xen (SL5)

Synopsis: Moderate: xen security and bug fix update
Issue Date: 2011-10-24
CVE Numbers: CVE-2011-3346

The xen packages contain administration tools and the xend service for
managing the kernel-xen kernel for virtualization on Red Hat Enterprise

A buffer overflow flaw was found in the Xen hypervisor SCSI subsystem
emulation. An unprivileged, local guest user could provide a large number
of bytes that are used to zero out a fixed-sized buffer via a SAI READ
CAPACITY SCSI command, overwriting memory and causing the guest to crash.

This update also fixes the following bugs:

* Prior to this update, the vif-bridge script used a maximum transmission
unit (MTU) of 1500 for a new Virtual Interface (VIF). As a result, the MTU
of the VIF could differ from that of the target bridge. This update fixes
the VIF hot-plug script so that the default MTU for new VIFs will match
that of the target Xen hypervisor bridge. In combination with a new enough
kernel (RHSA-2011:1386), this enables the use of jumbo frames in Xen
hypervisor guests. (BZ#738608)

* Prior to this update, the network-bridge script set the MTU of the bridge
to 1500. As a result, the MTU of the Xen hypervisor bridge could differ
from that of the physical interface. This update fixes the network script
so the MTU of the bridge can be set higher than 1500, thus also providing
support for jumbo frames. Now, the MTU of the Xen hypervisor bridge will
match that of the physical interface. (BZ#738610)

* Red Hat Enterprise Linux 5.6 introduced an optimized migration handling
that speeds up the migration of guests with large memory. However, the new
migration procedure can theoretically cause data corruption. While no cases
were observed in practice, with this update, the xend daemon properly waits
for correct device release before the guest is started on a destination
machine, thus fixing this bug. (BZ#743850)

Note: Before a guest is using a new enough kernel (RHSA-2011:1386), the MTU
of the VIF will drop back to 1500 (if it was set higher) after migration.

All xen users are advised to upgrade to these updated packages, which
contain backported patches to correct these issues. After installing the
updated packages, the xend service must be restarted for this update to
take effect.


– Scientific Linux Development Team