netdev - Re: [PATCH v3 2/2] sctp: fix ASCONF list handling

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Message-ID: <1433794190.4616.8.camel@stressinduktion.org>
Date:	Mon, 08 Jun 2015 22:09:50 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	mleitner@...hat.com
Cc:	Neil Horman <nhorman@...driver.com>, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>,
	Vlad Yasevich <vyasevich@...il.com>,
	Michio Honda <micchie@....wide.ad.jp>
Subject: Re: [PATCH v3 2/2] sctp: fix ASCONF list handling

On Fr, 2015-06-05 at 14:08 -0300, mleitner@...hat.com wrote:
>       if (sp->do_auto_asconf) {
> +             spin_lock_bh(&sock_net(sk)->sctp.addr_wq_lock);
>               sp->do_auto_asconf = 0;
> -             list_del(&sp->auto_asconf_list);
> +             list_del_rcu(&sp->auto_asconf_list);
> +             spin_unlock_bh(&sock_net(sk)->sctp.addr_wq_lock);
>       }

This also looks a bit unsafe to me:

My proposal would be to sock_hold/sock_put the sockets when pushing them
onto the auto_asconf_list and defer the modifications on the list until
we don't need to hold socket lock anymore (in syscalls we do have a reference
anyway).

addr_wq_lock then is only used either without lock_sock at all or only
in order addr_wq_lock -> lock_sock, which does not cause any locking
ordering issues.

Bye,
Hannes

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