1 /* $OpenBSD: bpf.c,v 1.19 2017/04/19 05:36:12 natano Exp $ */
2
3 /* BPF socket interface code, originally contributed by Archie Cobbs. */
4
5 /*
6 * Copyright (c) 1995, 1996, 1998, 1999
7 * The Internet Software Consortium. All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
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. Neither the name of The Internet Software Consortium nor the names
19 * of its contributors may be used to endorse or promote products derived
20 * from this software without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
23 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
24 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
25 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
26 * DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
27 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
28 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
29 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
30 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
31 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
32 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
33 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 *
36 * This software has been written for the Internet Software Consortium
37 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
38 * Enterprises. To learn more about the Internet Software Consortium,
39 * see ``http://www.vix.com/isc''. To learn more about Vixie
40 * Enterprises, see ``http://www.vix.com''.
41 */
42
43 #include <sys/types.h>
44 #include <sys/ioctl.h>
45 #include <sys/socket.h>
46
47 #include <net/bpf.h>
48 #include <net/if.h>
49
50 #include <netinet/in.h>
51 #include <netinet/if_ether.h>
52
53 #include <errno.h>
54 #include <fcntl.h>
55 #include <stdio.h>
56 #include <stdlib.h>
57 #include <string.h>
58 #include <unistd.h>
59
60 #include "dhcp.h"
61 #include "dhcpd.h"
62 #include "log.h"
63
64 /*
65 * Called by get_interface_list for each interface that's discovered.
66 * Opens a packet filter for each interface and adds it to the select
67 * mask.
68 */
69 int
if_register_bpf(struct interface_info * info)70 if_register_bpf(struct interface_info *info)
71 {
72 int sock;
73
74 /* Open the BPF device */
75 if ((sock = open("/dev/bpf", O_RDWR)) == -1)
76 fatal("Can't open bpf device");
77
78 /* Set the BPF device to point at this interface. */
79 if (ioctl(sock, BIOCSETIF, &info->ifr) == -1)
80 fatal("Can't attach interface %s to bpf device", info->name);
81
82 return (sock);
83 }
84
85 void
if_register_send(struct interface_info * info)86 if_register_send(struct interface_info *info)
87 {
88 /*
89 * If we're using the bpf API for sending and receiving, we
90 * don't need to register this interface twice.
91 */
92 info->wfdesc = info->rfdesc;
93 }
94
95 /*
96 * Packet filter program: 'ip and udp and dst port CLIENT_PORT'
97 */
98 struct bpf_insn dhcp_bpf_sfilter[] = {
99 /* Make sure this is an IP packet... */
100 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
101 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
102
103 /* Make sure it's a UDP packet... */
104 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
105 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
106
107 /* Make sure this isn't a fragment... */
108 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
109 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
110
111 /* Get the IP header length... */
112 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
113
114 /* Make sure it's to the right port... */
115 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
116 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, CLIENT_PORT, 0, 1),
117
118 /* If we passed all the tests, ask for the whole packet. */
119 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
120
121 /* Otherwise, drop it. */
122 BPF_STMT(BPF_RET+BPF_K, 0),
123 };
124
125 int dhcp_bpf_sfilter_len = sizeof(dhcp_bpf_sfilter) / sizeof(struct bpf_insn);
126
127 /*
128 * Packet filter program: 'ip and udp and dst port SERVER_PORT'
129 */
130 struct bpf_insn dhcp_bpf_filter[] = {
131 /* Make sure this is an IP packet... */
132 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
133 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
134
135 /* Make sure it's a UDP packet... */
136 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
137 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
138
139 /* Make sure this isn't a fragment... */
140 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
141 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
142
143 /* Get the IP header length... */
144 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
145
146 /* Make sure it's to the right port... */
147 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
148 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1),
149
150 /* If we passed all the tests, ask for the whole packet. */
151 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
152
153 /* Otherwise, drop it. */
154 BPF_STMT(BPF_RET+BPF_K, 0),
155 };
156
157 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
158
159 /*
160 * Packet filter program: encapsulated 'ip and udp and dst port SERVER_PORT'
161 */
162 struct bpf_insn dhcp_bpf_efilter[] = {
163 /* Make sure this is an encapsulated AF_INET packet... */
164 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, 0),
165 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, AF_INET << 24, 0, 10),
166
167 /* Make sure it's an IPIP packet... */
168 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 21),
169 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_IPIP, 0, 8),
170
171 /* Make sure it's an encapsulated UDP packet... */
172 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 41),
173 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
174
175 /* Make sure this isn't a fragment... */
176 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 38),
177 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
178
179 /* Get the IP header length... */
180 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 32),
181
182 /* Make sure it's to the right port... */
183 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 34),
184 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1),
185
186 /* If we passed all the tests, ask for the whole packet. */
187 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
188
189 /* Otherwise, drop it. */
190 BPF_STMT(BPF_RET+BPF_K, 0),
191 };
192
193 int dhcp_bpf_efilter_len = sizeof(dhcp_bpf_efilter) / sizeof(struct bpf_insn);
194
195 /*
196 * Packet write filter program: 'ip and udp and src port CLIENT_PORT'
197 */
198 struct bpf_insn dhcp_bpf_swfilter[] = {
199 /* Make sure this is an IP packet... */
200 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
201 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
202
203 /* Make sure it's a UDP packet... */
204 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
205 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
206
207 /* Make sure this isn't a fragment... */
208 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
209 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
210
211 /* Get the IP header length... */
212 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
213
214 /* Make sure it's from the right port... */
215 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
216 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, CLIENT_PORT, 0, 1),
217
218 /* If we passed all the tests, ask for the whole packet. */
219 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
220
221 /* Otherwise, drop it. */
222 BPF_STMT(BPF_RET+BPF_K, 0),
223 };
224
225 int dhcp_bpf_swfilter_len = sizeof(dhcp_bpf_swfilter) /
226 sizeof(struct bpf_insn);
227
228 /*
229 * Packet write filter program: 'ip and udp and src port SERVER_PORT'
230 */
231 struct bpf_insn dhcp_bpf_wfilter[] = {
232 /* Make sure this is an IP packet... */
233 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
234 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
235
236 /* Make sure it's a UDP packet... */
237 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
238 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
239
240 /* Make sure this isn't a fragment... */
241 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
242 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
243
244 /* Get the IP header length... */
245 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
246
247 /* Make sure it's from the right port... */
248 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
249 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1),
250
251 /* If we passed all the tests, ask for the whole packet. */
252 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
253
254 /* Otherwise, drop it. */
255 BPF_STMT(BPF_RET+BPF_K, 0),
256 };
257
258 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
259
260 void
if_register_receive(struct interface_info * info,int isserver)261 if_register_receive(struct interface_info *info, int isserver)
262 {
263 struct bpf_version v;
264 struct bpf_program p;
265 int flag = 1, sz, cmplt = 0;
266
267 /* Open a BPF device and hang it on this interface... */
268 info->rfdesc = if_register_bpf(info);
269
270 /* Make sure the BPF version is in range... */
271 if (ioctl(info->rfdesc, BIOCVERSION, &v) == -1)
272 fatal("Can't get BPF version");
273
274 if (v.bv_major != BPF_MAJOR_VERSION ||
275 v.bv_minor < BPF_MINOR_VERSION)
276 fatalx("Kernel BPF version out of range - recompile dhcpd!");
277
278 /*
279 * Set immediate mode so that reads return as soon as a packet
280 * comes in, rather than waiting for the input buffer to fill
281 * with packets.
282 */
283 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) == -1)
284 fatal("Can't set immediate mode on bpf device");
285
286 /* make sure kernel fills in the source ethernet address */
287 if (ioctl(info->rfdesc, BIOCSHDRCMPLT, &cmplt) == -1)
288 fatal("Can't set header complete flag on bpf device");
289
290 /* Get the required BPF buffer length from the kernel. */
291 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) == -1)
292 fatal("Can't get bpf buffer length");
293 info->rbuf_max = sz;
294 info->rbuf = malloc(info->rbuf_max);
295 if (!info->rbuf)
296 fatalx("Can't allocate %lu bytes for bpf input buffer.",
297 (unsigned long)info->rbuf_max);
298 info->rbuf_offset = 0;
299 info->rbuf_len = 0;
300
301 /* Set up the bpf filter program structure. */
302 if (isserver) {
303 p.bf_len = dhcp_bpf_sfilter_len;
304 p.bf_insns = dhcp_bpf_sfilter;
305 } else if (info->hw_address.htype == HTYPE_IPSEC_TUNNEL) {
306 p.bf_len = dhcp_bpf_efilter_len;
307 p.bf_insns = dhcp_bpf_efilter;
308 } else {
309 p.bf_len = dhcp_bpf_filter_len;
310 p.bf_insns = dhcp_bpf_filter;
311 }
312 if (ioctl(info->rfdesc, BIOCSETF, &p) == -1)
313 fatal("Can't install packet filter program");
314
315 /* Set up the bpf write filter program structure. */
316 if (isserver) {
317 p.bf_len = dhcp_bpf_swfilter_len;
318 p.bf_insns = dhcp_bpf_swfilter;
319 } else {
320 p.bf_len = dhcp_bpf_wfilter_len;
321 p.bf_insns = dhcp_bpf_wfilter;
322 }
323
324 if (ioctl(info->rfdesc, BIOCSETWF, &p) == -1)
325 fatal("Can't install write filter program");
326
327 /* make sure these settings cannot be changed after dropping privs */
328 if (ioctl(info->rfdesc, BIOCLOCK) == -1)
329 fatal("Failed to lock bpf descriptor");
330 }
331
332 ssize_t
send_packet(struct interface_info * interface,struct dhcp_packet * raw,size_t len,struct packet_ctx * pc)333 send_packet(struct interface_info *interface,
334 struct dhcp_packet *raw, size_t len, struct packet_ctx *pc)
335 {
336 unsigned char buf[256];
337 struct iovec iov[2];
338 ssize_t bufp;
339 int result;
340
341 result = -1;
342
343 if (interface->hw_address.htype == HTYPE_IPSEC_TUNNEL) {
344 socklen_t slen = pc->pc_dst.ss_len;
345 result = sendto(server_fd, raw, len, 0,
346 (struct sockaddr *)&pc->pc_dst, slen);
347 goto done;
348 }
349
350 /* Assemble the headers... */
351 if ((bufp = assemble_hw_header(buf, sizeof(buf), 0, pc,
352 interface->hw_address.htype)) == -1)
353 goto done;
354 if ((bufp = assemble_udp_ip_header(buf, sizeof(buf), bufp, pc,
355 (unsigned char *)raw, len)) == -1)
356 goto done;
357
358 /* Fire it off */
359 iov[0].iov_base = (char *)buf;
360 iov[0].iov_len = bufp;
361 iov[1].iov_base = (char *)raw;
362 iov[1].iov_len = len;
363
364 result = writev(interface->wfdesc, iov, 2);
365 done:
366 if (result == -1)
367 log_warn("send_packet");
368 return (result);
369 }
370
371 ssize_t
receive_packet(struct interface_info * interface,unsigned char * buf,size_t len,struct packet_ctx * pc)372 receive_packet(struct interface_info *interface, unsigned char *buf,
373 size_t len, struct packet_ctx *pc)
374 {
375 int length = 0;
376 ssize_t offset = 0;
377 struct bpf_hdr hdr;
378
379 /*
380 * All this complexity is because BPF doesn't guarantee that
381 * only one packet will be returned at a time. We're getting
382 * what we deserve, though - this is a terrible abuse of the BPF
383 * interface. Sigh.
384 */
385
386 /* Process packets until we get one we can return or until we've
387 * done a read and gotten nothing we can return...
388 */
389 do {
390 /* If the buffer is empty, fill it. */
391 if (interface->rbuf_offset == interface->rbuf_len) {
392 length = read(interface->rfdesc, interface->rbuf,
393 interface->rbuf_max);
394 if (length <= 0)
395 return (length);
396 interface->rbuf_offset = 0;
397 interface->rbuf_len = length;
398 }
399
400 /*
401 * If there isn't room for a whole bpf header, something
402 * went wrong, but we'll ignore it and hope it goes
403 * away... XXX
404 */
405 if (interface->rbuf_len - interface->rbuf_offset <
406 sizeof(hdr)) {
407 interface->rbuf_offset = interface->rbuf_len;
408 continue;
409 }
410
411 /* Copy out a bpf header... */
412 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
413 sizeof(hdr));
414
415 /*
416 * If the bpf header plus data doesn't fit in what's
417 * left of the buffer, stick head in sand yet again...
418 */
419 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
420 interface->rbuf_len) {
421 interface->rbuf_offset = interface->rbuf_len;
422 continue;
423 }
424
425 /*
426 * If the captured data wasn't the whole packet, or if
427 * the packet won't fit in the input buffer, all we can
428 * do is drop it.
429 */
430 if (hdr.bh_caplen != hdr.bh_datalen) {
431 interface->rbuf_offset += hdr.bh_hdrlen =
432 hdr.bh_caplen;
433 continue;
434 }
435
436 /* Skip over the BPF header... */
437 interface->rbuf_offset += hdr.bh_hdrlen;
438
439 /* Decode the physical header... */
440 offset = decode_hw_header(interface->rbuf,
441 interface->rbuf_len, interface->rbuf_offset, pc,
442 interface->hw_address.htype);
443
444 /*
445 * If decoding or a physical layer checksum failed
446 * (dunno of any physical layer that supports this, but WTH),
447 * skip this packet.
448 */
449 if (offset < 0) {
450 interface->rbuf_offset += hdr.bh_caplen;
451 continue;
452 }
453
454 /* Decode the IP and UDP headers... */
455 offset = decode_udp_ip_header(interface->rbuf,
456 interface->rbuf_len, offset, pc);
457
458 /* If the IP or UDP checksum was bad, skip the packet... */
459 if (offset < 0) {
460 interface->rbuf_offset += hdr.bh_caplen;
461 continue;
462 }
463
464 hdr.bh_caplen -= offset - interface->rbuf_offset;
465 interface->rbuf_offset = offset;
466
467 /*
468 * If there's not enough room to stash the packet data,
469 * we have to skip it (this shouldn't happen in real
470 * life, though).
471 */
472 if (hdr.bh_caplen > len) {
473 interface->rbuf_offset += hdr.bh_caplen;
474 continue;
475 }
476
477 /* Copy out the data in the packet... */
478 memcpy(buf, interface->rbuf + interface->rbuf_offset,
479 hdr.bh_caplen);
480 interface->rbuf_offset += hdr.bh_caplen;
481 return (hdr.bh_caplen);
482 } while (!length);
483 return (0);
484 }
485