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Subject: Re: [PATCH v2 00/10] userns: sysctl limits for namespaces
To: "Eric W. Biederman" <ebiederm@xmission.com>,
	Linux Containers <containers@lists.linux-foundation.org>
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From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
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Date: Tue, 26 Jul 2016 12:27:59 +0200
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Hello Eric,

On 07/21/2016 06:39 PM, Eric W. Biederman wrote:
>
> This patchset addresses two use cases:
> - Implement a sane upper bound on the number of namespaces.
> - Provide a way for sandboxes to limit the attack surface from
>   namespaces.
>
> The maximum sane case I can imagine is if every process is a fat
> process, so I set the maximum number of namespaces to the maximum
> number of threads.
>
> I make these limits recursive and per user namespace so that a
> usernamespace root can reduce the limits further.  If a user namespace
> root raises the limit the limit in the parent namespace will be honored.
>
> I have cut this implementation to the bare minimum needed to achieve
> these objectives.
>
> Does anyone know if there is a proper error code to return for resource
> limit exceeded?  I am currently using -EUSERS or -ENFILE but both of
> those feel a little wrong.

ENFILE certainly seems weird. I suppose my first question is: why two
different errors?

Some alternatives you might want to consider: E2BIG, EOVERFLOW,
or (maybe) ERANGE.

Cheers,

Michael