commit	ba7c2ab5f41599e006eb438849c2518cd1a4ceb2	[log] [tgz]
author	Vitaly Buka <vitalybuka@google.com>	Tue Jan 07 13:38:29 2020 -0800
committer	Vitaly Buka <vitalybuka@gmail.com>	Wed Jan 08 14:30:55 2020 -0800
tree	225a31e49d9232739df7a6ee4c8f29d840700428
parent	eb892f915384f67cd13812b2465f5969546a5fe9 [diff]

tree: 225a31e49d9232739df7a6ee4c8f29d840700428

README.md

libprotobuf-mutator

Overview

libprotobuf-mutator is a library to randomly mutate protobuffers.
It could be used together with guided fuzzing engines, such as libFuzzer.

Quick start on Debian/Ubuntu

Install prerequisites:

sudo apt-get update
sudo apt-get install protobuf-compiler libprotobuf-dev binutils cmake \
  ninja-build liblzma-dev libz-dev pkg-config autoconf libtool

Compile and test everything:

mkdir build
cd build
cmake .. -GNinja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_BUILD_TYPE=Debug
ninja check

Clang is only needed for libFuzzer integration.
By default, the system-installed version of protobuf is used. However, on some systems, the system version is too old. You can pass LIB_PROTO_MUTATOR_DOWNLOAD_PROTOBUF=ON to cmake to automatically download and build a working version of protobuf.

Installation:

ninja
sudo ninja install

This installs the headers, pkg-config, and static library. By default the headers are put in /usr/local/include/libprotobuf-mutator.

Usage

To use libprotobuf-mutator simply include mutator.h and mutator.cc into your build files.

The ProtobufMutator class implements mutations of the protobuf tree structure and mutations of individual fields. The field mutation logic is very basic -- for better results you should override the ProtobufMutator::Mutate* methods with more sophisticated logic, e.g. using libFuzzer's mutators.

To apply one mutation to a protobuf object do the following:

class MyProtobufMutator : public protobuf_mutator::Mutator {
 public:
  MyProtobufMutator(uint32_t seed) : protobuf_mutator::Mutator(seed) {}
  // Optionally redefine the Mutate* methods to perform more sophisticated mutations.
}
void Mutate(MyMessage* message) {
  MyProtobufMutator mutator(my_random_seed);
  mutator.Mutate(message, 200);
}

See also the ProtobufMutatorMessagesTest.UsageExample test from mutator_test.cc.

Integrating with libFuzzer

LibFuzzerProtobufMutator can help to integrate with libFuzzer. For example

#include "src/libfuzzer/libfuzzer_macro.h"

DEFINE_PROTO_FUZZER(const MyMessageType& input) {
  // Code which needs to be fuzzed.
  ConsumeMyMessageType(input);
}

Please see libfuzzer_example.cc as an example.

Mutation post-processing (experimental)

Sometimes it's necessary to keep particular values in some fields without which the proto is going to be rejected by fuzzed code. E.g. code may expect consistency between some fields or it may use some fields as checksums. Such constraints are going to be significant bottleneck for fuzzer even if it's capabale to get acceptable values with time.

PostProcessorRegistration can be used to avoid such issue and guide your fuzzer towards interesing code. It registers callback which will be called for each message of particular type after each mutation.

DEFINE_PROTO_FUZZER(const MyMessageType& input) {
  static PostProcessorRegistration reg = {
      [](MyMessageType* message, unsigned int seed) {
        TweakMyMessageType(message, seed);
      }};

  // Code which needs to be fuzzed.
  ConsumeMyMessageType(input);
}

Optional: Use seed if callback uses random numbers. It may help later with debuggin.

UTF-8 strings

"proto2" and "proto3" handle invalid UTF-8 strings differently. In both cases string should be UTF-8, however only "proto3" enforces that. So if fuzzer is applied to "proto2" type libprotobuf-mutator will generate any strings including invalid UTF-8. If it's a "proto3" message type, only valid UTF-8 will be used.

libprotobuf-mutator

Overview

Quick start on Debian/Ubuntu

Usage

Integrating with libFuzzer

Mutation post-processing (experimental)

UTF-8 strings

Users of the library

Bugs found with help of the library

Chromium

Envoy

Related materials