[mutter] xprops: Validate text properties that claim to be UTF8

[Marge Bot <marge-bot src gnome org>]

commit e4236530170b6c06b3c3832631f79f33f51703a9
Author: Sebastian Keller <skeller gnome org>
Date:   Tue May 4 01:42:58 2021 +0200

    xprops: Validate text properties that claim to be UTF8
    
    Some clients such as mpv might set the WM_TITLE as a UTF8_STRING based
    on some unconverted/unvalidated metadata that is not actually UTF8. This
    would then be set as the title of a MetaWindow (in the absence of a
    valid UTF8 _NET_WM_TITLE). The shell then tries to use this window title
    for things like the overview or the window switcher where it would
    trigger an UTF8 validation error and leave the shell in an unusable
    state.
    
    Fixes: https://gitlab.gnome.org/GNOME/mutter/-/issues/1794
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1850>

 src/x11/xprops.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)
---
diff --git a/src/x11/xprops.c b/src/x11/xprops.c
index 19f7a1cae0..729d5b684c 100644
--- a/src/x11/xprops.c
+++ b/src/x11/xprops.c
@@ -620,7 +620,7 @@ meta_prop_get_cardinal_with_atom_type (MetaX11Display *x11_display,
 }
 
 static char *
-text_property_to_utf8 (Display *xdisplay,
+text_property_to_utf8 (GetPropertyResults  *results,
                        const XTextProperty *prop)
 {
   char *ret = NULL;
@@ -629,7 +629,8 @@ text_property_to_utf8 (Display *xdisplay,
   int count = 0;
   int res;
 
-  res = XmbTextPropertyToTextList (xdisplay, prop, &local_list, &count);
+  res = XmbTextPropertyToTextList (results->x11_display->xdisplay, prop,
+                                   &local_list, &count);
   if (res == XNoMemory || res == XLocaleNotSupported || res == XConverterNotFound)
     goto out;
 
@@ -637,9 +638,26 @@ text_property_to_utf8 (Display *xdisplay,
     goto out;
 
   if (g_get_charset (&charset))
-    ret = g_strdup (local_list[0]);
+    {
+      if (!g_utf8_validate (local_list[0], -1, NULL))
+        {
+          char *name;
+
+          meta_x11_error_trap_push (results->x11_display);
+          name = XGetAtomName (results->x11_display->xdisplay, results->xatom);
+          meta_x11_error_trap_pop (results->x11_display);
+          meta_warning ("Property %s on window 0x%lx contained invalid UTF-8",
+                        name, results->xwindow);
+          meta_XFree (name);
+
+          goto out;
+        }
+      ret = g_strdup (local_list[0]);
+    }
   else
-    ret = g_convert (local_list[0], -1, "UTF-8", charset, NULL, NULL, NULL);
+    {
+      ret = g_convert (local_list[0], -1, "UTF-8", charset, NULL, NULL, NULL);
+    }
 
  out:
   XFreeStringList (local_list);
@@ -659,7 +677,7 @@ text_property_from_results (GetPropertyResults *results,
   tp.format = results->format;
   tp.nitems = results->n_items;
 
-  *utf8_str_p = text_property_to_utf8 (results->x11_display->xdisplay, &tp);
+  *utf8_str_p = text_property_to_utf8 (results, &tp);
 
   g_clear_pointer (&results->prop, g_free);