Re: [PATCH] kernel buffer overflow kmalloc_slab() fix

[J Freyensee <james_p_freyensee@linux.intel.com>]

Thank you for the collaboration work on the fix.  I like it.

Jay

On Fri, 2011-05-20 at 09:42 -0500, Christoph Lameter wrote:
> Subject: slub: Deal with hyperthetical case of PAGE_SIZE > 2M
> 
> kmalloc_index() currently returns -1 if the PAGE_SIZE is larger than 2M
> which seems to cause some concern since the callers do not check for -1.
> 
> Insert a BUG() and add a comment to the -1 explaining that the code
> cannot be reached.
> 
> Signed-off-by: Christoph Lameter <cl@linux.com>
> 
> ---
>  include/linux/slub_def.h |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/include/linux/slub_def.h
> ===================================================================
> --- linux-2.6.orig/include/linux/slub_def.h	2011-05-20 09:37:02.000000000 -0500
> +++ linux-2.6/include/linux/slub_def.h	2011-05-20 09:39:07.000000000 -0500
> @@ -179,7 +179,8 @@ static __always_inline int kmalloc_index
>  	if (size <=   4 * 1024) return 12;
>  /*
>   * The following is only needed to support architectures with a larger page
> - * size than 4k.
> + * size than 4k. We need to support 2 * PAGE_SIZE here. So for a 64k page
> + * size we would have to go up to 128k.
>   */
>  	if (size <=   8 * 1024) return 13;
>  	if (size <=  16 * 1024) return 14;
> @@ -190,7 +191,8 @@ static __always_inline int kmalloc_index
>  	if (size <= 512 * 1024) return 19;
>  	if (size <= 1024 * 1024) return 20;
>  	if (size <=  2 * 1024 * 1024) return 21;
> -	return -1;
> +	BUG();
> +	return -1; /* Will never be reached */
> 
>  /*
>   * What we really wanted to do and cannot do because of compiler issues is: