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 <redacted>
Acked-by: KOSAKI Motohiro <redacted>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: stable@kernel.org [2.6.36+]

For what it's worth, the stable address has changed to
stable@vger.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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