Subject: Re: [PATCH 3.8-rc] tuntap: refuse to re-attach to different tun_struct

From: Jason Wang <[email-masked]>
Date: Thu, 10 Jan 2013 18:43:20 +0800

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 <[email-masked]>
>> ---
>> 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()?
> Signed-off-by: Michael S. Tsirkin <[email-masked]>
>
> ---
>
> 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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