xwayland/present: Fix use-after-free in xwl_unrealize_window()

When a window is unrealized, Xwayland would destroy the Wayland surface
prior to unrealizing the present window.

xwl_present_flip() will then do a wl_surface_commit() of that surface,
hence causing a use-after-free:

 Invalid read of size 8
    at 0x49F7FD4: wl_proxy_marshal_array_flags (wayland-client.c:852)
    by 0x49F823A: wl_proxy_marshal_flags (wayland-client.c:784)
    by 0x42B877: wl_surface_commit (wayland-client-protocol.h:3914)
    by 0x42CAA7: xwl_present_flip (xwayland-present.c:717)
    by 0x42CD0E: xwl_present_execute (xwayland-present.c:783)
    by 0x42C26D: xwl_present_msc_bump (xwayland-present.c:416)
    by 0x42C2D1: xwl_present_timer_callback (xwayland-present.c:433)
    by 0x42BAC4: xwl_present_reset_timer (xwayland-present.c:149)
    by 0x42D1F8: xwl_present_unrealize_window (xwayland-present.c:945)
    by 0x4230E2: xwl_unrealize_window (xwayland-window.c:616)
    by 0x4FCDD8: compUnrealizeWindow (compwindow.c:292)
    by 0x4F3F5C: UnrealizeTree (window.c:2805)
  Address 0x1390b8d8 is 24 bytes inside a block of size 80 free'd
    at 0x48470E4: free (vg_replace_malloc.c:872)
    by 0x49F8029: wl_proxy_destroy_caller_locks (wayland-client.c:523)
    by 0x49F8029: wl_proxy_marshal_array_flags (wayland-client.c:861)
    by 0x49F823A: wl_proxy_marshal_flags (wayland-client.c:784)
    by 0x421984: wl_surface_destroy (wayland-client-protocol.h:3672)
    by 0x423052: xwl_unrealize_window (xwayland-window.c:599)
    by 0x4FCDD8: compUnrealizeWindow (compwindow.c:292)
    by 0x4F3F5C: UnrealizeTree (window.c:2805)
    by 0x4F424B: UnmapWindow (window.c:2863)
    by 0x4EF58C: DeleteWindow (window.c:1075)
    by 0x4E24B3: doFreeResource (resource.c:885)
    by 0x4E2ED7: FreeClientResources (resource.c:1151)
    by 0x4ACBA4: CloseDownClient (dispatch.c:3546)
  Block was alloc'd at
    at 0x4849464: calloc (vg_replace_malloc.c:1328)
    by 0x49F7F29: zalloc (wayland-private.h:233)
    by 0x49F7F29: proxy_create (wayland-client.c:422)
    by 0x49F7F29: create_outgoing_proxy (wayland-client.c:664)
    by 0x49F7F29: wl_proxy_marshal_array_flags (wayland-client.c:831)
    by 0x49F823A: wl_proxy_marshal_flags (wayland-client.c:784)
    by 0x4218CA: wl_compositor_create_surface (wayland-client-protocol.h:1291)
    by 0x422A0D: ensure_surface_for_window (xwayland-window.c:445)
    by 0x4231E8: xwl_window_set_window_pixmap (xwayland-window.c:647)
    by 0x5232D6: damageSetWindowPixmap (damage.c:1565)
    by 0x4FC7BC: compSetPixmapVisitWindow (compwindow.c:129)
    by 0x4EDB3F: TraverseTree (window.c:441)
    by 0x4FC851: compSetPixmap (compwindow.c:151)
    by 0x4F8C1A: compAllocPixmap (compalloc.c:616)
    by 0x4FC938: compCheckRedirect (compwindow.c:174)

To avoid that, call xwl_present_unrealize_window() before destroying the
Wayland surface.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
(cherry picked from commit 42113ab2894251376b2beab7e68f2705f5ce1084)

1 files changed, 10 insertions, 10 deletions

diff --git a/hw/xwayland/xwayland-window.c b/hw/xwayland/xwayland-window.c
index 152b4d0a6..92bcae326 100644
--- a/hw/xwayland/xwayland-window.c
+++ b/hw/xwayland/xwayland-window.c
@@ -605,16 +605,6 @@ xwl_unrealize_window(WindowPtr window)
     if (xwl_window_has_viewport_enabled(xwl_window))
         xwl_window_disable_viewport(xwl_window);
 
-    wl_surface_destroy(xwl_window->surface);
-    xorg_list_del(&xwl_window->link_damage);
-    xorg_list_del(&xwl_window->link_window);
-    unregister_damage(window);
-
-    xwl_window_buffers_dispose(xwl_window);
-
-    if (xwl_window->frame_callback)
-        wl_callback_destroy(xwl_window->frame_callback);
-
 #ifdef GLAMOR_HAS_GBM
     if (xwl_screen->present) {
         struct xwl_present_window *xwl_present_window, *tmp;
@@ -627,6 +617,16 @@ xwl_unrealize_window(WindowPtr window)
     }
 #endif
 
+    wl_surface_destroy(xwl_window->surface);
+    xorg_list_del(&xwl_window->link_damage);
+    xorg_list_del(&xwl_window->link_window);
+    unregister_damage(window);
+
+    xwl_window_buffers_dispose(xwl_window);
+
+    if (xwl_window->frame_callback)
+        wl_callback_destroy(xwl_window->frame_callback);
+
     free(xwl_window);
     dixSetPrivate(&window->devPrivates, &xwl_window_private_key, NULL);