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/* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of version 2 of the GNU General Public
* License as published by the Free Software Foundation.
*/
#include "vmlinux.h"
#include <string.h>
#include <linux/version.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_core_read.h>
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__type(key, struct sockaddr_in);
__type(value, struct sockaddr_in);
__uint(max_entries, 256);
} dnat_map SEC(".maps");
/* kprobe is NOT a stable ABI
* kernel functions can be removed, renamed or completely change semantics.
* Number of arguments and their positions can change, etc.
* In such case this bpf+kprobe example will no longer be meaningful
*
* This example sits on a syscall, and the syscall ABI is relatively stable
* of course, across platforms, and over time, the ABI may change.
*/
SEC("ksyscall/connect")
int BPF_KSYSCALL(bpf_prog1, int fd, struct sockaddr_in *uservaddr,
int addrlen)
{
struct sockaddr_in new_addr, orig_addr = {};
struct sockaddr_in *mapped_addr;
if (addrlen > sizeof(orig_addr))
return 0;
if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), uservaddr) != 0)
return 0;
mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr);
if (mapped_addr != NULL) {
memcpy(&new_addr, mapped_addr, sizeof(new_addr));
bpf_probe_write_user(uservaddr, &new_addr,
sizeof(new_addr));
}
return 0;
}
char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;
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