/* $OpenBSD: bpf_filter.c,v 1.27 2015/05/13 10:42:46 jsg 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 #include #include #ifndef _KERNEL #include #include #include "pcap.h" #else #include #endif #include #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 #define MINDEX(len, m, k) \ { \ len = m->m_len; \ while (k >= len) { \ k -= len; \ m = m->m_next; \ if (m == NULL) \ 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 == NULL || 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 == NULL) return 0; *err = 0; return (cp[0] << 8) | mtod(m0, u_char *)[0]; } #endif #include /* * 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