netdev - Re: [PATCH net] nfc: avoid potential race condition

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Date:   Mon, 27 Sep 2021 15:14:27 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Samuel Ortiz <sameo@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        "John W. Linville" <linville@...driver.com>,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] nfc: avoid potential race condition

On Fri, Sep 24, 2021 at 01:14:41PM -0700, Jakub Kicinski wrote:
> On Fri, 24 Sep 2021 10:21:33 +0200 Krzysztof Kozlowski wrote:
> > On 23/09/2021 14:22, Dan Carpenter wrote:
> > > On Thu, Sep 23, 2021 at 09:26:51AM +0200, Krzysztof Kozlowski wrote:  
> > >> On 23/09/2021 08:50, Dan Carpenter wrote:  
> >  [...]  
> > >>
> > >> I think the difference between this llcp_sock code and above transport,
> > >> is lack of writer to llcp_sock->local with whom you could race.
> > >>
> > >> Commits c0cfa2d8a788fcf4 and 6a2c0962105ae8ce causing the
> > >> multi-transport race show nicely assigns to vsk->transport when module
> > >> is unloaded.
> > >>
> > >> Here however there is no writer to llcp_sock->local, except bind and
> > >> connect and their error paths. The readers which you modify here, have
> > >> to happen after bind/connect. You cannot have getsockopt() or release()
> > >> before bind/connect, can you? Unless you mean here the bind error path,
> > >> where someone calls getsockopt() in the middle of bind()? Is it even
> > >> possible?
> > >>  
> > > 
> > > I don't know if this is a real issue either.
> > > 
> > > Racing with bind would be harmless.  The local pointer would be NULL and
> > > it would return harmlessly.  You would have to race with release and
> > > have a third trying to release local devices.  (Again that might be
> > > wild imagination.  It may not be possible).  
> > 
> > Indeed. The code looks reasonable, though, so even if race is not really
> > reproducible:
> > 
> > Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
> 
> Would you mind making a call if this is net (which will mean stable) or
> net-next material (without the Fixes tags) and reposting? Thanks! :)

This should be ported to stable.  The race is condition is real because
->release() can race with itself.  I don't know if expliotable or not
beyond just a denial of service.

regards,
dan carpenter