From 6fa46b71f7010ed17f6a44fe89bbc0cbcc2441f3 Mon Sep 17 00:00:00 2001 From: Petr Viktorin Date: Mon, 6 Mar 2023 17:24:24 +0100 Subject: [PATCH] CVE-2007-4559, PEP-706: Add filters for tarfile extraction (downstream) Add and test RHEL-specific ways of configuring the default behavior: environment variable and config file. --- Lib/tarfile.py | 47 +++++++++++++-- Lib/test/test_shutil.py | 2 +- Lib/test/test_tarfile.py | 122 ++++++++++++++++++++++++++++++++++++++- 3 files changed, 162 insertions(+), 9 deletions(-) diff --git a/Lib/tarfile.py b/Lib/tarfile.py index 3bbbcaa..91c7754 100755 --- a/Lib/tarfile.py +++ b/Lib/tarfile.py @@ -71,6 +71,13 @@ __all__ = ["TarFile", "TarInfo", "is_tarfile", "TarError", "ReadError", "OutsideDestinationError", "SpecialFileError", "AbsolutePathError", "LinkOutsideDestinationError"] +# If true, use the safer (but backwards-incompatible) 'tar' extraction filter, +# rather than 'fully_trusted', by default. +# The emitted warning is changed to match. +_RH_SAFER_DEFAULT = True + +# System-wide configuration file +_CONFIG_FILENAME = '/etc/python/tarfile.cfg' #--------------------------------------------------------- # tar constants @@ -2218,11 +2225,41 @@ class TarFile(object): if filter is None: filter = self.extraction_filter if filter is None: - warnings.warn( - 'Python 3.14 will, by default, filter extracted tar ' - + 'archives and reject files or modify their metadata. ' - + 'Use the filter argument to control this behavior.', - DeprecationWarning) + name = os.environ.get('PYTHON_TARFILE_EXTRACTION_FILTER') + if name is None: + try: + file = bltn_open(_CONFIG_FILENAME) + except FileNotFoundError: + pass + else: + import configparser + conf = configparser.ConfigParser( + interpolation=None, + comment_prefixes=('#', ), + ) + with file: + conf.read_file(file) + name = conf.get('tarfile', + 'PYTHON_TARFILE_EXTRACTION_FILTER', + fallback='') + if name: + try: + filter = _NAMED_FILTERS[name] + except KeyError: + raise ValueError(f"filter {filter!r} not found") from None + self.extraction_filter = filter + return filter + if _RH_SAFER_DEFAULT: + warnings.warn( + 'The default behavior of tarfile extraction has been ' + + 'changed to disallow common exploits ' + + '(including CVE-2007-4559). ' + + 'By default, absolute/parent paths are disallowed ' + + 'and some mode bits are cleared. ' + + 'See https://access.redhat.com/articles/7004769 ' + + 'for more details.', + RuntimeWarning) + return tar_filter return fully_trusted_filter if isinstance(filter, str): raise TypeError( diff --git a/Lib/test/test_shutil.py b/Lib/test/test_shutil.py index bf60f37..242f4af 100644 --- a/Lib/test/test_shutil.py +++ b/Lib/test/test_shutil.py @@ -1964,7 +1964,7 @@ class TestArchives(BaseTest, unittest.TestCase): self.check_unpack_archive(format, filter='fully_trusted') self.check_unpack_archive(format, filter='data') with warnings_helper.check_warnings( - ('Python 3.14', DeprecationWarning)): + ('.*CVE-2007-4559', RuntimeWarning)): self.check_unpack_archive(format) def test_unpack_archive_tar(self): diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py index 71489ea..1c08110 100644 --- a/Lib/test/test_tarfile.py +++ b/Lib/test/test_tarfile.py @@ -3098,8 +3098,8 @@ class NoneInfoExtractTests(ReadTest): tar.errorlevel = 0 with ExitStack() as cm: if cls.extraction_filter is None: - cm.enter_context(warnings.catch_warnings( - action="ignore", category=DeprecationWarning)) + cm.enter_context(warnings.catch_warnings()) + warnings.simplefilter(action="ignore", category=RuntimeWarning) tar.extractall(cls.control_dir, filter=cls.extraction_filter) tar.close() cls.control_paths = set( @@ -3920,7 +3920,7 @@ class TestExtractionFilters(unittest.TestCase): with ArchiveMaker() as arc: arc.add('foo') with warnings_helper.check_warnings( - ('Python 3.14', DeprecationWarning)): + ('.*CVE-2007-4559', RuntimeWarning)): with self.check_context(arc.open(), None): self.expect_file('foo') @@ -4089,6 +4089,122 @@ class TestExtractionFilters(unittest.TestCase): with self.check_context(arc.open(errorlevel='boo!'), filtererror_filter): self.expect_exception(TypeError) # errorlevel is not int + @contextmanager + def rh_config_context(self, config_lines=None): + """Set up for testing various ways of overriding the default filter + + return a triple with: + - temporary directory + - EnvironmentVarGuard() + - a test archive for use with check_* methods below + + If config_lines is given, write them to the config file. Otherwise + the config file is missing. + """ + tempdir = pathlib.Path(TEMPDIR) / 'tmp' + configfile = tempdir / 'tarfile.cfg' + with ArchiveMaker() as arc: + arc.add('good') + arc.add('ugly', symlink_to='/etc/passwd') + arc.add('../bad') + with ( + os_helper.temp_dir(tempdir), + support.swap_attr(tarfile, '_CONFIG_FILENAME', str(configfile)), + os_helper.EnvironmentVarGuard() as env, + arc.open() as tar, + ): + if config_lines is not None: + with configfile.open('w') as f: + for line in config_lines: + print(line, file=f) + yield tempdir, env, tar + + def check_rh_default_behavior(self, tar, tempdir): + """Check RH default: warn and refuse to extract dangerous files.""" + with ( + warnings_helper.check_warnings( + ('.*CVE-2007-4559', RuntimeWarning)), + self.assertRaises(tarfile.OutsideDestinationError), + ): + tar.extractall(tempdir / 'outdir') + + def check_trusted_default(self, tar, tempdir): + """Check 'fully_trusted' is configured as the default filter.""" + with ( + warnings_helper.check_no_warnings(self), + ): + tar.extractall(tempdir / 'outdir') + self.assertTrue((tempdir / 'outdir/good').exists()) + self.assertEqual((tempdir / 'outdir/ugly').readlink(), + pathlib.Path('/etc/passwd')) + self.assertTrue((tempdir / 'bad').exists()) + + def test_rh_default_no_conf(self): + with self.rh_config_context() as (tempdir, env, tar): + self.check_rh_default_behavior(tar, tempdir) + + def test_rh_default_from_file(self): + lines = ['[tarfile]', 'PYTHON_TARFILE_EXTRACTION_FILTER=fully_trusted'] + with self.rh_config_context(lines) as (tempdir, env, tar): + self.check_trusted_default(tar, tempdir) + + def test_rh_empty_config_file(self): + """Empty config file -> default behavior""" + lines = [] + with self.rh_config_context(lines) as (tempdir, env, tar): + self.check_rh_default_behavior(tar, tempdir) + + def test_empty_config_section(self): + """Empty section in config file -> default behavior""" + lines = ['[tarfile]'] + with self.rh_config_context(lines) as (tempdir, env, tar): + self.check_rh_default_behavior(tar, tempdir) + + def test_rh_default_empty_config_option(self): + """Empty option value in config file -> default behavior""" + lines = ['[tarfile]', 'PYTHON_TARFILE_EXTRACTION_FILTER='] + with self.rh_config_context(lines) as (tempdir, env, tar): + self.check_rh_default_behavior(tar, tempdir) + + def test_bad_config_option(self): + """Bad option value in config file -> ValueError""" + lines = ['[tarfile]', 'PYTHON_TARFILE_EXTRACTION_FILTER=unknown!'] + with self.rh_config_context(lines) as (tempdir, env, tar): + with self.assertRaises(ValueError): + tar.extractall(tempdir / 'outdir') + + def test_default_from_envvar(self): + with self.rh_config_context() as (tempdir, env, tar): + env['PYTHON_TARFILE_EXTRACTION_FILTER'] = 'fully_trusted' + self.check_trusted_default(tar, tempdir) + + def test_empty_envvar(self): + """Empty env variable -> default behavior""" + with self.rh_config_context() as (tempdir, env, tar): + env['PYTHON_TARFILE_EXTRACTION_FILTER'] = '' + self.check_rh_default_behavior(tar, tempdir) + + def test_bad_envvar(self): + with self.rh_config_context() as (tempdir, env, tar): + env['PYTHON_TARFILE_EXTRACTION_FILTER'] = 'unknown!' + with self.assertRaises(ValueError): + tar.extractall(tempdir / 'outdir') + + def test_envvar_overrides_file(self): + lines = ['[tarfile]', 'PYTHON_TARFILE_EXTRACTION_FILTER=data'] + with self.rh_config_context(lines) as (tempdir, env, tar): + env['PYTHON_TARFILE_EXTRACTION_FILTER'] = 'fully_trusted' + self.check_trusted_default(tar, tempdir) + + def test_monkeypatch_overrides_envvar(self): + with self.rh_config_context(None) as (tempdir, env, tar): + env['PYTHON_TARFILE_EXTRACTION_FILTER'] = 'data' + with support.swap_attr( + tarfile.TarFile, 'extraction_filter', + staticmethod(tarfile.fully_trusted_filter) + ): + self.check_trusted_default(tar, tempdir) + class OverwriteTests(archiver_tests.OverwriteTests, unittest.TestCase): testdir = os.path.join(TEMPDIR, "testoverwrite") -- 2.44.0