RHSA-2016:0212 - Security Advisory

Topic

Updated kernel-rt packages that fix two security issues, several bugs, and
add various enhancements are now available for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having Important security
impact. Common Vulnerability Scoring System (CVSS) base scores, which give
detailed severity ratings, are available for each vulnerability from the
CVE links in the References section.

Description

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.

Solution

Before applying this update, make sure all previously released errata
relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258

Affected Products

• Red Hat Enterprise Linux for Real Time 7 x86_64
• Red Hat Enterprise Linux for Real Time for x86_64 - Extended Life Cycle Support 7 x86_64

Fixes

• BZ - 1259577 - CVE-2015-5157 kernel: x86-64: IRET faults during NMIs processing
• BZ - 1272371 - CVE-2015-7872 kernel: Keyrings crash triggerable by unprivileged user
• BZ - 1282591 - kernel-rt: update to the RHEL7.2.z batch 2 source tree
• BZ - 1293229 - RCU stalls message on realtime kernel
• BZ - 1293230 - rt: netpoll: live lock with NAPI polling and busy polling on realtime kernel

CVEs

• CVE-2015-5157
• CVE-2015-7872

References

• http://www.redhat.com/security/updates/classification/#normal