diff options
Diffstat (limited to 'json4cpp/tests/fuzzing.md')
| -rw-r--r-- | json4cpp/tests/fuzzing.md | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/json4cpp/tests/fuzzing.md b/json4cpp/tests/fuzzing.md new file mode 100644 index 0000000000..cfbf4f2499 --- /dev/null +++ b/json4cpp/tests/fuzzing.md @@ -0,0 +1,81 @@ +# Fuzz testing + +Each parser of the library (JSON, BJData, BSON, CBOR, MessagePack, and UBJSON) can be fuzz tested. Currently, +[libFuzzer](https://llvm.org/docs/LibFuzzer.html) and [afl++](https://github.com/AFLplusplus/AFLplusplus) are supported. + +## Corpus creation + +For most effective fuzzing, a [corpus](https://llvm.org/docs/LibFuzzer.html#corpus) should be provided. A corpus is a +directory with some simple input files that cover several features of the parser and is hence a good starting point +for mutations. + +```shell +TEST_DATA_VERSION=3.1.0 +wget https://github.com/nlohmann/json_test_data/archive/refs/tags/v$TEST_DATA_VERSION.zip +unzip v$TEST_DATA_VERSION.zip +rm v$TEST_DATA_VERSION.zip +for FORMAT in json bjdata bson cbor msgpack ubjson +do + rm -fr corpus_$FORMAT + mkdir corpus_$FORMAT + find json_test_data-$TEST_DATA_VERSION -size -5k -name "*.$FORMAT" -exec cp "{}" "corpus_$FORMAT" \; +done +rm -fr json_test_data-$TEST_DATA_VERSION +``` + +The generated corpus can be used with both libFuzzer and afl++. The remainder of this documentation assumes the corpus +directories have been created in the `tests` directory. + +## libFuzzer + +To use libFuzzer, you need to pass `-fsanitize=fuzzer` as `FUZZER_ENGINE`. In the `tests` directory, call + +```shell +make fuzzers FUZZER_ENGINE="-fsanitize=fuzzer" +``` + +This creates a fuzz tester binary for each parser that supports these +[command line options](https://llvm.org/docs/LibFuzzer.html#options). + +In case your default compiler is not a Clang compiler that includes libFuzzer (Clang 6.0 or later), you need to set the +`CXX` variable accordingly. Note the compiler provided by Xcode (AppleClang) does not contain libFuzzer. Please install +Clang via Homebrew calling `brew install llvm` and add `CXX=$(brew --prefix llvm)/bin/clang` to the `make` call: + +```shell +make fuzzers FUZZER_ENGINE="-fsanitize=fuzzer" CXX=$(brew --prefix llvm)/bin/clang +``` + +Then pass the corpus directory as command-line argument (assuming it is located in `tests`): + +```shell +./parse_cbor_fuzzer corpus_cbor +``` + +The fuzzer should be able to run indefinitely without crashing. In case of a crash, the tested input is dumped into +a file starting with `crash-`. + +## afl++ + +To use afl++, you need to pass `-fsanitize=fuzzer` as `FUZZER_ENGINE`. It will be replaced by a `libAFLDriver.a` to +re-use the same code written for libFuzzer with afl++. Furthermore, set `afl-clang-fast++` as compiler. + +```shell +CXX=afl-clang-fast++ make fuzzers FUZZER_ENGINE="-fsanitize=fuzzer" +``` + +Then the fuzzer is called like this in the `tests` directory: + +```shell +afl-fuzz -i corpus_cbor -o out -- ./parse_cbor_fuzzer +``` + +The fuzzer should be able to run indefinitely without crashing. In case of a crash, the tested input is written to the +directory `out`. + +## OSS-Fuzz + +The library is further fuzz-tested 24/7 by Google's [OSS-Fuzz project](https://github.com/google/oss-fuzz). It uses +the same `fuzzers` target as above and also relies on the `FUZZER_ENGINE` variable. See the used +[build script](https://github.com/google/oss-fuzz/blob/master/projects/json/build.sh) for more information. + +In case the build at OSS-Fuzz fails, an issue will be created automatically. |