[PATCH v2 0/1] mdrestore: fix restore_v2() superblock length check

[PATCH v2 0/1] mdrestore: fix restore_v2() superblock length check

[Pavel Reichl]

Hi all,

On s390x (big-endian), running xfstests -g metadump currently fails
6 out of 9 tests. The failure is triggered by the superblock
extent-length validation in restore_v2(). The code rejects
xme_len == 1, but a length of 1 is the correct and expected value,
since the superblock fits within a single 512-byte sector.

On big-endian systems, this length decodes to 1 and the check aborts
the restore. On little-endian systems, the same on-disk bytes are
interpreted as 16777216, so the faulty logic never triggers there.

The patch removes the incorrect rejection of a valid extent length of
1 and applies proper logic so that the superblock extent length is
validated consistently across all architectures.

The outline of the fix was discussed with Chandan (thanks).

v2:
- xme.xme_len is an ondisk value so use be32_to_cpu() instead of
  cpu_to_be32()

Pavel Reichl (1):
  mdrestore: fix restore_v2() superblock length check

 mdrestore/xfs_mdrestore.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.52.0

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

[Pavel Reichl]

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>
---
 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

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

[Darrick J. Wong]

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
> 

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

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

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

[Chandan Babu R]

On Tue, Dec 09, 2025 at 11:58:52 PM +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>
> ---
>  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");

Thanks for fixing this,

Reviewed-by: Chandan Babu R <chandanbabu@kernel.org>

-- 
Chandan