netdev - Re: [PATCH net] mptcp: be careful on subflow creation

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Date:   Wed, 5 Aug 2020 11:14:25 +0200
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, mptcp@...ts.01.org,
        Nicolas Rybowski <nicolas.rybowski@...sares.net>
Subject: Re: [PATCH net] mptcp: be careful on subflow creation

Hi Paolo,

On 05/08/2020 11:10, Paolo Abeni wrote:
> On Tue, 2020-08-04 at 21:25 +0200, Matthieu Baerts wrote:
>> Hi Paolo,
>>
>> On 04/08/2020 18:31, Paolo Abeni wrote:
>>> Nicolas reported the following oops:
>>
>> (...)
>>
>>> on some unconventional configuration.
>>>
>>> The MPTCP protocol is trying to create a subflow for an
>>> unaccepted server socket. That is allowed by the RFC, even
>>> if subflow creation will likely fail.
>>> Unaccepted sockets have still a NULL sk_socket field,
>>> avoid the issue by failing earlier.
>>>
>>> Reported-and-tested-by: Nicolas Rybowski <nicolas.rybowski@...sares.net>
>>> Fixes: 7d14b0d2b9b3 ("mptcp: set correct vfs info for subflows")
>>
>> Thank you for the patch, the addition in the code looks very good to me!
>>
>> But are you sure the commit you mention introduces the issue you fix here?
> 
> AFAICS, the oops can be observed only with the mentioned commit - which
> unconditioanlly de-reference a NULL sk->sk_socket. [try to] create a
> subflow on server unaccepted socket is not a bug per-se, so I would not
> send the fix to older trees.

Sorry, my bad, I didn't see that in the mentioned commit, we were using 
sk->sk_socket without checking if it was not NULL...
Thank you for pointing that to me!

Bad idea to review patches on the evening :)

The patch is then good to go to me!

Reviewed-by: Matthieu Baerts <matthieu.baerts@...sares.net>

Cheers,
Matt
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