[arch-security] [ASA-201601-20] linux: privilege escalation

[Levente Polyak]

Arch Linux Security Advisory ASA-201601-20
==========================================

Severity: Critical
Date    : 2016-01-20
CVE-ID  : CVE-2016-0728
Package : linux
Type    : privilege escalation
Remote  : No
Link    : https://wiki.archlinux.org/index.php/CVE

Summary
=======

The package linux before version 4.3.3-3 is vulnerable to local
privilege escalation.

Resolution
==========

Upgrade to 4.3.3-3.

# pacman -Syu "linux>=4.3.3-3"

The problem has been fixed upstream but no release is available yet.

Workaround
==========

None.

Description
===========

It was reported that possible use-after-free vulnerability in keyring
facility, possibly leading to local privilege escalation, was found.
Function join_session_keyring in security/keys/process_keys.c holds a
reference to the requested keyring, but if that keyring is the same as
the one being currently used by the process, the kernel wouldn't
decrease keyring->usage before returning to userspace. The usage field
can be possibly overflowed causing use-after-free on the keyring object.

Impact
======

A local attacker is able to make use of this vulnerability to elevate
privileges and gain root access to the underlying system.

References
==========

https://access.redhat.com/security/cve/CVE-2016-0728
http://perception-point.io/2016/01/14/analysis-and-exploitation-of-a-linux-kernel-vulnerability-cve-2016-0728/
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=23567fd0
https://bugs.archlinux.org/task/47820

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