netdev - Re: [PATCH net-next] tun: Do SIOCGSKNS out of rtnl

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Date:   Wed, 9 May 2018 21:19:26 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>, davem@...emloft.net,
        edumazet@...gle.com, mst@...hat.com, brouer@...hat.com,
        peterpenkov96@...il.com, sd@...asysnail.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tun: Do SIOCGSKNS out of rtnl_lock()



On 2018年05月09日 17:00, Kirill Tkhai wrote:
> Hi, Jason,
>
> On 09.05.2018 10:18, Jason Wang wrote:
>>
>> On 2018年05月09日 00:21, Kirill Tkhai wrote:
>>> Since net ns of tun device is assigned on the device creation,
>>> and it never changes, we do not need to use any lock to get it
>>> from alive tun.
>>>
>>> Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
>>> ---
>>>    drivers/net/tun.c |   18 +++++++-----------
>>>    1 file changed, 7 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>> index d3c04ab9752a..44d4f3d25350 100644
>>> --- a/drivers/net/tun.c
>>> +++ b/drivers/net/tun.c
>>> @@ -2850,10 +2850,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
>>>                    unsigned long arg, int ifreq_len)
>>>    {
>>>        struct tun_file *tfile = file->private_data;
>>> +    struct net *net = sock_net(&tfile->sk);
>>>        struct tun_struct *tun;
>>>        void __user* argp = (void __user*)arg;
>>>        struct ifreq ifr;
>>> -    struct net *net;
>>>        kuid_t owner;
>>>        kgid_t group;
>>>        int sndbuf;
>>> @@ -2877,14 +2877,18 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
>>>             */
>>>            return put_user(IFF_TUN | IFF_TAP | TUN_FEATURES,
>>>                    (unsigned int __user*)argp);
>>> -    } else if (cmd == TUNSETQUEUE)
>>> +    } else if (cmd == TUNSETQUEUE) {
>>>            return tun_set_queue(file, &ifr);
>>> +    } else if (cmd == SIOCGSKNS) {
>> Not for this patch, reusing socket ioctl cmd is probably not good though they were probably not intersected (see ioctl-number.txt). We probably need to introduce TUN specific ioctls for SIOCGSKNS and SIOCGIFHWADDR and warn for socket ones.
> The most of socket ioctl cmds use 0x8900 type:
>
> #define SOCK_IOC_TYPE   0x89
>
> while tun cmd is 5400 ('T'). They should not intersect.
>
> The only exceptions are
>
> #define SIOCINQ         FIONREAD
> #define SIOCOUTQ        TIOCOUTQ
>
> #define TIOCOUTQ        0x5411
> #define FIONREAD        0x541B
>
> But they can't intersect even with exceptions, since tun nr starts from 200:
>
> #define TUNSETNOCSUM  _IOW('T', 200, int)
>
> and 200 > 0x1b (==27).
>
> I implemented SIOCGSKNS cmd in the same style as older socket cmds were used.
> I'm not sure, we can remove existing SIOCGIFHWADDR, since they are already used.

I think it's too late to remove it.

> If we add a warn, which time will we able to remove them? Some old software may
> use it, and in case of the program isn't developed any more, nobody can fix this
> warnings, even if he/she sees them..

I think this give a chance to push new wrote userspace to use new ioctl cmd.

Thanks

>
> Kirill
>
>>> +        if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
>>> +            return -EPERM;
>>> +        return open_related_ns(&net->ns, get_net_ns);
>>> +    }
>>>          ret = 0;
>>>        rtnl_lock();
>>>          tun = tun_get(tfile);
>>> -    net = sock_net(&tfile->sk);
>>>        if (cmd == TUNSETIFF) {
>>>            ret = -EEXIST;
>>>            if (tun)
>>> @@ -2914,14 +2918,6 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
>>>            tfile->ifindex = ifindex;
>>>            goto unlock;
>>>        }
>>> -    if (cmd == SIOCGSKNS) {
>>> -        ret = -EPERM;
>>> -        if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
>>> -            goto unlock;
>>> -
>>> -        ret = open_related_ns(&net->ns, get_net_ns);
>>> -        goto unlock;
>>> -    }
>>>          ret = -EBADFD;
>>>        if (!tun)
>>>