1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2001 McAfee, Inc. 5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by Jonathan Lemon 9 * and McAfee Research, the Security Research Division of McAfee, Inc. under 10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. [2001 McAfee, Inc.] 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 __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 TCP_BLACKBOX 94 #include <netinet/tcp_log_buf.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 #include <netinet/udp.h> 100 101 #include <netipsec/ipsec_support.h> 102 103 #include <machine/in_cksum.h> 104 105 #include <security/mac/mac_framework.h> 106 107 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1; 108 #define V_tcp_syncookies VNET(tcp_syncookies) 109 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 110 &VNET_NAME(tcp_syncookies), 0, 111 "Use TCP SYN cookies if the syncache overflows"); 112 113 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0; 114 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 116 &VNET_NAME(tcp_syncookiesonly), 0, 117 "Use only TCP SYN cookies"); 118 119 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 120 #define V_functions_inherit_listen_socket_stack \ 121 VNET(functions_inherit_listen_socket_stack) 122 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 123 CTLFLAG_VNET | CTLFLAG_RW, 124 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 125 "Inherit listen socket's stack"); 126 127 #ifdef TCP_OFFLOAD 128 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 129 #endif 130 131 static void syncache_drop(struct syncache *, struct syncache_head *); 132 static void syncache_free(struct syncache *); 133 static void syncache_insert(struct syncache *, struct syncache_head *); 134 static int syncache_respond(struct syncache *, const struct mbuf *, int); 135 static struct socket *syncache_socket(struct syncache *, struct socket *, 136 struct mbuf *m); 137 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 138 int docallout); 139 static void syncache_timer(void *); 140 141 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 142 uint8_t *, uintptr_t); 143 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 144 static struct syncache 145 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 146 struct syncache *, struct tcphdr *, struct tcpopt *, 147 struct socket *, uint16_t); 148 static void syncache_pause(struct in_conninfo *); 149 static void syncache_unpause(void *); 150 static void syncookie_reseed(void *); 151 #ifdef INVARIANTS 152 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 153 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 154 struct socket *lso, uint16_t port); 155 #endif 156 157 /* 158 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 159 * 3 retransmits corresponds to a timeout with default values of 160 * tcp_rexmit_initial * ( 1 + 161 * tcp_backoff[1] + 162 * tcp_backoff[2] + 163 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 164 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 165 * the odds are that the user has given up attempting to connect by then. 166 */ 167 #define SYNCACHE_MAXREXMTS 3 168 169 /* Arbitrary values */ 170 #define TCP_SYNCACHE_HASHSIZE 512 171 #define TCP_SYNCACHE_BUCKETLIMIT 30 172 173 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 174 #define V_tcp_syncache VNET(tcp_syncache) 175 176 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 177 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 178 "TCP SYN cache"); 179 180 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 181 &VNET_NAME(tcp_syncache.bucket_limit), 0, 182 "Per-bucket hash limit for syncache"); 183 184 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 185 &VNET_NAME(tcp_syncache.cache_limit), 0, 186 "Overall entry limit for syncache"); 187 188 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 189 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 190 191 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 192 &VNET_NAME(tcp_syncache.hashsize), 0, 193 "Size of TCP syncache hashtable"); 194 195 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 196 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 197 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 198 "and mac(4) checks"); 199 200 static int 201 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 202 { 203 int error; 204 u_int new; 205 206 new = V_tcp_syncache.rexmt_limit; 207 error = sysctl_handle_int(oidp, &new, 0, req); 208 if ((error == 0) && (req->newptr != NULL)) { 209 if (new > TCP_MAXRXTSHIFT) 210 error = EINVAL; 211 else 212 V_tcp_syncache.rexmt_limit = new; 213 } 214 return (error); 215 } 216 217 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 218 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 219 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 220 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 221 "Limit on SYN/ACK retransmissions"); 222 223 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 224 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 225 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 226 "Send reset on socket allocation failure"); 227 228 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 229 230 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 231 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 232 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 233 234 /* 235 * Requires the syncache entry to be already removed from the bucket list. 236 */ 237 static void 238 syncache_free(struct syncache *sc) 239 { 240 241 if (sc->sc_ipopts) 242 (void) m_free(sc->sc_ipopts); 243 if (sc->sc_cred) 244 crfree(sc->sc_cred); 245 #ifdef MAC 246 mac_syncache_destroy(&sc->sc_label); 247 #endif 248 249 uma_zfree(V_tcp_syncache.zone, sc); 250 } 251 252 void 253 syncache_init(void) 254 { 255 int i; 256 257 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 258 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 259 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 260 V_tcp_syncache.hash_secret = arc4random(); 261 262 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 263 &V_tcp_syncache.hashsize); 264 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 265 &V_tcp_syncache.bucket_limit); 266 if (!powerof2(V_tcp_syncache.hashsize) || 267 V_tcp_syncache.hashsize == 0) { 268 printf("WARNING: syncache hash size is not a power of 2.\n"); 269 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 270 } 271 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 272 273 /* Set limits. */ 274 V_tcp_syncache.cache_limit = 275 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 276 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 277 &V_tcp_syncache.cache_limit); 278 279 /* Allocate the hash table. */ 280 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 281 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 282 283 #ifdef VIMAGE 284 V_tcp_syncache.vnet = curvnet; 285 #endif 286 287 /* Initialize the hash buckets. */ 288 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 289 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 290 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 291 NULL, MTX_DEF); 292 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 293 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 294 V_tcp_syncache.hashbase[i].sch_length = 0; 295 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 296 V_tcp_syncache.hashbase[i].sch_last_overflow = 297 -(SYNCOOKIE_LIFETIME + 1); 298 } 299 300 /* Create the syncache entry zone. */ 301 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 302 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 303 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 304 V_tcp_syncache.cache_limit); 305 306 /* Start the SYN cookie reseeder callout. */ 307 callout_init(&V_tcp_syncache.secret.reseed, 1); 308 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 309 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 310 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 311 syncookie_reseed, &V_tcp_syncache); 312 313 /* Initialize the pause machinery. */ 314 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 315 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 316 0); 317 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 318 V_tcp_syncache.pause_backoff = 0; 319 V_tcp_syncache.paused = false; 320 } 321 322 #ifdef VIMAGE 323 void 324 syncache_destroy(void) 325 { 326 struct syncache_head *sch; 327 struct syncache *sc, *nsc; 328 int i; 329 330 /* 331 * Stop the re-seed timer before freeing resources. No need to 332 * possibly schedule it another time. 333 */ 334 callout_drain(&V_tcp_syncache.secret.reseed); 335 336 /* Stop the SYN cache pause callout. */ 337 mtx_lock(&V_tcp_syncache.pause_mtx); 338 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 339 mtx_unlock(&V_tcp_syncache.pause_mtx); 340 callout_drain(&V_tcp_syncache.pause_co); 341 } else 342 mtx_unlock(&V_tcp_syncache.pause_mtx); 343 344 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 345 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 346 sch = &V_tcp_syncache.hashbase[i]; 347 callout_drain(&sch->sch_timer); 348 349 SCH_LOCK(sch); 350 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 351 syncache_drop(sc, sch); 352 SCH_UNLOCK(sch); 353 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 354 ("%s: sch->sch_bucket not empty", __func__)); 355 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 356 __func__, sch->sch_length)); 357 mtx_destroy(&sch->sch_mtx); 358 } 359 360 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 361 ("%s: cache_count not 0", __func__)); 362 363 /* Free the allocated global resources. */ 364 uma_zdestroy(V_tcp_syncache.zone); 365 free(V_tcp_syncache.hashbase, M_SYNCACHE); 366 mtx_destroy(&V_tcp_syncache.pause_mtx); 367 } 368 #endif 369 370 /* 371 * Inserts a syncache entry into the specified bucket row. 372 * Locks and unlocks the syncache_head autonomously. 373 */ 374 static void 375 syncache_insert(struct syncache *sc, struct syncache_head *sch) 376 { 377 struct syncache *sc2; 378 379 SCH_LOCK(sch); 380 381 /* 382 * Make sure that we don't overflow the per-bucket limit. 383 * If the bucket is full, toss the oldest element. 384 */ 385 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 386 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 387 ("sch->sch_length incorrect")); 388 syncache_pause(&sc->sc_inc); 389 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 390 sch->sch_last_overflow = time_uptime; 391 syncache_drop(sc2, sch); 392 } 393 394 /* Put it into the bucket. */ 395 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 396 sch->sch_length++; 397 398 #ifdef TCP_OFFLOAD 399 if (ADDED_BY_TOE(sc)) { 400 struct toedev *tod = sc->sc_tod; 401 402 tod->tod_syncache_added(tod, sc->sc_todctx); 403 } 404 #endif 405 406 /* Reinitialize the bucket row's timer. */ 407 if (sch->sch_length == 1) 408 sch->sch_nextc = ticks + INT_MAX; 409 syncache_timeout(sc, sch, 1); 410 411 SCH_UNLOCK(sch); 412 413 TCPSTATES_INC(TCPS_SYN_RECEIVED); 414 TCPSTAT_INC(tcps_sc_added); 415 } 416 417 /* 418 * Remove and free entry from syncache bucket row. 419 * Expects locked syncache head. 420 */ 421 static void 422 syncache_drop(struct syncache *sc, struct syncache_head *sch) 423 { 424 425 SCH_LOCK_ASSERT(sch); 426 427 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 428 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 429 sch->sch_length--; 430 431 #ifdef TCP_OFFLOAD 432 if (ADDED_BY_TOE(sc)) { 433 struct toedev *tod = sc->sc_tod; 434 435 tod->tod_syncache_removed(tod, sc->sc_todctx); 436 } 437 #endif 438 439 syncache_free(sc); 440 } 441 442 /* 443 * Engage/reengage time on bucket row. 444 */ 445 static void 446 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 447 { 448 int rexmt; 449 450 if (sc->sc_rxmits == 0) 451 rexmt = tcp_rexmit_initial; 452 else 453 TCPT_RANGESET(rexmt, 454 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 455 tcp_rexmit_min, TCPTV_REXMTMAX); 456 sc->sc_rxttime = ticks + rexmt; 457 sc->sc_rxmits++; 458 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 459 sch->sch_nextc = sc->sc_rxttime; 460 if (docallout) 461 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 462 syncache_timer, (void *)sch); 463 } 464 } 465 466 /* 467 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 468 * If we have retransmitted an entry the maximum number of times, expire it. 469 * One separate timer for each bucket row. 470 */ 471 static void 472 syncache_timer(void *xsch) 473 { 474 struct syncache_head *sch = (struct syncache_head *)xsch; 475 struct syncache *sc, *nsc; 476 struct epoch_tracker et; 477 int tick = ticks; 478 char *s; 479 bool paused; 480 481 CURVNET_SET(sch->sch_sc->vnet); 482 483 /* NB: syncache_head has already been locked by the callout. */ 484 SCH_LOCK_ASSERT(sch); 485 486 /* 487 * In the following cycle we may remove some entries and/or 488 * advance some timeouts, so re-initialize the bucket timer. 489 */ 490 sch->sch_nextc = tick + INT_MAX; 491 492 /* 493 * If we have paused processing, unconditionally remove 494 * all syncache entries. 495 */ 496 mtx_lock(&V_tcp_syncache.pause_mtx); 497 paused = V_tcp_syncache.paused; 498 mtx_unlock(&V_tcp_syncache.pause_mtx); 499 500 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 501 if (paused) { 502 syncache_drop(sc, sch); 503 continue; 504 } 505 /* 506 * We do not check if the listen socket still exists 507 * and accept the case where the listen socket may be 508 * gone by the time we resend the SYN/ACK. We do 509 * not expect this to happens often. If it does, 510 * then the RST will be sent by the time the remote 511 * host does the SYN/ACK->ACK. 512 */ 513 if (TSTMP_GT(sc->sc_rxttime, tick)) { 514 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 515 sch->sch_nextc = sc->sc_rxttime; 516 continue; 517 } 518 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 519 sc->sc_flags &= ~SCF_ECN_MASK; 520 } 521 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 522 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 523 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 524 "giving up and removing syncache entry\n", 525 s, __func__); 526 free(s, M_TCPLOG); 527 } 528 syncache_drop(sc, sch); 529 TCPSTAT_INC(tcps_sc_stale); 530 continue; 531 } 532 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 533 log(LOG_DEBUG, "%s; %s: Response timeout, " 534 "retransmitting (%u) SYN|ACK\n", 535 s, __func__, sc->sc_rxmits); 536 free(s, M_TCPLOG); 537 } 538 539 NET_EPOCH_ENTER(et); 540 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 541 NET_EPOCH_EXIT(et); 542 TCPSTAT_INC(tcps_sc_retransmitted); 543 syncache_timeout(sc, sch, 0); 544 } 545 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 546 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 547 syncache_timer, (void *)(sch)); 548 CURVNET_RESTORE(); 549 } 550 551 /* 552 * Returns true if the system is only using cookies at the moment. 553 * This could be due to a sysadmin decision to only use cookies, or it 554 * could be due to the system detecting an attack. 555 */ 556 static inline bool 557 syncache_cookiesonly(void) 558 { 559 560 return (V_tcp_syncookies && (V_tcp_syncache.paused || 561 V_tcp_syncookiesonly)); 562 } 563 564 /* 565 * Find the hash bucket for the given connection. 566 */ 567 static struct syncache_head * 568 syncache_hashbucket(struct in_conninfo *inc) 569 { 570 uint32_t hash; 571 572 /* 573 * The hash is built on foreign port + local port + foreign address. 574 * We rely on the fact that struct in_conninfo starts with 16 bits 575 * of foreign port, then 16 bits of local port then followed by 128 576 * bits of foreign address. In case of IPv4 address, the first 3 577 * 32-bit words of the address always are zeroes. 578 */ 579 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 580 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 581 582 return (&V_tcp_syncache.hashbase[hash]); 583 } 584 585 /* 586 * Find an entry in the syncache. 587 * Returns always with locked syncache_head plus a matching entry or NULL. 588 */ 589 static struct syncache * 590 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 591 { 592 struct syncache *sc; 593 struct syncache_head *sch; 594 595 *schp = sch = syncache_hashbucket(inc); 596 SCH_LOCK(sch); 597 598 /* Circle through bucket row to find matching entry. */ 599 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 600 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 601 sizeof(struct in_endpoints)) == 0) 602 break; 603 604 return (sc); /* Always returns with locked sch. */ 605 } 606 607 /* 608 * This function is called when we get a RST for a 609 * non-existent connection, so that we can see if the 610 * connection is in the syn cache. If it is, zap it. 611 * If required send a challenge ACK. 612 */ 613 void 614 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 615 uint16_t port) 616 { 617 struct syncache *sc; 618 struct syncache_head *sch; 619 char *s = NULL; 620 621 if (syncache_cookiesonly()) 622 return; 623 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 624 SCH_LOCK_ASSERT(sch); 625 626 /* 627 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 628 * See RFC 793 page 65, section SEGMENT ARRIVES. 629 */ 630 if (tcp_get_flags(th) & (TH_ACK|TH_SYN|TH_FIN)) { 631 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 632 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 633 "FIN flag set, segment ignored\n", s, __func__); 634 TCPSTAT_INC(tcps_badrst); 635 goto done; 636 } 637 638 /* 639 * No corresponding connection was found in syncache. 640 * If syncookies are enabled and possibly exclusively 641 * used, or we are under memory pressure, a valid RST 642 * may not find a syncache entry. In that case we're 643 * done and no SYN|ACK retransmissions will happen. 644 * Otherwise the RST was misdirected or spoofed. 645 */ 646 if (sc == NULL) { 647 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 648 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 649 "syncache entry (possibly syncookie only), " 650 "segment ignored\n", s, __func__); 651 TCPSTAT_INC(tcps_badrst); 652 goto done; 653 } 654 655 /* The remote UDP encaps port does not match. */ 656 if (sc->sc_port != port) { 657 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 658 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 659 "syncache entry but non-matching UDP encaps port, " 660 "segment ignored\n", s, __func__); 661 TCPSTAT_INC(tcps_badrst); 662 goto done; 663 } 664 665 /* 666 * If the RST bit is set, check the sequence number to see 667 * if this is a valid reset segment. 668 * 669 * RFC 793 page 37: 670 * In all states except SYN-SENT, all reset (RST) segments 671 * are validated by checking their SEQ-fields. A reset is 672 * valid if its sequence number is in the window. 673 * 674 * RFC 793 page 69: 675 * There are four cases for the acceptability test for an incoming 676 * segment: 677 * 678 * Segment Receive Test 679 * Length Window 680 * ------- ------- ------------------------------------------- 681 * 0 0 SEG.SEQ = RCV.NXT 682 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 683 * >0 0 not acceptable 684 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 685 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 686 * 687 * Note that when receiving a SYN segment in the LISTEN state, 688 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 689 * described in RFC 793, page 66. 690 */ 691 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 692 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 693 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 694 if (V_tcp_insecure_rst || 695 th->th_seq == sc->sc_irs + 1) { 696 syncache_drop(sc, sch); 697 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 698 log(LOG_DEBUG, 699 "%s; %s: Our SYN|ACK was rejected, " 700 "connection attempt aborted by remote " 701 "endpoint\n", 702 s, __func__); 703 TCPSTAT_INC(tcps_sc_reset); 704 } else { 705 TCPSTAT_INC(tcps_badrst); 706 /* Send challenge ACK. */ 707 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 708 log(LOG_DEBUG, "%s; %s: RST with invalid " 709 " SEQ %u != NXT %u (+WND %u), " 710 "sending challenge ACK\n", 711 s, __func__, 712 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 713 syncache_respond(sc, m, TH_ACK); 714 } 715 } else { 716 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 717 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 718 "NXT %u (+WND %u), segment ignored\n", 719 s, __func__, 720 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 721 TCPSTAT_INC(tcps_badrst); 722 } 723 724 done: 725 if (s != NULL) 726 free(s, M_TCPLOG); 727 SCH_UNLOCK(sch); 728 } 729 730 void 731 syncache_badack(struct in_conninfo *inc, uint16_t port) 732 { 733 struct syncache *sc; 734 struct syncache_head *sch; 735 736 if (syncache_cookiesonly()) 737 return; 738 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 739 SCH_LOCK_ASSERT(sch); 740 if ((sc != NULL) && (sc->sc_port == port)) { 741 syncache_drop(sc, sch); 742 TCPSTAT_INC(tcps_sc_badack); 743 } 744 SCH_UNLOCK(sch); 745 } 746 747 void 748 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 749 { 750 struct syncache *sc; 751 struct syncache_head *sch; 752 753 if (syncache_cookiesonly()) 754 return; 755 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 756 SCH_LOCK_ASSERT(sch); 757 if (sc == NULL) 758 goto done; 759 760 /* If the port != sc_port, then it's a bogus ICMP msg */ 761 if (port != sc->sc_port) 762 goto done; 763 764 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 765 if (ntohl(th_seq) != sc->sc_iss) 766 goto done; 767 768 /* 769 * If we've rertransmitted 3 times and this is our second error, 770 * we remove the entry. Otherwise, we allow it to continue on. 771 * This prevents us from incorrectly nuking an entry during a 772 * spurious network outage. 773 * 774 * See tcp_notify(). 775 */ 776 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 777 sc->sc_flags |= SCF_UNREACH; 778 goto done; 779 } 780 syncache_drop(sc, sch); 781 TCPSTAT_INC(tcps_sc_unreach); 782 done: 783 SCH_UNLOCK(sch); 784 } 785 786 /* 787 * Build a new TCP socket structure from a syncache entry. 788 * 789 * On success return the newly created socket with its underlying inp locked. 790 */ 791 static struct socket * 792 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 793 { 794 struct tcp_function_block *blk; 795 struct inpcb *inp = NULL; 796 struct socket *so; 797 struct tcpcb *tp; 798 int error; 799 char *s; 800 801 NET_EPOCH_ASSERT(); 802 803 /* 804 * Ok, create the full blown connection, and set things up 805 * as they would have been set up if we had created the 806 * connection when the SYN arrived. 807 */ 808 if ((so = solisten_clone(lso)) == NULL) 809 goto allocfail; 810 #ifdef MAC 811 mac_socketpeer_set_from_mbuf(m, so); 812 #endif 813 error = in_pcballoc(so, &V_tcbinfo); 814 if (error) { 815 sodealloc(so); 816 goto allocfail; 817 } 818 inp = sotoinpcb(so); 819 if ((tp = tcp_newtcpcb(inp)) == NULL) { 820 in_pcbdetach(inp); 821 in_pcbfree(inp); 822 sodealloc(so); 823 goto allocfail; 824 } 825 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 826 #ifdef INET6 827 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 828 inp->inp_vflag &= ~INP_IPV4; 829 inp->inp_vflag |= INP_IPV6; 830 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 831 } else { 832 inp->inp_vflag &= ~INP_IPV6; 833 inp->inp_vflag |= INP_IPV4; 834 #endif 835 inp->inp_ip_ttl = sc->sc_ip_ttl; 836 inp->inp_ip_tos = sc->sc_ip_tos; 837 inp->inp_laddr = sc->sc_inc.inc_laddr; 838 #ifdef INET6 839 } 840 #endif 841 842 /* 843 * If there's an mbuf and it has a flowid, then let's initialise the 844 * inp with that particular flowid. 845 */ 846 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 847 inp->inp_flowid = m->m_pkthdr.flowid; 848 inp->inp_flowtype = M_HASHTYPE_GET(m); 849 #ifdef NUMA 850 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 851 #endif 852 } 853 854 inp->inp_lport = sc->sc_inc.inc_lport; 855 #ifdef INET6 856 if (inp->inp_vflag & INP_IPV6PROTO) { 857 struct inpcb *oinp = sotoinpcb(lso); 858 859 /* 860 * Inherit socket options from the listening socket. 861 * Note that in6p_inputopts are not (and should not be) 862 * copied, since it stores previously received options and is 863 * used to detect if each new option is different than the 864 * previous one and hence should be passed to a user. 865 * If we copied in6p_inputopts, a user would not be able to 866 * receive options just after calling the accept system call. 867 */ 868 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 869 if (oinp->in6p_outputopts) 870 inp->in6p_outputopts = 871 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 872 inp->in6p_hops = oinp->in6p_hops; 873 } 874 875 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 876 struct sockaddr_in6 sin6; 877 878 sin6.sin6_family = AF_INET6; 879 sin6.sin6_len = sizeof(sin6); 880 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 881 sin6.sin6_port = sc->sc_inc.inc_fport; 882 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 883 INP_HASH_WLOCK(&V_tcbinfo); 884 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 885 INP_HASH_WUNLOCK(&V_tcbinfo); 886 if (error != 0) 887 goto abort; 888 /* Override flowlabel from in6_pcbconnect. */ 889 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 890 inp->inp_flow |= sc->sc_flowlabel; 891 } 892 #endif /* INET6 */ 893 #if defined(INET) && defined(INET6) 894 else 895 #endif 896 #ifdef INET 897 { 898 struct sockaddr_in sin; 899 900 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 901 902 if (inp->inp_options == NULL) { 903 inp->inp_options = sc->sc_ipopts; 904 sc->sc_ipopts = NULL; 905 } 906 907 sin.sin_family = AF_INET; 908 sin.sin_len = sizeof(sin); 909 sin.sin_addr = sc->sc_inc.inc_faddr; 910 sin.sin_port = sc->sc_inc.inc_fport; 911 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 912 INP_HASH_WLOCK(&V_tcbinfo); 913 error = in_pcbconnect(inp, &sin, thread0.td_ucred, false); 914 INP_HASH_WUNLOCK(&V_tcbinfo); 915 if (error != 0) 916 goto abort; 917 } 918 #endif /* INET */ 919 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 920 /* Copy old policy into new socket's. */ 921 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 922 printf("syncache_socket: could not copy policy\n"); 923 #endif 924 tp->t_state = TCPS_SYN_RECEIVED; 925 tp->iss = sc->sc_iss; 926 tp->irs = sc->sc_irs; 927 tp->t_port = sc->sc_port; 928 tcp_rcvseqinit(tp); 929 tcp_sendseqinit(tp); 930 blk = sototcpcb(lso)->t_fb; 931 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 932 /* 933 * Our parents t_fb was not the default, 934 * we need to release our ref on tp->t_fb and 935 * pickup one on the new entry. 936 */ 937 struct tcp_function_block *rblk; 938 void *ptr = NULL; 939 940 rblk = find_and_ref_tcp_fb(blk); 941 KASSERT(rblk != NULL, 942 ("cannot find blk %p out of syncache?", blk)); 943 944 if (rblk->tfb_tcp_fb_init == NULL || 945 (*rblk->tfb_tcp_fb_init)(tp, &ptr) == 0) { 946 /* Release the old stack */ 947 if (tp->t_fb->tfb_tcp_fb_fini != NULL) 948 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 949 refcount_release(&tp->t_fb->tfb_refcnt); 950 /* Now set in all the pointers */ 951 tp->t_fb = rblk; 952 tp->t_fb_ptr = ptr; 953 } else { 954 /* 955 * Initialization failed. Release the reference count on 956 * the looked up default stack. 957 */ 958 refcount_release(&rblk->tfb_refcnt); 959 } 960 } 961 tp->snd_wl1 = sc->sc_irs; 962 tp->snd_max = tp->iss + 1; 963 tp->snd_nxt = tp->iss + 1; 964 tp->rcv_up = sc->sc_irs + 1; 965 tp->rcv_wnd = sc->sc_wnd; 966 tp->rcv_adv += tp->rcv_wnd; 967 tp->last_ack_sent = tp->rcv_nxt; 968 969 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 970 if (sc->sc_flags & SCF_NOOPT) 971 tp->t_flags |= TF_NOOPT; 972 else { 973 if (sc->sc_flags & SCF_WINSCALE) { 974 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 975 tp->snd_scale = sc->sc_requested_s_scale; 976 tp->request_r_scale = sc->sc_requested_r_scale; 977 } 978 if (sc->sc_flags & SCF_TIMESTAMP) { 979 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 980 tp->ts_recent = sc->sc_tsreflect; 981 tp->ts_recent_age = tcp_ts_getticks(); 982 tp->ts_offset = sc->sc_tsoff; 983 } 984 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 985 if (sc->sc_flags & SCF_SIGNATURE) 986 tp->t_flags |= TF_SIGNATURE; 987 #endif 988 if (sc->sc_flags & SCF_SACK) 989 tp->t_flags |= TF_SACK_PERMIT; 990 } 991 992 tcp_ecn_syncache_socket(tp, sc); 993 994 /* 995 * Set up MSS and get cached values from tcp_hostcache. 996 * This might overwrite some of the defaults we just set. 997 */ 998 tcp_mss(tp, sc->sc_peer_mss); 999 1000 /* 1001 * If the SYN,ACK was retransmitted, indicate that CWND to be 1002 * limited to one segment in cc_conn_init(). 1003 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1004 */ 1005 if (sc->sc_rxmits > 1) 1006 tp->snd_cwnd = 1; 1007 1008 #ifdef TCP_OFFLOAD 1009 /* 1010 * Allow a TOE driver to install its hooks. Note that we hold the 1011 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1012 * new connection before the TOE driver has done its thing. 1013 */ 1014 if (ADDED_BY_TOE(sc)) { 1015 struct toedev *tod = sc->sc_tod; 1016 1017 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1018 } 1019 #endif 1020 #ifdef TCP_BLACKBOX 1021 /* 1022 * Inherit the log state from the listening socket, if 1023 * - the log state of the listening socket is not off and 1024 * - the listening socket was not auto selected from all sessions and 1025 * - a log id is not set on the listening socket. 1026 * This avoids inheriting a log state which was automatically set. 1027 */ 1028 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 1029 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 1030 (sototcpcb(lso)->t_lib == NULL)) { 1031 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 1032 } 1033 #endif 1034 /* 1035 * Copy and activate timers. 1036 */ 1037 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 1038 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1039 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1040 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1041 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1042 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1043 1044 TCPSTAT_INC(tcps_accepts); 1045 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1046 1047 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1048 tp->t_flags |= TF_SONOTCONN; 1049 1050 return (so); 1051 1052 allocfail: 1053 /* 1054 * Drop the connection; we will either send a RST or have the peer 1055 * retransmit its SYN again after its RTO and try again. 1056 */ 1057 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1058 log(LOG_DEBUG, "%s; %s: Socket create failed " 1059 "due to limits or memory shortage\n", 1060 s, __func__); 1061 free(s, M_TCPLOG); 1062 } 1063 TCPSTAT_INC(tcps_listendrop); 1064 return (NULL); 1065 1066 abort: 1067 in_pcbdetach(inp); 1068 in_pcbfree(inp); 1069 sodealloc(so); 1070 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1071 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1072 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1073 error); 1074 free(s, M_TCPLOG); 1075 } 1076 TCPSTAT_INC(tcps_listendrop); 1077 return (NULL); 1078 } 1079 1080 /* 1081 * This function gets called when we receive an ACK for a 1082 * socket in the LISTEN state. We look up the connection 1083 * in the syncache, and if its there, we pull it out of 1084 * the cache and turn it into a full-blown connection in 1085 * the SYN-RECEIVED state. 1086 * 1087 * On syncache_socket() success the newly created socket 1088 * has its underlying inp locked. 1089 */ 1090 int 1091 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1092 struct socket **lsop, struct mbuf *m, uint16_t port) 1093 { 1094 struct syncache *sc; 1095 struct syncache_head *sch; 1096 struct syncache scs; 1097 char *s; 1098 bool locked; 1099 1100 NET_EPOCH_ASSERT(); 1101 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1102 ("%s: can handle only ACK", __func__)); 1103 1104 if (syncache_cookiesonly()) { 1105 sc = NULL; 1106 sch = syncache_hashbucket(inc); 1107 locked = false; 1108 } else { 1109 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1110 locked = true; 1111 SCH_LOCK_ASSERT(sch); 1112 } 1113 1114 #ifdef INVARIANTS 1115 /* 1116 * Test code for syncookies comparing the syncache stored 1117 * values with the reconstructed values from the cookie. 1118 */ 1119 if (sc != NULL) 1120 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1121 #endif 1122 1123 if (sc == NULL) { 1124 /* 1125 * There is no syncache entry, so see if this ACK is 1126 * a returning syncookie. To do this, first: 1127 * A. Check if syncookies are used in case of syncache 1128 * overflows 1129 * B. See if this socket has had a syncache entry dropped in 1130 * the recent past. We don't want to accept a bogus 1131 * syncookie if we've never received a SYN or accept it 1132 * twice. 1133 * C. check that the syncookie is valid. If it is, then 1134 * cobble up a fake syncache entry, and return. 1135 */ 1136 if (locked && !V_tcp_syncookies) { 1137 SCH_UNLOCK(sch); 1138 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1139 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1140 "segment rejected (syncookies disabled)\n", 1141 s, __func__); 1142 goto failed; 1143 } 1144 if (locked && !V_tcp_syncookiesonly && 1145 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1146 SCH_UNLOCK(sch); 1147 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1148 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1149 "segment rejected (no syncache entry)\n", 1150 s, __func__); 1151 goto failed; 1152 } 1153 bzero(&scs, sizeof(scs)); 1154 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1155 if (locked) 1156 SCH_UNLOCK(sch); 1157 if (sc == NULL) { 1158 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1159 log(LOG_DEBUG, "%s; %s: Segment failed " 1160 "SYNCOOKIE authentication, segment rejected " 1161 "(probably spoofed)\n", s, __func__); 1162 goto failed; 1163 } 1164 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1165 /* If received ACK has MD5 signature, check it. */ 1166 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1167 (!TCPMD5_ENABLED() || 1168 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1169 /* Drop the ACK. */ 1170 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1171 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1172 "MD5 signature doesn't match.\n", 1173 s, __func__); 1174 free(s, M_TCPLOG); 1175 } 1176 TCPSTAT_INC(tcps_sig_err_sigopt); 1177 return (-1); /* Do not send RST */ 1178 } 1179 #endif /* TCP_SIGNATURE */ 1180 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1181 } else { 1182 if (sc->sc_port != port) { 1183 SCH_UNLOCK(sch); 1184 return (0); 1185 } 1186 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1187 /* 1188 * If listening socket requested TCP digests, check that 1189 * received ACK has signature and it is correct. 1190 * If not, drop the ACK and leave sc entry in th cache, 1191 * because SYN was received with correct signature. 1192 */ 1193 if (sc->sc_flags & SCF_SIGNATURE) { 1194 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1195 /* No signature */ 1196 TCPSTAT_INC(tcps_sig_err_nosigopt); 1197 SCH_UNLOCK(sch); 1198 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1199 log(LOG_DEBUG, "%s; %s: Segment " 1200 "rejected, MD5 signature wasn't " 1201 "provided.\n", s, __func__); 1202 free(s, M_TCPLOG); 1203 } 1204 return (-1); /* Do not send RST */ 1205 } 1206 if (!TCPMD5_ENABLED() || 1207 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1208 /* Doesn't match or no SA */ 1209 SCH_UNLOCK(sch); 1210 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1211 log(LOG_DEBUG, "%s; %s: Segment " 1212 "rejected, MD5 signature doesn't " 1213 "match.\n", s, __func__); 1214 free(s, M_TCPLOG); 1215 } 1216 return (-1); /* Do not send RST */ 1217 } 1218 } 1219 #endif /* TCP_SIGNATURE */ 1220 1221 /* 1222 * RFC 7323 PAWS: If we have a timestamp on this segment and 1223 * it's less than ts_recent, drop it. 1224 * XXXMT: RFC 7323 also requires to send an ACK. 1225 * In tcp_input.c this is only done for TCP segments 1226 * with user data, so be consistent here and just drop 1227 * the segment. 1228 */ 1229 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1230 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1231 SCH_UNLOCK(sch); 1232 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1233 log(LOG_DEBUG, 1234 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1235 "segment dropped\n", s, __func__, 1236 to->to_tsval, sc->sc_tsreflect); 1237 free(s, M_TCPLOG); 1238 } 1239 return (-1); /* Do not send RST */ 1240 } 1241 1242 /* 1243 * If timestamps were not negotiated during SYN/ACK and a 1244 * segment with a timestamp is received, ignore the 1245 * timestamp and process the packet normally. 1246 * See section 3.2 of RFC 7323. 1247 */ 1248 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1249 (to->to_flags & TOF_TS)) { 1250 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1251 log(LOG_DEBUG, "%s; %s: Timestamp not " 1252 "expected, segment processed normally\n", 1253 s, __func__); 1254 free(s, M_TCPLOG); 1255 s = NULL; 1256 } 1257 } 1258 1259 /* 1260 * If timestamps were negotiated during SYN/ACK and a 1261 * segment without a timestamp is received, silently drop 1262 * the segment, unless the missing timestamps are tolerated. 1263 * See section 3.2 of RFC 7323. 1264 */ 1265 if ((sc->sc_flags & SCF_TIMESTAMP) && 1266 !(to->to_flags & TOF_TS)) { 1267 if (V_tcp_tolerate_missing_ts) { 1268 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1269 log(LOG_DEBUG, 1270 "%s; %s: Timestamp missing, " 1271 "segment processed normally\n", 1272 s, __func__); 1273 free(s, M_TCPLOG); 1274 } 1275 } else { 1276 SCH_UNLOCK(sch); 1277 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1278 log(LOG_DEBUG, 1279 "%s; %s: Timestamp missing, " 1280 "segment silently dropped\n", 1281 s, __func__); 1282 free(s, M_TCPLOG); 1283 } 1284 return (-1); /* Do not send RST */ 1285 } 1286 } 1287 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1288 sch->sch_length--; 1289 #ifdef TCP_OFFLOAD 1290 if (ADDED_BY_TOE(sc)) { 1291 struct toedev *tod = sc->sc_tod; 1292 1293 tod->tod_syncache_removed(tod, sc->sc_todctx); 1294 } 1295 #endif 1296 SCH_UNLOCK(sch); 1297 } 1298 1299 /* 1300 * Segment validation: 1301 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1302 */ 1303 if (th->th_ack != sc->sc_iss + 1) { 1304 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1305 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1306 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1307 goto failed; 1308 } 1309 1310 /* 1311 * The SEQ must fall in the window starting at the received 1312 * initial receive sequence number + 1 (the SYN). 1313 */ 1314 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1315 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1316 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1317 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1318 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1319 goto failed; 1320 } 1321 1322 *lsop = syncache_socket(sc, *lsop, m); 1323 1324 if (__predict_false(*lsop == NULL)) { 1325 TCPSTAT_INC(tcps_sc_aborted); 1326 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1327 } else 1328 TCPSTAT_INC(tcps_sc_completed); 1329 1330 /* how do we find the inp for the new socket? */ 1331 if (sc != &scs) 1332 syncache_free(sc); 1333 return (1); 1334 failed: 1335 if (sc != NULL) { 1336 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1337 if (sc != &scs) 1338 syncache_free(sc); 1339 } 1340 if (s != NULL) 1341 free(s, M_TCPLOG); 1342 *lsop = NULL; 1343 return (0); 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 syncache_head *sch; 1406 struct mbuf *ipopts = NULL; 1407 u_int ltflags; 1408 int win, ip_ttl, ip_tos; 1409 char *s; 1410 #ifdef INET6 1411 int autoflowlabel = 0; 1412 #endif 1413 #ifdef MAC 1414 struct label *maclabel; 1415 #endif 1416 struct syncache scs; 1417 struct ucred *cred; 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 && IS_FASTOPEN(tp->t_flags) && 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, m, 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 } 1604 SCH_UNLOCK(sch); 1605 goto donenoprobe; 1606 } 1607 1608 if (tfo_cookie_valid) { 1609 bzero(&scs, sizeof(scs)); 1610 sc = &scs; 1611 goto skip_alloc; 1612 } 1613 1614 /* 1615 * Skip allocating a syncache entry if we are just going to discard 1616 * it later. 1617 */ 1618 if (!locked) { 1619 bzero(&scs, sizeof(scs)); 1620 sc = &scs; 1621 } else 1622 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1623 if (sc == NULL) { 1624 /* 1625 * The zone allocator couldn't provide more entries. 1626 * Treat this as if the cache was full; drop the oldest 1627 * entry and insert the new one. 1628 */ 1629 TCPSTAT_INC(tcps_sc_zonefail); 1630 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1631 sch->sch_last_overflow = time_uptime; 1632 syncache_drop(sc, sch); 1633 syncache_pause(inc); 1634 } 1635 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1636 if (sc == NULL) { 1637 if (V_tcp_syncookies) { 1638 bzero(&scs, sizeof(scs)); 1639 sc = &scs; 1640 } else { 1641 KASSERT(locked, 1642 ("%s: bucket unexpectedly unlocked", 1643 __func__)); 1644 SCH_UNLOCK(sch); 1645 if (ipopts) 1646 (void) m_free(ipopts); 1647 goto done; 1648 } 1649 } 1650 } 1651 1652 skip_alloc: 1653 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1654 sc->sc_tfo_cookie = &tfo_response_cookie; 1655 1656 /* 1657 * Fill in the syncache values. 1658 */ 1659 #ifdef MAC 1660 sc->sc_label = maclabel; 1661 #endif 1662 sc->sc_cred = cred; 1663 sc->sc_port = port; 1664 cred = NULL; 1665 sc->sc_ipopts = ipopts; 1666 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1667 sc->sc_ip_tos = ip_tos; 1668 sc->sc_ip_ttl = ip_ttl; 1669 #ifdef TCP_OFFLOAD 1670 sc->sc_tod = tod; 1671 sc->sc_todctx = todctx; 1672 #endif 1673 sc->sc_irs = th->th_seq; 1674 sc->sc_flags = 0; 1675 sc->sc_flowlabel = 0; 1676 1677 /* 1678 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1679 * win was derived from socket earlier in the function. 1680 */ 1681 win = imax(win, 0); 1682 win = imin(win, TCP_MAXWIN); 1683 sc->sc_wnd = win; 1684 1685 if (V_tcp_do_rfc1323 && 1686 !(ltflags & TF_NOOPT)) { 1687 /* 1688 * A timestamp received in a SYN makes 1689 * it ok to send timestamp requests and replies. 1690 */ 1691 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1692 sc->sc_tsreflect = to->to_tsval; 1693 sc->sc_flags |= SCF_TIMESTAMP; 1694 sc->sc_tsoff = tcp_new_ts_offset(inc); 1695 } 1696 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1697 int wscale = 0; 1698 1699 /* 1700 * Pick the smallest possible scaling factor that 1701 * will still allow us to scale up to sb_max, aka 1702 * kern.ipc.maxsockbuf. 1703 * 1704 * We do this because there are broken firewalls that 1705 * will corrupt the window scale option, leading to 1706 * the other endpoint believing that our advertised 1707 * window is unscaled. At scale factors larger than 1708 * 5 the unscaled window will drop below 1500 bytes, 1709 * leading to serious problems when traversing these 1710 * broken firewalls. 1711 * 1712 * With the default maxsockbuf of 256K, a scale factor 1713 * of 3 will be chosen by this algorithm. Those who 1714 * choose a larger maxsockbuf should watch out 1715 * for the compatibility problems mentioned above. 1716 * 1717 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1718 * or <SYN,ACK>) segment itself is never scaled. 1719 */ 1720 while (wscale < TCP_MAX_WINSHIFT && 1721 (TCP_MAXWIN << wscale) < sb_max) 1722 wscale++; 1723 sc->sc_requested_r_scale = wscale; 1724 sc->sc_requested_s_scale = to->to_wscale; 1725 sc->sc_flags |= SCF_WINSCALE; 1726 } 1727 } 1728 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1729 /* 1730 * If incoming packet has an MD5 signature, flag this in the 1731 * syncache so that syncache_respond() will do the right thing 1732 * with the SYN+ACK. 1733 */ 1734 if (to->to_flags & TOF_SIGNATURE) 1735 sc->sc_flags |= SCF_SIGNATURE; 1736 #endif /* TCP_SIGNATURE */ 1737 if (to->to_flags & TOF_SACKPERM) 1738 sc->sc_flags |= SCF_SACK; 1739 if (to->to_flags & TOF_MSS) 1740 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1741 if (ltflags & TF_NOOPT) 1742 sc->sc_flags |= SCF_NOOPT; 1743 /* ECN Handshake */ 1744 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1745 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1746 1747 if (V_tcp_syncookies) 1748 sc->sc_iss = syncookie_generate(sch, sc); 1749 else 1750 sc->sc_iss = arc4random(); 1751 #ifdef INET6 1752 if (autoflowlabel) { 1753 if (V_tcp_syncookies) 1754 sc->sc_flowlabel = sc->sc_iss; 1755 else 1756 sc->sc_flowlabel = ip6_randomflowlabel(); 1757 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1758 } 1759 #endif 1760 if (locked) 1761 SCH_UNLOCK(sch); 1762 1763 if (tfo_cookie_valid) { 1764 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1765 /* INP_RUNLOCK(inp) will be performed by the caller */ 1766 goto tfo_expanded; 1767 } 1768 1769 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1770 /* 1771 * Do a standard 3-way handshake. 1772 */ 1773 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1774 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1775 syncache_free(sc); 1776 else if (sc != &scs) 1777 syncache_insert(sc, sch); /* locks and unlocks sch */ 1778 TCPSTAT_INC(tcps_sndacks); 1779 TCPSTAT_INC(tcps_sndtotal); 1780 } else { 1781 if (sc != &scs) 1782 syncache_free(sc); 1783 TCPSTAT_INC(tcps_sc_dropped); 1784 } 1785 goto donenoprobe; 1786 1787 done: 1788 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1789 donenoprobe: 1790 if (m) 1791 m_freem(m); 1792 /* 1793 * If tfo_pending is not NULL here, then a TFO SYN that did not 1794 * result in a new socket was processed and the associated pending 1795 * counter has not yet been decremented. All such TFO processing paths 1796 * transit this point. 1797 */ 1798 if (tfo_pending != NULL) 1799 tcp_fastopen_decrement_counter(tfo_pending); 1800 1801 tfo_expanded: 1802 if (cred != NULL) 1803 crfree(cred); 1804 #ifdef MAC 1805 if (sc == &scs) 1806 mac_syncache_destroy(&maclabel); 1807 #endif 1808 return (rv); 1809 } 1810 1811 /* 1812 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1813 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1814 */ 1815 static int 1816 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1817 { 1818 struct ip *ip = NULL; 1819 struct mbuf *m; 1820 struct tcphdr *th = NULL; 1821 struct udphdr *udp = NULL; 1822 int optlen, error = 0; /* Make compiler happy */ 1823 u_int16_t hlen, tlen, mssopt, ulen; 1824 struct tcpopt to; 1825 #ifdef INET6 1826 struct ip6_hdr *ip6 = NULL; 1827 #endif 1828 1829 NET_EPOCH_ASSERT(); 1830 1831 hlen = 1832 #ifdef INET6 1833 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1834 #endif 1835 sizeof(struct ip); 1836 tlen = hlen + sizeof(struct tcphdr); 1837 if (sc->sc_port) { 1838 tlen += sizeof(struct udphdr); 1839 } 1840 /* Determine MSS we advertize to other end of connection. */ 1841 mssopt = tcp_mssopt(&sc->sc_inc); 1842 if (sc->sc_port) 1843 mssopt -= V_tcp_udp_tunneling_overhead; 1844 mssopt = max(mssopt, V_tcp_minmss); 1845 1846 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1847 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1848 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1849 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1850 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1851 1852 /* Create the IP+TCP header from scratch. */ 1853 m = m_gethdr(M_NOWAIT, MT_DATA); 1854 if (m == NULL) 1855 return (ENOBUFS); 1856 #ifdef MAC 1857 mac_syncache_create_mbuf(sc->sc_label, m); 1858 #endif 1859 m->m_data += max_linkhdr; 1860 m->m_len = tlen; 1861 m->m_pkthdr.len = tlen; 1862 m->m_pkthdr.rcvif = NULL; 1863 1864 #ifdef INET6 1865 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1866 ip6 = mtod(m, struct ip6_hdr *); 1867 ip6->ip6_vfc = IPV6_VERSION; 1868 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1869 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1870 ip6->ip6_plen = htons(tlen - hlen); 1871 /* ip6_hlim is set after checksum */ 1872 /* Zero out traffic class and flow label. */ 1873 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1874 ip6->ip6_flow |= sc->sc_flowlabel; 1875 if (sc->sc_port != 0) { 1876 ip6->ip6_nxt = IPPROTO_UDP; 1877 udp = (struct udphdr *)(ip6 + 1); 1878 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1879 udp->uh_dport = sc->sc_port; 1880 ulen = (tlen - sizeof(struct ip6_hdr)); 1881 th = (struct tcphdr *)(udp + 1); 1882 } else { 1883 ip6->ip6_nxt = IPPROTO_TCP; 1884 th = (struct tcphdr *)(ip6 + 1); 1885 } 1886 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1887 } 1888 #endif 1889 #if defined(INET6) && defined(INET) 1890 else 1891 #endif 1892 #ifdef INET 1893 { 1894 ip = mtod(m, struct ip *); 1895 ip->ip_v = IPVERSION; 1896 ip->ip_hl = sizeof(struct ip) >> 2; 1897 ip->ip_len = htons(tlen); 1898 ip->ip_id = 0; 1899 ip->ip_off = 0; 1900 ip->ip_sum = 0; 1901 ip->ip_src = sc->sc_inc.inc_laddr; 1902 ip->ip_dst = sc->sc_inc.inc_faddr; 1903 ip->ip_ttl = sc->sc_ip_ttl; 1904 ip->ip_tos = sc->sc_ip_tos; 1905 1906 /* 1907 * See if we should do MTU discovery. Route lookups are 1908 * expensive, so we will only unset the DF bit if: 1909 * 1910 * 1) path_mtu_discovery is disabled 1911 * 2) the SCF_UNREACH flag has been set 1912 */ 1913 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1914 ip->ip_off |= htons(IP_DF); 1915 if (sc->sc_port == 0) { 1916 ip->ip_p = IPPROTO_TCP; 1917 th = (struct tcphdr *)(ip + 1); 1918 } else { 1919 ip->ip_p = IPPROTO_UDP; 1920 udp = (struct udphdr *)(ip + 1); 1921 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1922 udp->uh_dport = sc->sc_port; 1923 ulen = (tlen - sizeof(struct ip)); 1924 th = (struct tcphdr *)(udp + 1); 1925 } 1926 } 1927 #endif /* INET */ 1928 th->th_sport = sc->sc_inc.inc_lport; 1929 th->th_dport = sc->sc_inc.inc_fport; 1930 1931 if (flags & TH_SYN) 1932 th->th_seq = htonl(sc->sc_iss); 1933 else 1934 th->th_seq = htonl(sc->sc_iss + 1); 1935 th->th_ack = htonl(sc->sc_irs + 1); 1936 th->th_off = sizeof(struct tcphdr) >> 2; 1937 th->th_win = htons(sc->sc_wnd); 1938 th->th_urp = 0; 1939 1940 flags = tcp_ecn_syncache_respond(flags, sc); 1941 tcp_set_flags(th, flags); 1942 1943 /* Tack on the TCP options. */ 1944 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1945 to.to_flags = 0; 1946 1947 if (flags & TH_SYN) { 1948 to.to_mss = mssopt; 1949 to.to_flags = TOF_MSS; 1950 if (sc->sc_flags & SCF_WINSCALE) { 1951 to.to_wscale = sc->sc_requested_r_scale; 1952 to.to_flags |= TOF_SCALE; 1953 } 1954 if (sc->sc_flags & SCF_SACK) 1955 to.to_flags |= TOF_SACKPERM; 1956 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1957 if (sc->sc_flags & SCF_SIGNATURE) 1958 to.to_flags |= TOF_SIGNATURE; 1959 #endif 1960 if (sc->sc_tfo_cookie) { 1961 to.to_flags |= TOF_FASTOPEN; 1962 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1963 to.to_tfo_cookie = sc->sc_tfo_cookie; 1964 /* don't send cookie again when retransmitting response */ 1965 sc->sc_tfo_cookie = NULL; 1966 } 1967 } 1968 if (sc->sc_flags & SCF_TIMESTAMP) { 1969 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1970 to.to_tsecr = sc->sc_tsreflect; 1971 to.to_flags |= TOF_TS; 1972 } 1973 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1974 1975 /* Adjust headers by option size. */ 1976 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1977 m->m_len += optlen; 1978 m->m_pkthdr.len += optlen; 1979 #ifdef INET6 1980 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1981 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1982 else 1983 #endif 1984 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1985 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1986 if (sc->sc_flags & SCF_SIGNATURE) { 1987 KASSERT(to.to_flags & TOF_SIGNATURE, 1988 ("tcp_addoptions() didn't set tcp_signature")); 1989 1990 /* NOTE: to.to_signature is inside of mbuf */ 1991 if (!TCPMD5_ENABLED() || 1992 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1993 m_freem(m); 1994 return (EACCES); 1995 } 1996 } 1997 #endif 1998 } else 1999 optlen = 0; 2000 2001 if (udp) { 2002 ulen += optlen; 2003 udp->uh_ulen = htons(ulen); 2004 } 2005 M_SETFIB(m, sc->sc_inc.inc_fibnum); 2006 /* 2007 * If we have peer's SYN and it has a flowid, then let's assign it to 2008 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 2009 * to SYN|ACK due to lack of inp here. 2010 */ 2011 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 2012 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 2013 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 2014 } 2015 #ifdef INET6 2016 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2017 if (sc->sc_port) { 2018 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2019 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2020 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2021 IPPROTO_UDP, 0); 2022 th->th_sum = htons(0); 2023 } else { 2024 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2025 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2026 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2027 IPPROTO_TCP, 0); 2028 } 2029 ip6->ip6_hlim = sc->sc_ip_ttl; 2030 #ifdef TCP_OFFLOAD 2031 if (ADDED_BY_TOE(sc)) { 2032 struct toedev *tod = sc->sc_tod; 2033 2034 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2035 2036 return (error); 2037 } 2038 #endif 2039 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2040 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2041 } 2042 #endif 2043 #if defined(INET6) && defined(INET) 2044 else 2045 #endif 2046 #ifdef INET 2047 { 2048 if (sc->sc_port) { 2049 m->m_pkthdr.csum_flags = CSUM_UDP; 2050 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2051 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2052 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2053 th->th_sum = htons(0); 2054 } else { 2055 m->m_pkthdr.csum_flags = CSUM_TCP; 2056 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2057 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2058 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2059 } 2060 #ifdef TCP_OFFLOAD 2061 if (ADDED_BY_TOE(sc)) { 2062 struct toedev *tod = sc->sc_tod; 2063 2064 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2065 2066 return (error); 2067 } 2068 #endif 2069 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2070 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2071 } 2072 #endif 2073 return (error); 2074 } 2075 2076 /* 2077 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2078 * that exceed the capacity of the syncache by avoiding the storage of any 2079 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2080 * attacks where the attacker does not have access to our responses. 2081 * 2082 * Syncookies encode and include all necessary information about the 2083 * connection setup within the SYN|ACK that we send back. That way we 2084 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2085 * (if ever). Normally the syncache and syncookies are running in parallel 2086 * with the latter taking over when the former is exhausted. When matching 2087 * syncache entry is found the syncookie is ignored. 2088 * 2089 * The only reliable information persisting the 3WHS is our initial sequence 2090 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2091 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2092 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2093 * returns and signifies a legitimate connection if it matches the ACK. 2094 * 2095 * The available space of 32 bits to store the hash and to encode the SYN 2096 * option information is very tight and we should have at least 24 bits for 2097 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2098 * 2099 * SYN option information we have to encode to fully restore a connection: 2100 * MSS: is imporant to chose an optimal segment size to avoid IP level 2101 * fragmentation along the path. The common MSS values can be encoded 2102 * in a 3-bit table. Uncommon values are captured by the next lower value 2103 * in the table leading to a slight increase in packetization overhead. 2104 * WSCALE: is necessary to allow large windows to be used for high delay- 2105 * bandwidth product links. Not scaling the window when it was initially 2106 * negotiated is bad for performance as lack of scaling further decreases 2107 * the apparent available send window. We only need to encode the WSCALE 2108 * we received from the remote end. Our end can be recalculated at any 2109 * time. The common WSCALE values can be encoded in a 3-bit table. 2110 * Uncommon values are captured by the next lower value in the table 2111 * making us under-estimate the available window size halving our 2112 * theoretically possible maximum throughput for that connection. 2113 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2114 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2115 * that are included in all segments on a connection. We enable them when 2116 * the ACK has them. 2117 * 2118 * Security of syncookies and attack vectors: 2119 * 2120 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2121 * together with the gloabl secret to make it unique per connection attempt. 2122 * Thus any change of any of those parameters results in a different MAC output 2123 * in an unpredictable way unless a collision is encountered. 24 bits of the 2124 * MAC are embedded into the ISS. 2125 * 2126 * To prevent replay attacks two rotating global secrets are updated with a 2127 * new random value every 15 seconds. The life-time of a syncookie is thus 2128 * 15-30 seconds. 2129 * 2130 * Vector 1: Attacking the secret. This requires finding a weakness in the 2131 * MAC itself or the way it is used here. The attacker can do a chosen plain 2132 * text attack by varying and testing the all parameters under his control. 2133 * The strength depends on the size and randomness of the secret, and the 2134 * cryptographic security of the MAC function. Due to the constant updating 2135 * of the secret the attacker has at most 29.999 seconds to find the secret 2136 * and launch spoofed connections. After that he has to start all over again. 2137 * 2138 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2139 * size an average of 4,823 attempts are required for a 50% chance of success 2140 * to spoof a single syncookie (birthday collision paradox). However the 2141 * attacker is blind and doesn't know if one of his attempts succeeded unless 2142 * he has a side channel to interfere success from. A single connection setup 2143 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2144 * This many attempts are required for each one blind spoofed connection. For 2145 * every additional spoofed connection he has to launch another N attempts. 2146 * Thus for a sustained rate 100 spoofed connections per second approximately 2147 * 1,800,000 packets per second would have to be sent. 2148 * 2149 * NB: The MAC function should be fast so that it doesn't become a CPU 2150 * exhaustion attack vector itself. 2151 * 2152 * References: 2153 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2154 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2155 * http://cr.yp.to/syncookies.html (overview) 2156 * http://cr.yp.to/syncookies/archive (details) 2157 * 2158 * 2159 * Schematic construction of a syncookie enabled Initial Sequence Number: 2160 * 0 1 2 3 2161 * 12345678901234567890123456789012 2162 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2163 * 2164 * x 24 MAC (truncated) 2165 * W 3 Send Window Scale index 2166 * M 3 MSS index 2167 * S 1 SACK permitted 2168 * P 1 Odd/even secret 2169 */ 2170 2171 /* 2172 * Distribution and probability of certain MSS values. Those in between are 2173 * rounded down to the next lower one. 2174 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2175 * .2% .3% 5% 7% 7% 20% 15% 45% 2176 */ 2177 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2178 2179 /* 2180 * Distribution and probability of certain WSCALE values. We have to map the 2181 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2182 * bits based on prevalence of certain values. Where we don't have an exact 2183 * match for are rounded down to the next lower one letting us under-estimate 2184 * the true available window. At the moment this would happen only for the 2185 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2186 * and window size). The absence of the WSCALE option (no scaling in either 2187 * direction) is encoded with index zero. 2188 * [WSCALE values histograms, Allman, 2012] 2189 * X 10 10 35 5 6 14 10% by host 2190 * X 11 4 5 5 18 49 3% by connections 2191 */ 2192 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2193 2194 /* 2195 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2196 * and good cryptographic properties. 2197 */ 2198 static uint32_t 2199 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2200 uint8_t *secbits, uintptr_t secmod) 2201 { 2202 SIPHASH_CTX ctx; 2203 uint32_t siphash[2]; 2204 2205 SipHash24_Init(&ctx); 2206 SipHash_SetKey(&ctx, secbits); 2207 switch (inc->inc_flags & INC_ISIPV6) { 2208 #ifdef INET 2209 case 0: 2210 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2211 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2212 break; 2213 #endif 2214 #ifdef INET6 2215 case INC_ISIPV6: 2216 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2217 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2218 break; 2219 #endif 2220 } 2221 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2222 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2223 SipHash_Update(&ctx, &irs, sizeof(irs)); 2224 SipHash_Update(&ctx, &flags, sizeof(flags)); 2225 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2226 SipHash_Final((u_int8_t *)&siphash, &ctx); 2227 2228 return (siphash[0] ^ siphash[1]); 2229 } 2230 2231 static tcp_seq 2232 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2233 { 2234 u_int i, secbit, wscale; 2235 uint32_t iss, hash; 2236 uint8_t *secbits; 2237 union syncookie cookie; 2238 2239 cookie.cookie = 0; 2240 2241 /* Map our computed MSS into the 3-bit index. */ 2242 for (i = nitems(tcp_sc_msstab) - 1; 2243 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2244 i--) 2245 ; 2246 cookie.flags.mss_idx = i; 2247 2248 /* 2249 * Map the send window scale into the 3-bit index but only if 2250 * the wscale option was received. 2251 */ 2252 if (sc->sc_flags & SCF_WINSCALE) { 2253 wscale = sc->sc_requested_s_scale; 2254 for (i = nitems(tcp_sc_wstab) - 1; 2255 tcp_sc_wstab[i] > wscale && i > 0; 2256 i--) 2257 ; 2258 cookie.flags.wscale_idx = i; 2259 } 2260 2261 /* Can we do SACK? */ 2262 if (sc->sc_flags & SCF_SACK) 2263 cookie.flags.sack_ok = 1; 2264 2265 /* Which of the two secrets to use. */ 2266 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2267 cookie.flags.odd_even = secbit; 2268 2269 secbits = V_tcp_syncache.secret.key[secbit]; 2270 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2271 (uintptr_t)sch); 2272 2273 /* 2274 * Put the flags into the hash and XOR them to get better ISS number 2275 * variance. This doesn't enhance the cryptographic strength and is 2276 * done to prevent the 8 cookie bits from showing up directly on the 2277 * wire. 2278 */ 2279 iss = hash & ~0xff; 2280 iss |= cookie.cookie ^ (hash >> 24); 2281 2282 TCPSTAT_INC(tcps_sc_sendcookie); 2283 return (iss); 2284 } 2285 2286 static struct syncache * 2287 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2288 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2289 struct socket *lso, uint16_t port) 2290 { 2291 uint32_t hash; 2292 uint8_t *secbits; 2293 tcp_seq ack, seq; 2294 int wnd, wscale = 0; 2295 union syncookie cookie; 2296 2297 /* 2298 * Pull information out of SYN-ACK/ACK and revert sequence number 2299 * advances. 2300 */ 2301 ack = th->th_ack - 1; 2302 seq = th->th_seq - 1; 2303 2304 /* 2305 * Unpack the flags containing enough information to restore the 2306 * connection. 2307 */ 2308 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2309 2310 /* Which of the two secrets to use. */ 2311 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2312 2313 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2314 2315 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2316 if ((ack & ~0xff) != (hash & ~0xff)) 2317 return (NULL); 2318 2319 /* Fill in the syncache values. */ 2320 sc->sc_flags = 0; 2321 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2322 sc->sc_ipopts = NULL; 2323 2324 sc->sc_irs = seq; 2325 sc->sc_iss = ack; 2326 2327 switch (inc->inc_flags & INC_ISIPV6) { 2328 #ifdef INET 2329 case 0: 2330 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2331 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2332 break; 2333 #endif 2334 #ifdef INET6 2335 case INC_ISIPV6: 2336 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2337 sc->sc_flowlabel = 2338 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2339 break; 2340 #endif 2341 } 2342 2343 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2344 2345 /* We can simply recompute receive window scale we sent earlier. */ 2346 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2347 wscale++; 2348 2349 /* Only use wscale if it was enabled in the orignal SYN. */ 2350 if (cookie.flags.wscale_idx > 0) { 2351 sc->sc_requested_r_scale = wscale; 2352 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2353 sc->sc_flags |= SCF_WINSCALE; 2354 } 2355 2356 wnd = lso->sol_sbrcv_hiwat; 2357 wnd = imax(wnd, 0); 2358 wnd = imin(wnd, TCP_MAXWIN); 2359 sc->sc_wnd = wnd; 2360 2361 if (cookie.flags.sack_ok) 2362 sc->sc_flags |= SCF_SACK; 2363 2364 if (to->to_flags & TOF_TS) { 2365 sc->sc_flags |= SCF_TIMESTAMP; 2366 sc->sc_tsreflect = to->to_tsval; 2367 sc->sc_tsoff = tcp_new_ts_offset(inc); 2368 } 2369 2370 if (to->to_flags & TOF_SIGNATURE) 2371 sc->sc_flags |= SCF_SIGNATURE; 2372 2373 sc->sc_rxmits = 0; 2374 2375 sc->sc_port = port; 2376 2377 TCPSTAT_INC(tcps_sc_recvcookie); 2378 return (sc); 2379 } 2380 2381 #ifdef INVARIANTS 2382 static int 2383 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2384 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2385 struct socket *lso, uint16_t port) 2386 { 2387 struct syncache scs, *scx; 2388 char *s; 2389 2390 bzero(&scs, sizeof(scs)); 2391 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2392 2393 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2394 return (0); 2395 2396 if (scx != NULL) { 2397 if (sc->sc_peer_mss != scx->sc_peer_mss) 2398 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2399 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2400 2401 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2402 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2403 s, __func__, sc->sc_requested_r_scale, 2404 scx->sc_requested_r_scale); 2405 2406 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2407 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2408 s, __func__, sc->sc_requested_s_scale, 2409 scx->sc_requested_s_scale); 2410 2411 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2412 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2413 } 2414 2415 if (s != NULL) 2416 free(s, M_TCPLOG); 2417 return (0); 2418 } 2419 #endif /* INVARIANTS */ 2420 2421 static void 2422 syncookie_reseed(void *arg) 2423 { 2424 struct tcp_syncache *sc = arg; 2425 uint8_t *secbits; 2426 int secbit; 2427 2428 /* 2429 * Reseeding the secret doesn't have to be protected by a lock. 2430 * It only must be ensured that the new random values are visible 2431 * to all CPUs in a SMP environment. The atomic with release 2432 * semantics ensures that. 2433 */ 2434 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2435 secbits = sc->secret.key[secbit]; 2436 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2437 atomic_add_rel_int(&sc->secret.oddeven, 1); 2438 2439 /* Reschedule ourself. */ 2440 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2441 } 2442 2443 /* 2444 * We have overflowed a bucket. Let's pause dealing with the syncache. 2445 * This function will increment the bucketoverflow statistics appropriately 2446 * (once per pause when pausing is enabled; otherwise, once per overflow). 2447 */ 2448 static void 2449 syncache_pause(struct in_conninfo *inc) 2450 { 2451 time_t delta; 2452 const char *s; 2453 2454 /* XXX: 2455 * 2. Add sysctl read here so we don't get the benefit of this 2456 * change without the new sysctl. 2457 */ 2458 2459 /* 2460 * Try an unlocked read. If we already know that another thread 2461 * has activated the feature, there is no need to proceed. 2462 */ 2463 if (V_tcp_syncache.paused) 2464 return; 2465 2466 /* Are cookied enabled? If not, we can't pause. */ 2467 if (!V_tcp_syncookies) { 2468 TCPSTAT_INC(tcps_sc_bucketoverflow); 2469 return; 2470 } 2471 2472 /* 2473 * We may be the first thread to find an overflow. Get the lock 2474 * and evaluate if we need to take action. 2475 */ 2476 mtx_lock(&V_tcp_syncache.pause_mtx); 2477 if (V_tcp_syncache.paused) { 2478 mtx_unlock(&V_tcp_syncache.pause_mtx); 2479 return; 2480 } 2481 2482 /* Activate protection. */ 2483 V_tcp_syncache.paused = true; 2484 TCPSTAT_INC(tcps_sc_bucketoverflow); 2485 2486 /* 2487 * Determine the last backoff time. If we are seeing a re-newed 2488 * attack within that same time after last reactivating the syncache, 2489 * consider it an extension of the same attack. 2490 */ 2491 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2492 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2493 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2494 delta <<= 1; 2495 V_tcp_syncache.pause_backoff++; 2496 } 2497 } else { 2498 delta = TCP_SYNCACHE_PAUSE_TIME; 2499 V_tcp_syncache.pause_backoff = 0; 2500 } 2501 2502 /* Log a warning, including IP addresses, if able. */ 2503 if (inc != NULL) 2504 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2505 else 2506 s = (const char *)NULL; 2507 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2508 "the next %lld seconds%s%s%s\n", (long long)delta, 2509 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2510 (s != NULL) ? ")" : ""); 2511 free(__DECONST(void *, s), M_TCPLOG); 2512 2513 /* Use the calculated delta to set a new pause time. */ 2514 V_tcp_syncache.pause_until = time_uptime + delta; 2515 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2516 &V_tcp_syncache); 2517 mtx_unlock(&V_tcp_syncache.pause_mtx); 2518 } 2519 2520 /* Evaluate whether we need to unpause. */ 2521 static void 2522 syncache_unpause(void *arg) 2523 { 2524 struct tcp_syncache *sc; 2525 time_t delta; 2526 2527 sc = arg; 2528 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2529 callout_deactivate(&sc->pause_co); 2530 2531 /* 2532 * Check to make sure we are not running early. If the pause 2533 * time has expired, then deactivate the protection. 2534 */ 2535 if ((delta = sc->pause_until - time_uptime) > 0) 2536 callout_schedule(&sc->pause_co, delta * hz); 2537 else 2538 sc->paused = false; 2539 } 2540 2541 /* 2542 * Exports the syncache entries to userland so that netstat can display 2543 * them alongside the other sockets. This function is intended to be 2544 * called only from tcp_pcblist. 2545 * 2546 * Due to concurrency on an active system, the number of pcbs exported 2547 * may have no relation to max_pcbs. max_pcbs merely indicates the 2548 * amount of space the caller allocated for this function to use. 2549 */ 2550 int 2551 syncache_pcblist(struct sysctl_req *req) 2552 { 2553 struct xtcpcb xt; 2554 struct syncache *sc; 2555 struct syncache_head *sch; 2556 int error, i; 2557 2558 bzero(&xt, sizeof(xt)); 2559 xt.xt_len = sizeof(xt); 2560 xt.t_state = TCPS_SYN_RECEIVED; 2561 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2562 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2563 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2564 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2565 2566 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2567 sch = &V_tcp_syncache.hashbase[i]; 2568 SCH_LOCK(sch); 2569 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2570 if (sc->sc_cred != NULL && 2571 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2572 continue; 2573 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2574 xt.xt_inp.inp_vflag = INP_IPV6; 2575 else 2576 xt.xt_inp.inp_vflag = INP_IPV4; 2577 xt.xt_encaps_port = sc->sc_port; 2578 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2579 sizeof (struct in_conninfo)); 2580 error = SYSCTL_OUT(req, &xt, sizeof xt); 2581 if (error) { 2582 SCH_UNLOCK(sch); 2583 return (0); 2584 } 2585 } 2586 SCH_UNLOCK(sch); 2587 } 2588 2589 return (0); 2590 } 2591