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

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Message-Id: <20191206.204825.1293767323272186689.davem@davemloft.net>
Date:   Fri, 06 Dec 2019 20:48:25 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, soheil@...gle.com,
        ncardwell@...gle.com, ycheng@...gle.com, syzkaller@...glegroups.com
Subject: Re: [PATCH net] tcp: md5: fix potential overestimation of TCP
 option space

From: Eric Dumazet <edumazet@...gle.com>
Date: Thu,  5 Dec 2019 10:10:15 -0800

> 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>

Applied and queued up for -stable, thanks Eric.