Important: kernel security and bug fix update

Updated kernel packages that fix one security issue and three bugs are now
available for for Red Hat Enterprise Linux 6.

The Red Hat Security Response Team has rated this update as having
important security impact. Common Vulnerability Scoring System (CVSS) base
scores, which give detailed severity ratings, are available for each
vulnerability from the CVE links in the References section.

The kernel packages contain the Linux kernel, the core of any Linux
operating system.

This update fixes the following security issue:

* It was found that permissions were not checked properly in the Linux
kernel when handling the /proc/[pid]/mem writing functionality. A local,
unprivileged user could use this flaw to escalate their privileges. Refer
to Red Hat Knowledgebase article DOC-69129, linked to in the References,
for further information. (CVE-2012-0056, Important)

Red Hat would like to thank Jüri Aedla for reporting this issue.

This update fixes the following bugs:

* The RHSA-2011:1849 kernel update introduced a bug in the Linux kernel
scheduler, causing a "WARNING: at kernel/sched.c:5915 thread_return"
message and a call trace to be logged. This message was harmless, and was
not due to any system malfunctions or adverse behavior. With this update,
the WARN_ON_ONCE() call in the scheduler that caused this harmless message
has been removed. (BZ#768288)

* The RHSA-2011:1530 kernel update introduced a regression in the way
the Linux kernel maps ELF headers for kernel modules into kernel memory.
If a third-party kernel module is compiled on a Red Hat Enterprise Linux
system with a kernel prior to RHSA-2011:1530, then loading that module on
a system with RHSA-2011:1530 kernel would result in corruption of one byte
in the memory reserved for the module. In some cases, this could prevent
the module from functioning correctly. (BZ#769595)

* On some SMP systems the tsc may erroneously be marked as unstable during
early system boot or while the system is under heavy load. A "Clocksource
tsc unstable" message was logged when this occurred. As a result the system
would switch to the slower access, but higher precision HPET clock.

The "tsc=reliable" kernel parameter is supposed to avoid this problem by
indicating that the system has a known good clock, however, the parameter
only affected run time checks. A fix has been put in to avoid the boot
time checks so that the TSC remains as the clock for the duration of
system runtime. (BZ#755867)

Users should upgrade to these updated packages, which contain backported
patches to correct these issues. The system must be rebooted for this
update to take effect.

Before applying this update, make sure all previously-released errata
relevant to your system have been applied.

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
https://access.redhat.com/kb/docs/DOC-11259

782642 - CVE-2012-0056 kernel: proc: /proc/<pid>/mem mem_write insufficient permission checking

https://www.redhat.com/security/data/cve/CVE-2012-0056.html
https://access.redhat.com/security/updates/classification/#important
https://access.redhat.com/kb/docs/DOC-69129