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

[Jarek Poplawski <jarkao2@gmail.com>]

On Tue, May 19, 2009 at 05:32:29PM +0200, Eric Dumazet wrote:
> Jarek Poplawski a écrit :
> > On 19-05-2009 04:35, Stephen Hemminger wrote:
> >> Begin forwarded message:
> >>
> >> Date: Mon, 18 May 2009 14:10:20 GMT
> >> From: bugzilla-daemon@bugzilla.kernel.org
> >> To: shemminger@linux-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.
> 
> We could change rt_check_expire() to be smarter and handle any order in chains.
> 
> This would let rt_intern_hash() be simpler.
> 
> As its a more performance critical path, all would be good :)
> 
> >>
> >> 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?
> > 
> 
> Here is mine, only compiled, not tested yet.
> 
> All credits for Stephen for doing the analysis of course :)

- All credits for Stephen for doing the analysis of course :)
+ All credits for Alexander V. Lukyanov for doing the analysis of course :)

Jarek P.