netdev - Re: [PATCH net-next] neigh: fix a possible leak issue of neigh entry

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Message-ID: <1431522430.566.134.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 13 May 2015 06:07:10 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ying Xue <ying.xue@...driver.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH net-next] neigh: fix a possible leak issue of neigh entry

On Wed, 2015-05-13 at 18:32 +0800, Ying Xue wrote:
> On 05/13/2015 03:25 PM, Ying Xue wrote:
> > On 05/13/2015 02:20 PM, Eric Dumazet wrote:
> >> Have you hit this condition ?
> >>
> > 
> > No, I just found the issue when I was reading the code.
> > 
> >> If yes, there is a bug elsewhere and we need to fix it, not trying to
> >> recover.
> >>
> 
> After a search, it's found your mentioned bug probably should be:
> 
> https://patchwork.ozlabs.org/patch/458112/
> 
> But I think the bug should be a different issue that the patch is to be
> resolved. When the bug happened, neigh_add_timer() would take a reference on an
> object that already had a refcount of zero, which means somebody already
> decreased the refcount to zero before neigh_add_timer() was called. So, the bug
> should be unrelated to neigh_add_timer() although the bug really needs to be
> fixed. But the issue the patch tries to fix is wrong because it obviously
> violates the generic usage of how to take an object refcount in the object's
> timer handler as well as when its timer is started or deleted. Specially when a
> neighbour's timer to be modified is in pending state, we should not take its
> refcount, otherwise, the neighbour is leaked forever.
> 
> Therefore, the patch is needed for us even if your mentioned bug is not fixed.

Sorry, your patch is wrong.

As I said, if the issue is there, a different fix is needed.

Caller of the function must owns a refcount by definition.



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