Memory re-allocated could disclose the secret talloc magic. Instead use the fixed talloc magic for the 'was talloc, is now free' indication.
Created attachment 13902 [details] patch for master
We released this in talloc 2.1.11 with master commit efe317c59204af076bb500ad904d2a5f6a961509 for Samba 4.8. Patch is in 062309755888349afaa05dff7ac48ea8867110e0.