1 /* $OpenBSD: bpf.c,v 1.6 2005/07/29 17:26:28 krw 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 "dhcpd.h"
44 #include <sys/ioctl.h>
45 #include <sys/uio.h>
46
47 #include <net/bpf.h>
48 #include <netinet/in_systm.h>
49 #include <netinet/ip.h>
50 #include <netinet/udp.h>
51 #include <netinet/if_ether.h>
52
53 #define BPF_FORMAT "/dev/bpf%d"
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(struct interface_info * info)61 if_register_bpf(struct interface_info *info)
62 {
63 char filename[50];
64 int sock, b;
65
66 /* Open a BPF device */
67 for (b = 0; 1; b++) {
68 snprintf(filename, sizeof(filename), BPF_FORMAT, b);
69 sock = open(filename, O_RDWR, 0);
70 if (sock < 0) {
71 if (errno == EBUSY)
72 continue;
73 else
74 error("Can't find free bpf: %m");
75 } else
76 break;
77 }
78
79 /* Set the BPF device to point at this interface. */
80 if (ioctl(sock, BIOCSETIF, info->ifp) < 0)
81 error("Can't attach interface %s to bpf device %s: %m",
82 info->name, filename);
83
84 return (sock);
85 }
86
87 void
if_register_send(struct interface_info * info)88 if_register_send(struct interface_info *info)
89 {
90 /*
91 * If we're using the bpf API for sending and receiving, we
92 * don't need to register this interface twice.
93 */
94 info->wfdesc = info->rfdesc;
95 }
96
97 /*
98 * Packet read filter program: 'ip and udp and dst port bootps'
99 */
100 struct bpf_insn dhcp_bpf_filter[] = {
101 /* Make sure this is an IP packet... */
102 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
103 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
104
105 /* Make sure it's a UDP packet... */
106 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
107 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
108
109 /* Make sure this isn't a fragment... */
110 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
111 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
112
113 /* Get the IP header length... */
114 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
115
116 /* Make sure it's to the right port... */
117 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
118 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1),
119
120 /* If we passed all the tests, ask for the whole packet. */
121 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
122
123 /* Otherwise, drop it. */
124 BPF_STMT(BPF_RET+BPF_K, 0),
125 };
126
127 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
128
129
130 /*
131 * Packet write filter program:
132 * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
133 */
134 struct bpf_insn dhcp_bpf_wfilter[] = {
135 /* Make sure this is an IP packet... */
136 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
137 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 11),
138
139 /* Make sure it's a UDP packet... */
140 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
141 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 9),
142
143 /* Make sure this isn't a fragment... */
144 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
145 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 7, 0),
146
147 /* Get the IP header length... */
148 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
149
150 /* Make sure it's from the right port... */
151 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
152 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 4),
153
154 /* Make sure it is to the right ports ... */
155 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
156 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, CLIENT_PORT, 1, 0),
157 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1),
158
159 /* If we passed all the tests, ask for the whole packet. */
160 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
161
162 /* Otherwise, drop it. */
163 BPF_STMT(BPF_RET+BPF_K, 0),
164 };
165
166 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
167
168 void
if_register_receive(struct interface_info * info)169 if_register_receive(struct interface_info *info)
170 {
171 struct bpf_version v;
172 struct bpf_program p;
173 int flag = 1, sz, cmplt = 0;
174
175 /* Open a BPF device and hang it on this interface... */
176 info->rfdesc = if_register_bpf(info);
177
178 /* Make sure the BPF version is in range... */
179 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0)
180 error("Can't get BPF version: %m");
181
182 if (v.bv_major != BPF_MAJOR_VERSION ||
183 v.bv_minor < BPF_MINOR_VERSION)
184 error("Kernel BPF version out of range - recompile dhcpd!");
185
186 /*
187 * Set immediate mode so that reads return as soon as a packet
188 * comes in, rather than waiting for the input buffer to fill
189 * with packets.
190 */
191 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0)
192 error("Can't set immediate mode on bpf device: %m");
193
194 /* make sure kernel fills in the source ethernet address */
195 if (ioctl(info->rfdesc, BIOCSHDRCMPLT, &cmplt) < 0)
196 error("Can't set header complete flag on bpf device: %m");
197
198 /* Get the required BPF buffer length from the kernel. */
199 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0)
200 error("Can't get bpf buffer length: %m");
201 info->rbuf_max = sz;
202 info->rbuf = malloc(info->rbuf_max);
203 if (!info->rbuf)
204 error("Can't allocate %lu bytes for bpf input buffer.",
205 (unsigned long)info->rbuf_max);
206 info->rbuf_offset = 0;
207 info->rbuf_len = 0;
208
209 /* Set up the bpf filter program structure. */
210 p.bf_len = dhcp_bpf_filter_len;
211 p.bf_insns = dhcp_bpf_filter;
212
213 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
214 error("Can't install packet filter program: %m");
215
216 /* Set up the bpf write filter program structure. */
217 p.bf_len = dhcp_bpf_wfilter_len;
218 p.bf_insns = dhcp_bpf_wfilter;
219
220 if (ioctl(info->rfdesc, BIOCSETWF, &p) < 0)
221 error("Can't install write filter program: %m");
222
223 /* make sure these settings cannot be changed after dropping privs */
224 if (ioctl(info->rfdesc, BIOCLOCK) < 0)
225 error("Failed to lock bpf descriptor: %m");
226 }
227
228 ssize_t
send_packet(struct interface_info * interface,struct dhcp_packet * raw,size_t len,struct in_addr from,struct sockaddr_in * to,struct hardware * hto)229 send_packet(struct interface_info *interface, struct dhcp_packet *raw,
230 size_t len, struct in_addr from, struct sockaddr_in *to,
231 struct hardware *hto)
232 {
233 unsigned char buf[256];
234 struct iovec iov[2];
235 int result, bufp = 0;
236
237 /* Assemble the headers... */
238 assemble_hw_header(interface, buf, &bufp, hto);
239 assemble_udp_ip_header(interface, buf, &bufp, from.s_addr,
240 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len);
241
242 /* Fire it off */
243 iov[0].iov_base = (char *)buf;
244 iov[0].iov_len = bufp;
245 iov[1].iov_base = (char *)raw;
246 iov[1].iov_len = len;
247
248 result = writev(interface->wfdesc, iov, 2);
249 if (result < 0)
250 warning("send_packet: %m");
251 return (result);
252 }
253
254 ssize_t
receive_packet(struct interface_info * interface,unsigned char * buf,size_t len,struct sockaddr_in * from,struct hardware * hfrom)255 receive_packet(struct interface_info *interface, unsigned char *buf,
256 size_t len, struct sockaddr_in *from, struct hardware *hfrom)
257 {
258 int length = 0, offset = 0;
259 struct bpf_hdr hdr;
260
261 /*
262 * All this complexity is because BPF doesn't guarantee that
263 * only one packet will be returned at a time. We're getting
264 * what we deserve, though - this is a terrible abuse of the BPF
265 * interface. Sigh.
266 */
267
268 /* Process packets until we get one we can return or until we've
269 * done a read and gotten nothing we can return...
270 */
271 do {
272 /* If the buffer is empty, fill it. */
273 if (interface->rbuf_offset == interface->rbuf_len) {
274 length = read(interface->rfdesc, interface->rbuf,
275 interface->rbuf_max);
276 if (length <= 0)
277 return (length);
278 interface->rbuf_offset = 0;
279 interface->rbuf_len = BPF_WORDALIGN(length);
280 }
281
282 /*
283 * If there isn't room for a whole bpf header, something
284 * went wrong, but we'll ignore it and hope it goes
285 * away... XXX
286 */
287 if (interface->rbuf_len - interface->rbuf_offset <
288 sizeof(hdr)) {
289 interface->rbuf_offset = interface->rbuf_len;
290 continue;
291 }
292
293 /* Copy out a bpf header... */
294 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
295 sizeof(hdr));
296
297 /*
298 * If the bpf header plus data doesn't fit in what's
299 * left of the buffer, stick head in sand yet again...
300 */
301 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
302 interface->rbuf_len) {
303 interface->rbuf_offset = interface->rbuf_len;
304 continue;
305 }
306
307 /*
308 * If the captured data wasn't the whole packet, or if
309 * the packet won't fit in the input buffer, all we can
310 * do is drop it.
311 */
312 if (hdr.bh_caplen != hdr.bh_datalen) {
313 interface->rbuf_offset = BPF_WORDALIGN(
314 interface->rbuf_offset + hdr.bh_hdrlen +
315 hdr.bh_caplen);
316 continue;
317 }
318
319 /* Skip over the BPF header... */
320 interface->rbuf_offset += hdr.bh_hdrlen;
321
322 /* Decode the physical header... */
323 offset = decode_hw_header(interface,
324 interface->rbuf, interface->rbuf_offset, hfrom);
325
326 /*
327 * If a physical layer checksum failed (dunno of any
328 * physical layer that supports this, but WTH), skip
329 * this packet.
330 */
331 if (offset < 0) {
332 interface->rbuf_offset = BPF_WORDALIGN(
333 interface->rbuf_offset + hdr.bh_caplen);
334 continue;
335 }
336 interface->rbuf_offset += offset;
337 hdr.bh_caplen -= offset;
338
339 /* Decode the IP and UDP headers... */
340 offset = decode_udp_ip_header(interface, interface->rbuf,
341 interface->rbuf_offset, from, NULL, hdr.bh_caplen);
342
343 /* If the IP or UDP checksum was bad, skip the packet... */
344 if (offset < 0) {
345 interface->rbuf_offset = BPF_WORDALIGN(
346 interface->rbuf_offset + hdr.bh_caplen);
347 continue;
348 }
349 interface->rbuf_offset += offset;
350 hdr.bh_caplen -= offset;
351
352 /*
353 * If there's not enough room to stash the packet data,
354 * we have to skip it (this shouldn't happen in real
355 * life, though).
356 */
357 if (hdr.bh_caplen > len) {
358 interface->rbuf_offset = BPF_WORDALIGN(
359 interface->rbuf_offset + hdr.bh_caplen);
360 continue;
361 }
362
363 /* Copy out the data in the packet... */
364 memcpy(buf, interface->rbuf + interface->rbuf_offset,
365 hdr.bh_caplen);
366 interface->rbuf_offset = BPF_WORDALIGN(interface->rbuf_offset +
367 hdr.bh_caplen);
368 return (hdr.bh_caplen);
369 } while (!length);
370 return (0);
371 }
372