netdev - Re: [PATCH] xt_TCPMSS: SYN packets are allowed to contain data

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Message-ID: <alpine.LSU.2.01.1001202240350.18680@obet.zrqbmnf.qr>
Date:	Wed, 20 Jan 2010 22:41:59 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Simon Arlott <simon@...e.lp0.eu>
cc:	Patrick McHardy <kaber@...sh.net>,
	William Allen Simpson <william.allen.simpson@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH] xt_TCPMSS: SYN packets are allowed to contain data

On Wednesday 2010-01-20 22:39, Jan Engelhardt wrote:

>On Wednesday 2010-01-20 22:21, Simon Arlott wrote:
>
>>The TCPMSS target is dropping SYN packets where:
>>  1) There is data, or
>>  2) The data offset makes the TCP header larger than
>>  the packet.
>>
>>Both of these result in an error level printk.
>>
>>This change fixes the drop of SYN packets with data
>>(because the MSS option can safely be modified) and
>>passes packets with no MSS option instead of adding
>>one (which is not valid).
>
>Can you explain why the automatic addition of a MSS option is removed?

That is, of course, for the git log. If I followed the thread right, it 
was that adding the option could exceed the MTU. Well, can't we check 
for the outgoing MTU?
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