6. (9 points) Protection Given the access matrix below, answer questions (a)-(c)

Question

6. (9 points) Protection Given the access matrix below, answer questions (a)-(c). Domains Objects 2 D3 D4 read* write* write control owner read owner 3 read* write write control 4 a. Can a process in domain Di grant read privileges for object F3 to a process in domain D2? Why or why not? b. Can a process in domain D3 revoke the write privileges of a process in domain Di for object F3? Why or why not? c. Can a process in domain D2 give read, write, and execute privileges for object F2 to a process in domain Ds? Why or why not?

Explanation / Answer

Solution :-

a) A process in domain D1 performs the WRITE operation on object F3 and this process can not grant the read previleges to another process for object F3 in domain D2. The reason is that if one process is performing WRITE operation on an object then it can not grant permission to another process to read this object due to consistency. If one process is performing WRITE operation and another process is read the same object then the inconsistent value of the object can be read so it violate the consistency condition. Therefore, one process in domain D1 can not grant the read previleges to another process for object F3 in domain D2.

b) By the given access control matrix one process in Domain D3 performs the read operation on the object F3. While this operation the process can revoke the WRITE privileges of the another process in Domain D1. Because when a process is performs read operation then it not allow other process to write the same object for the consistency. If a process reading some object and another process write the same object at the same time then the process can read the inconsistent value.

c) In the the domain D2 the process is the owner of the object F2. So the process can give the read, write and execute previleges to the other process in domain D3. If a process is owned an object in a domain then it can grant the privileges to another process in another domain for the samer objects. Therfore, a process in domain D2 can give the read, write and execute previleges to the other process in domain D3.

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