Add nullptr guard in QStyleSheetStyle::drawPrimitive(PE_PanelLineEdit)

Drawing PE_PanelLineEdit in QStyleSheetStyle with the default argument
widget = nullptr causes a segfault.

drawPrimitive tries to fall back to a container widget's render rule
and therefore calls containerWidget() - which crashes when called with
nullptr.

Container widget fallback is pointless when drawPrimitive() is called
with widget == nullptr. This patch skips it in that case.

Fixes: QTBUG-104917
Pick-to: 6.4 6.3 6.2
Change-Id: I09e57dccfebb81a308944c233846d5b9ef58819e
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 8 insertions, 5 deletions

diff --git a/src/widgets/styles/qstylesheetstyle.cpp b/src/widgets/styles/qstylesheetstyle.cpp
index 0437561d13..6abef62835 100644
--- a/src/widgets/styles/qstylesheetstyle.cpp
+++ b/src/widgets/styles/qstylesheetstyle.cpp
@@ -4612,11 +4612,14 @@ void QStyleSheetStyle::drawPrimitive(PrimitiveElement pe, const QStyleOption *op
 
     case PE_PanelLineEdit:
         if (const QStyleOptionFrame *frm = qstyleoption_cast<const QStyleOptionFrame *>(opt)) {
-            if (QWidget *container = containerWidget(w); container != w) {
-                QRenderRule containerRule = renderRule(container, opt);
-                if (!containerRule.hasNativeBorder() || !containerRule.baseStyleCanDraw())
-                    return;
-                rule = containerRule;
+            // Fall back to container widget's render rule
+            if (w) {
+                if (QWidget *container = containerWidget(w); container != w) {
+                    QRenderRule containerRule = renderRule(container, opt);
+                    if (!containerRule.hasNativeBorder() || !containerRule.baseStyleCanDraw())
+                        return;
+                    rule = containerRule;
+                }
             }
 
             if (rule.hasNativeBorder()) {