linux-kernel - Re: [PATCH v3] ptrace: Fix fork event messages across pid namespaces

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Date:	Wed, 2 Apr 2014 15:37:33 -0700
From:	Matthew Dempsky <mdempsky@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Kees Cook <keescook@...omium.org>,
	Julien Tinnes <jln@...omium.org>,
	Roland McGrath <mcgrathr@...omium.org>,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] ptrace: Fix fork event messages across pid namespaces

On Wed, Apr 2, 2014 at 2:58 PM, Matthew Dempsky <mdempsky@...gle.com> wrote:
> Otherwise, it looks like (e.g.) the attempts to get the parent's pid
> in fill_prstatus() and tomoyo_sys_getppid() are also theoretical races
> of the same kind?

Doh, nevermind, those functions would potentially be use null "struct
pid" pointers, not "struct pid_namespace" pointers; and pid_nr_ns()
guards against pid being null.

Okay, I think I understand now why guarding against the
task_parent_pid_ns() here is consistent with other RCU code.  I'll
send a revised patch that does that.

Also, it looks like "0" is the conventional value for unrepresentable
pid_t values, so I'll change to do that too.
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