AllowClosedownGrabs enables Ctrl-Alt-Keypad
Multiply, which terminates any clients with keyboard or mouse grabs. The
HandleSpecialKeys entry ensures that these keys will be processed by the server
regardless of the keyboard map currently installed.
You can easily check that these key combinations are working by starting an xterm
and placing it in Secure Keyboard mode. Ctrl-Alt-Keypad Divide should cause the
xterm to come out of reverse video mode and permit you to type into other applications.
On the other hand, pressing Ctrl-Alt-Keypad Multiply terminates the xterm.
There is one situation where keyboard grabs shouldn??™t be overridden: when a locking
screensaver is in use. If the screensaver??™s keyboard grab can be released, a user
could then change VTs; if the X session was started from a shell prompt using the
startx command, it could be terminated with Ctrl-C, and the user would then have
access to a full shell prompt. An API has been written to guard against this, but it
doesn??™t work with xscreensaver (Section 6.13) because of permission issues, and it
won??™t work with older screensavers at all.
Therefore, a locking screensaver used in an X session started from a command
prompt allows a sophisticated user to bypass password protection if the
AllowDeactivateGrabs or AllowClosedownGrabs features are enabled.
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