ipv6: icmp6: add SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST

Hosts can often receive neighbour discovery messages
that are not for them.

Use a dedicated drop reason to make clear the packet is dropped
for this normal case.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dropreason.h

@@ -77,6 +77,7 @@
 	FN(IPV6_NDISC_HOP_LIMIT)	\
 	FN(IPV6_NDISC_BAD_CODE)		\
 	FN(IPV6_NDISC_BAD_OPTIONS)	\
+	FN(IPV6_NDISC_NS_OTHERHOST)	\
 	FNe(MAX)
 
 /**
@@ -333,6 +334,10 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_IPV6_NDISC_BAD_CODE,
 	/** @SKB_DROP_REASON_IPV6_NDISC_BAD_OPTIONS: invalid NDISC options. */
 	SKB_DROP_REASON_IPV6_NDISC_BAD_OPTIONS,
+	/** @SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST: NEIGHBOUR SOLICITATION
+	 * for another host.
+	 */
+	SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
 	 * used as a real 'reason'

net/ipv6/ndisc.c

@@ -921,9 +921,11 @@ static enum skb_drop_reason ndisc_recv_ns(struct sk_buff *skb)
 					pneigh_enqueue(&nd_tbl, idev->nd_parms, n);
 				goto out;
 			}
-		} else
+		} else {
+			SKB_DR_SET(reason, IPV6_NDISC_NS_OTHERHOST);
 			goto out;
 		}
+	}
 
 	if (is_router < 0)
 		is_router = idev->cnf.forwarding;