netdev - Re: [PATCH] vlan: Fix the b0rked ingress VLAN_FLAG_REORDER

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Date:	Tue, 24 May 2011 00:54:14 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	ebiederm@...ssion.com
Cc:	shemminger@...ux-foundation.org, greearb@...delatech.com,
	nicolas.2p.debian@...il.com, jpirko@...hat.com, xiaosuo@...il.com,
	netdev@...r.kernel.org, kaber@...sh.net, fubar@...ibm.com,
	eric.dumazet@...il.com, andy@...yhouse.net, jesse@...ira.com
Subject: Re: [PATCH] vlan: Fix the b0rked ingress VLAN_FLAG_REORDER_HDR
 check.

From: ebiederm@...ssion.com (Eric W. Biederman)
Date: Mon, 23 May 2011 17:11:51 -0700

> diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
> index 41495dc..c08dae7 100644
> --- a/net/8021q/vlan_core.c
> +++ b/net/8021q/vlan_core.c
> @@ -23,6 +23,11 @@ bool vlan_do_receive(struct sk_buff **skbp)
>  		return false;
>  
>  	skb->dev = vlan_dev;
> +	if (unlikely(!(vlan_dev_info(vlan_dev)->flags & VLAN_FLAG_REORDER_HDR))) {
> +		skb = *skbp = vlan_insert_tag(skb, skb->vlan_tci);
> +		if (!skb)
> +			return false;
> +	}
>  	skb->priority = vlan_get_ingress_priority(vlan_dev, skb->vlan_tci);
>  	skb->vlan_tci = 0;
>  

Below we do a eth_hdr(skb) based check on the ethernet address in the
PACKET_OTHERHOST case.

Won't this VLAN tag insertion change skb->mac_header and thus screw up
that test?

Touching this code requires surgical precision and long audits, because
there are so many subtble dependencies all over the place like this.
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