Re: [vserver] Problem with host process ending up to be child of guest process

From: Herbert Poetzl <>
Date: Mon 13 Oct 2014 - 12:37:15 BST
Message-ID: <>

On Mon, Oct 13, 2014 at 08:52:36AM +0000, Fiedler Roman wrote:
> Hello List,

> Analyzing a problem today, It seems the the root cause is, that
> a host process ended up being the child of a guest process
> after using "vserver exec".

Not sure what you expect from "vserver exec" but it is intended
to execute processes inside the guest after all.

If the guest has no reaper/init running, every top level guest
process will become a child of a host process.

> Since the guest process is in the guest's PID namespace, tools
> on the host fail to react accordingly, e.g. bash job-control
> gets stuck or start-stop-daemon reacts unexpected.

Maybe details about kernel/patch/util-vserver version as well
as the problematic command sequence which causes the "unexpected"
behaviour plus a description what the "expected" behaviour would
be would help a lot.

> Some questions to that:

> * Can someone give a hint, how this could happen, thus being
> able to attempt to fix the problem for now using a workaround?
> * Is this caused by known behavior of vserver exec and misuse
> from my side?
> * No matter if misuse or bug, should this case be prevented
> since it should also cause security risks?

> A host process uses the parent pid of itself or another host
> process, but parent pid is from guest namespace. So from my
> understanding it could collide with PIDs from host namespace,
> thus host process might operate on arbitrary other host
> process, e.g. signalling or modifying it or just like with
> bash, getting stuck running wait(-1) in endless loop?

Let's get some details first, thanks,

> Roman
Received on Mon Oct 13 12:37:26 2014

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