1 /* $OpenBSD: bpf.c,v 1.20 2007/01/08 02:51:13 krw Exp $ */
2 /* $DragonFly: src/sbin/dhclient/bpf.c,v 1.2 2008/11/05 14:08:41 sephe Exp $ */
3
4 /* BPF socket interface code, originally contributed by Archie Cobbs. */
5
6 /*
7 * Copyright (c) 1995, 1996, 1998, 1999
8 * The Internet Software Consortium. All rights reserved.
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 *
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
19 * 3. Neither the name of The Internet Software Consortium nor the names
20 * of its contributors may be used to endorse or promote products derived
21 * from this software without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
24 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
25 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
26 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
27 * DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
28 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
29 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
30 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
31 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
32 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
33 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
34 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * SUCH DAMAGE.
36 *
37 * This software has been written for the Internet Software Consortium
38 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
39 * Enterprises. To learn more about the Internet Software Consortium,
40 * see ``http://www.vix.com/isc''. To learn more about Vixie
41 * Enterprises, see ``http://www.vix.com''.
42 */
43
44 #include <sys/ioctl.h>
45 #include <sys/uio.h>
46
47 #include <net/bpf.h>
48 #include <netinet/if_ether.h>
49 #include <netinet/in_systm.h>
50 #include <netinet/ip.h>
51 #include <netinet/udp.h>
52
53 #include "dhcpd.h"
54
55 /*
56 * Called by get_interface_list for each interface that's discovered.
57 * Opens a packet filter for each interface and adds it to the select
58 * mask.
59 */
60 int
if_register_bpf(void)61 if_register_bpf(void)
62 {
63 char filename[50];
64 int sock, b;
65
66 /*
67 * Open a BPF device. Try auto-clone first (newer kernels),
68 * otherwise iterate (older kernels).
69 */
70 sock = open("/dev/bpf", O_RDWR, 0);
71 if (sock < 0) {
72 for (b = 0; 1; b++) {
73 snprintf(filename, sizeof(filename), "/dev/bpf%d", b);
74 sock = open(filename, O_RDWR, 0);
75 if (sock < 0) {
76 if (errno == EBUSY)
77 continue;
78 else
79 error("Can't find free bpf: %m");
80 } else {
81 break;
82 }
83 }
84 }
85
86 /* Set the BPF device to point at this interface. */
87 if (ioctl(sock, BIOCSETIF, ifi->ifp) < 0)
88 error("Can't attach interface %s to bpf device %s: %m",
89 ifi->name, filename);
90
91 return (sock);
92 }
93
94 void
if_register_send(void)95 if_register_send(void)
96 {
97 int sock, on = 1;
98
99 /*
100 * If we're using the bpf API for sending and receiving, we
101 * don't need to register this interface twice.
102 */
103 ifi->wfdesc = ifi->rfdesc;
104
105 /*
106 * Use raw socket for unicast send.
107 */
108 if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1)
109 error("socket(SOCK_RAW): %m");
110 if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on,
111 sizeof(on)) == -1)
112 error("setsockopt(IP_HDRINCL): %m");
113 ifi->ufdesc = sock;
114 }
115
116 /*
117 * Packet filter program...
118 *
119 * XXX: Changes to the filter program may require changes to the
120 * constant offsets used in if_register_send to patch the BPF program!
121 */
122 struct bpf_insn dhcp_bpf_filter[] = {
123 /* Make sure this is an IP packet... */
124 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
125 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
126
127 /* Make sure it's a UDP packet... */
128 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
129 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
130
131 /* Make sure this isn't a fragment... */
132 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
133 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
134
135 /* Get the IP header length... */
136 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
137
138 /* Make sure it's to the right port... */
139 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
140 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */
141
142 /* If we passed all the tests, ask for the whole packet. */
143 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
144
145 /* Otherwise, drop it. */
146 BPF_STMT(BPF_RET+BPF_K, 0),
147 };
148
149 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
150
151 /*
152 * Packet write filter program:
153 * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
154 */
155 struct bpf_insn dhcp_bpf_wfilter[] = {
156 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
157 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
158
159 /* Make sure this is an IP packet... */
160 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
161 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
162
163 /* Make sure it's a UDP packet... */
164 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
165 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
166
167 /* Make sure this isn't a fragment... */
168 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
169 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */
170
171 /* Get the IP header length... */
172 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
173
174 /* Make sure it's from the right port... */
175 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
176 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
177
178 /* Make sure it is to the right ports ... */
179 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
180 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
181
182 /* If we passed all the tests, ask for the whole packet. */
183 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
184
185 /* Otherwise, drop it. */
186 BPF_STMT(BPF_RET+BPF_K, 0),
187 };
188
189 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
190
191 void
if_register_receive(void)192 if_register_receive(void)
193 {
194 struct bpf_version v;
195 struct bpf_program p;
196 int flag = 1, sz;
197
198 /* Open a BPF device and hang it on this interface... */
199 ifi->rfdesc = if_register_bpf();
200
201 /* Make sure the BPF version is in range... */
202 if (ioctl(ifi->rfdesc, BIOCVERSION, &v) < 0)
203 error("Can't get BPF version: %m");
204
205 if (v.bv_major != BPF_MAJOR_VERSION ||
206 v.bv_minor < BPF_MINOR_VERSION)
207 error("Kernel BPF version out of range - recompile dhcpd!");
208
209 /*
210 * Set immediate mode so that reads return as soon as a packet
211 * comes in, rather than waiting for the input buffer to fill
212 * with packets.
213 */
214 if (ioctl(ifi->rfdesc, BIOCIMMEDIATE, &flag) < 0)
215 error("Can't set immediate mode on bpf device: %m");
216
217 /*if (ioctl(ifi->rfdesc, BIOCSFILDROP, &flag) < 0)
218 error("Can't set filter-drop mode on bpf device: %m");*/
219
220 /* Get the required BPF buffer length from the kernel. */
221 if (ioctl(ifi->rfdesc, BIOCGBLEN, &sz) < 0)
222 error("Can't get bpf buffer length: %m");
223 ifi->rbuf_max = sz;
224 ifi->rbuf = malloc(ifi->rbuf_max);
225 if (!ifi->rbuf)
226 error("Can't allocate %lu bytes for bpf input buffer.",
227 (unsigned long)ifi->rbuf_max);
228 ifi->rbuf_offset = 0;
229 ifi->rbuf_len = 0;
230
231 /* Set up the bpf filter program structure. */
232 p.bf_len = dhcp_bpf_filter_len;
233 p.bf_insns = dhcp_bpf_filter;
234
235 /* Patch the server port into the BPF program...
236 *
237 * XXX: changes to filter program may require changes to the
238 * insn number(s) used below!
239 */
240 dhcp_bpf_filter[8].k = LOCAL_PORT;
241
242 if (ioctl(ifi->rfdesc, BIOCSETF, &p) < 0)
243 error("Can't install packet filter program: %m");
244
245 /* Set up the bpf write filter program structure. */
246 p.bf_len = dhcp_bpf_wfilter_len;
247 p.bf_insns = dhcp_bpf_wfilter;
248
249 if (dhcp_bpf_wfilter[7].k == 0x1fff)
250 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
251
252 if (ioctl(ifi->rfdesc, BIOCSETWF, &p) < 0)
253 error("Can't install write filter program: %m");
254
255 if (ioctl(ifi->rfdesc, BIOCLOCK, NULL) < 0)
256 error("Cannot lock bpf");
257 }
258
259 ssize_t
send_packet(struct in_addr from,struct sockaddr_in * to,struct hardware * hto)260 send_packet(struct in_addr from, struct sockaddr_in *to,
261 struct hardware *hto)
262 {
263 #define IOVCNT 2
264 unsigned char buf[256];
265 struct iovec iov[IOVCNT];
266 struct msghdr msg;
267 int result, bufp = 0;
268
269 if (to->sin_addr.s_addr == INADDR_BROADCAST) {
270 assemble_hw_header(buf, &bufp, hto);
271 }
272
273 assemble_udp_ip_header(buf, &bufp, from.s_addr,
274 to->sin_addr.s_addr, to->sin_port,
275 (unsigned char *)&client->packet,
276 client->packet_length);
277
278 iov[0].iov_base = (char *)buf;
279 iov[0].iov_len = bufp;
280 iov[1].iov_base = (char *)&client->packet;
281 iov[1].iov_len = client->packet_length;
282
283 if (to->sin_addr.s_addr == INADDR_BROADCAST) {
284 result = writev(ifi->wfdesc, iov, IOVCNT);
285 } else {
286 struct ip *ip = (struct ip *)buf;
287
288 /*
289 * DragonFly's raw socket expects ip_len/ip_off
290 * in host byte order.
291 */
292 ip->ip_len = ntohs(ip->ip_len);
293 ip->ip_off = ntohs(ip->ip_off);
294
295 memset(&msg, 0, sizeof(msg));
296 msg.msg_name = (struct sockaddr *)to;
297 msg.msg_namelen = sizeof(*to);
298 msg.msg_iov = iov;
299 msg.msg_iovlen = IOVCNT;
300 result = sendmsg(ifi->ufdesc, &msg, 0);
301 }
302
303 if (result == -1)
304 warning("send_packet: %m");
305 return (result);
306 }
307
308 ssize_t
receive_packet(struct sockaddr_in * from,struct hardware * hfrom)309 receive_packet(struct sockaddr_in *from, struct hardware *hfrom)
310 {
311 int length = 0, offset = 0;
312 struct bpf_hdr hdr;
313
314 /*
315 * All this complexity is because BPF doesn't guarantee that
316 * only one packet will be returned at a time. We're getting
317 * what we deserve, though - this is a terrible abuse of the BPF
318 * interface. Sigh.
319 */
320
321 /* Process packets until we get one we can return or until we've
322 * done a read and gotten nothing we can return...
323 */
324 do {
325 /* If the buffer is empty, fill it. */
326 if (ifi->rbuf_offset >= ifi->rbuf_len) {
327 length = read(ifi->rfdesc, ifi->rbuf, ifi->rbuf_max);
328 if (length <= 0)
329 return (length);
330 ifi->rbuf_offset = 0;
331 ifi->rbuf_len = BPF_WORDALIGN(length);
332 }
333
334 /*
335 * If there isn't room for a whole bpf header, something
336 * went wrong, but we'll ignore it and hope it goes
337 * away... XXX
338 */
339 if (ifi->rbuf_len - ifi->rbuf_offset < sizeof(hdr)) {
340 ifi->rbuf_offset = ifi->rbuf_len;
341 continue;
342 }
343
344 /* Copy out a bpf header... */
345 memcpy(&hdr, &ifi->rbuf[ifi->rbuf_offset], sizeof(hdr));
346
347 /*
348 * If the bpf header plus data doesn't fit in what's
349 * left of the buffer, stick head in sand yet again...
350 */
351 if (ifi->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
352 ifi->rbuf_len) {
353 ifi->rbuf_offset = ifi->rbuf_len;
354 continue;
355 }
356
357 /*
358 * If the captured data wasn't the whole packet, or if
359 * the packet won't fit in the input buffer, all we can
360 * do is drop it.
361 */
362 if (hdr.bh_caplen != hdr.bh_datalen) {
363 ifi->rbuf_offset = BPF_WORDALIGN(
364 ifi->rbuf_offset + hdr.bh_hdrlen +
365 hdr.bh_caplen);
366 continue;
367 }
368
369 /* Skip over the BPF header... */
370 ifi->rbuf_offset += hdr.bh_hdrlen;
371
372 /* Decode the physical header... */
373 offset = decode_hw_header(ifi->rbuf, ifi->rbuf_offset, hfrom);
374
375 /*
376 * If a physical layer checksum failed (dunno of any
377 * physical layer that supports this, but WTH), skip
378 * this packet.
379 */
380 if (offset < 0) {
381 ifi->rbuf_offset = BPF_WORDALIGN(
382 ifi->rbuf_offset + hdr.bh_caplen);
383 continue;
384 }
385 ifi->rbuf_offset += offset;
386 hdr.bh_caplen -= offset;
387
388 /* Decode the IP and UDP headers... */
389 offset = decode_udp_ip_header(ifi->rbuf,
390 ifi->rbuf_offset, from, NULL, hdr.bh_caplen);
391
392 /* If the IP or UDP checksum was bad, skip the packet... */
393 if (offset < 0) {
394 ifi->rbuf_offset = BPF_WORDALIGN(
395 ifi->rbuf_offset + hdr.bh_caplen);
396 continue;
397 }
398 ifi->rbuf_offset += offset;
399 hdr.bh_caplen -= offset;
400
401 /*
402 * If there's not enough room to stash the packet data,
403 * we have to skip it (this shouldn't happen in real
404 * life, though).
405 */
406 if (hdr.bh_caplen > sizeof(client->packet)) {
407 ifi->rbuf_offset = BPF_WORDALIGN(
408 ifi->rbuf_offset + hdr.bh_caplen);
409 continue;
410 }
411
412 /* Copy out the data in the packet... */
413 memset(&client->packet, DHO_END, sizeof(client->packet));
414 memcpy(&client->packet, ifi->rbuf + ifi->rbuf_offset,
415 hdr.bh_caplen);
416 ifi->rbuf_offset = BPF_WORDALIGN(ifi->rbuf_offset +
417 hdr.bh_caplen);
418 return (hdr.bh_caplen);
419 } while (!length);
420 return (0);
421 }
422