Security Bulletin: Publicly disclosed vulnerability from Kernel affects IBM Netezza Host Management

Summary

Kernel is used by IBM Netezza Host Management. This bulletin provides mitigation for the reported CVE.

Vulnerability Details

CVEID:CVE-2020-14416
**DESCRIPTION:**Linux Kernel could allow a local attacker to execute arbitrary code on the system, caused by a race condition in tty->disc_data handling in the slip and slcan line discipline. By sending a specially-crafted request, an attacker could exploit this vulnerability to execute arbitrary code on the system.
CVSS Base score: 8.4
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/183915 for the current score.
CVSS Vector: (CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)

Affected Products and Versions

Remediation/Fixes

None

Workarounds and Mitigations

Mitigation of the reported CVE : CVE-2020-14416, blocklisting kernel moduleSlip to prevent it from loading automatically on PureData System for Analytics N200x and N3001 is as follows:
1. Change to user nz:
[root@nzhost1 ~]# su – nz

2. Check to see if Call Home is enabled:
[nz@nzhost1 ~]$ nzcallhome -status
If enabled, disable it:
[nz@nzhost1 ~]$nzcallhome –off Note: Ensure that nzcallhome returns status as disabled. If there are errors in the callHome.txt configuration file, errors are listed in the output, and call-Home is disabled.

3. Check the state of the Netezza system:
[nz@nzhost1 ~]$ nzstate

4. If the system state is online, stop the system using the command:
[nz@nzhost1 ~]$ nzstop

5. Wait for the system to stop, using the command:
[nz@nzhos1t ~]$ nzstate

System state is ‘Stopped’.

6. Exit from the nz session to return to user root:
[nz@nzhost1 ~]$ exit

7. Logged into the active host as root, type the following commands to stop the heartbeat processes:
[root@nzhost1 ~]# ssh ha2 /sbin/service heartbeat stop
[root@nzhost1 ~]# /sbin/service heartbeat stop

8. Run below commands as a root user to disable heartbeat from startup:
[root@nzhost1 ~]# ssh ha2 /sbin/chkconfig heartbeat off
[root@nzhost1 ~]# /sbin/chkconfig heartbeat off

9. Type the following commands to stop the DRBD processes:
[root@nzhost1 ~]# ssh ha2 /sbin/service drbd stop
[root@nzhost1 ~]# /sbin/service drbd stop

10. Run below commands as a root user to disable drbd from startup:
[root@nzhost1 ~]# ssh ha2 /sbin/chkconfig drbd off
[root@nzhost1 ~]# /sbin/chkconfig drbd off

Execute below steps using “root” user on both ha1/ha2 hosts

Step 1: Check if slip is loaded in the hosts

lsmod | grep slip

example:
[root@ nzhost1 ~]# lsmod | grep slip
slip 10466 0
slhc 5837 1 slip

Note: If there is no output skipStep 2, and proceed with** Step 3**

Step 2: Unload slip module

modprobe -rv slip

example:
[root@nzhost1 ~]# modprobe -rv slip
rmmod /lib/modules/2.6.32-754.33.1.el6.x86_64/kernel/drivers/net/slip.ko
rmmod /lib/modules/2.6.32-754.33.1.el6.x86_64/kernel/drivers/net/slhc.ko

Kernel module slip and its dependent modules will be unloaded in the reverse order that they are loaded, given that no processes depend on any of the modules being unloaded.

Step 3: To prevent a module from being loaded directly you add the blocklist line to a configuration file specific to the system configuration.

echo “blocklist slip” >> /etc/modprobe.d/local-blocklist.conf

example :
[root@nzhost1 ~]# echo “blocklist slip” >> /etc/modprobe.d/local-blocklist.conf
[root@nzhost1 ~]# cat /etc/modprobe.d/local-blocklist.conf | grep slip
blocklist slip

Step 4: Kernel modules can be loaded directly or loaded as a dependency from another module
To prevent installation as a dependency from another module follow below step:

echo “install slip /bin/false” >> /etc/modprobe.d/local-blocklist.conf

example:
[root@nzhost1 ~]# echo “install slip /bin/false” >> /etc/modprobe.d/local-blocklist.conf
[root@nzhost1 ~]# cat /etc/modprobe.d/local-blocklist.conf | grep slip
blocklist slip
install slip /bin/false

The install line simply causes /bin/false to be run instead of installing a module.

Step 5: Make a backup copy of your initramfs.

cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak

Example:
[root@nzhost1 ~]# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak
[root@nzhost1 ~]# uname -r
2.6.32-754.31.1.el6.x86_64
[root@nzhost1 ~]# ll /boot/initramfs-2.6.32-754.31.1.el6.x86_64.img.08-17-105347.bak
-rw------- 1 root root 21881438 Aug 17 10:53 /boot/initramfs-2.6.32-754.31.1.el6.x86_64.img.08-17-105347.bak

Step 6: If the kernel module is part of the initramfs (boot configuration), rebuild your initial ramdisk image, omitting the module to be avoided

dracut --omit-drivers slip -f

example:
[root@nzhost1 ~]# dracut --omit-drivers slip -f
[root@nzhost1 ~]# lsinitrd /boot/initramfs-2.6.32-754.31.1.el6.x86_64.img | grep slip

Step 7: Append module_name.blocklist to the kernel cmdline. We give it an invalid parameter of blocklist and set it to 1 as a way to preclude the kernel from loading it.

sed --follow-symlinks -i ‘/\s*kernel /vmlinuz/s/$/ slip.blocklist=1/’ /etc/grub.conf

example :
[root@nzhost1 ~]# sed --follow-symlinks -i ‘/\s*kernel /vmlinuz/s/$/ slip.blocklist=1/’ /etc/grub.conf

Step 8: blocklist the kernel module in kdump’s configuration file.

echo “blocklist slip” >> /etc/kdump.conf

example:
[root@nzhost1 ~]# echo “blocklist slip” >> /etc/kdump.conf
[root@nzhost1 ~]# cat /etc/kdump.conf | grep slip
blocklist slip

Note: PerformStep 9if kexec-tools is installed and kdump is configured else continue withStep 10.
Perform below commands to check if kexec-tools is installed and Kdump is operational
[root@nzhost1 ~]# rpm -qa | grep kexec-tools
[root@nzhost1 ~]# service kdump status

Step 9: Restart the kdump service to pick up the changes to kdump’s initrd.

service kdump restart

example:
[root@nzhost1 ~]# service kdump restart
Stopping kdump: [ OK ]
Detected change(s) the following file(s):

/etc/kdump.conf
Rebuilding /boot/initrd-2.6.32-754.31.1.el6.x86_64kdump.img
Starting kdump: [ OK ]

Step 10: Reboot the system at a convenient time to have the changes take effect.
Make sure the secondary host is up by pinging or logging in before rebooting the primary host.

/sbin/shutdown -r now

example:
[root@nzhost1 ~]# /sbin/shutdown -r now
Make sure the primary server comes up and is reachable before performing Mitigation steps on the secondary server.

After applying the mitigation:

1. Start the services using following:
[root@nzhost1 ~]# service heartbeat start
[root@nzhost1 ~]# ssh ha2 service heartbeat start
[root@nzhost1 ~]# service drbd start
[root@nzhost1 ~]# ssh ha2 service drbd start

2. Check the stat of the system. Type:
[root@nzhost1 ~]# crm_mon -i5

Result: When the cluster manager comes up and is ready, status appears as follows.
Make sure that nzinit has started before you proceed. (This could take a few minutes.)
Node: nps61074 (e890696b-ab7b-42c0-9e91-4c1cdacbe3f9): online
Node: nps61068 (72043b2e-9217-4666-be6f-79923aef2958): online
Resource Group: nps
drbd_exphome_device(heartbeat:drbddisk): Started nps61074
drbd_nz_device(heartbeat:drbddisk): Started nps61074
exphome_filesystem(heartbeat::ocf:Filesystem): Started nps61074
nz_filesystem (heartbeat::ocf:Filesystem): Started nps61074
fabric_ip (heartbeat::ocf:IPaddr): Started nps61074
wall_ip (heartbeat::ocf:IPaddr): Started nps61074
nzinit (lsb:nzinit): Started nps61074
fencing_route_to_ha1(stonith:apcmaster): Started nps61074
fencing_route_to_ha2(stonith:apcmaster): Started nps61068

3. From host 1 (ha1), press Ctrl+C to break out of crm_mon.

4. Turn on heartbeat and DRBD using the chkconfig:
ssh ha2 /sbin/chkconfig drbd on ** /sbin/chkconfig drbd on** ** ssh ha2 /sbin/chkconfig heartbeat on** ** /sbin/chkconfig heartbeat on**