(RHSA-2015:1507) Important: qemu-kvm security and bug fix update

KVM (Kernel-based Virtual Machine) is a full virtualization solution for
Linux on AMD64 and Intel 64 systems. The qemu-kvm package provides the
user-space component for running virtual machines using KVM.

A heap buffer overflow flaw was found in the way QEMU’s IDE subsystem
handled I/O buffer access while processing certain ATAPI commands.
A privileged guest user in a guest with the CDROM drive enabled could
potentially use this flaw to execute arbitrary code on the host with the
privileges of the host’s QEMU process corresponding to the guest.
(CVE-2015-5154)

An out-of-bounds memory access flaw, leading to memory corruption or
possibly an information leak, was found in QEMU’s pit_ioport_read()
function. A privileged guest user in a QEMU guest, which had QEMU PIT
emulation enabled, could potentially, in rare cases, use this flaw to
execute arbitrary code on the host with the privileges of the hosting QEMU
process. (CVE-2015-3214)

Red Hat would like to thank Matt Tait of Google’s Project Zero security
team for reporting the CVE-2015-3214 issue. The CVE-2015-5154 issue was
discovered by Kevin Wolf of Red Hat.

This update also fixes the following bug:

• Due to an incorrect implementation of portable memory barriers, the QEMU
  emulator in some cases terminated unexpectedly when a virtual disk was
  under heavy I/O load. This update fixes the implementation in order to
  achieve correct synchronization between QEMU’s threads. As a result, the
  described crash no longer occurs. (BZ#1233643)

All qemu-kvm users are advised to upgrade to these updated packages, which
contain backported patches to correct these issues. After installing this
update, shut down all running virtual machines. Once all virtual machines
have shut down, start them again for this update to take effect.