Deny GetObject for all S3 bucket-CodePudding

I want to create an IAM role with a read-only policy (arn:aws:iam::aws:policy/ReadOnlyAccess).

In order to prevent access to all objects on all buckets, I added a Deny section in Cloudformation template:

  ReadOnlyAccessRole:
    Type: AWS::IAM::Role
    Properties:
      Path: /
      RoleName: read-only-role
      AssumeRolePolicyDocument:
        Version: 2012-10-17
        Statement:
          - Effect: Allow
            Principal:
              AWS: !Ref AwsAccount
            Action: sts:AssumeRole
      
          - Effect: Deny
            Sid: DenyS3GetObject
            Action: s3:GetObject
            Resource: "arn:aws:s3:::/*"

      ManagedPolicyArns:
        - "arn:aws:iam::aws:policy/ReadOnlyAccess"

I get a "MalformedPolicyDocument" error in the Deny section (Resource).

I already tested these options :

Resource: "*"
Resource: "arn:aws:s3:::/*"
Resource: "arn:aws:s3:::prefix-bucket*"

Do you have any idea about this syntax error ?

EDIT :

Error from Cloudformation :

Blockquote Has prohibited field Resource (Service: AmazonIdentityManagement; Status Code: 400; Error Code: MalformedPolicyDocument; Request ID: ......; Proxy: null) enter code here

CodePudding user response：

You seem to be missing the Policies section.

Try something like this:

AWSTemplateFormatVersion: "2010-09-09"

Resources:
  MyTestRole:
    Type: AWS::IAM::Role
    Properties:
      RoleName: read-only-role
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
          - Effect: Allow
            Principal:
              AWS: !Ref AwsAccount
            Action: sts:AssumeRole
      Policies:
        - PolicyName: EmbeddedInlinePolicy
          PolicyDocument:
            Version: 2012-10-17
            Statement:
              - Effect: Deny
                Action: s3:GetObject
                Resource: '*'
      ManagedPolicyArns: 
        - arn:aws:iam::aws:policy/ReadOnlyAccess