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 
21 SEC("cgroup/sendmsg4")
22 int 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 
52 char _license[] SEC("license") = "GPL";
53