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
17 struct svc_addr {
18 __be32 addr;
19 __be16 port;
20 };
21
22 struct {
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
29 SEC("cgroup/connect4")
connect4(struct bpf_sock_addr * ctx)30 int 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
59 SEC("cgroup/getsockname4")
getsockname4(struct bpf_sock_addr * ctx)60 int 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
73 SEC("cgroup/getpeername4")
getpeername4(struct bpf_sock_addr * ctx)74 int 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