bpf_filter.c revision 182184 
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
37#include <sys/cdefs.h>
38__FBSDID("$FreeBSD: head/sys/net/bpf_filter.c 182184 2008-08-26 00:09:26Z jkim $");
39
40#include <sys/param.h>
41
42#if !defined(_KERNEL) || defined(sun)
43#include <netinet/in.h>
44#endif
45
46#ifndef __i386__
47#define BPF_ALIGN
48#endif
49
50#ifndef BPF_ALIGN
51#define EXTRACT_SHORT(p)	((u_int16_t)ntohs(*(u_int16_t *)p))
52#define EXTRACT_LONG(p)		(ntohl(*(u_int32_t *)p))
53#else
54#define EXTRACT_SHORT(p)\
55	((u_int16_t)\
56		((u_int16_t)*((u_char *)p+0)<<8|\
57		 (u_int16_t)*((u_char *)p+1)<<0))
58#define EXTRACT_LONG(p)\
59		((u_int32_t)*((u_char *)p+0)<<24|\
60		 (u_int32_t)*((u_char *)p+1)<<16|\
61		 (u_int32_t)*((u_char *)p+2)<<8|\
62		 (u_int32_t)*((u_char *)p+3)<<0)
63#endif
64
65#ifdef _KERNEL
66#include <sys/mbuf.h>
67#else
68#include <stdlib.h>
69#endif
70#include <net/bpf.h>
71#ifdef _KERNEL
72#define MINDEX(m, k) \
73{ \
74	register int len = m->m_len; \
75 \
76	while (k >= len) { \
77		k -= len; \
78		m = m->m_next; \
79		if (m == 0) \
80			return 0; \
81		len = m->m_len; \
82	} \
83}
84
85static u_int16_t	m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err);
86static u_int32_t	m_xword(struct mbuf *m, bpf_u_int32 k, int *err);
87
88static u_int32_t
89m_xword(struct mbuf *m, bpf_u_int32 k, int *err)
90{
91	size_t len;
92	u_char *cp, *np;
93	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	case 1:
115		return
116		    ((u_int32_t)cp[0] << 24) |
117		    ((u_int32_t)np[0] << 16) |
118		    ((u_int32_t)np[1] << 8)  |
119		    (u_int32_t)np[2];
120
121	case 2:
122		return
123		    ((u_int32_t)cp[0] << 24) |
124		    ((u_int32_t)cp[1] << 16) |
125		    ((u_int32_t)np[0] << 8) |
126		    (u_int32_t)np[1];
127
128	default:
129		return
130		    ((u_int32_t)cp[0] << 24) |
131		    ((u_int32_t)cp[1] << 16) |
132		    ((u_int32_t)cp[2] << 8) |
133		    (u_int32_t)np[0];
134	}
135    bad:
136	*err = 1;
137	return (0);
138}
139
140static u_int16_t
141m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err)
142{
143	size_t len;
144	u_char *cp;
145	struct mbuf *m0;
146
147	len = m->m_len;
148	while (k >= len) {
149		k -= len;
150		m = m->m_next;
151		if (m == 0)
152			goto bad;
153		len = m->m_len;
154	}
155	cp = mtod(m, u_char *) + k;
156	if (len - k >= 2) {
157		*err = 0;
158		return (EXTRACT_SHORT(cp));
159	}
160	m0 = m->m_next;
161	if (m0 == 0)
162		goto bad;
163	*err = 0;
164	return ((cp[0] << 8) | mtod(m0, u_char *)[0]);
165 bad:
166	*err = 1;
167	return (0);
168}
169#endif
170
171/*
172 * Execute the filter program starting at pc on the packet p
173 * wirelen is the length of the original packet
174 * buflen is the amount of data present
175 */
176u_int
177bpf_filter(const struct bpf_insn *pc, u_char *p, u_int wirelen, u_int buflen)
178{
179	u_int32_t A = 0, X = 0;
180	bpf_u_int32 k;
181	u_int32_t mem[BPF_MEMWORDS];
182
183	if (pc == NULL)
184		/*
185		 * No filter means accept all.
186		 */
187		return ((u_int)-1);
188
189	--pc;
190	while (1) {
191		++pc;
192		switch (pc->code) {
193		default:
194#ifdef _KERNEL
195			return 0;
196#else
197			abort();
198#endif
199
200		case BPF_RET|BPF_K:
201			return ((u_int)pc->k);
202
203		case BPF_RET|BPF_A:
204			return ((u_int)A);
205
206		case BPF_LD|BPF_W|BPF_ABS:
207			k = pc->k;
208			if (k > buflen || sizeof(int32_t) > buflen - k) {
209#ifdef _KERNEL
210				int merr;
211
212				if (buflen != 0)
213					return 0;
214				A = m_xword((struct mbuf *)p, k, &merr);
215				if (merr != 0)
216					return 0;
217				continue;
218#else
219				return (0);
220#endif
221			}
222#ifdef BPF_ALIGN
223			if (((intptr_t)(p + k) & 3) != 0)
224				A = EXTRACT_LONG(&p[k]);
225			else
226#endif
227				A = ntohl(*(int32_t *)(p + k));
228			continue;
229
230		case BPF_LD|BPF_H|BPF_ABS:
231			k = pc->k;
232			if (k > buflen || sizeof(int16_t) > buflen - k) {
233#ifdef _KERNEL
234				int merr;
235
236				if (buflen != 0)
237					return 0;
238				A = m_xhalf((struct mbuf *)p, k, &merr);
239				continue;
240#else
241				return 0;
242#endif
243			}
244			A = EXTRACT_SHORT(&p[k]);
245			continue;
246
247		case BPF_LD|BPF_B|BPF_ABS:
248			k = pc->k;
249			if (k >= buflen) {
250#ifdef _KERNEL
251				struct mbuf *m;
252
253				if (buflen != 0)
254					return 0;
255				m = (struct mbuf *)p;
256				MINDEX(m, k);
257				A = mtod(m, u_char *)[k];
258				continue;
259#else
260				return 0;
261#endif
262			}
263			A = p[k];
264			continue;
265
266		case BPF_LD|BPF_W|BPF_LEN:
267			A = wirelen;
268			continue;
269
270		case BPF_LDX|BPF_W|BPF_LEN:
271			X = wirelen;
272			continue;
273
274		case BPF_LD|BPF_W|BPF_IND:
275			k = X + pc->k;
276			if (pc->k > buflen || X > buflen - pc->k ||
277			    sizeof(int32_t) > buflen - k) {
278#ifdef _KERNEL
279				int merr;
280
281				if (buflen != 0)
282					return (0);
283				A = m_xword((struct mbuf *)p, k, &merr);
284				if (merr != 0)
285					return (0);
286				continue;
287#else
288				return (0);
289#endif
290			}
291#ifdef BPF_ALIGN
292			if (((intptr_t)(p + k) & 3) != 0)
293				A = EXTRACT_LONG(&p[k]);
294			else
295#endif
296				A = ntohl(*(int32_t *)(p + k));
297			continue;
298
299		case BPF_LD|BPF_H|BPF_IND:
300			k = X + pc->k;
301			if (X > buflen || pc->k > buflen - X ||
302			    sizeof(int16_t) > buflen - k) {
303#ifdef _KERNEL
304				int merr;
305
306				if (buflen != 0)
307					return 0;
308				A = m_xhalf((struct mbuf *)p, k, &merr);
309				if (merr != 0)
310					return (0);
311				continue;
312#else
313				return (0);
314#endif
315			}
316			A = EXTRACT_SHORT(&p[k]);
317			continue;
318
319		case BPF_LD|BPF_B|BPF_IND:
320			k = X + pc->k;
321			if (pc->k >= buflen || X >= buflen - pc->k) {
322#ifdef _KERNEL
323				struct mbuf *m;
324
325				if (buflen != 0)
326					return 0;
327				m = (struct mbuf *)p;
328				MINDEX(m, k);
329				A = mtod(m, u_char *)[k];
330				continue;
331#else
332				return (0);
333#endif
334			}
335			A = p[k];
336			continue;
337
338		case BPF_LDX|BPF_MSH|BPF_B:
339			k = pc->k;
340			if (k >= buflen) {
341#ifdef _KERNEL
342				register struct mbuf *m;
343
344				if (buflen != 0)
345					return 0;
346				m = (struct mbuf *)p;
347				MINDEX(m, k);
348				X = (mtod(m, u_char *)[k] & 0xf) << 2;
349				continue;
350#else
351				return 0;
352#endif
353			}
354			X = (p[pc->k] & 0xf) << 2;
355			continue;
356
357		case BPF_LD|BPF_IMM:
358			A = pc->k;
359			continue;
360
361		case BPF_LDX|BPF_IMM:
362			X = pc->k;
363			continue;
364
365		case BPF_LD|BPF_MEM:
366			A = mem[pc->k];
367			continue;
368
369		case BPF_LDX|BPF_MEM:
370			X = mem[pc->k];
371			continue;
372
373		case BPF_ST:
374			mem[pc->k] = A;
375			continue;
376
377		case BPF_STX:
378			mem[pc->k] = X;
379			continue;
380
381		case BPF_JMP|BPF_JA:
382			pc += pc->k;
383			continue;
384
385		case BPF_JMP|BPF_JGT|BPF_K:
386			pc += (A > pc->k) ? pc->jt : pc->jf;
387			continue;
388
389		case BPF_JMP|BPF_JGE|BPF_K:
390			pc += (A >= pc->k) ? pc->jt : pc->jf;
391			continue;
392
393		case BPF_JMP|BPF_JEQ|BPF_K:
394			pc += (A == pc->k) ? pc->jt : pc->jf;
395			continue;
396
397		case BPF_JMP|BPF_JSET|BPF_K:
398			pc += (A & pc->k) ? pc->jt : pc->jf;
399			continue;
400
401		case BPF_JMP|BPF_JGT|BPF_X:
402			pc += (A > X) ? pc->jt : pc->jf;
403			continue;
404
405		case BPF_JMP|BPF_JGE|BPF_X:
406			pc += (A >= X) ? pc->jt : pc->jf;
407			continue;
408
409		case BPF_JMP|BPF_JEQ|BPF_X:
410			pc += (A == X) ? pc->jt : pc->jf;
411			continue;
412
413		case BPF_JMP|BPF_JSET|BPF_X:
414			pc += (A & X) ? pc->jt : pc->jf;
415			continue;
416
417		case BPF_ALU|BPF_ADD|BPF_X:
418			A += X;
419			continue;
420
421		case BPF_ALU|BPF_SUB|BPF_X:
422			A -= X;
423			continue;
424
425		case BPF_ALU|BPF_MUL|BPF_X:
426			A *= X;
427			continue;
428
429		case BPF_ALU|BPF_DIV|BPF_X:
430			if (X == 0)
431				return 0;
432			A /= X;
433			continue;
434
435		case BPF_ALU|BPF_AND|BPF_X:
436			A &= X;
437			continue;
438
439		case BPF_ALU|BPF_OR|BPF_X:
440			A |= X;
441			continue;
442
443		case BPF_ALU|BPF_LSH|BPF_X:
444			A <<= X;
445			continue;
446
447		case BPF_ALU|BPF_RSH|BPF_X:
448			A >>= X;
449			continue;
450
451		case BPF_ALU|BPF_ADD|BPF_K:
452			A += pc->k;
453			continue;
454
455		case BPF_ALU|BPF_SUB|BPF_K:
456			A -= pc->k;
457			continue;
458
459		case BPF_ALU|BPF_MUL|BPF_K:
460			A *= pc->k;
461			continue;
462
463		case BPF_ALU|BPF_DIV|BPF_K:
464			A /= pc->k;
465			continue;
466
467		case BPF_ALU|BPF_AND|BPF_K:
468			A &= pc->k;
469			continue;
470
471		case BPF_ALU|BPF_OR|BPF_K:
472			A |= pc->k;
473			continue;
474
475		case BPF_ALU|BPF_LSH|BPF_K:
476			A <<= pc->k;
477			continue;
478
479		case BPF_ALU|BPF_RSH|BPF_K:
480			A >>= pc->k;
481			continue;
482
483		case BPF_ALU|BPF_NEG:
484			A = -A;
485			continue;
486
487		case BPF_MISC|BPF_TAX:
488			X = A;
489			continue;
490
491		case BPF_MISC|BPF_TXA:
492			A = X;
493			continue;
494		}
495	}
496}
497
498#ifdef _KERNEL
499/*
500 * Return true if the 'fcode' is a valid filter program.
501 * The constraints are that each jump be forward and to a valid
502 * code.  The code must terminate with either an accept or reject.
503 *
504 * The kernel needs to be able to verify an application's filter code.
505 * Otherwise, a bogus program could easily crash the system.
506 */
507int
508bpf_validate(f, len)
509	const struct bpf_insn *f;
510	int len;
511{
512	register int i;
513	register const struct bpf_insn *p;
514
515	/* Do not accept negative length filter. */
516	if (len < 0)
517		return 0;
518
519	/* An empty filter means accept all. */
520	if (len == 0)
521		return 1;
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
557