netdev - Re: [Patch net] ip: fix csum_sub() with csum_block

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Message-ID: <CAM_iQpVvczgezcWQ0awFUuj6gH-qeK05CXx=+AYcsxz_wkH1jQ@mail.gmail.com>
Date:   Thu, 8 Nov 2018 14:22:04 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Dimitris Michailidis <dmichail@...gle.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [Patch net] ip: fix csum_sub() with csum_block_sub()

On Thu, Nov 8, 2018 at 2:17 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Thu, Nov 8, 2018 at 2:04 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > When subtracting the checksum of a block of data,
> > csum_block_sub() must be used to respect the offset.
> >
> > We learned this lesson from both commit d55bef5059dd
> > ("net: fix pskb_trim_rcsum_slow() with odd trim offset") and
> > commit d48051c5b837 ("net/mlx5e: fix csum adjustments caused by RXFCS").
> >
> > Fixes: ca4ef4574f1e ("ip: fix IP_CHECKSUM handling")
>
> I do not believe you fix any bug here...
>
> I do not know of any inet protocol having odd header sizes.

That offset is payload offset, but yeah, the payload offset must be
aligned some way. Good point!

Let's drop it.