net-core: add InMacErrors counter

Increment InMacErrors counter when packet dropped due to incorrect dest
MAC addr.

example output from nstat:
\~# nstat -z "*InMac*"
\#kernel
Ip6InMacErrors                  0                  0.0
IpExtInMacErrors                1                  0.0

Tested: Created 2 netns, sent 1 packet using trafgen from 1 to the other
with "{eth(daddr=$INCORRECT_MAC...}", verified that nstat showed the
counter was incremented.

Signed-off-by: jeffreyji <jeffreyji@google.com>

include/uapi/linux/snmp.h

@@ -57,6 +57,7 @@ enum
 	IPSTATS_MIB_ECT0PKTS,			/* InECT0Pkts */
 	IPSTATS_MIB_CEPKTS,			/* InCEPkts */
 	IPSTATS_MIB_REASM_OVERLAPS,		/* ReasmOverlaps */
+	IPSTATS_MIB_INMACERRORS,		/* InMacErrors */
 	__IPSTATS_MIB_MAX
 };
 

net/ipv4/ip_input.c

@@ -441,8 +441,10 @@ static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
 	/* When the interface is in promisc. mode, drop all the crap
 	 * that it receives, do not try to analyse it.
 	 */
-	if (skb->pkt_type == PACKET_OTHERHOST)
+	if (skb->pkt_type == PACKET_OTHERHOST) {
+		__IP_INC_STATS(net, IPSTATS_MIB_INMACERRORS);
 		goto drop;
+	}
 
 	__IP_UPD_PO_STATS(net, IPSTATS_MIB_IN, skb->len);
 

net/ipv4/proc.c

@@ -117,6 +117,7 @@ static const struct snmp_mib snmp4_ipextstats_list[] = {
 	SNMP_MIB_ITEM("InECT0Pkts", IPSTATS_MIB_ECT0PKTS),
 	SNMP_MIB_ITEM("InCEPkts", IPSTATS_MIB_CEPKTS),
 	SNMP_MIB_ITEM("ReasmOverlaps", IPSTATS_MIB_REASM_OVERLAPS),
+	SNMP_MIB_ITEM("InMacErrors", IPSTATS_MIB_INMACERRORS),
 	SNMP_MIB_SENTINEL
 };
 

net/ipv6/ip6_input.c

@@ -150,6 +150,7 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
 	struct inet6_dev *idev;
 
 	if (skb->pkt_type == PACKET_OTHERHOST) {
+		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INMACERRORS);
 		kfree_skb(skb);
 		return NULL;
 	}

net/ipv6/proc.c

@@ -84,6 +84,7 @@ static const struct snmp_mib snmp6_ipstats_list[] = {
 	SNMP_MIB_ITEM("Ip6InECT1Pkts", IPSTATS_MIB_ECT1PKTS),
 	SNMP_MIB_ITEM("Ip6InECT0Pkts", IPSTATS_MIB_ECT0PKTS),
 	SNMP_MIB_ITEM("Ip6InCEPkts", IPSTATS_MIB_CEPKTS),
+	SNMP_MIB_ITEM("Ip6InMacErrors", IPSTATS_MIB_INMACERRORS),
 	SNMP_MIB_SENTINEL
 };