netdev - Re: net/arp: ARP cache aging failed.

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Date:   Wed, 23 Nov 2016 04:05:29 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Julian Anastasov <ja@....bg>
Cc:     yuehaibing <yuehaibing@...wei.com>, davem@...emloft.net,
        netdev@...r.kernel.org
Subject: Re: net/arp: ARP cache aging failed.

On Wed, 2016-11-23 at 10:33 +0200, Julian Anastasov wrote:
> 	Hello,
> 
> On Wed, 23 Nov 2016, yuehaibing wrote:
> 
> > 	As to my topo,HOST1 and HOST3 share one route on HOST2, tcp connection between HOST2 and HOST3 may call tcp_ack to set dst->pending_confirm.
> > 	
> > So dst_neigh_output may wrongly freshed  n->confirmed which stands for HOST1,however HOST1'MAC had been changed.
> > 
> > 	The possibility of this occurred Significantly increases ,when ping and TCP transaction are set the same processor affinity on the HOST2.
> > 
> > 	It seems that the issue is brought in commit 5110effee8fde2edfacac9cd12a9960ab2dc39ea ("net: Do delayed neigh confirmation.").
> 
> 	Bad news. Problem is not in delayed confirmation but
> in the mechanism to use same dst for different neighbours on
> LAN. We don't have a dst->neighbour reference anymore.
> 
> 	For IPv4 this is related to rt->rt_uses_gateway but
> also to DST_NOCACHE. In the other cases we can not call
> dst_confirm, may be we should lookup the neigh entry instead.
> But we need a way to reduce such lookups on every packet,
> for example, by remembering in struct sock and checking if
> some bits of jiffies (at least 4-5) are changed from
> previous lookup.


I thought bonding would keep the MAC address 'alive'.

If TCP packets are confirmed, this means the old MAC address is still
valid, what am I missing here ?