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Re: [PATCH 1/2] pidns: Don't allow new pids after the namespace is dead. [message #41725 is a reply to message #41719]

Tue, 15 February 2011 18:30

Oleg Nesterov
Messages: 143
Registered: August 2006

Senior Member

On 02/15, Daniel Lezcano wrote:
>
> In the case of unsharing or joining a pid namespace, it becomes
> possible to attempt to allocate a pid after zap_pid_namespace has
> killed everything in the namespace. Close the hole for now by simply
> not allowing any of those pid allocations to succeed.

Daniel, please explain more. It seems, a long ago I knew the reason
for this patch, but now I can't recall and can't understand this change.

> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -20,6 +20,7 @@ struct pid_namespace {
> struct kref kref;
> struct pidmap pidmap[PIDMAP_ENTRIES];
> int last_pid;
> + atomic_t dead;

Why atomic_t? It is used as a plain boolean.

And I can't unde

> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -282,6 +282,10 @@ struct pid *alloc_pid(struct pid_namespace *ns)
> struct pid_namespace *tmp;
> struct upid *upid;
>
> + pid = NULL;
> + if (atomic_read(&ns->dead))
> + goto out;
> +

So why this is needed?

If we see ns->dead != 0 we are already killed by zap_pid_ns_processes()
which sets ns->dead = 1.

Oleg.

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[Message index]

		[PATCH 1/2] pidns: Don't allow new pids after the namespace is dead. By: Daniel Lezcano on Tue, 15 February 2011 16:53
		[PATCH 2/2] pidns: Support unsharing the pid namespace. By: Daniel Lezcano on Tue, 15 February 2011 16:53
		Re: [PATCH 2/2] pidns: Support unsharing the pid namespace. By: Oleg Nesterov on Tue, 15 February 2011 19:01
		[PATCH 0/1] Was: pidns: Support unsharing the pid namespace. By: Oleg Nesterov on Tue, 15 February 2011 19:15
		[PATCH 1/1][3rd resend] sys_unshare: remove the dead CLONE_THREAD/SIGHAND/VM code By: Oleg Nesterov on Tue, 15 February 2011 19:17
		Re: [PATCH 1/1][3rd resend] sys_unshare: remove the dead CLONE_THREAD/SIGHAND/VM code By: serge on Mon, 21 February 2011 00:17
		Re: [PATCH 2/2] pidns: Support unsharing the pid namespace. By: Daniel Lezcano on Wed, 16 February 2011 23:47
		Re: [PATCH 2/2] pidns: Support unsharing the pid namespace. By: Oleg Nesterov on Thu, 17 February 2011 20:29
		Re: [PATCH 2/2] pidns: Support unsharing the pid namespace. By: Greg Kurz on Thu, 17 February 2011 22:35
		Re: [PATCH 2/2] pidns: Support unsharing the pid namespace. By: Oleg Nesterov on Fri, 18 February 2011 14:40
		Re: [PATCH 2/2] pidns: Support unsharing the pid namespace. By: Rob Landley on Thu, 24 February 2011 01:12
		Re: [PATCH 1/2] pidns: Don't allow new pids after the namespace is dead. By: Oleg Nesterov on Tue, 15 February 2011 18:30
		Re: [PATCH 1/2] pidns: Don't allow new pids after the namespace is dead. By: Daniel Lezcano on Wed, 16 February 2011 23:21
		Re: [PATCH 1/2] pidns: Don't allow new pids after the namespace is dead. By: Oleg Nesterov on Thu, 17 February 2011 20:54

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