RHSA-2016:0224 - 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 MRG 2.5.

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)

This update provides a build of the kernel-rt package for Red Hat
Enterprise MRG 2.5 that is layered on Red Hat Enterprise Linux 6, and
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#1277670)

The HP Smart Array (hpsa) SCSI driver has been updated to the latest
version included in a Red Hat release. (BZ#1224096)

This update also fixes the following bugs:

• A heavy load of incoming packets on a fast networking driver (like the

i40e) will both stress the softirq mechanism on the realtime kernel (as
described in BZ#1293229) and exercise the possible livelock in the netpoll
NAPI/busy polling routines (as described in BZ#1293230). The fixes applied
to both BZ#1293229 and BZ#1293230 will address these issues by hardening
the locking mechanism for the netpoll NAPI/busy polling and by enhancing
the way softirqs are serviced. These fixes also create a failsafe to
avoiding RCU stalls on a heavily loaded system and allows the networking
driver to work as expected. (BZ#1200766)

• The nohz_full code in older versions of the MRG-Realtime kernels was

incomplete and known to be problematic due to the way the old
implementation interacted with the real time features in the kernel.
The nohz_full kernel code has been updated enabling this feature to
function as expected and allowing this feature to be enabled in the
realtime kernel. (BZ#1278511)

• 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 were hardened to enforce the State
machine sanity to help ensure the system continues to function properly
under pressure. (BZ#1295884)

• 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 would be prevented from running on the
CPUs affected by the livelock. Among those lower priority threads are the
rcuc/ threads. 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 was
also updated to be more robust. These modifications allowed the rcuc/
threads to execute even under system pressure, mitigating the RCU stalls.
(BZ#1295885)

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

• MRG Realtime 2 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 - 1277670 - update the MRG 2.5.x 3.10 kernel-rt sources
• BZ - 1278511 - nohz_full still not working even with nohz=on

CVEs

• CVE-2015-7872
• CVE-2015-5157

References

• https://access.redhat.com/security/updates/classification/#important