The kernel packages contain the Linux kernel, the core of any Linux operating system.
A race condition was found in the way asynchronous I/O and fallocate() interacted when using the ext4 file system. A local, unprivileged user could use this flaw to expose random data from an extent whose data blocks have not yet been written, and thus contain data from a deleted file. (CVE-2012-4508, Important)
An information leak flaw was found in the way Linux kernel's device mapper subsystem, under certain conditions, interpreted data written to snapshot block devices. An attacker could use this flaw to read data from disk blocks in free space, which are normally inaccessible. (CVE-2013-4299, Moderate)
Red Hat would like to thank Theodore Ts'o for reporting CVE-2012-4508, and Fujitsu for reporting CVE-2013-4299. Upstream acknowledges Dmitry Monakhov as the original reporter of CVE-2012-4508.
This update also fixes the following bugs:
When the Audit subsystem was under heavy load, it could loop infinitely in the audit_log_start() function instead of failing over to the error recovery code. This would cause soft lockups in the kernel. With this update, the timeout condition in the audit_log_start() function has been modified to properly fail over when necessary. (BZ#1017898)
When handling Memory Type Range Registers (MTRRs), the stop_one_cpu_nowait() function could potentially be executed in parallel with the stop_machine() function, which resulted in a deadlock. The MTRR handling logic now uses the stop_machine() function and makes use of mutual exclusion to avoid the aforementioned deadlock. (BZ#1017902)
Power-limit notification interrupts were enabled by default. This could lead to degradation of system performance or even render the system unusable on certain platforms, such as Dell PowerEdge servers. Power-limit notification interrupts have been disabled by default and a new kernel command line parameter "int_pln_enable" has been added to allow users to observe these events using the existing system counters. Power-limit notification messages are also no longer displayed on the console. The affected platforms no longer suffer from degraded system performance due to this problem. (BZ#1020519)
Package level thermal and power limit events are not defined as MCE errors for the x86 architecture. However, the mcelog utility erroneously reported these events as MCE errors with the following message:
kernel: [Hardware Error]: Machine check events logged
Package level thermal and power limit events are no longer reported as MCE errors by mcelog. When these events are triggered, they are now reported only in the respective counters in sysfs (specifically, /sys/devices/system/cpu/cpu<number>/thermal_throttle/). (BZ#1021950)
All kernel users are advised to upgrade to these updated packages, which contain backported patches to correct these issues. The system must be rebooted for this update to take effect.