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Date: Sun, 20 Sep 2026 10:26:57 +0100
From: Simon Horman <horms@kernel.org>
To: Jakub Kicinski <kuba@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: <20260920092657.GB13925@horms.kernel.org>
References: <20260915083152.705309-1-xmei5@asu.edu>
 <20260919074535.GW51261@horms.kernel.org>
 <20260919154911.642616cf@kernel.org>
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In-Reply-To: <20260919154911.642616cf@kernel.org>

On Sat, Sep 19, 2026 at 03:49:11PM -0700, Jakub Kicinski wrote:
> 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.

Yes, I agree that seems likely.

> 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..