netdev - Re: [PATCH] net: implement emergency route cache rebulds when gc

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Date:	Tue, 30 Sep 2008 10:35:23 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	"Denis V. Lunev" <den@...allels.com>
Cc:	netdev@...r.kernel.org, kuznet@....inr.ac.ru, davem@...emloft.net,
	pekkas@...core.fi, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net
Subject: Re: [PATCH] net: implement emergency route cache rebulds when
	gc_elasticity is exceeded

On Tue, Sep 30, 2008 at 06:17:12PM +0400, Denis V. Lunev wrote:
> The patch is wrong in respect to
>   for_each_net
> usage.
> 
> It should be used under rtnl. It is not held at the moment :(
> 
Thank you, I'll be sure to take that into consideration when we determine what
the proper algorithm to implement here is.

Although, I used the rt_secret_rebuild timer function as my guide here, and it
doesn't hold the rtnl lock either, or is that because its running in a softirq
context?

Neil

> Regards,
> 	Den
> 
> On Mon, 2008-09-29 at 15:12 -0400, Neil Horman wrote:
> > Hey all-
> > 	We currently have the ability to disable our route cache secret interval
> > rebuild timer (by setting it to zero), but if we do that its possible for an
> > attacker (if they guess our route cache hash secret, to fill our system with
> > routes that all hash to the same bucket, destroying our performance.  This patch
> > provides a backstop for that issues.  In the event that our rebuild interval is
> > disabled (or very large), if any hash chain exceeds ip_rt_gc_elasticity, we do
> > an emergency hash rebuild.  During the hash rebuild we:
> > 1) warn the user of the emergency
> > 2) disable the rebuild timer
> > 3) invalidate the route caches
> > 4) re-enable the rebuild timer with its old value
> > 
> > Regards
> > Neil
> > 
> > Signed-off-by: Neil Horman <nhorman@...driver.com>
> > 
> > 
> >  route.c |   36 +++++++++++++++++++++++++++++++++++-
> >  1 file changed, 35 insertions(+), 1 deletion(-)
> > 
> > 
> > diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> > index 6ee5354..b95e02a 100644
> > --- a/net/ipv4/route.c
> > +++ b/net/ipv4/route.c
> > @@ -145,7 +145,7 @@ static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst);
> >  static void		 ipv4_link_failure(struct sk_buff *skb);
> >  static void		 ip_rt_update_pmtu(struct dst_entry *dst, u32 mtu);
> >  static int rt_garbage_collect(struct dst_ops *ops);
> > -
> > +static void rt_emergency_hash_rebuild(void);
> >  
> >  static struct dst_ops ipv4_dst_ops = {
> >  	.family =		AF_INET,
> > @@ -1056,6 +1056,15 @@ restart:
> >  			*candp = cand->u.dst.rt_next;
> >  			rt_free(cand);
> >  		}
> > +	} else if (chain_length > ip_rt_gc_elasticity) {
> > +		/*
> > +		 * We didn't find a route entry we could safely free,
> > +		 * yet our chain length is over our elasticity value.
> > +		 * Someone may have guessed our hash secret and is artifically
> > +		 * filling up our route cache.  Lets do an emergency rebuild
> > +		 * to be safe
> > +		 */
> > +		rt_emergency_hash_rebuild();
> >  	}
> >  
> >  	/* Try to bind route to arp only if it is output
> > @@ -2946,6 +2955,31 @@ static void rt_secret_reschedule(int old)
> >  	rtnl_unlock();
> >  }
> >  
> > +static void rt_secret_rebuild_oneshot(void) {
> > +	struct net *net;
> > +	int old_interval = ip_rt_secret_interval;
> > +
> > +	ip_rt_secret_interval = 0;
> > +
> > +	rt_secret_reschedule(old_interval);
> > +
> > +	for_each_net(net) 
> > +		rt_cache_invalidate(net);
> > +
> > +	ip_rt_secret_interval = old_interval;
> > +
> > +	rt_secret_reschedule(0);
> > +}
> > +
> > +static void rt_emergency_hash_rebuild(void) {
> > +	if (net_ratelimit()) {
> > +		printk(KERN_WARNING "Route hash chain too long!\n");
> > +		printk(KERN_WARNING "Adjust your secret_interval!\n");
> > +	}
> > +
> > +	rt_secret_rebuild_oneshot();
> > +}
> > +
> >  static int ipv4_sysctl_rt_secret_interval(ctl_table *ctl, int write,
> >  					  struct file *filp,
> >  					  void __user *buffer, size_t *lenp,
> 
> 

-- 
/****************************************************
 * Neil Horman <nhorman@...driver.com>
 * Software Engineer, Red Hat
 ****************************************************/
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