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63 lines
2.0 KiB
63 lines
2.0 KiB
4 months ago
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# Fuzzer for libstagefright_amrnbdec decoder
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## Plugin Design Considerations
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The fuzzer plugin for AMR-NB is designed based on the understanding of the
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codec and tries to achieve the following:
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##### Maximize code coverage
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The configuration parameters are not hardcoded, but instead selected based on
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incoming data. This ensures more code paths are reached by the fuzzer.
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AMR-NB supports the following parameters:
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1. Stream format (parameter name: `input_format`)
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2. 3GPP frame type (parameter name: `frame_type`)
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| Parameter| Valid Values| Configured Value|
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|------------- |-------------| ----- |
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| `input_format` | 0. `MIME_IETF` 1. `IF2` | Bit 0 (LSB) of 1st byte of data. |
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| `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. |
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This also ensures that the plugin is always deterministic for any given input.
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##### Maximize utilization of input data
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The plugin feeds the entire input data to the codec using a loop.
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If the decode operation was successful, the input is advanced by the frame size
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which is based on `input_format` and `frame_type` selected.
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If the decode operation was un-successful, the input is still advanced by frame size so
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that the fuzzer can proceed to feed the next frame.
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This ensures that the plugin tolerates any kind of input (empty, huge,
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malformed, etc) and doesnt `exit()` on any input and thereby increasing the
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chance of identifying vulnerabilities.
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## Build
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This describes steps to build amrnb_dec_fuzzer binary.
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### Android
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#### Steps to build
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Build the fuzzer
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```
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$ mm -j$(nproc) amrnb_dec_fuzzer
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```
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#### Steps to run
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Create a directory CORPUS_DIR and copy some amrnb files to that folder
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Push this directory to device.
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To run on device
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```
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$ adb sync data
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$ adb shell /data/fuzz/arm64/amrnb_dec_fuzzer/amrnb_dec_fuzzer CORPUS_DIR
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```
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To run on host
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```
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$ $ANDROID_HOST_OUT/fuzz/x86_64/amrnb_dec_fuzzer/amrnb_dec_fuzzer CORPUS_DIR
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```
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## References:
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* http://llvm.org/docs/LibFuzzer.html
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* https://github.com/google/oss-fuzz
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