net: add dst_pending_confirm flag to skbuff

Add new skbuff flag to allow protocols to confirm neighbour.
When same struct dst_entry can be used for many different
neighbours we can not use it for pending confirmations.

Add sock_confirm_neigh() helper to confirm the neighbour and
use it for IPv4, IPv6 and VRF before dst_neigh_output.
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vrf.c

@@ -378,6 +378,7 @@ static int vrf_finish_output6(struct net *net, struct sock *sk,
 	if (unlikely(!neigh))
 		neigh = __neigh_create(&nd_tbl, nexthop, dst->dev, false);
 	if (!IS_ERR(neigh)) {
+		sock_confirm_neigh(skb, neigh);
 		ret = dst_neigh_output(dst, neigh, skb);
 		rcu_read_unlock_bh();
 		return ret;
@@ -574,8 +575,10 @@ static int vrf_finish_output(struct net *net, struct sock *sk, struct sk_buff *s
 	neigh = __ipv4_neigh_lookup_noref(dev, nexthop);
 	if (unlikely(!neigh))
 		neigh = __neigh_create(&arp_tbl, &nexthop, dev, false);
-	if (!IS_ERR(neigh))
+	if (!IS_ERR(neigh)) {
+		sock_confirm_neigh(skb, neigh);
 		ret = dst_neigh_output(dst, neigh, skb);
+	}
 
 	rcu_read_unlock_bh();
 err:

include/linux/skbuff.h

@@ -612,6 +612,7 @@ static inline bool skb_mstamp_after(const struct skb_mstamp *t1,
  *	@wifi_acked_valid: wifi_acked was set
  *	@wifi_acked: whether frame was acked on wifi or not
  *	@no_fcs:  Request NIC to treat last 4 bytes as Ethernet FCS
+ *	@dst_pending_confirm: need to confirm neighbour
   *	@napi_id: id of the NAPI struct this skb came from
  *	@secmark: security marking
  *	@mark: Generic packet mark
@@ -741,6 +742,7 @@ struct sk_buff {
 	__u8			csum_level:2;
 	__u8			csum_bad:1;
 
+	__u8			dst_pending_confirm:1;
 #ifdef CONFIG_IPV6_NDISC_NODETYPE
 	__u8			ndisc_nodetype:2;
 #endif
@@ -3698,6 +3700,16 @@ static inline bool skb_rx_queue_recorded(const struct sk_buff *skb)
 	return skb->queue_mapping != 0;
 }
 
+static inline void skb_set_dst_pending_confirm(struct sk_buff *skb, u32 val)
+{
+	skb->dst_pending_confirm = val;
+}
+
+static inline bool skb_get_dst_pending_confirm(const struct sk_buff *skb)
+{
+	return skb->dst_pending_confirm != 0;
+}
+
 static inline struct sec_path *skb_sec_path(struct sk_buff *skb)
 {
 #ifdef CONFIG_XFRM

include/net/sock.h

@@ -1821,6 +1821,20 @@ static inline void sk_dst_confirm(struct sock *sk)
 		sk->sk_dst_pending_confirm = 1;
 }
 
+static inline void sock_confirm_neigh(struct sk_buff *skb, struct neighbour *n)
+{
+	if (skb_get_dst_pending_confirm(skb)) {
+		struct sock *sk = skb->sk;
+		unsigned long now = jiffies;
+
+		/* avoid dirtying neighbour */
+		if (n->confirmed != now)
+			n->confirmed = now;
+		if (sk && sk->sk_dst_pending_confirm)
+			sk->sk_dst_pending_confirm = 0;
+	}
+}
+
 bool sk_mc_loop(struct sock *sk);
 
 static inline bool sk_can_gso(const struct sock *sk)

net/ipv4/ip_output.c

@@ -222,7 +222,10 @@ static int ip_finish_output2(struct net *net, struct sock *sk, struct sk_buff *s
 	if (unlikely(!neigh))
 		neigh = __neigh_create(&arp_tbl, &nexthop, dev, false);
 	if (!IS_ERR(neigh)) {
-		int res = dst_neigh_output(dst, neigh, skb);
+		int res;
+
+		sock_confirm_neigh(skb, neigh);
+		res = dst_neigh_output(dst, neigh, skb);
 
 		rcu_read_unlock_bh();
 		return res;

net/ipv6/ip6_output.c

@@ -119,6 +119,7 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
 	if (unlikely(!neigh))
 		neigh = __neigh_create(&nd_tbl, nexthop, dst->dev, false);
 	if (!IS_ERR(neigh)) {
+		sock_confirm_neigh(skb, neigh);
 		ret = dst_neigh_output(dst, neigh, skb);
 		rcu_read_unlock_bh();
 		return ret;