Pawnyable LK06

bpf_example_filter.c

#include <linux/bpf.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
// https://pawnyable.cafe/linux-kernel/LK06/distfiles/bpf_insn.h
#include "bpf_insn.h"

void fatal(const char *msg) {
    perror(msg);
    exit(1);
}

int bpf(int cmd, union bpf_attr *attrs) {
    return syscall(__NR_bpf, cmd, attrs, sizeof(*attrs));
}

int main() {
    char verifier_log[0x10000];

    // prepare BPF program
    struct bpf_insn insns[] = {
        BPF_MOV64_IMM(BPF_REG_0, 4),
        BPF_EXIT_INSN(),
    };

    // set usage
    union bpf_attr prog_attr = {
        .prog_type = BPF_PROG_TYPE_SOCKET_FILTER,
        .insn_cnt = sizeof(insns) / sizeof(insns[0]),
        .insns = (uint64_t)insns,
        .license = (uint64_t) "GPL v2",
        .log_level = 2,
        .log_size = sizeof(verifier_log),
        .log_buf = (uint64_t)verifier_log};

    // load BPF program
    int progfd = bpf(BPF_PROG_LOAD, &prog_attr);
    if (progfd == -1)
        fatal("bpf(BPF_PROG_LOAD)");

    // create socket
    int socks[2];
    if (socketpair(AF_UNIX, SOCK_DGRAM, 0, socks))
        fatal("socketpair");
    if (setsockopt(socks[0], SOL_SOCKET, SO_ATTACH_BPF, &progfd, sizeof(int)))
        fatal("setsockopt");

    // use socket
    write(socks[1], "Hello", 5);
    char buf[0x10] = {};
    read(socks[0], buf, 0x10);
    printf("Received: %s\n", buf);

    return 0;
}