bpf_filter.c revision 153995 
198675Sdes/*-
298675Sdes * Copyright (c) 1990, 1991, 1993
398675Sdes *	The Regents of the University of California.  All rights reserved.
498675Sdes *
598675Sdes * This code is derived from the Stanford/CMU enet packet filter,
698675Sdes * (net/enet.c) distributed as part of 4.3BSD, and code contributed
798675Sdes * to Berkeley by Steven McCanne and Van Jacobson both of Lawrence
898675Sdes * Berkeley Laboratory.
998675Sdes *
1098675Sdes * Redistribution and use in source and binary forms, with or without
1198675Sdes * modification, are permitted provided that the following conditions
1298675Sdes * are met:
1398675Sdes * 1. Redistributions of source code must retain the above copyright
1498675Sdes *    notice, this list of conditions and the following disclaimer.
1598675Sdes * 2. Redistributions in binary form must reproduce the above copyright
1698675Sdes *    notice, this list of conditions and the following disclaimer in the
1798675Sdes *    documentation and/or other materials provided with the distribution.
1898675Sdes * 4. Neither the name of the University nor the names of its contributors
1998675Sdes *    may be used to endorse or promote products derived from this software
2098675Sdes *    without specific prior written permission.
2198675Sdes *
2298675Sdes * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
2398675Sdes * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
2498675Sdes * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
2598675Sdes * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
2698675Sdes * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
2798675Sdes * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
2898675Sdes * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
2998675Sdes * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
3098675Sdes * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
3198675Sdes * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
3298675Sdes * SUCH DAMAGE.
3398675Sdes *
3498675Sdes *      @(#)bpf_filter.c	8.1 (Berkeley) 6/10/93
3598675Sdes *
3698675Sdes * $FreeBSD: head/sys/net/bpf_filter.c 153995 2006-01-03 20:26:03Z jkim $
3798675Sdes */
3898675Sdes
3998675Sdes#include <sys/param.h>
4098675Sdes
4198675Sdes#ifdef sun
4298675Sdes#include <netinet/in.h>
4398675Sdes#endif
4498675Sdes
4598675Sdes#ifndef __i386__
4698675Sdes#define BPF_ALIGN
4798675Sdes#endif
4898675Sdes
4998675Sdes#ifndef BPF_ALIGN
5098675Sdes#define EXTRACT_SHORT(p)	((u_int16_t)ntohs(*(u_int16_t *)p))
5198675Sdes#define EXTRACT_LONG(p)		(ntohl(*(u_int32_t *)p))
5298675Sdes#else
5398675Sdes#define EXTRACT_SHORT(p)\
5498675Sdes	((u_int16_t)\
5598675Sdes		((u_int16_t)*((u_char *)p+0)<<8|\
5698675Sdes		 (u_int16_t)*((u_char *)p+1)<<0))
5798675Sdes#define EXTRACT_LONG(p)\
5898675Sdes		((u_int32_t)*((u_char *)p+0)<<24|\
5998675Sdes		 (u_int32_t)*((u_char *)p+1)<<16|\
6098675Sdes		 (u_int32_t)*((u_char *)p+2)<<8|\
6198675Sdes		 (u_int32_t)*((u_char *)p+3)<<0)
6298675Sdes#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
82static u_int16_t	m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err);
83static u_int32_t	m_xword(struct mbuf *m, bpf_u_int32 k, int *err);
84
85static u_int32_t
86m_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
141static u_int16_t
142m_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 */
180u_int
181bpf_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, 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, 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 */
515int
516bpf_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	if (len < 1)
524		return 1;
525
526	for (i = 0; i < len; ++i) {
527		/*
528		 * Check that that jumps are forward, and within
529		 * the code block.
530		 */
531		p = &f[i];
532		if (BPF_CLASS(p->code) == BPF_JMP) {
533			register int from = i + 1;
534
535			if (BPF_OP(p->code) == BPF_JA) {
536				if (from >= len || p->k >= len - from)
537					return 0;
538			}
539			else if (from >= len || p->jt >= len - from ||
540				 p->jf >= len - from)
541				return 0;
542		}
543		/*
544		 * Check that memory operations use valid addresses.
545		 */
546		if ((BPF_CLASS(p->code) == BPF_ST ||
547		     (BPF_CLASS(p->code) == BPF_LD &&
548		      (p->code & 0xe0) == BPF_MEM)) &&
549		    p->k >= BPF_MEMWORDS)
550			return 0;
551		/*
552		 * Check for constant division by 0.
553		 */
554		if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0)
555			return 0;
556	}
557	return BPF_CLASS(f[len - 1].code) == BPF_RET;
558}
559#endif
560