[PATCH 11/11] pidns: Support unsharing the pid namespace.

[Oleg Nesterov]

Hi Eric,

oleg at tv-sign.ru no longer works, so I just noticed these emails.

On 11/16, Eric W. Biederman wrote:
>
> Unsharing of the pid namespace unlike unsharing of other namespaces
> does not take affect immediately.  Instead it affects the children
> created with fork and clone.

I'll try to read this series later, but I am not sure I will ever
understand the code with these patches ;)

So alloc_pid() becomes the only user nsproxy->pid_ns and it is not
necessarily equal to task_active_pid_ns(). It seems to me that this
adds a lot of new corner cases.

Unless I missed something, at least we should not allow CLONE_THREAD
if active_pid_ns != nsproxy->pid_ns. If nothing else, copy_process()
initializes ->child_reaper only if thread_group_leader(child). And
->child_reaper == NULL can obviously lead to crash.

Oleg.