samples/bpf/test_probe_write_user_kern.c

   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;