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

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Date:   Thu, 23 Sep 2021 15:22:21 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     Samuel Ortiz <sameo@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "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 Thu, Sep 23, 2021 at 09:26:51AM +0200, Krzysztof Kozlowski wrote:
> On 23/09/2021 08:50, Dan Carpenter wrote:
> > This from static analysis inspired by CVE-2021-26708 where there was a
> > race condition because it didn't lock_sock(sk) before saving
> > "vsk->transport".  Here it is saving "llcp_sock->local" but the concept
> > is the same that it needs to take the lock first.
> 
> 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).

regards,
dan carpenter