userns: don't leak root user

Signed-off-by: NAlexey Dobriyan <adobriyan@sw.ru>
Acked-by: NCedric Le Goater <clg@fr.ibm.com>
Acked-by: NSerge Hallyn <serue@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/user_namespace.c

@@ -81,6 +81,7 @@ void free_user_ns(struct kref *kref)
 	struct user_namespace *ns;
 
 	ns = container_of(kref, struct user_namespace, kref);
+	free_uid(ns->root_user);
 	kfree(ns);
 }