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 * %sccs.include.redist.c%
11 *
12 * @(#)bpf_filter.c 8.1 (Berkeley) 06/10/93
13 *
14 * static char rcsid[] =
15 * "$Header: bpf_filter.c,v 1.16 91/10/27 21:22:35 mccanne Exp $";
16 */
17
18 #include <sys/param.h>
19 #include <sys/types.h>
20 #include <sys/time.h>
21
22 #ifdef sun
23 #include <netinet/in.h>
24 #endif
25
26 #if defined(sparc) || defined(mips) || defined(ibm032)
27 #define BPF_ALIGN
28 #endif
29
30 #ifndef BPF_ALIGN
31 #define EXTRACT_SHORT(p) ((u_short)ntohs(*(u_short *)p))
32 #define EXTRACT_LONG(p) (ntohl(*(u_long *)p))
33 #else
34 #define EXTRACT_SHORT(p)\
35 ((u_short)\
36 ((u_short)*((u_char *)p+0)<<8|\
37 (u_short)*((u_char *)p+1)<<0))
38 #define EXTRACT_LONG(p)\
39 ((u_long)*((u_char *)p+0)<<24|\
40 (u_long)*((u_char *)p+1)<<16|\
41 (u_long)*((u_char *)p+2)<<8|\
42 (u_long)*((u_char *)p+3)<<0)
43 #endif
44
45 #ifdef KERNEL
46 #include <sys/mbuf.h>
47 #define MINDEX(m, k) \
48 { \
49 register int len = m->m_len; \
50 \
51 while (k >= len) { \
52 k -= len; \
53 m = m->m_next; \
54 if (m == 0) \
55 return 0; \
56 len = m->m_len; \
57 } \
58 }
59
60 static int
m_xword(m,k,err)61 m_xword(m, k, err)
62 register struct mbuf *m;
63 register int k, *err;
64 {
65 register int len;
66 register u_char *cp, *np;
67 register struct mbuf *m0;
68
69 len = m->m_len;
70 while (k >= len) {
71 k -= len;
72 m = m->m_next;
73 if (m == 0)
74 goto bad;
75 len = m->m_len;
76 }
77 cp = mtod(m, u_char *) + k;
78 if (len - k >= 4) {
79 *err = 0;
80 return EXTRACT_LONG(cp);
81 }
82 m0 = m->m_next;
83 if (m0 == 0 || m0->m_len + len - k < 4)
84 goto bad;
85 *err = 0;
86 np = mtod(m0, u_char *);
87 switch (len - k) {
88
89 case 1:
90 return (cp[k] << 24) | (np[0] << 16) | (np[1] << 8) | np[2];
91
92 case 2:
93 return (cp[k] << 24) | (cp[k + 1] << 16) | (np[0] << 8) |
94 np[1];
95
96 default:
97 return (cp[k] << 24) | (cp[k + 1] << 16) | (cp[k + 2] << 8) |
98 np[0];
99 }
100 bad:
101 *err = 1;
102 return 0;
103 }
104
105 static int
m_xhalf(m,k,err)106 m_xhalf(m, k, err)
107 register struct mbuf *m;
108 register int k, *err;
109 {
110 register int len;
111 register u_char *cp;
112 register struct mbuf *m0;
113
114 len = m->m_len;
115 while (k >= len) {
116 k -= len;
117 m = m->m_next;
118 if (m == 0)
119 goto bad;
120 len = m->m_len;
121 }
122 cp = mtod(m, u_char *) + k;
123 if (len - k >= 2) {
124 *err = 0;
125 return EXTRACT_SHORT(cp);
126 }
127 m0 = m->m_next;
128 if (m0 == 0)
129 goto bad;
130 *err = 0;
131 return (cp[k] << 8) | mtod(m0, u_char *)[0];
132 bad:
133 *err = 1;
134 return 0;
135 }
136 #endif
137
138 #include <net/bpf.h>
139 /*
140 * Execute the filter program starting at pc on the packet p
141 * wirelen is the length of the original packet
142 * buflen is the amount of data present
143 */
144 u_int
bpf_filter(pc,p,wirelen,buflen)145 bpf_filter(pc, p, wirelen, buflen)
146 register struct bpf_insn *pc;
147 register u_char *p;
148 u_int wirelen;
149 register u_int buflen;
150 {
151 register u_long A, X;
152 register int k;
153 long mem[BPF_MEMWORDS];
154
155 if (pc == 0)
156 /*
157 * No filter means accept all.
158 */
159 return (u_int)-1;
160 #ifdef lint
161 A = 0;
162 X = 0;
163 #endif
164 --pc;
165 while (1) {
166 ++pc;
167 switch (pc->code) {
168
169 default:
170 #ifdef KERNEL
171 return 0;
172 #else
173 abort();
174 #endif
175 case BPF_RET|BPF_K:
176 return (u_int)pc->k;
177
178 case BPF_RET|BPF_A:
179 return (u_int)A;
180
181 case BPF_LD|BPF_W|BPF_ABS:
182 k = pc->k;
183 if (k + sizeof(long) > buflen) {
184 #ifdef KERNEL
185 int merr;
186
187 if (buflen != 0)
188 return 0;
189 A = m_xword((struct mbuf *)p, k, &merr);
190 if (merr != 0)
191 return 0;
192 continue;
193 #else
194 return 0;
195 #endif
196 }
197 #ifdef BPF_ALIGN
198 if (((int)(p + k) & 3) != 0)
199 A = EXTRACT_LONG(&p[k]);
200 else
201 #endif
202 A = ntohl(*(long *)(p + k));
203 continue;
204
205 case BPF_LD|BPF_H|BPF_ABS:
206 k = pc->k;
207 if (k + sizeof(short) > buflen) {
208 #ifdef KERNEL
209 int merr;
210
211 if (buflen != 0)
212 return 0;
213 A = m_xhalf((struct mbuf *)p, k, &merr);
214 continue;
215 #else
216 return 0;
217 #endif
218 }
219 A = EXTRACT_SHORT(&p[k]);
220 continue;
221
222 case BPF_LD|BPF_B|BPF_ABS:
223 k = pc->k;
224 if (k >= buflen) {
225 #ifdef KERNEL
226 register struct mbuf *m;
227
228 if (buflen != 0)
229 return 0;
230 m = (struct mbuf *)p;
231 MINDEX(m, k);
232 A = mtod(m, u_char *)[k];
233 continue;
234 #else
235 return 0;
236 #endif
237 }
238 A = p[k];
239 continue;
240
241 case BPF_LD|BPF_W|BPF_LEN:
242 A = wirelen;
243 continue;
244
245 case BPF_LDX|BPF_W|BPF_LEN:
246 X = wirelen;
247 continue;
248
249 case BPF_LD|BPF_W|BPF_IND:
250 k = X + pc->k;
251 if (k + sizeof(long) > buflen) {
252 #ifdef KERNEL
253 int merr;
254
255 if (buflen != 0)
256 return 0;
257 A = m_xword((struct mbuf *)p, k, &merr);
258 if (merr != 0)
259 return 0;
260 continue;
261 #else
262 return 0;
263 #endif
264 }
265 #ifdef BPF_ALIGN
266 if (((int)(p + k) & 3) != 0)
267 A = EXTRACT_LONG(&p[k]);
268 else
269 #endif
270 A = ntohl(*(long *)(p + k));
271 continue;
272
273 case BPF_LD|BPF_H|BPF_IND:
274 k = X + pc->k;
275 if (k + sizeof(short) > buflen) {
276 #ifdef KERNEL
277 int merr;
278
279 if (buflen != 0)
280 return 0;
281 A = m_xhalf((struct mbuf *)p, k, &merr);
282 if (merr != 0)
283 return 0;
284 continue;
285 #else
286 return 0;
287 #endif
288 }
289 A = EXTRACT_SHORT(&p[k]);
290 continue;
291
292 case BPF_LD|BPF_B|BPF_IND:
293 k = X + pc->k;
294 if (k >= buflen) {
295 #ifdef KERNEL
296 register struct mbuf *m;
297
298 if (buflen != 0)
299 return 0;
300 m = (struct mbuf *)p;
301 MINDEX(m, k);
302 A = mtod(m, char *)[k];
303 continue;
304 #else
305 return 0;
306 #endif
307 }
308 A = p[k];
309 continue;
310
311 case BPF_LDX|BPF_MSH|BPF_B:
312 k = pc->k;
313 if (k >= buflen) {
314 #ifdef KERNEL
315 register struct mbuf *m;
316
317 if (buflen != 0)
318 return 0;
319 m = (struct mbuf *)p;
320 MINDEX(m, k);
321 X = (mtod(m, char *)[k] & 0xf) << 2;
322 continue;
323 #else
324 return 0;
325 #endif
326 }
327 X = (p[pc->k] & 0xf) << 2;
328 continue;
329
330 case BPF_LD|BPF_IMM:
331 A = pc->k;
332 continue;
333
334 case BPF_LDX|BPF_IMM:
335 X = pc->k;
336 continue;
337
338 case BPF_LD|BPF_MEM:
339 A = mem[pc->k];
340 continue;
341
342 case BPF_LDX|BPF_MEM:
343 X = mem[pc->k];
344 continue;
345
346 case BPF_ST:
347 mem[pc->k] = A;
348 continue;
349
350 case BPF_STX:
351 mem[pc->k] = X;
352 continue;
353
354 case BPF_JMP|BPF_JA:
355 pc += pc->k;
356 continue;
357
358 case BPF_JMP|BPF_JGT|BPF_K:
359 pc += (A > pc->k) ? pc->jt : pc->jf;
360 continue;
361
362 case BPF_JMP|BPF_JGE|BPF_K:
363 pc += (A >= pc->k) ? pc->jt : pc->jf;
364 continue;
365
366 case BPF_JMP|BPF_JEQ|BPF_K:
367 pc += (A == pc->k) ? pc->jt : pc->jf;
368 continue;
369
370 case BPF_JMP|BPF_JSET|BPF_K:
371 pc += (A & pc->k) ? pc->jt : pc->jf;
372 continue;
373
374 case BPF_JMP|BPF_JGT|BPF_X:
375 pc += (A > X) ? pc->jt : pc->jf;
376 continue;
377
378 case BPF_JMP|BPF_JGE|BPF_X:
379 pc += (A >= X) ? pc->jt : pc->jf;
380 continue;
381
382 case BPF_JMP|BPF_JEQ|BPF_X:
383 pc += (A == X) ? pc->jt : pc->jf;
384 continue;
385
386 case BPF_JMP|BPF_JSET|BPF_X:
387 pc += (A & X) ? pc->jt : pc->jf;
388 continue;
389
390 case BPF_ALU|BPF_ADD|BPF_X:
391 A += X;
392 continue;
393
394 case BPF_ALU|BPF_SUB|BPF_X:
395 A -= X;
396 continue;
397
398 case BPF_ALU|BPF_MUL|BPF_X:
399 A *= X;
400 continue;
401
402 case BPF_ALU|BPF_DIV|BPF_X:
403 if (X == 0)
404 return 0;
405 A /= X;
406 continue;
407
408 case BPF_ALU|BPF_AND|BPF_X:
409 A &= X;
410 continue;
411
412 case BPF_ALU|BPF_OR|BPF_X:
413 A |= X;
414 continue;
415
416 case BPF_ALU|BPF_LSH|BPF_X:
417 A <<= X;
418 continue;
419
420 case BPF_ALU|BPF_RSH|BPF_X:
421 A >>= X;
422 continue;
423
424 case BPF_ALU|BPF_ADD|BPF_K:
425 A += pc->k;
426 continue;
427
428 case BPF_ALU|BPF_SUB|BPF_K:
429 A -= pc->k;
430 continue;
431
432 case BPF_ALU|BPF_MUL|BPF_K:
433 A *= pc->k;
434 continue;
435
436 case BPF_ALU|BPF_DIV|BPF_K:
437 A /= pc->k;
438 continue;
439
440 case BPF_ALU|BPF_AND|BPF_K:
441 A &= pc->k;
442 continue;
443
444 case BPF_ALU|BPF_OR|BPF_K:
445 A |= pc->k;
446 continue;
447
448 case BPF_ALU|BPF_LSH|BPF_K:
449 A <<= pc->k;
450 continue;
451
452 case BPF_ALU|BPF_RSH|BPF_K:
453 A >>= pc->k;
454 continue;
455
456 case BPF_ALU|BPF_NEG:
457 A = -A;
458 continue;
459
460 case BPF_MISC|BPF_TAX:
461 X = A;
462 continue;
463
464 case BPF_MISC|BPF_TXA:
465 A = X;
466 continue;
467 }
468 }
469 }
470
471 #ifdef KERNEL
472 /*
473 * Return true if the 'fcode' is a valid filter program.
474 * The constraints are that each jump be forward and to a valid
475 * code. The code must terminate with either an accept or reject.
476 * 'valid' is an array for use by the routine (it must be at least
477 * 'len' bytes long).
478 *
479 * The kernel needs to be able to verify an application's filter code.
480 * Otherwise, a bogus program could easily crash the system.
481 */
482 int
bpf_validate(f,len)483 bpf_validate(f, len)
484 struct bpf_insn *f;
485 int len;
486 {
487 register int i;
488 register struct bpf_insn *p;
489
490 for (i = 0; i < len; ++i) {
491 /*
492 * Check that that jumps are forward, and within
493 * the code block.
494 */
495 p = &f[i];
496 if (BPF_CLASS(p->code) == BPF_JMP) {
497 register int from = i + 1;
498
499 if (BPF_OP(p->code) == BPF_JA) {
500 if (from + p->k >= len)
501 return 0;
502 }
503 else if (from + p->jt >= len || from + p->jf >= len)
504 return 0;
505 }
506 /*
507 * Check that memory operations use valid addresses.
508 */
509 if ((BPF_CLASS(p->code) == BPF_ST ||
510 (BPF_CLASS(p->code) == BPF_LD &&
511 (p->code & 0xe0) == BPF_MEM)) &&
512 (p->k >= BPF_MEMWORDS || p->k < 0))
513 return 0;
514 /*
515 * Check for constant division by 0.
516 */
517 if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0)
518 return 0;
519 }
520 return BPF_CLASS(f[len - 1].code) == BPF_RET;
521 }
522 #endif
523