netdev - Re: [PATCH v12 nf-next 1/2] netfilter: bridge: Add conntrack double vlan and pppoe

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Message-ID: <aFhksV47fCiriwJ4@strlen.de>
Date: Sun, 22 Jun 2025 22:16:49 +0200
From: Florian Westphal <fw@...len.de>
To: Eric Woudstra <ericwouds@...il.com>
Cc: Pablo Neira Ayuso <pablo@...filter.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>,
	Nikolay Aleksandrov <razor@...ckwall.org>,
	Ido Schimmel <idosch@...dia.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, netfilter-devel@...r.kernel.org,
	bridge@...ts.linux.dev, netdev@...r.kernel.org
Subject: Re: [PATCH v12 nf-next 1/2] netfilter: bridge: Add conntrack double
 vlan and pppoe

Eric Woudstra <ericwouds@...il.com> wrote:
> -	if (ret != NF_ACCEPT)
> -		return ret;
> +	if (ret == NF_ACCEPT)
> +		ret = nf_conntrack_in(skb, &bridge_state);
>  
> -	return nf_conntrack_in(skb, &bridge_state);
> +do_not_track:
> +	if (offset) {
> +		__skb_push(skb, offset);

nf_conntrack_in() can free the skb, or steal it.

But aside from this, I'm not sure this is a good idea to begin with,
it feels like we start to reimplement br_netfilter.c .

Perhaps it would be better to not push/pull but instead rename

unsigned int
nf_conntrack_in(struct sk_buff *skb, const struct nf_hook_state *state)

 to

unsigned int 
nf_conntrack_inner(struct sk_buff *skb, const struct nf_hook_state *state,
		   unsigned int nhoff)

and add

unsigned int 
nf_conntrack_in(struct sk_buff *skb, const struct nf_hook_state *state)
{
	return nf_conntrack_inner(skb, state, skb_network_offset(skb));
}

Or, alternatively, add
struct nf_ct_pktoffs {
	u16 nhoff;
	u16 thoff;
};

then populate that from nf_ct_bridge_pre(), then pass that to
nf_conntrack_inner() (all names are suggestions, if you find something
better thats fine).

Its going to be more complicated than this, but my point is that e.g.
nf_ct_get_tuple() already gets the l4 offset, so why not pass l3
offset too?