SuSE Linux Advisory: kernel
Mar 25, 2003, 18:59 (0 Talkback[s])
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SuSE Security Announcement
Date: Tuesday, Mar 25 2003 18:00 MET
Affected products: 7.1, 7.2, 7.3, 8.0, 8.1
SuSE Linux Database Server,
SuSE eMail Server III, 3.1
SuSE Linux Enterprise Server 7,
SuSE Linux Enterprise Server 8,
SuSE Linux Firewall on CD/Admin host
SuSE Linux Connectivity Server
SuSE Linux Office Server
Vulnerability Type: local privilege escalation
Severity (1-10): 6
SuSE default package: yes
Cross References: CAN-2003-0127
Content of this advisory:
1) security vulnerability resolved: kernel
problem description, discussion, solution and upgrade information
2) pending vulnerabilities, solutions, workarounds:
- none in this security announcement
3) standard appendix (further information)
1) problem description, brief discussion, solution, upgrade information
The Linux kernel has a security flaw in all versions used on SuSE
products excluding the upcoming SuSE Linux 8.2 distribution. The flaw
is known as ptrace/modprobe bug: The local attacker can use ptrace and
attach to a modprobe process that is spawned if the user triggers the
loading of a kernel module using the kmod kernel module subsystem.
This can be done by asking for network protocols that are supplied by
kernel modules which are not loaded (yet). The vulnerability allows
the attacker to execute arbitrary commands as root.
There exists a temporary workaround against this flaw: It is possible
to temporaryly disable the kmod kernel module loading subsystem in the
kernel after all necessary kernel modules have been loaded (Note: SuSE
systems do not unload kernel modules in regular intervals.). If the
temporary workaround is chosen, it should be made sure that no
additional kernel modules need to be loaded afterwards (such as ISDN
drivers, scsi subsystem drivers or filesystem drivers such as the
iso9660 filesystem for cdroms and the language codepages).
To disable the kmod kernel module loading subsystem, use the following
command as root:
echo /no/such_file > /proc/sys/kernel/modprobe
If this command is inserted into a boot script that runs after all
services in a runlevel have been launched, it is an efficient
This workaround can be reverted by writing the original content
("/sbin/modprobe") back to the /proc/sys/kernel/modprobe file.
Please note that it is still possible for the root user to manually
load kernel modules.
As a permanent remedy for the problem we offer kernel update packages
for download from our ftp server. Please follow the guidelines that
are given in the extensive installation intructions below. The update
should be performed with special care in order to make sure that the
system will properly boot after the package update.
Note: Managing the necessary patches, building and mostly testing
kernel update packages is an extremely worksome and therefore also
time-consuming process. SuSE wishes to provide the same quality and
reliability in update packages as customers are used to from the
shipped original products. Even though our kernel updates are
thoroughly tested, the numerous possible hardware configurations for the
x86 platform give a certain probability for a functional failure of
parts of the kernel after the update has been performed. Some of the
possible failures cannot be handled by SuSE by definition. These
include (and are not limited to) possible problems with NVIDIA chipset
graphics boards that make use of hardware 3D acceleration. SuSE cannot
deliver the binary only driver for the NVIDIA graphics boards in the
The kernel of a Linux system is the most critical component with respect
to stability, reliability and security. By consequence, an update of that
component requires some care and full attention to succeed. If you do
not run a system where multiple users have access to, you may want to
consinder to not perform this update since the security risk imposed
by this bug is very small on a system with only one user.
SPECIAL INSTALL INSTRUCTIONS:
The following paragraphs will guide you through the installation
process in a step-by-step fashion. The character sequence "****"
marks the beginning of a new paragraph. In some cases, you decide
if the paragraph is needed for you or not. Please read through all
of the steps down to the end. All of the commands that need to be
executed are required to be run as the superuser (root). Each step
relies on the steps before to complete successfully.
**** Step 1: Determine the needed kernel type
Please use the following command to find the kernel type that is
installed on your system:
rpm -qf /boot/vmlinuz
The following options are possible (disregarding the version and build
number following the name, seperated by the "-" character):
k_deflt # default kernel, good for most systems.
k_i386 # kernel for older processors and chipsets
k_athlon # kernel made specifically for AMD Athlon family processors
k_orig # kernel built with unmodified sources
k_psmp # kernel for Pentium-I dual processor systems
k_smp # kernel for SMP systems (Pentium-II and above)
**** Step 2: Download the package for your system
Please download the kernel RPM package for your distribution with the
name starting as indicated by Step 1. The list of all kernel rpm
packages is appended below. Note: The kernel-source package does not
contain any binary kernel in bootable form. Instead, it contains the
sources that the binary kernel rpm packages are made from. It can be
used by administrators who have decided to build their own kernel.
Since the kernel-source.rpm is an installable (compiled) package that
contains sources for the linux kernel, it is not the source RPM for
the kernel RPM binary packages.
After downloading the kernel RPM package for your system, you should
verify the authenticity of the kernel rpm package using the methods as
listed in section 3) of each SuSE Security Announcement.
**** Step 3: Installing your kernel rpm package
Install the rpm package that you have downloaded in Steps 3 or 4 with
rpm -Uhv --nodeps --force
where is the name of the rpm package that you downloaded.
Warning: After performing this step, your system will likely not be
able to boot if the following steps have not been fully
**** Step 4: configuring and creating the initrd
The initrd is a ramdisk that is being loaded into the memory of your
system together with the kernel boot image by the bootloader. The
kernel uses the content of this ramdisk to execute commands that must
be run before the kernel can mount its actual root filesystem. It is
usually used to initialize scsi drivers or NIC drivers for diskless
The variable INITRD_MODULES (set in the files /etc/rc.config up to
7.3) or /etc/sysconfig/kernel (after and including 8.0)) determines
which kernel modules will be loaded in the initrd before the kernel
has mounted its actual root filesystem. The variable should contain
your scsi adapter (if any) or filesystem driver modules.
With the installation of the new kernel, the initrd has to be
re-packed with the update kernel modules. Please run the command
as root to create a new init rmadisk (initrd) for your system.
**** Step 5: bootloader
If you have a 7.x system, you must now run the command
as root to initialize the lilo bootloader for your system. Then
proceed to the next step.
If you run a SuSE Linux 8.x or a SLES8 system, there are two options:
Depending on your software configuration, you have the lilo bootloader
or the grub bootloader installed and initialized on your system.
The grub bootloader does not require any further actions to be
performed after the new kernel images have been moved in place by the
rpm Update command.
If you have a lilo bootloader installed and initialized, then the lilo
program must be run as root. Use the command
grep LOADER_TYPE /etc/sysconfig/bootloader
to find out which boot loader is configured. If it is lilo, then you
must run the lilo command as root. If grub is listed, then your system
does not require any bootloader initialization.
Warning: An improperly installed bootloader may render your system
**** Step 6: reboot
If all of the steps above have been successfully applied to your
system, then the new kernel including the kernel modules and the
initrd should be ready to boot. The system needs to be rebooted for
the changes to become active. Please make sure that all steps are
complete, then reboot using the command
shutdown -r now
Your system should now shut down and reboot with the new kernel.
Download sources for all kernel RPM packages:
Our maintenance customers are being notified individually. The packages
are being offered to install from the maintenance web.
2) Pending vulnerabilities in SuSE Distributions and Workarounds:
- there are no items listed in this security announcements.
3) standard appendix: authenticity verification, additional information
- Package authenticity verification:
SuSE update packages are available on many mirror ftp servers all over
the world. While this service is being considered valuable and important
to the free and open source software community, many users wish to be
sure about the origin of the package and its content before installing
the package. There are two verification methods that can be used
independently from each other to prove the authenticity of a downloaded
file or rpm package:
1) md5sums as provided in the (cryptographically signed) announcement.
2) using the internal gpg signatures of the rpm package.
1) execute the command
after you downloaded the file from a SuSE ftp server or its mirrors.
Then, compare the resulting md5sum with the one that is listed in the
announcement. Since the announcement containing the checksums is
cryptographically signed (usually using the key firstname.lastname@example.org),
the checksums show proof of the authenticity of the package.
We disrecommend to subscribe to security lists which cause the
email message containing the announcement to be modified so that
the signature does not match after transport through the mailing
Downsides: You must be able to verify the authenticity of the
announcement in the first place. If RPM packages are being rebuilt
and a new version of a package is published on the ftp server, all
md5 sums for the files are useless.
2) rpm package signatures provide an easy way to verify the authenticity
of an rpm package. Use the command
rpm -v --checksig
to verify the signature of the package, where is the
filename of the rpm package that you have downloaded. Of course,
package authenticity verification can only target an un-installed rpm
a) gpg is installed
b) The package is signed using a certain key. The public part of this
key must be installed by the gpg program in the directory
~/.gnupg/ under the user's home directory who performs the
signature verification (usually root). You can import the key
that is used by SuSE in rpm packages for SuSE Linux by saving
this announcement to a file ("announcement.txt") and
running the command (do "su -" to be root):
gpg --batch; gpg < announcement.txt | gpg --import
SuSE Linux distributions version 7.1 and thereafter install the
key "email@example.com" upon installation or upgrade, provided that
the package gpg is installed. The file containing the public key
is placed at the top-level directory of the first CD (pubring.gpg)
and at ftp://ftp.suse.com/pub/suse/pubring.gpg-build.suse.de .
- SuSE runs two security mailing lists to which any interested party may
- general/linux/SuSE security discussion.
All SuSE security announcements are sent to this list.
To subscribe, send an email to
- SuSE's announce-only mailing list.
Only SuSE's security announcements are sent to this list.
To subscribe, send an email to
For general information or the frequently asked questions (faq)
send mail to:
<<A HREF="mailto:firstname.lastname@example.org">email@example.com> or
<<A HREF="mailto:firstname.lastname@example.org">email@example.com> respectively.
SuSE's security contact is <<A HREF="mailto:firstname.lastname@example.org">email@example.com> or <<A HREF="mailto:firstname.lastname@example.org">email@example.com>.
The <<A HREF="mailto:firstname.lastname@example.org">email@example.com> public key is listed below.
The information in this advisory may be distributed or reproduced,
provided that the advisory is not modified in any way. In particular,
it is desired that the clear-text signature shows proof of the
authenticity of the text.
SuSE Linux AG makes no warranties of any kind whatsoever with respect
to the information contained in this security advisory.
Type Bits/KeyID Date User ID
pub 2048R/3D25D3D9 1999-03-06 SuSE Security Team <<A HREF="mailto:firstname.lastname@example.org">email@example.com>
pub 1024D/9C800ACA 2000-10-19 SuSE Package Signing Key <<A HREF="mailto:firstname.lastname@example.org">email@example.com>
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