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
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46#include "dhcpd.h"
47#include <sys/ioctl.h>
48#include <sys/uio.h>
49
50#include <net/bpf.h>
51#include <netinet/in_systm.h>
52#include <netinet/ip.h>
53#include <netinet/udp.h>
54#include <netinet/if_ether.h>
55
56#define BPF_FORMAT "/dev/bpf%d"
57
58/*
59 * Called by get_interface_list for each interface that's discovered.
60 * Opens a packet filter for each interface and adds it to the select
61 * mask.
62 */
63int
64if_register_bpf(struct interface_info *info)
65{
66 char filename[50];
67 int sock, b;
68
69 /* Open a BPF device */
70 for (b = 0; 1; b++) {
71 snprintf(filename, sizeof(filename), BPF_FORMAT, b);
72 sock = open(filename, O_RDWR, 0);
73 if (sock < 0) {
74 if (errno == EBUSY)
75 continue;
76 else
77 error("Can't find free bpf: %m");
78 } else
79 break;
80 }
81
82 /* Set the BPF device to point at this interface. */
83 if (ioctl(sock, BIOCSETIF, info->ifp) < 0)
84 error("Can't attach interface %s to bpf device %s: %m",
85 info->name, filename);
86
87 return (sock);
88}
89
90void
91if_register_send(struct interface_info *info)
92{
93 /*
94 * If we're using the bpf API for sending and receiving, we
95 * don't need to register this interface twice.
96 */
97 info->wfdesc = info->rfdesc;
98}
99
100/*
101 * Packet filter program...
102 *
103 * XXX: Changes to the filter program may require changes to the
104 * constant offsets used in if_register_send to patch the BPF program!
105 */
106struct bpf_insn dhcp_bpf_filter[] = {
107 /* Make sure this is an IP packet... */
108 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
109 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
110
111 /* Make sure it's a UDP packet... */
112 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
113 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
114
115 /* Make sure this isn't a fragment... */
116 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
117 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
118
119 /* Get the IP header length... */
120 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
121
122 /* Make sure it's to the right port... */
123 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
124 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */
125
126 /* If we passed all the tests, ask for the whole packet. */
127 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
128
129 /* Otherwise, drop it. */
130 BPF_STMT(BPF_RET+BPF_K, 0),
131};
132
133int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
134
135/*
136 * Packet write filter program:
137 * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
138 */
139struct bpf_insn dhcp_bpf_wfilter[] = {
140 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
141 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
142
143 /* Make sure this is an IP packet... */
144 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
145 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
146
147 /* Make sure it's a UDP packet... */
148 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
149 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
150
151 /* Make sure this isn't a fragment... */
152 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
153 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */
154
155 /* Get the IP header length... */
156 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
157
158 /* Make sure it's from the right port... */
159 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
160 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
161
162 /* Make sure it is to the right ports ... */
163 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
164 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
165
166 /* If we passed all the tests, ask for the whole packet. */
167 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
168
169 /* Otherwise, drop it. */
170 BPF_STMT(BPF_RET+BPF_K, 0),
171};
172
173int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
174
175void
176if_register_receive(struct interface_info *info)
177{
178 struct bpf_version v;
179 struct bpf_program p;
180 int flag = 1, sz;
181
182 /* Open a BPF device and hang it on this interface... */
183 info->rfdesc = if_register_bpf(info);
184
185 /* Make sure the BPF version is in range... */
186 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0)
187 error("Can't get BPF version: %m");
188
189 if (v.bv_major != BPF_MAJOR_VERSION ||
190 v.bv_minor < BPF_MINOR_VERSION)
191 error("Kernel BPF version out of range - recompile dhcpd!");
192
193 /*
194 * Set immediate mode so that reads return as soon as a packet
195 * comes in, rather than waiting for the input buffer to fill
196 * with packets.
197 */
198 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0)
199 error("Can't set immediate mode on bpf device: %m");
200
201 /* Get the required BPF buffer length from the kernel. */
202 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0)
203 error("Can't get bpf buffer length: %m");
204 info->rbuf_max = sz;
205 info->rbuf = malloc(info->rbuf_max);
206 if (!info->rbuf)
207 error("Can't allocate %lu bytes for bpf input buffer.",
208 (unsigned long)info->rbuf_max);
209 info->rbuf_offset = 0;
210 info->rbuf_len = 0;
211
212 /* Set up the bpf filter program structure. */
213 p.bf_len = dhcp_bpf_filter_len;
214 p.bf_insns = dhcp_bpf_filter;
215
216 /* Patch the server port into the BPF program...
217 *
218 * XXX: changes to filter program may require changes to the
219 * insn number(s) used below!
220 */
221 dhcp_bpf_filter[8].k = LOCAL_PORT;
222
223 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
224 error("Can't install packet filter program: %m");
225
226 /* Set up the bpf write filter program structure. */
227 p.bf_len = dhcp_bpf_wfilter_len;
228 p.bf_insns = dhcp_bpf_wfilter;
229
230 if (dhcp_bpf_wfilter[7].k == 0x1fff)
231 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
232
233 if (ioctl(info->rfdesc, BIOCSETWF, &p) < 0)
234 error("Can't install write filter program: %m");
235
236 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0)
237 error("Cannot lock bpf");
238}
239
240ssize_t
241send_packet(struct interface_info *interface, struct dhcp_packet *raw,
242 size_t len, struct in_addr from, struct sockaddr_in *to,
243 struct hardware *hto)
244{
245 unsigned char buf[256];
246 struct iovec iov[2];
247 int result, bufp = 0;
248
249 /* Assemble the headers... */
250 assemble_hw_header(interface, buf, &bufp, hto);
251 assemble_udp_ip_header(buf, &bufp, from.s_addr,
252 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len);
253
254 /* Fire it off */
255 iov[0].iov_base = (char *)buf;
256 iov[0].iov_len = bufp;
257 iov[1].iov_base = (char *)raw;
258 iov[1].iov_len = len;
259
260 result = writev(interface->wfdesc, iov, 2);
261 if (result < 0)
262 warning("send_packet: %m");
263 return (result);
264}
265
266ssize_t
267receive_packet(struct interface_info *interface, unsigned char *buf,
268 size_t len, struct sockaddr_in *from, struct hardware *hfrom)
269{
270 int length = 0, offset = 0;
271 struct bpf_hdr hdr;
272
273 /*
274 * All this complexity is because BPF doesn't guarantee that
275 * only one packet will be returned at a time. We're getting
276 * what we deserve, though - this is a terrible abuse of the BPF
277 * interface. Sigh.
278 */
279
280 /* Process packets until we get one we can return or until we've
281 * done a read and gotten nothing we can return...
282 */
283 do {
284 /* If the buffer is empty, fill it. */
285 if (interface->rbuf_offset == interface->rbuf_len) {
286 length = read(interface->rfdesc, interface->rbuf,
287 interface->rbuf_max);
288 if (length <= 0)
289 return (length);
290 interface->rbuf_offset = 0;
291 interface->rbuf_len = length;
292 }
293
294 /*
295 * If there isn't room for a whole bpf header, something
296 * went wrong, but we'll ignore it and hope it goes
297 * away... XXX
298 */
299 if (interface->rbuf_len - interface->rbuf_offset <
300 sizeof(hdr)) {
301 interface->rbuf_offset = interface->rbuf_len;
302 continue;
303 }
304
305 /* Copy out a bpf header... */
306 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
307 sizeof(hdr));
308
309 /*
310 * If the bpf header plus data doesn't fit in what's
311 * left of the buffer, stick head in sand yet again...
312 */
313 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
314 interface->rbuf_len) {
315 interface->rbuf_offset = interface->rbuf_len;
316 continue;
317 }
318
319 /* Skip over the BPF header... */
320 interface->rbuf_offset += hdr.bh_hdrlen;
321
322 /*
323 * If the captured data wasn't the whole packet, or if
324 * the packet won't fit in the input buffer, all we can
325 * do is drop it.
326 */
327 if (hdr.bh_caplen != hdr.bh_datalen) {
328 interface->rbuf_offset =
329 BPF_WORDALIGN(interface->rbuf_offset +
330 hdr.bh_caplen);
331 continue;
332 }
333
334 /* Decode the physical header... */
335 offset = decode_hw_header(interface->rbuf,
336 interface->rbuf_offset, hfrom);
337
338 /*
339 * If a physical layer checksum failed (dunno of any
340 * physical layer that supports this, but WTH), skip
341 * this packet.
342 */
343 if (offset < 0) {
344 interface->rbuf_offset =
345 BPF_WORDALIGN(interface->rbuf_offset +
346 hdr.bh_caplen);
347 continue;
348 }
349 interface->rbuf_offset += offset;
350 hdr.bh_caplen -= offset;
351
352 /* Decode the IP and UDP headers... */
353 offset = decode_udp_ip_header(interface->rbuf,
354 interface->rbuf_offset, from, NULL, hdr.bh_caplen);
355
356 /* If the IP or UDP checksum was bad, skip the packet... */
357 if (offset < 0) {
358 interface->rbuf_offset =
359 BPF_WORDALIGN(interface->rbuf_offset +
360 hdr.bh_caplen);
361 continue;
362 }
363 interface->rbuf_offset += offset;
364 hdr.bh_caplen -= offset;
365
366 /*
367 * If there's not enough room to stash the packet data,
368 * we have to skip it (this shouldn't happen in real
369 * life, though).
370 */
371 if (hdr.bh_caplen > len) {
372 interface->rbuf_offset =
373 BPF_WORDALIGN(interface->rbuf_offset +
374 hdr.bh_caplen);
375 continue;
376 }
377
378 /* Copy out the data in the packet... */
379 memcpy(buf, interface->rbuf + interface->rbuf_offset,
380 hdr.bh_caplen);
381 interface->rbuf_offset =
382 BPF_WORDALIGN(interface->rbuf_offset +
383 hdr.bh_caplen);
384 return (hdr.bh_caplen);
385 } while (!length);
386 return (0);
387}
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