Make QGuiApplicationPrivate::lastCursorPosition.toPoint() safe to use

QGuiApplicationPrivate::lastCursorPosition is initialized with qInf();
so before Qt has seen a mouse move event, attempting to convert to
QPoint is an error. It's best to have one place where we do the qIsInf()
check rather than several (and otherwise prefer using the QPointF as-is
rather than converting to QPoint at all).

Introduce a helper class that contains a QPointF, and provides a safe
conversion to QPoint, as well as simple accessors for clients using
QPointF.

Fixes: QTBUG-52472
Task-number: QTBUG-45045
Change-Id: I83fad1bfb658e03fa876344552f1d5bb751d9f81
Pick-to: 6.2 6.3
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 11 insertions, 2 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 7996883d06..da71580a73 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -130,6 +130,7 @@
 #include <qtgui_tracepoints_p.h>
 
 #include <ctype.h>
+#include <limits>
 
 QT_BEGIN_NAMESPACE
 
@@ -147,7 +148,7 @@ Q_GUI_EXPORT bool qt_is_tty_app = false;
 Qt::MouseButtons QGuiApplicationPrivate::mouse_buttons = Qt::NoButton;
 Qt::KeyboardModifiers QGuiApplicationPrivate::modifier_buttons = Qt::NoModifier;
 
-QPointF QGuiApplicationPrivate::lastCursorPosition(qt_inf(), qt_inf());
+QGuiApplicationPrivate::QLastCursorPosition QGuiApplicationPrivate::lastCursorPosition;
 
 QWindow *QGuiApplicationPrivate::currentMouseWindow = nullptr;
 
@@ -711,7 +712,7 @@ QGuiApplication::~QGuiApplication()
     QGuiApplicationPrivate::desktopFileName = nullptr;
     QGuiApplicationPrivate::mouse_buttons = Qt::NoButton;
     QGuiApplicationPrivate::modifier_buttons = Qt::NoModifier;
-    QGuiApplicationPrivate::lastCursorPosition = {qreal(qInf()), qreal(qInf())};
+    QGuiApplicationPrivate::lastCursorPosition.reset();
     QGuiApplicationPrivate::currentMousePressWindow = QGuiApplicationPrivate::currentMouseWindow = nullptr;
     QGuiApplicationPrivate::applicationState = Qt::ApplicationInactive;
     QGuiApplicationPrivate::currentDragWindow = nullptr;
@@ -4144,6 +4145,14 @@ QPixmap QGuiApplicationPrivate::getPixmapCursor(Qt::CursorShape cshape)
     return QPixmap();
 }
 
+QPoint QGuiApplicationPrivate::QLastCursorPosition::toPoint() const noexcept
+{
+    // Guard against the default initialization of qInf() (avoid UB or SIGFPE in conversion).
+    if (Q_UNLIKELY(qIsInf(thePoint.x())))
+        return QPoint(std::numeric_limits<int>::max(), std::numeric_limits<int>::max());
+    return thePoint.toPoint();
+}
+
 void QGuiApplicationPrivate::notifyThemeChanged()
 {
     updatePalette();