Gentoo Linux Security Advisory GLSA 200404-01
Severity: Normal
Title: Insecure sandbox temporary lockfile vulnerabilities in
Portage
Date: April 04, 2004
Bugs: #21923
ID: 200404-01
Synopsis
A flaw has been found in the temporary file handling algorithms
for the sandboxing code used within Portage. Lockfiles created
during normal Portage operation of portage could be manipulated by
local users resulting in the truncation of hard linked files;
causing a Denial of Service attack on the system.
Background
Portage is Gentoo’s package management system which is
responsible for installing, compiling and updating any ebuilds on
the system through the Gentoo rsync tree. Under default
configurations, most ebuilds run under a sandbox which prevent the
build process writing to the “real” system outside the build
directory – packages are installed into a temporary location and
then copied over safely by Portage instead. During the process the
sandbox wrapper creates lockfiles in the /tmp directory which are
vulnerable to a hard-link attack.
Affected packages
| Package | Vulnerable | Unaffected |
| sys-apps/portage | < 2.0.50-r3 | >= 2.0.50-r3 |
Description
A flaw in Portage’s sandbox wrapper has been found where the
temporary lockfiles are subject to a hard-link attack which allows
linkable files to be overwritten to an empty file. This can be used
to damage critical files on a system causing a Denial of Service,
or alternatively this attack may be used to cause other security
risks; for example firewall configuration data could be overwritten
without notice.
The vulnerable sandbox functions have been patched to test for
these new conditions: namely; for the existance of a hard-link
which would be removed before the sandbox process would continue,
for the existance of a world-writable lockfile in which case the
sandbox would also remove it, and also for any mismatches in the
UID ( anything but root ) and the GID ( anything but the group of
the sandbox process ).
If the vulnerable files cannot be removed by the sandbox, then
the sandbox would exit with a fatal error warning the adminstrator
of the issue. The patched functions also fix any other sandbox I/O
operations which do not explicitly include the mentioned
lockfile.
Impact
Any user with write access to the /tmp directory can hard-link a
file to /tmp/sandboxpids.tmp – this file would eventually be
replaced with an empty one; effectively wiping out the file it was
linked to as well with no prior warning. This could be used to
potentially disable a vital component of the system and cause a
path for other possible exploits.
This vulnerability only affects systems that have /tmp on the
root partition: since symbolic link attacks are filtered, /tmp has
to be on the same partition for an attack to take place.
Workaround
A workaround is not currently known for this issue. All users
are advised to upgrade to the latest version of Portage.
Resolution
Users should upgrade to Portage 2.0.50-r3 or later:
# emerge sync
# emerge -pv ">=sys-apps/portage-2.0.50-r3"
# emerge ">=sys-apps/portage-2.0.50-r3"
Concerns?
Security is a primary focus of Gentoo Linux and ensuring the
confidentiality and security of our users machines is of utmost
importance to us. Any security concerns should be addressed to
security@gentoo.org or
alternatively, you may file a bug at http://bugs.gentoo.org.