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SuSE Linux Advisory: kernel

Mar 25, 2003, 18:59 (0 Talkback[s])

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                        SuSE Security Announcement

        Package:                kernel
        Announcement-ID:        SuSE-SA:2003:021
        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
    permanent solution.
    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
    kernel RPM.
    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.

    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
    the command
        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
        init 6

    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,
       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 
       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
       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 "" 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 .

  - 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
                <<A HREF="">>.
        -   SuSE's announce-only mailing list.
            Only SuSE's security announcements are sent to this list.
            To subscribe, send an email to
                <<A HREF="">>.

    For general information or the frequently asked questions (faq)
    send mail to:
        <<A HREF="">> or
        <<A HREF="">> respectively.

    SuSE's security contact is <<A HREF="">> or <<A HREF="">>.
    The <<A HREF="">> 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="">>
pub  1024D/9C800ACA 2000-10-19 SuSE Package Signing Key <<A HREF="">>

Roman Drahtmüller,
SuSE Security.
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  SuSE Linux AG - Security       Phone: //             you need vision!"
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