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(bool, tcp_syncookies) = true; 106 #define V_tcp_syncookies VNET(tcp_syncookies) 107 SYSCTL_BOOL(_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(bool, tcp_syncookiesonly) = false; 112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 113 SYSCTL_BOOL(_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 void syncache_send_challenge_ack(struct syncache *, struct mbuf *); 126 static struct socket *syncache_socket(struct syncache *, struct socket *, 127 struct mbuf *m); 128 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 129 int docallout); 130 static void syncache_timer(void *); 131 132 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 133 uint8_t *, uintptr_t); 134 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 135 static bool syncookie_expand(struct in_conninfo *, 136 const struct syncache_head *, struct syncache *, 137 struct tcphdr *, struct tcpopt *, struct socket *, 138 uint16_t); 139 static void syncache_pause(struct in_conninfo *); 140 static void syncache_unpause(void *); 141 static void syncookie_reseed(void *); 142 #ifdef INVARIANTS 143 static void syncookie_cmp(struct in_conninfo *, 144 const struct syncache_head *, struct syncache *, 145 struct tcphdr *, struct tcpopt *, struct socket *, 146 uint16_t); 147 #endif 148 149 /* 150 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 151 * 3 retransmits corresponds to a timeout with default values of 152 * tcp_rexmit_initial * ( 1 + 153 * tcp_backoff[1] + 154 * tcp_backoff[2] + 155 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 156 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 157 * the odds are that the user has given up attempting to connect by then. 158 */ 159 #define SYNCACHE_MAXREXMTS 3 160 161 /* Arbitrary values */ 162 #define TCP_SYNCACHE_HASHSIZE 512 163 #define TCP_SYNCACHE_BUCKETLIMIT 30 164 165 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 166 #define V_tcp_syncache VNET(tcp_syncache) 167 168 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 169 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 170 "TCP SYN cache"); 171 172 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 173 &VNET_NAME(tcp_syncache.bucket_limit), 0, 174 "Per-bucket hash limit for syncache"); 175 176 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 177 &VNET_NAME(tcp_syncache.cache_limit), 0, 178 "Overall entry limit for syncache"); 179 180 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 181 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 182 183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 184 &VNET_NAME(tcp_syncache.hashsize), 0, 185 "Size of TCP syncache hashtable"); 186 187 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 188 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 189 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 190 "and mac(4) checks"); 191 192 static int 193 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 194 { 195 int error; 196 u_int new; 197 198 new = V_tcp_syncache.rexmt_limit; 199 error = sysctl_handle_int(oidp, &new, 0, req); 200 if ((error == 0) && (req->newptr != NULL)) { 201 if (new > TCP_MAXRXTSHIFT) 202 error = EINVAL; 203 else 204 V_tcp_syncache.rexmt_limit = new; 205 } 206 return (error); 207 } 208 209 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 210 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 211 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 212 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU", 213 "Limit on SYN/ACK retransmissions"); 214 215 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 216 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 217 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 218 "Send reset on socket allocation failure"); 219 220 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 221 222 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 223 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 224 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 225 226 /* 227 * Requires the syncache entry to be already removed from the bucket list. 228 */ 229 static void 230 syncache_free(struct syncache *sc) 231 { 232 233 if (sc->sc_ipopts) 234 (void)m_free(sc->sc_ipopts); 235 if (sc->sc_cred) 236 crfree(sc->sc_cred); 237 #ifdef MAC 238 mac_syncache_destroy(&sc->sc_label); 239 #endif 240 241 uma_zfree(V_tcp_syncache.zone, sc); 242 } 243 244 void 245 syncache_init(void) 246 { 247 int i; 248 249 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 250 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 251 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 252 V_tcp_syncache.hash_secret = arc4random(); 253 254 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 255 &V_tcp_syncache.hashsize); 256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 257 &V_tcp_syncache.bucket_limit); 258 if (!powerof2(V_tcp_syncache.hashsize) || 259 V_tcp_syncache.hashsize == 0) { 260 printf("WARNING: syncache hash size is not a power of 2.\n"); 261 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 262 } 263 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 264 265 /* Set limits. */ 266 V_tcp_syncache.cache_limit = 267 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 268 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 269 &V_tcp_syncache.cache_limit); 270 271 /* Allocate the hash table. */ 272 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 273 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 274 275 #ifdef VIMAGE 276 V_tcp_syncache.vnet = curvnet; 277 #endif 278 279 /* Initialize the hash buckets. */ 280 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 281 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 282 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 283 NULL, MTX_DEF); 284 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 285 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 286 V_tcp_syncache.hashbase[i].sch_length = 0; 287 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 288 V_tcp_syncache.hashbase[i].sch_last_overflow = 289 -(SYNCOOKIE_LIFETIME + 1); 290 } 291 292 /* Create the syncache entry zone. */ 293 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 294 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 295 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 296 V_tcp_syncache.cache_limit); 297 298 /* Start the SYN cookie reseeder callout. */ 299 callout_init(&V_tcp_syncache.secret.reseed, 1); 300 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 301 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 302 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 303 syncookie_reseed, &V_tcp_syncache); 304 305 /* Initialize the pause machinery. */ 306 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 307 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 308 0); 309 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 310 V_tcp_syncache.pause_backoff = 0; 311 V_tcp_syncache.paused = false; 312 } 313 314 #ifdef VIMAGE 315 void 316 syncache_destroy(void) 317 { 318 struct syncache_head *sch; 319 struct syncache *sc, *nsc; 320 int i; 321 322 /* 323 * Stop the re-seed timer before freeing resources. No need to 324 * possibly schedule it another time. 325 */ 326 callout_drain(&V_tcp_syncache.secret.reseed); 327 328 /* Stop the SYN cache pause callout. */ 329 mtx_lock(&V_tcp_syncache.pause_mtx); 330 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 331 mtx_unlock(&V_tcp_syncache.pause_mtx); 332 callout_drain(&V_tcp_syncache.pause_co); 333 } else 334 mtx_unlock(&V_tcp_syncache.pause_mtx); 335 336 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 337 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 338 sch = &V_tcp_syncache.hashbase[i]; 339 callout_drain(&sch->sch_timer); 340 341 SCH_LOCK(sch); 342 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 343 syncache_drop(sc, sch); 344 SCH_UNLOCK(sch); 345 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 346 ("%s: sch->sch_bucket not empty", __func__)); 347 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 348 __func__, sch->sch_length)); 349 mtx_destroy(&sch->sch_mtx); 350 } 351 352 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 353 ("%s: cache_count not 0", __func__)); 354 355 /* Free the allocated global resources. */ 356 uma_zdestroy(V_tcp_syncache.zone); 357 free(V_tcp_syncache.hashbase, M_SYNCACHE); 358 mtx_destroy(&V_tcp_syncache.pause_mtx); 359 } 360 #endif 361 362 /* 363 * Inserts a syncache entry into the specified bucket row. 364 * Locks and unlocks the syncache_head autonomously. 365 */ 366 static void 367 syncache_insert(struct syncache *sc, struct syncache_head *sch) 368 { 369 struct syncache *sc2; 370 371 SCH_LOCK(sch); 372 373 /* 374 * Make sure that we don't overflow the per-bucket limit. 375 * If the bucket is full, toss the oldest element. 376 */ 377 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 378 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 379 ("sch->sch_length incorrect")); 380 syncache_pause(&sc->sc_inc); 381 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 382 sch->sch_last_overflow = time_uptime; 383 syncache_drop(sc2, sch); 384 } 385 386 /* Put it into the bucket. */ 387 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 388 sch->sch_length++; 389 390 #ifdef TCP_OFFLOAD 391 if (ADDED_BY_TOE(sc)) { 392 struct toedev *tod = sc->sc_tod; 393 394 tod->tod_syncache_added(tod, sc->sc_todctx); 395 } 396 #endif 397 398 /* Reinitialize the bucket row's timer. */ 399 if (sch->sch_length == 1) 400 sch->sch_nextc = ticks + INT_MAX; 401 syncache_timeout(sc, sch, 1); 402 403 SCH_UNLOCK(sch); 404 405 TCPSTATES_INC(TCPS_SYN_RECEIVED); 406 TCPSTAT_INC(tcps_sc_added); 407 } 408 409 /* 410 * Remove and free entry from syncache bucket row. 411 * Expects locked syncache head. 412 */ 413 static void 414 syncache_drop(struct syncache *sc, struct syncache_head *sch) 415 { 416 417 SCH_LOCK_ASSERT(sch); 418 419 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 420 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 421 sch->sch_length--; 422 423 #ifdef TCP_OFFLOAD 424 if (ADDED_BY_TOE(sc)) { 425 struct toedev *tod = sc->sc_tod; 426 427 tod->tod_syncache_removed(tod, sc->sc_todctx); 428 } 429 #endif 430 431 syncache_free(sc); 432 } 433 434 /* 435 * Engage/reengage time on bucket row. 436 */ 437 static void 438 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 439 { 440 int rexmt; 441 442 if (sc->sc_rxmits == 0) 443 rexmt = tcp_rexmit_initial; 444 else 445 TCPT_RANGESET(rexmt, 446 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 447 tcp_rexmit_min, tcp_rexmit_max); 448 sc->sc_rxttime = ticks + rexmt; 449 sc->sc_rxmits++; 450 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 451 sch->sch_nextc = sc->sc_rxttime; 452 if (docallout) 453 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 454 syncache_timer, (void *)sch); 455 } 456 } 457 458 /* 459 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 460 * If we have retransmitted an entry the maximum number of times, expire it. 461 * One separate timer for each bucket row. 462 */ 463 static void 464 syncache_timer(void *xsch) 465 { 466 struct syncache_head *sch = (struct syncache_head *)xsch; 467 struct syncache *sc, *nsc; 468 struct epoch_tracker et; 469 int tick = ticks; 470 char *s; 471 bool paused; 472 473 CURVNET_SET(sch->sch_sc->vnet); 474 475 /* NB: syncache_head has already been locked by the callout. */ 476 SCH_LOCK_ASSERT(sch); 477 478 /* 479 * In the following cycle we may remove some entries and/or 480 * advance some timeouts, so re-initialize the bucket timer. 481 */ 482 sch->sch_nextc = tick + INT_MAX; 483 484 /* 485 * If we have paused processing, unconditionally remove 486 * all syncache entries. 487 */ 488 mtx_lock(&V_tcp_syncache.pause_mtx); 489 paused = V_tcp_syncache.paused; 490 mtx_unlock(&V_tcp_syncache.pause_mtx); 491 492 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 493 if (paused) { 494 syncache_drop(sc, sch); 495 continue; 496 } 497 /* 498 * We do not check if the listen socket still exists 499 * and accept the case where the listen socket may be 500 * gone by the time we resend the SYN/ACK. We do 501 * not expect this to happens often. If it does, 502 * then the RST will be sent by the time the remote 503 * host does the SYN/ACK->ACK. 504 */ 505 if (TSTMP_GT(sc->sc_rxttime, tick)) { 506 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 507 sch->sch_nextc = sc->sc_rxttime; 508 continue; 509 } 510 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 511 sc->sc_flags &= ~SCF_ECN_MASK; 512 } 513 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 514 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 515 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 516 "giving up and removing syncache entry\n", 517 s, __func__); 518 free(s, M_TCPLOG); 519 } 520 syncache_drop(sc, sch); 521 TCPSTAT_INC(tcps_sc_stale); 522 continue; 523 } 524 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 525 log(LOG_DEBUG, "%s; %s: Response timeout, " 526 "retransmitting (%u) SYN|ACK\n", 527 s, __func__, sc->sc_rxmits); 528 free(s, M_TCPLOG); 529 } 530 531 NET_EPOCH_ENTER(et); 532 if (syncache_respond(sc, NULL, TH_SYN|TH_ACK) == 0) { 533 syncache_timeout(sc, sch, 0); 534 TCPSTAT_INC(tcps_sndacks); 535 TCPSTAT_INC(tcps_sndtotal); 536 TCPSTAT_INC(tcps_sc_retransmitted); 537 } else { 538 /* 539 * Most likely we are memory constrained, so free 540 * resources. 541 */ 542 syncache_drop(sc, sch); 543 TCPSTAT_INC(tcps_sc_dropped); 544 } 545 NET_EPOCH_EXIT(et); 546 } 547 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 548 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 549 syncache_timer, (void *)(sch)); 550 CURVNET_RESTORE(); 551 } 552 553 /* 554 * Returns true if the system is only using cookies at the moment. 555 * This could be due to a sysadmin decision to only use cookies, or it 556 * could be due to the system detecting an attack. 557 */ 558 static inline bool 559 syncache_cookiesonly(void) 560 { 561 return ((V_tcp_syncookies && V_tcp_syncache.paused) || 562 V_tcp_syncookiesonly); 563 } 564 565 /* 566 * Find the hash bucket for the given connection. 567 */ 568 static struct syncache_head * 569 syncache_hashbucket(struct in_conninfo *inc) 570 { 571 uint32_t hash; 572 573 /* 574 * The hash is built on foreign port + local port + foreign address. 575 * We rely on the fact that struct in_conninfo starts with 16 bits 576 * of foreign port, then 16 bits of local port then followed by 128 577 * bits of foreign address. In case of IPv4 address, the first 3 578 * 32-bit words of the address always are zeroes. 579 */ 580 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 581 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 582 583 return (&V_tcp_syncache.hashbase[hash]); 584 } 585 586 /* 587 * Find an entry in the syncache. 588 * Returns always with locked syncache_head plus a matching entry or NULL. 589 */ 590 static struct syncache * 591 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 592 { 593 struct syncache *sc; 594 struct syncache_head *sch; 595 596 *schp = sch = syncache_hashbucket(inc); 597 SCH_LOCK(sch); 598 599 /* Circle through bucket row to find matching entry. */ 600 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 601 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 602 sizeof(struct in_endpoints)) == 0) 603 break; 604 605 return (sc); /* Always returns with locked sch. */ 606 } 607 608 /* 609 * This function is called when we get a RST for a 610 * non-existent connection, so that we can see if the 611 * connection is in the syn cache. If it is, zap it. 612 * If required send a challenge ACK. 613 */ 614 void 615 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 616 uint16_t port) 617 { 618 struct syncache *sc; 619 struct syncache_head *sch; 620 char *s = NULL; 621 622 if (syncache_cookiesonly()) 623 return; 624 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 625 SCH_LOCK_ASSERT(sch); 626 627 /* 628 * No corresponding connection was found in syncache. 629 * If syncookies are enabled and possibly exclusively 630 * used, or we are under memory pressure, a valid RST 631 * may not find a syncache entry. In that case we're 632 * done and no SYN|ACK retransmissions will happen. 633 * Otherwise the RST was misdirected or spoofed. 634 */ 635 if (sc == NULL) { 636 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 637 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 638 "syncache entry (possibly syncookie only), " 639 "segment ignored\n", s, __func__); 640 TCPSTAT_INC(tcps_badrst); 641 goto done; 642 } 643 644 /* The remote UDP encaps port does not match. */ 645 if (sc->sc_port != port) { 646 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 647 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 648 "syncache entry but non-matching UDP encaps port, " 649 "segment ignored\n", s, __func__); 650 TCPSTAT_INC(tcps_badrst); 651 goto done; 652 } 653 654 /* 655 * If the RST bit is set, check the sequence number to see 656 * if this is a valid reset segment. 657 * 658 * RFC 793 page 37: 659 * In all states except SYN-SENT, all reset (RST) segments 660 * are validated by checking their SEQ-fields. A reset is 661 * valid if its sequence number is in the window. 662 * 663 * RFC 793 page 69: 664 * There are four cases for the acceptability test for an incoming 665 * segment: 666 * 667 * Segment Receive Test 668 * Length Window 669 * ------- ------- ------------------------------------------- 670 * 0 0 SEG.SEQ = RCV.NXT 671 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 672 * >0 0 not acceptable 673 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 674 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 675 * 676 * Note that when receiving a SYN segment in the LISTEN state, 677 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 678 * described in RFC 793, page 66. 679 */ 680 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 681 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 682 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 683 if (V_tcp_insecure_rst || 684 th->th_seq == sc->sc_irs + 1) { 685 syncache_drop(sc, sch); 686 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 687 log(LOG_DEBUG, 688 "%s; %s: Our SYN|ACK was rejected, " 689 "connection attempt aborted by remote " 690 "endpoint\n", 691 s, __func__); 692 TCPSTAT_INC(tcps_sc_reset); 693 } else { 694 TCPSTAT_INC(tcps_badrst); 695 /* Send challenge ACK. */ 696 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 697 log(LOG_DEBUG, "%s; %s: RST with invalid " 698 " SEQ %u != NXT %u (+WND %u), " 699 "sending challenge ACK\n", 700 s, __func__, 701 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 702 syncache_send_challenge_ack(sc, m); 703 } 704 } else { 705 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 706 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 707 "NXT %u (+WND %u), segment ignored\n", 708 s, __func__, 709 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 710 TCPSTAT_INC(tcps_badrst); 711 } 712 713 done: 714 if (s != NULL) 715 free(s, M_TCPLOG); 716 SCH_UNLOCK(sch); 717 } 718 719 void 720 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 721 { 722 struct syncache *sc; 723 struct syncache_head *sch; 724 725 if (syncache_cookiesonly()) 726 return; 727 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 728 SCH_LOCK_ASSERT(sch); 729 if (sc == NULL) 730 goto done; 731 732 /* If the port != sc_port, then it's a bogus ICMP msg */ 733 if (port != sc->sc_port) 734 goto done; 735 736 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 737 if (ntohl(th_seq) != sc->sc_iss) 738 goto done; 739 740 /* 741 * If we've retransmitted 3 times and this is our second error, 742 * we remove the entry. Otherwise, we allow it to continue on. 743 * This prevents us from incorrectly nuking an entry during a 744 * spurious network outage. 745 * 746 * See tcp_notify(). 747 */ 748 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 749 sc->sc_flags |= SCF_UNREACH; 750 goto done; 751 } 752 syncache_drop(sc, sch); 753 TCPSTAT_INC(tcps_sc_unreach); 754 done: 755 SCH_UNLOCK(sch); 756 } 757 758 /* 759 * Build a new TCP socket structure from a syncache entry. 760 * 761 * On success return the newly created socket with its underlying inp locked. 762 */ 763 static struct socket * 764 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 765 { 766 struct inpcb *inp = NULL; 767 struct socket *so; 768 struct tcpcb *tp; 769 int error; 770 char *s; 771 772 NET_EPOCH_ASSERT(); 773 774 /* 775 * Ok, create the full blown connection, and set things up 776 * as they would have been set up if we had created the 777 * connection when the SYN arrived. 778 */ 779 if ((so = solisten_clone(lso)) == NULL) 780 goto allocfail; 781 #ifdef MAC 782 mac_socketpeer_set_from_mbuf(m, so); 783 #endif 784 error = in_pcballoc(so, &V_tcbinfo); 785 if (error) { 786 sodealloc(so); 787 goto allocfail; 788 } 789 inp = sotoinpcb(so); 790 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) { 791 in_pcbfree(inp); 792 sodealloc(so); 793 goto allocfail; 794 } 795 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 796 #ifdef INET6 797 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 798 inp->inp_vflag &= ~INP_IPV4; 799 inp->inp_vflag |= INP_IPV6; 800 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 801 } else { 802 inp->inp_vflag &= ~INP_IPV6; 803 inp->inp_vflag |= INP_IPV4; 804 #endif 805 inp->inp_ip_ttl = sc->sc_ip_ttl; 806 inp->inp_ip_tos = sc->sc_ip_tos; 807 inp->inp_laddr = sc->sc_inc.inc_laddr; 808 #ifdef INET6 809 } 810 #endif 811 812 /* 813 * If there's an mbuf and it has a flowid, then let's initialise the 814 * inp with that particular flowid. 815 */ 816 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 817 inp->inp_flowid = m->m_pkthdr.flowid; 818 inp->inp_flowtype = M_HASHTYPE_GET(m); 819 #ifdef NUMA 820 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 821 #endif 822 } 823 824 inp->inp_lport = sc->sc_inc.inc_lport; 825 #ifdef INET6 826 if (inp->inp_vflag & INP_IPV6PROTO) { 827 struct inpcb *oinp = sotoinpcb(lso); 828 829 /* 830 * Inherit socket options from the listening socket. 831 * Note that in6p_inputopts are not (and should not be) 832 * copied, since it stores previously received options and is 833 * used to detect if each new option is different than the 834 * previous one and hence should be passed to a user. 835 * If we copied in6p_inputopts, a user would not be able to 836 * receive options just after calling the accept system call. 837 */ 838 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 839 if (oinp->in6p_outputopts) 840 inp->in6p_outputopts = 841 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 842 inp->in6p_hops = oinp->in6p_hops; 843 } 844 845 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 846 struct sockaddr_in6 sin6; 847 848 sin6.sin6_family = AF_INET6; 849 sin6.sin6_len = sizeof(sin6); 850 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 851 sin6.sin6_port = sc->sc_inc.inc_fport; 852 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 853 INP_HASH_WLOCK(&V_tcbinfo); 854 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 855 INP_HASH_WUNLOCK(&V_tcbinfo); 856 if (error != 0) 857 goto abort; 858 /* Override flowlabel from in6_pcbconnect. */ 859 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 860 inp->inp_flow |= sc->sc_flowlabel; 861 } 862 #endif /* INET6 */ 863 #if defined(INET) && defined(INET6) 864 else 865 #endif 866 #ifdef INET 867 { 868 struct sockaddr_in sin; 869 870 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 871 872 if (inp->inp_options == NULL) { 873 inp->inp_options = sc->sc_ipopts; 874 sc->sc_ipopts = NULL; 875 } 876 877 sin.sin_family = AF_INET; 878 sin.sin_len = sizeof(sin); 879 sin.sin_addr = sc->sc_inc.inc_faddr; 880 sin.sin_port = sc->sc_inc.inc_fport; 881 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 882 INP_HASH_WLOCK(&V_tcbinfo); 883 error = in_pcbconnect(inp, &sin, thread0.td_ucred); 884 INP_HASH_WUNLOCK(&V_tcbinfo); 885 if (error != 0) 886 goto abort; 887 } 888 #endif /* INET */ 889 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 890 /* Copy old policy into new socket's. */ 891 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 892 printf("syncache_socket: could not copy policy\n"); 893 #endif 894 tp->t_state = TCPS_SYN_RECEIVED; 895 tp->iss = sc->sc_iss; 896 tp->irs = sc->sc_irs; 897 tp->t_port = sc->sc_port; 898 tcp_rcvseqinit(tp); 899 tcp_sendseqinit(tp); 900 tp->snd_wl1 = sc->sc_irs; 901 tp->snd_max = tp->iss + 1; 902 tp->snd_nxt = tp->iss + 1; 903 tp->rcv_up = sc->sc_irs + 1; 904 tp->rcv_wnd = sc->sc_wnd; 905 tp->rcv_adv += tp->rcv_wnd; 906 tp->last_ack_sent = tp->rcv_nxt; 907 908 tp->t_flags = sototcpcb(lso)->t_flags & 909 (TF_LRD|TF_NOPUSH|TF_NODELAY); 910 if (sc->sc_flags & SCF_NOOPT) 911 tp->t_flags |= TF_NOOPT; 912 else { 913 if (sc->sc_flags & SCF_WINSCALE) { 914 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 915 tp->snd_scale = sc->sc_requested_s_scale; 916 tp->request_r_scale = sc->sc_requested_r_scale; 917 } 918 if (sc->sc_flags & SCF_TIMESTAMP) { 919 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 920 tp->ts_recent = sc->sc_tsreflect; 921 tp->ts_recent_age = tcp_ts_getticks(); 922 tp->ts_offset = sc->sc_tsoff; 923 } 924 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 925 if (sc->sc_flags & SCF_SIGNATURE) 926 tp->t_flags |= TF_SIGNATURE; 927 #endif 928 if (sc->sc_flags & SCF_SACK) 929 tp->t_flags |= TF_SACK_PERMIT; 930 } 931 932 tcp_ecn_syncache_socket(tp, sc); 933 934 /* 935 * Set up MSS and get cached values from tcp_hostcache. 936 * This might overwrite some of the defaults we just set. 937 */ 938 tcp_mss(tp, sc->sc_peer_mss); 939 940 /* 941 * If the SYN,ACK was retransmitted, indicate that CWND to be 942 * limited to one segment in cc_conn_init(). 943 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 944 */ 945 if (sc->sc_rxmits > 1) 946 tp->snd_cwnd = 1; 947 948 /* Copy over the challenge ACK state. */ 949 tp->t_challenge_ack_end = sc->sc_challenge_ack_end; 950 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt; 951 952 #ifdef TCP_OFFLOAD 953 /* 954 * Allow a TOE driver to install its hooks. Note that we hold the 955 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 956 * new connection before the TOE driver has done its thing. 957 */ 958 if (ADDED_BY_TOE(sc)) { 959 struct toedev *tod = sc->sc_tod; 960 961 tod->tod_offload_socket(tod, sc->sc_todctx, so); 962 } 963 #endif 964 #ifdef TCP_BLACKBOX 965 /* 966 * Inherit the log state from the listening socket, if 967 * - the log state of the listening socket is not off and 968 * - the listening socket was not auto selected from all sessions and 969 * - a log id is not set on the listening socket. 970 * This avoids inheriting a log state which was automatically set. 971 */ 972 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 973 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 974 (sototcpcb(lso)->t_lib == NULL)) { 975 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 976 } 977 #endif 978 /* 979 * Copy and activate timers. 980 */ 981 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 982 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 983 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 984 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 985 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 986 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 987 988 TCPSTAT_INC(tcps_accepts); 989 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 990 991 if (!solisten_enqueue(so, SS_ISCONNECTED)) 992 tp->t_flags |= TF_SONOTCONN; 993 /* Can we inherit anything from the listener? */ 994 if (tp->t_fb->tfb_inherit != NULL) { 995 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 996 } 997 return (so); 998 999 allocfail: 1000 /* 1001 * Drop the connection; we will either send a RST or have the peer 1002 * retransmit its SYN again after its RTO and try again. 1003 */ 1004 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1005 log(LOG_DEBUG, "%s; %s: Socket create failed " 1006 "due to limits or memory shortage\n", 1007 s, __func__); 1008 free(s, M_TCPLOG); 1009 } 1010 TCPSTAT_INC(tcps_listendrop); 1011 return (NULL); 1012 1013 abort: 1014 tcp_discardcb(tp); 1015 in_pcbfree(inp); 1016 sodealloc(so); 1017 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1018 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1019 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1020 error); 1021 free(s, M_TCPLOG); 1022 } 1023 TCPSTAT_INC(tcps_listendrop); 1024 return (NULL); 1025 } 1026 1027 /* 1028 * This function gets called when we receive an ACK for a 1029 * socket in the LISTEN state. We look up the connection 1030 * in the syncache, and if its there, we pull it out of 1031 * the cache and turn it into a full-blown connection in 1032 * the SYN-RECEIVED state. 1033 * 1034 * On syncache_socket() success the newly created socket 1035 * has its underlying inp locked. 1036 * 1037 * *lsop is updated, if and only if 1 is returned. 1038 */ 1039 int 1040 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1041 struct socket **lsop, struct mbuf *m, uint16_t port) 1042 { 1043 struct syncache *sc; 1044 struct syncache_head *sch; 1045 struct syncache scs; 1046 char *s; 1047 bool locked; 1048 1049 NET_EPOCH_ASSERT(); 1050 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1051 ("%s: can handle only ACK", __func__)); 1052 1053 if (syncache_cookiesonly()) { 1054 sc = NULL; 1055 sch = syncache_hashbucket(inc); 1056 locked = false; 1057 } else { 1058 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1059 locked = true; 1060 SCH_LOCK_ASSERT(sch); 1061 } 1062 1063 #ifdef INVARIANTS 1064 /* 1065 * Test code for syncookies comparing the syncache stored 1066 * values with the reconstructed values from the cookie. 1067 */ 1068 if (sc != NULL) 1069 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1070 #endif 1071 1072 if (sc == NULL) { 1073 if (locked) { 1074 /* 1075 * The syncache is currently in use (neither disabled, 1076 * nor paused), but no entry was found. 1077 */ 1078 if (!V_tcp_syncookies) { 1079 /* 1080 * Since no syncookies are used in case of 1081 * a bucket overflow, don't even check for 1082 * a valid syncookie. 1083 */ 1084 SCH_UNLOCK(sch); 1085 TCPSTAT_INC(tcps_sc_spurcookie); 1086 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1087 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1088 "segment rejected " 1089 "(syncookies disabled)\n", 1090 s, __func__); 1091 free(s, M_TCPLOG); 1092 } 1093 return (0); 1094 } 1095 if (sch->sch_last_overflow < 1096 time_uptime - SYNCOOKIE_LIFETIME) { 1097 /* 1098 * Since the bucket did not overflow recently, 1099 * don't even check for a valid syncookie. 1100 */ 1101 SCH_UNLOCK(sch); 1102 TCPSTAT_INC(tcps_sc_spurcookie); 1103 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1104 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1105 "segment rejected " 1106 "(no syncache entry)\n", 1107 s, __func__); 1108 free(s, M_TCPLOG); 1109 } 1110 return (0); 1111 } 1112 SCH_UNLOCK(sch); 1113 } 1114 bzero(&scs, sizeof(scs)); 1115 /* 1116 * Now check, if the syncookie is valid. If it is, create an on 1117 * stack syncache entry. 1118 */ 1119 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) { 1120 sc = &scs; 1121 TCPSTAT_INC(tcps_sc_recvcookie); 1122 } else { 1123 TCPSTAT_INC(tcps_sc_failcookie); 1124 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1125 log(LOG_DEBUG, "%s; %s: Segment failed " 1126 "SYNCOOKIE authentication, segment rejected " 1127 "(probably spoofed)\n", s, __func__); 1128 free(s, M_TCPLOG); 1129 } 1130 return (0); 1131 } 1132 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1133 /* If received ACK has MD5 signature, check it. */ 1134 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1135 (!TCPMD5_ENABLED() || 1136 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1137 /* Drop the ACK. */ 1138 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1139 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1140 "MD5 signature doesn't match.\n", 1141 s, __func__); 1142 free(s, M_TCPLOG); 1143 } 1144 TCPSTAT_INC(tcps_sig_err_sigopt); 1145 return (-1); /* Do not send RST */ 1146 } 1147 #endif /* TCP_SIGNATURE */ 1148 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1149 } else { 1150 if (sc->sc_port != port) { 1151 SCH_UNLOCK(sch); 1152 return (0); 1153 } 1154 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1155 /* 1156 * If listening socket requested TCP digests, check that 1157 * received ACK has signature and it is correct. 1158 * If not, drop the ACK and leave sc entry in the cache, 1159 * because SYN was received with correct signature. 1160 */ 1161 if (sc->sc_flags & SCF_SIGNATURE) { 1162 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1163 /* No signature */ 1164 TCPSTAT_INC(tcps_sig_err_nosigopt); 1165 SCH_UNLOCK(sch); 1166 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1167 log(LOG_DEBUG, "%s; %s: Segment " 1168 "rejected, MD5 signature wasn't " 1169 "provided.\n", s, __func__); 1170 free(s, M_TCPLOG); 1171 } 1172 return (-1); /* Do not send RST */ 1173 } 1174 if (!TCPMD5_ENABLED() || 1175 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1176 /* Doesn't match or no SA */ 1177 SCH_UNLOCK(sch); 1178 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1179 log(LOG_DEBUG, "%s; %s: Segment " 1180 "rejected, MD5 signature doesn't " 1181 "match.\n", s, __func__); 1182 free(s, M_TCPLOG); 1183 } 1184 return (-1); /* Do not send RST */ 1185 } 1186 } 1187 #endif /* TCP_SIGNATURE */ 1188 1189 /* 1190 * RFC 7323 PAWS: If we have a timestamp on this segment and 1191 * it's less than ts_recent, drop it. 1192 * XXXMT: RFC 7323 also requires to send an ACK. 1193 * In tcp_input.c this is only done for TCP segments 1194 * with user data, so be consistent here and just drop 1195 * the segment. 1196 */ 1197 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1198 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1199 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1200 log(LOG_DEBUG, 1201 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1202 "segment dropped\n", s, __func__, 1203 to->to_tsval, sc->sc_tsreflect); 1204 } 1205 SCH_UNLOCK(sch); 1206 free(s, M_TCPLOG); 1207 return (-1); /* Do not send RST */ 1208 } 1209 1210 /* 1211 * If timestamps were not negotiated during SYN/ACK and a 1212 * segment with a timestamp is received, ignore the 1213 * timestamp and process the packet normally. 1214 * See section 3.2 of RFC 7323. 1215 */ 1216 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1217 (to->to_flags & TOF_TS)) { 1218 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1219 log(LOG_DEBUG, "%s; %s: Timestamp not " 1220 "expected, segment processed normally\n", 1221 s, __func__); 1222 free(s, M_TCPLOG); 1223 } 1224 } 1225 1226 /* 1227 * If timestamps were negotiated during SYN/ACK and a 1228 * segment without a timestamp is received, silently drop 1229 * the segment, unless the missing timestamps are tolerated. 1230 * See section 3.2 of RFC 7323. 1231 */ 1232 if ((sc->sc_flags & SCF_TIMESTAMP) && 1233 !(to->to_flags & TOF_TS)) { 1234 if (V_tcp_tolerate_missing_ts) { 1235 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1236 log(LOG_DEBUG, 1237 "%s; %s: Timestamp missing, " 1238 "segment processed normally\n", 1239 s, __func__); 1240 free(s, M_TCPLOG); 1241 } 1242 } else { 1243 SCH_UNLOCK(sch); 1244 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1245 log(LOG_DEBUG, 1246 "%s; %s: Timestamp missing, " 1247 "segment silently dropped\n", 1248 s, __func__); 1249 free(s, M_TCPLOG); 1250 } 1251 return (-1); /* Do not send RST */ 1252 } 1253 } 1254 1255 /* 1256 * SEG.SEQ validation: 1257 * The SEG.SEQ must be in the window starting at our 1258 * initial receive sequence number + 1. 1259 */ 1260 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1261 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1262 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1263 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, " 1264 "sending challenge ACK\n", 1265 s, __func__, th->th_seq, sc->sc_irs + 1); 1266 syncache_send_challenge_ack(sc, m); 1267 SCH_UNLOCK(sch); 1268 free(s, M_TCPLOG); 1269 return (-1); /* Do not send RST */ 1270 } 1271 1272 /* 1273 * SEG.ACK validation: 1274 * SEG.ACK must match our initial send sequence number + 1. 1275 */ 1276 if (th->th_ack != sc->sc_iss + 1) { 1277 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1278 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, " 1279 "segment rejected\n", 1280 s, __func__, th->th_ack, sc->sc_iss + 1); 1281 SCH_UNLOCK(sch); 1282 free(s, M_TCPLOG); 1283 return (0); /* Do send RST, do not free sc. */ 1284 } 1285 1286 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1287 sch->sch_length--; 1288 #ifdef TCP_OFFLOAD 1289 if (ADDED_BY_TOE(sc)) { 1290 struct toedev *tod = sc->sc_tod; 1291 1292 tod->tod_syncache_removed(tod, sc->sc_todctx); 1293 } 1294 #endif 1295 SCH_UNLOCK(sch); 1296 } 1297 1298 *lsop = syncache_socket(sc, *lsop, m); 1299 1300 if (__predict_false(*lsop == NULL)) { 1301 TCPSTAT_INC(tcps_sc_aborted); 1302 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1303 } else if (sc != &scs) 1304 TCPSTAT_INC(tcps_sc_completed); 1305 1306 if (sc != &scs) 1307 syncache_free(sc); 1308 return (1); 1309 } 1310 1311 static struct socket * 1312 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1313 uint64_t response_cookie) 1314 { 1315 struct inpcb *inp; 1316 struct tcpcb *tp; 1317 unsigned int *pending_counter; 1318 struct socket *so; 1319 1320 NET_EPOCH_ASSERT(); 1321 1322 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1323 so = syncache_socket(sc, lso, m); 1324 if (so == NULL) { 1325 TCPSTAT_INC(tcps_sc_aborted); 1326 atomic_subtract_int(pending_counter, 1); 1327 } else { 1328 soisconnected(so); 1329 inp = sotoinpcb(so); 1330 tp = intotcpcb(inp); 1331 tp->t_flags |= TF_FASTOPEN; 1332 tp->t_tfo_cookie.server = response_cookie; 1333 tp->snd_max = tp->iss; 1334 tp->snd_nxt = tp->iss; 1335 tp->t_tfo_pending = pending_counter; 1336 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1337 TCPSTAT_INC(tcps_sc_completed); 1338 } 1339 1340 return (so); 1341 } 1342 1343 /* 1344 * Given a LISTEN socket and an inbound SYN request, add 1345 * this to the syn cache, and send back a segment: 1346 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1347 * to the source. 1348 * 1349 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1350 * Doing so would require that we hold onto the data and deliver it 1351 * to the application. However, if we are the target of a SYN-flood 1352 * DoS attack, an attacker could send data which would eventually 1353 * consume all available buffer space if it were ACKed. By not ACKing 1354 * the data, we avoid this DoS scenario. 1355 * 1356 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1357 * cookie is processed and a new socket is created. In this case, any data 1358 * accompanying the SYN will be queued to the socket by tcp_input() and will 1359 * be ACKed either when the application sends response data or the delayed 1360 * ACK timer expires, whichever comes first. 1361 */ 1362 struct socket * 1363 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1364 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1365 void *todctx, uint8_t iptos, uint16_t port) 1366 { 1367 struct tcpcb *tp; 1368 struct socket *rv = NULL; 1369 struct syncache *sc = NULL; 1370 struct ucred *cred; 1371 struct syncache_head *sch; 1372 struct mbuf *ipopts = NULL; 1373 u_int ltflags; 1374 int win, ip_ttl, ip_tos; 1375 char *s; 1376 #ifdef INET6 1377 int autoflowlabel = 0; 1378 #endif 1379 #ifdef MAC 1380 struct label *maclabel = NULL; 1381 #endif 1382 struct syncache scs; 1383 uint64_t tfo_response_cookie; 1384 unsigned int *tfo_pending = NULL; 1385 int tfo_cookie_valid = 0; 1386 int tfo_response_cookie_valid = 0; 1387 bool locked; 1388 1389 INP_RLOCK_ASSERT(inp); /* listen socket */ 1390 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1391 ("%s: unexpected tcp flags", __func__)); 1392 1393 /* 1394 * Combine all so/tp operations very early to drop the INP lock as 1395 * soon as possible. 1396 */ 1397 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1398 tp = sototcpcb(so); 1399 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1400 1401 #ifdef INET6 1402 if (inc->inc_flags & INC_ISIPV6) { 1403 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1404 autoflowlabel = 1; 1405 } 1406 ip_ttl = in6_selecthlim(inp, NULL); 1407 if ((inp->in6p_outputopts == NULL) || 1408 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1409 ip_tos = 0; 1410 } else { 1411 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1412 } 1413 } 1414 #endif 1415 #if defined(INET6) && defined(INET) 1416 else 1417 #endif 1418 #ifdef INET 1419 { 1420 ip_ttl = inp->inp_ip_ttl; 1421 ip_tos = inp->inp_ip_tos; 1422 } 1423 #endif 1424 win = so->sol_sbrcv_hiwat; 1425 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1426 1427 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1428 (tp->t_tfo_pending != NULL) && 1429 (to->to_flags & TOF_FASTOPEN)) { 1430 /* 1431 * Limit the number of pending TFO connections to 1432 * approximately half of the queue limit. This prevents TFO 1433 * SYN floods from starving the service by filling the 1434 * listen queue with bogus TFO connections. 1435 */ 1436 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1437 (so->sol_qlimit / 2)) { 1438 int result; 1439 1440 result = tcp_fastopen_check_cookie(inc, 1441 to->to_tfo_cookie, to->to_tfo_len, 1442 &tfo_response_cookie); 1443 tfo_cookie_valid = (result > 0); 1444 tfo_response_cookie_valid = (result >= 0); 1445 } 1446 1447 /* 1448 * Remember the TFO pending counter as it will have to be 1449 * decremented below if we don't make it to syncache_tfo_expand(). 1450 */ 1451 tfo_pending = tp->t_tfo_pending; 1452 } 1453 1454 #ifdef MAC 1455 if (mac_syncache_init(&maclabel) != 0) { 1456 INP_RUNLOCK(inp); 1457 goto done; 1458 } else 1459 mac_syncache_create(maclabel, inp); 1460 #endif 1461 if (!tfo_cookie_valid) 1462 INP_RUNLOCK(inp); 1463 1464 /* 1465 * Remember the IP options, if any. 1466 */ 1467 #ifdef INET6 1468 if (!(inc->inc_flags & INC_ISIPV6)) 1469 #endif 1470 #ifdef INET 1471 ipopts = (m) ? ip_srcroute(m) : NULL; 1472 #else 1473 ipopts = NULL; 1474 #endif 1475 1476 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1477 /* 1478 * When the socket is TCP-MD5 enabled check that, 1479 * - a signed packet is valid 1480 * - a non-signed packet does not have a security association 1481 * 1482 * If a signed packet fails validation or a non-signed packet has a 1483 * security association, the packet will be dropped. 1484 */ 1485 if (ltflags & TF_SIGNATURE) { 1486 if (to->to_flags & TOF_SIGNATURE) { 1487 if (!TCPMD5_ENABLED() || 1488 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1489 goto done; 1490 } else { 1491 if (TCPMD5_ENABLED() && 1492 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1493 goto done; 1494 } 1495 } else if (to->to_flags & TOF_SIGNATURE) 1496 goto done; 1497 #endif /* TCP_SIGNATURE */ 1498 /* 1499 * See if we already have an entry for this connection. 1500 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1501 * 1502 * XXX: should the syncache be re-initialized with the contents 1503 * of the new SYN here (which may have different options?) 1504 * 1505 * XXX: We do not check the sequence number to see if this is a 1506 * real retransmit or a new connection attempt. The question is 1507 * how to handle such a case; either ignore it as spoofed, or 1508 * drop the current entry and create a new one? 1509 */ 1510 if (syncache_cookiesonly()) { 1511 sc = NULL; 1512 sch = syncache_hashbucket(inc); 1513 locked = false; 1514 } else { 1515 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1516 locked = true; 1517 SCH_LOCK_ASSERT(sch); 1518 } 1519 if (sc != NULL) { 1520 if (tfo_cookie_valid) 1521 INP_RUNLOCK(inp); 1522 TCPSTAT_INC(tcps_sc_dupsyn); 1523 if (ipopts) { 1524 /* 1525 * If we were remembering a previous source route, 1526 * forget it and use the new one we've been given. 1527 */ 1528 if (sc->sc_ipopts) 1529 (void)m_free(sc->sc_ipopts); 1530 sc->sc_ipopts = ipopts; 1531 } 1532 /* 1533 * Update timestamp if present. 1534 */ 1535 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1536 sc->sc_tsreflect = to->to_tsval; 1537 else 1538 sc->sc_flags &= ~SCF_TIMESTAMP; 1539 /* 1540 * Adjust ECN response if needed, e.g. different 1541 * IP ECN field, or a fallback by the remote host. 1542 */ 1543 if (sc->sc_flags & SCF_ECN_MASK) { 1544 sc->sc_flags &= ~SCF_ECN_MASK; 1545 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1546 } 1547 #ifdef MAC 1548 /* 1549 * Since we have already unconditionally allocated label 1550 * storage, free it up. The syncache entry will already 1551 * have an initialized label we can use. 1552 */ 1553 mac_syncache_destroy(&maclabel); 1554 #endif 1555 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1556 /* Retransmit SYN|ACK and reset retransmit count. */ 1557 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1558 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1559 "resetting timer and retransmitting SYN|ACK\n", 1560 s, __func__); 1561 free(s, M_TCPLOG); 1562 } 1563 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1564 sc->sc_rxmits = 0; 1565 syncache_timeout(sc, sch, 1); 1566 TCPSTAT_INC(tcps_sndacks); 1567 TCPSTAT_INC(tcps_sndtotal); 1568 } else { 1569 /* 1570 * Most likely we are memory constrained, so free 1571 * resources. 1572 */ 1573 syncache_drop(sc, sch); 1574 TCPSTAT_INC(tcps_sc_dropped); 1575 } 1576 SCH_UNLOCK(sch); 1577 goto donenoprobe; 1578 } 1579 1580 KASSERT(sc == NULL, ("sc(%p) != NULL", sc)); 1581 /* 1582 * Skip allocating a syncache entry if we are just going to discard 1583 * it later. 1584 */ 1585 if (!locked || tfo_cookie_valid) { 1586 bzero(&scs, sizeof(scs)); 1587 sc = &scs; 1588 } else { 1589 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1590 if (sc == NULL) { 1591 /* 1592 * The zone allocator couldn't provide more entries. 1593 * Treat this as if the cache was full; drop the oldest 1594 * entry and insert the new one. 1595 */ 1596 TCPSTAT_INC(tcps_sc_zonefail); 1597 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 1598 if (sc != NULL) { 1599 sch->sch_last_overflow = time_uptime; 1600 syncache_drop(sc, sch); 1601 syncache_pause(inc); 1602 } 1603 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1604 if (sc == NULL) { 1605 if (V_tcp_syncookies) { 1606 bzero(&scs, sizeof(scs)); 1607 sc = &scs; 1608 } else { 1609 KASSERT(locked, 1610 ("%s: bucket unexpectedly unlocked", 1611 __func__)); 1612 SCH_UNLOCK(sch); 1613 goto done; 1614 } 1615 } 1616 } 1617 } 1618 1619 KASSERT(sc != NULL, ("sc == NULL")); 1620 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1621 sc->sc_tfo_cookie = &tfo_response_cookie; 1622 1623 /* 1624 * Fill in the syncache values. 1625 */ 1626 #ifdef MAC 1627 sc->sc_label = maclabel; 1628 #endif 1629 /* 1630 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in 1631 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false. 1632 * Therefore, store the credentials only when needed: 1633 * - sc is allocated from the zone and not using the on stack instance. 1634 * - the sysctl variable net.inet.tcp.syncache.see_other is false. 1635 * The reference count is decremented when a zone allocated sc is 1636 * freed in syncache_free(). 1637 */ 1638 if (sc != &scs && !V_tcp_syncache.see_other) { 1639 sc->sc_cred = cred; 1640 cred = NULL; 1641 } else 1642 sc->sc_cred = NULL; 1643 sc->sc_port = port; 1644 sc->sc_ipopts = ipopts; 1645 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1646 sc->sc_ip_tos = ip_tos; 1647 sc->sc_ip_ttl = ip_ttl; 1648 #ifdef TCP_OFFLOAD 1649 sc->sc_tod = tod; 1650 sc->sc_todctx = todctx; 1651 #endif 1652 sc->sc_irs = th->th_seq; 1653 sc->sc_flags = 0; 1654 sc->sc_flowlabel = 0; 1655 1656 /* 1657 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1658 * win was derived from socket earlier in the function. 1659 */ 1660 win = imax(win, 0); 1661 win = imin(win, TCP_MAXWIN); 1662 sc->sc_wnd = win; 1663 1664 if (V_tcp_do_rfc1323 && 1665 !(ltflags & TF_NOOPT)) { 1666 /* 1667 * A timestamp received in a SYN makes 1668 * it ok to send timestamp requests and replies. 1669 */ 1670 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1671 sc->sc_tsreflect = to->to_tsval; 1672 sc->sc_flags |= SCF_TIMESTAMP; 1673 sc->sc_tsoff = tcp_new_ts_offset(inc); 1674 } 1675 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1676 u_int wscale = 0; 1677 1678 /* 1679 * Pick the smallest possible scaling factor that 1680 * will still allow us to scale up to sb_max, aka 1681 * kern.ipc.maxsockbuf. 1682 * 1683 * We do this because there are broken firewalls that 1684 * will corrupt the window scale option, leading to 1685 * the other endpoint believing that our advertised 1686 * window is unscaled. At scale factors larger than 1687 * 5 the unscaled window will drop below 1500 bytes, 1688 * leading to serious problems when traversing these 1689 * broken firewalls. 1690 * 1691 * With the default maxsockbuf of 256K, a scale factor 1692 * of 3 will be chosen by this algorithm. Those who 1693 * choose a larger maxsockbuf should watch out 1694 * for the compatibility problems mentioned above. 1695 * 1696 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1697 * or <SYN,ACK>) segment itself is never scaled. 1698 */ 1699 while (wscale < TCP_MAX_WINSHIFT && 1700 (TCP_MAXWIN << wscale) < sb_max) 1701 wscale++; 1702 sc->sc_requested_r_scale = wscale; 1703 sc->sc_requested_s_scale = to->to_wscale; 1704 sc->sc_flags |= SCF_WINSCALE; 1705 } 1706 } 1707 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1708 /* 1709 * If incoming packet has an MD5 signature, flag this in the 1710 * syncache so that syncache_respond() will do the right thing 1711 * with the SYN+ACK. 1712 */ 1713 if (to->to_flags & TOF_SIGNATURE) 1714 sc->sc_flags |= SCF_SIGNATURE; 1715 #endif /* TCP_SIGNATURE */ 1716 if (to->to_flags & TOF_SACKPERM) 1717 sc->sc_flags |= SCF_SACK; 1718 if (to->to_flags & TOF_MSS) 1719 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1720 if (ltflags & TF_NOOPT) 1721 sc->sc_flags |= SCF_NOOPT; 1722 /* ECN Handshake */ 1723 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1724 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1725 1726 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1727 sc->sc_iss = syncookie_generate(sch, sc); 1728 else 1729 sc->sc_iss = arc4random(); 1730 #ifdef INET6 1731 if (autoflowlabel) { 1732 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1733 sc->sc_flowlabel = sc->sc_iss; 1734 else 1735 sc->sc_flowlabel = ip6_randomflowlabel(); 1736 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1737 } 1738 #endif 1739 if (locked) 1740 SCH_UNLOCK(sch); 1741 1742 if (tfo_cookie_valid) { 1743 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1744 /* INP_RUNLOCK(inp) will be performed by the caller */ 1745 goto tfo_expanded; 1746 } 1747 1748 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1749 /* 1750 * Do a standard 3-way handshake. 1751 */ 1752 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1753 if (sc != &scs) 1754 syncache_insert(sc, sch); /* locks and unlocks sch */ 1755 TCPSTAT_INC(tcps_sndacks); 1756 TCPSTAT_INC(tcps_sndtotal); 1757 } else { 1758 /* 1759 * Most likely we are memory constrained, so free resources. 1760 */ 1761 if (sc != &scs) 1762 syncache_free(sc); 1763 TCPSTAT_INC(tcps_sc_dropped); 1764 } 1765 goto donenoprobe; 1766 1767 done: 1768 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1769 donenoprobe: 1770 if (m) 1771 m_freem(m); 1772 /* 1773 * If tfo_pending is not NULL here, then a TFO SYN that did not 1774 * result in a new socket was processed and the associated pending 1775 * counter has not yet been decremented. All such TFO processing paths 1776 * transit this point. 1777 */ 1778 if (tfo_pending != NULL) 1779 tcp_fastopen_decrement_counter(tfo_pending); 1780 1781 tfo_expanded: 1782 if (cred != NULL) 1783 crfree(cred); 1784 if (sc == NULL || sc == &scs) { 1785 #ifdef MAC 1786 mac_syncache_destroy(&maclabel); 1787 #endif 1788 if (ipopts) 1789 (void)m_free(ipopts); 1790 } 1791 return (rv); 1792 } 1793 1794 /* 1795 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1796 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1797 */ 1798 static int 1799 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1800 { 1801 struct ip *ip = NULL; 1802 struct mbuf *m; 1803 struct tcphdr *th = NULL; 1804 struct udphdr *udp = NULL; 1805 int optlen, error = 0; /* Make compiler happy */ 1806 u_int16_t hlen, tlen, mssopt, ulen; 1807 struct tcpopt to; 1808 #ifdef INET6 1809 struct ip6_hdr *ip6 = NULL; 1810 #endif 1811 1812 NET_EPOCH_ASSERT(); 1813 1814 hlen = 1815 #ifdef INET6 1816 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1817 #endif 1818 sizeof(struct ip); 1819 tlen = hlen + sizeof(struct tcphdr); 1820 if (sc->sc_port) { 1821 tlen += sizeof(struct udphdr); 1822 } 1823 /* Determine MSS we advertize to other end of connection. */ 1824 mssopt = tcp_mssopt(&sc->sc_inc); 1825 if (sc->sc_port) 1826 mssopt -= V_tcp_udp_tunneling_overhead; 1827 mssopt = max(mssopt, V_tcp_minmss); 1828 1829 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1830 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1831 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1832 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1833 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1834 1835 /* Create the IP+TCP header from scratch. */ 1836 m = m_gethdr(M_NOWAIT, MT_DATA); 1837 if (m == NULL) 1838 return (ENOBUFS); 1839 #ifdef MAC 1840 mac_syncache_create_mbuf(sc->sc_label, m); 1841 #endif 1842 m->m_data += max_linkhdr; 1843 m->m_len = tlen; 1844 m->m_pkthdr.len = tlen; 1845 m->m_pkthdr.rcvif = NULL; 1846 1847 #ifdef INET6 1848 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1849 ip6 = mtod(m, struct ip6_hdr *); 1850 ip6->ip6_vfc = IPV6_VERSION; 1851 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1852 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1853 ip6->ip6_plen = htons(tlen - hlen); 1854 /* ip6_hlim is set after checksum */ 1855 /* Zero out traffic class and flow label. */ 1856 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1857 ip6->ip6_flow |= sc->sc_flowlabel; 1858 if (sc->sc_port != 0) { 1859 ip6->ip6_nxt = IPPROTO_UDP; 1860 udp = (struct udphdr *)(ip6 + 1); 1861 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1862 udp->uh_dport = sc->sc_port; 1863 ulen = (tlen - sizeof(struct ip6_hdr)); 1864 th = (struct tcphdr *)(udp + 1); 1865 } else { 1866 ip6->ip6_nxt = IPPROTO_TCP; 1867 th = (struct tcphdr *)(ip6 + 1); 1868 } 1869 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1870 } 1871 #endif 1872 #if defined(INET6) && defined(INET) 1873 else 1874 #endif 1875 #ifdef INET 1876 { 1877 ip = mtod(m, struct ip *); 1878 ip->ip_v = IPVERSION; 1879 ip->ip_hl = sizeof(struct ip) >> 2; 1880 ip->ip_len = htons(tlen); 1881 ip->ip_id = 0; 1882 ip->ip_off = 0; 1883 ip->ip_sum = 0; 1884 ip->ip_src = sc->sc_inc.inc_laddr; 1885 ip->ip_dst = sc->sc_inc.inc_faddr; 1886 ip->ip_ttl = sc->sc_ip_ttl; 1887 ip->ip_tos = sc->sc_ip_tos; 1888 1889 /* 1890 * See if we should do MTU discovery. Route lookups are 1891 * expensive, so we will only unset the DF bit if: 1892 * 1893 * 1) path_mtu_discovery is disabled 1894 * 2) the SCF_UNREACH flag has been set 1895 */ 1896 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1897 ip->ip_off |= htons(IP_DF); 1898 if (sc->sc_port == 0) { 1899 ip->ip_p = IPPROTO_TCP; 1900 th = (struct tcphdr *)(ip + 1); 1901 } else { 1902 ip->ip_p = IPPROTO_UDP; 1903 udp = (struct udphdr *)(ip + 1); 1904 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1905 udp->uh_dport = sc->sc_port; 1906 ulen = (tlen - sizeof(struct ip)); 1907 th = (struct tcphdr *)(udp + 1); 1908 } 1909 } 1910 #endif /* INET */ 1911 th->th_sport = sc->sc_inc.inc_lport; 1912 th->th_dport = sc->sc_inc.inc_fport; 1913 1914 if (flags & TH_SYN) 1915 th->th_seq = htonl(sc->sc_iss); 1916 else 1917 th->th_seq = htonl(sc->sc_iss + 1); 1918 th->th_ack = htonl(sc->sc_irs + 1); 1919 th->th_off = sizeof(struct tcphdr) >> 2; 1920 th->th_win = htons(sc->sc_wnd); 1921 th->th_urp = 0; 1922 1923 flags = tcp_ecn_syncache_respond(flags, sc); 1924 tcp_set_flags(th, flags); 1925 1926 /* Tack on the TCP options. */ 1927 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1928 to.to_flags = 0; 1929 1930 if (flags & TH_SYN) { 1931 to.to_mss = mssopt; 1932 to.to_flags = TOF_MSS; 1933 if (sc->sc_flags & SCF_WINSCALE) { 1934 to.to_wscale = sc->sc_requested_r_scale; 1935 to.to_flags |= TOF_SCALE; 1936 } 1937 if (sc->sc_flags & SCF_SACK) 1938 to.to_flags |= TOF_SACKPERM; 1939 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1940 if (sc->sc_flags & SCF_SIGNATURE) 1941 to.to_flags |= TOF_SIGNATURE; 1942 #endif 1943 if (sc->sc_tfo_cookie) { 1944 to.to_flags |= TOF_FASTOPEN; 1945 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1946 to.to_tfo_cookie = sc->sc_tfo_cookie; 1947 /* don't send cookie again when retransmitting response */ 1948 sc->sc_tfo_cookie = NULL; 1949 } 1950 } 1951 if (sc->sc_flags & SCF_TIMESTAMP) { 1952 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1953 to.to_tsecr = sc->sc_tsreflect; 1954 to.to_flags |= TOF_TS; 1955 } 1956 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1957 1958 /* Adjust headers by option size. */ 1959 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1960 m->m_len += optlen; 1961 m->m_pkthdr.len += optlen; 1962 #ifdef INET6 1963 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1964 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1965 else 1966 #endif 1967 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1968 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1969 if (sc->sc_flags & SCF_SIGNATURE) { 1970 KASSERT(to.to_flags & TOF_SIGNATURE, 1971 ("tcp_addoptions() didn't set tcp_signature")); 1972 1973 /* NOTE: to.to_signature is inside of mbuf */ 1974 if (!TCPMD5_ENABLED() || 1975 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1976 m_freem(m); 1977 return (EACCES); 1978 } 1979 } 1980 #endif 1981 } else 1982 optlen = 0; 1983 1984 if (udp) { 1985 ulen += optlen; 1986 udp->uh_ulen = htons(ulen); 1987 } 1988 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1989 /* 1990 * If we have peer's SYN and it has a flowid, then let's assign it to 1991 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1992 * to SYN|ACK due to lack of inp here. 1993 */ 1994 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1995 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1996 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1997 } 1998 #ifdef INET6 1999 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2000 if (sc->sc_port) { 2001 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2002 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2003 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2004 IPPROTO_UDP, 0); 2005 th->th_sum = htons(0); 2006 } else { 2007 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2008 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2009 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2010 IPPROTO_TCP, 0); 2011 } 2012 ip6->ip6_hlim = sc->sc_ip_ttl; 2013 #ifdef TCP_OFFLOAD 2014 if (ADDED_BY_TOE(sc)) { 2015 struct toedev *tod = sc->sc_tod; 2016 2017 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2018 2019 return (error); 2020 } 2021 #endif 2022 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2023 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2024 } 2025 #endif 2026 #if defined(INET6) && defined(INET) 2027 else 2028 #endif 2029 #ifdef INET 2030 { 2031 if (sc->sc_port) { 2032 m->m_pkthdr.csum_flags = CSUM_UDP; 2033 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2034 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2035 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2036 th->th_sum = htons(0); 2037 } else { 2038 m->m_pkthdr.csum_flags = CSUM_TCP; 2039 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2040 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2041 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2042 } 2043 #ifdef TCP_OFFLOAD 2044 if (ADDED_BY_TOE(sc)) { 2045 struct toedev *tod = sc->sc_tod; 2046 2047 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2048 2049 return (error); 2050 } 2051 #endif 2052 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2053 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2054 } 2055 #endif 2056 return (error); 2057 } 2058 2059 static void 2060 syncache_send_challenge_ack(struct syncache *sc, struct mbuf *m) 2061 { 2062 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end, 2063 &sc->sc_challenge_ack_cnt)) { 2064 if (syncache_respond(sc, m, TH_ACK) == 0) { 2065 TCPSTAT_INC(tcps_sndacks); 2066 TCPSTAT_INC(tcps_sndtotal); 2067 } 2068 } 2069 } 2070 2071 /* 2072 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2073 * that exceed the capacity of the syncache by avoiding the storage of any 2074 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2075 * attacks where the attacker does not have access to our responses. 2076 * 2077 * Syncookies encode and include all necessary information about the 2078 * connection setup within the SYN|ACK that we send back. That way we 2079 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2080 * (if ever). Normally the syncache and syncookies are running in parallel 2081 * with the latter taking over when the former is exhausted. When matching 2082 * syncache entry is found the syncookie is ignored. 2083 * 2084 * The only reliable information persisting the 3WHS is our initial sequence 2085 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2086 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2087 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2088 * returns and signifies a legitimate connection if it matches the ACK. 2089 * 2090 * The available space of 32 bits to store the hash and to encode the SYN 2091 * option information is very tight and we should have at least 24 bits for 2092 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2093 * 2094 * SYN option information we have to encode to fully restore a connection: 2095 * MSS: is imporant to chose an optimal segment size to avoid IP level 2096 * fragmentation along the path. The common MSS values can be encoded 2097 * in a 3-bit table. Uncommon values are captured by the next lower value 2098 * in the table leading to a slight increase in packetization overhead. 2099 * WSCALE: is necessary to allow large windows to be used for high delay- 2100 * bandwidth product links. Not scaling the window when it was initially 2101 * negotiated is bad for performance as lack of scaling further decreases 2102 * the apparent available send window. We only need to encode the WSCALE 2103 * we received from the remote end. Our end can be recalculated at any 2104 * time. The common WSCALE values can be encoded in a 3-bit table. 2105 * Uncommon values are captured by the next lower value in the table 2106 * making us under-estimate the available window size halving our 2107 * theoretically possible maximum throughput for that connection. 2108 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2109 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2110 * that are included in all segments on a connection. We enable them when 2111 * the ACK has them. 2112 * 2113 * Security of syncookies and attack vectors: 2114 * 2115 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2116 * together with the gloabl secret to make it unique per connection attempt. 2117 * Thus any change of any of those parameters results in a different MAC output 2118 * in an unpredictable way unless a collision is encountered. 24 bits of the 2119 * MAC are embedded into the ISS. 2120 * 2121 * To prevent replay attacks two rotating global secrets are updated with a 2122 * new random value every 15 seconds. The life-time of a syncookie is thus 2123 * 15-30 seconds. 2124 * 2125 * Vector 1: Attacking the secret. This requires finding a weakness in the 2126 * MAC itself or the way it is used here. The attacker can do a chosen plain 2127 * text attack by varying and testing the all parameters under his control. 2128 * The strength depends on the size and randomness of the secret, and the 2129 * cryptographic security of the MAC function. Due to the constant updating 2130 * of the secret the attacker has at most 29.999 seconds to find the secret 2131 * and launch spoofed connections. After that he has to start all over again. 2132 * 2133 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2134 * size an average of 4,823 attempts are required for a 50% chance of success 2135 * to spoof a single syncookie (birthday collision paradox). However the 2136 * attacker is blind and doesn't know if one of his attempts succeeded unless 2137 * he has a side channel to interfere success from. A single connection setup 2138 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2139 * This many attempts are required for each one blind spoofed connection. For 2140 * every additional spoofed connection he has to launch another N attempts. 2141 * Thus for a sustained rate 100 spoofed connections per second approximately 2142 * 1,800,000 packets per second would have to be sent. 2143 * 2144 * NB: The MAC function should be fast so that it doesn't become a CPU 2145 * exhaustion attack vector itself. 2146 * 2147 * References: 2148 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2149 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2150 * http://cr.yp.to/syncookies.html (overview) 2151 * http://cr.yp.to/syncookies/archive (details) 2152 * 2153 * 2154 * Schematic construction of a syncookie enabled Initial Sequence Number: 2155 * 0 1 2 3 2156 * 12345678901234567890123456789012 2157 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2158 * 2159 * x 24 MAC (truncated) 2160 * W 3 Send Window Scale index 2161 * M 3 MSS index 2162 * S 1 SACK permitted 2163 * P 1 Odd/even secret 2164 */ 2165 2166 /* 2167 * Distribution and probability of certain MSS values. Those in between are 2168 * rounded down to the next lower one. 2169 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2170 * .2% .3% 5% 7% 7% 20% 15% 45% 2171 */ 2172 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2173 2174 /* 2175 * Distribution and probability of certain WSCALE values. We have to map the 2176 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2177 * bits based on prevalence of certain values. Where we don't have an exact 2178 * match for are rounded down to the next lower one letting us under-estimate 2179 * the true available window. At the moment this would happen only for the 2180 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2181 * and window size). The absence of the WSCALE option (no scaling in either 2182 * direction) is encoded with index zero. 2183 * [WSCALE values histograms, Allman, 2012] 2184 * X 10 10 35 5 6 14 10% by host 2185 * X 11 4 5 5 18 49 3% by connections 2186 */ 2187 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2188 2189 /* 2190 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2191 * and good cryptographic properties. 2192 */ 2193 static uint32_t 2194 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2195 uint8_t *secbits, uintptr_t secmod) 2196 { 2197 SIPHASH_CTX ctx; 2198 uint32_t siphash[2]; 2199 2200 SipHash24_Init(&ctx); 2201 SipHash_SetKey(&ctx, secbits); 2202 switch (inc->inc_flags & INC_ISIPV6) { 2203 #ifdef INET 2204 case 0: 2205 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2206 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2207 break; 2208 #endif 2209 #ifdef INET6 2210 case INC_ISIPV6: 2211 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2212 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2213 break; 2214 #endif 2215 } 2216 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2217 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2218 SipHash_Update(&ctx, &irs, sizeof(irs)); 2219 SipHash_Update(&ctx, &flags, sizeof(flags)); 2220 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2221 SipHash_Final((u_int8_t *)&siphash, &ctx); 2222 2223 return (siphash[0] ^ siphash[1]); 2224 } 2225 2226 static tcp_seq 2227 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2228 { 2229 u_int i, secbit, wscale; 2230 uint32_t iss, hash; 2231 uint8_t *secbits; 2232 union syncookie cookie; 2233 2234 cookie.cookie = 0; 2235 2236 /* Map our computed MSS into the 3-bit index. */ 2237 for (i = nitems(tcp_sc_msstab) - 1; 2238 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2239 i--) 2240 ; 2241 cookie.flags.mss_idx = i; 2242 2243 /* 2244 * Map the send window scale into the 3-bit index but only if 2245 * the wscale option was received. 2246 */ 2247 if (sc->sc_flags & SCF_WINSCALE) { 2248 wscale = sc->sc_requested_s_scale; 2249 for (i = nitems(tcp_sc_wstab) - 1; 2250 tcp_sc_wstab[i] > wscale && i > 0; 2251 i--) 2252 ; 2253 cookie.flags.wscale_idx = i; 2254 } 2255 2256 /* Can we do SACK? */ 2257 if (sc->sc_flags & SCF_SACK) 2258 cookie.flags.sack_ok = 1; 2259 2260 /* Which of the two secrets to use. */ 2261 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2262 cookie.flags.odd_even = secbit; 2263 2264 secbits = V_tcp_syncache.secret.key[secbit]; 2265 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2266 (uintptr_t)sch); 2267 2268 /* 2269 * Put the flags into the hash and XOR them to get better ISS number 2270 * variance. This doesn't enhance the cryptographic strength and is 2271 * done to prevent the 8 cookie bits from showing up directly on the 2272 * wire. 2273 */ 2274 iss = hash & ~0xff; 2275 iss |= cookie.cookie ^ (hash >> 24); 2276 2277 TCPSTAT_INC(tcps_sc_sendcookie); 2278 return (iss); 2279 } 2280 2281 static bool 2282 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch, 2283 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2284 struct socket *lso, uint16_t port) 2285 { 2286 uint32_t hash; 2287 uint8_t *secbits; 2288 tcp_seq ack, seq; 2289 int wnd; 2290 union syncookie cookie; 2291 2292 /* 2293 * Pull information out of SYN-ACK/ACK and revert sequence number 2294 * advances. 2295 */ 2296 ack = th->th_ack - 1; 2297 seq = th->th_seq - 1; 2298 2299 /* 2300 * Unpack the flags containing enough information to restore the 2301 * connection. 2302 */ 2303 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2304 2305 /* Which of the two secrets to use. */ 2306 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2307 2308 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2309 2310 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2311 if ((ack & ~0xff) != (hash & ~0xff)) 2312 return (false); 2313 2314 /* Fill in the syncache values. */ 2315 sc->sc_flags = 0; 2316 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2317 sc->sc_ipopts = NULL; 2318 2319 sc->sc_irs = seq; 2320 sc->sc_iss = ack; 2321 2322 switch (inc->inc_flags & INC_ISIPV6) { 2323 #ifdef INET 2324 case 0: 2325 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2326 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2327 break; 2328 #endif 2329 #ifdef INET6 2330 case INC_ISIPV6: 2331 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2332 sc->sc_flowlabel = 2333 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2334 break; 2335 #endif 2336 } 2337 2338 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2339 2340 /* Only use wscale if it was enabled in the orignal SYN. */ 2341 if (cookie.flags.wscale_idx > 0) { 2342 u_int wscale = 0; 2343 2344 /* Recompute the receive window scale that was sent earlier. */ 2345 while (wscale < TCP_MAX_WINSHIFT && 2346 (TCP_MAXWIN << wscale) < sb_max) 2347 wscale++; 2348 sc->sc_requested_r_scale = wscale; 2349 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2350 sc->sc_flags |= SCF_WINSCALE; 2351 } 2352 2353 wnd = lso->sol_sbrcv_hiwat; 2354 wnd = imax(wnd, 0); 2355 wnd = imin(wnd, TCP_MAXWIN); 2356 sc->sc_wnd = wnd; 2357 2358 if (cookie.flags.sack_ok) 2359 sc->sc_flags |= SCF_SACK; 2360 2361 if (to->to_flags & TOF_TS) { 2362 sc->sc_flags |= SCF_TIMESTAMP; 2363 sc->sc_tsreflect = to->to_tsval; 2364 sc->sc_tsoff = tcp_new_ts_offset(inc); 2365 } 2366 2367 if (to->to_flags & TOF_SIGNATURE) 2368 sc->sc_flags |= SCF_SIGNATURE; 2369 2370 sc->sc_rxmits = 0; 2371 2372 sc->sc_port = port; 2373 2374 return (true); 2375 } 2376 2377 #ifdef INVARIANTS 2378 static void 2379 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch, 2380 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2381 struct socket *lso, uint16_t port) 2382 { 2383 struct syncache scs; 2384 char *s; 2385 2386 bzero(&scs, sizeof(scs)); 2387 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) && 2388 (sc->sc_peer_mss != scs.sc_peer_mss || 2389 sc->sc_requested_r_scale != scs.sc_requested_r_scale || 2390 sc->sc_requested_s_scale != scs.sc_requested_s_scale || 2391 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) { 2392 2393 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2394 return; 2395 2396 if (sc->sc_peer_mss != scs.sc_peer_mss) 2397 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2398 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss); 2399 2400 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale) 2401 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2402 s, __func__, sc->sc_requested_r_scale, 2403 scs.sc_requested_r_scale); 2404 2405 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale) 2406 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2407 s, __func__, sc->sc_requested_s_scale, 2408 scs.sc_requested_s_scale); 2409 2410 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK)) 2411 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2412 2413 free(s, M_TCPLOG); 2414 } 2415 } 2416 #endif /* INVARIANTS */ 2417 2418 static void 2419 syncookie_reseed(void *arg) 2420 { 2421 struct tcp_syncache *sc = arg; 2422 uint8_t *secbits; 2423 int secbit; 2424 2425 /* 2426 * Reseeding the secret doesn't have to be protected by a lock. 2427 * It only must be ensured that the new random values are visible 2428 * to all CPUs in a SMP environment. The atomic with release 2429 * semantics ensures that. 2430 */ 2431 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2432 secbits = sc->secret.key[secbit]; 2433 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2434 atomic_add_rel_int(&sc->secret.oddeven, 1); 2435 2436 /* Reschedule ourself. */ 2437 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2438 } 2439 2440 /* 2441 * We have overflowed a bucket. Let's pause dealing with the syncache. 2442 * This function will increment the bucketoverflow statistics appropriately 2443 * (once per pause when pausing is enabled; otherwise, once per overflow). 2444 */ 2445 static void 2446 syncache_pause(struct in_conninfo *inc) 2447 { 2448 time_t delta; 2449 const char *s; 2450 2451 /* XXX: 2452 * 2. Add sysctl read here so we don't get the benefit of this 2453 * change without the new sysctl. 2454 */ 2455 2456 /* 2457 * Try an unlocked read. If we already know that another thread 2458 * has activated the feature, there is no need to proceed. 2459 */ 2460 if (V_tcp_syncache.paused) 2461 return; 2462 2463 /* Are cookied enabled? If not, we can't pause. */ 2464 if (!V_tcp_syncookies) { 2465 TCPSTAT_INC(tcps_sc_bucketoverflow); 2466 return; 2467 } 2468 2469 /* 2470 * We may be the first thread to find an overflow. Get the lock 2471 * and evaluate if we need to take action. 2472 */ 2473 mtx_lock(&V_tcp_syncache.pause_mtx); 2474 if (V_tcp_syncache.paused) { 2475 mtx_unlock(&V_tcp_syncache.pause_mtx); 2476 return; 2477 } 2478 2479 /* Activate protection. */ 2480 V_tcp_syncache.paused = true; 2481 TCPSTAT_INC(tcps_sc_bucketoverflow); 2482 2483 /* 2484 * Determine the last backoff time. If we are seeing a re-newed 2485 * attack within that same time after last reactivating the syncache, 2486 * consider it an extension of the same attack. 2487 */ 2488 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2489 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2490 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2491 delta <<= 1; 2492 V_tcp_syncache.pause_backoff++; 2493 } 2494 } else { 2495 delta = TCP_SYNCACHE_PAUSE_TIME; 2496 V_tcp_syncache.pause_backoff = 0; 2497 } 2498 2499 /* Log a warning, including IP addresses, if able. */ 2500 if (inc != NULL) 2501 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2502 else 2503 s = (const char *)NULL; 2504 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2505 "the next %lld seconds%s%s%s\n", (long long)delta, 2506 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2507 (s != NULL) ? ")" : ""); 2508 free(__DECONST(void *, s), M_TCPLOG); 2509 2510 /* Use the calculated delta to set a new pause time. */ 2511 V_tcp_syncache.pause_until = time_uptime + delta; 2512 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2513 &V_tcp_syncache); 2514 mtx_unlock(&V_tcp_syncache.pause_mtx); 2515 } 2516 2517 /* Evaluate whether we need to unpause. */ 2518 static void 2519 syncache_unpause(void *arg) 2520 { 2521 struct tcp_syncache *sc; 2522 time_t delta; 2523 2524 sc = arg; 2525 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2526 callout_deactivate(&sc->pause_co); 2527 2528 /* 2529 * Check to make sure we are not running early. If the pause 2530 * time has expired, then deactivate the protection. 2531 */ 2532 if ((delta = sc->pause_until - time_uptime) > 0) 2533 callout_schedule(&sc->pause_co, delta * hz); 2534 else 2535 sc->paused = false; 2536 } 2537 2538 /* 2539 * Exports the syncache entries to userland so that netstat can display 2540 * them alongside the other sockets. This function is intended to be 2541 * called only from tcp_pcblist. 2542 * 2543 * Due to concurrency on an active system, the number of pcbs exported 2544 * may have no relation to max_pcbs. max_pcbs merely indicates the 2545 * amount of space the caller allocated for this function to use. 2546 */ 2547 int 2548 syncache_pcblist(struct sysctl_req *req) 2549 { 2550 struct xtcpcb xt; 2551 struct syncache *sc; 2552 struct syncache_head *sch; 2553 int error, i; 2554 2555 bzero(&xt, sizeof(xt)); 2556 xt.xt_len = sizeof(xt); 2557 xt.t_state = TCPS_SYN_RECEIVED; 2558 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2559 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2560 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2561 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2562 2563 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2564 sch = &V_tcp_syncache.hashbase[i]; 2565 SCH_LOCK(sch); 2566 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2567 if (sc->sc_cred != NULL && 2568 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2569 continue; 2570 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2571 xt.xt_inp.inp_vflag = INP_IPV6; 2572 else 2573 xt.xt_inp.inp_vflag = INP_IPV4; 2574 xt.xt_encaps_port = sc->sc_port; 2575 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2576 sizeof (struct in_conninfo)); 2577 error = SYSCTL_OUT(req, &xt, sizeof xt); 2578 if (error) { 2579 SCH_UNLOCK(sch); 2580 return (0); 2581 } 2582 } 2583 SCH_UNLOCK(sch); 2584 } 2585 2586 return (0); 2587 } 2588