linux-kernel - Re: [PATCH v2] selinux: selinux_setprocattr()->ptrace_parent() needs rcu_read

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Date:	Mon, 16 Dec 2013 16:12:28 -0500
From:	Paul Moore <paul@...l-moore.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <james.l.morris@...cle.com>,
	Eric Paris <eparis@...isplace.org>,
	Evan McNabb <emcnabb@...hat.com>,
	Jan Stancek <jstancek@...hat.com>,
	linux-kernel@...r.kernel.org, selinux@...ho.nsa.gov
Subject: Re: [PATCH v2] selinux: selinux_setprocattr()->ptrace_parent() needs rcu_read_lock()

On Saturday, December 14, 2013 05:33:17 PM Oleg Nesterov wrote:
> selinux_setprocattr() does ptrace_parent(p) under task_lock(p),
> but task_struct->alloc_lock doesn't pin ->parent or ->ptrace,
> this looks confusing and triggers the "suspicious RCU usage"
> warning because ptrace_parent() does rcu_dereference_check().
> 
> And in theory this is wrong, spin_lock()->preempt_disable()
> doesn't necessarily imply rcu_read_lock() we need to access
> the ->parent.
> 
> Reported-by: Evan McNabb <emcnabb@...hat.com>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  security/selinux/hooks.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Applied, thanks.

> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -5503,11 +5503,11 @@ static int selinux_setprocattr(struct ta
>  		/* Check for ptracing, and update the task SID if ok.
>  		   Otherwise, leave SID unchanged and fail. */
>  		ptsid = 0;
> -		task_lock(p);
> +		rcu_read_lock();
>  		tracer = ptrace_parent(p);
>  		if (tracer)
>  			ptsid = task_sid(tracer);
> -		task_unlock(p);
> +		rcu_read_unlock();
> 
>  		if (tracer) {
>  			error = avc_has_perm(ptsid, sid, SECCLASS_PROCESS,

-- 
paul moore
www.paul-moore.com

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