netdev - Re: [PATCH] l2tp: prevent l2tp_tunnel_delete racing with userspace close

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Message-Id: <20130129.160331.1697248531078003094.davem@davemloft.net>
Date:	Tue, 29 Jan 2013 16:03:31 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	tparkin@...alix.com
Cc:	netdev@...r.kernel.org, celston@...alix.com, jchapman@...alix.com
Subject: Re: [PATCH] l2tp: prevent l2tp_tunnel_delete racing with userspace
 close

From: Tom Parkin <tparkin@...alix.com>
Date: Tue, 22 Jan 2013 15:13:48 +0000

> If a tunnel socket is created by userspace, l2tp hooks the socket destructor
> in order to clean up resources if userspace closes the socket or crashes.  It
> also caches a pointer to the struct sock for use in the data path and in the
> netlink interface.
> 
> While it is safe to use the cached sock pointer in the data path, where the
> skb references keep the socket alive, it is not safe to use it elsewhere as
> such access introduces a race with userspace closing the socket.  In
> particular, l2tp_tunnel_delete is prone to oopsing if a multithreaded
> userspace application closes a socket at the same time as sending a netlink
> delete command for the tunnel.
> 
> This patch fixes this oops by forcing l2tp_tunnel_delete to explicitly look up
> a tunnel socket held by userspace using sockfd_lookup().
> 
> Signed-off-by: Tom Parkin <tparkin@...alix.com>
> Signed-off-by: James Chapman <jchapman@...alix.com>

Applied.
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