netdev - Re: esp: Fix ESN generation under UDP encapsulation

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Date:	Thu, 23 Jun 2016 04:25:21 +0000
From:	Blair Steven <Blair.Steven@...iedtelesis.co.nz>
To:	Steffen Klassert <steffen.klassert@...unet.com>,
	Herbert Xu <herbert@...dor.apana.org.au>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: esp: Fix ESN generation under UDP encapsulation

This change tests okay in my setup.

Thanks very much
-Blair

On 06/20/2016 10:59 PM, Steffen Klassert wrote:
> 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@...iedtelesis.co.nz>
>> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
> Looks good.
> Blair could you please test this?
>
> Thanks!