bpf_filter.c

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/*-
 * Copyright (c) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
 *      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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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.c       7.5 (Berkeley) 7/15/91
 */

#if !(defined(lint) || defined(KERNEL) || defined(_KERNEL))
static const char rcsid[] =
    "@(#) $Header: /tcpdump/master/libpcap/bpf/net/bpf_filter.c,v 1.35 2000/10/23 19:32:21 fenner Exp $ (LBL)";
#endif

#include <sys/param.h>
#include <sys/types.h>
#include <sys/time.h>

#define SOLARIS (defined(sun) && (defined(__SVR4) || defined(__svr4__)))
#if defined(__hpux) || SOLARIS
# include <sys/sysmacros.h>
# include <sys/stream.h>
# define        mbuf    msgb
# define        m_next  b_cont
# define        MLEN(m) ((m)->b_wptr - (m)->b_rptr)
# define        mtod(m,t)       ((t)(m)->b_rptr)
#else
# define        MLEN(m) ((m)->m_len)
#endif

#include <net/bpf.h>

#if !defined(KERNEL) && !defined(_KERNEL)
#include <stdlib.h>
#endif

#define int32 bpf_int32
#define u_int32 bpf_u_int32

#ifndef LBL_ALIGN
#if defined(sparc) || defined(mips) || defined(ibm032) || \
    defined(__alpha) || defined(__hpux)
#define LBL_ALIGN
#endif
#endif

#ifndef LBL_ALIGN
#include <netinet/in.h>

#define EXTRACT_SHORT(p)        ((u_short)ntohs(*(u_short *)p))
#define EXTRACT_LONG(p)         (ntohl(*(u_int32 *)p))
#else
#define EXTRACT_SHORT(p)\
        ((u_short)\
                ((u_short)*((u_char *)p+0)<<8|\
                 (u_short)*((u_char *)p+1)<<0))
#define EXTRACT_LONG(p)\
                ((u_int32)*((u_char *)p+0)<<24|\
                 (u_int32)*((u_char *)p+1)<<16|\
                 (u_int32)*((u_char *)p+2)<<8|\
                 (u_int32)*((u_char *)p+3)<<0)
#endif

#if defined(KERNEL) || defined(_KERNEL)
# if !defined(__hpux) && !SOLARIS
#include <sys/mbuf.h>
# endif
#define MINDEX(len, _m, _k) \
{ \
        len = MLEN(m); \
        while ((_k) >= len) { \
                (_k) -= len; \
                (_m) = (_m)->m_next; \
                if ((_m) == 0) \
                        return 0; \
                len = MLEN(m); \
        } \
}

static int
m_xword(m, k, err)
        register struct mbuf *m;
        register int k, *err;
{
        register int len;
        register u_char *cp, *np;
        register struct mbuf *m0;

        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 || MLEN(m0) + len - k < 4)
                goto bad;
        *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];
        }
    bad:
        *err = 1;
        return 0;
}

static int
m_xhalf(m, k, err)
        register struct mbuf *m;
        register int k, *err;
{
        register int len;
        register u_char *cp;
        register struct mbuf *m0;

        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)
                goto bad;
        *err = 0;
        return (cp[0] << 8) | mtod(m0, u_char *)[0];
 bad:
        *err = 1;
        return 0;
}
#endif

/*
 * 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
 * For the kernel, p is assumed to be a pointer to an mbuf if buflen is 0,
 * in all other cases, p is a pointer to a buffer and buflen is its size.
 */
u_int
bpf_filter(pc, p, wirelen, buflen)
        register struct bpf_insn *pc;
        register u_char *p;
        u_int wirelen;
        register u_int buflen;
{
        register u_int32 A, X;
        register int k;
        int32 mem[BPF_MEMWORDS];
#if defined(KERNEL) || defined(_KERNEL)
        struct mbuf *m, *n;
        int merr, len;

        if (buflen == 0) {
                m = (struct mbuf *)p;
                p = mtod(m, u_char *);
                buflen = MLEN(m);
        } else
                m = NULL;
#endif

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

                default:
#if defined(KERNEL) || defined(_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) > buflen) {
#if defined(KERNEL) || defined(_KERNEL)
                                if (m == NULL)
                                        return 0;
                                A = m_xword(m, 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(short) > buflen) {
#if defined(KERNEL) || defined(_KERNEL)
                                if (m == NULL)
                                        return 0;
                                A = m_xhalf(m, 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) {
#if defined(KERNEL) || defined(_KERNEL)
                                if (m == NULL)
                                        return 0;
                                n = m;
                                MINDEX(len, n, k);
                                A = mtod(n, 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) > buflen) {
#if defined(KERNEL) || defined(_KERNEL)
                                if (m == NULL)
                                        return 0;
                                A = m_xword(m, 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(short) > buflen) {
#if defined(KERNEL) || defined(_KERNEL)
                                if (m == NULL)
                                        return 0;
                                A = m_xhalf(m, 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) {
#if defined(KERNEL) || defined(_KERNEL)
                                if (m == NULL)
                                        return 0;
                                n = m;
                                MINDEX(len, n, k);
                                A = mtod(n, 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) {
#if defined(KERNEL) || defined(_KERNEL)
                                if (m == NULL)
                                        return 0;
                                n = m;
                                MINDEX(len, n, k);
                                X = (mtod(n, 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;
                }
        }
}


/*
 * 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;
{
        register int i;
        register struct bpf_insn *p;

        for (i = 0; i < len; ++i) {
                /*
                 * Check that that jumps are forward, and within 
                 * the code block.
                 */
                p = &f[i];
                if (BPF_CLASS(p->code) == BPF_JMP) {
                        register int from = i + 1;

                        if (BPF_OP(p->code) == BPF_JA) {
                                if (from + p->k >= (unsigned)len)
                                        return 0;
                        }
                        else if (from + p->jt >= len || from + p->jf >= len)
                                return 0;
                }
                /*
                 * Check that memory operations use valid addresses.
                 */
                if ((BPF_CLASS(p->code) == BPF_ST ||
                     (BPF_CLASS(p->code) == BPF_LD && 
                      (p->code & 0xe0) == BPF_MEM)) &&
                    (p->k >= BPF_MEMWORDS || p->k < 0))
                        return 0;
                /*
                 * Check for constant division by 0.
                 */
                if (p->code == (BPF_ALU|BPF_DIV|BPF_K) && p->k == 0)
                        return 0;
        }
        return BPF_CLASS(f[len - 1].code) == BPF_RET;
}

---