Serverless AWS (Python) read from S3 : Access Denied

Question

I have a problem with getObject access from my lambda function (FrameWork serverless) to S3 service in AWS. here a sample of my code :

import boto3
import csv
def hello(event, context):
    s3 = boto3.resource('s3')
    bucket = s3.Bucket('myBucket')
    obj = bucket.Object(key='MOCK_DATA.csv')
    response = obj.get()
    lines = response['Body'].read().split()
    body = []
    for row in csv.DictReader(lines):
        body.append(row)
    return body

and in my serverless.yml, i gave to my lambda the full access to the bucket

  iamRoleStatements:
   - Effect: "Allow"
     Action:
       - "s3:*"
     Resource:
         - "arn:aws:s3:::myBucket"

but when i run the code, i receive the error:

START RequestId: a6c006b7-21e5-11e8-8193-c3378825927 Version: $LATEST
An error occurred (AccessDenied) when calling the GetObject operation: Access Denied: ClientError
Traceback (most recent call last):
  File "/var/task/handler.py", line 5, in hello
    response = obj.get()
  File "/var/runtime/boto3/resources/factory.py", line 520, in do_action
    response = action(self, *args, **kwargs)
  File "/var/runtime/boto3/resources/action.py", line 83, in __call__
    response = getattr(parent.meta.client, operation_name)(**params)
  File "/var/runtime/botocore/client.py", line 317, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "/var/runtime/botocore/client.py", line 615, in _make_api_call
    raise error_class(parsed_response, operation_name)
ClientError: An error occurred (AccessDenied) when calling the GetObject operation: Access Denied

do you have any idea why the boto3 dosent not take the permission from the iam role ? Because its working only if i declare boto3 with private and access keys:

s3 = boto3.resource('s3',aws_access_key_id='accesskey',aws_secret_access_key='privateKey')

Thank you in advance

Answer 1

For actions like s3:GetObject the resource should be arn:aws:s3:::myBucket/*. You are missing the trailing /*.