What kind of answer is this textbook question looking for in access control model?

Question

I'm going over a practice question and I have trouble understanding what it's asking.

Draw an access control matrix for the following Linux file system. Group A1 contains S1 and S3, group A2 contains S3. Only show users as subjects.

So is the answer to the question supposed to look like

What is the answer to the question?

Answer 1

So to summarize:

• Group 1 contains S1 and S3
• Group 2 contains S3

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Then it is pretty simple, if you know that in Linux, the 9-character permission scheme can be divided as follows:

• First three characters are the owner's permissions
• Next three characters are the group's permissions
• Last three characters are the permissions of all of the other users

Then, following the assumption I made, you know the following:

Permissions    a     b    c
S1             rwx   -    rwx (S1 is member of group 1: group 1 has rwx permission)
S2             rwx   rwx  - (due to explicit owner deny on the last row of the table)
S3             rwx   -    rwx (due to group inherited allow permission of group 1)