Re: [PATCH][DOCUMENTATION] The namespaces compatibility list doc

[Daniel Lezcano <dlezcano@fr.ibm.com>]

Pavel Emelyanov wrote:
>>From time to time people begin discussions about how the
> namespaces are working/going-to-work together.
> 
> Ted T'so proposed to create some document that describes what
> problems user may have when he/she creates some new namespace,
> but keeps others shared. I liked this idea, so here's the 
> initial version of such a document with the problems I currently 
> have in mind and can describe somewhat audibly - the "namespaces 
> compatibility list".
> 
> The Documentation/namespaces/ directory is about to contain more
> docs about the namespaces stuff.
> 
> Thanks to Cedirc for notes and spell checks on the doc.
> 
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
> 
> ---
> 
> commit 83061c56e1c4dcd54d48a62b108d219a7f5279a0
> Author: Pavel <pavel@xemulnb.sw.ru>
> Date:   Fri Nov 16 12:25:53 2007 +0300
> 
>     Namespaces compatibility list
> 
> diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
> index 910e511..3ead06b 100644
> --- a/Documentation/00-INDEX
> +++ b/Documentation/00-INDEX
> @@ -262,6 +262,8 @@ mtrr.txt
>  	- how to use PPro Memory Type Range Registers to increase performance.
>  mutex-design.txt
>  	- info on the generic mutex subsystem.
> +namespaces/
> +	- directory with various information about namespaces
>  nbd.txt
>  	- info on a TCP implementation of a network block device.
>  netlabel/
> diff --git a/Documentation/namespaces/compatibility-list.txt b/Documentation/namespaces/compatibility-list.txt
> new file mode 100644
> index 0000000..9c9e5c1
> --- /dev/null
> +++ b/Documentation/namespaces/compatibility-list.txt
> @@ -0,0 +1,33 @@
> +	Namespaces compatibility list
> +
> +This document contains the information about the problems user
> +may have when creating tasks living in different namespaces.
> +
> +Here's the summary. This matrix shows the known problems, that
> +occur when tasks share some namespace (the columns) while living
> +in different other namespaces (the rows):
> +
> +	UTS	IPC	VFS	PID	User	Net
> +UTS	 X
> +IPC		 X	 1               
> +VFS			 X
> +PID		 1	 1	 X               
> +User			 2		 X
> +Net						 
> +

	UTS	IPC	VFS	PID	User	Net
UTS	 X
IPC		 X	 1               3
VFS			 X
PID		 1	 1	 X
User			 2		 X
Net						

> +1. Both the IPC and the PID namespaces provide IDs to address
> +   object inside the kernel. E.g. semaphore with ipcid or
> +   process group with pid.
> +
> +   In both cases, tasks shouldn't try exposing this id to some
> +   other task living in a different namespace via a shared filesystem
> +   or IPC shmem/message. The fact is that this ID is only valid
> +   within the namespace it was obtained in and may refer to some
> +   other object in another namespace.
> +
> +2. Intentionnaly, two equal user ids in different user namespaces
       Intentionaly
> +   should not be equal from the VFS point of view. In other
> +   words, user 10 in one user namespace shouldn't have the same
> +   access permissions to files, beloging to user 10 in another
                                    belonging
> +   namespace. But currently this is not so.
> +

3. IPC and User

Two processes running in different user namespaces but with the same 
uids can access with the same permissions to the IPC created by one or 
other process