IAM deny policies in GCP - Mini Project: Build & Apply

IAM Deny Policies in GCP

📖 Scenario: You are managing access to a Google Cloud project. You want to create a policy that explicitly denies certain users from performing specific actions, even if other permissions allow them.

🎯 Goal: Build an IAM deny policy that blocks the storage.buckets.delete permission for a specific user on a Cloud Storage bucket.

📋 What You'll Learn

Create a deny policy binding for a user

Specify the permission storage.buckets.delete to deny

Attach the deny policy to a Cloud Storage bucket resource

💡 Why This Matters

🌍 Real World

IAM deny policies help prevent accidental or malicious access by explicitly blocking permissions, even if other roles grant them.

💼 Career

Cloud engineers and security specialists use deny policies to enforce strict access controls and protect critical resources.

1

Create the initial deny policy structure

Create a dictionary called deny_policy with a key denyRules that holds an empty list.

GCP

deny_policy = {
    "denyRules": []
}
# Your code here

Hint

Start by making a dictionary with a key named denyRules that is an empty list.

2

Add a deny rule for the delete permission

Add a dictionary to deny_policy["denyRules"] with keys deniedPrincipals set to ["user:[e-mail]"] and deniedPermissions set to ["storage.buckets.delete"].

GCP

deny_policy = {
    "denyRules": [
        # Add deny rule here
    ]
}
# Your code here

Hint

Add a deny rule that denies the user [e-mail] the permission to delete storage buckets.

3

Specify the resource to attach the deny policy

Create a variable called resource and set it to the string "//storage.googleapis.com/projects/_/buckets/my-bucket" representing the Cloud Storage bucket resource.

GCP

deny_policy = {
    "denyRules": [
        {
            "deniedPrincipals": ["user:[e-mail]"],
            "deniedPermissions": ["storage.buckets.delete"]
        }
    ]
}

# Your code here

Hint

Set the resource variable to the full resource name of the bucket.

4

Attach the deny policy to the resource

Create a dictionary called policy_request with keys resource set to the resource variable and policy set to the deny_policy dictionary.

GCP

deny_policy = {
    "denyRules": [
        {
            "deniedPrincipals": ["user:[e-mail]"],
            "deniedPermissions": ["storage.buckets.delete"]
        }
    ]
}

resource = "//storage.googleapis.com/projects/_/buckets/my-bucket"

# Your code here

Hint

Combine the resource and deny policy into a single request dictionary.

Practice

1. What is the main purpose of an IAM deny policy in Google Cloud?

easy

A. To monitor user activities without changing permissions

B. To grant additional permissions to users or groups

C. To explicitly block certain permissions even if other policies allow them

D. To automatically delete unused resources

Solution

1. Step 1: Understand IAM deny policy function and compare with other policy types

   An IAM deny policy explicitly blocks permissions, overriding any allow policies. Unlike allow policies that grant access, deny policies prevent actions even if allowed elsewhere.

2. Final Answer:

   To explicitly block certain permissions even if other policies allow them -> Option C

3. Quick Check:

   IAM deny policy blocks permissions [OK]

Hint: Deny policies block permissions regardless of other allows [OK]

Common Mistakes:

• Confusing deny policies with allow policies
• Thinking deny policies grant permissions
• Assuming deny policies only monitor actions

2. Which of the following is the correct way to specify a deny rule in an IAM policy JSON snippet?

easy

A. "denyRules": [{"deniedPermissions": ["storage.buckets.delete"]}]

B. "allowRules": [{"allowedPermissions": ["storage.buckets.delete"]}]

C. "denyRules": [{"allowedPermissions": ["storage.buckets.delete"]}]

D. "denyRules": [{"deniedPermissions": "storage.buckets.delete"}]

Solution

1. Step 1: Identify correct deny rule syntax and check each option

   Deny rules use "denyRules" with "deniedPermissions" as a list of strings. "denyRules": [{"deniedPermissions": ["storage.buckets.delete"]}] correctly uses a list for "deniedPermissions". "allowRules": [{"allowedPermissions": ["storage.buckets.delete"]}] uses allowRules, which is incorrect. "denyRules": [{"allowedPermissions": ["storage.buckets.delete"]}] mixes denyRules with allowedPermissions, which is invalid. "denyRules": [{"deniedPermissions": "storage.buckets.delete"}] uses a string instead of a list, which is invalid.

2. Final Answer:

   "denyRules": [{"deniedPermissions": ["storage.buckets.delete"]}] -> Option A

3. Quick Check:

   Deny rules need deniedPermissions as list [OK]

Hint: Deny permissions must be in a list under deniedPermissions [OK]

Common Mistakes:

• Using allowRules instead of denyRules
• Providing deniedPermissions as a string instead of list
• Mixing allowedPermissions inside denyRules

3. Given this deny policy snippet:

{"denyRules": [{"deniedPermissions": ["compute.instances.start"]}]}

What happens if a user has an allow policy for compute.instances.start but this deny policy is applied?

medium

A. The user can start instances because allow policies override deny policies

B. The deny policy has no effect unless combined with a condition

C. The user can start instances only during business hours

D. The user cannot start instances because deny policies block the permission

Solution

1. Step 1: Understand deny policy precedence and apply to the example

   Deny policies always override allow policies for the specified permissions. Even if the user has an allow for starting instances, the deny rule blocks it.

2. Final Answer:

   The user cannot start instances because deny policies block the permission -> Option D

3. Quick Check:

   Deny overrides allow for blocked permissions [OK]

Hint: Deny always beats allow for the same permission [OK]

Common Mistakes:

• Thinking allow policies override deny policies
• Assuming deny policies need conditions to work
• Believing deny policies only log actions

4. You wrote this deny policy JSON but it does not block the intended permission:

{"denyRules": [{"deniedPermissions": "storage.objects.delete"}]}

What is the error?

medium

A. denyRules should be named allowRules

B. deniedPermissions should be a list, not a string

C. storage.objects.delete is not a valid permission

D. The policy must include a condition to work

Solution

1. Step 1: Check deniedPermissions data type and identify the error in the JSON

   deniedPermissions must be a list of strings, not a single string. The policy uses a string instead of a list, so it is invalid and won't block the permission.

2. Final Answer:

   deniedPermissions should be a list, not a string -> Option B

3. Quick Check:

   deniedPermissions requires a list [OK]

Hint: Use brackets [] for deniedPermissions list [OK]

Common Mistakes:

• Using string instead of list for deniedPermissions
• Confusing denyRules with allowRules
• Thinking conditions are mandatory

5. You want to deny the permission storage.buckets.delete only for requests made after 2024-01-01T00:00:00Z. Which IAM deny policy condition should you use?

hard

A. Use a condition with request.time > '2024-01-01T00:00:00Z'

B. Use a condition with resource.name == 'storage.buckets.delete'

C. No condition is needed; deny applies to all users

D. Use a condition with request.ip != 'company-network-ip-range'

Solution

1. Step 1: Identify the condition to restrict by time and match condition syntax

   To deny only for requests after the date, use a condition checking request.time > '2024-01-01T00:00:00Z'. Use a condition with request.time > '2024-01-01T00:00:00Z' uses request.time with inequality to apply after the date, which is correct.

2. Final Answer:

   Use a condition with request.time > '2024-01-01T00:00:00Z' -> Option A

3. Quick Check:

   Condition on request.time restricts deny by time [OK]

Hint: Use request.time condition to limit deny by time [OK]

Common Mistakes:

• Using resource.name instead of request.time for time check
• Using IP condition unrelated to time
• Applying deny without condition blocks all users