LXR linux/samples/bpf/test_probe_write_user

   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
  13struct 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 */
  28SEC("kprobe/sys_connect")
  29int 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
  51char _license[] SEC("license") = "GPL";
  52u32 _version SEC("version") = LINUX_VERSION_CODE;
  53