Subject: Re: [Bugme-new] [Bug 9806] New: (tun dev) Impossible to deassert IFF_ONE_QUEUE or IFF_NO_PI

From: Andrew Morton <[email-masked]>
Date: Thu, 24 Jan 2008 00:33:56 -0800

> On Wed, 23 Jan 2008 13:13:13 -0800 (PST) [email-masked] wrote:
> http://bugzilla.kernel.org/show_bug.cgi?id=9806
> 
>            Summary: (tun dev) Impossible to deassert IFF_ONE_QUEUE or
>                     IFF_NO_PI
>            Product: Drivers
>            Version: 2.5
>      KernelVersion: 2.6.23
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: Network
>         AssignedTo: [email-masked]
>         ReportedBy: [email-masked]
> 
> 
> Problem Description:
> 
> 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).
> 

Thanks.   Could you please submit the patch via email?  Send it to
all recipients of this email.