Re: [PATCH] null_blk: set dma alignment to logical block size

[Christoph Hellwig <hch@lst.de>]

Maybe you can resend this with the Fixes tag and a blurb that this path
is exercised by xfstests since  851c4c96db00
("xfs: implement XFS_IOC_DIOINFO in terms of vfs_getattr") and causes
reproducible memory corruption?  Because that might help to get it
included ASAP..

On Wed, Oct 29, 2025 at 02:39:56PM +0100, Hans Holmberg wrote:
> This driver assumes that bio vectors are memory aligned to the logical
> block size, so set the queue limit to reflect that.
> 
> Unless we set up the limit based on the logical block size, we will go
> out of page bounds in copy_to_nullb / copy_from_nullb.
> 
> Signed-off-by: Hans Holmberg <hans.holmberg@wdc.com>
> ---
> 
> A fixes tag would be in order, but I have not figured out exactly when
> this became a problem.
> 
>  drivers/block/null_blk/main.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> index f982027e8c85..0ee55f889cfd 100644
> --- a/drivers/block/null_blk/main.c
> +++ b/drivers/block/null_blk/main.c
> @@ -1949,6 +1949,7 @@ static int null_add_dev(struct nullb_device *dev)
>  		.logical_block_size	= dev->blocksize,
>  		.physical_block_size	= dev->blocksize,
>  		.max_hw_sectors		= dev->max_sectors,
> +		.dma_alignment		= dev->blocksize - 1,
>  	};
>  
>  	struct nullb *nullb;
> -- 
> 2.34.1
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