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From: Luis Henriques <luis.henriques@canonical.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Willy Tarreau <w@1wt.eu>, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>,
        Colin King <colin.king@canonical.com>,
        Tim Gardner <tim.gardner@canonical.com>,
        John Johansen <john.johansen@canonical.com>
Subject: Re: [ 020/184] ptrace: ensure arch_ptrace/ptrace_request can never
References: <20130604172131.136042108@1wt.eu> <87sj0wucft.fsf@canonical.com>
	<20130605154051.GA23025@redhat.com>
	<20130607104640.GA30017@redhat.com>
Date: Fri, 07 Jun 2013 12:35:58 +0100
In-Reply-To: <20130607104640.GA30017@redhat.com> (Oleg Nesterov's message of
	"Fri, 7 Jun 2013 12:46:40 +0200")
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Oleg Nesterov <oleg@redhat.com> writes:

> On 06/05, Oleg Nesterov wrote:
>>
>> On 06/05, Luis Henriques wrote:
>> >
>> >  /* Ensure that nothing can wake it up, even SIGKILL */
>> > -static bool ptrace_freeze_traced(struct task_struct *task)
>> > +static bool ptrace_freeze_traced(struct task_struct *task, int kill)
>> >  {
>> > -	bool ret = false;
>> > +	bool ret = true;
>> >  
>> >  	spin_lock_irq(&task->sighand->siglock);
>> > -	if (task_is_traced(task) && !__fatal_signal_pending(task)) {
>> > +	if (task_is_stopped(task) && !__fatal_signal_pending(task))
>> >  		task->state = __TASK_TRACED;
>> > -		ret = true;
>> > +	else if (!kill) {
>> > +		if (task_is_traced(task) && !__fatal_signal_pending(task))
>> > +			task->state = __TASK_TRACED;
>> > +		else
>> > +			ret = false;
>> >  	}
>> >  	spin_unlock_irq(&task->sighand->siglock);
>> >  
>> > @@ -131,7 +135,7 @@ int ptrace_check_attach(struct task_struct *child, int kill)
>> >  		 * child->sighand can't be NULL, release_task()
>> >  		 * does ptrace_unlink() before __exit_signal().
>> >  		 */
>> > -		if (kill || ptrace_freeze_traced(child))
>> > +		if (ptrace_freeze_traced(child, kill))
>> >  			ret = 0;
>> 
>> I can't apply this patch, probably I misread it...
>> 
>> But it looks very wrong. It seems that ptrace_freeze_traced(kill => true)
>> always succeeds? Even if task is TASK_RUNNING/UNINTERRUPTIBLE/etc ?
>
> I am sorry for noise!
>
> Yes I misread the patch. Now I actually applied both patches and
> I believe the fix is fine.
>
> ptrace_freeze_traced(kill => true) succeeds, but this is correct.
> Somehow I confused this case with !kill.

Great, thanks a lot for clarifying this, Oleg.

Cheers,
-- 
Luis