Application: kcmshell4 ()
KDE Platform Version: 4.9.5
Qt Version: 4.8.4
Operating System: Linux 3.7.2-201.fc18.x86_64 x86_64
Distribution: "Fedora release 18 (Spherical Cow)"

-- Information about the crash:
- What I was doing when the application crashed:

1) I opened Login Screen settings (Directly)
2) I switch to "Convenience" tab (Not required)
3) I changed a setting (e.g. Enable Auto-Login)
4) I pressed Apply
5) Without providing root password and without closing the dialog requesting it, I press "OK" in "Login Screen" tab (It allow me to do this, I think it shouldn't allow me before closing the password dialog), an error message appear "Unable to authenticate/execute the action:  (code 6)"
6) I close the messege, "Login Screen" window gone, but password dialog is still open.
7) I enter ther root password and press Enter, the crash handler appears.

This can be reproduced using this exact procedure, also almost the same error happens when "Login Screen" is opened from "System Settings" (not directly), with some differences (no OK button, so we can press "Apply" again).

The crash can be reproduced every time.

-- Backtrace:
Application: KDE Control Module (kcmshell4), signal: Segmentation fault
Using host libthread_db library "/lib64/libthread_db.so.1".
81	T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
[Current thread is 1 (Thread 0x7f985b5f8880 (LWP 25927))]

Thread 2 (Thread 0x7f984daf7700 (LWP 25928)):
#0  0x0000003b136e998d in poll () at ../sysdeps/unix/syscall-template.S:81
#1  0x0000003b15247d44 in g_main_context_poll (n_fds=3, fds=0x7f98480010c0, timeout=-1, context=0x1248600, priority=<optimized out>) at gmain.c:3584
#2  g_main_context_iterate (context=0x1248600, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at gmain.c:3285
#3  0x0000003b152481a2 in g_main_loop_run (loop=0x1248590) at gmain.c:3484
#4  0x0000003b266cc546 in gdbus_shared_thread_func (user_data=0x12485d0) at gdbusprivate.c:277
#5  0x0000003b1526b5f5 in g_thread_proxy (data=0x1245320) at gthread.c:797
#6  0x0000003b13e07d15 in start_thread (arg=0x7f984daf7700) at pthread_create.c:308
#7  0x0000003b136f246d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:114

Thread 1 (Thread 0x7f985b5f8880 (LWP 25927)):
[KCrash Handler]
#6  isEmpty (this=<error reading variable: Cannot access memory at address 0xc8>) at ../../src/corelib/tools/qstring.h:705
#7  QTemporaryFile::fileName (this=0xc0) at io/qtemporaryfile.cpp:657
#8  0x00007f984e80146b in KDModule::save (this=0x108bd00) at /usr/src/debug/kde-workspace-4.9.5/kdm/kcm/main.cpp:374
#9  0x00000036678214e7 in KCModuleProxy::save (this=<optimized out>) at /usr/src/debug/kdelibs-4.9.5/kutils/kcmoduleproxy.cpp:279
#10 0x000000366781ee60 in KCMultiDialogPrivate::apply (this=<optimized out>) at /usr/src/debug/kdelibs-4.9.5/kutils/kcmultidialog.cpp:300
#11 0x000000366781ef67 in KCMultiDialog::slotOkClicked (this=0x1016d50) at /usr/src/debug/kdelibs-4.9.5/kutils/kcmultidialog.cpp:334
#12 0x0000003b18b8cebf in QMetaObject::activate (sender=0x1025230, m=<optimized out>, local_signal_index=<optimized out>, argv=0x7fffa72c83b0) at kernel/qobject.cpp:3539
#13 0x000000366490d07f in KPushButton::authorized (this=<optimized out>, _t1=0x121a9c0) at /usr/src/debug/kdelibs-4.9.5/x86_64-redhat-linux-gnu/kdeui/kpushbutton.moc:142
#14 0x0000003b18b8cebf in QMetaObject::activate (sender=0x1025230, m=<optimized out>, local_signal_index=<optimized out>, argv=0x7fffa72c8500) at kernel/qobject.cpp:3539
#15 0x0000003b1c42f222 in QAbstractButton::clicked (this=<optimized out>, _t1=false) at .moc/release-shared/moc_qabstractbutton.cpp:219
#16 0x0000003b1c183e9e in QAbstractButtonPrivate::emitClicked (this=this@entry=0x1087830) at widgets/qabstractbutton.cpp:548
#17 0x0000003b1c1844a0 in QAbstractButtonPrivate::click (this=this@entry=0x1087830) at widgets/qabstractbutton.cpp:541
#18 0x0000003b1c18470c in QAbstractButton::mouseReleaseEvent (this=0x1025230, e=0x7fffa72c8da0) at widgets/qabstractbutton.cpp:1123
#19 0x0000003b1be19f49 in QWidget::event (this=0x1025230, event=0x7fffa72c8da0) at kernel/qwidget.cpp:8375
#20 0x0000003b1bdca5cc in QApplicationPrivate::notify_helper (this=0xe60c20, receiver=0x1025230, e=0x7fffa72c8da0) at kernel/qapplication.cpp:4562
#21 0x0000003b1bdcf2ab in QApplication::notify (this=<optimized out>, receiver=0x1025230, e=0x7fffa72c8da0) at kernel/qapplication.cpp:4105
#22 0x0000003664846916 in KApplication::notify (this=0x7fffa72c9b90, receiver=0x1025230, event=0x7fffa72c8da0) at /usr/src/debug/kdelibs-4.9.5/kdeui/kernel/kapplication.cpp:311
#23 0x0000003b18b77a8e in QCoreApplication::notifyInternal (this=0x7fffa72c9b90, receiver=0x1025230, event=0x7fffa72c8da0) at kernel/qcoreapplication.cpp:946
#24 0x0000003b1bdcb40b in QApplicationPrivate::sendMouseEvent (receiver=0x1025230, event=0x7fffa72c8da0, alienWidget=0x1025230, nativeWidget=0x1016d50, buttonDown=0x3b1c89e268 <qt_button_down>, lastMouseReceiver=..., spontaneous=true) at ../../src/corelib/kernel/qcoreapplication.h:231
#25 0x0000003b1be45b74 in QETWidget::translateMouseEvent (this=0x1016d50, event=<optimized out>) at kernel/qapplication_x11.cpp:4537
#26 0x0000003b1be44901 in QApplication::x11ProcessEvent (this=0x7fffa72c9b90, event=0x7fffa72c9510) at kernel/qapplication_x11.cpp:3660
#27 0x0000003b1be6aa5c in x11EventSourceDispatch (s=s@entry=0xe5c320, callback=0x0, user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:148
#28 0x0000003b15247a75 in g_main_dispatch (context=0xe62100) at gmain.c:2715
#29 g_main_context_dispatch (context=context@entry=0xe62100) at gmain.c:3219
#30 0x0000003b15247da8 in g_main_context_iterate (context=context@entry=0xe62100, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at gmain.c:3290
#31 0x0000003b15247e64 in g_main_context_iteration (context=0xe62100, may_block=1) at gmain.c:3351
#32 0x0000003b18ba60d6 in QEventDispatcherGlib::processEvents (this=0xe37790, flags=...) at kernel/qeventdispatcher_glib.cpp:424
#33 0x0000003b1be6a73e in QGuiEventDispatcherGlib::processEvents (this=<optimized out>, flags=...) at kernel/qguieventdispatcher_glib.cpp:207
#34 0x0000003b18b767df in QEventLoop::processEvents (this=this@entry=0x7fffa72c98f0, flags=...) at kernel/qeventloop.cpp:149
#35 0x0000003b18b76a68 in QEventLoop::exec (this=0x7fffa72c98f0, flags=...) at kernel/qeventloop.cpp:204
#36 0x0000003b1c27e608 in QDialog::exec (this=0x1016d50) at dialogs/qdialog.cpp:554
#37 0x0000003664e07b7c in kdemain (_argc=14999712, _argv=<optimized out>) at /usr/src/debug/kde-runtime-4.9.5/kcmshell/main.cpp:292
#38 0x0000003b13621a05 in __libc_start_main (main=0x400790 <main(int, char**)>, argc=2, ubp_av=0x7fffa72c9cc8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffa72c9cb8) at libc-start.c:225
#39 0x00000000004007c1 in _start ()

Reported using DrKonqi