netdev - Re: [PATCH] netfilter: nft_paylaod: add base type NFT_PAYLOAD_LL_HEADER_NO

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Date:   Tue, 18 Jun 2019 12:04:23 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Florian Westphal <fw@...len.de>
Cc:     wenxu@...oud.cn, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] netfilter: nft_paylaod: add base type
 NFT_PAYLOAD_LL_HEADER_NO_TAG

On Tue, Jun 18, 2019 at 11:46:13AM +0200, Florian Westphal wrote:
> Pablo Neira Ayuso <pablo@...filter.org> wrote:
[...]
> > Could you describe this problem a bit more? Small example rule plus
> > scenario.
> 
> It was what wenxu reported originally:
> 
> nft add rule bridge filter forward ip protocol counter ..
> 
> The rule only matches if the ip packet is contained in an ethernet frame
> without vlan tag -- and thats neither expected nor desirable.
> 
> This rule works when using 'meta protocol ip' as dependency instead
> of ether type ip (what we do now), because VLAN stripping will fix/alter
> skb->protocol to the inner type when the VLAN tag gets removes.
> 
> It will still fail in case there are several VLAN tags, so we might
> need another meta expression that can figure out the l3 protocol type.

How would that new meta expression would look like?