Synopsis

Important: kernel security and bug fix update

Type/Severity

Security Advisory: Important

Topic

Updated kernel packages that fix one security issue and various bugs are
now available for Red Hat Enterprise Linux 6.

The Red Hat Security Response Team has rated this update as having
important security impact. A Common Vulnerability Scoring System (CVSS)
base score, which gives a detailed severity rating, is available from the
CVE link in the References section.

Description

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

Security fix:

• Using the SG_IO IOCTL to issue SCSI requests to partitions or LVM volumes

resulted in the requests being passed to the underlying block device. If a
privileged user only had access to a single partition or LVM volume, they
could use this flaw to bypass those restrictions and gain read and write
access (and be able to issue other SCSI commands) to the entire block
device.

In KVM (Kernel-based Virtual Machine) environments using raw format virtio
disks backed by a partition or LVM volume, a privileged guest user could
bypass intended restrictions and issue read and write requests (and other
SCSI commands) on the host, and possibly access the data of other guests
that reside on the same underlying block device. Partition-based and
LVM-based storage pools are not used by default. Refer to Red Hat Bugzilla
bug 752375 for further details and a mitigation script for users who cannot
apply this update immediately. (CVE-2011-4127, Important)

Bug fixes:

• Previously, idle load balancer kick requests from other CPUs could be

serviced without first receiving an inter-processor interrupt (IPI). This
could have led to a deadlock. (BZ#750459)

• This update fixes a performance regression that may have caused processes

(including KVM guests) to hang for a number of seconds. (BZ#751403)

• When md_raid1_unplug_device() was called while holding a spinlock, under

certain device failure conditions, it was possible for the lock to be
requested again, deeper in the call chain, causing a deadlock. Now,
md_raid1_unplug_device() is no longer called while holding a spinlock.
(BZ#755545)

• In hpet_next_event(), an interrupt could have occurred between the read

and write of the HPET (High Performance Event Timer) and the value of
HPET_COUNTER was then beyond that being written to the comparator
(HPET_Tn_CMP). Consequently, the timers were overdue for up to several
minutes. Now, a comparison is performed between the value of the counter
and the comparator in the HPET code. If the counter is beyond the
comparator, the "-ETIME" error code is returned. (BZ#756426)

• Index allocation in the virtio-blk module was based on a monotonically

increasing variable "index". Consequently, released indexes were not reused
and after a period of time, no new were available. Now, virtio-blk uses the
ida API to allocate indexes. (BZ#756427)

• A bug related to Context Caching existed in the Intel IOMMU support

module. On some newer Intel systems, the Context Cache mode has changed
from previous hardware versions, potentially exposing a Context coherency
race. The bug was exposed when performing a series of hot plug and unplug
operations of a Virtual Function network device which was immediately
configured into the network stack, i.e., successfully performed dynamic
host configuration protocol (DHCP). When the coherency race occurred, the
assigned device would not work properly in the guest virtual machine. With
this update, the Context coherency is corrected and the race and
potentially resulting device assignment failure no longer occurs.
(BZ#757671)

• The align_va_addr kernel parameter was ignored if secondary CPUs were

initialized. This happened because the parameter settings were overridden
during the initialization of secondary CPUs. Also, the align_va_addr
parameter documentation contained incorrect parameter arguments. With this
update, the underlying code has been modified to prevent the overriding and
the documentation has been updated. This update also removes the unused
code introduced by the patch for BZ#739456. (BZ#758028)

• Dell systems based on a future Intel processor with graphics acceleration

required the selection of the install system with basic video driver
installation option. This update removes this requirement. (BZ#758513)

Solution

Users should upgrade to these updated packages, which contain
backported patches to resolve these issues. The system must be
rebooted for this update to take effect.

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

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
https://access.redhat.com/kb/docs/DOC-11259

To install kernel packages manually, use "rpm -ivh [package]". Do not
use "rpm -Uvh" as that will remove the running kernel binaries from
your system. You may use "rpm -e" to remove old kernels after
determining that the new kernel functions properly on your system.

Affected Products

• Red Hat Enterprise Linux Server 6 x86_64
• Red Hat Enterprise Linux Server 6 i386
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.2 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.2 i386
• Red Hat Enterprise Linux Workstation 6 x86_64
• Red Hat Enterprise Linux Workstation 6 i386
• Red Hat Enterprise Linux Desktop 6 x86_64
• Red Hat Enterprise Linux Desktop 6 i386
• Red Hat Enterprise Linux for IBM z Systems 6 s390x
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 6.2 s390x
• Red Hat Enterprise Linux for Power, big endian 6 ppc64
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 6.2 ppc64
• Red Hat Enterprise Linux for Scientific Computing 6 x86_64
• Red Hat Enterprise Linux Server from RHUI 6 x86_64
• Red Hat Enterprise Linux Server from RHUI 6 i386
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.2 x86_64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.2 i386
• Red Hat Storage 2.0 x86_64
• Red Hat Gluster Storage Server for On-premise 2.0 x86_64
• Red Hat Storage for Public Cloud (via RHUI) 2.0 x86_64
• Red Hat Enterprise Linux Server - AUS 6.2 x86_64
• Red Hat Enterprise Linux Server - Extended Life Cycle Support 6 x86_64
• Red Hat Enterprise Linux Server - Extended Life Cycle Support 6 i386
• Red Hat Enterprise Linux Server - Extended Life Cycle Support (for IBM z Systems) 6 s390x

Fixes

• BZ - 752375 - CVE-2011-4127 kernel: possible privilege escalation via SG_IO ioctl

CVEs

• CVE-2011-4127
• CVE-2011-4621

References