kernel, perf, python security update

CentOS Errata and Security Advisory CESA-2011:1849

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)

Merged security bulletin from advisories:
https://lists.centos.org/pipermail/centos-announce/2011-December/080520.html

Affected packages:
kernel
kernel-debug
kernel-debug-devel
kernel-devel
kernel-doc
kernel-firmware
kernel-headers
perf
python-perf

Upstream details at:
https://access.redhat.com/errata/RHSA-2011:1849