avbroot/fuzz

Fuzzing

While avbroot's parsers are all memory-safe, it is still possible for panics or crashes to occur, for example due to excessive memory allocation, integer overflow, or division by zero. Fuzzing helps to identify these issues by randomizing inputs in a way that tries to increase code coverage.

Running the fuzzers

1. Install the cargo honggfuzz commands.

   cargo install honggfuzz
   

2. [Optional] Generate sample files to use as the initial fuzzing corpus.

   cargo xtask fuzz-corpus
   

3. Pick a fuzz target to run. A fuzz target is the name of the source file in src/bin/ without the .rs extension.

   The list of targets can be queried programmatically with:

   cargo read-manifest | jq -r '.targets[].name'
   

4. Run the fuzzer.

   cargo hfuzz run <fuzz target>
   

   This will run forever until it is manually killed. At the top of the screen, a summary section like the following is shown:

     Iterations : 31,243 [31.24k]
     Mode [1/3] : Feedback Driven Dry Run [2486/4085]
         Target : hfuzz_target/x86_64-unknown-linux-gnu/release/bootimage
        Threads : 8, CPUs: 16, CPU%: 800% [50%/CPU]
          Speed : 36,126/sec [avg: 31,243]
        Crashes : 53 [unique: 1, blocklist: 0, verified: 0]
       Timeouts : 0 [1 sec]
    Corpus Size : 1,424, max: 24,576 bytes, init: 4,085 files
     Cov Update : 0 days 00 hrs 00 mins 00 secs ago
       Coverage : edge: 897/224,621 [0%] pc: 2 cmp: 34,736
   

   When a crash occurs, the Crashes counter will increment and the input data that triggered the crash will be written to hfuzz_workspace/<fuzz target>/*.fuzz. New files are only written for unique crashes.

5. If a crash occurs, run the following command to trigger the crash in a debugger.

   cargo hfuzz run-debug <fuzz target> \
       hfuzz_workspace/<fuzz_target>/<input file>.fuzz
   

   This defaults to using rust-lldb. To use rust-gdb instead, set the HFUZZ_DEBUGGER environment variable to rust-gdb.

   Alternatively, just feed the input file to the appropriate avbroot command directly (eg. avbroot boot info -i hfuzz_workspace/<fuzz_target>/<input file>.fuzz for boot images).