-----BEGIN PGP SIGNED MESSAGE----- ______________________________________________________________________________ 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@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@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@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@suse.com>. suse-security-announce@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@suse.com>. 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. 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