linux-kernel - Re: [PATCH] oom: fix the unsafe proc_oom

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Date:	Thu, 1 Apr 2010 00:41:47 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	anfei <anfei.zhou@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	nishimura@....nes.nec.co.jp,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] oom: fix the unsafe proc_oom_score()->badness() call

On Wed, 31 Mar 2010, Oleg Nesterov wrote:

> But. Oh well. David, oom-badness-heuristic-rewrite.patch changed badness()
> to consult p->signal->oom_score_adj. Until recently this was wrong when it
> is called from proc_oom_score().
> 
> This means oom-badness-heuristic-rewrite.patch depends on
> signals-make-task_struct-signal-immutable-refcountable.patch, or we
> need the pid_alive() check again.
> 

oom-badness-heuristic-rewrite.patch didn't change anything, Linus' tree 
currently dereferences p->signal->oom_adj which is no different from 
dereferencing p->signal->oom_score_adj without a refcount on the 
signal_struct in -mm.  oom_adj was moved to struct signal_struct in 
2.6.32, see 28b83c5.

> oom_badness() gets the new argument, long totalpages, and the callers
> were updated. However, long uptime is not used any longer, probably
> it make sense to kill this arg and simplify the callers? Unless you
> are going to take run-time into account later.
> 
> So, I think -mm needs the patch below, but I have no idea how to
> write the changelog ;)
> 
> Oleg.
> 
> --- x/fs/proc/base.c
> +++ x/fs/proc/base.c
> @@ -430,12 +430,13 @@ static const struct file_operations proc
>  /* The badness from the OOM killer */
>  static int proc_oom_score(struct task_struct *task, char *buffer)
>  {
> -	unsigned long points;
> +	unsigned long points = 0;
>  	struct timespec uptime;
>  
>  	do_posix_clock_monotonic_gettime(&uptime);
>  	read_lock(&tasklist_lock);
> -	points = oom_badness(task->group_leader,
> +	if (pid_alive(task))
> +		points = oom_badness(task,
>  				global_page_state(NR_INACTIVE_ANON) +
>  				global_page_state(NR_ACTIVE_ANON) +
>  				global_page_state(NR_INACTIVE_FILE) +

This should be protected by the get_proc_task() on the inode before 
this function is called from proc_info_read().
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