(RHSA-2013:1519) Important: kernel security and bug fix update

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)

• An insufficiently designed calculation in the CPU accelerator could cause
  an arithmetic overflow in the set_cyc2ns_scale() function if the system
  uptime exceeded 208 days prior to using kexec to boot into a new kernel.
  This overflow led to a kernel panic on systems using the Time Stamp Counter
  (TSC) clock source, primarily systems using Intel Xeon E5 processors that
  do not reset TSC on soft power cycles. A patch has been applied to modify
  the calculation so that this arithmetic overflow and kernel panic can no
  longer occur under these circumstances. (BZ#1024453)

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.