"CreateBucket operation: Access Denied..." when calling Session.default_bucket() #1935

Describe the bug
Calling default_bucket() on a sagemaker.session.Session object, when specifying a custom default_bucket, raises:

• ClientError: An error occurred (AccessDenied) when calling the CreateBucket operation: Access Denied

when the default bucket already exists

possibly related to #1174

To reproduce

bucket = "bucket-that-exists"
boto_session = boto3.session.Session(region_name="ap-southeast-2")
sm_session = sagemaker.Session(boto_session, default_bucket=bucket)

sm_session.default_bucket()

• I added a command to L387 of src/sagemaker/session.py to display the number of keys in the bucket to verify that the intended default bucket is accessed:

• bucket.creation_date returns None even when the bucket exists
• could be tricky to reproduce, the execution role has limited permissions (can only list, upload/download, to/from this bucket), for example aws s3 ls is denied, let me know if there is any more info you need

Expected behavior
sm_session.default_bucket() should return the same default bucket name specified when constructing the sagemaker session object.

Screenshots or logs
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System information
A description of your system. Please provide:

• SageMaker Python SDK version: 2.12.0 (boto3 1.14.60)
• Python version: Python 3.6.10 :: Anaconda, Inc.