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 __u16 port = 0; 18 19 struct svc_addr { 20 __be32 addr; 21 __be16 port; 22 }; 23 24 struct { 25 __uint(type, BPF_MAP_TYPE_SK_STORAGE); 26 __uint(map_flags, BPF_F_NO_PREALLOC); 27 __type(key, int); 28 __type(value, struct svc_addr); 29 } service_mapping SEC(".maps"); 30 31 SEC("cgroup/connect4") 32 int connect4(struct bpf_sock_addr *ctx) 33 { 34 struct sockaddr_in sa = {}; 35 struct svc_addr *orig; 36 37 /* Force local address to 127.0.0.1:22222. */ 38 sa.sin_family = AF_INET; 39 sa.sin_port = bpf_htons(22222); 40 sa.sin_addr.s_addr = bpf_htonl(0x7f000001); 41 42 if (bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa)) != 0) 43 return 0; 44 45 /* Rewire service 1.2.3.4:60000 to backend 127.0.0.1:port. */ 46 if (ctx->user_port == bpf_htons(60000)) { 47 orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0, 48 BPF_SK_STORAGE_GET_F_CREATE); 49 if (!orig) 50 return 0; 51 52 orig->addr = ctx->user_ip4; 53 orig->port = ctx->user_port; 54 55 ctx->user_ip4 = bpf_htonl(0x7f000001); 56 ctx->user_port = bpf_htons(port); 57 } 58 return 1; 59 } 60 61 SEC("cgroup/getsockname4") 62 int getsockname4(struct bpf_sock_addr *ctx) 63 { 64 if (!get_set_sk_priority(ctx)) 65 return 1; 66 67 /* Expose local server as 1.2.3.4:60000 to client. */ 68 if (ctx->user_port == bpf_htons(port)) { 69 ctx->user_ip4 = bpf_htonl(0x01020304); 70 ctx->user_port = bpf_htons(60000); 71 } 72 return 1; 73 } 74 75 SEC("cgroup/getpeername4") 76 int getpeername4(struct bpf_sock_addr *ctx) 77 { 78 struct svc_addr *orig; 79 80 if (!get_set_sk_priority(ctx)) 81 return 1; 82 83 /* Expose service 1.2.3.4:60000 as peer instead of backend. */ 84 if (ctx->user_port == bpf_htons(port)) { 85 orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0, 0); 86 if (orig) { 87 ctx->user_ip4 = orig->addr; 88 ctx->user_port = orig->port; 89 } 90 } 91 return 1; 92 } 93