netdev - Re: DDoS attack causing bad effect on conntrack searches

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Message-ID: <1275388310.2738.2.camel@edumazet-laptop>
Date:	Tue, 01 Jun 2010 12:31:50 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Changli Gao <xiaosuo@...il.com>, hawk@...x.dk,
	Jesper Dangaard Brouer <hawk@...u.dk>,
	paulmck@...ux.vnet.ibm.com,
	Linux Kernel Network Hackers <netdev@...r.kernel.org>,
	Netfilter Developers <netfilter-devel@...r.kernel.org>
Subject: Re: DDoS attack causing bad effect on conntrack searches

Le mardi 01 juin 2010 à 12:18 +0200, Patrick McHardy a écrit :

> If a new conntrack is created in PRE_ROUTING or LOCAL_OUT, it will be
> added to the unconfirmed list and moved to the hash as soon as the
> packet passes POST_ROUTING. This means the number of unconfirmed entries
> created by the network is bound by the number of CPUs due to BH
> processing. The number created by locally generated packets is unbound
> in case of preemptible kernels however.
> 

OK, we should have a percpu list then.

BTW, I notice nf_conntrack_untracked is incorrectly annotated
'__read_mostly'.

It can be written very often :(

Should'nt we special case it and let be really const ?



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