Re: [PATCH v4 0/2] Add further ioctl() operations for namespace discovery

[Eric W. Biederman]

ebiederm@xxxxxxxxxxxx (Eric W. Biederman) writes:

> "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> writes:
>
>> Hi Eric,
>>
>> On 25 January 2017 at 14:58, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
>>> "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> writes:
>>>
>>>> I would like to write code that discovers the namespace setup on a live
>>>> system.  The NS_GET_PARENT and NS_GET_USERNS ioctl() operations added in
>>>> Linux 4.9 provide much of what I want, but there are still a couple of
>>>> small pieces missing. Those pieces are added with this patch series.
>>>
>>> So it looks like the -EOVERFLOW change broke your example program.
>>> Causing it to abort if -EOVERFLOW is hit.  Do we really want to return
>>> -EOVERFLOW?  Or do you want to fix your program?
>>
>> Bother! Yes, I should have kept the example program in sync. (I
>> overlooked that it was not any more in sync.)
>>
>> So, I want to make sure I understand correctly, before I aswer your
>> question. Suppose we have
>>
>> 1. Outer namespace owned by UID 0
>> 2. Inner namespace owned by UID 1000
>> 3. A UID mapping in the inner namespace that maps '0 1000 1'
>> 4. A processs, X, in the outer namespace with UID 0 (and all caps).
>>
>> That's the case you're meaning, right?
>
> I think so I just noticed you did not handle -EOVERFLOW in
> the one NS_GET_OWNER_UID call.
>
>> So, UID 0 doesn't have a
>> mapping into the inner namespace, but does have all capabilities in
>> that inner namespace, right?
>
> That is correct.

My concern is that the difference between returning -EOVERFLOW and
overflow_uid is primarily about usability.  If you haven't played with
the usability I don't trust that we have made the proper trade off.


Eric