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 SRC_REWRITE_IP6_0	0
14 #define SRC_REWRITE_IP6_1	0
15 #define SRC_REWRITE_IP6_2	0
16 #define SRC_REWRITE_IP6_3	6
17 
18 #define DST_REWRITE_IP6_0	0
19 #define DST_REWRITE_IP6_1	0
20 #define DST_REWRITE_IP6_2	0
21 #define DST_REWRITE_IP6_3	1
22 
23 #define DST_REWRITE_PORT6	6666
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 	if (!get_set_sk_priority(ctx))
32 		return 0;
33 
34 	/* Rewrite source. */
35 	if (ctx->msg_src_ip6[3] == bpf_htonl(1) ||
36 	    ctx->msg_src_ip6[3] == bpf_htonl(0)) {
37 		ctx->msg_src_ip6[0] = bpf_htonl(SRC_REWRITE_IP6_0);
38 		ctx->msg_src_ip6[1] = bpf_htonl(SRC_REWRITE_IP6_1);
39 		ctx->msg_src_ip6[2] = bpf_htonl(SRC_REWRITE_IP6_2);
40 		ctx->msg_src_ip6[3] = bpf_htonl(SRC_REWRITE_IP6_3);
41 	} else {
42 		/* Unexpected source. Reject sendmsg. */
43 		return 0;
44 	}
45 
46 	/* Rewrite destination. */
47 	if (ctx->user_ip6[0] == bpf_htonl(0xFACEB00C)) {
48 		ctx->user_ip6[0] = bpf_htonl(DST_REWRITE_IP6_0);
49 		ctx->user_ip6[1] = bpf_htonl(DST_REWRITE_IP6_1);
50 		ctx->user_ip6[2] = bpf_htonl(DST_REWRITE_IP6_2);
51 		ctx->user_ip6[3] = bpf_htonl(DST_REWRITE_IP6_3);
52 
53 		ctx->user_port = bpf_htons(DST_REWRITE_PORT6);
54 	} else {
55 		/* Unexpected destination. Reject sendmsg. */
56 		return 0;
57 	}
58 
59 	return 1;
60 }
61 
62 char _license[] SEC("license") = "GPL";
63