7.2 - RHSA-2016:1532

Problem Description:

An update for kernel-rt is now available for Red Hat Enterprise MRG 2.5.

Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

2. Relevant releases/architectures:

MRG Realtime for RHEL 6 Server v.2 - noarch, x86_64

3. Description:

The kernel-rt packages provide the Real Time Linux Kernel, which enables fine-tuning for systems with extremely high determinism requirements.

* A flaw was found in the Linux kernel's keyring handling code, where in key_reject_and_link() an uninitialised variable would eventually lead to arbitrary free address which could allow attacker to use a use-after-free style attack. (CVE-2016-4470, Important)

* The ovl_setattr function in fs/overlayfs/inode.c in the Linux kernel through 4.3.3 attempts to merge distinct setattr operations, which allows local users to bypass intended access restrictions and modify the attributes of arbitrary overlay files via a crafted application. (CVE-2015-8660, Moderate)

Red Hat would like to thank Nathan Williams for reporting CVE-2015-8660. The CVE-2016-4470 issue was discovered by David Howells (Red Hat Inc.).

The kernel-rt packages have been upgraded to upstream version 3.10.0-327.rt56.194.el6rt, which provides a number of bug fixes over the previous version. (BZ#1343658)

This update also fixes the following bugs:

* Previously, use of the get/put_cpu_var() function in function refill_stock() from the memcontrol cgroup code lead to a "scheduling while atomic" warning. With this update, refill_stock() uses the get/put_cpu_light() function instead, and the warnings no longer appear. (BZ#1348710)

* Prior to this update, if a real time task pinned to a given CPU was taking 100% of the CPU time, then calls to the lru_add_drain_all() function on other CPUs blocked for an undetermined amount of time. This caused latencies and undesired side effects. With this update, lru_add_drain_all() has been changed to drain the LRU pagevecs of remote CPUs. (BZ#1348711)

4. Solution:

For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.

5. Bugs fixed (https://bugzilla.redhat.com/):

1291329 - CVE-2015-8660 kernel: Permission bypass on overlayfs during copy_up 1341716 - CVE-2016-4470 kernel: Uninitialized variable in request_key handling causes kernel crash in error handling path 1343658 - update the MRG 2.5.z 3.10 kernel-rt sources