Re: [PATCH] xfs: check directory data block header padding in scrub

[Darrick J. Wong]

On Sat, Apr 04, 2026 at 01:50:33PM +0100, Yuto Ohnuki wrote:
> The pad field in xfs_dir3_data_hdr exists for 64-bit alignment and
> should always be zero. The scrub code already checks the pad field for
> leaf and free block headers but was missing the same check for data
> block headers. Add the missing check.
> 
> Signed-off-by: Yuto Ohnuki <ytohnuki@xxxxxxxxxx>
> ---
>  fs/xfs/scrub/dir.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/scrub/dir.c b/fs/xfs/scrub/dir.c
> index e09724cd3725..2db4def3358c 100644
> --- a/fs/xfs/scrub/dir.c
> +++ b/fs/xfs/scrub/dir.c
> @@ -492,7 +492,12 @@ xchk_directory_data_bestfree(
>  		goto out;
>  	xchk_buffer_recheck(sc, bp);
>  
> -	/* XXX: Check xfs_dir3_data_hdr.pad is zero once we start setting it. */

But where do we set xfs_dir3_data_hdr.pad to zero?  xfs_dir3_data_init
does not seem to do this...

> +	if (xfs_has_crc(sc->mp)) {
> +		struct xfs_dir3_data_hdr    *hdr3 = bp->b_addr;
> +
> +		if (hdr3->pad != cpu_to_be32(0))
> +			xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, lblk);

...and even if there is code that does the zero-initialization, it's
possible that old kernels wrote out garbage in the pad field and were
quite ok with that.  At best you can set XFS_SCRUB_OFLAG_PREEN to
indicate that this kernel should clean it out.

(For that you'd also want to add a new xchk_fblock_set_corrupt helper to
record which block tripped the "optimization possible" message.)

--D

> +	}
>  
>  	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
>  		goto out_buf;
> -- 
> 2.50.1
> 
> 
> 
> 
> Amazon Web Services EMEA SARL, 38 avenue John F. Kennedy, L-1855 Luxembourg, R.C.S. Luxembourg B186284
> 
> Amazon Web Services EMEA SARL, Irish Branch, One Burlington Plaza, Burlington Road, Dublin 4, Ireland, branch registration number 908705
> 
> 
> 
>