2.0 KiB
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