xfrm: interface: support IP6IP6 and IP6IP tunnels processing with .cb_handler

Similar to ip6_vti, IP6IP6 and IP6IP tunnels processing can easily
be done with .cb_handler for xfrm interface.

v1->v2:
  - no change.
v2-v3:
  - enable it only when CONFIG_INET6_XFRM_TUNNEL is defined, to fix
    the build error, reported by kbuild test robot.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_interface.c

@@ -798,6 +798,26 @@ static struct xfrm6_protocol xfrmi_ipcomp6_protocol __read_mostly = {
 	.priority	=	10,
 };
 
+#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+static int xfrmi6_rcv_tunnel(struct sk_buff *skb)
+{
+	const xfrm_address_t *saddr;
+	__be32 spi;
+
+	saddr = (const xfrm_address_t *)&ipv6_hdr(skb)->saddr;
+	spi = xfrm6_tunnel_spi_lookup(dev_net(skb->dev), saddr);
+
+	return xfrm6_rcv_spi(skb, IPPROTO_IPV6, spi, NULL);
+}
+
+static struct xfrm6_tunnel xfrmi_ipv6_handler __read_mostly = {
+	.handler	=	xfrmi6_rcv_tunnel,
+	.cb_handler	=	xfrmi_rcv_cb,
+	.err_handler	=	xfrmi6_err,
+	.priority	=	-1,
+};
+#endif
+
 static struct xfrm4_protocol xfrmi_esp4_protocol __read_mostly = {
 	.handler	=	xfrm4_rcv,
 	.input_handler	=	xfrm_input,
@@ -866,9 +886,23 @@ static int __init xfrmi6_init(void)
 	err = xfrm6_protocol_register(&xfrmi_ipcomp6_protocol, IPPROTO_COMP);
 	if (err < 0)
 		goto xfrm_proto_comp_failed;
+#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+	err = xfrm6_tunnel_register(&xfrmi_ipv6_handler, AF_INET6);
+	if (err < 0)
+		goto xfrm_tunnel_ipv6_failed;
+	err = xfrm6_tunnel_register(&xfrmi_ipv6_handler, AF_INET);
+	if (err < 0)
+		goto xfrm_tunnel_ip6ip_failed;
+#endif
 
 	return 0;
 
+#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+xfrm_tunnel_ip6ip_failed:
+	xfrm6_tunnel_deregister(&xfrmi_ipv6_handler, AF_INET6);
+xfrm_tunnel_ipv6_failed:
+	xfrm6_protocol_deregister(&xfrmi_ipcomp6_protocol, IPPROTO_COMP);
+#endif
 xfrm_proto_comp_failed:
 	xfrm6_protocol_deregister(&xfrmi_ah6_protocol, IPPROTO_AH);
 xfrm_proto_ah_failed:
@@ -879,6 +913,10 @@ xfrm_proto_esp_failed:
 
 static void xfrmi6_fini(void)
 {
+#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+	xfrm6_tunnel_deregister(&xfrmi_ipv6_handler, AF_INET);
+	xfrm6_tunnel_deregister(&xfrmi_ipv6_handler, AF_INET6);
+#endif
 	xfrm6_protocol_deregister(&xfrmi_ipcomp6_protocol, IPPROTO_COMP);
 	xfrm6_protocol_deregister(&xfrmi_ah6_protocol, IPPROTO_AH);
 	xfrm6_protocol_deregister(&xfrmi_esp6_protocol, IPPROTO_ESP);