Crash when deleting the parent of a context menu while it is being displayed

Asynchronous deletion of a widget (e.g. calling deleteLater() after a timeout)
could be caught by the context menu's event loop if called with exec() instead
of popup(). This causes the context menu to be deleted twice in some cases,
and a crash generally follows.

Although this introduces a minor behaviour change, we now use popup() with the
WA_DeleteOnClose attribute to display the context menu in all the
contextMenuEvent() bodies, except in those where the menu was already
protected by a QPointer. In QDialog::contextMenuEvent(), we use QWeakPointer
to reflect the fact that the menu was previously allocated in the stack.

QAbstractSpinBox, QDialog and QMdiSubWindow keep using QMenu::exec() in
contextMenuEvent() as they need the QAction returned.

Some auto-tests included.

Reviewed-by: Olivier
Task-number: QTBUG-7902

2 files changed, 6 insertions, 5 deletions

diff --git a/src/gui/dialogs/qdialog.cpp b/src/gui/dialogs/qdialog.cpp
index 9ff2ad8..fb0dba4 100644
--- a/src/gui/dialogs/qdialog.cpp
+++ b/src/gui/dialogs/qdialog.cpp
@@ -648,13 +648,14 @@ void QDialog::contextMenuEvent(QContextMenuEvent *e)
     while (w && w->whatsThis().size() == 0 && !w->testAttribute(Qt::WA_CustomWhatsThis))
         w = w->isWindow() ? 0 : w->parentWidget();
     if (w) {
-        QMenu p(this);
-        QAction *wt = p.addAction(tr("What's This?"));
-        if (p.exec(e->globalPos()) == wt) {
+        QWeakPointer<QMenu> p = new QMenu(this);
+        QAction *wt = p.data()->addAction(tr("What's This?"));
+        if (p.data()->exec(e->globalPos()) == wt) {
             QHelpEvent e(QEvent::WhatsThis, w->rect().center(),
                          w->mapToGlobal(w->rect().center()));
             QApplication::sendEvent(w, &e);
         }
+        delete p.data();
     }
 #endif
 }
diff --git a/src/gui/dialogs/qmessagebox.cpp b/src/gui/dialogs/qmessagebox.cpp
index d1b2e3f..ed437ff 100644
--- a/src/gui/dialogs/qmessagebox.cpp
+++ b/src/gui/dialogs/qmessagebox.cpp
@@ -92,8 +92,8 @@ public:
         {
 #ifndef QT_NO_CONTEXTMENU
             QMenu *menu = createStandardContextMenu();
-            menu->exec(e->globalPos());
-            delete menu;
+            menu->setAttribute(Qt::WA_DeleteOnClose);
+            menu->popup(e->globalPos());
 #else
             Q_UNUSED(e);
 #endif