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SubjectRe: [PATCH 3.8-rc] tuntap: refuse to re-attach to different tun_struct
On Thu, Jan 10, 2013 at 12:23:19PM +0200, Michael S. Tsirkin wrote:
> On Thu, Jan 10, 2013 at 08:59:48AM +0100, Stefan Hajnoczi wrote:
> > Multiqueue tun devices support detaching a tun_file from its tun_struct
> > and re-attaching at a later point in time. This allows users to disable
> > a specific queue temporarily.
> >
> > ioctl(TUNSETIFF) allows the user to specify the network interface to
> > attach by name. This means the user can attempt to attach to interface
> > "B" after detaching from interface "A".
> >
> > The driver is not designed to support this so check we are re-attaching
> > to the right tun_struct. Failure to do so may lead to oops.
> >
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> > This fix is for 3.8-rc.
> >
> > drivers/net/tun.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> > index fbd106e..cf6da6e 100644
> > --- a/drivers/net/tun.c
> > +++ b/drivers/net/tun.c
> > @@ -491,6 +491,8 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
> > err = -EINVAL;
> > if (rcu_dereference_protected(tfile->tun, lockdep_rtnl_is_held()))
> > goto out;
> > + if (tfile->detached && tun != tfile->detached)
> > + goto out;
> >
> > err = -EBUSY;
> > if (!(tun->flags & TUN_TAP_MQ) && tun->numqueues == 1)
> > --
> > 1.8.0.2
>
>
> I agree this is a bug but even with this patch, we still allow:
>
> SETIFF
> SETQUEUE (DISABLED)
> SETIFF
>
> Originally the rule always was that repeated setiff calls fail with
> EINVAL. We broke that when we set tun to NULL. It's probably worth
> preserving that, even if queue is disabled. Applying something like the below
> instead will address this concern, won't it?

Sounds good.

Stefan


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