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Fuzzing The Library
============================
Botan comes with a set of fuzzing endpoints which can be used to test
the library.
.. highlight:: shell
Fuzzing with libFuzzer
------------------------
To fuzz with libFuzzer (https://llvm.org/docs/LibFuzzer.html), you'll first
need to compile libFuzzer::
$ svn co https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/fuzzer libFuzzer
$ cd libFuzzer && clang -c -g -O2 -std=c++11 *.cpp
$ ar cr libFuzzer.a libFuzzer/*.o
Then build the fuzzers::
$ ./configure.py --cc=clang --build-fuzzer=libfuzzer --unsafe-fuzzer-mode \
--enable-sanitizers=coverage,address,undefined
$ make fuzzers
Enabling 'coverage' sanitizer flags is required for libFuzzer to work.
Address sanitizer and undefined sanitizer are optional.
The fuzzer binaries will be in `build/fuzzer`. Simply pick one and run it, optionally
also passing a directory containing corpus inputs.
Using `libfuzzer` build mode implicitly assumes the fuzzers need to
link with `libFuzzer`; if another library is needed (for example in
OSS-Fuzz, which uses `libFuzzingEngine`), use the flag
`--with-fuzzer-lib` to specify the desired name.
Fuzzing with AFL
--------------------
To fuzz with AFL (http://lcamtuf.coredump.cx/afl/)::
$ ./configure.py --with-sanitizers --build-fuzzer=afl --unsafe-fuzzer-mode --cc-bin=afl-g++
$ make fuzzers
For AFL sanitizers are optional. You can also use `afl-clang-fast++`
or `afl-clang++`, be sure to set `--cc=clang` also.
The fuzzer binaries will be in `build/fuzzer`. To run them you need to
run under `afl-fuzz`::
$ afl-fuzz -i corpus_path -o output_path ./build/fuzzer/binary
Fuzzing with TLS-Attacker
--------------------------
TLS-Attacker (https://github.com/RUB-NDS/TLS-Attacker) includes a mode for fuzzing
TLS servers. A prebuilt copy of TLS-Attacker is available in a git repository::
$ git clone --depth 1 https://github.com/randombit/botan-ci-tools.git
To run it against Botan's server::
$ ./configure.py --with-sanitizers
$ make botan
$ ./src/scripts/run_tls_attacker.py ./botan ./botan-ci-tools
Output and logs from the fuzzer are placed into `/tmp`. See the
TLS-Attacker documentation for more information about how to use this
tool.
Input Corpus
-----------------------
AFL requires an input corpus, and libFuzzer can certainly make good
use of it.
Some crypto corpus repositories include
* https://github.com/randombit/crypto-corpus
* https://github.com/mozilla/nss-fuzzing-corpus
* https://github.com/google/boringssl/tree/master/fuzz
* https://github.com/openssl/openssl/tree/master/fuzz/corpora
Adding new fuzzers
---------------------
New fuzzers are created by adding a source file to `src/fuzzers` which
have the signature:
``void fuzz(const uint8_t in[], size_t len)``
After adding your fuzzer, rerun `./configure.py` and build.
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