udp: increment UDP_MIB_INERRORS if copy failed

In UDP recvmsg(), we miss an increase of UDP_MIB_INERRORS if the copy
of skb to userspace failed for whatever reason.
Reported-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/udp.c

@@ -1226,6 +1226,11 @@ int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 
 	if (unlikely(err)) {
 		trace_kfree_skb(skb, udp_recvmsg);
+		if (!peeked) {
+			atomic_inc(&sk->sk_drops);
+			UDP_INC_STATS_USER(sock_net(sk),
+					   UDP_MIB_INERRORS, is_udplite);
+		}
 		goto out_free;
 	}
 

net/ipv6/udp.c

@@ -394,6 +394,17 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
 	}
 	if (unlikely(err)) {
 		trace_kfree_skb(skb, udpv6_recvmsg);
+		if (!peeked) {
+			atomic_inc(&sk->sk_drops);
+			if (is_udp4)
+				UDP_INC_STATS_USER(sock_net(sk),
+						   UDP_MIB_INERRORS,
+						   is_udplite);
+			else
+				UDP6_INC_STATS_USER(sock_net(sk),
+						    UDP_MIB_INERRORS,
+						    is_udplite);
+		}
 		goto out_free;
 	}
 	if (!peeked) {