netdev - Re: [PATCH] tcp: ensure non-empty connection request queue

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Message-ID: <572A3048.60802@hpe.com>
Date:	Wed, 4 May 2016 10:24:24 -0700
From:	Rick Jones <rick.jones2@....com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Peter Wu <peter@...ensteyn.nl>
Cc:	"David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Kui Zhang <kuizhang@...il.com>
Subject: Re: [PATCH] tcp: ensure non-empty connection request queue

On 05/03/2016 05:25 PM, Eric Dumazet wrote:
> On Tue, 2016-05-03 at 23:54 +0200, Peter Wu wrote:
>> When applications use listen() with a backlog of 0, the kernel would
>> set the maximum connection request queue to zero. This causes false
>> reports of SYN flooding (if tcp_syncookies is enabled) or packet drops
>> otherwise.
>>

> Well, I believe I already gave my opinion on this.
>
> listen backlog is not a hint. This is a limit.
>
> It is the limit of outstanding children in accept queue.
>
> If backlog is 0, no child can be put in the accept queue.
>
> It is therefore Working As Intented.

Dropping the connection attempt makes sense, but is entering/claiming 
synflood really indicated in the case of a zero-length accept queue?

rick