Re: esp: Fix ESN generation under UDP encapsulation

[Steffen Klassert <steffen.klassert@secunet.com>]

On Sat, Jun 18, 2016 at 01:03:36PM +0800, Herbert Xu wrote:
> On Fri, Jun 17, 2016 at 12:24:29PM +0200, Steffen Klassert wrote:
> > On Wed, Jun 15, 2016 at 12:44:54AM +0000, Blair Steven wrote:
> > > The restoration is happening - but being actioned on the wrong location.
> > > 
> > > The destination IP address is being saved and restored, and the SPI 
> > > being written directly after the destination IP address. From my 
> > > understanding though, the ESN shuffling should have saved and restored 
> > > the UDP source / dest ports + SPI.
> > 
> > Yes, looks like we copy with a wrong offset if udp encapsulation
> > is used, skb_transport_header() does not point to the esp header
> > in this case. Ccing Herbert, he changed this part when switching
> > to the new AEAD interface with
> > commit 7021b2e1cddd ("esp4: Switch to new AEAD interface").
> 
> Thanks for catching this!
> 
> I think rather than changing the transport header (which isn't
> quite right because UDP still is the transport protocol), we can
> just save the offset locally.  Something like this:
> 
> ---8<---
> Blair Steven noticed that ESN in conjunction with UDP encapsulation
> is broken because we set the temporary ESP header to the wrong spot.
> 
> This patch fixes this by first of all using the right spot, i.e.,
> 4 bytes off the real ESP header, and then saving this information
> so that after encryption we can restore it properly.
> 
> Fixes: 7021b2e1cddd ("esp4: Switch to new AEAD interface")
> Reported-by: Blair Steven <Blair.Steven@alliedtelesis.co.nz>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Looks good.
Blair could you please test this?

Thanks!