1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. The name of the author may not be used to endorse or promote 16 * products derived from this software without specific prior written 17 * permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 */ 31 32 /* 33 * ip_fastforward gets its speed from processing the forwarded packet to 34 * completion (if_output on the other side) without any queues or netisr's. 35 * The receiving interface DMAs the packet into memory, the upper half of 36 * driver calls ip_fastforward, we do our routing table lookup and directly 37 * send it off to the outgoing interface, which DMAs the packet to the 38 * network card. The only part of the packet we touch with the CPU is the 39 * IP header (unless there are complex firewall rules touching other parts 40 * of the packet, but that is up to you). We are essentially limited by bus 41 * bandwidth and how fast the network card/driver can set up receives and 42 * transmits. 43 * 44 * We handle basic errors, IP header errors, checksum errors, 45 * destination unreachable, fragmentation and fragmentation needed and 46 * report them via ICMP to the sender. 47 * 48 * Else if something is not pure IPv4 unicast forwarding we fall back to 49 * the normal ip_input processing path. We should only be called from 50 * interfaces connected to the outside world. 51 * 52 * Firewalling is fully supported including divert, ipfw fwd and ipfilter 53 * ipnat and address rewrite. 54 * 55 * IPSEC is not supported if this host is a tunnel broker. IPSEC is 56 * supported for connections to/from local host. 57 * 58 * We try to do the least expensive (in CPU ops) checks and operations 59 * first to catch junk with as little overhead as possible. 60 * 61 * We take full advantage of hardware support for IP checksum and 62 * fragmentation offloading. 63 */ 64 65 /* 66 * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which 67 * is being followed here. 68 */ 69 70 #include <sys/cdefs.h> 71 __FBSDID("$FreeBSD$"); 72 73 #include "opt_ipstealth.h" 74 75 #include <sys/param.h> 76 #include <sys/systm.h> 77 #include <sys/kernel.h> 78 #include <sys/malloc.h> 79 #include <sys/mbuf.h> 80 #include <sys/protosw.h> 81 #include <sys/sdt.h> 82 #include <sys/socket.h> 83 #include <sys/sysctl.h> 84 85 #include <net/if.h> 86 #include <net/if_types.h> 87 #include <net/if_var.h> 88 #include <net/if_dl.h> 89 #include <net/pfil.h> 90 #include <net/route.h> 91 #include <net/route/nhop.h> 92 #include <net/vnet.h> 93 94 #include <netinet/in.h> 95 #include <netinet/in_fib.h> 96 #include <netinet/in_kdtrace.h> 97 #include <netinet/in_systm.h> 98 #include <netinet/in_var.h> 99 #include <netinet/ip.h> 100 #include <netinet/ip_var.h> 101 #include <netinet/ip_icmp.h> 102 #include <netinet/ip_options.h> 103 104 #include <machine/in_cksum.h> 105 106 #define V_ipsendredirects VNET(ipsendredirects) 107 108 static struct mbuf * 109 ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, u_short ip_len, 110 struct in_addr *osrc, struct in_addr *newgw) 111 { 112 struct in_ifaddr *nh_ia; 113 struct mbuf *mcopy; 114 115 KASSERT(nh != NULL, ("%s: m %p nh is NULL\n", __func__, m)); 116 117 /* 118 * Only send a redirect if: 119 * - Redirects are not disabled (must be checked by caller), 120 * - We have not applied NAT (must be checked by caller as possible), 121 * - Neither a MCAST or BCAST packet (must be checked by caller) 122 * [RFC1009 Appendix A.2]. 123 * - The packet does not do IP source routing or having any other 124 * IP options (this case was handled already by ip_input() calling 125 * ip_dooptions() [RFC792, p13], 126 * - The packet is being forwarded out the same physical interface 127 * that it was received from [RFC1812, 5.2.7.2]. 128 */ 129 130 /* 131 * - The forwarding route was not created by a redirect 132 * [RFC1812, 5.2.7.2], or 133 * if it was to follow a default route (see below). 134 * - The next-hop is reachable by us [RFC1009 Appendix A.2]. 135 */ 136 if ((nh->nh_flags & (NHF_DEFAULT | NHF_REDIRECT | 137 NHF_BLACKHOLE | NHF_REJECT)) != 0) 138 return (NULL); 139 140 /* Get the new gateway. */ 141 if ((nh->nh_flags & NHF_GATEWAY) == 0 || nh->gw_sa.sa_family != AF_INET) 142 return (NULL); 143 newgw->s_addr = nh->gw4_sa.sin_addr.s_addr; 144 145 /* 146 * - The resulting forwarding destination is not "This host on this 147 * network" [RFC1122, Section 3.2.1.3] (default route check above). 148 */ 149 if (newgw->s_addr == 0) 150 return (NULL); 151 152 /* 153 * - We know how to reach the sender and the source address is 154 * directly connected to us [RFC792, p13]. 155 * + The new gateway address and the source address are on the same 156 * subnet [RFC1009 Appendix A.2, RFC1122 3.2.2.2, RFC1812, 5.2.7.2]. 157 * NB: if you think multiple logical subnets on the same wire should 158 * receive redirects read [RFC1812, APPENDIX C (14->15)]. 159 */ 160 nh_ia = (struct in_ifaddr *)nh->nh_ifa; 161 if ((ntohl(osrc->s_addr) & nh_ia->ia_subnetmask) != nh_ia->ia_subnet) 162 return (NULL); 163 164 /* Prepare for sending the redirect. */ 165 166 /* 167 * Make a copy of as much as we need of the packet as the original 168 * one will be forwarded but we need (a portion) for icmp_error(). 169 */ 170 mcopy = m_gethdr(M_NOWAIT, m->m_type); 171 if (mcopy == NULL) 172 return (NULL); 173 174 if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) { 175 /* 176 * It's probably ok if the pkthdr dup fails (because 177 * the deep copy of the tag chain failed), but for now 178 * be conservative and just discard the copy since 179 * code below may some day want the tags. 180 */ 181 m_free(mcopy); 182 return (NULL); 183 } 184 mcopy->m_len = min(ip_len, M_TRAILINGSPACE(mcopy)); 185 mcopy->m_pkthdr.len = mcopy->m_len; 186 m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t)); 187 188 return (mcopy); 189 } 190 191 192 static int 193 ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m) 194 { 195 struct nhop_object *nh; 196 197 nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE, 198 m->m_pkthdr.flowid); 199 if (nh == NULL) { 200 IPSTAT_INC(ips_noroute); 201 IPSTAT_INC(ips_cantforward); 202 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 203 return (EHOSTUNREACH); 204 } 205 /* 206 * Drop blackholed traffic and directed broadcasts. 207 */ 208 if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) { 209 IPSTAT_INC(ips_cantforward); 210 m_freem(m); 211 return (EHOSTUNREACH); 212 } 213 214 if (nh->nh_flags & NHF_REJECT) { 215 IPSTAT_INC(ips_cantforward); 216 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 217 return (EHOSTUNREACH); 218 } 219 220 *pnh = nh; 221 222 return (0); 223 } 224 225 /* 226 * Try to forward a packet based on the destination address. 227 * This is a fast path optimized for the plain forwarding case. 228 * If the packet is handled (and consumed) here then we return NULL; 229 * otherwise mbuf is returned and the packet should be delivered 230 * to ip_input for full processing. 231 */ 232 struct mbuf * 233 ip_tryforward(struct mbuf *m) 234 { 235 struct ip *ip; 236 struct mbuf *m0 = NULL; 237 struct nhop_object *nh = NULL; 238 struct route ro; 239 struct sockaddr_in *dst; 240 const struct sockaddr *gw; 241 struct in_addr dest, odest, rtdest, osrc; 242 uint16_t ip_len, ip_off; 243 int error = 0; 244 struct m_tag *fwd_tag = NULL; 245 struct mbuf *mcopy = NULL; 246 struct in_addr redest; 247 /* 248 * Are we active and forwarding packets? 249 */ 250 251 M_ASSERTVALID(m); 252 M_ASSERTPKTHDR(m); 253 254 /* 255 * Only IP packets without options 256 */ 257 ip = mtod(m, struct ip *); 258 259 if (ip->ip_hl != (sizeof(struct ip) >> 2)) { 260 if (V_ip_doopts == 1) 261 return m; 262 else if (V_ip_doopts == 2) { 263 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 264 0, 0); 265 return NULL; /* mbuf already free'd */ 266 } 267 /* else ignore IP options and continue */ 268 } 269 270 /* 271 * Only unicast IP, not from loopback, no L2 or IP broadcast, 272 * no multicast, no INADDR_ANY 273 * 274 * XXX: Probably some of these checks could be direct drop 275 * conditions. However it is not clear whether there are some 276 * hacks or obscure behaviours which make it necessary to 277 * let ip_input handle it. We play safe here and let ip_input 278 * deal with it until it is proven that we can directly drop it. 279 */ 280 if ((m->m_flags & (M_BCAST|M_MCAST)) || 281 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || 282 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST || 283 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST || 284 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 285 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 286 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) || 287 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) || 288 ip->ip_src.s_addr == INADDR_ANY || 289 ip->ip_dst.s_addr == INADDR_ANY ) 290 return m; 291 292 /* 293 * Is it for a local address on this host? 294 */ 295 if (in_localip(ip->ip_dst)) 296 return m; 297 298 IPSTAT_INC(ips_total); 299 300 /* 301 * Step 3: incoming packet firewall processing 302 */ 303 304 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; 305 osrc.s_addr = ip->ip_src.s_addr; 306 307 /* 308 * Run through list of ipfilter hooks for input packets 309 */ 310 if (!PFIL_HOOKED_IN(V_inet_pfil_head)) 311 goto passin; 312 313 if (pfil_mbuf_in(V_inet_pfil_head, &m, m->m_pkthdr.rcvif, 314 NULL) != PFIL_PASS) 315 goto drop; 316 317 M_ASSERTVALID(m); 318 M_ASSERTPKTHDR(m); 319 320 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ 321 dest.s_addr = ip->ip_dst.s_addr; 322 323 /* 324 * Destination address changed? 325 */ 326 if (odest.s_addr != dest.s_addr) { 327 /* 328 * Is it now for a local address on this host? 329 */ 330 if (in_localip(dest)) 331 goto forwardlocal; 332 /* 333 * Go on with new destination address 334 */ 335 } 336 337 if (m->m_flags & M_FASTFWD_OURS) { 338 /* 339 * ipfw changed it for a local address on this host. 340 */ 341 goto forwardlocal; 342 } 343 344 passin: 345 /* 346 * Step 4: decrement TTL and look up route 347 */ 348 349 /* 350 * Check TTL 351 */ 352 #ifdef IPSTEALTH 353 if (!V_ipstealth) { 354 #endif 355 if (ip->ip_ttl <= IPTTLDEC) { 356 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0); 357 return NULL; /* mbuf already free'd */ 358 } 359 360 /* 361 * Decrement the TTL and incrementally change the IP header checksum. 362 * Don't bother doing this with hw checksum offloading, it's faster 363 * doing it right here. 364 */ 365 ip->ip_ttl -= IPTTLDEC; 366 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) 367 ip->ip_sum -= ~htons(IPTTLDEC << 8); 368 else 369 ip->ip_sum += htons(IPTTLDEC << 8); 370 #ifdef IPSTEALTH 371 } 372 #endif 373 374 /* 375 * Next hop forced by pfil(9) hook? 376 */ 377 if ((m->m_flags & M_IP_NEXTHOP) && 378 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) { 379 /* 380 * Now we will find route to forced destination. 381 */ 382 dest.s_addr = ((struct sockaddr_in *) 383 (fwd_tag + 1))->sin_addr.s_addr; 384 m_tag_delete(m, fwd_tag); 385 m->m_flags &= ~M_IP_NEXTHOP; 386 } 387 388 /* 389 * Find route to destination. 390 */ 391 if (ip_findroute(&nh, dest, m) != 0) 392 return (NULL); /* icmp unreach already sent */ 393 394 /* 395 * Avoid second route lookup by caching destination. 396 */ 397 rtdest.s_addr = dest.s_addr; 398 399 /* 400 * Step 5: outgoing firewall packet processing 401 */ 402 if (!PFIL_HOOKED_OUT(V_inet_pfil_head)) 403 goto passout; 404 405 if (pfil_mbuf_out(V_inet_pfil_head, &m, nh->nh_ifp, 406 NULL) != PFIL_PASS) 407 goto drop; 408 409 M_ASSERTVALID(m); 410 M_ASSERTPKTHDR(m); 411 412 ip = mtod(m, struct ip *); 413 dest.s_addr = ip->ip_dst.s_addr; 414 415 /* 416 * Destination address changed? 417 */ 418 if (m->m_flags & M_IP_NEXTHOP) 419 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); 420 else 421 fwd_tag = NULL; 422 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { 423 /* 424 * Is it now for a local address on this host? 425 */ 426 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) { 427 forwardlocal: 428 /* 429 * Return packet for processing by ip_input(). 430 */ 431 m->m_flags |= M_FASTFWD_OURS; 432 return (m); 433 } 434 /* 435 * Redo route lookup with new destination address 436 */ 437 if (fwd_tag) { 438 dest.s_addr = ((struct sockaddr_in *) 439 (fwd_tag + 1))->sin_addr.s_addr; 440 m_tag_delete(m, fwd_tag); 441 m->m_flags &= ~M_IP_NEXTHOP; 442 } 443 if (dest.s_addr != rtdest.s_addr && 444 ip_findroute(&nh, dest, m) != 0) 445 return (NULL); /* icmp unreach already sent */ 446 } 447 448 passout: 449 /* 450 * Step 6: send off the packet 451 */ 452 ip_len = ntohs(ip->ip_len); 453 ip_off = ntohs(ip->ip_off); 454 455 bzero(&ro, sizeof(ro)); 456 dst = (struct sockaddr_in *)&ro.ro_dst; 457 dst->sin_family = AF_INET; 458 dst->sin_len = sizeof(*dst); 459 dst->sin_addr = dest; 460 if (nh->nh_flags & NHF_GATEWAY) { 461 gw = &nh->gw_sa; 462 ro.ro_flags |= RT_HAS_GW; 463 } else 464 gw = (const struct sockaddr *)dst; 465 466 /* Handle redirect case. */ 467 redest.s_addr = 0; 468 if (V_ipsendredirects && osrc.s_addr == ip->ip_src.s_addr && 469 nh->nh_ifp == m->m_pkthdr.rcvif) 470 mcopy = ip_redir_alloc(m, nh, ip_len, &osrc, &redest); 471 472 /* 473 * Check if packet fits MTU or if hardware will fragment for us 474 */ 475 if (ip_len <= nh->nh_mtu) { 476 /* 477 * Avoid confusing lower layers. 478 */ 479 m_clrprotoflags(m); 480 /* 481 * Send off the packet via outgoing interface 482 */ 483 IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL); 484 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro); 485 } else { 486 /* 487 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery 488 */ 489 if (ip_off & IP_DF) { 490 IPSTAT_INC(ips_cantfrag); 491 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 492 0, nh->nh_mtu); 493 goto consumed; 494 } else { 495 /* 496 * We have to fragment the packet 497 */ 498 m->m_pkthdr.csum_flags |= CSUM_IP; 499 if (ip_fragment(ip, &m, nh->nh_mtu, 500 nh->nh_ifp->if_hwassist) != 0) 501 goto drop; 502 KASSERT(m != NULL, ("null mbuf and no error")); 503 /* 504 * Send off the fragments via outgoing interface 505 */ 506 error = 0; 507 do { 508 m0 = m->m_nextpkt; 509 m->m_nextpkt = NULL; 510 /* 511 * Avoid confusing lower layers. 512 */ 513 m_clrprotoflags(m); 514 515 IP_PROBE(send, NULL, NULL, 516 mtod(m, struct ip *), nh->nh_ifp, 517 mtod(m, struct ip *), NULL); 518 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, 519 gw, &ro); 520 if (error) 521 break; 522 } while ((m = m0) != NULL); 523 if (error) { 524 /* Reclaim remaining fragments */ 525 for (m = m0; m; m = m0) { 526 m0 = m->m_nextpkt; 527 m_freem(m); 528 } 529 } else 530 IPSTAT_INC(ips_fragmented); 531 } 532 } 533 534 if (error != 0) 535 IPSTAT_INC(ips_odropped); 536 else { 537 IPSTAT_INC(ips_forward); 538 IPSTAT_INC(ips_fastforward); 539 } 540 541 /* Send required redirect */ 542 if (mcopy != NULL) { 543 icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0); 544 mcopy = NULL; /* Was consumed by callee. */ 545 } 546 547 consumed: 548 if (mcopy != NULL) 549 m_freem(mcopy); 550 return NULL; 551 drop: 552 if (m) 553 m_freem(m); 554 return NULL; 555 } 556