Fuzzer for libstagefright_amrnbdec decoder

Plugin Design Considerations

The fuzzer plugin for AMR-NB 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.

AMR-NB supports the following parameters:

Stream format (parameter name: input_format)
3GPP frame type (parameter name: frame_type)

Parameter	Valid Values	Configured Value
`input_format`	0. `MIME_IETF` 1. `IF2`	Bit 0 (LSB) of 1st byte of data.
`frame_type`	0. `AMR_475` 1. `AMR_515` 2. `AMR_59` 3. `AMR_67` 4. `AMR_74` 5. `AMR_795` 6. `AMR_102` 7. `AMR_122`	Bits 3, 4 and 5 of 1st 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 entire input data to the codec using a loop. If the decode operation was successful, the input is advanced by the frame size which is based on input_format and frame_type selected. If the decode operation was un-successful, the input is still advanced by frame size 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.

Build

This describes steps to build amrnb_dec_fuzzer binary.

Android

Steps to build

Build the fuzzer

  $ mm -j$(nproc) amrnb_dec_fuzzer

Steps to run

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

To run on device

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

To run on host

  $ $ANDROID_HOST_OUT/fuzz/x86_64/amrnb_dec_fuzzer/amrnb_dec_fuzzer CORPUS_DIR