tst_QWidget: Fix UB (invalid member access) in EnterTestMainDialog::eventFilter()

Found by UBSan:

  tst_qwidget.cpp:10207:29: runtime error: member access within address 0x6060000e8880 which does not point to an object of type 'EnterTestModalDialog'
  0x6060000e8880: note: object is of type 'QWidget'
   eb 00 80 45  10 4b 32 ab 11 2b 00 00  80 df 08 00 60 61 00 00  c0 4c 32 ab 11 2b 00 00  00 00 be be
                ^~~~~~~~~~~~~~~~~~~~~~~
                vptr for 'QWidget'
    #0 0x6ca13f in EnterTestMainDialog::eventFilter(QObject*, QEvent*) tst_qwidget.cpp:10207
    #1 0x2b11b8bc90c3 in QCoreApplicationPrivate::sendThroughApplicationEventFilters(QObject*, QEvent*) qcoreapplication.cpp:1081
    #2 0x2b11a3c49b4a in QApplicationPrivate::notify_helper(QObject*, QEvent*) qapplication.cpp:3716
    #3 0x2b11a3c8ec72 in QApplication::notify(QObject*, QEvent*) qapplication.cpp:3704
    #4 0x2b11b8bccd0f in QCoreApplication::notifyInternal2(QObject*, QEvent*) qcoreapplication.cpp:988
    #5 0x2b11aea5c34d in QCoreApplication::sendEvent(QObject*, QEvent*) qcoreapplication.h:231
    #6 0x2b11aea5c34d in QGuiApplicationPrivate::_q_updateFocusObject(QObject*) qguiapplication.cpp:3690
    #7 0x2b11aea61360 in QGuiApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) .moc/moc_qguiapplication.cpp:177
    #8 0x2b11b8d1dc86 in QMetaObject::activate(QObject*, int, int, void**) qobject.cpp:3787
    #9 0x2b11aea784a3 in QWindow::focusObjectChanged(QObject*) .moc/moc_qwindow.cpp:760
    #10 0x2b11a3fb24f2 in QWidget::clearFocus() qwidget.cpp:6705
    #11 0x2b11a3fc87b1 in QWidget::~QWidget() qwidget.cpp:1608
    #12 0x2b11a526688c in QDialog::~QDialog() qdialog.cpp:352
    #13 0x6c43e2 in EnterTestModalDialog::~EnterTestModalDialog() tst_qwidget.cpp:10160
    #14 0x6c43e2 in EnterTestModalDialog::~EnterTestModalDialog() tst_qwidget.cpp:10160
    #15 0x492be3 in EnterTestMainDialog::buttonPressed() tst_qwidget.cpp:10188
    #16 0x492be3 in EnterTestMainDialog::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) .moc/tst_qwidget.moc:2056
    #17 0x2b11b8d1dc86 in QMetaObject::activate(QObject*, int, int, void**) qobject.cpp:3787
    #18 0x2b11a45cb833 in QAbstractButton::clicked(bool) .moc/moc_qabstractbutton.cpp:307
    #19 0x2b11a45cd54b in QAbstractButtonPrivate::emitClicked() qabstractbutton.cpp:411
    #20 0x2b11a45df73a in QAbstractButtonPrivate::click() qabstractbutton.cpp:404
    [...]
    #41 0x6bb2cf in tst_QWidget::taskQTBUG_27643_enterEvents() tst_qwidget.cpp:10249
    [...]

Fix by checking the event type first, and accessing
modal->button only if it's QEvent::Enter.

Change-Id: I2c7df3a1f43ecbfe14741b5861729078a91a32d6
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 6 insertions, 7 deletions

diff --git a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp b/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
index e00e575c36..cc1aaa7d51 100644
--- a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
+++ b/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
@@ -10430,14 +10430,13 @@ public slots:
 
     bool eventFilter(QObject *o, QEvent *e)
     {
-        if (modal && modal->button && o == modal->button) {
-            switch (e->type()) {
-            case QEvent::Enter:
+        switch (e->type()) {
+        case QEvent::Enter:
+            if (modal && modal->button && o == modal->button)
                 enters++;
-                break;
-            default:
-                break;
-            }
+            break;
+        default:
+            break;
         }
         return QDialog::eventFilter(o, e);
     }