ipv6: Add reasons for skb drops to __udp6_lib_rcv

Add reasons to __udp6_lib_rcv for skb drops. The only twist is that the
NO_SOCKET takes precedence over the CSUM or other counters for that
path (motivation behind this patch - csum counter was misleading).
Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/udp.c

@@ -912,6 +912,7 @@ static int udp6_unicast_rcv_skb(struct sock *sk, struct sk_buff *skb,
 int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 		   int proto)
 {
+	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	const struct in6_addr *saddr, *daddr;
 	struct net *net = dev_net(skb->dev);
 	struct udphdr *uh;
@@ -988,6 +989,8 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 		return udp6_unicast_rcv_skb(sk, skb, uh);
 	}
 
+	reason = SKB_DROP_REASON_NO_SOCKET;
+
 	if (!uh->check)
 		goto report_csum_error;
 
@@ -1000,10 +1003,12 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	__UDP6_INC_STATS(net, UDP_MIB_NOPORTS, proto == IPPROTO_UDPLITE);
 	icmpv6_send(skb, ICMPV6_DEST_UNREACH, ICMPV6_PORT_UNREACH, 0);
 
-	kfree_skb(skb);
+	kfree_skb_reason(skb, reason);
 	return 0;
 
 short_packet:
+	if (reason == SKB_DROP_REASON_NOT_SPECIFIED)
+		reason = SKB_DROP_REASON_PKT_TOO_SMALL;
 	net_dbg_ratelimited("UDP%sv6: short packet: From [%pI6c]:%u %d/%d to [%pI6c]:%u\n",
 			    proto == IPPROTO_UDPLITE ? "-Lite" : "",
 			    saddr, ntohs(uh->source),
@@ -1014,10 +1019,12 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 report_csum_error:
 	udp6_csum_zero_error(skb);
 csum_error:
+	if (reason == SKB_DROP_REASON_NOT_SPECIFIED)
+		reason = SKB_DROP_REASON_UDP_CSUM;
 	__UDP6_INC_STATS(net, UDP_MIB_CSUMERRORS, proto == IPPROTO_UDPLITE);
 discard:
 	__UDP6_INC_STATS(net, UDP_MIB_INERRORS, proto == IPPROTO_UDPLITE);
-	kfree_skb(skb);
+	kfree_skb_reason(skb, reason);
 	return 0;
 }