KVM (Kernel-based Virtual Machine) is a full virtualization solution for Linux on AMD64 and Intel 64 systems. The qemu-kvm-rhev packages form the user-space component for running virtual machines using KVM.
A flaw was found in the way QEMU handled VT100 terminal escape sequences when emulating certain character devices. A guest user with privileges to write to a character device that is emulated on the host using a virtual console back-end could use this flaw to crash the qemu-kvm process on the host or, possibly, escalate their privileges on the host. (CVE-2012-3515)
When using qemu-kvm-rhev on a Red Hat Enterprise Linux 6 host not managed by Red Hat Enterprise Virtualization:
This flaw did not affect the default use of KVM. Affected configurations were:
When guests were started from the command line ("/usr/libexec/qemu-kvm") without the "-nodefaults" option, and also without specifying a serial or parallel device, or a virtio-console device, that specifically does not use a virtual console (vc) back-end. (Note that Red Hat does not support invoking "qemu-kvm" from the command line without "-nodefaults" on Red Hat Enterprise Linux 6.)
Guests that were managed via libvirt, such as when using Virtual Machine Manager (virt-manager), but that have a serial or parallel device, or a virtio-console device, that uses a virtual console back-end. By default, guests managed via libvirt will not use a virtual console back-end for such devices.
When using qemu-kvm-rhev on a Red Hat Enterprise Virtualization managed Red Hat Enterprise Linux 6 host:
To specify a virtual console back-end for a device and therefore be vulnerable to this issue, the device would have to be created another way, for example, by using a VDSM hook.
Red Hat would like to thank the Xen project for reporting this issue.
This update also fixes the following bugs:
Previously, the KVM modules were not loaded by the postinstall scriptlet of RPM scripts. This bug caused various issues and required the system to be rebooted to resolve them. With this update, the modules are loaded properly by the scriptlet and no unnecessary reboots are now required. (BZ#839897)
Previously, when a guest was started up with two serial devices, qemu-kvm returned an error message and terminated the boot because IRQ 4 for the ISA bus was being used by both devices. This update fixes the qemu-kvm code, which allows IRQ 4 to be used by more than one device on the ISA bus, and the boot now succeeds in the described scenario. (BZ#840054)
All users of qemu-kvm-rhev are advised to upgrade to these updated packages, which fix 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.