History

Victor Zverovich 7f723fbcb8 Consistently namespace qualify size_t		2020-05-07 15:59:46 -07:00
..
.gitignore	add oss-fuzz support	2019-06-30 06:10:07 -07:00
build.sh	add oss-fuzz support	2019-06-30 06:10:07 -07:00
chrono_duration.cpp	Consistently namespace qualify size_t	2020-05-07 15:59:46 -07:00
CMakeLists.txt	Apply clang format and other minor formatting tweaks	2019-06-30 08:52:15 -07:00
fuzzer_common.h	Apply clang format and other minor formatting tweaks	2019-06-30 08:52:15 -07:00
main.cpp	Consistently namespace qualify size_t	2020-05-07 15:59:46 -07:00
named_arg.cpp	Consistently namespace qualify size_t	2020-05-07 15:59:46 -07:00
one_arg.cpp	Consistently namespace qualify size_t	2020-05-07 15:59:46 -07:00
README.md	Replace FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION with fmt-specific macro (#1650 )	2020-04-29 09:12:43 -07:00
sprintf.cpp	Consistently namespace qualify size_t	2020-05-07 15:59:46 -07:00
two_args.cpp	Consistently namespace qualify size_t	2020-05-07 15:59:46 -07:00

README.md

FMT Fuzzer

Fuzzing has revealed several bugs in fmt. It is a part of the continous fuzzing at oss-fuzz.

The source code is modified to make the fuzzing possible without locking up on resource exhaustion:

#ifdef FMT_FUZZ
if(spec.precision>100000) {
  throw std::runtime_error("fuzz mode - avoiding large precision");
}
#endif

This macro FMT_FUZZ is enabled on OSS-Fuzz builds and makes fuzzing practically possible. It is used in fmt code to prevent resource exhaustion in fuzzing mode.
The macro FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION is the defacto standard for making fuzzing practically possible to disable certain fuzzing-unfriendly features (for example, randomness), see the libFuzzer documentation.

Running the fuzzers locally

There is a helper script to build the fuzzers, which has only been tested on Debian and Ubuntu linux so far. There should be no problems fuzzing on Windows (using clang>=8) or on Mac, but the script will probably not work out of the box.

Something along

mkdir build
cd build
export CXX=clang++
export CXXFLAGS="-fsanitize=fuzzer-no-link -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION= -g"
cmake ..  -DFMT_SAFE_DURATION_CAST=On -DFMT_FUZZ=On -DFMT_FUZZ_LINKMAIN=Off -DFMT_FUZZ_LDFLAGS="-fsanitize=fuzzer"
cmake --build .

should work to build the fuzzers for all platforms which clang supports.

Execute a fuzzer with for instance

cd build
export UBSAN_OPTIONS=halt_on_error=1
mkdir out_chrono
bin/fuzzer_chrono_duration  out_chrono