netdev - Re: [PATCH v2 net-next] tcp: avoid tx starvation by SYNACK packets

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Date:	Wed, 27 Jun 2012 23:39:20 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Florian Westphal <fw@...len.de>
Cc:	David Miller <davem@...emloft.net>, brouer@...hat.com,
	hans.schillstrom@...csson.com, subramanian.vijay@...il.com,
	dave.taht@...il.com, netdev@...r.kernel.org, ncardwell@...gle.com,
	therbert@...gle.com, mph@...h.dk
Subject: Re: [PATCH v2 net-next] tcp: avoid tx starvation by SYNACK packets

On Wed, 2012-06-27 at 21:50 +0200, Florian Westphal wrote:

> I doubt using jhash is safe for syncookies.
> 
> There a several differences to other uses in kernel:
> - all hash input except u32 cookie_secret[2] is known
> - we transmit hash result (i.e, its visible to 3rd party)
> - we do not re-seed the secret, ever
> 
> it should be quite easy to recompute cookie_secret[] from known syncookie
> values?

We could re-seed the secrets every MSL seconds a bit like in
tcp_cookie_generator()

This would require check_tcp_syn_cookie() doing two checks (most recent
seed, and previous one if first check failed)



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