Today I was told a tale by a Unix trainer a tale where the root password got leaked to the students, and one of the fellas removed the execute permission from /usr/bin/chmod itself. How do you recover chmod in this case and make it executable again? Let's say getting it from an external source or recompiling it is not a preferable option, is there some smart hack that can recover this chmod itself? Note that this happened a long time ago and I'm not looking for a solution for some current problem, just curious about what ways Unix provides us around such an issue. 
How to chmod without /usr/bin/chmod?
permissions;executable;chmod;system recovery