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Tasklist

FS#27993 - [xorg] Bypassing screensaver/locker program on xorg 1.11 and up

Attached to Project: Arch Linux
Opened by Vertlo Oraerk (oraerk) - Thursday, 19 January 2012, 10:15 GMT
Last edited by Eric Belanger (Snowman) - Monday, 23 January 2012, 20:15 GMT
Task Type Bug Report
Category Security
Status Closed
Assigned To No-one
Architecture All
Severity Critical
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 7
Private No

Details

Description:
Easily disable xlock with physical access to PC.
All details:
http://gu1.aeroxteam.fr/2012/01/19/bypass-screensaver-locker-program-xorg-111-and-up/

Additional info:
* package version(s): X.Org > 1.11
* config and/or log files etc.

Steps to reproduce:
1) Lock X.Org Session
2) Press Ctrl+Alt+Numpad Multiply
3) Session unlocked.

That is it, easily.
This task depends upon

Closed by  Eric Belanger (Snowman)
Monday, 23 January 2012, 20:15 GMT
Reason for closing:  Fixed
Additional comments about closing:  Fixed in xkeyboard-config 2.4.1-3
Comment by David J. Haines (dhaines) - Friday, 20 January 2012, 17:45 GMT
This method still works if you have a key set to send XF86ClearGrab, which defaults to CTRL+ALT+Numpad_Multiply (or KPMU in xkbcomp parlance).

Essentially, the bug remains, but it's not in [xorg], but rather [xscreensaver] and other screen-locking programs, as it's up to an individual program to disable the behavior (and screen-locking apps are exactly what should be doing that).
Comment by Ionut Biru (wonder) - Friday, 20 January 2012, 17:54 GMT
can you be more specific in your case? What do you use etc
Comment by David J. Haines (dhaines) - Friday, 20 January 2012, 18:01 GMT
I take back what I said about xscreensaver. It might not even be a bug.

I will say, however, that sending the XF86ClearGrab will cause a screen locking program to quit. I am now uncertain whether it is possible for a program to disable that behavior, as there is some discussion on arch-general stating that a linked article is incorrect.

My case is simply that CTRL+ALT+KPMU sends XF85ClearGrab, and will kill xscreensaver (or alock) if it's doing its screen locking job. I made a custom keyboard layout with xkbcomp (and judicious application of vi), which is attached hereto. As pointed out on arch-general, this may indeed simply be a case of a keybinding that just shouldn't be there unless you are debugging full screen programs and are OK with the consequences.

If there was a way to retract my reopen request, I would have before you acted on it.
Comment by Andrew S. Grigorev (eigrad) - Saturday, 21 January 2012, 01:55 GMT
Heey! Is it going to be fixed? Just disable ClearGrab/Ungrab in /usr/share/X11/xkb/compat/xfree86, why not?

44,49c44,49
< interpret XF86_Ungrab {
< action = Private(type=0x86, data="Ungrab");
< };
< interpret XF86_ClearGrab {
< action = Private(type=0x86, data="ClsGrb");
< };
---
> // interpret XF86_Ungrab {
> // action = Private(type=0x86, data="Ungrab");
> // };
> // interpret XF86_ClearGrab {
> // action = Private(type=0x86, data="ClsGrb");
> // };

Really, it is a security hole while it is not fixed in a *lock programs, but a such simple workaround is good enough for the moment, IMHO...
Comment by André Vitor Matos (andre.vmatos) - Saturday, 21 January 2012, 01:57 GMT
Please, close this bug. Fixed in xkeyboard-config 2.4.1-3

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