1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2001 McAfee, Inc. 5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by Jonathan Lemon 9 * and McAfee Research, the Security Research Division of McAfee, Inc. under 10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. [2001 McAfee, Inc.] 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/hash.h> 43 #include <sys/refcount.h> 44 #include <sys/kernel.h> 45 #include <sys/sysctl.h> 46 #include <sys/limits.h> 47 #include <sys/lock.h> 48 #include <sys/mutex.h> 49 #include <sys/malloc.h> 50 #include <sys/mbuf.h> 51 #include <sys/proc.h> /* for proc0 declaration */ 52 #include <sys/random.h> 53 #include <sys/socket.h> 54 #include <sys/socketvar.h> 55 #include <sys/syslog.h> 56 #include <sys/ucred.h> 57 58 #include <sys/md5.h> 59 #include <crypto/siphash/siphash.h> 60 61 #include <vm/uma.h> 62 63 #include <net/if.h> 64 #include <net/if_var.h> 65 #include <net/route.h> 66 #include <net/vnet.h> 67 68 #include <netinet/in.h> 69 #include <netinet/in_kdtrace.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 #include <netinet/tcp_fastopen.h> 85 #include <netinet/tcp_fsm.h> 86 #include <netinet/tcp_seq.h> 87 #include <netinet/tcp_timer.h> 88 #include <netinet/tcp_var.h> 89 #include <netinet/tcp_syncache.h> 90 #include <netinet/tcp_ecn.h> 91 #ifdef TCP_BLACKBOX 92 #include <netinet/tcp_log_buf.h> 93 #endif 94 #ifdef TCP_OFFLOAD 95 #include <netinet/toecore.h> 96 #endif 97 #include <netinet/udp.h> 98 99 #include <netipsec/ipsec_support.h> 100 101 #include <machine/in_cksum.h> 102 103 #include <security/mac/mac_framework.h> 104 105 VNET_DEFINE_STATIC(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 VNET_DEFINE_STATIC(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 *, const struct mbuf *, int); 125 static struct socket *syncache_socket(struct syncache *, struct socket *, 126 struct mbuf *m); 127 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 128 int docallout); 129 static void syncache_timer(void *); 130 131 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 132 uint8_t *, uintptr_t); 133 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 134 static struct syncache 135 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 136 struct syncache *, struct tcphdr *, struct tcpopt *, 137 struct socket *, uint16_t); 138 static void syncache_pause(struct in_conninfo *); 139 static void syncache_unpause(void *); 140 static void syncookie_reseed(void *); 141 #ifdef INVARIANTS 142 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 143 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 144 struct socket *lso, uint16_t port); 145 #endif 146 147 /* 148 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 149 * 3 retransmits corresponds to a timeout with default values of 150 * tcp_rexmit_initial * ( 1 + 151 * tcp_backoff[1] + 152 * tcp_backoff[2] + 153 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 154 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 155 * the odds are that the user has given up attempting to connect by then. 156 */ 157 #define SYNCACHE_MAXREXMTS 3 158 159 /* Arbitrary values */ 160 #define TCP_SYNCACHE_HASHSIZE 512 161 #define TCP_SYNCACHE_BUCKETLIMIT 30 162 163 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 164 #define V_tcp_syncache VNET(tcp_syncache) 165 166 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 167 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 168 "TCP SYN cache"); 169 170 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 171 &VNET_NAME(tcp_syncache.bucket_limit), 0, 172 "Per-bucket hash limit for syncache"); 173 174 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 175 &VNET_NAME(tcp_syncache.cache_limit), 0, 176 "Overall entry limit for syncache"); 177 178 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 179 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 180 181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 182 &VNET_NAME(tcp_syncache.hashsize), 0, 183 "Size of TCP syncache hashtable"); 184 185 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 186 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 187 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 188 "and mac(4) checks"); 189 190 static int 191 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 192 { 193 int error; 194 u_int new; 195 196 new = V_tcp_syncache.rexmt_limit; 197 error = sysctl_handle_int(oidp, &new, 0, req); 198 if ((error == 0) && (req->newptr != NULL)) { 199 if (new > TCP_MAXRXTSHIFT) 200 error = EINVAL; 201 else 202 V_tcp_syncache.rexmt_limit = new; 203 } 204 return (error); 205 } 206 207 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 208 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 209 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 210 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU", 211 "Limit on SYN/ACK retransmissions"); 212 213 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 214 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 215 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 216 "Send reset on socket allocation failure"); 217 218 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 219 220 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 221 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 222 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 223 224 /* 225 * Requires the syncache entry to be already removed from the bucket list. 226 */ 227 static void 228 syncache_free(struct syncache *sc) 229 { 230 231 if (sc->sc_ipopts) 232 (void)m_free(sc->sc_ipopts); 233 if (sc->sc_cred) 234 crfree(sc->sc_cred); 235 #ifdef MAC 236 mac_syncache_destroy(&sc->sc_label); 237 #endif 238 239 uma_zfree(V_tcp_syncache.zone, sc); 240 } 241 242 void 243 syncache_init(void) 244 { 245 int i; 246 247 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 248 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 249 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 250 V_tcp_syncache.hash_secret = arc4random(); 251 252 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 253 &V_tcp_syncache.hashsize); 254 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 255 &V_tcp_syncache.bucket_limit); 256 if (!powerof2(V_tcp_syncache.hashsize) || 257 V_tcp_syncache.hashsize == 0) { 258 printf("WARNING: syncache hash size is not a power of 2.\n"); 259 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 260 } 261 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 262 263 /* Set limits. */ 264 V_tcp_syncache.cache_limit = 265 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 266 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 267 &V_tcp_syncache.cache_limit); 268 269 /* Allocate the hash table. */ 270 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 271 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 272 273 #ifdef VIMAGE 274 V_tcp_syncache.vnet = curvnet; 275 #endif 276 277 /* Initialize the hash buckets. */ 278 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 279 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 280 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 281 NULL, MTX_DEF); 282 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 283 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 284 V_tcp_syncache.hashbase[i].sch_length = 0; 285 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 286 V_tcp_syncache.hashbase[i].sch_last_overflow = 287 -(SYNCOOKIE_LIFETIME + 1); 288 } 289 290 /* Create the syncache entry zone. */ 291 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 292 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 293 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 294 V_tcp_syncache.cache_limit); 295 296 /* Start the SYN cookie reseeder callout. */ 297 callout_init(&V_tcp_syncache.secret.reseed, 1); 298 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 299 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 300 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 301 syncookie_reseed, &V_tcp_syncache); 302 303 /* Initialize the pause machinery. */ 304 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 305 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 306 0); 307 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 308 V_tcp_syncache.pause_backoff = 0; 309 V_tcp_syncache.paused = false; 310 } 311 312 #ifdef VIMAGE 313 void 314 syncache_destroy(void) 315 { 316 struct syncache_head *sch; 317 struct syncache *sc, *nsc; 318 int i; 319 320 /* 321 * Stop the re-seed timer before freeing resources. No need to 322 * possibly schedule it another time. 323 */ 324 callout_drain(&V_tcp_syncache.secret.reseed); 325 326 /* Stop the SYN cache pause callout. */ 327 mtx_lock(&V_tcp_syncache.pause_mtx); 328 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 329 mtx_unlock(&V_tcp_syncache.pause_mtx); 330 callout_drain(&V_tcp_syncache.pause_co); 331 } else 332 mtx_unlock(&V_tcp_syncache.pause_mtx); 333 334 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 335 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 336 sch = &V_tcp_syncache.hashbase[i]; 337 callout_drain(&sch->sch_timer); 338 339 SCH_LOCK(sch); 340 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 341 syncache_drop(sc, sch); 342 SCH_UNLOCK(sch); 343 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 344 ("%s: sch->sch_bucket not empty", __func__)); 345 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 346 __func__, sch->sch_length)); 347 mtx_destroy(&sch->sch_mtx); 348 } 349 350 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 351 ("%s: cache_count not 0", __func__)); 352 353 /* Free the allocated global resources. */ 354 uma_zdestroy(V_tcp_syncache.zone); 355 free(V_tcp_syncache.hashbase, M_SYNCACHE); 356 mtx_destroy(&V_tcp_syncache.pause_mtx); 357 } 358 #endif 359 360 /* 361 * Inserts a syncache entry into the specified bucket row. 362 * Locks and unlocks the syncache_head autonomously. 363 */ 364 static void 365 syncache_insert(struct syncache *sc, struct syncache_head *sch) 366 { 367 struct syncache *sc2; 368 369 SCH_LOCK(sch); 370 371 /* 372 * Make sure that we don't overflow the per-bucket limit. 373 * If the bucket is full, toss the oldest element. 374 */ 375 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 376 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 377 ("sch->sch_length incorrect")); 378 syncache_pause(&sc->sc_inc); 379 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 380 sch->sch_last_overflow = time_uptime; 381 syncache_drop(sc2, sch); 382 } 383 384 /* Put it into the bucket. */ 385 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 386 sch->sch_length++; 387 388 #ifdef TCP_OFFLOAD 389 if (ADDED_BY_TOE(sc)) { 390 struct toedev *tod = sc->sc_tod; 391 392 tod->tod_syncache_added(tod, sc->sc_todctx); 393 } 394 #endif 395 396 /* Reinitialize the bucket row's timer. */ 397 if (sch->sch_length == 1) 398 sch->sch_nextc = ticks + INT_MAX; 399 syncache_timeout(sc, sch, 1); 400 401 SCH_UNLOCK(sch); 402 403 TCPSTATES_INC(TCPS_SYN_RECEIVED); 404 TCPSTAT_INC(tcps_sc_added); 405 } 406 407 /* 408 * Remove and free entry from syncache bucket row. 409 * Expects locked syncache head. 410 */ 411 static void 412 syncache_drop(struct syncache *sc, struct syncache_head *sch) 413 { 414 415 SCH_LOCK_ASSERT(sch); 416 417 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 418 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 419 sch->sch_length--; 420 421 #ifdef TCP_OFFLOAD 422 if (ADDED_BY_TOE(sc)) { 423 struct toedev *tod = sc->sc_tod; 424 425 tod->tod_syncache_removed(tod, sc->sc_todctx); 426 } 427 #endif 428 429 syncache_free(sc); 430 } 431 432 /* 433 * Engage/reengage time on bucket row. 434 */ 435 static void 436 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 437 { 438 int rexmt; 439 440 if (sc->sc_rxmits == 0) 441 rexmt = tcp_rexmit_initial; 442 else 443 TCPT_RANGESET(rexmt, 444 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 445 tcp_rexmit_min, TCPTV_REXMTMAX); 446 sc->sc_rxttime = ticks + rexmt; 447 sc->sc_rxmits++; 448 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 449 sch->sch_nextc = sc->sc_rxttime; 450 if (docallout) 451 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 452 syncache_timer, (void *)sch); 453 } 454 } 455 456 /* 457 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 458 * If we have retransmitted an entry the maximum number of times, expire it. 459 * One separate timer for each bucket row. 460 */ 461 static void 462 syncache_timer(void *xsch) 463 { 464 struct syncache_head *sch = (struct syncache_head *)xsch; 465 struct syncache *sc, *nsc; 466 struct epoch_tracker et; 467 int tick = ticks; 468 char *s; 469 bool paused; 470 471 CURVNET_SET(sch->sch_sc->vnet); 472 473 /* NB: syncache_head has already been locked by the callout. */ 474 SCH_LOCK_ASSERT(sch); 475 476 /* 477 * In the following cycle we may remove some entries and/or 478 * advance some timeouts, so re-initialize the bucket timer. 479 */ 480 sch->sch_nextc = tick + INT_MAX; 481 482 /* 483 * If we have paused processing, unconditionally remove 484 * all syncache entries. 485 */ 486 mtx_lock(&V_tcp_syncache.pause_mtx); 487 paused = V_tcp_syncache.paused; 488 mtx_unlock(&V_tcp_syncache.pause_mtx); 489 490 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 491 if (paused) { 492 syncache_drop(sc, sch); 493 continue; 494 } 495 /* 496 * We do not check if the listen socket still exists 497 * and accept the case where the listen socket may be 498 * gone by the time we resend the SYN/ACK. We do 499 * not expect this to happens often. If it does, 500 * then the RST will be sent by the time the remote 501 * host does the SYN/ACK->ACK. 502 */ 503 if (TSTMP_GT(sc->sc_rxttime, tick)) { 504 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 505 sch->sch_nextc = sc->sc_rxttime; 506 continue; 507 } 508 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 509 sc->sc_flags &= ~SCF_ECN_MASK; 510 } 511 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 512 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 513 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 514 "giving up and removing syncache entry\n", 515 s, __func__); 516 free(s, M_TCPLOG); 517 } 518 syncache_drop(sc, sch); 519 TCPSTAT_INC(tcps_sc_stale); 520 continue; 521 } 522 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 523 log(LOG_DEBUG, "%s; %s: Response timeout, " 524 "retransmitting (%u) SYN|ACK\n", 525 s, __func__, sc->sc_rxmits); 526 free(s, M_TCPLOG); 527 } 528 529 NET_EPOCH_ENTER(et); 530 if (syncache_respond(sc, NULL, TH_SYN|TH_ACK) == 0) { 531 syncache_timeout(sc, sch, 0); 532 TCPSTAT_INC(tcps_sndacks); 533 TCPSTAT_INC(tcps_sndtotal); 534 TCPSTAT_INC(tcps_sc_retransmitted); 535 } else { 536 syncache_drop(sc, sch); 537 TCPSTAT_INC(tcps_sc_dropped); 538 } 539 NET_EPOCH_EXIT(et); 540 } 541 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 542 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 543 syncache_timer, (void *)(sch)); 544 CURVNET_RESTORE(); 545 } 546 547 /* 548 * Returns true if the system is only using cookies at the moment. 549 * This could be due to a sysadmin decision to only use cookies, or it 550 * could be due to the system detecting an attack. 551 */ 552 static inline bool 553 syncache_cookiesonly(void) 554 { 555 556 return (V_tcp_syncookies && (V_tcp_syncache.paused || 557 V_tcp_syncookiesonly)); 558 } 559 560 /* 561 * Find the hash bucket for the given connection. 562 */ 563 static struct syncache_head * 564 syncache_hashbucket(struct in_conninfo *inc) 565 { 566 uint32_t hash; 567 568 /* 569 * The hash is built on foreign port + local port + foreign address. 570 * We rely on the fact that struct in_conninfo starts with 16 bits 571 * of foreign port, then 16 bits of local port then followed by 128 572 * bits of foreign address. In case of IPv4 address, the first 3 573 * 32-bit words of the address always are zeroes. 574 */ 575 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 576 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 577 578 return (&V_tcp_syncache.hashbase[hash]); 579 } 580 581 /* 582 * Find an entry in the syncache. 583 * Returns always with locked syncache_head plus a matching entry or NULL. 584 */ 585 static struct syncache * 586 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 587 { 588 struct syncache *sc; 589 struct syncache_head *sch; 590 591 *schp = sch = syncache_hashbucket(inc); 592 SCH_LOCK(sch); 593 594 /* Circle through bucket row to find matching entry. */ 595 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 596 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 597 sizeof(struct in_endpoints)) == 0) 598 break; 599 600 return (sc); /* Always returns with locked sch. */ 601 } 602 603 /* 604 * This function is called when we get a RST for a 605 * non-existent connection, so that we can see if the 606 * connection is in the syn cache. If it is, zap it. 607 * If required send a challenge ACK. 608 */ 609 void 610 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 611 uint16_t port) 612 { 613 struct syncache *sc; 614 struct syncache_head *sch; 615 char *s = NULL; 616 617 if (syncache_cookiesonly()) 618 return; 619 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 620 SCH_LOCK_ASSERT(sch); 621 622 /* 623 * No corresponding connection was found in syncache. 624 * If syncookies are enabled and possibly exclusively 625 * used, or we are under memory pressure, a valid RST 626 * may not find a syncache entry. In that case we're 627 * done and no SYN|ACK retransmissions will happen. 628 * Otherwise the RST was misdirected or spoofed. 629 */ 630 if (sc == NULL) { 631 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 632 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 633 "syncache entry (possibly syncookie only), " 634 "segment ignored\n", s, __func__); 635 TCPSTAT_INC(tcps_badrst); 636 goto done; 637 } 638 639 /* The remote UDP encaps port does not match. */ 640 if (sc->sc_port != port) { 641 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 642 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 643 "syncache entry but non-matching UDP encaps port, " 644 "segment ignored\n", s, __func__); 645 TCPSTAT_INC(tcps_badrst); 646 goto done; 647 } 648 649 /* 650 * If the RST bit is set, check the sequence number to see 651 * if this is a valid reset segment. 652 * 653 * RFC 793 page 37: 654 * In all states except SYN-SENT, all reset (RST) segments 655 * are validated by checking their SEQ-fields. A reset is 656 * valid if its sequence number is in the window. 657 * 658 * RFC 793 page 69: 659 * There are four cases for the acceptability test for an incoming 660 * segment: 661 * 662 * Segment Receive Test 663 * Length Window 664 * ------- ------- ------------------------------------------- 665 * 0 0 SEG.SEQ = RCV.NXT 666 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 667 * >0 0 not acceptable 668 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 669 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 670 * 671 * Note that when receiving a SYN segment in the LISTEN state, 672 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 673 * described in RFC 793, page 66. 674 */ 675 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 676 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 677 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 678 if (V_tcp_insecure_rst || 679 th->th_seq == sc->sc_irs + 1) { 680 syncache_drop(sc, sch); 681 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 682 log(LOG_DEBUG, 683 "%s; %s: Our SYN|ACK was rejected, " 684 "connection attempt aborted by remote " 685 "endpoint\n", 686 s, __func__); 687 TCPSTAT_INC(tcps_sc_reset); 688 } else { 689 TCPSTAT_INC(tcps_badrst); 690 /* Send challenge ACK. */ 691 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 692 log(LOG_DEBUG, "%s; %s: RST with invalid " 693 " SEQ %u != NXT %u (+WND %u), " 694 "sending challenge ACK\n", 695 s, __func__, 696 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 697 if (syncache_respond(sc, m, TH_ACK) == 0) { 698 TCPSTAT_INC(tcps_sndacks); 699 TCPSTAT_INC(tcps_sndtotal); 700 } else { 701 syncache_drop(sc, sch); 702 TCPSTAT_INC(tcps_sc_dropped); 703 } 704 } 705 } else { 706 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 707 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 708 "NXT %u (+WND %u), segment ignored\n", 709 s, __func__, 710 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 711 TCPSTAT_INC(tcps_badrst); 712 } 713 714 done: 715 if (s != NULL) 716 free(s, M_TCPLOG); 717 SCH_UNLOCK(sch); 718 } 719 720 void 721 syncache_badack(struct in_conninfo *inc, uint16_t port) 722 { 723 struct syncache *sc; 724 struct syncache_head *sch; 725 726 if (syncache_cookiesonly()) 727 return; 728 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 729 SCH_LOCK_ASSERT(sch); 730 if ((sc != NULL) && (sc->sc_port == port)) { 731 syncache_drop(sc, sch); 732 TCPSTAT_INC(tcps_sc_badack); 733 } 734 SCH_UNLOCK(sch); 735 } 736 737 void 738 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 739 { 740 struct syncache *sc; 741 struct syncache_head *sch; 742 743 if (syncache_cookiesonly()) 744 return; 745 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 746 SCH_LOCK_ASSERT(sch); 747 if (sc == NULL) 748 goto done; 749 750 /* If the port != sc_port, then it's a bogus ICMP msg */ 751 if (port != sc->sc_port) 752 goto done; 753 754 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 755 if (ntohl(th_seq) != sc->sc_iss) 756 goto done; 757 758 /* 759 * If we've rertransmitted 3 times and this is our second error, 760 * we remove the entry. Otherwise, we allow it to continue on. 761 * This prevents us from incorrectly nuking an entry during a 762 * spurious network outage. 763 * 764 * See tcp_notify(). 765 */ 766 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 767 sc->sc_flags |= SCF_UNREACH; 768 goto done; 769 } 770 syncache_drop(sc, sch); 771 TCPSTAT_INC(tcps_sc_unreach); 772 done: 773 SCH_UNLOCK(sch); 774 } 775 776 /* 777 * Build a new TCP socket structure from a syncache entry. 778 * 779 * On success return the newly created socket with its underlying inp locked. 780 */ 781 static struct socket * 782 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 783 { 784 struct inpcb *inp = NULL; 785 struct socket *so; 786 struct tcpcb *tp; 787 int error; 788 char *s; 789 790 NET_EPOCH_ASSERT(); 791 792 /* 793 * Ok, create the full blown connection, and set things up 794 * as they would have been set up if we had created the 795 * connection when the SYN arrived. 796 */ 797 if ((so = solisten_clone(lso)) == NULL) 798 goto allocfail; 799 #ifdef MAC 800 mac_socketpeer_set_from_mbuf(m, so); 801 #endif 802 error = in_pcballoc(so, &V_tcbinfo); 803 if (error) { 804 sodealloc(so); 805 goto allocfail; 806 } 807 inp = sotoinpcb(so); 808 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) { 809 in_pcbfree(inp); 810 sodealloc(so); 811 goto allocfail; 812 } 813 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 814 #ifdef INET6 815 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 816 inp->inp_vflag &= ~INP_IPV4; 817 inp->inp_vflag |= INP_IPV6; 818 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 819 } else { 820 inp->inp_vflag &= ~INP_IPV6; 821 inp->inp_vflag |= INP_IPV4; 822 #endif 823 inp->inp_ip_ttl = sc->sc_ip_ttl; 824 inp->inp_ip_tos = sc->sc_ip_tos; 825 inp->inp_laddr = sc->sc_inc.inc_laddr; 826 #ifdef INET6 827 } 828 #endif 829 830 /* 831 * If there's an mbuf and it has a flowid, then let's initialise the 832 * inp with that particular flowid. 833 */ 834 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 835 inp->inp_flowid = m->m_pkthdr.flowid; 836 inp->inp_flowtype = M_HASHTYPE_GET(m); 837 #ifdef NUMA 838 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 839 #endif 840 } 841 842 inp->inp_lport = sc->sc_inc.inc_lport; 843 #ifdef INET6 844 if (inp->inp_vflag & INP_IPV6PROTO) { 845 struct inpcb *oinp = sotoinpcb(lso); 846 847 /* 848 * Inherit socket options from the listening socket. 849 * Note that in6p_inputopts are not (and should not be) 850 * copied, since it stores previously received options and is 851 * used to detect if each new option is different than the 852 * previous one and hence should be passed to a user. 853 * If we copied in6p_inputopts, a user would not be able to 854 * receive options just after calling the accept system call. 855 */ 856 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 857 if (oinp->in6p_outputopts) 858 inp->in6p_outputopts = 859 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 860 inp->in6p_hops = oinp->in6p_hops; 861 } 862 863 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 864 struct sockaddr_in6 sin6; 865 866 sin6.sin6_family = AF_INET6; 867 sin6.sin6_len = sizeof(sin6); 868 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 869 sin6.sin6_port = sc->sc_inc.inc_fport; 870 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 871 INP_HASH_WLOCK(&V_tcbinfo); 872 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 873 INP_HASH_WUNLOCK(&V_tcbinfo); 874 if (error != 0) 875 goto abort; 876 /* Override flowlabel from in6_pcbconnect. */ 877 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 878 inp->inp_flow |= sc->sc_flowlabel; 879 } 880 #endif /* INET6 */ 881 #if defined(INET) && defined(INET6) 882 else 883 #endif 884 #ifdef INET 885 { 886 struct sockaddr_in sin; 887 888 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 889 890 if (inp->inp_options == NULL) { 891 inp->inp_options = sc->sc_ipopts; 892 sc->sc_ipopts = NULL; 893 } 894 895 sin.sin_family = AF_INET; 896 sin.sin_len = sizeof(sin); 897 sin.sin_addr = sc->sc_inc.inc_faddr; 898 sin.sin_port = sc->sc_inc.inc_fport; 899 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 900 INP_HASH_WLOCK(&V_tcbinfo); 901 error = in_pcbconnect(inp, &sin, thread0.td_ucred); 902 INP_HASH_WUNLOCK(&V_tcbinfo); 903 if (error != 0) 904 goto abort; 905 } 906 #endif /* INET */ 907 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 908 /* Copy old policy into new socket's. */ 909 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 910 printf("syncache_socket: could not copy policy\n"); 911 #endif 912 tp->t_state = TCPS_SYN_RECEIVED; 913 tp->iss = sc->sc_iss; 914 tp->irs = sc->sc_irs; 915 tp->t_port = sc->sc_port; 916 tcp_rcvseqinit(tp); 917 tcp_sendseqinit(tp); 918 tp->snd_wl1 = sc->sc_irs; 919 tp->snd_max = tp->iss + 1; 920 tp->snd_nxt = tp->iss + 1; 921 tp->rcv_up = sc->sc_irs + 1; 922 tp->rcv_wnd = sc->sc_wnd; 923 tp->rcv_adv += tp->rcv_wnd; 924 tp->last_ack_sent = tp->rcv_nxt; 925 926 tp->t_flags = sototcpcb(lso)->t_flags & 927 (TF_LRD|TF_NOPUSH|TF_NODELAY); 928 if (sc->sc_flags & SCF_NOOPT) 929 tp->t_flags |= TF_NOOPT; 930 else { 931 if (sc->sc_flags & SCF_WINSCALE) { 932 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 933 tp->snd_scale = sc->sc_requested_s_scale; 934 tp->request_r_scale = sc->sc_requested_r_scale; 935 } 936 if (sc->sc_flags & SCF_TIMESTAMP) { 937 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 938 tp->ts_recent = sc->sc_tsreflect; 939 tp->ts_recent_age = tcp_ts_getticks(); 940 tp->ts_offset = sc->sc_tsoff; 941 } 942 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 943 if (sc->sc_flags & SCF_SIGNATURE) 944 tp->t_flags |= TF_SIGNATURE; 945 #endif 946 if (sc->sc_flags & SCF_SACK) 947 tp->t_flags |= TF_SACK_PERMIT; 948 } 949 950 tcp_ecn_syncache_socket(tp, sc); 951 952 /* 953 * Set up MSS and get cached values from tcp_hostcache. 954 * This might overwrite some of the defaults we just set. 955 */ 956 tcp_mss(tp, sc->sc_peer_mss); 957 958 /* 959 * If the SYN,ACK was retransmitted, indicate that CWND to be 960 * limited to one segment in cc_conn_init(). 961 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 962 */ 963 if (sc->sc_rxmits > 1) 964 tp->snd_cwnd = 1; 965 966 #ifdef TCP_OFFLOAD 967 /* 968 * Allow a TOE driver to install its hooks. Note that we hold the 969 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 970 * new connection before the TOE driver has done its thing. 971 */ 972 if (ADDED_BY_TOE(sc)) { 973 struct toedev *tod = sc->sc_tod; 974 975 tod->tod_offload_socket(tod, sc->sc_todctx, so); 976 } 977 #endif 978 #ifdef TCP_BLACKBOX 979 /* 980 * Inherit the log state from the listening socket, if 981 * - the log state of the listening socket is not off and 982 * - the listening socket was not auto selected from all sessions and 983 * - a log id is not set on the listening socket. 984 * This avoids inheriting a log state which was automatically set. 985 */ 986 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 987 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 988 (sototcpcb(lso)->t_lib == NULL)) { 989 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 990 } 991 #endif 992 /* 993 * Copy and activate timers. 994 */ 995 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 996 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 997 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 998 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 999 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1000 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1001 1002 TCPSTAT_INC(tcps_accepts); 1003 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1004 1005 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1006 tp->t_flags |= TF_SONOTCONN; 1007 /* Can we inherit anything from the listener? */ 1008 if (tp->t_fb->tfb_inherit != NULL) { 1009 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 1010 } 1011 return (so); 1012 1013 allocfail: 1014 /* 1015 * Drop the connection; we will either send a RST or have the peer 1016 * retransmit its SYN again after its RTO and try again. 1017 */ 1018 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1019 log(LOG_DEBUG, "%s; %s: Socket create failed " 1020 "due to limits or memory shortage\n", 1021 s, __func__); 1022 free(s, M_TCPLOG); 1023 } 1024 TCPSTAT_INC(tcps_listendrop); 1025 return (NULL); 1026 1027 abort: 1028 tcp_discardcb(tp); 1029 in_pcbfree(inp); 1030 sodealloc(so); 1031 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1032 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1033 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1034 error); 1035 free(s, M_TCPLOG); 1036 } 1037 TCPSTAT_INC(tcps_listendrop); 1038 return (NULL); 1039 } 1040 1041 /* 1042 * This function gets called when we receive an ACK for a 1043 * socket in the LISTEN state. We look up the connection 1044 * in the syncache, and if its there, we pull it out of 1045 * the cache and turn it into a full-blown connection in 1046 * the SYN-RECEIVED state. 1047 * 1048 * On syncache_socket() success the newly created socket 1049 * has its underlying inp locked. 1050 */ 1051 int 1052 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1053 struct socket **lsop, struct mbuf *m, uint16_t port) 1054 { 1055 struct syncache *sc; 1056 struct syncache_head *sch; 1057 struct syncache scs; 1058 char *s; 1059 bool locked; 1060 1061 NET_EPOCH_ASSERT(); 1062 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1063 ("%s: can handle only ACK", __func__)); 1064 1065 if (syncache_cookiesonly()) { 1066 sc = NULL; 1067 sch = syncache_hashbucket(inc); 1068 locked = false; 1069 } else { 1070 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1071 locked = true; 1072 SCH_LOCK_ASSERT(sch); 1073 } 1074 1075 #ifdef INVARIANTS 1076 /* 1077 * Test code for syncookies comparing the syncache stored 1078 * values with the reconstructed values from the cookie. 1079 */ 1080 if (sc != NULL) 1081 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1082 #endif 1083 1084 if (sc == NULL) { 1085 /* 1086 * There is no syncache entry, so see if this ACK is 1087 * a returning syncookie. To do this, first: 1088 * A. Check if syncookies are used in case of syncache 1089 * overflows 1090 * B. See if this socket has had a syncache entry dropped in 1091 * the recent past. We don't want to accept a bogus 1092 * syncookie if we've never received a SYN or accept it 1093 * twice. 1094 * C. check that the syncookie is valid. If it is, then 1095 * cobble up a fake syncache entry, and return. 1096 */ 1097 if (locked && !V_tcp_syncookies) { 1098 SCH_UNLOCK(sch); 1099 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1100 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1101 "segment rejected (syncookies disabled)\n", 1102 s, __func__); 1103 goto failed; 1104 } 1105 if (locked && !V_tcp_syncookiesonly && 1106 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1107 SCH_UNLOCK(sch); 1108 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1109 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1110 "segment rejected (no syncache entry)\n", 1111 s, __func__); 1112 goto failed; 1113 } 1114 bzero(&scs, sizeof(scs)); 1115 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1116 if (locked) 1117 SCH_UNLOCK(sch); 1118 if (sc == NULL) { 1119 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1120 log(LOG_DEBUG, "%s; %s: Segment failed " 1121 "SYNCOOKIE authentication, segment rejected " 1122 "(probably spoofed)\n", s, __func__); 1123 goto failed; 1124 } 1125 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1126 /* If received ACK has MD5 signature, check it. */ 1127 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1128 (!TCPMD5_ENABLED() || 1129 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1130 /* Drop the ACK. */ 1131 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1132 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1133 "MD5 signature doesn't match.\n", 1134 s, __func__); 1135 free(s, M_TCPLOG); 1136 } 1137 TCPSTAT_INC(tcps_sig_err_sigopt); 1138 return (-1); /* Do not send RST */ 1139 } 1140 #endif /* TCP_SIGNATURE */ 1141 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1142 } else { 1143 if (sc->sc_port != port) { 1144 SCH_UNLOCK(sch); 1145 return (0); 1146 } 1147 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1148 /* 1149 * If listening socket requested TCP digests, check that 1150 * received ACK has signature and it is correct. 1151 * If not, drop the ACK and leave sc entry in th cache, 1152 * because SYN was received with correct signature. 1153 */ 1154 if (sc->sc_flags & SCF_SIGNATURE) { 1155 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1156 /* No signature */ 1157 TCPSTAT_INC(tcps_sig_err_nosigopt); 1158 SCH_UNLOCK(sch); 1159 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1160 log(LOG_DEBUG, "%s; %s: Segment " 1161 "rejected, MD5 signature wasn't " 1162 "provided.\n", s, __func__); 1163 free(s, M_TCPLOG); 1164 } 1165 return (-1); /* Do not send RST */ 1166 } 1167 if (!TCPMD5_ENABLED() || 1168 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1169 /* Doesn't match or no SA */ 1170 SCH_UNLOCK(sch); 1171 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1172 log(LOG_DEBUG, "%s; %s: Segment " 1173 "rejected, MD5 signature doesn't " 1174 "match.\n", s, __func__); 1175 free(s, M_TCPLOG); 1176 } 1177 return (-1); /* Do not send RST */ 1178 } 1179 } 1180 #endif /* TCP_SIGNATURE */ 1181 1182 /* 1183 * RFC 7323 PAWS: If we have a timestamp on this segment and 1184 * it's less than ts_recent, drop it. 1185 * XXXMT: RFC 7323 also requires to send an ACK. 1186 * In tcp_input.c this is only done for TCP segments 1187 * with user data, so be consistent here and just drop 1188 * the segment. 1189 */ 1190 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1191 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1192 SCH_UNLOCK(sch); 1193 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1194 log(LOG_DEBUG, 1195 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1196 "segment dropped\n", s, __func__, 1197 to->to_tsval, sc->sc_tsreflect); 1198 free(s, M_TCPLOG); 1199 } 1200 return (-1); /* Do not send RST */ 1201 } 1202 1203 /* 1204 * If timestamps were not negotiated during SYN/ACK and a 1205 * segment with a timestamp is received, ignore the 1206 * timestamp and process the packet normally. 1207 * See section 3.2 of RFC 7323. 1208 */ 1209 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1210 (to->to_flags & TOF_TS)) { 1211 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1212 log(LOG_DEBUG, "%s; %s: Timestamp not " 1213 "expected, segment processed normally\n", 1214 s, __func__); 1215 free(s, M_TCPLOG); 1216 s = NULL; 1217 } 1218 } 1219 1220 /* 1221 * If timestamps were negotiated during SYN/ACK and a 1222 * segment without a timestamp is received, silently drop 1223 * the segment, unless the missing timestamps are tolerated. 1224 * See section 3.2 of RFC 7323. 1225 */ 1226 if ((sc->sc_flags & SCF_TIMESTAMP) && 1227 !(to->to_flags & TOF_TS)) { 1228 if (V_tcp_tolerate_missing_ts) { 1229 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1230 log(LOG_DEBUG, 1231 "%s; %s: Timestamp missing, " 1232 "segment processed normally\n", 1233 s, __func__); 1234 free(s, M_TCPLOG); 1235 } 1236 } else { 1237 SCH_UNLOCK(sch); 1238 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1239 log(LOG_DEBUG, 1240 "%s; %s: Timestamp missing, " 1241 "segment silently dropped\n", 1242 s, __func__); 1243 free(s, M_TCPLOG); 1244 } 1245 return (-1); /* Do not send RST */ 1246 } 1247 } 1248 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1249 sch->sch_length--; 1250 #ifdef TCP_OFFLOAD 1251 if (ADDED_BY_TOE(sc)) { 1252 struct toedev *tod = sc->sc_tod; 1253 1254 tod->tod_syncache_removed(tod, sc->sc_todctx); 1255 } 1256 #endif 1257 SCH_UNLOCK(sch); 1258 } 1259 1260 /* 1261 * Segment validation: 1262 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1263 */ 1264 if (th->th_ack != sc->sc_iss + 1) { 1265 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1266 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1267 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1268 goto failed; 1269 } 1270 1271 /* 1272 * The SEQ must fall in the window starting at the received 1273 * initial receive sequence number + 1 (the SYN). 1274 */ 1275 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1276 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1277 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1278 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1279 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1280 goto failed; 1281 } 1282 1283 *lsop = syncache_socket(sc, *lsop, m); 1284 1285 if (__predict_false(*lsop == NULL)) { 1286 TCPSTAT_INC(tcps_sc_aborted); 1287 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1288 } else 1289 TCPSTAT_INC(tcps_sc_completed); 1290 1291 /* how do we find the inp for the new socket? */ 1292 if (sc != &scs) 1293 syncache_free(sc); 1294 return (1); 1295 failed: 1296 if (sc != NULL) { 1297 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1298 if (sc != &scs) 1299 syncache_free(sc); 1300 } 1301 if (s != NULL) 1302 free(s, M_TCPLOG); 1303 *lsop = NULL; 1304 return (0); 1305 } 1306 1307 static struct socket * 1308 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1309 uint64_t response_cookie) 1310 { 1311 struct inpcb *inp; 1312 struct tcpcb *tp; 1313 unsigned int *pending_counter; 1314 struct socket *so; 1315 1316 NET_EPOCH_ASSERT(); 1317 1318 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1319 so = syncache_socket(sc, lso, m); 1320 if (so == NULL) { 1321 TCPSTAT_INC(tcps_sc_aborted); 1322 atomic_subtract_int(pending_counter, 1); 1323 } else { 1324 soisconnected(so); 1325 inp = sotoinpcb(so); 1326 tp = intotcpcb(inp); 1327 tp->t_flags |= TF_FASTOPEN; 1328 tp->t_tfo_cookie.server = response_cookie; 1329 tp->snd_max = tp->iss; 1330 tp->snd_nxt = tp->iss; 1331 tp->t_tfo_pending = pending_counter; 1332 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1333 TCPSTAT_INC(tcps_sc_completed); 1334 } 1335 1336 return (so); 1337 } 1338 1339 /* 1340 * Given a LISTEN socket and an inbound SYN request, add 1341 * this to the syn cache, and send back a segment: 1342 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1343 * to the source. 1344 * 1345 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1346 * Doing so would require that we hold onto the data and deliver it 1347 * to the application. However, if we are the target of a SYN-flood 1348 * DoS attack, an attacker could send data which would eventually 1349 * consume all available buffer space if it were ACKed. By not ACKing 1350 * the data, we avoid this DoS scenario. 1351 * 1352 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1353 * cookie is processed and a new socket is created. In this case, any data 1354 * accompanying the SYN will be queued to the socket by tcp_input() and will 1355 * be ACKed either when the application sends response data or the delayed 1356 * ACK timer expires, whichever comes first. 1357 */ 1358 struct socket * 1359 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1360 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1361 void *todctx, uint8_t iptos, uint16_t port) 1362 { 1363 struct tcpcb *tp; 1364 struct socket *rv = NULL; 1365 struct syncache *sc = NULL; 1366 struct syncache_head *sch; 1367 struct mbuf *ipopts = NULL; 1368 u_int ltflags; 1369 int win, ip_ttl, ip_tos; 1370 char *s; 1371 #ifdef INET6 1372 int autoflowlabel = 0; 1373 #endif 1374 #ifdef MAC 1375 struct label *maclabel = NULL; 1376 #endif 1377 struct syncache scs; 1378 uint64_t tfo_response_cookie; 1379 unsigned int *tfo_pending = NULL; 1380 int tfo_cookie_valid = 0; 1381 int tfo_response_cookie_valid = 0; 1382 bool locked; 1383 1384 INP_RLOCK_ASSERT(inp); /* listen socket */ 1385 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1386 ("%s: unexpected tcp flags", __func__)); 1387 1388 /* 1389 * Combine all so/tp operations very early to drop the INP lock as 1390 * soon as possible. 1391 */ 1392 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1393 tp = sototcpcb(so); 1394 1395 #ifdef INET6 1396 if (inc->inc_flags & INC_ISIPV6) { 1397 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1398 autoflowlabel = 1; 1399 } 1400 ip_ttl = in6_selecthlim(inp, NULL); 1401 if ((inp->in6p_outputopts == NULL) || 1402 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1403 ip_tos = 0; 1404 } else { 1405 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1406 } 1407 } 1408 #endif 1409 #if defined(INET6) && defined(INET) 1410 else 1411 #endif 1412 #ifdef INET 1413 { 1414 ip_ttl = inp->inp_ip_ttl; 1415 ip_tos = inp->inp_ip_tos; 1416 } 1417 #endif 1418 win = so->sol_sbrcv_hiwat; 1419 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1420 1421 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1422 (tp->t_tfo_pending != NULL) && 1423 (to->to_flags & TOF_FASTOPEN)) { 1424 /* 1425 * Limit the number of pending TFO connections to 1426 * approximately half of the queue limit. This prevents TFO 1427 * SYN floods from starving the service by filling the 1428 * listen queue with bogus TFO connections. 1429 */ 1430 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1431 (so->sol_qlimit / 2)) { 1432 int result; 1433 1434 result = tcp_fastopen_check_cookie(inc, 1435 to->to_tfo_cookie, to->to_tfo_len, 1436 &tfo_response_cookie); 1437 tfo_cookie_valid = (result > 0); 1438 tfo_response_cookie_valid = (result >= 0); 1439 } 1440 1441 /* 1442 * Remember the TFO pending counter as it will have to be 1443 * decremented below if we don't make it to syncache_tfo_expand(). 1444 */ 1445 tfo_pending = tp->t_tfo_pending; 1446 } 1447 1448 #ifdef MAC 1449 if (mac_syncache_init(&maclabel) != 0) { 1450 INP_RUNLOCK(inp); 1451 goto done; 1452 } else 1453 mac_syncache_create(maclabel, inp); 1454 #endif 1455 if (!tfo_cookie_valid) 1456 INP_RUNLOCK(inp); 1457 1458 /* 1459 * Remember the IP options, if any. 1460 */ 1461 #ifdef INET6 1462 if (!(inc->inc_flags & INC_ISIPV6)) 1463 #endif 1464 #ifdef INET 1465 ipopts = (m) ? ip_srcroute(m) : NULL; 1466 #else 1467 ipopts = NULL; 1468 #endif 1469 1470 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1471 /* 1472 * When the socket is TCP-MD5 enabled check that, 1473 * - a signed packet is valid 1474 * - a non-signed packet does not have a security association 1475 * 1476 * If a signed packet fails validation or a non-signed packet has a 1477 * security association, the packet will be dropped. 1478 */ 1479 if (ltflags & TF_SIGNATURE) { 1480 if (to->to_flags & TOF_SIGNATURE) { 1481 if (!TCPMD5_ENABLED() || 1482 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1483 goto done; 1484 } else { 1485 if (TCPMD5_ENABLED() && 1486 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1487 goto done; 1488 } 1489 } else if (to->to_flags & TOF_SIGNATURE) 1490 goto done; 1491 #endif /* TCP_SIGNATURE */ 1492 /* 1493 * See if we already have an entry for this connection. 1494 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1495 * 1496 * XXX: should the syncache be re-initialized with the contents 1497 * of the new SYN here (which may have different options?) 1498 * 1499 * XXX: We do not check the sequence number to see if this is a 1500 * real retransmit or a new connection attempt. The question is 1501 * how to handle such a case; either ignore it as spoofed, or 1502 * drop the current entry and create a new one? 1503 */ 1504 if (syncache_cookiesonly()) { 1505 sc = NULL; 1506 sch = syncache_hashbucket(inc); 1507 locked = false; 1508 } else { 1509 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1510 locked = true; 1511 SCH_LOCK_ASSERT(sch); 1512 } 1513 if (sc != NULL) { 1514 if (tfo_cookie_valid) 1515 INP_RUNLOCK(inp); 1516 TCPSTAT_INC(tcps_sc_dupsyn); 1517 if (ipopts) { 1518 /* 1519 * If we were remembering a previous source route, 1520 * forget it and use the new one we've been given. 1521 */ 1522 if (sc->sc_ipopts) 1523 (void)m_free(sc->sc_ipopts); 1524 sc->sc_ipopts = ipopts; 1525 } 1526 /* 1527 * Update timestamp if present. 1528 */ 1529 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1530 sc->sc_tsreflect = to->to_tsval; 1531 else 1532 sc->sc_flags &= ~SCF_TIMESTAMP; 1533 /* 1534 * Adjust ECN response if needed, e.g. different 1535 * IP ECN field, or a fallback by the remote host. 1536 */ 1537 if (sc->sc_flags & SCF_ECN_MASK) { 1538 sc->sc_flags &= ~SCF_ECN_MASK; 1539 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1540 } 1541 #ifdef MAC 1542 /* 1543 * Since we have already unconditionally allocated label 1544 * storage, free it up. The syncache entry will already 1545 * have an initialized label we can use. 1546 */ 1547 mac_syncache_destroy(&maclabel); 1548 #endif 1549 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1550 /* Retransmit SYN|ACK and reset retransmit count. */ 1551 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1552 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1553 "resetting timer and retransmitting SYN|ACK\n", 1554 s, __func__); 1555 free(s, M_TCPLOG); 1556 } 1557 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1558 sc->sc_rxmits = 0; 1559 syncache_timeout(sc, sch, 1); 1560 TCPSTAT_INC(tcps_sndacks); 1561 TCPSTAT_INC(tcps_sndtotal); 1562 } else { 1563 syncache_drop(sc, sch); 1564 TCPSTAT_INC(tcps_sc_dropped); 1565 } 1566 SCH_UNLOCK(sch); 1567 goto donenoprobe; 1568 } 1569 1570 KASSERT(sc == NULL, ("sc(%p) != NULL", sc)); 1571 /* 1572 * Skip allocating a syncache entry if we are just going to discard 1573 * it later. 1574 */ 1575 if (!locked || tfo_cookie_valid) { 1576 bzero(&scs, sizeof(scs)); 1577 sc = &scs; 1578 } else { 1579 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1580 if (sc == NULL) { 1581 /* 1582 * The zone allocator couldn't provide more entries. 1583 * Treat this as if the cache was full; drop the oldest 1584 * entry and insert the new one. 1585 */ 1586 TCPSTAT_INC(tcps_sc_zonefail); 1587 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 1588 if (sc != NULL) { 1589 sch->sch_last_overflow = time_uptime; 1590 syncache_drop(sc, sch); 1591 syncache_pause(inc); 1592 } 1593 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1594 if (sc == NULL) { 1595 if (V_tcp_syncookies) { 1596 bzero(&scs, sizeof(scs)); 1597 sc = &scs; 1598 } else { 1599 KASSERT(locked, 1600 ("%s: bucket unexpectedly unlocked", 1601 __func__)); 1602 SCH_UNLOCK(sch); 1603 goto done; 1604 } 1605 } 1606 } 1607 } 1608 1609 KASSERT(sc != NULL, ("sc == NULL")); 1610 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1611 sc->sc_tfo_cookie = &tfo_response_cookie; 1612 1613 /* 1614 * Fill in the syncache values. 1615 */ 1616 #ifdef MAC 1617 sc->sc_label = maclabel; 1618 #endif 1619 /* 1620 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in 1621 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false. 1622 * Therefore, store the credentials and take a reference count only 1623 * when needed: 1624 * - sc is allocated from the zone and not using the on stack instance. 1625 * - the sysctl variable net.inet.tcp.syncache.see_other is false. 1626 * The reference count is decremented when a zone allocated sc is 1627 * freed in syncache_free(). 1628 */ 1629 if (sc != &scs && !V_tcp_syncache.see_other) 1630 sc->sc_cred = crhold(so->so_cred); 1631 else 1632 sc->sc_cred = NULL; 1633 sc->sc_port = port; 1634 sc->sc_ipopts = ipopts; 1635 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1636 sc->sc_ip_tos = ip_tos; 1637 sc->sc_ip_ttl = ip_ttl; 1638 #ifdef TCP_OFFLOAD 1639 sc->sc_tod = tod; 1640 sc->sc_todctx = todctx; 1641 #endif 1642 sc->sc_irs = th->th_seq; 1643 sc->sc_flags = 0; 1644 sc->sc_flowlabel = 0; 1645 1646 /* 1647 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1648 * win was derived from socket earlier in the function. 1649 */ 1650 win = imax(win, 0); 1651 win = imin(win, TCP_MAXWIN); 1652 sc->sc_wnd = win; 1653 1654 if (V_tcp_do_rfc1323 && 1655 !(ltflags & TF_NOOPT)) { 1656 /* 1657 * A timestamp received in a SYN makes 1658 * it ok to send timestamp requests and replies. 1659 */ 1660 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1661 sc->sc_tsreflect = to->to_tsval; 1662 sc->sc_flags |= SCF_TIMESTAMP; 1663 sc->sc_tsoff = tcp_new_ts_offset(inc); 1664 } 1665 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1666 int wscale = 0; 1667 1668 /* 1669 * Pick the smallest possible scaling factor that 1670 * will still allow us to scale up to sb_max, aka 1671 * kern.ipc.maxsockbuf. 1672 * 1673 * We do this because there are broken firewalls that 1674 * will corrupt the window scale option, leading to 1675 * the other endpoint believing that our advertised 1676 * window is unscaled. At scale factors larger than 1677 * 5 the unscaled window will drop below 1500 bytes, 1678 * leading to serious problems when traversing these 1679 * broken firewalls. 1680 * 1681 * With the default maxsockbuf of 256K, a scale factor 1682 * of 3 will be chosen by this algorithm. Those who 1683 * choose a larger maxsockbuf should watch out 1684 * for the compatibility problems mentioned above. 1685 * 1686 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1687 * or <SYN,ACK>) segment itself is never scaled. 1688 */ 1689 while (wscale < TCP_MAX_WINSHIFT && 1690 (TCP_MAXWIN << wscale) < sb_max) 1691 wscale++; 1692 sc->sc_requested_r_scale = wscale; 1693 sc->sc_requested_s_scale = to->to_wscale; 1694 sc->sc_flags |= SCF_WINSCALE; 1695 } 1696 } 1697 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1698 /* 1699 * If incoming packet has an MD5 signature, flag this in the 1700 * syncache so that syncache_respond() will do the right thing 1701 * with the SYN+ACK. 1702 */ 1703 if (to->to_flags & TOF_SIGNATURE) 1704 sc->sc_flags |= SCF_SIGNATURE; 1705 #endif /* TCP_SIGNATURE */ 1706 if (to->to_flags & TOF_SACKPERM) 1707 sc->sc_flags |= SCF_SACK; 1708 if (to->to_flags & TOF_MSS) 1709 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1710 if (ltflags & TF_NOOPT) 1711 sc->sc_flags |= SCF_NOOPT; 1712 /* ECN Handshake */ 1713 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1714 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1715 1716 if (V_tcp_syncookies) 1717 sc->sc_iss = syncookie_generate(sch, sc); 1718 else 1719 sc->sc_iss = arc4random(); 1720 #ifdef INET6 1721 if (autoflowlabel) { 1722 if (V_tcp_syncookies) 1723 sc->sc_flowlabel = sc->sc_iss; 1724 else 1725 sc->sc_flowlabel = ip6_randomflowlabel(); 1726 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1727 } 1728 #endif 1729 if (locked) 1730 SCH_UNLOCK(sch); 1731 1732 if (tfo_cookie_valid) { 1733 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1734 /* INP_RUNLOCK(inp) will be performed by the caller */ 1735 goto tfo_expanded; 1736 } 1737 1738 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1739 /* 1740 * Do a standard 3-way handshake. 1741 */ 1742 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1743 if (sc != &scs) 1744 syncache_insert(sc, sch); /* locks and unlocks sch */ 1745 TCPSTAT_INC(tcps_sndacks); 1746 TCPSTAT_INC(tcps_sndtotal); 1747 } else { 1748 if (sc != &scs) 1749 syncache_free(sc); 1750 TCPSTAT_INC(tcps_sc_dropped); 1751 } 1752 goto donenoprobe; 1753 1754 done: 1755 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1756 donenoprobe: 1757 if (m) 1758 m_freem(m); 1759 /* 1760 * If tfo_pending is not NULL here, then a TFO SYN that did not 1761 * result in a new socket was processed and the associated pending 1762 * counter has not yet been decremented. All such TFO processing paths 1763 * transit this point. 1764 */ 1765 if (tfo_pending != NULL) 1766 tcp_fastopen_decrement_counter(tfo_pending); 1767 1768 tfo_expanded: 1769 if (sc == NULL || sc == &scs) { 1770 #ifdef MAC 1771 mac_syncache_destroy(&maclabel); 1772 #endif 1773 if (ipopts) 1774 (void)m_free(ipopts); 1775 } 1776 return (rv); 1777 } 1778 1779 /* 1780 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1781 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1782 */ 1783 static int 1784 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1785 { 1786 struct ip *ip = NULL; 1787 struct mbuf *m; 1788 struct tcphdr *th = NULL; 1789 struct udphdr *udp = NULL; 1790 int optlen, error = 0; /* Make compiler happy */ 1791 u_int16_t hlen, tlen, mssopt, ulen; 1792 struct tcpopt to; 1793 #ifdef INET6 1794 struct ip6_hdr *ip6 = NULL; 1795 #endif 1796 1797 NET_EPOCH_ASSERT(); 1798 1799 hlen = 1800 #ifdef INET6 1801 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1802 #endif 1803 sizeof(struct ip); 1804 tlen = hlen + sizeof(struct tcphdr); 1805 if (sc->sc_port) { 1806 tlen += sizeof(struct udphdr); 1807 } 1808 /* Determine MSS we advertize to other end of connection. */ 1809 mssopt = tcp_mssopt(&sc->sc_inc); 1810 if (sc->sc_port) 1811 mssopt -= V_tcp_udp_tunneling_overhead; 1812 mssopt = max(mssopt, V_tcp_minmss); 1813 1814 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1815 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1816 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1817 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1818 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1819 1820 /* Create the IP+TCP header from scratch. */ 1821 m = m_gethdr(M_NOWAIT, MT_DATA); 1822 if (m == NULL) 1823 return (ENOBUFS); 1824 #ifdef MAC 1825 mac_syncache_create_mbuf(sc->sc_label, m); 1826 #endif 1827 m->m_data += max_linkhdr; 1828 m->m_len = tlen; 1829 m->m_pkthdr.len = tlen; 1830 m->m_pkthdr.rcvif = NULL; 1831 1832 #ifdef INET6 1833 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1834 ip6 = mtod(m, struct ip6_hdr *); 1835 ip6->ip6_vfc = IPV6_VERSION; 1836 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1837 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1838 ip6->ip6_plen = htons(tlen - hlen); 1839 /* ip6_hlim is set after checksum */ 1840 /* Zero out traffic class and flow label. */ 1841 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1842 ip6->ip6_flow |= sc->sc_flowlabel; 1843 if (sc->sc_port != 0) { 1844 ip6->ip6_nxt = IPPROTO_UDP; 1845 udp = (struct udphdr *)(ip6 + 1); 1846 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1847 udp->uh_dport = sc->sc_port; 1848 ulen = (tlen - sizeof(struct ip6_hdr)); 1849 th = (struct tcphdr *)(udp + 1); 1850 } else { 1851 ip6->ip6_nxt = IPPROTO_TCP; 1852 th = (struct tcphdr *)(ip6 + 1); 1853 } 1854 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1855 } 1856 #endif 1857 #if defined(INET6) && defined(INET) 1858 else 1859 #endif 1860 #ifdef INET 1861 { 1862 ip = mtod(m, struct ip *); 1863 ip->ip_v = IPVERSION; 1864 ip->ip_hl = sizeof(struct ip) >> 2; 1865 ip->ip_len = htons(tlen); 1866 ip->ip_id = 0; 1867 ip->ip_off = 0; 1868 ip->ip_sum = 0; 1869 ip->ip_src = sc->sc_inc.inc_laddr; 1870 ip->ip_dst = sc->sc_inc.inc_faddr; 1871 ip->ip_ttl = sc->sc_ip_ttl; 1872 ip->ip_tos = sc->sc_ip_tos; 1873 1874 /* 1875 * See if we should do MTU discovery. Route lookups are 1876 * expensive, so we will only unset the DF bit if: 1877 * 1878 * 1) path_mtu_discovery is disabled 1879 * 2) the SCF_UNREACH flag has been set 1880 */ 1881 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1882 ip->ip_off |= htons(IP_DF); 1883 if (sc->sc_port == 0) { 1884 ip->ip_p = IPPROTO_TCP; 1885 th = (struct tcphdr *)(ip + 1); 1886 } else { 1887 ip->ip_p = IPPROTO_UDP; 1888 udp = (struct udphdr *)(ip + 1); 1889 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1890 udp->uh_dport = sc->sc_port; 1891 ulen = (tlen - sizeof(struct ip)); 1892 th = (struct tcphdr *)(udp + 1); 1893 } 1894 } 1895 #endif /* INET */ 1896 th->th_sport = sc->sc_inc.inc_lport; 1897 th->th_dport = sc->sc_inc.inc_fport; 1898 1899 if (flags & TH_SYN) 1900 th->th_seq = htonl(sc->sc_iss); 1901 else 1902 th->th_seq = htonl(sc->sc_iss + 1); 1903 th->th_ack = htonl(sc->sc_irs + 1); 1904 th->th_off = sizeof(struct tcphdr) >> 2; 1905 th->th_win = htons(sc->sc_wnd); 1906 th->th_urp = 0; 1907 1908 flags = tcp_ecn_syncache_respond(flags, sc); 1909 tcp_set_flags(th, flags); 1910 1911 /* Tack on the TCP options. */ 1912 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1913 to.to_flags = 0; 1914 1915 if (flags & TH_SYN) { 1916 to.to_mss = mssopt; 1917 to.to_flags = TOF_MSS; 1918 if (sc->sc_flags & SCF_WINSCALE) { 1919 to.to_wscale = sc->sc_requested_r_scale; 1920 to.to_flags |= TOF_SCALE; 1921 } 1922 if (sc->sc_flags & SCF_SACK) 1923 to.to_flags |= TOF_SACKPERM; 1924 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1925 if (sc->sc_flags & SCF_SIGNATURE) 1926 to.to_flags |= TOF_SIGNATURE; 1927 #endif 1928 if (sc->sc_tfo_cookie) { 1929 to.to_flags |= TOF_FASTOPEN; 1930 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1931 to.to_tfo_cookie = sc->sc_tfo_cookie; 1932 /* don't send cookie again when retransmitting response */ 1933 sc->sc_tfo_cookie = NULL; 1934 } 1935 } 1936 if (sc->sc_flags & SCF_TIMESTAMP) { 1937 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1938 to.to_tsecr = sc->sc_tsreflect; 1939 to.to_flags |= TOF_TS; 1940 } 1941 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1942 1943 /* Adjust headers by option size. */ 1944 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1945 m->m_len += optlen; 1946 m->m_pkthdr.len += optlen; 1947 #ifdef INET6 1948 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1949 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1950 else 1951 #endif 1952 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1953 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1954 if (sc->sc_flags & SCF_SIGNATURE) { 1955 KASSERT(to.to_flags & TOF_SIGNATURE, 1956 ("tcp_addoptions() didn't set tcp_signature")); 1957 1958 /* NOTE: to.to_signature is inside of mbuf */ 1959 if (!TCPMD5_ENABLED() || 1960 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1961 m_freem(m); 1962 return (EACCES); 1963 } 1964 } 1965 #endif 1966 } else 1967 optlen = 0; 1968 1969 if (udp) { 1970 ulen += optlen; 1971 udp->uh_ulen = htons(ulen); 1972 } 1973 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1974 /* 1975 * If we have peer's SYN and it has a flowid, then let's assign it to 1976 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1977 * to SYN|ACK due to lack of inp here. 1978 */ 1979 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1980 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1981 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1982 } 1983 #ifdef INET6 1984 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1985 if (sc->sc_port) { 1986 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 1987 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 1988 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 1989 IPPROTO_UDP, 0); 1990 th->th_sum = htons(0); 1991 } else { 1992 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1993 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1994 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1995 IPPROTO_TCP, 0); 1996 } 1997 ip6->ip6_hlim = sc->sc_ip_ttl; 1998 #ifdef TCP_OFFLOAD 1999 if (ADDED_BY_TOE(sc)) { 2000 struct toedev *tod = sc->sc_tod; 2001 2002 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2003 2004 return (error); 2005 } 2006 #endif 2007 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2008 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2009 } 2010 #endif 2011 #if defined(INET6) && defined(INET) 2012 else 2013 #endif 2014 #ifdef INET 2015 { 2016 if (sc->sc_port) { 2017 m->m_pkthdr.csum_flags = CSUM_UDP; 2018 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2019 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2020 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2021 th->th_sum = htons(0); 2022 } else { 2023 m->m_pkthdr.csum_flags = CSUM_TCP; 2024 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2025 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2026 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2027 } 2028 #ifdef TCP_OFFLOAD 2029 if (ADDED_BY_TOE(sc)) { 2030 struct toedev *tod = sc->sc_tod; 2031 2032 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2033 2034 return (error); 2035 } 2036 #endif 2037 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2038 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2039 } 2040 #endif 2041 return (error); 2042 } 2043 2044 /* 2045 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2046 * that exceed the capacity of the syncache by avoiding the storage of any 2047 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2048 * attacks where the attacker does not have access to our responses. 2049 * 2050 * Syncookies encode and include all necessary information about the 2051 * connection setup within the SYN|ACK that we send back. That way we 2052 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2053 * (if ever). Normally the syncache and syncookies are running in parallel 2054 * with the latter taking over when the former is exhausted. When matching 2055 * syncache entry is found the syncookie is ignored. 2056 * 2057 * The only reliable information persisting the 3WHS is our initial sequence 2058 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2059 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2060 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2061 * returns and signifies a legitimate connection if it matches the ACK. 2062 * 2063 * The available space of 32 bits to store the hash and to encode the SYN 2064 * option information is very tight and we should have at least 24 bits for 2065 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2066 * 2067 * SYN option information we have to encode to fully restore a connection: 2068 * MSS: is imporant to chose an optimal segment size to avoid IP level 2069 * fragmentation along the path. The common MSS values can be encoded 2070 * in a 3-bit table. Uncommon values are captured by the next lower value 2071 * in the table leading to a slight increase in packetization overhead. 2072 * WSCALE: is necessary to allow large windows to be used for high delay- 2073 * bandwidth product links. Not scaling the window when it was initially 2074 * negotiated is bad for performance as lack of scaling further decreases 2075 * the apparent available send window. We only need to encode the WSCALE 2076 * we received from the remote end. Our end can be recalculated at any 2077 * time. The common WSCALE values can be encoded in a 3-bit table. 2078 * Uncommon values are captured by the next lower value in the table 2079 * making us under-estimate the available window size halving our 2080 * theoretically possible maximum throughput for that connection. 2081 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2082 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2083 * that are included in all segments on a connection. We enable them when 2084 * the ACK has them. 2085 * 2086 * Security of syncookies and attack vectors: 2087 * 2088 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2089 * together with the gloabl secret to make it unique per connection attempt. 2090 * Thus any change of any of those parameters results in a different MAC output 2091 * in an unpredictable way unless a collision is encountered. 24 bits of the 2092 * MAC are embedded into the ISS. 2093 * 2094 * To prevent replay attacks two rotating global secrets are updated with a 2095 * new random value every 15 seconds. The life-time of a syncookie is thus 2096 * 15-30 seconds. 2097 * 2098 * Vector 1: Attacking the secret. This requires finding a weakness in the 2099 * MAC itself or the way it is used here. The attacker can do a chosen plain 2100 * text attack by varying and testing the all parameters under his control. 2101 * The strength depends on the size and randomness of the secret, and the 2102 * cryptographic security of the MAC function. Due to the constant updating 2103 * of the secret the attacker has at most 29.999 seconds to find the secret 2104 * and launch spoofed connections. After that he has to start all over again. 2105 * 2106 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2107 * size an average of 4,823 attempts are required for a 50% chance of success 2108 * to spoof a single syncookie (birthday collision paradox). However the 2109 * attacker is blind and doesn't know if one of his attempts succeeded unless 2110 * he has a side channel to interfere success from. A single connection setup 2111 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2112 * This many attempts are required for each one blind spoofed connection. For 2113 * every additional spoofed connection he has to launch another N attempts. 2114 * Thus for a sustained rate 100 spoofed connections per second approximately 2115 * 1,800,000 packets per second would have to be sent. 2116 * 2117 * NB: The MAC function should be fast so that it doesn't become a CPU 2118 * exhaustion attack vector itself. 2119 * 2120 * References: 2121 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2122 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2123 * http://cr.yp.to/syncookies.html (overview) 2124 * http://cr.yp.to/syncookies/archive (details) 2125 * 2126 * 2127 * Schematic construction of a syncookie enabled Initial Sequence Number: 2128 * 0 1 2 3 2129 * 12345678901234567890123456789012 2130 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2131 * 2132 * x 24 MAC (truncated) 2133 * W 3 Send Window Scale index 2134 * M 3 MSS index 2135 * S 1 SACK permitted 2136 * P 1 Odd/even secret 2137 */ 2138 2139 /* 2140 * Distribution and probability of certain MSS values. Those in between are 2141 * rounded down to the next lower one. 2142 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2143 * .2% .3% 5% 7% 7% 20% 15% 45% 2144 */ 2145 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2146 2147 /* 2148 * Distribution and probability of certain WSCALE values. We have to map the 2149 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2150 * bits based on prevalence of certain values. Where we don't have an exact 2151 * match for are rounded down to the next lower one letting us under-estimate 2152 * the true available window. At the moment this would happen only for the 2153 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2154 * and window size). The absence of the WSCALE option (no scaling in either 2155 * direction) is encoded with index zero. 2156 * [WSCALE values histograms, Allman, 2012] 2157 * X 10 10 35 5 6 14 10% by host 2158 * X 11 4 5 5 18 49 3% by connections 2159 */ 2160 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2161 2162 /* 2163 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2164 * and good cryptographic properties. 2165 */ 2166 static uint32_t 2167 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2168 uint8_t *secbits, uintptr_t secmod) 2169 { 2170 SIPHASH_CTX ctx; 2171 uint32_t siphash[2]; 2172 2173 SipHash24_Init(&ctx); 2174 SipHash_SetKey(&ctx, secbits); 2175 switch (inc->inc_flags & INC_ISIPV6) { 2176 #ifdef INET 2177 case 0: 2178 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2179 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2180 break; 2181 #endif 2182 #ifdef INET6 2183 case INC_ISIPV6: 2184 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2185 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2186 break; 2187 #endif 2188 } 2189 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2190 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2191 SipHash_Update(&ctx, &irs, sizeof(irs)); 2192 SipHash_Update(&ctx, &flags, sizeof(flags)); 2193 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2194 SipHash_Final((u_int8_t *)&siphash, &ctx); 2195 2196 return (siphash[0] ^ siphash[1]); 2197 } 2198 2199 static tcp_seq 2200 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2201 { 2202 u_int i, secbit, wscale; 2203 uint32_t iss, hash; 2204 uint8_t *secbits; 2205 union syncookie cookie; 2206 2207 cookie.cookie = 0; 2208 2209 /* Map our computed MSS into the 3-bit index. */ 2210 for (i = nitems(tcp_sc_msstab) - 1; 2211 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2212 i--) 2213 ; 2214 cookie.flags.mss_idx = i; 2215 2216 /* 2217 * Map the send window scale into the 3-bit index but only if 2218 * the wscale option was received. 2219 */ 2220 if (sc->sc_flags & SCF_WINSCALE) { 2221 wscale = sc->sc_requested_s_scale; 2222 for (i = nitems(tcp_sc_wstab) - 1; 2223 tcp_sc_wstab[i] > wscale && i > 0; 2224 i--) 2225 ; 2226 cookie.flags.wscale_idx = i; 2227 } 2228 2229 /* Can we do SACK? */ 2230 if (sc->sc_flags & SCF_SACK) 2231 cookie.flags.sack_ok = 1; 2232 2233 /* Which of the two secrets to use. */ 2234 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2235 cookie.flags.odd_even = secbit; 2236 2237 secbits = V_tcp_syncache.secret.key[secbit]; 2238 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2239 (uintptr_t)sch); 2240 2241 /* 2242 * Put the flags into the hash and XOR them to get better ISS number 2243 * variance. This doesn't enhance the cryptographic strength and is 2244 * done to prevent the 8 cookie bits from showing up directly on the 2245 * wire. 2246 */ 2247 iss = hash & ~0xff; 2248 iss |= cookie.cookie ^ (hash >> 24); 2249 2250 TCPSTAT_INC(tcps_sc_sendcookie); 2251 return (iss); 2252 } 2253 2254 static struct syncache * 2255 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2256 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2257 struct socket *lso, uint16_t port) 2258 { 2259 uint32_t hash; 2260 uint8_t *secbits; 2261 tcp_seq ack, seq; 2262 int wnd, wscale = 0; 2263 union syncookie cookie; 2264 2265 /* 2266 * Pull information out of SYN-ACK/ACK and revert sequence number 2267 * advances. 2268 */ 2269 ack = th->th_ack - 1; 2270 seq = th->th_seq - 1; 2271 2272 /* 2273 * Unpack the flags containing enough information to restore the 2274 * connection. 2275 */ 2276 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2277 2278 /* Which of the two secrets to use. */ 2279 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2280 2281 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2282 2283 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2284 if ((ack & ~0xff) != (hash & ~0xff)) 2285 return (NULL); 2286 2287 /* Fill in the syncache values. */ 2288 sc->sc_flags = 0; 2289 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2290 sc->sc_ipopts = NULL; 2291 2292 sc->sc_irs = seq; 2293 sc->sc_iss = ack; 2294 2295 switch (inc->inc_flags & INC_ISIPV6) { 2296 #ifdef INET 2297 case 0: 2298 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2299 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2300 break; 2301 #endif 2302 #ifdef INET6 2303 case INC_ISIPV6: 2304 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2305 sc->sc_flowlabel = 2306 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2307 break; 2308 #endif 2309 } 2310 2311 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2312 2313 /* We can simply recompute receive window scale we sent earlier. */ 2314 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2315 wscale++; 2316 2317 /* Only use wscale if it was enabled in the orignal SYN. */ 2318 if (cookie.flags.wscale_idx > 0) { 2319 sc->sc_requested_r_scale = wscale; 2320 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2321 sc->sc_flags |= SCF_WINSCALE; 2322 } 2323 2324 wnd = lso->sol_sbrcv_hiwat; 2325 wnd = imax(wnd, 0); 2326 wnd = imin(wnd, TCP_MAXWIN); 2327 sc->sc_wnd = wnd; 2328 2329 if (cookie.flags.sack_ok) 2330 sc->sc_flags |= SCF_SACK; 2331 2332 if (to->to_flags & TOF_TS) { 2333 sc->sc_flags |= SCF_TIMESTAMP; 2334 sc->sc_tsreflect = to->to_tsval; 2335 sc->sc_tsoff = tcp_new_ts_offset(inc); 2336 } 2337 2338 if (to->to_flags & TOF_SIGNATURE) 2339 sc->sc_flags |= SCF_SIGNATURE; 2340 2341 sc->sc_rxmits = 0; 2342 2343 sc->sc_port = port; 2344 2345 TCPSTAT_INC(tcps_sc_recvcookie); 2346 return (sc); 2347 } 2348 2349 #ifdef INVARIANTS 2350 static int 2351 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2352 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2353 struct socket *lso, uint16_t port) 2354 { 2355 struct syncache scs, *scx; 2356 char *s; 2357 2358 bzero(&scs, sizeof(scs)); 2359 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2360 2361 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2362 return (0); 2363 2364 if (scx != NULL) { 2365 if (sc->sc_peer_mss != scx->sc_peer_mss) 2366 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2367 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2368 2369 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2370 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2371 s, __func__, sc->sc_requested_r_scale, 2372 scx->sc_requested_r_scale); 2373 2374 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2375 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2376 s, __func__, sc->sc_requested_s_scale, 2377 scx->sc_requested_s_scale); 2378 2379 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2380 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2381 } 2382 2383 if (s != NULL) 2384 free(s, M_TCPLOG); 2385 return (0); 2386 } 2387 #endif /* INVARIANTS */ 2388 2389 static void 2390 syncookie_reseed(void *arg) 2391 { 2392 struct tcp_syncache *sc = arg; 2393 uint8_t *secbits; 2394 int secbit; 2395 2396 /* 2397 * Reseeding the secret doesn't have to be protected by a lock. 2398 * It only must be ensured that the new random values are visible 2399 * to all CPUs in a SMP environment. The atomic with release 2400 * semantics ensures that. 2401 */ 2402 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2403 secbits = sc->secret.key[secbit]; 2404 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2405 atomic_add_rel_int(&sc->secret.oddeven, 1); 2406 2407 /* Reschedule ourself. */ 2408 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2409 } 2410 2411 /* 2412 * We have overflowed a bucket. Let's pause dealing with the syncache. 2413 * This function will increment the bucketoverflow statistics appropriately 2414 * (once per pause when pausing is enabled; otherwise, once per overflow). 2415 */ 2416 static void 2417 syncache_pause(struct in_conninfo *inc) 2418 { 2419 time_t delta; 2420 const char *s; 2421 2422 /* XXX: 2423 * 2. Add sysctl read here so we don't get the benefit of this 2424 * change without the new sysctl. 2425 */ 2426 2427 /* 2428 * Try an unlocked read. If we already know that another thread 2429 * has activated the feature, there is no need to proceed. 2430 */ 2431 if (V_tcp_syncache.paused) 2432 return; 2433 2434 /* Are cookied enabled? If not, we can't pause. */ 2435 if (!V_tcp_syncookies) { 2436 TCPSTAT_INC(tcps_sc_bucketoverflow); 2437 return; 2438 } 2439 2440 /* 2441 * We may be the first thread to find an overflow. Get the lock 2442 * and evaluate if we need to take action. 2443 */ 2444 mtx_lock(&V_tcp_syncache.pause_mtx); 2445 if (V_tcp_syncache.paused) { 2446 mtx_unlock(&V_tcp_syncache.pause_mtx); 2447 return; 2448 } 2449 2450 /* Activate protection. */ 2451 V_tcp_syncache.paused = true; 2452 TCPSTAT_INC(tcps_sc_bucketoverflow); 2453 2454 /* 2455 * Determine the last backoff time. If we are seeing a re-newed 2456 * attack within that same time after last reactivating the syncache, 2457 * consider it an extension of the same attack. 2458 */ 2459 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2460 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2461 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2462 delta <<= 1; 2463 V_tcp_syncache.pause_backoff++; 2464 } 2465 } else { 2466 delta = TCP_SYNCACHE_PAUSE_TIME; 2467 V_tcp_syncache.pause_backoff = 0; 2468 } 2469 2470 /* Log a warning, including IP addresses, if able. */ 2471 if (inc != NULL) 2472 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2473 else 2474 s = (const char *)NULL; 2475 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2476 "the next %lld seconds%s%s%s\n", (long long)delta, 2477 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2478 (s != NULL) ? ")" : ""); 2479 free(__DECONST(void *, s), M_TCPLOG); 2480 2481 /* Use the calculated delta to set a new pause time. */ 2482 V_tcp_syncache.pause_until = time_uptime + delta; 2483 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2484 &V_tcp_syncache); 2485 mtx_unlock(&V_tcp_syncache.pause_mtx); 2486 } 2487 2488 /* Evaluate whether we need to unpause. */ 2489 static void 2490 syncache_unpause(void *arg) 2491 { 2492 struct tcp_syncache *sc; 2493 time_t delta; 2494 2495 sc = arg; 2496 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2497 callout_deactivate(&sc->pause_co); 2498 2499 /* 2500 * Check to make sure we are not running early. If the pause 2501 * time has expired, then deactivate the protection. 2502 */ 2503 if ((delta = sc->pause_until - time_uptime) > 0) 2504 callout_schedule(&sc->pause_co, delta * hz); 2505 else 2506 sc->paused = false; 2507 } 2508 2509 /* 2510 * Exports the syncache entries to userland so that netstat can display 2511 * them alongside the other sockets. This function is intended to be 2512 * called only from tcp_pcblist. 2513 * 2514 * Due to concurrency on an active system, the number of pcbs exported 2515 * may have no relation to max_pcbs. max_pcbs merely indicates the 2516 * amount of space the caller allocated for this function to use. 2517 */ 2518 int 2519 syncache_pcblist(struct sysctl_req *req) 2520 { 2521 struct xtcpcb xt; 2522 struct syncache *sc; 2523 struct syncache_head *sch; 2524 int error, i; 2525 2526 bzero(&xt, sizeof(xt)); 2527 xt.xt_len = sizeof(xt); 2528 xt.t_state = TCPS_SYN_RECEIVED; 2529 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2530 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2531 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2532 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2533 2534 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2535 sch = &V_tcp_syncache.hashbase[i]; 2536 SCH_LOCK(sch); 2537 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2538 if (sc->sc_cred != NULL && 2539 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2540 continue; 2541 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2542 xt.xt_inp.inp_vflag = INP_IPV6; 2543 else 2544 xt.xt_inp.inp_vflag = INP_IPV4; 2545 xt.xt_encaps_port = sc->sc_port; 2546 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2547 sizeof (struct in_conninfo)); 2548 error = SYSCTL_OUT(req, &xt, sizeof xt); 2549 if (error) { 2550 SCH_UNLOCK(sch); 2551 return (0); 2552 } 2553 } 2554 SCH_UNLOCK(sch); 2555 } 2556 2557 return (0); 2558 } 2559