netdev - Re: [NETLINK] periodically rehash table, why?

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Message-Id: <E1HRdVX-0003fS-00@gondolin.me.apana.org.au>
Date:	Thu, 15 Mar 2007 11:07:51 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	holger@...eitzenberger.de (Holger Eitzenberger)
Cc:	netdev@...r.kernel.org
Subject: Re: [NETLINK] periodically rehash table, why?

Holger Eitzenberger <holger@...eitzenberger.de> wrote:
> 
> in nl_pid_hash_dilute() there is:
> 
>   if (unlikely(avg > 1) && nl_pid_hash_rehash(hash, 1))
>      return 1;
> 
>      if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
>         nl_pid_hash_rehash(hash, 0);
>         return 1;
>      }
> 
> I don't see a reason why periodically rehashing might help in any way
> (without resizing).  Is there a reason for that?

It's to prevent attackers from guessing the hash secret and causing
hash chains to grow excessively.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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