netdev - Re: [PATCH v2 net] tcp: make challenge acks less predictable

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Date:	Sun, 10 Jul 2016 08:55:57 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Yue Cao <ycao009@....edu>, David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Zhiyun Qian <zhiyunq@...ucr.edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH v2 net] tcp: make challenge acks less predictable

On Sun, Jul 10, 2016 at 4:04 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
>
> Yue Cao claims that current host rate limiting of challenge ACKS
> (RFC 5961) could leak enough information to allow a patient attacker
> to hijack TCP sessions. He will soon provide details in an academic
> paper.
>
> This patch increases the default limit from 100 to 1000, and adds
> some randomization so that the attacker can no longer hijack
> sessions without spending a considerable amount of probes.
>
> Based on initial analysis and patch from Linus.
>
> Note that we also have per socket rate limiting, so it is tempting
> to remove the host limit in the future.
>
> v2: randomize the count of challenge acks per second, not the period.
>
> Fixes: 282f23c6ee34 ("tcp: implement RFC 5961 3.2")
> Reported-by: Yue Cao <ycao009@....edu>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Yuchung Cheng <ycheng@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>

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

Thanks, Eric!

neal