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Date: Sat, 19 Sep 2026 15:49:11 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Simon Horman <horms@kernel.org>
Cc: Xiang Mei <xmei5@asu.edu>, andrew+netdev@lunn.ch, davem@davemloft.net,
 edumazet@google.com, pabeni@redhat.com, netdev@vger.kernel.org,
 bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jakub@cloudflare.com,
 stable@vger.kernel.org, co+0ea1ac045375cf05@bugs.sh
Subject: Re: [PATCH net] vlan: require the MAC header to be present in
 __vlan_insert_inner_tag()
Message-ID: <20260919154911.642616cf@kernel.org>
In-Reply-To: <20260919074535.GW51261@horms.kernel.org>
References: <20260915083152.705309-1-xmei5@asu.edu>
	<20260919074535.GW51261@horms.kernel.org>
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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..