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/bpf_helpers.h>
  12 #include <bpf/bpf_tracing.h>
  13 #include <bpf/bpf_core_read.h>
  14 #include "trace_common.h"
  15
  16 struct {
  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  */
  31 SEC("kprobe/" SYSCALL(sys_connect))
  32 int 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
  55 char _license[] SEC("license") = "GPL";
  56 u32 _version SEC("version") = LINUX_VERSION_CODE;