[RFC][PATCH] ns: Syscalls for better namespace sharing control.

Eric W. Biederman ebiederm at xmission.com
Tue Mar 2 14:13:37 PST 2010


Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com> writes:

> Pavel Emelyanov [xemul at parallels.com] wrote:
> | > I agree with all the points you and Pavel you talked about but I don't 
> | > feel comfortable to have the current process to switch the pid namespace 
> | > because of the process tree hierarchy (what will be the parent of the 
> | > process when you enter the pid namespace for example).
> | 
> | The answer is - the one, that used to be. I see no problems with it.
> | Do you?
>
> Just to be clear, when a process unshares its pid namespace, it takes
> on additional pid nr (== 1) in the new namespace but retains its original
> pid nr(s) in the parent (ancestor) namespaces right ?
>
> i.e the process becomes the container-init of the new namespace. When it
> exits, all its children belonging to the new namespace are killed too,
> but any children in the parent namespace (i.e children created before
> unshare()) are not killed.
>
> After the unshare() the process will not be able to signal any children
> it created before the unshare() (bc their active pid namespaces are
> different)

The only case that I see as being simple and unsurprising worked a bit
differently:

We currently have:

ns_of_pid(task_pid(tsk))
tsk->nsproxy->pid_ns


I would reduce the usage of tsk->nsproxy->pid_ns as much as possible,
and use ns_of_pid(task_pid(tsk)) for all of the routine things that
need to know the pid namespace of a process.  Possibly even to the point
or reversing the order of the upid array so using it is more efficient.

I would leave tsk->nsproxy->pid_ns for use by fork/clone when allocating
a childs pid number.

The unsharing process would have to become the child reaper.  I think the first
child would become pid 1 in that pid namespace.




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