ipe: return -ESTALE instead of -EINVAL on update when new policy has a lower version

When loading policies in userspace we want a recognizable error when an
update attempts to use an old policy, as that is an error that needs
to be treated differently from an invalid policy. Use -ESTALE as it is
clear enough for an update mechanism.
Signed-off-by: Luca Boccassi <bluca@debian.org>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Fan Wu <wufan@kernel.org>

security/ipe/policy.c

@@ -107,7 +107,7 @@ int ipe_update_policy(struct inode *root, const char *text, size_t textlen,
 	}
 
 	if (ver_to_u64(old) > ver_to_u64(new)) {
-		rc = -EINVAL;
+		rc = -ESTALE;
 		goto err;
 	}