blob: f033f36a13a389514d2bda36438c0b1a27b8136a [file] [log] [blame]
/* Copyright (c) 2016 Sargun Dhillon <>
* 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 <linux/skbuff.h>
#include <linux/netdevice.h>
#include <uapi/linux/bpf.h>
#include <linux/version.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
struct bpf_map_def SEC("maps") dnat_map = {
.key_size = sizeof(struct sockaddr_in),
.value_size = sizeof(struct sockaddr_in),
.max_entries = 256,
/* 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.
int bpf_prog1(struct pt_regs *ctx)
struct sockaddr_in new_addr, orig_addr = {};
struct sockaddr_in *mapped_addr;
void *sockaddr_arg = (void *)PT_REGS_PARM2(ctx);
int sockaddr_len = (int)PT_REGS_PARM3(ctx);
if (sockaddr_len > sizeof(orig_addr))
return 0;
if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), sockaddr_arg) != 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(sockaddr_arg, &new_addr,
return 0;
char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;