netdev - Re: [PATCH v2 net-next 1/1] driver: tun: Forbid to set IFF_TUN and IFF

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Date:   Fri, 21 Oct 2016 04:28:07 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     fgao@...ai8.com
Cc:     davem@...emloft.net, jasowang@...hat.com, edumazet@...gle.com,
        pabeni@...hat.com, netdev@...r.kernel.org, gfree.wind@...il.com
Subject: Re: [PATCH v2 net-next 1/1] driver: tun: Forbid to set IFF_TUN and
 IFF_TAP at the same time

On Fri, 2016-10-21 at 19:02 +0800, fgao@...ai8.com wrote:
> From: Gao Feng <fgao@...ai8.com>
> 
> Current tun driver permits the ifr_flags is set with IFF_TUN and
> IFF_TAP at the same time. But actually there is only IFF_TUN flag
> works. And it does not make sense these two flags are set, so add
> this check.
> 
> Signed-off-by: Gao Feng <fgao@...ai8.com>
> ---
>  v2: Remove useless {}
>  v1: Initial patch
> 
>  drivers/net/tun.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 8093e39..faaa189 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1752,6 +1752,9 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>  		if (err < 0)
>  			return err;
>  
> +		if ((ifr->ifr_flags & (IFF_TUN | IFF_TAP)) == (IFF_TUN | IFF_TAP))
> +			return -EINVAL;
> +
>  		/* Set dev type */
>  		if (ifr->ifr_flags & IFF_TUN) {
>  			/* TUN device */


This might break some applications.

It might be too late to add this check without a grace period.