KEYS: Fix use-after-free in assoc_array_gc()

An edit script should be considered inaccessible by a function once it has
called assoc_array_apply_edit() or assoc_array_cancel_edit().

However, assoc_array_gc() is accessing the edit script just after the
gc_complete: label.

Reported-by: Andreea-Cristina Bernat <bernat.ada@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Andreea-Cristina Bernat <bernat.ada@gmail.com>
cc: shemming@brocade.com
cc: paulmck@linux.vnet.ibm.com
Cc: stable@vger.kernel.org
Signed-off-by: James Morris <james.l.morris@oracle.com>

lib/assoc_array.c

@@ -1735,7 +1735,7 @@ ascend_old_tree:
 gc_complete:
 	edit->set[0].to = new_root;
 	assoc_array_apply_edit(edit);
-	edit->array->nr_leaves_on_tree = nr_leaves_on_tree;
+	array->nr_leaves_on_tree = nr_leaves_on_tree;
 	return 0;
 
 enomem: