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

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Message-ID: <87a8aea1pp.fsf@xmission.com>
Date:   Thu, 26 Jan 2017 17:23:46 +1300
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     "Michael Kerrisk \(man-pages\)" <mtk.manpages@...il.com>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        Linux API <linux-api@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Andrey Vagin <avagin@...nvz.org>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "W. Trevor King" <wking@...mily.us>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v4 0/2] Add further ioctl() operations for namespace discovery

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


> On 25 January 2017 at 15:28, Eric W. Biederman <ebiederm@...ssion.com> wrote:

>> 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.
>
> So, I had not initially included the no-UID-mapping case, and when you
> proposed -EOVERFLOW for that case, it seemed better.
>
> On reflection, mapping to the overflow_uid seems simpler. Taking the
> example shown in my other mail a short time ago, the unmapped UID 0
> from the outer namespace would map to the overflow_uid (which UID my
> program would print), but my program would still correctly report that
> the UID 0 process in the outer namespace might (subject to LSM checks)
> have capabilities in the inner namespace.
>
> So, it seems that reverting the EOVERFLOW change is in order (and my
> example program thus needs no changes). Does that sound reasonable to
> you?

It does.  I just care that you have thought through the tradeoffs of
that corner of the interface design.

Eric