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

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Message-ID: <20160317050359.GA3840@gondor.apana.org.au>
Date:	Thu, 17 Mar 2016 13:03:59 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Jiri Bohac <jbohac@...e.cz>
Cc:	Steffen Klassert <steffen.klassert@...unet.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] xfrm: don't segment UFO packets

On Wed, Mar 16, 2016 at 05:00:26PM +0100, Jiri Bohac wrote:
> xfrm_output() will segment GSO packets, including UDP (UFO) packets.
> this is wrong per RFC4303, section 3.3.4.  Fragmentation:
> 
>    If necessary, fragmentation is performed after ESP
>    processing within an IPsec implementation.  Thus,
>    transport mode ESP is applied only to whole IP
>    datagrams (not to IP fragments).
> 
> Prevent xfrm_output() from segmenting UFO packets so that they will be
> fragmented after the xfrm transforms.
> 
> Signed-off-by: Jiri Bohac <jbohac@...e.cz>

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.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt