MESSAGE
| DATE | 2001-10-29 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [hangout] Kernel Security alerts
|
http://linuxtoday.com/news_story.php3?ltsn=2001-10-27-001-20-SC-KN-SS
SuSE Security Announcement:
kernel
Oct 27, 2001, 00 :19 UTC (0 Talkback[s]) (1810 reads)
Date: Fri, 26 Oct 2001 18:31:01 +0200 (MEST)
From: Roman Drahtmueller
Subject: SuSE Security Announcement: kernel
(SuSE-SA:2001:036)
______________________________________________________________________________
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,
Verification
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.
Workarounds:
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
update.
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
command
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
systems.
Please download your kernel rpm from the location
ftp://ftp.suse.com/pub/suse/i386/update/7.3/kernel/2.4.10-20011026/
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
ftp://ftp.suse.com/pub/suse/i386/update/dist/kernel/
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
ftp://ftp.suse.com/pub/suse/i386/update/7.2/kernel/2.4.7-20011026/k_smp-2.4.7-22.i386.rpm
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 downloaded.
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
lsmod
or you should see the adapter in the output of the
command
lspci
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
/pub/suse/i386/update/dist/kernel/2.2.19-20011026/
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"), then
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
mk_initrd
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
initrd=/boot/initrd
Execute
lilo
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
or
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-at-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.
Prerequisites:
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-at-suse.de" upon installation or
upgrade, provided that
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
subscribe:
suse-security-at-suse.com
- general/linux/SuSE security discussion.
All SuSE security announcements are sent to
this list.
To subscribe, send an email to
suse-security-subscribe-at-suse.com
suse-security-announce-at-suse.com
- SuSE's announce-only mailing list.
Only SuSE's security annoucements are sent to
this list.
To subscribe, send an email to
suse-security-announce-subscribe-at-suse.com
For general information or the frequently asked
questions (faq)
send mail to:
suse-security-info-at-suse.com or
suse-security-faq-at-suse.com respectively.
===================================================
SuSE's security contact is security-at-suse.com.
The security-at-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
pub 1024D/9C800ACA 2000-10-19 SuSE Package Signing Key
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