netdev - Re: [PATCH net v2 2/2] net: ethernet: cortina: Bypass checksumming engine of alien ethertypes

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Date: Tue, 19 Dec 2023 15:22:57 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Eric Dumazet <edumazet@...gle.com>, Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: Hans Ulli Kroll <ulli.kroll@...glemail.com>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net v2 2/2] net: ethernet: cortina: Bypass checksumming
 engine of alien ethertypes

On Tue, Dec 19, 2023 at 10:15 AM Eric Dumazet <edumazet@...gle.com> wrote:
> On Tue, Dec 19, 2023 at 12:42 AM Linus Walleij <linus.walleij@...aro.org> wrote:

> > This is often what we want: DSA switches will "wash" custom ethertypes
> > before they go out, but in this case the custom ethertype upsets the
> > ethernet checksum engine used as conduit interface toward the DSA
> > switch.
>
>  Problem is that your code misses skb_header_pointer() or
> pskb_may_pull() call...
> Second "ethertype = ntohs(*p);" might access uninitialized data.

Yeah, needs to be done properly and look at skb->len etc.

> If this is a common operation, perhaps use a common helper from all drivers,
> this would help code review a bit...

You are right, Maxime opened a discussion on it in a parallel,
I'll cook something up!

Yours,
Linus Walleij