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

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

[Yuto Ohnuki]

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@amazon.com>
---
 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. */
+	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);
+	}
 
 	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
 		goto out_buf;
-- 
2.50.1




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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@amazon.com>
> ---
>  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
> 
> 
> 
>