Re: [PATCH v2 00/10] userns: sysctl limits for namespaces

[Colin Walters]

On Thu, Jul 21, 2016, at 12:39 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.

Perhaps this is obvious, but since you didn't quite explicitly state it;
do you see this as obsoleting the existing downstream patches
mentioned in:
https://lwn.net/Articles/673597/
It seems conceptually similar to Kees' original approach, right?

The high level makes sense to me...most interesting is
per-userns sysctls.  I'll note most current container managers
mount /proc/sys read-only, and Docker specifically drops
CAP_SYS_RESOURCE by default, so they'd likely need to learn
how to undo that if one wanted to support recursive container usage.
We'd probably need to evaluate the safety of having /proc/sys
writable generally.  (Also it's rather common to filter out CLONE_NEWUSER
via seccomp, but that's easy to undo)

But that's the flip side - if we're aiming primarily for an upstreamable
way to *limit* namespace usage, it seems sane to me.