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Message-ID: <710ab0ca79305c82013982d43250b0a1fd45824d@8b5064a13e22126c1b9329f0dc35b8915774b7c3.invalid> Date: Wed, 20 Jan 2010 12:59:16 -0000 From: "Simon Arlott" <simon@...e.lp0.eu> To: "William Allen Simpson" <william.allen.simpson@...il.com>, "Patrick McHardy" <kaber@...sh.net> Cc: "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 Tue, January 19, 2010 15:44, William Allen Simpson wrote: > Simon Arlott wrote: >> On Tue, January 19, 2010 09:17, William Allen Simpson wrote: >> I could change the comment too, but the same logic applies when >> there is data and no MSS option - the packet can't be increased >> in size if it would then exceed 576 bytes and/or the destination >> MTU. >> > Please change the comment. I've made a new version of the patch which I'll be able to test tonight. > If there is no MSS option, it should *not* be added, under *ANY* > circumstances. That violates the end-to-end arguments (some call > them principles). Agreed. The added MSS is likely to be larger than 536 too... I've removed this code. > MSS isn't about the _destination_ MTU, it's about the *source*. > If you cannot guarantee you know the source MTU, there's no basis > for deciding the MSS. I was referring to the SYN packet itself. It wouldn't always be possible to add an option without exceeding the MTU of that packet's destination if it had data. On 19/01/10 12:53, Patrick McHardy wrote: > Simon Arlott wrote: >> If this is 20 (IPv4 Header) + 20 (TCP Header) = 40 bytes, then >> there is no data and the header offset is wrong so it hasn't been >> checked. > > That's odd. If the packet is really only 40 bytes large, then there > are no TCP options, so your patch shouldn't have any effect. Except to remove the printk which fills up my serial console (because the header offset is wrong). -- Simon Arlott -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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