netdev - Re: [PATCH] ip6_gre: don't allow to remove the fb_tunnel

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Message-Id: <20140415.000404.2110427476393772943.davem@davemloft.net>
Date:	Tue, 15 Apr 2014 00:04:04 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	nicolas.dichtel@...nd.com
Cc:	netdev@...r.kernel.org, xeb@...l.ru
Subject: Re: [PATCH] ip6_gre: don't allow to remove the fb_tunnel_dev

From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Date: Mon, 14 Apr 2014 17:11:38 +0200

> It's possible to remove the FB tunnel with the command 'ip link del ip6gre0' but
> this is unsafe, the module always supposes that this device exists. For example,
> ip6gre_tunnel_lookup() may use it unconditionally.
> 
> Let's add a rtnl handler for dellink, which will never remove the FB tunnel (we
> let ip6gre_destroy_tunnels() do the job).
> 
> Introduced by commit c12b395a4664 ("gre: Support GRE over IPv6").
> 
> CC: Dmitry Kozlov <xeb@...l.ru>
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>

I don't see how we ever get rid of fb_tunnel_dev and can therefore
remove the module successfully.

It is created by the per-netns initialization, but since it isn't
added to the hashes I don't see how the per-netns exit code can
end up unregistering and freeing it up.

How is this supposed to work?
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