net: Add MIB counters for checksum errors

Add MIB counters for checksum errors in IP layer,
and TCP/UDP/ICMP layers, to help diagnose problems.

$ nstat -a | grep  Csum
IcmpInCsumErrors                72                 0.0
TcpInCsumErrors                 382                0.0
UdpInCsumErrors                 463221             0.0
Icmp6InCsumErrors               75                 0.0
Udp6InCsumErrors                173442             0.0
IpExtInCsumErrors               10884              0.0

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 2722db0..3159d16 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1131,6 +1131,8 @@
 	spin_lock_bh(&rcvq->lock);
 	while ((skb = skb_peek(rcvq)) != NULL &&
 		udp_lib_checksum_complete(skb)) {
+		UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_CSUMERRORS,
+				 IS_UDPLITE(sk));
 		UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_INERRORS,
 				 IS_UDPLITE(sk));
 		atomic_inc(&sk->sk_drops);
@@ -1286,8 +1288,10 @@
 
 csum_copy_err:
 	slow = lock_sock_fast(sk);
-	if (!skb_kill_datagram(sk, skb, flags))
+	if (!skb_kill_datagram(sk, skb, flags)) {
+		UDP_INC_STATS_USER(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
 		UDP_INC_STATS_USER(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
+	}
 	unlock_sock_fast(sk, slow);
 
 	if (noblock)
@@ -1513,7 +1517,7 @@
 
 	if (rcu_access_pointer(sk->sk_filter) &&
 	    udp_lib_checksum_complete(skb))
-		goto drop;
+		goto csum_error;
 
 
 	if (sk_rcvqueues_full(sk, skb, sk->sk_rcvbuf))
@@ -1533,6 +1537,8 @@
 
 	return rc;
 
+csum_error:
+	UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
 drop:
 	UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
 	atomic_inc(&sk->sk_drops);
@@ -1749,6 +1755,7 @@
 		       proto == IPPROTO_UDPLITE ? "Lite" : "",
 		       &saddr, ntohs(uh->source), &daddr, ntohs(uh->dest),
 		       ulen);
+	UDP_INC_STATS_BH(net, UDP_MIB_CSUMERRORS, proto == IPPROTO_UDPLITE);
 drop:
 	UDP_INC_STATS_BH(net, UDP_MIB_INERRORS, proto == IPPROTO_UDPLITE);
 	kfree_skb(skb);