Re: [PATCH v2 1/2] btrfs: Fix superblock csum type check.

[David Sterba <dsterba@suse.cz>]

On Mon, Apr 27, 2015 at 08:25:58AM +0800, Qu Wenruo wrote:
> 
> 
> -------- Original Message  --------
> Subject: Re: [PATCH v2 1/2] btrfs: Fix superblock csum type check.
> From: David Sterba <dsterba@suse.cz>
> To: Qu Wenruo <quwenruo@cn.fujitsu.com>
> Date: 2015年04月24日 23:05
> 
> > On Fri, Apr 24, 2015 at 09:12:40AM +0800, Qu Wenruo wrote:
> >> --- a/fs/btrfs/ctree.h
> >> +++ b/fs/btrfs/ctree.h
> >> @@ -173,6 +173,7 @@ struct btrfs_ordered_sum;
> >>
> >>   /* csum types */
> >>   #define BTRFS_CSUM_TYPE_CRC32	0
> >> +#define BTRFS_CSUM_LAST_TYPE	0
> >>
> >>   static int btrfs_csum_sizes[] = { 4, 0 };
> >
> > I'd prefer to fix it by removing the 0 from btrfs_csum_sizes instead of
> > introducing a define.
> >
> 
> Removing the zero seems not help for this case, as some one can still
> craft a strange csum_type to access outside the array.

The ARRAY_SIZE will be 1, so if a crafted csum will be anything than 0,
then the check will catch it, no?

> So I introduce the new macro and use the new macro to compare with 
> csum_type without acess the array.

The macro serves the same purpose as the ARRAY_SIZE macro and is always
in sync with the btrfs_csum_size.