Linux kernel 2.4.20-31.9 was the last erratum for Red Hat Linux 9:
http://www.redhat.com/security/updates/eol/
You can download the update packages on every FTP/HTTP mirror server, which carries Red Hat Linux.
The patch very likely also applies to the previous 2.4.20-30.9 kernel.
Since Red Hat Linux 9 has reach end-of-life long ago, you are advised to check out at least the additional community updates provided by
http://fedoralegacy.org