Fix UB in QGraphicsScene::wheelEvent()

operator--() would iterate before begin() if the list was empty. This is UB, and will crash in Qt 6, where begin()/end() can return an iterator pointing to a nullptr if the list is empty. Change-Id: I39c3a8ebb09fcad75d42019b02426ac5ac05eed9 Reviewed-by: Alex Blasche <[email protected]> Reviewed-by: Mårten Nordheim <[email protected]>
dxli · May 29, 2020 · f98fe1b · f98fe1b
1 parent d4ff606
commit f98fe1b
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/src/widgets/graphicsview/qgraphicsscene.cpp b/src/widgets/graphicsview/qgraphicsscene.cpp
@@ -4101,7 +4101,8 @@ void QGraphicsScene::wheelEvent(QGraphicsSceneWheelEvent *wheelEvent)
     // Remove all popups after the one found, or all or them if no popup is under the mouse.
     // Then continue with the event.
     QList<QGraphicsWidget *>::const_iterator iter = d->popupWidgets.constEnd();
-    while (--iter >= d->popupWidgets.constBegin() && !wheelCandidates.isEmpty()) {
+    while (iter > d->popupWidgets.constBegin() && !wheelCandidates.isEmpty()) {
+        --iter;
         if (wheelCandidates.first() == *iter || (*iter)->isAncestorOf(wheelCandidates.first()))
             break;
         d->removePopup(*iter);