apparmor: fix potential UAF in aa_replace_profiles

The function aa_replace_profiles was accessing udata->size after calling
aa_put_loaddata(udata), causing a potential UAF.

Fixed this by saving the size to a local variable before dropping the
reference.

Fixes: 5ac8c355ae ("apparmor: allow introspecting the loaded policy pre internal transform")
Reviewed-by: Georgia Garcia <[email protected]>
Signed-off-by: Maxime Bélair <[email protected]>
Signed-off-by: John Johansen <[email protected]>

security/apparmor/policy.c

@@ -1378,13 +1378,15 @@ ssize_t aa_replace_profiles(struct aa_ns *policy_ns, struct aa_label *label,
 	mutex_unlock(&ns->lock);
 
 out:
+	ssize_t udata_sz = udata->size;
+
 	aa_put_ns(ns);
 	aa_put_profile_loaddata(udata);
 	kfree(ns_name);
 
 	if (error)
 		return error;
-	return udata->size;
+	return udata_sz;
 
 fail_lock:
 	mutex_unlock(&ns->lock);