linux-kernel - Re: [PATCH 2/4] posix-timers: fix creation race

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Message-ID: <20070812195904.GB113@tv-sign.ru>
Date:	Sun, 12 Aug 2007 23:59:04 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	stable@...nel.org
Subject: Re: [PATCH 2/4] posix-timers: fix creation race

On 08/12, Oleg Nesterov wrote:
>
> > > -				spin_unlock_irqrestore(&process->sighand->siglock, flags);
> > >  				process = NULL;
> > >  			}
> > > +			spin_unlock_irqrestore(&process->sighand->siglock, flags);
> 
> i'll resend this patch tomorrow. We can't do spin_unlock_irqrestore(&process->...)
> if we set process = NULL above.

Another attempt, no cleanups, just a minimal fix for now.


[PATCH 2/4] posix-timers: fix creation race

sys_timer_create() sets ->it_process and unlocks ->siglock, then checks
tmr->it_sigev_notify to define if get_task_struct() is needed.

We already passed ->it_id to the caller, another thread can delete this
timer and free its memory in between.

As a minimal fix, move this code under ->siglock, sys_timer_delete() takes
it too before calling release_posix_timer(). A proper serialization would
be to take ->it_lock, we add a partly initialized timer on posix_timers_id,
not good.

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- t/kernel/posix-timers.c~	2007-08-12 23:50:46.000000000 +0400
+++ t/kernel/posix-timers.c	2007-08-12 23:52:07.000000000 +0400
@@ -547,9 +547,9 @@ sys_timer_create(const clockid_t which_c
 				new_timer->it_process = process;
 				list_add(&new_timer->list,
 					 &process->signal->posix_timers);
-				spin_unlock_irqrestore(&process->sighand->siglock, flags);
 				if (new_timer->it_sigev_notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID))
 					get_task_struct(process);
+				spin_unlock_irqrestore(&process->sighand->siglock, flags);
 			} else {
 				spin_unlock_irqrestore(&process->sighand->siglock, flags);
 				process = NULL;

-
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