S3 Private Bucket - amazon-web-services

Question

I'm trying to create a private S3 bucket with limited access. I only want myself as a user and an EC2 role to have access to the bucket. The purpose of the bucket is to store encrypted SSH keys that will be copied onto machines in an autoscaling group. Right now, when I run aws sync against the bucket, here is the output:
cogility#ip-10-10-200-113:~$ aws s3 sync s3://sshfolder.companycloud.com/cogility /home/cogility/.ssh
download failed: s3://sshfolder.companycloud.com/cogility/id_rsa to ../cogility/.ssh/id_rsa An error occurred (AccessDenied) when calling the GetObject operation: Access Denied
download failed: s3://sshfolder.companycloud.com/cogility/id_rsa.pub to ../cogility/.ssh/id_rsa.pub An error occurred (AccessDenied) when calling the GetObject operation: Access Denied
I create the EC2 instances with an EC2 role with the following permissions:
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "",
"Effect": "Allow",
"Action": [
"kms:List*",
"kms:Get*",
"kms:Describe*"
],
"Resource": "arn:aws:kms:us-west-2:0000000000:key/kms-id-01234567890"
},
{
"Sid": "",
"Effect": "Allow",
"Action": "s3:*",
"Resource": [
"arn:aws:s3:::sshfolder.companycloud.com/*",
"arn:aws:s3:::sshfolder.companycloud.com"
]
},
{
"Sid": "",
"Effect": "Allow",
"Action": [
"elasticloadbalancing:*",
"ec2:*",
"cloudwatch:*",
"autoscaling:*"
],
"Resource": "*"
},
{
"Sid": "",
"Effect": "Allow",
"Action": [
"lambda:List*",
"lambda:Invoke*",
"lambda:Get*"
],
"Resource": "*"
}
]
}
And here is the bucket policy:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Deny",
"Principal": "*",
"Action": "s3:*",
"Resource": [
"arn:aws:s3:::sshfolder.companycloud.com",
"arn:aws:s3:::sshfolder.companycloud.com/*"
],
"Condition": {
"StringNotLike": {
"aws:userId": [
"AROAXXXXXXXXXXXXXXXXX", <-- autoscaling-ec2-role user id
"AROAXXXXXXXXXXXXXXXXX",
"AIDAXXXXXXXXXXXXXXXXX",
"AIDAXXXXXXXXXXXXXXXXX"
],
"aws:sourceVpce": "vpce-abc82480d"
},
"ArnNotLike": {
"aws:SourceArn": "arn:aws:sts::000000000000:assumed-role/autoscaling-ec2-role/"
}
}
},
{
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::000000000000:root"
},
"Action": "s3:*",
"Resource": [
"arn:aws:s3:::sshfolder.companycloud.com",
"arn:aws:s3:::sshfolder.companycloud.com/*"
]
}
]
}
Any idea why I'm not able to access the S3 bucket from my EC2 instance?

Answer 1

Amazon S3 buckets are private by default. Therefore, one approach would be:
Do not use a Bucket Policy
Add permissions to your IAM User and the IAM Role to access the bucket
Alternatively:
Use a Bucket Policy to grant access to the IAM User and IAM Role
Both would be sufficient to meet your needs.
However, if you are further paranoid that somebody might accidentally grant access to the bucket (eg with s3:* and a principal of *), then your approach of explicitly Denying access to anyone other than that User & Role is a good approach.

Answer 2

deny trumps allow in your bucket policy. You need to use not principal to achieve this.
"Statement": [
{
"Effect": "Deny",
"NotPrincipal": {
"AWS": "arn:aws:iam::000000000000:root"
},
"Action": "s3:*",
"Resource": [
"arn:aws:s3:::sshfolder.companycloud.com",
"arn:aws:s3:::sshfolder.companycloud.com/*"
],
"Condition": {
"StringNotLike": {
"aws:userId": [
"AROAXXXXXXXXXXXXXXXXX", <-- autoscaling-ec2-role user id
"AROAXXXXXXXXXXXXXXXXX",
"AIDAXXXXXXXXXXXXXXXXX",
"AIDAXXXXXXXXXXXXXXXXX"
],
"aws:sourceVpce": "vpce-abc82480d"
},
"ArnNotLike": {
"aws:SourceArn": "arn:aws:sts::000000000000:assumed-role/autoscaling-ec2-role/"
}
}
}
]
It just inverts the principal element. You can similarly use NotAction and NotResource as appropriate. You could do away with your conditionals altogether and just use NotPrincipal for all of them, it's generally better practice than conditionals.
Here is a resource on it: https://aws.amazon.com/blogs/security/how-to-create-a-policy-that-whitelists-access-to-sensitive-amazon-s3-buckets/