From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A9052C0650E for ; Wed, 3 Jul 2019 14:31:42 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 817BD21850 for ; Wed, 3 Jul 2019 14:31:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 817BD21850 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:36372 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1higIP-0005n2-GH for qemu-devel@archiver.kernel.org; Wed, 03 Jul 2019 10:31:41 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55606) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1higGx-0005D8-Sp for qemu-devel@nongnu.org; Wed, 03 Jul 2019 10:30:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1higGw-0005el-CE for qemu-devel@nongnu.org; Wed, 03 Jul 2019 10:30:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54127) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1higGw-0005eK-2c for qemu-devel@nongnu.org; Wed, 03 Jul 2019 10:30:10 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 61F77A3B60; Wed, 3 Jul 2019 14:30:09 +0000 (UTC) Received: from redhat.com (unknown [10.42.17.95]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 711B9832B4; Wed, 3 Jul 2019 14:30:03 +0000 (UTC) Date: Wed, 3 Jul 2019 15:30:01 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Message-ID: <20190703143001.GE23082@redhat.com> References: <20190703135411.28436-1-berrange@redhat.com> <43fe3646-1ee5-238e-3f0b-dc0b2e976b6e@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <43fe3646-1ee5-238e-3f0b-dc0b2e976b6e@redhat.com> User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 03 Jul 2019 14:30:09 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH] doc: document that the monitor console is a privileged control interface X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Stefan Hajnoczi , P J P , qemu-devel@nongnu.org, Markus Armbruster , "Dr . David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 03, 2019 at 04:24:26PM +0200, Philippe Mathieu-Daud=C3=A9 wro= te: > On 7/3/19 3:54 PM, Daniel P. Berrang=C3=A9 wrote: > > A supposed exploit of QEMU was recently announced as CVE-2019-12928 > > claiming that the monitor console was insecure because the "migrate" > > comand enabled arbitrary command execution for a remote attacker. > >=20 > > For this to be a flaw the user launching QEMU must have configured > > the monitor in a way that allows for other userrs to access it. The > > exploit report quoted use of the "tcp" character device backend for > > QMP. > >=20 > > This would indeed allow any network user to connect to QEMU and > > execute arbitrary comamnds, however, this is not a flaw in QEMU. >=20 > comamnds -> commands >=20 > > It is the normal expected behaviour of the monitor console and the > > commands it supports. Given a monitor connection, there are many > > ways to access host filesystem content besides the migrate command. > >=20 > > The reality is that the monitor console (whether QMP or HMP) is > > considered a privileged interface to QEMU and as such must only > > be made available to trusted users. IOW, making it available with > > no authentication over TCP is simply a, very serious, user > > configuration error not a security flaw in QEMU itself. > >=20 > > The one thing this bogus security report highlights though is that > > we have not clearly documented the security implications around the > > use of the monitor. Add a few paragraphs of text to the security > > docs explaining why the monitor is a privileged interface and making > > a recommendation to only use the UNIX socket character device backend= . > >=20 > > Signed-off-by: Daniel P. Berrang=C3=A9 > > --- > > docs/security.texi | 36 ++++++++++++++++++++++++++++++++++++ > > 1 file changed, 36 insertions(+) > >=20 > > diff --git a/docs/security.texi b/docs/security.texi > > index 927764f1e6..5bff01449d 100644 > > --- a/docs/security.texi > > +++ b/docs/security.texi > > @@ -129,3 +129,39 @@ those resources that were granted to it. > > system calls that are not needed by QEMU, thereby reducing the host = kernel > > attack surface. > > @end itemize > > + > > +@section Sensitive configurations > > + > > +There are aspects of QEMU that can have non-obvious security implica= tions > > +which users & management applications must be aware of. > > + > > +@subsection Monitor console (QMP and HMP) > > + > > +The monitor console (whether used with QMP or HMP) provides an RPC i= nterface > > +to dynamically control many aspects of QEMU's runtime operation. Man= y of the > > +commands exposed will instruct QEMU to access content on the host fi= lesysystem > > +and/or trigger spawning of external processes. > > + > > +For example, the @code{migrate} command allows for the spawning of a= rbitrary > > +processes for the purpose of tunnelling the migration data stream. T= he > > +@code{blockdev-add} command instructs QEMU to open arbitrary files, = exposing > > +their content to the guest as a virtual disk. > > + > > +Unless QEMU is otherwise confined using technologies such as SELinux= , AppArmor, > > +or Linux namespaces, the monitor console should be considered to hav= e privileges > > +equivalent to those of the user account QEMU is running under. > > + > > +It is further important to consider the security of the character de= vice backend > > +over which the monitor console is exposed. It needs to have protecti= on against > > +malicious third parties which might try to make unauthorized connect= ions, or > > +perform man-in-the-middle attacks. Many of the character device back= ends do not > > +satisfy this requirement and so must not be used for the monitor con= sole. > > + > > +The general recommendation is that the monitor console should be exp= osed over > > +a UNIX domain socket backend to the local host only. Use of the TCP = based > > +character device backend is inappropriate unless configured to use b= oth TLS > > +encryption and authorization control policy on client connections. > > + > > +In summary the monitor console is considered a privileged control in= terface to >=20 > I'd have written "In summary, " or "In summary: " but I'm not sure this > is correct/better ;) Using a comma is a reasonable thing here. >=20 > > +QEMU and as such should only be made accessible to a trusted managem= ent > > +application or user. > >=20 >=20 > Thanks for writing this down. >=20 > Reviewed-by: Philippe Mathieu-Daud=C3=A9 Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|