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|
/* $OpenBSD: bpf_filter.c,v 1.26 2014/09/19 11:43:31 otto Exp $ */
/* $NetBSD: bpf_filter.c,v 1.12 1996/02/13 22:00:00 christos 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 <string.h>
#include "pcap.h"
#else
#include <sys/systm.h>
#endif
#include <sys/endian.h>
#ifdef __STRICT_ALIGNMENT
#define BPF_ALIGN
#endif
#ifndef BPF_ALIGN
#define EXTRACT_SHORT(p) ((u_int16_t)ntohs(*(u_int16_t *)p))
#define EXTRACT_LONG(p) (ntohl(*(u_int32_t *)p))
#else
#define EXTRACT_SHORT(p)\
((u_int16_t)\
((u_int16_t)*((u_char *)p+0)<<8|\
(u_int16_t)*((u_char *)p+1)<<0))
#define EXTRACT_LONG(p)\
((u_int32_t)*((u_char *)p+0)<<24|\
(u_int32_t)*((u_char *)p+1)<<16|\
(u_int32_t)*((u_char *)p+2)<<8|\
(u_int32_t)*((u_char *)p+3)<<0)
#endif
#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(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(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(struct bpf_insn *pc, u_char *p, u_int wirelen, u_int buflen)
{
u_int32_t A = 0, X = 0;
u_int32_t k;
int32_t mem[BPF_MEMWORDS];
bzero(mem, sizeof(mem));
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 > buflen || sizeof(int32_t) > buflen - k) {
#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 > buflen || sizeof(int16_t) > buflen - k) {
#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 > buflen || sizeof(int32_t) > buflen - k) {
#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 > buflen || sizeof(int16_t) > buflen - k) {
#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 and memory operations use valid addresses. The code
* must terminate with either an accept or reject.
*
* 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(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_MUL:
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_SRC(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
|