ip_vti: support IPIP tunnel processing with .cb_handler

With tunnel4_input_afinfo added, IPIP tunnel processing in
ip_vti can be easily done with .cb_handler. So replace the
processing by calling ip_tunnel_rcv() with it.

v1->v2:
  - no change.
v2-v3:
  - enable it only when CONFIG_INET_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/ipv4/ip_vti.c

@@ -91,32 +91,6 @@ static int vti_rcv_proto(struct sk_buff *skb)
 	return vti_rcv(skb, 0, false);
 }
 
-static int vti_rcv_tunnel(struct sk_buff *skb)
-{
-	struct ip_tunnel_net *itn = net_generic(dev_net(skb->dev), vti_net_id);
-	const struct iphdr *iph = ip_hdr(skb);
-	struct ip_tunnel *tunnel;
-
-	tunnel = ip_tunnel_lookup(itn, skb->dev->ifindex, TUNNEL_NO_KEY,
-				  iph->saddr, iph->daddr, 0);
-	if (tunnel) {
-		struct tnl_ptk_info tpi = {
-			.proto = htons(ETH_P_IP),
-		};
-
-		if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
-			goto drop;
-		if (iptunnel_pull_header(skb, 0, tpi.proto, false))
-			goto drop;
-		return ip_tunnel_rcv(tunnel, skb, &tpi, NULL, false);
-	}
-
-	return -EINVAL;
-drop:
-	kfree_skb(skb);
-	return 0;
-}
-
 static int vti_rcv_cb(struct sk_buff *skb, int err)
 {
 	unsigned short family;
@@ -495,11 +469,22 @@ static struct xfrm4_protocol vti_ipcomp4_protocol __read_mostly = {
 	.priority	=	100,
 };
 
-static struct xfrm_tunnel ipip_handler __read_mostly = {
+#if IS_ENABLED(CONFIG_INET_XFRM_TUNNEL)
+static int vti_rcv_tunnel(struct sk_buff *skb)
+{
+	XFRM_SPI_SKB_CB(skb)->family = AF_INET;
+	XFRM_SPI_SKB_CB(skb)->daddroff = offsetof(struct iphdr, daddr);
+
+	return vti_input(skb, IPPROTO_IPIP, ip_hdr(skb)->saddr, 0, false);
+}
+
+static struct xfrm_tunnel vti_ipip_handler __read_mostly = {
 	.handler	=	vti_rcv_tunnel,
+	.cb_handler	=	vti_rcv_cb,
 	.err_handler	=	vti4_err,
 	.priority	=	0,
 };
+#endif
 
 static int __net_init vti_init_net(struct net *net)
 {
@@ -669,10 +654,12 @@ static int __init vti_init(void)
 	if (err < 0)
 		goto xfrm_proto_comp_failed;
 
+#if IS_ENABLED(CONFIG_INET_XFRM_TUNNEL)
 	msg = "ipip tunnel";
-	err = xfrm4_tunnel_register(&ipip_handler, AF_INET);
+	err = xfrm4_tunnel_register(&vti_ipip_handler, AF_INET);
 	if (err < 0)
 		goto xfrm_tunnel_failed;
+#endif
 
 	msg = "netlink interface";
 	err = rtnl_link_register(&vti_link_ops);
@@ -682,8 +669,10 @@ static int __init vti_init(void)
 	return err;
 
 rtnl_link_failed:
-	xfrm4_tunnel_deregister(&ipip_handler, AF_INET);
+#if IS_ENABLED(CONFIG_INET_XFRM_TUNNEL)
+	xfrm4_tunnel_deregister(&vti_ipip_handler, AF_INET);
 xfrm_tunnel_failed:
+#endif
 	xfrm4_protocol_deregister(&vti_ipcomp4_protocol, IPPROTO_COMP);
 xfrm_proto_comp_failed:
 	xfrm4_protocol_deregister(&vti_ah4_protocol, IPPROTO_AH);
@@ -699,7 +688,9 @@ static int __init vti_init(void)
 static void __exit vti_fini(void)
 {
 	rtnl_link_unregister(&vti_link_ops);
-	xfrm4_tunnel_deregister(&ipip_handler, AF_INET);
+#if IS_ENABLED(CONFIG_INET_XFRM_TUNNEL)
+	xfrm4_tunnel_deregister(&vti_ipip_handler, AF_INET);
+#endif
 	xfrm4_protocol_deregister(&vti_ipcomp4_protocol, IPPROTO_COMP);
 	xfrm4_protocol_deregister(&vti_ah4_protocol, IPPROTO_AH);
 	xfrm4_protocol_deregister(&vti_esp4_protocol, IPPROTO_ESP);