Fix out-of-bounds write

Change ac210c73e4 introduced the requirement that all input devices with
Scroll capability must have a QXcbScrollingDevicePrivate as their d_ptr.
However, this was not enforced, and would fail for the "Virtual core
pointer".

To fix this, always use qobject_cast to verify that the device is of the
correct type.

Change-Id: I4a6b1d4d79308eb04e9f52dda00294fffe377bdf
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index b62d461170..1e402a37de 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -78,7 +78,7 @@ class QXcbScreen;
 class QXcbWindow;
 class QXcbDrag;
 class QXcbKeyboard;
-class QXcbScrollingDevicePrivate;
+class QXcbScrollingDevice;
 class QXcbClipboard;
 class QXcbWMSupport;
 class QXcbNativeInterface;
@@ -316,8 +316,8 @@ private:
     TabletData *tabletDataForDevice(int id);
 #endif // QT_CONFIG(tabletevent)
     void xi2HandleScrollEvent(void *event, const QPointingDevice *scrollingDevice);
-    void xi2UpdateScrollingDevice(QXcbScrollingDevicePrivate *scrollingDevice);
-    QXcbScrollingDevicePrivate *scrollingDeviceForId(int id);
+    void xi2UpdateScrollingDevice(QInputDevice *scrollingDevice);
+    QXcbScrollingDevice *scrollingDeviceForId(int id);
 
     static bool xi2GetValuatorValueIfSet(const void *event, int valuatorNum, double *value);