netdev - Re: [Patch net v2] mlx5: fixup checksum for short ethernet frame padding

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Message-ID: <CAM_iQpWXXM3F28b8XLURCJJQaTVK++P9U+u=dehCbqqKEE8VHA@mail.gmail.com>
Date:   Wed, 28 Nov 2018 15:57:09 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [Patch net v2] mlx5: fixup checksum for short ethernet frame padding

On Wed, Nov 28, 2018 at 3:50 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Wed, Nov 28, 2018 at 2:16 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > On Wed, Nov 28, 2018 at 7:00 AM Eric Dumazet <edumazet@...gle.com> wrote:
> > >
> > > Nice packet of death alert.
> > >
> > > pad_len can be 0xFFFFFF67  here, if frame_len is smaller than pad_offset.
> >
> > Unless IP header is malformed, how could it be?
>
> This is totally something an attacker can forge.

Of course, as in the email I sent to mellanox guys,__vlan_get_protocol()
could _literately_ exhaust all skb->len. If no sufficient skb tail room,
we could even possibly crash.

But again, I kinda feel the hardware already does the sanity check,
otherwise we have much more serious trouble in mlx5e_lro_update_hdr()
which parses into TCP header.

Thanks.