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. Dave. > 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. Dave. -- 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
