Sicherheit: ptrace-Problem im Kernel
Aktuelle Meldungen Distributionen
Name: ptrace-Problem im Kernel
ID: SuSE-SA:2001:036
Distribution: SUSE
Plattformen: Keine Angabe
Datum: Sa, 27. Oktober 2001, 13:00
Referenzen: Keine Angabe
Applikationen: Linux




SuSE Security Announcement

Package: kernel
Announcement-ID: SuSE-SA:2001:036
Date: Friday, Oct 26th 2001 18:00 MEST
Affected SuSE versions: 6.3, 6.4, 7.0, 7.1, 7.2, 7.3
Vulnerability Type: local privilege escalation
Severity (1-10): 8
SuSE default package: yes
Other affected systems: all Linux systems, all kernel versions

Content of this advisory:
1) security vulnerability resolved: kernel
problem description, discussion, solution and upgrade information
2) pending vulnerabilities, solutions, workarounds
3) standard appendix (further information)


1) The Problem, Workaround, Recommended solution, Instructions, Notes,

The Problem:

The SuSE Linux kernel is a standard kernel, enhanced with a set of
additional drivers and other improvements, to suit the end-user's
demand for a great variety of drivers for all kind of hardware.

Two security related problems have been found in both the 2.2 and
2.4 series kernels:

1) A recursive symlink structure can cause the kernel to consume excessive
CPU time, causing the machine to halt for an arbitrary amount of time.
2) ptrace(2), the system call used to trace processes as done by the
strace(1) command, must not be given permissions to trace setuid or
setgid programs (processes with a different effective uid or gid than
the caller's uid/gid). A race condition in the ptrace() kernel code
was the reason for the kernel update in May 2001. The flaw fixed with
this kernel update is based on the assumption that the calling process
is allowed to trace a running process. The fix consists of disallowing
a ptrace() system call for all setuid/setgid binaries, regardless
of the capabilities of the calling process.

Bug 1) can lead to a local DoS.
Bug 2) can allow a local attacker to gain root privileges.


It is possible to work around bug 2) by removing the setuid bit from the
programs newgrp, su, su1, sudo and possibly more programs in the system
that will start another program with different pivileges.
In order to completely solve the security problems, it is recommended to
update the kernel to a newer version as described below.

Recommended solution:

We have provided update kernels for our supported distributions
6.3, 6.4, 7.0, 7.1, 7.2 and the freshly released 7.3. Currently,
only kernel update packages for the Intel i386 distributions are
available. The update should be performed with special care in order
to make sure that the system will properly boot after the package

Step-By-Step Installation Instructions:

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.
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 version

SuSE-6.3, 6.4 and 7.0 are built for kernels of version 2.2, 7.1 and
up are also ready for a 2.4 kernel. You should use the same major kernel
version for the update as you are using already.

Determine the kernel version that is running on your system with the
uname -r

If your running kernel is version 2.2.x, you should use a 2.2.19 kernel
to update, if you use a 2.4 series kernel, use a 2.4 kernel to update
SuSE-7.3 users: See Step 3!).
Cross-version updates _may_ work in your installation but are dis-
recommended in order to preserve a properly running system.

**** Step 2: Determine the needed kernel type

After you have determined which version to install, you must select the
type of kernel rpm package to install. There are four types offered:

k_i386 a kernel that runs on i386 processors.
k_smp the kernel for computers with more than one CPU
k_psmp for dual Pentium-I processor computers
k_deflt the default kernel for most systems, includes support
for APM (laptops).

You can use the command
rpm -qf `awk -F= '/image/{print $2}' < /etc/lilo.conf`
to find the name of the kernel RPM package that is installed on
your system. In the case of inconclusive results, pick one from the
four choices above: k_deflt works on most systems, k_smp is for
multi processor computers.

Step 1 and 2 will lead you to one of these possiblities:

2.2-default 2.2-smp 2.2-psmp 2.2-i386
2.4-default 2.4-smp 2.4-psmp 2.4-i386

**** Step 3: SuSE-7.3 special: Download

If you have a SuSE-7.3 system, continue to read this paragraph,
otherwise jump to Step 4.
SuSE Linux 7.3 comes with a kernel version 2.4.10. We have made
a set of patched kernels of this particular version to seamlessly
fit into a 7.3 installation. SuSE Linux releases before 7.3 should
receive a 2.4.7 kernel update - we provide both versions for the update.
It should be possible though to run both 2.4 kernels on all 2.4 based

Please download your kernel rpm from the location
After downloading the rpm package, you might want to verify the
authenticity of the rpm package according to Section 3 of this and every
SuSE Security announcement.
Then go to Step 5, omitting Step 4.

**** Step 4: Download your kernel rpm

Your kernel rpm package is available for download from


where <dist> is the release version of your distribution.
If you need to download a 2.4 series kernel, enter the directory
called 2.4.7-20011026/ and download the kernel rpm type that you
have selected in Step 2.
If you need to download a 2.2 series kernel, enter the directory
called 2.2.19-20011026/ and download the kernel rpm type that you
have selected in Step 2.

An example: For a SuSE-7.2 distribution installed on an SMP system
that is running a 2.4 series kernel, you should download the file

After downloading the rpm package, you might want to verify the
authenticity of the rpm package according to Section 3 of this
SuSE Security announcement at the bottom of this message.

**** Step 5: SuSE-6.3 special: Installing your kernel rpm package

If you have a SuSE-6.3 system, continue to read this paragraph,
otherwise jump to Step 6.
In SuSE Linux version 6.3, the kernel and the kernel modules are
packaged in two different packages. This will change with the success
of this update: Both kernel images and kernel modules will be contained
in the same package. For the update to succeed, you will have to either
remove the existing kernel package from your system using the command
rpm -e `rpm -qf /boot/vmlinuz`
or two kernel rpm packages will be installed on your system.

**** Step 6: Installing your kernel rpm package

Install the rpm package that you have downloaded in Steps 3 or 4 with
the command
rpm -Uhv --nodeps --force <K_FILE.RPM>
where <K_FILE.RPM> is the name of the rpm package that you

Notice: After performing this step, your system will likely not be
able to boot if the following steps have not been fully applied.

**** Step 7: aic7xxx

If you use an Adaptec aic7xxx SCSI host adapter, continue to read
this paragraph, otherwise jump to Step 8.
The new kernel comes with two versions for the Adaptec aic7xxx driver.
If you have such a card, you should see the driver listed in the
output from the command
or you should see the adapter in the output of the command
The new driver is known to work reliably. However, if you encounter
any problems with CDROM drives or other removeable devices (CD-RW
drives, tapes, etc) after this kernel upgrade, then you should try to
use the old driver which is called aic7xxx_old instead of aic7xxx.
If you decide to make this change, then the steps 10 and 11 are
mandatory for the update to succeed, regardless if you get back to
this paragraph after your first reboot or not.
To use the old driver, please use your favourite editor to edit
the file /etc/rc.config. Change aic7xxx into aic7xxx_old at the line
that starts with INITRD_MODULES. You should find it near the top of the
file. Do not forget to save your changes. Then go to Steps 10 and 11.

If you want to use the new driver, then do not change anything.

**** Step 8: LVM

If you use LVM, then continue to read this paragraph,
otherwise jump to Step 9.
If you use LVM (Logical Volume Manager) in your installation of SuSE
Linux before and including SuSE-7.1, then you need the updated lvm
package from the
directory for your distribution as well. The package contains the
userspace utilities to manage the Logical Volume Manager driver.
An update package is needed because the LVM data format/structure on
disk has changed with the new version of the LVM kernel driver.
Install the package as usual using the command
rpm -Uhv lvm-0.9.1_beta4-12.i386.rpm
Be sure you have downloaded the package for the explicit version
of your SuSE Linux Installation. The package names are identical
for all distribution versions.

With this kernel upgrade, the lvm driver is configured as a module,
it is _not_ compiled into the kernel image any more. Therefore, you
should use your favourite editor and edit /etc/rc.config. In this
file, the variable INITRD_MODULES must contain the word "lvm-mod".
Example: you have an NCR scsi hostadapter and use lvm and reiserfs.
The line in /etc/rc.config should look like
INITRD_MODULES="sym53c8xx lvm-mod"
Be careful about the double quotes!

WARNING: After the first boot with the new kernel you will not be able
to downgrade to older versions of LVM any more.

**** Step 9: reiserfs

If you use reiserfs, then continue to read this paragraph,
otherwise jump to Step 10.

If you use reiserfs (find out via "grep reiserfs /proc/mounts"),
make sure that the variable INITRD_MODULES from /etc/rc.config contains
the word "reiserfs", like in the example in Step 8.

**** Step 10: configuring and creating the initrd

Upon kernel boot (after lilo runs), the kernel needs to use the
drivers for the device (disk/raid) where the root filesystem
is located in order to access it for mounting. If this driver is
not compiled into the kernel, it is supplied as a kernel module
that must be loaded _before_ the root filesystem is mounted. This
is done using a ramdisk that is loaded along with the kernel by lilo
(which is subject to the next Step).

The modules that will be packed into this initial ramdisk (initrd)
must be listed in the variable INITRD_MODULES in the file
/etc/rc.config . This ramdisk, called "initrd", must be generated
using the command
If the driver for the device containing your root device is not
compiled directly into the kernel, then your system will most likely
not boot any more. If you have followed the above steps, you should be
safe. Special care should be taken with scsi hostadapters, logical volume
manager (lvm) and reiserfs.

**** Step 11: lilo

lilo is responsible for loading the kernel image and the initrd
ramdisk image into the system and for transferring control of the
system to the kernel. Therefore, a proper installation of the
bootloader (by calling the program lilo) is essential for the
system to boot (!).
Manually changed settings in /etc/lilo.conf require the admin to make
sure that /boot/vmlinuz is listed in the first "image" line in that
file. Verify that the line starting with initrd= is set to
and you should see your label(s) in an output like
Added linux *
Every other output should be considered an error and requires
attention. If your system managed to reboot before the upgrade, you
should not see any additional output from lilo at this stage.

**** Step 12: SuSE-7.0 special

If you have a SuSE Linux 7.0 distribution, then continue to read this
paragraph, otherwise jump to Step 13.
If you have performed the kernel upgrade as described in the last kernel
SuSE Security announcement SuSE-SA:2001:18 and if you have performed
the upgrade of the glibc as described in Step 8 of SuSE-SA:2001:18, then
you are done and you should go to Step 13. Otherwise, please read
SuSE-SA:2001:18 (from
http://www.suse.de/de/support/security/2001_018_kernel_txt.txt) and
return to the Step 13 in this announcement.

**** Step 13: 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
init 6


2) Pending vulnerabilities in SuSE Distributions and Workarounds:

- openssh
After stabilizing the openssh package, updates for the distributions
6.4-7.2 are currently being prepared. The update packages fix a security
problem related to the recently discovered problems with source ip
based access restrictions in a user's ~/.ssh/authorized_keys2 file.
The packages will appear shortly on our ftp servers. Please note that
packages for the distributions 6.3 and up including 7.0 containing
cryptographic software are located on the German ftp server ftp.suse.de,
all other packages can be found on ftp.suse.com at the usual location.

- squid
A squid server can be brought to a crash upon receipt of certain
requests. The attacker must have request access to the running squid
proxy to be able to take advantage of this weakness. The only effect
of an attack is the Denial of Service (DoS). After an attack, the
squid proxy must be restarted.
Update packages are available on our ftp server that eliminate the
problem. The security announcement for this issue will follow soon.


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
md5sum <name-of-the-file.rpm>
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 security@suse.de),
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
list software.
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 <file.rpm>
to verify the signature of the package, where <file.rpm> is the
filename of the rpm package that you have downloaded. Of course,
package authenticity verification can only target an uninstalled rpm
package file.
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 "build@suse.de" upon installation or upgrade, provided
the package gpg is installed. The file containing the public key
is placed at the toplevel 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 annoucements are sent to this list.
To subscribe, send an email to

For general information or the frequently asked questions (faq)
send mail to:
<suse-security-info@suse.com> or
<suse-security-faq@suse.com> respectively.

SuSE's security contact is <security@suse.com>.
The <security@suse.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 cleartext signature shows proof of the
authenticity of the text.
SuSE GmbH 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 <security@suse.de>
pub 1024D/9C800ACA 2000-10-19 SuSE Package Signing Key <build@suse.de>

Version: GnuPG v1.0.6 (GNU/Linux)
Comment: For info see http://www.gnupg.org


Version: 2.6.3i
Charset: noconv


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