(RHSA-2012:1233) Important: qemu-kvm-rhev 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-rhev packages form the
user-space component for running virtual machines using KVM.

A flaw was found in the way QEMU handled VT100 terminal escape sequences
when emulating certain character devices. A guest user with privileges to
write to a character device that is emulated on the host using a virtual
console back-end could use this flaw to crash the qemu-kvm process on the
host or, possibly, escalate their privileges on the host. (CVE-2012-3515)

When using qemu-kvm-rhev on a Red Hat Enterprise Linux 6 host not managed
by Red Hat Enterprise Virtualization:

• This flaw did not affect the default use of KVM. Affected configurations
  were:

• When guests were started from the command line (“/usr/libexec/qemu-kvm”)
  without the “-nodefaults” option, and also without specifying a
  serial or parallel device, or a virtio-console device, that specifically
  does not use a virtual console (vc) back-end. (Note that Red Hat does not
  support invoking “qemu-kvm” from the command line without “-nodefaults” on
  Red Hat Enterprise Linux 6.)

• Guests that were managed via libvirt, such as when using Virtual Machine
  Manager (virt-manager), but that have a serial or parallel device, or a
  virtio-console device, that uses a virtual console back-end. By default,
  guests managed via libvirt will not use a virtual console back-end for such
  devices.

When using qemu-kvm-rhev on a Red Hat Enterprise Virtualization managed Red
Hat Enterprise Linux 6 host:

• This flaw did not affect the default use of a Red Hat Enterprise
  Virtualization host: it is not possible to add a device that uses a virtual
  console back-end via Red Hat Enterprise Virtualization Manager.

To specify a virtual console back-end for a device and therefore be
vulnerable to this issue, the device would have to be created another way,
for example, by using a VDSM hook.

Red Hat would like to thank the Xen project for reporting this issue.

This update also fixes the following bugs:

• Previously, the KVM modules were not loaded by the postinstall scriptlet
  of RPM scripts. This bug caused various issues and required the system to
  be rebooted to resolve them. With this update, the modules are loaded
  properly by the scriptlet and no unnecessary reboots are now required.
  (BZ#839897)

• Previously, when a guest was started up with two serial devices, qemu-kvm
  returned an error message and terminated the boot because IRQ 4 for the ISA
  bus was being used by both devices. This update fixes the qemu-kvm code,
  which allows IRQ 4 to be used by more than one device on the ISA bus, and
  the boot now succeeds in the described scenario. (BZ#840054)

All users of qemu-kvm-rhev are advised to upgrade to these updated
packages, which fix 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.