Chapter 11. Protecting systems against intrusive USB devices

Procedure

1. Install the usbguard package:

   # dnf install usbguard

2. Create an initial rule set:

   # usbguard generate-policy > /etc/usbguard/rules.conf

3. Start the usbguard daemon and ensure that it starts automatically on boot:

   # systemctl enable --now usbguard

Verification

1. Verify that the usbguard service is running:

   # systemctl status usbguard
   ● usbguard.service - USBGuard daemon
      Loaded: loaded (/usr/lib/systemd/system/usbguard.service; enabled; vendor preset: disabled)
      Active: active (running) since Thu 2019-11-07 09:44:07 CET; 3min 16s ago
        Docs: man:usbguard-daemon(8)
    Main PID: 6122 (usbguard-daemon)
       Tasks: 3 (limit: 11493)
      Memory: 1.2M
      CGroup: /system.slice/usbguard.service
              └─6122 /usr/sbin/usbguard-daemon -f -s -c /etc/usbguard/usbguard-daemon.conf
   
   Nov 07 09:44:06 localhost.localdomain systemd[1]: Starting USBGuard daemon...
   Nov 07 09:44:07 localhost.localdomain systemd[1]: Started USBGuard daemon.

2. List USB devices recognized by USBGuard:

   # usbguard list-devices
   4: allow id 1d6b:0002 serial "0000:02:00.0" name "xHCI Host Controller" hash...

Procedure

1. Determine the ID of the USB device by listing the devices recognized by USBGuard:

   # usbguard list-devices
   1: allow id 1d6b:0002 serial "0000:00:06.7" name "EHCI Host Controller" hash "JDOb0BiktYs2ct3mSQKopnOOV2h9MGYADwhT+oUtF2s=" parent-hash "4PHGcaDKWtPjKDwYpIRG722cB9SlGz9l9Iea93+Gt9c=" via-port "usb1" with-interface 09:00:00
   ...
   6: block id 1b1c:1ab1 serial "000024937962" name "Voyager" hash "CrXgiaWIf2bZAU+5WkzOE7y0rdSO82XMzubn7HDb95Q=" parent-hash "JDOb0BiktYs2ct3mSQKopnOOV2h9MGYADwhT+oUtF2s=" via-port "1-3" with-interface 08:06:50

2. Authorize a device to interact with the system:

   # usbguard allow-device <ID>

3. Deauthorize and remove a device:

   # usbguard reject-device <ID>

4. Deauthorize and retain a device:

   # usbguard block-device <ID>

Procedure

1. Configure SELinux to allow the usbguard daemon to write rules.

   1. Display the semanage Booleans relevant to usbguard.

      # semanage boolean -l | grep usbguard
      usbguard_daemon_write_conf     (off  ,  off)  Allow usbguard to daemon write conf
      usbguard_daemon_write_rules    (on   ,   on)  Allow usbguard to daemon write rules

   2. If the usbguard_daemon_write_rules Boolean is turned off, turn it on.

      # semanage boolean -m --on usbguard_daemon_write_rules

2. Determine the ID of the USB device by listing the devices recognized by USBGuard:

   # usbguard list-devices
   1: allow id 1d6b:0002 serial "0000:00:06.7" name "EHCI Host Controller" hash "JDOb0BiktYs2ct3mSQKopnOOV2h9MGYADwhT+oUtF2s=" parent-hash "4PHGcaDKWtPjKDwYpIRG722cB9SlGz9l9Iea93+Gt9c=" via-port "usb1" with-interface 09:00:00
   ...
   6: block id 1b1c:1ab1 serial "000024937962" name "Voyager" hash "CrXgiaWIf2bZAU+5WkzOE7y0rdSO82XMzubn7HDb95Q=" parent-hash "JDOb0BiktYs2ct3mSQKopnOOV2h9MGYADwhT+oUtF2s=" via-port "1-3" with-interface 08:06:50

3. Permanently authorize a device to interact with the system:

   # usbguard allow-device <ID> -p

4. Permanently deauthorize and remove a device:

   # usbguard reject-device <ID> -p

5. Permanently deauthorize and retain a device:

   # usbguard block-device <ID> -p

Verification

1. Check that the USBGuard rules include the changes you made.

   # usbguard list-rules

Procedure

1. Create a policy which authorizes the currently connected USB devices, and store the generated rules to the rules.conf file:

   # usbguard generate-policy --no-hashes > ./rules.conf

   The --no-hashes option does not generate hash attributes for devices. Avoid hash attributes in your configuration settings because they might not be persistent.

2. In the rules.conf file, add, remove, or edit the rules as required by using a text editor. For example, the following rule allows only devices with a single mass storage interface to interact with the system:

   allow with-interface equals { 08:*:* }

   See the usbguard-rules.conf(5) man page for a detailed rule-language description and more examples.

3. Install the updated policy:

   # install -m 0600 -o root -g root rules.conf /etc/usbguard/rules.conf

4. Restart the usbguard daemon to apply your changes:

   # systemctl restart usbguard

Verification

1. Check that your custom rules are in the active policy, for example:

   # usbguard list-rules
   …
   4: allow with-interface 08:*:*
   …

Procedure

1. Create a policy which authorizes the currently connected USB devices, and store the generated rules to a new .conf file, for example, <policy.conf>.

   # usbguard generate-policy --no-hashes > ./<policy.conf>

   The --no-hashes option does not generate hash attributes for devices. Avoid hash attributes in your configuration settings because they might not be persistent.

2. Open the <policy.conf> file with a text editor of your choice, and select the lines with the rules that you want to record, for example:

   …
   allow id 04f2:0833 serial "" name "USB Keyboard" via-port "7-2" with-interface { 03:01:01 03:00:00 } with-connect-type "unknown"
   …

3. Copy the selected lines into a separate .conf file.

   Note

   The two digits at the beginning of the file name specify the order in which the daemon reads the configuration files.

   For example, to copy the rules for your keyboards into a new .conf file:

   # grep "USB Keyboard" ./<policy.conf> > ./<10keyboards.conf>

4. Install the new policy to the /etc/usbguard/rules.d/ directory.

   # install -m 0600 -o root -g root <10keyboards.conf> /etc/usbguard/rules.d/<10keyboards.conf>

5. Move the rest of the lines to the main rules.conf file.

   # grep -v "USB Keyboard" ./policy.conf > ./rules.conf

6. Install the remaining rules.

   # install -m 0600 -o root -g root rules.conf /etc/usbguard/rules.conf

7. Restart the usbguard daemon to apply your changes.

   # systemctl restart usbguard

Verification

1. Display all active USBGuard rules.

   # usbguard list-rules
   …
   15: allow id 04f2:0833 serial "" name "USB Keyboard" hash "kxM/iddRe/WSCocgiuQlVs6Dn0VEza7KiHoDeTz0fyg=" parent-hash "2i6ZBJfTl5BakXF7Gba84/Cp1gslnNc1DM6vWQpie3s=" via-port "7-2" with-interface { 03:01:01 03:00:00 } with-connect-type "unknown"
   …

2. Display the contents of the rules.conf file and all the .conf files in the /etc/usbguard/rules.d/ directory.

   # cat /etc/usbguard/rules.conf /etc/usbguard/rules.d/*.conf

3. Verify that the active rules contain all the rules from the files and are in the correct order.

Procedure

1. Edit the /etc/usbguard/usbguard-daemon.conf file with the rules you want to add. For example, to allow all users in the wheel group to use the IPC interface, add this line:

   IPCAllowGroups=wheel

2. You can add users or groups also with the usbguard command. For example, the following command enables a user to have full access to the Devices and Exceptions sections and to list and modify the current policy:

   # usbguard add-user <user_name> --devices ALL --policy modify,list --exceptions ALL

   Replace <user_name> with the user name that should receive these permissions.

   You can remove the granted permissions for a user by using the usbguard remove-user <user_name> command.

3. Restart the usbguard daemon to apply your changes:

   # systemctl restart usbguard

Procedure

1. In the /etc/usbguard/usbguard-daemon.conf file, change the AuditBackend option from FileAudit to LinuxAudit:

   AuditBackend=LinuxAudit

2. Restart the usbguard daemon to apply the configuration change:

   # systemctl restart usbguard

Verification

1. Query the audit daemon log for a USB authorization event, for example:

   # ausearch -ts recent -m USER_DEVICE