Fuzzer for libFLAC decoder

Plugin Design Considerations

The fuzzer plugin for FLAC decoder is designed based on the understanding of the codec and tries to achieve the following:

Maximize code coverage

The configuration parameters are not hardcoded, but instead selected based on incoming data. This ensures more code paths are reached by the fuzzer.

FLAC supports the following two decoder API's for native mode:

FLAC__stream_decoder_process_single (frame by frame decoding)
FLAC__stream_decoder_process_until_end_of_stream (decoding entire stream)

One of these two decoder API's will be called based on LSB of 5th byte of data.

This also ensures that the plugin is always deterministic for any given input.

Maximize utilization of input data

The plugin feeds the input data to the codec using a read_callback as and when requested by the decoder. The read_callback feeds the input data to the decoder until the end of stream.

This ensures that the plugin tolerates any kind of input (empty, huge, malformed, etc) and doesnt exit() on any input and thereby increasing the chance of identifying vulnerabilities.

Build

This describes steps to build flac_dec_fuzzer binary.

Android

Steps to build

Build the fuzzer

  $ mm -j$(nproc) flac_dec_fuzzer

Steps to run

Create a directory CORPUS_DIR and copy some flac files to that folder Push this directory to device.

To run on device

  $ adb sync data
  $ adb shell /data/fuzz/arm64/flac_dec_fuzzer/flac_dec_fuzzer CORPUS_DIR

To run on host

  $ $ANDROID_HOST_OUT/fuzz/x86_64/flac_dec_fuzzer/flac_dec_fuzzer CORPUS_DIR