netdev - Re: [PATCH v3 4/5] net: tun: fix tun_xdp_one() for IFF

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Date:   Mon, 28 Jun 2021 11:43:30 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org
Cc:     Eugenio Pérez <eperezma@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH v3 4/5] net: tun: fix tun_xdp_one() for IFF_TUN mode

On Mon, 2021-06-28 at 12:27 +0800, Jason Wang wrote:
> > If we're going to continue to *not* check on the XDP path, we similarly
> > need a proof that it can't be fragmented. And also a reason to bother
> > with the "optimisation", of course.
> 
> 
> For XDP path, we simply need to add a length check since the packet is 
> always a linear memory.

Sure, but in that case skb_headlen is going to be enough to cover
ETH_HLEN, and that's the very first thing that the standard inline
version of pskb_may_pull() checks, without ever even having to make an
out-of-line call.

So there's just no reason ever for us *not* to keep it really simple,
and use pskb_may_pull() in all cases.

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