Bug 45796 - null pointer dereference in ProcXTestFakeInput when all input devices are disabled
Summary: null pointer dereference in ProcXTestFakeInput when all input devices are dis...
Alias: None
Product: xorg
Classification: Unclassified
Component: Server/General (show other bugs)
Version: unspecified
Hardware: Other All
: medium normal
Assignee: Xorg Project Team
QA Contact: Xorg Project Team
Depends on:
Reported: 2012-02-08 09:56 UTC by Andy Lutomirski
Modified: 2012-06-12 03:58 UTC (History)
1 user (show)

See Also:
i915 platform:
i915 features:


Description Andy Lutomirski 2012-02-08 09:56:52 UTC
This is xorg-x11-server-1.11.3-1.fc16 from Fedora 16.

I want to use x11vnc or vino-server in a way that's reasonably secure against attackers sitting at the keyboard.  The best idea I have is to turn off local input devices, like this:

for dev in `xinput list |perl -ane '$_ =~ /id=(\d+)\s/ and print "$1\n"'`; do
    xinput set-prop "$dev" 'Device Enabled' "$1"

This works until a remote user actually tries to send input.  Then I get an instant segfault in the server.  gdb says:

Program received signal SIGSEGV, Segmentation fault.
0x00000000004db52e in ProcXTestFakeInput (client=0x2057c60) at xtest.c:375
375	            if (!dev->valuator)
(gdb) bt
#0  0x00000000004db52e in ProcXTestFakeInput (client=0x2057c60) at xtest.c:375
#1  0x0000000000433ae1 in Dispatch () at dispatch.c:447
#2  0x0000000000422e15 in main (argc=<optimized out>, argv=0x7fff821baa48, 
    envp=<optimized out>) at main.c:287
(gdb) list
370	            }
372	            need_ptr_update = 0;
373	            break;
374	        case MotionNotify:
375	            if (!dev->valuator)
376	                return BadDevice;
378	            if (!(extension || ev->u.keyButtonPointer.root == None))
379	            {
(gdb) print dev
$1 = (DeviceIntPtr) 0x0

(It would be nice to have a better way to do this.  For example, turning off all non-Xtest input and setting dpms off *without telling client software that dpms is off* so that the compositor continues to draw things.)
Comment 1 Peter Hutterer 2012-02-15 21:15:30 UTC
Proposed patch: http://patchwork.freedesktop.org/patch/9116/
Comment 2 Jeremy Huddleston Sequoia 2012-06-12 03:58:59 UTC
This is fixed on 1.12.1

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