tcp_syncache.c revision 253210
1/*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 4 * All rights reserved. 5 * 6 * This software was developed for the FreeBSD Project by Jonathan Lemon 7 * and McAfee Research, the Security Research Division of McAfee, Inc. under 8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 9 * DARPA CHATS research program. [2001 McAfee, Inc.] 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33#include <sys/cdefs.h> 34__FBSDID("$FreeBSD: head/sys/netinet/tcp_syncache.c 253210 2013-07-11 15:29:25Z andre $"); 35 36#include "opt_inet.h" 37#include "opt_inet6.h" 38#include "opt_ipsec.h" 39#include "opt_pcbgroup.h" 40 41#include <sys/param.h> 42#include <sys/systm.h> 43#include <sys/kernel.h> 44#include <sys/sysctl.h> 45#include <sys/limits.h> 46#include <sys/lock.h> 47#include <sys/mutex.h> 48#include <sys/malloc.h> 49#include <sys/mbuf.h> 50#include <sys/proc.h> /* for proc0 declaration */ 51#include <sys/random.h> 52#include <sys/socket.h> 53#include <sys/socketvar.h> 54#include <sys/syslog.h> 55#include <sys/ucred.h> 56 57#include <sys/md5.h> 58#include <crypto/siphash/siphash.h> 59 60#include <vm/uma.h> 61 62#include <net/if.h> 63#include <net/route.h> 64#include <net/vnet.h> 65 66#include <netinet/in.h> 67#include <netinet/in_systm.h> 68#include <netinet/ip.h> 69#include <netinet/in_var.h> 70#include <netinet/in_pcb.h> 71#include <netinet/ip_var.h> 72#include <netinet/ip_options.h> 73#ifdef INET6 74#include <netinet/ip6.h> 75#include <netinet/icmp6.h> 76#include <netinet6/nd6.h> 77#include <netinet6/ip6_var.h> 78#include <netinet6/in6_pcb.h> 79#endif 80#include <netinet/tcp.h> 81#include <netinet/tcp_fsm.h> 82#include <netinet/tcp_seq.h> 83#include <netinet/tcp_timer.h> 84#include <netinet/tcp_var.h> 85#include <netinet/tcp_syncache.h> 86#ifdef INET6 87#include <netinet6/tcp6_var.h> 88#endif 89#ifdef TCP_OFFLOAD 90#include <netinet/toecore.h> 91#endif 92 93#ifdef IPSEC 94#include <netipsec/ipsec.h> 95#ifdef INET6 96#include <netipsec/ipsec6.h> 97#endif 98#include <netipsec/key.h> 99#endif /*IPSEC*/ 100 101#include <machine/in_cksum.h> 102 103#include <security/mac/mac_framework.h> 104 105static VNET_DEFINE(int, tcp_syncookies) = 1; 106#define V_tcp_syncookies VNET(tcp_syncookies) 107SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 108 &VNET_NAME(tcp_syncookies), 0, 109 "Use TCP SYN cookies if the syncache overflows"); 110 111static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 112#define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 113SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 114 &VNET_NAME(tcp_syncookiesonly), 0, 115 "Use only TCP SYN cookies"); 116 117#ifdef TCP_OFFLOAD 118#define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 119#endif 120 121static void syncache_drop(struct syncache *, struct syncache_head *); 122static void syncache_free(struct syncache *); 123static void syncache_insert(struct syncache *, struct syncache_head *); 124struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 125static int syncache_respond(struct syncache *); 126static struct socket *syncache_socket(struct syncache *, struct socket *, 127 struct mbuf *m); 128static int syncache_sysctl_count(SYSCTL_HANDLER_ARGS); 129static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 130 int docallout); 131static void syncache_timer(void *); 132 133static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 134 uint8_t *, uintptr_t); 135static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 136static struct syncache 137 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 138 struct syncache *, struct tcphdr *, struct tcpopt *, 139 struct socket *); 140static void syncookie_reseed(void *); 141#ifdef INVARIANTS 142static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 143 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 144 struct socket *lso); 145#endif 146 147/* 148 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 149 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 150 * the odds are that the user has given up attempting to connect by then. 151 */ 152#define SYNCACHE_MAXREXMTS 3 153 154/* Arbitrary values */ 155#define TCP_SYNCACHE_HASHSIZE 512 156#define TCP_SYNCACHE_BUCKETLIMIT 30 157 158static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 159#define V_tcp_syncache VNET(tcp_syncache) 160 161static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 162 "TCP SYN cache"); 163 164SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 165 &VNET_NAME(tcp_syncache.bucket_limit), 0, 166 "Per-bucket hash limit for syncache"); 167 168SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 169 &VNET_NAME(tcp_syncache.cache_limit), 0, 170 "Overall entry limit for syncache"); 171 172SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD), 173 NULL, 0, &syncache_sysctl_count, "IU", 174 "Current number of entries in syncache"); 175 176SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 177 &VNET_NAME(tcp_syncache.hashsize), 0, 178 "Size of TCP syncache hashtable"); 179 180SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 181 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 182 "Limit on SYN/ACK retransmissions"); 183 184VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 185SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 186 CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 187 "Send reset on socket allocation failure"); 188 189static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 190 191#define SYNCACHE_HASH(inc, mask) \ 192 ((V_tcp_syncache.hash_secret ^ \ 193 (inc)->inc_faddr.s_addr ^ \ 194 ((inc)->inc_faddr.s_addr >> 16) ^ \ 195 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 196 197#define SYNCACHE_HASH6(inc, mask) \ 198 ((V_tcp_syncache.hash_secret ^ \ 199 (inc)->inc6_faddr.s6_addr32[0] ^ \ 200 (inc)->inc6_faddr.s6_addr32[3] ^ \ 201 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 202 203#define ENDPTS_EQ(a, b) ( \ 204 (a)->ie_fport == (b)->ie_fport && \ 205 (a)->ie_lport == (b)->ie_lport && \ 206 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 207 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 208) 209 210#define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 211 212#define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 213#define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 214#define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 215 216/* 217 * Requires the syncache entry to be already removed from the bucket list. 218 */ 219static void 220syncache_free(struct syncache *sc) 221{ 222 223 if (sc->sc_ipopts) 224 (void) m_free(sc->sc_ipopts); 225 if (sc->sc_cred) 226 crfree(sc->sc_cred); 227#ifdef MAC 228 mac_syncache_destroy(&sc->sc_label); 229#endif 230 231 uma_zfree(V_tcp_syncache.zone, sc); 232} 233 234void 235syncache_init(void) 236{ 237 int i; 238 239 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 240 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 241 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 242 V_tcp_syncache.hash_secret = arc4random(); 243 244 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 245 &V_tcp_syncache.hashsize); 246 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 247 &V_tcp_syncache.bucket_limit); 248 if (!powerof2(V_tcp_syncache.hashsize) || 249 V_tcp_syncache.hashsize == 0) { 250 printf("WARNING: syncache hash size is not a power of 2.\n"); 251 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 252 } 253 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 254 255 /* Set limits. */ 256 V_tcp_syncache.cache_limit = 257 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 258 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 259 &V_tcp_syncache.cache_limit); 260 261 /* Allocate the hash table. */ 262 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 263 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 264 265#ifdef VIMAGE 266 V_tcp_syncache.vnet = curvnet; 267#endif 268 269 /* Initialize the hash buckets. */ 270 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 271 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 272 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 273 NULL, MTX_DEF); 274 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 275 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 276 V_tcp_syncache.hashbase[i].sch_length = 0; 277 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 278 } 279 280 /* Create the syncache entry zone. */ 281 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 282 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 283 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 284 V_tcp_syncache.cache_limit); 285 286 /* Start the SYN cookie reseeder callout. */ 287 callout_init(&V_tcp_syncache.secret.reseed, 1); 288 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 289 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 290 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 291 syncookie_reseed, &V_tcp_syncache); 292} 293 294#ifdef VIMAGE 295void 296syncache_destroy(void) 297{ 298 struct syncache_head *sch; 299 struct syncache *sc, *nsc; 300 int i; 301 302 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 303 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 304 305 sch = &V_tcp_syncache.hashbase[i]; 306 callout_drain(&sch->sch_timer); 307 308 SCH_LOCK(sch); 309 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 310 syncache_drop(sc, sch); 311 SCH_UNLOCK(sch); 312 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 313 ("%s: sch->sch_bucket not empty", __func__)); 314 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 315 __func__, sch->sch_length)); 316 mtx_destroy(&sch->sch_mtx); 317 } 318 319 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 320 ("%s: cache_count not 0", __func__)); 321 322 /* Free the allocated global resources. */ 323 uma_zdestroy(V_tcp_syncache.zone); 324 free(V_tcp_syncache.hashbase, M_SYNCACHE); 325 326 callout_drain(&V_tcp_syncache.secret.reseed); 327} 328#endif 329 330static int 331syncache_sysctl_count(SYSCTL_HANDLER_ARGS) 332{ 333 int count; 334 335 count = uma_zone_get_cur(V_tcp_syncache.zone); 336 return (sysctl_handle_int(oidp, &count, 0, req)); 337} 338 339/* 340 * Inserts a syncache entry into the specified bucket row. 341 * Locks and unlocks the syncache_head autonomously. 342 */ 343static void 344syncache_insert(struct syncache *sc, struct syncache_head *sch) 345{ 346 struct syncache *sc2; 347 348 SCH_LOCK(sch); 349 350 /* 351 * Make sure that we don't overflow the per-bucket limit. 352 * If the bucket is full, toss the oldest element. 353 */ 354 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 355 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 356 ("sch->sch_length incorrect")); 357 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 358 syncache_drop(sc2, sch); 359 TCPSTAT_INC(tcps_sc_bucketoverflow); 360 } 361 362 /* Put it into the bucket. */ 363 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 364 sch->sch_length++; 365 366#ifdef TCP_OFFLOAD 367 if (ADDED_BY_TOE(sc)) { 368 struct toedev *tod = sc->sc_tod; 369 370 tod->tod_syncache_added(tod, sc->sc_todctx); 371 } 372#endif 373 374 /* Reinitialize the bucket row's timer. */ 375 if (sch->sch_length == 1) 376 sch->sch_nextc = ticks + INT_MAX; 377 syncache_timeout(sc, sch, 1); 378 379 SCH_UNLOCK(sch); 380 381 TCPSTAT_INC(tcps_sc_added); 382} 383 384/* 385 * Remove and free entry from syncache bucket row. 386 * Expects locked syncache head. 387 */ 388static void 389syncache_drop(struct syncache *sc, struct syncache_head *sch) 390{ 391 392 SCH_LOCK_ASSERT(sch); 393 394 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 395 sch->sch_length--; 396 397#ifdef TCP_OFFLOAD 398 if (ADDED_BY_TOE(sc)) { 399 struct toedev *tod = sc->sc_tod; 400 401 tod->tod_syncache_removed(tod, sc->sc_todctx); 402 } 403#endif 404 405 syncache_free(sc); 406} 407 408/* 409 * Engage/reengage time on bucket row. 410 */ 411static void 412syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 413{ 414 sc->sc_rxttime = ticks + 415 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 416 sc->sc_rxmits++; 417 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 418 sch->sch_nextc = sc->sc_rxttime; 419 if (docallout) 420 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 421 syncache_timer, (void *)sch); 422 } 423} 424 425/* 426 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 427 * If we have retransmitted an entry the maximum number of times, expire it. 428 * One separate timer for each bucket row. 429 */ 430static void 431syncache_timer(void *xsch) 432{ 433 struct syncache_head *sch = (struct syncache_head *)xsch; 434 struct syncache *sc, *nsc; 435 int tick = ticks; 436 char *s; 437 438 CURVNET_SET(sch->sch_sc->vnet); 439 440 /* NB: syncache_head has already been locked by the callout. */ 441 SCH_LOCK_ASSERT(sch); 442 443 /* 444 * In the following cycle we may remove some entries and/or 445 * advance some timeouts, so re-initialize the bucket timer. 446 */ 447 sch->sch_nextc = tick + INT_MAX; 448 449 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 450 /* 451 * We do not check if the listen socket still exists 452 * and accept the case where the listen socket may be 453 * gone by the time we resend the SYN/ACK. We do 454 * not expect this to happens often. If it does, 455 * then the RST will be sent by the time the remote 456 * host does the SYN/ACK->ACK. 457 */ 458 if (TSTMP_GT(sc->sc_rxttime, tick)) { 459 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 460 sch->sch_nextc = sc->sc_rxttime; 461 continue; 462 } 463 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 464 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 465 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 466 "giving up and removing syncache entry\n", 467 s, __func__); 468 free(s, M_TCPLOG); 469 } 470 syncache_drop(sc, sch); 471 TCPSTAT_INC(tcps_sc_stale); 472 continue; 473 } 474 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 475 log(LOG_DEBUG, "%s; %s: Response timeout, " 476 "retransmitting (%u) SYN|ACK\n", 477 s, __func__, sc->sc_rxmits); 478 free(s, M_TCPLOG); 479 } 480 481 (void) syncache_respond(sc); 482 TCPSTAT_INC(tcps_sc_retransmitted); 483 syncache_timeout(sc, sch, 0); 484 } 485 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 486 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 487 syncache_timer, (void *)(sch)); 488 CURVNET_RESTORE(); 489} 490 491/* 492 * Find an entry in the syncache. 493 * Returns always with locked syncache_head plus a matching entry or NULL. 494 */ 495struct syncache * 496syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 497{ 498 struct syncache *sc; 499 struct syncache_head *sch; 500 501#ifdef INET6 502 if (inc->inc_flags & INC_ISIPV6) { 503 sch = &V_tcp_syncache.hashbase[ 504 SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)]; 505 *schp = sch; 506 507 SCH_LOCK(sch); 508 509 /* Circle through bucket row to find matching entry. */ 510 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 511 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 512 return (sc); 513 } 514 } else 515#endif 516 { 517 sch = &V_tcp_syncache.hashbase[ 518 SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)]; 519 *schp = sch; 520 521 SCH_LOCK(sch); 522 523 /* Circle through bucket row to find matching entry. */ 524 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 525#ifdef INET6 526 if (sc->sc_inc.inc_flags & INC_ISIPV6) 527 continue; 528#endif 529 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 530 return (sc); 531 } 532 } 533 SCH_LOCK_ASSERT(*schp); 534 return (NULL); /* always returns with locked sch */ 535} 536 537/* 538 * This function is called when we get a RST for a 539 * non-existent connection, so that we can see if the 540 * connection is in the syn cache. If it is, zap it. 541 */ 542void 543syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 544{ 545 struct syncache *sc; 546 struct syncache_head *sch; 547 char *s = NULL; 548 549 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 550 SCH_LOCK_ASSERT(sch); 551 552 /* 553 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 554 * See RFC 793 page 65, section SEGMENT ARRIVES. 555 */ 556 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 557 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 558 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 559 "FIN flag set, segment ignored\n", s, __func__); 560 TCPSTAT_INC(tcps_badrst); 561 goto done; 562 } 563 564 /* 565 * No corresponding connection was found in syncache. 566 * If syncookies are enabled and possibly exclusively 567 * used, or we are under memory pressure, a valid RST 568 * may not find a syncache entry. In that case we're 569 * done and no SYN|ACK retransmissions will happen. 570 * Otherwise the RST was misdirected or spoofed. 571 */ 572 if (sc == NULL) { 573 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 574 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 575 "syncache entry (possibly syncookie only), " 576 "segment ignored\n", s, __func__); 577 TCPSTAT_INC(tcps_badrst); 578 goto done; 579 } 580 581 /* 582 * If the RST bit is set, check the sequence number to see 583 * if this is a valid reset segment. 584 * RFC 793 page 37: 585 * In all states except SYN-SENT, all reset (RST) segments 586 * are validated by checking their SEQ-fields. A reset is 587 * valid if its sequence number is in the window. 588 * 589 * The sequence number in the reset segment is normally an 590 * echo of our outgoing acknowlegement numbers, but some hosts 591 * send a reset with the sequence number at the rightmost edge 592 * of our receive window, and we have to handle this case. 593 */ 594 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 595 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 596 syncache_drop(sc, sch); 597 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 598 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 599 "connection attempt aborted by remote endpoint\n", 600 s, __func__); 601 TCPSTAT_INC(tcps_sc_reset); 602 } else { 603 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 604 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 605 "IRS %u (+WND %u), segment ignored\n", 606 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 607 TCPSTAT_INC(tcps_badrst); 608 } 609 610done: 611 if (s != NULL) 612 free(s, M_TCPLOG); 613 SCH_UNLOCK(sch); 614} 615 616void 617syncache_badack(struct in_conninfo *inc) 618{ 619 struct syncache *sc; 620 struct syncache_head *sch; 621 622 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 623 SCH_LOCK_ASSERT(sch); 624 if (sc != NULL) { 625 syncache_drop(sc, sch); 626 TCPSTAT_INC(tcps_sc_badack); 627 } 628 SCH_UNLOCK(sch); 629} 630 631void 632syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 633{ 634 struct syncache *sc; 635 struct syncache_head *sch; 636 637 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 638 SCH_LOCK_ASSERT(sch); 639 if (sc == NULL) 640 goto done; 641 642 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 643 if (ntohl(th->th_seq) != sc->sc_iss) 644 goto done; 645 646 /* 647 * If we've rertransmitted 3 times and this is our second error, 648 * we remove the entry. Otherwise, we allow it to continue on. 649 * This prevents us from incorrectly nuking an entry during a 650 * spurious network outage. 651 * 652 * See tcp_notify(). 653 */ 654 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 655 sc->sc_flags |= SCF_UNREACH; 656 goto done; 657 } 658 syncache_drop(sc, sch); 659 TCPSTAT_INC(tcps_sc_unreach); 660done: 661 SCH_UNLOCK(sch); 662} 663 664/* 665 * Build a new TCP socket structure from a syncache entry. 666 */ 667static struct socket * 668syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 669{ 670 struct inpcb *inp = NULL; 671 struct socket *so; 672 struct tcpcb *tp; 673 int error; 674 char *s; 675 676 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 677 678 /* 679 * Ok, create the full blown connection, and set things up 680 * as they would have been set up if we had created the 681 * connection when the SYN arrived. If we can't create 682 * the connection, abort it. 683 */ 684 so = sonewconn(lso, SS_ISCONNECTED); 685 if (so == NULL) { 686 /* 687 * Drop the connection; we will either send a RST or 688 * have the peer retransmit its SYN again after its 689 * RTO and try again. 690 */ 691 TCPSTAT_INC(tcps_listendrop); 692 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 693 log(LOG_DEBUG, "%s; %s: Socket create failed " 694 "due to limits or memory shortage\n", 695 s, __func__); 696 free(s, M_TCPLOG); 697 } 698 goto abort2; 699 } 700#ifdef MAC 701 mac_socketpeer_set_from_mbuf(m, so); 702#endif 703 704 inp = sotoinpcb(so); 705 inp->inp_inc.inc_fibnum = so->so_fibnum; 706 INP_WLOCK(inp); 707 INP_HASH_WLOCK(&V_tcbinfo); 708 709 /* Insert new socket into PCB hash list. */ 710 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 711#ifdef INET6 712 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 713 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 714 } else { 715 inp->inp_vflag &= ~INP_IPV6; 716 inp->inp_vflag |= INP_IPV4; 717#endif 718 inp->inp_laddr = sc->sc_inc.inc_laddr; 719#ifdef INET6 720 } 721#endif 722 723 /* 724 * Install in the reservation hash table for now, but don't yet 725 * install a connection group since the full 4-tuple isn't yet 726 * configured. 727 */ 728 inp->inp_lport = sc->sc_inc.inc_lport; 729 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 730 /* 731 * Undo the assignments above if we failed to 732 * put the PCB on the hash lists. 733 */ 734#ifdef INET6 735 if (sc->sc_inc.inc_flags & INC_ISIPV6) 736 inp->in6p_laddr = in6addr_any; 737 else 738#endif 739 inp->inp_laddr.s_addr = INADDR_ANY; 740 inp->inp_lport = 0; 741 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 742 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 743 "with error %i\n", 744 s, __func__, error); 745 free(s, M_TCPLOG); 746 } 747 INP_HASH_WUNLOCK(&V_tcbinfo); 748 goto abort; 749 } 750#ifdef IPSEC 751 /* Copy old policy into new socket's. */ 752 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 753 printf("syncache_socket: could not copy policy\n"); 754#endif 755#ifdef INET6 756 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 757 struct inpcb *oinp = sotoinpcb(lso); 758 struct in6_addr laddr6; 759 struct sockaddr_in6 sin6; 760 /* 761 * Inherit socket options from the listening socket. 762 * Note that in6p_inputopts are not (and should not be) 763 * copied, since it stores previously received options and is 764 * used to detect if each new option is different than the 765 * previous one and hence should be passed to a user. 766 * If we copied in6p_inputopts, a user would not be able to 767 * receive options just after calling the accept system call. 768 */ 769 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 770 if (oinp->in6p_outputopts) 771 inp->in6p_outputopts = 772 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 773 774 sin6.sin6_family = AF_INET6; 775 sin6.sin6_len = sizeof(sin6); 776 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 777 sin6.sin6_port = sc->sc_inc.inc_fport; 778 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 779 laddr6 = inp->in6p_laddr; 780 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 781 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 782 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 783 thread0.td_ucred, m)) != 0) { 784 inp->in6p_laddr = laddr6; 785 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 786 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 787 "with error %i\n", 788 s, __func__, error); 789 free(s, M_TCPLOG); 790 } 791 INP_HASH_WUNLOCK(&V_tcbinfo); 792 goto abort; 793 } 794 /* Override flowlabel from in6_pcbconnect. */ 795 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 796 inp->inp_flow |= sc->sc_flowlabel; 797 } 798#endif /* INET6 */ 799#if defined(INET) && defined(INET6) 800 else 801#endif 802#ifdef INET 803 { 804 struct in_addr laddr; 805 struct sockaddr_in sin; 806 807 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 808 809 if (inp->inp_options == NULL) { 810 inp->inp_options = sc->sc_ipopts; 811 sc->sc_ipopts = NULL; 812 } 813 814 sin.sin_family = AF_INET; 815 sin.sin_len = sizeof(sin); 816 sin.sin_addr = sc->sc_inc.inc_faddr; 817 sin.sin_port = sc->sc_inc.inc_fport; 818 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 819 laddr = inp->inp_laddr; 820 if (inp->inp_laddr.s_addr == INADDR_ANY) 821 inp->inp_laddr = sc->sc_inc.inc_laddr; 822 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 823 thread0.td_ucred, m)) != 0) { 824 inp->inp_laddr = laddr; 825 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 826 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 827 "with error %i\n", 828 s, __func__, error); 829 free(s, M_TCPLOG); 830 } 831 INP_HASH_WUNLOCK(&V_tcbinfo); 832 goto abort; 833 } 834 } 835#endif /* INET */ 836 INP_HASH_WUNLOCK(&V_tcbinfo); 837 tp = intotcpcb(inp); 838 tp->t_state = TCPS_SYN_RECEIVED; 839 tp->iss = sc->sc_iss; 840 tp->irs = sc->sc_irs; 841 tcp_rcvseqinit(tp); 842 tcp_sendseqinit(tp); 843 tp->snd_wl1 = sc->sc_irs; 844 tp->snd_max = tp->iss + 1; 845 tp->snd_nxt = tp->iss + 1; 846 tp->rcv_up = sc->sc_irs + 1; 847 tp->rcv_wnd = sc->sc_wnd; 848 tp->rcv_adv += tp->rcv_wnd; 849 tp->last_ack_sent = tp->rcv_nxt; 850 851 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 852 if (sc->sc_flags & SCF_NOOPT) 853 tp->t_flags |= TF_NOOPT; 854 else { 855 if (sc->sc_flags & SCF_WINSCALE) { 856 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 857 tp->snd_scale = sc->sc_requested_s_scale; 858 tp->request_r_scale = sc->sc_requested_r_scale; 859 } 860 if (sc->sc_flags & SCF_TIMESTAMP) { 861 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 862 tp->ts_recent = sc->sc_tsreflect; 863 tp->ts_recent_age = tcp_ts_getticks(); 864 tp->ts_offset = sc->sc_tsoff; 865 } 866#ifdef TCP_SIGNATURE 867 if (sc->sc_flags & SCF_SIGNATURE) 868 tp->t_flags |= TF_SIGNATURE; 869#endif 870 if (sc->sc_flags & SCF_SACK) 871 tp->t_flags |= TF_SACK_PERMIT; 872 } 873 874 if (sc->sc_flags & SCF_ECN) 875 tp->t_flags |= TF_ECN_PERMIT; 876 877 /* 878 * Set up MSS and get cached values from tcp_hostcache. 879 * This might overwrite some of the defaults we just set. 880 */ 881 tcp_mss(tp, sc->sc_peer_mss); 882 883 /* 884 * If the SYN,ACK was retransmitted, indicate that CWND to be 885 * limited to one segment in cc_conn_init(). 886 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 887 */ 888 if (sc->sc_rxmits > 1) 889 tp->snd_cwnd = 1; 890 891#ifdef TCP_OFFLOAD 892 /* 893 * Allow a TOE driver to install its hooks. Note that we hold the 894 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 895 * new connection before the TOE driver has done its thing. 896 */ 897 if (ADDED_BY_TOE(sc)) { 898 struct toedev *tod = sc->sc_tod; 899 900 tod->tod_offload_socket(tod, sc->sc_todctx, so); 901 } 902#endif 903 /* 904 * Copy and activate timers. 905 */ 906 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 907 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 908 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 909 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 910 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 911 912 INP_WUNLOCK(inp); 913 914 TCPSTAT_INC(tcps_accepts); 915 return (so); 916 917abort: 918 INP_WUNLOCK(inp); 919abort2: 920 if (so != NULL) 921 soabort(so); 922 return (NULL); 923} 924 925/* 926 * This function gets called when we receive an ACK for a 927 * socket in the LISTEN state. We look up the connection 928 * in the syncache, and if its there, we pull it out of 929 * the cache and turn it into a full-blown connection in 930 * the SYN-RECEIVED state. 931 */ 932int 933syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 934 struct socket **lsop, struct mbuf *m) 935{ 936 struct syncache *sc; 937 struct syncache_head *sch; 938 struct syncache scs; 939 char *s; 940 941 /* 942 * Global TCP locks are held because we manipulate the PCB lists 943 * and create a new socket. 944 */ 945 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 946 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 947 ("%s: can handle only ACK", __func__)); 948 949 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 950 SCH_LOCK_ASSERT(sch); 951 952#ifdef INVARIANTS 953 /* 954 * Test code for syncookies comparing the syncache stored 955 * values with the reconstructed values from the cookie. 956 */ 957 if (sc != NULL) 958 syncookie_cmp(inc, sch, sc, th, to, *lsop); 959#endif 960 961 if (sc == NULL) { 962 /* 963 * There is no syncache entry, so see if this ACK is 964 * a returning syncookie. To do this, first: 965 * A. See if this socket has had a syncache entry dropped in 966 * the past. We don't want to accept a bogus syncookie 967 * if we've never received a SYN. 968 * B. check that the syncookie is valid. If it is, then 969 * cobble up a fake syncache entry, and return. 970 */ 971 if (!V_tcp_syncookies) { 972 SCH_UNLOCK(sch); 973 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 974 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 975 "segment rejected (syncookies disabled)\n", 976 s, __func__); 977 goto failed; 978 } 979 bzero(&scs, sizeof(scs)); 980 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 981 SCH_UNLOCK(sch); 982 if (sc == NULL) { 983 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 984 log(LOG_DEBUG, "%s; %s: Segment failed " 985 "SYNCOOKIE authentication, segment rejected " 986 "(probably spoofed)\n", s, __func__); 987 goto failed; 988 } 989 } else { 990 /* Pull out the entry to unlock the bucket row. */ 991 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 992 sch->sch_length--; 993#ifdef TCP_OFFLOAD 994 if (ADDED_BY_TOE(sc)) { 995 struct toedev *tod = sc->sc_tod; 996 997 tod->tod_syncache_removed(tod, sc->sc_todctx); 998 } 999#endif 1000 SCH_UNLOCK(sch); 1001 } 1002 1003 /* 1004 * Segment validation: 1005 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1006 */ 1007 if (th->th_ack != sc->sc_iss + 1) { 1008 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1009 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1010 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1011 goto failed; 1012 } 1013 1014 /* 1015 * The SEQ must fall in the window starting at the received 1016 * initial receive sequence number + 1 (the SYN). 1017 */ 1018 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1019 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1020 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1021 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1022 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1023 goto failed; 1024 } 1025 1026 /* 1027 * If timestamps were not negotiated during SYN/ACK they 1028 * must not appear on any segment during this session. 1029 */ 1030 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1031 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1032 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1033 "segment rejected\n", s, __func__); 1034 goto failed; 1035 } 1036 1037 /* 1038 * If timestamps were negotiated during SYN/ACK they should 1039 * appear on every segment during this session. 1040 * XXXAO: This is only informal as there have been unverified 1041 * reports of non-compliants stacks. 1042 */ 1043 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1044 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1045 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1046 "no action\n", s, __func__); 1047 } 1048 1049 /* 1050 * If timestamps were negotiated the reflected timestamp 1051 * must be equal to what we actually sent in the SYN|ACK. 1052 */ 1053 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 1054 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1055 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1056 "segment rejected\n", 1057 s, __func__, to->to_tsecr, sc->sc_ts); 1058 goto failed; 1059 } 1060 1061 *lsop = syncache_socket(sc, *lsop, m); 1062 1063 if (*lsop == NULL) 1064 TCPSTAT_INC(tcps_sc_aborted); 1065 else 1066 TCPSTAT_INC(tcps_sc_completed); 1067 1068/* how do we find the inp for the new socket? */ 1069 if (sc != &scs) 1070 syncache_free(sc); 1071 return (1); 1072failed: 1073 if (sc != NULL && sc != &scs) 1074 syncache_free(sc); 1075 if (s != NULL) 1076 free(s, M_TCPLOG); 1077 *lsop = NULL; 1078 return (0); 1079} 1080 1081/* 1082 * Given a LISTEN socket and an inbound SYN request, add 1083 * this to the syn cache, and send back a segment: 1084 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1085 * to the source. 1086 * 1087 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1088 * Doing so would require that we hold onto the data and deliver it 1089 * to the application. However, if we are the target of a SYN-flood 1090 * DoS attack, an attacker could send data which would eventually 1091 * consume all available buffer space if it were ACKed. By not ACKing 1092 * the data, we avoid this DoS scenario. 1093 */ 1094void 1095syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1096 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1097 void *todctx) 1098{ 1099 struct tcpcb *tp; 1100 struct socket *so; 1101 struct syncache *sc = NULL; 1102 struct syncache_head *sch; 1103 struct mbuf *ipopts = NULL; 1104 u_int ltflags; 1105 int win, sb_hiwat, ip_ttl, ip_tos; 1106 char *s; 1107#ifdef INET6 1108 int autoflowlabel = 0; 1109#endif 1110#ifdef MAC 1111 struct label *maclabel; 1112#endif 1113 struct syncache scs; 1114 struct ucred *cred; 1115 1116 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 1117 INP_WLOCK_ASSERT(inp); /* listen socket */ 1118 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1119 ("%s: unexpected tcp flags", __func__)); 1120 1121 /* 1122 * Combine all so/tp operations very early to drop the INP lock as 1123 * soon as possible. 1124 */ 1125 so = *lsop; 1126 tp = sototcpcb(so); 1127 cred = crhold(so->so_cred); 1128 1129#ifdef INET6 1130 if ((inc->inc_flags & INC_ISIPV6) && 1131 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1132 autoflowlabel = 1; 1133#endif 1134 ip_ttl = inp->inp_ip_ttl; 1135 ip_tos = inp->inp_ip_tos; 1136 win = sbspace(&so->so_rcv); 1137 sb_hiwat = so->so_rcv.sb_hiwat; 1138 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1139 1140 /* By the time we drop the lock these should no longer be used. */ 1141 so = NULL; 1142 tp = NULL; 1143 1144#ifdef MAC 1145 if (mac_syncache_init(&maclabel) != 0) { 1146 INP_WUNLOCK(inp); 1147 INP_INFO_WUNLOCK(&V_tcbinfo); 1148 goto done; 1149 } else 1150 mac_syncache_create(maclabel, inp); 1151#endif 1152 INP_WUNLOCK(inp); 1153 INP_INFO_WUNLOCK(&V_tcbinfo); 1154 1155 /* 1156 * Remember the IP options, if any. 1157 */ 1158#ifdef INET6 1159 if (!(inc->inc_flags & INC_ISIPV6)) 1160#endif 1161#ifdef INET 1162 ipopts = (m) ? ip_srcroute(m) : NULL; 1163#else 1164 ipopts = NULL; 1165#endif 1166 1167 /* 1168 * See if we already have an entry for this connection. 1169 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1170 * 1171 * XXX: should the syncache be re-initialized with the contents 1172 * of the new SYN here (which may have different options?) 1173 * 1174 * XXX: We do not check the sequence number to see if this is a 1175 * real retransmit or a new connection attempt. The question is 1176 * how to handle such a case; either ignore it as spoofed, or 1177 * drop the current entry and create a new one? 1178 */ 1179 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1180 SCH_LOCK_ASSERT(sch); 1181 if (sc != NULL) { 1182 TCPSTAT_INC(tcps_sc_dupsyn); 1183 if (ipopts) { 1184 /* 1185 * If we were remembering a previous source route, 1186 * forget it and use the new one we've been given. 1187 */ 1188 if (sc->sc_ipopts) 1189 (void) m_free(sc->sc_ipopts); 1190 sc->sc_ipopts = ipopts; 1191 } 1192 /* 1193 * Update timestamp if present. 1194 */ 1195 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1196 sc->sc_tsreflect = to->to_tsval; 1197 else 1198 sc->sc_flags &= ~SCF_TIMESTAMP; 1199#ifdef MAC 1200 /* 1201 * Since we have already unconditionally allocated label 1202 * storage, free it up. The syncache entry will already 1203 * have an initialized label we can use. 1204 */ 1205 mac_syncache_destroy(&maclabel); 1206#endif 1207 /* Retransmit SYN|ACK and reset retransmit count. */ 1208 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1209 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1210 "resetting timer and retransmitting SYN|ACK\n", 1211 s, __func__); 1212 free(s, M_TCPLOG); 1213 } 1214 if (syncache_respond(sc) == 0) { 1215 sc->sc_rxmits = 0; 1216 syncache_timeout(sc, sch, 1); 1217 TCPSTAT_INC(tcps_sndacks); 1218 TCPSTAT_INC(tcps_sndtotal); 1219 } 1220 SCH_UNLOCK(sch); 1221 goto done; 1222 } 1223 1224 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1225 if (sc == NULL) { 1226 /* 1227 * The zone allocator couldn't provide more entries. 1228 * Treat this as if the cache was full; drop the oldest 1229 * entry and insert the new one. 1230 */ 1231 TCPSTAT_INC(tcps_sc_zonefail); 1232 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1233 syncache_drop(sc, sch); 1234 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1235 if (sc == NULL) { 1236 if (V_tcp_syncookies) { 1237 bzero(&scs, sizeof(scs)); 1238 sc = &scs; 1239 } else { 1240 SCH_UNLOCK(sch); 1241 if (ipopts) 1242 (void) m_free(ipopts); 1243 goto done; 1244 } 1245 } 1246 } 1247 1248 /* 1249 * Fill in the syncache values. 1250 */ 1251#ifdef MAC 1252 sc->sc_label = maclabel; 1253#endif 1254 sc->sc_cred = cred; 1255 cred = NULL; 1256 sc->sc_ipopts = ipopts; 1257 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1258#ifdef INET6 1259 if (!(inc->inc_flags & INC_ISIPV6)) 1260#endif 1261 { 1262 sc->sc_ip_tos = ip_tos; 1263 sc->sc_ip_ttl = ip_ttl; 1264 } 1265#ifdef TCP_OFFLOAD 1266 sc->sc_tod = tod; 1267 sc->sc_todctx = todctx; 1268#endif 1269 sc->sc_irs = th->th_seq; 1270 sc->sc_iss = arc4random(); 1271 sc->sc_flags = 0; 1272 sc->sc_flowlabel = 0; 1273 1274 /* 1275 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1276 * win was derived from socket earlier in the function. 1277 */ 1278 win = imax(win, 0); 1279 win = imin(win, TCP_MAXWIN); 1280 sc->sc_wnd = win; 1281 1282 if (V_tcp_do_rfc1323) { 1283 /* 1284 * A timestamp received in a SYN makes 1285 * it ok to send timestamp requests and replies. 1286 */ 1287 if (to->to_flags & TOF_TS) { 1288 sc->sc_tsreflect = to->to_tsval; 1289 sc->sc_ts = tcp_ts_getticks(); 1290 sc->sc_flags |= SCF_TIMESTAMP; 1291 } 1292 if (to->to_flags & TOF_SCALE) { 1293 int wscale = 0; 1294 1295 /* 1296 * Pick the smallest possible scaling factor that 1297 * will still allow us to scale up to sb_max, aka 1298 * kern.ipc.maxsockbuf. 1299 * 1300 * We do this because there are broken firewalls that 1301 * will corrupt the window scale option, leading to 1302 * the other endpoint believing that our advertised 1303 * window is unscaled. At scale factors larger than 1304 * 5 the unscaled window will drop below 1500 bytes, 1305 * leading to serious problems when traversing these 1306 * broken firewalls. 1307 * 1308 * With the default maxsockbuf of 256K, a scale factor 1309 * of 3 will be chosen by this algorithm. Those who 1310 * choose a larger maxsockbuf should watch out 1311 * for the compatiblity problems mentioned above. 1312 * 1313 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1314 * or <SYN,ACK>) segment itself is never scaled. 1315 */ 1316 while (wscale < TCP_MAX_WINSHIFT && 1317 (TCP_MAXWIN << wscale) < sb_max) 1318 wscale++; 1319 sc->sc_requested_r_scale = wscale; 1320 sc->sc_requested_s_scale = to->to_wscale; 1321 sc->sc_flags |= SCF_WINSCALE; 1322 } 1323 } 1324#ifdef TCP_SIGNATURE 1325 /* 1326 * If listening socket requested TCP digests, and received SYN 1327 * contains the option, flag this in the syncache so that 1328 * syncache_respond() will do the right thing with the SYN+ACK. 1329 * XXX: Currently we always record the option by default and will 1330 * attempt to use it in syncache_respond(). 1331 */ 1332 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1333 sc->sc_flags |= SCF_SIGNATURE; 1334#endif 1335 if (to->to_flags & TOF_SACKPERM) 1336 sc->sc_flags |= SCF_SACK; 1337 if (to->to_flags & TOF_MSS) 1338 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1339 if (ltflags & TF_NOOPT) 1340 sc->sc_flags |= SCF_NOOPT; 1341 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1342 sc->sc_flags |= SCF_ECN; 1343 1344 if (V_tcp_syncookies) 1345 sc->sc_iss = syncookie_generate(sch, sc); 1346#ifdef INET6 1347 if (autoflowlabel) { 1348 if (V_tcp_syncookies) 1349 sc->sc_flowlabel = sc->sc_iss; 1350 else 1351 sc->sc_flowlabel = ip6_randomflowlabel(); 1352 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1353 } 1354#endif 1355 SCH_UNLOCK(sch); 1356 1357 /* 1358 * Do a standard 3-way handshake. 1359 */ 1360 if (syncache_respond(sc) == 0) { 1361 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1362 syncache_free(sc); 1363 else if (sc != &scs) 1364 syncache_insert(sc, sch); /* locks and unlocks sch */ 1365 TCPSTAT_INC(tcps_sndacks); 1366 TCPSTAT_INC(tcps_sndtotal); 1367 } else { 1368 if (sc != &scs) 1369 syncache_free(sc); 1370 TCPSTAT_INC(tcps_sc_dropped); 1371 } 1372 1373done: 1374 if (cred != NULL) 1375 crfree(cred); 1376#ifdef MAC 1377 if (sc == &scs) 1378 mac_syncache_destroy(&maclabel); 1379#endif 1380 if (m) { 1381 1382 *lsop = NULL; 1383 m_freem(m); 1384 } 1385} 1386 1387static int 1388syncache_respond(struct syncache *sc) 1389{ 1390 struct ip *ip = NULL; 1391 struct mbuf *m; 1392 struct tcphdr *th = NULL; 1393 int optlen, error = 0; /* Make compiler happy */ 1394 u_int16_t hlen, tlen, mssopt; 1395 struct tcpopt to; 1396#ifdef INET6 1397 struct ip6_hdr *ip6 = NULL; 1398#endif 1399 1400 hlen = 1401#ifdef INET6 1402 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1403#endif 1404 sizeof(struct ip); 1405 tlen = hlen + sizeof(struct tcphdr); 1406 1407 /* Determine MSS we advertize to other end of connection. */ 1408 mssopt = tcp_mssopt(&sc->sc_inc); 1409 if (sc->sc_peer_mss) 1410 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1411 1412 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1413 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1414 ("syncache: mbuf too small")); 1415 1416 /* Create the IP+TCP header from scratch. */ 1417 m = m_gethdr(M_NOWAIT, MT_DATA); 1418 if (m == NULL) 1419 return (ENOBUFS); 1420#ifdef MAC 1421 mac_syncache_create_mbuf(sc->sc_label, m); 1422#endif 1423 m->m_data += max_linkhdr; 1424 m->m_len = tlen; 1425 m->m_pkthdr.len = tlen; 1426 m->m_pkthdr.rcvif = NULL; 1427 1428#ifdef INET6 1429 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1430 ip6 = mtod(m, struct ip6_hdr *); 1431 ip6->ip6_vfc = IPV6_VERSION; 1432 ip6->ip6_nxt = IPPROTO_TCP; 1433 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1434 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1435 ip6->ip6_plen = htons(tlen - hlen); 1436 /* ip6_hlim is set after checksum */ 1437 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1438 ip6->ip6_flow |= sc->sc_flowlabel; 1439 1440 th = (struct tcphdr *)(ip6 + 1); 1441 } 1442#endif 1443#if defined(INET6) && defined(INET) 1444 else 1445#endif 1446#ifdef INET 1447 { 1448 ip = mtod(m, struct ip *); 1449 ip->ip_v = IPVERSION; 1450 ip->ip_hl = sizeof(struct ip) >> 2; 1451 ip->ip_len = htons(tlen); 1452 ip->ip_id = 0; 1453 ip->ip_off = 0; 1454 ip->ip_sum = 0; 1455 ip->ip_p = IPPROTO_TCP; 1456 ip->ip_src = sc->sc_inc.inc_laddr; 1457 ip->ip_dst = sc->sc_inc.inc_faddr; 1458 ip->ip_ttl = sc->sc_ip_ttl; 1459 ip->ip_tos = sc->sc_ip_tos; 1460 1461 /* 1462 * See if we should do MTU discovery. Route lookups are 1463 * expensive, so we will only unset the DF bit if: 1464 * 1465 * 1) path_mtu_discovery is disabled 1466 * 2) the SCF_UNREACH flag has been set 1467 */ 1468 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1469 ip->ip_off |= htons(IP_DF); 1470 1471 th = (struct tcphdr *)(ip + 1); 1472 } 1473#endif /* INET */ 1474 th->th_sport = sc->sc_inc.inc_lport; 1475 th->th_dport = sc->sc_inc.inc_fport; 1476 1477 th->th_seq = htonl(sc->sc_iss); 1478 th->th_ack = htonl(sc->sc_irs + 1); 1479 th->th_off = sizeof(struct tcphdr) >> 2; 1480 th->th_x2 = 0; 1481 th->th_flags = TH_SYN|TH_ACK; 1482 th->th_win = htons(sc->sc_wnd); 1483 th->th_urp = 0; 1484 1485 if (sc->sc_flags & SCF_ECN) { 1486 th->th_flags |= TH_ECE; 1487 TCPSTAT_INC(tcps_ecn_shs); 1488 } 1489 1490 /* Tack on the TCP options. */ 1491 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1492 to.to_flags = 0; 1493 1494 to.to_mss = mssopt; 1495 to.to_flags = TOF_MSS; 1496 if (sc->sc_flags & SCF_WINSCALE) { 1497 to.to_wscale = sc->sc_requested_r_scale; 1498 to.to_flags |= TOF_SCALE; 1499 } 1500 if (sc->sc_flags & SCF_TIMESTAMP) { 1501 /* Virgin timestamp or TCP cookie enhanced one. */ 1502 to.to_tsval = sc->sc_ts; 1503 to.to_tsecr = sc->sc_tsreflect; 1504 to.to_flags |= TOF_TS; 1505 } 1506 if (sc->sc_flags & SCF_SACK) 1507 to.to_flags |= TOF_SACKPERM; 1508#ifdef TCP_SIGNATURE 1509 if (sc->sc_flags & SCF_SIGNATURE) 1510 to.to_flags |= TOF_SIGNATURE; 1511#endif 1512 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1513 1514 /* Adjust headers by option size. */ 1515 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1516 m->m_len += optlen; 1517 m->m_pkthdr.len += optlen; 1518 1519#ifdef TCP_SIGNATURE 1520 if (sc->sc_flags & SCF_SIGNATURE) 1521 tcp_signature_compute(m, 0, 0, optlen, 1522 to.to_signature, IPSEC_DIR_OUTBOUND); 1523#endif 1524#ifdef INET6 1525 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1526 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1527 else 1528#endif 1529 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1530 } else 1531 optlen = 0; 1532 1533 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1534 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1535#ifdef INET6 1536 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1537 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1538 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1539 IPPROTO_TCP, 0); 1540 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1541#ifdef TCP_OFFLOAD 1542 if (ADDED_BY_TOE(sc)) { 1543 struct toedev *tod = sc->sc_tod; 1544 1545 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1546 1547 return (error); 1548 } 1549#endif 1550 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1551 } 1552#endif 1553#if defined(INET6) && defined(INET) 1554 else 1555#endif 1556#ifdef INET 1557 { 1558 m->m_pkthdr.csum_flags = CSUM_TCP; 1559 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1560 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1561#ifdef TCP_OFFLOAD 1562 if (ADDED_BY_TOE(sc)) { 1563 struct toedev *tod = sc->sc_tod; 1564 1565 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1566 1567 return (error); 1568 } 1569#endif 1570 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1571 } 1572#endif 1573 return (error); 1574} 1575 1576/* 1577 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1578 * that exceed the capacity of the syncache by avoiding the storage of any 1579 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1580 * attacks where the attacker does not have access to our responses. 1581 * 1582 * Syncookies encode and include all necessary information about the 1583 * connection setup within the SYN|ACK that we send back. That way we 1584 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1585 * (if ever). Normally the syncache and syncookies are running in parallel 1586 * with the latter taking over when the former is exhausted. When matching 1587 * syncache entry is found the syncookie is ignored. 1588 * 1589 * The only reliable information persisting the 3WHS is our inital sequence 1590 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1591 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1592 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1593 * returns and signifies a legitimate connection if it matches the ACK. 1594 * 1595 * The available space of 32 bits to store the hash and to encode the SYN 1596 * option information is very tight and we should have at least 24 bits for 1597 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1598 * 1599 * SYN option information we have to encode to fully restore a connection: 1600 * MSS: is imporant to chose an optimal segment size to avoid IP level 1601 * fragmentation along the path. The common MSS values can be encoded 1602 * in a 3-bit table. Uncommon values are captured by the next lower value 1603 * in the table leading to a slight increase in packetization overhead. 1604 * WSCALE: is necessary to allow large windows to be used for high delay- 1605 * bandwidth product links. Not scaling the window when it was initially 1606 * negotiated is bad for performance as lack of scaling further decreases 1607 * the apparent available send window. We only need to encode the WSCALE 1608 * we received from the remote end. Our end can be recalculated at any 1609 * time. The common WSCALE values can be encoded in a 3-bit table. 1610 * Uncommon values are captured by the next lower value in the table 1611 * making us under-estimate the available window size halving our 1612 * theoretically possible maximum throughput for that connection. 1613 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1614 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1615 * that are included in all segments on a connection. We enable them when 1616 * the ACK has them. 1617 * 1618 * Security of syncookies and attack vectors: 1619 * 1620 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1621 * together with the gloabl secret to make it unique per connection attempt. 1622 * Thus any change of any of those parameters results in a different MAC output 1623 * in an unpredictable way unless a collision is encountered. 24 bits of the 1624 * MAC are embedded into the ISS. 1625 * 1626 * To prevent replay attacks two rotating global secrets are updated with a 1627 * new random value every 15 seconds. The life-time of a syncookie is thus 1628 * 15-30 seconds. 1629 * 1630 * Vector 1: Attacking the secret. This requires finding a weakness in the 1631 * MAC itself or the way it is used here. The attacker can do a chosen plain 1632 * text attack by varying and testing the all parameters under his control. 1633 * The strength depends on the size and randomness of the secret, and the 1634 * cryptographic security of the MAC function. Due to the constant updating 1635 * of the secret the attacker has at most 29.999 seconds to find the secret 1636 * and launch spoofed connections. After that he has to start all over again. 1637 * 1638 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1639 * size an average of 4,823 attempts are required for a 50% chance of success 1640 * to spoof a single syncookie (birthday collision paradox). However the 1641 * attacker is blind and doesn't know if one of his attempts succeeded unless 1642 * he has a side channel to interfere success from. A single connection setup 1643 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1644 * This many attempts are required for each one blind spoofed connection. For 1645 * every additional spoofed connection he has to launch another N attempts. 1646 * Thus for a sustained rate 100 spoofed connections per second approximately 1647 * 1,800,000 packets per second would have to be sent. 1648 * 1649 * NB: The MAC function should be fast so that it doesn't become a CPU 1650 * exhaustion attack vector itself. 1651 * 1652 * References: 1653 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1654 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1655 * http://cr.yp.to/syncookies.html (overview) 1656 * http://cr.yp.to/syncookies/archive (details) 1657 * 1658 * 1659 * Schematic construction of a syncookie enabled Initial Sequence Number: 1660 * 0 1 2 3 1661 * 12345678901234567890123456789012 1662 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1663 * 1664 * x 24 MAC (truncated) 1665 * W 3 Send Window Scale index 1666 * M 3 MSS index 1667 * S 1 SACK permitted 1668 * P 1 Odd/even secret 1669 */ 1670 1671/* 1672 * Distribution and probability of certain MSS values. Those in between are 1673 * rounded down to the next lower one. 1674 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1675 * .2% .3% 5% 7% 7% 20% 15% 45% 1676 */ 1677static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1678 1679/* 1680 * Distribution and probability of certain WSCALE values. We have to map the 1681 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1682 * bits based on prevalence of certain values. Where we don't have an exact 1683 * match for are rounded down to the next lower one letting us under-estimate 1684 * the true available window. At the moment this would happen only for the 1685 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1686 * and window size). The absence of the WSCALE option (no scaling in either 1687 * direction) is encoded with index zero. 1688 * [WSCALE values histograms, Allman, 2012] 1689 * X 10 10 35 5 6 14 10% by host 1690 * X 11 4 5 5 18 49 3% by connections 1691 */ 1692static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1693 1694/* 1695 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1696 * and good cryptographic properties. 1697 */ 1698static uint32_t 1699syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1700 uint8_t *secbits, uintptr_t secmod) 1701{ 1702 SIPHASH_CTX ctx; 1703 uint32_t siphash[2]; 1704 1705 SipHash24_Init(&ctx); 1706 SipHash_SetKey(&ctx, secbits); 1707 switch (inc->inc_flags & INC_ISIPV6) { 1708#ifdef INET 1709 case 0: 1710 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1711 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1712 break; 1713#endif 1714#ifdef INET6 1715 case INC_ISIPV6: 1716 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1717 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1718 break; 1719#endif 1720 } 1721 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1722 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1723 SipHash_Update(&ctx, &flags, sizeof(flags)); 1724 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1725 SipHash_Final((u_int8_t *)&siphash, &ctx); 1726 1727 return (siphash[0] ^ siphash[1]); 1728} 1729 1730static tcp_seq 1731syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1732{ 1733 u_int i, mss, secbit, wscale; 1734 uint32_t iss, hash; 1735 uint8_t *secbits; 1736 union syncookie cookie; 1737 1738 SCH_LOCK_ASSERT(sch); 1739 1740 cookie.cookie = 0; 1741 1742 /* Map our computed MSS into the 3-bit index. */ 1743 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1744 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1; 1745 tcp_sc_msstab[i] > mss && i > 0; 1746 i--) 1747 ; 1748 cookie.flags.mss_idx = i; 1749 1750 /* 1751 * Map the send window scale into the 3-bit index but only if 1752 * the wscale option was received. 1753 */ 1754 if (sc->sc_flags & SCF_WINSCALE) { 1755 wscale = sc->sc_requested_s_scale; 1756 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1; 1757 tcp_sc_wstab[i] > wscale && i > 0; 1758 i--) 1759 ; 1760 cookie.flags.wscale_idx = i; 1761 } 1762 1763 /* Can we do SACK? */ 1764 if (sc->sc_flags & SCF_SACK) 1765 cookie.flags.sack_ok = 1; 1766 1767 /* Which of the two secrets to use. */ 1768 secbit = sch->sch_sc->secret.oddeven & 0x1; 1769 cookie.flags.odd_even = secbit; 1770 1771 secbits = sch->sch_sc->secret.key[secbit]; 1772 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1773 (uintptr_t)sch); 1774 1775 /* 1776 * Put the flags into the hash and XOR them to get better ISS number 1777 * variance. This doesn't enhance the cryptographic strength and is 1778 * done to prevent the 8 cookie bits from showing up directly on the 1779 * wire. 1780 */ 1781 iss = hash & ~0xff; 1782 iss |= cookie.cookie ^ (hash >> 24); 1783 1784 /* Randomize the timestamp. */ 1785 if (sc->sc_flags & SCF_TIMESTAMP) { 1786 sc->sc_ts = arc4random(); 1787 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1788 } 1789 1790 TCPSTAT_INC(tcps_sc_sendcookie); 1791 return (iss); 1792} 1793 1794static struct syncache * 1795syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1796 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1797 struct socket *lso) 1798{ 1799 uint32_t hash; 1800 uint8_t *secbits; 1801 tcp_seq ack, seq; 1802 int wnd, wscale = 0; 1803 union syncookie cookie; 1804 1805 SCH_LOCK_ASSERT(sch); 1806 1807 /* 1808 * Pull information out of SYN-ACK/ACK and revert sequence number 1809 * advances. 1810 */ 1811 ack = th->th_ack - 1; 1812 seq = th->th_seq - 1; 1813 1814 /* 1815 * Unpack the flags containing enough information to restore the 1816 * connection. 1817 */ 1818 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 1819 1820 /* Which of the two secrets to use. */ 1821 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 1822 1823 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 1824 1825 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 1826 if ((ack & ~0xff) != (hash & ~0xff)) 1827 return (NULL); 1828 1829 /* Fill in the syncache values. */ 1830 sc->sc_flags = 0; 1831 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1832 sc->sc_ipopts = NULL; 1833 1834 sc->sc_irs = seq; 1835 sc->sc_iss = ack; 1836 1837 switch (inc->inc_flags & INC_ISIPV6) { 1838#ifdef INET 1839 case 0: 1840 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 1841 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 1842 break; 1843#endif 1844#ifdef INET6 1845 case INC_ISIPV6: 1846 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 1847 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 1848 break; 1849#endif 1850 } 1851 1852 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 1853 1854 /* We can simply recompute receive window scale we sent earlier. */ 1855 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 1856 wscale++; 1857 1858 /* Only use wscale if it was enabled in the orignal SYN. */ 1859 if (cookie.flags.wscale_idx > 0) { 1860 sc->sc_requested_r_scale = wscale; 1861 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 1862 sc->sc_flags |= SCF_WINSCALE; 1863 } 1864 1865 wnd = sbspace(&lso->so_rcv); 1866 wnd = imax(wnd, 0); 1867 wnd = imin(wnd, TCP_MAXWIN); 1868 sc->sc_wnd = wnd; 1869 1870 if (cookie.flags.sack_ok) 1871 sc->sc_flags |= SCF_SACK; 1872 1873 if (to->to_flags & TOF_TS) { 1874 sc->sc_flags |= SCF_TIMESTAMP; 1875 sc->sc_tsreflect = to->to_tsval; 1876 sc->sc_ts = to->to_tsecr; 1877 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 1878 } 1879 1880 if (to->to_flags & TOF_SIGNATURE) 1881 sc->sc_flags |= SCF_SIGNATURE; 1882 1883 sc->sc_rxmits = 0; 1884 1885 TCPSTAT_INC(tcps_sc_recvcookie); 1886 return (sc); 1887} 1888 1889#ifdef INVARIANTS 1890static int 1891syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 1892 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1893 struct socket *lso) 1894{ 1895 struct syncache scs, *scx; 1896 char *s; 1897 1898 bzero(&scs, sizeof(scs)); 1899 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 1900 1901 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 1902 return (0); 1903 1904 if (scx != NULL) { 1905 if (sc->sc_peer_mss != scx->sc_peer_mss) 1906 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 1907 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 1908 1909 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 1910 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 1911 s, __func__, sc->sc_requested_r_scale, 1912 scx->sc_requested_r_scale); 1913 1914 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 1915 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 1916 s, __func__, sc->sc_requested_s_scale, 1917 scx->sc_requested_s_scale); 1918 1919 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 1920 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 1921 } 1922 1923 if (s != NULL) 1924 free(s, M_TCPLOG); 1925 return (0); 1926} 1927#endif /* INVARIANTS */ 1928 1929static void 1930syncookie_reseed(void *arg) 1931{ 1932 struct tcp_syncache *sc = arg; 1933 uint8_t *secbits; 1934 int secbit; 1935 1936 /* 1937 * Reseeding the secret doesn't have to be protected by a lock. 1938 * It only must be ensured that the new random values are visible 1939 * to all CPUs in a SMP environment. The atomic with release 1940 * semantics ensures that. 1941 */ 1942 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 1943 secbits = sc->secret.key[secbit]; 1944 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 1945 atomic_add_rel_int(&sc->secret.oddeven, 1); 1946 1947 /* Reschedule ourself. */ 1948 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 1949} 1950 1951/* 1952 * Returns the current number of syncache entries. This number 1953 * will probably change before you get around to calling 1954 * syncache_pcblist. 1955 */ 1956int 1957syncache_pcbcount(void) 1958{ 1959 struct syncache_head *sch; 1960 int count, i; 1961 1962 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1963 /* No need to lock for a read. */ 1964 sch = &V_tcp_syncache.hashbase[i]; 1965 count += sch->sch_length; 1966 } 1967 return count; 1968} 1969 1970/* 1971 * Exports the syncache entries to userland so that netstat can display 1972 * them alongside the other sockets. This function is intended to be 1973 * called only from tcp_pcblist. 1974 * 1975 * Due to concurrency on an active system, the number of pcbs exported 1976 * may have no relation to max_pcbs. max_pcbs merely indicates the 1977 * amount of space the caller allocated for this function to use. 1978 */ 1979int 1980syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 1981{ 1982 struct xtcpcb xt; 1983 struct syncache *sc; 1984 struct syncache_head *sch; 1985 int count, error, i; 1986 1987 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1988 sch = &V_tcp_syncache.hashbase[i]; 1989 SCH_LOCK(sch); 1990 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 1991 if (count >= max_pcbs) { 1992 SCH_UNLOCK(sch); 1993 goto exit; 1994 } 1995 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 1996 continue; 1997 bzero(&xt, sizeof(xt)); 1998 xt.xt_len = sizeof(xt); 1999 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2000 xt.xt_inp.inp_vflag = INP_IPV6; 2001 else 2002 xt.xt_inp.inp_vflag = INP_IPV4; 2003 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2004 xt.xt_tp.t_inpcb = &xt.xt_inp; 2005 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2006 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2007 xt.xt_socket.xso_len = sizeof (struct xsocket); 2008 xt.xt_socket.so_type = SOCK_STREAM; 2009 xt.xt_socket.so_state = SS_ISCONNECTING; 2010 error = SYSCTL_OUT(req, &xt, sizeof xt); 2011 if (error) { 2012 SCH_UNLOCK(sch); 2013 goto exit; 2014 } 2015 count++; 2016 } 2017 SCH_UNLOCK(sch); 2018 } 2019exit: 2020 *pcbs_exported = count; 2021 return error; 2022} 2023