netdev - Re: [patch 2/2] tun: impossible to deassert IFF_ONE_QUEUE or IFF_NO

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Message-Id: <20080205.030547.156453415.davem@davemloft.net>
Date:	Tue, 05 Feb 2008 03:05:47 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	akpm@...ux-foundation.org
Cc:	netdev@...r.kernel.org, nwfilardo@...il.com, jeff@...zik.org,
	maxk@...lcomm.com
Subject: Re: [patch 2/2] tun: impossible to deassert IFF_ONE_QUEUE or
 IFF_NO_PI

From: akpm@...ux-foundation.org
Date: Mon, 04 Feb 2008 23:45:21 -0800

> From: "Nathaniel Filardo" <nwfilardo@...il.com>
> 
> Taken from http://bugzilla.kernel.org/show_bug.cgi?id=9806
> 
> The TUN/TAP driver only permits one-way transitions of IFF_NO_PI or
> IFF_ONE_QUEUE during the lifetime of a tap/tun interface.  Note that
> tun_set_iff contains
> 
>  541         if (ifr->ifr_flags & IFF_NO_PI)
>  542                 tun->flags |= TUN_NO_PI;
>  543 
>  544         if (ifr->ifr_flags & IFF_ONE_QUEUE)
>  545                 tun->flags |= TUN_ONE_QUEUE;
> 
> This is easily fixed by adding else branches which clear these bits.
> 
> Steps to reproduce:
> 
> This is easily reproduced by setting an interface persistant using tunctl then
> attempting to open it as IFF_TAP or IFF_TUN, without asserting the IFF_NO_PI
> flag.  The ioctl() will succeed and the ifr.flags word is not modified, but the
> interface remains in IFF_NO_PI mode (as it was set by tunctl).
> 
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Jeff Garzik <jeff@...zik.org>
> Acked-by: Maxim Krasnyansky <maxk@...lcomm.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

Applied.
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