1 /*- 2 * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. The name of the author may not be used to endorse or promote 14 * products derived from this software without specific prior written 15 * permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 */ 29 30 /* 31 * ip_fastforward gets its speed from processing the forwarded packet to 32 * completion (if_output on the other side) without any queues or netisr's. 33 * The receiving interface DMAs the packet into memory, the upper half of 34 * driver calls ip_fastforward, we do our routing table lookup and directly 35 * send it off to the outgoing interface, which DMAs the packet to the 36 * network card. The only part of the packet we touch with the CPU is the 37 * IP header (unless there are complex firewall rules touching other parts 38 * of the packet, but that is up to you). We are essentially limited by bus 39 * bandwidth and how fast the network card/driver can set up receives and 40 * transmits. 41 * 42 * We handle basic errors, IP header errors, checksum errors, 43 * destination unreachable, fragmentation and fragmentation needed and 44 * report them via ICMP to the sender. 45 * 46 * Else if something is not pure IPv4 unicast forwarding we fall back to 47 * the normal ip_input processing path. We should only be called from 48 * interfaces connected to the outside world. 49 * 50 * Firewalling is fully supported including divert, ipfw fwd and ipfilter 51 * ipnat and address rewrite. 52 * 53 * IPSEC is not supported if this host is a tunnel broker. IPSEC is 54 * supported for connections to/from local host. 55 * 56 * We try to do the least expensive (in CPU ops) checks and operations 57 * first to catch junk with as little overhead as possible. 58 * 59 * We take full advantage of hardware support for IP checksum and 60 * fragmentation offloading. 61 * 62 * We don't do ICMP redirect in the fast forwarding path. I have had my own 63 * cases where two core routers with Zebra routing suite would send millions 64 * ICMP redirects to connected hosts if the destination router was not the 65 * default gateway. In one case it was filling the routing table of a host 66 * with approximately 300.000 cloned redirect entries until it ran out of 67 * kernel memory. However the networking code proved very robust and it didn't 68 * crash or fail in other ways. 69 */ 70 71 /* 72 * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which 73 * is being followed here. 74 */ 75 76 #include <sys/cdefs.h> 77 __FBSDID("$FreeBSD$"); 78 79 #include "opt_ipfw.h" 80 #include "opt_ipstealth.h" 81 82 #include <sys/param.h> 83 #include <sys/systm.h> 84 #include <sys/kernel.h> 85 #include <sys/malloc.h> 86 #include <sys/mbuf.h> 87 #include <sys/protosw.h> 88 #include <sys/socket.h> 89 #include <sys/sysctl.h> 90 91 #include <net/pfil.h> 92 #include <net/if.h> 93 #include <net/if_types.h> 94 #include <net/if_var.h> 95 #include <net/if_dl.h> 96 #include <net/route.h> 97 #include <net/vnet.h> 98 99 #include <netinet/in.h> 100 #include <netinet/in_systm.h> 101 #include <netinet/in_var.h> 102 #include <netinet/ip.h> 103 #include <netinet/ip_var.h> 104 #include <netinet/ip_icmp.h> 105 #include <netinet/ip_options.h> 106 107 #include <machine/in_cksum.h> 108 109 static VNET_DEFINE(int, ipfastforward_active); 110 #define V_ipfastforward_active VNET(ipfastforward_active) 111 112 SYSCTL_VNET_INT(_net_inet_ip, OID_AUTO, fastforwarding, CTLFLAG_RW, 113 &VNET_NAME(ipfastforward_active), 0, "Enable fast IP forwarding"); 114 115 static struct sockaddr_in * 116 ip_findroute(struct route *ro, struct in_addr dest, struct mbuf *m) 117 { 118 struct sockaddr_in *dst; 119 struct rtentry *rt; 120 121 /* 122 * Find route to destination. 123 */ 124 bzero(ro, sizeof(*ro)); 125 dst = (struct sockaddr_in *)&ro->ro_dst; 126 dst->sin_family = AF_INET; 127 dst->sin_len = sizeof(*dst); 128 dst->sin_addr.s_addr = dest.s_addr; 129 in_rtalloc_ign(ro, 0, M_GETFIB(m)); 130 131 /* 132 * Route there and interface still up? 133 */ 134 rt = ro->ro_rt; 135 if (rt && (rt->rt_flags & RTF_UP) && 136 (rt->rt_ifp->if_flags & IFF_UP) && 137 (rt->rt_ifp->if_drv_flags & IFF_DRV_RUNNING)) { 138 if (rt->rt_flags & RTF_GATEWAY) 139 dst = (struct sockaddr_in *)rt->rt_gateway; 140 } else { 141 IPSTAT_INC(ips_noroute); 142 IPSTAT_INC(ips_cantforward); 143 if (rt) 144 RTFREE(rt); 145 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 146 return NULL; 147 } 148 return dst; 149 } 150 151 /* 152 * Try to forward a packet based on the destination address. 153 * This is a fast path optimized for the plain forwarding case. 154 * If the packet is handled (and consumed) here then we return NULL; 155 * otherwise mbuf is returned and the packet should be delivered 156 * to ip_input for full processing. 157 */ 158 struct mbuf * 159 ip_fastforward(struct mbuf *m) 160 { 161 struct ip *ip; 162 struct mbuf *m0 = NULL; 163 struct route ro; 164 struct sockaddr_in *dst = NULL; 165 struct ifnet *ifp; 166 struct in_addr odest, dest; 167 u_short sum, ip_len; 168 int error = 0; 169 int hlen, mtu; 170 #ifdef IPFIREWALL_FORWARD 171 struct m_tag *fwd_tag; 172 #endif 173 174 /* 175 * Are we active and forwarding packets? 176 */ 177 if (!V_ipfastforward_active || !V_ipforwarding) 178 return m; 179 180 M_ASSERTVALID(m); 181 M_ASSERTPKTHDR(m); 182 183 bzero(&ro, sizeof(ro)); 184 185 /* 186 * Step 1: check for packet drop conditions (and sanity checks) 187 */ 188 189 /* 190 * Is entire packet big enough? 191 */ 192 if (m->m_pkthdr.len < sizeof(struct ip)) { 193 IPSTAT_INC(ips_tooshort); 194 goto drop; 195 } 196 197 /* 198 * Is first mbuf large enough for ip header and is header present? 199 */ 200 if (m->m_len < sizeof (struct ip) && 201 (m = m_pullup(m, sizeof (struct ip))) == NULL) { 202 IPSTAT_INC(ips_toosmall); 203 return NULL; /* mbuf already free'd */ 204 } 205 206 ip = mtod(m, struct ip *); 207 208 /* 209 * Is it IPv4? 210 */ 211 if (ip->ip_v != IPVERSION) { 212 IPSTAT_INC(ips_badvers); 213 goto drop; 214 } 215 216 /* 217 * Is IP header length correct and is it in first mbuf? 218 */ 219 hlen = ip->ip_hl << 2; 220 if (hlen < sizeof(struct ip)) { /* minimum header length */ 221 IPSTAT_INC(ips_badhlen); 222 goto drop; 223 } 224 if (hlen > m->m_len) { 225 if ((m = m_pullup(m, hlen)) == NULL) { 226 IPSTAT_INC(ips_badhlen); 227 return NULL; /* mbuf already free'd */ 228 } 229 ip = mtod(m, struct ip *); 230 } 231 232 /* 233 * Checksum correct? 234 */ 235 if (m->m_pkthdr.csum_flags & CSUM_IP_CHECKED) 236 sum = !(m->m_pkthdr.csum_flags & CSUM_IP_VALID); 237 else { 238 if (hlen == sizeof(struct ip)) 239 sum = in_cksum_hdr(ip); 240 else 241 sum = in_cksum(m, hlen); 242 } 243 if (sum) { 244 IPSTAT_INC(ips_badsum); 245 goto drop; 246 } 247 248 /* 249 * Remember that we have checked the IP header and found it valid. 250 */ 251 m->m_pkthdr.csum_flags |= (CSUM_IP_CHECKED | CSUM_IP_VALID); 252 253 ip_len = ntohs(ip->ip_len); 254 255 /* 256 * Is IP length longer than packet we have got? 257 */ 258 if (m->m_pkthdr.len < ip_len) { 259 IPSTAT_INC(ips_tooshort); 260 goto drop; 261 } 262 263 /* 264 * Is packet longer than IP header tells us? If yes, truncate packet. 265 */ 266 if (m->m_pkthdr.len > ip_len) { 267 if (m->m_len == m->m_pkthdr.len) { 268 m->m_len = ip_len; 269 m->m_pkthdr.len = ip_len; 270 } else 271 m_adj(m, ip_len - m->m_pkthdr.len); 272 } 273 274 /* 275 * Is packet from or to 127/8? 276 */ 277 if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET || 278 (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) { 279 IPSTAT_INC(ips_badaddr); 280 goto drop; 281 } 282 283 #ifdef ALTQ 284 /* 285 * Is packet dropped by traffic conditioner? 286 */ 287 if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0) 288 goto drop; 289 #endif 290 291 /* 292 * Step 2: fallback conditions to normal ip_input path processing 293 */ 294 295 /* 296 * Only IP packets without options 297 */ 298 if (ip->ip_hl != (sizeof(struct ip) >> 2)) { 299 if (ip_doopts == 1) 300 return m; 301 else if (ip_doopts == 2) { 302 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 303 0, 0); 304 return NULL; /* mbuf already free'd */ 305 } 306 /* else ignore IP options and continue */ 307 } 308 309 /* 310 * Only unicast IP, not from loopback, no L2 or IP broadcast, 311 * no multicast, no INADDR_ANY 312 * 313 * XXX: Probably some of these checks could be direct drop 314 * conditions. However it is not clear whether there are some 315 * hacks or obscure behaviours which make it neccessary to 316 * let ip_input handle it. We play safe here and let ip_input 317 * deal with it until it is proven that we can directly drop it. 318 */ 319 if ((m->m_flags & (M_BCAST|M_MCAST)) || 320 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || 321 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST || 322 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST || 323 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 324 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 325 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) || 326 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) || 327 ip->ip_src.s_addr == INADDR_ANY || 328 ip->ip_dst.s_addr == INADDR_ANY ) 329 return m; 330 331 /* 332 * Is it for a local address on this host? 333 */ 334 if (in_localip(ip->ip_dst)) 335 return m; 336 337 IPSTAT_INC(ips_total); 338 339 /* 340 * Step 3: incoming packet firewall processing 341 */ 342 343 /* 344 * Convert to host representation 345 */ 346 ip->ip_len = ntohs(ip->ip_len); 347 ip->ip_off = ntohs(ip->ip_off); 348 349 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; 350 351 /* 352 * Run through list of ipfilter hooks for input packets 353 */ 354 if (!PFIL_HOOKED(&V_inet_pfil_hook)) 355 goto passin; 356 357 if (pfil_run_hooks( 358 &V_inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN, NULL) || 359 m == NULL) 360 goto drop; 361 362 M_ASSERTVALID(m); 363 M_ASSERTPKTHDR(m); 364 365 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ 366 dest.s_addr = ip->ip_dst.s_addr; 367 368 /* 369 * Destination address changed? 370 */ 371 if (odest.s_addr != dest.s_addr) { 372 /* 373 * Is it now for a local address on this host? 374 */ 375 if (in_localip(dest)) 376 goto forwardlocal; 377 /* 378 * Go on with new destination address 379 */ 380 } 381 #ifdef IPFIREWALL_FORWARD 382 if (m->m_flags & M_FASTFWD_OURS) { 383 /* 384 * ipfw changed it for a local address on this host. 385 */ 386 goto forwardlocal; 387 } 388 #endif /* IPFIREWALL_FORWARD */ 389 390 passin: 391 /* 392 * Step 4: decrement TTL and look up route 393 */ 394 395 /* 396 * Check TTL 397 */ 398 #ifdef IPSTEALTH 399 if (!V_ipstealth) { 400 #endif 401 if (ip->ip_ttl <= IPTTLDEC) { 402 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0); 403 return NULL; /* mbuf already free'd */ 404 } 405 406 /* 407 * Decrement the TTL and incrementally change the IP header checksum. 408 * Don't bother doing this with hw checksum offloading, it's faster 409 * doing it right here. 410 */ 411 ip->ip_ttl -= IPTTLDEC; 412 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) 413 ip->ip_sum -= ~htons(IPTTLDEC << 8); 414 else 415 ip->ip_sum += htons(IPTTLDEC << 8); 416 #ifdef IPSTEALTH 417 } 418 #endif 419 420 /* 421 * Find route to destination. 422 */ 423 if ((dst = ip_findroute(&ro, dest, m)) == NULL) 424 return NULL; /* icmp unreach already sent */ 425 ifp = ro.ro_rt->rt_ifp; 426 427 /* 428 * Immediately drop blackholed traffic, and directed broadcasts 429 * for either the all-ones or all-zero subnet addresses on 430 * locally attached networks. 431 */ 432 if ((ro.ro_rt->rt_flags & (RTF_BLACKHOLE|RTF_BROADCAST)) != 0) 433 goto drop; 434 435 /* 436 * Step 5: outgoing firewall packet processing 437 */ 438 439 /* 440 * Run through list of hooks for output packets. 441 */ 442 if (!PFIL_HOOKED(&V_inet_pfil_hook)) 443 goto passout; 444 445 if (pfil_run_hooks(&V_inet_pfil_hook, &m, ifp, PFIL_OUT, NULL) || m == NULL) { 446 goto drop; 447 } 448 449 M_ASSERTVALID(m); 450 M_ASSERTPKTHDR(m); 451 452 ip = mtod(m, struct ip *); 453 dest.s_addr = ip->ip_dst.s_addr; 454 455 /* 456 * Destination address changed? 457 */ 458 #ifndef IPFIREWALL_FORWARD 459 if (odest.s_addr != dest.s_addr) { 460 #else 461 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); 462 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { 463 #endif /* IPFIREWALL_FORWARD */ 464 /* 465 * Is it now for a local address on this host? 466 */ 467 #ifndef IPFIREWALL_FORWARD 468 if (in_localip(dest)) { 469 #else 470 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) { 471 #endif /* IPFIREWALL_FORWARD */ 472 forwardlocal: 473 /* 474 * Return packet for processing by ip_input(). 475 * Keep host byte order as expected at ip_input's 476 * "ours"-label. 477 */ 478 m->m_flags |= M_FASTFWD_OURS; 479 if (ro.ro_rt) 480 RTFREE(ro.ro_rt); 481 return m; 482 } 483 /* 484 * Redo route lookup with new destination address 485 */ 486 #ifdef IPFIREWALL_FORWARD 487 if (fwd_tag) { 488 dest.s_addr = ((struct sockaddr_in *) 489 (fwd_tag + 1))->sin_addr.s_addr; 490 m_tag_delete(m, fwd_tag); 491 } 492 #endif /* IPFIREWALL_FORWARD */ 493 RTFREE(ro.ro_rt); 494 if ((dst = ip_findroute(&ro, dest, m)) == NULL) 495 return NULL; /* icmp unreach already sent */ 496 ifp = ro.ro_rt->rt_ifp; 497 } 498 499 passout: 500 /* 501 * Step 6: send off the packet 502 */ 503 504 /* 505 * Check if route is dampned (when ARP is unable to resolve) 506 */ 507 if ((ro.ro_rt->rt_flags & RTF_REJECT) && 508 (ro.ro_rt->rt_rmx.rmx_expire == 0 || 509 time_uptime < ro.ro_rt->rt_rmx.rmx_expire)) { 510 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 511 goto consumed; 512 } 513 514 #ifndef ALTQ 515 /* 516 * Check if there is enough space in the interface queue 517 */ 518 if ((ifp->if_snd.ifq_len + ip->ip_len / ifp->if_mtu + 1) >= 519 ifp->if_snd.ifq_maxlen) { 520 IPSTAT_INC(ips_odropped); 521 /* would send source quench here but that is depreciated */ 522 goto drop; 523 } 524 #endif 525 526 /* 527 * Check if media link state of interface is not down 528 */ 529 if (ifp->if_link_state == LINK_STATE_DOWN) { 530 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 531 goto consumed; 532 } 533 534 /* 535 * Check if packet fits MTU or if hardware will fragment for us 536 */ 537 if (ro.ro_rt->rt_rmx.rmx_mtu) 538 mtu = min(ro.ro_rt->rt_rmx.rmx_mtu, ifp->if_mtu); 539 else 540 mtu = ifp->if_mtu; 541 542 if (ip->ip_len <= mtu || 543 (ifp->if_hwassist & CSUM_FRAGMENT && (ip->ip_off & IP_DF) == 0)) { 544 /* 545 * Restore packet header fields to original values 546 */ 547 ip->ip_len = htons(ip->ip_len); 548 ip->ip_off = htons(ip->ip_off); 549 /* 550 * Send off the packet via outgoing interface 551 */ 552 error = (*ifp->if_output)(ifp, m, 553 (struct sockaddr *)dst, &ro); 554 } else { 555 /* 556 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery 557 */ 558 if (ip->ip_off & IP_DF) { 559 IPSTAT_INC(ips_cantfrag); 560 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 561 0, mtu); 562 goto consumed; 563 } else { 564 /* 565 * We have to fragment the packet 566 */ 567 m->m_pkthdr.csum_flags |= CSUM_IP; 568 /* 569 * ip_fragment expects ip_len and ip_off in host byte 570 * order but returns all packets in network byte order 571 */ 572 if (ip_fragment(ip, &m, mtu, ifp->if_hwassist, 573 (~ifp->if_hwassist & CSUM_DELAY_IP))) { 574 goto drop; 575 } 576 KASSERT(m != NULL, ("null mbuf and no error")); 577 /* 578 * Send off the fragments via outgoing interface 579 */ 580 error = 0; 581 do { 582 m0 = m->m_nextpkt; 583 m->m_nextpkt = NULL; 584 585 error = (*ifp->if_output)(ifp, m, 586 (struct sockaddr *)dst, &ro); 587 if (error) 588 break; 589 } while ((m = m0) != NULL); 590 if (error) { 591 /* Reclaim remaining fragments */ 592 for (m = m0; m; m = m0) { 593 m0 = m->m_nextpkt; 594 m_freem(m); 595 } 596 } else 597 IPSTAT_INC(ips_fragmented); 598 } 599 } 600 601 if (error != 0) 602 IPSTAT_INC(ips_odropped); 603 else { 604 ro.ro_rt->rt_rmx.rmx_pksent++; 605 IPSTAT_INC(ips_forward); 606 IPSTAT_INC(ips_fastforward); 607 } 608 consumed: 609 RTFREE(ro.ro_rt); 610 return NULL; 611 drop: 612 if (m) 613 m_freem(m); 614 if (ro.ro_rt) 615 RTFREE(ro.ro_rt); 616 return NULL; 617 } 618