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