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

Security Bulletin


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

Vulnerability Details

CVEID:   CVE-2020-10781
DESCRIPTION:   Linux Kernel is vulnerable to a denial of service. By continually reading the /sys/class/zram-control/hot_add file, a local authenticated attacker could exploit this vulnerability to cause the system OOM killer to activate, terminating userspace processes possibly making the system inoperable.
CVSS Base score: 5.5
CVSS Temporal Score: See: for the current score.
CVSS Vector: (CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)

Affected Products and Versions

Affected Product(s)Version(s)
IBM Netezza Host ManagementAll IBM Netezza Host Management starting




Workarounds and Mitigations

Mitigation of the reported CVE : CVE-2020-10781, blacklisting kernel module zram 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 zram is loaded in the hosts

lsmod | grep zram

[root@ nzhost1 ~]# lsmod | grep zram
zram 15996 0
lzo_decompress 2343 1 zram
lzo_compress 2368 1 zram

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

Step 2: Unload zram module

modprobe -rv zram

[root@nzhost1 ~]# modprobe -rv zram
rmmod /lib/modules/2.6.32-754.35.1.el6.x86_64/kernel/drivers/staging/zram/zram.ko
rmmod /lib/modules/2.6.32-754.35.1.el6.x86_64/kernel/lib/lzo/lzo_decompress.ko
rmmod /lib/modules/2.6.32-754.35.1.el6.x86_64/kernel/lib/lzo/lzo_compress.ko

Kernel module zram 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 blacklist line to a configuration file specific to the system configuration.

echo "blacklist zram" >> /etc/modprobe.d/local-blacklist.conf

example :
[root@nzhost1 ~]# echo "blacklist zram" >> /etc/modprobe.d/local-blacklist.conf
[root@nzhost1 ~]# cat /etc/modprobe.d/local-blacklist.conf | grep zram
blacklist zram

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 zram /bin/false" >> /etc/modprobe.d/local-blacklist.conf

[root@nzhost1 ~]# echo "install zram /bin/false" >> /etc/modprobe.d/local-blacklist.conf
[root@nzhost1 ~]# cat /etc/modprobe.d/local-blacklist.conf | grep zram
blacklist zram
install zram /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

[root@nzhost1 ~]# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak
[root@nzhost1 ~]# uname -r
[root@nzhost1 ~]# ll /boot/initramfs-2.6.32-754.35.1.el6.x86_64.img.08-17-105347.bak
-rw------- 1 root root 21881438 Aug 17 10:53 /boot/initramfs-2.6.32-754.35.1.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 zram -f

[root@nzhost1 ~]# dracut --omit-drivers zram -f
[root@nzhost1 ~]# lsinitrd /boot/initramfs-2.6.32-754.35.1.el6.x86_64.img | grep zram

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

sed --follow-symlinks -i '/\s*kernel \/vmlinuz/s/$/ zram.blacklist=1/' /etc/grub.conf

example :
[root@nzhost1 ~]# sed --follow-symlinks -i '/\s*kernel \/vmlinuz/s/$/ zram.blacklist=1/' /etc/grub.conf

Step 8: Blacklist the kernel module in kdump's configuration file.

echo "blacklist zram" >> /etc/kdump.conf

[root@nzhost1 ~]# echo "blacklist zram" >> /etc/kdump.conf
[root@nzhost1 ~]# cat /etc/kdump.conf | grep zram
blacklist zram

Note: Perform Step 9 if kexec-tools is installed and kdump is configured else continue with Step 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

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

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

[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

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Change History

21 Oct 2020: Initial Publication

*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.


According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES ""AS IS"" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY.

Document Location


[{"Business Unit":{"code":"BU004","label":"Hybrid Cloud"},"Product":{"code":"SSULQD","label":"PureData System for Analytics"},"Component":"","Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"All Versions","Edition":""}]

Document Information

Modified date:
21 October 2020