From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Airlie Subject: Re: Securing non-root X input Date: Sun, 31 Jan 2010 18:38:51 +1000 Message-ID: <21d7e9971001310038y11a936f2g778f4a3119652692@mail.gmail.com> References: <20100129232437.GB6992@parisc-linux.org> <20100130074546.GB30378@core.coreip.homeip.net> <20100131013534.GA1331@parisc-linux.org> <20100131071307.GB12320@core.coreip.homeip.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail-iw0-f173.google.com ([209.85.223.173]:37686 "EHLO mail-iw0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750728Ab0AaIiw convert rfc822-to-8bit (ORCPT ); Sun, 31 Jan 2010 03:38:52 -0500 Received: by iwn3 with SMTP id 3so3334350iwn.23 for ; Sun, 31 Jan 2010 00:38:51 -0800 (PST) In-Reply-To: <20100131071307.GB12320@core.coreip.homeip.net> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Dmitry Torokhov Cc: Matthew Wilcox , peter.hutterer@who-t.net, linux-input@vger.kernel.org, xorg@freedesktop.org On Sun, Jan 31, 2010 at 5:13 PM, Dmitry Torokhov wrote: > On Sat, Jan 30, 2010 at 06:35:47PM -0700, Matthew Wilcox wrote: >> On Fri, Jan 29, 2010 at 11:45:46PM -0800, Dmitry Torokhov wrote: >> > Hi Matthew, >> > >> > On Fri, Jan 29, 2010 at 04:24:38PM -0700, Matthew Wilcox wrote: >> > > This tiny patch allows the X server to ask how many times the de= vice has >> > > been opened. =A0If it's more than one, the X server can ask the = user what >> > > they want to do about it. =A0For bonus points, the X server can = also run >> > > programs like lsof or fuser to find out which other processes ha= ve the >> > > device open, and tell the user that information too. =A0At that = point, >> > > the sysadmin can call in the ICBM strike on the offending user. >> > > >> > > Does this approach work for everyone? >> > >> > I do not think so. What about the cases when event devices are >> > legitimately opened by several processes, like this: >> > >> > [dtor@dtor-d630 work]$ ps aux | grep hald-addon-input >> > root =A0 =A0 =A01132 =A00.0 =A00.0 =A022200 =A0 824 ? =A0 =A0 =A0 = =A0S =A0 =A0Jan22 =A0 0:29 >> > hald-addon-input: Listening on /dev/input/event7 /dev/input/event2= /dev/input/event1 /dev/input/event6 /dev/input/event0 /dev/input/event= 12 /dev/input/event4 >> > dtor =A0 =A0 30424 =A00.0 =A00.0 102736 =A0 808 pts/3 =A0 =A0S+ =A0= 23:23 =A0 0:00 grep hald-addon-input >> > [dtor@dtor-d630 work]$ >> > >> > It might not be hald but some other daemon monitoring key presses >> > (sleep, hibernate, wifi keys and switches, etc). >> > >> > If it was just about ensuring that only oneprocess accesses the de= vice >> > then we could just use EVIOCGRAB but as experience shows it is not= a >> > workable solution. >> >> Yes, that's right. =A0I didn't quite go far enough in my explanation >> above ... =A0the X server can look around the system to see what tru= sted >> daemons (running as either root or the same user as the one running = X) >> currently have the device open, and notify the user if there's addit= ional >> openers that it isn't expecting. >> > > Then it will be constant race between X and the rest of the world wit= h X > pretty much always behind. Kind of like SELinux - as soon as try movi= ng > left or right the thing starts screaming at you... > >> Maybe we don't need a kernel patch to make this work after all, just >> a suid helper for X that uses the code from lsof/fuser to list all t= he >> current openers of /dev/input/eventN. >> > > But what about the case where malicious user opens the devices after = the > X done its scan? That can't happen since we remove privs from the previous users of the node before starting the new X server via ConsoleKit or at least thats = the plan, The problem is only a user holding open the evdev device after they've = lost perms on the device. Dave. > mknod is a privileged operation, requiring CAP_MKNOD. Otherwise evcen > current setup would be completely insecure if any user could just mkn= od > in his home directory and snoop root's keypresses at console. Its more the other devices the kernel might make, or udev. Not sure if that ever happens though. Dave. -- To unsubscribe from this list: send the line "unsubscribe linux-input" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html