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

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Message-ID: <47358bea-e761-b823-dfbd-cd8e0a2a69a6@canonical.com>
Date:   Fri, 24 Sep 2021 10:21:33 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Dan Carpenter <dan.carpenter@...cle.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 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:
>>> 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).

Indeed. The code looks reasonable, though, so even if race is not really
reproducible:

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>


Best regards,
Krzysztof