch); 1095 goto done; 1096 } 1097 1098 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1099 if (sc == NULL) { 1100 /* 1101 * The zone allocator couldn't provide more entries. 1102 * Treat this as if the cache was full; drop the oldest 1103 * entry and insert the new one. 1104 */ 1105 tcpstat.tcps_sc_zonefail++; 1106 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1107 syncache_drop(sc, sch); 1108 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1109 if (sc == NULL) { 1110 if (tcp_syncookies) { 1111 bzero(&scs, sizeof(scs)); 1112 sc = &scs; 1113 } else { 1114 SCH_UNLOCK(sch); 1115 if (ipopts) 1116 (void) m_free(ipopts); 1117 goto done; 1118 } 1119 } 1120 } 1121 1122 /* 1123 * Fill in the syncache values. 1124 */ 1125 #ifdef MAC 1126 sc->sc_label = maclabel; 1127 #endif 1128 sc->sc_ipopts = ipopts; 1129 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1130 #ifdef INET6 1131 if (!inc->inc_isipv6) 1132 #endif 1133 { 1134 sc->sc_ip_tos = ip_tos; 1135 sc->sc_ip_ttl = ip_ttl; 1136 } 1137 #ifndef TCP_OFFLOAD_DISABLE 1138 sc->sc_tu = tu; 1139 sc->sc_toepcb = toepcb; 1140 #endif 1141 sc->sc_irs = th->th_seq; 1142 sc->sc_iss = arc4random(); 1143 sc->sc_flags = 0; 1144 sc->sc_flowlabel = 0; 1145 1146 /* 1147 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1148 * win was derived from socket earlier in the function. 1149 */ 1150 win = imax(win, 0); 1151 win = imin(win, TCP_MAXWIN); 1152 sc->sc_wnd = win; 1153 1154 if (tcp_do_rfc1323) { 1155 /* 1156 * A timestamp received in a SYN makes 1157 * it ok to send timestamp requests and replies. 1158 */ 1159 if (to->to_flags & TOF_TS) { 1160 sc->sc_tsreflect = to->to_tsval; 1161 sc->sc_ts = ticks; 1162 sc->sc_flags |= SCF_TIMESTAMP; 1163 } 1164 if (to->to_flags & TOF_SCALE) { 1165 int wscale = 0; 1166 1167 /* 1168 * Pick the smallest possible scaling factor that 1169 * will still allow us to scale up to sb_max, aka 1170 * kern.ipc.maxsockbuf. 1171 * 1172 * We do this because there are broken firewalls that 1173 * will corrupt the window scale option, leading to 1174 * the other endpoint believing that our advertised 1175 * window is unscaled. At scale factors larger than 1176 * 5 the unscaled window will drop below 1500 bytes, 1177 * leading to serious problems when traversing these 1178 * broken firewalls. 1179 * 1180 * With the default maxsockbuf of 256K, a scale factor 1181 * of 3 will be chosen by this algorithm. Those who 1182 * choose a larger maxsockbuf should watch out 1183 * for the compatiblity problems mentioned above. 1184 * 1185 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1186 * or <SYN,ACK>) segment itself is never scaled. 1187 */ 1188 while (wscale < TCP_MAX_WINSHIFT && 1189 (TCP_MAXWIN << wscale) < sb_max) 1190 wscale++; 1191 sc->sc_requested_r_scale = wscale; 1192 sc->sc_requested_s_scale = to->to_wscale; 1193 sc->sc_flags |= SCF_WINSCALE; 1194 } 1195 } 1196 #ifdef TCP_SIGNATURE 1197 /* 1198 * If listening socket requested TCP digests, and received SYN 1199 * contains the option, flag this in the syncache so that 1200 * syncache_respond() will do the right thing with the SYN+ACK. 1201 * XXX: Currently we always record the option by default and will 1202 * attempt to use it in syncache_respond(). 1203 */ 1204 if (to->to_flags & TOF_SIGNATURE) 1205 sc->sc_flags |= SCF_SIGNATURE; 1206 #endif 1207 if (to->to_flags & TOF_SACKPERM) 1208 sc->sc_flags |= SCF_SACK; 1209 if (to->to_flags & TOF_MSS) 1210 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1211 if (noopt) 1212 sc->sc_flags |= SCF_NOOPT; 1213 1214 if (tcp_syncookies) { 1215 syncookie_generate(sch, sc, &flowtmp); 1216 #ifdef INET6 1217 if (autoflowlabel) 1218 sc->sc_flowlabel = flowtmp; 1219 #endif 1220 } else { 1221 #ifdef INET6 1222 if (autoflowlabel) 1223 sc->sc_flowlabel = 1224 (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK); 1225 #endif 1226 } 1227 SCH_UNLOCK(sch); 1228 1229 /* 1230 * Do a standard 3-way handshake. 1231 */ 1232 if (TOEPCB_ISSET(sc) || syncache_respond(sc) == 0) { 1233 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs) 1234 syncache_free(sc); 1235 else if (sc != &scs) 1236 syncache_insert(sc, sch); /* locks and unlocks sch */ 1237 tcpstat.tcps_sndacks++; 1238 tcpstat.tcps_sndtotal++; 1239 } else { 1240 if (sc != &scs) 1241 syncache_free(sc); 1242 tcpstat.tcps_sc_dropped++; 1243 } 1244 1245 done: 1246 #ifdef MAC 1247 if (sc == &scs) 1248 mac_syncache_destroy(&maclabel); 1249 #endif 1250 if (m) { 1251 1252 *lsop = NULL; 1253 m_freem(m); 1254 } 1255 return; 1256 } 1257 1258 static int 1259 syncache_respond(struct syncache *sc) 1260 { 1261 struct ip *ip = NULL; 1262 struct mbuf *m; 1263 struct tcphdr *th; 1264 int optlen, error; 1265 u_int16_t hlen, tlen, mssopt; 1266 struct tcpopt to; 1267 #ifdef INET6 1268 struct ip6_hdr *ip6 = NULL; 1269 #endif 1270 1271 hlen = 1272 #ifdef INET6 1273 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) : 1274 #endif 1275 sizeof(struct ip); 1276 tlen = hlen + sizeof(struct tcphdr); 1277 1278 /* Determine MSS we advertize to other end of connection. */ 1279 mssopt = tcp_mssopt(&sc->sc_inc); 1280 if (sc->sc_peer_mss) 1281 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss); 1282 1283 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1284 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1285 ("syncache: mbuf too small")); 1286 1287 /* Create the IP+TCP header from scratch. */ 1288 m = m_gethdr(M_DONTWAIT, MT_DATA); 1289 if (m == NULL) 1290 return (ENOBUFS); 1291 #ifdef MAC 1292 mac_syncache_create_mbuf(sc->sc_label, m); 1293 #endif 1294 m->m_data += max_linkhdr; 1295 m->m_len = tlen; 1296 m->m_pkthdr.len = tlen; 1297 m->m_pkthdr.rcvif = NULL; 1298 1299 #ifdef INET6 1300 if (sc->sc_inc.inc_isipv6) { 1301 ip6 = mtod(m, struct ip6_hdr *); 1302 ip6->ip6_vfc = IPV6_VERSION; 1303 ip6->ip6_nxt = IPPROTO_TCP; 1304 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1305 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1306 ip6->ip6_plen = htons(tlen - hlen); 1307 /* ip6_hlim is set after checksum */ 1308 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1309 ip6->ip6_flow |= sc->sc_flowlabel; 1310 1311 th = (struct tcphdr *)(ip6 + 1); 1312 } else 1313 #endif 1314 { 1315 ip = mtod(m, struct ip *); 1316 ip->ip_v = IPVERSION; 1317 ip->ip_hl = sizeof(struct ip) >> 2; 1318 ip->ip_len = tlen; 1319 ip->ip_id = 0; 1320 ip->ip_off = 0; 1321 ip->ip_sum = 0; 1322 ip->ip_p = IPPROTO_TCP; 1323 ip->ip_src = sc->sc_inc.inc_laddr; 1324 ip->ip_dst = sc->sc_inc.inc_faddr; 1325 ip->ip_ttl = sc->sc_ip_ttl; 1326 ip->ip_tos = sc->sc_ip_tos; 1327 1328 /* 1329 * See if we should do MTU discovery. Route lookups are 1330 * expensive, so we will only unset the DF bit if: 1331 * 1332 * 1) path_mtu_discovery is disabled 1333 * 2) the SCF_UNREACH flag has been set 1334 */ 1335 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1336 ip->ip_off |= IP_DF; 1337 1338 th = (struct tcphdr *)(ip + 1); 1339 } 1340 th->th_sport = sc->sc_inc.inc_lport; 1341 th->th_dport = sc->sc_inc.inc_fport; 1342 1343 th->th_seq = htonl(sc->sc_iss); 1344 th->th_ack = htonl(sc->sc_irs + 1); 1345 th->th_off = sizeof(struct tcphdr) >> 2; 1346 th->th_x2 = 0; 1347 th->th_flags = TH_SYN|TH_ACK; 1348 th->th_win = htons(sc->sc_wnd); 1349 th->th_urp = 0; 1350 1351 /* Tack on the TCP options. */ 1352 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1353 to.to_flags = 0; 1354 1355 to.to_mss = mssopt; 1356 to.to_flags = TOF_MSS; 1357 if (sc->sc_flags & SCF_WINSCALE) { 1358 to.to_wscale = sc->sc_requested_r_scale; 1359 to.to_flags |= TOF_SCALE; 1360 } 1361 if (sc->sc_flags & SCF_TIMESTAMP) { 1362 /* Virgin timestamp or TCP cookie enhanced one. */ 1363 to.to_tsval = sc->sc_ts; 1364 to.to_tsecr = sc->sc_tsreflect; 1365 to.to_flags |= TOF_TS; 1366 } 1367 if (sc->sc_flags & SCF_SACK) 1368 to.to_flags |= TOF_SACKPERM; 1369 #ifdef TCP_SIGNATURE 1370 if (sc->sc_flags & SCF_SIGNATURE) 1371 to.to_flags |= TOF_SIGNATURE; 1372 #endif 1373 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1374 1375 /* Adjust headers by option size. */ 1376 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1377 m->m_len += optlen; 1378 m->m_pkthdr.len += optlen; 1379 1380 #ifdef TCP_SIGNATURE 1381 if (sc->sc_flags & SCF_SIGNATURE) 1382 tcp_signature_compute(m, sizeof(struct ip), 0, optlen, 1383 to.to_signature, IPSEC_DIR_OUTBOUND); 1384 #endif 1385 #ifdef INET6 1386 if (sc->sc_inc.inc_isipv6) 1387 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1388 else 1389 #endif 1390 ip->ip_len += optlen; 1391 } else 1392 optlen = 0; 1393 1394 #ifdef INET6 1395 if (sc->sc_inc.inc_isipv6) { 1396 th->th_sum = 0; 1397 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, 1398 tlen + optlen - hlen); 1399 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1400 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1401 } else 1402 #endif 1403 { 1404 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1405 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1406 m->m_pkthdr.csum_flags = CSUM_TCP; 1407 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1408 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1409 } 1410 return (error); 1411 } 1412 1413 void 1414 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1415 struct inpcb *inp, struct socket **lsop, struct mbuf *m) 1416 { 1417 _syncache_add(inc, to, th, inp, lsop, m, NULL, NULL); 1418 } 1419 1420 void 1421 syncache_offload_add(struct in_conninfo *inc, struct tcpopt *to, 1422 struct tcphdr *th, struct inpcb *inp, struct socket **lsop, 1423 struct toe_usrreqs *tu, void *toepcb) 1424 { 1425 _syncache_add(inc, to, th, inp, lsop, NULL, tu, toepcb); 1426 } 1427 1428 /* 1429 * The purpose of SYN cookies is to avoid keeping track of all SYN's we 1430 * receive and to be able to handle SYN floods from bogus source addresses 1431 * (where we will never receive any reply). SYN floods try to exhaust all 1432 * our memory and available slots in the SYN cache table to cause a denial 1433 * of service to legitimate users of the local host. 1434 * 1435 * The idea of SYN cookies is to encode and include all necessary information 1436 * about the connection setup state within the SYN-ACK we send back and thus 1437 * to get along without keeping any local state until the ACK to the SYN-ACK 1438 * arrives (if ever). Everything we need to know should be available from 1439 * the information we encoded in the SYN-ACK. 1440 * 1441 * More information about the theory behind SYN cookies and its first 1442 * discussion and specification can be found at: 1443 * http://cr.yp.to/syncookies.html (overview) 1444 * http://cr.yp.to/syncookies/archive (gory details) 1445 * 1446 * This implementation extends the orginal idea and first implementation 1447 * of FreeBSD by using not only the initial sequence number field to store 1448 * information but also the timestamp field if present. This way we can 1449 * keep track of the entire state we need to know to recreate the session in 1450 * its original form. Almost all TCP speakers implement RFC1323 timestamps 1451 * these days. For those that do not we still have to live with the known 1452 * shortcomings of the ISN only SYN cookies. 1453 * 1454 * Cookie layers: 1455 * 1456 * Initial sequence number we send: 1457 * 31|................................|0 1458 * DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP 1459 * D = MD5 Digest (first dword) 1460 * M = MSS index 1461 * R = Rotation of secret 1462 * P = Odd or Even secret 1463 * 1464 * The MD5 Digest is computed with over following parameters: 1465 * a) randomly rotated secret 1466 * b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6) 1467 * c) the received initial sequence number from remote host 1468 * d) the rotation offset and odd/even bit 1469 * 1470 * Timestamp we send: 1471 * 31|................................|0 1472 * DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5 1473 * D = MD5 Digest (third dword) (only as filler) 1474 * S = Requested send window scale 1475 * R = Requested receive window scale 1476 * A = SACK allowed 1477 * 5 = TCP-MD5 enabled (not implemented yet) 1478 * XORed with MD5 Digest (forth dword) 1479 * 1480 * The timestamp isn't cryptographically secure and doesn't need to be. 1481 * The double use of the MD5 digest dwords ties it to a specific remote/ 1482 * local host/port, remote initial sequence number and our local time 1483 * limited secret. A received timestamp is reverted (XORed) and then 1484 * the contained MD5 dword is compared to the computed one to ensure the 1485 * timestamp belongs to the SYN-ACK we sent. The other parameters may 1486 * have been tampered with but this isn't different from supplying bogus 1487 * values in the SYN in the first place. 1488 * 1489 * Some problems with SYN cookies remain however: 1490 * Consider the problem of a recreated (and retransmitted) cookie. If the 1491 * original SYN was accepted, the connection is established. The second 1492 * SYN is inflight, and if it arrives with an ISN that falls within the 1493 * receive window, the connection is killed. 1494 * 1495 * Notes: 1496 * A heuristic to determine when to accept syn cookies is not necessary. 1497 * An ACK flood would cause the syncookie verification to be attempted, 1498 * but a SYN flood causes syncookies to be generated. Both are of equal 1499 * cost, so there's no point in trying to optimize the ACK flood case. 1500 * Also, if you don't process certain ACKs for some reason, then all someone 1501 * would have to do is launch a SYN and ACK flood at the same time, which 1502 * would stop cookie verification and defeat the entire purpose of syncookies. 1503 */ 1504 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 }; 1505 1506 static void 1507 syncookie_generate(struct syncache_head *sch, struct syncache *sc, 1508 u_int32_t *flowlabel) 1509 { 1510 MD5_CTX ctx; 1511 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1512 u_int32_t data; 1513 u_int32_t *secbits; 1514 u_int off, pmss, mss; 1515 int i; 1516 1517 SCH_LOCK_ASSERT(sch); 1518 1519 /* Which of the two secrets to use. */ 1520 secbits = sch->sch_oddeven ? 1521 sch->sch_secbits_odd : sch->sch_secbits_even; 1522 1523 /* Reseed secret if too old. */ 1524 if (sch->sch_reseed < time_uptime) { 1525 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */ 1526 secbits = sch->sch_oddeven ? 1527 sch->sch_secbits_odd : sch->sch_secbits_even; 1528 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++) 1529 secbits[i] = arc4random(); 1530 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME; 1531 } 1532 1533 /* Secret rotation offset. */ 1534 off = sc->sc_iss & 0x7; /* iss was randomized before */ 1535 1536 /* Maximum segment size calculation. */ 1537 pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss); 1538 for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--) 1539 if (tcp_sc_msstab[mss] <= pmss) 1540 break; 1541 1542 /* Fold parameters and MD5 digest into the ISN we will send. */ 1543 data = sch->sch_oddeven;/* odd or even secret, 1 bit */ 1544 data |= off << 1; /* secret offset, derived from iss, 3 bits */ 1545 data |= mss << 4; /* mss, 3 bits */ 1546 1547 MD5Init(&ctx); 1548 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1549 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1550 MD5Update(&ctx, secbits, off); 1551 MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc)); 1552 MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs)); 1553 MD5Update(&ctx, &data, sizeof(data)); 1554 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1555 1556 data |= (md5_buffer[0] << 7); 1557 sc->sc_iss = data; 1558 1559 #ifdef INET6 1560 *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1561 #endif 1562 1563 /* Additional parameters are stored in the timestamp if present. */ 1564 if (sc->sc_flags & SCF_TIMESTAMP) { 1565 data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */ 1566 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */ 1567 data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */ 1568 data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */ 1569 data |= md5_buffer[2] << 10; /* more digest bits */ 1570 data ^= md5_buffer[3]; 1571 sc->sc_ts = data; 1572 sc->sc_tsoff = data - ticks; /* after XOR */ 1573 } 1574 1575 tcpstat.tcps_sc_sendcookie++; 1576 return; 1577 } 1578 1579 static struct syncache * 1580 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1581 struct syncache *sc, struct tcpopt *to, struct tcphdr *th, 1582 struct socket *so) 1583 { 1584 MD5_CTX ctx; 1585 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1586 u_int32_t data = 0; 1587 u_int32_t *secbits; 1588 tcp_seq ack, seq; 1589 int off, mss, wnd, flags; 1590 1591 SCH_LOCK_ASSERT(sch); 1592 1593 /* 1594 * Pull information out of SYN-ACK/ACK and 1595 * revert sequence number advances. 1596 */ 1597 ack = th->th_ack - 1; 1598 seq = th->th_seq - 1; 1599 off = (ack >> 1) & 0x7; 1600 mss = (ack >> 4) & 0x7; 1601 flags = ack & 0x7f; 1602 1603 /* Which of the two secrets to use. */ 1604 secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even; 1605 1606 /* 1607 * The secret wasn't updated for the lifetime of a syncookie, 1608 * so this SYN-ACK/ACK is either too old (replay) or totally bogus. 1609 */ 1610 if (sch->sch_reseed < time_uptime) { 1611 return (NULL); 1612 } 1613 1614 /* Recompute the digest so we can compare it. */ 1615 MD5Init(&ctx); 1616 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1617 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1618 MD5Update(&ctx, secbits, off); 1619 MD5Update(&ctx, inc, sizeof(*inc)); 1620 MD5Update(&ctx, &seq, sizeof(seq)); 1621 MD5Update(&ctx, &flags, sizeof(flags)); 1622 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1623 1624 /* Does the digest part of or ACK'ed ISS match? */ 1625 if ((ack & (~0x7f)) != (md5_buffer[0] << 7)) 1626 return (NULL); 1627 1628 /* Does the digest part of our reflected timestamp match? */ 1629 if (to->to_flags & TOF_TS) { 1630 data = md5_buffer[3] ^ to->to_tsecr; 1631 if ((data & (~0x3ff)) != (md5_buffer[2] << 10)) 1632 return (NULL); 1633 } 1634 1635 /* Fill in the syncache values. */ 1636 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1637 sc->sc_ipopts = NULL; 1638 1639 sc->sc_irs = seq; 1640 sc->sc_iss = ack; 1641 1642 #ifdef INET6 1643 if (inc->inc_isipv6) { 1644 if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL) 1645 sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1646 } else 1647 #endif 1648 { 1649 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl; 1650 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos; 1651 } 1652 1653 /* Additional parameters that were encoded in the timestamp. */ 1654 if (data) { 1655 sc->sc_flags |= SCF_TIMESTAMP; 1656 sc->sc_tsreflect = to->to_tsval; 1657 sc->sc_ts = to->to_tsecr; 1658 sc->sc_tsoff = to->to_tsecr - ticks; 1659 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0; 1660 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0; 1661 sc->sc_requested_s_scale = min((data >> 2) & 0xf, 1662 TCP_MAX_WINSHIFT); 1663 sc->sc_requested_r_scale = min((data >> 6) & 0xf, 1664 TCP_MAX_WINSHIFT); 1665 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale) 1666 sc->sc_flags |= SCF_WINSCALE; 1667 } else 1668 sc->sc_flags |= SCF_NOOPT; 1669 1670 wnd = sbspace(&so->so_rcv); 1671 wnd = imax(wnd, 0); 1672 wnd = imin(wnd, TCP_MAXWIN); 1673 sc->sc_wnd = wnd; 1674 1675 sc->sc_rxmits = 0; 1676 sc->sc_peer_mss = tcp_sc_msstab[mss]; 1677 1678 tcpstat.tcps_sc_recvcookie++; 1679 return (sc); 1680 } 1681 1682 /* 1683 * Returns the current number of syncache entries. This number 1684 * will probably change before you get around to calling 1685 * syncache_pcblist. 1686 */ 1687 1688 int 1689 syncache_pcbcount(void) 1690 { 1691 struct syncache_head *sch; 1692 int count, i; 1693 1694 for (count = 0, i = 0; i < tcp_syncache.hashsize; i++) { 1695 /* No need to lock for a read. */ 1696 sch = &tcp_syncache.hashbase[i]; 1697 count += sch->sch_length; 1698 } 1699 return count; 1700 } 1701 1702 /* 1703 * Exports the syncache entries to userland so that netstat can display 1704 * them alongside the other sockets. This function is intended to be 1705 * called only from tcp_pcblist. 1706 * 1707 * Due to concurrency on an active system, the number of pcbs exported 1708 * may have no relation to max_pcbs. max_pcbs merely indicates the 1709 * amount of space the caller allocated for this function to use. 1710 */ 1711 int 1712 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 1713 { 1714 struct xtcpcb xt; 1715 struct syncache *sc; 1716 struct syncache_head *sch; 1717 int count, error, i; 1718 1719 for (count = 0, error = 0, i = 0; i < tcp_syncache.hashsize; i++) { 1720 sch = &tcp_syncache.hashbase[i]; 1721 SCH_LOCK(sch); 1722 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 1723 if (count >= max_pcbs) { 1724 SCH_UNLOCK(sch); 1725 goto exit; 1726 } 1727 bzero(&xt, sizeof(xt)); 1728 xt.xt_len = sizeof(xt); 1729 if (sc->sc_inc.inc_isipv6) 1730 xt.xt_inp.inp_vflag = INP_IPV6; 1731 else 1732 xt.xt_inp.inp_vflag = INP_IPV4; 1733 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 1734 xt.xt_tp.t_inpcb = &xt.xt_inp; 1735 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 1736 xt.xt_socket.xso_protocol = IPPROTO_TCP; 1737 xt.xt_socket.xso_len = sizeof (struct xsocket); 1738 xt.xt_socket.so_type = SOCK_STREAM; 1739 xt.xt_socket.so_state = SS_ISCONNECTING; 1740 error = SYSCTL_OUT(req, &xt, sizeof xt); 1741 if (error) { 1742 SCH_UNLOCK(sch); 1743 goto exit; 1744 } 1745 count++; 1746 } 1747 SCH_UNLOCK(sch); 1748 } 1749 exit: 1750 *pcbs_exported = count; 1751 return error; 1752 } 1753