[PATCH 4/6] xfs: fix zero byte checking in the superblock scrubber

Darrick J. Wong
2024-12-04T03:03:17Z

From: Darrick J. Wong <djwong@kernel.org>

The logic to check that the region past the end of the superblock is all
zeroes is wrong -- we don't want to check only the bytes past the end of
the maximally sized ondisk superblock structure as currently defined in
xfs_format.h; we want to check the bytes beyond the end of the ondisk as
defined by the feature bits.

Port the superblock size logic from xfs_repair and then put it to use in
xfs_scrub.

Cc: <stable@vger.kernel.org> # v4.15
Fixes: 21fb4cb1981ef7 ("xfs: scrub the secondary superblocks")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
fs/xfs/scrub/agheader.c | 26 ++++++++++++++++++++++++--
1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/scrub/agheader.c b/fs/xfs/scrub/agheader.c
index 88063d67cb5fd4..190d56f8134463 100644
--- a/fs/xfs/scrub/agheader.c
+++ b/fs/xfs/scrub/agheader.c
@@ -59,6 +59,27 @@ xchk_superblock_xref(
/* scrub teardown will take care of sc->sa for us */
}

+/* Calculate the ondisk superblock size in bytes */
+STATIC size_t
+xchk_superblock_ondisk_size(
+ struct xfs_mount *mp)
+{
+ if (xfs_has_metadir(mp))
+ return offsetofend(struct xfs_dsb, sb_pad);
+ if (xfs_has_metauuid(mp))
+ return offsetofend(struct xfs_dsb, sb_meta_uuid);
+ if (xfs_has_crc(mp))
+ return offsetofend(struct xfs_dsb, sb_lsn);
+ if (xfs_sb_version_hasmorebits(&mp->m_sb))
+ return offsetofend(struct xfs_dsb, sb_bad_features2);
+ if (xfs_has_logv2(mp))
+ return offsetofend(struct xfs_dsb, sb_logsunit);
+ if (xfs_has_sector(mp))
+ return offsetofend(struct xfs_dsb, sb_logsectsize);
+ /* only support dirv2 or more recent */
+ return offsetofend(struct xfs_dsb, sb_dirblklog);
+}
+
/*
* Scrub the filesystem superblock.
*
@@ -75,6 +96,7 @@ xchk_superblock(
struct xfs_buf *bp;
struct xfs_dsb *sb;
struct xfs_perag *pag;
+ size_t sblen;
xfs_agnumber_t agno;
uint32_t v2_ok;
__be32 features_mask;
@@ -388,8 +410,8 @@ xchk_superblock(
}

/* Everything else must be zero. */
- if (memchr_inv(sb + 1, 0,
- BBTOB(bp->b_length) - sizeof(struct xfs_dsb)))
+ sblen = xchk_superblock_ondisk_size(mp);
+ if (memchr_inv((char *)sb + sblen, 0, BBTOB(bp->b_length) - sblen))
xchk_block_set_corrupt(sc, bp);

xchk_superblock_xref(sc, bp);