2 * Copyright (c) 1990, 1991, 1993
3 * The Regents of the University of California. All rights reserved.
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
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
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 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.
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
34 * @(#)bpf_filter.c 8.1 (Berkeley) 6/10/93
36 * $FreeBSD: src/sys/net/bpf_filter.c,v 1.17 1999/12/29 04:38:31 peter Exp $
39 #include <sys/systm.h>
40 #include <sys/param.h>
42 #if defined(sparc) || defined(mips) || defined(ibm032)
47 #define EXTRACT_SHORT(p) ((u_int16_t)ntohs(*(u_int16_t *)p))
48 #define EXTRACT_LONG(p) (ntohl(*(u_int32_t *)p))
50 #define EXTRACT_SHORT(p)\
52 ((u_int16_t)*((u_char *)p+0)<<8|\
53 (u_int16_t)*((u_char *)p+1)<<0))
54 #define EXTRACT_LONG(p)\
55 ((u_int32_t)*((u_char *)p+0)<<24|\
56 (u_int32_t)*((u_char *)p+1)<<16|\
57 (u_int32_t)*((u_char *)p+2)<<8|\
58 (u_int32_t)*((u_char *)p+3)<<0)
66 #define MINDEX(m, k) \
79 extern int bpf_maxbufsize;
81 static u_int16_t m_xhalf (struct mbuf *m, bpf_u_int32 k, int *err);
82 static u_int32_t m_xword (struct mbuf *m, bpf_u_int32 k, int *err);
85 m_xword(struct mbuf *m, bpf_u_int32 k, int *err)
99 cp = mtod(m, u_char *) + k;
102 return EXTRACT_LONG(cp);
105 if (m0 == NULL || m0->m_len + len - k < 4)
108 np = mtod(m0, u_char *);
113 ((u_int32_t)cp[0] << 24) |
114 ((u_int32_t)np[0] << 16) |
115 ((u_int32_t)np[1] << 8) |
120 ((u_int32_t)cp[0] << 24) |
121 ((u_int32_t)cp[1] << 16) |
122 ((u_int32_t)np[0] << 8) |
127 ((u_int32_t)cp[0] << 24) |
128 ((u_int32_t)cp[1] << 16) |
129 ((u_int32_t)cp[2] << 8) |
138 m_xhalf(struct mbuf *m, bpf_u_int32 k, int *err)
152 cp = mtod(m, u_char *) + k;
155 return EXTRACT_SHORT(cp);
161 return (cp[0] << 8) | mtod(m0, u_char *)[0];
169 * Execute the filter program starting at pc on the packet p
170 * wirelen is the length of the original packet
171 * buflen is the amount of data present
174 bpf_filter(const struct bpf_insn *pc, u_char *p, u_int wirelen, u_int buflen)
176 u_int32_t A = 0, X = 0;
178 u_int32_t mem[BPF_MEMWORDS];
180 bzero(mem, sizeof(mem));
184 * No filter means accept all.
206 case BPF_LD|BPF_W|BPF_ABS:
208 if (k > buflen || sizeof(int32_t) > buflen - k) {
214 A = m_xword((struct mbuf *)p, k, &merr);
223 if (((intptr_t)(p + k) & 3) != 0)
224 A = EXTRACT_LONG(&p[k]);
227 A = ntohl(*(int32_t *)(p + k));
230 case BPF_LD|BPF_H|BPF_ABS:
232 if (k > buflen || sizeof(int16_t) > buflen - k) {
238 A = m_xhalf((struct mbuf *)p, k, &merr);
244 A = EXTRACT_SHORT(&p[k]);
247 case BPF_LD|BPF_B|BPF_ABS:
255 m = (struct mbuf *)p;
257 A = mtod(m, u_char *)[k];
266 case BPF_LD|BPF_W|BPF_LEN:
270 case BPF_LDX|BPF_W|BPF_LEN:
274 case BPF_LD|BPF_W|BPF_IND:
276 if (pc->k > buflen || X > buflen - pc->k ||
277 sizeof(int32_t) > buflen - k) {
283 A = m_xword((struct mbuf *)p, k, &merr);
292 if (((intptr_t)(p + k) & 3) != 0)
293 A = EXTRACT_LONG(&p[k]);
296 A = ntohl(*(int32_t *)(p + k));
299 case BPF_LD|BPF_H|BPF_IND:
301 if (X > buflen || pc->k > buflen - X ||
302 sizeof(int16_t) > buflen - k) {
308 A = m_xhalf((struct mbuf *)p, k, &merr);
316 A = EXTRACT_SHORT(&p[k]);
319 case BPF_LD|BPF_B|BPF_IND:
321 if (pc->k >= buflen || X >= buflen - pc->k) {
327 m = (struct mbuf *)p;
329 A = mtod(m, u_char *)[k];
338 case BPF_LDX|BPF_MSH|BPF_B:
346 m = (struct mbuf *)p;
348 X = (mtod(m, char *)[k] & 0xf) << 2;
354 X = (p[pc->k] & 0xf) << 2;
361 case BPF_LDX|BPF_IMM:
369 case BPF_LDX|BPF_MEM:
385 case BPF_JMP|BPF_JGT|BPF_K:
386 pc += (A > pc->k) ? pc->jt : pc->jf;
389 case BPF_JMP|BPF_JGE|BPF_K:
390 pc += (A >= pc->k) ? pc->jt : pc->jf;
393 case BPF_JMP|BPF_JEQ|BPF_K:
394 pc += (A == pc->k) ? pc->jt : pc->jf;
397 case BPF_JMP|BPF_JSET|BPF_K:
398 pc += (A & pc->k) ? pc->jt : pc->jf;
401 case BPF_JMP|BPF_JGT|BPF_X:
402 pc += (A > X) ? pc->jt : pc->jf;
405 case BPF_JMP|BPF_JGE|BPF_X:
406 pc += (A >= X) ? pc->jt : pc->jf;
409 case BPF_JMP|BPF_JEQ|BPF_X:
410 pc += (A == X) ? pc->jt : pc->jf;
413 case BPF_JMP|BPF_JSET|BPF_X:
414 pc += (A & X) ? pc->jt : pc->jf;
417 case BPF_ALU|BPF_ADD|BPF_X:
421 case BPF_ALU|BPF_SUB|BPF_X:
425 case BPF_ALU|BPF_MUL|BPF_X:
429 case BPF_ALU|BPF_DIV|BPF_X:
435 case BPF_ALU|BPF_AND|BPF_X:
439 case BPF_ALU|BPF_OR|BPF_X:
443 case BPF_ALU|BPF_LSH|BPF_X:
447 case BPF_ALU|BPF_RSH|BPF_X:
451 case BPF_ALU|BPF_ADD|BPF_K:
455 case BPF_ALU|BPF_SUB|BPF_K:
459 case BPF_ALU|BPF_MUL|BPF_K:
463 case BPF_ALU|BPF_DIV|BPF_K:
467 case BPF_ALU|BPF_AND|BPF_K:
471 case BPF_ALU|BPF_OR|BPF_K:
475 case BPF_ALU|BPF_LSH|BPF_K:
479 case BPF_ALU|BPF_RSH|BPF_K:
483 case BPF_ALU|BPF_NEG:
487 case BPF_MISC|BPF_TAX:
491 case BPF_MISC|BPF_TXA:
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, that memory accesses are within valid ranges (to the
503 * extent that this can be checked statically; loads of packet
504 * data have to be, and are, also checked at run time), and that
505 * the code terminates with either an accept or reject.
507 * The kernel needs to be able to verify an application's filter code.
508 * Otherwise, a bogus program could easily crash the system.
511 bpf_validate(const struct bpf_insn *f, int len)
514 const struct bpf_insn *p;
516 if (len < 1 || len > BPF_MAXINSNS)
519 for (i = 0; i < len; ++i) {
521 switch (BPF_CLASS(p->code)) {
523 * Check that memory operations use valid addresses.
527 switch (BPF_MODE(p->code)) {
534 * More strict check with actual packet length
537 if (p->k >= bpf_maxbufsize)
541 if (p->k >= BPF_MEMWORDS)
552 if (p->k >= BPF_MEMWORDS)
556 switch (BPF_OP(p->code)) {
568 * Check for constant division by 0.
570 if (BPF_SRC(p->code) == BPF_K && p->k == 0)
579 * Check that jumps are within the code block,
580 * and that unconditional branches don't go
581 * backwards as a result of an overflow.
582 * Unconditional branches have a 32-bit offset,
583 * so they could overflow; we check to make
584 * sure they don't. Conditional branches have
585 * an 8-bit offset, and the from address is <=
586 * BPF_MAXINSNS, and we assume that BPF_MAXINSNS
587 * is sufficiently small that adding 255 to it
590 * We know that len is <= BPF_MAXINSNS, and we
591 * assume that BPF_MAXINSNS is < the maximum size
592 * of a u_int, so that i + 1 doesn't overflow.
595 switch (BPF_OP(p->code)) {
597 if (from + p->k < from || from + p->k >= len)
604 if (from + p->jt >= len || from + p->jf >= len)
619 return BPF_CLASS(f[len - 1].code) == BPF_RET;