netdev - Re: [PATCH net-next] kcm: do not attach sockets if sk_user

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Date:   Wed, 17 Jan 2018 11:13:33 +0000
From:   James Chapman <jchapman@...alix.com>
To:     David Miller <davem@...emloft.net>
Cc:     tom@...bertland.com, netdev@...r.kernel.org,
        Guillaume Nault <g.nault@...halink.fr>
Subject: Re: [PATCH net-next] kcm: do not attach sockets if sk_user_data is
 already used

On 16 January 2018 at 19:00, David Miller <davem@...emloft.net> wrote:
> From: Tom Herbert <tom@...bertland.com>
> Date: Tue, 16 Jan 2018 09:36:41 -0800
>
>> sk_user_data is set with the sk_callback lock held in code below.
>> Should be able to take the lock earlier can do this check under the
>> lock.
>
> csock, and this csk, is obtained from an arbitrary one of the
> process's FDs.  It can be any socket type or family, and that socket's
> family might set sk_user_data without the callback lock.
>
> The only socket type check is making sure it is not another PF_KCM
> socket.  So that doesn't help with this problem.

Is it the intention to update all socket code over time to write
sk_user_data within the sk_callback lock? If so, I'm happy to address
that in the l2tp code (and update the kcm patch to check sk_user_data
within the sk_callback lock). Or is the preferred solution to restrict
KCM to specific socket families, as suggested by Guillaume earlier in
the thread?