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

ebiederm@xmission.com (Eric W. Biederman) writes:

"Michael Kerrisk (man-pages)" [off-list ref] writes:

quoted

Hi Eric,

On 25 January 2017 at 14:58, Eric W. Biederman [off-list ref] wrote:

quoted

"Michael Kerrisk (man-pages)" [off-list ref] writes:

quoted

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.

quoted

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