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Date: Sun, 22 Feb 2026 18:27:06 +0100
From: Florian Westphal <fw@strlen.de>
To: Eric Woudstra <ericwouds@gmail.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>, Phil Sutter <phil@nwl.cc>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Simon Horman <horms@kernel.org>, netfilter-devel@vger.kernel.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH RFC v1 nf-next] netfilter: nf_flow_table_ip: Introduce
 nf_flow_vlan_push()
Message-ID: <aZs8atSEZTjkzzQ3@strlen.de>
References: <20260222155251.76886-1-ericwouds@gmail.com>
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In-Reply-To: <20260222155251.76886-1-ericwouds@gmail.com>

Eric Woudstra <ericwouds@gmail.com> wrote:
> With double vlan tagged packets in the fastpath, getting the error:
> 
> skb_vlan_push got skb with skb->data not at mac header (offset 18)
> 
> Introduce nf_flow_vlan_push, that can push the inner vlan in the
> fastpath.
> 
> Fixes: c653d5a78f34 ("netfilter: flowtable: inline vlan encapsulation in xmit path")

This change is in net/nf tree, so why are you targetting nf-next?
Are you proposing a revert for nf?  If so, please first send a revert
for nf.

Is there a test case for this that demonstrages the breakage?

And why is this tagged as RFC, what is the problem with this patch?

> +	if (skb_vlan_tag_present(skb)) {
> +		struct vlan_hdr *vhdr;
> +
> +		if (skb_cow_head(skb, VLAN_HLEN))
> +			return -1;
> +
> +		__skb_push(skb, VLAN_HLEN);
> +		skb_reset_network_header(skb);
> +
> +		vhdr = (struct vlan_hdr *)(skb->data);
> +		vhdr->h_vlan_TCI = htons(id);
> +		vhdr->h_vlan_encapsulated_proto = skb->protocol;
> +		skb->protocol = proto;

Ok, I see, this opencodes a variant of skb_vlan_push().
Would it be possible to correct skb->data so it points to the mac header
temporarily?  skb->data always points to network header so this cannot
have worked, ever.