(RHSA-2011:1401) Moderate: xen security and bug fix update

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

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.
(CVE-2011-3346)

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.