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

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Message-ID: <20201127110649.62563a6c@kicinski-fedora-pc1c0hjn.DHCP.thefacebook.com>
Date:   Fri, 27 Nov 2020 11:06:49 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Matthieu Baerts <matthieu.baerts@...sares.net>
Cc:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        mptcp@...ts.01.org
Subject: Re: [PATCH net] mptcp: fix NULL ptr dereference on bad MPJ

On Thu, 26 Nov 2020 16:23:08 +0100 Matthieu Baerts wrote:
> 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>

Applied, thanks!