[mutter] x11: Check for XCB reply

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

commit 445373d028c896b557d03d4f416e7a50a972cf08
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Mon Feb 8 18:19:01 2021 +0100

    x11: Check for XCB reply
    
    Now that mutter can survive Xwayland vanishing in mid-flight, we need to
    actually check if the Xserver reply fetched though XCB is not NULL,
    otherwise we may crash, that would be a shame.
    
    Close: https://gitlab.gnome.org/GNOME/mutter/-/issues/1638
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1718>

 src/x11/group.c  |  4 ++--
 src/x11/xprops.c | 12 ++++--------
 2 files changed, 6 insertions(+), 10 deletions(-)
---
diff --git a/src/x11/group.c b/src/x11/group.c
index 57b79e96e5..27f21d0682 100644
--- a/src/x11/group.c
+++ b/src/x11/group.c
@@ -56,12 +56,12 @@ meta_group_new (MetaX11Display *x11_display,
   group->refcount = 1; /* owned by caller, hash table has only weak ref */
 
   xcb_connection_t *xcb_conn = XGetXCBConnection (x11_display->xdisplay);
-  xcb_generic_error_t *e;
+  g_autofree xcb_generic_error_t *e = NULL;
   g_autofree xcb_get_window_attributes_reply_t *attrs =
     xcb_get_window_attributes_reply (xcb_conn,
                                      xcb_get_window_attributes (xcb_conn, group_leader),
                                      &e);
-  if (e)
+  if (e || !attrs)
     return NULL;
 
   const uint32_t events[] = { attrs->your_event_mask | XCB_EVENT_MASK_PROPERTY_CHANGE };
diff --git a/src/x11/xprops.c b/src/x11/xprops.c
index ad74538534..19f7a1cae0 100644
--- a/src/x11/xprops.c
+++ b/src/x11/xprops.c
@@ -191,16 +191,13 @@ async_get_property_finish (xcb_connection_t          *xcb_conn,
                            xcb_get_property_cookie_t  cookie,
                            GetPropertyResults        *results)
 {
-  xcb_get_property_reply_t *reply;
-  xcb_generic_error_t *error;
+  g_autofree xcb_get_property_reply_t *reply = NULL;
+  g_autofree xcb_generic_error_t *error = NULL;
   int length;
 
   reply = xcb_get_property_reply (xcb_conn, cookie, &error);
-  if (error)
-    {
-      free (error);
-      return FALSE;
-    }
+  if (error || !reply)
+    return FALSE;
 
   results->n_items = reply->value_len;
   results->type = reply->type;
@@ -219,7 +216,6 @@ async_get_property_finish (xcb_connection_t          *xcb_conn,
       results->prop[length] = '\0';
     }
 
-  free (reply);
   return (results->prop != NULL);
 }