[PATCH 6/6] xfs_repair: check plausibility of root dir pointer before trashing it

Darrick J. Wong
2019-12-04T17:05:09Z

From: Darrick J. Wong <darrick.wong@oracle.com>

If sb_rootino doesn't point to where we think mkfs should have allocated
the root directory, check to see if the alleged root directory actually
looks like a root directory. If so, we'll let it live because someone
could have changed sunit since formatting time, and that changes the
root directory inode estimate.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
repair/xfs_repair.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)

diff --git a/repair/xfs_repair.c b/repair/xfs_repair.c
index abd568c9..b0407f4b 100644
--- a/repair/xfs_repair.c
+++ b/repair/xfs_repair.c
@@ -426,6 +426,37 @@ _("would reset superblock %s inode pointer to %"PRIu64"\n"),
*ino = expected_ino;
}

+/* Does the root directory inode look like a plausible root directory? */
+static bool
+has_plausible_rootdir(
+ struct xfs_mount *mp)
+{
+ struct xfs_inode *ip;
+ xfs_ino_t ino;
+ int error;
+ bool ret = false;
+
+ error = -libxfs_iget(mp, NULL, mp->m_sb.sb_rootino, 0, &ip,
+ &xfs_default_ifork_ops);
+ if (error)
+ goto out;
+ if (!S_ISDIR(VFS_I(ip)->i_mode))
+ goto out_rele;
+
+ error = -libxfs_dir_lookup(NULL, ip, &xfs_name_dotdot, &ino, NULL);
+ if (error)
+ goto out_rele;
+
+ /* The root directory '..' entry points to the directory. */
+ if (ino == mp->m_sb.sb_rootino)
+ ret = true;
+
+out_rele:
+ libxfs_irele(ip);
+out:
+ return ret;
+}
+
/*
* Make sure that the first 3 inodes in the filesystem are the root directory,
* the realtime bitmap, and the realtime summary, in that order.
@@ -436,6 +467,20 @@ calc_mkfs(
{
xfs_ino_t rootino = libxfs_ialloc_calc_rootino(mp, -1);

+ /*
+ * If the root inode isn't where we think it is, check its plausibility
+ * as a root directory. It's possible that somebody changed sunit
+ * since the filesystem was created, which can change the value of the
+ * above computation. Don't blow up the root directory if this is the
+ * case.
+ */
+ if (mp->m_sb.sb_rootino != rootino && has_plausible_rootdir(mp)) {
+ do_warn(
+_("sb root inode value %" PRIu64 " inconsistent with alignment (expected %"PRIu64")\n"),
+ mp->m_sb.sb_rootino, rootino);
+ rootino = mp->m_sb.sb_rootino;
+ }
+
ensure_fixed_ino(&mp->m_sb.sb_rootino, rootino,
_("root"));
ensure_fixed_ino(&mp->m_sb.sb_rbmino, rootino + 1,