qbdi-based binary-only instrumentation for afl-fuzz

NOTE: this code is outdated and first would need to be adapted to the current AFL++ versions. Try frida_mode or fpicker https://github.com/ttdennis/fpicker/ first, maybe they suite your need.

1) Introduction

The code in ./qbdi_mode allows you to build a standalone feature that using the QBDI framework to fuzz android native library.

2) Build

First download the Android NDK

https://developer.android.com/ndk/downloads
https://dl.google.com/android/repository/android-ndk-r20-linux-x86_64.zip

Then unzip it and build the standalone-toolchain For x86_64 standalone-toolchain

unzip android-ndk-r20-linux-x86_64.zip
cd android-ndk-r20/
./build/tools/make_standalone_toolchain.py --arch x86_64 --api 21 --install-dir ../android-standalone-toolchain-x86_64

For x86 standalone-toolchain

./build/tools/make_standalone_toolchain.py --arch x86 --api 21 --install-dir ../android-standalone-toolchain-x86

In alternative you can also use the prebuilt toolchain, in that case make sure to set the proper CC and CXX env variables because there are many different compilers for each API version in the prebuilt toolchain.

For example:

export STANDALONE_TOOLCHAIN_PATH=~/Android/Sdk/ndk/20.1.5948944/toolchains/llvm/prebuilt/linux-x86_64/
export CC=x86_64-linux-android21-clang
export CXX=x86_64-linux-android21-clang++

Then download the QBDI SDK from website

https://qbdi.quarkslab.com/

For Android x86_64

https://github.com/QBDI/QBDI/releases/download/v0.7.0/QBDI-0.7.0-android-X86_64.tar.gz

Then decompress the sdk

mkdir android-qbdi-sdk-x86_64
cp QBDI-0.7.0-android-X86_64.tar.gz android-qbdi-sdk-x86_64/
cd android-qbdi-sdk-x86_64/
tar xvf QBDI-0.7.0-android-X86_64.tar.gz

Now set the STANDALONE_TOOLCHAIN_PATH to the path of standalone-toolchain

export STANDALONE_TOOLCHAIN_PATH=/home/hac425/workspace/android-standalone-toolchain-x86_64

set the QBDI_SDK_PATH to the path of QBDI SDK

export QBDI_SDK_PATH=/home/hac425/workspace/AFLplusplus/qbdi_mode/android-qbdi-sdk-x86_64/

Then run the build.sh

./build.sh x86_64

this could build the afl-fuzz and also the qbdi template for android x86_64

Example

The demo-so.c is an vulnerable library, it has a function for test

int target_func(char *buf, int size) {

  printf("buffer:%p, size:%p\n", buf, size);
  switch (buf[0]) {

    case 1:
      puts("222");
      if (buf[1] == '\x44') {

        puts("null ptr deference");
        *(char *)(0) = 1;

      }

      break;
    case 0xff:
      if (buf[2] == '\xff') {

        if (buf[1] == '\x44') {

          puts("crash....");
          *(char *)(0xdeadbeef) = 1;

        }

      }

      break;
    default: puts("default action"); break;

  }

  return 1;

}

This could be build to libdemo.so.

Then we should load the library in template.cpp and find the target function address.

    void *handle = dlopen(lib_path, RTLD_LAZY);
	..........................................
	..........................................
	..........................................
    p_target_func = (target_func)dlsym(handle, "target_func");

then we read the data from file and call the function in fuzz_func

QBDI_NOINLINE int fuzz_func() {

  if (afl_setup()) { afl_forkserver(); }

  /* Read the input from file */
  unsigned long len = 0;
  char *        data = read_file(input_pathname, &len);

  /* Call the target function with the input data */
  p_target_func(data, len);
  return 1;

}

Just compile it

./build.sh x86_64

Then push the afl-fuzz, loader, libdemo.so, the libQBDI.so from the QBDI SDK and the libc++_shared.so from android-standalone-toolchain to android device

adb push afl-fuzz /data/local/tmp
adb push libdemo.so /data/local/tmp
adb push loader /data/local/tmp
adb push android-qbdi-sdk-x86_64/usr/local/lib/libQBDI.so /data/local/tmp
adb push ../../android-standalone-toolchain-x86_64/sysroot/usr/lib/x86_64-linux-android/libc++_shared.so
/data/local/tmp

In android adb shell, run the loader to test if it runs

cd /data/local/tmp
export LD_LIBRARY_PATH=/data/local/tmp
mkdir in
echo 0000 > in/1
./loader libdemo.so in/1
p_target_func:0x716d96a98600
	offset:0x600
	offset:0x580
buffer:0x716d96609050, size:0x5
	offset:0x628
	offset:0x646
	offset:0x64b
	offset:0x65c
	offset:0x6df
	offset:0x590
default action
	offset:0x6eb

Now run afl-fuzz to fuzz the demo library

./afl-fuzz -i in -o out -- ./loader /data/local/tmp/libdemo.so @@