Test suite of Flatbuffers library has fuzzer section with tests are based on libFuzzer library.
LibFuzzer is in-process, coverage-guided, evolutionary fuzzing engine. LibFuzzer is linked with the library under test, and feeds fuzzed inputs to the library via a specific fuzzing entrypoint (aka “target function”); the fuzzer then tracks which areas of the code are reached, and generates mutations on the corpus of input data in order to maximize the code coverage. The code coverage information for libFuzzer is provided by LLVM’s SanitizerCoverage instrumentation.
For details about libFuzzer see: https://llvm.org/docs/LibFuzzer.html
To build and run these tests LLVM compiler (with clang frontend) and CMake should be installed before.
The fuzzer section include three tests:
verifier_fuzzerchecks stability of deserialization engine for
parser_fuzzerchecks stability of schema and json parser under various inputs;
scalar_parserfocused on validation of the parser while parse numeric scalars in schema and/or json files;
The grammar of the Flatbuffers library is based on printable-ASCII characters. By design, the Flatbuffers library should be independent of the global or thread locales used by an end-user application. Set environment variable
FLATBUFFERS_TEST_LOCALE to run a fuzzer with a specific C-locale:
>FLATBUFFERS_TEST_LOCALE="" ./scalar_parser >FLATBUFFERS_TEST_LOCALE="ru_RU.CP1251" ./parser_fuzzer
These are examples of running a fuzzer. Flags may vary and depend on a version of the libFuzzer library. For details, run a fuzzer with
./verifier_fuzzer -reduce_depth=1 -use_value_profile=1 -shrink=1 ../.corpus_verifier/
./parser_fuzzer -reduce_depth=1 -use_value_profile=1 -shrink=1 ../.corpus_parser/
./scalar_fuzzer -reduce_depth=1 -use_value_profile=1 -shrink=1 -max_len=3000 ../.corpus_parser/ ../.seed_parser/
-only_ascii=1 is useful for fast number-compatibility checking while run
./scalar_fuzzer -only_ascii=1 -reduce_depth=1 -use_value_profile=1 -shrink=1 -max_len=3000 -timeout=10 -rss_limit_mb=2048 -jobs=2 ../.corpus_parser/ ../.seed_parser/
Run with a specific C-locale:
FLATBUFFERS_TEST_LOCALE="ru_RU.CP1251" ./scalar_fuzzer -reduce_depth=1 -use_value_profile=1 -shrink=1 -max_len=3000 -timeout=10 -rss_limit_mb=2048 ../.corpus_parser/ ../.seed_parser/
The libFuzzer allow to filter (minimize) corpus with help of
-merge If set to 1, any corpus inputs from the 2nd, 3rd etc. corpus directories that trigger new code coverage will be merged into the first corpus directory. Defaults to 0. This flag can be used to minimize a corpus.
Merge several seeds to one (a new collected corpus to the seed collection, for example):
./scalar_fuzzer -merge=1 ../.seed_parser/ ../.corpus_parser/
scalar_fuzzerrun should be limited to 3000. Example: