From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:54347) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SgXUB-0001iN-Ge for qemu-devel@nongnu.org; Mon, 18 Jun 2012 04:39:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SgXU6-0004mY-DF for qemu-devel@nongnu.org; Mon, 18 Jun 2012 04:38:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:12265) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SgXU6-0004mN-55 for qemu-devel@nongnu.org; Mon, 18 Jun 2012 04:38:54 -0400 Date: Mon, 18 Jun 2012 09:38:46 +0100 From: "Daniel P. Berrange" Message-ID: <20120618083846.GE28026@redhat.com> References: <20120613203028.GB6019@redhat.com> <5022524.gIe1TV6Uvp@sifl> <20120618083103.GC28026@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20120618083103.GC28026@redhat.com> Subject: Re: [Qemu-devel] [RFC] [PATCHv2 2/2] Adding basic calls to libseccomp in vl.c Reply-To: "Daniel P. Berrange" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paul Moore Cc: Blue Swirl , qemu-devel@nongnu.org, Eduardo Otubo On Mon, Jun 18, 2012 at 09:31:03AM +0100, Daniel P. Berrange wrote: > On Fri, Jun 15, 2012 at 05:02:19PM -0400, Paul Moore wrote: > > On Friday, June 15, 2012 07:06:10 PM Blue Swirl wrote: > > > I think allowing execve() would render seccomp pretty much useless. > > > > Not necessarily. > > > > I'll agree that it does seem a bit odd to allow execve(), but there is still > > value in enabling seccomp to disable potentially buggy/exploitable syscalls. > > Let's not forget that we have over 300 syscalls on x86_64, not including the > > 32 bit versions, and even if we add all of the new syscalls suggested in this > > thread we are still talking about a small subset of syscalls. As far as > > security goes, the old adage of "less is more" applies. > > I can sort of see this argument, but *only* if the QEMU process is being > run under a dedicated, fully unprivileged (from a DAC pov) user, completely > separate from anything else on the system. Or, of course, for a QEMU already confined by SELinux. > If QEMU were being run as root, then even with seccomp, it could trivially > just overwrite some binary in /bin, update /proc/core-pattern to point to > this binary, and then crash itself. Now that core handling binary will > execute without any of the seccomp filters applied. > > Similarly if QEMU is being run in the user's desktop session, I'm sure there > is some kind of similar attack possible by changing a config setting for the > user's GNOME/KDE session, and then waiting for GNOME/KDE to execute the script > that QEMU just wrote out, once again bypassing seccomp. Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|