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CVE-2007-4559 python: ensure sanity in our tarfiles

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Python's tarfile module is not very careful about paths that step out
of the target directory. We can be a bit better at little cost.

This was reported in 2007[1], and has recently been publicised [2, for
example].

We were informed of this bug in December 2021 by Luis Alberto López
Alvar, but decided then that there were no circumstances under which
this was a security concern. That is, if you can alter the backup
files, you can already do worse things. But there is a case to guard
against an administrator being tricked into trying to restore a file
that isn't based on a real backup.

[1] https://nvd.nist.gov/vuln/detail/CVE-2007-4559
[2] https://www.theregister.com/2022/09/22/python_vulnerability_tarfile/

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15185

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Tue Oct  4 03:48:43 UTC 2022 on sn-devel-184
This commit is contained in:
Douglas Bagnall
2022-09-23 12:32:25 +12:00
committed by Andrew Bartlett
parent 6a5d03e2f7
commit 37406b9d97
7 changed files with 117 additions and 4 deletions
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43
python/samba/safe_tarfile.py Normal file
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# Unix SMB/CIFS implementation.
# Copyright (C) Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
from tarfile import ExtractError, TarInfo, TarFile as UnsafeTarFile
class TarFile(UnsafeTarFile):
"""This TarFile implementation is trying to ameliorate CVE-2007-4559,
where tarfile.TarFiles can step outside of the target directory
using '../../'.
"""
def extract(self, member, path="", set_attrs=True, *, numeric_owner=False):
if isinstance(member, TarInfo):
name = member.name
else:
name = member
if '../' in name:
raise ExtractError(f"'../' is not allowed in path '{name}'")
if name.startswith('/'):
raise ExtractError(f"path '{name}' should not start with '/'")
super().extract(member, path, set_attrs=set_attrs,
numeric_owner=numeric_owner)
open = TarFile.open