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

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Date:	Sun, 12 Aug 2007 21:05:55 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Oleg Nesterov <oleg@...sign.ru>
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 Sun, 2007-08-12 at 21:05 +0400, Oleg Nesterov wrote:
> 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>

Acked-by: Thomas Gleixner <tglx@...utronix.de>

> --- t/kernel/posix-timers.c~2_CREATE	2007-08-12 17:59:17.000000000 +0400
> +++ t/kernel/posix-timers.c	2007-08-12 18:11:33.000000000 +0400
> @@ -547,13 +547,12 @@ 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);
>  			} else {
> -				spin_unlock_irqrestore(&process->sighand->siglock, flags);
>  				process = NULL;
>  			}
> +			spin_unlock_irqrestore(&process->sighand->siglock, flags);
>  		}
>  		read_unlock(&tasklist_lock);
>  		if (!process) {
> 

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