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 #include <bpf_sockopt_helpers.h>
14 
15 char _license[] SEC("license") = "GPL";
16 int _version SEC("version") = 1;
17 
18 struct svc_addr {
19 	__be32 addr;
20 	__be16 port;
21 };
22 
23 struct {
24 	__uint(type, BPF_MAP_TYPE_SK_STORAGE);
25 	__uint(map_flags, BPF_F_NO_PREALLOC);
26 	__type(key, int);
27 	__type(value, struct svc_addr);
28 } service_mapping SEC(".maps");
29 
30 SEC("cgroup/connect4")
31 int connect4(struct bpf_sock_addr *ctx)
32 {
33 	struct sockaddr_in sa = {};
34 	struct svc_addr *orig;
35 
36 	/* Force local address to 127.0.0.1:22222. */
37 	sa.sin_family = AF_INET;
38 	sa.sin_port = bpf_htons(22222);
39 	sa.sin_addr.s_addr = bpf_htonl(0x7f000001);
40 
41 	if (bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa)) != 0)
42 		return 0;
43 
44 	/* Rewire service 1.2.3.4:60000 to backend 127.0.0.1:60123. */
45 	if (ctx->user_port == bpf_htons(60000)) {
46 		orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0,
47 					  BPF_SK_STORAGE_GET_F_CREATE);
48 		if (!orig)
49 			return 0;
50 
51 		orig->addr = ctx->user_ip4;
52 		orig->port = ctx->user_port;
53 
54 		ctx->user_ip4 = bpf_htonl(0x7f000001);
55 		ctx->user_port = bpf_htons(60123);
56 	}
57 	return 1;
58 }
59 
60 SEC("cgroup/getsockname4")
61 int getsockname4(struct bpf_sock_addr *ctx)
62 {
63 	if (!get_set_sk_priority(ctx))
64 		return 1;
65 
66 	/* Expose local server as 1.2.3.4:60000 to client. */
67 	if (ctx->user_port == bpf_htons(60123)) {
68 		ctx->user_ip4 = bpf_htonl(0x01020304);
69 		ctx->user_port = bpf_htons(60000);
70 	}
71 	return 1;
72 }
73 
74 SEC("cgroup/getpeername4")
75 int getpeername4(struct bpf_sock_addr *ctx)
76 {
77 	struct svc_addr *orig;
78 
79 	if (!get_set_sk_priority(ctx))
80 		return 1;
81 
82 	/* Expose service 1.2.3.4:60000 as peer instead of backend. */
83 	if (ctx->user_port == bpf_htons(60123)) {
84 		orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0, 0);
85 		if (orig) {
86 			ctx->user_ip4 = orig->addr;
87 			ctx->user_port = orig->port;
88 		}
89 	}
90 	return 1;
91 }
92