(RHSA-2013:0896) Moderate: qemu-kvm security and bug fix update

ID RHSA-2013:0896
Type redhat
Reporter RedHat
Modified 2017-11-24T18:38:45


KVM (Kernel-based Virtual Machine) is a full virtualization solution for Linux on AMD64 and Intel 64 systems. qemu-kvm is the user-space component for running virtual machines using KVM.

It was found that QEMU Guest Agent (the "qemu-ga" service) created certain files with world-writable permissions when run in daemon mode (the default mode). An unprivileged guest user could use this flaw to consume all free space on the partition containing the qemu-ga log file, or modify the contents of the log. When a UNIX domain socket transport was explicitly configured to be used (not the default), an unprivileged guest user could potentially use this flaw to escalate their privileges in the guest. This update requires manual action. Refer below for details. (CVE-2013-2007)

This update does not change the permissions of the existing log file or the UNIX domain socket. For these to be changed, stop the qemu-ga service, and then manually remove all "group" and "other" permissions on the affected files, or remove the files.

Note that after installing this update, files created by the guest-file-open QEMU Monitor Protocol (QMP) command will still continue to be created with world-writable permissions for backwards compatibility.

This issue was discovered by Laszlo Ersek of Red Hat.

This update also fixes the following bugs:

  • Previously, due to integer overflow in code calculations, the qemu-kvm utility was reporting incorrect memory size on QMP events when using the virtio balloon driver with more than 4 GB of memory. This update fixes the overflow in the code and qemu-kvm works as expected in the described scenario. (BZ#958750)

  • When the set_link flag is set to "off" to change the status of a network card, the status is changed to "down" on the respective guest. Previously, with certain network cards, when such a guest was restarted, the status of the network card was unexpectedly reset to "up", even though the network was unavailable. A patch has been provided to address this bug and the link status change is now preserved across restarts for all network cards. (BZ#927591)

All users of qemu-kvm should upgrade to these updated packages, which contain backported patches to correct 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.