xfs: check for bogus values in btree block headers

When we're reading a btree block, make sure that what we retrieved
matches the owner and level; and has a plausible number of records.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_btree.c

@@ -1769,8 +1769,28 @@ xfs_btree_lookup_get_block(
 	if (error)
 		return error;
 
+	/* Check the inode owner since the verifiers don't. */
+	if (xfs_sb_version_hascrc(&cur->bc_mp->m_sb) &&
+	    (cur->bc_flags & XFS_BTREE_LONG_PTRS) &&
+	    be64_to_cpu((*blkp)->bb_u.l.bb_owner) !=
+			cur->bc_private.b.ip->i_ino)
+		goto out_bad;
+
+	/* Did we get the level we were looking for? */
+	if (be16_to_cpu((*blkp)->bb_level) != level)
+		goto out_bad;
+
+	/* Check that internal nodes have at least one record. */
+	if (level != 0 && be16_to_cpu((*blkp)->bb_numrecs) == 0)
+		goto out_bad;
+
 	xfs_btree_setbuf(cur, level, bp);
 	return 0;
+
+out_bad:
+	*blkp = NULL;
+	xfs_trans_brelse(cur->bc_tp, bp);
+	return -EFSCORRUPTED;
 }
 
 /*