Re: namespaces compatibility list

[Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

Cedric Le Goater wrote:
> Pavel Emelyanov wrote:
>> Cedric Le Goater wrote:
>>> Pavel Emelyanov wrote:
>>>> Hi guys!
>>>>
>>>> As you might have seen, recently there was some spontaneous 
>>>> discussion about the namespaces-working-together problems.
>>>>
>>>> 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 like this idea, so here's the draft
>>>> with the problems I currently have in mind and can describe 
>>>> somewhat audibly - the "namespaces compatibility list".
>>> that compatibility list could be encoded in the way we check
>>> the clone flags in copy_process() and unshare(). It would 
>>> also be good to have it as a comment somewhere in kernel/fork.c
>> How can we insure, that a new task will not share the files
>> with its parent to address the PID namespaces vs VFS namespaces
>> interaction? There's no way to do it. We can only keep them in
>> one IPC namespace...
> 
> ? I'm not sure I understand you.

As far as I understand, you propose the check for the clone flags
in the copy_process()/sys_unshare() and return -EINVAL for the cases
we consider to be unsafe. E.g. when a user wants to clone new pid
namespace, he must clone the ipc namespace as well.

But my point is that this check is not enough - user may kill himself
by cloning a pid namespace and sharing the pids via the filesystem 
(like with the example with futexes) and there's no way to check for 
this situation in the copy_process()/sys_unchare.

I mean that this list cannot be encoded. But we can warn user, that
some stuff will stop working if he violates some rules.

> C.
>