linux-kernel - Re: [PATCH v2 RESEND] oom: fix integer overflow of points in oom

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Message-ID: <20111202190019.GA13283@suse.de>
Date:	Fri, 2 Dec 2011 11:00:19 -0800
From:	Greg KH <gregkh@...e.de>
To:	Frantisek Hrbata <fhrbata@...hat.com>
Cc:	rientjes@...gle.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	kosaki.motohiro@...fujitsu.com, oleg@...hat.com,
	minchan.kim@...il.com, stable@...nel.org, eteo@...hat.com,
	pmatouse@...hat.com
Subject: Re: [PATCH v2 RESEND] oom: fix integer overflow of points in
 oom_badness

On Fri, Dec 02, 2011 at 06:45:27PM +0100, Frantisek Hrbata wrote:
> An integer overflow will happen on 64bit archs if task's sum of rss, swapents
> and nr_ptes exceeds (2^31)/1000 value. This was introduced by commit
> 
> f755a04 oom: use pte pages in OOM score
> 
> where the oom score computation was divided into several steps and it's no
> longer computed as one expression in unsigned long(rss, swapents, nr_pte are
> unsigned long), where the result value assigned to points(int) is in
> range(1..1000). So there could be an int overflow while computing
> 
> 176          points *= 1000;
> 
> and points may have negative value. Meaning the oom score for a mem hog task
> will be one.
> 
> 196          if (points <= 0)
> 197                  return 1;
> 
> For example:
> [ 3366]     0  3366 35390480 24303939   5       0             0 oom01
> Out of memory: Kill process 3366 (oom01) score 1 or sacrifice child
> 
> Here the oom1 process consumes more than 24303939(rss)*4096~=92GB physical
> memory, but it's oom score is one.
> 
> In this situation the mem hog task is skipped and oom killer kills another and
> most probably innocent task with oom score greater than one.
> 
> The points variable should be of type long instead of int to prevent the int
> overflow.
> 
> Signed-off-by: Frantisek Hrbata <fhrbata@...hat.com>
> Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Acked-by: Oleg Nesterov <oleg@...hat.com>
> Acked-by: David Rientjes <rientjes@...gle.com>
> Cc: stable@...nel.org [2.6.36+]

For what it's worth, the stable address has changed to
stable@...r.kernel.org so you might want to fix that up in future
submissions.

I still catch patches that are tagged with this marking, but you will
not end up posting stuff to the list this way :)

thanks,

greg k-h
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