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128 lines
3.3 KiB
C
128 lines
3.3 KiB
C
// bpf.c: bpf packet filter for linux/freebsd
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#include "config.h"
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/types.h>
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#include "dat.h"
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#include "fns.h"
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struct bpf_insn {
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ushort code;
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uchar jt;
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uchar jf;
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u_int32_t k;
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};
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struct bpf_program {
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uint bf_len;
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struct bpf_insn *bf_insns;
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};
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/* instruction classes */
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#define BPF_CLASS(code) ((code) & 0x07)
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#define BPF_LD 0x00
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#define BPF_LDX 0x01
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#define BPF_ST 0x02
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#define BPF_STX 0x03
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#define BPF_ALU 0x04
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#define BPF_JMP 0x05
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#define BPF_RET 0x06
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#define BPF_MISC 0x07
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/* ld/ldx fields */
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#define BPF_SIZE(code) ((code) & 0x18)
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#define BPF_W 0x00
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#define BPF_H 0x08
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#define BPF_B 0x10
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#define BPF_MODE(code) ((code) & 0xe0)
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#define BPF_IMM 0x00
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#define BPF_ABS 0x20
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#define BPF_IND 0x40
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#define BPF_MEM 0x60
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#define BPF_LEN 0x80
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#define BPF_MSH 0xa0
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/* alu/jmp fields */
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#define BPF_OP(code) ((code) & 0xf0)
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#define BPF_ADD 0x00
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#define BPF_SUB 0x10
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#define BPF_MUL 0x20
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#define BPF_DIV 0x30
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#define BPF_OR 0x40
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#define BPF_AND 0x50
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#define BPF_LSH 0x60
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#define BPF_RSH 0x70
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#define BPF_NEG 0x80
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#define BPF_JA 0x00
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#define BPF_JEQ 0x10
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#define BPF_JGT 0x20
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#define BPF_JGE 0x30
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#define BPF_JSET 0x40
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#define BPF_SRC(code) ((code) & 0x08)
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#define BPF_K 0x00
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#define BPF_X 0x08
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/* ret - BPF_K and BPF_X also apply */
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#define BPF_RVAL(code) ((code) & 0x18)
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#define BPF_A 0x10
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/* misc */
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#define BPF_MISCOP(code) ((code) & 0xf8)
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#define BPF_TAX 0x00
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#define BPF_TXA 0x80
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/* macros for insn array initializers */
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#define BPF_STMT(code, k) { (ushort)(code), 0, 0, k }
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#define BPF_JUMP(code, k, jt, jf) { (ushort)(code), jt, jf, k }
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void *
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create_bpf_program(int shelf, int slot)
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{
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struct bpf_program *bpf_program;
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struct bpf_insn insns[] = {
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/* CHECKTYPE: Load the type into register */
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BPF_STMT(BPF_LD+BPF_H+BPF_ABS, 12),
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/* Does it match AoE Type (0x88a2)? No, goto INVALID */
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0x88a2, 0, 10),
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/* Load the flags into register */
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BPF_STMT(BPF_LD+BPF_B+BPF_ABS, 14),
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/* Check to see if the Resp flag is set */
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BPF_STMT(BPF_ALU+BPF_AND+BPF_K, Resp),
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/* Yes, goto INVALID */
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 7),
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/* CHECKSHELF: Load the shelf number into register */
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BPF_STMT(BPF_LD+BPF_H+BPF_ABS, 16),
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/* Does it match shelf number? Yes, goto CHECKSLOT */
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, shelf, 1, 0),
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/* Does it match broadcast? No, goto INVALID */
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0xffff, 0, 4),
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/* CHECKSLOT: Load the slot number into register */
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BPF_STMT(BPF_LD+BPF_B+BPF_ABS, 18),
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/* Does it match shelf number? Yes, goto VALID */
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, slot, 1, 0),
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/* Does it match broadcast? No, goto INVALID */
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0xff, 0, 1),
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/* VALID: return -1 (allow the packet to be read) */
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BPF_STMT(BPF_RET+BPF_K, -1),
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/* INVALID: return 0 (ignore the packet) */
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BPF_STMT(BPF_RET+BPF_K, 0),
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};
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if ((bpf_program = malloc(sizeof(struct bpf_program))) == NULL
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|| (bpf_program->bf_insns = malloc(sizeof(insns))) == NULL) {
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perror("malloc");
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exit(1);
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}
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bpf_program->bf_len = sizeof(insns)/sizeof(struct bpf_insn);
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memcpy(bpf_program->bf_insns, insns, sizeof(insns));
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return (void *)bpf_program;
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}
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void
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free_bpf_program(void *bpf_program)
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{
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free(((struct bpf_program *) bpf_program)->bf_insns);
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free(bpf_program);
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}
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