[dm-devel] dm-crypt: don't decrease device limits

[Mike Snitzer]

On Fri, Aug 10 2018 at 11:23am -0400,
Mikulas Patocka <mpatocka at redhat.com> wrote:

> dm-crypt should only increase device limits, it should not decrease them.
> 
> This fixes a bug where the user could create a crypt device with 1024
> sector size on the top of scsi device that had 4096 logical sectors. The
> limit 4096 would be lost and the user could incorrectly send 1024-I/Os to
> the crypt device.
> 
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> 
> ---
>  drivers/md/dm-crypt.c |    8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> Index: linux-2.6/drivers/md/dm-crypt.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-crypt.c	2018-08-10 15:02:26.700000000 +0200
> +++ linux-2.6/drivers/md/dm-crypt.c	2018-08-10 15:28:02.170000000 +0200
> @@ -3072,11 +3072,9 @@ static void crypt_io_hints(struct dm_tar
>  	 */
>  	limits->max_segment_size = PAGE_SIZE;
>  
> -	if (cc->sector_size != (1 << SECTOR_SHIFT)) {
> -		limits->logical_block_size = cc->sector_size;
> -		limits->physical_block_size = cc->sector_size;
> -		blk_limits_io_min(limits, cc->sector_size);
> -	}
> +	limits->logical_block_size = max(limits->logical_block_size, cc->sector_size);
> +	limits->physical_block_size = max(limits->physical_block_size, (unsigned)cc->sector_size);
> +	blk_limits_io_min(limits, cc->sector_size);
>  }
>  
>  static struct target_type crypt_target = {

tweaked and staged for 4.19 here:
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.19&id=08575fd060d7f88f674509461b32d86b272093d9

I switched to using max_t() and stacked io_min rather than impose that
it is cc->sector_size.