1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 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 __FBSDID("$FreeBSD$"); 37 38 #include "opt_inet.h" 39 #include "opt_inet6.h" 40 #include "opt_ipsec.h" 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/hash.h> 45 #include <sys/refcount.h> 46 #include <sys/kernel.h> 47 #include <sys/sysctl.h> 48 #include <sys/limits.h> 49 #include <sys/lock.h> 50 #include <sys/mutex.h> 51 #include <sys/malloc.h> 52 #include <sys/mbuf.h> 53 #include <sys/proc.h> /* for proc0 declaration */ 54 #include <sys/random.h> 55 #include <sys/socket.h> 56 #include <sys/socketvar.h> 57 #include <sys/syslog.h> 58 #include <sys/ucred.h> 59 60 #include <sys/md5.h> 61 #include <crypto/siphash/siphash.h> 62 63 #include <vm/uma.h> 64 65 #include <net/if.h> 66 #include <net/if_var.h> 67 #include <net/route.h> 68 #include <net/vnet.h> 69 70 #include <netinet/in.h> 71 #include <netinet/in_kdtrace.h> 72 #include <netinet/in_systm.h> 73 #include <netinet/ip.h> 74 #include <netinet/in_var.h> 75 #include <netinet/in_pcb.h> 76 #include <netinet/ip_var.h> 77 #include <netinet/ip_options.h> 78 #ifdef INET6 79 #include <netinet/ip6.h> 80 #include <netinet/icmp6.h> 81 #include <netinet6/nd6.h> 82 #include <netinet6/ip6_var.h> 83 #include <netinet6/in6_pcb.h> 84 #endif 85 #include <netinet/tcp.h> 86 #include <netinet/tcp_fastopen.h> 87 #include <netinet/tcp_fsm.h> 88 #include <netinet/tcp_seq.h> 89 #include <netinet/tcp_timer.h> 90 #include <netinet/tcp_var.h> 91 #include <netinet/tcp_syncache.h> 92 #include <netinet/tcp_ecn.h> 93 #ifdef INET6 94 #include <netinet6/tcp6_var.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 #include <netinet/udp.h> 100 #include <netinet/udp_var.h> 101 102 #include <netipsec/ipsec_support.h> 103 104 #include <machine/in_cksum.h> 105 106 #include <security/mac/mac_framework.h> 107 108 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1; 109 #define V_tcp_syncookies VNET(tcp_syncookies) 110 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 111 &VNET_NAME(tcp_syncookies), 0, 112 "Use TCP SYN cookies if the syncache overflows"); 113 114 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0; 115 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 116 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 117 &VNET_NAME(tcp_syncookiesonly), 0, 118 "Use only TCP SYN cookies"); 119 120 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 121 #define V_functions_inherit_listen_socket_stack \ 122 VNET(functions_inherit_listen_socket_stack) 123 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 124 CTLFLAG_VNET | CTLFLAG_RW, 125 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 126 "Inherit listen socket's stack"); 127 128 #ifdef TCP_OFFLOAD 129 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 130 #endif 131 132 static void syncache_drop(struct syncache *, struct syncache_head *); 133 static void syncache_free(struct syncache *); 134 static void syncache_insert(struct syncache *, struct syncache_head *); 135 static int syncache_respond(struct syncache *, const struct mbuf *, int); 136 static struct socket *syncache_socket(struct syncache *, struct socket *, 137 struct mbuf *m); 138 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 139 int docallout); 140 static void syncache_timer(void *); 141 142 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 143 uint8_t *, uintptr_t); 144 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 145 static struct syncache 146 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 147 struct syncache *, struct tcphdr *, struct tcpopt *, 148 struct socket *, uint16_t); 149 static void syncache_pause(struct in_conninfo *); 150 static void syncache_unpause(void *); 151 static void syncookie_reseed(void *); 152 #ifdef INVARIANTS 153 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 154 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 155 struct socket *lso, uint16_t port); 156 #endif 157 158 /* 159 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 160 * 3 retransmits corresponds to a timeout with default values of 161 * tcp_rexmit_initial * ( 1 + 162 * tcp_backoff[1] + 163 * tcp_backoff[2] + 164 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 165 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 166 * the odds are that the user has given up attempting to connect by then. 167 */ 168 #define SYNCACHE_MAXREXMTS 3 169 170 /* Arbitrary values */ 171 #define TCP_SYNCACHE_HASHSIZE 512 172 #define TCP_SYNCACHE_BUCKETLIMIT 30 173 174 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 175 #define V_tcp_syncache VNET(tcp_syncache) 176 177 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 178 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 179 "TCP SYN cache"); 180 181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 182 &VNET_NAME(tcp_syncache.bucket_limit), 0, 183 "Per-bucket hash limit for syncache"); 184 185 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 186 &VNET_NAME(tcp_syncache.cache_limit), 0, 187 "Overall entry limit for syncache"); 188 189 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 190 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 191 192 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 193 &VNET_NAME(tcp_syncache.hashsize), 0, 194 "Size of TCP syncache hashtable"); 195 196 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 197 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 198 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 199 "and mac(4) checks"); 200 201 static int 202 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 203 { 204 int error; 205 u_int new; 206 207 new = V_tcp_syncache.rexmt_limit; 208 error = sysctl_handle_int(oidp, &new, 0, req); 209 if ((error == 0) && (req->newptr != NULL)) { 210 if (new > TCP_MAXRXTSHIFT) 211 error = EINVAL; 212 else 213 V_tcp_syncache.rexmt_limit = new; 214 } 215 return (error); 216 } 217 218 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 219 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 220 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 221 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 222 "Limit on SYN/ACK retransmissions"); 223 224 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 225 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 226 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 227 "Send reset on socket allocation failure"); 228 229 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 230 231 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 232 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 233 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 234 235 /* 236 * Requires the syncache entry to be already removed from the bucket list. 237 */ 238 static void 239 syncache_free(struct syncache *sc) 240 { 241 242 if (sc->sc_ipopts) 243 (void) m_free(sc->sc_ipopts); 244 if (sc->sc_cred) 245 crfree(sc->sc_cred); 246 #ifdef MAC 247 mac_syncache_destroy(&sc->sc_label); 248 #endif 249 250 uma_zfree(V_tcp_syncache.zone, sc); 251 } 252 253 void 254 syncache_init(void) 255 { 256 int i; 257 258 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 259 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 260 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 261 V_tcp_syncache.hash_secret = arc4random(); 262 263 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 264 &V_tcp_syncache.hashsize); 265 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 266 &V_tcp_syncache.bucket_limit); 267 if (!powerof2(V_tcp_syncache.hashsize) || 268 V_tcp_syncache.hashsize == 0) { 269 printf("WARNING: syncache hash size is not a power of 2.\n"); 270 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 271 } 272 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 273 274 /* Set limits. */ 275 V_tcp_syncache.cache_limit = 276 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 277 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 278 &V_tcp_syncache.cache_limit); 279 280 /* Allocate the hash table. */ 281 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 282 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 283 284 #ifdef VIMAGE 285 V_tcp_syncache.vnet = curvnet; 286 #endif 287 288 /* Initialize the hash buckets. */ 289 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 290 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 291 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 292 NULL, MTX_DEF); 293 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 294 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 295 V_tcp_syncache.hashbase[i].sch_length = 0; 296 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 297 V_tcp_syncache.hashbase[i].sch_last_overflow = 298 -(SYNCOOKIE_LIFETIME + 1); 299 } 300 301 /* Create the syncache entry zone. */ 302 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 303 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 304 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 305 V_tcp_syncache.cache_limit); 306 307 /* Start the SYN cookie reseeder callout. */ 308 callout_init(&V_tcp_syncache.secret.reseed, 1); 309 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 310 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 311 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 312 syncookie_reseed, &V_tcp_syncache); 313 314 /* Initialize the pause machinery. */ 315 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 316 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 317 0); 318 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 319 V_tcp_syncache.pause_backoff = 0; 320 V_tcp_syncache.paused = false; 321 } 322 323 #ifdef VIMAGE 324 void 325 syncache_destroy(void) 326 { 327 struct syncache_head *sch; 328 struct syncache *sc, *nsc; 329 int i; 330 331 /* 332 * Stop the re-seed timer before freeing resources. No need to 333 * possibly schedule it another time. 334 */ 335 callout_drain(&V_tcp_syncache.secret.reseed); 336 337 /* Stop the SYN cache pause callout. */ 338 mtx_lock(&V_tcp_syncache.pause_mtx); 339 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 340 mtx_unlock(&V_tcp_syncache.pause_mtx); 341 callout_drain(&V_tcp_syncache.pause_co); 342 } else 343 mtx_unlock(&V_tcp_syncache.pause_mtx); 344 345 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 346 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 347 sch = &V_tcp_syncache.hashbase[i]; 348 callout_drain(&sch->sch_timer); 349 350 SCH_LOCK(sch); 351 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 352 syncache_drop(sc, sch); 353 SCH_UNLOCK(sch); 354 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 355 ("%s: sch->sch_bucket not empty", __func__)); 356 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 357 __func__, sch->sch_length)); 358 mtx_destroy(&sch->sch_mtx); 359 } 360 361 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 362 ("%s: cache_count not 0", __func__)); 363 364 /* Free the allocated global resources. */ 365 uma_zdestroy(V_tcp_syncache.zone); 366 free(V_tcp_syncache.hashbase, M_SYNCACHE); 367 mtx_destroy(&V_tcp_syncache.pause_mtx); 368 } 369 #endif 370 371 /* 372 * Inserts a syncache entry into the specified bucket row. 373 * Locks and unlocks the syncache_head autonomously. 374 */ 375 static void 376 syncache_insert(struct syncache *sc, struct syncache_head *sch) 377 { 378 struct syncache *sc2; 379 380 SCH_LOCK(sch); 381 382 /* 383 * Make sure that we don't overflow the per-bucket limit. 384 * If the bucket is full, toss the oldest element. 385 */ 386 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 387 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 388 ("sch->sch_length incorrect")); 389 syncache_pause(&sc->sc_inc); 390 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 391 sch->sch_last_overflow = time_uptime; 392 syncache_drop(sc2, sch); 393 } 394 395 /* Put it into the bucket. */ 396 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 397 sch->sch_length++; 398 399 #ifdef TCP_OFFLOAD 400 if (ADDED_BY_TOE(sc)) { 401 struct toedev *tod = sc->sc_tod; 402 403 tod->tod_syncache_added(tod, sc->sc_todctx); 404 } 405 #endif 406 407 /* Reinitialize the bucket row's timer. */ 408 if (sch->sch_length == 1) 409 sch->sch_nextc = ticks + INT_MAX; 410 syncache_timeout(sc, sch, 1); 411 412 SCH_UNLOCK(sch); 413 414 TCPSTATES_INC(TCPS_SYN_RECEIVED); 415 TCPSTAT_INC(tcps_sc_added); 416 } 417 418 /* 419 * Remove and free entry from syncache bucket row. 420 * Expects locked syncache head. 421 */ 422 static void 423 syncache_drop(struct syncache *sc, struct syncache_head *sch) 424 { 425 426 SCH_LOCK_ASSERT(sch); 427 428 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 429 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 430 sch->sch_length--; 431 432 #ifdef TCP_OFFLOAD 433 if (ADDED_BY_TOE(sc)) { 434 struct toedev *tod = sc->sc_tod; 435 436 tod->tod_syncache_removed(tod, sc->sc_todctx); 437 } 438 #endif 439 440 syncache_free(sc); 441 } 442 443 /* 444 * Engage/reengage time on bucket row. 445 */ 446 static void 447 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 448 { 449 int rexmt; 450 451 if (sc->sc_rxmits == 0) 452 rexmt = tcp_rexmit_initial; 453 else 454 TCPT_RANGESET(rexmt, 455 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 456 tcp_rexmit_min, TCPTV_REXMTMAX); 457 sc->sc_rxttime = ticks + rexmt; 458 sc->sc_rxmits++; 459 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 460 sch->sch_nextc = sc->sc_rxttime; 461 if (docallout) 462 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 463 syncache_timer, (void *)sch); 464 } 465 } 466 467 /* 468 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 469 * If we have retransmitted an entry the maximum number of times, expire it. 470 * One separate timer for each bucket row. 471 */ 472 static void 473 syncache_timer(void *xsch) 474 { 475 struct syncache_head *sch = (struct syncache_head *)xsch; 476 struct syncache *sc, *nsc; 477 struct epoch_tracker et; 478 int tick = ticks; 479 char *s; 480 bool paused; 481 482 CURVNET_SET(sch->sch_sc->vnet); 483 484 /* NB: syncache_head has already been locked by the callout. */ 485 SCH_LOCK_ASSERT(sch); 486 487 /* 488 * In the following cycle we may remove some entries and/or 489 * advance some timeouts, so re-initialize the bucket timer. 490 */ 491 sch->sch_nextc = tick + INT_MAX; 492 493 /* 494 * If we have paused processing, unconditionally remove 495 * all syncache entries. 496 */ 497 mtx_lock(&V_tcp_syncache.pause_mtx); 498 paused = V_tcp_syncache.paused; 499 mtx_unlock(&V_tcp_syncache.pause_mtx); 500 501 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 502 if (paused) { 503 syncache_drop(sc, sch); 504 continue; 505 } 506 /* 507 * We do not check if the listen socket still exists 508 * and accept the case where the listen socket may be 509 * gone by the time we resend the SYN/ACK. We do 510 * not expect this to happens often. If it does, 511 * then the RST will be sent by the time the remote 512 * host does the SYN/ACK->ACK. 513 */ 514 if (TSTMP_GT(sc->sc_rxttime, tick)) { 515 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 516 sch->sch_nextc = sc->sc_rxttime; 517 continue; 518 } 519 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 520 sc->sc_flags &= ~SCF_ECN; 521 } 522 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 523 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 524 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 525 "giving up and removing syncache entry\n", 526 s, __func__); 527 free(s, M_TCPLOG); 528 } 529 syncache_drop(sc, sch); 530 TCPSTAT_INC(tcps_sc_stale); 531 continue; 532 } 533 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 534 log(LOG_DEBUG, "%s; %s: Response timeout, " 535 "retransmitting (%u) SYN|ACK\n", 536 s, __func__, sc->sc_rxmits); 537 free(s, M_TCPLOG); 538 } 539 540 NET_EPOCH_ENTER(et); 541 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 542 NET_EPOCH_EXIT(et); 543 TCPSTAT_INC(tcps_sc_retransmitted); 544 syncache_timeout(sc, sch, 0); 545 } 546 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 547 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 548 syncache_timer, (void *)(sch)); 549 CURVNET_RESTORE(); 550 } 551 552 /* 553 * Returns true if the system is only using cookies at the moment. 554 * This could be due to a sysadmin decision to only use cookies, or it 555 * could be due to the system detecting an attack. 556 */ 557 static inline bool 558 syncache_cookiesonly(void) 559 { 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 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 629 * See RFC 793 page 65, section SEGMENT ARRIVES. 630 */ 631 if (tcp_get_flags(th) & (TH_ACK|TH_SYN|TH_FIN)) { 632 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 633 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 634 "FIN flag set, segment ignored\n", s, __func__); 635 TCPSTAT_INC(tcps_badrst); 636 goto done; 637 } 638 639 /* 640 * No corresponding connection was found in syncache. 641 * If syncookies are enabled and possibly exclusively 642 * used, or we are under memory pressure, a valid RST 643 * may not find a syncache entry. In that case we're 644 * done and no SYN|ACK retransmissions will happen. 645 * Otherwise the RST was misdirected or spoofed. 646 */ 647 if (sc == NULL) { 648 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 649 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 650 "syncache entry (possibly syncookie only), " 651 "segment ignored\n", s, __func__); 652 TCPSTAT_INC(tcps_badrst); 653 goto done; 654 } 655 656 /* The remote UDP encaps port does not match. */ 657 if (sc->sc_port != port) { 658 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 659 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 660 "syncache entry but non-matching UDP encaps port, " 661 "segment ignored\n", s, __func__); 662 TCPSTAT_INC(tcps_badrst); 663 goto done; 664 } 665 666 /* 667 * If the RST bit is set, check the sequence number to see 668 * if this is a valid reset segment. 669 * 670 * RFC 793 page 37: 671 * In all states except SYN-SENT, all reset (RST) segments 672 * are validated by checking their SEQ-fields. A reset is 673 * valid if its sequence number is in the window. 674 * 675 * RFC 793 page 69: 676 * There are four cases for the acceptability test for an incoming 677 * segment: 678 * 679 * Segment Receive Test 680 * Length Window 681 * ------- ------- ------------------------------------------- 682 * 0 0 SEG.SEQ = RCV.NXT 683 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 684 * >0 0 not acceptable 685 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 686 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 687 * 688 * Note that when receiving a SYN segment in the LISTEN state, 689 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 690 * described in RFC 793, page 66. 691 */ 692 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 693 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 694 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 695 if (V_tcp_insecure_rst || 696 th->th_seq == sc->sc_irs + 1) { 697 syncache_drop(sc, sch); 698 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 699 log(LOG_DEBUG, 700 "%s; %s: Our SYN|ACK was rejected, " 701 "connection attempt aborted by remote " 702 "endpoint\n", 703 s, __func__); 704 TCPSTAT_INC(tcps_sc_reset); 705 } else { 706 TCPSTAT_INC(tcps_badrst); 707 /* Send challenge ACK. */ 708 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 709 log(LOG_DEBUG, "%s; %s: RST with invalid " 710 " SEQ %u != NXT %u (+WND %u), " 711 "sending challenge ACK\n", 712 s, __func__, 713 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 714 syncache_respond(sc, m, TH_ACK); 715 } 716 } else { 717 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 718 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 719 "NXT %u (+WND %u), segment ignored\n", 720 s, __func__, 721 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 722 TCPSTAT_INC(tcps_badrst); 723 } 724 725 done: 726 if (s != NULL) 727 free(s, M_TCPLOG); 728 SCH_UNLOCK(sch); 729 } 730 731 void 732 syncache_badack(struct in_conninfo *inc, uint16_t port) 733 { 734 struct syncache *sc; 735 struct syncache_head *sch; 736 737 if (syncache_cookiesonly()) 738 return; 739 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 740 SCH_LOCK_ASSERT(sch); 741 if ((sc != NULL) && (sc->sc_port == port)) { 742 syncache_drop(sc, sch); 743 TCPSTAT_INC(tcps_sc_badack); 744 } 745 SCH_UNLOCK(sch); 746 } 747 748 void 749 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 750 { 751 struct syncache *sc; 752 struct syncache_head *sch; 753 754 if (syncache_cookiesonly()) 755 return; 756 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 757 SCH_LOCK_ASSERT(sch); 758 if (sc == NULL) 759 goto done; 760 761 /* If the port != sc_port, then it's a bogus ICMP msg */ 762 if (port != sc->sc_port) 763 goto done; 764 765 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 766 if (ntohl(th_seq) != sc->sc_iss) 767 goto done; 768 769 /* 770 * If we've rertransmitted 3 times and this is our second error, 771 * we remove the entry. Otherwise, we allow it to continue on. 772 * This prevents us from incorrectly nuking an entry during a 773 * spurious network outage. 774 * 775 * See tcp_notify(). 776 */ 777 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 778 sc->sc_flags |= SCF_UNREACH; 779 goto done; 780 } 781 syncache_drop(sc, sch); 782 TCPSTAT_INC(tcps_sc_unreach); 783 done: 784 SCH_UNLOCK(sch); 785 } 786 787 /* 788 * Build a new TCP socket structure from a syncache entry. 789 * 790 * On success return the newly created socket with its underlying inp locked. 791 */ 792 static struct socket * 793 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 794 { 795 struct tcp_function_block *blk; 796 struct inpcb *inp = NULL; 797 struct socket *so; 798 struct tcpcb *tp; 799 int error; 800 char *s; 801 802 NET_EPOCH_ASSERT(); 803 804 /* 805 * Ok, create the full blown connection, and set things up 806 * as they would have been set up if we had created the 807 * connection when the SYN arrived. If we can't create 808 * the connection, abort it. 809 */ 810 so = sonewconn(lso, 0); 811 if (so == NULL) { 812 /* 813 * Drop the connection; we will either send a RST or 814 * have the peer retransmit its SYN again after its 815 * RTO and try again. 816 */ 817 TCPSTAT_INC(tcps_listendrop); 818 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 819 log(LOG_DEBUG, "%s; %s: Socket create failed " 820 "due to limits or memory shortage\n", 821 s, __func__); 822 free(s, M_TCPLOG); 823 } 824 goto abort2; 825 } 826 #ifdef MAC 827 mac_socketpeer_set_from_mbuf(m, so); 828 #endif 829 830 inp = sotoinpcb(so); 831 inp->inp_inc.inc_fibnum = so->so_fibnum; 832 INP_WLOCK(inp); 833 /* 834 * Exclusive pcbinfo lock is not required in syncache socket case even 835 * if two inpcb locks can be acquired simultaneously: 836 * - the inpcb in LISTEN state, 837 * - the newly created inp. 838 * 839 * In this case, an inp cannot be at same time in LISTEN state and 840 * just created by an accept() call. 841 */ 842 INP_HASH_WLOCK(&V_tcbinfo); 843 844 /* Insert new socket into PCB hash list. */ 845 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 846 #ifdef INET6 847 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 848 inp->inp_vflag &= ~INP_IPV4; 849 inp->inp_vflag |= INP_IPV6; 850 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 851 } else { 852 inp->inp_vflag &= ~INP_IPV6; 853 inp->inp_vflag |= INP_IPV4; 854 #endif 855 inp->inp_ip_ttl = sc->sc_ip_ttl; 856 inp->inp_ip_tos = sc->sc_ip_tos; 857 inp->inp_laddr = sc->sc_inc.inc_laddr; 858 #ifdef INET6 859 } 860 #endif 861 862 /* 863 * If there's an mbuf and it has a flowid, then let's initialise the 864 * inp with that particular flowid. 865 */ 866 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 867 inp->inp_flowid = m->m_pkthdr.flowid; 868 inp->inp_flowtype = M_HASHTYPE_GET(m); 869 #ifdef NUMA 870 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 871 #endif 872 } 873 874 inp->inp_lport = sc->sc_inc.inc_lport; 875 #ifdef INET6 876 if (inp->inp_vflag & INP_IPV6PROTO) { 877 struct inpcb *oinp = sotoinpcb(lso); 878 879 /* 880 * Inherit socket options from the listening socket. 881 * Note that in6p_inputopts are not (and should not be) 882 * copied, since it stores previously received options and is 883 * used to detect if each new option is different than the 884 * previous one and hence should be passed to a user. 885 * If we copied in6p_inputopts, a user would not be able to 886 * receive options just after calling the accept system call. 887 */ 888 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 889 if (oinp->in6p_outputopts) 890 inp->in6p_outputopts = 891 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 892 inp->in6p_hops = oinp->in6p_hops; 893 } 894 895 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 896 struct in6_addr laddr6; 897 struct sockaddr_in6 sin6; 898 899 sin6.sin6_family = AF_INET6; 900 sin6.sin6_len = sizeof(sin6); 901 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 902 sin6.sin6_port = sc->sc_inc.inc_fport; 903 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 904 laddr6 = inp->in6p_laddr; 905 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 906 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 907 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 908 thread0.td_ucred, m, false)) != 0) { 909 inp->in6p_laddr = laddr6; 910 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 911 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 912 "with error %i\n", 913 s, __func__, error); 914 free(s, M_TCPLOG); 915 } 916 INP_HASH_WUNLOCK(&V_tcbinfo); 917 goto abort; 918 } 919 /* Override flowlabel from in6_pcbconnect. */ 920 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 921 inp->inp_flow |= sc->sc_flowlabel; 922 } 923 #endif /* INET6 */ 924 #if defined(INET) && defined(INET6) 925 else 926 #endif 927 #ifdef INET 928 { 929 struct in_addr laddr; 930 struct sockaddr_in sin; 931 932 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 933 934 if (inp->inp_options == NULL) { 935 inp->inp_options = sc->sc_ipopts; 936 sc->sc_ipopts = NULL; 937 } 938 939 sin.sin_family = AF_INET; 940 sin.sin_len = sizeof(sin); 941 sin.sin_addr = sc->sc_inc.inc_faddr; 942 sin.sin_port = sc->sc_inc.inc_fport; 943 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 944 laddr = inp->inp_laddr; 945 if (inp->inp_laddr.s_addr == INADDR_ANY) 946 inp->inp_laddr = sc->sc_inc.inc_laddr; 947 if ((error = in_pcbconnect(inp, (struct sockaddr *)&sin, 948 thread0.td_ucred, false)) != 0) { 949 inp->inp_laddr = laddr; 950 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 951 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 952 "with error %i\n", 953 s, __func__, error); 954 free(s, M_TCPLOG); 955 } 956 INP_HASH_WUNLOCK(&V_tcbinfo); 957 goto abort; 958 } 959 } 960 #endif /* INET */ 961 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 962 /* Copy old policy into new socket's. */ 963 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 964 printf("syncache_socket: could not copy policy\n"); 965 #endif 966 INP_HASH_WUNLOCK(&V_tcbinfo); 967 tp = intotcpcb(inp); 968 tcp_state_change(tp, TCPS_SYN_RECEIVED); 969 tp->iss = sc->sc_iss; 970 tp->irs = sc->sc_irs; 971 tp->t_port = sc->sc_port; 972 tcp_rcvseqinit(tp); 973 tcp_sendseqinit(tp); 974 blk = sototcpcb(lso)->t_fb; 975 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 976 /* 977 * Our parents t_fb was not the default, 978 * we need to release our ref on tp->t_fb and 979 * pickup one on the new entry. 980 */ 981 struct tcp_function_block *rblk; 982 983 rblk = find_and_ref_tcp_fb(blk); 984 KASSERT(rblk != NULL, 985 ("cannot find blk %p out of syncache?", blk)); 986 if (tp->t_fb->tfb_tcp_fb_fini) 987 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 988 refcount_release(&tp->t_fb->tfb_refcnt); 989 tp->t_fb = rblk; 990 /* 991 * XXXrrs this is quite dangerous, it is possible 992 * for the new function to fail to init. We also 993 * are not asking if the handoff_is_ok though at 994 * the very start thats probalbly ok. 995 */ 996 if (tp->t_fb->tfb_tcp_fb_init) { 997 (*tp->t_fb->tfb_tcp_fb_init)(tp); 998 } 999 } 1000 tp->snd_wl1 = sc->sc_irs; 1001 tp->snd_max = tp->iss + 1; 1002 tp->snd_nxt = tp->iss + 1; 1003 tp->rcv_up = sc->sc_irs + 1; 1004 tp->rcv_wnd = sc->sc_wnd; 1005 tp->rcv_adv += tp->rcv_wnd; 1006 tp->last_ack_sent = tp->rcv_nxt; 1007 1008 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 1009 if (sc->sc_flags & SCF_NOOPT) 1010 tp->t_flags |= TF_NOOPT; 1011 else { 1012 if (sc->sc_flags & SCF_WINSCALE) { 1013 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 1014 tp->snd_scale = sc->sc_requested_s_scale; 1015 tp->request_r_scale = sc->sc_requested_r_scale; 1016 } 1017 if (sc->sc_flags & SCF_TIMESTAMP) { 1018 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 1019 tp->ts_recent = sc->sc_tsreflect; 1020 tp->ts_recent_age = tcp_ts_getticks(); 1021 tp->ts_offset = sc->sc_tsoff; 1022 } 1023 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1024 if (sc->sc_flags & SCF_SIGNATURE) 1025 tp->t_flags |= TF_SIGNATURE; 1026 #endif 1027 if (sc->sc_flags & SCF_SACK) 1028 tp->t_flags |= TF_SACK_PERMIT; 1029 } 1030 1031 tcp_ecn_syncache_socket(tp, sc); 1032 1033 /* 1034 * Set up MSS and get cached values from tcp_hostcache. 1035 * This might overwrite some of the defaults we just set. 1036 */ 1037 tcp_mss(tp, sc->sc_peer_mss); 1038 1039 /* 1040 * If the SYN,ACK was retransmitted, indicate that CWND to be 1041 * limited to one segment in cc_conn_init(). 1042 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1043 */ 1044 if (sc->sc_rxmits > 1) 1045 tp->snd_cwnd = 1; 1046 1047 #ifdef TCP_OFFLOAD 1048 /* 1049 * Allow a TOE driver to install its hooks. Note that we hold the 1050 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1051 * new connection before the TOE driver has done its thing. 1052 */ 1053 if (ADDED_BY_TOE(sc)) { 1054 struct toedev *tod = sc->sc_tod; 1055 1056 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1057 } 1058 #endif 1059 /* 1060 * Copy and activate timers. 1061 */ 1062 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1063 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1064 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1065 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1066 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1067 1068 TCPSTAT_INC(tcps_accepts); 1069 return (so); 1070 1071 abort: 1072 INP_WUNLOCK(inp); 1073 abort2: 1074 if (so != NULL) 1075 soabort(so); 1076 return (NULL); 1077 } 1078 1079 /* 1080 * This function gets called when we receive an ACK for a 1081 * socket in the LISTEN state. We look up the connection 1082 * in the syncache, and if its there, we pull it out of 1083 * the cache and turn it into a full-blown connection in 1084 * the SYN-RECEIVED state. 1085 * 1086 * On syncache_socket() success the newly created socket 1087 * has its underlying inp locked. 1088 */ 1089 int 1090 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1091 struct socket **lsop, struct mbuf *m, uint16_t port) 1092 { 1093 struct syncache *sc; 1094 struct syncache_head *sch; 1095 struct syncache scs; 1096 char *s; 1097 bool locked; 1098 1099 NET_EPOCH_ASSERT(); 1100 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1101 ("%s: can handle only ACK", __func__)); 1102 1103 if (syncache_cookiesonly()) { 1104 sc = NULL; 1105 sch = syncache_hashbucket(inc); 1106 locked = false; 1107 } else { 1108 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1109 locked = true; 1110 SCH_LOCK_ASSERT(sch); 1111 } 1112 1113 #ifdef INVARIANTS 1114 /* 1115 * Test code for syncookies comparing the syncache stored 1116 * values with the reconstructed values from the cookie. 1117 */ 1118 if (sc != NULL) 1119 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1120 #endif 1121 1122 if (sc == NULL) { 1123 /* 1124 * There is no syncache entry, so see if this ACK is 1125 * a returning syncookie. To do this, first: 1126 * A. Check if syncookies are used in case of syncache 1127 * overflows 1128 * B. See if this socket has had a syncache entry dropped in 1129 * the recent past. We don't want to accept a bogus 1130 * syncookie if we've never received a SYN or accept it 1131 * twice. 1132 * C. check that the syncookie is valid. If it is, then 1133 * cobble up a fake syncache entry, and return. 1134 */ 1135 if (locked && !V_tcp_syncookies) { 1136 SCH_UNLOCK(sch); 1137 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1138 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1139 "segment rejected (syncookies disabled)\n", 1140 s, __func__); 1141 goto failed; 1142 } 1143 if (locked && !V_tcp_syncookiesonly && 1144 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1145 SCH_UNLOCK(sch); 1146 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1147 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1148 "segment rejected (no syncache entry)\n", 1149 s, __func__); 1150 goto failed; 1151 } 1152 bzero(&scs, sizeof(scs)); 1153 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1154 if (locked) 1155 SCH_UNLOCK(sch); 1156 if (sc == NULL) { 1157 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1158 log(LOG_DEBUG, "%s; %s: Segment failed " 1159 "SYNCOOKIE authentication, segment rejected " 1160 "(probably spoofed)\n", s, __func__); 1161 goto failed; 1162 } 1163 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1164 /* If received ACK has MD5 signature, check it. */ 1165 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1166 (!TCPMD5_ENABLED() || 1167 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1168 /* Drop the ACK. */ 1169 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1170 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1171 "MD5 signature doesn't match.\n", 1172 s, __func__); 1173 free(s, M_TCPLOG); 1174 } 1175 TCPSTAT_INC(tcps_sig_err_sigopt); 1176 return (-1); /* Do not send RST */ 1177 } 1178 #endif /* TCP_SIGNATURE */ 1179 } else { 1180 if (sc->sc_port != port) { 1181 SCH_UNLOCK(sch); 1182 return (0); 1183 } 1184 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1185 /* 1186 * If listening socket requested TCP digests, check that 1187 * received ACK has signature and it is correct. 1188 * If not, drop the ACK and leave sc entry in th cache, 1189 * because SYN was received with correct signature. 1190 */ 1191 if (sc->sc_flags & SCF_SIGNATURE) { 1192 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1193 /* No signature */ 1194 TCPSTAT_INC(tcps_sig_err_nosigopt); 1195 SCH_UNLOCK(sch); 1196 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1197 log(LOG_DEBUG, "%s; %s: Segment " 1198 "rejected, MD5 signature wasn't " 1199 "provided.\n", s, __func__); 1200 free(s, M_TCPLOG); 1201 } 1202 return (-1); /* Do not send RST */ 1203 } 1204 if (!TCPMD5_ENABLED() || 1205 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1206 /* Doesn't match or no SA */ 1207 SCH_UNLOCK(sch); 1208 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1209 log(LOG_DEBUG, "%s; %s: Segment " 1210 "rejected, MD5 signature doesn't " 1211 "match.\n", s, __func__); 1212 free(s, M_TCPLOG); 1213 } 1214 return (-1); /* Do not send RST */ 1215 } 1216 } 1217 #endif /* TCP_SIGNATURE */ 1218 1219 /* 1220 * RFC 7323 PAWS: If we have a timestamp on this segment and 1221 * it's less than ts_recent, drop it. 1222 * XXXMT: RFC 7323 also requires to send an ACK. 1223 * In tcp_input.c this is only done for TCP segments 1224 * with user data, so be consistent here and just drop 1225 * the segment. 1226 */ 1227 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1228 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1229 SCH_UNLOCK(sch); 1230 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1231 log(LOG_DEBUG, 1232 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1233 "segment dropped\n", s, __func__, 1234 to->to_tsval, sc->sc_tsreflect); 1235 free(s, M_TCPLOG); 1236 } 1237 return (-1); /* Do not send RST */ 1238 } 1239 1240 /* 1241 * If timestamps were not negotiated during SYN/ACK and a 1242 * segment with a timestamp is received, ignore the 1243 * timestamp and process the packet normally. 1244 * See section 3.2 of RFC 7323. 1245 */ 1246 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1247 (to->to_flags & TOF_TS)) { 1248 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1249 log(LOG_DEBUG, "%s; %s: Timestamp not " 1250 "expected, segment processed normally\n", 1251 s, __func__); 1252 free(s, M_TCPLOG); 1253 s = NULL; 1254 } 1255 } 1256 1257 /* 1258 * If timestamps were negotiated during SYN/ACK and a 1259 * segment without a timestamp is received, silently drop 1260 * the segment, unless the missing timestamps are tolerated. 1261 * See section 3.2 of RFC 7323. 1262 */ 1263 if ((sc->sc_flags & SCF_TIMESTAMP) && 1264 !(to->to_flags & TOF_TS)) { 1265 if (V_tcp_tolerate_missing_ts) { 1266 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1267 log(LOG_DEBUG, 1268 "%s; %s: Timestamp missing, " 1269 "segment processed normally\n", 1270 s, __func__); 1271 free(s, M_TCPLOG); 1272 } 1273 } else { 1274 SCH_UNLOCK(sch); 1275 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1276 log(LOG_DEBUG, 1277 "%s; %s: Timestamp missing, " 1278 "segment silently dropped\n", 1279 s, __func__); 1280 free(s, M_TCPLOG); 1281 } 1282 return (-1); /* Do not send RST */ 1283 } 1284 } 1285 1286 /* 1287 * Pull out the entry to unlock the bucket row. 1288 * 1289 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1290 * tcp_state_change(). The tcpcb is not existent at this 1291 * moment. A new one will be allocated via syncache_socket-> 1292 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1293 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1294 */ 1295 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1296 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1297 sch->sch_length--; 1298 #ifdef TCP_OFFLOAD 1299 if (ADDED_BY_TOE(sc)) { 1300 struct toedev *tod = sc->sc_tod; 1301 1302 tod->tod_syncache_removed(tod, sc->sc_todctx); 1303 } 1304 #endif 1305 SCH_UNLOCK(sch); 1306 } 1307 1308 /* 1309 * Segment validation: 1310 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1311 */ 1312 if (th->th_ack != sc->sc_iss + 1) { 1313 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1314 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1315 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1316 goto failed; 1317 } 1318 1319 /* 1320 * The SEQ must fall in the window starting at the received 1321 * initial receive sequence number + 1 (the SYN). 1322 */ 1323 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1324 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1325 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1326 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1327 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1328 goto failed; 1329 } 1330 1331 *lsop = syncache_socket(sc, *lsop, m); 1332 1333 if (*lsop == NULL) 1334 TCPSTAT_INC(tcps_sc_aborted); 1335 else 1336 TCPSTAT_INC(tcps_sc_completed); 1337 1338 /* how do we find the inp for the new socket? */ 1339 if (sc != &scs) 1340 syncache_free(sc); 1341 return (1); 1342 failed: 1343 if (sc != NULL && sc != &scs) 1344 syncache_free(sc); 1345 if (s != NULL) 1346 free(s, M_TCPLOG); 1347 *lsop = NULL; 1348 return (0); 1349 } 1350 1351 static struct socket * 1352 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1353 uint64_t response_cookie) 1354 { 1355 struct inpcb *inp; 1356 struct tcpcb *tp; 1357 unsigned int *pending_counter; 1358 struct socket *so; 1359 1360 NET_EPOCH_ASSERT(); 1361 1362 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1363 so = syncache_socket(sc, lso, m); 1364 if (so == NULL) { 1365 TCPSTAT_INC(tcps_sc_aborted); 1366 atomic_subtract_int(pending_counter, 1); 1367 } else { 1368 soisconnected(so); 1369 inp = sotoinpcb(so); 1370 tp = intotcpcb(inp); 1371 tp->t_flags |= TF_FASTOPEN; 1372 tp->t_tfo_cookie.server = response_cookie; 1373 tp->snd_max = tp->iss; 1374 tp->snd_nxt = tp->iss; 1375 tp->t_tfo_pending = pending_counter; 1376 TCPSTAT_INC(tcps_sc_completed); 1377 } 1378 1379 return (so); 1380 } 1381 1382 /* 1383 * Given a LISTEN socket and an inbound SYN request, add 1384 * this to the syn cache, and send back a segment: 1385 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1386 * to the source. 1387 * 1388 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1389 * Doing so would require that we hold onto the data and deliver it 1390 * to the application. However, if we are the target of a SYN-flood 1391 * DoS attack, an attacker could send data which would eventually 1392 * consume all available buffer space if it were ACKed. By not ACKing 1393 * the data, we avoid this DoS scenario. 1394 * 1395 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1396 * cookie is processed and a new socket is created. In this case, any data 1397 * accompanying the SYN will be queued to the socket by tcp_input() and will 1398 * be ACKed either when the application sends response data or the delayed 1399 * ACK timer expires, whichever comes first. 1400 */ 1401 struct socket * 1402 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1403 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1404 void *todctx, uint8_t iptos, uint16_t port) 1405 { 1406 struct tcpcb *tp; 1407 struct socket *rv = NULL; 1408 struct syncache *sc = NULL; 1409 struct syncache_head *sch; 1410 struct mbuf *ipopts = NULL; 1411 u_int ltflags; 1412 int win, ip_ttl, ip_tos; 1413 char *s; 1414 #ifdef INET6 1415 int autoflowlabel = 0; 1416 #endif 1417 #ifdef MAC 1418 struct label *maclabel; 1419 #endif 1420 struct syncache scs; 1421 struct ucred *cred; 1422 uint64_t tfo_response_cookie; 1423 unsigned int *tfo_pending = NULL; 1424 int tfo_cookie_valid = 0; 1425 int tfo_response_cookie_valid = 0; 1426 bool locked; 1427 1428 INP_RLOCK_ASSERT(inp); /* listen socket */ 1429 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1430 ("%s: unexpected tcp flags", __func__)); 1431 1432 /* 1433 * Combine all so/tp operations very early to drop the INP lock as 1434 * soon as possible. 1435 */ 1436 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1437 tp = sototcpcb(so); 1438 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1439 1440 #ifdef INET6 1441 if (inc->inc_flags & INC_ISIPV6) { 1442 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1443 autoflowlabel = 1; 1444 } 1445 ip_ttl = in6_selecthlim(inp, NULL); 1446 if ((inp->in6p_outputopts == NULL) || 1447 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1448 ip_tos = 0; 1449 } else { 1450 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1451 } 1452 } 1453 #endif 1454 #if defined(INET6) && defined(INET) 1455 else 1456 #endif 1457 #ifdef INET 1458 { 1459 ip_ttl = inp->inp_ip_ttl; 1460 ip_tos = inp->inp_ip_tos; 1461 } 1462 #endif 1463 win = so->sol_sbrcv_hiwat; 1464 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1465 1466 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1467 (tp->t_tfo_pending != NULL) && 1468 (to->to_flags & TOF_FASTOPEN)) { 1469 /* 1470 * Limit the number of pending TFO connections to 1471 * approximately half of the queue limit. This prevents TFO 1472 * SYN floods from starving the service by filling the 1473 * listen queue with bogus TFO connections. 1474 */ 1475 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1476 (so->sol_qlimit / 2)) { 1477 int result; 1478 1479 result = tcp_fastopen_check_cookie(inc, 1480 to->to_tfo_cookie, to->to_tfo_len, 1481 &tfo_response_cookie); 1482 tfo_cookie_valid = (result > 0); 1483 tfo_response_cookie_valid = (result >= 0); 1484 } 1485 1486 /* 1487 * Remember the TFO pending counter as it will have to be 1488 * decremented below if we don't make it to syncache_tfo_expand(). 1489 */ 1490 tfo_pending = tp->t_tfo_pending; 1491 } 1492 1493 #ifdef MAC 1494 if (mac_syncache_init(&maclabel) != 0) { 1495 INP_RUNLOCK(inp); 1496 goto done; 1497 } else 1498 mac_syncache_create(maclabel, inp); 1499 #endif 1500 if (!tfo_cookie_valid) 1501 INP_RUNLOCK(inp); 1502 1503 /* 1504 * Remember the IP options, if any. 1505 */ 1506 #ifdef INET6 1507 if (!(inc->inc_flags & INC_ISIPV6)) 1508 #endif 1509 #ifdef INET 1510 ipopts = (m) ? ip_srcroute(m) : NULL; 1511 #else 1512 ipopts = NULL; 1513 #endif 1514 1515 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1516 /* 1517 * When the socket is TCP-MD5 enabled check that, 1518 * - a signed packet is valid 1519 * - a non-signed packet does not have a security association 1520 * 1521 * If a signed packet fails validation or a non-signed packet has a 1522 * security association, the packet will be dropped. 1523 */ 1524 if (ltflags & TF_SIGNATURE) { 1525 if (to->to_flags & TOF_SIGNATURE) { 1526 if (!TCPMD5_ENABLED() || 1527 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1528 goto done; 1529 } else { 1530 if (TCPMD5_ENABLED() && 1531 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1532 goto done; 1533 } 1534 } else if (to->to_flags & TOF_SIGNATURE) 1535 goto done; 1536 #endif /* TCP_SIGNATURE */ 1537 /* 1538 * See if we already have an entry for this connection. 1539 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1540 * 1541 * XXX: should the syncache be re-initialized with the contents 1542 * of the new SYN here (which may have different options?) 1543 * 1544 * XXX: We do not check the sequence number to see if this is a 1545 * real retransmit or a new connection attempt. The question is 1546 * how to handle such a case; either ignore it as spoofed, or 1547 * drop the current entry and create a new one? 1548 */ 1549 if (syncache_cookiesonly()) { 1550 sc = NULL; 1551 sch = syncache_hashbucket(inc); 1552 locked = false; 1553 } else { 1554 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1555 locked = true; 1556 SCH_LOCK_ASSERT(sch); 1557 } 1558 if (sc != NULL) { 1559 if (tfo_cookie_valid) 1560 INP_RUNLOCK(inp); 1561 TCPSTAT_INC(tcps_sc_dupsyn); 1562 if (ipopts) { 1563 /* 1564 * If we were remembering a previous source route, 1565 * forget it and use the new one we've been given. 1566 */ 1567 if (sc->sc_ipopts) 1568 (void) m_free(sc->sc_ipopts); 1569 sc->sc_ipopts = ipopts; 1570 } 1571 /* 1572 * Update timestamp if present. 1573 */ 1574 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1575 sc->sc_tsreflect = to->to_tsval; 1576 else 1577 sc->sc_flags &= ~SCF_TIMESTAMP; 1578 /* 1579 * Disable ECN if needed. 1580 */ 1581 if ((sc->sc_flags & SCF_ECN) && 1582 ((tcp_get_flags(th) & (TH_ECE|TH_CWR)) != (TH_ECE|TH_CWR))) { 1583 sc->sc_flags &= ~SCF_ECN; 1584 } 1585 #ifdef MAC 1586 /* 1587 * Since we have already unconditionally allocated label 1588 * storage, free it up. The syncache entry will already 1589 * have an initialized label we can use. 1590 */ 1591 mac_syncache_destroy(&maclabel); 1592 #endif 1593 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1594 /* Retransmit SYN|ACK and reset retransmit count. */ 1595 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1596 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1597 "resetting timer and retransmitting SYN|ACK\n", 1598 s, __func__); 1599 free(s, M_TCPLOG); 1600 } 1601 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1602 sc->sc_rxmits = 0; 1603 syncache_timeout(sc, sch, 1); 1604 TCPSTAT_INC(tcps_sndacks); 1605 TCPSTAT_INC(tcps_sndtotal); 1606 } 1607 SCH_UNLOCK(sch); 1608 goto donenoprobe; 1609 } 1610 1611 if (tfo_cookie_valid) { 1612 bzero(&scs, sizeof(scs)); 1613 sc = &scs; 1614 goto skip_alloc; 1615 } 1616 1617 /* 1618 * Skip allocating a syncache entry if we are just going to discard 1619 * it later. 1620 */ 1621 if (!locked) { 1622 bzero(&scs, sizeof(scs)); 1623 sc = &scs; 1624 } else 1625 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1626 if (sc == NULL) { 1627 /* 1628 * The zone allocator couldn't provide more entries. 1629 * Treat this as if the cache was full; drop the oldest 1630 * entry and insert the new one. 1631 */ 1632 TCPSTAT_INC(tcps_sc_zonefail); 1633 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != 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 if (ipopts) 1649 (void) m_free(ipopts); 1650 goto done; 1651 } 1652 } 1653 } 1654 1655 skip_alloc: 1656 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1657 sc->sc_tfo_cookie = &tfo_response_cookie; 1658 1659 /* 1660 * Fill in the syncache values. 1661 */ 1662 #ifdef MAC 1663 sc->sc_label = maclabel; 1664 #endif 1665 sc->sc_cred = cred; 1666 sc->sc_port = port; 1667 cred = NULL; 1668 sc->sc_ipopts = ipopts; 1669 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1670 sc->sc_ip_tos = ip_tos; 1671 sc->sc_ip_ttl = ip_ttl; 1672 #ifdef TCP_OFFLOAD 1673 sc->sc_tod = tod; 1674 sc->sc_todctx = todctx; 1675 #endif 1676 sc->sc_irs = th->th_seq; 1677 sc->sc_flags = 0; 1678 sc->sc_flowlabel = 0; 1679 1680 /* 1681 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1682 * win was derived from socket earlier in the function. 1683 */ 1684 win = imax(win, 0); 1685 win = imin(win, TCP_MAXWIN); 1686 sc->sc_wnd = win; 1687 1688 if (V_tcp_do_rfc1323 && 1689 !(ltflags & TF_NOOPT)) { 1690 /* 1691 * A timestamp received in a SYN makes 1692 * it ok to send timestamp requests and replies. 1693 */ 1694 if (to->to_flags & TOF_TS) { 1695 sc->sc_tsreflect = to->to_tsval; 1696 sc->sc_flags |= SCF_TIMESTAMP; 1697 sc->sc_tsoff = tcp_new_ts_offset(inc); 1698 } 1699 if (to->to_flags & TOF_SCALE) { 1700 int wscale = 0; 1701 1702 /* 1703 * Pick the smallest possible scaling factor that 1704 * will still allow us to scale up to sb_max, aka 1705 * kern.ipc.maxsockbuf. 1706 * 1707 * We do this because there are broken firewalls that 1708 * will corrupt the window scale option, leading to 1709 * the other endpoint believing that our advertised 1710 * window is unscaled. At scale factors larger than 1711 * 5 the unscaled window will drop below 1500 bytes, 1712 * leading to serious problems when traversing these 1713 * broken firewalls. 1714 * 1715 * With the default maxsockbuf of 256K, a scale factor 1716 * of 3 will be chosen by this algorithm. Those who 1717 * choose a larger maxsockbuf should watch out 1718 * for the compatibility problems mentioned above. 1719 * 1720 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1721 * or <SYN,ACK>) segment itself is never scaled. 1722 */ 1723 while (wscale < TCP_MAX_WINSHIFT && 1724 (TCP_MAXWIN << wscale) < sb_max) 1725 wscale++; 1726 sc->sc_requested_r_scale = wscale; 1727 sc->sc_requested_s_scale = to->to_wscale; 1728 sc->sc_flags |= SCF_WINSCALE; 1729 } 1730 } 1731 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1732 /* 1733 * If incoming packet has an MD5 signature, flag this in the 1734 * syncache so that syncache_respond() will do the right thing 1735 * with the SYN+ACK. 1736 */ 1737 if (to->to_flags & TOF_SIGNATURE) 1738 sc->sc_flags |= SCF_SIGNATURE; 1739 #endif /* TCP_SIGNATURE */ 1740 if (to->to_flags & TOF_SACKPERM) 1741 sc->sc_flags |= SCF_SACK; 1742 if (to->to_flags & TOF_MSS) 1743 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1744 if (ltflags & TF_NOOPT) 1745 sc->sc_flags |= SCF_NOOPT; 1746 /* ECN Handshake */ 1747 if (V_tcp_do_ecn) 1748 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1749 1750 if (V_tcp_syncookies) 1751 sc->sc_iss = syncookie_generate(sch, sc); 1752 else 1753 sc->sc_iss = arc4random(); 1754 #ifdef INET6 1755 if (autoflowlabel) { 1756 if (V_tcp_syncookies) 1757 sc->sc_flowlabel = sc->sc_iss; 1758 else 1759 sc->sc_flowlabel = ip6_randomflowlabel(); 1760 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1761 } 1762 #endif 1763 if (locked) 1764 SCH_UNLOCK(sch); 1765 1766 if (tfo_cookie_valid) { 1767 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1768 /* INP_RUNLOCK(inp) will be performed by the caller */ 1769 goto tfo_expanded; 1770 } 1771 1772 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1773 /* 1774 * Do a standard 3-way handshake. 1775 */ 1776 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1777 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1778 syncache_free(sc); 1779 else if (sc != &scs) 1780 syncache_insert(sc, sch); /* locks and unlocks sch */ 1781 TCPSTAT_INC(tcps_sndacks); 1782 TCPSTAT_INC(tcps_sndtotal); 1783 } else { 1784 if (sc != &scs) 1785 syncache_free(sc); 1786 TCPSTAT_INC(tcps_sc_dropped); 1787 } 1788 goto donenoprobe; 1789 1790 done: 1791 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1792 donenoprobe: 1793 if (m) 1794 m_freem(m); 1795 /* 1796 * If tfo_pending is not NULL here, then a TFO SYN that did not 1797 * result in a new socket was processed and the associated pending 1798 * counter has not yet been decremented. All such TFO processing paths 1799 * transit this point. 1800 */ 1801 if (tfo_pending != NULL) 1802 tcp_fastopen_decrement_counter(tfo_pending); 1803 1804 tfo_expanded: 1805 if (cred != NULL) 1806 crfree(cred); 1807 #ifdef MAC 1808 if (sc == &scs) 1809 mac_syncache_destroy(&maclabel); 1810 #endif 1811 return (rv); 1812 } 1813 1814 /* 1815 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1816 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1817 */ 1818 static int 1819 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1820 { 1821 struct ip *ip = NULL; 1822 struct mbuf *m; 1823 struct tcphdr *th = NULL; 1824 struct udphdr *udp = NULL; 1825 int optlen, error = 0; /* Make compiler happy */ 1826 u_int16_t hlen, tlen, mssopt, ulen; 1827 struct tcpopt to; 1828 #ifdef INET6 1829 struct ip6_hdr *ip6 = NULL; 1830 #endif 1831 1832 NET_EPOCH_ASSERT(); 1833 1834 hlen = 1835 #ifdef INET6 1836 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1837 #endif 1838 sizeof(struct ip); 1839 tlen = hlen + sizeof(struct tcphdr); 1840 if (sc->sc_port) { 1841 tlen += sizeof(struct udphdr); 1842 } 1843 /* Determine MSS we advertize to other end of connection. */ 1844 mssopt = tcp_mssopt(&sc->sc_inc); 1845 if (sc->sc_port) 1846 mssopt -= V_tcp_udp_tunneling_overhead; 1847 mssopt = max(mssopt, V_tcp_minmss); 1848 1849 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1850 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1851 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1852 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1853 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1854 1855 /* Create the IP+TCP header from scratch. */ 1856 m = m_gethdr(M_NOWAIT, MT_DATA); 1857 if (m == NULL) 1858 return (ENOBUFS); 1859 #ifdef MAC 1860 mac_syncache_create_mbuf(sc->sc_label, m); 1861 #endif 1862 m->m_data += max_linkhdr; 1863 m->m_len = tlen; 1864 m->m_pkthdr.len = tlen; 1865 m->m_pkthdr.rcvif = NULL; 1866 1867 #ifdef INET6 1868 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1869 ip6 = mtod(m, struct ip6_hdr *); 1870 ip6->ip6_vfc = IPV6_VERSION; 1871 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1872 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1873 ip6->ip6_plen = htons(tlen - hlen); 1874 /* ip6_hlim is set after checksum */ 1875 /* Zero out traffic class and flow label. */ 1876 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1877 ip6->ip6_flow |= sc->sc_flowlabel; 1878 if (sc->sc_port != 0) { 1879 ip6->ip6_nxt = IPPROTO_UDP; 1880 udp = (struct udphdr *)(ip6 + 1); 1881 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1882 udp->uh_dport = sc->sc_port; 1883 ulen = (tlen - sizeof(struct ip6_hdr)); 1884 th = (struct tcphdr *)(udp + 1); 1885 } else { 1886 ip6->ip6_nxt = IPPROTO_TCP; 1887 th = (struct tcphdr *)(ip6 + 1); 1888 } 1889 ip6->ip6_flow |= htonl(sc->sc_ip_tos << 20); 1890 } 1891 #endif 1892 #if defined(INET6) && defined(INET) 1893 else 1894 #endif 1895 #ifdef INET 1896 { 1897 ip = mtod(m, struct ip *); 1898 ip->ip_v = IPVERSION; 1899 ip->ip_hl = sizeof(struct ip) >> 2; 1900 ip->ip_len = htons(tlen); 1901 ip->ip_id = 0; 1902 ip->ip_off = 0; 1903 ip->ip_sum = 0; 1904 ip->ip_src = sc->sc_inc.inc_laddr; 1905 ip->ip_dst = sc->sc_inc.inc_faddr; 1906 ip->ip_ttl = sc->sc_ip_ttl; 1907 ip->ip_tos = sc->sc_ip_tos; 1908 1909 /* 1910 * See if we should do MTU discovery. Route lookups are 1911 * expensive, so we will only unset the DF bit if: 1912 * 1913 * 1) path_mtu_discovery is disabled 1914 * 2) the SCF_UNREACH flag has been set 1915 */ 1916 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1917 ip->ip_off |= htons(IP_DF); 1918 if (sc->sc_port == 0) { 1919 ip->ip_p = IPPROTO_TCP; 1920 th = (struct tcphdr *)(ip + 1); 1921 } else { 1922 ip->ip_p = IPPROTO_UDP; 1923 udp = (struct udphdr *)(ip + 1); 1924 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1925 udp->uh_dport = sc->sc_port; 1926 ulen = (tlen - sizeof(struct ip)); 1927 th = (struct tcphdr *)(udp + 1); 1928 } 1929 } 1930 #endif /* INET */ 1931 th->th_sport = sc->sc_inc.inc_lport; 1932 th->th_dport = sc->sc_inc.inc_fport; 1933 1934 if (flags & TH_SYN) 1935 th->th_seq = htonl(sc->sc_iss); 1936 else 1937 th->th_seq = htonl(sc->sc_iss + 1); 1938 th->th_ack = htonl(sc->sc_irs + 1); 1939 th->th_off = sizeof(struct tcphdr) >> 2; 1940 th->th_win = htons(sc->sc_wnd); 1941 th->th_urp = 0; 1942 1943 flags = tcp_ecn_syncache_respond(flags, sc); 1944 tcp_set_flags(th, flags); 1945 1946 /* Tack on the TCP options. */ 1947 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1948 to.to_flags = 0; 1949 1950 if (flags & TH_SYN) { 1951 to.to_mss = mssopt; 1952 to.to_flags = TOF_MSS; 1953 if (sc->sc_flags & SCF_WINSCALE) { 1954 to.to_wscale = sc->sc_requested_r_scale; 1955 to.to_flags |= TOF_SCALE; 1956 } 1957 if (sc->sc_flags & SCF_SACK) 1958 to.to_flags |= TOF_SACKPERM; 1959 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1960 if (sc->sc_flags & SCF_SIGNATURE) 1961 to.to_flags |= TOF_SIGNATURE; 1962 #endif 1963 if (sc->sc_tfo_cookie) { 1964 to.to_flags |= TOF_FASTOPEN; 1965 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1966 to.to_tfo_cookie = sc->sc_tfo_cookie; 1967 /* don't send cookie again when retransmitting response */ 1968 sc->sc_tfo_cookie = NULL; 1969 } 1970 } 1971 if (sc->sc_flags & SCF_TIMESTAMP) { 1972 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1973 to.to_tsecr = sc->sc_tsreflect; 1974 to.to_flags |= TOF_TS; 1975 } 1976 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1977 1978 /* Adjust headers by option size. */ 1979 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1980 m->m_len += optlen; 1981 m->m_pkthdr.len += optlen; 1982 #ifdef INET6 1983 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1984 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1985 else 1986 #endif 1987 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1988 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1989 if (sc->sc_flags & SCF_SIGNATURE) { 1990 KASSERT(to.to_flags & TOF_SIGNATURE, 1991 ("tcp_addoptions() didn't set tcp_signature")); 1992 1993 /* NOTE: to.to_signature is inside of mbuf */ 1994 if (!TCPMD5_ENABLED() || 1995 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1996 m_freem(m); 1997 return (EACCES); 1998 } 1999 } 2000 #endif 2001 } else 2002 optlen = 0; 2003 2004 if (udp) { 2005 ulen += optlen; 2006 udp->uh_ulen = htons(ulen); 2007 } 2008 M_SETFIB(m, sc->sc_inc.inc_fibnum); 2009 /* 2010 * If we have peer's SYN and it has a flowid, then let's assign it to 2011 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 2012 * to SYN|ACK due to lack of inp here. 2013 */ 2014 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 2015 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 2016 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 2017 } 2018 #ifdef INET6 2019 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2020 if (sc->sc_port) { 2021 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2022 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2023 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2024 IPPROTO_UDP, 0); 2025 th->th_sum = htons(0); 2026 } else { 2027 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2028 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2029 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2030 IPPROTO_TCP, 0); 2031 } 2032 ip6->ip6_hlim = sc->sc_ip_ttl; 2033 #ifdef TCP_OFFLOAD 2034 if (ADDED_BY_TOE(sc)) { 2035 struct toedev *tod = sc->sc_tod; 2036 2037 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2038 2039 return (error); 2040 } 2041 #endif 2042 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2043 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2044 } 2045 #endif 2046 #if defined(INET6) && defined(INET) 2047 else 2048 #endif 2049 #ifdef INET 2050 { 2051 if (sc->sc_port) { 2052 m->m_pkthdr.csum_flags = CSUM_UDP; 2053 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2054 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2055 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2056 th->th_sum = htons(0); 2057 } else { 2058 m->m_pkthdr.csum_flags = CSUM_TCP; 2059 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2060 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2061 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2062 } 2063 #ifdef TCP_OFFLOAD 2064 if (ADDED_BY_TOE(sc)) { 2065 struct toedev *tod = sc->sc_tod; 2066 2067 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2068 2069 return (error); 2070 } 2071 #endif 2072 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2073 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2074 } 2075 #endif 2076 return (error); 2077 } 2078 2079 /* 2080 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2081 * that exceed the capacity of the syncache by avoiding the storage of any 2082 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2083 * attacks where the attacker does not have access to our responses. 2084 * 2085 * Syncookies encode and include all necessary information about the 2086 * connection setup within the SYN|ACK that we send back. That way we 2087 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2088 * (if ever). Normally the syncache and syncookies are running in parallel 2089 * with the latter taking over when the former is exhausted. When matching 2090 * syncache entry is found the syncookie is ignored. 2091 * 2092 * The only reliable information persisting the 3WHS is our initial sequence 2093 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2094 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2095 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2096 * returns and signifies a legitimate connection if it matches the ACK. 2097 * 2098 * The available space of 32 bits to store the hash and to encode the SYN 2099 * option information is very tight and we should have at least 24 bits for 2100 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2101 * 2102 * SYN option information we have to encode to fully restore a connection: 2103 * MSS: is imporant to chose an optimal segment size to avoid IP level 2104 * fragmentation along the path. The common MSS values can be encoded 2105 * in a 3-bit table. Uncommon values are captured by the next lower value 2106 * in the table leading to a slight increase in packetization overhead. 2107 * WSCALE: is necessary to allow large windows to be used for high delay- 2108 * bandwidth product links. Not scaling the window when it was initially 2109 * negotiated is bad for performance as lack of scaling further decreases 2110 * the apparent available send window. We only need to encode the WSCALE 2111 * we received from the remote end. Our end can be recalculated at any 2112 * time. The common WSCALE values can be encoded in a 3-bit table. 2113 * Uncommon values are captured by the next lower value in the table 2114 * making us under-estimate the available window size halving our 2115 * theoretically possible maximum throughput for that connection. 2116 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2117 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2118 * that are included in all segments on a connection. We enable them when 2119 * the ACK has them. 2120 * 2121 * Security of syncookies and attack vectors: 2122 * 2123 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2124 * together with the gloabl secret to make it unique per connection attempt. 2125 * Thus any change of any of those parameters results in a different MAC output 2126 * in an unpredictable way unless a collision is encountered. 24 bits of the 2127 * MAC are embedded into the ISS. 2128 * 2129 * To prevent replay attacks two rotating global secrets are updated with a 2130 * new random value every 15 seconds. The life-time of a syncookie is thus 2131 * 15-30 seconds. 2132 * 2133 * Vector 1: Attacking the secret. This requires finding a weakness in the 2134 * MAC itself or the way it is used here. The attacker can do a chosen plain 2135 * text attack by varying and testing the all parameters under his control. 2136 * The strength depends on the size and randomness of the secret, and the 2137 * cryptographic security of the MAC function. Due to the constant updating 2138 * of the secret the attacker has at most 29.999 seconds to find the secret 2139 * and launch spoofed connections. After that he has to start all over again. 2140 * 2141 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2142 * size an average of 4,823 attempts are required for a 50% chance of success 2143 * to spoof a single syncookie (birthday collision paradox). However the 2144 * attacker is blind and doesn't know if one of his attempts succeeded unless 2145 * he has a side channel to interfere success from. A single connection setup 2146 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2147 * This many attempts are required for each one blind spoofed connection. For 2148 * every additional spoofed connection he has to launch another N attempts. 2149 * Thus for a sustained rate 100 spoofed connections per second approximately 2150 * 1,800,000 packets per second would have to be sent. 2151 * 2152 * NB: The MAC function should be fast so that it doesn't become a CPU 2153 * exhaustion attack vector itself. 2154 * 2155 * References: 2156 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2157 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2158 * http://cr.yp.to/syncookies.html (overview) 2159 * http://cr.yp.to/syncookies/archive (details) 2160 * 2161 * 2162 * Schematic construction of a syncookie enabled Initial Sequence Number: 2163 * 0 1 2 3 2164 * 12345678901234567890123456789012 2165 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2166 * 2167 * x 24 MAC (truncated) 2168 * W 3 Send Window Scale index 2169 * M 3 MSS index 2170 * S 1 SACK permitted 2171 * P 1 Odd/even secret 2172 */ 2173 2174 /* 2175 * Distribution and probability of certain MSS values. Those in between are 2176 * rounded down to the next lower one. 2177 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2178 * .2% .3% 5% 7% 7% 20% 15% 45% 2179 */ 2180 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2181 2182 /* 2183 * Distribution and probability of certain WSCALE values. We have to map the 2184 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2185 * bits based on prevalence of certain values. Where we don't have an exact 2186 * match for are rounded down to the next lower one letting us under-estimate 2187 * the true available window. At the moment this would happen only for the 2188 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2189 * and window size). The absence of the WSCALE option (no scaling in either 2190 * direction) is encoded with index zero. 2191 * [WSCALE values histograms, Allman, 2012] 2192 * X 10 10 35 5 6 14 10% by host 2193 * X 11 4 5 5 18 49 3% by connections 2194 */ 2195 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2196 2197 /* 2198 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2199 * and good cryptographic properties. 2200 */ 2201 static uint32_t 2202 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2203 uint8_t *secbits, uintptr_t secmod) 2204 { 2205 SIPHASH_CTX ctx; 2206 uint32_t siphash[2]; 2207 2208 SipHash24_Init(&ctx); 2209 SipHash_SetKey(&ctx, secbits); 2210 switch (inc->inc_flags & INC_ISIPV6) { 2211 #ifdef INET 2212 case 0: 2213 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2214 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2215 break; 2216 #endif 2217 #ifdef INET6 2218 case INC_ISIPV6: 2219 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2220 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2221 break; 2222 #endif 2223 } 2224 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2225 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2226 SipHash_Update(&ctx, &irs, sizeof(irs)); 2227 SipHash_Update(&ctx, &flags, sizeof(flags)); 2228 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2229 SipHash_Final((u_int8_t *)&siphash, &ctx); 2230 2231 return (siphash[0] ^ siphash[1]); 2232 } 2233 2234 static tcp_seq 2235 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2236 { 2237 u_int i, secbit, wscale; 2238 uint32_t iss, hash; 2239 uint8_t *secbits; 2240 union syncookie cookie; 2241 2242 cookie.cookie = 0; 2243 2244 /* Map our computed MSS into the 3-bit index. */ 2245 for (i = nitems(tcp_sc_msstab) - 1; 2246 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2247 i--) 2248 ; 2249 cookie.flags.mss_idx = i; 2250 2251 /* 2252 * Map the send window scale into the 3-bit index but only if 2253 * the wscale option was received. 2254 */ 2255 if (sc->sc_flags & SCF_WINSCALE) { 2256 wscale = sc->sc_requested_s_scale; 2257 for (i = nitems(tcp_sc_wstab) - 1; 2258 tcp_sc_wstab[i] > wscale && i > 0; 2259 i--) 2260 ; 2261 cookie.flags.wscale_idx = i; 2262 } 2263 2264 /* Can we do SACK? */ 2265 if (sc->sc_flags & SCF_SACK) 2266 cookie.flags.sack_ok = 1; 2267 2268 /* Which of the two secrets to use. */ 2269 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2270 cookie.flags.odd_even = secbit; 2271 2272 secbits = V_tcp_syncache.secret.key[secbit]; 2273 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2274 (uintptr_t)sch); 2275 2276 /* 2277 * Put the flags into the hash and XOR them to get better ISS number 2278 * variance. This doesn't enhance the cryptographic strength and is 2279 * done to prevent the 8 cookie bits from showing up directly on the 2280 * wire. 2281 */ 2282 iss = hash & ~0xff; 2283 iss |= cookie.cookie ^ (hash >> 24); 2284 2285 TCPSTAT_INC(tcps_sc_sendcookie); 2286 return (iss); 2287 } 2288 2289 static struct syncache * 2290 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2291 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2292 struct socket *lso, uint16_t port) 2293 { 2294 uint32_t hash; 2295 uint8_t *secbits; 2296 tcp_seq ack, seq; 2297 int wnd, wscale = 0; 2298 union syncookie cookie; 2299 2300 /* 2301 * Pull information out of SYN-ACK/ACK and revert sequence number 2302 * advances. 2303 */ 2304 ack = th->th_ack - 1; 2305 seq = th->th_seq - 1; 2306 2307 /* 2308 * Unpack the flags containing enough information to restore the 2309 * connection. 2310 */ 2311 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2312 2313 /* Which of the two secrets to use. */ 2314 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2315 2316 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2317 2318 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2319 if ((ack & ~0xff) != (hash & ~0xff)) 2320 return (NULL); 2321 2322 /* Fill in the syncache values. */ 2323 sc->sc_flags = 0; 2324 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2325 sc->sc_ipopts = NULL; 2326 2327 sc->sc_irs = seq; 2328 sc->sc_iss = ack; 2329 2330 switch (inc->inc_flags & INC_ISIPV6) { 2331 #ifdef INET 2332 case 0: 2333 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2334 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2335 break; 2336 #endif 2337 #ifdef INET6 2338 case INC_ISIPV6: 2339 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2340 sc->sc_flowlabel = 2341 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2342 break; 2343 #endif 2344 } 2345 2346 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2347 2348 /* We can simply recompute receive window scale we sent earlier. */ 2349 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2350 wscale++; 2351 2352 /* Only use wscale if it was enabled in the orignal SYN. */ 2353 if (cookie.flags.wscale_idx > 0) { 2354 sc->sc_requested_r_scale = wscale; 2355 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2356 sc->sc_flags |= SCF_WINSCALE; 2357 } 2358 2359 wnd = lso->sol_sbrcv_hiwat; 2360 wnd = imax(wnd, 0); 2361 wnd = imin(wnd, TCP_MAXWIN); 2362 sc->sc_wnd = wnd; 2363 2364 if (cookie.flags.sack_ok) 2365 sc->sc_flags |= SCF_SACK; 2366 2367 if (to->to_flags & TOF_TS) { 2368 sc->sc_flags |= SCF_TIMESTAMP; 2369 sc->sc_tsreflect = to->to_tsval; 2370 sc->sc_tsoff = tcp_new_ts_offset(inc); 2371 } 2372 2373 if (to->to_flags & TOF_SIGNATURE) 2374 sc->sc_flags |= SCF_SIGNATURE; 2375 2376 sc->sc_rxmits = 0; 2377 2378 sc->sc_port = port; 2379 2380 TCPSTAT_INC(tcps_sc_recvcookie); 2381 return (sc); 2382 } 2383 2384 #ifdef INVARIANTS 2385 static int 2386 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2387 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2388 struct socket *lso, uint16_t port) 2389 { 2390 struct syncache scs, *scx; 2391 char *s; 2392 2393 bzero(&scs, sizeof(scs)); 2394 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2395 2396 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2397 return (0); 2398 2399 if (scx != NULL) { 2400 if (sc->sc_peer_mss != scx->sc_peer_mss) 2401 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2402 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2403 2404 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2405 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2406 s, __func__, sc->sc_requested_r_scale, 2407 scx->sc_requested_r_scale); 2408 2409 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2410 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2411 s, __func__, sc->sc_requested_s_scale, 2412 scx->sc_requested_s_scale); 2413 2414 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2415 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2416 } 2417 2418 if (s != NULL) 2419 free(s, M_TCPLOG); 2420 return (0); 2421 } 2422 #endif /* INVARIANTS */ 2423 2424 static void 2425 syncookie_reseed(void *arg) 2426 { 2427 struct tcp_syncache *sc = arg; 2428 uint8_t *secbits; 2429 int secbit; 2430 2431 /* 2432 * Reseeding the secret doesn't have to be protected by a lock. 2433 * It only must be ensured that the new random values are visible 2434 * to all CPUs in a SMP environment. The atomic with release 2435 * semantics ensures that. 2436 */ 2437 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2438 secbits = sc->secret.key[secbit]; 2439 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2440 atomic_add_rel_int(&sc->secret.oddeven, 1); 2441 2442 /* Reschedule ourself. */ 2443 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2444 } 2445 2446 /* 2447 * We have overflowed a bucket. Let's pause dealing with the syncache. 2448 * This function will increment the bucketoverflow statistics appropriately 2449 * (once per pause when pausing is enabled; otherwise, once per overflow). 2450 */ 2451 static void 2452 syncache_pause(struct in_conninfo *inc) 2453 { 2454 time_t delta; 2455 const char *s; 2456 2457 /* XXX: 2458 * 2. Add sysctl read here so we don't get the benefit of this 2459 * change without the new sysctl. 2460 */ 2461 2462 /* 2463 * Try an unlocked read. If we already know that another thread 2464 * has activated the feature, there is no need to proceed. 2465 */ 2466 if (V_tcp_syncache.paused) 2467 return; 2468 2469 /* Are cookied enabled? If not, we can't pause. */ 2470 if (!V_tcp_syncookies) { 2471 TCPSTAT_INC(tcps_sc_bucketoverflow); 2472 return; 2473 } 2474 2475 /* 2476 * We may be the first thread to find an overflow. Get the lock 2477 * and evaluate if we need to take action. 2478 */ 2479 mtx_lock(&V_tcp_syncache.pause_mtx); 2480 if (V_tcp_syncache.paused) { 2481 mtx_unlock(&V_tcp_syncache.pause_mtx); 2482 return; 2483 } 2484 2485 /* Activate protection. */ 2486 V_tcp_syncache.paused = true; 2487 TCPSTAT_INC(tcps_sc_bucketoverflow); 2488 2489 /* 2490 * Determine the last backoff time. If we are seeing a re-newed 2491 * attack within that same time after last reactivating the syncache, 2492 * consider it an extension of the same attack. 2493 */ 2494 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2495 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2496 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2497 delta <<= 1; 2498 V_tcp_syncache.pause_backoff++; 2499 } 2500 } else { 2501 delta = TCP_SYNCACHE_PAUSE_TIME; 2502 V_tcp_syncache.pause_backoff = 0; 2503 } 2504 2505 /* Log a warning, including IP addresses, if able. */ 2506 if (inc != NULL) 2507 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2508 else 2509 s = (const char *)NULL; 2510 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2511 "the next %lld seconds%s%s%s\n", (long long)delta, 2512 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2513 (s != NULL) ? ")" : ""); 2514 free(__DECONST(void *, s), M_TCPLOG); 2515 2516 /* Use the calculated delta to set a new pause time. */ 2517 V_tcp_syncache.pause_until = time_uptime + delta; 2518 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2519 &V_tcp_syncache); 2520 mtx_unlock(&V_tcp_syncache.pause_mtx); 2521 } 2522 2523 /* Evaluate whether we need to unpause. */ 2524 static void 2525 syncache_unpause(void *arg) 2526 { 2527 struct tcp_syncache *sc; 2528 time_t delta; 2529 2530 sc = arg; 2531 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2532 callout_deactivate(&sc->pause_co); 2533 2534 /* 2535 * Check to make sure we are not running early. If the pause 2536 * time has expired, then deactivate the protection. 2537 */ 2538 if ((delta = sc->pause_until - time_uptime) > 0) 2539 callout_schedule(&sc->pause_co, delta * hz); 2540 else 2541 sc->paused = false; 2542 } 2543 2544 /* 2545 * Exports the syncache entries to userland so that netstat can display 2546 * them alongside the other sockets. This function is intended to be 2547 * called only from tcp_pcblist. 2548 * 2549 * Due to concurrency on an active system, the number of pcbs exported 2550 * may have no relation to max_pcbs. max_pcbs merely indicates the 2551 * amount of space the caller allocated for this function to use. 2552 */ 2553 int 2554 syncache_pcblist(struct sysctl_req *req) 2555 { 2556 struct xtcpcb xt; 2557 struct syncache *sc; 2558 struct syncache_head *sch; 2559 int error, i; 2560 2561 bzero(&xt, sizeof(xt)); 2562 xt.xt_len = sizeof(xt); 2563 xt.t_state = TCPS_SYN_RECEIVED; 2564 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2565 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2566 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2567 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2568 2569 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2570 sch = &V_tcp_syncache.hashbase[i]; 2571 SCH_LOCK(sch); 2572 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2573 if (sc->sc_cred != NULL && 2574 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2575 continue; 2576 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2577 xt.xt_inp.inp_vflag = INP_IPV6; 2578 else 2579 xt.xt_inp.inp_vflag = INP_IPV4; 2580 xt.xt_encaps_port = sc->sc_port; 2581 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2582 sizeof (struct in_conninfo)); 2583 error = SYSCTL_OUT(req, &xt, sizeof xt); 2584 if (error) { 2585 SCH_UNLOCK(sch); 2586 return (0); 2587 } 2588 } 2589 SCH_UNLOCK(sch); 2590 } 2591 2592 return (0); 2593 } 2594