Compiz crashes with SIGSEGV in PrivateWindow::configure

An override redirect which is stacked at the bottom and receives a ConfigureNotify event to restack higher up will cause compiz to crash.

The following patch fixe sthat

:=== modified file 'src/window.cpp'
--- src/window.cpp 2011-10-19 04:08:25 +0000
+++ src/window.cpp 2012-01-19 15:53:39 +0000
@@ -1997,8 +1997,16 @@
     if (priv->geometry.border () != ce->border_width)
  valueMask |= CWBorderWidth;

- if (ROOTPARENT (window->prev) != ce->above)
- valueMask |= CWSibling | CWStackMode;
+ if (window->prev)
+ {
+ if (ROOTPARENT (window->prev) != ce->above)
+ valueMask |= CWSibling | CWStackMode;
+ }
+ else
+ {
+ if (ce->above != 0)
+ valueMask |= CWSibling | CWStackMode;
+ }

     priv->attrib.override_redirect = ce->override_redirect;

Program received signal SIGSEGV, Segmentation fault.
0x00000000004cdcdc in CompWindow::frame (this=0x0) at /home/miso-work/unity/source/compiz-core/src/window.cpp:5954
5954 return priv->serverFrame;
#0 0x00000000004cdcdc in CompWindow::frame (this=0x0) at /home/miso-work/unity/source/compiz-core/src/window.cpp:5954
#1 0x00000000004c0df9 in PrivateWindow::configure (this=0x89aca0, ce=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/window.cpp:2000
#2 0x00000000004ec81f in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:1050
#3 0x00007fffebb9f93b in PrivateCompositeScreen::handleEvent (this=0x928d40, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/plugins/composite/src/screen.cpp:102
#4 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#5 0x00007fffeb940825 in PrivateGLScreen::handleEvent (this=0xaf0150, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/plugins/opengl/src/screen.cpp:607
#6 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#7 0x00007fffe8969525 in DecorScreen::handleEvent (this=0xb7b6c0, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/plugins/decor/src/decor.cpp:1614
#8 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#9 0x00007fffe8521170 in RegexScreen::handleEvent (this=0xafe390, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/plugins/regex/src/regex.cpp:250
#10 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#11 0x00007fffe80ea0e3 in ResizeScreen::handleEvent (this=0xb688e0, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/plugins/resize/src/resize.cpp:1498
#12 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#13 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#14 0x00007fffe779d9de in PlaceScreen::handleEvent (this=0xc17890, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/plugins/place/src/place.cpp:392
#15 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#16 0x00007fffe7574fd0 in SessionScreen::handleEvent (this=0xbc35d0, event=0x9b1a430) at /home/miso-work/unity/source/compiz-plugins-main/session/src/session.cpp:707
#17 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#18 0x00007fffe71369d7 in MoveScreen::handleEvent (this=0xba5600, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/plugins/move/src/move.cpp:672
#19 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#20 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#21 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#22 0x00007fffe646feca in UnityMTGrabHandlesScreen::handleEvent (this=0xbad040, event=0x9b1a430) at /home/miso-work/unity/source/unity/plugins/unity-mt-grab-handles/src/unity-mt-grab-handles.cpp:360
#23 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#24 0x00007fffe5423aae in FadeScreen::handleEvent (this=0xd0d130, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/plugins/fade/src/fade.cpp:67
#25 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#26 0x00007fffe51f971d in WorkaroundsScreen::handleEvent (this=0xd4a440, event=0x9b1a430) at /home/miso-work/unity/source/compiz-plugins-main/workarounds/src/workarounds.cpp:941
#27 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#28 0x00007fffe4fbc9e0 in PrivateScaleScreen::handleEvent (this=0xd47400, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/plugins/scale/src/scale.cpp:1594
#29 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#30 0x00007fffe44d8e03 in unity::UnityScreen::handleEvent (this=0xe38370, event=0x9b1a430) at /home/miso-work/unity/source/unity/plugins/unityshell/src/unityshell.cpp:1164
#31 0x00000000004ec503 in CompScreen::handleEvent (this=0x787370, event=0x9b1a430) at /home/miso-work/unity/source/compiz-core/src/event.cpp:987
#32 0x0000000000494898 in PrivateScreen::processEvents (this=0x87f5f0) at /home/miso-work/unity/source/compiz-core/src/screen.cpp:748
#33 0x00000000004fa623 in CompEventSource::callback (this=0x8e9c70) at /home/miso-work/unity/source/compiz-core/src/eventsource.cpp:71
#34 0x00000000004fad17 in sigc::bound_mem_functor0<bool, CompEventSource>::operator() (this=0x927b48) at /usr/include/sigc++-2.0/sigc++/functors/mem_fun.h:1787
#35 0x00000000004fac5e in sigc::adaptor_functor<sigc::bound_mem_functor0<bool, CompEventSource> >::operator() (this=0x927b40) at /usr/include/sigc++-2.0/sigc++/adaptors/adaptor_trait.h:251
#36 0x00000000004fab39 in sigc::internal::slot_call0<sigc::bound_mem_functor0<bool, CompEventSource>, bool>::call_it (rep=0x927b10) at /usr/include/sigc++-2.0/sigc++/functors/slot.h:103
#37 0x000000000048cc90 in sigc::slot0<bool>::operator() (this=0x8f4020) at /usr/include/sigc++-2.0/sigc++/functors/slot.h:440
#38 0x00000000004fa6c8 in CompEventSource::dispatch (this=0x8e9c70, slot=0x8f4020) at /home/miso-work/unity/source/compiz-core/src/eventsource.cpp:94
#39 0x00007ffff67a348f in Glib::Source::dispatch_vfunc(_GSource*, int (*)(void*), void*) () from /usr/lib/x86_64-linux-gnu/libglibmm-2.4.so.1
#40 0x00007ffff62ad6ca in g_main_dispatch (context=0x793c50) at /build/buildd/glib2.0-2.31.8/./glib/gmain.c:2513
#41 g_main_context_dispatch (context=0x793c50) at /build/buildd/glib2.0-2.31.8/./glib/gmain.c:3050
#42 0x00007ffff62ada90 in g_main_context_iterate (dispatch=1, block=<optimized out>, context=0x793c50, self=<optimized out>) at /build/buildd/glib2.0-2.31.8/./glib/gmain.c:3121
#43 g_main_context_iterate (context=0x793c50, block=<optimized out>, dispatch=1, self=<optimized out>) at /build/buildd/glib2.0-2.31.8/./glib/gmain.c:3058
#44 0x00007ffff62ade8a in g_main_loop_run (loop=0xb0fa40) at /build/buildd/glib2.0-2.31.8/./glib/gmain.c:3315
#45 0x00000000004926f8 in CompScreen::eventLoop (this=0x787370) at /home/miso-work/unity/source/compiz-core/src/screen.cpp:129
#46 0x000000000048eceb in CompManager::run (this=0x7fffffffd970) at /home/miso-work/unity/source/compiz-core/src/main.cpp:261
#47 0x000000000048ee63 in main (argc=2, argv=0x7fffffffda98) at /home/miso-work/unity/source/compiz-core/src/main.cpp:306

No testcase available, but a fairly straightforward fix (null check)