From: jamal <redacted>
Date: Tue, 03 Jul 2007 09:09:48 -0400

[It sounds very dangerous to me the way skb->cb is being used by the
vlan code (i.e requires human intervention/knowledge to catch it as an
issue). I had no freaking idea the vlan code was using it. Maybe a huge
comment somewhere on how these cbs are being used by drivers would help
or even a registration on startup to just make sure there is no conflict
at a layer (i have been meaning to do the later for years now). In any
case this is is a digression]. 

This is how the VLAN layer passed in the tag for the transmit
function.

The CB is owned by the caller until you spam it with your local
data at your level, so if you need any information the previous
layer provides you have to sample it before using the ->cb[]

So you can simply fix this by reading the VLAN tag, then using
the ->cb[] however you like.

It's always been like this, don't be surprised :)