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// SPDX-License-Identifier: GPL-2.0
#include <string.h>
#include <stdbool.h>
#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/in6.h>
#include <sys/socket.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
char _license[] SEC("license") = "GPL";
int _version SEC("version") = 1;
struct svc_addr {
__be32 addr;
__be16 port;
};
struct {
__uint(type, BPF_MAP_TYPE_SK_STORAGE);
__uint(map_flags, BPF_F_NO_PREALLOC);
__type(key, int);
__type(value, struct svc_addr);
} service_mapping SEC(".maps");
SEC("cgroup/connect4")
int connect4(struct bpf_sock_addr *ctx)
{
struct sockaddr_in sa = {};
struct svc_addr *orig;
/* Force local address to 127.0.0.1:22222. */
sa.sin_family = AF_INET;
sa.sin_port = bpf_htons(22222);
sa.sin_addr.s_addr = bpf_htonl(0x7f000001);
if (bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa)) != 0)
return 0;
/* Rewire service 1.2.3.4:60000 to backend 127.0.0.1:60123. */
if (ctx->user_port == bpf_htons(60000)) {
orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0,
BPF_SK_STORAGE_GET_F_CREATE);
if (!orig)
return 0;
orig->addr = ctx->user_ip4;
orig->port = ctx->user_port;
ctx->user_ip4 = bpf_htonl(0x7f000001);
ctx->user_port = bpf_htons(60123);
}
return 1;
}
SEC("cgroup/getsockname4")
int getsockname4(struct bpf_sock_addr *ctx)
{
/* Expose local server as 1.2.3.4:60000 to client. */
if (ctx->user_port == bpf_htons(60123)) {
ctx->user_ip4 = bpf_htonl(0x01020304);
ctx->user_port = bpf_htons(60000);
}
return 1;
}
SEC("cgroup/getpeername4")
int getpeername4(struct bpf_sock_addr *ctx)
{
struct svc_addr *orig;
/* Expose service 1.2.3.4:60000 as peer instead of backend. */
if (ctx->user_port == bpf_htons(60123)) {
orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0, 0);
if (orig) {
ctx->user_ip4 = orig->addr;
ctx->user_port = orig->port;
}
}
return 1;
}
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