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default	Integrating a Python project	Setting up a new project	Getting started	3	/getting-started/new-project-guide/python-lang/

Integrating a Python project

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The process of integrating a project written in Python with OSS-Fuzz is very similar to the general [Setting up a new project]({{ site.baseurl }}/getting-started/new-project-guide/) process. The key specifics of integrating a Python project are outlined below.

Atheris

Python fuzzing in OSS-Fuzz depends on Atheris. Fuzzers will depend on the atheris package, and dependencies are pre-installed on the OSS-Fuzz base docker images.

Project files

Example project

We recommending viewing ujson as an example of a simple Python fuzzing project.

project.yaml

The language attribute must be specified.

language: python

The only supported fuzzing engine is libFuzzer (libfuzzer). The supported sanitizers are AddressSanitizer (address) and UndefinedBehaviorSanitizer (undefined). These must be explicitly specified.

fuzzing_engines:
  - libfuzzer
sanitizers:
  - address
  - undefined

Dockerfile

Because most dependencies are already pre-installed on the images, no significant changes are needed in the Dockerfile for Python fuzzing projects. You should simply clone the project, set a WORKDIR, and copy any necessary files, or install any project-specific dependencies here as you normally would.

build.sh

For Python projects, build.sh does need some more significant modifications over normal projects. The following is an annotated example build script, explaining why each step is necessary and when they can be omitted.

# Build and install project (using current CFLAGS, CXXFLAGS). This is required
# for projects with C extensions so that they're built with the proper flags.
pip3 install .

# Build fuzzers into $OUT. These could be detected in other ways.
for fuzzer in $(find $SRC -name '*_fuzzer.py'); do
  fuzzer_basename=$(basename -s .py $fuzzer)
  fuzzer_package=${fuzzer_basename}.pkg

  # To avoid issues with Python version conflicts, or changes in environment
  # over time on the OSS-Fuzz bots, we use pyinstaller to create a standalone
  # package. Though not necessarily required for reproducing issues, this is
  # required to keep fuzzers working properly in OSS-Fuzz.
  pyinstaller --distpath $OUT --onefile --name $fuzzer_package $fuzzer

  # Create execution wrapper. Atheris requires that certain libraries are
  # preloaded, so this is also done here to ensure compatibility and simplify
  # test case reproduction. Since this helper script is what OSS-Fuzz will
  # actually execute, it is also always required.
  # NOTE: If you are fuzzing python-only code and do not have native C/C++
  # extensions, then remove the LD_PRELOAD line below as preloading sanitizer
  # library is not required and can lead to unexpected startup crashes.
  echo "#!/bin/sh
# LLVMFuzzerTestOneInput for fuzzer detection.
LD_PRELOAD=\$(dirname "\$0")/sanitizer_with_fuzzer.so  \
ASAN_OPTIONS=\$ASAN_OPTIONS:symbolize=1:detect_leaks=0 \
\$(dirname "\$0")/$fuzzer_package \$@" > $OUT/$fuzzer_basename
  chmod u+x $OUT/$fuzzer_basename
done

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