netdev - Re: [PATCH] xfrm: don't segment UFO packets

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Message-ID: <20160318080528.GK3347@gauss.secunet.com>
Date:	Fri, 18 Mar 2016 09:05:28 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	Jiri Bohac <jbohac@...e.cz>,
	"David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>
Subject: Re: [PATCH] xfrm: don't segment UFO packets

On Fri, Mar 18, 2016 at 10:36:53AM +0800, Herbert Xu wrote:
> On Thu, Mar 17, 2016 at 06:08:55PM +0100, Jiri Bohac wrote:
> > On Thu, Mar 17, 2016 at 11:24:59AM +0100, Steffen Klassert wrote:
> > > In IPv6 this check is missing, so this could be the
> > > problem if this is IPv6.
> > 
> > indeed, this patch also fixes my problem:
> 
> Hmm, is this what you really want? If I understood you correctly,
> you want the fragmentation to occur after IPsec.

The main problem was probably that UFO handling does not work at
all on IPv6 IPsec. 

> So while this
> might generate the same output, it is still going to prefragment
> the data, only to merge them back for IPsec and then refragment
> again.

This is far away from being optimal, but this is what usually
happens if a local application sends data that we need to
fragment.

We currently work on avoiding the linearization on IPsec,
but having a skb with a fraglist is really the worst case.