Re: [PATCH 0/2] Add further ioctl() operations for namespace discovery

From: ebiederm@xmission.com (Eric W. Biederman)
To: "Michael Kerrisk \(man-pages\)" <mtk.manpages@gmail.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
	linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, Andrey Vagin <avagin@openvz.org>,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	"W. Trevor King" <wking@tremily.us>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jonathan Corbet <corbet@lwn.net>,
	Andrei Vagin <avagin@virtuozzo.com>
Subject: Re: [PATCH 0/2] Add further ioctl() operations for namespace discovery
Date: Thu, 22 Dec 2016 23:28:39 +1300	[thread overview]
Message-ID: <87vauc9s14.fsf@xmission.com> (raw)
In-Reply-To: <142285b7-225b-fd15-3c8e-9ae2d02e82b5@gmail.com> (Michael Kerrisk's message of "Thu, 22 Dec 2016 08:20:33 +0100")

"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> writes:

> Hi Eric,
>
> On 12/22/2016 01:27 AM, Eric W. Biederman wrote:
>> "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> writes:
>> 
>>> Hi Eric,
>>>
>>> On 12/21/2016 01:17 AM, Eric W. Biederman wrote:
>>>> "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> writes:
>>>>
>>>>> Hi Eric,
>>>>>
>>>>> On 12/20/2016 09:22 PM, Eric W. Biederman wrote:
>>>>>> "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> writes:
>>>>>>
>>>>>>> Hello Eric,
>>>>>>>
>>>>>>> On 12/19/2016 11:53 PM, Eric W. Biederman wrote:
>>>>>>>> "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> writes:
>>>>>>>>
>> 
>>>> Now the question becomes who are the users of this?  Because it just
>>>> occurred to me that we now have an interesting complication.  Userspace
>>>> extending the meaning of the capability bits, and using to protect
>>>> additional things.  Ugh.  That could be a maintenance problem of another
>>>> flavor.  Definitely not my favorite.
>>>
>>> I don't follow you here. Could you say some more about what you mean?
>> 
>> I have seen user space userspace do thing such as extend CAP_SYS_REBOOT
>> to things such as permission to invoke "shutdown -r now".  Which
>> depending on what a clean reboot entails could be greately increasing
>> the scope of CAP_SYS_REBOOT.
>> 
>> I am concerned for that and similar situations that userspace
>> applications could lead us into situation that one wrong decision could
>> wind up being an unfixable mistake because fixing the mistake would
>> break userspsace.
>
> Okay.
>
>>>> So why are we asking the questions about what permissions a process has?
>>>
>>> My main interest here is monitoring/discovery/debugging on a running
>>> system. NS_GET_PARENT, NS_GET_USERNS, NS_GET_CREATOR_UID, and 
>>> NS_GET_NSTYPE provide most of what I'd like to see. Being able to ask
>>> "does this process have permissions in that namespace?" would be nice 
>>> to have in terms of understanding/debugging a system.
>> 
>> If we are just looking at explanations then I seem to have been
>> over-engineering things.  So let's just aim at the two ioctls.
>> Or at least the information in those ioctls.
>
> Okay.
>
>> With at least a comment on the ioctl returning the OWNER_UID that
>> describes why it is not a problem to if the owners uid is something like
>> ((uid_t)-3).  Which overlaps with the space for error return codes.
>>
>> I don't know if we are fine or not, but that review comment definitely
>> deserves some consideration.
>
>
> See my reply just sent to Andrei. We should instead then just return 
> the UID via a buffer pointed to by the ioctl() argument:
>
> ioctl(fd, NS_GET_OWNER_UID, &uid);

That will work without problem.  Especially as unsigned int is the same
on both 32bit and 64bit so we won't need a compat ioctl.

Eric