Re: [PATCH net] vlan: require the MAC header to be present in __vlan_insert_inner_tag()

[Jakub Kicinski]

On Sat, 19 Sep 2026 08:45:35 +0100 Simon Horman wrote:
> > +	if (unlikely(!pskb_may_pull(skb, mac_len)))
> > +		return -EINVAL;
> > +
> >  	if (skb_cow_head(skb, meta_len + VLAN_HLEN) < 0)
> >  		return -ENOMEM;  
> 
> TBH I am surprised that we have a bug like this in this function.
> But your analysis matches my understanding of the code.

FWIW I suspect it's because non-ethernet packets shouldn't normally
reach ethernet helpers. But I'm not sure how practical it would be
to push mac_len checks to the callers or anything of the sort,
so we can as well check here..