netdev - Re: [PATCH v13 nf-next 3/3] netfilter: nft_chain_filter: Add bridge double vlan and pppoe

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Message-ID: <aGgzUe9X_0hXN2Ok@strlen.de>
Date: Fri, 4 Jul 2025 22:02:25 +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 v13 nf-next 3/3] netfilter: nft_chain_filter: Add bridge
 double vlan and pppoe

Eric Woudstra <ericwouds@...il.com> wrote:
> This adds the capability to evaluate 802.1ad, QinQ, PPPoE and PPPoE-in-Q
> packets in the bridge filter chain.
> 
> Signed-off-by: Eric Woudstra <ericwouds@...il.com>
> ---
>  net/netfilter/nft_chain_filter.c | 52 +++++++++++++++++++++++++++++++-
>  1 file changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/net/netfilter/nft_chain_filter.c b/net/netfilter/nft_chain_filter.c
> index 19a553550c76..8445ddfb9cea 100644
> --- a/net/netfilter/nft_chain_filter.c
> +++ b/net/netfilter/nft_chain_filter.c
> @@ -232,11 +232,55 @@ nft_do_chain_bridge(void *priv,
>  		    struct sk_buff *skb,
>  		    const struct nf_hook_state *state)
>  {
> +	__be16 outer_proto, proto = 0;
>  	struct nft_pktinfo pkt;
> +	int ret, offset = 0;
>  
>  	nft_set_pktinfo(&pkt, skb, state);
>  
>  	switch (eth_hdr(skb)->h_proto) {
> +	case htons(ETH_P_PPP_SES): {
> +		struct ppp_hdr {
> +			struct pppoe_hdr hdr;
> +			__be16 proto;
> +		} *ph;
> +
> +		if (!pskb_may_pull(skb, PPPOE_SES_HLEN))
> +			break;
> +		offset = PPPOE_SES_HLEN;
> +		outer_proto = skb->protocol;
> +		ph = (struct ppp_hdr *)(skb->data);
> +		switch (ph->proto) {
> +		case htons(PPP_IP):
> +			proto = htons(ETH_P_IP);
> +			break;
> +		case htons(PPP_IPV6):
> +			proto = htons(ETH_P_IPV6);
> +			break;
> +		}

What if ph->proto is neither ipv4 nor ipv6?  I don't think
we should clobber skb->protocol or set a new network header in that
case.

> +      ret = nft_do_chain(&pkt, priv);
> +
> +      if (offset) {
> +               skb_reset_network_header(skb);

if ret == NF_STOLEN, skb has already been free'd or is queued
elsewhere and must not be modified anymore.

I would restrict this to ret == NF_ACCEPT.