Chapter 9: Process Credentials

Exercise 9-1

My solution is in ex9_1.c.

To compile and link this solution, use sudo make ex9_1.

Exercise 9-1 (a)

To answer this part of the exercise, use ./ex9_1 a. The output should be similar to:

Initial UIDs:
Uid:	1000	0	0	0
UIDs after setuid(1001):
Uid:	1001	1001	1001	1001

Exercise 9-1 (b)

To answer this part of the exercise, use ./ex9_1 b. The output should be similar to:

Initial UIDs:
Uid:	1000	0	0	0
UIDs after setreuid(-1, 1001):
Uid:	1000	1001	1001	1001

Exercise 9-1 (c)

To answer this part of the exercise, use ./ex9_1 c. The output should be similar to:

Initial UIDs:
Uid:	1000	0	0	0
UIDs after seteuid(1001):
Uid:	1000	1001	0	1001

Exercise 9-1 (d)

To answer this part of the exercise, use ./ex9_1 d. The output should be similar to:

Initial UIDs:
Uid:	1000	0	0	0
UIDs after setfsuid(1001):
Uid:	1000	0	0	1001

Exercise 9-1 (e)

To answer this part of the exercise, use ./ex9_1 e. The output should be similar to:

Initial UIDs:
Uid:	1000	0	0	0
UIDs after setresuid(-1, 1001, 1002):
Uid:	1000	1001	1002	1001

Exercise 9-2

The answer is NO. The reason is given on p.168:

A process whose effective user ID is 0 (the user ID of root) has all of the privileges of the superuser. Such a process is referred to as a privileged process. ...

Exercise 9-3

My solution is in my_initgroups.c.

To run this solution:

Use make my_initgroups to compile and link this code.
Use sudo ./my_initgroups to execute this solution.

On successful execution, there is no output.

Exercise 9-4

My solution is in ex9_4.c.

To compile and link this solution, use sudo make ex9_4.

Exercise 9-4 (a)

To answer this part of the exercise, use ./ex9_4 a. The output should be similar to:

Initial UIDs:
Uid:    1000    1002    1002    1002
UIDs after seteuid(1000):
Uid:    1000    1000    1002    1000
UIDs after seteuid(1002):
Uid:    1000    1002    1002    1002

Exercise 9-4 (b)

To answer this part of the exercise, use ./ex9_4 b. The output should be similar to:

Initial UIDs:
Uid:    1000    1002    1002    1002
UIDs after setresuid(-1, 1000, 1000):
Uid:    1000    1000    1000    1000

Exercise 9-5

My solution is in ex9_4.c.

To compile and link this solution, use sudo make ex9_5.

Exercise 9-5 (a)

To answer this part of the exercise, use ./ex9_5 a. The output should be similar to:

Initial UIDs:
Uid:    1000    0       0       0
UIDs after seteuid(1000):
Uid:    1000    1000    0       1000
UIDs after seteuid(0):
Uid:    1000    0       0       0

Exercise 9-5 (b)

To answer this part of the exercise, use ./ex9_5 b. The output should be similar to:

Initial UIDs:
Uid:    1000    0       0       0
UIDs after setresuid(-1, 1000, 1000):
Uid:    1000    1000    1000    1000