1 // SPDX-License-Identifier: GPL-2.0
2 #include <string.h>
3 #include <stdbool.h>
4 
5 #include <linux/bpf.h>
6 #include <linux/in.h>
7 #include <linux/in6.h>
8 #include <sys/socket.h>
9 
10 #include <bpf/bpf_helpers.h>
11 #include <bpf/bpf_endian.h>
12 
13 char _license[] SEC("license") = "GPL";
14 int _version SEC("version") = 1;
15 
16 struct svc_addr {
17 	__be32 addr;
18 	__be16 port;
19 };
20 
21 struct {
22 	__uint(type, BPF_MAP_TYPE_SK_STORAGE);
23 	__uint(map_flags, BPF_F_NO_PREALLOC);
24 	__type(key, int);
25 	__type(value, struct svc_addr);
26 } service_mapping SEC(".maps");
27 
28 SEC("cgroup/connect4")
29 int connect4(struct bpf_sock_addr *ctx)
30 {
31 	struct sockaddr_in sa = {};
32 	struct svc_addr *orig;
33 
34 	/* Force local address to 127.0.0.1:22222. */
35 	sa.sin_family = AF_INET;
36 	sa.sin_port = bpf_htons(22222);
37 	sa.sin_addr.s_addr = bpf_htonl(0x7f000001);
38 
39 	if (bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa)) != 0)
40 		return 0;
41 
42 	/* Rewire service 1.2.3.4:60000 to backend 127.0.0.1:60123. */
43 	if (ctx->user_port == bpf_htons(60000)) {
44 		orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0,
45 					  BPF_SK_STORAGE_GET_F_CREATE);
46 		if (!orig)
47 			return 0;
48 
49 		orig->addr = ctx->user_ip4;
50 		orig->port = ctx->user_port;
51 
52 		ctx->user_ip4 = bpf_htonl(0x7f000001);
53 		ctx->user_port = bpf_htons(60123);
54 	}
55 	return 1;
56 }
57 
58 SEC("cgroup/getsockname4")
59 int getsockname4(struct bpf_sock_addr *ctx)
60 {
61 	/* Expose local server as 1.2.3.4:60000 to client. */
62 	if (ctx->user_port == bpf_htons(60123)) {
63 		ctx->user_ip4 = bpf_htonl(0x01020304);
64 		ctx->user_port = bpf_htons(60000);
65 	}
66 	return 1;
67 }
68 
69 SEC("cgroup/getpeername4")
70 int getpeername4(struct bpf_sock_addr *ctx)
71 {
72 	struct svc_addr *orig;
73 
74 	/* Expose service 1.2.3.4:60000 as peer instead of backend. */
75 	if (ctx->user_port == bpf_htons(60123)) {
76 		orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0, 0);
77 		if (orig) {
78 			ctx->user_ip4 = orig->addr;
79 			ctx->user_port = orig->port;
80 		}
81 	}
82 	return 1;
83 }
84