(RHSA-2016:0212) Important: kernel-rt security, bug fix, and enhancement update

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

• It was found that the Linux kernel’s keys subsystem did not correctly
  garbage collect uninstantiated keyrings. A local attacker could use this
  flaw to crash the system or, potentially, escalate their privileges on the
  system. (CVE-2015-7872, Important)

• A flaw was found in the way the Linux kernel handled IRET faults during
  the processing of NMIs. An unprivileged, local user could use this flaw to
  crash the system or, potentially (although highly unlikely), escalate their
  privileges on the system. (CVE-2015-5157, Moderate)

The kernel-rt packages have been upgraded to version 3.10.0-327.10.1, which
provides a number of bug fixes and enhancements, including:

• [md] dm: fix AB-BA deadlock in __dm_destroy()

• [md] revert "dm-mpath: fix stalls when handling invalid ioctl

• [cpufreq] intel_pstate: Fix limits->max_perf and limits->max_policy_pct
  rounding errors

• [cpufreq] revert “intel_pstate: fix rounding error in max_freq_pct”

• [crypto] nx: 842 - Add CRC and validation support

• [of] return NUMA_NO_NODE from fallback of_node_to_nid()

(BZ#1282591)

This update also fixes the following bugs:

• Because the realtime kernel replaces most of the spinlocks with
  rtmutexes, the locking scheme used in both NAPI polling and busy polling
  could become out of synchronization with the State Machine they protected.
  This could cause system performance degradation or even a livelock
  situation when a machine with faster NICs (10g or 40g) was subject to a
  heavy pressure receiving network packets. The locking schemes on NAPI
  polling and busy polling routines have been hardened to enforce the State
  machine sanity to help ensure the system continues to function properly
  under pressure. (BZ#1293230)

• A possible livelock in the NAPI polling and busy polling routines could
  lead the system to a livelock on threads running at high, realtime,
  priorities. The threads running at priorities lower than the ones of the
  threads involved in the livelock were prevented from running on the CPUs
  affected by the livelock. Among those lower priority threads are the rcuc/
  threads. With this update, right before (4 jiffies) a RCU stall is
  detected, the rcuc/ threads on the CPUs facing the livelock have their
  priorities boosted above the priority of the threads involved in the
  livelock. The softirq code has also been updated to be more robust.
  These modifications allow the rcuc/ threads to execute even under system
  pressure, mitigating the RCU stalls. (BZ#1293229)

• Multiple CPUs trying to take an rq lock previously caused large latencies
  on machines with many CPUs. On systems with more than 32 cores, this update
  uses the “push” rather than “pull” approach and provides multiple changes
  to the scheduling of rq locks. As a result, machines no longer suffer from
  multiplied latencies on large CPU systems. (BZ#1282597)

• Previously, the SFC driver for 10 GB cards executed polling in NAPI mode,
  using a locking mechanism similar to a “trylock”. Consequently, when
  running on a Realtime kernel, a livelock could occur. This update modifies
  the locking mechanism so that once the lock is taken it is not released
  until the operation is complete. (BZ#1282609)

All kernel-rt users are advised to upgrade to these updated packages, which
correct these issues and add these enhancements. The system must be
rebooted for this update to take effect.