Synopsis: Important: kernel security and bug fix update
Advisory ID: SLSA-2016:0185-1
Issue Date: 2016-02-16
CVE Numbers: CVE-2015-7872
* 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
* 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.
* 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.
* 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.
* 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.
* 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.
* 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
* 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.
* 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.
The system must be rebooted for this update to take effect.
– Scientific Linux Development Team