From: asxpi <asxpi@narayana.im>
Subject: [PATCH] wayland/touch: Don't crash on grab requests for cancelled touches (traced)

The same NULL check as mutter-touch-cancelled-grab.patch (mutter!5375):
a touch cancelled while the finger is still down keeps its
MetaWaylandTouchInfo with focus_surface NULL (deliberately, since !5057),
and a grab request with its serial must be refused rather than crash in
touch_can_grab_surface().

LOCAL TEST ONLY: three g_message lines say which path cancelled the touch
(CLUTTER_TOUCH_CANCEL or the seat's focus change) and when a grab for a
cancelled touch was refused, to answer the open question on !5375 of how a
resize reaches touch_can_grab_surface() with no focus surface.

Upstream: https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/5375
---
--- a/src/wayland/meta-wayland-touch.c
+++ b/src/wayland/meta-wayland-touch.c
@@ -524,6 +524,7 @@
       break;

     case CLUTTER_TOUCH_CANCEL:
+      g_message ("touch-trace: cancel via CLUTTER_TOUCH_CANCEL");
       meta_wayland_touch_cancel (touch);
       break;

@@ -656,6 +657,13 @@
 {
   MetaWaylandSurface *subsurface;

+  /* Cleared by meta_wayland_touch_cancel() while the touch is still down */
+  if (!touch_info->focus_surface)
+    {
+      g_message ("touch-trace: grab refused for a cancelled touch");
+      return FALSE;
+    }
+
   if (touch_info->focus_surface->surface == surface)
     return TRUE;

--- a/src/wayland/meta-wayland-seat.c
+++ b/src/wayland/meta-wayland-seat.c
@@ -259,7 +259,10 @@
         sequence = clutter_sprite_get_sequence (CLUTTER_SPRITE (focus));

         if (surface != meta_wayland_touch_get_focus_surface (seat->touch, sequence))
-          meta_wayland_touch_cancel (seat->touch);
+          {
+            g_message ("touch-trace: cancel via seat focus change");
+            meta_wayland_touch_cancel (seat->touch);
+          }

         break;
       }