Constraining the memory used by an unprivilged mount of tmpfs.

[Serge Hallyn]

Quoting Glauber Costa (glommer at parallels.com):
> On 01/17/2013 11:01 PM, Eric W. Biederman wrote:
> > What are the practical problems with control groups that makes them
> > undesirable/hard to use with namespaces?
> > 
> > What would it take to fix the problems with control groups?
> There aren't, from my PoV.
> When I run containers, for instance, I basically join all namespaces,
> configure all groups, and everything I can.
> 
> I do know, however, that not every use case is like that, and those
> things tends to be very loosely coupled.
> 
> So what I am worried about, is not a valid container usage where you
> have your constraints configured. But if I login into a box as a normal
> user, and that now allows me to create a userns, and maliciously fire a
> big tmpfs from there, cgroups will not gonna be there for me - it's not
> a container box, is just something I am trying to break.

Hm.  So basically we would, ideally, find a way to make it so that if
uid 500 creates a new userns and, therein, mounts a tmpfs, then that
tmpfs gets accounted and limited along with uid 500's RSS?

-serge