netdev - Re: [PATCH,v2,net-next 2/2] tun: enable napi_gro

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Date:   Fri, 22 Sep 2017 13:50:20 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Petar Penkov <peterpenkov96@...il.com>
Cc:     Mahesh Bandewar (महेश बंडेवार) 
        <maheshb@...gle.com>, Network Development <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        David Miller <davem@...emloft.net>,
        Petar Bozhidarov Penkov <ppenkov@...nford.edu>
Subject: Re: [PATCH,v2,net-next 2/2] tun: enable napi_gro_frags() for TUN/TAP driver

On Fri, Sep 22, 2017 at 1:48 PM, Petar Penkov <peterpenkov96@...il.com> wrote:
> On Fri, Sep 22, 2017 at 9:51 AM, Mahesh Bandewar (महेश बंडेवार)
> <maheshb@...gle.com> wrote:
>> On Fri, Sep 22, 2017 at 7:06 AM, Willem de Bruijn
>> <willemdebruijn.kernel@...il.com> wrote:
>>>> @@ -2061,6 +2174,9 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>>>>         if (tfile->detached)
>>>>                 return -EINVAL;
>>>>
>>>> +       if ((ifr->ifr_flags & IFF_NAPI_FRAGS) && !capable(CAP_NET_ADMIN))
>>>> +               return -EPERM;
>>>> +
>>>
>>> This should perhaps be moved into the !dev branch, directly below the
>>> ns_capable check.
>>>
>> Hmm, does that mean fail only on creation but allow to attach if
>> exists? That would be wrong, isn't it? Correct me if I'm wrong but we
>> want to prevent both these scenarios if user does not have sufficient
>> privileges (i.e. NET_ADMIN in init-ns).

Ok.

>>
> My understanding is we want to protect both scenarios.
>>>>         dev = __dev_get_by_name(net, ifr->ifr_name);
>>>>         if (dev) {
>>>>                 if (ifr->ifr_flags & IFF_TUN_EXCL)
>>>> @@ -2185,6 +2301,9 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>>>>         tun->flags = (tun->flags & ~TUN_FEATURES) |
>>>>                 (ifr->ifr_flags & TUN_FEATURES);
>>>>
>>>> +       if (!(tun->flags & IFF_NAPI) || (tun->flags & TUN_TYPE_MASK) != IFF_TAP)
>>>> +               tun->flags = tun->flags & ~IFF_NAPI_FRAGS;
>>>> +
>>>
>>> Similarly, this check only need to be performed in that branch.
>>> Instead of reverting to non-frags mode, a tun_set_iff with the wrong
>>> set of flags should probably fail hard.
>> Yes, agree, wrong set of flags should fail hard and probably be done
>> before attach or open, no?
> Agreed, in v3 I will push this check before the conditional so both
> branches can be rejected with EINVAL.

Sounds great.