Operating Systems & Privileges Flashcards
TCB has 3 requirements. Which of the following is not one of the requirements?
a. Complete mediation between the os and hardware resources and applications. In addition, the os must make sure the applications have the necessary authorizations
b. Os must be tamper proof
c. Os must be able to go from user to kernel mode without errors
d. OS must be correct and ensure the resources are used properly
c. Os must be able to go from user to kernel mode without errors
What is a file INODE?
a. An INODE is part of a linked list design for memory storage
b. An INODE is a special directory only to be seen by root
c. An INODE is a control structure that contains information needed by the OS for a file
d. A user permission for a given user group
c. An INODE is a control structure that contains information needed by the OS for a file
In a DBMS, what happens in the following scenario assuming each of these steps are followed sequentially? Assume the grant option is always used.
Ann grants access right to Bob. Ann grants access right to Chris. Bob grants access right to David. David grants access right to Ellen. Chris grants access right to David. David grants access right to Frank. Ellen grants access right to Jim. Bob revokes access right from David.
A. David no longer has the access right.
B. David, Ellen, Frank, and Jim no longer have the access right.
C. David, Ellen, and Jim no longer have the access right.
D. Ellen and Jim no longer have the access right.
Answer D
In most implementations, the revocation is cascaded. In this case, since Chris also granted access to David, then David won’t have his access revoked, but Ellen since her access was granted after Bob (and before Chris) had granted access to David. Frank’s access remains since David granted access to him after Chris granted access to David. In general terms, if the access right would exist anyway, then the revoke is not cascaded.
Source: Book pg. 163
Most of the operating systems use _____. In addition to this ____ is more efficient for finding access rights
A.) ACLs & C-List
B.) TCB & Chmod
C.) Revocation & ACL
D.) C-List & ACLs
Answer A
Source: Lecture 5 notes
An attacker exploits a program and launches a shell. With which privilege level are the instructions executed?
A. User
B. Root
C. System
D. Host Program
Answer D
The attacker’s shellcode is run with the privileges of the exploited program. Source: L2 “Shellcode Privileges”
T/F: When an applicant applies to a registration authority (RA) to become a subscriber of a credential service provider (CSP), the RA is responsible for issuing an electronic credential
Answer False
The CSP issues the electronic credential to the subscriber.
Source: Book pg. 65
Which of the following is not a common physical characteristic used for biometric authentication?
A. Fingerprints B. Hair color C. Voice D. Signature E. Iris F. All of the above G. None of the above
Answer B
Facial characteristics are used, but that does not include a person’s hair color.
Source: Book pg. 88
What is the purpose of a nonce used in a challenge-response password protocol?
A. Prevent the hash of the password from being transmitted directly. B. Eliminate need for host to store user’s password. C. Defend against a replay attack. D. All of the above E. A & B F. B & C G. A & C H. None of the above.
Answer G
The nonce is used in generating a hash which the client sends to the server. The nonce is also randomly generated at the start of the session, so if an attacker tried a replay attack, they have a different nonce and thus would fail.
Source: Book pg. 93-94
Which of the following is NOT true with regards to operating systems?
a. We use operating systems to manage hardware
b. Operating systems such as Linux, Windows, and macOS handles access of low-level hardware resources
c. Operating systems can be a hinderance to users which is why they’re generally optional on most modern CPUs
d. Browsers, Word processors, and the like sit on top of the OS
Correct Answer: C
Without controlled hardware access in an operating system:
a. It would be easy for one application to overwrite data in another
b. One application could hog the CPU
c. Application running would not be cohesive
d. A & C
e. All of the above
Correct Answer: E
Which of the following are true about process isolation within operating systems?
a. All of the different applications are running on the same system and sharing the same physical resources
b. From the perspective of the application, it “thinks” it has complete and exclusive access to the entire hardware
c. The operating system does keep the applications aware of each other to avoid bandwidth hogging
d. A & B
e. All of the above
Correct Answer: D
C is incorrect - processes need not necessarily be aware of other processes
A system call allows application code to gain access to functionality implemented by the OS. A system call is often called a protected procedure call. The cost of a system call is:
a. The same as a regular call
b. Higher than a regular call
Correct Answer: B
A system call requires control transfer from the calling process into the OS, which then must perform authentication / authorization checks before granting access and transferring control back. This is more costly than a regular call, which incurs none of this overhead.
Complete mediation ensures that the OS cannot be bypassed when accessing a protected resource. How does the OS know who is making the request for the resource?
a. Process runs on behalf of a user who must have previously logged in
b. Requested resource allows us to find out who must be requesting it
c. All of the above
Correct Answer: A
Processes run on behalf of users. Users must login to the system to run applications/processes.
We have established that an OS must be tamper-proof. But how does an OS maintain this?
a. Modern CPUs default to privilege mode “0” which is least-privilege
b. CPUs have different execution modes or execution rings which have varying privileges
c. CPUs have different execution modes (least privilege set to “0”) and higher privileges are granted as you move up to higher modes
d. A & C
e. All of the above
Correct Answer: B
“0” mode is most privileged. Privileges are revoked as you move higher in execution modes or rings.
System calls are used to transfer control between user and system code. In the x86 architecture, we have explicit instructions to cross this system boundary. They are:
a. _enter & _exit
b. sys_enter & sys_exit
c. sysenter & sysexit
d. None of the above
Correct Answer: C
