tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1/* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me>
2 *
3 * This program is free software; you can redistribute it and/or
4 * modify it under the terms of version 2 of the GNU General Public
5 * License as published by the Free Software Foundation.
6 */
7#include <linux/skbuff.h>
8#include <linux/netdevice.h>
9#include <uapi/linux/bpf.h>
10#include <linux/version.h>
11#include <bpf/bpf_helpers.h>
12#include <bpf/bpf_tracing.h>
13
14struct bpf_map_def SEC("maps") dnat_map = {
15 .type = BPF_MAP_TYPE_HASH,
16 .key_size = sizeof(struct sockaddr_in),
17 .value_size = sizeof(struct sockaddr_in),
18 .max_entries = 256,
19};
20
21/* kprobe is NOT a stable ABI
22 * kernel functions can be removed, renamed or completely change semantics.
23 * Number of arguments and their positions can change, etc.
24 * In such case this bpf+kprobe example will no longer be meaningful
25 *
26 * This example sits on a syscall, and the syscall ABI is relatively stable
27 * of course, across platforms, and over time, the ABI may change.
28 */
29SEC("kprobe/sys_connect")
30int bpf_prog1(struct pt_regs *ctx)
31{
32 struct sockaddr_in new_addr, orig_addr = {};
33 struct sockaddr_in *mapped_addr;
34 void *sockaddr_arg = (void *)PT_REGS_PARM2(ctx);
35 int sockaddr_len = (int)PT_REGS_PARM3(ctx);
36
37 if (sockaddr_len > sizeof(orig_addr))
38 return 0;
39
40 if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), sockaddr_arg) != 0)
41 return 0;
42
43 mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr);
44 if (mapped_addr != NULL) {
45 memcpy(&new_addr, mapped_addr, sizeof(new_addr));
46 bpf_probe_write_user(sockaddr_arg, &new_addr,
47 sizeof(new_addr));
48 }
49 return 0;
50}
51
52char _license[] SEC("license") = "GPL";
53u32 _version SEC("version") = LINUX_VERSION_CODE;