Re: [PATCH] memcg: avoid "free" overflow inmemcg_hierarchical_free_pages()

[Johannes Weiner]

On Tue, Nov 09, 2010 at 12:54:13AM -0800, Greg Thelen wrote:
> memcg limit and usage values are stored in res_counter, as 64-bit
> numbers, even on 32-bit machines.  The "free" variable in
> memcg_hierarchical_free_pages() stores the difference between two
> 64-bit numbers (limit - current_usage), and thus should be stored
> in a 64-bit local rather than a machine defined unsigned long.

It is converted to pages before the assignment, but even that might
overflow on 32-bit if the difference is sufficiently large (> 1<<44).

> Reported-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>

Reviewed-by: Johannes Weiner <hannes@xxxxxxxxxxx>
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