netdev - Re: [PATCH 3.8-rc] tuntap: refuse to re-attach to different tun

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Date:	Thu, 10 Jan 2013 21:53:59 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Stefan Hajnoczi <stefanha@...hat.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3.8-rc] tuntap: refuse to re-attach to different tun_struct

On 01/10/2013 07:07 PM, Michael S. Tsirkin wrote:
> 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@...hat.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.

Will post a patch, thanks.
>>> Signed-off-by: Michael S. Tsirkin <mst@...hat.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());
>>> --
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