1 /*- 2 * Copyright (c) 2001 Networks Associates Technology, Inc. 3 * All rights reserved. 4 * 5 * This software was developed for the FreeBSD Project by Jonathan Lemon 6 * and NAI Labs, the Security Research Division of Network Associates, Inc. 7 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 8 * DARPA CHATS research program. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. The name of the author may not be used to endorse or promote 19 * products derived from this software without specific prior written 20 * permission. 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 * $FreeBSD$ 35 */ 36 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/kernel.h> 43 #include <sys/sysctl.h> 44 #include <sys/malloc.h> 45 #include <sys/mbuf.h> 46 #include <sys/md5.h> 47 #include <sys/proc.h> /* for proc0 declaration */ 48 #include <sys/random.h> 49 #include <sys/socket.h> 50 #include <sys/socketvar.h> 51 52 #include <net/if.h> 53 #include <net/route.h> 54 55 #include <netinet/in.h> 56 #include <netinet/in_systm.h> 57 #include <netinet/ip.h> 58 #include <netinet/in_var.h> 59 #include <netinet/in_pcb.h> 60 #include <netinet/ip_var.h> 61 #ifdef INET6 62 #include <netinet/ip6.h> 63 #include <netinet/icmp6.h> 64 #include <netinet6/nd6.h> 65 #include <netinet6/ip6_var.h> 66 #include <netinet6/in6_pcb.h> 67 #endif 68 #include <netinet/tcp.h> 69 #include <netinet/tcp_fsm.h> 70 #include <netinet/tcp_seq.h> 71 #include <netinet/tcp_timer.h> 72 #include <netinet/tcp_var.h> 73 #ifdef INET6 74 #include <netinet6/tcp6_var.h> 75 #endif 76 77 #ifdef IPSEC 78 #include <netinet6/ipsec.h> 79 #ifdef INET6 80 #include <netinet6/ipsec6.h> 81 #endif 82 #include <netkey/key.h> 83 #endif /*IPSEC*/ 84 85 #include <machine/in_cksum.h> 86 #include <vm/uma.h> 87 88 static int tcp_syncookies = 1; 89 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 90 &tcp_syncookies, 0, 91 "Use TCP SYN cookies if the syncache overflows"); 92 93 static void syncache_drop(struct syncache *, struct syncache_head *); 94 static void syncache_free(struct syncache *); 95 static void syncache_insert(struct syncache *, struct syncache_head *); 96 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 97 static int syncache_respond(struct syncache *, struct mbuf *); 98 static struct socket *syncache_socket(struct syncache *, struct socket *, 99 struct mbuf *m); 100 static void syncache_timer(void *); 101 static u_int32_t syncookie_generate(struct syncache *); 102 static struct syncache *syncookie_lookup(struct in_conninfo *, 103 struct tcphdr *, struct socket *); 104 105 /* 106 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 107 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds, 108 * the odds are that the user has given up attempting to connect by then. 109 */ 110 #define SYNCACHE_MAXREXMTS 3 111 112 /* Arbitrary values */ 113 #define TCP_SYNCACHE_HASHSIZE 512 114 #define TCP_SYNCACHE_BUCKETLIMIT 30 115 116 struct tcp_syncache { 117 struct syncache_head *hashbase; 118 uma_zone_t zone; 119 u_int hashsize; 120 u_int hashmask; 121 u_int bucket_limit; 122 u_int cache_count; 123 u_int cache_limit; 124 u_int rexmt_limit; 125 u_int hash_secret; 126 u_int next_reseed; 127 TAILQ_HEAD(, syncache) timerq[SYNCACHE_MAXREXMTS + 1]; 128 struct callout tt_timerq[SYNCACHE_MAXREXMTS + 1]; 129 }; 130 static struct tcp_syncache tcp_syncache; 131 132 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 133 134 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RD, 135 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 136 137 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RD, 138 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 139 140 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 141 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 142 143 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RD, 144 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 145 146 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 147 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 148 149 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 150 151 #define SYNCACHE_HASH(inc, mask) \ 152 ((tcp_syncache.hash_secret ^ \ 153 (inc)->inc_faddr.s_addr ^ \ 154 ((inc)->inc_faddr.s_addr >> 16) ^ \ 155 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 156 157 #define SYNCACHE_HASH6(inc, mask) \ 158 ((tcp_syncache.hash_secret ^ \ 159 (inc)->inc6_faddr.s6_addr32[0] ^ \ 160 (inc)->inc6_faddr.s6_addr32[3] ^ \ 161 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 162 163 #define ENDPTS_EQ(a, b) ( \ 164 (a)->ie_fport == (b)->ie_fport && \ 165 (a)->ie_lport == (b)->ie_lport && \ 166 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 167 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 168 ) 169 170 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 171 172 #define SYNCACHE_TIMEOUT(sc, slot) do { \ 173 sc->sc_rxtslot = slot; \ 174 sc->sc_rxttime = ticks + TCPTV_RTOBASE * tcp_backoff[slot]; \ 175 TAILQ_INSERT_TAIL(&tcp_syncache.timerq[slot], sc, sc_timerq); \ 176 if (!callout_active(&tcp_syncache.tt_timerq[slot])) \ 177 callout_reset(&tcp_syncache.tt_timerq[slot], \ 178 TCPTV_RTOBASE * tcp_backoff[slot], \ 179 syncache_timer, (void *)((intptr_t)slot)); \ 180 } while (0) 181 182 static void 183 syncache_free(struct syncache *sc) 184 { 185 struct rtentry *rt; 186 187 if (sc->sc_ipopts) 188 (void) m_free(sc->sc_ipopts); 189 #ifdef INET6 190 if (sc->sc_inc.inc_isipv6) 191 rt = sc->sc_route6.ro_rt; 192 else 193 #endif 194 rt = sc->sc_route.ro_rt; 195 if (rt != NULL) { 196 /* 197 * If this is the only reference to a protocol cloned 198 * route, remove it immediately. 199 */ 200 if (rt->rt_flags & RTF_WASCLONED && 201 (sc->sc_flags & SCF_KEEPROUTE) == 0 && 202 rt->rt_refcnt == 1) 203 rtrequest(RTM_DELETE, rt_key(rt), 204 rt->rt_gateway, rt_mask(rt), 205 rt->rt_flags, NULL); 206 RTFREE(rt); 207 } 208 uma_zfree(tcp_syncache.zone, sc); 209 } 210 211 void 212 syncache_init(void) 213 { 214 int i; 215 216 tcp_syncache.cache_count = 0; 217 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 218 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 219 tcp_syncache.cache_limit = 220 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 221 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 222 tcp_syncache.next_reseed = 0; 223 tcp_syncache.hash_secret = arc4random(); 224 225 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 226 &tcp_syncache.hashsize); 227 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 228 &tcp_syncache.cache_limit); 229 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 230 &tcp_syncache.bucket_limit); 231 if (!powerof2(tcp_syncache.hashsize)) { 232 printf("WARNING: syncache hash size is not a power of 2.\n"); 233 tcp_syncache.hashsize = 512; /* safe default */ 234 } 235 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 236 237 /* Allocate the hash table. */ 238 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 239 tcp_syncache.hashsize * sizeof(struct syncache_head), 240 M_SYNCACHE, M_WAITOK); 241 242 /* Initialize the hash buckets. */ 243 for (i = 0; i < tcp_syncache.hashsize; i++) { 244 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 245 tcp_syncache.hashbase[i].sch_length = 0; 246 } 247 248 /* Initialize the timer queues. */ 249 for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) { 250 TAILQ_INIT(&tcp_syncache.timerq[i]); 251 callout_init(&tcp_syncache.tt_timerq[i], 0); 252 } 253 254 /* 255 * Allocate the syncache entries. Allow the zone to allocate one 256 * more entry than cache limit, so a new entry can bump out an 257 * older one. 258 */ 259 tcp_syncache.cache_limit -= 1; 260 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 261 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE); 262 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); 263 } 264 265 static void 266 syncache_insert(sc, sch) 267 struct syncache *sc; 268 struct syncache_head *sch; 269 { 270 struct syncache *sc2; 271 int s, i; 272 273 /* 274 * Make sure that we don't overflow the per-bucket 275 * limit or the total cache size limit. 276 */ 277 s = splnet(); 278 if (sch->sch_length >= tcp_syncache.bucket_limit) { 279 /* 280 * The bucket is full, toss the oldest element. 281 */ 282 sc2 = TAILQ_FIRST(&sch->sch_bucket); 283 sc2->sc_tp->ts_recent = ticks; 284 syncache_drop(sc2, sch); 285 tcpstat.tcps_sc_bucketoverflow++; 286 } else if (tcp_syncache.cache_count >= tcp_syncache.cache_limit) { 287 /* 288 * The cache is full. Toss the oldest entry in the 289 * entire cache. This is the front entry in the 290 * first non-empty timer queue with the largest 291 * timeout value. 292 */ 293 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) { 294 sc2 = TAILQ_FIRST(&tcp_syncache.timerq[i]); 295 if (sc2 != NULL) 296 break; 297 } 298 sc2->sc_tp->ts_recent = ticks; 299 syncache_drop(sc2, NULL); 300 tcpstat.tcps_sc_cacheoverflow++; 301 } 302 303 /* Initialize the entry's timer. */ 304 SYNCACHE_TIMEOUT(sc, 0); 305 306 /* Put it into the bucket. */ 307 TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash); 308 sch->sch_length++; 309 tcp_syncache.cache_count++; 310 tcpstat.tcps_sc_added++; 311 splx(s); 312 } 313 314 static void 315 syncache_drop(sc, sch) 316 struct syncache *sc; 317 struct syncache_head *sch; 318 { 319 int s; 320 321 if (sch == NULL) { 322 #ifdef INET6 323 if (sc->sc_inc.inc_isipv6) { 324 sch = &tcp_syncache.hashbase[ 325 SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)]; 326 } else 327 #endif 328 { 329 sch = &tcp_syncache.hashbase[ 330 SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)]; 331 } 332 } 333 334 s = splnet(); 335 336 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 337 sch->sch_length--; 338 tcp_syncache.cache_count--; 339 340 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], sc, sc_timerq); 341 if (TAILQ_EMPTY(&tcp_syncache.timerq[sc->sc_rxtslot])) 342 callout_stop(&tcp_syncache.tt_timerq[sc->sc_rxtslot]); 343 splx(s); 344 345 syncache_free(sc); 346 } 347 348 /* 349 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 350 * If we have retransmitted an entry the maximum number of times, expire it. 351 */ 352 static void 353 syncache_timer(xslot) 354 void *xslot; 355 { 356 intptr_t slot = (intptr_t)xslot; 357 struct syncache *sc, *nsc; 358 struct inpcb *inp; 359 int s; 360 361 s = splnet(); 362 if (callout_pending(&tcp_syncache.tt_timerq[slot]) || 363 !callout_active(&tcp_syncache.tt_timerq[slot])) { 364 splx(s); 365 return; 366 } 367 callout_deactivate(&tcp_syncache.tt_timerq[slot]); 368 369 nsc = TAILQ_FIRST(&tcp_syncache.timerq[slot]); 370 INP_INFO_RLOCK(&tcbinfo); 371 while (nsc != NULL) { 372 if (ticks < nsc->sc_rxttime) 373 break; 374 sc = nsc; 375 inp = sc->sc_tp->t_inpcb; 376 INP_LOCK(inp); 377 if (slot == SYNCACHE_MAXREXMTS || 378 slot >= tcp_syncache.rexmt_limit || 379 inp->inp_gencnt != sc->sc_inp_gencnt) { 380 nsc = TAILQ_NEXT(sc, sc_timerq); 381 syncache_drop(sc, NULL); 382 tcpstat.tcps_sc_stale++; 383 INP_UNLOCK(inp); 384 continue; 385 } 386 /* 387 * syncache_respond() may call back into the syncache to 388 * to modify another entry, so do not obtain the next 389 * entry on the timer chain until it has completed. 390 */ 391 (void) syncache_respond(sc, NULL); 392 INP_UNLOCK(inp); 393 nsc = TAILQ_NEXT(sc, sc_timerq); 394 tcpstat.tcps_sc_retransmitted++; 395 TAILQ_REMOVE(&tcp_syncache.timerq[slot], sc, sc_timerq); 396 SYNCACHE_TIMEOUT(sc, slot + 1); 397 } 398 INP_INFO_RUNLOCK(&tcbinfo); 399 if (nsc != NULL) 400 callout_reset(&tcp_syncache.tt_timerq[slot], 401 nsc->sc_rxttime - ticks, syncache_timer, (void *)(slot)); 402 splx(s); 403 } 404 405 /* 406 * Find an entry in the syncache. 407 */ 408 struct syncache * 409 syncache_lookup(inc, schp) 410 struct in_conninfo *inc; 411 struct syncache_head **schp; 412 { 413 struct syncache *sc; 414 struct syncache_head *sch; 415 int s; 416 417 #ifdef INET6 418 if (inc->inc_isipv6) { 419 sch = &tcp_syncache.hashbase[ 420 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 421 *schp = sch; 422 s = splnet(); 423 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 424 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) { 425 splx(s); 426 return (sc); 427 } 428 } 429 splx(s); 430 } else 431 #endif 432 { 433 sch = &tcp_syncache.hashbase[ 434 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 435 *schp = sch; 436 s = splnet(); 437 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 438 #ifdef INET6 439 if (sc->sc_inc.inc_isipv6) 440 continue; 441 #endif 442 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) { 443 splx(s); 444 return (sc); 445 } 446 } 447 splx(s); 448 } 449 return (NULL); 450 } 451 452 /* 453 * This function is called when we get a RST for a 454 * non-existent connection, so that we can see if the 455 * connection is in the syn cache. If it is, zap it. 456 */ 457 void 458 syncache_chkrst(inc, th) 459 struct in_conninfo *inc; 460 struct tcphdr *th; 461 { 462 struct syncache *sc; 463 struct syncache_head *sch; 464 465 sc = syncache_lookup(inc, &sch); 466 if (sc == NULL) 467 return; 468 /* 469 * If the RST bit is set, check the sequence number to see 470 * if this is a valid reset segment. 471 * RFC 793 page 37: 472 * In all states except SYN-SENT, all reset (RST) segments 473 * are validated by checking their SEQ-fields. A reset is 474 * valid if its sequence number is in the window. 475 * 476 * The sequence number in the reset segment is normally an 477 * echo of our outgoing acknowlegement numbers, but some hosts 478 * send a reset with the sequence number at the rightmost edge 479 * of our receive window, and we have to handle this case. 480 */ 481 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 482 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 483 syncache_drop(sc, sch); 484 tcpstat.tcps_sc_reset++; 485 } 486 } 487 488 void 489 syncache_badack(inc) 490 struct in_conninfo *inc; 491 { 492 struct syncache *sc; 493 struct syncache_head *sch; 494 495 sc = syncache_lookup(inc, &sch); 496 if (sc != NULL) { 497 syncache_drop(sc, sch); 498 tcpstat.tcps_sc_badack++; 499 } 500 } 501 502 void 503 syncache_unreach(inc, th) 504 struct in_conninfo *inc; 505 struct tcphdr *th; 506 { 507 struct syncache *sc; 508 struct syncache_head *sch; 509 510 /* we are called at splnet() here */ 511 sc = syncache_lookup(inc, &sch); 512 if (sc == NULL) 513 return; 514 515 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 516 if (ntohl(th->th_seq) != sc->sc_iss) 517 return; 518 519 /* 520 * If we've rertransmitted 3 times and this is our second error, 521 * we remove the entry. Otherwise, we allow it to continue on. 522 * This prevents us from incorrectly nuking an entry during a 523 * spurious network outage. 524 * 525 * See tcp_notify(). 526 */ 527 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) { 528 sc->sc_flags |= SCF_UNREACH; 529 return; 530 } 531 syncache_drop(sc, sch); 532 tcpstat.tcps_sc_unreach++; 533 } 534 535 /* 536 * Build a new TCP socket structure from a syncache entry. 537 */ 538 static struct socket * 539 syncache_socket(sc, lso, m) 540 struct syncache *sc; 541 struct socket *lso; 542 struct mbuf *m; 543 { 544 struct inpcb *inp = NULL; 545 struct socket *so; 546 struct tcpcb *tp; 547 548 /* 549 * Ok, create the full blown connection, and set things up 550 * as they would have been set up if we had created the 551 * connection when the SYN arrived. If we can't create 552 * the connection, abort it. 553 */ 554 so = sonewconn(lso, SS_ISCONNECTED); 555 if (so == NULL) { 556 /* 557 * Drop the connection; we will send a RST if the peer 558 * retransmits the ACK, 559 */ 560 tcpstat.tcps_listendrop++; 561 goto abort; 562 } 563 564 inp = sotoinpcb(so); 565 566 /* 567 * Insert new socket into hash list. 568 */ 569 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 570 #ifdef INET6 571 if (sc->sc_inc.inc_isipv6) { 572 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 573 } else { 574 inp->inp_vflag &= ~INP_IPV6; 575 inp->inp_vflag |= INP_IPV4; 576 #endif 577 inp->inp_laddr = sc->sc_inc.inc_laddr; 578 #ifdef INET6 579 } 580 #endif 581 inp->inp_lport = sc->sc_inc.inc_lport; 582 if (in_pcbinshash(inp) != 0) { 583 /* 584 * Undo the assignments above if we failed to 585 * put the PCB on the hash lists. 586 */ 587 #ifdef INET6 588 if (sc->sc_inc.inc_isipv6) 589 inp->in6p_laddr = in6addr_any; 590 else 591 #endif 592 inp->inp_laddr.s_addr = INADDR_ANY; 593 inp->inp_lport = 0; 594 goto abort; 595 } 596 #ifdef IPSEC 597 /* copy old policy into new socket's */ 598 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 599 printf("syncache_expand: could not copy policy\n"); 600 #endif 601 #ifdef INET6 602 if (sc->sc_inc.inc_isipv6) { 603 struct inpcb *oinp = sotoinpcb(lso); 604 struct in6_addr laddr6; 605 struct sockaddr_in6 *sin6; 606 /* 607 * Inherit socket options from the listening socket. 608 * Note that in6p_inputopts are not (and should not be) 609 * copied, since it stores previously received options and is 610 * used to detect if each new option is different than the 611 * previous one and hence should be passed to a user. 612 * If we copied in6p_inputopts, a user would not be able to 613 * receive options just after calling the accept system call. 614 */ 615 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 616 if (oinp->in6p_outputopts) 617 inp->in6p_outputopts = 618 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 619 inp->in6p_route = sc->sc_route6; 620 sc->sc_route6.ro_rt = NULL; 621 622 MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6, 623 M_SONAME, M_NOWAIT | M_ZERO); 624 if (sin6 == NULL) 625 goto abort; 626 sin6->sin6_family = AF_INET6; 627 sin6->sin6_len = sizeof(*sin6); 628 sin6->sin6_addr = sc->sc_inc.inc6_faddr; 629 sin6->sin6_port = sc->sc_inc.inc_fport; 630 laddr6 = inp->in6p_laddr; 631 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 632 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 633 if (in6_pcbconnect(inp, (struct sockaddr *)sin6, &thread0)) { 634 inp->in6p_laddr = laddr6; 635 FREE(sin6, M_SONAME); 636 goto abort; 637 } 638 FREE(sin6, M_SONAME); 639 } else 640 #endif 641 { 642 struct in_addr laddr; 643 struct sockaddr_in *sin; 644 645 inp->inp_options = ip_srcroute(); 646 if (inp->inp_options == NULL) { 647 inp->inp_options = sc->sc_ipopts; 648 sc->sc_ipopts = NULL; 649 } 650 inp->inp_route = sc->sc_route; 651 sc->sc_route.ro_rt = NULL; 652 653 MALLOC(sin, struct sockaddr_in *, sizeof *sin, 654 M_SONAME, M_NOWAIT | M_ZERO); 655 if (sin == NULL) 656 goto abort; 657 sin->sin_family = AF_INET; 658 sin->sin_len = sizeof(*sin); 659 sin->sin_addr = sc->sc_inc.inc_faddr; 660 sin->sin_port = sc->sc_inc.inc_fport; 661 bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero)); 662 laddr = inp->inp_laddr; 663 if (inp->inp_laddr.s_addr == INADDR_ANY) 664 inp->inp_laddr = sc->sc_inc.inc_laddr; 665 if (in_pcbconnect(inp, (struct sockaddr *)sin, &thread0)) { 666 inp->inp_laddr = laddr; 667 FREE(sin, M_SONAME); 668 goto abort; 669 } 670 FREE(sin, M_SONAME); 671 } 672 673 tp = intotcpcb(inp); 674 tp->t_state = TCPS_SYN_RECEIVED; 675 tp->iss = sc->sc_iss; 676 tp->irs = sc->sc_irs; 677 tcp_rcvseqinit(tp); 678 tcp_sendseqinit(tp); 679 tp->snd_wl1 = sc->sc_irs; 680 tp->rcv_up = sc->sc_irs + 1; 681 tp->rcv_wnd = sc->sc_wnd; 682 tp->rcv_adv += tp->rcv_wnd; 683 684 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 685 if (sc->sc_flags & SCF_NOOPT) 686 tp->t_flags |= TF_NOOPT; 687 if (sc->sc_flags & SCF_WINSCALE) { 688 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 689 tp->requested_s_scale = sc->sc_requested_s_scale; 690 tp->request_r_scale = sc->sc_request_r_scale; 691 } 692 if (sc->sc_flags & SCF_TIMESTAMP) { 693 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 694 tp->ts_recent = sc->sc_tsrecent; 695 tp->ts_recent_age = ticks; 696 } 697 if (sc->sc_flags & SCF_CC) { 698 /* 699 * Initialization of the tcpcb for transaction; 700 * set SND.WND = SEG.WND, 701 * initialize CCsend and CCrecv. 702 */ 703 tp->t_flags |= TF_REQ_CC|TF_RCVD_CC; 704 tp->cc_send = sc->sc_cc_send; 705 tp->cc_recv = sc->sc_cc_recv; 706 } 707 708 tcp_mss(tp, sc->sc_peer_mss); 709 710 /* 711 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 712 */ 713 if (sc->sc_rxtslot != 0) 714 tp->snd_cwnd = tp->t_maxseg; 715 callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp); 716 717 tcpstat.tcps_accepts++; 718 return (so); 719 720 abort: 721 if (so != NULL) 722 (void) soabort(so); 723 return (NULL); 724 } 725 726 /* 727 * This function gets called when we receive an ACK for a 728 * socket in the LISTEN state. We look up the connection 729 * in the syncache, and if its there, we pull it out of 730 * the cache and turn it into a full-blown connection in 731 * the SYN-RECEIVED state. 732 */ 733 int 734 syncache_expand(inc, th, sop, m) 735 struct in_conninfo *inc; 736 struct tcphdr *th; 737 struct socket **sop; 738 struct mbuf *m; 739 { 740 struct syncache *sc; 741 struct syncache_head *sch; 742 struct socket *so; 743 744 sc = syncache_lookup(inc, &sch); 745 if (sc == NULL) { 746 /* 747 * There is no syncache entry, so see if this ACK is 748 * a returning syncookie. To do this, first: 749 * A. See if this socket has had a syncache entry dropped in 750 * the past. We don't want to accept a bogus syncookie 751 * if we've never received a SYN. 752 * B. check that the syncookie is valid. If it is, then 753 * cobble up a fake syncache entry, and return. 754 */ 755 if (!tcp_syncookies) 756 return (0); 757 sc = syncookie_lookup(inc, th, *sop); 758 if (sc == NULL) 759 return (0); 760 sch = NULL; 761 tcpstat.tcps_sc_recvcookie++; 762 } 763 764 /* 765 * If seg contains an ACK, but not for our SYN/ACK, send a RST. 766 */ 767 if (th->th_ack != sc->sc_iss + 1) 768 return (0); 769 770 so = syncache_socket(sc, *sop, m); 771 if (so == NULL) { 772 #if 0 773 resetandabort: 774 /* XXXjlemon check this - is this correct? */ 775 (void) tcp_respond(NULL, m, m, th, 776 th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK); 777 #endif 778 m_freem(m); /* XXX only needed for above */ 779 tcpstat.tcps_sc_aborted++; 780 } else { 781 sc->sc_flags |= SCF_KEEPROUTE; 782 tcpstat.tcps_sc_completed++; 783 } 784 if (sch == NULL) 785 syncache_free(sc); 786 else 787 syncache_drop(sc, sch); 788 *sop = so; 789 return (1); 790 } 791 792 /* 793 * Given a LISTEN socket and an inbound SYN request, add 794 * this to the syn cache, and send back a segment: 795 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 796 * to the source. 797 * 798 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 799 * Doing so would require that we hold onto the data and deliver it 800 * to the application. However, if we are the target of a SYN-flood 801 * DoS attack, an attacker could send data which would eventually 802 * consume all available buffer space if it were ACKed. By not ACKing 803 * the data, we avoid this DoS scenario. 804 */ 805 int 806 syncache_add(inc, to, th, sop, m) 807 struct in_conninfo *inc; 808 struct tcpopt *to; 809 struct tcphdr *th; 810 struct socket **sop; 811 struct mbuf *m; 812 { 813 struct tcpcb *tp; 814 struct socket *so; 815 struct syncache *sc = NULL; 816 struct syncache_head *sch; 817 struct mbuf *ipopts = NULL; 818 struct rmxp_tao *taop; 819 int i, s, win; 820 821 so = *sop; 822 tp = sototcpcb(so); 823 824 /* 825 * Remember the IP options, if any. 826 */ 827 #ifdef INET6 828 if (!inc->inc_isipv6) 829 #endif 830 ipopts = ip_srcroute(); 831 832 /* 833 * See if we already have an entry for this connection. 834 * If we do, resend the SYN,ACK, and reset the retransmit timer. 835 * 836 * XXX 837 * should the syncache be re-initialized with the contents 838 * of the new SYN here (which may have different options?) 839 */ 840 sc = syncache_lookup(inc, &sch); 841 if (sc != NULL) { 842 tcpstat.tcps_sc_dupsyn++; 843 if (ipopts) { 844 /* 845 * If we were remembering a previous source route, 846 * forget it and use the new one we've been given. 847 */ 848 if (sc->sc_ipopts) 849 (void) m_free(sc->sc_ipopts); 850 sc->sc_ipopts = ipopts; 851 } 852 /* 853 * Update timestamp if present. 854 */ 855 if (sc->sc_flags & SCF_TIMESTAMP) 856 sc->sc_tsrecent = to->to_tsval; 857 /* 858 * PCB may have changed, pick up new values. 859 */ 860 sc->sc_tp = tp; 861 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt; 862 if (syncache_respond(sc, m) == 0) { 863 s = splnet(); 864 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], 865 sc, sc_timerq); 866 SYNCACHE_TIMEOUT(sc, sc->sc_rxtslot); 867 splx(s); 868 tcpstat.tcps_sndacks++; 869 tcpstat.tcps_sndtotal++; 870 } 871 *sop = NULL; 872 return (1); 873 } 874 875 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT); 876 if (sc == NULL) { 877 /* 878 * The zone allocator couldn't provide more entries. 879 * Treat this as if the cache was full; drop the oldest 880 * entry and insert the new one. 881 */ 882 s = splnet(); 883 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) { 884 sc = TAILQ_FIRST(&tcp_syncache.timerq[i]); 885 if (sc != NULL) 886 break; 887 } 888 sc->sc_tp->ts_recent = ticks; 889 syncache_drop(sc, NULL); 890 splx(s); 891 tcpstat.tcps_sc_zonefail++; 892 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT); 893 if (sc == NULL) { 894 if (ipopts) 895 (void) m_free(ipopts); 896 return (0); 897 } 898 } 899 900 /* 901 * Fill in the syncache values. 902 */ 903 bzero(sc, sizeof(*sc)); 904 sc->sc_tp = tp; 905 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt; 906 sc->sc_ipopts = ipopts; 907 sc->sc_inc.inc_fport = inc->inc_fport; 908 sc->sc_inc.inc_lport = inc->inc_lport; 909 #ifdef INET6 910 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; 911 if (inc->inc_isipv6) { 912 sc->sc_inc.inc6_faddr = inc->inc6_faddr; 913 sc->sc_inc.inc6_laddr = inc->inc6_laddr; 914 sc->sc_route6.ro_rt = NULL; 915 } else 916 #endif 917 { 918 sc->sc_inc.inc_faddr = inc->inc_faddr; 919 sc->sc_inc.inc_laddr = inc->inc_laddr; 920 sc->sc_route.ro_rt = NULL; 921 } 922 sc->sc_irs = th->th_seq; 923 if (tcp_syncookies) 924 sc->sc_iss = syncookie_generate(sc); 925 else 926 sc->sc_iss = arc4random(); 927 928 /* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN] */ 929 win = sbspace(&so->so_rcv); 930 win = imax(win, 0); 931 win = imin(win, TCP_MAXWIN); 932 sc->sc_wnd = win; 933 934 sc->sc_flags = 0; 935 sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0; 936 if (tcp_do_rfc1323) { 937 /* 938 * A timestamp received in a SYN makes 939 * it ok to send timestamp requests and replies. 940 */ 941 if (to->to_flags & TOF_TS) { 942 sc->sc_tsrecent = to->to_tsval; 943 sc->sc_flags |= SCF_TIMESTAMP; 944 } 945 if (to->to_flags & TOF_SCALE) { 946 int wscale = 0; 947 948 /* Compute proper scaling value from buffer space */ 949 while (wscale < TCP_MAX_WINSHIFT && 950 (TCP_MAXWIN << wscale) < so->so_rcv.sb_hiwat) 951 wscale++; 952 sc->sc_request_r_scale = wscale; 953 sc->sc_requested_s_scale = to->to_requested_s_scale; 954 sc->sc_flags |= SCF_WINSCALE; 955 } 956 } 957 if (tcp_do_rfc1644) { 958 /* 959 * A CC or CC.new option received in a SYN makes 960 * it ok to send CC in subsequent segments. 961 */ 962 if (to->to_flags & (TOF_CC|TOF_CCNEW)) { 963 sc->sc_cc_recv = to->to_cc; 964 sc->sc_cc_send = CC_INC(tcp_ccgen); 965 sc->sc_flags |= SCF_CC; 966 } 967 } 968 if (tp->t_flags & TF_NOOPT) 969 sc->sc_flags = SCF_NOOPT; 970 971 /* 972 * XXX 973 * We have the option here of not doing TAO (even if the segment 974 * qualifies) and instead fall back to a normal 3WHS via the syncache. 975 * This allows us to apply synflood protection to TAO-qualifying SYNs 976 * also. However, there should be a hueristic to determine when to 977 * do this, and is not present at the moment. 978 */ 979 980 /* 981 * Perform TAO test on incoming CC (SEG.CC) option, if any. 982 * - compare SEG.CC against cached CC from the same host, if any. 983 * - if SEG.CC > chached value, SYN must be new and is accepted 984 * immediately: save new CC in the cache, mark the socket 985 * connected, enter ESTABLISHED state, turn on flag to 986 * send a SYN in the next segment. 987 * A virtual advertised window is set in rcv_adv to 988 * initialize SWS prevention. Then enter normal segment 989 * processing: drop SYN, process data and FIN. 990 * - otherwise do a normal 3-way handshake. 991 */ 992 taop = tcp_gettaocache(&sc->sc_inc); 993 if ((to->to_flags & TOF_CC) != 0) { 994 if (((tp->t_flags & TF_NOPUSH) != 0) && 995 sc->sc_flags & SCF_CC && 996 taop != NULL && taop->tao_cc != 0 && 997 CC_GT(to->to_cc, taop->tao_cc)) { 998 sc->sc_rxtslot = 0; 999 so = syncache_socket(sc, *sop, m); 1000 if (so != NULL) { 1001 sc->sc_flags |= SCF_KEEPROUTE; 1002 taop->tao_cc = to->to_cc; 1003 *sop = so; 1004 } 1005 syncache_free(sc); 1006 return (so != NULL); 1007 } 1008 } else { 1009 /* 1010 * No CC option, but maybe CC.NEW: invalidate cached value. 1011 */ 1012 if (taop != NULL) 1013 taop->tao_cc = 0; 1014 } 1015 /* 1016 * TAO test failed or there was no CC option, 1017 * do a standard 3-way handshake. 1018 */ 1019 if (syncache_respond(sc, m) == 0) { 1020 syncache_insert(sc, sch); 1021 tcpstat.tcps_sndacks++; 1022 tcpstat.tcps_sndtotal++; 1023 } else { 1024 syncache_free(sc); 1025 tcpstat.tcps_sc_dropped++; 1026 } 1027 *sop = NULL; 1028 return (1); 1029 } 1030 1031 static int 1032 syncache_respond(sc, m) 1033 struct syncache *sc; 1034 struct mbuf *m; 1035 { 1036 u_int8_t *optp; 1037 int optlen, error; 1038 u_int16_t tlen, hlen, mssopt; 1039 struct ip *ip = NULL; 1040 struct rtentry *rt; 1041 struct tcphdr *th; 1042 #ifdef INET6 1043 struct ip6_hdr *ip6 = NULL; 1044 #endif 1045 1046 #ifdef INET6 1047 if (sc->sc_inc.inc_isipv6) { 1048 rt = tcp_rtlookup6(&sc->sc_inc); 1049 if (rt != NULL) 1050 mssopt = rt->rt_ifp->if_mtu - 1051 (sizeof(struct ip6_hdr) + sizeof(struct tcphdr)); 1052 else 1053 mssopt = tcp_v6mssdflt; 1054 hlen = sizeof(struct ip6_hdr); 1055 } else 1056 #endif 1057 { 1058 rt = tcp_rtlookup(&sc->sc_inc); 1059 if (rt != NULL) 1060 mssopt = rt->rt_ifp->if_mtu - 1061 (sizeof(struct ip) + sizeof(struct tcphdr)); 1062 else 1063 mssopt = tcp_mssdflt; 1064 hlen = sizeof(struct ip); 1065 } 1066 1067 /* Compute the size of the TCP options. */ 1068 if (sc->sc_flags & SCF_NOOPT) { 1069 optlen = 0; 1070 } else { 1071 optlen = TCPOLEN_MAXSEG + 1072 ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) + 1073 ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0) + 1074 ((sc->sc_flags & SCF_CC) ? TCPOLEN_CC_APPA * 2 : 0); 1075 } 1076 tlen = hlen + sizeof(struct tcphdr) + optlen; 1077 1078 /* 1079 * XXX 1080 * assume that the entire packet will fit in a header mbuf 1081 */ 1082 KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small")); 1083 1084 /* 1085 * XXX shouldn't this reuse the mbuf if possible ? 1086 * Create the IP+TCP header from scratch. 1087 */ 1088 if (m) 1089 m_freem(m); 1090 1091 m = m_gethdr(M_DONTWAIT, MT_HEADER); 1092 if (m == NULL) 1093 return (ENOBUFS); 1094 m->m_data += max_linkhdr; 1095 m->m_len = tlen; 1096 m->m_pkthdr.len = tlen; 1097 m->m_pkthdr.rcvif = NULL; 1098 1099 #ifdef IPSEC 1100 /* use IPsec policy on listening socket to send SYN,ACK */ 1101 if (ipsec_setsocket(m, sc->sc_tp->t_inpcb->inp_socket) != 0) { 1102 m_freem(m); 1103 return (ENOBUFS); 1104 } 1105 #endif 1106 1107 #ifdef INET6 1108 if (sc->sc_inc.inc_isipv6) { 1109 ip6 = mtod(m, struct ip6_hdr *); 1110 ip6->ip6_vfc = IPV6_VERSION; 1111 ip6->ip6_nxt = IPPROTO_TCP; 1112 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1113 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1114 ip6->ip6_plen = htons(tlen - hlen); 1115 /* ip6_hlim is set after checksum */ 1116 /* ip6_flow = ??? */ 1117 1118 th = (struct tcphdr *)(ip6 + 1); 1119 } else 1120 #endif 1121 { 1122 ip = mtod(m, struct ip *); 1123 ip->ip_v = IPVERSION; 1124 ip->ip_hl = sizeof(struct ip) >> 2; 1125 ip->ip_len = tlen; 1126 ip->ip_id = 0; 1127 ip->ip_off = 0; 1128 ip->ip_sum = 0; 1129 ip->ip_p = IPPROTO_TCP; 1130 ip->ip_src = sc->sc_inc.inc_laddr; 1131 ip->ip_dst = sc->sc_inc.inc_faddr; 1132 ip->ip_ttl = sc->sc_tp->t_inpcb->inp_ip_ttl; /* XXX */ 1133 ip->ip_tos = sc->sc_tp->t_inpcb->inp_ip_tos; /* XXX */ 1134 1135 /* 1136 * See if we should do MTU discovery. We do it only if the following 1137 * are true: 1138 * 1) we have a valid route to the destination 1139 * 2) the MTU is not locked (if it is, then discovery has been 1140 * disabled) 1141 */ 1142 if (path_mtu_discovery 1143 && (rt != NULL) 1144 && rt->rt_flags & RTF_UP 1145 && !(rt->rt_rmx.rmx_locks & RTV_MTU)) { 1146 ip->ip_off |= IP_DF; 1147 } 1148 1149 th = (struct tcphdr *)(ip + 1); 1150 } 1151 th->th_sport = sc->sc_inc.inc_lport; 1152 th->th_dport = sc->sc_inc.inc_fport; 1153 1154 th->th_seq = htonl(sc->sc_iss); 1155 th->th_ack = htonl(sc->sc_irs + 1); 1156 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1157 th->th_x2 = 0; 1158 th->th_flags = TH_SYN|TH_ACK; 1159 th->th_win = htons(sc->sc_wnd); 1160 th->th_urp = 0; 1161 1162 /* Tack on the TCP options. */ 1163 if (optlen == 0) 1164 goto no_options; 1165 optp = (u_int8_t *)(th + 1); 1166 *optp++ = TCPOPT_MAXSEG; 1167 *optp++ = TCPOLEN_MAXSEG; 1168 *optp++ = (mssopt >> 8) & 0xff; 1169 *optp++ = mssopt & 0xff; 1170 1171 if (sc->sc_flags & SCF_WINSCALE) { 1172 *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 | 1173 TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 | 1174 sc->sc_request_r_scale); 1175 optp += 4; 1176 } 1177 1178 if (sc->sc_flags & SCF_TIMESTAMP) { 1179 u_int32_t *lp = (u_int32_t *)(optp); 1180 1181 /* Form timestamp option as shown in appendix A of RFC 1323. */ 1182 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 1183 *lp++ = htonl(ticks); 1184 *lp = htonl(sc->sc_tsrecent); 1185 optp += TCPOLEN_TSTAMP_APPA; 1186 } 1187 1188 /* 1189 * Send CC and CC.echo if we received CC from our peer. 1190 */ 1191 if (sc->sc_flags & SCF_CC) { 1192 u_int32_t *lp = (u_int32_t *)(optp); 1193 1194 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CC)); 1195 *lp++ = htonl(sc->sc_cc_send); 1196 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CCECHO)); 1197 *lp = htonl(sc->sc_cc_recv); 1198 optp += TCPOLEN_CC_APPA * 2; 1199 } 1200 no_options: 1201 1202 #ifdef INET6 1203 if (sc->sc_inc.inc_isipv6) { 1204 struct route_in6 *ro6 = &sc->sc_route6; 1205 1206 th->th_sum = 0; 1207 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen); 1208 ip6->ip6_hlim = in6_selecthlim(NULL, 1209 ro6->ro_rt ? ro6->ro_rt->rt_ifp : NULL); 1210 error = ip6_output(m, NULL, ro6, 0, NULL, NULL); 1211 } else 1212 #endif 1213 { 1214 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1215 htons(tlen - hlen + IPPROTO_TCP)); 1216 m->m_pkthdr.csum_flags = CSUM_TCP; 1217 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1218 error = ip_output(m, sc->sc_ipopts, &sc->sc_route, 0, NULL); 1219 } 1220 return (error); 1221 } 1222 1223 /* 1224 * cookie layers: 1225 * 1226 * |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .| 1227 * | peer iss | 1228 * | MD5(laddr,faddr,lport,fport,secret) |. . . . . . .| 1229 * | 0 |(A)| | 1230 * (A): peer mss index 1231 */ 1232 1233 /* 1234 * The values below are chosen to minimize the size of the tcp_secret 1235 * table, as well as providing roughly a 4 second lifetime for the cookie. 1236 */ 1237 1238 #define SYNCOOKIE_HASHSHIFT 2 /* log2(# of 32bit words from hash) */ 1239 #define SYNCOOKIE_WNDBITS 7 /* exposed bits for window indexing */ 1240 #define SYNCOOKIE_TIMESHIFT 5 /* scale ticks to window time units */ 1241 1242 #define SYNCOOKIE_HASHMASK ((1 << SYNCOOKIE_HASHSHIFT) - 1) 1243 #define SYNCOOKIE_WNDMASK ((1 << SYNCOOKIE_WNDBITS) - 1) 1244 #define SYNCOOKIE_NSECRETS (1 << (SYNCOOKIE_WNDBITS - SYNCOOKIE_HASHSHIFT)) 1245 #define SYNCOOKIE_TIMEOUT \ 1246 (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT)) 1247 #define SYNCOOKIE_DATAMASK ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK) 1248 1249 static struct { 1250 u_int32_t ts_secbits; 1251 u_int ts_expire; 1252 } tcp_secret[SYNCOOKIE_NSECRETS]; 1253 1254 static int tcp_msstab[] = { 0, 536, 1460, 8960 }; 1255 1256 static MD5_CTX syn_ctx; 1257 1258 #define MD5Add(v) MD5Update(&syn_ctx, (u_char *)&v, sizeof(v)) 1259 1260 /* 1261 * Consider the problem of a recreated (and retransmitted) cookie. If the 1262 * original SYN was accepted, the connection is established. The second 1263 * SYN is inflight, and if it arrives with an ISN that falls within the 1264 * receive window, the connection is killed. 1265 * 1266 * However, since cookies have other problems, this may not be worth 1267 * worrying about. 1268 */ 1269 1270 static u_int32_t 1271 syncookie_generate(struct syncache *sc) 1272 { 1273 u_int32_t md5_buffer[4]; 1274 u_int32_t data; 1275 int wnd, idx; 1276 1277 wnd = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK; 1278 idx = wnd >> SYNCOOKIE_HASHSHIFT; 1279 if (tcp_secret[idx].ts_expire < ticks) { 1280 tcp_secret[idx].ts_secbits = arc4random(); 1281 tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT; 1282 } 1283 for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--) 1284 if (tcp_msstab[data] <= sc->sc_peer_mss) 1285 break; 1286 data = (data << SYNCOOKIE_WNDBITS) | wnd; 1287 data ^= sc->sc_irs; /* peer's iss */ 1288 MD5Init(&syn_ctx); 1289 #ifdef INET6 1290 if (sc->sc_inc.inc_isipv6) { 1291 MD5Add(sc->sc_inc.inc6_laddr); 1292 MD5Add(sc->sc_inc.inc6_faddr); 1293 } else 1294 #endif 1295 { 1296 MD5Add(sc->sc_inc.inc_laddr); 1297 MD5Add(sc->sc_inc.inc_faddr); 1298 } 1299 MD5Add(sc->sc_inc.inc_lport); 1300 MD5Add(sc->sc_inc.inc_fport); 1301 MD5Add(tcp_secret[idx].ts_secbits); 1302 MD5Final((u_char *)&md5_buffer, &syn_ctx); 1303 data ^= (md5_buffer[wnd & SYNCOOKIE_HASHMASK] & ~SYNCOOKIE_WNDMASK); 1304 return (data); 1305 } 1306 1307 static struct syncache * 1308 syncookie_lookup(inc, th, so) 1309 struct in_conninfo *inc; 1310 struct tcphdr *th; 1311 struct socket *so; 1312 { 1313 u_int32_t md5_buffer[4]; 1314 struct syncache *sc; 1315 u_int32_t data; 1316 int wnd, idx; 1317 1318 data = (th->th_ack - 1) ^ (th->th_seq - 1); /* remove ISS */ 1319 wnd = data & SYNCOOKIE_WNDMASK; 1320 idx = wnd >> SYNCOOKIE_HASHSHIFT; 1321 if (tcp_secret[idx].ts_expire < ticks || 1322 sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks) 1323 return (NULL); 1324 MD5Init(&syn_ctx); 1325 #ifdef INET6 1326 if (inc->inc_isipv6) { 1327 MD5Add(inc->inc6_laddr); 1328 MD5Add(inc->inc6_faddr); 1329 } else 1330 #endif 1331 { 1332 MD5Add(inc->inc_laddr); 1333 MD5Add(inc->inc_faddr); 1334 } 1335 MD5Add(inc->inc_lport); 1336 MD5Add(inc->inc_fport); 1337 MD5Add(tcp_secret[idx].ts_secbits); 1338 MD5Final((u_char *)&md5_buffer, &syn_ctx); 1339 data ^= md5_buffer[wnd & SYNCOOKIE_HASHMASK]; 1340 if ((data & ~SYNCOOKIE_DATAMASK) != 0) 1341 return (NULL); 1342 data = data >> SYNCOOKIE_WNDBITS; 1343 1344 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT); 1345 if (sc == NULL) 1346 return (NULL); 1347 /* 1348 * Fill in the syncache values. 1349 * XXX duplicate code from syncache_add 1350 */ 1351 sc->sc_ipopts = NULL; 1352 sc->sc_inc.inc_fport = inc->inc_fport; 1353 sc->sc_inc.inc_lport = inc->inc_lport; 1354 #ifdef INET6 1355 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; 1356 if (inc->inc_isipv6) { 1357 sc->sc_inc.inc6_faddr = inc->inc6_faddr; 1358 sc->sc_inc.inc6_laddr = inc->inc6_laddr; 1359 sc->sc_route6.ro_rt = NULL; 1360 } else 1361 #endif 1362 { 1363 sc->sc_inc.inc_faddr = inc->inc_faddr; 1364 sc->sc_inc.inc_laddr = inc->inc_laddr; 1365 sc->sc_route.ro_rt = NULL; 1366 } 1367 sc->sc_irs = th->th_seq - 1; 1368 sc->sc_iss = th->th_ack - 1; 1369 wnd = sbspace(&so->so_rcv); 1370 wnd = imax(wnd, 0); 1371 wnd = imin(wnd, TCP_MAXWIN); 1372 sc->sc_wnd = wnd; 1373 sc->sc_flags = 0; 1374 sc->sc_rxtslot = 0; 1375 sc->sc_peer_mss = tcp_msstab[data]; 1376 return (sc); 1377 } 1378