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Date:	Wed, 24 Dec 2014 19:06:54 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Stijn Volckaert <Stijn.Volckaert@...s.ugent.be>
Cc:	Roland McGrath <roland@...k.frob.com>,
	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] Allow introspection to already attached ptracer in
	__ptrace_may_access

On 12/24, Stijn Volckaert wrote:
>
> The question now is whether or not it's the security module's
> responsibility to check whether a tracee relationship is already in
> place or if ptrace itself should do it.

Honestly, I have no idea

> --- a/kernel/ptrace.c	2014-12-24 13:53:23.055346526 +0100
> +++ b/kernel/ptrace.c	2014-12-24 14:17:20.617824840 +0100
> @@ -232,6 +232,9 @@ static int __ptrace_may_access(struct ta
>  	/* Don't let security modules deny introspection */
>  	if (same_thread_group(task, current))
>  		return 0;
> +	/* Don't deny introspection to already attached ptracer */
> +	if (!ptrace_check_attach(task, true))
> +	        return 0;

Perhaps this makes sense, probably security checks do not make sense
if the target is traced.

But in this case I'd suggest to simply

	if (ptrace_parent(task) == current)
		return 0;


Oleg.

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