Kernel is used by IBM Netezza Host Management. This bulletin provides mitigation for the reported CVE.
CVEID:CVE-2021-3715
**DESCRIPTION:**Linux Kernel could allow a local authenticated attacker to gain elevated privileges on the system, caused by a use-after-free in route4_change() in net/sched/cls_route.c. By sending a specially-crafted request, an attacker could exploit this vulnerability to escalate privileges.
CVSS Base score: 7.8
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/208836 for the current score.
CVSS Vector: (CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
Affected Product(s) | Version(s) |
---|---|
IBM Netezza Host Management | All IBM Netezza Host Management starting 5.4.9.0 |
None
Mitigation of the reported CVEs : CVE-2021-3715 blocklisting kernel modulecls_route to prevent them 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 kernel modules cls_route is loaded in the hosts
lsmod | grep cls_route
example:
lsmod | grep cls_route
cls_route 6515 0
Note: No output onStep 1for any module indicates, that module is not loaded hence skipStep 2for that module, and proceed withStep 3
Step 2: Unload kernel module cls_route if it is loaded
modprobe -rv cls_route
example:
[root@nzhost1 ~]# modprobe -rv cls_route
rmmod /lib/modules/2.6.32-754.41.2.el6.x86_64/kernel/net/sched/cls_route.ko
Kernel modules and their 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 modules from being loaded directly you add the blocklist line to a configuration file specific to the system configuration.
echo “blocklist cls_route” >> /etc/modprobe.d/local-blocklist.conf
example :
[root@nzhost1 ~]# echo “blocklist cls_route” >> /etc/modprobe.d/local-blocklist.conf
[root@nzhost1 ~]# cat /etc/modprobe.d/local-blocklist.conf | grep cls_route
blocklist cls_route
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 cls_route /bin/false” >> /etc/modprobe.d/local-blocklist.conf
example:
[root@nzhost1 ~]# echo “install cls_route /bin/false” >> /etc/modprobe.d/local-blocklist.conf
[root@nzhost1 ~]# cat /etc/modprobe.d/local-blocklist.conf | grep cls_route
blocklist cls_route
install cls_route /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
2.6.32-754.41.2.el6.x86_64
[root@nzhost1 ~]# ll /boot/initramfs-2.6.32-754.41.2.el6.x86_64.img.10-01-041951.bak
-rw------- 1 root root 22126152 Sep 17 03:52 /boot/initramfs-2.6.32-754.41.2.el6.x86_64.img.10-01-041951.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 cls_route -f
example:
[root@nzhost1 ~]# dracut --omit-drivers cls_route -f
[root@nzhost1 ~]# lsinitrd /boot/initramfs-2.6.32-754.41.2.el6.x86_64.img | grep cls_route
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/$/ cls_route.blocklist=1/’ /etc/grub.conf
example :
[root@nzhost1 ~]# sed --follow-symlinks -i ‘/\s*kernel /vmlinuz/s/$/ cls_route.blocklist=1/’ /etc/grub.conf
Step 8: blocklist the kernel module in kdump’s configuration file.
echo “blocklist cls_route” >> /etc/kdump.conf
example:
[root@nzhost1 ~]# echo “blocklist cls_route” >> /etc/kdump.conf
[root@nzhost1 ~]# cat /etc/kdump.conf | grep cls_route
blocklist cls_route
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**