P1L5 Access Control

Question 1

Two parts to Access Control

Answer 1

1. Decide who should have access to certain resources. An access control policy.
2. Enforcement–only accesses defined by the access control policy are granted

Question 2

Access Control Matrix (ACM)

Answer 2

Rows correspond to sources of the request (users/subjects/groups)
Columns correspond to the resources that need protected

Question 3

Discretionary Access Control

Answer 3

Access is at the discretion of its owner. Owner can grant access to other users and also allow or not allow the other users to propagate this access.

Question 4

Flaw with DAC

Answer 4

Other user can copy to another file and then share with third party.

Question 5

Access Control List (ACL)

Answer 5

Columns for an object that define each users rights of that object.

Question 6

Capability List (C-List)

Answer 6

Rows for a user that define that user’s rights for each object.

Question 7

Where should ACL be stored?

Answer 7

• -In trusted part of system
• -Consists of access control entries
• -Should be stored along with other object meta-data
• -Checking requires traversal of the ACL

Question 8

Where should C-List be stored?

Answer 8

• -It is per user
• -A capability is an unforgeable reference/handle for a resource
• -User catalogue of capabilities defines what a certain user can access
• -Can be stored in objects/resources themselves

Question 9

ACL vs C-List

Answer 9

Efficiency–ACL are not as efficient as C-List
Accountability–Can be found easily in ACL. With C-List, each user’s catalog must be checked to see if access ok.
Revocation–Revoking access in ACL is easy

Most OS uses ACL

Question 10

How does OS implement ACL?

Answer 10

The OS keeps track of info about each file and its metadata, called an i-node. Open files are stored in the meta-data table. The file must be active.

Question 11

Role Based Access Control (RBAC)

Answer 11

The access rights are associated by roles/jobs. Users can have more than one role.

Question 12

RBAC benefits

Answer 12

• -Policy need not be updated when a certain person leaves
• -new employee should be able to activate the desired role.
• -Start with minimum access

SELinux supports RBAC

Question 13

Fail-safe defaults

Answer 13

Implies that when an access control policy is silent about access to a certain user, that access must be denied.