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 19:32:26 +0800
From:   Gao Feng <fgao@...ai8.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>, jasowang@...hat.com,
        edumazet@...gle.com, pabeni@...hat.com,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next 1/1] driver: tun: Forbid to set IFF_TUN and
 IFF_TAP at the same time

Hi Eric,

On Fri, Oct 21, 2016 at 7:28 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> 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.

Yes. I consider about this case.
But I think there should be very least applications which set these
two flags at the same time.

>
> It might be too late to add this check without a grace period.
>
>
>
Yes, It needs some discussions.

Regards
Feng