netdev - Re: Fw: [Bug 13339] New: rtable leak in ipv4/route.c

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Date:	Tue, 19 May 2009 11:12:07 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	lav@....ru, Stephen Hemminger <shemminger@...ux-foundation.org>,
	netdev@...r.kernel.org
Subject: Re: Fw: [Bug 13339] New: rtable leak in ipv4/route.c

On Tue, May 19, 2009 at 12:34:17PM +0000, Jarek Poplawski wrote:
> On 19-05-2009 04:35, Stephen Hemminger wrote:
> > 
> > Begin forwarded message:
> > 
> > Date: Mon, 18 May 2009 14:10:20 GMT
> > From: bugzilla-daemon@...zilla.kernel.org
> > To: shemminger@...ux-foundation.org
> > Subject: [Bug 13339] New: rtable leak in ipv4/route.c
> > 
> > 
> > http://bugzilla.kernel.org/show_bug.cgi?id=13339
> ...
> > 2.6.29 patch has introduced flexible route cache rebuilding. Unfortunately the
> > patch has at least one critical flaw, and another problem.
> > 
> > rt_intern_hash calculates rthi pointer, which is later used for new entry
> > insertion. The same loop calculates cand pointer which is used to clean the
> > list. If the pointers are the same, rtable leak occurs, as first the cand is
> > removed then the new entry is appended to it.
> > 
> > This leak leads to unregister_netdevice problem (usage count > 0).
> > 
> > Another problem of the patch is that it tries to insert the entries in certain
> > order, to facilitate counting of entries distinct by all but QoS parameters.
> > Unfortunately, referencing an existing rtable entry moves it to list beginning,
> > to speed up further lookups, so the carefully built order is destroyed.
> > 
> > For the first problem the simplest patch it to set rthi=0 when rthi==cand, but
> > it will also destroy the ordering.
> 
> I think fixing this bug fast is more important than this
> ordering or counting. Could you send your patch proposal?


I agree that the corner case in which cand and rthi is a problem (although as
you point out easily fixable), and with an alteration to your proposal it can be
done without destroying the order.

As for the reordering by reference however, I don't see any move to front
heuristic being implemented anywhere in the routing path.  Where do you see this
happening?

Neil

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