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("$FreeBSD$"); 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 #ifdef IPSEC 100 #include <netipsec/ipsec.h> 101 #ifdef INET6 102 #include <netipsec/ipsec6.h> 103 #endif 104 #include <netipsec/key.h> 105 #endif /*IPSEC*/ 106 107 #include <machine/in_cksum.h> 108 109 #include <security/mac/mac_framework.h> 110 111 static VNET_DEFINE(int, tcp_syncookies) = 1; 112 #define V_tcp_syncookies VNET(tcp_syncookies) 113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 114 &VNET_NAME(tcp_syncookies), 0, 115 "Use TCP SYN cookies if the syncache overflows"); 116 117 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 118 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 120 &VNET_NAME(tcp_syncookiesonly), 0, 121 "Use only TCP SYN cookies"); 122 123 #ifdef TCP_OFFLOAD 124 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 125 #endif 126 127 static void syncache_drop(struct syncache *, struct syncache_head *); 128 static void syncache_free(struct syncache *); 129 static void syncache_insert(struct syncache *, struct syncache_head *); 130 static int syncache_respond(struct syncache *, struct syncache_head *, int); 131 static struct socket *syncache_socket(struct syncache *, struct socket *, 132 struct mbuf *m); 133 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 134 int docallout); 135 static void syncache_timer(void *); 136 137 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 138 uint8_t *, uintptr_t); 139 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 140 static struct syncache 141 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 142 struct syncache *, struct tcphdr *, struct tcpopt *, 143 struct socket *); 144 static void syncookie_reseed(void *); 145 #ifdef INVARIANTS 146 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 147 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 148 struct socket *lso); 149 #endif 150 151 /* 152 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 153 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 154 * the odds are that the user has given up attempting to connect by then. 155 */ 156 #define SYNCACHE_MAXREXMTS 3 157 158 /* Arbitrary values */ 159 #define TCP_SYNCACHE_HASHSIZE 512 160 #define TCP_SYNCACHE_BUCKETLIMIT 30 161 162 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 163 #define V_tcp_syncache VNET(tcp_syncache) 164 165 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 166 "TCP SYN cache"); 167 168 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 169 &VNET_NAME(tcp_syncache.bucket_limit), 0, 170 "Per-bucket hash limit for syncache"); 171 172 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 173 &VNET_NAME(tcp_syncache.cache_limit), 0, 174 "Overall entry limit for syncache"); 175 176 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 177 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 178 179 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 180 &VNET_NAME(tcp_syncache.hashsize), 0, 181 "Size of TCP syncache hashtable"); 182 183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW, 184 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 185 "Limit on SYN/ACK retransmissions"); 186 187 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 188 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 189 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 190 "Send reset on socket allocation failure"); 191 192 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 193 194 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 195 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 196 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 197 198 /* 199 * Requires the syncache entry to be already removed from the bucket list. 200 */ 201 static void 202 syncache_free(struct syncache *sc) 203 { 204 205 if (sc->sc_ipopts) 206 (void) m_free(sc->sc_ipopts); 207 if (sc->sc_cred) 208 crfree(sc->sc_cred); 209 #ifdef MAC 210 mac_syncache_destroy(&sc->sc_label); 211 #endif 212 213 uma_zfree(V_tcp_syncache.zone, sc); 214 } 215 216 void 217 syncache_init(void) 218 { 219 int i; 220 221 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 222 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 223 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 224 V_tcp_syncache.hash_secret = arc4random(); 225 226 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 227 &V_tcp_syncache.hashsize); 228 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 229 &V_tcp_syncache.bucket_limit); 230 if (!powerof2(V_tcp_syncache.hashsize) || 231 V_tcp_syncache.hashsize == 0) { 232 printf("WARNING: syncache hash size is not a power of 2.\n"); 233 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 234 } 235 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 236 237 /* Set limits. */ 238 V_tcp_syncache.cache_limit = 239 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 240 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 241 &V_tcp_syncache.cache_limit); 242 243 /* Allocate the hash table. */ 244 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 245 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 246 247 #ifdef VIMAGE 248 V_tcp_syncache.vnet = curvnet; 249 #endif 250 251 /* Initialize the hash buckets. */ 252 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 253 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 254 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 255 NULL, MTX_DEF); 256 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 257 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 258 V_tcp_syncache.hashbase[i].sch_length = 0; 259 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 260 } 261 262 /* Create the syncache entry zone. */ 263 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 264 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 265 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 266 V_tcp_syncache.cache_limit); 267 268 /* Start the SYN cookie reseeder callout. */ 269 callout_init(&V_tcp_syncache.secret.reseed, 1); 270 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 271 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 272 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 273 syncookie_reseed, &V_tcp_syncache); 274 } 275 276 #ifdef VIMAGE 277 void 278 syncache_destroy(void) 279 { 280 struct syncache_head *sch; 281 struct syncache *sc, *nsc; 282 int i; 283 284 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 285 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 286 287 sch = &V_tcp_syncache.hashbase[i]; 288 callout_drain(&sch->sch_timer); 289 290 SCH_LOCK(sch); 291 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 292 syncache_drop(sc, sch); 293 SCH_UNLOCK(sch); 294 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 295 ("%s: sch->sch_bucket not empty", __func__)); 296 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 297 __func__, sch->sch_length)); 298 mtx_destroy(&sch->sch_mtx); 299 } 300 301 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 302 ("%s: cache_count not 0", __func__)); 303 304 /* Free the allocated global resources. */ 305 uma_zdestroy(V_tcp_syncache.zone); 306 free(V_tcp_syncache.hashbase, M_SYNCACHE); 307 308 callout_drain(&V_tcp_syncache.secret.reseed); 309 } 310 #endif 311 312 /* 313 * Inserts a syncache entry into the specified bucket row. 314 * Locks and unlocks the syncache_head autonomously. 315 */ 316 static void 317 syncache_insert(struct syncache *sc, struct syncache_head *sch) 318 { 319 struct syncache *sc2; 320 321 SCH_LOCK(sch); 322 323 /* 324 * Make sure that we don't overflow the per-bucket limit. 325 * If the bucket is full, toss the oldest element. 326 */ 327 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 328 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 329 ("sch->sch_length incorrect")); 330 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 331 syncache_drop(sc2, sch); 332 TCPSTAT_INC(tcps_sc_bucketoverflow); 333 } 334 335 /* Put it into the bucket. */ 336 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 337 sch->sch_length++; 338 339 #ifdef TCP_OFFLOAD 340 if (ADDED_BY_TOE(sc)) { 341 struct toedev *tod = sc->sc_tod; 342 343 tod->tod_syncache_added(tod, sc->sc_todctx); 344 } 345 #endif 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 TCPSTAT_INC(tcps_states[TCPS_SYN_RECEIVED]); 355 TCPSTAT_INC(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 TCPSTAT_DEC(tcps_states[TCPS_SYN_RECEIVED]); 369 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 370 sch->sch_length--; 371 372 #ifdef TCP_OFFLOAD 373 if (ADDED_BY_TOE(sc)) { 374 struct toedev *tod = sc->sc_tod; 375 376 tod->tod_syncache_removed(tod, sc->sc_todctx); 377 } 378 #endif 379 380 syncache_free(sc); 381 } 382 383 /* 384 * Engage/reengage time on bucket row. 385 */ 386 static void 387 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 388 { 389 sc->sc_rxttime = ticks + 390 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 391 sc->sc_rxmits++; 392 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 393 sch->sch_nextc = sc->sc_rxttime; 394 if (docallout) 395 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 396 syncache_timer, (void *)sch); 397 } 398 } 399 400 /* 401 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 402 * If we have retransmitted an entry the maximum number of times, expire it. 403 * One separate timer for each bucket row. 404 */ 405 static void 406 syncache_timer(void *xsch) 407 { 408 struct syncache_head *sch = (struct syncache_head *)xsch; 409 struct syncache *sc, *nsc; 410 int tick = ticks; 411 char *s; 412 413 CURVNET_SET(sch->sch_sc->vnet); 414 415 /* NB: syncache_head has already been locked by the callout. */ 416 SCH_LOCK_ASSERT(sch); 417 418 /* 419 * In the following cycle we may remove some entries and/or 420 * advance some timeouts, so re-initialize the bucket timer. 421 */ 422 sch->sch_nextc = tick + INT_MAX; 423 424 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 425 /* 426 * We do not check if the listen socket still exists 427 * and accept the case where the listen socket may be 428 * gone by the time we resend the SYN/ACK. We do 429 * not expect this to happens often. If it does, 430 * then the RST will be sent by the time the remote 431 * host does the SYN/ACK->ACK. 432 */ 433 if (TSTMP_GT(sc->sc_rxttime, tick)) { 434 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 435 sch->sch_nextc = sc->sc_rxttime; 436 continue; 437 } 438 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 439 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 440 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 441 "giving up and removing syncache entry\n", 442 s, __func__); 443 free(s, M_TCPLOG); 444 } 445 syncache_drop(sc, sch); 446 TCPSTAT_INC(tcps_sc_stale); 447 continue; 448 } 449 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 450 log(LOG_DEBUG, "%s; %s: Response timeout, " 451 "retransmitting (%u) SYN|ACK\n", 452 s, __func__, sc->sc_rxmits); 453 free(s, M_TCPLOG); 454 } 455 456 syncache_respond(sc, sch, 1); 457 TCPSTAT_INC(tcps_sc_retransmitted); 458 syncache_timeout(sc, sch, 0); 459 } 460 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 461 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 462 syncache_timer, (void *)(sch)); 463 CURVNET_RESTORE(); 464 } 465 466 /* 467 * Find an entry in the syncache. 468 * Returns always with locked syncache_head plus a matching entry or NULL. 469 */ 470 static struct syncache * 471 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 472 { 473 struct syncache *sc; 474 struct syncache_head *sch; 475 uint32_t hash; 476 477 /* 478 * The hash is built on foreign port + local port + foreign address. 479 * We rely on the fact that struct in_conninfo starts with 16 bits 480 * of foreign port, then 16 bits of local port then followed by 128 481 * bits of foreign address. In case of IPv4 address, the first 3 482 * 32-bit words of the address always are zeroes. 483 */ 484 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 485 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 486 487 sch = &V_tcp_syncache.hashbase[hash]; 488 *schp = sch; 489 SCH_LOCK(sch); 490 491 /* Circle through bucket row to find matching entry. */ 492 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 493 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 494 sizeof(struct in_endpoints)) == 0) 495 break; 496 497 return (sc); /* Always returns with locked sch. */ 498 } 499 500 /* 501 * This function is called when we get a RST for a 502 * non-existent connection, so that we can see if the 503 * connection is in the syn cache. If it is, zap it. 504 */ 505 void 506 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 507 { 508 struct syncache *sc; 509 struct syncache_head *sch; 510 char *s = NULL; 511 512 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 513 SCH_LOCK_ASSERT(sch); 514 515 /* 516 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 517 * See RFC 793 page 65, section SEGMENT ARRIVES. 518 */ 519 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 520 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 521 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 522 "FIN flag set, segment ignored\n", s, __func__); 523 TCPSTAT_INC(tcps_badrst); 524 goto done; 525 } 526 527 /* 528 * No corresponding connection was found in syncache. 529 * If syncookies are enabled and possibly exclusively 530 * used, or we are under memory pressure, a valid RST 531 * may not find a syncache entry. In that case we're 532 * done and no SYN|ACK retransmissions will happen. 533 * Otherwise the RST was misdirected or spoofed. 534 */ 535 if (sc == NULL) { 536 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 537 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 538 "syncache entry (possibly syncookie only), " 539 "segment ignored\n", s, __func__); 540 TCPSTAT_INC(tcps_badrst); 541 goto done; 542 } 543 544 /* 545 * If the RST bit is set, check the sequence number to see 546 * if this is a valid reset segment. 547 * RFC 793 page 37: 548 * In all states except SYN-SENT, all reset (RST) segments 549 * are validated by checking their SEQ-fields. A reset is 550 * valid if its sequence number is in the window. 551 * 552 * The sequence number in the reset segment is normally an 553 * echo of our outgoing acknowlegement numbers, but some hosts 554 * send a reset with the sequence number at the rightmost edge 555 * of our receive window, and we have to handle this case. 556 */ 557 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 558 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 559 syncache_drop(sc, sch); 560 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 561 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 562 "connection attempt aborted by remote endpoint\n", 563 s, __func__); 564 TCPSTAT_INC(tcps_sc_reset); 565 } else { 566 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 567 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 568 "IRS %u (+WND %u), segment ignored\n", 569 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 570 TCPSTAT_INC(tcps_badrst); 571 } 572 573 done: 574 if (s != NULL) 575 free(s, M_TCPLOG); 576 SCH_UNLOCK(sch); 577 } 578 579 void 580 syncache_badack(struct in_conninfo *inc) 581 { 582 struct syncache *sc; 583 struct syncache_head *sch; 584 585 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 586 SCH_LOCK_ASSERT(sch); 587 if (sc != NULL) { 588 syncache_drop(sc, sch); 589 TCPSTAT_INC(tcps_sc_badack); 590 } 591 SCH_UNLOCK(sch); 592 } 593 594 void 595 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 596 { 597 struct syncache *sc; 598 struct syncache_head *sch; 599 600 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 601 SCH_LOCK_ASSERT(sch); 602 if (sc == NULL) 603 goto done; 604 605 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 606 if (ntohl(th->th_seq) != sc->sc_iss) 607 goto done; 608 609 /* 610 * If we've rertransmitted 3 times and this is our second error, 611 * we remove the entry. Otherwise, we allow it to continue on. 612 * This prevents us from incorrectly nuking an entry during a 613 * spurious network outage. 614 * 615 * See tcp_notify(). 616 */ 617 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 618 sc->sc_flags |= SCF_UNREACH; 619 goto done; 620 } 621 syncache_drop(sc, sch); 622 TCPSTAT_INC(tcps_sc_unreach); 623 done: 624 SCH_UNLOCK(sch); 625 } 626 627 /* 628 * Build a new TCP socket structure from a syncache entry. 629 * 630 * On success return the newly created socket with its underlying inp locked. 631 */ 632 static struct socket * 633 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 634 { 635 struct tcp_function_block *blk; 636 struct inpcb *inp = NULL; 637 struct socket *so; 638 struct tcpcb *tp; 639 int error; 640 char *s; 641 642 INP_INFO_RLOCK_ASSERT(&V_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, 0); 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_INC(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 mac_socketpeer_set_from_mbuf(m, so); 668 #endif 669 670 inp = sotoinpcb(so); 671 inp->inp_inc.inc_fibnum = so->so_fibnum; 672 INP_WLOCK(inp); 673 /* 674 * Exclusive pcbinfo lock is not required in syncache socket case even 675 * if two inpcb locks can be acquired simultaneously: 676 * - the inpcb in LISTEN state, 677 * - the newly created inp. 678 * 679 * In this case, an inp cannot be at same time in LISTEN state and 680 * just created by an accept() call. 681 */ 682 INP_HASH_WLOCK(&V_tcbinfo); 683 684 /* Insert new socket into PCB hash list. */ 685 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 686 #ifdef INET6 687 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 688 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 689 } else { 690 inp->inp_vflag &= ~INP_IPV6; 691 inp->inp_vflag |= INP_IPV4; 692 #endif 693 inp->inp_laddr = sc->sc_inc.inc_laddr; 694 #ifdef INET6 695 } 696 #endif 697 698 /* 699 * If there's an mbuf and it has a flowid, then let's initialise the 700 * inp with that particular flowid. 701 */ 702 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 703 inp->inp_flowid = m->m_pkthdr.flowid; 704 inp->inp_flowtype = M_HASHTYPE_GET(m); 705 } 706 707 /* 708 * Install in the reservation hash table for now, but don't yet 709 * install a connection group since the full 4-tuple isn't yet 710 * configured. 711 */ 712 inp->inp_lport = sc->sc_inc.inc_lport; 713 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 714 /* 715 * Undo the assignments above if we failed to 716 * put the PCB on the hash lists. 717 */ 718 #ifdef INET6 719 if (sc->sc_inc.inc_flags & INC_ISIPV6) 720 inp->in6p_laddr = in6addr_any; 721 else 722 #endif 723 inp->inp_laddr.s_addr = INADDR_ANY; 724 inp->inp_lport = 0; 725 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 726 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 727 "with error %i\n", 728 s, __func__, error); 729 free(s, M_TCPLOG); 730 } 731 INP_HASH_WUNLOCK(&V_tcbinfo); 732 goto abort; 733 } 734 #ifdef IPSEC 735 /* Copy old policy into new socket's. */ 736 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 737 printf("syncache_socket: could not copy policy\n"); 738 #endif 739 #ifdef INET6 740 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 741 struct inpcb *oinp = sotoinpcb(lso); 742 struct in6_addr laddr6; 743 struct sockaddr_in6 sin6; 744 /* 745 * Inherit socket options from the listening socket. 746 * Note that in6p_inputopts are not (and should not be) 747 * copied, since it stores previously received options and is 748 * used to detect if each new option is different than the 749 * previous one and hence should be passed to a user. 750 * If we copied in6p_inputopts, a user would not be able to 751 * receive options just after calling the accept system call. 752 */ 753 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 754 if (oinp->in6p_outputopts) 755 inp->in6p_outputopts = 756 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 757 758 sin6.sin6_family = AF_INET6; 759 sin6.sin6_len = sizeof(sin6); 760 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 761 sin6.sin6_port = sc->sc_inc.inc_fport; 762 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 763 laddr6 = inp->in6p_laddr; 764 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 765 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 766 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 767 thread0.td_ucred, m)) != 0) { 768 inp->in6p_laddr = laddr6; 769 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 770 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 771 "with error %i\n", 772 s, __func__, error); 773 free(s, M_TCPLOG); 774 } 775 INP_HASH_WUNLOCK(&V_tcbinfo); 776 goto abort; 777 } 778 /* Override flowlabel from in6_pcbconnect. */ 779 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 780 inp->inp_flow |= sc->sc_flowlabel; 781 } 782 #endif /* INET6 */ 783 #if defined(INET) && defined(INET6) 784 else 785 #endif 786 #ifdef INET 787 { 788 struct in_addr laddr; 789 struct sockaddr_in sin; 790 791 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 792 793 if (inp->inp_options == NULL) { 794 inp->inp_options = sc->sc_ipopts; 795 sc->sc_ipopts = NULL; 796 } 797 798 sin.sin_family = AF_INET; 799 sin.sin_len = sizeof(sin); 800 sin.sin_addr = sc->sc_inc.inc_faddr; 801 sin.sin_port = sc->sc_inc.inc_fport; 802 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 803 laddr = inp->inp_laddr; 804 if (inp->inp_laddr.s_addr == INADDR_ANY) 805 inp->inp_laddr = sc->sc_inc.inc_laddr; 806 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 807 thread0.td_ucred, m)) != 0) { 808 inp->inp_laddr = laddr; 809 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 810 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 811 "with error %i\n", 812 s, __func__, error); 813 free(s, M_TCPLOG); 814 } 815 INP_HASH_WUNLOCK(&V_tcbinfo); 816 goto abort; 817 } 818 } 819 #endif /* INET */ 820 INP_HASH_WUNLOCK(&V_tcbinfo); 821 tp = intotcpcb(inp); 822 tcp_state_change(tp, TCPS_SYN_RECEIVED); 823 tp->iss = sc->sc_iss; 824 tp->irs = sc->sc_irs; 825 tcp_rcvseqinit(tp); 826 tcp_sendseqinit(tp); 827 blk = sototcpcb(lso)->t_fb; 828 if (blk != tp->t_fb) { 829 /* 830 * Our parents t_fb was not the default, 831 * we need to release our ref on tp->t_fb and 832 * pickup one on the new entry. 833 */ 834 struct tcp_function_block *rblk; 835 836 rblk = find_and_ref_tcp_fb(blk); 837 KASSERT(rblk != NULL, 838 ("cannot find blk %p out of syncache?", blk)); 839 if (tp->t_fb->tfb_tcp_fb_fini) 840 (*tp->t_fb->tfb_tcp_fb_fini)(tp); 841 refcount_release(&tp->t_fb->tfb_refcnt); 842 tp->t_fb = rblk; 843 if (tp->t_fb->tfb_tcp_fb_init) { 844 (*tp->t_fb->tfb_tcp_fb_init)(tp); 845 } 846 } 847 tp->snd_wl1 = sc->sc_irs; 848 tp->snd_max = tp->iss + 1; 849 tp->snd_nxt = tp->iss + 1; 850 tp->rcv_up = sc->sc_irs + 1; 851 tp->rcv_wnd = sc->sc_wnd; 852 tp->rcv_adv += tp->rcv_wnd; 853 tp->last_ack_sent = tp->rcv_nxt; 854 855 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 856 if (sc->sc_flags & SCF_NOOPT) 857 tp->t_flags |= TF_NOOPT; 858 else { 859 if (sc->sc_flags & SCF_WINSCALE) { 860 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 861 tp->snd_scale = sc->sc_requested_s_scale; 862 tp->request_r_scale = sc->sc_requested_r_scale; 863 } 864 if (sc->sc_flags & SCF_TIMESTAMP) { 865 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 866 tp->ts_recent = sc->sc_tsreflect; 867 tp->ts_recent_age = tcp_ts_getticks(); 868 tp->ts_offset = sc->sc_tsoff; 869 } 870 #ifdef TCP_SIGNATURE 871 if (sc->sc_flags & SCF_SIGNATURE) 872 tp->t_flags |= TF_SIGNATURE; 873 #endif 874 if (sc->sc_flags & SCF_SACK) 875 tp->t_flags |= TF_SACK_PERMIT; 876 } 877 878 if (sc->sc_flags & SCF_ECN) 879 tp->t_flags |= TF_ECN_PERMIT; 880 881 /* 882 * Set up MSS and get cached values from tcp_hostcache. 883 * This might overwrite some of the defaults we just set. 884 */ 885 tcp_mss(tp, sc->sc_peer_mss); 886 887 /* 888 * If the SYN,ACK was retransmitted, indicate that CWND to be 889 * limited to one segment in cc_conn_init(). 890 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 891 */ 892 if (sc->sc_rxmits > 1) 893 tp->snd_cwnd = 1; 894 895 #ifdef TCP_OFFLOAD 896 /* 897 * Allow a TOE driver to install its hooks. Note that we hold the 898 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 899 * new connection before the TOE driver has done its thing. 900 */ 901 if (ADDED_BY_TOE(sc)) { 902 struct toedev *tod = sc->sc_tod; 903 904 tod->tod_offload_socket(tod, sc->sc_todctx, so); 905 } 906 #endif 907 /* 908 * Copy and activate timers. 909 */ 910 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 911 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 912 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 913 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 914 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 915 916 soisconnected(so); 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. See if this socket has had a syncache entry dropped in 973 * the past. We don't want to accept a bogus syncookie 974 * if we've never received a SYN. 975 * B. check that the syncookie is valid. If it is, then 976 * cobble up a fake syncache entry, and return. 977 */ 978 if (!V_tcp_syncookies) { 979 SCH_UNLOCK(sch); 980 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 981 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 982 "segment rejected (syncookies disabled)\n", 983 s, __func__); 984 goto failed; 985 } 986 bzero(&scs, sizeof(scs)); 987 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 988 SCH_UNLOCK(sch); 989 if (sc == NULL) { 990 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 991 log(LOG_DEBUG, "%s; %s: Segment failed " 992 "SYNCOOKIE authentication, segment rejected " 993 "(probably spoofed)\n", s, __func__); 994 goto failed; 995 } 996 } else { 997 /* 998 * Pull out the entry to unlock the bucket row. 999 * 1000 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1001 * tcp_state_change(). The tcpcb is not existent at this 1002 * moment. A new one will be allocated via syncache_socket-> 1003 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1004 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1005 */ 1006 TCPSTAT_DEC(tcps_states[TCPS_SYN_RECEIVED]); 1007 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1008 sch->sch_length--; 1009 #ifdef TCP_OFFLOAD 1010 if (ADDED_BY_TOE(sc)) { 1011 struct toedev *tod = sc->sc_tod; 1012 1013 tod->tod_syncache_removed(tod, sc->sc_todctx); 1014 } 1015 #endif 1016 SCH_UNLOCK(sch); 1017 } 1018 1019 /* 1020 * Segment validation: 1021 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1022 */ 1023 if (th->th_ack != sc->sc_iss + 1) { 1024 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1025 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1026 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1027 goto failed; 1028 } 1029 1030 /* 1031 * The SEQ must fall in the window starting at the received 1032 * initial receive sequence number + 1 (the SYN). 1033 */ 1034 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1035 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1036 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1037 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1038 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1039 goto failed; 1040 } 1041 1042 /* 1043 * If timestamps were not negotiated during SYN/ACK they 1044 * must not appear on any segment during this session. 1045 */ 1046 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1047 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1048 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1049 "segment rejected\n", s, __func__); 1050 goto failed; 1051 } 1052 1053 /* 1054 * If timestamps were negotiated during SYN/ACK they should 1055 * appear on every segment during this session. 1056 * XXXAO: This is only informal as there have been unverified 1057 * reports of non-compliants stacks. 1058 */ 1059 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1060 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1061 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1062 "no action\n", s, __func__); 1063 free(s, M_TCPLOG); 1064 s = NULL; 1065 } 1066 } 1067 1068 /* 1069 * If timestamps were negotiated the reflected timestamp 1070 * must be equal to what we actually sent in the SYN|ACK. 1071 */ 1072 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 1073 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1074 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1075 "segment rejected\n", 1076 s, __func__, to->to_tsecr, sc->sc_ts); 1077 goto failed; 1078 } 1079 1080 *lsop = syncache_socket(sc, *lsop, m); 1081 1082 if (*lsop == NULL) 1083 TCPSTAT_INC(tcps_sc_aborted); 1084 else 1085 TCPSTAT_INC(tcps_sc_completed); 1086 1087 /* how do we find the inp for the new socket? */ 1088 if (sc != &scs) 1089 syncache_free(sc); 1090 return (1); 1091 failed: 1092 if (sc != NULL && sc != &scs) 1093 syncache_free(sc); 1094 if (s != NULL) 1095 free(s, M_TCPLOG); 1096 *lsop = NULL; 1097 return (0); 1098 } 1099 1100 #ifdef TCP_RFC7413 1101 static void 1102 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1103 uint64_t response_cookie) 1104 { 1105 struct inpcb *inp; 1106 struct tcpcb *tp; 1107 unsigned int *pending_counter; 1108 1109 /* 1110 * Global TCP locks are held because we manipulate the PCB lists 1111 * and create a new socket. 1112 */ 1113 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 1114 1115 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1116 *lsop = syncache_socket(sc, *lsop, m); 1117 if (*lsop == NULL) { 1118 TCPSTAT_INC(tcps_sc_aborted); 1119 atomic_subtract_int(pending_counter, 1); 1120 } else { 1121 inp = sotoinpcb(*lsop); 1122 tp = intotcpcb(inp); 1123 tp->t_flags |= TF_FASTOPEN; 1124 tp->t_tfo_cookie = response_cookie; 1125 tp->snd_max = tp->iss; 1126 tp->snd_nxt = tp->iss; 1127 tp->t_tfo_pending = pending_counter; 1128 TCPSTAT_INC(tcps_sc_completed); 1129 } 1130 } 1131 #endif /* TCP_RFC7413 */ 1132 1133 /* 1134 * Given a LISTEN socket and an inbound SYN request, add 1135 * this to the syn cache, and send back a segment: 1136 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1137 * to the source. 1138 * 1139 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1140 * Doing so would require that we hold onto the data and deliver it 1141 * to the application. However, if we are the target of a SYN-flood 1142 * DoS attack, an attacker could send data which would eventually 1143 * consume all available buffer space if it were ACKed. By not ACKing 1144 * the data, we avoid this DoS scenario. 1145 * 1146 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1147 * cookie is processed, V_tcp_fastopen_enabled set to true, and the 1148 * TCP_FASTOPEN socket option is set. In this case, a new socket is created 1149 * and returned via lsop, the mbuf is not freed so that tcp_input() can 1150 * queue its data to the socket, and 1 is returned to indicate the 1151 * TFO-socket-creation path was taken. 1152 */ 1153 int 1154 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1155 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1156 void *todctx) 1157 { 1158 struct tcpcb *tp; 1159 struct socket *so; 1160 struct syncache *sc = NULL; 1161 struct syncache_head *sch; 1162 struct mbuf *ipopts = NULL; 1163 u_int ltflags; 1164 int win, sb_hiwat, ip_ttl, ip_tos; 1165 char *s; 1166 int rv = 0; 1167 #ifdef INET6 1168 int autoflowlabel = 0; 1169 #endif 1170 #ifdef MAC 1171 struct label *maclabel; 1172 #endif 1173 struct syncache scs; 1174 struct ucred *cred; 1175 #ifdef TCP_RFC7413 1176 uint64_t tfo_response_cookie; 1177 int tfo_cookie_valid = 0; 1178 int tfo_response_cookie_valid = 0; 1179 #endif 1180 1181 INP_WLOCK_ASSERT(inp); /* listen socket */ 1182 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1183 ("%s: unexpected tcp flags", __func__)); 1184 1185 /* 1186 * Combine all so/tp operations very early to drop the INP lock as 1187 * soon as possible. 1188 */ 1189 so = *lsop; 1190 tp = sototcpcb(so); 1191 cred = crhold(so->so_cred); 1192 1193 #ifdef INET6 1194 if ((inc->inc_flags & INC_ISIPV6) && 1195 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1196 autoflowlabel = 1; 1197 #endif 1198 ip_ttl = inp->inp_ip_ttl; 1199 ip_tos = inp->inp_ip_tos; 1200 win = sbspace(&so->so_rcv); 1201 sb_hiwat = so->so_rcv.sb_hiwat; 1202 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1203 1204 #ifdef TCP_RFC7413 1205 if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) && 1206 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) { 1207 /* 1208 * Limit the number of pending TFO connections to 1209 * approximately half of the queue limit. This prevents TFO 1210 * SYN floods from starving the service by filling the 1211 * listen queue with bogus TFO connections. 1212 */ 1213 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1214 (so->so_qlimit / 2)) { 1215 int result; 1216 1217 result = tcp_fastopen_check_cookie(inc, 1218 to->to_tfo_cookie, to->to_tfo_len, 1219 &tfo_response_cookie); 1220 tfo_cookie_valid = (result > 0); 1221 tfo_response_cookie_valid = (result >= 0); 1222 } else 1223 atomic_subtract_int(tp->t_tfo_pending, 1); 1224 } 1225 #endif 1226 1227 /* By the time we drop the lock these should no longer be used. */ 1228 so = NULL; 1229 tp = NULL; 1230 1231 #ifdef MAC 1232 if (mac_syncache_init(&maclabel) != 0) { 1233 INP_WUNLOCK(inp); 1234 goto done; 1235 } else 1236 mac_syncache_create(maclabel, inp); 1237 #endif 1238 #ifdef TCP_RFC7413 1239 if (!tfo_cookie_valid) 1240 #endif 1241 INP_WUNLOCK(inp); 1242 1243 /* 1244 * Remember the IP options, if any. 1245 */ 1246 #ifdef INET6 1247 if (!(inc->inc_flags & INC_ISIPV6)) 1248 #endif 1249 #ifdef INET 1250 ipopts = (m) ? ip_srcroute(m) : NULL; 1251 #else 1252 ipopts = NULL; 1253 #endif 1254 1255 /* 1256 * See if we already have an entry for this connection. 1257 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1258 * 1259 * XXX: should the syncache be re-initialized with the contents 1260 * of the new SYN here (which may have different options?) 1261 * 1262 * XXX: We do not check the sequence number to see if this is a 1263 * real retransmit or a new connection attempt. The question is 1264 * how to handle such a case; either ignore it as spoofed, or 1265 * drop the current entry and create a new one? 1266 */ 1267 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1268 SCH_LOCK_ASSERT(sch); 1269 if (sc != NULL) { 1270 #ifdef TCP_RFC7413 1271 if (tfo_cookie_valid) 1272 INP_WUNLOCK(inp); 1273 #endif 1274 TCPSTAT_INC(tcps_sc_dupsyn); 1275 if (ipopts) { 1276 /* 1277 * If we were remembering a previous source route, 1278 * forget it and use the new one we've been given. 1279 */ 1280 if (sc->sc_ipopts) 1281 (void) m_free(sc->sc_ipopts); 1282 sc->sc_ipopts = ipopts; 1283 } 1284 /* 1285 * Update timestamp if present. 1286 */ 1287 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1288 sc->sc_tsreflect = to->to_tsval; 1289 else 1290 sc->sc_flags &= ~SCF_TIMESTAMP; 1291 #ifdef MAC 1292 /* 1293 * Since we have already unconditionally allocated label 1294 * storage, free it up. The syncache entry will already 1295 * have an initialized label we can use. 1296 */ 1297 mac_syncache_destroy(&maclabel); 1298 #endif 1299 /* Retransmit SYN|ACK and reset retransmit count. */ 1300 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1301 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1302 "resetting timer and retransmitting SYN|ACK\n", 1303 s, __func__); 1304 free(s, M_TCPLOG); 1305 } 1306 if (syncache_respond(sc, sch, 1) == 0) { 1307 sc->sc_rxmits = 0; 1308 syncache_timeout(sc, sch, 1); 1309 TCPSTAT_INC(tcps_sndacks); 1310 TCPSTAT_INC(tcps_sndtotal); 1311 } 1312 SCH_UNLOCK(sch); 1313 goto done; 1314 } 1315 1316 #ifdef TCP_RFC7413 1317 if (tfo_cookie_valid) { 1318 bzero(&scs, sizeof(scs)); 1319 sc = &scs; 1320 goto skip_alloc; 1321 } 1322 #endif 1323 1324 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1325 if (sc == NULL) { 1326 /* 1327 * The zone allocator couldn't provide more entries. 1328 * Treat this as if the cache was full; drop the oldest 1329 * entry and insert the new one. 1330 */ 1331 TCPSTAT_INC(tcps_sc_zonefail); 1332 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1333 syncache_drop(sc, sch); 1334 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1335 if (sc == NULL) { 1336 if (V_tcp_syncookies) { 1337 bzero(&scs, sizeof(scs)); 1338 sc = &scs; 1339 } else { 1340 SCH_UNLOCK(sch); 1341 if (ipopts) 1342 (void) m_free(ipopts); 1343 goto done; 1344 } 1345 } 1346 } 1347 1348 #ifdef TCP_RFC7413 1349 skip_alloc: 1350 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1351 sc->sc_tfo_cookie = &tfo_response_cookie; 1352 #endif 1353 1354 /* 1355 * Fill in the syncache values. 1356 */ 1357 #ifdef MAC 1358 sc->sc_label = maclabel; 1359 #endif 1360 sc->sc_cred = cred; 1361 cred = NULL; 1362 sc->sc_ipopts = ipopts; 1363 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1364 #ifdef INET6 1365 if (!(inc->inc_flags & INC_ISIPV6)) 1366 #endif 1367 { 1368 sc->sc_ip_tos = ip_tos; 1369 sc->sc_ip_ttl = ip_ttl; 1370 } 1371 #ifdef TCP_OFFLOAD 1372 sc->sc_tod = tod; 1373 sc->sc_todctx = todctx; 1374 #endif 1375 sc->sc_irs = th->th_seq; 1376 sc->sc_iss = arc4random(); 1377 sc->sc_flags = 0; 1378 sc->sc_flowlabel = 0; 1379 1380 /* 1381 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1382 * win was derived from socket earlier in the function. 1383 */ 1384 win = imax(win, 0); 1385 win = imin(win, TCP_MAXWIN); 1386 sc->sc_wnd = win; 1387 1388 if (V_tcp_do_rfc1323) { 1389 /* 1390 * A timestamp received in a SYN makes 1391 * it ok to send timestamp requests and replies. 1392 */ 1393 if (to->to_flags & TOF_TS) { 1394 sc->sc_tsreflect = to->to_tsval; 1395 sc->sc_ts = tcp_ts_getticks(); 1396 sc->sc_flags |= SCF_TIMESTAMP; 1397 } 1398 if (to->to_flags & TOF_SCALE) { 1399 int wscale = 0; 1400 1401 /* 1402 * Pick the smallest possible scaling factor that 1403 * will still allow us to scale up to sb_max, aka 1404 * kern.ipc.maxsockbuf. 1405 * 1406 * We do this because there are broken firewalls that 1407 * will corrupt the window scale option, leading to 1408 * the other endpoint believing that our advertised 1409 * window is unscaled. At scale factors larger than 1410 * 5 the unscaled window will drop below 1500 bytes, 1411 * leading to serious problems when traversing these 1412 * broken firewalls. 1413 * 1414 * With the default maxsockbuf of 256K, a scale factor 1415 * of 3 will be chosen by this algorithm. Those who 1416 * choose a larger maxsockbuf should watch out 1417 * for the compatiblity problems mentioned above. 1418 * 1419 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1420 * or <SYN,ACK>) segment itself is never scaled. 1421 */ 1422 while (wscale < TCP_MAX_WINSHIFT && 1423 (TCP_MAXWIN << wscale) < sb_max) 1424 wscale++; 1425 sc->sc_requested_r_scale = wscale; 1426 sc->sc_requested_s_scale = to->to_wscale; 1427 sc->sc_flags |= SCF_WINSCALE; 1428 } 1429 } 1430 #ifdef TCP_SIGNATURE 1431 /* 1432 * If listening socket requested TCP digests, OR received SYN 1433 * contains the option, flag this in the syncache so that 1434 * syncache_respond() will do the right thing with the SYN+ACK. 1435 */ 1436 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1437 sc->sc_flags |= SCF_SIGNATURE; 1438 #endif 1439 if (to->to_flags & TOF_SACKPERM) 1440 sc->sc_flags |= SCF_SACK; 1441 if (to->to_flags & TOF_MSS) 1442 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1443 if (ltflags & TF_NOOPT) 1444 sc->sc_flags |= SCF_NOOPT; 1445 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1446 sc->sc_flags |= SCF_ECN; 1447 1448 if (V_tcp_syncookies) 1449 sc->sc_iss = syncookie_generate(sch, sc); 1450 #ifdef INET6 1451 if (autoflowlabel) { 1452 if (V_tcp_syncookies) 1453 sc->sc_flowlabel = sc->sc_iss; 1454 else 1455 sc->sc_flowlabel = ip6_randomflowlabel(); 1456 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1457 } 1458 #endif 1459 SCH_UNLOCK(sch); 1460 1461 #ifdef TCP_RFC7413 1462 if (tfo_cookie_valid) { 1463 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1464 /* INP_WUNLOCK(inp) will be performed by the called */ 1465 rv = 1; 1466 goto tfo_done; 1467 } 1468 #endif 1469 1470 /* 1471 * Do a standard 3-way handshake. 1472 */ 1473 if (syncache_respond(sc, sch, 0) == 0) { 1474 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1475 syncache_free(sc); 1476 else if (sc != &scs) 1477 syncache_insert(sc, sch); /* locks and unlocks sch */ 1478 TCPSTAT_INC(tcps_sndacks); 1479 TCPSTAT_INC(tcps_sndtotal); 1480 } else { 1481 if (sc != &scs) 1482 syncache_free(sc); 1483 TCPSTAT_INC(tcps_sc_dropped); 1484 } 1485 1486 done: 1487 if (m) { 1488 *lsop = NULL; 1489 m_freem(m); 1490 } 1491 #ifdef TCP_RFC7413 1492 tfo_done: 1493 #endif 1494 if (cred != NULL) 1495 crfree(cred); 1496 #ifdef MAC 1497 if (sc == &scs) 1498 mac_syncache_destroy(&maclabel); 1499 #endif 1500 return (rv); 1501 } 1502 1503 static int 1504 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked) 1505 { 1506 struct ip *ip = NULL; 1507 struct mbuf *m; 1508 struct tcphdr *th = NULL; 1509 int optlen, error = 0; /* Make compiler happy */ 1510 u_int16_t hlen, tlen, mssopt; 1511 struct tcpopt to; 1512 #ifdef INET6 1513 struct ip6_hdr *ip6 = NULL; 1514 #endif 1515 #ifdef TCP_SIGNATURE 1516 struct secasvar *sav; 1517 #endif 1518 1519 hlen = 1520 #ifdef INET6 1521 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1522 #endif 1523 sizeof(struct ip); 1524 tlen = hlen + sizeof(struct tcphdr); 1525 1526 /* Determine MSS we advertize to other end of connection. */ 1527 mssopt = tcp_mssopt(&sc->sc_inc); 1528 if (sc->sc_peer_mss) 1529 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1530 1531 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1532 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1533 ("syncache: mbuf too small")); 1534 1535 /* Create the IP+TCP header from scratch. */ 1536 m = m_gethdr(M_NOWAIT, MT_DATA); 1537 if (m == NULL) 1538 return (ENOBUFS); 1539 #ifdef MAC 1540 mac_syncache_create_mbuf(sc->sc_label, m); 1541 #endif 1542 m->m_data += max_linkhdr; 1543 m->m_len = tlen; 1544 m->m_pkthdr.len = tlen; 1545 m->m_pkthdr.rcvif = NULL; 1546 1547 #ifdef INET6 1548 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1549 ip6 = mtod(m, struct ip6_hdr *); 1550 ip6->ip6_vfc = IPV6_VERSION; 1551 ip6->ip6_nxt = IPPROTO_TCP; 1552 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1553 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1554 ip6->ip6_plen = htons(tlen - hlen); 1555 /* ip6_hlim is set after checksum */ 1556 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1557 ip6->ip6_flow |= sc->sc_flowlabel; 1558 1559 th = (struct tcphdr *)(ip6 + 1); 1560 } 1561 #endif 1562 #if defined(INET6) && defined(INET) 1563 else 1564 #endif 1565 #ifdef INET 1566 { 1567 ip = mtod(m, struct ip *); 1568 ip->ip_v = IPVERSION; 1569 ip->ip_hl = sizeof(struct ip) >> 2; 1570 ip->ip_len = htons(tlen); 1571 ip->ip_id = 0; 1572 ip->ip_off = 0; 1573 ip->ip_sum = 0; 1574 ip->ip_p = IPPROTO_TCP; 1575 ip->ip_src = sc->sc_inc.inc_laddr; 1576 ip->ip_dst = sc->sc_inc.inc_faddr; 1577 ip->ip_ttl = sc->sc_ip_ttl; 1578 ip->ip_tos = sc->sc_ip_tos; 1579 1580 /* 1581 * See if we should do MTU discovery. Route lookups are 1582 * expensive, so we will only unset the DF bit if: 1583 * 1584 * 1) path_mtu_discovery is disabled 1585 * 2) the SCF_UNREACH flag has been set 1586 */ 1587 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1588 ip->ip_off |= htons(IP_DF); 1589 1590 th = (struct tcphdr *)(ip + 1); 1591 } 1592 #endif /* INET */ 1593 th->th_sport = sc->sc_inc.inc_lport; 1594 th->th_dport = sc->sc_inc.inc_fport; 1595 1596 th->th_seq = htonl(sc->sc_iss); 1597 th->th_ack = htonl(sc->sc_irs + 1); 1598 th->th_off = sizeof(struct tcphdr) >> 2; 1599 th->th_x2 = 0; 1600 th->th_flags = TH_SYN|TH_ACK; 1601 th->th_win = htons(sc->sc_wnd); 1602 th->th_urp = 0; 1603 1604 if (sc->sc_flags & SCF_ECN) { 1605 th->th_flags |= TH_ECE; 1606 TCPSTAT_INC(tcps_ecn_shs); 1607 } 1608 1609 /* Tack on the TCP options. */ 1610 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1611 to.to_flags = 0; 1612 1613 to.to_mss = mssopt; 1614 to.to_flags = TOF_MSS; 1615 if (sc->sc_flags & SCF_WINSCALE) { 1616 to.to_wscale = sc->sc_requested_r_scale; 1617 to.to_flags |= TOF_SCALE; 1618 } 1619 if (sc->sc_flags & SCF_TIMESTAMP) { 1620 /* Virgin timestamp or TCP cookie enhanced one. */ 1621 to.to_tsval = sc->sc_ts; 1622 to.to_tsecr = sc->sc_tsreflect; 1623 to.to_flags |= TOF_TS; 1624 } 1625 if (sc->sc_flags & SCF_SACK) 1626 to.to_flags |= TOF_SACKPERM; 1627 #ifdef TCP_SIGNATURE 1628 sav = NULL; 1629 if (sc->sc_flags & SCF_SIGNATURE) { 1630 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND); 1631 if (sav != NULL) 1632 to.to_flags |= TOF_SIGNATURE; 1633 else { 1634 1635 /* 1636 * We've got SCF_SIGNATURE flag 1637 * inherited from listening socket, 1638 * but no SADB key for given source 1639 * address. Assume signature is not 1640 * required and remove signature flag 1641 * instead of silently dropping 1642 * connection. 1643 */ 1644 if (locked == 0) 1645 SCH_LOCK(sch); 1646 sc->sc_flags &= ~SCF_SIGNATURE; 1647 if (locked == 0) 1648 SCH_UNLOCK(sch); 1649 } 1650 } 1651 #endif 1652 1653 #ifdef TCP_RFC7413 1654 if (sc->sc_tfo_cookie) { 1655 to.to_flags |= TOF_FASTOPEN; 1656 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1657 to.to_tfo_cookie = sc->sc_tfo_cookie; 1658 /* don't send cookie again when retransmitting response */ 1659 sc->sc_tfo_cookie = NULL; 1660 } 1661 #endif 1662 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1663 1664 /* Adjust headers by option size. */ 1665 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1666 m->m_len += optlen; 1667 m->m_pkthdr.len += optlen; 1668 1669 #ifdef TCP_SIGNATURE 1670 if (sc->sc_flags & SCF_SIGNATURE) 1671 tcp_signature_do_compute(m, 0, optlen, 1672 to.to_signature, sav); 1673 #endif 1674 #ifdef INET6 1675 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1676 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1677 else 1678 #endif 1679 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1680 } else 1681 optlen = 0; 1682 1683 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1684 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1685 #ifdef INET6 1686 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1687 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1688 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1689 IPPROTO_TCP, 0); 1690 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1691 #ifdef TCP_OFFLOAD 1692 if (ADDED_BY_TOE(sc)) { 1693 struct toedev *tod = sc->sc_tod; 1694 1695 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1696 1697 return (error); 1698 } 1699 #endif 1700 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1701 } 1702 #endif 1703 #if defined(INET6) && defined(INET) 1704 else 1705 #endif 1706 #ifdef INET 1707 { 1708 m->m_pkthdr.csum_flags = CSUM_TCP; 1709 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1710 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1711 #ifdef TCP_OFFLOAD 1712 if (ADDED_BY_TOE(sc)) { 1713 struct toedev *tod = sc->sc_tod; 1714 1715 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1716 1717 return (error); 1718 } 1719 #endif 1720 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1721 } 1722 #endif 1723 return (error); 1724 } 1725 1726 /* 1727 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1728 * that exceed the capacity of the syncache by avoiding the storage of any 1729 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1730 * attacks where the attacker does not have access to our responses. 1731 * 1732 * Syncookies encode and include all necessary information about the 1733 * connection setup within the SYN|ACK that we send back. That way we 1734 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1735 * (if ever). Normally the syncache and syncookies are running in parallel 1736 * with the latter taking over when the former is exhausted. When matching 1737 * syncache entry is found the syncookie is ignored. 1738 * 1739 * The only reliable information persisting the 3WHS is our inital sequence 1740 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1741 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1742 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1743 * returns and signifies a legitimate connection if it matches the ACK. 1744 * 1745 * The available space of 32 bits to store the hash and to encode the SYN 1746 * option information is very tight and we should have at least 24 bits for 1747 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1748 * 1749 * SYN option information we have to encode to fully restore a connection: 1750 * MSS: is imporant to chose an optimal segment size to avoid IP level 1751 * fragmentation along the path. The common MSS values can be encoded 1752 * in a 3-bit table. Uncommon values are captured by the next lower value 1753 * in the table leading to a slight increase in packetization overhead. 1754 * WSCALE: is necessary to allow large windows to be used for high delay- 1755 * bandwidth product links. Not scaling the window when it was initially 1756 * negotiated is bad for performance as lack of scaling further decreases 1757 * the apparent available send window. We only need to encode the WSCALE 1758 * we received from the remote end. Our end can be recalculated at any 1759 * time. The common WSCALE values can be encoded in a 3-bit table. 1760 * Uncommon values are captured by the next lower value in the table 1761 * making us under-estimate the available window size halving our 1762 * theoretically possible maximum throughput for that connection. 1763 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1764 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1765 * that are included in all segments on a connection. We enable them when 1766 * the ACK has them. 1767 * 1768 * Security of syncookies and attack vectors: 1769 * 1770 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1771 * together with the gloabl secret to make it unique per connection attempt. 1772 * Thus any change of any of those parameters results in a different MAC output 1773 * in an unpredictable way unless a collision is encountered. 24 bits of the 1774 * MAC are embedded into the ISS. 1775 * 1776 * To prevent replay attacks two rotating global secrets are updated with a 1777 * new random value every 15 seconds. The life-time of a syncookie is thus 1778 * 15-30 seconds. 1779 * 1780 * Vector 1: Attacking the secret. This requires finding a weakness in the 1781 * MAC itself or the way it is used here. The attacker can do a chosen plain 1782 * text attack by varying and testing the all parameters under his control. 1783 * The strength depends on the size and randomness of the secret, and the 1784 * cryptographic security of the MAC function. Due to the constant updating 1785 * of the secret the attacker has at most 29.999 seconds to find the secret 1786 * and launch spoofed connections. After that he has to start all over again. 1787 * 1788 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1789 * size an average of 4,823 attempts are required for a 50% chance of success 1790 * to spoof a single syncookie (birthday collision paradox). However the 1791 * attacker is blind and doesn't know if one of his attempts succeeded unless 1792 * he has a side channel to interfere success from. A single connection setup 1793 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1794 * This many attempts are required for each one blind spoofed connection. For 1795 * every additional spoofed connection he has to launch another N attempts. 1796 * Thus for a sustained rate 100 spoofed connections per second approximately 1797 * 1,800,000 packets per second would have to be sent. 1798 * 1799 * NB: The MAC function should be fast so that it doesn't become a CPU 1800 * exhaustion attack vector itself. 1801 * 1802 * References: 1803 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1804 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1805 * http://cr.yp.to/syncookies.html (overview) 1806 * http://cr.yp.to/syncookies/archive (details) 1807 * 1808 * 1809 * Schematic construction of a syncookie enabled Initial Sequence Number: 1810 * 0 1 2 3 1811 * 12345678901234567890123456789012 1812 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1813 * 1814 * x 24 MAC (truncated) 1815 * W 3 Send Window Scale index 1816 * M 3 MSS index 1817 * S 1 SACK permitted 1818 * P 1 Odd/even secret 1819 */ 1820 1821 /* 1822 * Distribution and probability of certain MSS values. Those in between are 1823 * rounded down to the next lower one. 1824 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1825 * .2% .3% 5% 7% 7% 20% 15% 45% 1826 */ 1827 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1828 1829 /* 1830 * Distribution and probability of certain WSCALE values. We have to map the 1831 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1832 * bits based on prevalence of certain values. Where we don't have an exact 1833 * match for are rounded down to the next lower one letting us under-estimate 1834 * the true available window. At the moment this would happen only for the 1835 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1836 * and window size). The absence of the WSCALE option (no scaling in either 1837 * direction) is encoded with index zero. 1838 * [WSCALE values histograms, Allman, 2012] 1839 * X 10 10 35 5 6 14 10% by host 1840 * X 11 4 5 5 18 49 3% by connections 1841 */ 1842 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1843 1844 /* 1845 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1846 * and good cryptographic properties. 1847 */ 1848 static uint32_t 1849 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1850 uint8_t *secbits, uintptr_t secmod) 1851 { 1852 SIPHASH_CTX ctx; 1853 uint32_t siphash[2]; 1854 1855 SipHash24_Init(&ctx); 1856 SipHash_SetKey(&ctx, secbits); 1857 switch (inc->inc_flags & INC_ISIPV6) { 1858 #ifdef INET 1859 case 0: 1860 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1861 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1862 break; 1863 #endif 1864 #ifdef INET6 1865 case INC_ISIPV6: 1866 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1867 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1868 break; 1869 #endif 1870 } 1871 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1872 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1873 SipHash_Update(&ctx, &irs, sizeof(irs)); 1874 SipHash_Update(&ctx, &flags, sizeof(flags)); 1875 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1876 SipHash_Final((u_int8_t *)&siphash, &ctx); 1877 1878 return (siphash[0] ^ siphash[1]); 1879 } 1880 1881 static tcp_seq 1882 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1883 { 1884 u_int i, mss, secbit, wscale; 1885 uint32_t iss, hash; 1886 uint8_t *secbits; 1887 union syncookie cookie; 1888 1889 SCH_LOCK_ASSERT(sch); 1890 1891 cookie.cookie = 0; 1892 1893 /* Map our computed MSS into the 3-bit index. */ 1894 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1895 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1; 1896 tcp_sc_msstab[i] > mss && i > 0; 1897 i--) 1898 ; 1899 cookie.flags.mss_idx = i; 1900 1901 /* 1902 * Map the send window scale into the 3-bit index but only if 1903 * the wscale option was received. 1904 */ 1905 if (sc->sc_flags & SCF_WINSCALE) { 1906 wscale = sc->sc_requested_s_scale; 1907 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1; 1908 tcp_sc_wstab[i] > wscale && i > 0; 1909 i--) 1910 ; 1911 cookie.flags.wscale_idx = i; 1912 } 1913 1914 /* Can we do SACK? */ 1915 if (sc->sc_flags & SCF_SACK) 1916 cookie.flags.sack_ok = 1; 1917 1918 /* Which of the two secrets to use. */ 1919 secbit = sch->sch_sc->secret.oddeven & 0x1; 1920 cookie.flags.odd_even = secbit; 1921 1922 secbits = sch->sch_sc->secret.key[secbit]; 1923 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1924 (uintptr_t)sch); 1925 1926 /* 1927 * Put the flags into the hash and XOR them to get better ISS number 1928 * variance. This doesn't enhance the cryptographic strength and is 1929 * done to prevent the 8 cookie bits from showing up directly on the 1930 * wire. 1931 */ 1932 iss = hash & ~0xff; 1933 iss |= cookie.cookie ^ (hash >> 24); 1934 1935 /* Randomize the timestamp. */ 1936 if (sc->sc_flags & SCF_TIMESTAMP) { 1937 sc->sc_ts = arc4random(); 1938 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1939 } 1940 1941 TCPSTAT_INC(tcps_sc_sendcookie); 1942 return (iss); 1943 } 1944 1945 static struct syncache * 1946 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1947 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1948 struct socket *lso) 1949 { 1950 uint32_t hash; 1951 uint8_t *secbits; 1952 tcp_seq ack, seq; 1953 int wnd, wscale = 0; 1954 union syncookie cookie; 1955 1956 SCH_LOCK_ASSERT(sch); 1957 1958 /* 1959 * Pull information out of SYN-ACK/ACK and revert sequence number 1960 * advances. 1961 */ 1962 ack = th->th_ack - 1; 1963 seq = th->th_seq - 1; 1964 1965 /* 1966 * Unpack the flags containing enough information to restore the 1967 * connection. 1968 */ 1969 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 1970 1971 /* Which of the two secrets to use. */ 1972 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 1973 1974 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 1975 1976 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 1977 if ((ack & ~0xff) != (hash & ~0xff)) 1978 return (NULL); 1979 1980 /* Fill in the syncache values. */ 1981 sc->sc_flags = 0; 1982 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1983 sc->sc_ipopts = NULL; 1984 1985 sc->sc_irs = seq; 1986 sc->sc_iss = ack; 1987 1988 switch (inc->inc_flags & INC_ISIPV6) { 1989 #ifdef INET 1990 case 0: 1991 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 1992 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 1993 break; 1994 #endif 1995 #ifdef INET6 1996 case INC_ISIPV6: 1997 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 1998 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 1999 break; 2000 #endif 2001 } 2002 2003 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2004 2005 /* We can simply recompute receive window scale we sent earlier. */ 2006 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2007 wscale++; 2008 2009 /* Only use wscale if it was enabled in the orignal SYN. */ 2010 if (cookie.flags.wscale_idx > 0) { 2011 sc->sc_requested_r_scale = wscale; 2012 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2013 sc->sc_flags |= SCF_WINSCALE; 2014 } 2015 2016 wnd = sbspace(&lso->so_rcv); 2017 wnd = imax(wnd, 0); 2018 wnd = imin(wnd, TCP_MAXWIN); 2019 sc->sc_wnd = wnd; 2020 2021 if (cookie.flags.sack_ok) 2022 sc->sc_flags |= SCF_SACK; 2023 2024 if (to->to_flags & TOF_TS) { 2025 sc->sc_flags |= SCF_TIMESTAMP; 2026 sc->sc_tsreflect = to->to_tsval; 2027 sc->sc_ts = to->to_tsecr; 2028 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 2029 } 2030 2031 if (to->to_flags & TOF_SIGNATURE) 2032 sc->sc_flags |= SCF_SIGNATURE; 2033 2034 sc->sc_rxmits = 0; 2035 2036 TCPSTAT_INC(tcps_sc_recvcookie); 2037 return (sc); 2038 } 2039 2040 #ifdef INVARIANTS 2041 static int 2042 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2043 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2044 struct socket *lso) 2045 { 2046 struct syncache scs, *scx; 2047 char *s; 2048 2049 bzero(&scs, sizeof(scs)); 2050 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2051 2052 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2053 return (0); 2054 2055 if (scx != NULL) { 2056 if (sc->sc_peer_mss != scx->sc_peer_mss) 2057 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2058 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2059 2060 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2061 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2062 s, __func__, sc->sc_requested_r_scale, 2063 scx->sc_requested_r_scale); 2064 2065 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2066 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2067 s, __func__, sc->sc_requested_s_scale, 2068 scx->sc_requested_s_scale); 2069 2070 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2071 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2072 } 2073 2074 if (s != NULL) 2075 free(s, M_TCPLOG); 2076 return (0); 2077 } 2078 #endif /* INVARIANTS */ 2079 2080 static void 2081 syncookie_reseed(void *arg) 2082 { 2083 struct tcp_syncache *sc = arg; 2084 uint8_t *secbits; 2085 int secbit; 2086 2087 /* 2088 * Reseeding the secret doesn't have to be protected by a lock. 2089 * It only must be ensured that the new random values are visible 2090 * to all CPUs in a SMP environment. The atomic with release 2091 * semantics ensures that. 2092 */ 2093 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2094 secbits = sc->secret.key[secbit]; 2095 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2096 atomic_add_rel_int(&sc->secret.oddeven, 1); 2097 2098 /* Reschedule ourself. */ 2099 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2100 } 2101 2102 /* 2103 * Exports the syncache entries to userland so that netstat can display 2104 * them alongside the other sockets. This function is intended to be 2105 * called only from tcp_pcblist. 2106 * 2107 * Due to concurrency on an active system, the number of pcbs exported 2108 * may have no relation to max_pcbs. max_pcbs merely indicates the 2109 * amount of space the caller allocated for this function to use. 2110 */ 2111 int 2112 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2113 { 2114 struct xtcpcb xt; 2115 struct syncache *sc; 2116 struct syncache_head *sch; 2117 int count, error, i; 2118 2119 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2120 sch = &V_tcp_syncache.hashbase[i]; 2121 SCH_LOCK(sch); 2122 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2123 if (count >= max_pcbs) { 2124 SCH_UNLOCK(sch); 2125 goto exit; 2126 } 2127 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2128 continue; 2129 bzero(&xt, sizeof(xt)); 2130 xt.xt_len = sizeof(xt); 2131 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2132 xt.xt_inp.inp_vflag = INP_IPV6; 2133 else 2134 xt.xt_inp.inp_vflag = INP_IPV4; 2135 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2136 xt.xt_tp.t_inpcb = &xt.xt_inp; 2137 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2138 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2139 xt.xt_socket.xso_len = sizeof (struct xsocket); 2140 xt.xt_socket.so_type = SOCK_STREAM; 2141 xt.xt_socket.so_state = SS_ISCONNECTING; 2142 error = SYSCTL_OUT(req, &xt, sizeof xt); 2143 if (error) { 2144 SCH_UNLOCK(sch); 2145 goto exit; 2146 } 2147 count++; 2148 } 2149 SCH_UNLOCK(sch); 2150 } 2151 exit: 2152 *pcbs_exported = count; 2153 return error; 2154 } 2155