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 "opt_inet.h" 36 #include "opt_inet6.h" 37 #include "opt_ipsec.h" 38 39 #include <sys/param.h> 40 #include <sys/systm.h> 41 #include <sys/hash.h> 42 #include <sys/refcount.h> 43 #include <sys/kernel.h> 44 #include <sys/sysctl.h> 45 #include <sys/limits.h> 46 #include <sys/lock.h> 47 #include <sys/mutex.h> 48 #include <sys/malloc.h> 49 #include <sys/mbuf.h> 50 #include <sys/proc.h> /* for proc0 declaration */ 51 #include <sys/random.h> 52 #include <sys/socket.h> 53 #include <sys/socketvar.h> 54 #include <sys/syslog.h> 55 #include <sys/ucred.h> 56 57 #include <sys/md5.h> 58 #include <crypto/siphash/siphash.h> 59 60 #include <vm/uma.h> 61 62 #include <net/if.h> 63 #include <net/if_var.h> 64 #include <net/route.h> 65 #include <net/vnet.h> 66 67 #include <netinet/in.h> 68 #include <netinet/in_kdtrace.h> 69 #include <netinet/in_systm.h> 70 #include <netinet/ip.h> 71 #include <netinet/in_var.h> 72 #include <netinet/in_pcb.h> 73 #include <netinet/in_rss.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 #include <netinet6/in6_rss.h> 83 #endif 84 #include <netinet/tcp.h> 85 #include <netinet/tcp_fastopen.h> 86 #include <netinet/tcp_fsm.h> 87 #include <netinet/tcp_seq.h> 88 #include <netinet/tcp_timer.h> 89 #include <netinet/tcp_var.h> 90 #include <netinet/tcp_syncache.h> 91 #include <netinet/tcp_ecn.h> 92 #ifdef TCP_BLACKBOX 93 #include <netinet/tcp_log_buf.h> 94 #endif 95 #ifdef TCP_OFFLOAD 96 #include <netinet/toecore.h> 97 #endif 98 #include <netinet/udp.h> 99 100 #include <netipsec/ipsec_support.h> 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 VNET_DEFINE_STATIC(bool, tcp_syncookies) = true; 107 #define V_tcp_syncookies VNET(tcp_syncookies) 108 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 109 &VNET_NAME(tcp_syncookies), 0, 110 "Use TCP SYN cookies if the syncache overflows"); 111 112 VNET_DEFINE_STATIC(bool, tcp_syncookiesonly) = false; 113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 114 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 115 &VNET_NAME(tcp_syncookiesonly), 0, 116 "Use only TCP SYN cookies"); 117 118 #ifdef TCP_OFFLOAD 119 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 120 #endif 121 122 static void syncache_drop(struct syncache *, struct syncache_head *); 123 static void syncache_free(struct syncache *); 124 static void syncache_insert(struct syncache *, struct syncache_head *); 125 static int syncache_respond(struct syncache *, int); 126 static void syncache_send_challenge_ack(struct syncache *); 127 static struct socket *syncache_socket(struct syncache *, struct socket *, 128 struct mbuf *m); 129 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 130 int docallout); 131 static void syncache_timer(void *); 132 133 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 134 uint8_t *, uintptr_t); 135 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 136 static bool syncookie_expand(struct in_conninfo *, 137 const struct syncache_head *, struct syncache *, 138 struct tcphdr *, struct tcpopt *, struct socket *, 139 uint16_t); 140 static void syncache_pause(struct in_conninfo *); 141 static void syncache_unpause(void *); 142 static void syncookie_reseed(void *); 143 #ifdef INVARIANTS 144 static void syncookie_cmp(struct in_conninfo *, 145 const struct syncache_head *, struct syncache *, 146 struct tcphdr *, struct tcpopt *, struct socket *, 147 uint16_t); 148 #endif 149 150 /* 151 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 152 * 3 retransmits corresponds to a timeout with default values of 153 * tcp_rexmit_initial * ( 1 + 154 * tcp_backoff[1] + 155 * tcp_backoff[2] + 156 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 157 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 158 * the odds are that the user has given up attempting to connect by then. 159 */ 160 #define SYNCACHE_MAXREXMTS 3 161 162 /* Arbitrary values */ 163 #define TCP_SYNCACHE_HASHSIZE 512 164 #define TCP_SYNCACHE_BUCKETLIMIT 30 165 166 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 167 #define V_tcp_syncache VNET(tcp_syncache) 168 169 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 170 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 171 "TCP SYN cache"); 172 173 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 174 &VNET_NAME(tcp_syncache.bucket_limit), 0, 175 "Per-bucket hash limit for syncache"); 176 177 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 178 &VNET_NAME(tcp_syncache.cache_limit), 0, 179 "Overall entry limit for syncache"); 180 181 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 182 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 183 184 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 185 &VNET_NAME(tcp_syncache.hashsize), 0, 186 "Size of TCP syncache hashtable"); 187 188 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 189 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 190 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 191 "and mac(4) checks"); 192 193 static int 194 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 195 { 196 int error; 197 u_int new; 198 199 new = V_tcp_syncache.rexmt_limit; 200 error = sysctl_handle_int(oidp, &new, 0, req); 201 if ((error == 0) && (req->newptr != NULL)) { 202 if (new > TCP_MAXRXTSHIFT) 203 error = EINVAL; 204 else 205 V_tcp_syncache.rexmt_limit = new; 206 } 207 return (error); 208 } 209 210 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 211 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 212 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 213 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU", 214 "Limit on SYN/ACK retransmissions"); 215 216 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 217 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 218 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 219 "Send reset on socket allocation failure"); 220 221 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 222 223 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 224 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 225 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 226 227 /* 228 * Requires the syncache entry to be already removed from the bucket list. 229 */ 230 static void 231 syncache_free(struct syncache *sc) 232 { 233 234 if (sc->sc_ipopts) 235 (void)m_free(sc->sc_ipopts); 236 if (sc->sc_cred) 237 crfree(sc->sc_cred); 238 #ifdef MAC 239 mac_syncache_destroy(&sc->sc_label); 240 #endif 241 242 uma_zfree(V_tcp_syncache.zone, sc); 243 } 244 245 void 246 syncache_init(void) 247 { 248 int i; 249 250 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 251 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 252 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 253 V_tcp_syncache.hash_secret = arc4random(); 254 255 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 256 &V_tcp_syncache.hashsize); 257 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 258 &V_tcp_syncache.bucket_limit); 259 if (!powerof2(V_tcp_syncache.hashsize) || 260 V_tcp_syncache.hashsize == 0) { 261 printf("WARNING: syncache hash size is not a power of 2.\n"); 262 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 263 } 264 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 265 266 /* Set limits. */ 267 V_tcp_syncache.cache_limit = 268 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 269 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 270 &V_tcp_syncache.cache_limit); 271 272 /* Allocate the hash table. */ 273 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 274 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 275 276 #ifdef VIMAGE 277 V_tcp_syncache.vnet = curvnet; 278 #endif 279 280 /* Initialize the hash buckets. */ 281 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 282 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 283 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 284 NULL, MTX_DEF); 285 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 286 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 287 V_tcp_syncache.hashbase[i].sch_length = 0; 288 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 289 V_tcp_syncache.hashbase[i].sch_last_overflow = 290 -(SYNCOOKIE_LIFETIME + 1); 291 } 292 293 /* Create the syncache entry zone. */ 294 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 295 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 296 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 297 V_tcp_syncache.cache_limit); 298 299 /* Start the SYN cookie reseeder callout. */ 300 callout_init(&V_tcp_syncache.secret.reseed, 1); 301 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 302 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 303 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 304 syncookie_reseed, &V_tcp_syncache); 305 306 /* Initialize the pause machinery. */ 307 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 308 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 309 0); 310 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 311 V_tcp_syncache.pause_backoff = 0; 312 V_tcp_syncache.paused = false; 313 } 314 315 #ifdef VIMAGE 316 void 317 syncache_destroy(void) 318 { 319 struct syncache_head *sch; 320 struct syncache *sc, *nsc; 321 int i; 322 323 /* 324 * Stop the re-seed timer before freeing resources. No need to 325 * possibly schedule it another time. 326 */ 327 callout_drain(&V_tcp_syncache.secret.reseed); 328 329 /* Stop the SYN cache pause callout. */ 330 mtx_lock(&V_tcp_syncache.pause_mtx); 331 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 332 mtx_unlock(&V_tcp_syncache.pause_mtx); 333 callout_drain(&V_tcp_syncache.pause_co); 334 } else 335 mtx_unlock(&V_tcp_syncache.pause_mtx); 336 337 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 338 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 339 sch = &V_tcp_syncache.hashbase[i]; 340 callout_drain(&sch->sch_timer); 341 342 SCH_LOCK(sch); 343 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 344 syncache_drop(sc, sch); 345 SCH_UNLOCK(sch); 346 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 347 ("%s: sch->sch_bucket not empty", __func__)); 348 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 349 __func__, sch->sch_length)); 350 mtx_destroy(&sch->sch_mtx); 351 } 352 353 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 354 ("%s: cache_count not 0", __func__)); 355 356 /* Free the allocated global resources. */ 357 uma_zdestroy(V_tcp_syncache.zone); 358 free(V_tcp_syncache.hashbase, M_SYNCACHE); 359 mtx_destroy(&V_tcp_syncache.pause_mtx); 360 } 361 #endif 362 363 /* 364 * Inserts a syncache entry into the specified bucket row. 365 * Locks and unlocks the syncache_head autonomously. 366 */ 367 static void 368 syncache_insert(struct syncache *sc, struct syncache_head *sch) 369 { 370 struct syncache *sc2; 371 372 SCH_LOCK(sch); 373 374 /* 375 * Make sure that we don't overflow the per-bucket limit. 376 * If the bucket is full, toss the oldest element. 377 */ 378 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 379 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 380 ("sch->sch_length incorrect")); 381 syncache_pause(&sc->sc_inc); 382 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 383 sch->sch_last_overflow = time_uptime; 384 syncache_drop(sc2, sch); 385 } 386 387 /* Put it into the bucket. */ 388 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 389 sch->sch_length++; 390 391 #ifdef TCP_OFFLOAD 392 if (ADDED_BY_TOE(sc)) { 393 struct toedev *tod = sc->sc_tod; 394 395 tod->tod_syncache_added(tod, sc->sc_todctx); 396 } 397 #endif 398 399 /* Reinitialize the bucket row's timer. */ 400 if (sch->sch_length == 1) 401 sch->sch_nextc = ticks + INT_MAX; 402 syncache_timeout(sc, sch, 1); 403 404 SCH_UNLOCK(sch); 405 406 TCPSTATES_INC(TCPS_SYN_RECEIVED); 407 TCPSTAT_INC(tcps_sc_added); 408 } 409 410 /* 411 * Remove and free entry from syncache bucket row. 412 * Expects locked syncache head. 413 */ 414 static void 415 syncache_drop(struct syncache *sc, struct syncache_head *sch) 416 { 417 418 SCH_LOCK_ASSERT(sch); 419 420 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 421 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 422 sch->sch_length--; 423 424 #ifdef TCP_OFFLOAD 425 if (ADDED_BY_TOE(sc)) { 426 struct toedev *tod = sc->sc_tod; 427 428 tod->tod_syncache_removed(tod, sc->sc_todctx); 429 } 430 #endif 431 432 syncache_free(sc); 433 } 434 435 /* 436 * Engage/reengage time on bucket row. 437 */ 438 static void 439 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 440 { 441 int rexmt; 442 443 if (sc->sc_rxmits == 0) 444 rexmt = tcp_rexmit_initial; 445 else 446 TCPT_RANGESET(rexmt, 447 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 448 tcp_rexmit_min, tcp_rexmit_max); 449 sc->sc_rxttime = ticks + rexmt; 450 sc->sc_rxmits++; 451 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 452 sch->sch_nextc = sc->sc_rxttime; 453 if (docallout) 454 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 455 syncache_timer, (void *)sch); 456 } 457 } 458 459 /* 460 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 461 * If we have retransmitted an entry the maximum number of times, expire it. 462 * One separate timer for each bucket row. 463 */ 464 static void 465 syncache_timer(void *xsch) 466 { 467 struct syncache_head *sch = (struct syncache_head *)xsch; 468 struct syncache *sc, *nsc; 469 struct epoch_tracker et; 470 int tick = ticks; 471 char *s; 472 bool paused; 473 474 CURVNET_SET(sch->sch_sc->vnet); 475 476 /* NB: syncache_head has already been locked by the callout. */ 477 SCH_LOCK_ASSERT(sch); 478 479 /* 480 * In the following cycle we may remove some entries and/or 481 * advance some timeouts, so re-initialize the bucket timer. 482 */ 483 sch->sch_nextc = tick + INT_MAX; 484 485 /* 486 * If we have paused processing, unconditionally remove 487 * all syncache entries. 488 */ 489 mtx_lock(&V_tcp_syncache.pause_mtx); 490 paused = V_tcp_syncache.paused; 491 mtx_unlock(&V_tcp_syncache.pause_mtx); 492 493 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 494 if (paused) { 495 syncache_drop(sc, sch); 496 continue; 497 } 498 /* 499 * We do not check if the listen socket still exists 500 * and accept the case where the listen socket may be 501 * gone by the time we resend the SYN/ACK. We do 502 * not expect this to happens often. If it does, 503 * then the RST will be sent by the time the remote 504 * host does the SYN/ACK->ACK. 505 */ 506 if (TSTMP_GT(sc->sc_rxttime, tick)) { 507 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 508 sch->sch_nextc = sc->sc_rxttime; 509 continue; 510 } 511 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 512 sc->sc_flags &= ~SCF_ECN_MASK; 513 } 514 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 515 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 516 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 517 "giving up and removing syncache entry\n", 518 s, __func__); 519 free(s, M_TCPLOG); 520 } 521 syncache_drop(sc, sch); 522 TCPSTAT_INC(tcps_sc_stale); 523 continue; 524 } 525 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 526 log(LOG_DEBUG, "%s; %s: Response timeout, " 527 "retransmitting (%u) SYN|ACK\n", 528 s, __func__, sc->sc_rxmits); 529 free(s, M_TCPLOG); 530 } 531 532 NET_EPOCH_ENTER(et); 533 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) { 534 syncache_timeout(sc, sch, 0); 535 TCPSTAT_INC(tcps_sndacks); 536 TCPSTAT_INC(tcps_sndtotal); 537 TCPSTAT_INC(tcps_sc_retransmitted); 538 } else { 539 /* 540 * Most likely we are memory constrained, so free 541 * resources. 542 */ 543 syncache_drop(sc, sch); 544 TCPSTAT_INC(tcps_sc_dropped); 545 } 546 NET_EPOCH_EXIT(et); 547 } 548 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 549 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 550 syncache_timer, (void *)(sch)); 551 CURVNET_RESTORE(); 552 } 553 554 /* 555 * Returns true if the system is only using cookies at the moment. 556 * This could be due to a sysadmin decision to only use cookies, or it 557 * could be due to the system detecting an attack. 558 */ 559 static inline bool 560 syncache_cookiesonly(void) 561 { 562 return ((V_tcp_syncookies && V_tcp_syncache.paused) || 563 V_tcp_syncookiesonly); 564 } 565 566 /* 567 * Find the hash bucket for the given connection. 568 */ 569 static struct syncache_head * 570 syncache_hashbucket(struct in_conninfo *inc) 571 { 572 uint32_t hash; 573 574 /* 575 * The hash is built on foreign port + local port + foreign address. 576 * We rely on the fact that struct in_conninfo starts with 16 bits 577 * of foreign port, then 16 bits of local port then followed by 128 578 * bits of foreign address. In case of IPv4 address, the first 3 579 * 32-bit words of the address always are zeroes. 580 */ 581 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 582 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 583 584 return (&V_tcp_syncache.hashbase[hash]); 585 } 586 587 /* 588 * Find an entry in the syncache. 589 * Returns always with locked syncache_head plus a matching entry or NULL. 590 */ 591 static struct syncache * 592 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 593 { 594 struct syncache *sc; 595 struct syncache_head *sch; 596 597 *schp = sch = syncache_hashbucket(inc); 598 SCH_LOCK(sch); 599 600 /* Circle through bucket row to find matching entry. */ 601 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 602 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 603 sizeof(struct in_endpoints)) == 0) 604 break; 605 606 return (sc); /* Always returns with locked sch. */ 607 } 608 609 /* 610 * This function is called when we get a RST for a 611 * non-existent connection, so that we can see if the 612 * connection is in the syn cache. If it is, zap it. 613 * If required send a challenge ACK. 614 */ 615 void 616 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, 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); 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 * Creation of a socket via solisten_clone() bypasses call to pr_attach. 776 * That's why there is some pasted code from soattach() and from 777 * tcp_usr_attach() here. This should improve once TCP is PR_SOCKBUF. 778 */ 779 if ((so = solisten_clone(lso)) == NULL) 780 goto allocfail; 781 mtx_init(&so->so_snd_mtx, "so_snd", NULL, MTX_DEF); 782 mtx_init(&so->so_rcv_mtx, "so_rcv", NULL, MTX_DEF); 783 so->so_snd.sb_mtx = &so->so_snd_mtx; 784 so->so_rcv.sb_mtx = &so->so_rcv_mtx; 785 error = soreserve(so, lso->sol_sbsnd_hiwat, lso->sol_sbrcv_hiwat); 786 if (error) { 787 sodealloc(so); 788 goto allocfail; 789 } 790 #ifdef MAC 791 mac_socketpeer_set_from_mbuf(m, so); 792 #endif 793 error = in_pcballoc(so, &V_tcbinfo); 794 if (error) { 795 sodealloc(so); 796 goto allocfail; 797 } 798 inp = sotoinpcb(so); 799 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) { 800 in_pcbfree(inp); 801 sodealloc(so); 802 goto allocfail; 803 } 804 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 805 #ifdef INET6 806 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 807 inp->inp_vflag &= ~INP_IPV4; 808 inp->inp_vflag |= INP_IPV6; 809 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 810 } else { 811 inp->inp_vflag &= ~INP_IPV6; 812 inp->inp_vflag |= INP_IPV4; 813 #endif 814 inp->inp_ip_ttl = sc->sc_ip_ttl; 815 inp->inp_ip_tos = sc->sc_ip_tos; 816 inp->inp_laddr = sc->sc_inc.inc_laddr; 817 #ifdef INET6 818 } 819 #endif 820 inp->inp_lport = sc->sc_inc.inc_lport; 821 #ifdef INET6 822 if (inp->inp_vflag & INP_IPV6PROTO) { 823 struct inpcb *oinp = sotoinpcb(lso); 824 825 /* 826 * Inherit socket options from the listening socket. 827 * Note that in6p_inputopts are not (and should not be) 828 * copied, since it stores previously received options and is 829 * used to detect if each new option is different than the 830 * previous one and hence should be passed to a user. 831 * If we copied in6p_inputopts, a user would not be able to 832 * receive options just after calling the accept system call. 833 */ 834 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 835 if (oinp->in6p_outputopts) 836 inp->in6p_outputopts = 837 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 838 inp->in6p_hops = oinp->in6p_hops; 839 } 840 841 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 842 struct sockaddr_in6 sin6; 843 844 sin6.sin6_family = AF_INET6; 845 sin6.sin6_len = sizeof(sin6); 846 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 847 sin6.sin6_port = sc->sc_inc.inc_fport; 848 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 849 INP_HASH_WLOCK(&V_tcbinfo); 850 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 851 INP_HASH_WUNLOCK(&V_tcbinfo); 852 if (error != 0) 853 goto abort; 854 /* Override flowlabel from in6_pcbconnect. */ 855 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 856 inp->inp_flow |= sc->sc_flowlabel; 857 } 858 #endif /* INET6 */ 859 #if defined(INET) && defined(INET6) 860 else 861 #endif 862 #ifdef INET 863 { 864 struct sockaddr_in sin; 865 866 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 867 868 if (inp->inp_options == NULL) { 869 inp->inp_options = sc->sc_ipopts; 870 sc->sc_ipopts = NULL; 871 } 872 873 sin.sin_family = AF_INET; 874 sin.sin_len = sizeof(sin); 875 sin.sin_addr = sc->sc_inc.inc_faddr; 876 sin.sin_port = sc->sc_inc.inc_fport; 877 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 878 INP_HASH_WLOCK(&V_tcbinfo); 879 error = in_pcbconnect(inp, &sin, thread0.td_ucred); 880 INP_HASH_WUNLOCK(&V_tcbinfo); 881 if (error != 0) 882 goto abort; 883 } 884 #endif /* INET */ 885 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 886 /* Copy old policy into new socket's. */ 887 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 888 printf("syncache_socket: could not copy policy\n"); 889 #endif 890 if (sc->sc_flowtype != M_HASHTYPE_NONE) { 891 inp->inp_flowid = sc->sc_flowid; 892 inp->inp_flowtype = sc->sc_flowtype; 893 } else { 894 /* assign flowid by software RSS hash */ 895 #ifdef INET6 896 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 897 rss_proto_software_hash_v6(&inp->in6p_faddr, 898 &inp->in6p_laddr, 899 inp->inp_fport, 900 inp->inp_lport, 901 IPPROTO_TCP, 902 &inp->inp_flowid, 903 &inp->inp_flowtype); 904 } else 905 #endif /* INET6 */ 906 { 907 #ifdef INET 908 rss_proto_software_hash_v4(inp->inp_faddr, 909 inp->inp_laddr, 910 inp->inp_fport, 911 inp->inp_lport, 912 IPPROTO_TCP, 913 &inp->inp_flowid, 914 &inp->inp_flowtype); 915 #endif /* INET */ 916 } 917 } 918 #ifdef NUMA 919 inp->inp_numa_domain = sc->sc_numa_domain; 920 #endif 921 922 tp->t_state = TCPS_SYN_RECEIVED; 923 tp->iss = sc->sc_iss; 924 tp->irs = sc->sc_irs; 925 tp->t_port = sc->sc_port; 926 tcp_rcvseqinit(tp); 927 tcp_sendseqinit(tp); 928 tp->snd_wl1 = sc->sc_irs; 929 tp->snd_max = tp->iss + 1; 930 tp->snd_nxt = tp->iss + 1; 931 tp->rcv_up = sc->sc_irs + 1; 932 tp->rcv_wnd = sc->sc_wnd; 933 tp->rcv_adv += tp->rcv_wnd; 934 tp->last_ack_sent = tp->rcv_nxt; 935 936 tp->t_flags = sototcpcb(lso)->t_flags & 937 (TF_LRD|TF_NOPUSH|TF_NODELAY); 938 if (sc->sc_flags & SCF_NOOPT) 939 tp->t_flags |= TF_NOOPT; 940 else { 941 if (sc->sc_flags & SCF_WINSCALE) { 942 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 943 tp->snd_scale = sc->sc_requested_s_scale; 944 tp->request_r_scale = sc->sc_requested_r_scale; 945 } 946 if (sc->sc_flags & SCF_TIMESTAMP) { 947 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 948 tp->ts_recent = sc->sc_tsreflect; 949 tp->ts_recent_age = tcp_ts_getticks(); 950 tp->ts_offset = sc->sc_tsoff; 951 } 952 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 953 if (sc->sc_flags & SCF_SIGNATURE) 954 tp->t_flags |= TF_SIGNATURE; 955 #endif 956 if (sc->sc_flags & SCF_SACK) 957 tp->t_flags |= TF_SACK_PERMIT; 958 } 959 960 tcp_ecn_syncache_socket(tp, sc); 961 962 /* 963 * Set up MSS and get cached values from tcp_hostcache. 964 * This might overwrite some of the defaults we just set. 965 */ 966 tcp_mss(tp, sc->sc_peer_mss); 967 968 /* 969 * If the SYN,ACK was retransmitted, indicate that CWND to be 970 * limited to one segment in cc_conn_init(). 971 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 972 */ 973 if (sc->sc_rxmits > 1) 974 tp->snd_cwnd = 1; 975 976 /* Copy over the challenge ACK state. */ 977 tp->t_challenge_ack_end = sc->sc_challenge_ack_end; 978 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt; 979 980 #ifdef TCP_OFFLOAD 981 /* 982 * Allow a TOE driver to install its hooks. Note that we hold the 983 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 984 * new connection before the TOE driver has done its thing. 985 */ 986 if (ADDED_BY_TOE(sc)) { 987 struct toedev *tod = sc->sc_tod; 988 989 tod->tod_offload_socket(tod, sc->sc_todctx, so); 990 } 991 #endif 992 #ifdef TCP_BLACKBOX 993 /* 994 * Inherit the log state from the listening socket, if 995 * - the log state of the listening socket is not off and 996 * - the listening socket was not auto selected from all sessions and 997 * - a log id is not set on the listening socket. 998 * This avoids inheriting a log state which was automatically set. 999 */ 1000 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 1001 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 1002 (sototcpcb(lso)->t_lib == NULL)) { 1003 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 1004 } 1005 #endif 1006 /* 1007 * Copy and activate timers. 1008 */ 1009 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 1010 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1011 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1012 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1013 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1014 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1015 1016 TCPSTAT_INC(tcps_accepts); 1017 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1018 1019 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1020 tp->t_flags |= TF_SONOTCONN; 1021 /* Can we inherit anything from the listener? */ 1022 if (tp->t_fb->tfb_inherit != NULL) { 1023 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 1024 } 1025 return (so); 1026 1027 allocfail: 1028 /* 1029 * Drop the connection; we will either send a RST or have the peer 1030 * retransmit its SYN again after its RTO and try again. 1031 */ 1032 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1033 log(LOG_DEBUG, "%s; %s: Socket create failed " 1034 "due to limits or memory shortage\n", 1035 s, __func__); 1036 free(s, M_TCPLOG); 1037 } 1038 TCPSTAT_INC(tcps_listendrop); 1039 return (NULL); 1040 1041 abort: 1042 tcp_discardcb(tp); 1043 in_pcbfree(inp); 1044 sodealloc(so); 1045 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1046 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1047 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1048 error); 1049 free(s, M_TCPLOG); 1050 } 1051 TCPSTAT_INC(tcps_listendrop); 1052 return (NULL); 1053 } 1054 1055 /* 1056 * This function gets called when we receive an ACK for a 1057 * socket in the LISTEN state. We look up the connection 1058 * in the syncache, and if its there, we pull it out of 1059 * the cache and turn it into a full-blown connection in 1060 * the SYN-RECEIVED state. 1061 * 1062 * On syncache_socket() success the newly created socket 1063 * has its underlying inp locked. 1064 * 1065 * *lsop is updated, if and only if 1 is returned. 1066 */ 1067 int 1068 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1069 struct socket **lsop, struct mbuf *m, uint16_t port) 1070 { 1071 struct syncache *sc; 1072 struct syncache_head *sch; 1073 struct syncache scs; 1074 char *s; 1075 bool locked; 1076 1077 NET_EPOCH_ASSERT(); 1078 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1079 ("%s: can handle only ACK", __func__)); 1080 1081 if (syncache_cookiesonly()) { 1082 sc = NULL; 1083 sch = syncache_hashbucket(inc); 1084 locked = false; 1085 } else { 1086 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1087 locked = true; 1088 SCH_LOCK_ASSERT(sch); 1089 } 1090 1091 #ifdef INVARIANTS 1092 /* 1093 * Test code for syncookies comparing the syncache stored 1094 * values with the reconstructed values from the cookie. 1095 */ 1096 if (sc != NULL) 1097 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1098 #endif 1099 1100 if (sc == NULL) { 1101 if (locked) { 1102 /* 1103 * The syncache is currently in use (neither disabled, 1104 * nor paused), but no entry was found. 1105 */ 1106 if (!V_tcp_syncookies) { 1107 /* 1108 * Since no syncookies are used in case of 1109 * a bucket overflow, don't even check for 1110 * a valid syncookie. 1111 */ 1112 SCH_UNLOCK(sch); 1113 TCPSTAT_INC(tcps_sc_spurcookie); 1114 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1115 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1116 "segment rejected " 1117 "(syncookies disabled)\n", 1118 s, __func__); 1119 free(s, M_TCPLOG); 1120 } 1121 return (0); 1122 } 1123 if (sch->sch_last_overflow < 1124 time_uptime - SYNCOOKIE_LIFETIME) { 1125 /* 1126 * Since the bucket did not overflow recently, 1127 * don't even check for a valid syncookie. 1128 */ 1129 SCH_UNLOCK(sch); 1130 TCPSTAT_INC(tcps_sc_spurcookie); 1131 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1132 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1133 "segment rejected " 1134 "(no syncache entry)\n", 1135 s, __func__); 1136 free(s, M_TCPLOG); 1137 } 1138 return (0); 1139 } 1140 SCH_UNLOCK(sch); 1141 } 1142 bzero(&scs, sizeof(scs)); 1143 /* 1144 * Now check, if the syncookie is valid. If it is, create an on 1145 * stack syncache entry. 1146 */ 1147 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) { 1148 sc = &scs; 1149 TCPSTAT_INC(tcps_sc_recvcookie); 1150 } else { 1151 TCPSTAT_INC(tcps_sc_failcookie); 1152 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1153 log(LOG_DEBUG, "%s; %s: Segment failed " 1154 "SYNCOOKIE authentication, segment rejected " 1155 "(probably spoofed)\n", s, __func__); 1156 free(s, M_TCPLOG); 1157 } 1158 return (0); 1159 } 1160 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1161 /* If received ACK has MD5 signature, check it. */ 1162 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1163 (!TCPMD5_ENABLED() || 1164 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1165 /* Drop the ACK. */ 1166 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1167 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1168 "MD5 signature doesn't match.\n", 1169 s, __func__); 1170 free(s, M_TCPLOG); 1171 } 1172 TCPSTAT_INC(tcps_sig_err_sigopt); 1173 return (-1); /* Do not send RST */ 1174 } 1175 #endif /* TCP_SIGNATURE */ 1176 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 1177 sc->sc_flowid = m->m_pkthdr.flowid; 1178 sc->sc_flowtype = M_HASHTYPE_GET(m); 1179 } 1180 #ifdef NUMA 1181 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM; 1182 #endif 1183 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1184 } else { 1185 if (sc->sc_port != port) { 1186 SCH_UNLOCK(sch); 1187 return (0); 1188 } 1189 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1190 /* 1191 * If listening socket requested TCP digests, check that 1192 * received ACK has signature and it is correct. 1193 * If not, drop the ACK and leave sc entry in the cache, 1194 * because SYN was received with correct signature. 1195 */ 1196 if (sc->sc_flags & SCF_SIGNATURE) { 1197 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1198 /* No signature */ 1199 TCPSTAT_INC(tcps_sig_err_nosigopt); 1200 SCH_UNLOCK(sch); 1201 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1202 log(LOG_DEBUG, "%s; %s: Segment " 1203 "rejected, MD5 signature wasn't " 1204 "provided.\n", s, __func__); 1205 free(s, M_TCPLOG); 1206 } 1207 return (-1); /* Do not send RST */ 1208 } 1209 if (!TCPMD5_ENABLED() || 1210 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1211 /* Doesn't match or no SA */ 1212 SCH_UNLOCK(sch); 1213 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1214 log(LOG_DEBUG, "%s; %s: Segment " 1215 "rejected, MD5 signature doesn't " 1216 "match.\n", s, __func__); 1217 free(s, M_TCPLOG); 1218 } 1219 return (-1); /* Do not send RST */ 1220 } 1221 } 1222 #endif /* TCP_SIGNATURE */ 1223 1224 /* 1225 * RFC 7323 PAWS: If we have a timestamp on this segment and 1226 * it's less than ts_recent, drop it. 1227 * XXXMT: RFC 7323 also requires to send an ACK. 1228 * In tcp_input.c this is only done for TCP segments 1229 * with user data, so be consistent here and just drop 1230 * the segment. 1231 */ 1232 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1233 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1234 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1235 log(LOG_DEBUG, 1236 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1237 "segment dropped\n", s, __func__, 1238 to->to_tsval, sc->sc_tsreflect); 1239 } 1240 SCH_UNLOCK(sch); 1241 free(s, M_TCPLOG); 1242 return (-1); /* Do not send RST */ 1243 } 1244 1245 /* 1246 * If timestamps were not negotiated during SYN/ACK and a 1247 * segment with a timestamp is received, ignore the 1248 * timestamp and process the packet normally. 1249 * See section 3.2 of RFC 7323. 1250 */ 1251 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1252 (to->to_flags & TOF_TS)) { 1253 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1254 log(LOG_DEBUG, "%s; %s: Timestamp not " 1255 "expected, segment processed normally\n", 1256 s, __func__); 1257 free(s, M_TCPLOG); 1258 } 1259 } 1260 1261 /* 1262 * If timestamps were negotiated during SYN/ACK and a 1263 * segment without a timestamp is received, silently drop 1264 * the segment, unless the missing timestamps are tolerated. 1265 * See section 3.2 of RFC 7323. 1266 */ 1267 if ((sc->sc_flags & SCF_TIMESTAMP) && 1268 !(to->to_flags & TOF_TS)) { 1269 if (V_tcp_tolerate_missing_ts) { 1270 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1271 log(LOG_DEBUG, 1272 "%s; %s: Timestamp missing, " 1273 "segment processed normally\n", 1274 s, __func__); 1275 free(s, M_TCPLOG); 1276 } 1277 } else { 1278 SCH_UNLOCK(sch); 1279 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1280 log(LOG_DEBUG, 1281 "%s; %s: Timestamp missing, " 1282 "segment silently dropped\n", 1283 s, __func__); 1284 free(s, M_TCPLOG); 1285 } 1286 return (-1); /* Do not send RST */ 1287 } 1288 } 1289 1290 /* 1291 * SEG.SEQ validation: 1292 * The SEG.SEQ must be in the window starting at our 1293 * initial receive sequence number + 1. 1294 */ 1295 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1296 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1297 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1298 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, " 1299 "sending challenge ACK\n", 1300 s, __func__, th->th_seq, sc->sc_irs + 1); 1301 syncache_send_challenge_ack(sc); 1302 SCH_UNLOCK(sch); 1303 free(s, M_TCPLOG); 1304 return (-1); /* Do not send RST */ 1305 } 1306 1307 /* 1308 * SEG.ACK validation: 1309 * SEG.ACK must match our initial send sequence number + 1. 1310 */ 1311 if (th->th_ack != sc->sc_iss + 1) { 1312 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1313 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, " 1314 "segment rejected\n", 1315 s, __func__, th->th_ack, sc->sc_iss + 1); 1316 SCH_UNLOCK(sch); 1317 free(s, M_TCPLOG); 1318 return (0); /* Do send RST, do not free sc. */ 1319 } 1320 1321 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1322 sch->sch_length--; 1323 #ifdef TCP_OFFLOAD 1324 if (ADDED_BY_TOE(sc)) { 1325 struct toedev *tod = sc->sc_tod; 1326 1327 tod->tod_syncache_removed(tod, sc->sc_todctx); 1328 } 1329 #endif 1330 SCH_UNLOCK(sch); 1331 } 1332 1333 *lsop = syncache_socket(sc, *lsop, m); 1334 1335 if (__predict_false(*lsop == NULL)) { 1336 TCPSTAT_INC(tcps_sc_aborted); 1337 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1338 } else if (sc != &scs) 1339 TCPSTAT_INC(tcps_sc_completed); 1340 1341 if (sc != &scs) 1342 syncache_free(sc); 1343 return (1); 1344 } 1345 1346 static struct socket * 1347 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1348 uint64_t response_cookie) 1349 { 1350 struct inpcb *inp; 1351 struct tcpcb *tp; 1352 unsigned int *pending_counter; 1353 struct socket *so; 1354 1355 NET_EPOCH_ASSERT(); 1356 1357 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1358 so = syncache_socket(sc, lso, m); 1359 if (so == NULL) { 1360 TCPSTAT_INC(tcps_sc_aborted); 1361 atomic_subtract_int(pending_counter, 1); 1362 } else { 1363 soisconnected(so); 1364 inp = sotoinpcb(so); 1365 tp = intotcpcb(inp); 1366 tp->t_flags |= TF_FASTOPEN; 1367 tp->t_tfo_cookie.server = response_cookie; 1368 tp->snd_max = tp->iss; 1369 tp->snd_nxt = tp->iss; 1370 tp->t_tfo_pending = pending_counter; 1371 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1372 TCPSTAT_INC(tcps_sc_completed); 1373 } 1374 1375 return (so); 1376 } 1377 1378 /* 1379 * Given a LISTEN socket and an inbound SYN request, add 1380 * this to the syn cache, and send back a segment: 1381 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1382 * to the source. 1383 * 1384 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1385 * Doing so would require that we hold onto the data and deliver it 1386 * to the application. However, if we are the target of a SYN-flood 1387 * DoS attack, an attacker could send data which would eventually 1388 * consume all available buffer space if it were ACKed. By not ACKing 1389 * the data, we avoid this DoS scenario. 1390 * 1391 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1392 * cookie is processed and a new socket is created. In this case, any data 1393 * accompanying the SYN will be queued to the socket by tcp_input() and will 1394 * be ACKed either when the application sends response data or the delayed 1395 * ACK timer expires, whichever comes first. 1396 */ 1397 struct socket * 1398 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1399 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1400 void *todctx, uint8_t iptos, uint16_t port) 1401 { 1402 struct tcpcb *tp; 1403 struct socket *rv = NULL; 1404 struct syncache *sc = NULL; 1405 struct ucred *cred; 1406 struct syncache_head *sch; 1407 struct mbuf *ipopts = NULL; 1408 u_int ltflags; 1409 int win, ip_ttl, ip_tos; 1410 char *s; 1411 #ifdef INET6 1412 int autoflowlabel = 0; 1413 #endif 1414 #ifdef MAC 1415 struct label *maclabel = NULL; 1416 #endif 1417 struct syncache scs; 1418 uint64_t tfo_response_cookie; 1419 unsigned int *tfo_pending = NULL; 1420 int tfo_cookie_valid = 0; 1421 int tfo_response_cookie_valid = 0; 1422 bool locked; 1423 1424 INP_RLOCK_ASSERT(inp); /* listen socket */ 1425 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1426 ("%s: unexpected tcp flags", __func__)); 1427 1428 /* 1429 * Combine all so/tp operations very early to drop the INP lock as 1430 * soon as possible. 1431 */ 1432 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1433 tp = sototcpcb(so); 1434 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1435 1436 #ifdef INET6 1437 if (inc->inc_flags & INC_ISIPV6) { 1438 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1439 autoflowlabel = 1; 1440 } 1441 ip_ttl = in6_selecthlim(inp, NULL); 1442 if ((inp->in6p_outputopts == NULL) || 1443 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1444 ip_tos = 0; 1445 } else { 1446 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1447 } 1448 } 1449 #endif 1450 #if defined(INET6) && defined(INET) 1451 else 1452 #endif 1453 #ifdef INET 1454 { 1455 ip_ttl = inp->inp_ip_ttl; 1456 ip_tos = inp->inp_ip_tos; 1457 } 1458 #endif 1459 win = so->sol_sbrcv_hiwat; 1460 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1461 1462 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1463 (tp->t_tfo_pending != NULL) && 1464 (to->to_flags & TOF_FASTOPEN)) { 1465 /* 1466 * Limit the number of pending TFO connections to 1467 * approximately half of the queue limit. This prevents TFO 1468 * SYN floods from starving the service by filling the 1469 * listen queue with bogus TFO connections. 1470 */ 1471 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1472 (so->sol_qlimit / 2)) { 1473 int result; 1474 1475 result = tcp_fastopen_check_cookie(inc, 1476 to->to_tfo_cookie, to->to_tfo_len, 1477 &tfo_response_cookie); 1478 tfo_cookie_valid = (result > 0); 1479 tfo_response_cookie_valid = (result >= 0); 1480 } 1481 1482 /* 1483 * Remember the TFO pending counter as it will have to be 1484 * decremented below if we don't make it to syncache_tfo_expand(). 1485 */ 1486 tfo_pending = tp->t_tfo_pending; 1487 } 1488 1489 #ifdef MAC 1490 if (mac_syncache_init(&maclabel) != 0) { 1491 INP_RUNLOCK(inp); 1492 goto done; 1493 } else 1494 mac_syncache_create(maclabel, inp); 1495 #endif 1496 if (!tfo_cookie_valid) 1497 INP_RUNLOCK(inp); 1498 1499 /* 1500 * Remember the IP options, if any. 1501 */ 1502 #ifdef INET6 1503 if (!(inc->inc_flags & INC_ISIPV6)) 1504 #endif 1505 #ifdef INET 1506 ipopts = (m) ? ip_srcroute(m) : NULL; 1507 #else 1508 ipopts = NULL; 1509 #endif 1510 1511 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1512 /* 1513 * When the socket is TCP-MD5 enabled check that, 1514 * - a signed packet is valid 1515 * - a non-signed packet does not have a security association 1516 * 1517 * If a signed packet fails validation or a non-signed packet has a 1518 * security association, the packet will be dropped. 1519 */ 1520 if (ltflags & TF_SIGNATURE) { 1521 if (to->to_flags & TOF_SIGNATURE) { 1522 if (!TCPMD5_ENABLED() || 1523 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1524 goto done; 1525 } else { 1526 if (TCPMD5_ENABLED() && 1527 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1528 goto done; 1529 } 1530 } else if (to->to_flags & TOF_SIGNATURE) 1531 goto done; 1532 #endif /* TCP_SIGNATURE */ 1533 /* 1534 * See if we already have an entry for this connection. 1535 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1536 * 1537 * XXX: should the syncache be re-initialized with the contents 1538 * of the new SYN here (which may have different options?) 1539 * 1540 * XXX: We do not check the sequence number to see if this is a 1541 * real retransmit or a new connection attempt. The question is 1542 * how to handle such a case; either ignore it as spoofed, or 1543 * drop the current entry and create a new one? 1544 */ 1545 if (syncache_cookiesonly()) { 1546 sc = NULL; 1547 sch = syncache_hashbucket(inc); 1548 locked = false; 1549 } else { 1550 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1551 locked = true; 1552 SCH_LOCK_ASSERT(sch); 1553 } 1554 if (sc != NULL) { 1555 if (tfo_cookie_valid) 1556 INP_RUNLOCK(inp); 1557 TCPSTAT_INC(tcps_sc_dupsyn); 1558 if (ipopts) { 1559 /* 1560 * If we were remembering a previous source route, 1561 * forget it and use the new one we've been given. 1562 */ 1563 if (sc->sc_ipopts) 1564 (void)m_free(sc->sc_ipopts); 1565 sc->sc_ipopts = ipopts; 1566 } 1567 /* 1568 * Update timestamp if present. 1569 */ 1570 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1571 sc->sc_tsreflect = to->to_tsval; 1572 else 1573 sc->sc_flags &= ~SCF_TIMESTAMP; 1574 /* 1575 * Adjust ECN response if needed, e.g. different 1576 * IP ECN field, or a fallback by the remote host. 1577 */ 1578 if (sc->sc_flags & SCF_ECN_MASK) { 1579 sc->sc_flags &= ~SCF_ECN_MASK; 1580 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1581 } 1582 #ifdef MAC 1583 /* 1584 * Since we have already unconditionally allocated label 1585 * storage, free it up. The syncache entry will already 1586 * have an initialized label we can use. 1587 */ 1588 mac_syncache_destroy(&maclabel); 1589 #endif 1590 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1591 /* Retransmit SYN|ACK and reset retransmit count. */ 1592 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1593 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1594 "resetting timer and retransmitting SYN|ACK\n", 1595 s, __func__); 1596 free(s, M_TCPLOG); 1597 } 1598 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) { 1599 sc->sc_rxmits = 0; 1600 syncache_timeout(sc, sch, 1); 1601 TCPSTAT_INC(tcps_sndacks); 1602 TCPSTAT_INC(tcps_sndtotal); 1603 } else { 1604 /* 1605 * Most likely we are memory constrained, so free 1606 * resources. 1607 */ 1608 syncache_drop(sc, sch); 1609 TCPSTAT_INC(tcps_sc_dropped); 1610 } 1611 SCH_UNLOCK(sch); 1612 goto donenoprobe; 1613 } 1614 1615 KASSERT(sc == NULL, ("sc(%p) != NULL", sc)); 1616 /* 1617 * Skip allocating a syncache entry if we are just going to discard 1618 * it later. 1619 */ 1620 if (!locked || tfo_cookie_valid) { 1621 bzero(&scs, sizeof(scs)); 1622 sc = &scs; 1623 } else { 1624 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1625 if (sc == NULL) { 1626 /* 1627 * The zone allocator couldn't provide more entries. 1628 * Treat this as if the cache was full; drop the oldest 1629 * entry and insert the new one. 1630 */ 1631 TCPSTAT_INC(tcps_sc_zonefail); 1632 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 1633 if (sc != NULL) { 1634 sch->sch_last_overflow = time_uptime; 1635 syncache_drop(sc, sch); 1636 syncache_pause(inc); 1637 } 1638 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1639 if (sc == NULL) { 1640 if (V_tcp_syncookies) { 1641 bzero(&scs, sizeof(scs)); 1642 sc = &scs; 1643 } else { 1644 KASSERT(locked, 1645 ("%s: bucket unexpectedly unlocked", 1646 __func__)); 1647 SCH_UNLOCK(sch); 1648 goto done; 1649 } 1650 } 1651 } 1652 } 1653 1654 KASSERT(sc != NULL, ("sc == NULL")); 1655 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1656 sc->sc_tfo_cookie = &tfo_response_cookie; 1657 1658 /* 1659 * Fill in the syncache values. 1660 */ 1661 #ifdef MAC 1662 sc->sc_label = maclabel; 1663 #endif 1664 /* 1665 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in 1666 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false. 1667 * Therefore, store the credentials only when needed: 1668 * - sc is allocated from the zone and not using the on stack instance. 1669 * - the sysctl variable net.inet.tcp.syncache.see_other is false. 1670 * The reference count is decremented when a zone allocated sc is 1671 * freed in syncache_free(). 1672 */ 1673 if (sc != &scs && !V_tcp_syncache.see_other) { 1674 sc->sc_cred = cred; 1675 cred = NULL; 1676 } else 1677 sc->sc_cred = NULL; 1678 sc->sc_port = port; 1679 sc->sc_ipopts = ipopts; 1680 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1681 sc->sc_ip_tos = ip_tos; 1682 sc->sc_ip_ttl = ip_ttl; 1683 #ifdef TCP_OFFLOAD 1684 sc->sc_tod = tod; 1685 sc->sc_todctx = todctx; 1686 #endif 1687 sc->sc_irs = th->th_seq; 1688 sc->sc_flags = 0; 1689 sc->sc_flowlabel = 0; 1690 1691 /* 1692 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1693 * win was derived from socket earlier in the function. 1694 */ 1695 win = imax(win, 0); 1696 win = imin(win, TCP_MAXWIN); 1697 sc->sc_wnd = win; 1698 1699 if (V_tcp_do_rfc1323 && 1700 !(ltflags & TF_NOOPT)) { 1701 /* 1702 * A timestamp received in a SYN makes 1703 * it ok to send timestamp requests and replies. 1704 */ 1705 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1706 sc->sc_tsreflect = to->to_tsval; 1707 sc->sc_flags |= SCF_TIMESTAMP; 1708 sc->sc_tsoff = tcp_new_ts_offset(inc); 1709 } 1710 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1711 u_int wscale = 0; 1712 1713 /* 1714 * Pick the smallest possible scaling factor that 1715 * will still allow us to scale up to sb_max, aka 1716 * kern.ipc.maxsockbuf. 1717 * 1718 * We do this because there are broken firewalls that 1719 * will corrupt the window scale option, leading to 1720 * the other endpoint believing that our advertised 1721 * window is unscaled. At scale factors larger than 1722 * 5 the unscaled window will drop below 1500 bytes, 1723 * leading to serious problems when traversing these 1724 * broken firewalls. 1725 * 1726 * With the default maxsockbuf of 256K, a scale factor 1727 * of 3 will be chosen by this algorithm. Those who 1728 * choose a larger maxsockbuf should watch out 1729 * for the compatibility problems mentioned above. 1730 * 1731 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1732 * or <SYN,ACK>) segment itself is never scaled. 1733 */ 1734 while (wscale < TCP_MAX_WINSHIFT && 1735 (TCP_MAXWIN << wscale) < sb_max) 1736 wscale++; 1737 sc->sc_requested_r_scale = wscale; 1738 sc->sc_requested_s_scale = to->to_wscale; 1739 sc->sc_flags |= SCF_WINSCALE; 1740 } 1741 } 1742 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1743 /* 1744 * If incoming packet has an MD5 signature, flag this in the 1745 * syncache so that syncache_respond() will do the right thing 1746 * with the SYN+ACK. 1747 */ 1748 if (to->to_flags & TOF_SIGNATURE) 1749 sc->sc_flags |= SCF_SIGNATURE; 1750 #endif /* TCP_SIGNATURE */ 1751 if (to->to_flags & TOF_SACKPERM) 1752 sc->sc_flags |= SCF_SACK; 1753 if (to->to_flags & TOF_MSS) 1754 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1755 if (ltflags & TF_NOOPT) 1756 sc->sc_flags |= SCF_NOOPT; 1757 /* ECN Handshake */ 1758 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1759 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1760 1761 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1762 sc->sc_iss = syncookie_generate(sch, sc); 1763 else 1764 sc->sc_iss = arc4random(); 1765 #ifdef INET6 1766 if (autoflowlabel) { 1767 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1768 sc->sc_flowlabel = sc->sc_iss; 1769 else 1770 sc->sc_flowlabel = ip6_randomflowlabel(); 1771 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1772 } 1773 #endif 1774 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 1775 sc->sc_flowid = m->m_pkthdr.flowid; 1776 sc->sc_flowtype = M_HASHTYPE_GET(m); 1777 } 1778 #ifdef NUMA 1779 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM; 1780 #endif 1781 if (locked) 1782 SCH_UNLOCK(sch); 1783 1784 if (tfo_cookie_valid) { 1785 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1786 /* INP_RUNLOCK(inp) will be performed by the caller */ 1787 goto tfo_expanded; 1788 } 1789 1790 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1791 /* 1792 * Do a standard 3-way handshake. 1793 */ 1794 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) { 1795 if (sc != &scs) 1796 syncache_insert(sc, sch); /* locks and unlocks sch */ 1797 TCPSTAT_INC(tcps_sndacks); 1798 TCPSTAT_INC(tcps_sndtotal); 1799 } else { 1800 /* 1801 * Most likely we are memory constrained, so free resources. 1802 */ 1803 if (sc != &scs) 1804 syncache_free(sc); 1805 TCPSTAT_INC(tcps_sc_dropped); 1806 } 1807 goto donenoprobe; 1808 1809 done: 1810 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1811 donenoprobe: 1812 if (m) 1813 m_freem(m); 1814 /* 1815 * If tfo_pending is not NULL here, then a TFO SYN that did not 1816 * result in a new socket was processed and the associated pending 1817 * counter has not yet been decremented. All such TFO processing paths 1818 * transit this point. 1819 */ 1820 if (tfo_pending != NULL) 1821 tcp_fastopen_decrement_counter(tfo_pending); 1822 1823 tfo_expanded: 1824 if (cred != NULL) 1825 crfree(cred); 1826 if (sc == NULL || sc == &scs) { 1827 #ifdef MAC 1828 mac_syncache_destroy(&maclabel); 1829 #endif 1830 if (ipopts) 1831 (void)m_free(ipopts); 1832 } 1833 return (rv); 1834 } 1835 1836 /* 1837 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment 1838 * or upon 3WHS ACK timeout. 1839 */ 1840 static int 1841 syncache_respond(struct syncache *sc, int flags) 1842 { 1843 struct ip *ip = NULL; 1844 struct mbuf *m; 1845 struct tcphdr *th = NULL; 1846 struct udphdr *udp = NULL; 1847 int optlen, error = 0; /* Make compiler happy */ 1848 u_int16_t hlen, tlen, mssopt, ulen; 1849 struct tcpopt to; 1850 #ifdef INET6 1851 struct ip6_hdr *ip6 = NULL; 1852 #endif 1853 1854 NET_EPOCH_ASSERT(); 1855 1856 hlen = 1857 #ifdef INET6 1858 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1859 #endif 1860 sizeof(struct ip); 1861 tlen = hlen + sizeof(struct tcphdr); 1862 if (sc->sc_port) { 1863 tlen += sizeof(struct udphdr); 1864 } 1865 /* Determine MSS we advertize to other end of connection. */ 1866 mssopt = tcp_mssopt(&sc->sc_inc); 1867 if (sc->sc_port) 1868 mssopt -= V_tcp_udp_tunneling_overhead; 1869 mssopt = max(mssopt, V_tcp_minmss); 1870 1871 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1872 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1873 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1874 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1875 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1876 1877 /* Create the IP+TCP header from scratch. */ 1878 m = m_gethdr(M_NOWAIT, MT_DATA); 1879 if (m == NULL) 1880 return (ENOBUFS); 1881 #ifdef MAC 1882 mac_syncache_create_mbuf(sc->sc_label, m); 1883 #endif 1884 m->m_data += max_linkhdr; 1885 m->m_len = tlen; 1886 m->m_pkthdr.len = tlen; 1887 m->m_pkthdr.rcvif = NULL; 1888 1889 #ifdef INET6 1890 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1891 ip6 = mtod(m, struct ip6_hdr *); 1892 ip6->ip6_vfc = IPV6_VERSION; 1893 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1894 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1895 ip6->ip6_plen = htons(tlen - hlen); 1896 /* ip6_hlim is set after checksum */ 1897 /* Zero out traffic class and flow label. */ 1898 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1899 ip6->ip6_flow |= sc->sc_flowlabel; 1900 if (sc->sc_port != 0) { 1901 ip6->ip6_nxt = IPPROTO_UDP; 1902 udp = (struct udphdr *)(ip6 + 1); 1903 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1904 udp->uh_dport = sc->sc_port; 1905 ulen = (tlen - sizeof(struct ip6_hdr)); 1906 th = (struct tcphdr *)(udp + 1); 1907 } else { 1908 ip6->ip6_nxt = IPPROTO_TCP; 1909 th = (struct tcphdr *)(ip6 + 1); 1910 } 1911 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1912 } 1913 #endif 1914 #if defined(INET6) && defined(INET) 1915 else 1916 #endif 1917 #ifdef INET 1918 { 1919 ip = mtod(m, struct ip *); 1920 ip->ip_v = IPVERSION; 1921 ip->ip_hl = sizeof(struct ip) >> 2; 1922 ip->ip_len = htons(tlen); 1923 ip->ip_id = 0; 1924 ip->ip_off = 0; 1925 ip->ip_sum = 0; 1926 ip->ip_src = sc->sc_inc.inc_laddr; 1927 ip->ip_dst = sc->sc_inc.inc_faddr; 1928 ip->ip_ttl = sc->sc_ip_ttl; 1929 ip->ip_tos = sc->sc_ip_tos; 1930 1931 /* 1932 * See if we should do MTU discovery. Route lookups are 1933 * expensive, so we will only unset the DF bit if: 1934 * 1935 * 1) path_mtu_discovery is disabled 1936 * 2) the SCF_UNREACH flag has been set 1937 */ 1938 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1939 ip->ip_off |= htons(IP_DF); 1940 if (sc->sc_port == 0) { 1941 ip->ip_p = IPPROTO_TCP; 1942 th = (struct tcphdr *)(ip + 1); 1943 } else { 1944 ip->ip_p = IPPROTO_UDP; 1945 udp = (struct udphdr *)(ip + 1); 1946 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1947 udp->uh_dport = sc->sc_port; 1948 ulen = (tlen - sizeof(struct ip)); 1949 th = (struct tcphdr *)(udp + 1); 1950 } 1951 } 1952 #endif /* INET */ 1953 th->th_sport = sc->sc_inc.inc_lport; 1954 th->th_dport = sc->sc_inc.inc_fport; 1955 1956 if (flags & TH_SYN) 1957 th->th_seq = htonl(sc->sc_iss); 1958 else 1959 th->th_seq = htonl(sc->sc_iss + 1); 1960 th->th_ack = htonl(sc->sc_irs + 1); 1961 th->th_off = sizeof(struct tcphdr) >> 2; 1962 th->th_win = htons(sc->sc_wnd); 1963 th->th_urp = 0; 1964 1965 flags = tcp_ecn_syncache_respond(flags, sc); 1966 tcp_set_flags(th, flags); 1967 1968 /* Tack on the TCP options. */ 1969 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1970 to.to_flags = 0; 1971 1972 if (flags & TH_SYN) { 1973 to.to_mss = mssopt; 1974 to.to_flags = TOF_MSS; 1975 if (sc->sc_flags & SCF_WINSCALE) { 1976 to.to_wscale = sc->sc_requested_r_scale; 1977 to.to_flags |= TOF_SCALE; 1978 } 1979 if (sc->sc_flags & SCF_SACK) 1980 to.to_flags |= TOF_SACKPERM; 1981 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1982 if (sc->sc_flags & SCF_SIGNATURE) 1983 to.to_flags |= TOF_SIGNATURE; 1984 #endif 1985 if (sc->sc_tfo_cookie) { 1986 to.to_flags |= TOF_FASTOPEN; 1987 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1988 to.to_tfo_cookie = sc->sc_tfo_cookie; 1989 /* don't send cookie again when retransmitting response */ 1990 sc->sc_tfo_cookie = NULL; 1991 } 1992 } 1993 if (sc->sc_flags & SCF_TIMESTAMP) { 1994 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1995 to.to_tsecr = sc->sc_tsreflect; 1996 to.to_flags |= TOF_TS; 1997 } 1998 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1999 2000 /* Adjust headers by option size. */ 2001 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 2002 m->m_len += optlen; 2003 m->m_pkthdr.len += optlen; 2004 #ifdef INET6 2005 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2006 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 2007 else 2008 #endif 2009 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 2010 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 2011 if (sc->sc_flags & SCF_SIGNATURE) { 2012 KASSERT(to.to_flags & TOF_SIGNATURE, 2013 ("tcp_addoptions() didn't set tcp_signature")); 2014 2015 /* NOTE: to.to_signature is inside of mbuf */ 2016 if (!TCPMD5_ENABLED() || 2017 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 2018 m_freem(m); 2019 return (EACCES); 2020 } 2021 } 2022 #endif 2023 } else 2024 optlen = 0; 2025 2026 if (udp) { 2027 ulen += optlen; 2028 udp->uh_ulen = htons(ulen); 2029 } 2030 M_SETFIB(m, sc->sc_inc.inc_fibnum); 2031 m->m_pkthdr.flowid = sc->sc_flowid; 2032 M_HASHTYPE_SET(m, sc->sc_flowtype); 2033 #ifdef NUMA 2034 m->m_pkthdr.numa_domain = sc->sc_numa_domain; 2035 #endif 2036 #ifdef INET6 2037 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2038 if (sc->sc_port) { 2039 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2040 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2041 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2042 IPPROTO_UDP, 0); 2043 th->th_sum = htons(0); 2044 } else { 2045 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2046 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2047 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2048 IPPROTO_TCP, 0); 2049 } 2050 ip6->ip6_hlim = sc->sc_ip_ttl; 2051 #ifdef TCP_OFFLOAD 2052 if (ADDED_BY_TOE(sc)) { 2053 struct toedev *tod = sc->sc_tod; 2054 2055 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2056 2057 return (error); 2058 } 2059 #endif 2060 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2061 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2062 } 2063 #endif 2064 #if defined(INET6) && defined(INET) 2065 else 2066 #endif 2067 #ifdef INET 2068 { 2069 if (sc->sc_port) { 2070 m->m_pkthdr.csum_flags = CSUM_UDP; 2071 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2072 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2073 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2074 th->th_sum = htons(0); 2075 } else { 2076 m->m_pkthdr.csum_flags = CSUM_TCP; 2077 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2078 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2079 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2080 } 2081 #ifdef TCP_OFFLOAD 2082 if (ADDED_BY_TOE(sc)) { 2083 struct toedev *tod = sc->sc_tod; 2084 2085 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2086 2087 return (error); 2088 } 2089 #endif 2090 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2091 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2092 } 2093 #endif 2094 return (error); 2095 } 2096 2097 static void 2098 syncache_send_challenge_ack(struct syncache *sc) 2099 { 2100 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end, 2101 &sc->sc_challenge_ack_cnt)) { 2102 if (syncache_respond(sc, TH_ACK) == 0) { 2103 TCPSTAT_INC(tcps_sndacks); 2104 TCPSTAT_INC(tcps_sndtotal); 2105 } 2106 } 2107 } 2108 2109 /* 2110 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2111 * that exceed the capacity of the syncache by avoiding the storage of any 2112 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2113 * attacks where the attacker does not have access to our responses. 2114 * 2115 * Syncookies encode and include all necessary information about the 2116 * connection setup within the SYN|ACK that we send back. That way we 2117 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2118 * (if ever). Normally the syncache and syncookies are running in parallel 2119 * with the latter taking over when the former is exhausted. When matching 2120 * syncache entry is found the syncookie is ignored. 2121 * 2122 * The only reliable information persisting the 3WHS is our initial sequence 2123 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2124 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2125 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2126 * returns and signifies a legitimate connection if it matches the ACK. 2127 * 2128 * The available space of 32 bits to store the hash and to encode the SYN 2129 * option information is very tight and we should have at least 24 bits for 2130 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2131 * 2132 * SYN option information we have to encode to fully restore a connection: 2133 * MSS: is imporant to chose an optimal segment size to avoid IP level 2134 * fragmentation along the path. The common MSS values can be encoded 2135 * in a 3-bit table. Uncommon values are captured by the next lower value 2136 * in the table leading to a slight increase in packetization overhead. 2137 * WSCALE: is necessary to allow large windows to be used for high delay- 2138 * bandwidth product links. Not scaling the window when it was initially 2139 * negotiated is bad for performance as lack of scaling further decreases 2140 * the apparent available send window. We only need to encode the WSCALE 2141 * we received from the remote end. Our end can be recalculated at any 2142 * time. The common WSCALE values can be encoded in a 3-bit table. 2143 * Uncommon values are captured by the next lower value in the table 2144 * making us under-estimate the available window size halving our 2145 * theoretically possible maximum throughput for that connection. 2146 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2147 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2148 * that are included in all segments on a connection. We enable them when 2149 * the ACK has them. 2150 * 2151 * Security of syncookies and attack vectors: 2152 * 2153 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2154 * together with the gloabl secret to make it unique per connection attempt. 2155 * Thus any change of any of those parameters results in a different MAC output 2156 * in an unpredictable way unless a collision is encountered. 24 bits of the 2157 * MAC are embedded into the ISS. 2158 * 2159 * To prevent replay attacks two rotating global secrets are updated with a 2160 * new random value every 15 seconds. The life-time of a syncookie is thus 2161 * 15-30 seconds. 2162 * 2163 * Vector 1: Attacking the secret. This requires finding a weakness in the 2164 * MAC itself or the way it is used here. The attacker can do a chosen plain 2165 * text attack by varying and testing the all parameters under his control. 2166 * The strength depends on the size and randomness of the secret, and the 2167 * cryptographic security of the MAC function. Due to the constant updating 2168 * of the secret the attacker has at most 29.999 seconds to find the secret 2169 * and launch spoofed connections. After that he has to start all over again. 2170 * 2171 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2172 * size an average of 4,823 attempts are required for a 50% chance of success 2173 * to spoof a single syncookie (birthday collision paradox). However the 2174 * attacker is blind and doesn't know if one of his attempts succeeded unless 2175 * he has a side channel to interfere success from. A single connection setup 2176 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2177 * This many attempts are required for each one blind spoofed connection. For 2178 * every additional spoofed connection he has to launch another N attempts. 2179 * Thus for a sustained rate 100 spoofed connections per second approximately 2180 * 1,800,000 packets per second would have to be sent. 2181 * 2182 * NB: The MAC function should be fast so that it doesn't become a CPU 2183 * exhaustion attack vector itself. 2184 * 2185 * References: 2186 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2187 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2188 * http://cr.yp.to/syncookies.html (overview) 2189 * http://cr.yp.to/syncookies/archive (details) 2190 * 2191 * 2192 * Schematic construction of a syncookie enabled Initial Sequence Number: 2193 * 0 1 2 3 2194 * 12345678901234567890123456789012 2195 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2196 * 2197 * x 24 MAC (truncated) 2198 * W 3 Send Window Scale index 2199 * M 3 MSS index 2200 * S 1 SACK permitted 2201 * P 1 Odd/even secret 2202 */ 2203 2204 /* 2205 * Distribution and probability of certain MSS values. Those in between are 2206 * rounded down to the next lower one. 2207 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2208 * .2% .3% 5% 7% 7% 20% 15% 45% 2209 */ 2210 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2211 2212 /* 2213 * Distribution and probability of certain WSCALE values. We have to map the 2214 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2215 * bits based on prevalence of certain values. Where we don't have an exact 2216 * match for are rounded down to the next lower one letting us under-estimate 2217 * the true available window. At the moment this would happen only for the 2218 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2219 * and window size). The absence of the WSCALE option (no scaling in either 2220 * direction) is encoded with index zero. 2221 * [WSCALE values histograms, Allman, 2012] 2222 * X 10 10 35 5 6 14 10% by host 2223 * X 11 4 5 5 18 49 3% by connections 2224 */ 2225 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2226 2227 /* 2228 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2229 * and good cryptographic properties. 2230 */ 2231 static uint32_t 2232 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2233 uint8_t *secbits, uintptr_t secmod) 2234 { 2235 SIPHASH_CTX ctx; 2236 uint32_t siphash[2]; 2237 2238 SipHash24_Init(&ctx); 2239 SipHash_SetKey(&ctx, secbits); 2240 switch (inc->inc_flags & INC_ISIPV6) { 2241 #ifdef INET 2242 case 0: 2243 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2244 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2245 break; 2246 #endif 2247 #ifdef INET6 2248 case INC_ISIPV6: 2249 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2250 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2251 break; 2252 #endif 2253 } 2254 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2255 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2256 SipHash_Update(&ctx, &irs, sizeof(irs)); 2257 SipHash_Update(&ctx, &flags, sizeof(flags)); 2258 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2259 SipHash_Final((u_int8_t *)&siphash, &ctx); 2260 2261 return (siphash[0] ^ siphash[1]); 2262 } 2263 2264 static tcp_seq 2265 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2266 { 2267 u_int i, secbit, wscale; 2268 uint32_t iss, hash; 2269 uint8_t *secbits; 2270 union syncookie cookie; 2271 2272 cookie.cookie = 0; 2273 2274 /* Map our computed MSS into the 3-bit index. */ 2275 for (i = nitems(tcp_sc_msstab) - 1; 2276 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2277 i--) 2278 ; 2279 cookie.flags.mss_idx = i; 2280 2281 /* 2282 * Map the send window scale into the 3-bit index but only if 2283 * the wscale option was received. 2284 */ 2285 if (sc->sc_flags & SCF_WINSCALE) { 2286 wscale = sc->sc_requested_s_scale; 2287 for (i = nitems(tcp_sc_wstab) - 1; 2288 tcp_sc_wstab[i] > wscale && i > 0; 2289 i--) 2290 ; 2291 cookie.flags.wscale_idx = i; 2292 } 2293 2294 /* Can we do SACK? */ 2295 if (sc->sc_flags & SCF_SACK) 2296 cookie.flags.sack_ok = 1; 2297 2298 /* Which of the two secrets to use. */ 2299 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2300 cookie.flags.odd_even = secbit; 2301 2302 secbits = V_tcp_syncache.secret.key[secbit]; 2303 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2304 (uintptr_t)sch); 2305 2306 /* 2307 * Put the flags into the hash and XOR them to get better ISS number 2308 * variance. This doesn't enhance the cryptographic strength and is 2309 * done to prevent the 8 cookie bits from showing up directly on the 2310 * wire. 2311 */ 2312 iss = hash & ~0xff; 2313 iss |= cookie.cookie ^ (hash >> 24); 2314 2315 TCPSTAT_INC(tcps_sc_sendcookie); 2316 return (iss); 2317 } 2318 2319 static bool 2320 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch, 2321 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2322 struct socket *lso, uint16_t port) 2323 { 2324 uint32_t hash; 2325 uint8_t *secbits; 2326 tcp_seq ack, seq; 2327 int wnd; 2328 union syncookie cookie; 2329 2330 /* 2331 * Pull information out of SYN-ACK/ACK and revert sequence number 2332 * advances. 2333 */ 2334 ack = th->th_ack - 1; 2335 seq = th->th_seq - 1; 2336 2337 /* 2338 * Unpack the flags containing enough information to restore the 2339 * connection. 2340 */ 2341 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2342 2343 /* Which of the two secrets to use. */ 2344 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2345 2346 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2347 2348 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2349 if ((ack & ~0xff) != (hash & ~0xff)) 2350 return (false); 2351 2352 /* Fill in the syncache values. */ 2353 sc->sc_flags = 0; 2354 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2355 sc->sc_ipopts = NULL; 2356 2357 sc->sc_irs = seq; 2358 sc->sc_iss = ack; 2359 2360 switch (inc->inc_flags & INC_ISIPV6) { 2361 #ifdef INET 2362 case 0: 2363 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2364 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2365 break; 2366 #endif 2367 #ifdef INET6 2368 case INC_ISIPV6: 2369 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2370 sc->sc_flowlabel = 2371 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2372 break; 2373 #endif 2374 } 2375 2376 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2377 2378 /* Only use wscale if it was enabled in the orignal SYN. */ 2379 if (cookie.flags.wscale_idx > 0) { 2380 u_int wscale = 0; 2381 2382 /* Recompute the receive window scale that was sent earlier. */ 2383 while (wscale < TCP_MAX_WINSHIFT && 2384 (TCP_MAXWIN << wscale) < sb_max) 2385 wscale++; 2386 sc->sc_requested_r_scale = wscale; 2387 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2388 sc->sc_flags |= SCF_WINSCALE; 2389 } 2390 2391 wnd = lso->sol_sbrcv_hiwat; 2392 wnd = imax(wnd, 0); 2393 wnd = imin(wnd, TCP_MAXWIN); 2394 sc->sc_wnd = wnd; 2395 2396 if (cookie.flags.sack_ok) 2397 sc->sc_flags |= SCF_SACK; 2398 2399 if (to->to_flags & TOF_TS) { 2400 sc->sc_flags |= SCF_TIMESTAMP; 2401 sc->sc_tsreflect = to->to_tsval; 2402 sc->sc_tsoff = tcp_new_ts_offset(inc); 2403 } 2404 2405 if (to->to_flags & TOF_SIGNATURE) 2406 sc->sc_flags |= SCF_SIGNATURE; 2407 2408 sc->sc_rxmits = 0; 2409 2410 sc->sc_port = port; 2411 2412 return (true); 2413 } 2414 2415 #ifdef INVARIANTS 2416 static void 2417 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch, 2418 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2419 struct socket *lso, uint16_t port) 2420 { 2421 struct syncache scs; 2422 char *s; 2423 2424 bzero(&scs, sizeof(scs)); 2425 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) && 2426 (sc->sc_peer_mss != scs.sc_peer_mss || 2427 sc->sc_requested_r_scale != scs.sc_requested_r_scale || 2428 sc->sc_requested_s_scale != scs.sc_requested_s_scale || 2429 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) { 2430 2431 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2432 return; 2433 2434 if (sc->sc_peer_mss != scs.sc_peer_mss) 2435 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2436 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss); 2437 2438 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale) 2439 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2440 s, __func__, sc->sc_requested_r_scale, 2441 scs.sc_requested_r_scale); 2442 2443 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale) 2444 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2445 s, __func__, sc->sc_requested_s_scale, 2446 scs.sc_requested_s_scale); 2447 2448 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK)) 2449 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2450 2451 free(s, M_TCPLOG); 2452 } 2453 } 2454 #endif /* INVARIANTS */ 2455 2456 static void 2457 syncookie_reseed(void *arg) 2458 { 2459 struct tcp_syncache *sc = arg; 2460 uint8_t *secbits; 2461 int secbit; 2462 2463 /* 2464 * Reseeding the secret doesn't have to be protected by a lock. 2465 * It only must be ensured that the new random values are visible 2466 * to all CPUs in a SMP environment. The atomic with release 2467 * semantics ensures that. 2468 */ 2469 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2470 secbits = sc->secret.key[secbit]; 2471 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2472 atomic_add_rel_int(&sc->secret.oddeven, 1); 2473 2474 /* Reschedule ourself. */ 2475 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2476 } 2477 2478 /* 2479 * We have overflowed a bucket. Let's pause dealing with the syncache. 2480 * This function will increment the bucketoverflow statistics appropriately 2481 * (once per pause when pausing is enabled; otherwise, once per overflow). 2482 */ 2483 static void 2484 syncache_pause(struct in_conninfo *inc) 2485 { 2486 time_t delta; 2487 const char *s; 2488 2489 /* XXX: 2490 * 2. Add sysctl read here so we don't get the benefit of this 2491 * change without the new sysctl. 2492 */ 2493 2494 /* 2495 * Try an unlocked read. If we already know that another thread 2496 * has activated the feature, there is no need to proceed. 2497 */ 2498 if (V_tcp_syncache.paused) 2499 return; 2500 2501 /* Are cookied enabled? If not, we can't pause. */ 2502 if (!V_tcp_syncookies) { 2503 TCPSTAT_INC(tcps_sc_bucketoverflow); 2504 return; 2505 } 2506 2507 /* 2508 * We may be the first thread to find an overflow. Get the lock 2509 * and evaluate if we need to take action. 2510 */ 2511 mtx_lock(&V_tcp_syncache.pause_mtx); 2512 if (V_tcp_syncache.paused) { 2513 mtx_unlock(&V_tcp_syncache.pause_mtx); 2514 return; 2515 } 2516 2517 /* Activate protection. */ 2518 V_tcp_syncache.paused = true; 2519 TCPSTAT_INC(tcps_sc_bucketoverflow); 2520 2521 /* 2522 * Determine the last backoff time. If we are seeing a re-newed 2523 * attack within that same time after last reactivating the syncache, 2524 * consider it an extension of the same attack. 2525 */ 2526 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2527 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2528 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2529 delta <<= 1; 2530 V_tcp_syncache.pause_backoff++; 2531 } 2532 } else { 2533 delta = TCP_SYNCACHE_PAUSE_TIME; 2534 V_tcp_syncache.pause_backoff = 0; 2535 } 2536 2537 /* Log a warning, including IP addresses, if able. */ 2538 if (inc != NULL) 2539 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2540 else 2541 s = (const char *)NULL; 2542 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2543 "the next %lld seconds%s%s%s\n", (long long)delta, 2544 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2545 (s != NULL) ? ")" : ""); 2546 free(__DECONST(void *, s), M_TCPLOG); 2547 2548 /* Use the calculated delta to set a new pause time. */ 2549 V_tcp_syncache.pause_until = time_uptime + delta; 2550 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2551 &V_tcp_syncache); 2552 mtx_unlock(&V_tcp_syncache.pause_mtx); 2553 } 2554 2555 /* Evaluate whether we need to unpause. */ 2556 static void 2557 syncache_unpause(void *arg) 2558 { 2559 struct tcp_syncache *sc; 2560 time_t delta; 2561 2562 sc = arg; 2563 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2564 callout_deactivate(&sc->pause_co); 2565 2566 /* 2567 * Check to make sure we are not running early. If the pause 2568 * time has expired, then deactivate the protection. 2569 */ 2570 if ((delta = sc->pause_until - time_uptime) > 0) 2571 callout_schedule(&sc->pause_co, delta * hz); 2572 else 2573 sc->paused = false; 2574 } 2575 2576 /* 2577 * Exports the syncache entries to userland so that netstat can display 2578 * them alongside the other sockets. This function is intended to be 2579 * called only from tcp_pcblist. 2580 * 2581 * Due to concurrency on an active system, the number of pcbs exported 2582 * may have no relation to max_pcbs. max_pcbs merely indicates the 2583 * amount of space the caller allocated for this function to use. 2584 */ 2585 int 2586 syncache_pcblist(struct sysctl_req *req) 2587 { 2588 struct xtcpcb xt; 2589 struct syncache *sc; 2590 struct syncache_head *sch; 2591 int error, i; 2592 2593 bzero(&xt, sizeof(xt)); 2594 xt.xt_len = sizeof(xt); 2595 xt.t_state = TCPS_SYN_RECEIVED; 2596 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2597 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2598 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2599 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2600 2601 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2602 sch = &V_tcp_syncache.hashbase[i]; 2603 SCH_LOCK(sch); 2604 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2605 if (sc->sc_cred != NULL && 2606 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2607 continue; 2608 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2609 xt.xt_inp.inp_vflag = INP_IPV6; 2610 else 2611 xt.xt_inp.inp_vflag = INP_IPV4; 2612 xt.xt_encaps_port = sc->sc_port; 2613 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2614 sizeof (struct in_conninfo)); 2615 error = SYSCTL_OUT(req, &xt, sizeof xt); 2616 if (error) { 2617 SCH_UNLOCK(sch); 2618 return (0); 2619 } 2620 } 2621 SCH_UNLOCK(sch); 2622 } 2623 2624 return (0); 2625 } 2626