Or, how to fuzz OpenSSL with libfuzzer.
Starting from a vanilla+OpenSSH server Ubuntu install.
Use Chrome's handy recent build of clang. Older versions may also work.
$ sudo apt-get install git $ mkdir git-work $ git clone https://chromium.googlesource.com/chromium/src/tools/clang $ clang/scripts/update.py
You may want to git pull and re-run the update from time to time.
Update your path:
$ PATH=~/third_party/llvm-build/Release+Asserts/bin/:$PATH
Get and build libFuzzer (there is a git mirror at https://github.com/llvm-mirror/llvm/tree/master/lib/Fuzzer if you prefer):
$ cd $ sudo apt-get install subversion $ mkdir svn-work $ cd svn-work $ svn co http://llvm.org/svn/llvm-project/llvm/trunk/lib/Fuzzer $ cd Fuzzer $ clang++ -c -g -O2 -std=c++11 *.cpp $ ar r libFuzzer.a *.o $ ranlib libFuzzer.a
Configure for fuzzing:
$ CC=clang ./config enable-fuzz-libfuzzer \
--with-fuzzer-include=../../svn-work/Fuzzer \
--with-fuzzer-lib=../../svn-work/Fuzzer/libFuzzer \
-DPEDANTIC enable-asan enable-ubsan no-shared \
-DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION \
-fsanitize-coverage=edge,indirect-calls,8bit-counters \
enable-ec_nistp_64_gcc_128 -fno-sanitize=alignment enable-tls1_3 \
enable-weak-ssl-ciphers enable-rc5 enable-md2 \
enable-ssl3 enable-ssl3-method enable-nextprotoneg
$ sudo apt-get install make
$ LDCMD=clang++ make -j
$ fuzz/helper.py $FUZZER
Where $FUZZER is one of the executables in fuzz/.
If you get a crash, you should find a corresponding input file in fuzz/corpora/$FUZZER-crash/. You can reproduce the crash with
$ fuzz/$FUZZER <crashfile>
Configure for fuzzing:
$ sudo apt-get install afl-clang
$ CC=afl-clang-fast ./config enable-fuzz-afl no-shared -DPEDANTIC \
enable-tls1_3 enable-weak-ssl-ciphers enable-rc5 enable-md2 \
enable-ssl3 enable-ssl3-method enable-nextprotoneg \
enable-ec_nistp_64_gcc_128
$ make
The following options can also be enabled: enable-asan, enable-ubsan, enable-msan
Run one of the fuzzers:
$ afl-fuzz -i fuzz/corpora/$FUZZER -o fuzz/corpora/$FUZZER/out fuzz/$FUZZER
Where $FUZZER is one of the executables in fuzz/.