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From:   Jeffrey Ji <jeffreyjilinux@gmail.com>
To:     Eric Dumazet <edumazet@google.com>,
        "David S . Miller" <davem@davemloft.net>
Cc:     Brian Vazquez <brianvv@google.com>, kuba@kernel.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        jeffreyji <jeffreyji@google.com>
Subject: [PATCH v5 net-next] net-core: add InMacErrors counter
Date:   Mon, 31 Jan 2022 18:15:07 +0000
Message-Id: <20220131181507.3470388-1-jeffreyji@google.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: jeffreyji <jeffreyji@google.com>

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

An example when this drop can occur is when manually crafting raw
packets that will be consumed by a user space application via a tap
device. For testing purposes local traffic was generated using trafgen
for the client and netcat to start a server

example output from nstat:
\~# nstat -a | grep InMac
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.

changelog:

v5:
Change from SKB_DROP_REASON_BAD_DEST_MAC to SKB_DROP_REASON_OTHERHOST

v3-4:
Remove Change-Id

v2:
Use skb_free_reason() for tracing
Add real-life example in patch msg

Signed-off-by: jeffreyji <jeffreyji@google.com>
---
 include/linux/skbuff.h    |  1 +
 include/uapi/linux/snmp.h |  1 +
 net/ipv4/ip_input.c       |  7 +++++--
 net/ipv4/proc.c           |  1 +
 net/ipv6/ip6_input.c      | 12 +++++++-----
 net/ipv6/proc.c           |  1 +
 6 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index bf11e1fbd69b..c831e3a502f2 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -320,6 +320,7 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_TCP_CSUM,
 	SKB_DROP_REASON_TCP_FILTER,
 	SKB_DROP_REASON_UDP_CSUM,
+	SKB_DROP_REASON_OTHERHOST,
 	SKB_DROP_REASON_MAX,
 };
 
diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index 904909d020e2..ac2fac12dd7d 100644
--- a/include/uapi/linux/snmp.h
+++ b/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
 };
 
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index 3a025c011971..780892526166 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -441,8 +441,11 @@ 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)
-		goto drop;
+	if (skb->pkt_type == PACKET_OTHERHOST) {
+		__IP_INC_STATS(net, IPSTATS_MIB_INMACERRORS);
+		kfree_skb_reason(skb, SKB_DROP_REASON_OTHERHOST);
+		return NULL;
+	}
 
 	__IP_UPD_PO_STATS(net, IPSTATS_MIB_IN, skb->len);
 
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index f30273afb539..dfe0a1dbf8e9 100644
--- a/net/ipv4/proc.c
+++ b/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
 };
 
diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
index 80256717868e..da18d9159647 100644
--- a/net/ipv6/ip6_input.c
+++ b/net/ipv6/ip6_input.c
@@ -149,15 +149,17 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
 	u32 pkt_len;
 	struct inet6_dev *idev;
 
-	if (skb->pkt_type == PACKET_OTHERHOST) {
-		kfree_skb(skb);
-		return NULL;
-	}
-
 	rcu_read_lock();
 
 	idev = __in6_dev_get(skb->dev);
 
+	if (skb->pkt_type == PACKET_OTHERHOST) {
+		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INMACERRORS);
+		rcu_read_unlock();
+		kfree_skb_reason(skb, SKB_DROP_REASON_OTHERHOST);
+		return NULL;
+	}
+
 	__IP6_UPD_PO_STATS(net, idev, IPSTATS_MIB_IN, skb->len);
 
 	if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL ||
diff --git a/net/ipv6/proc.c b/net/ipv6/proc.c
index d6306aa46bb1..76e6119ba558 100644
--- a/net/ipv6/proc.c
+++ b/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
 };
 
-- 
2.35.0.rc2.247.g8bbb082509-goog