From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next-2.6] syncookies: check decoded options against
 sysctl settings
Date: Wed, 16 Jun 2010 13:52:48 -0700 (PDT)
Message-ID: <20100616.135248.39186709.davem@davemloft.net>
References: <1276464875-4460-1-git-send-email-fw@strlen.de>
	<20100615.180947.241927235.davem@davemloft.net>
	<20100616080309.GC20287@Chamillionaire.breakpoint.cc>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: netdev@vger.kernel.org
To: fw@strlen.de
Return-path: <netdev-owner@vger.kernel.org>
Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:40067
	"EHLO sunset.davemloft.net" rhost-flags-OK-OK-OK-OK)
	by vger.kernel.org with ESMTP id S1753576Ab0FPUwg (ORCPT
	<rfc822;netdev@vger.kernel.org>); Wed, 16 Jun 2010 16:52:36 -0400
In-Reply-To: <20100616080309.GC20287@Chamillionaire.breakpoint.cc>
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

From: Florian Westphal <fw@strlen.de>
Date: Wed, 16 Jun 2010 10:03:09 +0200

> David Miller <davem@davemloft.net> wrote:
>> From: Florian Westphal <fw@strlen.de>
>> Date: Sun, 13 Jun 2010 23:34:35 +0200
>> 
>> > -	if (tcp_opt->sack_ok)
>> > -		tcp_sack_reset(tcp_opt);
>> > +	if (tcp_opt->sack_ok && !sysctl_tcp_sack)
>> > +		return false;
>> >  
>> 
>> If you remove the tcp_sack_reset() call here, who is going to
>> do it?
> 
> Right, I should have mentioned that in the changelog, sorry about that.
> 
> Bottom line is that I failed to find out why its needed.
> Both call sites of this function (cookie_v4_check, cookie_v6_check)
> allocate the "struct tcp_options_received" argument on the stack, zero it,
> hand it to tcp_parse_options() and then call cookie_check_timestamp().
> 
> I did not find any place in tcp_parse_options that would cause
> tcp_opt->num_sacks/dsack to become nonzero.
> 
> Even if it can turn nonzero, I do not see any ill effects that might
> happen then. The structure is on the stack and after tcp_parse_options()
> returns only a few selected members are copied to the inet_request_sock.

Please resubmit your patch with these explanations in the commit
message.

Thank you.