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python-tuf/tests/test_indefinite_freeze_attack.py
Martin Vrachev 028d1bc9f7 Make "utils" import more definite 
Currently, we are importing the "utils" module in tests/utils
with "import utils".
This could become a problem when there is another module with
the same general name "utils" and could lead to import mistakes.

Signed-off-by: Martin Vrachev <mvrachev@vmware.com>
2020-11-23 22:17:31 +02:00

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#!/usr/bin/env python
# Copyright 2012 - 2017, New York University and the TUF contributors
# SPDX-License-Identifier: MIT OR Apache-2.0
"""
<Program Name>
test_indefinite_freeze_attack.py
<Author>
Konstantin Andrianov.
<Started>
March 10, 2012.
April 1, 2014.
Refactored to use the 'unittest' module (test conditions in code, rather
than verifying text output), use pre-generated repository files, and
discontinue use of the old repository tools. -vladimir.v.diaz
March 9, 2016.
Additional test added relating to issue:
https://github.com/theupdateframework/tuf/issues/322
If a metadata file is not updated (no indication of a new version
available), the expiration of the pre-existing, locally trusted metadata
must still be detected. This additional test complains if such does not
occur, and accompanies code in tuf.client.updater:refresh() to detect it.
-sebastien.awwad
<Copyright>
See LICENSE-MIT OR LICENSE for licensing information.
<Purpose>
Simulate an indefinite freeze attack. In an indefinite freeze attack,
attacker is able to respond to client's requests with the same, outdated
metadata without the client being aware.
"""
# Help with Python 3 compatibility, where the print statement is a function, an
# implicit relative import is invalid, and the '/' operator performs true
# division. Example: print 'hello world' raises a 'SyntaxError' exception.
from __future__ import print_function
from __future__ import absolute_import
from __future__ import division
from __future__ import unicode_literals
import datetime
import os
import time
import tempfile
import shutil
import json
import logging
import unittest
import sys
if sys.version_info >= (3, 3):
import unittest.mock as mock
else:
import mock
import tuf.formats
import tuf.log
import tuf.client.updater as updater
import tuf.repository_tool as repo_tool
import tuf.unittest_toolbox as unittest_toolbox
import tuf.roledb
import tuf.keydb
import tuf.exceptions
from tests import utils
import securesystemslib
import six
# The repository tool is imported and logs console messages by default. Disable
# console log messages generated by this unit test.
repo_tool.disable_console_log_messages()
logger = logging.getLogger(__name__)
class TestIndefiniteFreezeAttack(unittest_toolbox.Modified_TestCase):
@classmethod
def setUpClass(cls):
# Create a temporary directory to store the repository, metadata, and target
# files. 'temporary_directory' must be deleted in TearDownModule() so that
# temporary files are always removed, even when exceptions occur.
cls.temporary_directory = tempfile.mkdtemp(dir=os.getcwd())
# Launch a SimpleHTTPServer (serves files in the current directory).
# Test cases will request metadata and target files that have been
# pre-generated in 'tuf/tests/repository_data', which will be served by the
# SimpleHTTPServer launched here. The test cases of this unit test assume
# the pre-generated metadata files have a specific structure, such
# as a delegated role 'targets/role1', three target files, five key files,
# etc.
cls.server_process_handler = utils.TestServerProcess(log=logger)
@classmethod
def tearDownClass(cls):
# Cleans the resources and flush the logged lines (if any).
cls.server_process_handler.clean()
# Remove the temporary repository directory, which should contain all the
# metadata, targets, and key files generated of all the test cases.
shutil.rmtree(cls.temporary_directory)
def setUp(self):
# We are inheriting from custom class.
unittest_toolbox.Modified_TestCase.setUp(self)
self.repository_name = 'test_repository1'
# Copy the original repository files provided in the test folder so that
# any modifications made to repository files are restricted to the copies.
# The 'repository_data' directory is expected to exist in 'tuf/tests/'.
original_repository_files = os.path.join(os.getcwd(), 'repository_data')
temporary_repository_root = \
self.make_temp_directory(directory=self.temporary_directory)
# The original repository, keystore, and client directories will be copied
# for each test case.
original_repository = os.path.join(original_repository_files, 'repository')
original_client = os.path.join(original_repository_files, 'client')
original_keystore = os.path.join(original_repository_files, 'keystore')
# Save references to the often-needed client repository directories.
# Test cases need these references to access metadata and target files.
self.repository_directory = \
os.path.join(temporary_repository_root, 'repository')
self.client_directory = os.path.join(temporary_repository_root, 'client')
self.keystore_directory = os.path.join(temporary_repository_root, 'keystore')
# Copy the original 'repository', 'client', and 'keystore' directories
# to the temporary repository the test cases can use.
shutil.copytree(original_repository, self.repository_directory)
shutil.copytree(original_client, self.client_directory)
shutil.copytree(original_keystore, self.keystore_directory)
# Set the url prefix required by the 'tuf/client/updater.py' updater.
# 'path/to/tmp/repository' -> 'localhost:8001/tmp/repository'.
repository_basepath = self.repository_directory[len(os.getcwd()):]
url_prefix = 'http://localhost:' \
+ str(self.server_process_handler.port) + repository_basepath
# Setting 'tuf.settings.repository_directory' with the temporary client
# directory copied from the original repository files.
tuf.settings.repositories_directory = self.client_directory
self.repository_mirrors = {'mirror1': {'url_prefix': url_prefix,
'metadata_path': 'metadata',
'targets_path': 'targets'}}
# Create the repository instance. The test cases will use this client
# updater to refresh metadata, fetch target files, etc.
self.repository_updater = updater.Updater(self.repository_name,
self.repository_mirrors)
def tearDown(self):
# Modified_TestCase.tearDown() automatically deletes temporary files and
# directories that may have been created during each test case.
unittest_toolbox.Modified_TestCase.tearDown(self)
tuf.roledb.clear_roledb(clear_all=True)
tuf.keydb.clear_keydb(clear_all=True)
# Logs stdout and stderr from the sever subprocess.
self.server_process_handler.flush_log()
def test_without_tuf(self):
# Without TUF, Test 1 and Test 2 are functionally equivalent, so we skip
# Test 1 and only perform Test 2.
#
# Test 1: If we find that the timestamp acquired from a mirror indicates
# that there is no new snapshot file, and our current snapshot
# file is expired, is it recognized as such?
# Test 2: If an expired timestamp is downloaded, is it recognized as such?
# Test 2 Begin:
#
# 'timestamp.json' specifies the latest version of the repository files. A
# client should only accept the same version of this file up to a certain
# point, or else it cannot detect that new files are available for
# download. Modify the repository's timestamp.json' so that it expires
# soon, copy it over to the client, and attempt to re-fetch the same
# expired version.
#
# A non-TUF client (without a way to detect when metadata has expired) is
# expected to download the same version, and thus the same outdated files.
# Verify that the downloaded 'timestamp.json' contains the same file size
# and hash as the one available locally.
timestamp_path = os.path.join(self.repository_directory, 'metadata',
'timestamp.json')
timestamp_metadata = securesystemslib.util.load_json_file(timestamp_path)
expiry_time = time.time() - 10
expires = tuf.formats.unix_timestamp_to_datetime(int(expiry_time))
expires = expires.isoformat() + 'Z'
timestamp_metadata['signed']['expires'] = expires
tuf.formats.check_signable_object_format(timestamp_metadata)
with open(timestamp_path, 'wb') as file_object:
# Explicitly specify the JSON separators for Python 2 + 3 consistency.
timestamp_content = \
json.dumps(timestamp_metadata, indent=1, separators=(',', ': '),
sort_keys=True).encode('utf-8')
file_object.write(timestamp_content)
client_timestamp_path = os.path.join(self.client_directory, 'timestamp.json')
shutil.copy(timestamp_path, client_timestamp_path)
length, hashes = securesystemslib.util.get_file_details(timestamp_path)
fileinfo = tuf.formats.make_targets_fileinfo(length, hashes)
url_prefix = self.repository_mirrors['mirror1']['url_prefix']
url_file = os.path.join(url_prefix, 'metadata', 'timestamp.json')
six.moves.urllib.request.urlretrieve(url_file.replace('\\', '/'), client_timestamp_path)
length, hashes = securesystemslib.util.get_file_details(client_timestamp_path)
download_fileinfo = tuf.formats.make_targets_fileinfo(length, hashes)
# Verify 'download_fileinfo' is equal to the current local file.
self.assertEqual(download_fileinfo, fileinfo)
def test_with_tuf(self):
# Three tests are conducted here.
#
# Test 1: If we find that the timestamp acquired from a mirror indicates
# that there is no new snapshot file, and our current snapshot
# file is expired, is it recognized as such?
# Test 2: If an expired timestamp is downloaded, is it recognized as such?
# Test 3: If an expired Snapshot is downloaded, is it (1) rejected? (2) the
# local Snapshot file deleted? (3) and is the client able to recover when
# given a new, valid Snapshot?
# Test 1 Begin:
#
# Addresses this issue: https://github.com/theupdateframework/tuf/issues/322
#
# If time has passed and our snapshot or targets role is expired, and
# the mirror whose timestamp we fetched doesn't indicate the existence of a
# new snapshot version, we still need to check that it's expired and notify
# the software update system / application / user. This test creates that
# scenario. The correct behavior is to raise an exception.
#
# Background: Expiration checks (updater._ensure_not_expired) were
# previously conducted when the metadata file was downloaded. If no new
# metadata file was downloaded, no expiry check would occur. In particular,
# while root was checked for expiration at the beginning of each
# updater.refresh() cycle, and timestamp was always checked because it was
# always fetched, snapshot and targets were never checked if the user did
# not receive evidence that they had changed. This bug allowed a class of
# freeze attacks.
# That bug was fixed and this test tests that fix going forward.
# Modify the timestamp file on the remote repository. 'timestamp.json'
# must be properly updated and signed with 'repository_tool.py', otherwise
# the client will reject it as invalid metadata.
# Load the repository
repository = repo_tool.load_repository(self.repository_directory)
# Load the snapshot and timestamp keys
key_file = os.path.join(self.keystore_directory, 'timestamp_key')
timestamp_private = repo_tool.import_ed25519_privatekey_from_file(key_file,
'password')
repository.timestamp.load_signing_key(timestamp_private)
key_file = os.path.join(self.keystore_directory, 'snapshot_key')
snapshot_private = repo_tool.import_ed25519_privatekey_from_file(key_file,
'password')
repository.snapshot.load_signing_key(snapshot_private)
# sign snapshot with expiry in near future (earlier than e.g. timestamp)
expiry = int(time.time() + 60*60)
repository.snapshot.expiration = tuf.formats.unix_timestamp_to_datetime(
expiry)
repository.mark_dirty(['snapshot', 'timestamp'])
repository.writeall()
# And move the staged metadata to the "live" metadata.
shutil.rmtree(os.path.join(self.repository_directory, 'metadata'))
shutil.copytree(os.path.join(self.repository_directory, 'metadata.staged'),
os.path.join(self.repository_directory, 'metadata'))
# Refresh metadata on the client. For this refresh, all data is not expired.
logger.info('Test: Refreshing #1 - Initial metadata refresh occurring.')
self.repository_updater.refresh()
logger.info('Test: Refreshing #2 - refresh after local snapshot expiry.')
# mock current time to one second after snapshot expiry
mock_time = mock.Mock()
mock_time.return_value = expiry + 1
with mock.patch('time.time', mock_time):
try:
self.repository_updater.refresh() # We expect this to fail!
except tuf.exceptions.ExpiredMetadataError:
logger.info('Test: Refresh #2 - failed as expected. Expired local'
' snapshot case generated a tuf.exceptions.ExpiredMetadataError'
' exception as expected. Test pass.')
else:
self.fail('TUF failed to detect expired stale snapshot metadata. Freeze'
' attack successful.')
# Test 2 Begin:
#
# 'timestamp.json' specifies the latest version of the repository files.
# A client should only accept the same version of this file up to a certain
# point, or else it cannot detect that new files are available for download.
# Modify the repository's 'timestamp.json' so that it is about to expire,
# copy it over the to client, wait a moment until it expires, and attempt to
# re-fetch the same expired version.
# The same scenario as in test_without_tuf() is followed here, except with
# a TUF client. The TUF client performs a refresh of top-level metadata,
# which includes 'timestamp.json', and should detect a freeze attack if
# the repository serves an outdated 'timestamp.json'.
# Modify the timestamp file on the remote repository. 'timestamp.json'
# must be properly updated and signed with 'repository_tool.py', otherwise
# the client will reject it as invalid metadata. The resulting
# 'timestamp.json' should be valid metadata, but expired (as intended).
repository = repo_tool.load_repository(self.repository_directory)
key_file = os.path.join(self.keystore_directory, 'timestamp_key')
timestamp_private = repo_tool.import_ed25519_privatekey_from_file(key_file,
'password')
repository.timestamp.load_signing_key(timestamp_private)
# Set timestamp metadata to expire soon.
# We cannot set the timestamp expiration with
# 'repository.timestamp.expiration = ...' with already-expired timestamp
# metadata because of consistency checks that occur during that assignment.
expiry_time = time.time() + 60*60
datetime_object = tuf.formats.unix_timestamp_to_datetime(int(expiry_time))
repository.timestamp.expiration = datetime_object
repository.writeall()
# Move the staged metadata to the "live" metadata.
shutil.rmtree(os.path.join(self.repository_directory, 'metadata'))
shutil.copytree(os.path.join(self.repository_directory, 'metadata.staged'),
os.path.join(self.repository_directory, 'metadata'))
# mock current time to one second after timestamp expiry
mock_time = mock.Mock()
mock_time.return_value = expiry_time + 1
with mock.patch('time.time', mock_time):
try:
self.repository_updater.refresh() # We expect NoWorkingMirrorError.
except tuf.exceptions.NoWorkingMirrorError as e:
# Make sure the contained error is ExpiredMetadataError
for mirror_url, mirror_error in six.iteritems(e.mirror_errors):
self.assertTrue(isinstance(mirror_error, tuf.exceptions.ExpiredMetadataError))
else:
self.fail('TUF failed to detect expired, stale timestamp metadata.'
' Freeze attack successful.')
# Test 3 Begin:
#
# Serve the client expired Snapshot. The client should reject the given,
# expired Snapshot and the locally trusted one, which should now be out of
# date.
# After the attack, attempt to re-issue a valid Snapshot to verify that
# the client is still able to update. A bug previously caused snapshot
# expiration or replay to result in an indefinite freeze; see
# github.com/theupdateframework/tuf/issues/736
repository = repo_tool.load_repository(self.repository_directory)
ts_key_file = os.path.join(self.keystore_directory, 'timestamp_key')
snapshot_key_file = os.path.join(self.keystore_directory, 'snapshot_key')
timestamp_private = repo_tool.import_ed25519_privatekey_from_file(
ts_key_file, 'password')
snapshot_private = repo_tool.import_ed25519_privatekey_from_file(
snapshot_key_file, 'password')
repository.timestamp.load_signing_key(timestamp_private)
repository.snapshot.load_signing_key(snapshot_private)
# Set ts to expire in 1 month.
ts_expiry_time = time.time() + 2630000
# Set snapshot to expire in 1 hour.
snapshot_expiry_time = time.time() + 60*60
ts_datetime_object = tuf.formats.unix_timestamp_to_datetime(
int(ts_expiry_time))
snapshot_datetime_object = tuf.formats.unix_timestamp_to_datetime(
int(snapshot_expiry_time))
repository.timestamp.expiration = ts_datetime_object
repository.snapshot.expiration = snapshot_datetime_object
repository.writeall()
# Move the staged metadata to the "live" metadata.
shutil.rmtree(os.path.join(self.repository_directory, 'metadata'))
shutil.copytree(os.path.join(self.repository_directory, 'metadata.staged'),
os.path.join(self.repository_directory, 'metadata'))
# mock current time to one second after snapshot expiry
mock_time = mock.Mock()
mock_time.return_value = snapshot_expiry_time + 1
with mock.patch('time.time', mock_time):
try:
# We expect the following refresh() to raise a NoWorkingMirrorError.
self.repository_updater.refresh()
except tuf.exceptions.NoWorkingMirrorError as e:
# Make sure the contained error is ExpiredMetadataError
for mirror_url, mirror_error in six.iteritems(e.mirror_errors):
self.assertTrue(isinstance(mirror_error, tuf.exceptions.ExpiredMetadataError))
self.assertTrue(mirror_url.endswith('snapshot.json'))
else:
self.fail('TUF failed to detect expired, stale Snapshot metadata.'
' Freeze attack successful.')
# The client should have rejected the malicious Snapshot metadata, and
# distrusted the local snapshot file that is no longer valid.
self.assertTrue('snapshot' not in self.repository_updater.metadata['current'])
self.assertEqual(sorted(['root', 'targets', 'timestamp']),
sorted(self.repository_updater.metadata['current']))
# Verify that the client is able to recover from the malicious Snapshot.
# Re-sign a valid Snapshot file that the client should accept.
repository = repo_tool.load_repository(self.repository_directory)
repository.timestamp.load_signing_key(timestamp_private)
repository.snapshot.load_signing_key(snapshot_private)
# Set snapshot to expire in 1 month.
snapshot_expiry_time = time.time() + 2630000
snapshot_datetime_object = tuf.formats.unix_timestamp_to_datetime(
int(snapshot_expiry_time))
repository.snapshot.expiration = snapshot_datetime_object
repository.writeall()
# Move the staged metadata to the "live" metadata.
shutil.rmtree(os.path.join(self.repository_directory, 'metadata'))
shutil.copytree(os.path.join(self.repository_directory, 'metadata.staged'),
os.path.join(self.repository_directory, 'metadata'))
# Verify that the client accepts the valid metadata file.
self.repository_updater.refresh()
self.assertTrue('snapshot' in self.repository_updater.metadata['current'])
self.assertEqual(sorted(['root', 'targets', 'timestamp', 'snapshot']),
sorted(self.repository_updater.metadata['current']))
if __name__ == '__main__':
utils.configure_test_logging(sys.argv)
unittest.main()
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