Q. In some systems a subdirectory is able to be read and written by an authorized user just as ordinary files can be.
a. Explain the protection problems that could arise.
b. Suggest a scheme for dealing with every of the protection problems you named in part a.
Answer:
a. One piece of information reserved in a directory entry is file location. If a user could alter this location then he could access other files defeating the access-protection scheme.
b. Don't allow the user to directly write onto the subdirectory. Rather offer system operations to do so.