bpf_filter.c

/*	$OpenBSD: bpf_filter.c,v 1.19 2007/08/06 08:28:09 tom Exp $	*/
/*	$NetBSD: bpf_filter.c,v 1.12 1996/02/13 22:00:00 christos Exp $	*/
/*	$Id: bpf_filter.c,v 1.4 2007/10/01 21:12:08 canacar Exp $	*/

/*
 * Copyright (c) 1990, 1991, 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from the Stanford/CMU enet packet filter,
 * (net/enet.c) distributed as part of 4.3BSD, and code contributed
 * to Berkeley by Steven McCanne and Van Jacobson both of Lawrence
 * Berkeley Laboratory.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)bpf_filter.c	8.1 (Berkeley) 6/10/93
 */

#include <sys/param.h>
#include <sys/types.h>
#include <sys/time.h>
#ifndef _KERNEL
#include <stdlib.h>
#include "pcap.h"
#endif

#include <sys/endian.h>
#ifdef __STRICT_ALIGNMENT
#define BPF_ALIGN
#endif

/* XXX this means we are no longer compatible with BPF */
#define EXTRACT_SHORT(p)	(*(u_int16_t *)p)
#define EXTRACT_LONG(p)		(*(u_int32_t *)p)

#ifdef _KERNEL
#include <sys/mbuf.h>
#define MINDEX(len, m, k) \
{ \
	len = m->m_len; \
	while (k >= len) { \
		k -= len; \
		m = m->m_next; \
		if (m == 0) \
			return 0; \
		len = m->m_len; \
	} \
}

extern int bpf_maxbufsize;

int	bpf_m_xword(struct mbuf *, u_int32_t, int *);
int	bpf_m_xhalf(struct mbuf *, u_int32_t, int *);

int
bpf_m_xword(m, k, err)
	struct mbuf *m;
	u_int32_t k;
	int *err;
{
	int len;
	u_char *cp, *np;
	struct mbuf *m0;

	*err = 1;
	MINDEX(len, m, k);
	cp = mtod(m, u_char *) + k;
	if (len >= k + 4) {
		*err = 0;
		return EXTRACT_LONG(cp);
	}
	m0 = m->m_next;
	if (m0 == 0 || m0->m_len + len - k < 4)
		return 0;
	*err = 0;
	np = mtod(m0, u_char *);
	switch (len - k) {

	case 1:
		return (cp[0] << 24) | (np[0] << 16) | (np[1] << 8) | np[2];

	case 2:
		return (cp[0] << 24) | (cp[1] << 16) | (np[0] << 8) | np[1];

	default:
		return (cp[0] << 24) | (cp[1] << 16) | (cp[2] << 8) | np[0];
	}
}

int
bpf_m_xhalf(m, k, err)
	struct mbuf *m;
	u_int32_t k;
	int *err;
{
	int len;
	u_char *cp;
	struct mbuf *m0;

	*err = 1;
	MINDEX(len, m, k);
	cp = mtod(m, u_char *) + k;
	if (len >= k + 2) {
		*err = 0;
		return EXTRACT_SHORT(cp);
	}
	m0 = m->m_next;
	if (m0 == 0)
		return 0;
	*err = 0;
	return (cp[0] << 8) | mtod(m0, u_char *)[0];
}
#endif

#include <net/bpf.h>

/*
 * Execute the filter program starting at pc on the packet p
 * wirelen is the length of the original packet
 * buflen is the amount of data present
 */
u_int
bpf_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen, u_int buflen)
{
	u_int64_t A = 0, X = 0;
	u_int64_t k;
	int64_t mem[BPF_MEMWORDS];

	if (pc == 0)
		/*
		 * No filter means accept all.
		 */
		return (u_int)-1;
	--pc;
	while (1) {
		++pc;
		switch (pc->code) {

		default:
#ifdef _KERNEL
			return 0;
#else
			abort();
#endif			
		case BPF_RET|BPF_K:
			return (u_int)pc->k;

		case BPF_RET|BPF_A:
			return (u_int)A;

		case BPF_LD|BPF_W|BPF_ABS:
			k = pc->k;
			if (k + sizeof(int32_t) > buflen) {
#ifdef _KERNEL
				int merr;

				if (buflen != 0)
					return 0;
				A = bpf_m_xword((struct mbuf *)p, k, &merr);
				if (merr != 0)
					return 0;
				continue;
#else
				return 0;
#endif
			}
			A = EXTRACT_LONG(&p[k]);
			continue;

		case BPF_LD|BPF_H|BPF_ABS:
			k = pc->k;
			if (k + sizeof(int16_t) > buflen) {
#ifdef _KERNEL
				int merr;

				if (buflen != 0)
					return 0;
				A = bpf_m_xhalf((struct mbuf *)p, k, &merr);
				if (merr != 0)
					return 0;
				continue;
#else
				return 0;
#endif
			}
			A = EXTRACT_SHORT(&p[k]);
			continue;

		case BPF_LD|BPF_B|BPF_ABS:
			k = pc->k;
			if (k >= buflen) {
#ifdef _KERNEL
				struct mbuf *m;
				int len;

				if (buflen != 0)
					return 0;
				m = (struct mbuf *)p;
				MINDEX(len, m, k);
				A = mtod(m, u_char *)[k];
				continue;
#else
				return 0;
#endif
			}
			A = p[k];
			continue;

		case BPF_LD|BPF_W|BPF_LEN:
			A = wirelen;
			continue;

		case BPF_LDX|BPF_W|BPF_LEN:
			X = wirelen;
			continue;

		case BPF_LD|BPF_W|BPF_IND:
			k = X + pc->k;
			if (k + sizeof(int32_t) > buflen) {
#ifdef _KERNEL
				int merr;

				if (buflen != 0)
					return 0;
				A = bpf_m_xword((struct mbuf *)p, k, &merr);
				if (merr != 0)
					return 0;
				continue;
#else
				return 0;
#endif
			}
			A = EXTRACT_LONG(&p[k]);
			continue;

		case BPF_LD|BPF_H|BPF_IND:
			k = X + pc->k;
			if (k + sizeof(int16_t) > buflen) {
#ifdef _KERNEL
				int merr;

				if (buflen != 0)
					return 0;
				A = bpf_m_xhalf((struct mbuf *)p, k, &merr);
				if (merr != 0)
					return 0;
				continue;
#else
				return 0;
#endif
			}
			A = EXTRACT_SHORT(&p[k]);
			continue;

		case BPF_LD|BPF_B|BPF_IND:
			k = X + pc->k;
			if (k >= buflen) {
#ifdef _KERNEL
				struct mbuf *m;
				int len;

				if (buflen != 0)
					return 0;
				m = (struct mbuf *)p;
				MINDEX(len, m, k);
				A = mtod(m, u_char *)[k];
				continue;
#else
				return 0;
#endif
			}
			A = p[k];
			continue;

		case BPF_LDX|BPF_MSH|BPF_B:
			k = pc->k;
			if (k >= buflen) {
#ifdef _KERNEL
				struct mbuf *m;
				int len;

				if (buflen != 0)
					return 0;
				m = (struct mbuf *)p;
				MINDEX(len, m, k);
				X = (mtod(m, u_char *)[k] & 0xf) << 2;
				continue;
#else
				return 0;
#endif
			}
			X = (p[pc->k] & 0xf) << 2;
			continue;

		case BPF_LD|BPF_IMM:
			A = pc->k;
			continue;

		case BPF_LDX|BPF_IMM:
			X = pc->k;
			continue;

		case BPF_LD|BPF_MEM:
			A = mem[pc->k];
			continue;
			
		case BPF_LDX|BPF_MEM:
			X = mem[pc->k];
			continue;

		case BPF_ST:
			mem[pc->k] = A;
			continue;

		case BPF_STX:
			mem[pc->k] = X;
			continue;

		case BPF_JMP|BPF_JA:
			pc += pc->k;
			continue;

		case BPF_JMP|BPF_JGT|BPF_K:
			pc += (A > pc->k) ? pc->jt : pc->jf;
			continue;

		case BPF_JMP|BPF_JGE|BPF_K:
			pc += (A >= pc->k) ? pc->jt : pc->jf;
			continue;

		case BPF_JMP|BPF_JEQ|BPF_K:
			pc += (A == pc->k) ? pc->jt : pc->jf;
			continue;

		case BPF_JMP|BPF_JSET|BPF_K:
			pc += (A & pc->k) ? pc->jt : pc->jf;
			continue;

		case BPF_JMP|BPF_JGT|BPF_X:
			pc += (A > X) ? pc->jt : pc->jf;
			continue;

		case BPF_JMP|BPF_JGE|BPF_X:
			pc += (A >= X) ? pc->jt : pc->jf;
			continue;

		case BPF_JMP|BPF_JEQ|BPF_X:
			pc += (A == X) ? pc->jt : pc->jf;
			continue;

		case BPF_JMP|BPF_JSET|BPF_X:
			pc += (A & X) ? pc->jt : pc->jf;
			continue;

		case BPF_ALU|BPF_ADD|BPF_X:
			A += X;
			continue;
			
		case BPF_ALU|BPF_SUB|BPF_X:
			A -= X;
			continue;
			
		case BPF_ALU|BPF_MUL|BPF_X:
			A *= X;
			continue;
			
		case BPF_ALU|BPF_DIV|BPF_X:
			if (X == 0)
				return 0;
			A /= X;
			continue;
			
		case BPF_ALU|BPF_AND|BPF_X:
			A &= X;
			continue;
			
		case BPF_ALU|BPF_OR|BPF_X:
			A |= X;
			continue;

		case BPF_ALU|BPF_LSH|BPF_X:
			A <<= X;
			continue;

		case BPF_ALU|BPF_RSH|BPF_X:
			A >>= X;
			continue;

		case BPF_ALU|BPF_ADD|BPF_K:
			A += pc->k;
			continue;
			
		case BPF_ALU|BPF_SUB|BPF_K:
			A -= pc->k;
			continue;
			
		case BPF_ALU|BPF_MUL|BPF_K:
			A *= pc->k;
			continue;
			
		case BPF_ALU|BPF_DIV|BPF_K:
			A /= pc->k;
			continue;
			
		case BPF_ALU|BPF_AND|BPF_K:
			A &= pc->k;
			continue;
			
		case BPF_ALU|BPF_OR|BPF_K:
			A |= pc->k;
			continue;

		case BPF_ALU|BPF_LSH|BPF_K:
			A <<= pc->k;
			continue;

		case BPF_ALU|BPF_RSH|BPF_K:
			A >>= pc->k;
			continue;

		case BPF_ALU|BPF_NEG:
			A = -A;
			continue;

		case BPF_MISC|BPF_TAX:
			X = A;
			continue;

		case BPF_MISC|BPF_TXA:
			A = X;
			continue;
		}
	}
}

#ifdef _KERNEL
/*
 * Return true if the 'fcode' is a valid filter program.
 * The constraints are that each jump be forward and to a valid
 * code.  The code must terminate with either an accept or reject. 
 * 'valid' is an array for use by the routine (it must be at least
 * 'len' bytes long).  
 *
 * The kernel needs to be able to verify an application's filter code.
 * Otherwise, a bogus program could easily crash the system.
 */
int
bpf_validate(f, len)
	struct bpf_insn *f;
	int len;
{
	u_int i, from;
	struct bpf_insn *p;

	if (len < 1 || len > BPF_MAXINSNS)
		return 0;

	for (i = 0; i < len; ++i) {
		p = &f[i];
		switch (BPF_CLASS(p->code)) {
		/*
		 * Check that memory operations use valid addresses.
		 */
		case BPF_LD:
		case BPF_LDX:
			switch (BPF_MODE(p->code)) {
			case BPF_IMM:
				break;
			case BPF_ABS:
			case BPF_IND:
			case BPF_MSH:
				/*
				 * More strict check with actual packet length
				 * is done runtime.
				 */
				if (p->k >= bpf_maxbufsize)
					return 0;
				break;
			case BPF_MEM:
				if (p->k >= BPF_MEMWORDS)
					return 0;
				break;
			case BPF_LEN:
				break;
			default:
				return 0;
			}
			break;
		case BPF_ST:
		case BPF_STX:
			if (p->k >= BPF_MEMWORDS)
				return 0;
			break;
		case BPF_ALU:
			switch (BPF_OP(p->code)) {
			case BPF_ADD:
			case BPF_SUB:
			case BPF_OR:
			case BPF_AND:
			case BPF_LSH:
			case BPF_RSH:
			case BPF_NEG:
				break;
			case BPF_DIV:
				/*
				 * Check for constant division by 0.
				 */
				if (BPF_RVAL(p->code) == BPF_K && p->k == 0)
					return 0;
				break;
			default:
				return 0;
			}
			break;
		case BPF_JMP:
			/*
			 * Check that jumps are forward, and within 
			 * the code block.
			 */
			from = i + 1;
			switch (BPF_OP(p->code)) {
			case BPF_JA:
				if (from + p->k < from || from + p->k >= len)
					return 0;
				break;
			case BPF_JEQ:
			case BPF_JGT:
			case BPF_JGE:
			case BPF_JSET:
				if (from + p->jt >= len || from + p->jf >= len)
					return 0;
				break;
			default:
				return 0;
			}
			break;
		case BPF_RET:
			break;
		case BPF_MISC:
			break;
		default:
			return 0;
		}

	}
	return BPF_CLASS(f[len - 1].code) == BPF_RET;
}
#endif