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 "vmlinux.h"
8 #include <string.h>
9 #include <linux/version.h>
10 #include <bpf/bpf_helpers.h>
11 #include <bpf/bpf_tracing.h>
12 #include <bpf/bpf_core_read.h>
13
14 struct {
15 __uint(type, BPF_MAP_TYPE_HASH);
16 __type(key, struct sockaddr_in);
17 __type(value, struct sockaddr_in);
18 __uint(max_entries, 256);
19 } dnat_map SEC(".maps");
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 */
29 SEC("ksyscall/connect")
30 int BPF_KSYSCALL(bpf_prog1, int fd, struct sockaddr_in *uservaddr,
31 int addrlen)
32 {
33 struct sockaddr_in new_addr, orig_addr = {};
34 struct sockaddr_in *mapped_addr;
35
36 if (addrlen > sizeof(orig_addr))
37 return 0;
38
39 if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), uservaddr) != 0)
40 return 0;
41
42 mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr);
43 if (mapped_addr != NULL) {
44 memcpy(&new_addr, mapped_addr, sizeof(new_addr));
45 bpf_probe_write_user(uservaddr, &new_addr,
46 sizeof(new_addr));
47 }
48 return 0;
49 }
50
51 char _license[] SEC("license") = "GPL";
52 u32 _version SEC("version") = LINUX_VERSION_CODE;
53
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.