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#define SRC1_IP4		0xAC100001U /* 172.16.0.1 */
12#define SRC2_IP4		0x00000000U
13#define SRC_REWRITE_IP4		0x7f000004U
14#define DST_IP4			0xC0A801FEU /* 192.168.1.254 */
15#define DST_REWRITE_IP4		0x7f000001U
16#define DST_PORT		4040
17#define DST_REWRITE_PORT4	4444
18
19int _version SEC("version") = 1;
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	/* Rewrite source. */
28	if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) ||
29	    ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) {
30		ctx->msg_src_ip4 = bpf_htonl(SRC_REWRITE_IP4);
31	} else {
32		/* Unexpected source. Reject sendmsg. */
33		return 0;
34	}
35
36	/* Rewrite destination. */
37	if ((ctx->user_ip4 >> 24) == (bpf_htonl(DST_IP4) >> 24) &&
38	     ctx->user_port == bpf_htons(DST_PORT)) {
39		ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4);
40		ctx->user_port = bpf_htons(DST_REWRITE_PORT4);
41	} else {
42		/* Unexpected source. Reject sendmsg. */
43		return 0;
44	}
45
46	return 1;
47}
48
49char _license[] SEC("license") = "GPL";