(RHSA-2010:0615) Low: libvirt security and bug fix update

The libvirt library is a C API for managing and interacting with the
virtualization capabilities of Linux and other operating systems. In
addition, libvirt provides tools for remotely managing virtualized systems.

It was found that libvirt did not set the user-defined backing store format
when creating a new image, possibly resulting in applications having to
probe the backing store to discover the format. A privileged guest user
could use this flaw to read arbitrary files on the host. (CVE-2010-2239)

It was found that libvirt created insecure iptables rules on the host when
a guest system was configured for IP masquerading, allowing the guest to
use privileged ports on the host when accessing network resources. A
privileged guest user could use this flaw to access network resources that
would otherwise not be accessible to the guest. (CVE-2010-2242)

Red Hat would like to thank Jeremy Nickurak for reporting the CVE-2010-2242
issue.

This update also fixes the following bugs:

• a Linux software bridge assumes the MAC address of the enslaved interface
  with the numerically lowest MAC address. When the bridge changes its MAC
  address, for a period of time it does not relay packets across network
  segments, resulting in a temporary network “blackout”. The bridge should
  thus avoid changing its MAC address in order not to disrupt network
  communications.

The Linux kernel assigns network TAP devices a random MAC address.
Occasionally, this random MAC address is lower than that of the physical
interface which is enslaved (for example, eth0 or eth1), which causes the
bridge to change its MAC address, thereby disrupting network communications
for a period of time.

With this update, libvirt now sets an explicit MAC address for all TAP
devices created using the configured MAC address from the XML, but with the
high bit set to 0xFE. The result is that TAP device MAC addresses are now
numerically greater than those for physical interfaces, and bridges should
no longer attempt to switch their MAC address to that of the TAP device,
thus avoiding potential spurious network disruptions. (BZ#617243)

• a memory leak in the libvirt driver for the Xen hypervisor has been fixed
  with this update. (BZ#619711)

• the xm and virsh management user interfaces for virtual guests can be
  called on the command line to list the number of active guests. However,
  under certain circumstances, running the “virsh list” command resulted in
  virsh not listing all of the virtual guests that were active (that is,
  running) at the time. This update incorporates a fix that matches the logic
  used for determining active guests with that of “xm list”, such that both
  commands should now list the same number of active virtual guests under all
  circumstances. (BZ#618200)

All users of libvirt are advised to upgrade to these updated packages,
which contain backported patches to correct these issues. After installing
the updated packages, the system must be rebooted for the update to take
effect.