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

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Message-ID: <CAFLxGvyKMbJyfk5oiRZ6-67yHH=f+3mkY=gd3AsZC1G_o0Xhxg@mail.gmail.com>
Date:	Tue, 3 May 2016 12:35:12 +0200
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Guillaume Nault <g.nault@...halink.fr>
Cc:	Wang Shanker <shankerwangmiao@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Question] Should `CAP_NET_ADMIN` be needed when opening `/dev/ppp`?

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?

-- 
Thanks,
//richard