Awesome

What is this?

bun is a tool for integrating fuzzer-based tests into a conventional CI pipeline. The popular afl-fuzz tool in particular is designed to use only one CPU core per invocation and keep records on persistent storage for later examination by an analyst; this particular workflow is ill-suited for cloud-based CI testing services, which do not persist storage for users and unceremoniously kill long-running processes. It also makes using available compute resources (two CPU cores even for free-tier Travis CI) challenging. bun attempts to solve these problems.

How does it work?

bun uses afl-gotcpu to detect the number of free CPU cores and then launches that number of afl-fuzz processes, configured in the correct manner to cooperate exploring the program's state space. bun monitors the progress of running afl-fuzz instances with afl-whatsup. afl-fuzz instances launched by bun run in a mode where they will stop when they find a crash or afl-fuzz determines that there is a low likelihood of finding one with additional work.

When crashes are detected on any afl-fuzz process, bun will stop the others and report the crash information. If no crashes are detected, bun will continue running until the last afl-fuzz gives up. (You may wish to limit the wall-clock time consumed with timeout when initially launching bun.)

How do I use the output?

When crashes are detected, bun will base64-encode them and output them on the console. You can then copy the text chunks and base64-decode them into reproduction cases to run locally.

How do I run it?

See bun --help for the most current information.

Here's an example of fuzzing one of Crowbar's packaged examples, calendar:

$ bun -i input/ -o output/ ./calendar
The last (or only) fuzzer (28129) has finished!
Crashes found! Take a look; copy/paste to save for reproduction:
echo UN5QAd5Q3t7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u | base64 -d > crash_0.$(date -u +%s)
$ echo UN5QAd5Q3t7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u7u | base64 -d > crash_0.$(date -u +%s)
$ ./calendar crash_0.1508880277 
calendar: ....
calendar: FAIL

When given the input:

    [1825-01-30 22:50:45; 1825-03-17 04:05:41]
    
the test failed:

    1825-03-20 04:05:41 != 1825-03-17 04:05:41
    
Fatal error: exception Crowbar.TestFailure

Building

The usual dune command should be sufficient:

dune build

For CI

For an example of using bun in a CI environment, see ocaml-test-stdlib, which uses bun to manage its Crowbar tests in Travis CI.