ip6_vti: support IP6IP6 tunnel processing with .cb_handler

Similar to IPIP tunnel's processing, this patch is to support
IP6IP6 tunnel processing with .cb_handler.

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/ipv6/ip6_vti.c

@@ -1218,6 +1218,26 @@ static struct xfrm6_protocol vti_ipcomp6_protocol __read_mostly = {
 	.priority	=	100,
 };
 
+#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+static int vti6_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 vti6_input_proto(skb, IPPROTO_IPV6, spi, 0);
+}
+
+static struct xfrm6_tunnel vti_ipv6_handler __read_mostly = {
+	.handler	=	vti6_rcv_tunnel,
+	.cb_handler	=	vti6_rcv_cb,
+	.err_handler	=	vti6_err,
+	.priority	=	0,
+};
+#endif
+
 /**
  * vti6_tunnel_init - register protocol and reserve needed resources
  *
@@ -1243,6 +1263,12 @@ static int __init vti6_tunnel_init(void)
 	err = xfrm6_protocol_register(&vti_ipcomp6_protocol, IPPROTO_COMP);
 	if (err < 0)
 		goto xfrm_proto_comp_failed;
+#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+	msg = "ipv6 tunnel";
+	err = xfrm6_tunnel_register(&vti_ipv6_handler, AF_INET6);
+	if (err < 0)
+		goto vti_tunnel_failed;
+#endif
 
 	msg = "netlink interface";
 	err = rtnl_link_register(&vti6_link_ops);
@@ -1252,6 +1278,10 @@ static int __init vti6_tunnel_init(void)
 	return 0;
 
 rtnl_link_failed:
+#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+	err = xfrm6_tunnel_deregister(&vti_ipv6_handler, AF_INET6);
+vti_tunnel_failed:
+#endif
 	xfrm6_protocol_deregister(&vti_ipcomp6_protocol, IPPROTO_COMP);
 xfrm_proto_comp_failed:
 	xfrm6_protocol_deregister(&vti_ah6_protocol, IPPROTO_AH);
@@ -1270,6 +1300,9 @@ static int __init vti6_tunnel_init(void)
 static void __exit vti6_tunnel_cleanup(void)
 {
 	rtnl_link_unregister(&vti6_link_ops);
+#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+	xfrm6_tunnel_deregister(&vti_ipv6_handler, AF_INET6);
+#endif
 	xfrm6_protocol_deregister(&vti_ipcomp6_protocol, IPPROTO_COMP);
 	xfrm6_protocol_deregister(&vti_ah6_protocol, IPPROTO_AH);
 	xfrm6_protocol_deregister(&vti_esp6_protocol, IPPROTO_ESP);