On Sun, Jan 31, 2010 at 06:38:51PM +1000, Dave Airlie wrote: > On Sun, Jan 31, 2010 at 5:13 PM, Dmitry Torokhov > <dmitry.torokhov@xxxxxxxxx> 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 device has > >> > > been opened. If it's more than one, the X server can ask the user what > >> > > they want to do about it. For bonus points, the X server can also run > >> > > programs like lsof or fuser to find out which other processes have the > >> > > device open, and tell the user that information too. At 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 1132 0.0 0.0 22200 824 ? S Jan22 0:29 > >> > hald-addon-input: Listening on /dev/input/event7 /dev/input/event2 /dev/input/event1 /dev/input/event6 /dev/input/event0 /dev/input/event12 /dev/input/event4 > >> > dtor 30424 0.0 0.0 102736 808 pts/3 S+ 23:23 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 device > >> > then we could just use EVIOCGRAB but as experience shows it is not a > >> > workable solution. > >> > >> Yes, that's right. I didn't quite go far enough in my explanation > >> above ... the X server can look around the system to see what trusted > >> 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 additional > >> openers that it isn't expecting. > >> > > > > Then it will be constant race between X and the rest of the world with X > > pretty much always behind. Kind of like SELinux - as soon as try moving > > 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 the > >> 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. > I see. How revoke will help here though? How will we know which descriptors shoudl be revoked and which should be left alone? > > mknod is a privileged operation, requiring CAP_MKNOD. Otherwise evcen > > current setup would be completely insecure if any user could just mknod > > 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. > This is distro config and may happen now (udev creates a non-root device if misconfigured etc). -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
