netdev - Re: [net-next PATCH 1/3] net: fix race bug in fragmentation create code

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Date:	Fri, 19 Apr 2013 10:09:24 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [net-next PATCH 1/3] net: fix race bug in fragmentation create
 code

On Fri, 2013-04-19 at 03:00 +0200, Hannes Frederic Sowa wrote:
> On Thu, Apr 18, 2013 at 11:37:27PM +0200, Jesper Dangaard Brouer wrote:
> > During creation of a new inet_frag_queue, the lru_list pointer is
> > updated after releasing the hash bucket lock, which can lead to a
> > race condition (and panic), if the inet_frag_queue is deleted
> > (very quickly) before the lru_list is valid.
> > 
> > This race condition is should not be able to occur with current
> > LRU based evictor.  For the planned direct hash based
> > evictor/clean strategy, this race condition is more likely to
> > occur.
> > 
> > Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> > ---
> > 
> >  net/ipv4/inet_fragment.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
> > index e97d66a..beec05b 100644
> > --- a/net/ipv4/inet_fragment.c
> > +++ b/net/ipv4/inet_fragment.c
> > @@ -283,9 +283,9 @@ static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf,
> >  
> >  	atomic_inc(&qp->refcnt);
> >  	hlist_add_head(&qp->list, &hb->chain);
> > +	inet_frag_lru_add(nf, qp);
> >  	spin_unlock(&hb->chain_lock);
> >  	read_unlock(&f->lock);
> > -	inet_frag_lru_add(nf, qp);
> >  	return qp;
> >  }
> 
> If I checked correctly, the current code does not have the race
> condition? I think this change is ok but maybe we can defer it until
> the direct hash cleanup patches land?

Lets hear what others think of collapsing it into the next patch?
(I don't have a problem with doing so)

--Jesper


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