Red Hat 7 RHSA-2016:0185 Important: Kernel Critical Security Update

The kernel 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)
This update also fixes the following bugs:
* Previously, processing packets with a lot of different IPv6 source addresses caused the kernel to return warnings concerning soft-lockups due to high lock contention and latency increase. With this update, lock contention is reduced by backing off concurrent waiting threads on the lock. As a result, the kernel no longer issues warnings in the described scenario. (BZ#1285370)
* Prior to this update, block device readahead was artificially limited. As a consequence, the read performance was poor, especially on RAID devices. Now, per-device readahead limits are used for each device instead of a global limit. As a result, read performance has improved, especially on RAID devices. (BZ#1287550)
* After injecting an EEH error, the host was previously not recovering and observing I/O hangs in HTX tool logs. This update makes sure that when one or both of EEH_STATE_MMIO_ACTIVE and EEH_STATE_MMIO_ENABLED flags is marked in the PE state, the PE's IO path is regarded as enabled as well. As a result, the host no longer hangs and recovers as expected. (BZ#1289101)
* The genwqe device driver was previously using the GFP_ATOMIC flag for allocating consecutive memory pages from the kernel's atomic memory pool, even in non-atomic situations. This could lead to allocation failures during memory pressure. With this update, the genwqe driver's memory allocations use the GFP_KERNEL flag, and the driver can allocate memory even during memory pressure situations. (BZ#1289450)
* The nx842 co-processor for IBM Power Systems could in some circumstances provide invalid data due to a data corruption bug during uncompression. With this update, all compression and uncompression calls to the nx842 co-processor contain a cyclic redundancy check (CRC) flag, which forces all compression and uncompression operations to check data integrity and prevents the co-processor from providing corrupted data. (BZ#1289451)
* A failed "updatepp" operation on the little-endian variant of IBM Power Systems could previously cause a wrong hash value to be used for the next hash insert operation in the page table. This could result in a missing hash pte update or invalidate operation, potentially causing memory corruption. With this update, the hash value is always recalculated after a failed "updatepp" operation, avoiding memory corruption. (BZ#1289452)
* Large Receive Offload (LRO) flag disabling was not being propagated downwards from above devices in vlan and bond hierarchy, breaking the flow of traffic. This problem has been fixed and LRO flags now propagate correctly. (BZ#1292072)
* Due to rounding errors in the CPU frequency of the intel_pstate driver, the CPU frequency never reached the value requested by the user. A kernel patch has been applied to fix these rounding errors. (BZ#1296276)
* When running several containers (up to 100), reports of hung tasks were previously reported. This update fixes the AB-BA deadlock in the dm_destroy() function, and the hung reports no longer occur. (BZ#1296566)
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.