netdev - Re: [PATCH net] tcp: md5: fix potential overestimation of TCP option space

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Date:   Fri, 6 Dec 2019 09:49:39 -0500
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] tcp: md5: fix potential overestimation of TCP option space

On Thu, Dec 5, 2019 at 1:10 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Back in 2008, Adam Langley fixed the corner case of packets for flows
> having all of the following options : MD5 TS SACK
>
> Since MD5 needs 20 bytes, and TS needs 12 bytes, no sack block
> can be cooked from the remaining 8 bytes.
>
> tcp_established_options() correctly sets opts->num_sack_blocks
> to zero, but returns 36 instead of 32.
>
> This means TCP cooks packets with 4 extra bytes at the end
> of options, containing unitialized bytes.
>
> Fixes: 33ad798c924b ("tcp: options clean up")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> ---

Acked-by: Neal Cardwell <ncardwell@...gle.com>

Thanks, Eric!

neal