Xen Security Advisory 221 - NULL pointer deref in event channel poll

classic Classic list List threaded Threaded
1 message Options
Reply | Threaded
Open this post in threaded view
|

Xen Security Advisory 221 - NULL pointer deref in event channel poll

Xen.org security team
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

                    Xen Security Advisory XSA-221
                              version 2

               NULL pointer deref in event channel poll

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

Public release.

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

When polling event channels, in general arbitrary port numbers can be
specified.  Specifically, there is no requirement that a polled event
channel ports has ever been created.  When the code was generalised
from an earlier implementation, introducing some intermediate
pointers, a check should have been made that these intermediate
pointers are non-NULL.  However, that check was omitted.

IMPACT
======

A malicious or buggy guest may cause the hypervisor to access
addresses it doesn't control, usually leading to a host crash (Denial
of Service).  Information leaks cannot be excluded.

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

Xen versions 4.4 and newer are vulnerable.  Xen versions 4.3 and
earlier are not affected.

Both x86 and ARM systems are vulnerable.

While all guest kinds can cause a Denial of Service, only x86 PV guests
may be able to leverage the possible information leaks.

MITIGATION
==========

There is no known mitigation.

CREDITS
=======

This issue was discovered by Ankur Arora of Oracle.

RESOLUTION
==========

Applying the appropriate attached patch resolves this issue.

xsa221.patch           Xen 4.4.x and later, including xen-unstable

$ sha256sum xsa221*
2425396a713466808b0f75f91337be4dd20a4dee7733972b04489773c6e97655  xsa221.patch
$

DEPLOYMENT DURING EMBARGO
=========================

Deployment of the patches and/or mitigations described above (or
others which are substantially similar) is permitted during the
embargo, even on public-facing systems with untrusted guest users and
administrators.

But: Distribution of updated software is prohibited (except to other
members of the predisclosure list).

Predisclosure list members who wish to deploy significantly different
patches and/or mitigations, please contact the Xen Project Security
Team.

(Note: this during-embargo deployment notice is retained in
post-embargo publicly released Xen Project advisories, even though it
is then no longer applicable.  This is to enable the community to have
oversight of the Xen Project Security Team's decisionmaking.)

For more information about permissible uses of embargoed information,
consult the Xen Project community's agreed Security Policy:
  http://www.xenproject.org/security-policy.html
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQEcBAEBCAAGBQJZSQ3TAAoJEIP+FMlX6CvZw20H/jCUm+eX4rPUCQ6CL+Ya/dXH
th34nPKQnq60gm3469sDQQMNbuvfgBItAAAjO87NC6P2BSyYPMny5SvqSsmkWow1
8OkAWq5ZZ3L7ksPhkP6aco+ks1a99SxJX4YfjwOFq9ct6/zfrcW1ThEqs9j87JeP
6RGPYgXc0mP9IOk27JnUVgiej7/v4a8v5FcWrG3bHpw2vp9tY3hdvkfc6wJiuplx
kkqIVkqTpCNu7QYGv3de1RpDeI5mN8TGY+6ahs9eZFEFmRGWiAahhZRnwGVNE7Tl
QcHzaphlzp/etub8sHgZPH90xLaeILJ+9oz29b/SLUVqahRxzTD1bLUElEu2su0=
=xR3U
-----END PGP SIGNATURE-----

_______________________________________________
Xen-announce mailing list
[hidden email]
https://lists.xen.org/xen-announce

xsa221.patch (9K) Download Attachment