I'm facing a challenge with an IAM role named "foo" that has a policy allowing s3:* across all resources, which I can't change. I need to limit its permissions to only s3:ListBucket and s3:GetObject for a specific path in the bucket (/1/2/3/4). My trial and error suggests that to enforce this restriction, I must explicitly list actions like s3:Put* in a Deny statement, which seems illogical to me. Am I missing something here?
3 Answers
Just a heads-up, if both the IAM role and bucket are within the same account, permissions can come from either the bucket policy or your IAM policy. Even if you can't change the role policy, you might consider creating a bucket policy that includes explicit denies, as you'd need those to block any unwanted permissions effectively. Just make sure to test your denies thoroughly to avoid accidentally restricting valid actions. Here's a basic structure you might use for your bucket policy, which includes denies for actions you don't want to allow.
Keep in mind that if you're truly unable to modify the IAM policy, you could explore options like boundary policies, Service Control Policies (SCPs), or Resource Control Policies (RCPs) to manage permissions. It's a more complex route, but worth considering if you're stuck with that broad IAM policy.
It sounds like you're trying to impose restrictions on a very permissive IAM role, which can be tricky. Ideally, you should be able to create a more specific policy that only grants s3:ListBucket and s3:GetObject permissions for those prefixes. Adding denies might become messy if you can't adjust the higher-level policy. If that policy can't be changed for some odd business reasons, you're left with a convoluted setup of denies to restrict access, which I agree is less than ideal.
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