The safety problem Flashcards
What is the definition of the safety problem?
Any computer system is safe with respect to the right r if the system cannot leak r.
What is right leakage?
Right leakage is simply a phenomenon in which a given right r is added to an element in the ACM not already having the right r.
Let S1 and S2 be subjects and O be an object. S1 can read O whilst S2 has no rights over O. This is the original state of the ACM. A leakage would occur if a new right was given to any of the subjects, say S2 is given write permission. Then the system would leak the right w.
Is right leakage always bad?
No, leakage is not always bad. Whenever a subject has a legitimate need for a right it does not hold, granting that right is will constitute leakage even if it is of no harm to the system.
What is the fundamental safety question?
Is there a generic algorithm that allows us to determine whether a given protection state Q0 is safe with respect to a given right r.
The answer to the question is no, unless the system is mono-operational.