mirror of https://github.com/google/oss-fuzz.git
321 lines
12 KiB
Python
321 lines
12 KiB
Python
# Copyright 2020 Google LLC
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""A module to handle running a fuzz target for a specified amount of time."""
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import collections
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import logging
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import os
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import re
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import shutil
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import stat
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import subprocess
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import sys
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import base_runner_utils
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# pylint: disable=wrong-import-position,import-error
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sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
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import utils
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logging.basicConfig(
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format='%(asctime)s - %(name)s - %(levelname)s - %(message)s',
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level=logging.DEBUG)
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# Use a fixed seed for determinism. Use len_control=0 since we don't have enough
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# time fuzzing for len_control to make sense (probably).
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LIBFUZZER_OPTIONS = ['-seed=1337', '-len_control=0']
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# The number of reproduce attempts for a crash.
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REPRODUCE_ATTEMPTS = 10
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# Seconds on top of duration until a timeout error is raised.
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BUFFER_TIME = 10
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# Log message if we can't check if crash reproduces on an recent build.
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COULD_NOT_TEST_ON_CLUSTERFUZZ_MESSAGE = (
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'Could not run previous build of target to determine if this code change '
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'(pr/commit) introduced crash. Assuming crash was newly introduced.')
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FuzzResult = collections.namedtuple('FuzzResult',
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['testcase', 'stacktrace', 'corpus_path'])
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class ReproduceError(Exception):
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"""Error for when we can't attempt to reproduce a crash."""
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def get_fuzz_target_corpus_dir(workspace, target_name):
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"""Returns the directory for storing |target_name|'s corpus in |workspace|."""
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return os.path.join(workspace.corpora, target_name)
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def get_fuzz_target_pruned_corpus_dir(workspace, target_name):
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"""Returns the directory for storing |target_name|'s puned corpus in
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|workspace|."""
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return os.path.join(workspace.pruned_corpora, target_name)
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class FuzzTarget: # pylint: disable=too-many-instance-attributes
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"""A class to manage a single fuzz target.
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Attributes:
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target_name: The name of the fuzz target.
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duration: The length of time in seconds that the target should run.
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target_path: The location of the fuzz target binary.
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workspace: The workspace for storing things related to fuzzing.
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"""
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# pylint: disable=too-many-arguments
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def __init__(self, target_path, duration, workspace, clusterfuzz_deployment,
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config):
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"""Represents a single fuzz target.
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Args:
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target_path: The location of the fuzz target binary.
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duration: The length of time in seconds the target should run.
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workspace: The path used for storing things needed for fuzzing.
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clusterfuzz_deployment: The object representing the ClusterFuzz
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deployment.
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config: The config of this project.
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"""
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self.target_path = target_path
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self.target_name = os.path.basename(self.target_path)
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self.duration = int(duration)
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self.workspace = workspace
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self.clusterfuzz_deployment = clusterfuzz_deployment
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self.config = config
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self.latest_corpus_path = get_fuzz_target_corpus_dir(
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self.workspace, self.target_name)
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os.makedirs(self.latest_corpus_path, exist_ok=True)
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self.pruned_corpus_path = get_fuzz_target_pruned_corpus_dir(
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self.workspace, self.target_name)
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os.makedirs(self.pruned_corpus_path, exist_ok=True)
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def _download_corpus(self):
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"""Downloads the corpus for the target from ClusterFuzz and returns the path
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to the corpus. An empty directory is provided if the corpus can't be
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downloaded or is empty."""
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self.clusterfuzz_deployment.download_corpus(self.target_name,
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self.latest_corpus_path)
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return self.latest_corpus_path
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def prune(self):
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"""Prunes the corpus and returns the result."""
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self._download_corpus()
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prune_options = [
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'-merge=1', self.pruned_corpus_path, self.latest_corpus_path
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]
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result = self.fuzz(use_corpus=False, extra_libfuzzer_options=prune_options)
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return FuzzResult(result.testcase, result.stacktrace,
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self.pruned_corpus_path)
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def fuzz(self, use_corpus=True, extra_libfuzzer_options=None):
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"""Starts the fuzz target run for the length of time specified by duration.
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Returns:
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FuzzResult namedtuple with stacktrace and testcase if applicable.
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"""
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logging.info('Running fuzzer: %s.', self.target_name)
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if extra_libfuzzer_options is None:
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extra_libfuzzer_options = []
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env = base_runner_utils.get_env(self.config, self.workspace)
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# TODO(metzman): Is this needed?
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env['RUN_FUZZER_MODE'] = 'interactive'
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if use_corpus:
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# If corpus can be downloaded, use it for fuzzing.
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self._download_corpus()
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env['CORPUS_DIR'] = self.latest_corpus_path
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options = LIBFUZZER_OPTIONS.copy() + [
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f'-max_total_time={self.duration}',
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# Make sure libFuzzer artifact files don't pollute $OUT.
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f'-artifact_prefix={self.workspace.artifacts}/'
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] + extra_libfuzzer_options
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command = ['run_fuzzer', self.target_name] + options
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logging.info('Running command: %s', command)
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process = subprocess.Popen(command,
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env=env,
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stdout=subprocess.PIPE,
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stderr=subprocess.PIPE)
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try:
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_, stderr = process.communicate(timeout=self.duration + BUFFER_TIME)
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except subprocess.TimeoutExpired:
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logging.error('Fuzzer %s timed out, ending fuzzing.', self.target_name)
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return FuzzResult(None, None, self.latest_corpus_path)
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# Libfuzzer timeout was reached.
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if not process.returncode:
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logging.info('Fuzzer %s finished with no crashes discovered.',
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self.target_name)
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return FuzzResult(None, None, self.latest_corpus_path)
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# Crash was discovered.
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logging.info('Fuzzer %s, ended before timeout.', self.target_name)
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testcase = get_testcase(stderr)
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if not testcase:
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logging.error(b'No testcase found in stacktrace: %s.', stderr)
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return FuzzResult(None, None, self.latest_corpus_path)
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utils.binary_print(b'Fuzzer: %s. Detected bug:\n%s' %
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(self.target_name.encode(), stderr))
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if self.is_crash_reportable(testcase):
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# We found a bug in the fuzz target and we will report it.
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return FuzzResult(testcase, stderr, self.latest_corpus_path)
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# We found a bug but we won't report it.
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return FuzzResult(None, None, self.latest_corpus_path)
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def free_disk_if_needed(self, delete_fuzz_target=True):
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"""Deletes things that are no longer needed from fuzzing this fuzz target to
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save disk space if needed."""
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if not self.config.low_disk_space:
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logging.info('Not freeing disk space after running fuzz target.')
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return
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logging.info('Deleting corpus and seed corpus of %s to save disk.',
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self.target_name)
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# Delete the seed corpus, corpus, and fuzz target.
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for corpus_path in [self.latest_corpus_path, self.pruned_corpus_path]:
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# Use ignore_errors=True to fix
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# https://github.com/google/oss-fuzz/issues/5383.
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shutil.rmtree(corpus_path, ignore_errors=True)
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target_seed_corpus_path = self.target_path + '_seed_corpus.zip'
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if os.path.exists(target_seed_corpus_path):
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os.remove(target_seed_corpus_path)
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if delete_fuzz_target:
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logging.info('Deleting fuzz target: %s.', self.target_name)
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os.remove(self.target_path)
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logging.info('Done deleting.')
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def is_reproducible(self, testcase, target_path):
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"""Checks if the testcase reproduces.
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Args:
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testcase: The path to the testcase to be tested.
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target_path: The path to the fuzz target to be tested
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Returns:
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True if crash is reproducible and we were able to run the
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binary.
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Raises:
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ReproduceError if we can't attempt to reproduce the crash.
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"""
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if not os.path.exists(target_path):
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logging.info('Target: %s does not exist.', target_path)
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raise ReproduceError(f'Target {target_path} not found.')
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os.chmod(target_path, stat.S_IRWXO)
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env = base_runner_utils.get_env(self.config, self.workspace)
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env['TESTCASE'] = testcase
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command = ['reproduce', self.target_name, '-runs=100']
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logging.info('Running reproduce command: %s.', ' '.join(command))
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for _ in range(REPRODUCE_ATTEMPTS):
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_, _, returncode = utils.execute(command, env=env)
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if returncode != 0:
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logging.info('Reproduce command returned: %s. Reproducible on %s.',
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returncode, target_path)
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return True
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logging.info('Reproduce command returned 0. Not reproducible on %s.',
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target_path)
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return False
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def is_crash_reportable(self, testcase):
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"""Returns True if a crash is reportable. This means the crash is
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reproducible but not reproducible on a build from the ClusterFuzz deployment
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(meaning the crash was introduced by this PR/commit/code change).
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Args:
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testcase: The path to the testcase that triggered the crash.
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Returns:
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True if the crash was introduced by the current pull request.
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Raises:
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ReproduceError if we can't attempt to reproduce the crash on the PR build.
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"""
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if not os.path.exists(testcase):
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raise ReproduceError(f'Testcase {testcase} not found.')
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try:
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reproducible_on_code_change = self.is_reproducible(
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testcase, self.target_path)
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except ReproduceError as error:
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logging.error('Could not check for crash reproducibility.'
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'Please file an issue:'
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'https://github.com/google/oss-fuzz/issues/new.')
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raise error
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if not reproducible_on_code_change:
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logging.info('Crash is not reproducible.')
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return self.config.report_unreproducible_crashes
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logging.info('Crash is reproducible.')
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return self.is_crash_novel(testcase)
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def is_crash_novel(self, testcase):
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"""Returns whether or not the crash is new. A crash is considered new if it
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can't be reproduced on an older ClusterFuzz build of the target."""
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if not os.path.exists(testcase):
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raise ReproduceError('Testcase %s not found.' % testcase)
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clusterfuzz_build_dir = self.clusterfuzz_deployment.download_latest_build()
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if not clusterfuzz_build_dir:
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# Crash is reproducible on PR build and we can't test on a recent
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# ClusterFuzz/OSS-Fuzz build.
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logging.info(COULD_NOT_TEST_ON_CLUSTERFUZZ_MESSAGE)
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return True
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clusterfuzz_target_path = os.path.join(clusterfuzz_build_dir,
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self.target_name)
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try:
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reproducible_on_clusterfuzz_build = self.is_reproducible(
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testcase, clusterfuzz_target_path)
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except ReproduceError:
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# This happens if the project has ClusterFuzz builds, but the fuzz target
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# is not in it (e.g. because the fuzz target is new).
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logging.info(COULD_NOT_TEST_ON_CLUSTERFUZZ_MESSAGE)
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return True
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if reproducible_on_clusterfuzz_build:
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logging.info('The crash is reproducible on previous build. '
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'Code change (pr/commit) did not introduce crash.')
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return False
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logging.info('The crash is not reproducible on previous build. '
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'Code change (pr/commit) introduced crash.')
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return True
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def get_testcase(stderr_bytes):
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"""Gets the file from a fuzzer run stacktrace.
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Args:
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stderr_bytes: The bytes containing the output from the fuzzer.
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Returns:
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The path to the testcase or None if not found.
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"""
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match = re.search(rb'\bTest unit written to (.+)', stderr_bytes)
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if match:
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return match.group(1).decode('utf-8')
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return None
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