netdev - Re: [PATCH v2] xfrm: interface: Don't hide plain packets from netfilter

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Date:   Thu, 10 Dec 2020 18:57:40 +0100
From:   Phil Sutter <phil@....cc>
To:     Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc:     Eyal Birger <eyal.birger@...il.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        linux-crypto@...r.kernel.org, netfilter-devel@...r.kernel.org,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v2] xfrm: interface: Don't hide plain packets from
 netfilter

Hi Nicolas,

On Thu, Dec 10, 2020 at 02:18:45PM +0100, Nicolas Dichtel wrote:
> Le 10/12/2020 à 12:48, Eyal Birger a écrit :
> > On Thu, Dec 10, 2020 at 1:10 PM Nicolas Dichtel
> > <nicolas.dichtel@...nd.com> wrote:
> [snip]
> > I also think they should be consistent. But it'd still be confusing to me
> > to get an OUTPUT hook on the inner packet in the forwarding case.
> I re-read the whole thread and I agree with you. There is no reason to pass the
> inner packet through the OUTPUT hook (my comment about the consistency with ip
> tunnels is still valid ;-)).
> Sorry for the confusion.
> 
> Phil, with nftables, you can match the 'kind' of the interface, that should be
> enough to match packets, isn't it?

Yes, sure. Also, the inner packet passes POSTROUTING hook with ipsec
context present, it's just not visible in OUTPUT. Of course the broader
question is what do people use ipsec context matches for. If it's really
just to ensure traffic is encrypted, xfrm_interface alone is sufficient.

Originally this was reported as "ipsec match stops working if
xfrm_interface is used" and I suspected it's a bug in the driver.
Knowing the behaviour is expected (and at least consistent with vti),
the case is closed from my side. :)

Thanks, Phil