SuSE: 'kernel' local privilege escalation vulnerabilities

    Date 26 Oct 2001
    Posted By LinuxSecurity Advisories
    Two security-related vulnerabilities have been found that affect every Linux kernel since 2.2.
                            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  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 
        where  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 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,
        all other packages can be found on 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
           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 This email address is being protected from spambots. You need JavaScript enabled to view it.),
           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 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 "This email address is being protected from spambots. You need JavaScript enabled to view it." 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 .
      - SuSE runs two security mailing lists to which any interested party may
        This email address is being protected from spambots. You need JavaScript enabled to view it.
            -   general/linux/SuSE security discussion.
                All SuSE security announcements are sent to this list.
                To subscribe, send an email to
                    <This email address is being protected from spambots. You need JavaScript enabled to view it.>.
        This email address is being protected from spambots. You need JavaScript enabled to view it.
            -   SuSE's announce-only mailing list.
                Only SuSE's security annoucements are sent to this list.
                To subscribe, send an email to
                    <This email address is being protected from spambots. You need JavaScript enabled to view it.>.
        For general information or the frequently asked questions (faq)
        send mail to:
            <This email address is being protected from spambots. You need JavaScript enabled to view it.> or
            <This email address is being protected from spambots. You need JavaScript enabled to view it.> respectively.
        SuSE's security contact is <This email address is being protected from spambots. You need JavaScript enabled to view it.>.
        The <This email address is being protected from spambots. You need JavaScript enabled to view it.> 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 <This email address is being protected from spambots. You need JavaScript enabled to view it.>
    pub  1024D/9C800ACA 2000-10-19 SuSE Package Signing Key <This email address is being protected from spambots. You need JavaScript enabled to view it.>
    Version: GnuPG v1.0.6 (GNU/Linux)
    Comment: For info see
    - -----END PGP PUBLIC KEY BLOCK-----

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