linux-kernel - Re: [PATCH] sanitize task->comm to avoid leaking escape codes

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Date:	Tue, 29 Jun 2010 07:58:25 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>, john stultz <johnstul@...ibm.com>
Cc:	Kees Cook <kees.cook@...onical.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Neil Horman <nhorman@...driver.com>,
	Roland McGrath <roland@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sanitize task->comm to avoid leaking escape codes

On Wed, 2010-06-23 at 21:41 +0200, Oleg Nesterov wrote:
> On 06/23, Kees Cook wrote:
> >
> > @@ -956,7 +957,15 @@ void set_task_comm(struct task_struct *tsk, char *buf)
> >  	 */
> >  	memset(tsk->comm, 0, TASK_COMM_LEN);
> >  	wmb();
> 
> Off-topic. I'd wish I could understand this barrier. Since the lockless
> reader doesn't do rmb() I don't see how this can help.

This wmb() looks wrong to me as well. To achieve what the comment in
this function says, it should be smp_wmb() and we should have smp_rmb()
in the reading side, AFAIU.

>  OTOH, I don't
> understand why it is needed, we never change ->comm[TASK_COMM_LEN-1] == '0'.

I think the idea was that readers can see incomplete names, but not
messed up names, consisting of old and new ones.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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