1// SPDX-License-Identifier: GPL-2.0
2// Copyright (c) 2018 Facebook
3
4#include <linux/stddef.h>
5#include <linux/bpf.h>
6#include <sys/socket.h>
7
8#include <bpf/bpf_helpers.h>
9#include <bpf/bpf_endian.h>
10
11#include <bpf_sockopt_helpers.h>
12
13#define SRC1_IP4		0xAC100001U /* 172.16.0.1 */
14#define SRC2_IP4		0x00000000U
15#define SRC_REWRITE_IP4		0x7f000004U
16#define DST_IP4			0xC0A801FEU /* 192.168.1.254 */
17#define DST_REWRITE_IP4		0x7f000001U
18#define DST_PORT		4040
19#define DST_REWRITE_PORT4	4444
20
21SEC("cgroup/sendmsg4")
22int sendmsg_v4_prog(struct bpf_sock_addr *ctx)
23{
24	if (ctx->type != SOCK_DGRAM)
25		return 0;
26
27	if (!get_set_sk_priority(ctx))
28		return 0;
29
30	/* Rewrite source. */
31	if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) ||
32	    ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) {
33		ctx->msg_src_ip4 = bpf_htonl(SRC_REWRITE_IP4);
34	} else {
35		/* Unexpected source. Reject sendmsg. */
36		return 0;
37	}
38
39	/* Rewrite destination. */
40	if ((ctx->user_ip4 >> 24) == (bpf_htonl(DST_IP4) >> 24) &&
41	     ctx->user_port == bpf_htons(DST_PORT)) {
42		ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4);
43		ctx->user_port = bpf_htons(DST_REWRITE_PORT4);
44	} else {
45		/* Unexpected source. Reject sendmsg. */
46		return 0;
47	}
48
49	return 1;
50}
51
52SEC("cgroup/sendmsg4")
53int sendmsg_v4_deny_prog(struct bpf_sock_addr *ctx)
54{
55	return 0;
56}
57
58char _license[] SEC("license") = "GPL";
59