netdev - Re: [PATCH net-next] tcp: accept RST if SEQ matches right edge of SACK block

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Date:	Fri, 3 Jun 2016 17:59:27 +0200
From:	Pau Espin <pau.espin@...sares.net>
To:	Neal Cardwell <ncardwell@...gle.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next] tcp: accept RST if SEQ matches right edge of
 SACK block

Hi Neal,
Sorry I saw your email just after sending the second version of the patch.
Indeed, it could make sense to do it as you say. I'll try to do some
tests in my environment and send a new version with those changes if I
don't find any problem with it.

On Fri, Jun 3, 2016 at 5:45 PM, Neal Cardwell <ncardwell@...gle.com> wrote:
> On Fri, Jun 3, 2016 at 11:13 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> I have no strict opinion on this.
>>
>> It seems to me that checking at most 4 right edges (at least in current
>> linux implementation) is not adding a huge risk, and allows for better
>> interoperability.
>>
>> I vote for no extra sysctl.
>
> I vote for no extra sysctl as well.
>
> But I would also vote to tighten up the proposed logic slightly, and
> only check the seq of the incoming RST against the right edge of the
> *right-most* SACK block. That is, the code could loop through the
> tp->selective_acks to find the right-most of the right edges of the
> SACK blocks (the end_seq that has no other end_seq after() it). AFAICT
> it makes sense to expect that a legitimate incoming RST might match
> rcv_nxt, or might match the right-most edge of the right-most SACK.
> But allowing a RST to match a sequence of some SACK in the middle of
> the sequence range would seem to only increase the attack surface for
> RST attacks.
>
> neal



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Pau Espin Pedrol | R&D Engineer - External
pau.espin@...sares.net | +32 487 43 36 50
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www.tessares.net
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