Question

1. [Linux permissions] Suppose that you are a superuser on a Linux system, and there is a file “/home/alice/foo”, which is owned by an ordinary user Alice. You need to give a permission to read a this file to an ordinary user Bob, but no one else (of course, you as superuser will be able to read it too). Explain how you will do it.

Note: You do not have to provide specific commands, just a short description will suffice.

2. [Limitations of integrity models] Suppose that some operating system (OS) implements the Biba integrity model in its original form (i.e., as described in the lectures). Also, supposed that there are only two integrity levels: “High” (for the system itself and the superuser) and “Low” for the ordinary users. Describe what issues the ordinary users may have with working on this OS?

Hint: Answer the following question: Will such the system run programs compiled by the ordinary users? (Explain your answer.) Specifically, what rule will be used to allow or deny it?

Answer 1

Answer 1)

In order to achieve this problem, at first we can create a group; add the user Bob to that particular group and then change the ownership of that file to the specific user and later at the end, we can give the user 'Bob' particular read permissions so that he can read it and me as being a superuser has access to that file too.

Commands to be used:

So to achieve this, we first create a group by using the command:

addgroup NewGroup

Then we add Bob of that group

usermod -G NewGroup Bob

Then we change the file permissions to allow read access to the members of the NewGroup group.

chgrp Bob /home/alice/foo

chmod 400 /home/alice/foo

This file will remain owned by super user, but be readable by Bob and not by the other users.

Note: Since we have given limited time to solve the question, So I have solved 1, please upload remaining separately.