netdev - Re: [PATCH net] mptcp: fix NULL ptr dereference on bad MPJ

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Message-ID: <2c3eecf9-c3b9-861a-cb8c-2f103496abfc@tessares.net>
Date:   Thu, 26 Nov 2020 16:23:08 +0100
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     Jakub Kicinski <kuba@...nel.org>, mptcp@...ts.01.org
Subject: Re: [PATCH net] mptcp: fix NULL ptr dereference on bad MPJ

Hi Paolo,

On 26/11/2020 15:17, Paolo Abeni wrote:
> If an msk listener receives an MPJ carrying an invalid token, it
> will zero the request socket msk entry. That should later
> cause fallback and subflow reset - as per RFC - at
> subflow_syn_recv_sock() time due to failing hmac validation.
> 
> Since commit 4cf8b7e48a09 ("subflow: introduce and use
> mptcp_can_accept_new_subflow()"), we unconditionally dereference
> - in mptcp_can_accept_new_subflow - the subflow request msk
> before performing hmac validation. In the above scenario we
> hit a NULL ptr dereference.
> 
> Address the issue doing the hmac validation earlier.
> 
> Fixes: 4cf8b7e48a09 ("subflow: introduce and use mptcp_can_accept_new_subflow()")
> Tested-by: Davide Caratti <dcaratti@...hat.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

Good catch! Thank you for the patch!

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

Cheers,
Matt
-- 
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