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/bpf_helpers.h>
  12#include <bpf/bpf_tracing.h>
  13#include <bpf/bpf_core_read.h>
  14#include "trace_common.h"
  15
  16struct {
  17        __uint(type, BPF_MAP_TYPE_HASH);
  18        __type(key, struct sockaddr_in);
  19        __type(value, struct sockaddr_in);
  20        __uint(max_entries, 256);
  21} dnat_map SEC(".maps");
  22
  23/* kprobe is NOT a stable ABI
  24 * kernel functions can be removed, renamed or completely change semantics.
  25 * Number of arguments and their positions can change, etc.
  26 * In such case this bpf+kprobe example will no longer be meaningful
  27 *
  28 * This example sits on a syscall, and the syscall ABI is relatively stable
  29 * of course, across platforms, and over time, the ABI may change.
  30 */
  31SEC("kprobe/" SYSCALL(sys_connect))
  32int bpf_prog1(struct pt_regs *ctx)
  33{
  34        struct pt_regs *real_regs = (struct pt_regs *)PT_REGS_PARM1_CORE(ctx);
  35        void *sockaddr_arg = (void *)PT_REGS_PARM2_CORE(real_regs);
  36        int sockaddr_len = (int)PT_REGS_PARM3_CORE(real_regs);
  37        struct sockaddr_in new_addr, orig_addr = {};
  38        struct sockaddr_in *mapped_addr;
  39
  40        if (sockaddr_len > sizeof(orig_addr))
  41                return 0;
  42
  43        if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), sockaddr_arg) != 0)
  44                return 0;
  45
  46        mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr);
  47        if (mapped_addr != NULL) {
  48                memcpy(&new_addr, mapped_addr, sizeof(new_addr));
  49                bpf_probe_write_user(sockaddr_arg, &new_addr,
  50                                     sizeof(new_addr));
  51        }
  52        return 0;
  53}
  54
  55char _license[] SEC("license") = "GPL";
  56u32 _version SEC("version") = LINUX_VERSION_CODE;
  57