[gnome-shell] screenShield: Only allow graphs to lift shield when locked

[Florian Müllner <fmuellner src gnome org>]

commit 205880e74e1bcecb66b79f2399c77ccf8f1ae94a
Author: Florian Müllner <fmuellner gnome org>
Date:   Fri Oct 21 18:03:44 2016 +0200

    screenShield: Only allow graphs to lift shield when locked
    
    Since commit 67615a0cbc, any printable key can be used to lift the
    screen shield rather than just escape/enter/space. While this is
    convenient for unlocking where the input is forwarded to the password
    entry, it is potentially dangerous when the screen is inactive but
    not locked: If the user types her password, the first character will
    lift the shield and the remaining input will go to the focused window.
    To prevent this from happening, only allow printable keys when the
    screen is actually locked and restrict the key presses that lift the
    shield to the original set of escape/enter/space otherwise.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=773328

 js/ui/screenShield.js |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/js/ui/screenShield.js b/js/ui/screenShield.js
index c6202fe..db53382 100644
--- a/js/ui/screenShield.js
+++ b/js/ui/screenShield.js
@@ -665,7 +665,10 @@ const ScreenShield = new Lang.Class({
         let isEnter = (symbol == Clutter.KEY_Return ||
                        symbol == Clutter.KEY_KP_Enter ||
                        symbol == Clutter.KEY_ISO_Enter);
-        if (!isEnter && !(GLib.unichar_isprint(unichar) || symbol == Clutter.KEY_Escape))
+        let isEscape = (symbol == Clutter.KEY_Escape);
+        let isLiftChar = (GLib.unichar_isprint(unichar) &&
+                          (this._isLocked || !GLib.unichar_isgraph(unichar)));
+        if (!isEnter && !isEscape && !isLiftChar)
             return Clutter.EVENT_PROPAGATE;
 
         if (this._isLocked &&