Re: [PATCH] namespaces: introduce sys_hijack (v4)

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

>> hmm, I'm wondering how this is going to work for a process which 
>> would have unshared its device (pts) namespace. How are we going 
>> to link the pts living in different namespaces if the stdios of the
>> hijacked process is using them ? like in the case of a shell, which
>> is certainly something we would like to hijacked.
>>
>> it looks like a challenge for me. maybe I'm wrong.
> 
> Might be a problem, but tough to address that until we actually
> have a dev ns or devpts ns and established semantics.
> 
> Note the filestruct comes from current, not the hijack target, so
> presumably we can work around the tty issue in any case by
> keeping an open file across the hijack?
> 
> For instance, use the attached modified version of hijack.c
> which puts a writeable fd for /tmp/helloworld in fd 5, then
> does hijack, then from the resulting shell do
> 
> 	echo ab >&5
> 
> So we should easily be able to work around it.

yes. it should. 

> Or am i missing something?

I guess we need to work a little more on the pts/device namespace
to see how it interacts. 

>>> The effect is a sort of namespace enter.  The following program
>>> uses sys_hijack to 'enter' all namespaces of the specified pid.
>>> For instance in one terminal, do
>>>
>>> 	mount -t cgroup -ons /cgroup
>>> 	hostname
>>> 	  qemu
>>> 	ns_exec -u /bin/sh
>>> 	  hostname serge
>>>           echo $$
>>>             1073
>>> 	  cat /proc/$$/cgroup
>>> 	    ns:/node_1073
>> Is there a reason to have the 'node_' prefix ? couldn't we just
>> use $pid ? 
> 
> Good question.  It's just how the ns-cgroup does it...  If you want to
> send in a patch to change that, I'll ack it.

just below. 

I gave a quick look to the ns subsystem and didn't see how the node_$pid 
was destroyed. do we have to do a rmdir ?

Thanks,


C.

Signed-off-by: Cedric Le Goater <clg-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org>
---
 kernel/cgroup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: 2.6.23-mm1/kernel/cgroup.c
===================================================================
--- 2.6.23-mm1.orig/kernel/cgroup.c
+++ 2.6.23-mm1/kernel/cgroup.c
@@ -2604,7 +2604,7 @@ int cgroup_clone(struct task_struct *tsk
        cg = tsk->cgroups;
        parent = task_cgroup(tsk, subsys->subsys_id);
 
-       snprintf(nodename, MAX_CGROUP_TYPE_NAMELEN, "node_%d", tsk->pid);
+       snprintf(nodename, MAX_CGROUP_TYPE_NAMELEN, "%d", tsk->pid);
 
        /* Pin the hierarchy */
        atomic_inc(&parent->root->sb->s_active);