Add support for C extension fuzzing on macOS

[mschwager]

Hi all,

I recently added similar support in Ruzzy, so I thought it might be useful here too.

I also added a new target in example_fuzzers to test this functionality out and prove it's working as intended:

$ cd example_fuzzers/native_extension_example/
$ CC=/opt/homebrew/opt/llvm/bin/clang CXX=/opt/homebrew/opt/llvm/bin/clang++ CFLAGS="-fsanitize=address,fuzzer-no-link" CXXFLAGS="-fsanitize=address,fuzzer-no-link" python -m pip install --no-build-isolation --force-reinstall .

$ DYLD_INSERT_LIBRARIES="$(python -c 'import atheris; print(atheris.path())')/asan_with_fuzzer.dylib" python fuzzer.py
INFO: Using preloaded libfuzzer
INFO: Running with entropic power schedule (0xFF, 100).
INFO: Seed: 3715284803
INFO: Loaded 1 modules   (4811 inline 8-bit counters): 4811 [0x10badac78, 0x10badbf43), 
INFO: Loaded 1 PC tables (4811 PCs): 4811 [0x10badbf48,0x10baeebf8), 
INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes
INFO: A corpus is not provided, starting from an empty corpus
#2	INITED cov: 60 ft: 60 corp: 1/1b exec/s: 0 rss: 68Mb
#32	NEW    cov: 61 ft: 61 corp: 2/5b lim: 4 exec/s: 0 rss: 68Mb L: 4/4 MS: 5 CrossOver-ShuffleBytes-InsertByte-InsertByte-InsertByte-
#1119	NEW    cov: 62 ft: 62 corp: 3/9b lim: 14 exec/s: 0 rss: 68Mb L: 4/4 MS: 2 ShuffleBytes-ChangeByte-
#382945	NEW    cov: 63 ft: 63 corp: 4/13b lim: 3810 exec/s: 0 rss: 96Mb L: 4/4 MS: 1 ChangeByte-
#388938	NEW    cov: 64 ft: 64 corp: 5/17b lim: 3865 exec/s: 0 rss: 96Mb L: 4/4 MS: 3 ShuffleBytes-CopyPart-CrossOver-
=================================================================
==3513==ERROR: AddressSanitizer: heap-use-after-free on address 0x60c000264d00 at pc 0x00010ba78dac bp 0x00016bdb8130 sp 0x00016bdb8128
READ of size 1 at 0x60c000264d00 thread T0
...

[mschwager]

Switching to the stdlib's venv library avoids this third-party dependency.

[mschwager]

Use venv here.

[mschwager]

Hey @TheShiftedBit 👋, I see development of Atheris has slowed a bit. Is this project still open to outside PRs?

[TheShiftedBit]

Atheris already has C extension fuzzing support. I'm not sure I understand - what was the issue you were experiencing?

[mschwager]

Atheris already has C extension fuzzing support. I'm not sure I understand - what was the issue you were experiencing?

As far as I can tell, C extension fuzzing is only supported on Linux:

(However, this option is not yet supported on Mac).

So this PR adds support for C extension fuzzing on macOS.