FreeBSD/Linux Kernel Cross Reference
sys/net/bpf_filter.c
1 /*-
2 * Copyright (c) 1990, 1991, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * This code is derived from the Stanford/CMU enet packet filter,
6 * (net/enet.c) distributed as part of 4.3BSD, and code contributed
7 * to Berkeley by Steven McCanne and Van Jacobson both of Lawrence
8 * Berkeley Laboratory.
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 * 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 * 4. Neither the name of the University nor the names of its contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 *
34 * @(#)bpf_filter.c 8.1 (Berkeley) 6/10/93
35 *
36 * $FreeBSD$
37 */
38
39 #include <sys/param.h>
40
41 #ifdef sun
42 #include <netinet/in.h>
43 #endif
44
45 #ifndef __i386__
46 #define BPF_ALIGN
47 #endif
48
49 #ifndef BPF_ALIGN
50 #define EXTRACT_SHORT(p) ((u_int16_t)ntohs(*(u_int16_t *)p))
51 #define EXTRACT_LONG(p) (ntohl(*(u_int32_t *)p))
52 #else
53 #define EXTRACT_SHORT(p)\
54 ((u_int16_t)\
55 ((u_int16_t)*((u_char *)p+0)<<8|\
56 (u_int16_t)*((u_char *)p+1)<<0))
57 #define EXTRACT_LONG(p)\
58 ((u_int32_t)*((u_char *)p+0)<<24|\
59 (u_int32_t)*((u_char *)p+1)<<16|\
60 (u_int32_t)*((u_char *)p+2)<<8|\
61 (u_int32_t)*((u_char *)p+3)<<0)
62 #endif
63
64 #ifdef _KERNEL
65 #include <sys/mbuf.h>
66 #endif
67 #include <net/bpf.h>
68 #ifdef _KERNEL
69 #define MINDEX(m, k) \
70 { \
71 register int len = m->m_len; \
72 \
73 while (k >= len) { \
74 k -= len; \
75 m = m->m_next; \
76 if (m == 0) \
77 return 0; \
78 len = m->m_len; \
79 } \
80 }
81
82 static u_int16_t m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err);
83 static u_int32_t m_xword(struct mbuf *m, bpf_u_int32 k, int *err);
84
85 static u_int32_t
86 m_xword(m, k, err)
87 register struct mbuf *m;
88 register bpf_u_int32 k;
89 register int *err;
90 {
91 register size_t len;
92 register u_char *cp, *np;
93 register struct mbuf *m0;
94
95 len = m->m_len;
96 while (k >= len) {
97 k -= len;
98 m = m->m_next;
99 if (m == 0)
100 goto bad;
101 len = m->m_len;
102 }
103 cp = mtod(m, u_char *) + k;
104 if (len - k >= 4) {
105 *err = 0;
106 return EXTRACT_LONG(cp);
107 }
108 m0 = m->m_next;
109 if (m0 == 0 || m0->m_len + len - k < 4)
110 goto bad;
111 *err = 0;
112 np = mtod(m0, u_char *);
113 switch (len - k) {
114
115 case 1:
116 return
117 ((u_int32_t)cp[0] << 24) |
118 ((u_int32_t)np[0] << 16) |
119 ((u_int32_t)np[1] << 8) |
120 (u_int32_t)np[2];
121
122 case 2:
123 return
124 ((u_int32_t)cp[0] << 24) |
125 ((u_int32_t)cp[1] << 16) |
126 ((u_int32_t)np[0] << 8) |
127 (u_int32_t)np[1];
128
129 default:
130 return
131 ((u_int32_t)cp[0] << 24) |
132 ((u_int32_t)cp[1] << 16) |
133 ((u_int32_t)cp[2] << 8) |
134 (u_int32_t)np[0];
135 }
136 bad:
137 *err = 1;
138 return 0;
139 }
140
141 static u_int16_t
142 m_xhalf(m, k, err)
143 register struct mbuf *m;
144 register bpf_u_int32 k;
145 register int *err;
146 {
147 register size_t len;
148 register u_char *cp;
149 register struct mbuf *m0;
150
151 len = m->m_len;
152 while (k >= len) {
153 k -= len;
154 m = m->m_next;
155 if (m == 0)
156 goto bad;
157 len = m->m_len;
158 }
159 cp = mtod(m, u_char *) + k;
160 if (len - k >= 2) {
161 *err = 0;
162 return EXTRACT_SHORT(cp);
163 }
164 m0 = m->m_next;
165 if (m0 == 0)
166 goto bad;
167 *err = 0;
168 return (cp[0] << 8) | mtod(m0, u_char *)[0];
169 bad:
170 *err = 1;
171 return 0;
172 }
173 #endif
174
175 /*
176 * Execute the filter program starting at pc on the packet p
177 * wirelen is the length of the original packet
178 * buflen is the amount of data present
179 */
180 u_int
181 bpf_filter(pc, p, wirelen, buflen)
182 register const struct bpf_insn *pc;
183 register u_char *p;
184 u_int wirelen;
185 register u_int buflen;
186 {
187 register u_int32_t A = 0, X = 0;
188 register bpf_u_int32 k;
189 int32_t mem[BPF_MEMWORDS];
190
191 if (pc == 0)
192 /*
193 * No filter means accept all.
194 */
195 return (u_int)-1;
196
197 --pc;
198 while (1) {
199 ++pc;
200 switch (pc->code) {
201
202 default:
203 #ifdef _KERNEL
204 return 0;
205 #else
206 abort();
207 #endif
208 case BPF_RET|BPF_K:
209 return (u_int)pc->k;
210
211 case BPF_RET|BPF_A:
212 return (u_int)A;
213
214 case BPF_LD|BPF_W|BPF_ABS:
215 k = pc->k;
216 if (k > buflen || sizeof(int32_t) > buflen - k) {
217 #ifdef _KERNEL
218 int merr;
219
220 if (buflen != 0)
221 return 0;
222 A = m_xword((struct mbuf *)p, k, &merr);
223 if (merr != 0)
224 return 0;
225 continue;
226 #else
227 return 0;
228 #endif
229 }
230 #ifdef BPF_ALIGN
231 if (((intptr_t)(p + k) & 3) != 0)
232 A = EXTRACT_LONG(&p[k]);
233 else
234 #endif
235 A = ntohl(*(int32_t *)(p + k));
236 continue;
237
238 case BPF_LD|BPF_H|BPF_ABS:
239 k = pc->k;
240 if (k > buflen || sizeof(int16_t) > buflen - k) {
241 #ifdef _KERNEL
242 int merr;
243
244 if (buflen != 0)
245 return 0;
246 A = m_xhalf((struct mbuf *)p, k, &merr);
247 continue;
248 #else
249 return 0;
250 #endif
251 }
252 A = EXTRACT_SHORT(&p[k]);
253 continue;
254
255 case BPF_LD|BPF_B|BPF_ABS:
256 k = pc->k;
257 if (k >= buflen) {
258 #ifdef _KERNEL
259 register struct mbuf *m;
260
261 if (buflen != 0)
262 return 0;
263 m = (struct mbuf *)p;
264 MINDEX(m, k);
265 A = mtod(m, u_char *)[k];
266 continue;
267 #else
268 return 0;
269 #endif
270 }
271 A = p[k];
272 continue;
273
274 case BPF_LD|BPF_W|BPF_LEN:
275 A = wirelen;
276 continue;
277
278 case BPF_LDX|BPF_W|BPF_LEN:
279 X = wirelen;
280 continue;
281
282 case BPF_LD|BPF_W|BPF_IND:
283 k = X + pc->k;
284 if (pc->k > buflen || X > buflen - pc->k ||
285 sizeof(int32_t) > buflen - k) {
286 #ifdef _KERNEL
287 int merr;
288
289 if (buflen != 0)
290 return 0;
291 A = m_xword((struct mbuf *)p, k, &merr);
292 if (merr != 0)
293 return 0;
294 continue;
295 #else
296 return 0;
297 #endif
298 }
299 #ifdef BPF_ALIGN
300 if (((intptr_t)(p + k) & 3) != 0)
301 A = EXTRACT_LONG(&p[k]);
302 else
303 #endif
304 A = ntohl(*(int32_t *)(p + k));
305 continue;
306
307 case BPF_LD|BPF_H|BPF_IND:
308 k = X + pc->k;
309 if (X > buflen || pc->k > buflen - X ||
310 sizeof(int16_t) > buflen - k) {
311 #ifdef _KERNEL
312 int merr;
313
314 if (buflen != 0)
315 return 0;
316 A = m_xhalf((struct mbuf *)p, k, &merr);
317 if (merr != 0)
318 return 0;
319 continue;
320 #else
321 return 0;
322 #endif
323 }
324 A = EXTRACT_SHORT(&p[k]);
325 continue;
326
327 case BPF_LD|BPF_B|BPF_IND:
328 k = X + pc->k;
329 if (pc->k >= buflen || X >= buflen - pc->k) {
330 #ifdef _KERNEL
331 register struct mbuf *m;
332
333 if (buflen != 0)
334 return 0;
335 m = (struct mbuf *)p;
336 MINDEX(m, k);
337 A = mtod(m, u_char *)[k];
338 continue;
339 #else
340 return 0;
341 #endif
342 }
343 A = p[k];
344 continue;
345
346 case BPF_LDX|BPF_MSH|BPF_B:
347 k = pc->k;
348 if (k >= buflen) {
349 #ifdef _KERNEL
350 register struct mbuf *m;
351
352 if (buflen != 0)
353 return 0;
354 m = (struct mbuf *)p;
355 MINDEX(m, k);
356 X = (mtod(m, u_char *)[k] & 0xf) << 2;
357 continue;
358 #else
359 return 0;
360 #endif
361 }
362 X = (p[pc->k] & 0xf) << 2;
363 continue;
364
365 case BPF_LD|BPF_IMM:
366 A = pc->k;
367 continue;
368
369 case BPF_LDX|BPF_IMM:
370 X = pc->k;
371 continue;
372
373 case BPF_LD|BPF_MEM:
374 A = mem[pc->k];
375 continue;
376
377 case BPF_LDX|BPF_MEM:
378 X = mem[pc->k];
379 continue;
380
381 case BPF_ST:
382 mem[pc->k] = A;
383 continue;
384
385 case BPF_STX:
386 mem[pc->k] = X;
387 continue;
388
389 case BPF_JMP|BPF_JA:
390 pc += pc->k;
391 continue;
392
393 case BPF_JMP|BPF_JGT|BPF_K:
394 pc += (A > pc->k) ? pc->jt : pc->jf;
395 continue;
396
397 case BPF_JMP|BPF_JGE|BPF_K:
398 pc += (A >= pc->k) ? pc->jt : pc->jf;
399 continue;
400
401 case BPF_JMP|BPF_JEQ|BPF_K:
402 pc += (A == pc->k) ? pc->jt : pc->jf;
403 continue;
404
405 case BPF_JMP|BPF_JSET|BPF_K:
406 pc += (A & pc->k) ? pc->jt : pc->jf;
407 continue;
408
409 case BPF_JMP|BPF_JGT|BPF_X:
410 pc += (A > X) ? pc->jt : pc->jf;
411 continue;
412
413 case BPF_JMP|BPF_JGE|BPF_X:
414 pc += (A >= X) ? pc->jt : pc->jf;
415 continue;
416
417 case BPF_JMP|BPF_JEQ|BPF_X:
418 pc += (A == X) ? pc->jt : pc->jf;
419 continue;
420
421 case BPF_JMP|BPF_JSET|BPF_X:
422 pc += (A & X) ? pc->jt : pc->jf;
423 continue;
424
425 case BPF_ALU|BPF_ADD|BPF_X:
426 A += X;
427 continue;
428
429 case BPF_ALU|BPF_SUB|BPF_X:
430 A -= X;
431 continue;
432
433 case BPF_ALU|BPF_MUL|BPF_X:
434 A *= X;
435 continue;
436
437 case BPF_ALU|BPF_DIV|BPF_X:
438 if (X == 0)
439 return 0;
440 A /= X;
441 continue;
442
443 case BPF_ALU|BPF_AND|BPF_X:
444 A &= X;
445 continue;
446
447 case BPF_ALU|BPF_OR|BPF_X:
448 A |= X;
449 continue;
450
451 case BPF_ALU|BPF_LSH|BPF_X:
452 A <<= X;
453 continue;
454
455 case BPF_ALU|BPF_RSH|BPF_X:
456 A >>= X;
457 continue;
458
459 case BPF_ALU|BPF_ADD|BPF_K:
460 A += pc->k;
461 continue;
462
463 case BPF_ALU|BPF_SUB|BPF_K:
464 A -= pc->k;
465 continue;
466
467 case BPF_ALU|BPF_MUL|BPF_K:
468 A *= pc->k;
469 continue;
470
471 case BPF_ALU|BPF_DIV|BPF_K:
472 A /= pc->k;
473 continue;
474
475 case BPF_ALU|BPF_AND|BPF_K:
476 A &= pc->k;
477 continue;
478
479 case BPF_ALU|BPF_OR|BPF_K:
480 A |= pc->k;
481 continue;
482
483 case BPF_ALU|BPF_LSH|BPF_K:
484 A <<= pc->k;
485 continue;
486
487 case BPF_ALU|BPF_RSH|BPF_K:
488 A >>= pc->k;
489 continue;
490
491 case BPF_ALU|BPF_NEG:
492 A = -A;
493 continue;
494
495 case BPF_MISC|BPF_TAX:
496 X = A;
497 continue;
498
499 case BPF_MISC|BPF_TXA:
500 A = X;
501 continue;
502 }
503 }
504 }
505
506 #ifdef _KERNEL
507 /*
508 * Return true if the 'fcode' is a valid filter program.
509 * The constraints are that each jump be forward and to a valid
510 * code. The code must terminate with either an accept or reject.
511 *
512 * The kernel needs to be able to verify an application's filter code.
513 * Otherwise, a bogus program could easily crash the system.
514 */
515 int
516 bpf_validate(f, len)
517 const struct bpf_insn *f;
518 int len;
519 {
520 register int i;
521 register const struct bpf_insn *p;
522
523 for (i = 0; i < len; ++i) {
524 /*
525 * Check that that jumps are forward, and within
526 * the code block.
527 */
528 p = &f[i];
529 if (BPF_CLASS(p->code) == BPF_JMP) {
530 register int from = i + 1;
531
532 if (BPF_OP(p->code) == BPF_JA) {
533 if (from >= len || p->k >= len - from)
534 return 0;
535 }
536 else if (from >= len || p->jt >= len - from ||
537 p->jf >= len - from)
538 return 0;
539 }
540 /*
541 * Check that memory operations use valid addresses.
542 */
543 if ((BPF_CLASS(p->code) == BPF_ST ||
544 (BPF_CLASS(p->code) == BPF_LD &&
545 (p->code & 0xe0) == BPF_MEM)) &&
546 p->k >= BPF_MEMWORDS)
547 return 0;
548 /*
549 * Check for constant division by 0.
550 */
551 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0)
552 return 0;
553 }
554 return BPF_CLASS(f[len - 1].code) == BPF_RET;
555 }
556 #endif
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