Re: [PATCH] mm/gup_benchmark: prevent integer overflow in ioctl

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Thu, Oct 25, 2018 at 09:15:46AM +0300, Dan Carpenter wrote:
> The concern here is that "gup->size" is a u64 and "nr_pages" is unsigned
> long.  On 32 bit systems we could trick the kernel into allocating fewer
> pages than expected.
> 
> Fixes: 64c349f4ae78 ("mm: add infrastructure for get_user_pages_fast() benchmarking")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>  mm/gup_benchmark.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
> index debf11388a60..5b42d3d4b60a 100644
> --- a/mm/gup_benchmark.c
> +++ b/mm/gup_benchmark.c
> @@ -27,6 +27,9 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
>  	int nr;
>  	struct page **pages;
>  
> +	if (gup->size > ULONG_MAX)
> +		return -EINVAL;
> +

Strictly speaking gup->size / PAGE_SIZE has to be <= ULONG_MAX, but it
should be fine this way too.

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov