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Alloy Access Control
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| one sig Person { | |
| roles: set Role | |
| } | |
| sig Role {} | |
| sig Resource { | |
| , access: set Person + Role | |
| , parent: lone Resource | |
| } | |
| fact "No cycles" { | |
| no r: Resource | | |
| r in r.^parent | |
| } | |
| pred can_access[p: Person, r: Resource] { | |
| direct_access[p, r] or role_access[p, r] | |
| } | |
| pred direct_access[p: Person, r: Resource] { | |
| p in (r.access + r.parent.access) | |
| } | |
| pred role_access[p: Person, r: Resource] { | |
| some role: p.roles | | |
| role in (r.access + r.parent.access) | |
| } | |
| some_direct_access: run {some p: Person, r: Resource | direct_access[p, r]} | |
| some_role_access: run {some p: Person, r: Resource | role_access[p, r]} | |
| assert access_rules { | |
| all p: Person, r: Resource | | |
| can_access[p, r] => direct_access[p, r] or role_access[p, r] | |
| } | |
| //if you can access the parent, you can access all its children | |
| assert parent_implies_child { | |
| all p: Person, r: Resource | | |
| can_access[p, r] => all child: parent.r | can_access[p, child] | |
| } | |
| check access_rules | |
| check parent_implies_child |
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A counterexample to
parent_implies_child, showing it's possible to access a parent without being able to access that parent's child: