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cf9b1199 SD |
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_helpers.h" | |
12 | ||
13 | struct bpf_map_def SEC("maps") dnat_map = { | |
14 | .type = BPF_MAP_TYPE_HASH, | |
15 | .key_size = sizeof(struct sockaddr_in), | |
16 | .value_size = sizeof(struct sockaddr_in), | |
17 | .max_entries = 256, | |
18 | }; | |
19 | ||
20 | /* kprobe is NOT a stable ABI | |
21 | * kernel functions can be removed, renamed or completely change semantics. | |
22 | * Number of arguments and their positions can change, etc. | |
23 | * In such case this bpf+kprobe example will no longer be meaningful | |
24 | * | |
25 | * This example sits on a syscall, and the syscall ABI is relatively stable | |
26 | * of course, across platforms, and over time, the ABI may change. | |
27 | */ | |
28 | SEC("kprobe/sys_connect") | |
29 | int bpf_prog1(struct pt_regs *ctx) | |
30 | { | |
31 | struct sockaddr_in new_addr, orig_addr = {}; | |
32 | struct sockaddr_in *mapped_addr; | |
33 | void *sockaddr_arg = (void *)PT_REGS_PARM2(ctx); | |
34 | int sockaddr_len = (int)PT_REGS_PARM3(ctx); | |
35 | ||
36 | if (sockaddr_len > sizeof(orig_addr)) | |
37 | return 0; | |
38 | ||
39 | if (bpf_probe_read(&orig_addr, sizeof(orig_addr), sockaddr_arg) != 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(sockaddr_arg, &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; |