1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright (c) 2018 Facebook
3 
4 #include <string.h>
5 
6 #include <linux/stddef.h>
7 #include <linux/bpf.h>
8 #include <linux/in.h>
9 #include <linux/in6.h>
10 #include <sys/socket.h>
11 
12 #include <bpf/bpf_helpers.h>
13 #include <bpf/bpf_endian.h>
14 
15 #define SRC_REWRITE_IP4		0x7f000004U
16 #define DST_REWRITE_IP4		0x7f000001U
17 #define DST_REWRITE_PORT4	4444
18 
19 int _version SEC("version") = 1;
20 
21 SEC("cgroup/connect4")
22 int connect_v4_prog(struct bpf_sock_addr *ctx)
23 {
24 	struct bpf_sock_tuple tuple = {};
25 	struct sockaddr_in sa;
26 	struct bpf_sock *sk;
27 
28 	/* Verify that new destination is available. */
29 	memset(&tuple.ipv4.saddr, 0, sizeof(tuple.ipv4.saddr));
30 	memset(&tuple.ipv4.sport, 0, sizeof(tuple.ipv4.sport));
31 
32 	tuple.ipv4.daddr = bpf_htonl(DST_REWRITE_IP4);
33 	tuple.ipv4.dport = bpf_htons(DST_REWRITE_PORT4);
34 
35 	if (ctx->type != SOCK_STREAM && ctx->type != SOCK_DGRAM)
36 		return 0;
37 	else if (ctx->type == SOCK_STREAM)
38 		sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof(tuple.ipv4),
39 				       BPF_F_CURRENT_NETNS, 0);
40 	else
41 		sk = bpf_sk_lookup_udp(ctx, &tuple, sizeof(tuple.ipv4),
42 				       BPF_F_CURRENT_NETNS, 0);
43 
44 	if (!sk)
45 		return 0;
46 
47 	if (sk->src_ip4 != tuple.ipv4.daddr ||
48 	    sk->src_port != DST_REWRITE_PORT4) {
49 		bpf_sk_release(sk);
50 		return 0;
51 	}
52 
53 	bpf_sk_release(sk);
54 
55 	/* Rewrite destination. */
56 	ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4);
57 	ctx->user_port = bpf_htons(DST_REWRITE_PORT4);
58 
59 	/* Rewrite source. */
60 	memset(&sa, 0, sizeof(sa));
61 
62 	sa.sin_family = AF_INET;
63 	sa.sin_port = bpf_htons(0);
64 	sa.sin_addr.s_addr = bpf_htonl(SRC_REWRITE_IP4);
65 
66 	if (bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa)) != 0)
67 		return 0;
68 
69 	return 1;
70 }
71 
72 char _license[] SEC("license") = "GPL";
73