Re: [PATCH v2] oom: fix integer overflow of points in oom_badness

[David Rientjes]

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@xxxxxxxxxx>

Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx [2.6.36+]
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/