How to Block USB Storage Devices in Linux Servers
In order to protect sensitive data extraction from servers by users who have physical access to machines, it’s a best practice to disable all USB storage support in Linux kernel.
In order to disable USB storage support, we first need to identify if the storage driver is loaded into Linux kernel and the name of the driver (module) responsible with storage driver.
Run the lsmod command to list all loaded kernel drivers and filter the output via grep command with the search string “usb_storage”.
# lsmod | grep usb_storage
From lsmod command, we can see that the sub_storage module is in use by UAS module. Next, unload both USB storage modules from kernel and verify if the removal has been successfully completed, by issuing the below commands.
# modprobe -r usb_storage # modprobe -r uas # lsmod | grep usb
Next, list the content of the current runtime kernel usb storage modules directory by issuing the below command and identify the usb-storage driver name. Usually this module should be named usb-storage.ko.xz or usb-storage.ko.
# ls /lib/modules/`uname -r`/kernel/drivers/usb/storage/
In order to block USB storage module form loading into kernel, change directory to kernel usb storage modules path and rename the usb-storage.ko.xz module to usb-storage.ko.xz.blacklist, by issuing the below commands.
# cd /lib/modules/`uname -r`/kernel/drivers/usb/storage/ # ls # mv usb-storage.ko.xz usb-storage.ko.xz.blacklist
In Debian based Linux distributions, issue the below commands to block usb-storage module from loading into Linux kernel.
# cd /lib/modules/`uname -r`/kernel/drivers/usb/storage/ # ls # mv usb-storage.ko usb-storage.ko.blacklist
Now, whenever you plug-in a USB storage device, the kernel will be fail to load the storage device driver intro kernel. To revert changes, just rename the usb module blacklisted back to its old name.
# cd /lib/modules/`uname -r`/kernel/drivers/usb/storage/ # mv usb-storage.ko.xz.blacklist usb-storage.ko.xz
However, this method applies only to runtime kernel modules. In case you want to blacklist USB storage modules form all available kernels in the system, enter each kernel module directory version path and rename the usb-storage.ko.xz to usb-storage.ko.xz.blacklist.