Fuzzer for libstagefright_m4vh263dec decoder

Plugin Design Considerations

The fuzzer plugin for MPEG4/H263 is designed based on the understanding of the codec and tries to achieve the following:

Maximize code coverage

Dict files (dictionary files) are created for MPEG4 and H263 to ensure that the required start bytes are present in every input file that goes to the fuzzer. This ensures that decoder does not reject any input file in the first check

Maximize utilization of input data

The plugin feeds the entire input data to the codec using a loop.

If the decode operation was successful, the input is advanced by the number of bytes consumed in the decode call.
If the decode operation was un-successful, the input is advanced by 1 byte so that the fuzzer can proceed to feed the next frame.

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.

Other considerations

Two fuzzer binaries - mpeg4_dec_fuzzer and h263_dec_fuzzer are generated based on the presence of a flag - ‘MPEG4’
The number of decode calls are kept to a maximum of 100 so that the fuzzer does not timeout.

Build

This describes steps to build mpeg4_dec_fuzzer and h263_dec_fuzzer binary.

Android

Steps to build

Build the fuzzer

  $ mm -j$(nproc) mpeg4_dec_fuzzer
  $ mm -j$(nproc) h263_dec_fuzzer

Steps to run

Create a directory CORPUS_DIR and copy some MPEG4 or H263 files to that folder Push this directory to device.

To run on device

  $ adb sync data
  $ adb shell /data/fuzz/arm64/mpeg4_dec_fuzzer/mpeg4_dec_fuzzer CORPUS_DIR
  $ adb shell /data/fuzz/arm64/h263_dec_fuzzer/h263_dec_fuzzer CORPUS_DIR

To run on host

  $ $ANDROID_HOST_OUT/fuzz/x86_64/mpeg4_dec_fuzzer/mpeg4_dec_fuzzer CORPUS_DIR
  $ $ANDROID_HOST_OUT/fuzz/x86_64/h263_dec_fuzzer/h263_dec_fuzzer CORPUS_DIR