netdev - Re: [PATCH] ipv4: remove ip_rt

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Date:	Thu, 06 May 2010 23:08:05 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, kuznet@....inr.ac.ru,
	jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net
Subject: Re: [PATCH] ipv4: remove ip_rt_secret timer (v2)

Le jeudi 06 mai 2010 à 16:29 -0400, Neil Horman a écrit :
> Version 2 of this patch, taking Erics comment about making the rt_genid non-zero
> when a netns is created.  This makes sense, and helps prevent attackers from
> guessing our initial secret value
> 
> 
> 
> A while back there was a discussion regarding the rt_secret_interval timer.
> Given that we've had the ability to do emergency route cache rebuilds for awhile
> now, based on a statistical analysis of the various hash chain lengths in the
> cache, the use of the flush timer is somewhat redundant.  This patch removes the
> rt_secret_interval sysctl, allowing us to rely solely on the statistical
> analysis mechanism to determine the need for route cache flushes.
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> 

> -
> -static __net_init int rt_secret_timer_init(struct net *net)
> +static __net_init int rt_genid_init(struct net *net)
>  {
> -	atomic_set(&net->ipv4.rt_genid,
> -			(int) ((num_physpages ^ (num_physpages>>8)) ^
> -			(jiffies ^ (jiffies >> 7))));
> -


> +	/*
> +	 * This just serves to start off each new net namespace
> +	 * with a non-zero rt_genid value, making it harder to guess
> +	 */
> +	rt_cache_invalidate(net);
>  	return 0;
>  }
>  

I am _sorry_ to be such a paranoiac guy.

Could you please feed more than 8 bits here ?

like :

get_random_bytes(&net->ipv4.rt_genid, sizeof(net->ipv4.rt_genid));

There is no need to comment this in the code, this kind of rnd init is
very common in net tree.





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