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    SubjectRe: [PATCH 3.8-rc] tuntap: refuse to re-attach to different tun_struct
    On Thu, Jan 10, 2013 at 06:43:20PM +0800, Jason Wang wrote:
    > On 01/10/2013 06:23 PM, 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?
    > >
    > > Note: works with regular userspace but I didn't test
    > > multiqueue userspace. What do you think.
    >
    > Or just fail when tun->detached is not NULL at the beginning of
    > tun_set_iff()?

    Yes that'll also work I think. If you prefer this pls send patch.

    > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    > >
    > > ---
    > >
    > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c
    > > index fbd106e..5ec8b08 100644
    > > --- a/drivers/net/tun.c
    > > +++ b/drivers/net/tun.c
    > > @@ -483,7 +483,7 @@ static void tun_detach_all(struct net_device *dev)
    > > BUG_ON(tun->numdisabled != 0);
    > > }
    > >
    > > -static int tun_attach(struct tun_struct *tun, struct file *file)
    > > +static int tun_attach(struct tun_struct *tun, struct file *file, bool setiff)
    > > {
    > > struct tun_file *tfile = file->private_data;
    > > int err;
    > > @@ -492,6 +492,9 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
    > > if (rcu_dereference_protected(tfile->tun, lockdep_rtnl_is_held()))
    > > goto out;
    > >
    > > + if (setiff && tfile->detached)
    > > + goto out;
    > > +
    > > err = -EBUSY;
    > > if (!(tun->flags & TUN_TAP_MQ) && tun->numqueues == 1)
    > > goto out;
    > > @@ -1561,7 +1564,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
    > > if (err < 0)
    > > return err;
    > >
    > > - err = tun_attach(tun, file);
    > > + err = tun_attach(tun, file, true);
    > > if (err < 0)
    > > return err;
    > >
    > > @@ -1627,7 +1630,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
    > > dev->features = dev->hw_features;
    > >
    > > INIT_LIST_HEAD(&tun->disabled);
    > > - err = tun_attach(tun, file);
    > > + err = tun_attach(tun, file, true);
    > > if (err < 0)
    > > goto err_free_dev;
    > >
    > > @@ -1792,7 +1795,7 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr)
    > > else if (tun_not_capable(tun))
    > > ret = -EPERM;
    > > else
    > > - ret = tun_attach(tun, file);
    > > + ret = tun_attach(tun, file, false);
    > > } else if (ifr->ifr_flags & IFF_DETACH_QUEUE) {
    > > tun = rcu_dereference_protected(tfile->tun,
    > > lockdep_rtnl_is_held());
    > > --
    > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    > > the body of a message to majordomo@vger.kernel.org
    > > More majordomo info at http://vger.kernel.org/majordomo-info.html
    > > Please read the FAQ at http://www.tux.org/lkml/


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