Syntax of Fine-Grained Permissions Policies

Policy Structure

A fine-grained policy consists of a Version and a Statement. Each policy can have multiple statements.

Figure 1 Policy structure

Policy Syntax

In the navigation pane on the IAM console, click Policies and then click the name of a policy to view its details. The DWS ReadOnlyAccess policy is used as an example to describe the syntax of fine-grained policies.

Figure 2 Setting the policy

{
        "Version": "1.1",
        "Statement": [
                {
                        "Effect": "Allow",
                        "Action": [
                                "dws:*:get*",
                                "dws:*:list*",
                                "ecs:*:get*",
                                "ecs:*:list*",
                                "vpc:*:get*",
                                "vpc:*:list*",
                                "evs:*:get*",
                                "evs:*:list*",
                                "mrs:*:get*",
                                "bss:*:list*",
                                "bss:*:get*"
                        ]
                }
        ]
}

• Version: Distinguishes between role-based access control (RBAC) and fine-grained policies.
  • 1.0: RBAC policies. An RBAC policy consists of permissions for an entire service. Users in a group with such a policy assigned are granted all of the permissions required for that service.
  • 1.1: Fine-grained policies. A fine-grained policy consists of API-based permissions for operations on specific resource types. Fine-grained policies, as the name suggests, allow for more fine-grained control than RBAC policies. Users granted permissions of such a policy can only perform specific operations on the corresponding service. Fine-grained policies include system and custom policies.
• Statement: Permissions defined by a policy, including Effect and Action.
  • Effect

    The valid values for Effect are Allow and Deny. System policies contain only Allow statements. For custom policies containing both Allow and Deny statements, the Deny statements take precedence.

  • Action

    Permissions in the format of Service name:Resource type:Operation. A policy can contain one or more permissions. The wildcard (*) is allowed to indicate all of the services, resource types, or operations depending on its location in the action.

    Example: dws:cluster:create, permissions for create data warehouse clusters.

Multi-Action Policy

A custom policy can contain actions of multiple services that are all of the global or project-level type. The following is a policy with multiple statements:

{ 
    "Version": "1.1", 
    "Statement": [ 
        { 
            "Effect": "Allow", 
            "Action": [ 
                "ecs:cloudServers:resize", 
                "ecs:cloudServers:delete", 
                "ecs:cloudServers:rebuild" 
            ] 
        }, 
        { 
            "Effect": "Allow", 
            "Action": [ 
                "dws:*:get*",
                "dws:*:list*",
                "dws:cluster:create" 
            ] 
        } 
    ] 
}

Deny Policy

A deny policy must be used in conjunction with other policies to take effect. If the permissions assigned to a user contain both Allow and Deny actions, the Deny actions take precedence over the Allow actions.

Authentication Logic

If a user is granted permissions of multiple policies or of only one policy containing both Allow and Deny statements, then authentication starts from the Deny statements. The following figure shows the authentication logic for resource access.

Figure 3 Authentication logic

The actions in each policy bear the OR relationship.

1. A user accesses the system and makes an operation request.
2. The system evaluates all the permissions policies assigned to the user.
3. In these policies, the system looks for explicit deny permissions. If the system finds an explicit deny that applies, it returns a decision of Deny, and the authentication ends.
4. If no explicit deny is found, the system looks for allow permissions that would apply to the request. If the system finds an explicit allow permission that applies, it returns a decision of Allow, and the authentication ends.
5. If no explicit allow permission is found, IAM returns a decision of Deny, and the authentication ends.