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

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Date:	Tue, 29 Jun 2010 15:32:11 -0700
From:	john stultz <johnstul@...ibm.com>
To:	dedekind1@...il.com
Cc:	Oleg Nesterov <oleg@...hat.com>,
	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 Tue, 2010-06-29 at 07:58 +0300, Artem Bityutskiy wrote:
> 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.

Yes, that was the intent, but I do see how it is unnecessary.

So I'm fine with it and the memset being removed.

Thanks for catching this!
-john
 

 

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