Add Atheris fuzzers

.clusterfuzzlite/Dockerfile

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+FROM gcr.io/oss-fuzz-base/base-builder-python
+COPY . $SRC/jupytext
+WORKDIR jupytext
+COPY .clusterfuzzlite/build.sh $SRC/

.clusterfuzzlite/build.sh

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+#!/bin/bash -eu
+pip3 install --upgrade pip
+pip3 install .
+
+for fuzzer in $(find $SRC -name 'fuzz_*.py'); do
+  fuzzer_basename=$(basename -s .py $fuzzer)
+  fuzzer_package=${fuzzer_basename}.pkg
+  pyinstaller --distpath $OUT --onefile --name $fuzzer_package $fuzzer
+
+  # Create execution wrapper.
+  echo "#!/bin/sh
+# LLVMFuzzerTestOneInput for fuzzer detection.
+this_dir=\$(dirname \"\$0\")
+LD_PRELOAD=\$this_dir/sanitizer_with_fuzzer.so \
+ASAN_OPTIONS=\$ASAN_OPTIONS:symbolize=1:external_symbolizer_path=\$this_dir/llvm-symbolizer:detect_leaks=0 \
+\$this_dir/$fuzzer_package \$@" > $OUT/$fuzzer_basename
+  chmod +x $OUT/$fuzzer_basename
+done

.clusterfuzzlite/project.yaml

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+language: python

.github/workflows/cflite.yml

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+name: ClusterFuzzLite PR fuzzing
+on:
+  workflow_dispatch:
+  pull_request:
+    paths:
+      - '**'
+permissions: read-all
+jobs:
+  PR:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sanitizer: [address]
+    steps:
+    - name: Build Fuzzers (${{ matrix.sanitizer }})
+      id: build
+      uses: google/clusterfuzzlite/actions/build_fuzzers@v1
+      with:
+        sanitizer: ${{ matrix.sanitizer }}
+        language: python
+    - name: Run Fuzzers (${{ matrix.sanitizer }})
+      id: run
+      uses: google/clusterfuzzlite/actions/run_fuzzers@v1
+      with:
+        github-token: ${{ secrets.GITHUB_TOKEN }}
+        fuzz-seconds: 400
+        mode: 'code-change'
+        sanitizer: ${{ matrix.sanitizer }}

tests/fuzzing/fuzz_LightScriptCellReader.py

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+import sys
+
+import atheris
+
+with atheris.instrument_imports():
+    from jupytext.cell_reader import LightScriptCellReader
+
+def TestOneInput(data):
+    fdp = atheris.FuzzedDataProvider(data)
+    text = fdp.ConsumeString(len(data))
+    lines = text.splitlines()
+    _ = LightScriptCellReader().read(lines)
+
+
+
+def main():
+    atheris.Setup(sys.argv, TestOneInput, enable_python_coverage=True)
+    atheris.Fuzz()
+
+if __name__ == "__main__":
+    main()

tests/fuzzing/fuzz_RMarkdownCellReader.py

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+import sys
+
+import atheris
+
+with atheris.instrument_imports():
+    from jupytext.cell_reader import RMarkdownCellReader
+
+def TestOneInput(data):
+    fdp = atheris.FuzzedDataProvider(data)
+    text = fdp.ConsumeString(len(data))
+    lines = text.splitlines()
+    _ = RMarkdownCellReader().read(lines)
+
+
+def main():
+    atheris.Setup(sys.argv, TestOneInput, enable_python_coverage=True)
+    atheris.Fuzz()
+
+if __name__ == "__main__":
+    main()