Red Hat Enterprise Linux 6: RHSA-2012:0052-01 Critical Local Escalation

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.