linux-kernel - Re: [PATCH] tun: avoid owner checks on IFF_ATTACH

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Date:	Thu, 10 Jan 2013 22:08:03 +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, Paul Moore <pmoore@...hat.com>
Subject: Re: [PATCH] tun: avoid owner checks on IFF_ATTACH_QUEUE

On 01/10/2013 07:31 PM, Michael S. Tsirkin wrote:
> At the moment, we check owner when we enable queue in tun.
> This seems redundant and will break some valid uses
> where fd is passed around: I think TUNSETOWNER is there
> to prevent others from attaching to a persistent device not
> owned by them. Here the fd is already attached,
> enabling/disabling queue is more like read/write.

It also change the number of queues of the tuntap, maybe we should limit
this. Note that if management layer does not call TUNSETOWNER, the check
is just a nop. So if management layer want to limit the behavior, it's
its duty to do this correctly.
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>
> ---
>
> Note: this is unrelated to Stefan's bugfix.
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index fbd106e..78e3225 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1789,10 +1792,8 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr)
>  		tun = tfile->detached;
>  		if (!tun)
>  			ret = -EINVAL;
> -		else if (tun_not_capable(tun))
> -			ret = -EPERM;
>  		else
>  			ret = tun_attach(tun, file);
>  	} else if (ifr->ifr_flags & IFF_DETACH_QUEUE) {
>  		tun = rcu_dereference_protected(tfile->tun,
>  						lockdep_rtnl_is_held());


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