From mboxrd@z Thu Jan  1 00:00:00 1970
From: Patrick McHardy <kaber@trash.net>
Subject: Re: [PATCH 1/2] [NETFILTER]: xt_TCPMSS: Consider incoming device's
 MTU in clamp-to-pmtu
Date: Sun, 20 Jan 2008 14:48:23 +0100
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References: <Pine.LNX.4.64.0801201318040.14598@fbirervta.pbzchgretzou.qr>
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Cc: Netfilter Developer Mailing List <netfilter-devel@vger.kernel.org>
To: Jan Engelhardt <jengelh@computergmbh.de>
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Jan Engelhardt wrote:
> commit 1ed78bbf75455dfe77a028f2da2f351cff4028f2
> Author: Jan Engelhardt <jengelh@computergmbh.de>
> Date:   Sun Jan 20 13:13:33 2008 +0100
> 
>     [NETFILTER]: xt_TCPMSS: Consider incoming device's MTU in clamp-to-pmtu
>     
>     The TCPMSS target in Xtables should consider the MTU of the input
>     device on forwarded packets as part of the path MTU.
>     
>     Point in case: IN=ppp0, OUT=eth0. MSS set to 1460 in spite of MTU of
>     ppp0 being 1392.


> -				   sizeof(*ipv6h) + sizeof(struct tcphdr));
> +	ret = tcpmss_mangle_packet(skb, targinfo, (in == NULL) ? ~0U : in->mtu,
> +	      tcphoff, sizeof(*ipv6h) + sizeof(struct tcphdr));


This is slightly better than what we currently have, but it should
actually use the MTU from the dst_entry for the reverse direction.
I've tried adding this not too long ago and ran into some problems,
but I can't remember the exact details.