1# Fuzzer for libstagefright_amrnbenc encoder
2
3## Plugin Design Considerations
4The fuzzer plugin for AMR-NB is designed based on the understanding of the
5codec and tries to achieve the following:
6
7##### Maximize code coverage
8The configuration parameters are not hardcoded, but instead selected based on
9incoming data. This ensures more code paths are reached by the fuzzer.
10
11AMR-WB supports the following parameters:
121. Output Format (parameter name: `outputFormat`)
132. Mode (parameter name: `mode`)
14
15| Parameter| Valid Values| Configured Value|
16|------------- |-------------| ----- |
17| `outputFormat` | 0. `AMR_TX_WMF` 1. `AMR_TX_IF2` 2. `AMR_TX_ETS` | Bits 0, 1 and 2 of 1st byte of data. |
18| `mode`   | 0. `MR475` 1. `MR515` 2. `MR59` 3. `MR67`  4. `MR74 ` 5. `MR795` 6. `MR102` 7. `MR122` 8. `MRDTX` | Bits 3, 4, 5 and 6 of 1st byte of data. |
19
20This also ensures that the plugin is always deterministic for any given input.
21
22##### Maximize utilization of input data
23The plugin feeds the entire input data to the codec using a loop.
24If the encode operation was successful, the input is advanced by the frame size.
25If the encode operation was un-successful, the input is still advanced by frame size so
26that the fuzzer can proceed to feed the next frame.
27
28This ensures that the plugin tolerates any kind of input (empty, huge,
29malformed, etc) and doesnt `exit()` on any input and thereby increasing the
30chance of identifying vulnerabilities.
31
32## Build
33
34This describes steps to build amrnb_enc_fuzzer binary.
35
36### Android
37
38#### Steps to build
39Build the fuzzer
40```
41  $ mm -j$(nproc) amrnb_enc_fuzzer
42```
43
44#### Steps to run
45Create a directory CORPUS_DIR and copy some pcm files to that folder
46Push this directory to device.
47
48To run on device
49```
50  $ adb sync data
51  $ adb shell /data/fuzz/arm64/amrnb_enc_fuzzer/amrnb_enc_fuzzer CORPUS_DIR
52```
53To run on host
54```
55  $ $ANDROID_HOST_OUT/fuzz/x86_64/amrnb_enc_fuzzer/amrnb_enc_fuzzer CORPUS_DIR
56```
57
58## References:
59 * http://llvm.org/docs/LibFuzzer.html
60 * https://github.com/google/oss-fuzz
61