linux-kernel - Re: [PATCH net] ip6tnl: fix use after free of fb_tnl

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Date:	Thu, 14 Nov 2013 10:40:41 -0500
From:	Willem de Bruijn <willemb@...gle.com>
To:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc:	rostedt@...dmis.org, linux-kernel <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org, gregkh@...uxfoundation.org,
	williams@...hat.com, linux-rt-users@...r.kernel.org,
	lclaudio@...g.org, David Miller <davem@...emloft.net>,
	netdev@...r.kernel.org
Subject: Re: [PATCH net] ip6tnl: fix use after free of fb_tnl_dev

On Thu, Nov 14, 2013 at 9:47 AM, Nicolas Dichtel
<nicolas.dichtel@...nd.com> wrote:
> Bug has been introduced by commit bb8140947a24 ("ip6tnl: allow to use rtnl ops
> on fb tunnel").
>
> When ip6_tunnel.ko is unloaded, FB device is delete by rtnl_link_unregister()
> and then we try to use the pointer in ip6_tnl_destroy_tunnels().
>
> Let's add an handler for dellink, which will never remove the FB tunnel. With
> this patch it will no more be possible to remove it via 'ip link del ip6tnl0',
> but it's safer.
>
> The same fix was already proposed by Willem de Bruijn <willemb@...gle.com> for
> sit interfaces.
>
> CC: Willem de Bruijn <willemb@...gle.com>
> Reported-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>

Acked-by: Willem de Bruijn <willemb@...gle.com>

Also ran a test similar to the one for sit: `modprobe ip6_tunnel;
rmmod ip6_tunnel` with CONFIG_DEBUG_SLAB=y. This exposed the bug at
HEAD, completes successfully with the patch applied.
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