Xen Security Advisory XSA-83
                              version 2

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

UPDATES IN VERSION 2
====================

Public release.

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.

MITIGATION
==========

This issue can be avoided by not assigning PCI devices to untrusted guests on
systems supporting Intel VT-d or AMD Vi.

CREDITS
=======

This issue was discovered by Coverity Scan, prompted by modelling
improvements contributed by Andrew Coooper.  The issue was diagnosed
by Matthew Daley and Andrew Coooper.  The patch was prepared by Andrew
Cooper.

RESOLUTION
==========

Applying the attached patch resolves this issue.

xsa83.patch                 Xen 4.2.x, Xen 4.3.x, xen-unstable

$ sha256sum xsa83*.patch
71ba62c024ed867f99f335ed63d7e04a7981d348cc29a3718e5c48f15a1e0fb1  xsa83.patch
$