linux-kernel - Re: [Question] Should `CAP_NET_ADMIN` be needed when opening `/dev/ppp`?

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Message-Id: <04054B5D-AD85-47ED-8666-21C7399BC121@gmail.com>
Date:	Tue, 3 May 2016 21:08:45 +0800
From:	王邈 <shankerwangmiao@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Richard Weinberger <richard.weinberger@...il.com>,
	Guillaume Nault <g.nault@...halink.fr>, netdev@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Question] Should `CAP_NET_ADMIN` be needed when opening `/dev/ppp`?


> 在 2016年5月3日，下午7:23，Hannes Frederic Sowa <hannes@...essinduktion.org> 写道：
> 
> On Tue, May 3, 2016, at 12:35, Richard Weinberger wrote:
>> On Tue, May 3, 2016 at 12:12 PM, Guillaume Nault <g.nault@...halink.fr>
>> wrote:
>>> On Sun, May 01, 2016 at 09:38:57PM +0800, Wang Shanker wrote:
>>>> static int ppp_open(struct inode *inode, struct file *file)
>>>> {
>>>>      /*
>>>>       * This could (should?) be enforced by the permissions on /dev/ppp.
>>>>       */
>>>>      if (!capable(CAP_NET_ADMIN))
>>>>              return -EPERM;
>>>>      return 0;
>>>> }
>>>> ```
>>>> 
>>>> I wonder why CAP_NET_ADMIN is needed here, rather than leaving it to the
>>>> permission of the device node. If there is no need, I suggest that the
>>>> CAP_NET_ADMIN check be removed.
>>>> 
>>> If this test was removed here, then it'd have to be added again in the
>>> PPPIOCNEWUNIT ioctl, at the very least, because creating a netdevice
>>> should require CAP_NET_ADMIN. Therefore that wouldn't help for your
>>> case.
>>> I don't know why the test was placed in ppp_open() in the first place,
>>> but changing it now would have side effects on user space. So I'd
>>> rather leave the code as is.
>> 
>> I think the question is whether we really require having CAP_NET_ADMIN
>> in the initial namespace and not just in the current one.
>> Is ppp not network namespace aware?
> 
> I agree, ns_capable(net->user_ns, CAP_NET_ADMIN), would probably make
> more sense.
I agree with that.
> 
> Bye,
> Hannes