3 Each fuzzing target can be built with multiple engines.
4 Zstd provides a fuzz corpus for each target that can be downloaded with
11 It will download each corpus into `./corpora/TARGET`.
15 `fuzz.py` is a helper script for building and running fuzzers.
16 Run `./fuzz.py -h` for the commands and run `./fuzz.py COMMAND -h` for
17 command specific help.
21 `fuzz.py` provides a utility to generate seed data for each fuzzer.
24 make -C ../tests decodecorpus
28 By default it outputs 100 samples, each at most 8KB into `corpora/TARGET-seed`,
29 but that can be configured with the `--number`, `--max-size-log` and `--seed`
33 It respects the usual build environment variables `CC`, `CFLAGS`, etc.
34 The environment variables can be overridden with the corresponding flags
35 `--cc`, `--cflags`, etc.
36 The specific fuzzing engine is selected with `LIB_FUZZING_ENGINE` or
37 `--lib-fuzzing-engine`, the default is `libregression.a`.
38 Alternatively, you can use Clang's built in fuzzing engine with
40 It has flags that can easily set up sanitizers `--enable-{a,ub,m}san`, and
41 coverage instrumentation `--enable-coverage`.
42 It sets sane defaults which can be overridden with flags `--debug`,
43 `--enable-ubsan-pointer-overflow`, etc.
44 Run `./fuzz.py build -h` for help.
48 `./fuzz.py` can run `libfuzzer`, `afl`, and `regression` tests.
49 See the help of the relevant command for options.
50 Flags not parsed by `fuzz.py` are passed to the fuzzing engine.
51 The command used to run the fuzzer is printed for debugging.
53 Here's a helpful command to fuzz each target across all cores,
54 stopping only if a bug is found:
56 for target in $(./fuzz.py list); do
57 ./fuzz.py libfuzzer $target -jobs=10 -workers=10 -max_total_time=1000 || break;
60 Alternatively, you can fuzz all targets in parallel, using one core per target:
62 python3 ./fuzz.py list | xargs -P$(python3 ./fuzz.py list | wc -l) -I__ sh -c "python3 ./fuzz.py libfuzzer __ 2>&1 | tee __.log"
64 Either way, to double-check that no crashes were found, run `ls corpora/*crash`.
65 If any crashes were found, you can use the hashes to reproduce them.
70 # Build the fuzz targets
71 ./fuzz.py build all --enable-fuzzer --enable-asan --enable-ubsan --cc clang --cxx clang++
73 CC=clang CXX=clang++ ./fuzz.py build all --enable-fuzzer --enable-asan --enable-ubsan
75 ./fuzz.py libfuzzer TARGET <libfuzzer args like -jobs=4>
78 where `TARGET` could be `simple_decompress`, `stream_round_trip`, etc.
82 Fuzzing with `libFuzzer` and `MSAN` is as easy as:
85 CC=clang CXX=clang++ ./fuzz.py build all --enable-fuzzer --enable-msan
86 ./fuzz.py libfuzzer TARGET <libfuzzer args>
89 `fuzz.py` respects the environment variables / flags `MSAN_EXTRA_CPPFLAGS`,
90 `MSAN_EXTRA_CFLAGS`, `MSAN_EXTRA_CXXFLAGS`, `MSAN_EXTRA_LDFLAGS` to easily pass
91 the extra parameters only for MSAN.
95 The default `LIB_FUZZING_ENGINE` is `libregression.a`, which produces a binary
99 # Build the fuzz targets
100 CC=afl-clang CXX=afl-clang++ ./fuzz.py build all --enable-asan --enable-ubsan
101 # Run the fuzzer without a memory limit because of ASAN
102 ./fuzz.py afl TARGET -m none
105 ## Regression Testing
107 The regression test supports the `all` target to run all the fuzzers in one
111 CC=clang CXX=clang++ ./fuzz.py build all --enable-asan --enable-ubsan
112 ./fuzz.py regression all
113 CC=clang CXX=clang++ ./fuzz.py build all --enable-msan
114 ./fuzz.py regression all
117 ## Fuzzing a custom sequence producer plugin
118 Sequence producer plugin authors can use the zstd fuzzers to stress-test their code.
119 See the documentation in `fuzz_third_party_seq_prod.h` for details.
121 ## Adding a new fuzzer
122 There are several steps involved in adding a new fuzzer harness.
124 ### Build your harness
125 1. Create a new your fuzzer harness `tests/fuzz/your_harness.c`.
127 2. Add your harness to the Makefile
129 2.1 Follow [this example](https://github.com/facebook/zstd/blob/e124e39301381de8f323436a3e4c46539747ba24/tests/fuzz/Makefile#L216) if your fuzzer requires both compression and decompression symbols (prefix `rt_`). If your fuzzer only requires decompression symbols, follow [this example](https://github.com/facebook/zstd/blob/6a0052a409e2604bd40354b76b86272b712edd7d/tests/fuzz/Makefile#L194) (prefix `d_`).
131 2.2 Add your target to [`FUZZ_TARGETS`](https://github.com/facebook/zstd/blob/6a0052a409e2604bd40354b76b86272b712edd7d/tests/fuzz/Makefile#L108).
133 3. Add your harness to [`fuzz.py`](https://github.com/facebook/zstd/blob/6a0052a409e2604bd40354b76b86272b712edd7d/tests/fuzz/fuzz.py#L48).
135 ### Generate seed data
136 Follow the instructions above to generate seed data:
138 make -C ../tests decodecorpus
139 ./fuzz.py gen your_harness
143 Follow the instructions above to run your harness and fix any crashes:
145 ./fuzz.py build your_harness --enable-fuzzer --enable-asan --enable-ubsan --cc clang --cxx clang++
146 ./fuzz.py libfuzzer your_harness
149 ### Minimize and zip the corpus
150 After running the fuzzer for a while, you will have a large corpus at `tests/fuzz/corpora/your_harness*`.
151 This corpus must be minimized and zipped before uploading to GitHub for regression testing:
153 ./fuzz.py minimize your_harness
154 ./fuzz.py zip your_harness
157 ### Upload the zip file to GitHub
158 The previous step should produce a `.zip` file containing the corpus for your new harness.
159 This corpus must be uploaded to GitHub here: https://github.com/facebook/zstd/releases/tag/fuzz-corpora