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 	int prio;
25 
26 	if (ctx->type != SOCK_DGRAM)
27 		return 0;
28 
29 	if (!get_set_sk_priority(ctx))
30 		return 0;
31 
32 	/* Rewrite source. */
33 	if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) ||
34 	    ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) {
35 		ctx->msg_src_ip4 = bpf_htonl(SRC_REWRITE_IP4);
36 	} else {
37 		/* Unexpected source. Reject sendmsg. */
38 		return 0;
39 	}
40 
41 	/* Rewrite destination. */
42 	if ((ctx->user_ip4 >> 24) == (bpf_htonl(DST_IP4) >> 24) &&
43 	     ctx->user_port == bpf_htons(DST_PORT)) {
44 		ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4);
45 		ctx->user_port = bpf_htons(DST_REWRITE_PORT4);
46 	} else {
47 		/* Unexpected source. Reject sendmsg. */
48 		return 0;
49 	}
50 
51 	return 1;
52 }
53 
54 char _license[] SEC("license") = "GPL";
55