Re: [PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

From: Paolo Abeni <pabeni@redhat.com>
To: "Li, James Zheng" <James.Z.Li@Dell.com>,
	Eric Dumazet <edumazet@google.com>,
	 Zheng Li <lizheng043@gmail.com>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"davem@davemloft.net" <davem@davemloft.net>,
	 "jmorris@namei.org" <jmorris@namei.org>,
	"kuba@kernel.org" <kuba@kernel.org>
Subject: Re: [PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full
Date: Thu, 18 Apr 2024 11:33:46 +0200	[thread overview]
Message-ID: <3f487ef495da476e5b0564dbb024dca54e8bee10.camel@redhat.com> (raw)
In-Reply-To: <IA1PR19MB6545F5F1940C0B326058987ABB082@IA1PR19MB6545.namprd19.prod.outlook.com>

On Tue, 2024-04-16 at 10:36 +0000, Li, James Zheng wrote:
> On Tuesday, April 16, 2024 6:02 PM Eric Dumazet <edumazet@google.com> wrote:
> > Hmmm...
> 
> > Loopback IPv4 can hold 2^24 different addresses, that is 16384 * 1024
> 
> There is only one Loopback neigh "0.0.0.0 dev lo lladdr 00:00:00:00:00:00 NOARP"
> existing even you have configured 2^24 different addresses on the loopback device.

Eric, I think James is right, in __ipv4_neigh_lookup_noref():

	if (dev->flags & (IFF_LOOPBACK | IFF_POINTOPOINT))
                key = INADDR_ANY;

	return ___neigh_lookup_noref(&arp_tbl, neigh_key_eq32, arp_hashfn, &key, dev);

So there should be at most one neigh entry over the loopback device.
The patch looks safe to me, am I missing something?

Thanks,

Paolo