Answer:
afile bfile cfile
Alice --x r-- ---
Bob r-- --x ---
Cathy r-- rw- rwx
The above table has - sign which represents the access that is not provided to the user. For example r-- in bfile means that Alice can only read bfile and two dash -- after this show that Alice cannot write and execute bfile.
If you want the access control matrix to show the owner, group and other permission too then you can alter this table as given in Explanation section.
Step-by-step explanation:
In the table
r = read
w = write
x = execute
There are three users:
Alice
Bob
Cathy
There are 3 files
afile owned by Alice
bfile owned by Bob
cfile owned by Cathy
First statement:
Alice owns the file afile, and Bob and Cathy can read it
This means Bob and Cathy has read (r) access to afile
afile -> [(Bob,r) (Cathy,r)]
Second statement:
Cathy can read and write Bob's file bfile:
bfile -> [Cathy, rw)]
This means Cathy has read write (rw) access to bfile
Third statement:
Alice can only read Bob's file bfile
bfile -> [(Alice, r)]
This means Alice has only read (r) access to bfile
Fourth statement:
Only Cathy can read and write her file cfile
cfile -> [(Cathy, rw)]
Fifth statement:
owner of each of these files can execute his/her file
afile -> [(Alice, x)]
bfile -> [(Bob, x)]
cfile -> [(Cathy, x)]
So this makes the matrix:
afile bfile cfile
Alice --xo r--- ----
Bob r--- --xo ----
Cathy r--- rw-- rwxo