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

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Message-Id: <20160711.133400.1349480895641773377.davem@davemloft.net>
Date:	Mon, 11 Jul 2016 13:34:00 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	ycao009@....edu, netdev@...r.kernel.org, zhiyunq@...ucr.edu,
	torvalds@...ux-foundation.org, ycheng@...gle.com,
	ncardwell@...gle.com
Subject: Re: [PATCH v2 net] tcp: make challenge acks less predictable

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sun, 10 Jul 2016 10:04:02 +0200

> 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>

Applied and queued up for -stable, thanks Eric.