linux-kernel - Re: [patch 5/9] security: Use get_task_cred() in keyctl_session_to

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Date:	Wed, 9 Dec 2009 18:45:27 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Al Viro <viro@...iv.linux.org.uk>,
	James Morris <jmorris@...ei.org>,
	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-security-module@...r.kernel.org
Subject: Re: [patch 5/9] security: Use get_task_cred() in
	keyctl_session_to_parent()

On Thu, Dec 10, 2009 at 12:53:12AM -0000, Thomas Gleixner wrote:
> Strictly this is not necessary today, but according to Paul McKenney
> it's not guaranteed that irq disabled regions will prevent RCU
> progress. That's a property of the current implementation. In
> preempt-rt this assumption is not true anymore.
> 
> Use get_task_cred() to make this future proof.

Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> from RCU perspective.

> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: James Morris <jmorris@...ei.org>
> Cc: linux-security-module@...r.kernel.org
> ---
>  security/keys/keyctl.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6-tip/security/keys/keyctl.c
> ===================================================================
> --- linux-2.6-tip.orig/security/keys/keyctl.c
> +++ linux-2.6-tip/security/keys/keyctl.c
> @@ -1237,7 +1237,7 @@ long keyctl_get_security(key_serial_t ke
>  long keyctl_session_to_parent(void)
>  {
>  	struct task_struct *me, *parent;
> -	const struct cred *mycred, *pcred;
> +	const struct cred *mycred, *pcred = NULL;
>  	struct cred *cred, *oldcred;
>  	key_ref_t keyring_r;
>  	int ret;
> @@ -1274,7 +1274,7 @@ long keyctl_session_to_parent(void)
>  	/* the parent and the child must have different session keyrings or
>  	 * there's no point */
>  	mycred = current_cred();
> -	pcred = __task_cred(parent);
> +	pcred = get_task_cred(parent);
>  	if (mycred == pcred ||
>  	    mycred->tgcred->session_keyring == pcred->tgcred->session_keyring)
>  		goto already_same;
> @@ -1312,6 +1312,7 @@ long keyctl_session_to_parent(void)
>  	set_ti_thread_flag(task_thread_info(parent), TIF_NOTIFY_RESUME);
> 
>  	write_unlock_irq(&tasklist_lock);
> +	put_cred(pcred);
>  	if (oldcred)
>  		put_cred(oldcred);
>  	return 0;
> @@ -1321,6 +1322,8 @@ already_same:
>  not_permitted:
>  	write_unlock_irq(&tasklist_lock);
>  	put_cred(cred);
> +	if (pcred)
> +		put_cred(pcred);
>  	return ret;
> 
>  error_keyring:
> 
> 
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