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