Amazon S3 bucket policy, what am I doing wrong?

Question

I used the Policy Generator to create a simple rule for my bucket; the rules should allow the following intended effect:

• root access
• limit access to given IAM user
• allow read-only access to everyone

To this purpose I wrote the following rule, but somethng didnt work as expected, and in particular, I have totally lost access to the bucket elements, was getting "Access Denied" in all cases, root included:

edit : with @jarmod answer I was able to set the intended functionality, however it trigger a warning, about the bucket being public, I do not see the difference respect having no policy, the bucket is still publicly accessible for read-only. What is the difference?

Answer 1

Perhaps you could do this as follows:

1. for all users, allow action s3:GetObject
2. for all users except root and your specific IAM user, deny all actions except s3:GetObject

You could do this with a policy something like this:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": "*",
            "Action": "s3:GetObject",
            "Resource": [
                "arn:aws:s3:::mybucket/*"
            ]
        },
        {
            "Effect": "Deny",
            "Principal": "*",
            "NotAction": "s3:GetObject",
            "Resource": [
                "arn:aws:s3:::mybucket/*"
            ],
            "Condition": {
                "StringNotLike": {
                    "aws:userId": [
                        "iam-userid-here",
                        "root-userid-here"
                    ]
                }
            }
        }
    ]
}

To get iam-userid-here , run aws iam list-users and retrieve the UserId for the IAM user.

Similarly, to get root-userid-here , simply retrieve the account number from the Arn of the previous aws iam list-users output. The root account userId is the AWS account number.

The IAM user indicated by iam-userid-here could then have an IAM policy allowing S3 access.