How to blacklist or disable USB module in Red Hat 7

To improve security in our environment many times we have to blacklist certain modules from getting loaded in our setup to avoid any security leak.

The provided procedure is tested with Red Hat Enterprise Linux 7

Before starting with the blacklisting let us validate our usb module is properly loaded

# lsmod | grep -i usb
usb_storage            66762  0

So the module looks to be loaded just fine and the below command will show us any usb device which is mounted currently on the blade

# lsscsi
[0:0:0:0]    storage HP       P244br           4.52  -
[0:1:0:0]    disk    HP       LOGICAL VOLUME   4.52  /dev/sda
[1:0:0:0]    cd/dvd  HP       Virtual DVD-ROM        /dev/sr0

 

Lets start blacklisting this module

Below file must be used to blacklist any module

/etc/modprobe.d/local-blacklist.conf

The syntax to be used here is

blacklist <module name>

For eg to blacklist usb module:

# vim /etc/modprobe.d/local-blacklist.conf
blacklist usb-storage

save and exit the file.

Now the above syntax used will blacklist a module only if it is not a part of any dependency.

For eg. firewire module is a dependency for network drivers like be2net so if I blacklist firewire module but still since it is needed by be2net driver, the be2net will activate the blacklisted module during system startup

To avoid this append below line. Here for eg I used firewire module, the same can be replaced with usb-storage.ko

# vim /etc/modprobe.d/local-blacklist.conf
blacklist firewire
install firewire /bin/false

save the file and exit

Next you must rebuild the initramfs, this is needed to keep your changes persistent across reboot

IMPORTANT NOTE : Take backup of your existing initramfs just in case the new initramfs fails or has any issue
# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.before_update.bak

Next run below command to rebuild the initramfs

# dracut -v -f

Next proceed with the reboot of the node but in case you plan to reboot the node later, doing so the active session will still have the usb module enabled so to disable the usb module from the active session

 

Disable usb module from the current session

# rmmod usb-storage.ko

This will remove the us module from the kernel

OR

usb module can also be removed using

# modprobe -r usb-storage.ko

Now regenerate your kernel list of dependencies and the loaded modules.

# depmod -a

This will probe all the modules

Now you can validate if the usb module is still loaded on your system

# lsmod | grep -i usb_storage

The output should give you nothing so your module is successfully removed and blacklisted

I hope the article was helpful

 

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