Out-of-memory condition yielding memory corruption during IRQ setup

ISSUE DESCRIPTION

When setting up the IRQ for a passed through physical device, a flaw in the error handling could result in a memory allocation being used after it is freed, and then freed a second time. This would typically result in memory corruption.

IMPACT

Malicious guest administrators can trigger a use-after-free error, resulting in hypervisor memory corruption. The effects of memory corruption could be anything, including a host-wide denial of service, or privilege escalation.

VULNERABLE SYSTEMS

Xen 4.2.x and later are vulnerable. Xen 4.1.x and earlier are not vulnerable.
Only systems making use of device passthrough are vulnerable.
Only systems with a 64-bit hypervisor configured to support more than 128 CPUs or with a 32-bit hypervisor configured to support more than 64 CPUs are vulnerable.