vrf: Increment Icmp6InMsgs on the original netdev

Get the ingress interface and increment ICMP counters based on that
instead of skb->dev when the the dev is a VRF device.

This is a follow up on the following message:
https://www.spinics.net/lists/netdev/msg560268.html

v2: Avoid changing skb->dev since it has unintended effect for local
    delivery (David Ahern).
Signed-off-by: Stephen Suryaputra <ssuryaextr@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/addrconf.h

@@ -309,6 +309,22 @@ static inline struct inet6_dev *__in6_dev_get(const struct net_device *dev)
 	return rcu_dereference_rtnl(dev->ip6_ptr);
 }
 
+/**
+ * __in6_dev_stats_get - get inet6_dev pointer for stats
+ * @dev: network device
+ * @skb: skb for original incoming interface if neeeded
+ *
+ * Caller must hold rcu_read_lock or RTNL, because this function
+ * does not take a reference on the inet6_dev.
+ */
+static inline struct inet6_dev *__in6_dev_stats_get(const struct net_device *dev,
+						    const struct sk_buff *skb)
+{
+	if (netif_is_l3_master(dev))
+		dev = dev_get_by_index_rcu(dev_net(dev), inet6_iif(skb));
+	return __in6_dev_get(dev);
+}
+
 /**
  * __in6_dev_get_safely - get inet6_dev pointer from netdevice
  * @dev: network device

net/ipv6/icmp.c

@@ -393,23 +393,28 @@ relookup_failed:
 	return ERR_PTR(err);
 }
 
-static int icmp6_iif(const struct sk_buff *skb)
+static struct net_device *icmp6_dev(const struct sk_buff *skb)
 {
-	int iif = skb->dev->ifindex;
+	struct net_device *dev = skb->dev;
 
 	/* for local traffic to local address, skb dev is the loopback
 	 * device. Check if there is a dst attached to the skb and if so
 	 * get the real device index. Same is needed for replies to a link
 	 * local address on a device enslaved to an L3 master device
 	 */
-	if (unlikely(iif == LOOPBACK_IFINDEX || netif_is_l3_master(skb->dev))) {
+	if (unlikely(dev->ifindex == LOOPBACK_IFINDEX || netif_is_l3_master(skb->dev))) {
 		const struct rt6_info *rt6 = skb_rt6_info(skb);
 
 		if (rt6)
-			iif = rt6->rt6i_idev->dev->ifindex;
+			dev = rt6->rt6i_idev->dev;
 	}
 
-	return iif;
+	return dev;
+}
+
+static int icmp6_iif(const struct sk_buff *skb)
+{
+	return icmp6_dev(skb)->ifindex;
 }
 
 /*
@@ -810,7 +815,7 @@ out:
 static int icmpv6_rcv(struct sk_buff *skb)
 {
 	struct net *net = dev_net(skb->dev);
-	struct net_device *dev = skb->dev;
+	struct net_device *dev = icmp6_dev(skb);
 	struct inet6_dev *idev = __in6_dev_get(dev);
 	const struct in6_addr *saddr, *daddr;
 	struct icmp6hdr *hdr;

net/ipv6/reassembly.c

@@ -298,7 +298,7 @@ static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
 			   skb_network_header_len(skb));
 
 	rcu_read_lock();
-	__IP6_INC_STATS(net, __in6_dev_get(dev), IPSTATS_MIB_REASMOKS);
+	__IP6_INC_STATS(net, __in6_dev_stats_get(dev, skb), IPSTATS_MIB_REASMOKS);
 	rcu_read_unlock();
 	fq->q.rb_fragments = RB_ROOT;
 	fq->q.fragments_tail = NULL;
@@ -312,7 +312,7 @@ out_oom:
 	net_dbg_ratelimited("ip6_frag_reasm: no memory for reassembly\n");
 out_fail:
 	rcu_read_lock();
-	__IP6_INC_STATS(net, __in6_dev_get(dev), IPSTATS_MIB_REASMFAILS);
+	__IP6_INC_STATS(net, __in6_dev_stats_get(dev, skb), IPSTATS_MIB_REASMFAILS);
 	rcu_read_unlock();
 	inet_frag_kill(&fq->q);
 	return -1;