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# Fuzzer for libFraunhoferAAC decoder
## Plugin Design Considerations
The fuzzer plugin for aac decoder is designed based on the understanding of the
codec and tries to achieve the following:
##### Maximize code coverage
This fuzzer makes use of the following config parameters:
1. Transport type (parameter name: `TRANSPORT_TYPE`)
| Parameter| Valid Values| Configured Value|
|------------- |-------------| ----- |
| `TRANSPORT_TYPE` | 0.`TT_UNKNOWN ` 1.`TT_MP4_RAW ` 2.`TT_MP4_ADIF ` 3.`TT_MP4_ADTS ` 4.`TT_MP4_LATM_MCP1 ` 5.`TT_MP4_LATM_MCP0 ` 6.`TT_MP4_LOAS ` 7.`TT_DRM ` | `TT_MP4_ADIF ` |
Note: Value of `TRANSPORT_TYPE` could be set to any of these values.
It is set to `TT_MP4_ADIF` in the fuzzer plugin.
##### 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 an
offset calculated using valid bytes.
* If the decode operation was un-successful, the input is advanced by 1 byte
till it reaches a valid frame or 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 aac_dec_fuzzer binary.
## Android
### Steps to build
Build the fuzzer
```
$ mm -j$(nproc) aac_dec_fuzzer
```
### Steps to run
Create a directory CORPUS_DIR and copy some aac files to that folder.
Push this directory to device.
To run on device
```
$ adb sync data
$ adb shell /data/fuzz/arm64/aac_dec_fuzzer/aac_dec_fuzzer CORPUS_DIR
```
To run on host
```
$ $ANDROID_HOST_OUT/fuzz/x86_64/aac_dec_fuzzer/aac_dec_fuzzer CORPUS_DIR
```
## References:
* http://llvm.org/docs/LibFuzzer.html
* https://github.com/google/oss-fuzz
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