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 #include "opt_pcbgroup.h" 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/hash.h> 46 #include <sys/refcount.h> 47 #include <sys/kernel.h> 48 #include <sys/sysctl.h> 49 #include <sys/limits.h> 50 #include <sys/lock.h> 51 #include <sys/mutex.h> 52 #include <sys/malloc.h> 53 #include <sys/mbuf.h> 54 #include <sys/proc.h> /* for proc0 declaration */ 55 #include <sys/random.h> 56 #include <sys/socket.h> 57 #include <sys/socketvar.h> 58 #include <sys/syslog.h> 59 #include <sys/ucred.h> 60 61 #include <sys/md5.h> 62 #include <crypto/siphash/siphash.h> 63 64 #include <vm/uma.h> 65 66 #include <net/if.h> 67 #include <net/if_var.h> 68 #include <net/route.h> 69 #include <net/vnet.h> 70 71 #include <netinet/in.h> 72 #include <netinet/in_kdtrace.h> 73 #include <netinet/in_systm.h> 74 #include <netinet/ip.h> 75 #include <netinet/in_var.h> 76 #include <netinet/in_pcb.h> 77 #include <netinet/ip_var.h> 78 #include <netinet/ip_options.h> 79 #ifdef INET6 80 #include <netinet/ip6.h> 81 #include <netinet/icmp6.h> 82 #include <netinet6/nd6.h> 83 #include <netinet6/ip6_var.h> 84 #include <netinet6/in6_pcb.h> 85 #endif 86 #include <netinet/tcp.h> 87 #include <netinet/tcp_fastopen.h> 88 #include <netinet/tcp_fsm.h> 89 #include <netinet/tcp_seq.h> 90 #include <netinet/tcp_timer.h> 91 #include <netinet/tcp_var.h> 92 #include <netinet/tcp_syncache.h> 93 #ifdef INET6 94 #include <netinet6/tcp6_var.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 100 #include <netipsec/ipsec_support.h> 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1; 107 #define V_tcp_syncookies VNET(tcp_syncookies) 108 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 109 &VNET_NAME(tcp_syncookies), 0, 110 "Use TCP SYN cookies if the syncache overflows"); 111 112 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0; 113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 115 &VNET_NAME(tcp_syncookiesonly), 0, 116 "Use only TCP SYN cookies"); 117 118 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 119 #define V_functions_inherit_listen_socket_stack \ 120 VNET(functions_inherit_listen_socket_stack) 121 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 122 CTLFLAG_VNET | CTLFLAG_RW, 123 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 124 "Inherit listen socket's stack"); 125 126 #ifdef TCP_OFFLOAD 127 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 128 #endif 129 130 static void syncache_drop(struct syncache *, struct syncache_head *); 131 static void syncache_free(struct syncache *); 132 static void syncache_insert(struct syncache *, struct syncache_head *); 133 static int syncache_respond(struct syncache *, const struct mbuf *, int); 134 static struct socket *syncache_socket(struct syncache *, struct socket *, 135 struct mbuf *m); 136 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 137 int docallout); 138 static void syncache_timer(void *); 139 140 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 141 uint8_t *, uintptr_t); 142 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 143 static struct syncache 144 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 145 struct syncache *, struct tcphdr *, struct tcpopt *, 146 struct socket *); 147 static void syncache_pause(struct in_conninfo *); 148 static void syncache_unpause(void *); 149 static void syncookie_reseed(void *); 150 #ifdef INVARIANTS 151 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 152 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 153 struct socket *lso); 154 #endif 155 156 /* 157 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 158 * 3 retransmits corresponds to a timeout with default values of 159 * tcp_rexmit_initial * ( 1 + 160 * tcp_backoff[1] + 161 * tcp_backoff[2] + 162 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 163 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 164 * the odds are that the user has given up attempting to connect by then. 165 */ 166 #define SYNCACHE_MAXREXMTS 3 167 168 /* Arbitrary values */ 169 #define TCP_SYNCACHE_HASHSIZE 512 170 #define TCP_SYNCACHE_BUCKETLIMIT 30 171 172 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 173 #define V_tcp_syncache VNET(tcp_syncache) 174 175 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 176 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 177 "TCP SYN cache"); 178 179 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 180 &VNET_NAME(tcp_syncache.bucket_limit), 0, 181 "Per-bucket hash limit for syncache"); 182 183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 184 &VNET_NAME(tcp_syncache.cache_limit), 0, 185 "Overall entry limit for syncache"); 186 187 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 188 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 189 190 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 191 &VNET_NAME(tcp_syncache.hashsize), 0, 192 "Size of TCP syncache hashtable"); 193 194 static int 195 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 196 { 197 int error; 198 u_int new; 199 200 new = V_tcp_syncache.rexmt_limit; 201 error = sysctl_handle_int(oidp, &new, 0, req); 202 if ((error == 0) && (req->newptr != NULL)) { 203 if (new > TCP_MAXRXTSHIFT) 204 error = EINVAL; 205 else 206 V_tcp_syncache.rexmt_limit = new; 207 } 208 return (error); 209 } 210 211 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 212 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 213 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 214 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 215 "Limit on SYN/ACK retransmissions"); 216 217 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 218 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 219 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 220 "Send reset on socket allocation failure"); 221 222 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 223 224 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 225 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 226 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 227 228 /* 229 * Requires the syncache entry to be already removed from the bucket list. 230 */ 231 static void 232 syncache_free(struct syncache *sc) 233 { 234 235 if (sc->sc_ipopts) 236 (void) m_free(sc->sc_ipopts); 237 if (sc->sc_cred) 238 crfree(sc->sc_cred); 239 #ifdef MAC 240 mac_syncache_destroy(&sc->sc_label); 241 #endif 242 243 uma_zfree(V_tcp_syncache.zone, sc); 244 } 245 246 void 247 syncache_init(void) 248 { 249 int i; 250 251 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 252 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 253 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 254 V_tcp_syncache.hash_secret = arc4random(); 255 256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 257 &V_tcp_syncache.hashsize); 258 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 259 &V_tcp_syncache.bucket_limit); 260 if (!powerof2(V_tcp_syncache.hashsize) || 261 V_tcp_syncache.hashsize == 0) { 262 printf("WARNING: syncache hash size is not a power of 2.\n"); 263 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 264 } 265 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 266 267 /* Set limits. */ 268 V_tcp_syncache.cache_limit = 269 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 270 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 271 &V_tcp_syncache.cache_limit); 272 273 /* Allocate the hash table. */ 274 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 275 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 276 277 #ifdef VIMAGE 278 V_tcp_syncache.vnet = curvnet; 279 #endif 280 281 /* Initialize the hash buckets. */ 282 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 283 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 284 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 285 NULL, MTX_DEF); 286 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 287 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 288 V_tcp_syncache.hashbase[i].sch_length = 0; 289 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 290 V_tcp_syncache.hashbase[i].sch_last_overflow = 291 -(SYNCOOKIE_LIFETIME + 1); 292 } 293 294 /* Create the syncache entry zone. */ 295 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 296 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 297 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 298 V_tcp_syncache.cache_limit); 299 300 /* Start the SYN cookie reseeder callout. */ 301 callout_init(&V_tcp_syncache.secret.reseed, 1); 302 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 303 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 304 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 305 syncookie_reseed, &V_tcp_syncache); 306 307 /* Initialize the pause machinery. */ 308 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 309 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 310 0); 311 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 312 V_tcp_syncache.pause_backoff = 0; 313 V_tcp_syncache.paused = false; 314 } 315 316 #ifdef VIMAGE 317 void 318 syncache_destroy(void) 319 { 320 struct syncache_head *sch; 321 struct syncache *sc, *nsc; 322 int i; 323 324 /* 325 * Stop the re-seed timer before freeing resources. No need to 326 * possibly schedule it another time. 327 */ 328 callout_drain(&V_tcp_syncache.secret.reseed); 329 330 /* Stop the SYN cache pause callout. */ 331 mtx_lock(&V_tcp_syncache.pause_mtx); 332 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 333 mtx_unlock(&V_tcp_syncache.pause_mtx); 334 callout_drain(&V_tcp_syncache.pause_co); 335 } else 336 mtx_unlock(&V_tcp_syncache.pause_mtx); 337 338 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 339 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 340 341 sch = &V_tcp_syncache.hashbase[i]; 342 callout_drain(&sch->sch_timer); 343 344 SCH_LOCK(sch); 345 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 346 syncache_drop(sc, sch); 347 SCH_UNLOCK(sch); 348 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 349 ("%s: sch->sch_bucket not empty", __func__)); 350 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 351 __func__, sch->sch_length)); 352 mtx_destroy(&sch->sch_mtx); 353 } 354 355 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 356 ("%s: cache_count not 0", __func__)); 357 358 /* Free the allocated global resources. */ 359 uma_zdestroy(V_tcp_syncache.zone); 360 free(V_tcp_syncache.hashbase, M_SYNCACHE); 361 mtx_destroy(&V_tcp_syncache.pause_mtx); 362 } 363 #endif 364 365 /* 366 * Inserts a syncache entry into the specified bucket row. 367 * Locks and unlocks the syncache_head autonomously. 368 */ 369 static void 370 syncache_insert(struct syncache *sc, struct syncache_head *sch) 371 { 372 struct syncache *sc2; 373 374 SCH_LOCK(sch); 375 376 /* 377 * Make sure that we don't overflow the per-bucket limit. 378 * If the bucket is full, toss the oldest element. 379 */ 380 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 381 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 382 ("sch->sch_length incorrect")); 383 syncache_pause(&sc->sc_inc); 384 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 385 sch->sch_last_overflow = time_uptime; 386 syncache_drop(sc2, sch); 387 } 388 389 /* Put it into the bucket. */ 390 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 391 sch->sch_length++; 392 393 #ifdef TCP_OFFLOAD 394 if (ADDED_BY_TOE(sc)) { 395 struct toedev *tod = sc->sc_tod; 396 397 tod->tod_syncache_added(tod, sc->sc_todctx); 398 } 399 #endif 400 401 /* Reinitialize the bucket row's timer. */ 402 if (sch->sch_length == 1) 403 sch->sch_nextc = ticks + INT_MAX; 404 syncache_timeout(sc, sch, 1); 405 406 SCH_UNLOCK(sch); 407 408 TCPSTATES_INC(TCPS_SYN_RECEIVED); 409 TCPSTAT_INC(tcps_sc_added); 410 } 411 412 /* 413 * Remove and free entry from syncache bucket row. 414 * Expects locked syncache head. 415 */ 416 static void 417 syncache_drop(struct syncache *sc, struct syncache_head *sch) 418 { 419 420 SCH_LOCK_ASSERT(sch); 421 422 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 423 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 424 sch->sch_length--; 425 426 #ifdef TCP_OFFLOAD 427 if (ADDED_BY_TOE(sc)) { 428 struct toedev *tod = sc->sc_tod; 429 430 tod->tod_syncache_removed(tod, sc->sc_todctx); 431 } 432 #endif 433 434 syncache_free(sc); 435 } 436 437 /* 438 * Engage/reengage time on bucket row. 439 */ 440 static void 441 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 442 { 443 int rexmt; 444 445 if (sc->sc_rxmits == 0) 446 rexmt = tcp_rexmit_initial; 447 else 448 TCPT_RANGESET(rexmt, 449 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 450 tcp_rexmit_min, TCPTV_REXMTMAX); 451 sc->sc_rxttime = ticks + rexmt; 452 sc->sc_rxmits++; 453 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 454 sch->sch_nextc = sc->sc_rxttime; 455 if (docallout) 456 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 457 syncache_timer, (void *)sch); 458 } 459 } 460 461 /* 462 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 463 * If we have retransmitted an entry the maximum number of times, expire it. 464 * One separate timer for each bucket row. 465 */ 466 static void 467 syncache_timer(void *xsch) 468 { 469 struct syncache_head *sch = (struct syncache_head *)xsch; 470 struct syncache *sc, *nsc; 471 struct epoch_tracker et; 472 int tick = ticks; 473 char *s; 474 bool paused; 475 476 CURVNET_SET(sch->sch_sc->vnet); 477 478 /* NB: syncache_head has already been locked by the callout. */ 479 SCH_LOCK_ASSERT(sch); 480 481 /* 482 * In the following cycle we may remove some entries and/or 483 * advance some timeouts, so re-initialize the bucket timer. 484 */ 485 sch->sch_nextc = tick + INT_MAX; 486 487 /* 488 * If we have paused processing, unconditionally remove 489 * all syncache entries. 490 */ 491 mtx_lock(&V_tcp_syncache.pause_mtx); 492 paused = V_tcp_syncache.paused; 493 mtx_unlock(&V_tcp_syncache.pause_mtx); 494 495 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 496 if (paused) { 497 syncache_drop(sc, sch); 498 continue; 499 } 500 /* 501 * We do not check if the listen socket still exists 502 * and accept the case where the listen socket may be 503 * gone by the time we resend the SYN/ACK. We do 504 * not expect this to happens often. If it does, 505 * then the RST will be sent by the time the remote 506 * host does the SYN/ACK->ACK. 507 */ 508 if (TSTMP_GT(sc->sc_rxttime, tick)) { 509 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 510 sch->sch_nextc = sc->sc_rxttime; 511 continue; 512 } 513 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 514 sc->sc_flags &= ~SCF_ECN; 515 } 516 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 517 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 518 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 519 "giving up and removing syncache entry\n", 520 s, __func__); 521 free(s, M_TCPLOG); 522 } 523 syncache_drop(sc, sch); 524 TCPSTAT_INC(tcps_sc_stale); 525 continue; 526 } 527 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 528 log(LOG_DEBUG, "%s; %s: Response timeout, " 529 "retransmitting (%u) SYN|ACK\n", 530 s, __func__, sc->sc_rxmits); 531 free(s, M_TCPLOG); 532 } 533 534 NET_EPOCH_ENTER(et); 535 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 536 NET_EPOCH_EXIT(et); 537 TCPSTAT_INC(tcps_sc_retransmitted); 538 syncache_timeout(sc, sch, 0); 539 } 540 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 541 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 542 syncache_timer, (void *)(sch)); 543 CURVNET_RESTORE(); 544 } 545 546 /* 547 * Returns true if the system is only using cookies at the moment. 548 * This could be due to a sysadmin decision to only use cookies, or it 549 * could be due to the system detecting an attack. 550 */ 551 static inline bool 552 syncache_cookiesonly(void) 553 { 554 555 return (V_tcp_syncookies && (V_tcp_syncache.paused || 556 V_tcp_syncookiesonly)); 557 } 558 559 /* 560 * Find the hash bucket for the given connection. 561 */ 562 static struct syncache_head * 563 syncache_hashbucket(struct in_conninfo *inc) 564 { 565 uint32_t hash; 566 567 /* 568 * The hash is built on foreign port + local port + foreign address. 569 * We rely on the fact that struct in_conninfo starts with 16 bits 570 * of foreign port, then 16 bits of local port then followed by 128 571 * bits of foreign address. In case of IPv4 address, the first 3 572 * 32-bit words of the address always are zeroes. 573 */ 574 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 575 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 576 577 return (&V_tcp_syncache.hashbase[hash]); 578 } 579 580 /* 581 * Find an entry in the syncache. 582 * Returns always with locked syncache_head plus a matching entry or NULL. 583 */ 584 static struct syncache * 585 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 586 { 587 struct syncache *sc; 588 struct syncache_head *sch; 589 590 *schp = sch = syncache_hashbucket(inc); 591 SCH_LOCK(sch); 592 593 /* Circle through bucket row to find matching entry. */ 594 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 595 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 596 sizeof(struct in_endpoints)) == 0) 597 break; 598 599 return (sc); /* Always returns with locked sch. */ 600 } 601 602 /* 603 * This function is called when we get a RST for a 604 * non-existent connection, so that we can see if the 605 * connection is in the syn cache. If it is, zap it. 606 * If required send a challenge ACK. 607 */ 608 void 609 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m) 610 { 611 struct syncache *sc; 612 struct syncache_head *sch; 613 char *s = NULL; 614 615 if (syncache_cookiesonly()) 616 return; 617 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 618 SCH_LOCK_ASSERT(sch); 619 620 /* 621 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 622 * See RFC 793 page 65, section SEGMENT ARRIVES. 623 */ 624 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 625 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 626 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 627 "FIN flag set, segment ignored\n", s, __func__); 628 TCPSTAT_INC(tcps_badrst); 629 goto done; 630 } 631 632 /* 633 * No corresponding connection was found in syncache. 634 * If syncookies are enabled and possibly exclusively 635 * used, or we are under memory pressure, a valid RST 636 * may not find a syncache entry. In that case we're 637 * done and no SYN|ACK retransmissions will happen. 638 * Otherwise the RST was misdirected or spoofed. 639 */ 640 if (sc == NULL) { 641 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 642 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 643 "syncache entry (possibly syncookie only), " 644 "segment ignored\n", s, __func__); 645 TCPSTAT_INC(tcps_badrst); 646 goto done; 647 } 648 649 /* 650 * If the RST bit is set, check the sequence number to see 651 * if this is a valid reset segment. 652 * 653 * RFC 793 page 37: 654 * In all states except SYN-SENT, all reset (RST) segments 655 * are validated by checking their SEQ-fields. A reset is 656 * valid if its sequence number is in the window. 657 * 658 * RFC 793 page 69: 659 * There are four cases for the acceptability test for an incoming 660 * segment: 661 * 662 * Segment Receive Test 663 * Length Window 664 * ------- ------- ------------------------------------------- 665 * 0 0 SEG.SEQ = RCV.NXT 666 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 667 * >0 0 not acceptable 668 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 669 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 670 * 671 * Note that when receiving a SYN segment in the LISTEN state, 672 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 673 * described in RFC 793, page 66. 674 */ 675 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 676 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 677 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 678 if (V_tcp_insecure_rst || 679 th->th_seq == sc->sc_irs + 1) { 680 syncache_drop(sc, sch); 681 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 682 log(LOG_DEBUG, 683 "%s; %s: Our SYN|ACK was rejected, " 684 "connection attempt aborted by remote " 685 "endpoint\n", 686 s, __func__); 687 TCPSTAT_INC(tcps_sc_reset); 688 } else { 689 TCPSTAT_INC(tcps_badrst); 690 /* Send challenge ACK. */ 691 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 692 log(LOG_DEBUG, "%s; %s: RST with invalid " 693 " SEQ %u != NXT %u (+WND %u), " 694 "sending challenge ACK\n", 695 s, __func__, 696 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 697 syncache_respond(sc, m, TH_ACK); 698 } 699 } else { 700 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 701 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 702 "NXT %u (+WND %u), segment ignored\n", 703 s, __func__, 704 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 705 TCPSTAT_INC(tcps_badrst); 706 } 707 708 done: 709 if (s != NULL) 710 free(s, M_TCPLOG); 711 SCH_UNLOCK(sch); 712 } 713 714 void 715 syncache_badack(struct in_conninfo *inc) 716 { 717 struct syncache *sc; 718 struct syncache_head *sch; 719 720 if (syncache_cookiesonly()) 721 return; 722 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 723 SCH_LOCK_ASSERT(sch); 724 if (sc != NULL) { 725 syncache_drop(sc, sch); 726 TCPSTAT_INC(tcps_sc_badack); 727 } 728 SCH_UNLOCK(sch); 729 } 730 731 void 732 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq) 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) 742 goto done; 743 744 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 745 if (ntohl(th_seq) != sc->sc_iss) 746 goto done; 747 748 /* 749 * If we've rertransmitted 3 times and this is our second error, 750 * we remove the entry. Otherwise, we allow it to continue on. 751 * This prevents us from incorrectly nuking an entry during a 752 * spurious network outage. 753 * 754 * See tcp_notify(). 755 */ 756 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 757 sc->sc_flags |= SCF_UNREACH; 758 goto done; 759 } 760 syncache_drop(sc, sch); 761 TCPSTAT_INC(tcps_sc_unreach); 762 done: 763 SCH_UNLOCK(sch); 764 } 765 766 /* 767 * Build a new TCP socket structure from a syncache entry. 768 * 769 * On success return the newly created socket with its underlying inp locked. 770 */ 771 static struct socket * 772 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 773 { 774 struct tcp_function_block *blk; 775 struct inpcb *inp = NULL; 776 struct socket *so; 777 struct tcpcb *tp; 778 int error; 779 char *s; 780 781 NET_EPOCH_ASSERT(); 782 783 /* 784 * Ok, create the full blown connection, and set things up 785 * as they would have been set up if we had created the 786 * connection when the SYN arrived. If we can't create 787 * the connection, abort it. 788 */ 789 so = sonewconn(lso, 0); 790 if (so == NULL) { 791 /* 792 * Drop the connection; we will either send a RST or 793 * have the peer retransmit its SYN again after its 794 * RTO and try again. 795 */ 796 TCPSTAT_INC(tcps_listendrop); 797 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 798 log(LOG_DEBUG, "%s; %s: Socket create failed " 799 "due to limits or memory shortage\n", 800 s, __func__); 801 free(s, M_TCPLOG); 802 } 803 goto abort2; 804 } 805 #ifdef MAC 806 mac_socketpeer_set_from_mbuf(m, so); 807 #endif 808 809 inp = sotoinpcb(so); 810 inp->inp_inc.inc_fibnum = so->so_fibnum; 811 INP_WLOCK(inp); 812 /* 813 * Exclusive pcbinfo lock is not required in syncache socket case even 814 * if two inpcb locks can be acquired simultaneously: 815 * - the inpcb in LISTEN state, 816 * - the newly created inp. 817 * 818 * In this case, an inp cannot be at same time in LISTEN state and 819 * just created by an accept() call. 820 */ 821 INP_HASH_WLOCK(&V_tcbinfo); 822 823 /* Insert new socket into PCB hash list. */ 824 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 825 #ifdef INET6 826 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 827 inp->inp_vflag &= ~INP_IPV4; 828 inp->inp_vflag |= INP_IPV6; 829 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 830 } else { 831 inp->inp_vflag &= ~INP_IPV6; 832 inp->inp_vflag |= INP_IPV4; 833 #endif 834 inp->inp_laddr = sc->sc_inc.inc_laddr; 835 #ifdef INET6 836 } 837 #endif 838 839 /* 840 * If there's an mbuf and it has a flowid, then let's initialise the 841 * inp with that particular flowid. 842 */ 843 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 844 inp->inp_flowid = m->m_pkthdr.flowid; 845 inp->inp_flowtype = M_HASHTYPE_GET(m); 846 #ifdef NUMA 847 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 848 #endif 849 } 850 851 inp->inp_lport = sc->sc_inc.inc_lport; 852 #ifdef INET6 853 if (inp->inp_vflag & INP_IPV6PROTO) { 854 struct inpcb *oinp = sotoinpcb(lso); 855 856 /* 857 * Inherit socket options from the listening socket. 858 * Note that in6p_inputopts are not (and should not be) 859 * copied, since it stores previously received options and is 860 * used to detect if each new option is different than the 861 * previous one and hence should be passed to a user. 862 * If we copied in6p_inputopts, a user would not be able to 863 * receive options just after calling the accept system call. 864 */ 865 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 866 if (oinp->in6p_outputopts) 867 inp->in6p_outputopts = 868 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 869 } 870 871 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 872 struct in6_addr laddr6; 873 struct sockaddr_in6 sin6; 874 875 sin6.sin6_family = AF_INET6; 876 sin6.sin6_len = sizeof(sin6); 877 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 878 sin6.sin6_port = sc->sc_inc.inc_fport; 879 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 880 laddr6 = inp->in6p_laddr; 881 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 882 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 883 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 884 thread0.td_ucred, m, false)) != 0) { 885 inp->in6p_laddr = laddr6; 886 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 887 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 888 "with error %i\n", 889 s, __func__, error); 890 free(s, M_TCPLOG); 891 } 892 INP_HASH_WUNLOCK(&V_tcbinfo); 893 goto abort; 894 } 895 /* Override flowlabel from in6_pcbconnect. */ 896 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 897 inp->inp_flow |= sc->sc_flowlabel; 898 } 899 #endif /* INET6 */ 900 #if defined(INET) && defined(INET6) 901 else 902 #endif 903 #ifdef INET 904 { 905 struct in_addr laddr; 906 struct sockaddr_in sin; 907 908 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 909 910 if (inp->inp_options == NULL) { 911 inp->inp_options = sc->sc_ipopts; 912 sc->sc_ipopts = NULL; 913 } 914 915 sin.sin_family = AF_INET; 916 sin.sin_len = sizeof(sin); 917 sin.sin_addr = sc->sc_inc.inc_faddr; 918 sin.sin_port = sc->sc_inc.inc_fport; 919 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 920 laddr = inp->inp_laddr; 921 if (inp->inp_laddr.s_addr == INADDR_ANY) 922 inp->inp_laddr = sc->sc_inc.inc_laddr; 923 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 924 thread0.td_ucred, m, false)) != 0) { 925 inp->inp_laddr = laddr; 926 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 927 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 928 "with error %i\n", 929 s, __func__, error); 930 free(s, M_TCPLOG); 931 } 932 INP_HASH_WUNLOCK(&V_tcbinfo); 933 goto abort; 934 } 935 } 936 #endif /* INET */ 937 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 938 /* Copy old policy into new socket's. */ 939 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 940 printf("syncache_socket: could not copy policy\n"); 941 #endif 942 INP_HASH_WUNLOCK(&V_tcbinfo); 943 tp = intotcpcb(inp); 944 tcp_state_change(tp, TCPS_SYN_RECEIVED); 945 tp->iss = sc->sc_iss; 946 tp->irs = sc->sc_irs; 947 tcp_rcvseqinit(tp); 948 tcp_sendseqinit(tp); 949 blk = sototcpcb(lso)->t_fb; 950 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 951 /* 952 * Our parents t_fb was not the default, 953 * we need to release our ref on tp->t_fb and 954 * pickup one on the new entry. 955 */ 956 struct tcp_function_block *rblk; 957 958 rblk = find_and_ref_tcp_fb(blk); 959 KASSERT(rblk != NULL, 960 ("cannot find blk %p out of syncache?", blk)); 961 if (tp->t_fb->tfb_tcp_fb_fini) 962 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 963 refcount_release(&tp->t_fb->tfb_refcnt); 964 tp->t_fb = rblk; 965 /* 966 * XXXrrs this is quite dangerous, it is possible 967 * for the new function to fail to init. We also 968 * are not asking if the handoff_is_ok though at 969 * the very start thats probalbly ok. 970 */ 971 if (tp->t_fb->tfb_tcp_fb_init) { 972 (*tp->t_fb->tfb_tcp_fb_init)(tp); 973 } 974 } 975 tp->snd_wl1 = sc->sc_irs; 976 tp->snd_max = tp->iss + 1; 977 tp->snd_nxt = tp->iss + 1; 978 tp->rcv_up = sc->sc_irs + 1; 979 tp->rcv_wnd = sc->sc_wnd; 980 tp->rcv_adv += tp->rcv_wnd; 981 tp->last_ack_sent = tp->rcv_nxt; 982 983 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 984 if (sc->sc_flags & SCF_NOOPT) 985 tp->t_flags |= TF_NOOPT; 986 else { 987 if (sc->sc_flags & SCF_WINSCALE) { 988 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 989 tp->snd_scale = sc->sc_requested_s_scale; 990 tp->request_r_scale = sc->sc_requested_r_scale; 991 } 992 if (sc->sc_flags & SCF_TIMESTAMP) { 993 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 994 tp->ts_recent = sc->sc_tsreflect; 995 tp->ts_recent_age = tcp_ts_getticks(); 996 tp->ts_offset = sc->sc_tsoff; 997 } 998 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 999 if (sc->sc_flags & SCF_SIGNATURE) 1000 tp->t_flags |= TF_SIGNATURE; 1001 #endif 1002 if (sc->sc_flags & SCF_SACK) 1003 tp->t_flags |= TF_SACK_PERMIT; 1004 } 1005 1006 if (sc->sc_flags & SCF_ECN) 1007 tp->t_flags2 |= TF2_ECN_PERMIT; 1008 1009 /* 1010 * Set up MSS and get cached values from tcp_hostcache. 1011 * This might overwrite some of the defaults we just set. 1012 */ 1013 tcp_mss(tp, sc->sc_peer_mss); 1014 1015 /* 1016 * If the SYN,ACK was retransmitted, indicate that CWND to be 1017 * limited to one segment in cc_conn_init(). 1018 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1019 */ 1020 if (sc->sc_rxmits > 1) 1021 tp->snd_cwnd = 1; 1022 1023 #ifdef TCP_OFFLOAD 1024 /* 1025 * Allow a TOE driver to install its hooks. Note that we hold the 1026 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1027 * new connection before the TOE driver has done its thing. 1028 */ 1029 if (ADDED_BY_TOE(sc)) { 1030 struct toedev *tod = sc->sc_tod; 1031 1032 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1033 } 1034 #endif 1035 /* 1036 * Copy and activate timers. 1037 */ 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 return (so); 1046 1047 abort: 1048 INP_WUNLOCK(inp); 1049 abort2: 1050 if (so != NULL) 1051 soabort(so); 1052 return (NULL); 1053 } 1054 1055 /* 1056 * This function gets called when we receive an ACK for a 1057 * socket in the LISTEN state. We look up the connection 1058 * in the syncache, and if its there, we pull it out of 1059 * the cache and turn it into a full-blown connection in 1060 * the SYN-RECEIVED state. 1061 * 1062 * On syncache_socket() success the newly created socket 1063 * has its underlying inp locked. 1064 */ 1065 int 1066 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1067 struct socket **lsop, struct mbuf *m) 1068 { 1069 struct syncache *sc; 1070 struct syncache_head *sch; 1071 struct syncache scs; 1072 char *s; 1073 bool locked; 1074 1075 NET_EPOCH_ASSERT(); 1076 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1077 ("%s: can handle only ACK", __func__)); 1078 1079 if (syncache_cookiesonly()) { 1080 sc = NULL; 1081 sch = syncache_hashbucket(inc); 1082 locked = false; 1083 } else { 1084 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1085 locked = true; 1086 SCH_LOCK_ASSERT(sch); 1087 } 1088 1089 #ifdef INVARIANTS 1090 /* 1091 * Test code for syncookies comparing the syncache stored 1092 * values with the reconstructed values from the cookie. 1093 */ 1094 if (sc != NULL) 1095 syncookie_cmp(inc, sch, sc, th, to, *lsop); 1096 #endif 1097 1098 if (sc == NULL) { 1099 /* 1100 * There is no syncache entry, so see if this ACK is 1101 * a returning syncookie. To do this, first: 1102 * A. Check if syncookies are used in case of syncache 1103 * overflows 1104 * B. See if this socket has had a syncache entry dropped in 1105 * the recent past. We don't want to accept a bogus 1106 * syncookie if we've never received a SYN or accept it 1107 * twice. 1108 * C. check that the syncookie is valid. If it is, then 1109 * cobble up a fake syncache entry, and return. 1110 */ 1111 if (locked && !V_tcp_syncookies) { 1112 SCH_UNLOCK(sch); 1113 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1114 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1115 "segment rejected (syncookies disabled)\n", 1116 s, __func__); 1117 goto failed; 1118 } 1119 if (locked && !V_tcp_syncookiesonly && 1120 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1121 SCH_UNLOCK(sch); 1122 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1123 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1124 "segment rejected (no syncache entry)\n", 1125 s, __func__); 1126 goto failed; 1127 } 1128 bzero(&scs, sizeof(scs)); 1129 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 1130 if (locked) 1131 SCH_UNLOCK(sch); 1132 if (sc == NULL) { 1133 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1134 log(LOG_DEBUG, "%s; %s: Segment failed " 1135 "SYNCOOKIE authentication, segment rejected " 1136 "(probably spoofed)\n", s, __func__); 1137 goto failed; 1138 } 1139 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1140 /* If received ACK has MD5 signature, check it. */ 1141 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1142 (!TCPMD5_ENABLED() || 1143 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1144 /* Drop the ACK. */ 1145 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1146 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1147 "MD5 signature doesn't match.\n", 1148 s, __func__); 1149 free(s, M_TCPLOG); 1150 } 1151 TCPSTAT_INC(tcps_sig_err_sigopt); 1152 return (-1); /* Do not send RST */ 1153 } 1154 #endif /* TCP_SIGNATURE */ 1155 } else { 1156 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1157 /* 1158 * If listening socket requested TCP digests, check that 1159 * received ACK has signature and it is correct. 1160 * If not, drop the ACK and leave sc entry in th cache, 1161 * because SYN was received with correct signature. 1162 */ 1163 if (sc->sc_flags & SCF_SIGNATURE) { 1164 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1165 /* No signature */ 1166 TCPSTAT_INC(tcps_sig_err_nosigopt); 1167 SCH_UNLOCK(sch); 1168 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1169 log(LOG_DEBUG, "%s; %s: Segment " 1170 "rejected, MD5 signature wasn't " 1171 "provided.\n", s, __func__); 1172 free(s, M_TCPLOG); 1173 } 1174 return (-1); /* Do not send RST */ 1175 } 1176 if (!TCPMD5_ENABLED() || 1177 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1178 /* Doesn't match or no SA */ 1179 SCH_UNLOCK(sch); 1180 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1181 log(LOG_DEBUG, "%s; %s: Segment " 1182 "rejected, MD5 signature doesn't " 1183 "match.\n", s, __func__); 1184 free(s, M_TCPLOG); 1185 } 1186 return (-1); /* Do not send RST */ 1187 } 1188 } 1189 #endif /* TCP_SIGNATURE */ 1190 1191 /* 1192 * RFC 7323 PAWS: If we have a timestamp on this segment and 1193 * it's less than ts_recent, drop it. 1194 * XXXMT: RFC 7323 also requires to send an ACK. 1195 * In tcp_input.c this is only done for TCP segments 1196 * with user data, so be consistent here and just drop 1197 * the segment. 1198 */ 1199 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1200 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1201 SCH_UNLOCK(sch); 1202 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1203 log(LOG_DEBUG, 1204 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1205 "segment dropped\n", s, __func__, 1206 to->to_tsval, sc->sc_tsreflect); 1207 free(s, M_TCPLOG); 1208 } 1209 return (-1); /* Do not send RST */ 1210 } 1211 1212 /* 1213 * Pull out the entry to unlock the bucket row. 1214 * 1215 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1216 * tcp_state_change(). The tcpcb is not existent at this 1217 * moment. A new one will be allocated via syncache_socket-> 1218 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1219 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1220 */ 1221 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1222 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1223 sch->sch_length--; 1224 #ifdef TCP_OFFLOAD 1225 if (ADDED_BY_TOE(sc)) { 1226 struct toedev *tod = sc->sc_tod; 1227 1228 tod->tod_syncache_removed(tod, sc->sc_todctx); 1229 } 1230 #endif 1231 SCH_UNLOCK(sch); 1232 } 1233 1234 /* 1235 * Segment validation: 1236 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1237 */ 1238 if (th->th_ack != sc->sc_iss + 1) { 1239 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1240 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1241 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1242 goto failed; 1243 } 1244 1245 /* 1246 * The SEQ must fall in the window starting at the received 1247 * initial receive sequence number + 1 (the SYN). 1248 */ 1249 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1250 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1251 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1252 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1253 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1254 goto failed; 1255 } 1256 1257 /* 1258 * If timestamps were not negotiated during SYN/ACK they 1259 * must not appear on any segment during this session. 1260 */ 1261 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1262 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1263 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1264 "segment rejected\n", s, __func__); 1265 goto failed; 1266 } 1267 1268 /* 1269 * If timestamps were negotiated during SYN/ACK they should 1270 * appear on every segment during this session. 1271 * XXXAO: This is only informal as there have been unverified 1272 * reports of non-compliants stacks. 1273 */ 1274 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1275 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1276 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1277 "no action\n", s, __func__); 1278 free(s, M_TCPLOG); 1279 s = NULL; 1280 } 1281 } 1282 1283 *lsop = syncache_socket(sc, *lsop, m); 1284 1285 if (*lsop == NULL) 1286 TCPSTAT_INC(tcps_sc_aborted); 1287 else 1288 TCPSTAT_INC(tcps_sc_completed); 1289 1290 /* how do we find the inp for the new socket? */ 1291 if (sc != &scs) 1292 syncache_free(sc); 1293 return (1); 1294 failed: 1295 if (sc != NULL && sc != &scs) 1296 syncache_free(sc); 1297 if (s != NULL) 1298 free(s, M_TCPLOG); 1299 *lsop = NULL; 1300 return (0); 1301 } 1302 1303 static void 1304 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1305 uint64_t response_cookie) 1306 { 1307 struct inpcb *inp; 1308 struct tcpcb *tp; 1309 unsigned int *pending_counter; 1310 1311 NET_EPOCH_ASSERT(); 1312 1313 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1314 *lsop = syncache_socket(sc, *lsop, m); 1315 if (*lsop == NULL) { 1316 TCPSTAT_INC(tcps_sc_aborted); 1317 atomic_subtract_int(pending_counter, 1); 1318 } else { 1319 soisconnected(*lsop); 1320 inp = sotoinpcb(*lsop); 1321 tp = intotcpcb(inp); 1322 tp->t_flags |= TF_FASTOPEN; 1323 tp->t_tfo_cookie.server = response_cookie; 1324 tp->snd_max = tp->iss; 1325 tp->snd_nxt = tp->iss; 1326 tp->t_tfo_pending = pending_counter; 1327 TCPSTAT_INC(tcps_sc_completed); 1328 } 1329 } 1330 1331 /* 1332 * Given a LISTEN socket and an inbound SYN request, add 1333 * this to the syn cache, and send back a segment: 1334 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1335 * to the source. 1336 * 1337 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1338 * Doing so would require that we hold onto the data and deliver it 1339 * to the application. However, if we are the target of a SYN-flood 1340 * DoS attack, an attacker could send data which would eventually 1341 * consume all available buffer space if it were ACKed. By not ACKing 1342 * the data, we avoid this DoS scenario. 1343 * 1344 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1345 * cookie is processed and a new socket is created. In this case, any data 1346 * accompanying the SYN will be queued to the socket by tcp_input() and will 1347 * be ACKed either when the application sends response data or the delayed 1348 * ACK timer expires, whichever comes first. 1349 */ 1350 int 1351 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1352 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1353 void *todctx, uint8_t iptos) 1354 { 1355 struct tcpcb *tp; 1356 struct socket *so; 1357 struct syncache *sc = NULL; 1358 struct syncache_head *sch; 1359 struct mbuf *ipopts = NULL; 1360 u_int ltflags; 1361 int win, ip_ttl, ip_tos; 1362 char *s; 1363 int rv = 0; 1364 #ifdef INET6 1365 int autoflowlabel = 0; 1366 #endif 1367 #ifdef MAC 1368 struct label *maclabel; 1369 #endif 1370 struct syncache scs; 1371 struct ucred *cred; 1372 uint64_t tfo_response_cookie; 1373 unsigned int *tfo_pending = NULL; 1374 int tfo_cookie_valid = 0; 1375 int tfo_response_cookie_valid = 0; 1376 bool locked; 1377 1378 INP_WLOCK_ASSERT(inp); /* listen socket */ 1379 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1380 ("%s: unexpected tcp flags", __func__)); 1381 1382 /* 1383 * Combine all so/tp operations very early to drop the INP lock as 1384 * soon as possible. 1385 */ 1386 so = *lsop; 1387 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1388 tp = sototcpcb(so); 1389 cred = crhold(so->so_cred); 1390 1391 #ifdef INET6 1392 if ((inc->inc_flags & INC_ISIPV6) && 1393 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1394 autoflowlabel = 1; 1395 #endif 1396 ip_ttl = inp->inp_ip_ttl; 1397 ip_tos = inp->inp_ip_tos; 1398 win = so->sol_sbrcv_hiwat; 1399 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1400 1401 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1402 (tp->t_tfo_pending != NULL) && 1403 (to->to_flags & TOF_FASTOPEN)) { 1404 /* 1405 * Limit the number of pending TFO connections to 1406 * approximately half of the queue limit. This prevents TFO 1407 * SYN floods from starving the service by filling the 1408 * listen queue with bogus TFO connections. 1409 */ 1410 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1411 (so->sol_qlimit / 2)) { 1412 int result; 1413 1414 result = tcp_fastopen_check_cookie(inc, 1415 to->to_tfo_cookie, to->to_tfo_len, 1416 &tfo_response_cookie); 1417 tfo_cookie_valid = (result > 0); 1418 tfo_response_cookie_valid = (result >= 0); 1419 } 1420 1421 /* 1422 * Remember the TFO pending counter as it will have to be 1423 * decremented below if we don't make it to syncache_tfo_expand(). 1424 */ 1425 tfo_pending = tp->t_tfo_pending; 1426 } 1427 1428 /* By the time we drop the lock these should no longer be used. */ 1429 so = NULL; 1430 tp = NULL; 1431 1432 #ifdef MAC 1433 if (mac_syncache_init(&maclabel) != 0) { 1434 INP_WUNLOCK(inp); 1435 goto done; 1436 } else 1437 mac_syncache_create(maclabel, inp); 1438 #endif 1439 if (!tfo_cookie_valid) 1440 INP_WUNLOCK(inp); 1441 1442 /* 1443 * Remember the IP options, if any. 1444 */ 1445 #ifdef INET6 1446 if (!(inc->inc_flags & INC_ISIPV6)) 1447 #endif 1448 #ifdef INET 1449 ipopts = (m) ? ip_srcroute(m) : NULL; 1450 #else 1451 ipopts = NULL; 1452 #endif 1453 1454 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1455 /* 1456 * If listening socket requested TCP digests, check that received 1457 * SYN has signature and it is correct. If signature doesn't match 1458 * or TCP_SIGNATURE support isn't enabled, drop the packet. 1459 */ 1460 if (ltflags & TF_SIGNATURE) { 1461 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1462 TCPSTAT_INC(tcps_sig_err_nosigopt); 1463 goto done; 1464 } 1465 if (!TCPMD5_ENABLED() || 1466 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1467 goto done; 1468 } 1469 #endif /* TCP_SIGNATURE */ 1470 /* 1471 * See if we already have an entry for this connection. 1472 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1473 * 1474 * XXX: should the syncache be re-initialized with the contents 1475 * of the new SYN here (which may have different options?) 1476 * 1477 * XXX: We do not check the sequence number to see if this is a 1478 * real retransmit or a new connection attempt. The question is 1479 * how to handle such a case; either ignore it as spoofed, or 1480 * drop the current entry and create a new one? 1481 */ 1482 if (syncache_cookiesonly()) { 1483 sc = NULL; 1484 sch = syncache_hashbucket(inc); 1485 locked = false; 1486 } else { 1487 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1488 locked = true; 1489 SCH_LOCK_ASSERT(sch); 1490 } 1491 if (sc != NULL) { 1492 if (tfo_cookie_valid) 1493 INP_WUNLOCK(inp); 1494 TCPSTAT_INC(tcps_sc_dupsyn); 1495 if (ipopts) { 1496 /* 1497 * If we were remembering a previous source route, 1498 * forget it and use the new one we've been given. 1499 */ 1500 if (sc->sc_ipopts) 1501 (void) m_free(sc->sc_ipopts); 1502 sc->sc_ipopts = ipopts; 1503 } 1504 /* 1505 * Update timestamp if present. 1506 */ 1507 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1508 sc->sc_tsreflect = to->to_tsval; 1509 else 1510 sc->sc_flags &= ~SCF_TIMESTAMP; 1511 /* 1512 * Disable ECN if needed. 1513 */ 1514 if ((sc->sc_flags & SCF_ECN) && 1515 ((th->th_flags & (TH_ECE|TH_CWR)) != (TH_ECE|TH_CWR))) { 1516 sc->sc_flags &= ~SCF_ECN; 1517 } 1518 #ifdef MAC 1519 /* 1520 * Since we have already unconditionally allocated label 1521 * storage, free it up. The syncache entry will already 1522 * have an initialized label we can use. 1523 */ 1524 mac_syncache_destroy(&maclabel); 1525 #endif 1526 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1527 /* Retransmit SYN|ACK and reset retransmit count. */ 1528 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1529 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1530 "resetting timer and retransmitting SYN|ACK\n", 1531 s, __func__); 1532 free(s, M_TCPLOG); 1533 } 1534 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1535 sc->sc_rxmits = 0; 1536 syncache_timeout(sc, sch, 1); 1537 TCPSTAT_INC(tcps_sndacks); 1538 TCPSTAT_INC(tcps_sndtotal); 1539 } 1540 SCH_UNLOCK(sch); 1541 goto donenoprobe; 1542 } 1543 1544 if (tfo_cookie_valid) { 1545 bzero(&scs, sizeof(scs)); 1546 sc = &scs; 1547 goto skip_alloc; 1548 } 1549 1550 /* 1551 * Skip allocating a syncache entry if we are just going to discard 1552 * it later. 1553 */ 1554 if (!locked) { 1555 bzero(&scs, sizeof(scs)); 1556 sc = &scs; 1557 } else 1558 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1559 if (sc == NULL) { 1560 /* 1561 * The zone allocator couldn't provide more entries. 1562 * Treat this as if the cache was full; drop the oldest 1563 * entry and insert the new one. 1564 */ 1565 TCPSTAT_INC(tcps_sc_zonefail); 1566 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1567 sch->sch_last_overflow = time_uptime; 1568 syncache_drop(sc, sch); 1569 syncache_pause(inc); 1570 } 1571 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1572 if (sc == NULL) { 1573 if (V_tcp_syncookies) { 1574 bzero(&scs, sizeof(scs)); 1575 sc = &scs; 1576 } else { 1577 KASSERT(locked, 1578 ("%s: bucket unexpectedly unlocked", 1579 __func__)); 1580 SCH_UNLOCK(sch); 1581 if (ipopts) 1582 (void) m_free(ipopts); 1583 goto done; 1584 } 1585 } 1586 } 1587 1588 skip_alloc: 1589 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1590 sc->sc_tfo_cookie = &tfo_response_cookie; 1591 1592 /* 1593 * Fill in the syncache values. 1594 */ 1595 #ifdef MAC 1596 sc->sc_label = maclabel; 1597 #endif 1598 sc->sc_cred = cred; 1599 cred = NULL; 1600 sc->sc_ipopts = ipopts; 1601 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1602 #ifdef INET6 1603 if (!(inc->inc_flags & INC_ISIPV6)) 1604 #endif 1605 { 1606 sc->sc_ip_tos = ip_tos; 1607 sc->sc_ip_ttl = ip_ttl; 1608 } 1609 #ifdef TCP_OFFLOAD 1610 sc->sc_tod = tod; 1611 sc->sc_todctx = todctx; 1612 #endif 1613 sc->sc_irs = th->th_seq; 1614 sc->sc_flags = 0; 1615 sc->sc_flowlabel = 0; 1616 1617 /* 1618 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1619 * win was derived from socket earlier in the function. 1620 */ 1621 win = imax(win, 0); 1622 win = imin(win, TCP_MAXWIN); 1623 sc->sc_wnd = win; 1624 1625 if (V_tcp_do_rfc1323) { 1626 /* 1627 * A timestamp received in a SYN makes 1628 * it ok to send timestamp requests and replies. 1629 */ 1630 if (to->to_flags & TOF_TS) { 1631 sc->sc_tsreflect = to->to_tsval; 1632 sc->sc_flags |= SCF_TIMESTAMP; 1633 sc->sc_tsoff = tcp_new_ts_offset(inc); 1634 } 1635 if (to->to_flags & TOF_SCALE) { 1636 int wscale = 0; 1637 1638 /* 1639 * Pick the smallest possible scaling factor that 1640 * will still allow us to scale up to sb_max, aka 1641 * kern.ipc.maxsockbuf. 1642 * 1643 * We do this because there are broken firewalls that 1644 * will corrupt the window scale option, leading to 1645 * the other endpoint believing that our advertised 1646 * window is unscaled. At scale factors larger than 1647 * 5 the unscaled window will drop below 1500 bytes, 1648 * leading to serious problems when traversing these 1649 * broken firewalls. 1650 * 1651 * With the default maxsockbuf of 256K, a scale factor 1652 * of 3 will be chosen by this algorithm. Those who 1653 * choose a larger maxsockbuf should watch out 1654 * for the compatibility problems mentioned above. 1655 * 1656 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1657 * or <SYN,ACK>) segment itself is never scaled. 1658 */ 1659 while (wscale < TCP_MAX_WINSHIFT && 1660 (TCP_MAXWIN << wscale) < sb_max) 1661 wscale++; 1662 sc->sc_requested_r_scale = wscale; 1663 sc->sc_requested_s_scale = to->to_wscale; 1664 sc->sc_flags |= SCF_WINSCALE; 1665 } 1666 } 1667 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1668 /* 1669 * If listening socket requested TCP digests, flag this in the 1670 * syncache so that syncache_respond() will do the right thing 1671 * with the SYN+ACK. 1672 */ 1673 if (ltflags & TF_SIGNATURE) 1674 sc->sc_flags |= SCF_SIGNATURE; 1675 #endif /* TCP_SIGNATURE */ 1676 if (to->to_flags & TOF_SACKPERM) 1677 sc->sc_flags |= SCF_SACK; 1678 if (to->to_flags & TOF_MSS) 1679 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1680 if (ltflags & TF_NOOPT) 1681 sc->sc_flags |= SCF_NOOPT; 1682 if (((th->th_flags & (TH_ECE|TH_CWR)) == (TH_ECE|TH_CWR)) && 1683 V_tcp_do_ecn) 1684 sc->sc_flags |= SCF_ECN; 1685 1686 if (V_tcp_syncookies) 1687 sc->sc_iss = syncookie_generate(sch, sc); 1688 else 1689 sc->sc_iss = arc4random(); 1690 #ifdef INET6 1691 if (autoflowlabel) { 1692 if (V_tcp_syncookies) 1693 sc->sc_flowlabel = sc->sc_iss; 1694 else 1695 sc->sc_flowlabel = ip6_randomflowlabel(); 1696 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1697 } 1698 #endif 1699 if (locked) 1700 SCH_UNLOCK(sch); 1701 1702 if (tfo_cookie_valid) { 1703 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1704 /* INP_WUNLOCK(inp) will be performed by the caller */ 1705 rv = 1; 1706 goto tfo_expanded; 1707 } 1708 1709 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1710 /* 1711 * Do a standard 3-way handshake. 1712 */ 1713 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1714 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1715 syncache_free(sc); 1716 else if (sc != &scs) 1717 syncache_insert(sc, sch); /* locks and unlocks sch */ 1718 TCPSTAT_INC(tcps_sndacks); 1719 TCPSTAT_INC(tcps_sndtotal); 1720 } else { 1721 if (sc != &scs) 1722 syncache_free(sc); 1723 TCPSTAT_INC(tcps_sc_dropped); 1724 } 1725 goto donenoprobe; 1726 1727 done: 1728 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1729 donenoprobe: 1730 if (m) { 1731 *lsop = NULL; 1732 m_freem(m); 1733 } 1734 /* 1735 * If tfo_pending is not NULL here, then a TFO SYN that did not 1736 * result in a new socket was processed and the associated pending 1737 * counter has not yet been decremented. All such TFO processing paths 1738 * transit this point. 1739 */ 1740 if (tfo_pending != NULL) 1741 tcp_fastopen_decrement_counter(tfo_pending); 1742 1743 tfo_expanded: 1744 if (cred != NULL) 1745 crfree(cred); 1746 #ifdef MAC 1747 if (sc == &scs) 1748 mac_syncache_destroy(&maclabel); 1749 #endif 1750 return (rv); 1751 } 1752 1753 /* 1754 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1755 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1756 */ 1757 static int 1758 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1759 { 1760 struct ip *ip = NULL; 1761 struct mbuf *m; 1762 struct tcphdr *th = NULL; 1763 int optlen, error = 0; /* Make compiler happy */ 1764 u_int16_t hlen, tlen, mssopt; 1765 struct tcpopt to; 1766 #ifdef INET6 1767 struct ip6_hdr *ip6 = NULL; 1768 #endif 1769 1770 NET_EPOCH_ASSERT(); 1771 1772 hlen = 1773 #ifdef INET6 1774 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1775 #endif 1776 sizeof(struct ip); 1777 tlen = hlen + sizeof(struct tcphdr); 1778 1779 /* Determine MSS we advertize to other end of connection. */ 1780 mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss); 1781 1782 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1783 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1784 ("syncache: mbuf too small")); 1785 1786 /* Create the IP+TCP header from scratch. */ 1787 m = m_gethdr(M_NOWAIT, MT_DATA); 1788 if (m == NULL) 1789 return (ENOBUFS); 1790 #ifdef MAC 1791 mac_syncache_create_mbuf(sc->sc_label, m); 1792 #endif 1793 m->m_data += max_linkhdr; 1794 m->m_len = tlen; 1795 m->m_pkthdr.len = tlen; 1796 m->m_pkthdr.rcvif = NULL; 1797 1798 #ifdef INET6 1799 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1800 ip6 = mtod(m, struct ip6_hdr *); 1801 ip6->ip6_vfc = IPV6_VERSION; 1802 ip6->ip6_nxt = IPPROTO_TCP; 1803 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1804 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1805 ip6->ip6_plen = htons(tlen - hlen); 1806 /* ip6_hlim is set after checksum */ 1807 /* Zero out traffic class and flow label. */ 1808 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1809 ip6->ip6_flow |= sc->sc_flowlabel; 1810 1811 th = (struct tcphdr *)(ip6 + 1); 1812 } 1813 #endif 1814 #if defined(INET6) && defined(INET) 1815 else 1816 #endif 1817 #ifdef INET 1818 { 1819 ip = mtod(m, struct ip *); 1820 ip->ip_v = IPVERSION; 1821 ip->ip_hl = sizeof(struct ip) >> 2; 1822 ip->ip_len = htons(tlen); 1823 ip->ip_id = 0; 1824 ip->ip_off = 0; 1825 ip->ip_sum = 0; 1826 ip->ip_p = IPPROTO_TCP; 1827 ip->ip_src = sc->sc_inc.inc_laddr; 1828 ip->ip_dst = sc->sc_inc.inc_faddr; 1829 ip->ip_ttl = sc->sc_ip_ttl; 1830 ip->ip_tos = sc->sc_ip_tos; 1831 1832 /* 1833 * See if we should do MTU discovery. Route lookups are 1834 * expensive, so we will only unset the DF bit if: 1835 * 1836 * 1) path_mtu_discovery is disabled 1837 * 2) the SCF_UNREACH flag has been set 1838 */ 1839 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1840 ip->ip_off |= htons(IP_DF); 1841 1842 th = (struct tcphdr *)(ip + 1); 1843 } 1844 #endif /* INET */ 1845 th->th_sport = sc->sc_inc.inc_lport; 1846 th->th_dport = sc->sc_inc.inc_fport; 1847 1848 if (flags & TH_SYN) 1849 th->th_seq = htonl(sc->sc_iss); 1850 else 1851 th->th_seq = htonl(sc->sc_iss + 1); 1852 th->th_ack = htonl(sc->sc_irs + 1); 1853 th->th_off = sizeof(struct tcphdr) >> 2; 1854 th->th_x2 = 0; 1855 th->th_flags = flags; 1856 th->th_win = htons(sc->sc_wnd); 1857 th->th_urp = 0; 1858 1859 if ((flags & TH_SYN) && (sc->sc_flags & SCF_ECN)) { 1860 th->th_flags |= TH_ECE; 1861 TCPSTAT_INC(tcps_ecn_shs); 1862 } 1863 1864 /* Tack on the TCP options. */ 1865 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1866 to.to_flags = 0; 1867 1868 if (flags & TH_SYN) { 1869 to.to_mss = mssopt; 1870 to.to_flags = TOF_MSS; 1871 if (sc->sc_flags & SCF_WINSCALE) { 1872 to.to_wscale = sc->sc_requested_r_scale; 1873 to.to_flags |= TOF_SCALE; 1874 } 1875 if (sc->sc_flags & SCF_SACK) 1876 to.to_flags |= TOF_SACKPERM; 1877 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1878 if (sc->sc_flags & SCF_SIGNATURE) 1879 to.to_flags |= TOF_SIGNATURE; 1880 #endif 1881 if (sc->sc_tfo_cookie) { 1882 to.to_flags |= TOF_FASTOPEN; 1883 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1884 to.to_tfo_cookie = sc->sc_tfo_cookie; 1885 /* don't send cookie again when retransmitting response */ 1886 sc->sc_tfo_cookie = NULL; 1887 } 1888 } 1889 if (sc->sc_flags & SCF_TIMESTAMP) { 1890 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1891 to.to_tsecr = sc->sc_tsreflect; 1892 to.to_flags |= TOF_TS; 1893 } 1894 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1895 1896 /* Adjust headers by option size. */ 1897 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1898 m->m_len += optlen; 1899 m->m_pkthdr.len += optlen; 1900 #ifdef INET6 1901 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1902 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1903 else 1904 #endif 1905 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1906 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1907 if (sc->sc_flags & SCF_SIGNATURE) { 1908 KASSERT(to.to_flags & TOF_SIGNATURE, 1909 ("tcp_addoptions() didn't set tcp_signature")); 1910 1911 /* NOTE: to.to_signature is inside of mbuf */ 1912 if (!TCPMD5_ENABLED() || 1913 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1914 m_freem(m); 1915 return (EACCES); 1916 } 1917 } 1918 #endif 1919 } else 1920 optlen = 0; 1921 1922 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1923 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1924 /* 1925 * If we have peer's SYN and it has a flowid, then let's assign it to 1926 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1927 * to SYN|ACK due to lack of inp here. 1928 */ 1929 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1930 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1931 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1932 } 1933 #ifdef INET6 1934 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1935 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1936 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1937 IPPROTO_TCP, 0); 1938 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1939 #ifdef TCP_OFFLOAD 1940 if (ADDED_BY_TOE(sc)) { 1941 struct toedev *tod = sc->sc_tod; 1942 1943 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1944 1945 return (error); 1946 } 1947 #endif 1948 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 1949 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1950 } 1951 #endif 1952 #if defined(INET6) && defined(INET) 1953 else 1954 #endif 1955 #ifdef INET 1956 { 1957 m->m_pkthdr.csum_flags = CSUM_TCP; 1958 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1959 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1960 #ifdef TCP_OFFLOAD 1961 if (ADDED_BY_TOE(sc)) { 1962 struct toedev *tod = sc->sc_tod; 1963 1964 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1965 1966 return (error); 1967 } 1968 #endif 1969 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 1970 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1971 } 1972 #endif 1973 return (error); 1974 } 1975 1976 /* 1977 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1978 * that exceed the capacity of the syncache by avoiding the storage of any 1979 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1980 * attacks where the attacker does not have access to our responses. 1981 * 1982 * Syncookies encode and include all necessary information about the 1983 * connection setup within the SYN|ACK that we send back. That way we 1984 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1985 * (if ever). Normally the syncache and syncookies are running in parallel 1986 * with the latter taking over when the former is exhausted. When matching 1987 * syncache entry is found the syncookie is ignored. 1988 * 1989 * The only reliable information persisting the 3WHS is our initial sequence 1990 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1991 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1992 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1993 * returns and signifies a legitimate connection if it matches the ACK. 1994 * 1995 * The available space of 32 bits to store the hash and to encode the SYN 1996 * option information is very tight and we should have at least 24 bits for 1997 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1998 * 1999 * SYN option information we have to encode to fully restore a connection: 2000 * MSS: is imporant to chose an optimal segment size to avoid IP level 2001 * fragmentation along the path. The common MSS values can be encoded 2002 * in a 3-bit table. Uncommon values are captured by the next lower value 2003 * in the table leading to a slight increase in packetization overhead. 2004 * WSCALE: is necessary to allow large windows to be used for high delay- 2005 * bandwidth product links. Not scaling the window when it was initially 2006 * negotiated is bad for performance as lack of scaling further decreases 2007 * the apparent available send window. We only need to encode the WSCALE 2008 * we received from the remote end. Our end can be recalculated at any 2009 * time. The common WSCALE values can be encoded in a 3-bit table. 2010 * Uncommon values are captured by the next lower value in the table 2011 * making us under-estimate the available window size halving our 2012 * theoretically possible maximum throughput for that connection. 2013 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2014 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2015 * that are included in all segments on a connection. We enable them when 2016 * the ACK has them. 2017 * 2018 * Security of syncookies and attack vectors: 2019 * 2020 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2021 * together with the gloabl secret to make it unique per connection attempt. 2022 * Thus any change of any of those parameters results in a different MAC output 2023 * in an unpredictable way unless a collision is encountered. 24 bits of the 2024 * MAC are embedded into the ISS. 2025 * 2026 * To prevent replay attacks two rotating global secrets are updated with a 2027 * new random value every 15 seconds. The life-time of a syncookie is thus 2028 * 15-30 seconds. 2029 * 2030 * Vector 1: Attacking the secret. This requires finding a weakness in the 2031 * MAC itself or the way it is used here. The attacker can do a chosen plain 2032 * text attack by varying and testing the all parameters under his control. 2033 * The strength depends on the size and randomness of the secret, and the 2034 * cryptographic security of the MAC function. Due to the constant updating 2035 * of the secret the attacker has at most 29.999 seconds to find the secret 2036 * and launch spoofed connections. After that he has to start all over again. 2037 * 2038 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2039 * size an average of 4,823 attempts are required for a 50% chance of success 2040 * to spoof a single syncookie (birthday collision paradox). However the 2041 * attacker is blind and doesn't know if one of his attempts succeeded unless 2042 * he has a side channel to interfere success from. A single connection setup 2043 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2044 * This many attempts are required for each one blind spoofed connection. For 2045 * every additional spoofed connection he has to launch another N attempts. 2046 * Thus for a sustained rate 100 spoofed connections per second approximately 2047 * 1,800,000 packets per second would have to be sent. 2048 * 2049 * NB: The MAC function should be fast so that it doesn't become a CPU 2050 * exhaustion attack vector itself. 2051 * 2052 * References: 2053 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2054 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2055 * http://cr.yp.to/syncookies.html (overview) 2056 * http://cr.yp.to/syncookies/archive (details) 2057 * 2058 * 2059 * Schematic construction of a syncookie enabled Initial Sequence Number: 2060 * 0 1 2 3 2061 * 12345678901234567890123456789012 2062 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2063 * 2064 * x 24 MAC (truncated) 2065 * W 3 Send Window Scale index 2066 * M 3 MSS index 2067 * S 1 SACK permitted 2068 * P 1 Odd/even secret 2069 */ 2070 2071 /* 2072 * Distribution and probability of certain MSS values. Those in between are 2073 * rounded down to the next lower one. 2074 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2075 * .2% .3% 5% 7% 7% 20% 15% 45% 2076 */ 2077 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2078 2079 /* 2080 * Distribution and probability of certain WSCALE values. We have to map the 2081 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2082 * bits based on prevalence of certain values. Where we don't have an exact 2083 * match for are rounded down to the next lower one letting us under-estimate 2084 * the true available window. At the moment this would happen only for the 2085 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2086 * and window size). The absence of the WSCALE option (no scaling in either 2087 * direction) is encoded with index zero. 2088 * [WSCALE values histograms, Allman, 2012] 2089 * X 10 10 35 5 6 14 10% by host 2090 * X 11 4 5 5 18 49 3% by connections 2091 */ 2092 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2093 2094 /* 2095 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2096 * and good cryptographic properties. 2097 */ 2098 static uint32_t 2099 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2100 uint8_t *secbits, uintptr_t secmod) 2101 { 2102 SIPHASH_CTX ctx; 2103 uint32_t siphash[2]; 2104 2105 SipHash24_Init(&ctx); 2106 SipHash_SetKey(&ctx, secbits); 2107 switch (inc->inc_flags & INC_ISIPV6) { 2108 #ifdef INET 2109 case 0: 2110 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2111 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2112 break; 2113 #endif 2114 #ifdef INET6 2115 case INC_ISIPV6: 2116 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2117 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2118 break; 2119 #endif 2120 } 2121 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2122 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2123 SipHash_Update(&ctx, &irs, sizeof(irs)); 2124 SipHash_Update(&ctx, &flags, sizeof(flags)); 2125 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2126 SipHash_Final((u_int8_t *)&siphash, &ctx); 2127 2128 return (siphash[0] ^ siphash[1]); 2129 } 2130 2131 static tcp_seq 2132 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2133 { 2134 u_int i, secbit, wscale; 2135 uint32_t iss, hash; 2136 uint8_t *secbits; 2137 union syncookie cookie; 2138 2139 cookie.cookie = 0; 2140 2141 /* Map our computed MSS into the 3-bit index. */ 2142 for (i = nitems(tcp_sc_msstab) - 1; 2143 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2144 i--) 2145 ; 2146 cookie.flags.mss_idx = i; 2147 2148 /* 2149 * Map the send window scale into the 3-bit index but only if 2150 * the wscale option was received. 2151 */ 2152 if (sc->sc_flags & SCF_WINSCALE) { 2153 wscale = sc->sc_requested_s_scale; 2154 for (i = nitems(tcp_sc_wstab) - 1; 2155 tcp_sc_wstab[i] > wscale && i > 0; 2156 i--) 2157 ; 2158 cookie.flags.wscale_idx = i; 2159 } 2160 2161 /* Can we do SACK? */ 2162 if (sc->sc_flags & SCF_SACK) 2163 cookie.flags.sack_ok = 1; 2164 2165 /* Which of the two secrets to use. */ 2166 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2167 cookie.flags.odd_even = secbit; 2168 2169 secbits = V_tcp_syncache.secret.key[secbit]; 2170 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2171 (uintptr_t)sch); 2172 2173 /* 2174 * Put the flags into the hash and XOR them to get better ISS number 2175 * variance. This doesn't enhance the cryptographic strength and is 2176 * done to prevent the 8 cookie bits from showing up directly on the 2177 * wire. 2178 */ 2179 iss = hash & ~0xff; 2180 iss |= cookie.cookie ^ (hash >> 24); 2181 2182 TCPSTAT_INC(tcps_sc_sendcookie); 2183 return (iss); 2184 } 2185 2186 static struct syncache * 2187 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2188 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2189 struct socket *lso) 2190 { 2191 uint32_t hash; 2192 uint8_t *secbits; 2193 tcp_seq ack, seq; 2194 int wnd, wscale = 0; 2195 union syncookie cookie; 2196 2197 /* 2198 * Pull information out of SYN-ACK/ACK and revert sequence number 2199 * advances. 2200 */ 2201 ack = th->th_ack - 1; 2202 seq = th->th_seq - 1; 2203 2204 /* 2205 * Unpack the flags containing enough information to restore the 2206 * connection. 2207 */ 2208 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2209 2210 /* Which of the two secrets to use. */ 2211 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2212 2213 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2214 2215 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2216 if ((ack & ~0xff) != (hash & ~0xff)) 2217 return (NULL); 2218 2219 /* Fill in the syncache values. */ 2220 sc->sc_flags = 0; 2221 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2222 sc->sc_ipopts = NULL; 2223 2224 sc->sc_irs = seq; 2225 sc->sc_iss = ack; 2226 2227 switch (inc->inc_flags & INC_ISIPV6) { 2228 #ifdef INET 2229 case 0: 2230 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2231 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2232 break; 2233 #endif 2234 #ifdef INET6 2235 case INC_ISIPV6: 2236 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2237 sc->sc_flowlabel = 2238 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2239 break; 2240 #endif 2241 } 2242 2243 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2244 2245 /* We can simply recompute receive window scale we sent earlier. */ 2246 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2247 wscale++; 2248 2249 /* Only use wscale if it was enabled in the orignal SYN. */ 2250 if (cookie.flags.wscale_idx > 0) { 2251 sc->sc_requested_r_scale = wscale; 2252 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2253 sc->sc_flags |= SCF_WINSCALE; 2254 } 2255 2256 wnd = lso->sol_sbrcv_hiwat; 2257 wnd = imax(wnd, 0); 2258 wnd = imin(wnd, TCP_MAXWIN); 2259 sc->sc_wnd = wnd; 2260 2261 if (cookie.flags.sack_ok) 2262 sc->sc_flags |= SCF_SACK; 2263 2264 if (to->to_flags & TOF_TS) { 2265 sc->sc_flags |= SCF_TIMESTAMP; 2266 sc->sc_tsreflect = to->to_tsval; 2267 sc->sc_tsoff = tcp_new_ts_offset(inc); 2268 } 2269 2270 if (to->to_flags & TOF_SIGNATURE) 2271 sc->sc_flags |= SCF_SIGNATURE; 2272 2273 sc->sc_rxmits = 0; 2274 2275 TCPSTAT_INC(tcps_sc_recvcookie); 2276 return (sc); 2277 } 2278 2279 #ifdef INVARIANTS 2280 static int 2281 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2282 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2283 struct socket *lso) 2284 { 2285 struct syncache scs, *scx; 2286 char *s; 2287 2288 bzero(&scs, sizeof(scs)); 2289 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2290 2291 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2292 return (0); 2293 2294 if (scx != NULL) { 2295 if (sc->sc_peer_mss != scx->sc_peer_mss) 2296 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2297 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2298 2299 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2300 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2301 s, __func__, sc->sc_requested_r_scale, 2302 scx->sc_requested_r_scale); 2303 2304 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2305 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2306 s, __func__, sc->sc_requested_s_scale, 2307 scx->sc_requested_s_scale); 2308 2309 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2310 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2311 } 2312 2313 if (s != NULL) 2314 free(s, M_TCPLOG); 2315 return (0); 2316 } 2317 #endif /* INVARIANTS */ 2318 2319 static void 2320 syncookie_reseed(void *arg) 2321 { 2322 struct tcp_syncache *sc = arg; 2323 uint8_t *secbits; 2324 int secbit; 2325 2326 /* 2327 * Reseeding the secret doesn't have to be protected by a lock. 2328 * It only must be ensured that the new random values are visible 2329 * to all CPUs in a SMP environment. The atomic with release 2330 * semantics ensures that. 2331 */ 2332 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2333 secbits = sc->secret.key[secbit]; 2334 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2335 atomic_add_rel_int(&sc->secret.oddeven, 1); 2336 2337 /* Reschedule ourself. */ 2338 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2339 } 2340 2341 /* 2342 * We have overflowed a bucket. Let's pause dealing with the syncache. 2343 * This function will increment the bucketoverflow statistics appropriately 2344 * (once per pause when pausing is enabled; otherwise, once per overflow). 2345 */ 2346 static void 2347 syncache_pause(struct in_conninfo *inc) 2348 { 2349 time_t delta; 2350 const char *s; 2351 2352 /* XXX: 2353 * 2. Add sysctl read here so we don't get the benefit of this 2354 * change without the new sysctl. 2355 */ 2356 2357 /* 2358 * Try an unlocked read. If we already know that another thread 2359 * has activated the feature, there is no need to proceed. 2360 */ 2361 if (V_tcp_syncache.paused) 2362 return; 2363 2364 /* Are cookied enabled? If not, we can't pause. */ 2365 if (!V_tcp_syncookies) { 2366 TCPSTAT_INC(tcps_sc_bucketoverflow); 2367 return; 2368 } 2369 2370 /* 2371 * We may be the first thread to find an overflow. Get the lock 2372 * and evaluate if we need to take action. 2373 */ 2374 mtx_lock(&V_tcp_syncache.pause_mtx); 2375 if (V_tcp_syncache.paused) { 2376 mtx_unlock(&V_tcp_syncache.pause_mtx); 2377 return; 2378 } 2379 2380 /* Activate protection. */ 2381 V_tcp_syncache.paused = true; 2382 TCPSTAT_INC(tcps_sc_bucketoverflow); 2383 2384 /* 2385 * Determine the last backoff time. If we are seeing a re-newed 2386 * attack within that same time after last reactivating the syncache, 2387 * consider it an extension of the same attack. 2388 */ 2389 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2390 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2391 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2392 delta <<= 1; 2393 V_tcp_syncache.pause_backoff++; 2394 } 2395 } else { 2396 delta = TCP_SYNCACHE_PAUSE_TIME; 2397 V_tcp_syncache.pause_backoff = 0; 2398 } 2399 2400 /* Log a warning, including IP addresses, if able. */ 2401 if (inc != NULL) 2402 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2403 else 2404 s = (const char *)NULL; 2405 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2406 "the next %lld seconds%s%s%s\n", (long long)delta, 2407 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2408 (s != NULL) ? ")" : ""); 2409 free(__DECONST(void *, s), M_TCPLOG); 2410 2411 /* Use the calculated delta to set a new pause time. */ 2412 V_tcp_syncache.pause_until = time_uptime + delta; 2413 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2414 &V_tcp_syncache); 2415 mtx_unlock(&V_tcp_syncache.pause_mtx); 2416 } 2417 2418 /* Evaluate whether we need to unpause. */ 2419 static void 2420 syncache_unpause(void *arg) 2421 { 2422 struct tcp_syncache *sc; 2423 time_t delta; 2424 2425 sc = arg; 2426 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2427 callout_deactivate(&sc->pause_co); 2428 2429 /* 2430 * Check to make sure we are not running early. If the pause 2431 * time has expired, then deactivate the protection. 2432 */ 2433 if ((delta = sc->pause_until - time_uptime) > 0) 2434 callout_schedule(&sc->pause_co, delta * hz); 2435 else 2436 sc->paused = false; 2437 } 2438 2439 /* 2440 * Exports the syncache entries to userland so that netstat can display 2441 * them alongside the other sockets. This function is intended to be 2442 * called only from tcp_pcblist. 2443 * 2444 * Due to concurrency on an active system, the number of pcbs exported 2445 * may have no relation to max_pcbs. max_pcbs merely indicates the 2446 * amount of space the caller allocated for this function to use. 2447 */ 2448 int 2449 syncache_pcblist(struct sysctl_req *req) 2450 { 2451 struct xtcpcb xt; 2452 struct syncache *sc; 2453 struct syncache_head *sch; 2454 int error, i; 2455 2456 bzero(&xt, sizeof(xt)); 2457 xt.xt_len = sizeof(xt); 2458 xt.t_state = TCPS_SYN_RECEIVED; 2459 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2460 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2461 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2462 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2463 2464 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2465 sch = &V_tcp_syncache.hashbase[i]; 2466 SCH_LOCK(sch); 2467 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2468 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2469 continue; 2470 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2471 xt.xt_inp.inp_vflag = INP_IPV6; 2472 else 2473 xt.xt_inp.inp_vflag = INP_IPV4; 2474 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2475 sizeof (struct in_conninfo)); 2476 error = SYSCTL_OUT(req, &xt, sizeof xt); 2477 if (error) { 2478 SCH_UNLOCK(sch); 2479 return (0); 2480 } 2481 } 2482 SCH_UNLOCK(sch); 2483 } 2484 2485 return (0); 2486 } 2487