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 #include "opt_ipstealth.h"
72
73 #include <sys/param.h>
74 #include <sys/systm.h>
75 #include <sys/kernel.h>
76 #include <sys/malloc.h>
77 #include <sys/mbuf.h>
78 #include <sys/protosw.h>
79 #include <sys/sdt.h>
80 #include <sys/socket.h>
81 #include <sys/sysctl.h>
82
83 #include <net/if.h>
84 #include <net/if_types.h>
85 #include <net/if_var.h>
86 #include <net/if_dl.h>
87 #include <net/if_private.h>
88 #include <net/pfil.h>
89 #include <net/route.h>
90 #include <net/route/nhop.h>
91 #include <net/vnet.h>
92
93 #include <netinet/in.h>
94 #include <netinet/in_fib.h>
95 #include <netinet/in_kdtrace.h>
96 #include <netinet/in_systm.h>
97 #include <netinet/in_var.h>
98 #include <netinet/ip.h>
99 #include <netinet/ip_var.h>
100 #include <netinet/ip_icmp.h>
101 #include <netinet/ip_options.h>
102
103 #include <machine/in_cksum.h>
104
105 #define V_ipsendredirects VNET(ipsendredirects)
106
107 static struct mbuf *
ip_redir_alloc(struct mbuf * m,struct nhop_object * nh,u_short ip_len,struct in_addr * osrc,struct in_addr * newgw)108 ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, u_short ip_len,
109 struct in_addr *osrc, struct in_addr *newgw)
110 {
111 struct in_ifaddr *nh_ia;
112 struct mbuf *mcopy;
113
114 KASSERT(nh != NULL, ("%s: m %p nh is NULL\n", __func__, m));
115
116 /*
117 * Only send a redirect if:
118 * - Redirects are not disabled (must be checked by caller),
119 * - We have not applied NAT (must be checked by caller as possible),
120 * - Neither a MCAST or BCAST packet (must be checked by caller)
121 * [RFC1009 Appendix A.2].
122 * - The packet does not do IP source routing or having any other
123 * IP options (this case was handled already by ip_input() calling
124 * ip_dooptions() [RFC792, p13],
125 * - The packet is being forwarded out the same physical interface
126 * that it was received from [RFC1812, 5.2.7.2].
127 */
128
129 /*
130 * - The forwarding route was not created by a redirect
131 * [RFC1812, 5.2.7.2], or
132 * if it was to follow a default route (see below).
133 * - The next-hop is reachable by us [RFC1009 Appendix A.2].
134 */
135 if ((nh->nh_flags & (NHF_DEFAULT | NHF_REDIRECT |
136 NHF_BLACKHOLE | NHF_REJECT)) != 0)
137 return (NULL);
138
139 /* Get the new gateway. */
140 if ((nh->nh_flags & NHF_GATEWAY) == 0 || nh->gw_sa.sa_family != AF_INET)
141 return (NULL);
142 newgw->s_addr = nh->gw4_sa.sin_addr.s_addr;
143
144 /*
145 * - The resulting forwarding destination is not "This host on this
146 * network" [RFC1122, Section 3.2.1.3] (default route check above).
147 */
148 if (newgw->s_addr == 0)
149 return (NULL);
150
151 /*
152 * - We know how to reach the sender and the source address is
153 * directly connected to us [RFC792, p13].
154 * + The new gateway address and the source address are on the same
155 * subnet [RFC1009 Appendix A.2, RFC1122 3.2.2.2, RFC1812, 5.2.7.2].
156 * NB: if you think multiple logical subnets on the same wire should
157 * receive redirects read [RFC1812, APPENDIX C (14->15)].
158 */
159 nh_ia = (struct in_ifaddr *)nh->nh_ifa;
160 if ((ntohl(osrc->s_addr) & nh_ia->ia_subnetmask) != nh_ia->ia_subnet)
161 return (NULL);
162
163 /* Prepare for sending the redirect. */
164
165 /*
166 * Make a copy of as much as we need of the packet as the original
167 * one will be forwarded but we need (a portion) for icmp_error().
168 */
169 mcopy = m_gethdr(M_NOWAIT, m->m_type);
170 if (mcopy == NULL)
171 return (NULL);
172
173 if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) {
174 /*
175 * It's probably ok if the pkthdr dup fails (because
176 * the deep copy of the tag chain failed), but for now
177 * be conservative and just discard the copy since
178 * code below may some day want the tags.
179 */
180 m_free(mcopy);
181 return (NULL);
182 }
183 mcopy->m_len = min(ip_len, M_TRAILINGSPACE(mcopy));
184 mcopy->m_pkthdr.len = mcopy->m_len;
185 m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t));
186
187 return (mcopy);
188 }
189
190
191 static int
ip_findroute(struct nhop_object ** pnh,struct in_addr dest,struct mbuf * m)192 ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m)
193 {
194 struct nhop_object *nh;
195
196 nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE,
197 m->m_pkthdr.flowid);
198 if (nh == NULL) {
199 IPSTAT_INC(ips_noroute);
200 IPSTAT_INC(ips_cantforward);
201 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
202 return (EHOSTUNREACH);
203 }
204 /*
205 * Drop blackholed traffic and directed broadcasts.
206 */
207 if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) {
208 IPSTAT_INC(ips_cantforward);
209 m_freem(m);
210 return (EHOSTUNREACH);
211 }
212
213 if (nh->nh_flags & NHF_REJECT) {
214 IPSTAT_INC(ips_cantforward);
215 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
216 return (EHOSTUNREACH);
217 }
218
219 *pnh = nh;
220
221 return (0);
222 }
223
224 /*
225 * Try to forward a packet based on the destination address.
226 * This is a fast path optimized for the plain forwarding case.
227 * If the packet is handled (and consumed) here then we return NULL;
228 * otherwise mbuf is returned and the packet should be delivered
229 * to ip_input for full processing.
230 */
231 struct mbuf *
ip_tryforward(struct mbuf * m)232 ip_tryforward(struct mbuf *m)
233 {
234 struct ip *ip;
235 struct mbuf *m0 = NULL;
236 struct nhop_object *nh = NULL;
237 struct route ro;
238 struct sockaddr_in *dst;
239 const struct sockaddr *gw;
240 struct in_addr dest, odest, rtdest, osrc;
241 uint16_t ip_len, ip_off;
242 int error = 0;
243 struct m_tag *fwd_tag = NULL;
244 struct mbuf *mcopy = NULL;
245 struct in_addr redest;
246 /*
247 * Are we active and forwarding packets?
248 */
249
250 M_ASSERTVALID(m);
251 M_ASSERTPKTHDR(m);
252
253 /*
254 * Only IP packets without options
255 */
256 ip = mtod(m, struct ip *);
257
258 if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
259 if (V_ip_doopts == 1)
260 return m;
261 else if (V_ip_doopts == 2) {
262 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
263 0, 0);
264 return NULL; /* mbuf already free'd */
265 }
266 /* else ignore IP options and continue */
267 }
268
269 /*
270 * Only unicast IP, not from loopback, no L2 or IP broadcast,
271 * no multicast, no INADDR_ANY
272 *
273 * XXX: Probably some of these checks could be direct drop
274 * conditions. However it is not clear whether there are some
275 * hacks or obscure behaviours which make it necessary to
276 * let ip_input handle it. We play safe here and let ip_input
277 * deal with it until it is proven that we can directly drop it.
278 */
279 if ((m->m_flags & (M_BCAST|M_MCAST)) ||
280 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) ||
281 in_broadcast(ip->ip_src) ||
282 in_broadcast(ip->ip_dst) ||
283 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
284 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
285 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) ||
286 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) )
287 return m;
288
289 /*
290 * Is it for a local address on this host?
291 */
292 if (in_localip(ip->ip_dst))
293 return m;
294
295 IPSTAT_INC(ips_total);
296
297 /*
298 * Step 3: incoming packet firewall processing
299 */
300
301 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;
302 osrc.s_addr = ip->ip_src.s_addr;
303
304 /*
305 * Run through list of ipfilter hooks for input packets
306 */
307 if (!PFIL_HOOKED_IN(V_inet_pfil_head))
308 goto passin;
309
310 if (pfil_mbuf_in(V_inet_pfil_head, &m, m->m_pkthdr.rcvif,
311 NULL) != PFIL_PASS)
312 goto drop;
313
314 M_ASSERTVALID(m);
315 M_ASSERTPKTHDR(m);
316
317 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */
318 dest.s_addr = ip->ip_dst.s_addr;
319
320 /*
321 * Destination address changed?
322 */
323 if (odest.s_addr != dest.s_addr) {
324 /*
325 * Is it now for a local address on this host?
326 */
327 if (in_localip(dest))
328 goto forwardlocal;
329 /*
330 * Go on with new destination address
331 */
332 }
333
334 if (m->m_flags & M_FASTFWD_OURS) {
335 /*
336 * ipfw changed it for a local address on this host.
337 */
338 goto forwardlocal;
339 }
340
341 passin:
342 /*
343 * Step 4: decrement TTL and look up route
344 */
345
346 /*
347 * Check TTL
348 */
349 #ifdef IPSTEALTH
350 if (!V_ipstealth) {
351 #endif
352 if (ip->ip_ttl <= IPTTLDEC) {
353 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0);
354 return NULL; /* mbuf already free'd */
355 }
356
357 /*
358 * Decrement the TTL and incrementally change the IP header checksum.
359 * Don't bother doing this with hw checksum offloading, it's faster
360 * doing it right here.
361 */
362 ip->ip_ttl -= IPTTLDEC;
363 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8))
364 ip->ip_sum -= ~htons(IPTTLDEC << 8);
365 else
366 ip->ip_sum += htons(IPTTLDEC << 8);
367 #ifdef IPSTEALTH
368 }
369 #endif
370
371 /*
372 * Next hop forced by pfil(9) hook?
373 */
374 if ((m->m_flags & M_IP_NEXTHOP) &&
375 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) {
376 /*
377 * Now we will find route to forced destination.
378 */
379 dest.s_addr = ((struct sockaddr_in *)
380 (fwd_tag + 1))->sin_addr.s_addr;
381 m_tag_delete(m, fwd_tag);
382 m->m_flags &= ~M_IP_NEXTHOP;
383 }
384
385 /*
386 * Find route to destination.
387 */
388 if (ip_findroute(&nh, dest, m) != 0)
389 return (NULL); /* icmp unreach already sent */
390
391 /*
392 * Avoid second route lookup by caching destination.
393 */
394 rtdest.s_addr = dest.s_addr;
395
396 /*
397 * Step 5: outgoing firewall packet processing
398 */
399 if (!PFIL_HOOKED_OUT(V_inet_pfil_head))
400 goto passout;
401
402 if (pfil_mbuf_fwd(V_inet_pfil_head, &m, nh->nh_ifp,
403 NULL) != PFIL_PASS)
404 goto drop;
405
406 M_ASSERTVALID(m);
407 M_ASSERTPKTHDR(m);
408
409 ip = mtod(m, struct ip *);
410 dest.s_addr = ip->ip_dst.s_addr;
411
412 /*
413 * Destination address changed?
414 */
415 if (m->m_flags & M_IP_NEXTHOP)
416 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
417 else
418 fwd_tag = NULL;
419 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) {
420 /*
421 * Is it now for a local address on this host?
422 */
423 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) {
424 forwardlocal:
425 /*
426 * Return packet for processing by ip_input().
427 */
428 m->m_flags |= M_FASTFWD_OURS;
429 return (m);
430 }
431 /*
432 * Redo route lookup with new destination address
433 */
434 if (fwd_tag) {
435 dest.s_addr = ((struct sockaddr_in *)
436 (fwd_tag + 1))->sin_addr.s_addr;
437 m_tag_delete(m, fwd_tag);
438 m->m_flags &= ~M_IP_NEXTHOP;
439 }
440 if (dest.s_addr != rtdest.s_addr &&
441 ip_findroute(&nh, dest, m) != 0)
442 return (NULL); /* icmp unreach already sent */
443 }
444
445 passout:
446 /*
447 * Step 6: send off the packet
448 */
449 ip_len = ntohs(ip->ip_len);
450 ip_off = ntohs(ip->ip_off);
451
452 bzero(&ro, sizeof(ro));
453 dst = (struct sockaddr_in *)&ro.ro_dst;
454 dst->sin_family = AF_INET;
455 dst->sin_len = sizeof(*dst);
456 dst->sin_addr = dest;
457 if (nh->nh_flags & NHF_GATEWAY) {
458 gw = &nh->gw_sa;
459 ro.ro_flags |= RT_HAS_GW;
460 } else
461 gw = (const struct sockaddr *)dst;
462
463 /* Handle redirect case. */
464 redest.s_addr = 0;
465 if (V_ipsendredirects && osrc.s_addr == ip->ip_src.s_addr &&
466 nh->nh_ifp == m->m_pkthdr.rcvif)
467 mcopy = ip_redir_alloc(m, nh, ip_len, &osrc, &redest);
468
469 /*
470 * Check if packet fits MTU or if hardware will fragment for us
471 */
472 if (ip_len <= nh->nh_mtu) {
473 /*
474 * Avoid confusing lower layers.
475 */
476 m_clrprotoflags(m);
477 /*
478 * Send off the packet via outgoing interface
479 */
480 IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL);
481 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro);
482 } else {
483 /*
484 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
485 */
486 if (ip_off & IP_DF) {
487 IPSTAT_INC(ips_cantfrag);
488 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
489 0, nh->nh_mtu);
490 goto consumed;
491 } else {
492 /*
493 * We have to fragment the packet
494 */
495 m->m_pkthdr.csum_flags |= CSUM_IP;
496 if (ip_fragment(ip, &m, nh->nh_mtu,
497 nh->nh_ifp->if_hwassist) != 0)
498 goto drop;
499 KASSERT(m != NULL, ("null mbuf and no error"));
500 /*
501 * Send off the fragments via outgoing interface
502 */
503 error = 0;
504 do {
505 m0 = m->m_nextpkt;
506 m->m_nextpkt = NULL;
507 /*
508 * Avoid confusing lower layers.
509 */
510 m_clrprotoflags(m);
511
512 IP_PROBE(send, NULL, NULL,
513 mtod(m, struct ip *), nh->nh_ifp,
514 mtod(m, struct ip *), NULL);
515 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m,
516 gw, &ro);
517 if (error)
518 break;
519 } while ((m = m0) != NULL);
520 if (error) {
521 /* Reclaim remaining fragments */
522 for (m = m0; m; m = m0) {
523 m0 = m->m_nextpkt;
524 m_freem(m);
525 }
526 } else
527 IPSTAT_INC(ips_fragmented);
528 }
529 }
530
531 if (error != 0)
532 IPSTAT_INC(ips_odropped);
533 else {
534 IPSTAT_INC(ips_forward);
535 IPSTAT_INC(ips_fastforward);
536 }
537
538 /* Send required redirect */
539 if (mcopy != NULL) {
540 icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0);
541 mcopy = NULL; /* Was consumed by callee. */
542 }
543
544 consumed:
545 if (mcopy != NULL)
546 m_freem(mcopy);
547 return NULL;
548 drop:
549 if (m)
550 m_freem(m);
551 return NULL;
552 }
553