linux-kernel - Re: [PATCH v4] ptrace: Fix fork event messages across pid namespaces

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Message-ID: <20140407190610.GA24607@redhat.com>
Date:	Mon, 7 Apr 2014 21:06:10 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Matthew Dempsky <mdempsky@...omium.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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 v4] ptrace: Fix fork event messages across pid
	namespaces

On 04/03, Matthew Dempsky wrote:
>
> On Thu, Apr 3, 2014 at 8:44 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> > Some notes for potential future changes...
> >
> >         - I do not not see any potential user of ptrace_event_pid() outside
> >           of fork.c, so perhaps this helper should not be exported.
> >
> >           In fact I wouldn't mind if you send v5 which moves it into fork.c ;)
>
> Like you mentioned, it's potentially used by fs/exec.c too, which I
> was intending to send a followup patch for.

OK, agreed. Probably we can tolerate the extra get/put_pid() but make
this code look better.

> >         - OTOH, calculating pid_nr in the namespace of ->parent can probably
> >           go into another simple (exported) helper. do_notify_parent_*() and
> >           exec_binprm() could use it, even they do not have the problem with
> >           task_active_pid_ns(parent) == NULL. Not sure.
>
> I think do_notify_parent_*() are safe from task_active_pid_ns(parent)
> == NULL because they're under tasklist_lock,

Yes, they are fine correctness-wise, just this task_pid_nr_ns(...) doesn't
look readable. OK, please forget, from_kuid_munged() doesn't look better.

> but it looks like
> exec_binprm() is theoretically racy

No (if you meant task_pid_nr_ns() == NULL). Note that __task_pid_nr_ns()
checks ns != NULL. In fact this is bad, this just reminds that we have
too many helpers with the subtle differences ;)

But if you meant that it can report the wrong pid then yes, of course,
it can race with detach/attach too.

Oleg.

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