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") 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") 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") 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