Run 'python3-libraries' fuzzer in CI using CIFuzz

python · hugovk · Jan 16, 2026 · Jan 12, 2026 · Jan 12, 2026 · Jan 12, 2026
commit 2623d6047a21089896b6662d611bb4e1b83c54b1
@@ -676,6 +676,45 @@ jobs:
           sarif_file: cifuzz-sarif/results.sarif
           checkout_path: cifuzz-sarif
 
+  cifuzz-libraries:
+    name: CIFuzz-libraries
+    runs-on: ubuntu-latest
+    timeout-minutes: 60
+    needs: build-context
+    if: needs.build-context.outputs.run-ci-fuzz-libraries == 'true'
+    permissions:
+      security-events: write
+    strategy:
+      fail-fast: false
+      matrix:
+        sanitizer: [address, undefined, memory]
+    steps:
+      - name: Build fuzzers (${{ matrix.sanitizer }})
+        id: build
+        uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@master
+        with:
+          oss-fuzz-project-name: python3-libraries
+          sanitizer: ${{ matrix.sanitizer }}
+      - name: Run fuzzers (${{ matrix.sanitizer }})
+        uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
+        with:
+          fuzz-seconds: 600
+          oss-fuzz-project-name: python3-libraries
+          output-sarif: true
+          sanitizer: ${{ matrix.sanitizer }}
+      - name: Upload crash
+        if: failure() && steps.build.outcome == 'success'
+        uses: actions/upload-artifact@v4
+        with:
+          name: ${{ matrix.sanitizer }}-artifacts
+          path: ./out/artifacts
+      - name: Upload SARIF
+        if: always() && steps.build.outcome == 'success'
+        uses: github/codeql-action/upload-sarif@v3
+        with:
+          sarif_file: cifuzz-sarif/results.sarif
+          checkout_path: cifuzz-sarif
+
   all-required-green:  # This job does nothing and is only used for the branch protection
     name: All required checks pass
     runs-on: ubuntu-latest
@@ -698,6 +737,7 @@ jobs:
     - build-san
     - cross-build-linux
     - cifuzz
+    - cifuzz-libraries
     if: always()
 
     steps:

diff --git a/Misc/NEWS.d/next/Tools-Demos/2026-01-12-13-37-14.gh-issue-143572.WKV_Jk.rst b/Misc/NEWS.d/next/Tools-Demos/2026-01-12-13-37-14.gh-issue-143572.WKV_Jk.rst
@@ -0,0 +1,2 @@
+Run the 'python3-libraries' fuzzer using CIFuzz. Automatically detect when
+modules are changed.
@@ -50,11 +50,57 @@
 MACOS_DIRS = frozenset({"Mac"})
 WASI_DIRS = frozenset({Path("Tools", "wasm")})
 
+LIBRARY_FUZZER_PATHS = frozenset({
+    # All C/CPP fuzzers.
+    Path("configure"),
+    # ast
+    Path("Lib/ast.py"),
+    Path("Python/ast.c"),
+    # configparser
+    Path("Lib/configparser.py"),
+    # csv
+    Path("Lib/csv.py"),
+    Path("Modules/_csv.c"),
+    # decode
+    Path("Lib/encodings/"),
+    Path("Modules/_codecsmodule.c"),
+    Path("Modules/cjkcodecs/"),
+    Path("Modules/unicodedata*"),
+    # difflib
+    Path("Lib/difflib.py"),
+    # email
+    Path("Lib/email/"),
+    # html
+    Path("Lib/html/"),
+    Path("Lib/_markupbase.py"),
+    # http.client
+    Path("Lib/http/client.py"),
+    # json
+    Path("Lib/json/"),
+    Path("Modules/_json.c"),
+    # plist
+    Path("Lib/plistlib.py"),
+    # re
+    Path("Lib/re/"),
+    Path("Modules/_sre/"),
+    # tarfile
+    Path("Lib/tarfile.py"),
+    # tomllib
+    Path("Modules/tomllib/"),
+    # xml
+    Path("Lib/xml/"),
+    Path("Lib/_markupbase.py"),
+    Path("Modules/expat/"),
+    # zipfile
+    Path("Lib/zipfile/"),
+})
+
 
 @dataclass(kw_only=True, slots=True)
 class Outputs:
     run_android: bool = False
     run_ci_fuzz: bool = False
+    run_ci_fuzz_libraries: bool = False
     run_docs: bool = False
     run_ios: bool = False
     run_macos: bool = False
@@ -94,6 +140,11 @@ def compute_changes() -> None:
     else:
         print("Branch too old for CIFuzz tests; or no C files were changed")
 
+    if outputs.run_ci_fuzz_libraries:
+        print("Run CIFuzz tests for libraries")
+    else:
+        print("Branch too old for CIFuzz tests; or no library files were changed")
+
     if outputs.run_docs:
         print("Build documentation")
 
@@ -144,9 +195,18 @@ def get_file_platform(file: Path) -> str | None:
     return None
 
 
+def is_fuzzable_library_file(file: Path) -> bool:
+    return any(
+        (file.is_relative_to(needs_fuzz) and needs_fuzz.is_dir())
+        or (file == needs_fuzz and file.is_file())
+        for needs_fuzz in LIBRARY_FUZZER_PATHS
+    )
+
+
 def process_changed_files(changed_files: Set[Path]) -> Outputs:
     run_tests = False
     run_ci_fuzz = False
+    run_ci_fuzz_libraries = False
     run_docs = False
     run_windows_tests = False
     run_windows_msi = False
@@ -161,7 +221,7 @@ def process_changed_files(changed_files: Set[Path]) -> Outputs:
 
         if file.parent == GITHUB_WORKFLOWS_PATH:
             if file.name == "build.yml":
-                run_tests = run_ci_fuzz = True
+                run_tests = run_ci_fuzz = run_ci_fuzz_libraries = True
                 has_platform_specific_change = False
             if file.name == "reusable-docs.yml":
                 run_docs = True
@@ -196,6 +256,8 @@ def process_changed_files(changed_files: Set[Path]) -> Outputs:
             ("Modules", "_xxtestfuzz"),
         }:
             run_ci_fuzz = True
+        if not run_ci_fuzz_libraries and is_fuzzable_library_file(file):
+            run_ci_fuzz_libraries = True
 
         # Check for changed documentation-related files
         if doc_file:
@@ -229,6 +291,7 @@ def process_changed_files(changed_files: Set[Path]) -> Outputs:
     return Outputs(
         run_android=run_android,
         run_ci_fuzz=run_ci_fuzz,
+        run_ci_fuzz_libraries=run_ci_fuzz_libraries,
         run_docs=run_docs,
         run_ios=run_ios,
         run_macos=run_macos,
@@ -265,6 +328,7 @@ def write_github_output(outputs: Outputs) -> None:
     with open(os.environ["GITHUB_OUTPUT"], "a", encoding="utf-8") as f:
         f.write(f"run-android={bool_lower(outputs.run_android)}\n")
         f.write(f"run-ci-fuzz={bool_lower(outputs.run_ci_fuzz)}\n")
+        f.write(f"run-ci-fuzz-libraries={bool_lower(outputs.run_ci_fuzz_libraries)}\n")
         f.write(f"run-docs={bool_lower(outputs.run_docs)}\n")
         f.write(f"run-ios={bool_lower(outputs.run_ios)}\n")
         f.write(f"run-macos={bool_lower(outputs.run_macos)}\n")
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Run the 'python3-libraries' fuzzer using CIFuzz. Automatically detect when
		modules are changed.