linux-kernel - Re: [PATCH 1/6] fill_tgid: fix task

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Message-ID: <45460302.4080904@in.ibm.com>
Date:	Mon, 30 Oct 2006 19:19:54 +0530
From:	Balbir Singh <balbir@...ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
CC:	Andrew Morton <akpm@...l.org>,
	Shailabh Nagar <nagar@...son.ibm.com>, Jay Lan <jlan@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] fill_tgid: fix task_struct leak and possible oops

Oleg Nesterov wrote:
> 1. fill_tgid() forgets to do put_task_struct(first).
> 

Looks good!

> 2. release_task(first) can happen after fill_tgid() drops tasklist_lock,
>    it is unsafe to dereference first->signal.
> 

But, we have a reference to first via get_task_struct(). release_task()
would do just a put_task_struct(). Am I missing something?


> This is a temporary fix, imho the locking should be reworked.
> 
> Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
> 
> --- STATS/kernel/taskstats.c~1_fix_sig	2006-10-22 18:24:03.000000000 +0400
> +++ STATS/kernel/taskstats.c	2006-10-26 23:44:32.000000000 +0400
> @@ -237,14 +237,17 @@ static int fill_tgid(pid_t tgid, struct 
>  	} else
>  		get_task_struct(first);
>  
> -	/* Start with stats from dead tasks */
> -	spin_lock_irqsave(&first->signal->stats_lock, flags);
> -	if (first->signal->stats)
> -		memcpy(stats, first->signal->stats, sizeof(*stats));
> -	spin_unlock_irqrestore(&first->signal->stats_lock, flags);
>  
>  	tsk = first;
>  	read_lock(&tasklist_lock);
> +	/* Start with stats from dead tasks */
> +	if (first->signal) {
> +		spin_lock_irqsave(&first->signal->stats_lock, flags);
> +		if (first->signal->stats)
> +			memcpy(stats, first->signal->stats, sizeof(*stats));
> +		spin_unlock_irqrestore(&first->signal->stats_lock, flags);
> +	}
> +
>  	do {
>  		if (tsk->exit_state == EXIT_ZOMBIE && thread_group_leader(tsk))
>  			continue;
> @@ -264,7 +267,7 @@ static int fill_tgid(pid_t tgid, struct 
>  	 * Accounting subsytems can also add calls here to modify
>  	 * fields of taskstats.
>  	 */
> -
> +	put_task_struct(first);
>  	return 0;
>  }
>  
> 


-- 

	Balbir Singh,
	Linux Technology Center,
	IBM Software Labs
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