Hi,

When creating a custom wayland surface, by getting a wl_compositor and calling wl_compositor_create_surface, it's userdata is not filled with what Qt expects.

Thus, as there is no check of ownership, when the pointer enters a non-Qt wl_surface running on the same wayland client connection, Qt tries to cast the userdata and it results in a segfault.

Here is the relevant code in src/client/qwaylandinputdevice.cpp:447

void QWaylandInputDevice::Pointer::pointer_enter(uint32_t serial, struct wl_surface *surface,
                                                  wl_fixed_t sx, wl_fixed_t sy)
 {
     if (!surface)
         return;
 
     QWaylandWindow *window = QWaylandWindow::fromWlSurface(surface);
     mFocus = window;
     mSurfacePos = QPointF(wl_fixed_to_double(sx), wl_fixed_to_double(sy));
     mGlobalPos = window->window()->mapToGlobal(mSurfacePos.toPoint()); 

I haven't tested many QtWayland version but I believe It should happens in every QtWayland versions.

Maybe something derived from this can be done to fix this issue?

https://github.com/alexandre-janniaux/qtwayland/pull/1/files

Stacktrace is attached: stacktrace_qt_pointer.md