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, CTLFLAG_RW, 0, 176 "TCP SYN cache"); 177 178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 179 &VNET_NAME(tcp_syncache.bucket_limit), 0, 180 "Per-bucket hash limit for syncache"); 181 182 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 183 &VNET_NAME(tcp_syncache.cache_limit), 0, 184 "Overall entry limit for syncache"); 185 186 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 187 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 188 189 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 190 &VNET_NAME(tcp_syncache.hashsize), 0, 191 "Size of TCP syncache hashtable"); 192 193 static int 194 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 195 { 196 int error; 197 u_int new; 198 199 new = V_tcp_syncache.rexmt_limit; 200 error = sysctl_handle_int(oidp, &new, 0, req); 201 if ((error == 0) && (req->newptr != NULL)) { 202 if (new > TCP_MAXRXTSHIFT) 203 error = EINVAL; 204 else 205 V_tcp_syncache.rexmt_limit = new; 206 } 207 return (error); 208 } 209 210 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 211 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW, 212 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 213 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 214 "Limit on SYN/ACK retransmissions"); 215 216 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 217 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 218 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 219 "Send reset on socket allocation failure"); 220 221 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 222 223 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 224 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 225 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 226 227 /* 228 * Requires the syncache entry to be already removed from the bucket list. 229 */ 230 static void 231 syncache_free(struct syncache *sc) 232 { 233 234 if (sc->sc_ipopts) 235 (void) m_free(sc->sc_ipopts); 236 if (sc->sc_cred) 237 crfree(sc->sc_cred); 238 #ifdef MAC 239 mac_syncache_destroy(&sc->sc_label); 240 #endif 241 242 uma_zfree(V_tcp_syncache.zone, sc); 243 } 244 245 void 246 syncache_init(void) 247 { 248 int i; 249 250 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 251 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 252 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 253 V_tcp_syncache.hash_secret = arc4random(); 254 255 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 256 &V_tcp_syncache.hashsize); 257 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 258 &V_tcp_syncache.bucket_limit); 259 if (!powerof2(V_tcp_syncache.hashsize) || 260 V_tcp_syncache.hashsize == 0) { 261 printf("WARNING: syncache hash size is not a power of 2.\n"); 262 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 263 } 264 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 265 266 /* Set limits. */ 267 V_tcp_syncache.cache_limit = 268 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 269 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 270 &V_tcp_syncache.cache_limit); 271 272 /* Allocate the hash table. */ 273 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 274 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 275 276 #ifdef VIMAGE 277 V_tcp_syncache.vnet = curvnet; 278 #endif 279 280 /* Initialize the hash buckets. */ 281 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 282 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 283 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 284 NULL, MTX_DEF); 285 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 286 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 287 V_tcp_syncache.hashbase[i].sch_length = 0; 288 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 289 V_tcp_syncache.hashbase[i].sch_last_overflow = 290 -(SYNCOOKIE_LIFETIME + 1); 291 } 292 293 /* Create the syncache entry zone. */ 294 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 295 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 296 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 297 V_tcp_syncache.cache_limit); 298 299 /* Start the SYN cookie reseeder callout. */ 300 callout_init(&V_tcp_syncache.secret.reseed, 1); 301 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 302 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 303 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 304 syncookie_reseed, &V_tcp_syncache); 305 306 /* Initialize the pause machinery. */ 307 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 308 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 309 0); 310 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 311 V_tcp_syncache.pause_backoff = 0; 312 V_tcp_syncache.paused = false; 313 } 314 315 #ifdef VIMAGE 316 void 317 syncache_destroy(void) 318 { 319 struct syncache_head *sch; 320 struct syncache *sc, *nsc; 321 int i; 322 323 /* 324 * Stop the re-seed timer before freeing resources. No need to 325 * possibly schedule it another time. 326 */ 327 callout_drain(&V_tcp_syncache.secret.reseed); 328 329 /* Stop the SYN cache pause callout. */ 330 mtx_lock(&V_tcp_syncache.pause_mtx); 331 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 332 mtx_unlock(&V_tcp_syncache.pause_mtx); 333 callout_drain(&V_tcp_syncache.pause_co); 334 } else 335 mtx_unlock(&V_tcp_syncache.pause_mtx); 336 337 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 338 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 339 340 sch = &V_tcp_syncache.hashbase[i]; 341 callout_drain(&sch->sch_timer); 342 343 SCH_LOCK(sch); 344 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 345 syncache_drop(sc, sch); 346 SCH_UNLOCK(sch); 347 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 348 ("%s: sch->sch_bucket not empty", __func__)); 349 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 350 __func__, sch->sch_length)); 351 mtx_destroy(&sch->sch_mtx); 352 } 353 354 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 355 ("%s: cache_count not 0", __func__)); 356 357 /* Free the allocated global resources. */ 358 uma_zdestroy(V_tcp_syncache.zone); 359 free(V_tcp_syncache.hashbase, M_SYNCACHE); 360 mtx_destroy(&V_tcp_syncache.pause_mtx); 361 } 362 #endif 363 364 /* 365 * Inserts a syncache entry into the specified bucket row. 366 * Locks and unlocks the syncache_head autonomously. 367 */ 368 static void 369 syncache_insert(struct syncache *sc, struct syncache_head *sch) 370 { 371 struct syncache *sc2; 372 373 SCH_LOCK(sch); 374 375 /* 376 * Make sure that we don't overflow the per-bucket limit. 377 * If the bucket is full, toss the oldest element. 378 */ 379 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 380 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 381 ("sch->sch_length incorrect")); 382 syncache_pause(&sc->sc_inc); 383 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 384 sch->sch_last_overflow = time_uptime; 385 syncache_drop(sc2, sch); 386 } 387 388 /* Put it into the bucket. */ 389 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 390 sch->sch_length++; 391 392 #ifdef TCP_OFFLOAD 393 if (ADDED_BY_TOE(sc)) { 394 struct toedev *tod = sc->sc_tod; 395 396 tod->tod_syncache_added(tod, sc->sc_todctx); 397 } 398 #endif 399 400 /* Reinitialize the bucket row's timer. */ 401 if (sch->sch_length == 1) 402 sch->sch_nextc = ticks + INT_MAX; 403 syncache_timeout(sc, sch, 1); 404 405 SCH_UNLOCK(sch); 406 407 TCPSTATES_INC(TCPS_SYN_RECEIVED); 408 TCPSTAT_INC(tcps_sc_added); 409 } 410 411 /* 412 * Remove and free entry from syncache bucket row. 413 * Expects locked syncache head. 414 */ 415 static void 416 syncache_drop(struct syncache *sc, struct syncache_head *sch) 417 { 418 419 SCH_LOCK_ASSERT(sch); 420 421 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 422 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 423 sch->sch_length--; 424 425 #ifdef TCP_OFFLOAD 426 if (ADDED_BY_TOE(sc)) { 427 struct toedev *tod = sc->sc_tod; 428 429 tod->tod_syncache_removed(tod, sc->sc_todctx); 430 } 431 #endif 432 433 syncache_free(sc); 434 } 435 436 /* 437 * Engage/reengage time on bucket row. 438 */ 439 static void 440 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 441 { 442 int rexmt; 443 444 if (sc->sc_rxmits == 0) 445 rexmt = tcp_rexmit_initial; 446 else 447 TCPT_RANGESET(rexmt, 448 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 449 tcp_rexmit_min, TCPTV_REXMTMAX); 450 sc->sc_rxttime = ticks + rexmt; 451 sc->sc_rxmits++; 452 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 453 sch->sch_nextc = sc->sc_rxttime; 454 if (docallout) 455 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 456 syncache_timer, (void *)sch); 457 } 458 } 459 460 /* 461 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 462 * If we have retransmitted an entry the maximum number of times, expire it. 463 * One separate timer for each bucket row. 464 */ 465 static void 466 syncache_timer(void *xsch) 467 { 468 struct syncache_head *sch = (struct syncache_head *)xsch; 469 struct syncache *sc, *nsc; 470 int tick = ticks; 471 char *s; 472 bool paused; 473 474 CURVNET_SET(sch->sch_sc->vnet); 475 476 /* NB: syncache_head has already been locked by the callout. */ 477 SCH_LOCK_ASSERT(sch); 478 479 /* 480 * In the following cycle we may remove some entries and/or 481 * advance some timeouts, so re-initialize the bucket timer. 482 */ 483 sch->sch_nextc = tick + INT_MAX; 484 485 /* 486 * If we have paused processing, unconditionally remove 487 * all syncache entries. 488 */ 489 mtx_lock(&V_tcp_syncache.pause_mtx); 490 paused = V_tcp_syncache.paused; 491 mtx_unlock(&V_tcp_syncache.pause_mtx); 492 493 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 494 if (paused) { 495 syncache_drop(sc, sch); 496 continue; 497 } 498 /* 499 * We do not check if the listen socket still exists 500 * and accept the case where the listen socket may be 501 * gone by the time we resend the SYN/ACK. We do 502 * not expect this to happens often. If it does, 503 * then the RST will be sent by the time the remote 504 * host does the SYN/ACK->ACK. 505 */ 506 if (TSTMP_GT(sc->sc_rxttime, tick)) { 507 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 508 sch->sch_nextc = sc->sc_rxttime; 509 continue; 510 } 511 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 512 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 513 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 514 "giving up and removing syncache entry\n", 515 s, __func__); 516 free(s, M_TCPLOG); 517 } 518 syncache_drop(sc, sch); 519 TCPSTAT_INC(tcps_sc_stale); 520 continue; 521 } 522 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 523 log(LOG_DEBUG, "%s; %s: Response timeout, " 524 "retransmitting (%u) SYN|ACK\n", 525 s, __func__, sc->sc_rxmits); 526 free(s, M_TCPLOG); 527 } 528 529 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 530 TCPSTAT_INC(tcps_sc_retransmitted); 531 syncache_timeout(sc, sch, 0); 532 } 533 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 534 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 535 syncache_timer, (void *)(sch)); 536 CURVNET_RESTORE(); 537 } 538 539 /* 540 * Returns true if the system is only using cookies at the moment. 541 * This could be due to a sysadmin decision to only use cookies, or it 542 * could be due to the system detecting an attack. 543 */ 544 static inline bool 545 syncache_cookiesonly(void) 546 { 547 548 return (V_tcp_syncookies && (V_tcp_syncache.paused || 549 V_tcp_syncookiesonly)); 550 } 551 552 /* 553 * Find the hash bucket for the given connection. 554 */ 555 static struct syncache_head * 556 syncache_hashbucket(struct in_conninfo *inc) 557 { 558 uint32_t hash; 559 560 /* 561 * The hash is built on foreign port + local port + foreign address. 562 * We rely on the fact that struct in_conninfo starts with 16 bits 563 * of foreign port, then 16 bits of local port then followed by 128 564 * bits of foreign address. In case of IPv4 address, the first 3 565 * 32-bit words of the address always are zeroes. 566 */ 567 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 568 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 569 570 return (&V_tcp_syncache.hashbase[hash]); 571 } 572 573 /* 574 * Find an entry in the syncache. 575 * Returns always with locked syncache_head plus a matching entry or NULL. 576 */ 577 static struct syncache * 578 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 579 { 580 struct syncache *sc; 581 struct syncache_head *sch; 582 583 *schp = sch = syncache_hashbucket(inc); 584 SCH_LOCK(sch); 585 586 /* Circle through bucket row to find matching entry. */ 587 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 588 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 589 sizeof(struct in_endpoints)) == 0) 590 break; 591 592 return (sc); /* Always returns with locked sch. */ 593 } 594 595 /* 596 * This function is called when we get a RST for a 597 * non-existent connection, so that we can see if the 598 * connection is in the syn cache. If it is, zap it. 599 * If required send a challenge ACK. 600 */ 601 void 602 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m) 603 { 604 struct syncache *sc; 605 struct syncache_head *sch; 606 char *s = NULL; 607 608 if (syncache_cookiesonly()) 609 return; 610 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 611 SCH_LOCK_ASSERT(sch); 612 613 /* 614 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 615 * See RFC 793 page 65, section SEGMENT ARRIVES. 616 */ 617 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 618 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 619 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 620 "FIN flag set, segment ignored\n", s, __func__); 621 TCPSTAT_INC(tcps_badrst); 622 goto done; 623 } 624 625 /* 626 * No corresponding connection was found in syncache. 627 * If syncookies are enabled and possibly exclusively 628 * used, or we are under memory pressure, a valid RST 629 * may not find a syncache entry. In that case we're 630 * done and no SYN|ACK retransmissions will happen. 631 * Otherwise the RST was misdirected or spoofed. 632 */ 633 if (sc == NULL) { 634 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 635 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 636 "syncache entry (possibly syncookie only), " 637 "segment ignored\n", s, __func__); 638 TCPSTAT_INC(tcps_badrst); 639 goto done; 640 } 641 642 /* 643 * If the RST bit is set, check the sequence number to see 644 * if this is a valid reset segment. 645 * 646 * RFC 793 page 37: 647 * In all states except SYN-SENT, all reset (RST) segments 648 * are validated by checking their SEQ-fields. A reset is 649 * valid if its sequence number is in the window. 650 * 651 * RFC 793 page 69: 652 * There are four cases for the acceptability test for an incoming 653 * segment: 654 * 655 * Segment Receive Test 656 * Length Window 657 * ------- ------- ------------------------------------------- 658 * 0 0 SEG.SEQ = RCV.NXT 659 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 660 * >0 0 not acceptable 661 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 662 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 663 * 664 * Note that when receiving a SYN segment in the LISTEN state, 665 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 666 * described in RFC 793, page 66. 667 */ 668 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 669 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 670 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 671 if (V_tcp_insecure_rst || 672 th->th_seq == sc->sc_irs + 1) { 673 syncache_drop(sc, sch); 674 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 675 log(LOG_DEBUG, 676 "%s; %s: Our SYN|ACK was rejected, " 677 "connection attempt aborted by remote " 678 "endpoint\n", 679 s, __func__); 680 TCPSTAT_INC(tcps_sc_reset); 681 } else { 682 TCPSTAT_INC(tcps_badrst); 683 /* Send challenge ACK. */ 684 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 685 log(LOG_DEBUG, "%s; %s: RST with invalid " 686 " SEQ %u != NXT %u (+WND %u), " 687 "sending challenge ACK\n", 688 s, __func__, 689 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 690 syncache_respond(sc, m, TH_ACK); 691 } 692 } else { 693 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 694 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 695 "NXT %u (+WND %u), segment ignored\n", 696 s, __func__, 697 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 698 TCPSTAT_INC(tcps_badrst); 699 } 700 701 done: 702 if (s != NULL) 703 free(s, M_TCPLOG); 704 SCH_UNLOCK(sch); 705 } 706 707 void 708 syncache_badack(struct in_conninfo *inc) 709 { 710 struct syncache *sc; 711 struct syncache_head *sch; 712 713 if (syncache_cookiesonly()) 714 return; 715 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 716 SCH_LOCK_ASSERT(sch); 717 if (sc != NULL) { 718 syncache_drop(sc, sch); 719 TCPSTAT_INC(tcps_sc_badack); 720 } 721 SCH_UNLOCK(sch); 722 } 723 724 void 725 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq) 726 { 727 struct syncache *sc; 728 struct syncache_head *sch; 729 730 if (syncache_cookiesonly()) 731 return; 732 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 733 SCH_LOCK_ASSERT(sch); 734 if (sc == NULL) 735 goto done; 736 737 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 738 if (ntohl(th_seq) != sc->sc_iss) 739 goto done; 740 741 /* 742 * If we've rertransmitted 3 times and this is our second error, 743 * we remove the entry. Otherwise, we allow it to continue on. 744 * This prevents us from incorrectly nuking an entry during a 745 * spurious network outage. 746 * 747 * See tcp_notify(). 748 */ 749 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 750 sc->sc_flags |= SCF_UNREACH; 751 goto done; 752 } 753 syncache_drop(sc, sch); 754 TCPSTAT_INC(tcps_sc_unreach); 755 done: 756 SCH_UNLOCK(sch); 757 } 758 759 /* 760 * Build a new TCP socket structure from a syncache entry. 761 * 762 * On success return the newly created socket with its underlying inp locked. 763 */ 764 static struct socket * 765 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 766 { 767 struct tcp_function_block *blk; 768 struct inpcb *inp = NULL; 769 struct socket *so; 770 struct tcpcb *tp; 771 int error; 772 char *s; 773 774 NET_EPOCH_ASSERT(); 775 776 /* 777 * Ok, create the full blown connection, and set things up 778 * as they would have been set up if we had created the 779 * connection when the SYN arrived. If we can't create 780 * the connection, abort it. 781 */ 782 so = sonewconn(lso, 0); 783 if (so == NULL) { 784 /* 785 * Drop the connection; we will either send a RST or 786 * have the peer retransmit its SYN again after its 787 * RTO and try again. 788 */ 789 TCPSTAT_INC(tcps_listendrop); 790 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 791 log(LOG_DEBUG, "%s; %s: Socket create failed " 792 "due to limits or memory shortage\n", 793 s, __func__); 794 free(s, M_TCPLOG); 795 } 796 goto abort2; 797 } 798 #ifdef MAC 799 mac_socketpeer_set_from_mbuf(m, so); 800 #endif 801 802 inp = sotoinpcb(so); 803 inp->inp_inc.inc_fibnum = so->so_fibnum; 804 INP_WLOCK(inp); 805 /* 806 * Exclusive pcbinfo lock is not required in syncache socket case even 807 * if two inpcb locks can be acquired simultaneously: 808 * - the inpcb in LISTEN state, 809 * - the newly created inp. 810 * 811 * In this case, an inp cannot be at same time in LISTEN state and 812 * just created by an accept() call. 813 */ 814 INP_HASH_WLOCK(&V_tcbinfo); 815 816 /* Insert new socket into PCB hash list. */ 817 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 818 #ifdef INET6 819 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 820 inp->inp_vflag &= ~INP_IPV4; 821 inp->inp_vflag |= INP_IPV6; 822 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 823 } else { 824 inp->inp_vflag &= ~INP_IPV6; 825 inp->inp_vflag |= INP_IPV4; 826 #endif 827 inp->inp_laddr = sc->sc_inc.inc_laddr; 828 #ifdef INET6 829 } 830 #endif 831 832 /* 833 * If there's an mbuf and it has a flowid, then let's initialise the 834 * inp with that particular flowid. 835 */ 836 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 837 inp->inp_flowid = m->m_pkthdr.flowid; 838 inp->inp_flowtype = M_HASHTYPE_GET(m); 839 #ifdef NUMA 840 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 841 #endif 842 } 843 844 inp->inp_lport = sc->sc_inc.inc_lport; 845 #ifdef INET6 846 if (inp->inp_vflag & INP_IPV6PROTO) { 847 struct inpcb *oinp = sotoinpcb(lso); 848 849 /* 850 * Inherit socket options from the listening socket. 851 * Note that in6p_inputopts are not (and should not be) 852 * copied, since it stores previously received options and is 853 * used to detect if each new option is different than the 854 * previous one and hence should be passed to a user. 855 * If we copied in6p_inputopts, a user would not be able to 856 * receive options just after calling the accept system call. 857 */ 858 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 859 if (oinp->in6p_outputopts) 860 inp->in6p_outputopts = 861 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 862 } 863 864 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 865 struct in6_addr laddr6; 866 struct sockaddr_in6 sin6; 867 868 sin6.sin6_family = AF_INET6; 869 sin6.sin6_len = sizeof(sin6); 870 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 871 sin6.sin6_port = sc->sc_inc.inc_fport; 872 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 873 laddr6 = inp->in6p_laddr; 874 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 875 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 876 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 877 thread0.td_ucred, m, false)) != 0) { 878 inp->in6p_laddr = laddr6; 879 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 880 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 881 "with error %i\n", 882 s, __func__, error); 883 free(s, M_TCPLOG); 884 } 885 INP_HASH_WUNLOCK(&V_tcbinfo); 886 goto abort; 887 } 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 in_addr laddr; 899 struct sockaddr_in sin; 900 901 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 902 903 if (inp->inp_options == NULL) { 904 inp->inp_options = sc->sc_ipopts; 905 sc->sc_ipopts = NULL; 906 } 907 908 sin.sin_family = AF_INET; 909 sin.sin_len = sizeof(sin); 910 sin.sin_addr = sc->sc_inc.inc_faddr; 911 sin.sin_port = sc->sc_inc.inc_fport; 912 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 913 laddr = inp->inp_laddr; 914 if (inp->inp_laddr.s_addr == INADDR_ANY) 915 inp->inp_laddr = sc->sc_inc.inc_laddr; 916 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 917 thread0.td_ucred, m, false)) != 0) { 918 inp->inp_laddr = laddr; 919 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 920 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 921 "with error %i\n", 922 s, __func__, error); 923 free(s, M_TCPLOG); 924 } 925 INP_HASH_WUNLOCK(&V_tcbinfo); 926 goto abort; 927 } 928 } 929 #endif /* INET */ 930 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 931 /* Copy old policy into new socket's. */ 932 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 933 printf("syncache_socket: could not copy policy\n"); 934 #endif 935 INP_HASH_WUNLOCK(&V_tcbinfo); 936 tp = intotcpcb(inp); 937 tcp_state_change(tp, TCPS_SYN_RECEIVED); 938 tp->iss = sc->sc_iss; 939 tp->irs = sc->sc_irs; 940 tcp_rcvseqinit(tp); 941 tcp_sendseqinit(tp); 942 blk = sototcpcb(lso)->t_fb; 943 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 944 /* 945 * Our parents t_fb was not the default, 946 * we need to release our ref on tp->t_fb and 947 * pickup one on the new entry. 948 */ 949 struct tcp_function_block *rblk; 950 951 rblk = find_and_ref_tcp_fb(blk); 952 KASSERT(rblk != NULL, 953 ("cannot find blk %p out of syncache?", blk)); 954 if (tp->t_fb->tfb_tcp_fb_fini) 955 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 956 refcount_release(&tp->t_fb->tfb_refcnt); 957 tp->t_fb = rblk; 958 /* 959 * XXXrrs this is quite dangerous, it is possible 960 * for the new function to fail to init. We also 961 * are not asking if the handoff_is_ok though at 962 * the very start thats probalbly ok. 963 */ 964 if (tp->t_fb->tfb_tcp_fb_init) { 965 (*tp->t_fb->tfb_tcp_fb_init)(tp); 966 } 967 } 968 tp->snd_wl1 = sc->sc_irs; 969 tp->snd_max = tp->iss + 1; 970 tp->snd_nxt = tp->iss + 1; 971 tp->rcv_up = sc->sc_irs + 1; 972 tp->rcv_wnd = sc->sc_wnd; 973 tp->rcv_adv += tp->rcv_wnd; 974 tp->last_ack_sent = tp->rcv_nxt; 975 976 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 977 if (sc->sc_flags & SCF_NOOPT) 978 tp->t_flags |= TF_NOOPT; 979 else { 980 if (sc->sc_flags & SCF_WINSCALE) { 981 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 982 tp->snd_scale = sc->sc_requested_s_scale; 983 tp->request_r_scale = sc->sc_requested_r_scale; 984 } 985 if (sc->sc_flags & SCF_TIMESTAMP) { 986 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 987 tp->ts_recent = sc->sc_tsreflect; 988 tp->ts_recent_age = tcp_ts_getticks(); 989 tp->ts_offset = sc->sc_tsoff; 990 } 991 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 992 if (sc->sc_flags & SCF_SIGNATURE) 993 tp->t_flags |= TF_SIGNATURE; 994 #endif 995 if (sc->sc_flags & SCF_SACK) 996 tp->t_flags |= TF_SACK_PERMIT; 997 } 998 999 if (sc->sc_flags & SCF_ECN) 1000 tp->t_flags2 |= TF2_ECN_PERMIT; 1001 1002 /* 1003 * Set up MSS and get cached values from tcp_hostcache. 1004 * This might overwrite some of the defaults we just set. 1005 */ 1006 tcp_mss(tp, sc->sc_peer_mss); 1007 1008 /* 1009 * If the SYN,ACK was retransmitted, indicate that CWND to be 1010 * limited to one segment in cc_conn_init(). 1011 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1012 */ 1013 if (sc->sc_rxmits > 1) 1014 tp->snd_cwnd = 1; 1015 1016 #ifdef TCP_OFFLOAD 1017 /* 1018 * Allow a TOE driver to install its hooks. Note that we hold the 1019 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1020 * new connection before the TOE driver has done its thing. 1021 */ 1022 if (ADDED_BY_TOE(sc)) { 1023 struct toedev *tod = sc->sc_tod; 1024 1025 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1026 } 1027 #endif 1028 /* 1029 * Copy and activate timers. 1030 */ 1031 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1032 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1033 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1034 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1035 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1036 1037 TCPSTAT_INC(tcps_accepts); 1038 return (so); 1039 1040 abort: 1041 INP_WUNLOCK(inp); 1042 abort2: 1043 if (so != NULL) 1044 soabort(so); 1045 return (NULL); 1046 } 1047 1048 /* 1049 * This function gets called when we receive an ACK for a 1050 * socket in the LISTEN state. We look up the connection 1051 * in the syncache, and if its there, we pull it out of 1052 * the cache and turn it into a full-blown connection in 1053 * the SYN-RECEIVED state. 1054 * 1055 * On syncache_socket() success the newly created socket 1056 * has its underlying inp locked. 1057 */ 1058 int 1059 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1060 struct socket **lsop, struct mbuf *m) 1061 { 1062 struct syncache *sc; 1063 struct syncache_head *sch; 1064 struct syncache scs; 1065 char *s; 1066 bool locked; 1067 1068 NET_EPOCH_ASSERT(); 1069 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1070 ("%s: can handle only ACK", __func__)); 1071 1072 if (syncache_cookiesonly()) { 1073 sc = NULL; 1074 sch = syncache_hashbucket(inc); 1075 locked = false; 1076 } else { 1077 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1078 locked = true; 1079 SCH_LOCK_ASSERT(sch); 1080 } 1081 1082 #ifdef INVARIANTS 1083 /* 1084 * Test code for syncookies comparing the syncache stored 1085 * values with the reconstructed values from the cookie. 1086 */ 1087 if (sc != NULL) 1088 syncookie_cmp(inc, sch, sc, th, to, *lsop); 1089 #endif 1090 1091 if (sc == NULL) { 1092 /* 1093 * There is no syncache entry, so see if this ACK is 1094 * a returning syncookie. To do this, first: 1095 * A. Check if syncookies are used in case of syncache 1096 * overflows 1097 * B. See if this socket has had a syncache entry dropped in 1098 * the recent past. We don't want to accept a bogus 1099 * syncookie if we've never received a SYN or accept it 1100 * twice. 1101 * C. check that the syncookie is valid. If it is, then 1102 * cobble up a fake syncache entry, and return. 1103 */ 1104 if (locked && !V_tcp_syncookies) { 1105 SCH_UNLOCK(sch); 1106 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1107 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1108 "segment rejected (syncookies disabled)\n", 1109 s, __func__); 1110 goto failed; 1111 } 1112 if (locked && !V_tcp_syncookiesonly && 1113 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1114 SCH_UNLOCK(sch); 1115 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1116 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1117 "segment rejected (no syncache entry)\n", 1118 s, __func__); 1119 goto failed; 1120 } 1121 bzero(&scs, sizeof(scs)); 1122 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 1123 if (locked) 1124 SCH_UNLOCK(sch); 1125 if (sc == NULL) { 1126 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1127 log(LOG_DEBUG, "%s; %s: Segment failed " 1128 "SYNCOOKIE authentication, segment rejected " 1129 "(probably spoofed)\n", s, __func__); 1130 goto failed; 1131 } 1132 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1133 /* If received ACK has MD5 signature, check it. */ 1134 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1135 (!TCPMD5_ENABLED() || 1136 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1137 /* Drop the ACK. */ 1138 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1139 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1140 "MD5 signature doesn't match.\n", 1141 s, __func__); 1142 free(s, M_TCPLOG); 1143 } 1144 TCPSTAT_INC(tcps_sig_err_sigopt); 1145 return (-1); /* Do not send RST */ 1146 } 1147 #endif /* TCP_SIGNATURE */ 1148 } else { 1149 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1150 /* 1151 * If listening socket requested TCP digests, check that 1152 * received ACK has signature and it is correct. 1153 * If not, drop the ACK and leave sc entry in th cache, 1154 * because SYN was received with correct signature. 1155 */ 1156 if (sc->sc_flags & SCF_SIGNATURE) { 1157 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1158 /* No signature */ 1159 TCPSTAT_INC(tcps_sig_err_nosigopt); 1160 SCH_UNLOCK(sch); 1161 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1162 log(LOG_DEBUG, "%s; %s: Segment " 1163 "rejected, MD5 signature wasn't " 1164 "provided.\n", s, __func__); 1165 free(s, M_TCPLOG); 1166 } 1167 return (-1); /* Do not send RST */ 1168 } 1169 if (!TCPMD5_ENABLED() || 1170 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1171 /* Doesn't match or no SA */ 1172 SCH_UNLOCK(sch); 1173 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1174 log(LOG_DEBUG, "%s; %s: Segment " 1175 "rejected, MD5 signature doesn't " 1176 "match.\n", s, __func__); 1177 free(s, M_TCPLOG); 1178 } 1179 return (-1); /* Do not send RST */ 1180 } 1181 } 1182 #endif /* TCP_SIGNATURE */ 1183 1184 /* 1185 * RFC 7323 PAWS: If we have a timestamp on this segment and 1186 * it's less than ts_recent, drop it. 1187 * XXXMT: RFC 7323 also requires to send an ACK. 1188 * In tcp_input.c this is only done for TCP segments 1189 * with user data, so be consistent here and just drop 1190 * the segment. 1191 */ 1192 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1193 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1194 SCH_UNLOCK(sch); 1195 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1196 log(LOG_DEBUG, 1197 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1198 "segment dropped\n", s, __func__, 1199 to->to_tsval, sc->sc_tsreflect); 1200 free(s, M_TCPLOG); 1201 } 1202 return (-1); /* Do not send RST */ 1203 } 1204 1205 /* 1206 * Pull out the entry to unlock the bucket row. 1207 * 1208 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1209 * tcp_state_change(). The tcpcb is not existent at this 1210 * moment. A new one will be allocated via syncache_socket-> 1211 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1212 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1213 */ 1214 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1215 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1216 sch->sch_length--; 1217 #ifdef TCP_OFFLOAD 1218 if (ADDED_BY_TOE(sc)) { 1219 struct toedev *tod = sc->sc_tod; 1220 1221 tod->tod_syncache_removed(tod, sc->sc_todctx); 1222 } 1223 #endif 1224 SCH_UNLOCK(sch); 1225 } 1226 1227 /* 1228 * Segment validation: 1229 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1230 */ 1231 if (th->th_ack != sc->sc_iss + 1) { 1232 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1233 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1234 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1235 goto failed; 1236 } 1237 1238 /* 1239 * The SEQ must fall in the window starting at the received 1240 * initial receive sequence number + 1 (the SYN). 1241 */ 1242 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1243 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1244 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1245 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1246 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1247 goto failed; 1248 } 1249 1250 /* 1251 * If timestamps were not negotiated during SYN/ACK they 1252 * must not appear on any segment during this session. 1253 */ 1254 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1255 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1256 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1257 "segment rejected\n", s, __func__); 1258 goto failed; 1259 } 1260 1261 /* 1262 * If timestamps were negotiated during SYN/ACK they should 1263 * appear on every segment during this session. 1264 * XXXAO: This is only informal as there have been unverified 1265 * reports of non-compliants stacks. 1266 */ 1267 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1268 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1269 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1270 "no action\n", s, __func__); 1271 free(s, M_TCPLOG); 1272 s = NULL; 1273 } 1274 } 1275 1276 *lsop = syncache_socket(sc, *lsop, m); 1277 1278 if (*lsop == NULL) 1279 TCPSTAT_INC(tcps_sc_aborted); 1280 else 1281 TCPSTAT_INC(tcps_sc_completed); 1282 1283 /* how do we find the inp for the new socket? */ 1284 if (sc != &scs) 1285 syncache_free(sc); 1286 return (1); 1287 failed: 1288 if (sc != NULL && sc != &scs) 1289 syncache_free(sc); 1290 if (s != NULL) 1291 free(s, M_TCPLOG); 1292 *lsop = NULL; 1293 return (0); 1294 } 1295 1296 static void 1297 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1298 uint64_t response_cookie) 1299 { 1300 struct inpcb *inp; 1301 struct tcpcb *tp; 1302 unsigned int *pending_counter; 1303 1304 NET_EPOCH_ASSERT(); 1305 1306 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1307 *lsop = syncache_socket(sc, *lsop, m); 1308 if (*lsop == NULL) { 1309 TCPSTAT_INC(tcps_sc_aborted); 1310 atomic_subtract_int(pending_counter, 1); 1311 } else { 1312 soisconnected(*lsop); 1313 inp = sotoinpcb(*lsop); 1314 tp = intotcpcb(inp); 1315 tp->t_flags |= TF_FASTOPEN; 1316 tp->t_tfo_cookie.server = response_cookie; 1317 tp->snd_max = tp->iss; 1318 tp->snd_nxt = tp->iss; 1319 tp->t_tfo_pending = pending_counter; 1320 TCPSTAT_INC(tcps_sc_completed); 1321 } 1322 } 1323 1324 /* 1325 * Given a LISTEN socket and an inbound SYN request, add 1326 * this to the syn cache, and send back a segment: 1327 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1328 * to the source. 1329 * 1330 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1331 * Doing so would require that we hold onto the data and deliver it 1332 * to the application. However, if we are the target of a SYN-flood 1333 * DoS attack, an attacker could send data which would eventually 1334 * consume all available buffer space if it were ACKed. By not ACKing 1335 * the data, we avoid this DoS scenario. 1336 * 1337 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1338 * cookie is processed and a new socket is created. In this case, any data 1339 * accompanying the SYN will be queued to the socket by tcp_input() and will 1340 * be ACKed either when the application sends response data or the delayed 1341 * ACK timer expires, whichever comes first. 1342 */ 1343 int 1344 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1345 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1346 void *todctx, uint8_t iptos) 1347 { 1348 struct tcpcb *tp; 1349 struct socket *so; 1350 struct syncache *sc = NULL; 1351 struct syncache_head *sch; 1352 struct mbuf *ipopts = NULL; 1353 u_int ltflags; 1354 int win, ip_ttl, ip_tos; 1355 char *s; 1356 int rv = 0; 1357 #ifdef INET6 1358 int autoflowlabel = 0; 1359 #endif 1360 #ifdef MAC 1361 struct label *maclabel; 1362 #endif 1363 struct syncache scs; 1364 struct ucred *cred; 1365 uint64_t tfo_response_cookie; 1366 unsigned int *tfo_pending = NULL; 1367 int tfo_cookie_valid = 0; 1368 int tfo_response_cookie_valid = 0; 1369 bool locked; 1370 1371 INP_WLOCK_ASSERT(inp); /* listen socket */ 1372 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1373 ("%s: unexpected tcp flags", __func__)); 1374 1375 /* 1376 * Combine all so/tp operations very early to drop the INP lock as 1377 * soon as possible. 1378 */ 1379 so = *lsop; 1380 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1381 tp = sototcpcb(so); 1382 cred = crhold(so->so_cred); 1383 1384 #ifdef INET6 1385 if ((inc->inc_flags & INC_ISIPV6) && 1386 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1387 autoflowlabel = 1; 1388 #endif 1389 ip_ttl = inp->inp_ip_ttl; 1390 ip_tos = inp->inp_ip_tos; 1391 win = so->sol_sbrcv_hiwat; 1392 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1393 1394 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1395 (tp->t_tfo_pending != NULL) && 1396 (to->to_flags & TOF_FASTOPEN)) { 1397 /* 1398 * Limit the number of pending TFO connections to 1399 * approximately half of the queue limit. This prevents TFO 1400 * SYN floods from starving the service by filling the 1401 * listen queue with bogus TFO connections. 1402 */ 1403 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1404 (so->sol_qlimit / 2)) { 1405 int result; 1406 1407 result = tcp_fastopen_check_cookie(inc, 1408 to->to_tfo_cookie, to->to_tfo_len, 1409 &tfo_response_cookie); 1410 tfo_cookie_valid = (result > 0); 1411 tfo_response_cookie_valid = (result >= 0); 1412 } 1413 1414 /* 1415 * Remember the TFO pending counter as it will have to be 1416 * decremented below if we don't make it to syncache_tfo_expand(). 1417 */ 1418 tfo_pending = tp->t_tfo_pending; 1419 } 1420 1421 /* By the time we drop the lock these should no longer be used. */ 1422 so = NULL; 1423 tp = NULL; 1424 1425 #ifdef MAC 1426 if (mac_syncache_init(&maclabel) != 0) { 1427 INP_WUNLOCK(inp); 1428 goto done; 1429 } else 1430 mac_syncache_create(maclabel, inp); 1431 #endif 1432 if (!tfo_cookie_valid) 1433 INP_WUNLOCK(inp); 1434 1435 /* 1436 * Remember the IP options, if any. 1437 */ 1438 #ifdef INET6 1439 if (!(inc->inc_flags & INC_ISIPV6)) 1440 #endif 1441 #ifdef INET 1442 ipopts = (m) ? ip_srcroute(m) : NULL; 1443 #else 1444 ipopts = NULL; 1445 #endif 1446 1447 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1448 /* 1449 * If listening socket requested TCP digests, check that received 1450 * SYN has signature and it is correct. If signature doesn't match 1451 * or TCP_SIGNATURE support isn't enabled, drop the packet. 1452 */ 1453 if (ltflags & TF_SIGNATURE) { 1454 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1455 TCPSTAT_INC(tcps_sig_err_nosigopt); 1456 goto done; 1457 } 1458 if (!TCPMD5_ENABLED() || 1459 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1460 goto done; 1461 } 1462 #endif /* TCP_SIGNATURE */ 1463 /* 1464 * See if we already have an entry for this connection. 1465 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1466 * 1467 * XXX: should the syncache be re-initialized with the contents 1468 * of the new SYN here (which may have different options?) 1469 * 1470 * XXX: We do not check the sequence number to see if this is a 1471 * real retransmit or a new connection attempt. The question is 1472 * how to handle such a case; either ignore it as spoofed, or 1473 * drop the current entry and create a new one? 1474 */ 1475 if (syncache_cookiesonly()) { 1476 sc = NULL; 1477 sch = syncache_hashbucket(inc); 1478 locked = false; 1479 } else { 1480 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1481 locked = true; 1482 SCH_LOCK_ASSERT(sch); 1483 } 1484 if (sc != NULL) { 1485 if (tfo_cookie_valid) 1486 INP_WUNLOCK(inp); 1487 TCPSTAT_INC(tcps_sc_dupsyn); 1488 if (ipopts) { 1489 /* 1490 * If we were remembering a previous source route, 1491 * forget it and use the new one we've been given. 1492 */ 1493 if (sc->sc_ipopts) 1494 (void) m_free(sc->sc_ipopts); 1495 sc->sc_ipopts = ipopts; 1496 } 1497 /* 1498 * Update timestamp if present. 1499 */ 1500 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1501 sc->sc_tsreflect = to->to_tsval; 1502 else 1503 sc->sc_flags &= ~SCF_TIMESTAMP; 1504 #ifdef MAC 1505 /* 1506 * Since we have already unconditionally allocated label 1507 * storage, free it up. The syncache entry will already 1508 * have an initialized label we can use. 1509 */ 1510 mac_syncache_destroy(&maclabel); 1511 #endif 1512 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1513 /* Retransmit SYN|ACK and reset retransmit count. */ 1514 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1515 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1516 "resetting timer and retransmitting SYN|ACK\n", 1517 s, __func__); 1518 free(s, M_TCPLOG); 1519 } 1520 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1521 sc->sc_rxmits = 0; 1522 syncache_timeout(sc, sch, 1); 1523 TCPSTAT_INC(tcps_sndacks); 1524 TCPSTAT_INC(tcps_sndtotal); 1525 } 1526 SCH_UNLOCK(sch); 1527 goto donenoprobe; 1528 } 1529 1530 if (tfo_cookie_valid) { 1531 bzero(&scs, sizeof(scs)); 1532 sc = &scs; 1533 goto skip_alloc; 1534 } 1535 1536 /* 1537 * Skip allocating a syncache entry if we are just going to discard 1538 * it later. 1539 */ 1540 if (!locked) { 1541 bzero(&scs, sizeof(scs)); 1542 sc = &scs; 1543 } else 1544 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1545 if (sc == NULL) { 1546 /* 1547 * The zone allocator couldn't provide more entries. 1548 * Treat this as if the cache was full; drop the oldest 1549 * entry and insert the new one. 1550 */ 1551 TCPSTAT_INC(tcps_sc_zonefail); 1552 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1553 sch->sch_last_overflow = time_uptime; 1554 syncache_drop(sc, sch); 1555 syncache_pause(inc); 1556 } 1557 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1558 if (sc == NULL) { 1559 if (V_tcp_syncookies) { 1560 bzero(&scs, sizeof(scs)); 1561 sc = &scs; 1562 } else { 1563 KASSERT(locked, 1564 ("%s: bucket unexpectedly unlocked", 1565 __func__)); 1566 SCH_UNLOCK(sch); 1567 if (ipopts) 1568 (void) m_free(ipopts); 1569 goto done; 1570 } 1571 } 1572 } 1573 1574 skip_alloc: 1575 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1576 sc->sc_tfo_cookie = &tfo_response_cookie; 1577 1578 /* 1579 * Fill in the syncache values. 1580 */ 1581 #ifdef MAC 1582 sc->sc_label = maclabel; 1583 #endif 1584 sc->sc_cred = cred; 1585 cred = NULL; 1586 sc->sc_ipopts = ipopts; 1587 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1588 #ifdef INET6 1589 if (!(inc->inc_flags & INC_ISIPV6)) 1590 #endif 1591 { 1592 sc->sc_ip_tos = ip_tos; 1593 sc->sc_ip_ttl = ip_ttl; 1594 } 1595 #ifdef TCP_OFFLOAD 1596 sc->sc_tod = tod; 1597 sc->sc_todctx = todctx; 1598 #endif 1599 sc->sc_irs = th->th_seq; 1600 sc->sc_flags = 0; 1601 sc->sc_flowlabel = 0; 1602 1603 /* 1604 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1605 * win was derived from socket earlier in the function. 1606 */ 1607 win = imax(win, 0); 1608 win = imin(win, TCP_MAXWIN); 1609 sc->sc_wnd = win; 1610 1611 if (V_tcp_do_rfc1323) { 1612 /* 1613 * A timestamp received in a SYN makes 1614 * it ok to send timestamp requests and replies. 1615 */ 1616 if (to->to_flags & TOF_TS) { 1617 sc->sc_tsreflect = to->to_tsval; 1618 sc->sc_flags |= SCF_TIMESTAMP; 1619 sc->sc_tsoff = tcp_new_ts_offset(inc); 1620 } 1621 if (to->to_flags & TOF_SCALE) { 1622 int wscale = 0; 1623 1624 /* 1625 * Pick the smallest possible scaling factor that 1626 * will still allow us to scale up to sb_max, aka 1627 * kern.ipc.maxsockbuf. 1628 * 1629 * We do this because there are broken firewalls that 1630 * will corrupt the window scale option, leading to 1631 * the other endpoint believing that our advertised 1632 * window is unscaled. At scale factors larger than 1633 * 5 the unscaled window will drop below 1500 bytes, 1634 * leading to serious problems when traversing these 1635 * broken firewalls. 1636 * 1637 * With the default maxsockbuf of 256K, a scale factor 1638 * of 3 will be chosen by this algorithm. Those who 1639 * choose a larger maxsockbuf should watch out 1640 * for the compatibility problems mentioned above. 1641 * 1642 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1643 * or <SYN,ACK>) segment itself is never scaled. 1644 */ 1645 while (wscale < TCP_MAX_WINSHIFT && 1646 (TCP_MAXWIN << wscale) < sb_max) 1647 wscale++; 1648 sc->sc_requested_r_scale = wscale; 1649 sc->sc_requested_s_scale = to->to_wscale; 1650 sc->sc_flags |= SCF_WINSCALE; 1651 } 1652 } 1653 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1654 /* 1655 * If listening socket requested TCP digests, flag this in the 1656 * syncache so that syncache_respond() will do the right thing 1657 * with the SYN+ACK. 1658 */ 1659 if (ltflags & TF_SIGNATURE) 1660 sc->sc_flags |= SCF_SIGNATURE; 1661 #endif /* TCP_SIGNATURE */ 1662 if (to->to_flags & TOF_SACKPERM) 1663 sc->sc_flags |= SCF_SACK; 1664 if (to->to_flags & TOF_MSS) 1665 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1666 if (ltflags & TF_NOOPT) 1667 sc->sc_flags |= SCF_NOOPT; 1668 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1669 sc->sc_flags |= SCF_ECN; 1670 1671 if (V_tcp_syncookies) 1672 sc->sc_iss = syncookie_generate(sch, sc); 1673 else 1674 sc->sc_iss = arc4random(); 1675 #ifdef INET6 1676 if (autoflowlabel) { 1677 if (V_tcp_syncookies) 1678 sc->sc_flowlabel = sc->sc_iss; 1679 else 1680 sc->sc_flowlabel = ip6_randomflowlabel(); 1681 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1682 } 1683 #endif 1684 if (locked) 1685 SCH_UNLOCK(sch); 1686 1687 if (tfo_cookie_valid) { 1688 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1689 /* INP_WUNLOCK(inp) will be performed by the caller */ 1690 rv = 1; 1691 goto tfo_expanded; 1692 } 1693 1694 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1695 /* 1696 * Do a standard 3-way handshake. 1697 */ 1698 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1699 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1700 syncache_free(sc); 1701 else if (sc != &scs) 1702 syncache_insert(sc, sch); /* locks and unlocks sch */ 1703 TCPSTAT_INC(tcps_sndacks); 1704 TCPSTAT_INC(tcps_sndtotal); 1705 } else { 1706 if (sc != &scs) 1707 syncache_free(sc); 1708 TCPSTAT_INC(tcps_sc_dropped); 1709 } 1710 goto donenoprobe; 1711 1712 done: 1713 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1714 donenoprobe: 1715 if (m) { 1716 *lsop = NULL; 1717 m_freem(m); 1718 } 1719 /* 1720 * If tfo_pending is not NULL here, then a TFO SYN that did not 1721 * result in a new socket was processed and the associated pending 1722 * counter has not yet been decremented. All such TFO processing paths 1723 * transit this point. 1724 */ 1725 if (tfo_pending != NULL) 1726 tcp_fastopen_decrement_counter(tfo_pending); 1727 1728 tfo_expanded: 1729 if (cred != NULL) 1730 crfree(cred); 1731 #ifdef MAC 1732 if (sc == &scs) 1733 mac_syncache_destroy(&maclabel); 1734 #endif 1735 return (rv); 1736 } 1737 1738 /* 1739 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1740 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1741 */ 1742 static int 1743 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1744 { 1745 struct ip *ip = NULL; 1746 struct mbuf *m; 1747 struct tcphdr *th = NULL; 1748 int optlen, error = 0; /* Make compiler happy */ 1749 u_int16_t hlen, tlen, mssopt; 1750 struct tcpopt to; 1751 #ifdef INET6 1752 struct ip6_hdr *ip6 = NULL; 1753 #endif 1754 1755 NET_EPOCH_ASSERT(); 1756 1757 hlen = 1758 #ifdef INET6 1759 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1760 #endif 1761 sizeof(struct ip); 1762 tlen = hlen + sizeof(struct tcphdr); 1763 1764 /* Determine MSS we advertize to other end of connection. */ 1765 mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss); 1766 1767 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1768 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1769 ("syncache: mbuf too small")); 1770 1771 /* Create the IP+TCP header from scratch. */ 1772 m = m_gethdr(M_NOWAIT, MT_DATA); 1773 if (m == NULL) 1774 return (ENOBUFS); 1775 #ifdef MAC 1776 mac_syncache_create_mbuf(sc->sc_label, m); 1777 #endif 1778 m->m_data += max_linkhdr; 1779 m->m_len = tlen; 1780 m->m_pkthdr.len = tlen; 1781 m->m_pkthdr.rcvif = NULL; 1782 1783 #ifdef INET6 1784 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1785 ip6 = mtod(m, struct ip6_hdr *); 1786 ip6->ip6_vfc = IPV6_VERSION; 1787 ip6->ip6_nxt = IPPROTO_TCP; 1788 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1789 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1790 ip6->ip6_plen = htons(tlen - hlen); 1791 /* ip6_hlim is set after checksum */ 1792 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1793 ip6->ip6_flow |= sc->sc_flowlabel; 1794 1795 th = (struct tcphdr *)(ip6 + 1); 1796 } 1797 #endif 1798 #if defined(INET6) && defined(INET) 1799 else 1800 #endif 1801 #ifdef INET 1802 { 1803 ip = mtod(m, struct ip *); 1804 ip->ip_v = IPVERSION; 1805 ip->ip_hl = sizeof(struct ip) >> 2; 1806 ip->ip_len = htons(tlen); 1807 ip->ip_id = 0; 1808 ip->ip_off = 0; 1809 ip->ip_sum = 0; 1810 ip->ip_p = IPPROTO_TCP; 1811 ip->ip_src = sc->sc_inc.inc_laddr; 1812 ip->ip_dst = sc->sc_inc.inc_faddr; 1813 ip->ip_ttl = sc->sc_ip_ttl; 1814 ip->ip_tos = sc->sc_ip_tos; 1815 1816 /* 1817 * See if we should do MTU discovery. Route lookups are 1818 * expensive, so we will only unset the DF bit if: 1819 * 1820 * 1) path_mtu_discovery is disabled 1821 * 2) the SCF_UNREACH flag has been set 1822 */ 1823 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1824 ip->ip_off |= htons(IP_DF); 1825 1826 th = (struct tcphdr *)(ip + 1); 1827 } 1828 #endif /* INET */ 1829 th->th_sport = sc->sc_inc.inc_lport; 1830 th->th_dport = sc->sc_inc.inc_fport; 1831 1832 if (flags & TH_SYN) 1833 th->th_seq = htonl(sc->sc_iss); 1834 else 1835 th->th_seq = htonl(sc->sc_iss + 1); 1836 th->th_ack = htonl(sc->sc_irs + 1); 1837 th->th_off = sizeof(struct tcphdr) >> 2; 1838 th->th_x2 = 0; 1839 th->th_flags = flags; 1840 th->th_win = htons(sc->sc_wnd); 1841 th->th_urp = 0; 1842 1843 if ((flags & TH_SYN) && (sc->sc_flags & SCF_ECN)) { 1844 th->th_flags |= TH_ECE; 1845 TCPSTAT_INC(tcps_ecn_shs); 1846 } 1847 1848 /* Tack on the TCP options. */ 1849 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1850 to.to_flags = 0; 1851 1852 if (flags & TH_SYN) { 1853 to.to_mss = mssopt; 1854 to.to_flags = TOF_MSS; 1855 if (sc->sc_flags & SCF_WINSCALE) { 1856 to.to_wscale = sc->sc_requested_r_scale; 1857 to.to_flags |= TOF_SCALE; 1858 } 1859 if (sc->sc_flags & SCF_SACK) 1860 to.to_flags |= TOF_SACKPERM; 1861 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1862 if (sc->sc_flags & SCF_SIGNATURE) 1863 to.to_flags |= TOF_SIGNATURE; 1864 #endif 1865 if (sc->sc_tfo_cookie) { 1866 to.to_flags |= TOF_FASTOPEN; 1867 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1868 to.to_tfo_cookie = sc->sc_tfo_cookie; 1869 /* don't send cookie again when retransmitting response */ 1870 sc->sc_tfo_cookie = NULL; 1871 } 1872 } 1873 if (sc->sc_flags & SCF_TIMESTAMP) { 1874 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1875 to.to_tsecr = sc->sc_tsreflect; 1876 to.to_flags |= TOF_TS; 1877 } 1878 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1879 1880 /* Adjust headers by option size. */ 1881 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1882 m->m_len += optlen; 1883 m->m_pkthdr.len += optlen; 1884 #ifdef INET6 1885 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1886 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1887 else 1888 #endif 1889 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1890 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1891 if (sc->sc_flags & SCF_SIGNATURE) { 1892 KASSERT(to.to_flags & TOF_SIGNATURE, 1893 ("tcp_addoptions() didn't set tcp_signature")); 1894 1895 /* NOTE: to.to_signature is inside of mbuf */ 1896 if (!TCPMD5_ENABLED() || 1897 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1898 m_freem(m); 1899 return (EACCES); 1900 } 1901 } 1902 #endif 1903 } else 1904 optlen = 0; 1905 1906 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1907 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1908 /* 1909 * If we have peer's SYN and it has a flowid, then let's assign it to 1910 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1911 * to SYN|ACK due to lack of inp here. 1912 */ 1913 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1914 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1915 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1916 } 1917 #ifdef INET6 1918 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1919 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1920 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1921 IPPROTO_TCP, 0); 1922 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1923 #ifdef TCP_OFFLOAD 1924 if (ADDED_BY_TOE(sc)) { 1925 struct toedev *tod = sc->sc_tod; 1926 1927 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1928 1929 return (error); 1930 } 1931 #endif 1932 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 1933 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1934 } 1935 #endif 1936 #if defined(INET6) && defined(INET) 1937 else 1938 #endif 1939 #ifdef INET 1940 { 1941 m->m_pkthdr.csum_flags = CSUM_TCP; 1942 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1943 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1944 #ifdef TCP_OFFLOAD 1945 if (ADDED_BY_TOE(sc)) { 1946 struct toedev *tod = sc->sc_tod; 1947 1948 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1949 1950 return (error); 1951 } 1952 #endif 1953 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 1954 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1955 } 1956 #endif 1957 return (error); 1958 } 1959 1960 /* 1961 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1962 * that exceed the capacity of the syncache by avoiding the storage of any 1963 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1964 * attacks where the attacker does not have access to our responses. 1965 * 1966 * Syncookies encode and include all necessary information about the 1967 * connection setup within the SYN|ACK that we send back. That way we 1968 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1969 * (if ever). Normally the syncache and syncookies are running in parallel 1970 * with the latter taking over when the former is exhausted. When matching 1971 * syncache entry is found the syncookie is ignored. 1972 * 1973 * The only reliable information persisting the 3WHS is our initial sequence 1974 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1975 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1976 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1977 * returns and signifies a legitimate connection if it matches the ACK. 1978 * 1979 * The available space of 32 bits to store the hash and to encode the SYN 1980 * option information is very tight and we should have at least 24 bits for 1981 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1982 * 1983 * SYN option information we have to encode to fully restore a connection: 1984 * MSS: is imporant to chose an optimal segment size to avoid IP level 1985 * fragmentation along the path. The common MSS values can be encoded 1986 * in a 3-bit table. Uncommon values are captured by the next lower value 1987 * in the table leading to a slight increase in packetization overhead. 1988 * WSCALE: is necessary to allow large windows to be used for high delay- 1989 * bandwidth product links. Not scaling the window when it was initially 1990 * negotiated is bad for performance as lack of scaling further decreases 1991 * the apparent available send window. We only need to encode the WSCALE 1992 * we received from the remote end. Our end can be recalculated at any 1993 * time. The common WSCALE values can be encoded in a 3-bit table. 1994 * Uncommon values are captured by the next lower value in the table 1995 * making us under-estimate the available window size halving our 1996 * theoretically possible maximum throughput for that connection. 1997 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1998 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1999 * that are included in all segments on a connection. We enable them when 2000 * the ACK has them. 2001 * 2002 * Security of syncookies and attack vectors: 2003 * 2004 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2005 * together with the gloabl secret to make it unique per connection attempt. 2006 * Thus any change of any of those parameters results in a different MAC output 2007 * in an unpredictable way unless a collision is encountered. 24 bits of the 2008 * MAC are embedded into the ISS. 2009 * 2010 * To prevent replay attacks two rotating global secrets are updated with a 2011 * new random value every 15 seconds. The life-time of a syncookie is thus 2012 * 15-30 seconds. 2013 * 2014 * Vector 1: Attacking the secret. This requires finding a weakness in the 2015 * MAC itself or the way it is used here. The attacker can do a chosen plain 2016 * text attack by varying and testing the all parameters under his control. 2017 * The strength depends on the size and randomness of the secret, and the 2018 * cryptographic security of the MAC function. Due to the constant updating 2019 * of the secret the attacker has at most 29.999 seconds to find the secret 2020 * and launch spoofed connections. After that he has to start all over again. 2021 * 2022 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2023 * size an average of 4,823 attempts are required for a 50% chance of success 2024 * to spoof a single syncookie (birthday collision paradox). However the 2025 * attacker is blind and doesn't know if one of his attempts succeeded unless 2026 * he has a side channel to interfere success from. A single connection setup 2027 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2028 * This many attempts are required for each one blind spoofed connection. For 2029 * every additional spoofed connection he has to launch another N attempts. 2030 * Thus for a sustained rate 100 spoofed connections per second approximately 2031 * 1,800,000 packets per second would have to be sent. 2032 * 2033 * NB: The MAC function should be fast so that it doesn't become a CPU 2034 * exhaustion attack vector itself. 2035 * 2036 * References: 2037 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2038 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2039 * http://cr.yp.to/syncookies.html (overview) 2040 * http://cr.yp.to/syncookies/archive (details) 2041 * 2042 * 2043 * Schematic construction of a syncookie enabled Initial Sequence Number: 2044 * 0 1 2 3 2045 * 12345678901234567890123456789012 2046 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2047 * 2048 * x 24 MAC (truncated) 2049 * W 3 Send Window Scale index 2050 * M 3 MSS index 2051 * S 1 SACK permitted 2052 * P 1 Odd/even secret 2053 */ 2054 2055 /* 2056 * Distribution and probability of certain MSS values. Those in between are 2057 * rounded down to the next lower one. 2058 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2059 * .2% .3% 5% 7% 7% 20% 15% 45% 2060 */ 2061 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2062 2063 /* 2064 * Distribution and probability of certain WSCALE values. We have to map the 2065 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2066 * bits based on prevalence of certain values. Where we don't have an exact 2067 * match for are rounded down to the next lower one letting us under-estimate 2068 * the true available window. At the moment this would happen only for the 2069 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2070 * and window size). The absence of the WSCALE option (no scaling in either 2071 * direction) is encoded with index zero. 2072 * [WSCALE values histograms, Allman, 2012] 2073 * X 10 10 35 5 6 14 10% by host 2074 * X 11 4 5 5 18 49 3% by connections 2075 */ 2076 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2077 2078 /* 2079 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2080 * and good cryptographic properties. 2081 */ 2082 static uint32_t 2083 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2084 uint8_t *secbits, uintptr_t secmod) 2085 { 2086 SIPHASH_CTX ctx; 2087 uint32_t siphash[2]; 2088 2089 SipHash24_Init(&ctx); 2090 SipHash_SetKey(&ctx, secbits); 2091 switch (inc->inc_flags & INC_ISIPV6) { 2092 #ifdef INET 2093 case 0: 2094 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2095 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2096 break; 2097 #endif 2098 #ifdef INET6 2099 case INC_ISIPV6: 2100 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2101 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2102 break; 2103 #endif 2104 } 2105 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2106 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2107 SipHash_Update(&ctx, &irs, sizeof(irs)); 2108 SipHash_Update(&ctx, &flags, sizeof(flags)); 2109 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2110 SipHash_Final((u_int8_t *)&siphash, &ctx); 2111 2112 return (siphash[0] ^ siphash[1]); 2113 } 2114 2115 static tcp_seq 2116 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2117 { 2118 u_int i, secbit, wscale; 2119 uint32_t iss, hash; 2120 uint8_t *secbits; 2121 union syncookie cookie; 2122 2123 cookie.cookie = 0; 2124 2125 /* Map our computed MSS into the 3-bit index. */ 2126 for (i = nitems(tcp_sc_msstab) - 1; 2127 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2128 i--) 2129 ; 2130 cookie.flags.mss_idx = i; 2131 2132 /* 2133 * Map the send window scale into the 3-bit index but only if 2134 * the wscale option was received. 2135 */ 2136 if (sc->sc_flags & SCF_WINSCALE) { 2137 wscale = sc->sc_requested_s_scale; 2138 for (i = nitems(tcp_sc_wstab) - 1; 2139 tcp_sc_wstab[i] > wscale && i > 0; 2140 i--) 2141 ; 2142 cookie.flags.wscale_idx = i; 2143 } 2144 2145 /* Can we do SACK? */ 2146 if (sc->sc_flags & SCF_SACK) 2147 cookie.flags.sack_ok = 1; 2148 2149 /* Which of the two secrets to use. */ 2150 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2151 cookie.flags.odd_even = secbit; 2152 2153 secbits = V_tcp_syncache.secret.key[secbit]; 2154 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2155 (uintptr_t)sch); 2156 2157 /* 2158 * Put the flags into the hash and XOR them to get better ISS number 2159 * variance. This doesn't enhance the cryptographic strength and is 2160 * done to prevent the 8 cookie bits from showing up directly on the 2161 * wire. 2162 */ 2163 iss = hash & ~0xff; 2164 iss |= cookie.cookie ^ (hash >> 24); 2165 2166 TCPSTAT_INC(tcps_sc_sendcookie); 2167 return (iss); 2168 } 2169 2170 static struct syncache * 2171 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2172 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2173 struct socket *lso) 2174 { 2175 uint32_t hash; 2176 uint8_t *secbits; 2177 tcp_seq ack, seq; 2178 int wnd, wscale = 0; 2179 union syncookie cookie; 2180 2181 /* 2182 * Pull information out of SYN-ACK/ACK and revert sequence number 2183 * advances. 2184 */ 2185 ack = th->th_ack - 1; 2186 seq = th->th_seq - 1; 2187 2188 /* 2189 * Unpack the flags containing enough information to restore the 2190 * connection. 2191 */ 2192 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2193 2194 /* Which of the two secrets to use. */ 2195 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2196 2197 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2198 2199 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2200 if ((ack & ~0xff) != (hash & ~0xff)) 2201 return (NULL); 2202 2203 /* Fill in the syncache values. */ 2204 sc->sc_flags = 0; 2205 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2206 sc->sc_ipopts = NULL; 2207 2208 sc->sc_irs = seq; 2209 sc->sc_iss = ack; 2210 2211 switch (inc->inc_flags & INC_ISIPV6) { 2212 #ifdef INET 2213 case 0: 2214 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2215 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2216 break; 2217 #endif 2218 #ifdef INET6 2219 case INC_ISIPV6: 2220 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2221 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 2222 break; 2223 #endif 2224 } 2225 2226 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2227 2228 /* We can simply recompute receive window scale we sent earlier. */ 2229 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2230 wscale++; 2231 2232 /* Only use wscale if it was enabled in the orignal SYN. */ 2233 if (cookie.flags.wscale_idx > 0) { 2234 sc->sc_requested_r_scale = wscale; 2235 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2236 sc->sc_flags |= SCF_WINSCALE; 2237 } 2238 2239 wnd = lso->sol_sbrcv_hiwat; 2240 wnd = imax(wnd, 0); 2241 wnd = imin(wnd, TCP_MAXWIN); 2242 sc->sc_wnd = wnd; 2243 2244 if (cookie.flags.sack_ok) 2245 sc->sc_flags |= SCF_SACK; 2246 2247 if (to->to_flags & TOF_TS) { 2248 sc->sc_flags |= SCF_TIMESTAMP; 2249 sc->sc_tsreflect = to->to_tsval; 2250 sc->sc_tsoff = tcp_new_ts_offset(inc); 2251 } 2252 2253 if (to->to_flags & TOF_SIGNATURE) 2254 sc->sc_flags |= SCF_SIGNATURE; 2255 2256 sc->sc_rxmits = 0; 2257 2258 TCPSTAT_INC(tcps_sc_recvcookie); 2259 return (sc); 2260 } 2261 2262 #ifdef INVARIANTS 2263 static int 2264 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2265 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2266 struct socket *lso) 2267 { 2268 struct syncache scs, *scx; 2269 char *s; 2270 2271 bzero(&scs, sizeof(scs)); 2272 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2273 2274 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2275 return (0); 2276 2277 if (scx != NULL) { 2278 if (sc->sc_peer_mss != scx->sc_peer_mss) 2279 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2280 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2281 2282 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2283 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2284 s, __func__, sc->sc_requested_r_scale, 2285 scx->sc_requested_r_scale); 2286 2287 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2288 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2289 s, __func__, sc->sc_requested_s_scale, 2290 scx->sc_requested_s_scale); 2291 2292 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2293 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2294 } 2295 2296 if (s != NULL) 2297 free(s, M_TCPLOG); 2298 return (0); 2299 } 2300 #endif /* INVARIANTS */ 2301 2302 static void 2303 syncookie_reseed(void *arg) 2304 { 2305 struct tcp_syncache *sc = arg; 2306 uint8_t *secbits; 2307 int secbit; 2308 2309 /* 2310 * Reseeding the secret doesn't have to be protected by a lock. 2311 * It only must be ensured that the new random values are visible 2312 * to all CPUs in a SMP environment. The atomic with release 2313 * semantics ensures that. 2314 */ 2315 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2316 secbits = sc->secret.key[secbit]; 2317 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2318 atomic_add_rel_int(&sc->secret.oddeven, 1); 2319 2320 /* Reschedule ourself. */ 2321 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2322 } 2323 2324 /* 2325 * We have overflowed a bucket. Let's pause dealing with the syncache. 2326 * This function will increment the bucketoverflow statistics appropriately 2327 * (once per pause when pausing is enabled; otherwise, once per overflow). 2328 */ 2329 static void 2330 syncache_pause(struct in_conninfo *inc) 2331 { 2332 time_t delta; 2333 const char *s; 2334 2335 /* XXX: 2336 * 2. Add sysctl read here so we don't get the benefit of this 2337 * change without the new sysctl. 2338 */ 2339 2340 /* 2341 * Try an unlocked read. If we already know that another thread 2342 * has activated the feature, there is no need to proceed. 2343 */ 2344 if (V_tcp_syncache.paused) 2345 return; 2346 2347 /* Are cookied enabled? If not, we can't pause. */ 2348 if (!V_tcp_syncookies) { 2349 TCPSTAT_INC(tcps_sc_bucketoverflow); 2350 return; 2351 } 2352 2353 /* 2354 * We may be the first thread to find an overflow. Get the lock 2355 * and evaluate if we need to take action. 2356 */ 2357 mtx_lock(&V_tcp_syncache.pause_mtx); 2358 if (V_tcp_syncache.paused) { 2359 mtx_unlock(&V_tcp_syncache.pause_mtx); 2360 return; 2361 } 2362 2363 /* Activate protection. */ 2364 V_tcp_syncache.paused = true; 2365 TCPSTAT_INC(tcps_sc_bucketoverflow); 2366 2367 /* 2368 * Determine the last backoff time. If we are seeing a re-newed 2369 * attack within that same time after last reactivating the syncache, 2370 * consider it an extension of the same attack. 2371 */ 2372 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2373 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2374 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2375 delta <<= 1; 2376 V_tcp_syncache.pause_backoff++; 2377 } 2378 } else { 2379 delta = TCP_SYNCACHE_PAUSE_TIME; 2380 V_tcp_syncache.pause_backoff = 0; 2381 } 2382 2383 /* Log a warning, including IP addresses, if able. */ 2384 if (inc != NULL) 2385 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2386 else 2387 s = (const char *)NULL; 2388 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2389 "the next %lld seconds%s%s%s\n", (long long)delta, 2390 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2391 (s != NULL) ? ")" : ""); 2392 free(__DECONST(void *, s), M_TCPLOG); 2393 2394 /* Use the calculated delta to set a new pause time. */ 2395 V_tcp_syncache.pause_until = time_uptime + delta; 2396 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2397 &V_tcp_syncache); 2398 mtx_unlock(&V_tcp_syncache.pause_mtx); 2399 } 2400 2401 /* Evaluate whether we need to unpause. */ 2402 static void 2403 syncache_unpause(void *arg) 2404 { 2405 struct tcp_syncache *sc; 2406 time_t delta; 2407 2408 sc = arg; 2409 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2410 callout_deactivate(&sc->pause_co); 2411 2412 /* 2413 * Check to make sure we are not running early. If the pause 2414 * time has expired, then deactivate the protection. 2415 */ 2416 if ((delta = sc->pause_until - time_uptime) > 0) 2417 callout_schedule(&sc->pause_co, delta * hz); 2418 else 2419 sc->paused = false; 2420 } 2421 2422 /* 2423 * Exports the syncache entries to userland so that netstat can display 2424 * them alongside the other sockets. This function is intended to be 2425 * called only from tcp_pcblist. 2426 * 2427 * Due to concurrency on an active system, the number of pcbs exported 2428 * may have no relation to max_pcbs. max_pcbs merely indicates the 2429 * amount of space the caller allocated for this function to use. 2430 */ 2431 int 2432 syncache_pcblist(struct sysctl_req *req) 2433 { 2434 struct xtcpcb xt; 2435 struct syncache *sc; 2436 struct syncache_head *sch; 2437 int error, i; 2438 2439 bzero(&xt, sizeof(xt)); 2440 xt.xt_len = sizeof(xt); 2441 xt.t_state = TCPS_SYN_RECEIVED; 2442 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2443 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2444 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2445 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2446 2447 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2448 sch = &V_tcp_syncache.hashbase[i]; 2449 SCH_LOCK(sch); 2450 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2451 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2452 continue; 2453 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2454 xt.xt_inp.inp_vflag = INP_IPV6; 2455 else 2456 xt.xt_inp.inp_vflag = INP_IPV4; 2457 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2458 sizeof (struct in_conninfo)); 2459 error = SYSCTL_OUT(req, &xt, sizeof xt); 2460 if (error) { 2461 SCH_UNLOCK(sch); 2462 return (0); 2463 } 2464 } 2465 SCH_UNLOCK(sch); 2466 } 2467 2468 return (0); 2469 } 2470