Fuzzer for libcmd_fuzzer

Plugin Design Considerations

The fuzzer plugin for libcmd is designed based on the understanding of the library 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.

libcmd supports the following parameters:

1. In (parameter name: in)
2. Out (parameter name: out)
3. Err (parameter name: err)
4. Run Mode (parameter name: runMode)

Parameter	Valid Values	Configured Value
in	INT32_MIN to INT32_MAX	Value obtained from FuzzedDataProvider
out	INT32_MIN to INT32_MAX	Value obtained from FuzzedDataProvider
err	INT32_MIN to INT32_MAX	Value obtained from FuzzedDataProvider
runMode	1.RunMode::kStandalone 2. RunMode::kLibrary	Value chosen from valid values using FuzzedDataProvider

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 cmd module. 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 cmd_fuzzer binary.

Android

Steps to build

Build the fuzzer

  $ mm -j$(nproc) cmd_fuzzer

Steps to run

To run on device

  $ adb sync data
  $ adb shell /data/fuzz/${TARGET_ARCH}/cmd_fuzzer/cmd_fuzzer

References:

• http://llvm.org/docs/LibFuzzer.html
• https://github.com/google/oss-fuzz