[Lxc-users] Kernel 2.6.33-rc6, 3 bugs container specific.

Serge E. Hallyn serue at us.ibm.com
Tue Feb 2 21:32:54 UTC 2010

Quoting Jean-Marc Pigeon (jmp at safe.ca):
> Hello,
> > 
> > I was wondering out loud about the best design to solve his problem.
> > 
> > If we try to redirect kernel-generated messages to containers, we have
> > several problems, including whether we need to duplicate the messages
> > to the host container.  So in one sense it seems more flexible to
> > 	1. send everything to host syslog
> 		No, if we do that all CONTs message will reach
> 		the same bucket and it will be difficult to sort
> 		them out..
> 		CONT sys_admin and HOST sys_admin could be different
> 		"entity", so you debug CONT config and critical
> 		needed information reach HOST (which you do not 
> 		have access to).

Yes, so a privileged task on HOST must pass that information back to
you on CONT.  That is not a valid complaint imo.  But how to sort the
msgs out is a valid question.

We need some sort of identifier, unique system-wide, attached to.. something.
Is ifindex unique system-wide right now?  Oh, IIRC it is, but we wnat it to
be containerized, so that would be a bad choice :)

> > 	2. clamp down on syslog use by processes not in the init_user_ns
> 		Could give me more detail??...

Simplest choices would be to just refuse sys_syslog() and open(/proc/kmsg)
altogether from a container, or to only allow reading/writing messages
to own syslog.  (I had hoped to find time to try out the second option but
simply haven't had the time, and it doesn't look like I will very soon.
So if anyone else wants to, pls jump at it...)

Then /proc/kmsg can provide what I described above through a FUSE file,
and if, as you mentioned, the container unmounts the FUSE fs and gets
to real procfs, they just get nothing.

> > 	3. let the userspace on the host copy messages into a socket or
> > 	   file so child container can pretend it has real syslog.
> 		So you trap printk message from CONT on the HOST and 
> 		redirect them on CONT but on a standard syslog channel.
> 		Seem OK to me, as long /proc/kmsg is not existing
> 		(/dev/null) in the CONT file tree.
> -- 
> A bientôt
> ==========================================================================
> Jean-Marc Pigeon                                   Internet: jmp at safe.ca
> SAFE Inc.                                          Phone: (514) 493-4280
>                                                    Fax:   (514) 493-1946
>         Clement, 'a kiss solution' to get rid of SPAM (at last)
>            Clement' Home base <"http://www.clement.safe.ca">
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