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

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Message-ID: <20160317102459.GG3347@gauss.secunet.com>
Date:	Thu, 17 Mar 2016 11:24:59 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Jiri Bohac <jbohac@...e.cz>
CC:	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>
Subject: Re: [PATCH] xfrm: don't segment UFO packets

On Thu, Mar 17, 2016 at 10:41:15AM +0100, Jiri Bohac wrote:
> On Thu, Mar 17, 2016 at 01:03:59PM +0800, Herbert Xu wrote:
> > On Wed, Mar 16, 2016 at 05:00:26PM +0100, Jiri Bohac wrote:
> > > Prevent xfrm_output() from segmenting UFO packets so that they will be
> > > fragmented after the xfrm transforms.
> > 
> > Fair enough.  But I wonder if this is enough.  Wouldn't UDP notice
> > that we're doing IPsec and prefragment the packet anyway? So I think
> > this check may also be needed in the UDP output path.
> 
> Fixes my broken case. 

Is this IPv4 or IPv6? IPv4 should not create a GSO skb
if IPsec is done. It checks for rt->dst.header_len
in __ip_append_data() and does a fallback to the
standard case if rt->dst.header_len is non zero.

In IPv6 this check is missing, so this could be the
problem if this is IPv6.