From mboxrd@z Thu Jan  1 00:00:00 1970
From: Artem Bityutskiy <dedekind1@gmail.com>
Subject: Re: [PATCH] sanitize task->comm to avoid leaking escape codes
Date: Tue, 29 Jun 2010 07:58:25 +0300
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References: <20100623181129.GM5876@outflux.net>
	 <20100623194145.GA19628@redhat.com>
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Cc: Kees Cook <kees.cook@canonical.com>, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	Neil Horman <nhorman@tuxdriver.com>,
	Roland McGrath <roland@redhat.com>,
	Ingo Molnar <mingo@elte.hu>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>
To: Oleg Nesterov <oleg@redhat.com>, john stultz <johnstul@us.ibm.com>
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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, ch=
ar *buf)
> >  	 */
> >  	memset(tsk->comm, 0, TASK_COMM_LEN);
> >  	wmb();
>=20
> Off-topic. I'd wish I could understand this barrier. Since the lockle=
ss
> 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] =
=3D=3D '0'.

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

--=20
Best Regards,
Artem Bityutskiy (=D0=90=D1=80=D1=82=D1=91=D0=BC =D0=91=D0=B8=D1=82=D1=8E=
=D1=86=D0=BA=D0=B8=D0=B9)

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