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 SRC_REWRITE_IP6_0	0
12 #define SRC_REWRITE_IP6_1	0
13 #define SRC_REWRITE_IP6_2	0
14 #define SRC_REWRITE_IP6_3	6
15 
16 #define DST_REWRITE_IP6_0	0
17 #define DST_REWRITE_IP6_1	0
18 #define DST_REWRITE_IP6_2	0
19 #define DST_REWRITE_IP6_3	1
20 
21 #define DST_REWRITE_PORT6	6666
22 
23 int _version SEC("version") = 1;
24 
25 SEC("cgroup/sendmsg6")
26 int sendmsg_v6_prog(struct bpf_sock_addr *ctx)
27 {
28 	if (ctx->type != SOCK_DGRAM)
29 		return 0;
30 
31 	/* Rewrite source. */
32 	if (ctx->msg_src_ip6[3] == bpf_htonl(1) ||
33 	    ctx->msg_src_ip6[3] == bpf_htonl(0)) {
34 		ctx->msg_src_ip6[0] = bpf_htonl(SRC_REWRITE_IP6_0);
35 		ctx->msg_src_ip6[1] = bpf_htonl(SRC_REWRITE_IP6_1);
36 		ctx->msg_src_ip6[2] = bpf_htonl(SRC_REWRITE_IP6_2);
37 		ctx->msg_src_ip6[3] = bpf_htonl(SRC_REWRITE_IP6_3);
38 	} else {
39 		/* Unexpected source. Reject sendmsg. */
40 		return 0;
41 	}
42 
43 	/* Rewrite destination. */
44 	if (ctx->user_ip6[0] == bpf_htonl(0xFACEB00C)) {
45 		ctx->user_ip6[0] = bpf_htonl(DST_REWRITE_IP6_0);
46 		ctx->user_ip6[1] = bpf_htonl(DST_REWRITE_IP6_1);
47 		ctx->user_ip6[2] = bpf_htonl(DST_REWRITE_IP6_2);
48 		ctx->user_ip6[3] = bpf_htonl(DST_REWRITE_IP6_3);
49 
50 		ctx->user_port = bpf_htons(DST_REWRITE_PORT6);
51 	} else {
52 		/* Unexpected destination. Reject sendmsg. */
53 		return 0;
54 	}
55 
56 	return 1;
57 }
58 
59 char _license[] SEC("license") = "GPL";
60