Re: [patch -mm 1/5] mqueue namespace : add struct mq_namespace

[Cedric Le Goater <clg-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org>]

sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org wrote:
> Cedric Le Goater [clg-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org] wrote:
> | 
> | >> however, we have an issue with the signal notification in __do_notify()
> | >> we could kill a process in a different pid namespace.
> | > 
> | > So I took a quick look at the code as it is (before this patchset)
> | > and the taking a reference to a socket and the taking a reference to
> | > a struct pid should do the right thing when we intersect with other
> | > namespaces.  It certainly does not look like a fundamental issue.
> 
> | 
> | right. this should be covered when the pid namespace signal handling is 
> | complete. kill_pid_info() should fail to send a signal to a sibling or 
> | a parent pid namespace. 
> | 
> | I guess we should add a WARNING() to say that we're attempting to do so.
> 
> Just want to clarify how a signal is sent to a parent ns.
> 
> 	A process P1 sets itself up to be notified when a message arrives
> 	on a queue.
> 
> 	P1 then clones P2 with CLONE_NEWPID.
> 
> 	P2 writes to the message queue and thus signals P1
> 
> What should the semantics be here ?
> 
> I guess it makes less sense for two namespaces to be dependent on the same
> message queue this way.  But, if P2 writes to the queue, technically, the
> queue is not empty, so P1 should be notified, no ? 
> 
> This sounds similar to the SIGIO signal case (F_SETOWN). My understanding
> was that we would notify whoever was set to receive the notification, even
> if they were in a parent ns (again my reasoning was its based on the state
> of a file).

yes

> IOW,  should we change kill_pid_info() ?  If the caller can 'see' the
> 'struct pid' they can signal it. The expectation was that callers would
> call find_vpid() and thus only see processes in their namespace.

I think we have to decide on some limitations with signals and make sure 
that we cannot send a signal to a sibling pid namespace. This can occur
in some special namespaces unshare configuration which should never be used 
but to make sure, let's add a big WARNING when we detect such a pid namespace
violation.

If it is what you mean, I agree :)

Thanks,

C.