1/* eBPF example program:
 2 *
 3 * - Loads eBPF program
 4 *
 5 *   The eBPF program sets the sk_bound_dev_if index in new AF_INET{6}
 6 *   sockets opened by processes in the cgroup.
 7 *
 8 * - Attaches the new program to a cgroup using BPF_PROG_ATTACH
 9 */
10
11#define _GNU_SOURCE
12
13#include <stdio.h>
14#include <stdlib.h>
15#include <stddef.h>
16#include <string.h>
17#include <unistd.h>
18#include <assert.h>
19#include <errno.h>
20#include <fcntl.h>
21#include <net/if.h>
22#include <linux/bpf.h>
23
24#include "libbpf.h"
25
26char bpf_log_buf[BPF_LOG_BUF_SIZE];
27
28static int prog_load(int idx)
29{
30	struct bpf_insn prog[] = {
31		BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
32		BPF_MOV64_IMM(BPF_REG_3, idx),
33		BPF_MOV64_IMM(BPF_REG_2, offsetof(struct bpf_sock, bound_dev_if)),
34		BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_3, offsetof(struct bpf_sock, bound_dev_if)),
35		BPF_MOV64_IMM(BPF_REG_0, 1), /* r0 = verdict */
36		BPF_EXIT_INSN(),
37	};
38	size_t insns_cnt = sizeof(prog) / sizeof(struct bpf_insn);
39
40	return bpf_load_program(BPF_PROG_TYPE_CGROUP_SOCK, prog, insns_cnt,
41				"GPL", 0, bpf_log_buf, BPF_LOG_BUF_SIZE);
42}
43
44static int usage(const char *argv0)
45{
46	printf("Usage: %s cg-path device-index\n", argv0);
47	return EXIT_FAILURE;
48}
49
50int main(int argc, char **argv)
51{
52	int cg_fd, prog_fd, ret;
53	unsigned int idx;
54
55	if (argc < 2)
56		return usage(argv[0]);
57
58	idx = if_nametoindex(argv[2]);
59	if (!idx) {
60		printf("Invalid device name\n");
61		return EXIT_FAILURE;
62	}
63
64	cg_fd = open(argv[1], O_DIRECTORY | O_RDONLY);
65	if (cg_fd < 0) {
66		printf("Failed to open cgroup path: '%s'\n", strerror(errno));
67		return EXIT_FAILURE;
68	}
69
70	prog_fd = prog_load(idx);
71	printf("Output from kernel verifier:\n%s\n-------\n", bpf_log_buf);
72
73	if (prog_fd < 0) {
74		printf("Failed to load prog: '%s'\n", strerror(errno));
75		return EXIT_FAILURE;
76	}
77
78	ret = bpf_prog_attach(prog_fd, cg_fd, BPF_CGROUP_INET_SOCK_CREATE, 0);
79	if (ret < 0) {
80		printf("Failed to attach prog to cgroup: '%s'\n",
81		       strerror(errno));
82		return EXIT_FAILURE;
83	}
84
85	return EXIT_SUCCESS;
86}