flask: add flask-cors extension (#7676)

* flask: add cors extension

* give more appropriate function name

* add license header

* nit

projects/flask/Dockerfile

@@ -16,5 +16,6 @@
 
 FROM gcr.io/oss-fuzz-base/base-builder-python
 RUN git clone https://github.com/pallets/flask
+RUN git clone https://github.com/corydolphin/flask-cors
 RUN git clone --depth=1 https://github.com/google/fuzzing/
-COPY build.sh fuzz_* $SRC/
+COPY build.sh *.py $SRC/

projects/flask/build.sh

@@ -14,11 +14,23 @@
 # limitations under the License.
 #
 ################################################################################
-cd flask
+
+# Build flask
+cd $SRC/flask
 python3 -m pip install importlib_metadata
 pip3 install -r ./requirements/tests-pallets-min.in
 pip3 install .
 
+# Build flask-cors
+cd $SRC/flask-cors
+pip3 install requests
+pip3 install .
+
+# Build flask-cors fuzzers
+cd $SRC/flask-cors
+compile_python_fuzzer $SRC/cors_fuzz_flask.py
+
+# Build flask fuzzers
 # Build fuzzers in $OUT.
 for fuzzer in $(find $SRC -name 'fuzz_*.py'); do
   compile_python_fuzzer $fuzzer

projects/flask/cors_fuzz_flask.py

@@ -0,0 +1,88 @@
+#!/usr/bin/python3
+# Copyright 2022 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import requests
+import threading
+import time
+import atheris
+
+with atheris.instrument_imports():
+  from flask import Flask
+  from flask_cors import CORS
+  from flask import request
+
+app = Flask(__name__)
+CORS(app)
+output = ""
+
+@app.errorhandler(500)
+def internal_error(error):
+  print(
+    "Catching exception error from flask. The exception is likely "
+    "printed already right above this message in the log."
+  )
+  return str(error), 500
+
+@app.route("/")
+def fuzz_echo():
+  global output
+  return output
+
+def shutdown_server():
+  func = request.environ.get('werkzeug.server.shutdown')
+  if func is None:
+    raise RuntimeError('Not running with the Werkzeug Server')
+  func()
+
+# We use this to force a shutdown of the app. This is to
+# have a clean exit when a crash is found.
+@app.route('/shutdown')
+def shutdown():
+  shutdown_server()
+  return "Server shutdown"
+
+class ServerThread(threading.Thread):
+  def __init__(self):
+    threading.Thread.__init__(self)
+
+  def run(self):
+    global app
+    app.run()
+
+def TestOneInput(data):
+  global output
+  output = data
+
+  try:
+    r = requests.get('http://127.0.0.1:5000', timeout=0.5)
+    if r.status_code == 500:
+        raise Exception(r.text)
+  except requests.exceptions.ConnectionError:
+    None
+  except Exception as e:
+    # Every other exception is raised, but we need to shutdown
+    # the server before raising it.
+    requests.get('http://127.0.0.1:5000/shutdown', timeout=1.02)
+    raise e
+
+def main():
+  t1 = ServerThread()
+  t1.start()
+  atheris.Setup(sys.argv, TestOneInput, enable_python_coverage=True)
+  atheris.Fuzz()
+  t1.join()
+
+if __name__ == "__main__":
+  main()