xfs: detect empty attr leaf blocks in xfs_attr3_leaf_verify

xfs_repair flags these as a corruption error, so the verifier should
catch software bugs that result in empty leaf blocks being written
to disk, too.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>

Author: dgchinner

fs/xfs/libxfs/xfs_attr_leaf.c

@@ -310,6 +310,15 @@ xfs_attr3_leaf_verify(
 	if (fa)
 		return fa;
 
+	/*
+	 * Empty leaf blocks should never occur;  they imply the existence of a
+	 * software bug that needs fixing. xfs_repair also flags them as a
+	 * corruption that needs fixing, so we should never let these go to
+	 * disk.
+	 */
+	if (ichdr.count == 0)
+		return __this_address;
+
 	/*
 	 * firstused is the block offset of the first name info structure.
 	 * Make sure it doesn't go off the block or crash into the header.