1*4882a593Smuzhiyun /* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me>
2*4882a593Smuzhiyun *
3*4882a593Smuzhiyun * This program is free software; you can redistribute it and/or
4*4882a593Smuzhiyun * modify it under the terms of version 2 of the GNU General Public
5*4882a593Smuzhiyun * License as published by the Free Software Foundation.
6*4882a593Smuzhiyun */
7*4882a593Smuzhiyun #include <linux/skbuff.h>
8*4882a593Smuzhiyun #include <linux/netdevice.h>
9*4882a593Smuzhiyun #include <uapi/linux/bpf.h>
10*4882a593Smuzhiyun #include <linux/version.h>
11*4882a593Smuzhiyun #include <bpf/bpf_helpers.h>
12*4882a593Smuzhiyun #include <bpf/bpf_tracing.h>
13*4882a593Smuzhiyun #include <bpf/bpf_core_read.h>
14*4882a593Smuzhiyun #include "trace_common.h"
15*4882a593Smuzhiyun
16*4882a593Smuzhiyun struct {
17*4882a593Smuzhiyun __uint(type, BPF_MAP_TYPE_HASH);
18*4882a593Smuzhiyun __type(key, struct sockaddr_in);
19*4882a593Smuzhiyun __type(value, struct sockaddr_in);
20*4882a593Smuzhiyun __uint(max_entries, 256);
21*4882a593Smuzhiyun } dnat_map SEC(".maps");
22*4882a593Smuzhiyun
23*4882a593Smuzhiyun /* kprobe is NOT a stable ABI
24*4882a593Smuzhiyun * kernel functions can be removed, renamed or completely change semantics.
25*4882a593Smuzhiyun * Number of arguments and their positions can change, etc.
26*4882a593Smuzhiyun * In such case this bpf+kprobe example will no longer be meaningful
27*4882a593Smuzhiyun *
28*4882a593Smuzhiyun * This example sits on a syscall, and the syscall ABI is relatively stable
29*4882a593Smuzhiyun * of course, across platforms, and over time, the ABI may change.
30*4882a593Smuzhiyun */
SYSCALL(sys_connect)31*4882a593Smuzhiyun SEC("kprobe/" SYSCALL(sys_connect))
32*4882a593Smuzhiyun int bpf_prog1(struct pt_regs *ctx)
33*4882a593Smuzhiyun {
34*4882a593Smuzhiyun struct pt_regs *real_regs = (struct pt_regs *)PT_REGS_PARM1_CORE(ctx);
35*4882a593Smuzhiyun void *sockaddr_arg = (void *)PT_REGS_PARM2_CORE(real_regs);
36*4882a593Smuzhiyun int sockaddr_len = (int)PT_REGS_PARM3_CORE(real_regs);
37*4882a593Smuzhiyun struct sockaddr_in new_addr, orig_addr = {};
38*4882a593Smuzhiyun struct sockaddr_in *mapped_addr;
39*4882a593Smuzhiyun
40*4882a593Smuzhiyun if (sockaddr_len > sizeof(orig_addr))
41*4882a593Smuzhiyun return 0;
42*4882a593Smuzhiyun
43*4882a593Smuzhiyun if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), sockaddr_arg) != 0)
44*4882a593Smuzhiyun return 0;
45*4882a593Smuzhiyun
46*4882a593Smuzhiyun mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr);
47*4882a593Smuzhiyun if (mapped_addr != NULL) {
48*4882a593Smuzhiyun memcpy(&new_addr, mapped_addr, sizeof(new_addr));
49*4882a593Smuzhiyun bpf_probe_write_user(sockaddr_arg, &new_addr,
50*4882a593Smuzhiyun sizeof(new_addr));
51*4882a593Smuzhiyun }
52*4882a593Smuzhiyun return 0;
53*4882a593Smuzhiyun }
54*4882a593Smuzhiyun
55*4882a593Smuzhiyun char _license[] SEC("license") = "GPL";
56*4882a593Smuzhiyun u32 _version SEC("version") = LINUX_VERSION_CODE;
57