netdev - Re: [PATCH net] l2tp: fix use-after-free during module unload

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Message-Id: <20160901.163416.76744449780953103.davem@davemloft.net>
Date:   Thu, 01 Sep 2016 16:34:16 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     sd@...asysnail.net
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net] l2tp: fix use-after-free during module unload

From: Sabrina Dubroca <sd@...asysnail.net>
Date: Tue, 30 Aug 2016 16:05:16 +0200

> Tunnel deletion is delayed by both a workqueue (l2tp_tunnel_delete -> wq
>  -> l2tp_tunnel_del_work) and RCU (sk_destruct -> RCU ->
> l2tp_tunnel_destruct).
> 
> By the time l2tp_tunnel_destruct() runs to destroy the tunnel and finish
> destroying the socket, the private data reserved via the net_generic
> mechanism has already been freed, but l2tp_tunnel_destruct() actually
> uses this data.
> 
> Make sure tunnel deletion for the netns has completed before returning
> from l2tp_net_exit() by first flushing the tunnel removal workqueue, and
> then waiting for RCU callbacks to complete.
> 
> Fixes: 167eb17e0b17 ("l2tp: create tunnel sockets in the right namespace")
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>

Please resubmit this with Sergei's feedback addressed.

Thanks.