Re: [PATCH v2 1/1] mdrestore: fix restore_v2() superblock length check

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Dec 09, 2025 at 11:58:52PM +0100, Pavel Reichl wrote:
> On big-endian architectures (e.g. s390x), restoring a filesystem from a
> v2 metadump fails with "Invalid superblock disk address/length". This is
> caused by restore_v2() treating a superblock extent length of 1 as an
> error, even though a length of 1 is expected because the superblock fits
> within a 512-byte sector.
> 
> On little-endian systems, the same raw extent length bytes that represent
> a value of 1 on big-endian are misinterpreted as 16777216 due to byte
> ordering, so the faulty check never triggers there and the bug is hidden.
> 
> Fix the issue by using an endian-correct comparison of xme_len so that
> the superblock extent length is validated properly and consistently on
> all architectures.
> 
> Signed-off-by: Pavel Reichl <preichl@redhat.com>

Looks good!
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  mdrestore/xfs_mdrestore.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mdrestore/xfs_mdrestore.c b/mdrestore/xfs_mdrestore.c
> index f10c4bef..b6e8a619 100644
> --- a/mdrestore/xfs_mdrestore.c
> +++ b/mdrestore/xfs_mdrestore.c
> @@ -437,7 +437,7 @@ restore_v2(
>  	if (fread(&xme, sizeof(xme), 1, md_fp) != 1)
>  		fatal("error reading from metadump file\n");
>  
> -	if (xme.xme_addr != 0 || xme.xme_len == 1 ||
> +	if (xme.xme_addr != 0 || be32_to_cpu(xme.xme_len) != 1 ||
>  	    (be64_to_cpu(xme.xme_addr) & XME_ADDR_DEVICE_MASK) !=
>  			XME_ADDR_DATA_DEVICE)
>  		fatal("Invalid superblock disk address/length\n");
> -- 
> 2.52.0
>