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252 lines
10 KiB
252 lines
10 KiB
From 8b70605b594b3831331a9340ba764ff751871612 Mon Sep 17 00:00:00 2001
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From: Petr Viktorin <encukou@gmail.com>
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Date: Mon, 6 Mar 2023 17:24:24 +0100
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Subject: [PATCH] CVE-2007-4559, PEP-706: Add filters for tarfile extraction
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(downstream)
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Add and test RHEL-specific ways of configuring the default behavior: environment
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variable and config file.
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---
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Lib/tarfile.py | 42 +++++++++++++
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Lib/test/test_shutil.py | 3 +-
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Lib/test/test_tarfile.py | 128 ++++++++++++++++++++++++++++++++++++++-
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3 files changed, 169 insertions(+), 4 deletions(-)
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diff --git a/Lib/tarfile.py b/Lib/tarfile.py
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index 130b5e0..3b7d8d5 100755
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--- a/Lib/tarfile.py
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+++ b/Lib/tarfile.py
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@@ -72,6 +72,13 @@ __all__ = ["TarFile", "TarInfo", "is_tarfile", "TarError", "ReadError",
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"ENCODING", "USTAR_FORMAT", "GNU_FORMAT", "PAX_FORMAT",
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"DEFAULT_FORMAT", "open"]
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+# If true, use the safer (but backwards-incompatible) 'tar' extraction filter,
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+# rather than 'fully_trusted', by default.
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+# The emitted warning is changed to match.
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+_RH_SAFER_DEFAULT = True
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+
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+# System-wide configuration file
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+_CONFIG_FILENAME = '/etc/python/tarfile.cfg'
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#---------------------------------------------------------
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# tar constants
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@@ -2211,6 +2218,41 @@ class TarFile(object):
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if filter is None:
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filter = self.extraction_filter
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if filter is None:
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+ name = os.environ.get('PYTHON_TARFILE_EXTRACTION_FILTER')
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+ if name is None:
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+ try:
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+ file = bltn_open(_CONFIG_FILENAME)
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+ except FileNotFoundError:
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+ pass
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+ else:
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+ import configparser
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+ conf = configparser.ConfigParser(
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+ interpolation=None,
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+ comment_prefixes=('#', ),
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+ )
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+ with file:
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+ conf.read_file(file)
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+ name = conf.get('tarfile',
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+ 'PYTHON_TARFILE_EXTRACTION_FILTER',
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+ fallback='')
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+ if name:
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+ try:
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+ filter = _NAMED_FILTERS[name]
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+ except KeyError:
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+ raise ValueError(f"filter {filter!r} not found") from None
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+ self.extraction_filter = filter
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+ return filter
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+ if _RH_SAFER_DEFAULT:
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+ warnings.warn(
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+ 'The default behavior of tarfile extraction has been '
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+ + 'changed to disallow common exploits '
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+ + '(including CVE-2007-4559). '
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+ + 'By default, absolute/parent paths are disallowed '
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+ + 'and some mode bits are cleared. '
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+ + 'See https://access.redhat.com/articles/7004769 '
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+ + 'for more details.',
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+ RuntimeWarning)
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+ return tar_filter
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return fully_trusted_filter
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if isinstance(filter, str):
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raise TypeError(
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diff --git a/Lib/test/test_shutil.py b/Lib/test/test_shutil.py
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index 9bf4145..f247b82 100644
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--- a/Lib/test/test_shutil.py
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+++ b/Lib/test/test_shutil.py
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@@ -1665,7 +1665,8 @@ class TestArchives(BaseTest, unittest.TestCase):
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def check_unpack_tarball(self, format):
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self.check_unpack_archive(format, filter='fully_trusted')
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self.check_unpack_archive(format, filter='data')
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- with warnings_helper.check_no_warnings(self):
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+ with warnings_helper.check_warnings(
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+ ('.*CVE-2007-4559', RuntimeWarning)):
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self.check_unpack_archive(format)
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def test_unpack_archive_tar(self):
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diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
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index cdea033..4724285 100644
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--- a/Lib/test/test_tarfile.py
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+++ b/Lib/test/test_tarfile.py
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@@ -2,7 +2,7 @@ import sys
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import os
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import io
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from hashlib import sha256
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-from contextlib import contextmanager
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+from contextlib import contextmanager, ExitStack
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from random import Random
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import pathlib
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import shutil
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@@ -2999,7 +2999,11 @@ class NoneInfoExtractTests(ReadTest):
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tar = tarfile.open(tarname, mode='r', encoding="iso8859-1")
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cls.control_dir = pathlib.Path(TEMPDIR) / "extractall_ctrl"
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tar.errorlevel = 0
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- tar.extractall(cls.control_dir, filter=cls.extraction_filter)
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+ with ExitStack() as cm:
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+ if cls.extraction_filter is None:
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+ cm.enter_context(warnings.catch_warnings())
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+ warnings.simplefilter(action="ignore", category=RuntimeWarning)
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+ tar.extractall(cls.control_dir, filter=cls.extraction_filter)
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tar.close()
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cls.control_paths = set(
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p.relative_to(cls.control_dir)
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@@ -3674,7 +3678,8 @@ class TestExtractionFilters(unittest.TestCase):
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"""Ensure the default filter does not warn (like in 3.12)"""
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with ArchiveMaker() as arc:
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arc.add('foo')
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- with warnings_helper.check_no_warnings(self):
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+ with warnings_helper.check_warnings(
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+ ('.*CVE-2007-4559', RuntimeWarning)):
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with self.check_context(arc.open(), None):
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self.expect_file('foo')
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@@ -3844,6 +3849,123 @@ class TestExtractionFilters(unittest.TestCase):
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self.expect_exception(TypeError) # errorlevel is not int
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+ @contextmanager
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+ def rh_config_context(self, config_lines=None):
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+ """Set up for testing various ways of overriding the default filter
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+
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+ return a triple with:
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+ - temporary directory
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+ - EnvironmentVarGuard()
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+ - a test archive for use with check_* methods below
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+
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+ If config_lines is given, write them to the config file. Otherwise
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+ the config file is missing.
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+ """
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+ tempdir = pathlib.Path(TEMPDIR) / 'tmp'
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+ configfile = tempdir / 'tarfile.cfg'
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+ with ArchiveMaker() as arc:
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+ arc.add('good')
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+ arc.add('ugly', symlink_to='/etc/passwd')
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+ arc.add('../bad')
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+ with (
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+ os_helper.temp_dir(tempdir),
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+ support.swap_attr(tarfile, '_CONFIG_FILENAME', str(configfile)),
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+ os_helper.EnvironmentVarGuard() as env,
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+ arc.open() as tar,
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+ ):
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+ if config_lines is not None:
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+ with configfile.open('w') as f:
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+ for line in config_lines:
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+ print(line, file=f)
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+ yield tempdir, env, tar
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+
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+ def check_rh_default_behavior(self, tar, tempdir):
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+ """Check RH default: warn and refuse to extract dangerous files."""
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+ with (
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+ warnings_helper.check_warnings(
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+ ('.*CVE-2007-4559', RuntimeWarning)),
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+ self.assertRaises(tarfile.OutsideDestinationError),
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+ ):
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+ tar.extractall(tempdir / 'outdir')
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+
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+ def check_trusted_default(self, tar, tempdir):
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+ """Check 'fully_trusted' is configured as the default filter."""
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+ with (
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+ warnings_helper.check_no_warnings(self),
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+ ):
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+ tar.extractall(tempdir / 'outdir')
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+ self.assertTrue((tempdir / 'outdir/good').exists())
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+ self.assertEqual((tempdir / 'outdir/ugly').readlink(),
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+ pathlib.Path('/etc/passwd'))
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+ self.assertTrue((tempdir / 'bad').exists())
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+
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+ def test_rh_default_no_conf(self):
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+ with self.rh_config_context() as (tempdir, env, tar):
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+ self.check_rh_default_behavior(tar, tempdir)
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+
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+ def test_rh_default_from_file(self):
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+ lines = ['[tarfile]', 'PYTHON_TARFILE_EXTRACTION_FILTER=fully_trusted']
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+ with self.rh_config_context(lines) as (tempdir, env, tar):
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+ self.check_trusted_default(tar, tempdir)
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+
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+ def test_rh_empty_config_file(self):
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+ """Empty config file -> default behavior"""
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+ lines = []
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+ with self.rh_config_context(lines) as (tempdir, env, tar):
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+ self.check_rh_default_behavior(tar, tempdir)
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+
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+ def test_empty_config_section(self):
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+ """Empty section in config file -> default behavior"""
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+ lines = ['[tarfile]']
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+ with self.rh_config_context(lines) as (tempdir, env, tar):
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+ self.check_rh_default_behavior(tar, tempdir)
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+
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+ def test_rh_default_empty_config_option(self):
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+ """Empty option value in config file -> default behavior"""
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+ lines = ['[tarfile]', 'PYTHON_TARFILE_EXTRACTION_FILTER=']
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+ with self.rh_config_context(lines) as (tempdir, env, tar):
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+ self.check_rh_default_behavior(tar, tempdir)
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+
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+ def test_bad_config_option(self):
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+ """Bad option value in config file -> ValueError"""
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+ lines = ['[tarfile]', 'PYTHON_TARFILE_EXTRACTION_FILTER=unknown!']
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+ with self.rh_config_context(lines) as (tempdir, env, tar):
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+ with self.assertRaises(ValueError):
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+ tar.extractall(tempdir / 'outdir')
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+
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+ def test_default_from_envvar(self):
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+ with self.rh_config_context() as (tempdir, env, tar):
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+ env['PYTHON_TARFILE_EXTRACTION_FILTER'] = 'fully_trusted'
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+ self.check_trusted_default(tar, tempdir)
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+
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+ def test_empty_envvar(self):
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+ """Empty env variable -> default behavior"""
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+ with self.rh_config_context() as (tempdir, env, tar):
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+ env['PYTHON_TARFILE_EXTRACTION_FILTER'] = ''
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+ self.check_rh_default_behavior(tar, tempdir)
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+
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+ def test_bad_envvar(self):
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+ with self.rh_config_context() as (tempdir, env, tar):
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+ env['PYTHON_TARFILE_EXTRACTION_FILTER'] = 'unknown!'
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+ with self.assertRaises(ValueError):
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+ tar.extractall(tempdir / 'outdir')
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+
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+ def test_envvar_overrides_file(self):
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+ lines = ['[tarfile]', 'PYTHON_TARFILE_EXTRACTION_FILTER=data']
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+ with self.rh_config_context(lines) as (tempdir, env, tar):
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+ env['PYTHON_TARFILE_EXTRACTION_FILTER'] = 'fully_trusted'
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+ self.check_trusted_default(tar, tempdir)
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+
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+ def test_monkeypatch_overrides_envvar(self):
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+ with self.rh_config_context(None) as (tempdir, env, tar):
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+ env['PYTHON_TARFILE_EXTRACTION_FILTER'] = 'data'
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+ with support.swap_attr(
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+ tarfile.TarFile, 'extraction_filter',
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+ staticmethod(tarfile.fully_trusted_filter)
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+ ):
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+ self.check_trusted_default(tar, tempdir)
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+
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+
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def setUpModule():
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os_helper.unlink(TEMPDIR)
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os.makedirs(TEMPDIR)
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--
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2.41.0
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