root shell exploit still working in kernel 2.4.21

[Thomas Frase]

hello!

the problem:
i tried an exploit (url given below) with debian woody kernel 2.4.18
and self compiled kernel 2.4.21 resulting in a root shell.

exploit code url: (found via google)
http://isec.pl/cliph/isec-ptrace-kmod-exploit.c

as described in the source the exploit uses the well known ptrace bug
which i thought was fixed in kernel 2.4.21.

i don't know why it still works or how to fix it. i told someone people
in #debian.de (quakenet) about the results of the exploit and they
asked me to post a bug report here.

greetings
    thomas f.
    (germany)

Kernel 2.4.21 infos:

Output from ver_linux:
-------------------------------------------------
Linux xXxXx 2.4.21 #1 SMP Fri Jun 20 14:25:09 CEST 2003 i686 unknown

Gnu C                  2.95.4
Gnu make               3.80
util-linux             2.11z
mount                  2.11z
modutils               2.4.21
e2fsprogs              1.27
PPP                    2.4.1
Linux C Library        2.3.1
Dynamic linker (ldd)   2.3.1
Procps                 3.1.9
Net-tools              1.60
Console-tools          0.2.3
Sh-utils               2.0.11
Modules Loaded
-------------------------------------------------

Output from /proc/version:
-------------------------------------------------
Linux version 2.4.21 (root@xXxXx) (gcc version 2.95.4 20011002 (Debian
prerelease)) #1 SMP Fri Jun 20 14:25:09 CEST 2003
-------------------------------------------------