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Fuzz-testing Bitcoin Core
A special test harness `test_bitcoin_fuzzy` is provided to provide an easy
entry point for fuzzers and the like. In this document we'll describe how to
use it with AFL.
Building AFL
It is recommended to always use the latest version of afl:
tar -zxvf afl-latest.tgz
cd afl-<version>
To build Bitcoin Core using AFL instrumentation (this assumes that the
`AFLPATH` was set as above):
./configure --disable-ccache --disable-shared --enable-tests CC=${AFLPATH}/afl-gcc CXX=${AFLPATH}/afl-g++
export AFL_HARDEN=1
cd src/
make test/test_bitcoin_fuzzy
We disable ccache because we don't want to pollute the ccache with instrumented
objects, and similarly don't want to use non-instrumented cached objects linked
Preparing fuzzing
AFL needs an input directory with examples, and an output directory where it
will place examples that it found. These can be anywhere in the file system,
we'll define environment variables to make it easy to reference them.
mkdir inputs
mkdir outputs
Example inputs are available from:
Extract these (or other starting inputs) into the `inputs` directory before starting fuzzing.
To start the actual fuzzing use:
$AFLPATH/afl-fuzz -i ${AFLIN} -o ${AFLOUT} -m52 -- test/test_bitcoin_fuzzy
You may have to change a few kernel parameters to test optimally - `afl-fuzz`
will print an error and suggestion if so.