v811_spc009/external/flac/fuzzer

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:

1. FLAC__stream_decoder_process_single (frame by frame decoding)
2. 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

Fuzzer for libFLAC encoder

Plugin Design Considerations

The fuzzer plugin for flac encoder 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.

Follwing functions were called in initEncoder to configure the encoder:

Function name	Parameter	Valid Values	Configured Value
FLAC__stream_encoder_set_sample_rate	sampleRate	1 to 655350	All the bits of 1st, 2nd and 3rd byte of data
FLAC__stream_encoder_set_channels	mChannels	1 2	bit 0 of 4th byte of data
FLAC__stream_encoder_set_compression_level	compression	1 2	bit 0 of 5th byte of data
FLAC__stream_encoder_set_bits_per_sample	bitsPerSample	16 24	bit 0 of 6th byte of data
FLAC__stream_encoder_set_verify	-	false true	bit 0 of 7th byte of data
FLAC__stream_encoder_set_streamable_subset	-	false true	bit 0 of 8th byte of data
FLAC__stream_encoder_set_do_mid_side_stereo	-	false true	bit 0 of 9th byte of data
FLAC__stream_encoder_set_loose_mid_side_stereo	-	false true	bit 0 of 10th byte of data
FLAC__stream_encoder_set_max_lpc_order	-	false true	bit 0 of 11th byte of data
FLAC__stream_encoder_set_qlp_coeff_precision	-	0 1	bit 0 of 12th byte of data
FLAC__stream_encoder_set_do_qlp_coeff_prec_search	-	false true	bit 0 of 13th byte of data
FLAC__stream_encoder_set_do_escape_coding	-	false true	bit 0 of 14th byte of data
FLAC__stream_encoder_set_do_exhaustive_model_search	-	false true	bit 0 of 15th byte of data
FLAC__stream_encoder_set_min_residual_partition_order	-	0 1	bit 0 of 16th byte of data
FLAC__stream_encoder_set_max_residual_partition_order	-	0 1	bit 0 of 17th byte of data
FLAC__stream_encoder_set_rice_parameter_search_dist	-	0 1	bit 0 of 18th byte of data
FLAC__stream_encoder_set_total_samples_estimate	-	0 1	bit 0 of 19th byte of data

Maximize utilization of input data

The plugin feeds the entire input data to the codec and continues with the encoding even on a failure. This ensures that the plugin tolerates any kind of input (empty, huge, malformed, etc) and doesn't exit() on any input and thereby increasing the chance of identifying vulnerabilities.

Build

This describes steps to build flac_enc_fuzzer binary.

Android

Steps to build

Build the fuzzer

  $ mm -j$(nproc) flac_enc_fuzzer

Steps to run

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

To run on device

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

To run on host

  $ $ANDROID_HOST_OUT/fuzz/x86_64/flac_enc_fuzzer/flac_enc_fuzzer CORPUS_DIR

References:

• http://llvm.org/docs/LibFuzzer.html
• https://github.com/google/oss-fuzz