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. 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. 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 , 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. * a memory leak in the libvirt driver for the Xen hypervisor has been fixed with this update. * 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 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. 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.