Re: [PATCH v10 nf-next 2/3] netfilter: nft_chain_filter: Add bridge double vlan and pppoe

[Pablo Neira Ayuso <pablo@netfilter.org>]

Hi,

On Sat, Mar 15, 2025 at 09:00:32PM +0100, Eric Woudstra wrote:
> This adds the capability to evaluate 802.1ad, QinQ, PPPoE and PPPoE-in-Q
> packets in the bridge filter chain.
> 
> Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
> Signed-off-by: Eric Woudstra <ericwouds@gmail.com>
> ---
>  net/netfilter/nft_chain_filter.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/net/netfilter/nft_chain_filter.c b/net/netfilter/nft_chain_filter.c
> index 19a553550c76..7c7080c1a67d 100644
> --- a/net/netfilter/nft_chain_filter.c
> +++ b/net/netfilter/nft_chain_filter.c
> @@ -232,11 +232,27 @@ nft_do_chain_bridge(void *priv,
>  		    struct sk_buff *skb,
>  		    const struct nf_hook_state *state)
>  {
> +	struct ethhdr *ethh = eth_hdr(skb);
>  	struct nft_pktinfo pkt;
> +	int thoff;
>  
>  	nft_set_pktinfo(&pkt, skb, state);
>  
> -	switch (eth_hdr(skb)->h_proto) {
> +	switch (ethh->h_proto) {
> +	case htons(ETH_P_PPP_SES):
> +		thoff = PPPOE_SES_HLEN;
> +		ethh += thoff;

This pointer arithmetics does not look correct, ethh is struct ethhdr,
neither void nor char.

> +		break;
> +	case htons(ETH_P_8021Q):
> +		thoff = VLAN_HLEN;
> +		ethh += thoff;

Same here.

> +		break;
> +	default:
> +		thoff = 0;
> +		break;
> +	}
> +
> +	switch (ethh->h_proto) {

This switch will match on the wrong offset.

>  	case htons(ETH_P_IP):
>  		nft_set_pktinfo_ipv4_validate(&pkt);
>  		break;
> @@ -248,6 +264,8 @@ nft_do_chain_bridge(void *priv,
>  		break;
>  	}
>  
> +	pkt.thoff += thoff;

And only transport offset is adjusted here.

>  	return nft_do_chain(&pkt, priv);
>  }
>  
> -- 
> 2.47.1
>