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

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Date:	Mon, 31 Oct 2011 11:22:42 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Frantisek Hrbata <fhrbata@...hat.com>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>, stable@...nel.org,
	eteo@...hat.com, pmatouse@...hat.com
Subject: Re: [PATCH v2] oom: fix integer overflow of points in oom_badness

On Mon, 31 Oct 2011, 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
> 

This commit was introduced in 2.6.39 but also backported to stable since 
2.6.36, so presumably we'd need to mark this for stable as well going back 
that far.

> 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: David Rientjes <rientjes@...gle.com>
Cc: stable@...nel.org [2.6.36+]
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