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