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

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Message-ID: <1272001478.7895.7545.camel@edumazet-laptop>
Date:	Fri, 23 Apr 2010 07:44:38 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	hawk@...u.dk, paulmck@...ux.vnet.ibm.com, kaber@...sh.net,
	xiaosuo@...il.com, hawk@...x.dk, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: DDoS attack causing bad effect on conntrack searches

Le jeudi 22 avril 2010 à 16:44 -0700, David Miller a écrit :
> Eric, I wonder if we run into some kind of issue on 32-bit systems
> because we always lose a bit of the conntrack hash value when we store
> it into the 'nulls' area?
> 
> Wouldn't that make the "get_nulls_value(n) != hash" fail?
> --


Well, 'hash' at this time is not the result of the jhash() transform [0
- 0xFFFFFFFF], but a slot number in htable [0 - (300032-1)].


And we can have a nulls_value up to 0x7FFFFFFF  (31 bits)

static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
{
        return ((unsigned long)ptr) >> 1;
}




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