linux - Can't login as root after changing permissions of /usr/bin

I changed the folder permissions of /usr/bin to 777. Now when I login to root user it shows "incorrect password".

Now I'm not able to do anything on this PC. How can I revert the permissions of /usr/bin without a terminal? I think I need to change them to 751.

I can login via CtrlAltF1, but not into root.

Answer

Boot off the install CD but dont install, mount the folder, and change the permissions back.