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SuSE Security Announcement: kernel

Oct 27, 2001, 00:19 (0 Talkback[s])
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,

  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 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
    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"), 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
    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 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

        -   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 
pub  1024D/9C800ACA 2000-10-19 SuSE Package Signing Key 

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


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