Mailing List Archive

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Xen Security Advisory XSA-73
version 2

Lock order reversal between page allocation and grant table locks

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

Corrected typo in xsa73-4.1.patch. The other patches were already
correct.

NOTE REGARDING LACK OF EMBARGO
==============================

While the response to this issue was being prepared by the security
team, the bug was independently discovered by a third party who
publicly disclosed it without realising the security impact.

ISSUE DESCRIPTION
=================

The locks page_alloc_lock and grant_table.lock are not always taken in
the same order. This opens the possibility of deadlock.

IMPACT
======

A malicious guest administrator can deny service to the entire host.

VULNERABLE SYSTEMS
==================

Xen versions going back to at least Xen 3.2 are vulnerable.

To exploit the vulnerability, the attacker must have control of more
than one vcpu, either by controlling a malicious multi-vcpu guest, or
by controlling more than one guest.

MITIGATION
==========

There is no practical mitigation for this issue.

CREDITS
=======

This issue was discovered by Coverity Scan and diagnosed by Andrew
Cooper.

RESOLUTION
==========

Applying the appropriate attached patch resolves this issue.

xsa73-4.3-unstable.patch Xen 4.3.x, xen-unstable
xsa73-4.2.patch Xen 4.2.x
xsa73-4.1.patch Xen 4.1.x

$ sha256sum xsa73*.patch
c9284e2c12b1c4f8c63d11b8802b4f408e6623f857f120b04e47840f433e4823 xsa73-4.1.patch
10b809c39582a7f29150f0635b78bc2ce40df0bded963b78f42db3e21775da8c xsa73-4.2.patch
48411cd6b15e4e4fa3c4335298179a4b1094c5e1ae8dc7582bbfb9439d97037b xsa73-4.3-unstable.patch
$
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