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sys/netinet/tcp_syncache.c
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1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 4 * All rights reserved. 5 * 6 * This software was developed for the FreeBSD Project by Jonathan Lemon 7 * and McAfee Research, the Security Research Division of McAfee, Inc. under 8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 9 * DARPA CHATS research program. [2001 McAfee, Inc.] 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 __FBSDID("$FreeBSD: releng/11.1/sys/netinet/tcp_syncache.c 319654 2017-06-07 12:50:54Z tuexen $"); 35 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 #include "opt_pcbgroup.h" 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/hash.h> 44 #include <sys/refcount.h> 45 #include <sys/kernel.h> 46 #include <sys/sysctl.h> 47 #include <sys/limits.h> 48 #include <sys/lock.h> 49 #include <sys/mutex.h> 50 #include <sys/malloc.h> 51 #include <sys/mbuf.h> 52 #include <sys/proc.h> /* for proc0 declaration */ 53 #include <sys/random.h> 54 #include <sys/socket.h> 55 #include <sys/socketvar.h> 56 #include <sys/syslog.h> 57 #include <sys/ucred.h> 58 59 #include <sys/md5.h> 60 #include <crypto/siphash/siphash.h> 61 62 #include <vm/uma.h> 63 64 #include <net/if.h> 65 #include <net/if_var.h> 66 #include <net/route.h> 67 #include <net/vnet.h> 68 69 #include <netinet/in.h> 70 #include <netinet/in_systm.h> 71 #include <netinet/ip.h> 72 #include <netinet/in_var.h> 73 #include <netinet/in_pcb.h> 74 #include <netinet/ip_var.h> 75 #include <netinet/ip_options.h> 76 #ifdef INET6 77 #include <netinet/ip6.h> 78 #include <netinet/icmp6.h> 79 #include <netinet6/nd6.h> 80 #include <netinet6/ip6_var.h> 81 #include <netinet6/in6_pcb.h> 82 #endif 83 #include <netinet/tcp.h> 84 #ifdef TCP_RFC7413 85 #include <netinet/tcp_fastopen.h> 86 #endif 87 #include <netinet/tcp_fsm.h> 88 #include <netinet/tcp_seq.h> 89 #include <netinet/tcp_timer.h> 90 #include <netinet/tcp_var.h> 91 #include <netinet/tcp_syncache.h> 92 #ifdef INET6 93 #include <netinet6/tcp6_var.h> 94 #endif 95 #ifdef TCP_OFFLOAD 96 #include <netinet/toecore.h> 97 #endif 98 99 #include <netipsec/ipsec_support.h> 100 101 #include <machine/in_cksum.h> 102 103 #include <security/mac/mac_framework.h> 104 105 static VNET_DEFINE(int, tcp_syncookies) = 1; 106 #define V_tcp_syncookies VNET(tcp_syncookies) 107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 108 &VNET_NAME(tcp_syncookies), 0, 109 "Use TCP SYN cookies if the syncache overflows"); 110 111 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 114 &VNET_NAME(tcp_syncookiesonly), 0, 115 "Use only TCP SYN cookies"); 116 117 #ifdef TCP_OFFLOAD 118 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 119 #endif 120 121 static void syncache_drop(struct syncache *, struct syncache_head *); 122 static void syncache_free(struct syncache *); 123 static void syncache_insert(struct syncache *, struct syncache_head *); 124 static int syncache_respond(struct syncache *, struct syncache_head *, int, 125 const struct mbuf *); 126 static struct socket *syncache_socket(struct syncache *, struct socket *, 127 struct mbuf *m); 128 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 129 int docallout); 130 static void syncache_timer(void *); 131 132 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 133 uint8_t *, uintptr_t); 134 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 135 static struct syncache 136 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 137 struct syncache *, struct tcphdr *, struct tcpopt *, 138 struct socket *); 139 static void syncookie_reseed(void *); 140 #ifdef INVARIANTS 141 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 142 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 143 struct socket *lso); 144 #endif 145 146 /* 147 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 148 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 149 * the odds are that the user has given up attempting to connect by then. 150 */ 151 #define SYNCACHE_MAXREXMTS 3 152 153 /* Arbitrary values */ 154 #define TCP_SYNCACHE_HASHSIZE 512 155 #define TCP_SYNCACHE_BUCKETLIMIT 30 156 157 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 158 #define V_tcp_syncache VNET(tcp_syncache) 159 160 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 161 "TCP SYN cache"); 162 163 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 164 &VNET_NAME(tcp_syncache.bucket_limit), 0, 165 "Per-bucket hash limit for syncache"); 166 167 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 168 &VNET_NAME(tcp_syncache.cache_limit), 0, 169 "Overall entry limit for syncache"); 170 171 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 172 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 173 174 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 175 &VNET_NAME(tcp_syncache.hashsize), 0, 176 "Size of TCP syncache hashtable"); 177 178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW, 179 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 180 "Limit on SYN/ACK retransmissions"); 181 182 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 183 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 184 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 185 "Send reset on socket allocation failure"); 186 187 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 188 189 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 190 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 191 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 192 193 /* 194 * Requires the syncache entry to be already removed from the bucket list. 195 */ 196 static void 197 syncache_free(struct syncache *sc) 198 { 199 200 if (sc->sc_ipopts) 201 (void) m_free(sc->sc_ipopts); 202 if (sc->sc_cred) 203 crfree(sc->sc_cred); 204 #ifdef MAC 205 mac_syncache_destroy(&sc->sc_label); 206 #endif 207 208 uma_zfree(V_tcp_syncache.zone, sc); 209 } 210 211 void 212 syncache_init(void) 213 { 214 int i; 215 216 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 217 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 218 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 219 V_tcp_syncache.hash_secret = arc4random(); 220 221 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 222 &V_tcp_syncache.hashsize); 223 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 224 &V_tcp_syncache.bucket_limit); 225 if (!powerof2(V_tcp_syncache.hashsize) || 226 V_tcp_syncache.hashsize == 0) { 227 printf("WARNING: syncache hash size is not a power of 2.\n"); 228 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 229 } 230 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 231 232 /* Set limits. */ 233 V_tcp_syncache.cache_limit = 234 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 235 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 236 &V_tcp_syncache.cache_limit); 237 238 /* Allocate the hash table. */ 239 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 240 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 241 242 #ifdef VIMAGE 243 V_tcp_syncache.vnet = curvnet; 244 #endif 245 246 /* Initialize the hash buckets. */ 247 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 248 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 249 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 250 NULL, MTX_DEF); 251 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 252 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 253 V_tcp_syncache.hashbase[i].sch_length = 0; 254 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 255 V_tcp_syncache.hashbase[i].sch_last_overflow = 256 -(SYNCOOKIE_LIFETIME + 1); 257 } 258 259 /* Create the syncache entry zone. */ 260 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 261 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 262 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 263 V_tcp_syncache.cache_limit); 264 265 /* Start the SYN cookie reseeder callout. */ 266 callout_init(&V_tcp_syncache.secret.reseed, 1); 267 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 268 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 269 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 270 syncookie_reseed, &V_tcp_syncache); 271 } 272 273 #ifdef VIMAGE 274 void 275 syncache_destroy(void) 276 { 277 struct syncache_head *sch; 278 struct syncache *sc, *nsc; 279 int i; 280 281 /* 282 * Stop the re-seed timer before freeing resources. No need to 283 * possibly schedule it another time. 284 */ 285 callout_drain(&V_tcp_syncache.secret.reseed); 286 287 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 288 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 289 290 sch = &V_tcp_syncache.hashbase[i]; 291 callout_drain(&sch->sch_timer); 292 293 SCH_LOCK(sch); 294 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 295 syncache_drop(sc, sch); 296 SCH_UNLOCK(sch); 297 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 298 ("%s: sch->sch_bucket not empty", __func__)); 299 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 300 __func__, sch->sch_length)); 301 mtx_destroy(&sch->sch_mtx); 302 } 303 304 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 305 ("%s: cache_count not 0", __func__)); 306 307 /* Free the allocated global resources. */ 308 uma_zdestroy(V_tcp_syncache.zone); 309 free(V_tcp_syncache.hashbase, M_SYNCACHE); 310 } 311 #endif 312 313 /* 314 * Inserts a syncache entry into the specified bucket row. 315 * Locks and unlocks the syncache_head autonomously. 316 */ 317 static void 318 syncache_insert(struct syncache *sc, struct syncache_head *sch) 319 { 320 struct syncache *sc2; 321 322 SCH_LOCK(sch); 323 324 /* 325 * Make sure that we don't overflow the per-bucket limit. 326 * If the bucket is full, toss the oldest element. 327 */ 328 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 329 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 330 ("sch->sch_length incorrect")); 331 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 332 sch->sch_last_overflow = time_uptime; 333 syncache_drop(sc2, sch); 334 TCPSTAT_INC(tcps_sc_bucketoverflow); 335 } 336 337 /* Put it into the bucket. */ 338 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 339 sch->sch_length++; 340 341 #ifdef TCP_OFFLOAD 342 if (ADDED_BY_TOE(sc)) { 343 struct toedev *tod = sc->sc_tod; 344 345 tod->tod_syncache_added(tod, sc->sc_todctx); 346 } 347 #endif 348 349 /* Reinitialize the bucket row's timer. */ 350 if (sch->sch_length == 1) 351 sch->sch_nextc = ticks + INT_MAX; 352 syncache_timeout(sc, sch, 1); 353 354 SCH_UNLOCK(sch); 355 356 TCPSTATES_INC(TCPS_SYN_RECEIVED); 357 TCPSTAT_INC(tcps_sc_added); 358 } 359 360 /* 361 * Remove and free entry from syncache bucket row. 362 * Expects locked syncache head. 363 */ 364 static void 365 syncache_drop(struct syncache *sc, struct syncache_head *sch) 366 { 367 368 SCH_LOCK_ASSERT(sch); 369 370 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 371 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 372 sch->sch_length--; 373 374 #ifdef TCP_OFFLOAD 375 if (ADDED_BY_TOE(sc)) { 376 struct toedev *tod = sc->sc_tod; 377 378 tod->tod_syncache_removed(tod, sc->sc_todctx); 379 } 380 #endif 381 382 syncache_free(sc); 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_syn_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 CURVNET_SET(sch->sch_sc->vnet); 416 417 /* NB: syncache_head has already been locked by the callout. */ 418 SCH_LOCK_ASSERT(sch); 419 420 /* 421 * In the following cycle we may remove some entries and/or 422 * advance some timeouts, so re-initialize the bucket timer. 423 */ 424 sch->sch_nextc = tick + INT_MAX; 425 426 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 427 /* 428 * We do not check if the listen socket still exists 429 * and accept the case where the listen socket may be 430 * gone by the time we resend the SYN/ACK. We do 431 * not expect this to happens often. If it does, 432 * then the RST will be sent by the time the remote 433 * host does the SYN/ACK->ACK. 434 */ 435 if (TSTMP_GT(sc->sc_rxttime, tick)) { 436 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 437 sch->sch_nextc = sc->sc_rxttime; 438 continue; 439 } 440 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 441 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 442 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 443 "giving up and removing syncache entry\n", 444 s, __func__); 445 free(s, M_TCPLOG); 446 } 447 syncache_drop(sc, sch); 448 TCPSTAT_INC(tcps_sc_stale); 449 continue; 450 } 451 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 452 log(LOG_DEBUG, "%s; %s: Response timeout, " 453 "retransmitting (%u) SYN|ACK\n", 454 s, __func__, sc->sc_rxmits); 455 free(s, M_TCPLOG); 456 } 457 458 syncache_respond(sc, sch, 1, NULL); 459 TCPSTAT_INC(tcps_sc_retransmitted); 460 syncache_timeout(sc, sch, 0); 461 } 462 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 463 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 464 syncache_timer, (void *)(sch)); 465 CURVNET_RESTORE(); 466 } 467 468 /* 469 * Find an entry in the syncache. 470 * Returns always with locked syncache_head plus a matching entry or NULL. 471 */ 472 static struct syncache * 473 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 474 { 475 struct syncache *sc; 476 struct syncache_head *sch; 477 uint32_t hash; 478 479 /* 480 * The hash is built on foreign port + local port + foreign address. 481 * We rely on the fact that struct in_conninfo starts with 16 bits 482 * of foreign port, then 16 bits of local port then followed by 128 483 * bits of foreign address. In case of IPv4 address, the first 3 484 * 32-bit words of the address always are zeroes. 485 */ 486 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 487 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 488 489 sch = &V_tcp_syncache.hashbase[hash]; 490 *schp = sch; 491 SCH_LOCK(sch); 492 493 /* Circle through bucket row to find matching entry. */ 494 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 495 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 496 sizeof(struct in_endpoints)) == 0) 497 break; 498 499 return (sc); /* Always returns with locked sch. */ 500 } 501 502 /* 503 * This function is called when we get a RST for a 504 * non-existent connection, so that we can see if the 505 * connection is in the syn cache. If it is, zap it. 506 */ 507 void 508 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 509 { 510 struct syncache *sc; 511 struct syncache_head *sch; 512 char *s = NULL; 513 514 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 515 SCH_LOCK_ASSERT(sch); 516 517 /* 518 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 519 * See RFC 793 page 65, section SEGMENT ARRIVES. 520 */ 521 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 522 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 523 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 524 "FIN flag set, segment ignored\n", s, __func__); 525 TCPSTAT_INC(tcps_badrst); 526 goto done; 527 } 528 529 /* 530 * No corresponding connection was found in syncache. 531 * If syncookies are enabled and possibly exclusively 532 * used, or we are under memory pressure, a valid RST 533 * may not find a syncache entry. In that case we're 534 * done and no SYN|ACK retransmissions will happen. 535 * Otherwise the RST was misdirected or spoofed. 536 */ 537 if (sc == NULL) { 538 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 539 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 540 "syncache entry (possibly syncookie only), " 541 "segment ignored\n", s, __func__); 542 TCPSTAT_INC(tcps_badrst); 543 goto done; 544 } 545 546 /* 547 * If the RST bit is set, check the sequence number to see 548 * if this is a valid reset segment. 549 * RFC 793 page 37: 550 * In all states except SYN-SENT, all reset (RST) segments 551 * are validated by checking their SEQ-fields. A reset is 552 * valid if its sequence number is in the window. 553 * 554 * The sequence number in the reset segment is normally an 555 * echo of our outgoing acknowlegement numbers, but some hosts 556 * send a reset with the sequence number at the rightmost edge 557 * of our receive window, and we have to handle this case. 558 */ 559 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 560 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 561 syncache_drop(sc, sch); 562 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 563 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 564 "connection attempt aborted by remote endpoint\n", 565 s, __func__); 566 TCPSTAT_INC(tcps_sc_reset); 567 } else { 568 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 569 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 570 "IRS %u (+WND %u), segment ignored\n", 571 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 572 TCPSTAT_INC(tcps_badrst); 573 } 574 575 done: 576 if (s != NULL) 577 free(s, M_TCPLOG); 578 SCH_UNLOCK(sch); 579 } 580 581 void 582 syncache_badack(struct in_conninfo *inc) 583 { 584 struct syncache *sc; 585 struct syncache_head *sch; 586 587 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 588 SCH_LOCK_ASSERT(sch); 589 if (sc != NULL) { 590 syncache_drop(sc, sch); 591 TCPSTAT_INC(tcps_sc_badack); 592 } 593 SCH_UNLOCK(sch); 594 } 595 596 void 597 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq) 598 { 599 struct syncache *sc; 600 struct syncache_head *sch; 601 602 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 603 SCH_LOCK_ASSERT(sch); 604 if (sc == NULL) 605 goto done; 606 607 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 608 if (ntohl(th_seq) != sc->sc_iss) 609 goto done; 610 611 /* 612 * If we've rertransmitted 3 times and this is our second error, 613 * we remove the entry. Otherwise, we allow it to continue on. 614 * This prevents us from incorrectly nuking an entry during a 615 * spurious network outage. 616 * 617 * See tcp_notify(). 618 */ 619 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 620 sc->sc_flags |= SCF_UNREACH; 621 goto done; 622 } 623 syncache_drop(sc, sch); 624 TCPSTAT_INC(tcps_sc_unreach); 625 done: 626 SCH_UNLOCK(sch); 627 } 628 629 /* 630 * Build a new TCP socket structure from a syncache entry. 631 * 632 * On success return the newly created socket with its underlying inp locked. 633 */ 634 static struct socket * 635 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 636 { 637 struct tcp_function_block *blk; 638 struct inpcb *inp = NULL; 639 struct socket *so; 640 struct tcpcb *tp; 641 int error; 642 char *s; 643 644 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 645 646 /* 647 * Ok, create the full blown connection, and set things up 648 * as they would have been set up if we had created the 649 * connection when the SYN arrived. If we can't create 650 * the connection, abort it. 651 */ 652 so = sonewconn(lso, 0); 653 if (so == NULL) { 654 /* 655 * Drop the connection; we will either send a RST or 656 * have the peer retransmit its SYN again after its 657 * RTO and try again. 658 */ 659 TCPSTAT_INC(tcps_listendrop); 660 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 661 log(LOG_DEBUG, "%s; %s: Socket create failed " 662 "due to limits or memory shortage\n", 663 s, __func__); 664 free(s, M_TCPLOG); 665 } 666 goto abort2; 667 } 668 #ifdef MAC 669 mac_socketpeer_set_from_mbuf(m, so); 670 #endif 671 672 inp = sotoinpcb(so); 673 inp->inp_inc.inc_fibnum = so->so_fibnum; 674 INP_WLOCK(inp); 675 /* 676 * Exclusive pcbinfo lock is not required in syncache socket case even 677 * if two inpcb locks can be acquired simultaneously: 678 * - the inpcb in LISTEN state, 679 * - the newly created inp. 680 * 681 * In this case, an inp cannot be at same time in LISTEN state and 682 * just created by an accept() call. 683 */ 684 INP_HASH_WLOCK(&V_tcbinfo); 685 686 /* Insert new socket into PCB hash list. */ 687 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 688 #ifdef INET6 689 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 690 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 691 } else { 692 inp->inp_vflag &= ~INP_IPV6; 693 inp->inp_vflag |= INP_IPV4; 694 #endif 695 inp->inp_laddr = sc->sc_inc.inc_laddr; 696 #ifdef INET6 697 } 698 #endif 699 700 /* 701 * If there's an mbuf and it has a flowid, then let's initialise the 702 * inp with that particular flowid. 703 */ 704 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 705 inp->inp_flowid = m->m_pkthdr.flowid; 706 inp->inp_flowtype = M_HASHTYPE_GET(m); 707 } 708 709 /* 710 * Install in the reservation hash table for now, but don't yet 711 * install a connection group since the full 4-tuple isn't yet 712 * configured. 713 */ 714 inp->inp_lport = sc->sc_inc.inc_lport; 715 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 716 /* 717 * Undo the assignments above if we failed to 718 * put the PCB on the hash lists. 719 */ 720 #ifdef INET6 721 if (sc->sc_inc.inc_flags & INC_ISIPV6) 722 inp->in6p_laddr = in6addr_any; 723 else 724 #endif 725 inp->inp_laddr.s_addr = INADDR_ANY; 726 inp->inp_lport = 0; 727 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 728 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 729 "with error %i\n", 730 s, __func__, error); 731 free(s, M_TCPLOG); 732 } 733 INP_HASH_WUNLOCK(&V_tcbinfo); 734 goto abort; 735 } 736 #ifdef INET6 737 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 738 struct inpcb *oinp = sotoinpcb(lso); 739 struct in6_addr laddr6; 740 struct sockaddr_in6 sin6; 741 /* 742 * Inherit socket options from the listening socket. 743 * Note that in6p_inputopts are not (and should not be) 744 * copied, since it stores previously received options and is 745 * used to detect if each new option is different than the 746 * previous one and hence should be passed to a user. 747 * If we copied in6p_inputopts, a user would not be able to 748 * receive options just after calling the accept system call. 749 */ 750 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 751 if (oinp->in6p_outputopts) 752 inp->in6p_outputopts = 753 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 754 755 sin6.sin6_family = AF_INET6; 756 sin6.sin6_len = sizeof(sin6); 757 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 758 sin6.sin6_port = sc->sc_inc.inc_fport; 759 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 760 laddr6 = inp->in6p_laddr; 761 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 762 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 763 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 764 thread0.td_ucred, m)) != 0) { 765 inp->in6p_laddr = laddr6; 766 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 767 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 768 "with error %i\n", 769 s, __func__, error); 770 free(s, M_TCPLOG); 771 } 772 INP_HASH_WUNLOCK(&V_tcbinfo); 773 goto abort; 774 } 775 /* Override flowlabel from in6_pcbconnect. */ 776 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 777 inp->inp_flow |= sc->sc_flowlabel; 778 } 779 #endif /* INET6 */ 780 #if defined(INET) && defined(INET6) 781 else 782 #endif 783 #ifdef INET 784 { 785 struct in_addr laddr; 786 struct sockaddr_in sin; 787 788 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 789 790 if (inp->inp_options == NULL) { 791 inp->inp_options = sc->sc_ipopts; 792 sc->sc_ipopts = NULL; 793 } 794 795 sin.sin_family = AF_INET; 796 sin.sin_len = sizeof(sin); 797 sin.sin_addr = sc->sc_inc.inc_faddr; 798 sin.sin_port = sc->sc_inc.inc_fport; 799 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 800 laddr = inp->inp_laddr; 801 if (inp->inp_laddr.s_addr == INADDR_ANY) 802 inp->inp_laddr = sc->sc_inc.inc_laddr; 803 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 804 thread0.td_ucred, m)) != 0) { 805 inp->inp_laddr = laddr; 806 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 807 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 808 "with error %i\n", 809 s, __func__, error); 810 free(s, M_TCPLOG); 811 } 812 INP_HASH_WUNLOCK(&V_tcbinfo); 813 goto abort; 814 } 815 } 816 #endif /* INET */ 817 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 818 /* Copy old policy into new socket's. */ 819 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 820 printf("syncache_socket: could not copy policy\n"); 821 #endif 822 INP_HASH_WUNLOCK(&V_tcbinfo); 823 tp = intotcpcb(inp); 824 tcp_state_change(tp, TCPS_SYN_RECEIVED); 825 tp->iss = sc->sc_iss; 826 tp->irs = sc->sc_irs; 827 tcp_rcvseqinit(tp); 828 tcp_sendseqinit(tp); 829 blk = sototcpcb(lso)->t_fb; 830 if (blk != tp->t_fb) { 831 /* 832 * Our parents t_fb was not the default, 833 * we need to release our ref on tp->t_fb and 834 * pickup one on the new entry. 835 */ 836 struct tcp_function_block *rblk; 837 838 rblk = find_and_ref_tcp_fb(blk); 839 KASSERT(rblk != NULL, 840 ("cannot find blk %p out of syncache?", blk)); 841 if (tp->t_fb->tfb_tcp_fb_fini) 842 (*tp->t_fb->tfb_tcp_fb_fini)(tp); 843 refcount_release(&tp->t_fb->tfb_refcnt); 844 tp->t_fb = rblk; 845 if (tp->t_fb->tfb_tcp_fb_init) { 846 (*tp->t_fb->tfb_tcp_fb_init)(tp); 847 } 848 } 849 tp->snd_wl1 = sc->sc_irs; 850 tp->snd_max = tp->iss + 1; 851 tp->snd_nxt = tp->iss + 1; 852 tp->rcv_up = sc->sc_irs + 1; 853 tp->rcv_wnd = sc->sc_wnd; 854 tp->rcv_adv += tp->rcv_wnd; 855 tp->last_ack_sent = tp->rcv_nxt; 856 857 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 858 if (sc->sc_flags & SCF_NOOPT) 859 tp->t_flags |= TF_NOOPT; 860 else { 861 if (sc->sc_flags & SCF_WINSCALE) { 862 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 863 tp->snd_scale = sc->sc_requested_s_scale; 864 tp->request_r_scale = sc->sc_requested_r_scale; 865 } 866 if (sc->sc_flags & SCF_TIMESTAMP) { 867 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 868 tp->ts_recent = sc->sc_tsreflect; 869 tp->ts_recent_age = tcp_ts_getticks(); 870 tp->ts_offset = sc->sc_tsoff; 871 } 872 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 873 if (sc->sc_flags & SCF_SIGNATURE) 874 tp->t_flags |= TF_SIGNATURE; 875 #endif 876 if (sc->sc_flags & SCF_SACK) 877 tp->t_flags |= TF_SACK_PERMIT; 878 } 879 880 if (sc->sc_flags & SCF_ECN) 881 tp->t_flags |= TF_ECN_PERMIT; 882 883 /* 884 * Set up MSS and get cached values from tcp_hostcache. 885 * This might overwrite some of the defaults we just set. 886 */ 887 tcp_mss(tp, sc->sc_peer_mss); 888 889 /* 890 * If the SYN,ACK was retransmitted, indicate that CWND to be 891 * limited to one segment in cc_conn_init(). 892 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 893 */ 894 if (sc->sc_rxmits > 1) 895 tp->snd_cwnd = 1; 896 897 #ifdef TCP_OFFLOAD 898 /* 899 * Allow a TOE driver to install its hooks. Note that we hold the 900 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 901 * new connection before the TOE driver has done its thing. 902 */ 903 if (ADDED_BY_TOE(sc)) { 904 struct toedev *tod = sc->sc_tod; 905 906 tod->tod_offload_socket(tod, sc->sc_todctx, so); 907 } 908 #endif 909 /* 910 * Copy and activate timers. 911 */ 912 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 913 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 914 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 915 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 916 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 917 918 TCPSTAT_INC(tcps_accepts); 919 return (so); 920 921 abort: 922 INP_WUNLOCK(inp); 923 abort2: 924 if (so != NULL) 925 soabort(so); 926 return (NULL); 927 } 928 929 /* 930 * This function gets called when we receive an ACK for a 931 * socket in the LISTEN state. We look up the connection 932 * in the syncache, and if its there, we pull it out of 933 * the cache and turn it into a full-blown connection in 934 * the SYN-RECEIVED state. 935 * 936 * On syncache_socket() success the newly created socket 937 * has its underlying inp locked. 938 */ 939 int 940 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 941 struct socket **lsop, struct mbuf *m) 942 { 943 struct syncache *sc; 944 struct syncache_head *sch; 945 struct syncache scs; 946 char *s; 947 948 /* 949 * Global TCP locks are held because we manipulate the PCB lists 950 * and create a new socket. 951 */ 952 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 953 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 954 ("%s: can handle only ACK", __func__)); 955 956 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 957 SCH_LOCK_ASSERT(sch); 958 959 #ifdef INVARIANTS 960 /* 961 * Test code for syncookies comparing the syncache stored 962 * values with the reconstructed values from the cookie. 963 */ 964 if (sc != NULL) 965 syncookie_cmp(inc, sch, sc, th, to, *lsop); 966 #endif 967 968 if (sc == NULL) { 969 /* 970 * There is no syncache entry, so see if this ACK is 971 * a returning syncookie. To do this, first: 972 * A. Check if syncookies are used in case of syncache 973 * overflows 974 * B. See if this socket has had a syncache entry dropped in 975 * the recent past. We don't want to accept a bogus 976 * syncookie if we've never received a SYN or accept it 977 * twice. 978 * C. check that the syncookie is valid. If it is, then 979 * cobble up a fake syncache entry, and return. 980 */ 981 if (!V_tcp_syncookies) { 982 SCH_UNLOCK(sch); 983 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 984 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 985 "segment rejected (syncookies disabled)\n", 986 s, __func__); 987 goto failed; 988 } 989 if (!V_tcp_syncookiesonly && 990 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 991 SCH_UNLOCK(sch); 992 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 993 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 994 "segment rejected (no syncache entry)\n", 995 s, __func__); 996 goto failed; 997 } 998 bzero(&scs, sizeof(scs)); 999 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 1000 SCH_UNLOCK(sch); 1001 if (sc == NULL) { 1002 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1003 log(LOG_DEBUG, "%s; %s: Segment failed " 1004 "SYNCOOKIE authentication, segment rejected " 1005 "(probably spoofed)\n", s, __func__); 1006 goto failed; 1007 } 1008 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1009 /* If received ACK has MD5 signature, check it. */ 1010 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1011 (!TCPMD5_ENABLED() || 1012 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1013 /* Drop the ACK. */ 1014 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1015 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1016 "MD5 signature doesn't match.\n", 1017 s, __func__); 1018 free(s, M_TCPLOG); 1019 } 1020 TCPSTAT_INC(tcps_sig_err_sigopt); 1021 return (-1); /* Do not send RST */ 1022 } 1023 #endif /* TCP_SIGNATURE */ 1024 } else { 1025 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1026 /* 1027 * If listening socket requested TCP digests, check that 1028 * received ACK has signature and it is correct. 1029 * If not, drop the ACK and leave sc entry in th cache, 1030 * because SYN was received with correct signature. 1031 */ 1032 if (sc->sc_flags & SCF_SIGNATURE) { 1033 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1034 /* No signature */ 1035 TCPSTAT_INC(tcps_sig_err_nosigopt); 1036 SCH_UNLOCK(sch); 1037 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1038 log(LOG_DEBUG, "%s; %s: Segment " 1039 "rejected, MD5 signature wasn't " 1040 "provided.\n", s, __func__); 1041 free(s, M_TCPLOG); 1042 } 1043 return (-1); /* Do not send RST */ 1044 } 1045 if (!TCPMD5_ENABLED() || 1046 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1047 /* Doesn't match or no SA */ 1048 SCH_UNLOCK(sch); 1049 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1050 log(LOG_DEBUG, "%s; %s: Segment " 1051 "rejected, MD5 signature doesn't " 1052 "match.\n", s, __func__); 1053 free(s, M_TCPLOG); 1054 } 1055 return (-1); /* Do not send RST */ 1056 } 1057 } 1058 #endif /* TCP_SIGNATURE */ 1059 /* 1060 * Pull out the entry to unlock the bucket row. 1061 * 1062 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1063 * tcp_state_change(). The tcpcb is not existent at this 1064 * moment. A new one will be allocated via syncache_socket-> 1065 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1066 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1067 */ 1068 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1069 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1070 sch->sch_length--; 1071 #ifdef TCP_OFFLOAD 1072 if (ADDED_BY_TOE(sc)) { 1073 struct toedev *tod = sc->sc_tod; 1074 1075 tod->tod_syncache_removed(tod, sc->sc_todctx); 1076 } 1077 #endif 1078 SCH_UNLOCK(sch); 1079 } 1080 1081 /* 1082 * Segment validation: 1083 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1084 */ 1085 if (th->th_ack != sc->sc_iss + 1) { 1086 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1087 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1088 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1089 goto failed; 1090 } 1091 1092 /* 1093 * The SEQ must fall in the window starting at the received 1094 * initial receive sequence number + 1 (the SYN). 1095 */ 1096 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1097 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1098 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1099 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1100 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1101 goto failed; 1102 } 1103 1104 /* 1105 * If timestamps were not negotiated during SYN/ACK they 1106 * must not appear on any segment during this session. 1107 */ 1108 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1109 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1110 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1111 "segment rejected\n", s, __func__); 1112 goto failed; 1113 } 1114 1115 /* 1116 * If timestamps were negotiated during SYN/ACK they should 1117 * appear on every segment during this session. 1118 * XXXAO: This is only informal as there have been unverified 1119 * reports of non-compliants stacks. 1120 */ 1121 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1122 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1123 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1124 "no action\n", s, __func__); 1125 free(s, M_TCPLOG); 1126 s = NULL; 1127 } 1128 } 1129 1130 /* 1131 * If timestamps were negotiated, the reflected timestamp 1132 * must be equal to what we actually sent in the SYN|ACK 1133 * except in the case of 0. Some boxes are known for sending 1134 * broken timestamp replies during the 3whs (and potentially 1135 * during the connection also). 1136 * 1137 * Accept the final ACK of 3whs with reflected timestamp of 0 1138 * instead of sending a RST and deleting the syncache entry. 1139 */ 1140 if ((to->to_flags & TOF_TS) && to->to_tsecr && 1141 to->to_tsecr != sc->sc_ts) { 1142 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1143 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1144 "segment rejected\n", 1145 s, __func__, to->to_tsecr, sc->sc_ts); 1146 goto failed; 1147 } 1148 1149 *lsop = syncache_socket(sc, *lsop, m); 1150 1151 if (*lsop == NULL) 1152 TCPSTAT_INC(tcps_sc_aborted); 1153 else 1154 TCPSTAT_INC(tcps_sc_completed); 1155 1156 /* how do we find the inp for the new socket? */ 1157 if (sc != &scs) 1158 syncache_free(sc); 1159 return (1); 1160 failed: 1161 if (sc != NULL && sc != &scs) 1162 syncache_free(sc); 1163 if (s != NULL) 1164 free(s, M_TCPLOG); 1165 *lsop = NULL; 1166 return (0); 1167 } 1168 1169 #ifdef TCP_RFC7413 1170 static void 1171 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1172 uint64_t response_cookie) 1173 { 1174 struct inpcb *inp; 1175 struct tcpcb *tp; 1176 unsigned int *pending_counter; 1177 1178 /* 1179 * Global TCP locks are held because we manipulate the PCB lists 1180 * and create a new socket. 1181 */ 1182 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 1183 1184 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1185 *lsop = syncache_socket(sc, *lsop, m); 1186 if (*lsop == NULL) { 1187 TCPSTAT_INC(tcps_sc_aborted); 1188 atomic_subtract_int(pending_counter, 1); 1189 } else { 1190 inp = sotoinpcb(*lsop); 1191 tp = intotcpcb(inp); 1192 tp->t_flags |= TF_FASTOPEN; 1193 tp->t_tfo_cookie = response_cookie; 1194 tp->snd_max = tp->iss; 1195 tp->snd_nxt = tp->iss; 1196 tp->t_tfo_pending = pending_counter; 1197 TCPSTAT_INC(tcps_sc_completed); 1198 } 1199 } 1200 #endif /* TCP_RFC7413 */ 1201 1202 /* 1203 * Given a LISTEN socket and an inbound SYN request, add 1204 * this to the syn cache, and send back a segment: 1205 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1206 * to the source. 1207 * 1208 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1209 * Doing so would require that we hold onto the data and deliver it 1210 * to the application. However, if we are the target of a SYN-flood 1211 * DoS attack, an attacker could send data which would eventually 1212 * consume all available buffer space if it were ACKed. By not ACKing 1213 * the data, we avoid this DoS scenario. 1214 * 1215 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1216 * cookie is processed, V_tcp_fastopen_enabled set to true, and the 1217 * TCP_FASTOPEN socket option is set. In this case, a new socket is created 1218 * and returned via lsop, the mbuf is not freed so that tcp_input() can 1219 * queue its data to the socket, and 1 is returned to indicate the 1220 * TFO-socket-creation path was taken. 1221 */ 1222 int 1223 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1224 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1225 void *todctx) 1226 { 1227 struct tcpcb *tp; 1228 struct socket *so; 1229 struct syncache *sc = NULL; 1230 struct syncache_head *sch; 1231 struct mbuf *ipopts = NULL; 1232 u_int ltflags; 1233 int win, sb_hiwat, ip_ttl, ip_tos; 1234 char *s; 1235 int rv = 0; 1236 #ifdef INET6 1237 int autoflowlabel = 0; 1238 #endif 1239 #ifdef MAC 1240 struct label *maclabel; 1241 #endif 1242 struct syncache scs; 1243 struct ucred *cred; 1244 #ifdef TCP_RFC7413 1245 uint64_t tfo_response_cookie; 1246 int tfo_cookie_valid = 0; 1247 int tfo_response_cookie_valid = 0; 1248 #endif 1249 1250 INP_WLOCK_ASSERT(inp); /* listen socket */ 1251 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1252 ("%s: unexpected tcp flags", __func__)); 1253 1254 /* 1255 * Combine all so/tp operations very early to drop the INP lock as 1256 * soon as possible. 1257 */ 1258 so = *lsop; 1259 tp = sototcpcb(so); 1260 cred = crhold(so->so_cred); 1261 1262 #ifdef INET6 1263 if ((inc->inc_flags & INC_ISIPV6) && 1264 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1265 autoflowlabel = 1; 1266 #endif 1267 ip_ttl = inp->inp_ip_ttl; 1268 ip_tos = inp->inp_ip_tos; 1269 win = sbspace(&so->so_rcv); 1270 sb_hiwat = so->so_rcv.sb_hiwat; 1271 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1272 1273 #ifdef TCP_RFC7413 1274 if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) && 1275 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) { 1276 /* 1277 * Limit the number of pending TFO connections to 1278 * approximately half of the queue limit. This prevents TFO 1279 * SYN floods from starving the service by filling the 1280 * listen queue with bogus TFO connections. 1281 */ 1282 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1283 (so->so_qlimit / 2)) { 1284 int result; 1285 1286 result = tcp_fastopen_check_cookie(inc, 1287 to->to_tfo_cookie, to->to_tfo_len, 1288 &tfo_response_cookie); 1289 tfo_cookie_valid = (result > 0); 1290 tfo_response_cookie_valid = (result >= 0); 1291 } else 1292 atomic_subtract_int(tp->t_tfo_pending, 1); 1293 } 1294 #endif 1295 1296 /* By the time we drop the lock these should no longer be used. */ 1297 so = NULL; 1298 tp = NULL; 1299 1300 #ifdef MAC 1301 if (mac_syncache_init(&maclabel) != 0) { 1302 INP_WUNLOCK(inp); 1303 goto done; 1304 } else 1305 mac_syncache_create(maclabel, inp); 1306 #endif 1307 #ifdef TCP_RFC7413 1308 if (!tfo_cookie_valid) 1309 #endif 1310 INP_WUNLOCK(inp); 1311 1312 /* 1313 * Remember the IP options, if any. 1314 */ 1315 #ifdef INET6 1316 if (!(inc->inc_flags & INC_ISIPV6)) 1317 #endif 1318 #ifdef INET 1319 ipopts = (m) ? ip_srcroute(m) : NULL; 1320 #else 1321 ipopts = NULL; 1322 #endif 1323 1324 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1325 /* 1326 * If listening socket requested TCP digests, check that received 1327 * SYN has signature and it is correct. If signature doesn't match 1328 * or TCP_SIGNATURE support isn't enabled, drop the packet. 1329 */ 1330 if (ltflags & TF_SIGNATURE) { 1331 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1332 TCPSTAT_INC(tcps_sig_err_nosigopt); 1333 goto done; 1334 } 1335 if (!TCPMD5_ENABLED() || 1336 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1337 goto done; 1338 } 1339 #endif /* TCP_SIGNATURE */ 1340 /* 1341 * See if we already have an entry for this connection. 1342 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1343 * 1344 * XXX: should the syncache be re-initialized with the contents 1345 * of the new SYN here (which may have different options?) 1346 * 1347 * XXX: We do not check the sequence number to see if this is a 1348 * real retransmit or a new connection attempt. The question is 1349 * how to handle such a case; either ignore it as spoofed, or 1350 * drop the current entry and create a new one? 1351 */ 1352 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1353 SCH_LOCK_ASSERT(sch); 1354 if (sc != NULL) { 1355 #ifdef TCP_RFC7413 1356 if (tfo_cookie_valid) 1357 INP_WUNLOCK(inp); 1358 #endif 1359 TCPSTAT_INC(tcps_sc_dupsyn); 1360 if (ipopts) { 1361 /* 1362 * If we were remembering a previous source route, 1363 * forget it and use the new one we've been given. 1364 */ 1365 if (sc->sc_ipopts) 1366 (void) m_free(sc->sc_ipopts); 1367 sc->sc_ipopts = ipopts; 1368 } 1369 /* 1370 * Update timestamp if present. 1371 */ 1372 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1373 sc->sc_tsreflect = to->to_tsval; 1374 else 1375 sc->sc_flags &= ~SCF_TIMESTAMP; 1376 #ifdef MAC 1377 /* 1378 * Since we have already unconditionally allocated label 1379 * storage, free it up. The syncache entry will already 1380 * have an initialized label we can use. 1381 */ 1382 mac_syncache_destroy(&maclabel); 1383 #endif 1384 /* Retransmit SYN|ACK and reset retransmit count. */ 1385 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1386 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1387 "resetting timer and retransmitting SYN|ACK\n", 1388 s, __func__); 1389 free(s, M_TCPLOG); 1390 } 1391 if (syncache_respond(sc, sch, 1, m) == 0) { 1392 sc->sc_rxmits = 0; 1393 syncache_timeout(sc, sch, 1); 1394 TCPSTAT_INC(tcps_sndacks); 1395 TCPSTAT_INC(tcps_sndtotal); 1396 } 1397 SCH_UNLOCK(sch); 1398 goto done; 1399 } 1400 1401 #ifdef TCP_RFC7413 1402 if (tfo_cookie_valid) { 1403 bzero(&scs, sizeof(scs)); 1404 sc = &scs; 1405 goto skip_alloc; 1406 } 1407 #endif 1408 1409 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1410 if (sc == NULL) { 1411 /* 1412 * The zone allocator couldn't provide more entries. 1413 * Treat this as if the cache was full; drop the oldest 1414 * entry and insert the new one. 1415 */ 1416 TCPSTAT_INC(tcps_sc_zonefail); 1417 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1418 sch->sch_last_overflow = time_uptime; 1419 syncache_drop(sc, sch); 1420 } 1421 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1422 if (sc == NULL) { 1423 if (V_tcp_syncookies) { 1424 bzero(&scs, sizeof(scs)); 1425 sc = &scs; 1426 } else { 1427 SCH_UNLOCK(sch); 1428 if (ipopts) 1429 (void) m_free(ipopts); 1430 goto done; 1431 } 1432 } 1433 } 1434 1435 #ifdef TCP_RFC7413 1436 skip_alloc: 1437 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1438 sc->sc_tfo_cookie = &tfo_response_cookie; 1439 #endif 1440 1441 /* 1442 * Fill in the syncache values. 1443 */ 1444 #ifdef MAC 1445 sc->sc_label = maclabel; 1446 #endif 1447 sc->sc_cred = cred; 1448 cred = NULL; 1449 sc->sc_ipopts = ipopts; 1450 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1451 #ifdef INET6 1452 if (!(inc->inc_flags & INC_ISIPV6)) 1453 #endif 1454 { 1455 sc->sc_ip_tos = ip_tos; 1456 sc->sc_ip_ttl = ip_ttl; 1457 } 1458 #ifdef TCP_OFFLOAD 1459 sc->sc_tod = tod; 1460 sc->sc_todctx = todctx; 1461 #endif 1462 sc->sc_irs = th->th_seq; 1463 sc->sc_iss = arc4random(); 1464 sc->sc_flags = 0; 1465 sc->sc_flowlabel = 0; 1466 1467 /* 1468 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1469 * win was derived from socket earlier in the function. 1470 */ 1471 win = imax(win, 0); 1472 win = imin(win, TCP_MAXWIN); 1473 sc->sc_wnd = win; 1474 1475 if (V_tcp_do_rfc1323) { 1476 /* 1477 * A timestamp received in a SYN makes 1478 * it ok to send timestamp requests and replies. 1479 */ 1480 if (to->to_flags & TOF_TS) { 1481 sc->sc_tsreflect = to->to_tsval; 1482 sc->sc_ts = tcp_ts_getticks(); 1483 sc->sc_flags |= SCF_TIMESTAMP; 1484 } 1485 if (to->to_flags & TOF_SCALE) { 1486 int wscale = 0; 1487 1488 /* 1489 * Pick the smallest possible scaling factor that 1490 * will still allow us to scale up to sb_max, aka 1491 * kern.ipc.maxsockbuf. 1492 * 1493 * We do this because there are broken firewalls that 1494 * will corrupt the window scale option, leading to 1495 * the other endpoint believing that our advertised 1496 * window is unscaled. At scale factors larger than 1497 * 5 the unscaled window will drop below 1500 bytes, 1498 * leading to serious problems when traversing these 1499 * broken firewalls. 1500 * 1501 * With the default maxsockbuf of 256K, a scale factor 1502 * of 3 will be chosen by this algorithm. Those who 1503 * choose a larger maxsockbuf should watch out 1504 * for the compatibility problems mentioned above. 1505 * 1506 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1507 * or <SYN,ACK>) segment itself is never scaled. 1508 */ 1509 while (wscale < TCP_MAX_WINSHIFT && 1510 (TCP_MAXWIN << wscale) < sb_max) 1511 wscale++; 1512 sc->sc_requested_r_scale = wscale; 1513 sc->sc_requested_s_scale = to->to_wscale; 1514 sc->sc_flags |= SCF_WINSCALE; 1515 } 1516 } 1517 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1518 /* 1519 * If listening socket requested TCP digests, flag this in the 1520 * syncache so that syncache_respond() will do the right thing 1521 * with the SYN+ACK. 1522 */ 1523 if (ltflags & TF_SIGNATURE) 1524 sc->sc_flags |= SCF_SIGNATURE; 1525 #endif /* TCP_SIGNATURE */ 1526 if (to->to_flags & TOF_SACKPERM) 1527 sc->sc_flags |= SCF_SACK; 1528 if (to->to_flags & TOF_MSS) 1529 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1530 if (ltflags & TF_NOOPT) 1531 sc->sc_flags |= SCF_NOOPT; 1532 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1533 sc->sc_flags |= SCF_ECN; 1534 1535 if (V_tcp_syncookies) 1536 sc->sc_iss = syncookie_generate(sch, sc); 1537 #ifdef INET6 1538 if (autoflowlabel) { 1539 if (V_tcp_syncookies) 1540 sc->sc_flowlabel = sc->sc_iss; 1541 else 1542 sc->sc_flowlabel = ip6_randomflowlabel(); 1543 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1544 } 1545 #endif 1546 SCH_UNLOCK(sch); 1547 1548 #ifdef TCP_RFC7413 1549 if (tfo_cookie_valid) { 1550 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1551 /* INP_WUNLOCK(inp) will be performed by the called */ 1552 rv = 1; 1553 goto tfo_done; 1554 } 1555 #endif 1556 1557 /* 1558 * Do a standard 3-way handshake. 1559 */ 1560 if (syncache_respond(sc, sch, 0, m) == 0) { 1561 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1562 syncache_free(sc); 1563 else if (sc != &scs) 1564 syncache_insert(sc, sch); /* locks and unlocks sch */ 1565 TCPSTAT_INC(tcps_sndacks); 1566 TCPSTAT_INC(tcps_sndtotal); 1567 } else { 1568 if (sc != &scs) 1569 syncache_free(sc); 1570 TCPSTAT_INC(tcps_sc_dropped); 1571 } 1572 1573 done: 1574 if (m) { 1575 *lsop = NULL; 1576 m_freem(m); 1577 } 1578 #ifdef TCP_RFC7413 1579 tfo_done: 1580 #endif 1581 if (cred != NULL) 1582 crfree(cred); 1583 #ifdef MAC 1584 if (sc == &scs) 1585 mac_syncache_destroy(&maclabel); 1586 #endif 1587 return (rv); 1588 } 1589 1590 /* 1591 * Send SYN|ACK to the peer. Either in response to the peer's SYN, 1592 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1593 */ 1594 static int 1595 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked, 1596 const struct mbuf *m0) 1597 { 1598 struct ip *ip = NULL; 1599 struct mbuf *m; 1600 struct tcphdr *th = NULL; 1601 int optlen, error = 0; /* Make compiler happy */ 1602 u_int16_t hlen, tlen, mssopt; 1603 struct tcpopt to; 1604 #ifdef INET6 1605 struct ip6_hdr *ip6 = NULL; 1606 #endif 1607 hlen = 1608 #ifdef INET6 1609 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1610 #endif 1611 sizeof(struct ip); 1612 tlen = hlen + sizeof(struct tcphdr); 1613 1614 /* Determine MSS we advertize to other end of connection. */ 1615 mssopt = tcp_mssopt(&sc->sc_inc); 1616 if (sc->sc_peer_mss) 1617 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1618 1619 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1620 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1621 ("syncache: mbuf too small")); 1622 1623 /* Create the IP+TCP header from scratch. */ 1624 m = m_gethdr(M_NOWAIT, MT_DATA); 1625 if (m == NULL) 1626 return (ENOBUFS); 1627 #ifdef MAC 1628 mac_syncache_create_mbuf(sc->sc_label, m); 1629 #endif 1630 m->m_data += max_linkhdr; 1631 m->m_len = tlen; 1632 m->m_pkthdr.len = tlen; 1633 m->m_pkthdr.rcvif = NULL; 1634 1635 #ifdef INET6 1636 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1637 ip6 = mtod(m, struct ip6_hdr *); 1638 ip6->ip6_vfc = IPV6_VERSION; 1639 ip6->ip6_nxt = IPPROTO_TCP; 1640 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1641 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1642 ip6->ip6_plen = htons(tlen - hlen); 1643 /* ip6_hlim is set after checksum */ 1644 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1645 ip6->ip6_flow |= sc->sc_flowlabel; 1646 1647 th = (struct tcphdr *)(ip6 + 1); 1648 } 1649 #endif 1650 #if defined(INET6) && defined(INET) 1651 else 1652 #endif 1653 #ifdef INET 1654 { 1655 ip = mtod(m, struct ip *); 1656 ip->ip_v = IPVERSION; 1657 ip->ip_hl = sizeof(struct ip) >> 2; 1658 ip->ip_len = htons(tlen); 1659 ip->ip_id = 0; 1660 ip->ip_off = 0; 1661 ip->ip_sum = 0; 1662 ip->ip_p = IPPROTO_TCP; 1663 ip->ip_src = sc->sc_inc.inc_laddr; 1664 ip->ip_dst = sc->sc_inc.inc_faddr; 1665 ip->ip_ttl = sc->sc_ip_ttl; 1666 ip->ip_tos = sc->sc_ip_tos; 1667 1668 /* 1669 * See if we should do MTU discovery. Route lookups are 1670 * expensive, so we will only unset the DF bit if: 1671 * 1672 * 1) path_mtu_discovery is disabled 1673 * 2) the SCF_UNREACH flag has been set 1674 */ 1675 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1676 ip->ip_off |= htons(IP_DF); 1677 1678 th = (struct tcphdr *)(ip + 1); 1679 } 1680 #endif /* INET */ 1681 th->th_sport = sc->sc_inc.inc_lport; 1682 th->th_dport = sc->sc_inc.inc_fport; 1683 1684 th->th_seq = htonl(sc->sc_iss); 1685 th->th_ack = htonl(sc->sc_irs + 1); 1686 th->th_off = sizeof(struct tcphdr) >> 2; 1687 th->th_x2 = 0; 1688 th->th_flags = TH_SYN|TH_ACK; 1689 th->th_win = htons(sc->sc_wnd); 1690 th->th_urp = 0; 1691 1692 if (sc->sc_flags & SCF_ECN) { 1693 th->th_flags |= TH_ECE; 1694 TCPSTAT_INC(tcps_ecn_shs); 1695 } 1696 1697 /* Tack on the TCP options. */ 1698 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1699 to.to_flags = 0; 1700 1701 to.to_mss = mssopt; 1702 to.to_flags = TOF_MSS; 1703 if (sc->sc_flags & SCF_WINSCALE) { 1704 to.to_wscale = sc->sc_requested_r_scale; 1705 to.to_flags |= TOF_SCALE; 1706 } 1707 if (sc->sc_flags & SCF_TIMESTAMP) { 1708 /* Virgin timestamp or TCP cookie enhanced one. */ 1709 to.to_tsval = sc->sc_ts; 1710 to.to_tsecr = sc->sc_tsreflect; 1711 to.to_flags |= TOF_TS; 1712 } 1713 if (sc->sc_flags & SCF_SACK) 1714 to.to_flags |= TOF_SACKPERM; 1715 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1716 if (sc->sc_flags & SCF_SIGNATURE) 1717 to.to_flags |= TOF_SIGNATURE; 1718 #endif 1719 #ifdef TCP_RFC7413 1720 if (sc->sc_tfo_cookie) { 1721 to.to_flags |= TOF_FASTOPEN; 1722 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1723 to.to_tfo_cookie = sc->sc_tfo_cookie; 1724 /* don't send cookie again when retransmitting response */ 1725 sc->sc_tfo_cookie = NULL; 1726 } 1727 #endif 1728 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1729 1730 /* Adjust headers by option size. */ 1731 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1732 m->m_len += optlen; 1733 m->m_pkthdr.len += optlen; 1734 #ifdef INET6 1735 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1736 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1737 else 1738 #endif 1739 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1740 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1741 if (sc->sc_flags & SCF_SIGNATURE) { 1742 KASSERT(to.to_flags & TOF_SIGNATURE, 1743 ("tcp_addoptions() didn't set tcp_signature")); 1744 1745 /* NOTE: to.to_signature is inside of mbuf */ 1746 if (!TCPMD5_ENABLED() || 1747 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1748 m_freem(m); 1749 return (EACCES); 1750 } 1751 } 1752 #endif 1753 } else 1754 optlen = 0; 1755 1756 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1757 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1758 /* 1759 * If we have peer's SYN and it has a flowid, then let's assign it to 1760 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1761 * to SYN|ACK due to lack of inp here. 1762 */ 1763 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1764 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1765 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1766 } 1767 #ifdef INET6 1768 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1769 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1770 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1771 IPPROTO_TCP, 0); 1772 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1773 #ifdef TCP_OFFLOAD 1774 if (ADDED_BY_TOE(sc)) { 1775 struct toedev *tod = sc->sc_tod; 1776 1777 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1778 1779 return (error); 1780 } 1781 #endif 1782 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1783 } 1784 #endif 1785 #if defined(INET6) && defined(INET) 1786 else 1787 #endif 1788 #ifdef INET 1789 { 1790 m->m_pkthdr.csum_flags = CSUM_TCP; 1791 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1792 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1793 #ifdef TCP_OFFLOAD 1794 if (ADDED_BY_TOE(sc)) { 1795 struct toedev *tod = sc->sc_tod; 1796 1797 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1798 1799 return (error); 1800 } 1801 #endif 1802 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1803 } 1804 #endif 1805 return (error); 1806 } 1807 1808 /* 1809 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1810 * that exceed the capacity of the syncache by avoiding the storage of any 1811 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1812 * attacks where the attacker does not have access to our responses. 1813 * 1814 * Syncookies encode and include all necessary information about the 1815 * connection setup within the SYN|ACK that we send back. That way we 1816 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1817 * (if ever). Normally the syncache and syncookies are running in parallel 1818 * with the latter taking over when the former is exhausted. When matching 1819 * syncache entry is found the syncookie is ignored. 1820 * 1821 * The only reliable information persisting the 3WHS is our initial sequence 1822 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1823 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1824 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1825 * returns and signifies a legitimate connection if it matches the ACK. 1826 * 1827 * The available space of 32 bits to store the hash and to encode the SYN 1828 * option information is very tight and we should have at least 24 bits for 1829 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1830 * 1831 * SYN option information we have to encode to fully restore a connection: 1832 * MSS: is imporant to chose an optimal segment size to avoid IP level 1833 * fragmentation along the path. The common MSS values can be encoded 1834 * in a 3-bit table. Uncommon values are captured by the next lower value 1835 * in the table leading to a slight increase in packetization overhead. 1836 * WSCALE: is necessary to allow large windows to be used for high delay- 1837 * bandwidth product links. Not scaling the window when it was initially 1838 * negotiated is bad for performance as lack of scaling further decreases 1839 * the apparent available send window. We only need to encode the WSCALE 1840 * we received from the remote end. Our end can be recalculated at any 1841 * time. The common WSCALE values can be encoded in a 3-bit table. 1842 * Uncommon values are captured by the next lower value in the table 1843 * making us under-estimate the available window size halving our 1844 * theoretically possible maximum throughput for that connection. 1845 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1846 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1847 * that are included in all segments on a connection. We enable them when 1848 * the ACK has them. 1849 * 1850 * Security of syncookies and attack vectors: 1851 * 1852 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1853 * together with the gloabl secret to make it unique per connection attempt. 1854 * Thus any change of any of those parameters results in a different MAC output 1855 * in an unpredictable way unless a collision is encountered. 24 bits of the 1856 * MAC are embedded into the ISS. 1857 * 1858 * To prevent replay attacks two rotating global secrets are updated with a 1859 * new random value every 15 seconds. The life-time of a syncookie is thus 1860 * 15-30 seconds. 1861 * 1862 * Vector 1: Attacking the secret. This requires finding a weakness in the 1863 * MAC itself or the way it is used here. The attacker can do a chosen plain 1864 * text attack by varying and testing the all parameters under his control. 1865 * The strength depends on the size and randomness of the secret, and the 1866 * cryptographic security of the MAC function. Due to the constant updating 1867 * of the secret the attacker has at most 29.999 seconds to find the secret 1868 * and launch spoofed connections. After that he has to start all over again. 1869 * 1870 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1871 * size an average of 4,823 attempts are required for a 50% chance of success 1872 * to spoof a single syncookie (birthday collision paradox). However the 1873 * attacker is blind and doesn't know if one of his attempts succeeded unless 1874 * he has a side channel to interfere success from. A single connection setup 1875 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1876 * This many attempts are required for each one blind spoofed connection. For 1877 * every additional spoofed connection he has to launch another N attempts. 1878 * Thus for a sustained rate 100 spoofed connections per second approximately 1879 * 1,800,000 packets per second would have to be sent. 1880 * 1881 * NB: The MAC function should be fast so that it doesn't become a CPU 1882 * exhaustion attack vector itself. 1883 * 1884 * References: 1885 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1886 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1887 * http://cr.yp.to/syncookies.html (overview) 1888 * http://cr.yp.to/syncookies/archive (details) 1889 * 1890 * 1891 * Schematic construction of a syncookie enabled Initial Sequence Number: 1892 * 0 1 2 3 1893 * 12345678901234567890123456789012 1894 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1895 * 1896 * x 24 MAC (truncated) 1897 * W 3 Send Window Scale index 1898 * M 3 MSS index 1899 * S 1 SACK permitted 1900 * P 1 Odd/even secret 1901 */ 1902 1903 /* 1904 * Distribution and probability of certain MSS values. Those in between are 1905 * rounded down to the next lower one. 1906 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1907 * .2% .3% 5% 7% 7% 20% 15% 45% 1908 */ 1909 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1910 1911 /* 1912 * Distribution and probability of certain WSCALE values. We have to map the 1913 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1914 * bits based on prevalence of certain values. Where we don't have an exact 1915 * match for are rounded down to the next lower one letting us under-estimate 1916 * the true available window. At the moment this would happen only for the 1917 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1918 * and window size). The absence of the WSCALE option (no scaling in either 1919 * direction) is encoded with index zero. 1920 * [WSCALE values histograms, Allman, 2012] 1921 * X 10 10 35 5 6 14 10% by host 1922 * X 11 4 5 5 18 49 3% by connections 1923 */ 1924 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1925 1926 /* 1927 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1928 * and good cryptographic properties. 1929 */ 1930 static uint32_t 1931 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1932 uint8_t *secbits, uintptr_t secmod) 1933 { 1934 SIPHASH_CTX ctx; 1935 uint32_t siphash[2]; 1936 1937 SipHash24_Init(&ctx); 1938 SipHash_SetKey(&ctx, secbits); 1939 switch (inc->inc_flags & INC_ISIPV6) { 1940 #ifdef INET 1941 case 0: 1942 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1943 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1944 break; 1945 #endif 1946 #ifdef INET6 1947 case INC_ISIPV6: 1948 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1949 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1950 break; 1951 #endif 1952 } 1953 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1954 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1955 SipHash_Update(&ctx, &irs, sizeof(irs)); 1956 SipHash_Update(&ctx, &flags, sizeof(flags)); 1957 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1958 SipHash_Final((u_int8_t *)&siphash, &ctx); 1959 1960 return (siphash[0] ^ siphash[1]); 1961 } 1962 1963 static tcp_seq 1964 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1965 { 1966 u_int i, mss, secbit, wscale; 1967 uint32_t iss, hash; 1968 uint8_t *secbits; 1969 union syncookie cookie; 1970 1971 SCH_LOCK_ASSERT(sch); 1972 1973 cookie.cookie = 0; 1974 1975 /* Map our computed MSS into the 3-bit index. */ 1976 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1977 for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0; 1978 i--) 1979 ; 1980 cookie.flags.mss_idx = i; 1981 1982 /* 1983 * Map the send window scale into the 3-bit index but only if 1984 * the wscale option was received. 1985 */ 1986 if (sc->sc_flags & SCF_WINSCALE) { 1987 wscale = sc->sc_requested_s_scale; 1988 for (i = nitems(tcp_sc_wstab) - 1; 1989 tcp_sc_wstab[i] > wscale && i > 0; 1990 i--) 1991 ; 1992 cookie.flags.wscale_idx = i; 1993 } 1994 1995 /* Can we do SACK? */ 1996 if (sc->sc_flags & SCF_SACK) 1997 cookie.flags.sack_ok = 1; 1998 1999 /* Which of the two secrets to use. */ 2000 secbit = sch->sch_sc->secret.oddeven & 0x1; 2001 cookie.flags.odd_even = secbit; 2002 2003 secbits = sch->sch_sc->secret.key[secbit]; 2004 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2005 (uintptr_t)sch); 2006 2007 /* 2008 * Put the flags into the hash and XOR them to get better ISS number 2009 * variance. This doesn't enhance the cryptographic strength and is 2010 * done to prevent the 8 cookie bits from showing up directly on the 2011 * wire. 2012 */ 2013 iss = hash & ~0xff; 2014 iss |= cookie.cookie ^ (hash >> 24); 2015 2016 /* Randomize the timestamp. */ 2017 if (sc->sc_flags & SCF_TIMESTAMP) { 2018 sc->sc_ts = arc4random(); 2019 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 2020 } 2021 2022 TCPSTAT_INC(tcps_sc_sendcookie); 2023 return (iss); 2024 } 2025 2026 static struct syncache * 2027 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2028 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2029 struct socket *lso) 2030 { 2031 uint32_t hash; 2032 uint8_t *secbits; 2033 tcp_seq ack, seq; 2034 int wnd, wscale = 0; 2035 union syncookie cookie; 2036 2037 SCH_LOCK_ASSERT(sch); 2038 2039 /* 2040 * Pull information out of SYN-ACK/ACK and revert sequence number 2041 * advances. 2042 */ 2043 ack = th->th_ack - 1; 2044 seq = th->th_seq - 1; 2045 2046 /* 2047 * Unpack the flags containing enough information to restore the 2048 * connection. 2049 */ 2050 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2051 2052 /* Which of the two secrets to use. */ 2053 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 2054 2055 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2056 2057 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2058 if ((ack & ~0xff) != (hash & ~0xff)) 2059 return (NULL); 2060 2061 /* Fill in the syncache values. */ 2062 sc->sc_flags = 0; 2063 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2064 sc->sc_ipopts = NULL; 2065 2066 sc->sc_irs = seq; 2067 sc->sc_iss = ack; 2068 2069 switch (inc->inc_flags & INC_ISIPV6) { 2070 #ifdef INET 2071 case 0: 2072 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2073 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2074 break; 2075 #endif 2076 #ifdef INET6 2077 case INC_ISIPV6: 2078 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2079 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 2080 break; 2081 #endif 2082 } 2083 2084 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2085 2086 /* We can simply recompute receive window scale we sent earlier. */ 2087 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2088 wscale++; 2089 2090 /* Only use wscale if it was enabled in the orignal SYN. */ 2091 if (cookie.flags.wscale_idx > 0) { 2092 sc->sc_requested_r_scale = wscale; 2093 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2094 sc->sc_flags |= SCF_WINSCALE; 2095 } 2096 2097 wnd = sbspace(&lso->so_rcv); 2098 wnd = imax(wnd, 0); 2099 wnd = imin(wnd, TCP_MAXWIN); 2100 sc->sc_wnd = wnd; 2101 2102 if (cookie.flags.sack_ok) 2103 sc->sc_flags |= SCF_SACK; 2104 2105 if (to->to_flags & TOF_TS) { 2106 sc->sc_flags |= SCF_TIMESTAMP; 2107 sc->sc_tsreflect = to->to_tsval; 2108 sc->sc_ts = to->to_tsecr; 2109 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 2110 } 2111 2112 if (to->to_flags & TOF_SIGNATURE) 2113 sc->sc_flags |= SCF_SIGNATURE; 2114 2115 sc->sc_rxmits = 0; 2116 2117 TCPSTAT_INC(tcps_sc_recvcookie); 2118 return (sc); 2119 } 2120 2121 #ifdef INVARIANTS 2122 static int 2123 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2124 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2125 struct socket *lso) 2126 { 2127 struct syncache scs, *scx; 2128 char *s; 2129 2130 bzero(&scs, sizeof(scs)); 2131 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2132 2133 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2134 return (0); 2135 2136 if (scx != NULL) { 2137 if (sc->sc_peer_mss != scx->sc_peer_mss) 2138 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2139 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2140 2141 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2142 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2143 s, __func__, sc->sc_requested_r_scale, 2144 scx->sc_requested_r_scale); 2145 2146 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2147 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2148 s, __func__, sc->sc_requested_s_scale, 2149 scx->sc_requested_s_scale); 2150 2151 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2152 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2153 } 2154 2155 if (s != NULL) 2156 free(s, M_TCPLOG); 2157 return (0); 2158 } 2159 #endif /* INVARIANTS */ 2160 2161 static void 2162 syncookie_reseed(void *arg) 2163 { 2164 struct tcp_syncache *sc = arg; 2165 uint8_t *secbits; 2166 int secbit; 2167 2168 /* 2169 * Reseeding the secret doesn't have to be protected by a lock. 2170 * It only must be ensured that the new random values are visible 2171 * to all CPUs in a SMP environment. The atomic with release 2172 * semantics ensures that. 2173 */ 2174 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2175 secbits = sc->secret.key[secbit]; 2176 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2177 atomic_add_rel_int(&sc->secret.oddeven, 1); 2178 2179 /* Reschedule ourself. */ 2180 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2181 } 2182 2183 /* 2184 * Exports the syncache entries to userland so that netstat can display 2185 * them alongside the other sockets. This function is intended to be 2186 * called only from tcp_pcblist. 2187 * 2188 * Due to concurrency on an active system, the number of pcbs exported 2189 * may have no relation to max_pcbs. max_pcbs merely indicates the 2190 * amount of space the caller allocated for this function to use. 2191 */ 2192 int 2193 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2194 { 2195 struct xtcpcb xt; 2196 struct syncache *sc; 2197 struct syncache_head *sch; 2198 int count, error, i; 2199 2200 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2201 sch = &V_tcp_syncache.hashbase[i]; 2202 SCH_LOCK(sch); 2203 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2204 if (count >= max_pcbs) { 2205 SCH_UNLOCK(sch); 2206 goto exit; 2207 } 2208 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2209 continue; 2210 bzero(&xt, sizeof(xt)); 2211 xt.xt_len = sizeof(xt); 2212 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2213 xt.xt_inp.inp_vflag = INP_IPV6; 2214 else 2215 xt.xt_inp.inp_vflag = INP_IPV4; 2216 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2217 xt.xt_tp.t_inpcb = &xt.xt_inp; 2218 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2219 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2220 xt.xt_socket.xso_len = sizeof (struct xsocket); 2221 xt.xt_socket.so_type = SOCK_STREAM; 2222 xt.xt_socket.so_state = SS_ISCONNECTING; 2223 error = SYSCTL_OUT(req, &xt, sizeof xt); 2224 if (error) { 2225 SCH_UNLOCK(sch); 2226 goto exit; 2227 } 2228 count++; 2229 } 2230 SCH_UNLOCK(sch); 2231 } 2232 exit: 2233 *pcbs_exported = count; 2234 return error; 2235 }
Cache object: 4cc887cd9b71f42403ade666c76e365f
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