xfs: log recovery needs to validate against sb_meta_uuid

Now that sb_uuid can be changed by the user, we cannot use this to
validate the metadata blocks being recovered belong to this
filesystem. We must check against the sb_meta_uuid as that will
remain unchanged.

There is a complication in this code - the superblock itself. We can
not check the sb_meta_uuid unconditionally, as that may not be set
on disk. Hence we must verify the superblock sb_uuid matches between
the log record and the in-core superblock.

Found by inspection after the previous two problems were found.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_log_recover.c

@@ -1890,15 +1890,25 @@ xlog_recover_get_buf_lsn(
 		uuid = &((struct xfs_attr3_rmt_hdr *)blk)->rm_uuid;
 		break;
 	case XFS_SB_MAGIC:
+		/*
+		 * superblock uuids are magic. We may or may not have a
+		 * sb_meta_uuid on disk, but it will be set in the in-core
+		 * superblock. We set the uuid pointer for verification
+		 * according to the superblock feature mask to ensure we check
+		 * the relevant UUID in the superblock.
+		 */
 		lsn = be64_to_cpu(((struct xfs_dsb *)blk)->sb_lsn);
-		uuid = &((struct xfs_dsb *)blk)->sb_uuid;
+		if (xfs_sb_version_hasmetauuid(&mp->m_sb))
+			uuid = &((struct xfs_dsb *)blk)->sb_meta_uuid;
+		else
+			uuid = &((struct xfs_dsb *)blk)->sb_uuid;
 		break;
 	default:
 		break;
 	}
 
 	if (lsn != (xfs_lsn_t)-1) {
-		if (!uuid_equal(&mp->m_sb.sb_uuid, uuid))
+		if (!uuid_equal(&mp->m_sb.sb_meta_uuid, uuid))
 			goto recover_immediately;
 		return lsn;
 	}