Re: [PATCH v2] xfs: sanitize da node pad field on write

[Carlos Maiolino]

On Thu, Apr 23, 2026 at 09:18:44AM +0100, Yuto Ohnuki wrote:
> The DA node block header (xfs_da3_node_hdr) contains a __pad32 field
> that should always be zero. Prior to commit a45086e27dfa21 ("xfs:
> validate metadata LSNs against log on v5 superblocks"),
> xfs_da3_node_create() did not zero the full header, so __pad32 could
> contain stale data on older filesystems.
> 
> Clear this field in the write verifier to ensure it is corrected
> whenever the block is next written to disk.
> 
> Suggested-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
> Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
> Signed-off-by: Yuto Ohnuki <ytohnuki@xxxxxxxxxx>
> ---
> Changes in v2:
> - Added comments explaining why __pad32 is cleared unconditionally.
> - Link to v1: https://lore.kernel.org/all/20260421054311.25301-2-ytohnuki@xxxxxxxxxx/
> ---
>  fs/xfs/libxfs/xfs_da_btree.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
> index ad801b7bd2dd..4edbf4bb5c7f 100644
> --- a/fs/xfs/libxfs/xfs_da_btree.c
> +++ b/fs/xfs/libxfs/xfs_da_btree.c
> @@ -318,6 +318,12 @@ xfs_da3_node_write_verify(
>  	if (bip)
>  		hdr3->info.lsn = cpu_to_be64(bip->bli_item.li_lsn);
>  
> +	/*
> +	 * Old kernels may not have zeroed the padding field in the header,
> +	 * so clear it unconditionally to sanitize stale data on disk.
> +	 */
> +	hdr3->__pad32 = 0;
> +
>  	xfs_buf_update_cksum(bp, XFS_DA3_NODE_CRC_OFF);
>  }
>  

Looks good.

Reviewed-by: Carlos Maiolino <cmaiolino@xxxxxxxxxx>

> -- 
> 2.50.1
> 
> 
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