[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-Id: <E1WS4V3-0001Xh-Se@xenbits.xen.org>
Date: Mon, 24 Mar 2014 13:01:09 +0000
From: Xen.org security team <security@....org>
To: xen-announce@...ts.xen.org, xen-devel@...ts.xen.org,
xen-users@...ts.xen.org, oss-security@...ts.openwall.com
CC: Xen.org security team <security@....org>
Subject: Xen Security Advisory 90 - Linux netback crash trying to disable
due to malformed packet
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Xen Security Advisory XSA-90
Linux netback crash trying to disable due to malformed packet
ISSUE DESCRIPTION
=================
When Linux's netback sees a malformed packet, it tries to disable the
interface which serves the misbehaving frontend.
This involves taking a mutex, which might sleep. But in recent
versions of Linux the guest transmit path is handled by NAPI in
softirq context, where sleeping is not allowed. The end result is
that the backend domain (often, Dom0) crashes with "scheduling while
atomic".
IMPACT
======
Malicious guest administrators can cause denial of service. If driver
domains are not in use, the impact is a host crash.
VULNERABLE SYSTEMS
==================
This bug affects systems using Linux as the driver domain, including
non-disaggregated systems using Linux as dom0.
Only versions of Linux whose netback uses NAPI are affected. In Linux
mainline this is all versions of Linux containing git changeset
b3f980bd82, which was introduced between Linux 3.11 and 3.12-rc1.
Systems using a different OS as dom0 (eg, NetBSD, Solaris) are not
vulnerable.
Both x86 and ARM systems are affected.
MITIGATION
==========
Using driver domains may limit the scope of the denial of service, and
may make it possible to resume service without restarting guests (by
restarting the driver domain). Advice on reconfiguring a system to
use driver domains is beyond the reasonable scope of this advisory.
In the case of an x86 HVM guest, the exploit can be prevented by
disabling the PV IO paths; normally this would come with a substantial
performance cost, and it may involve reconfiguring the guest as well
as the host. This is not recommended.
NOTE REGARDING LACK OF EMBARGO
==============================
This bug was publicly reported on xen-devel, before it was appreciated
that there was a security problem. The public mailing list thread
nevertheless contains information strongly suggestive of a security
bug, and a different security bug (with CVE) is suggested as seeming
"similar".
For these reasons we (the Xen Project Security Team) have concluded
that the presence of this bug, as a security problem, is not (any
longer) a secret.
CREDITS
=======
This issue was discovered as a bug by Török Edwin and analysed by
Wei Liu of Citrix.
RESOLUTION
==========
Applying the appropriate attached patch resolves this issue.
$ sha256sum xsa90*.patch
07341ffb7f577d32510602797a08009eade817009b425a124413ee743bdb6f05 xsa90.patch
$
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.12 (GNU/Linux)
iQEcBAEBAgAGBQJTMCxRAAoJEIP+FMlX6CvZaAEIAIIVfNdz3CwFYbiSwa51RJ3L
YFarP71/0EjNJKSaRwf6EQjDNnApqq6ep4+WKFvlMbm515jyQXp6mAbb8ffqnLUQ
2SDOlQXOpbnZrJrgo4YcT5ru8ZusauYz36TkFVcXBmcKWq29KoUARo5zG7YGyh9H
aWajaZs6RQPv3QE8IInNSP0oitRQZg/5xAW+Lz4Kn8xpO/IJuYW3ROH6JQcFF67H
r7xVAzxjrNQ3P5mN0iiOkQYK39PqhwGUhWaa6JlejsjUgU1nsGIBOHH+ISCaZrtL
e/6XK3awaDiu1dAL4Py1SdhPiA0sTeqA3bf6ARd7ymoIFqGuxrqYlupcUKTupjE=
=LrLN
-----END PGP SIGNATURE-----
Download attachment "xsa90.patch" of type "application/octet-stream" (4106 bytes)
Powered by blists - more mailing lists
Please check out the
Open Source Software Security Wiki, which is counterpart to this
mailing list.
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
