Re: [PATCH] Allow signalling container-init

[sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org]

Oleg Nesterov [oleg-6lXkIZvqkOAvJsYlp49lxw@public.gmane.org] wrote:
| On 08/08, sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org wrote:
| > 
| > From: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
| > Subject: [PATCH] Allow signalling container-init
| > 
| > Only the global-init process must be special - any other container-init
| > process must be killable to prevent run-away processes in the system.
| 
| I think you are right, but....
| 
| > --- lx26-23-rc1-mm1.orig/kernel/signal.c	2007-08-07 13:52:12.000000000 -0700
| > +++ lx26-23-rc1-mm1/kernel/signal.c	2007-08-08 15:09:27.000000000 -0700
| > @@ -1861,11 +1861,9 @@ relock:
| >  			continue;
| >  
| >  		/*
| > -		 * Init of a pid space gets no signals it doesn't want from
| > -		 * within that pid space. It can of course get signals from
| > -		 * its parent pid space.
| > +		 * Global init gets no signals it doesn't want.
| >  		 */
| > -		if (current == task_child_reaper(current))
| > +		if (is_global_init(current->group_leader))
| >  			continue;
| 
| ...this breaks exec() from /sbin/init. Note that de_thread() kills other
| sub-threads with SIGKILL. With this patch de_thread() will hang waiting
| for other threads to die.

Again for threaded-init I guess :-(

Well, we discussed last week about allowing non-root users to clone their
pid namespace. The user can then create a container-init and this
process would become immune to signal even by a root user ?

| 
| I think it is better to not change the current behaviour which is not
| perfect (buggy), until we actually protect /sbin/init from unwanted
| signals.

Can we preserve the existing behavior by checking only the main thread
of global init (i.e pass in 'current' rather than 'current->group_leader'
to is_global_init()) ?

| 
| (That said, I am not sure what behaviour is better (worse :), with or
|  without this patch)
| 
| Oleg.