RHSA-2012:1233 - Security Advisory

Topic

Updated qemu-kvm-rhev packages that fix one security issue and two 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

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.

Solution

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/knowledge/articles/11258

Affected Products

• Red Hat Virtualization 3 for RHEL 6 x86_64

Fixes

• BZ - 851252 - CVE-2012-3515 qemu: VT100 emulation vulnerability

CVEs

• CVE-2012-3515

References

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