xfs: abort directory parent scrub scans if we encounter a zapped directory

In a previous patch, we added some code to perform sufficient repairs
to an ondisk inode record such that the inode cache would be willing to
load the inode.  If the broken inode was a shortform directory, it will
reset the directory to something plausible, which is to say an empty
subdirectory of the root.  The telltale signs that something is
seriously wrong is the broken link count.

Such directories look clean, but they shouldn't participate in a
filesystem scan to find or confirm a directory parent pointer.  Create a
predicate that identifies such directories and abort the scrub.

Found by fuzzing xfs/1554 with multithreaded xfs_scrub enabled and
u3.bmx[0].startblock = zeroes.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 17 insertions, 0 deletions

diff --git a/fs/xfs/scrub/parent.c b/fs/xfs/scrub/parent.c
index e6155d86f791..7db873672146 100644
--- a/fs/xfs/scrub/parent.c
+++ b/fs/xfs/scrub/parent.c
@@ -156,6 +156,16 @@ xchk_parent_validate(
 		goto out_rele;
 	}
 
+	/*
+	 * We cannot yet validate this parent pointer if the directory looks as
+	 * though it has been zapped by the inode record repair code.
+	 */
+	if (xchk_dir_looks_zapped(dp)) {
+		error = -EBUSY;
+		xchk_set_incomplete(sc);
+		goto out_unlock;
+	}
+
 	/* Look for a directory entry in the parent pointing to the child. */
 	error = xchk_dir_walk(sc, dp, xchk_parent_actor, &spc);
 	if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
@@ -217,6 +227,13 @@ xchk_parent(
 		 */
 		error = xchk_parent_validate(sc, parent_ino);
 	} while (error == -EAGAIN);
+	if (error == -EBUSY) {
+		/*
+		 * We could not scan a directory, so we marked the check
+		 * incomplete.  No further error return is necessary.
+		 */
+		return 0;
+	}
 
 	return error;
 }