CGROUP means Control group.
In my case, usb-redir works fine while usb-host not.
https://www.kernel.org/doc/Documentation/cgroups/devices.txt

Just do it

# sed -i 's/devices /#devices /'
# reboot

Add fine control list

Review the rules to libvirt, and leave all the character device to it

# cgget libvirt
To remove "c" device
# echo c > /sys/fs/cgroup/libvirt/devices.deny
To add all the "c" devices
# echo "c *:* rwm" > /sys/fs/cgroup/libvirt/devices.allow

devices.deny/allow is something like end-point.

About hierarchy

A child will not have more permission than its parent.