[Bug]: aws_sns_topic fails to plan if the deployed resource policy references IAM roles which have been deleted or recreated

[rhowe]

Terraform Core Version

1.5.7

AWS Provider Version

5.10.0

Affected Resource(s)

• aws_sns_topic

Expected Behavior

A broken policy should have been retrieved from AWS without causing the plan to fail

Actual Behavior

The Terraform run failed with an error when preparing the plan

Relevant Error/Panic Output Snippet

Error: reading SNS Topic (arn:...): contains invalid principals

Terraform Configuration Files

# This has been hand-copied from a restricted environment I can't copy & paste from
# It might have a few silly errors but hopefully is still useful

resource "aws_iam_role" "role" {
  name = "role"
}

resource "aws_sns_topic" "topic" {
  name = "mytopic"
  display_name = "mytopic"
}

resource "aws_sns_topic_policy" "policy" {
  arn = aws_sns_topic.topic.arn
  policy = jsonencode({
  Id = "topic-policy"
  Statement = [{
    Sid = "sid"
    Action = "sns:Subscribe"
    Effect = "Allow"
    Principal = {
      AWS = aws_iam_role.role.arn
    }
    Resource = aws_sns_topic.topic.arn
  ]})
}

Steps to Reproduce

This is an approximation of what I was doing to trigger the issue

terraform apply
terraform -target aws_sns_topic.topic plan # Expect to succeed
terraform -target aws_iam_role.role destroy
terraform -target aws_sns_topic.topic plan # Expect to fail when reading the existing topic policy
terraform -target aws_iam_role.role apply
terraform -target aws_sns_topic.topic plan # Expect to fail when reading the existing topic policy

Debug Output

No response

Panic Output

No response

Important Factoids

No response

References

No response

Would you like to implement a fix?

None

[github-actions]

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[rhowe]

Also confirmed on provider 5.55.0

[MDBeudekerCN]

Is there any update on this, now we cannot do any operations on our SNS queues after we modify a role name, which is weird....

[MDBeudekerCN]

Apparently this is a feature that prevents privilege escalation on the AWS side:
https://repost.aws/articles/ARSqFcxvd7R9u-gcFD9nmA5g/understanding-aws-s-handling-of-deleted-iam-roles-in-policies

But this does built a dependency between IAM and SNS access policies where our terraform setup breaks if we change an IAM role 🤔

[mk4dir]

Recently, I experienced the same issue.

╷
│ Error: reading SNS Topic (arn:aws:sns:eu-central-1:123456789123:my-cool-sns): contains invalid principals
│ 
│   with module.my-cool-sns.aws_sns_topic.this[0],
│   on .terraform/modules/my-cool-sns/main.tf line 11, in resource "aws_sns_topic" "this":
│   11: resource "aws_sns_topic" "this" {
│ 
╵

When I checked the Access Policy of SNS itself, I saw that the principal of one of the statements was some kind of ID as below:

{
      "Sid": "AllowPublish",
      "Effect": "Allow",
      "Principal": {
        "AWS": "AROAQ2VQR17XTKL6QP3WA"
      },
      "Action": "sns:Publish",
      "Resource": "arn:aws:sns:eu-central-1:123456789123:my-cool-sns"
}

Idk how it happened, but the IAM Role in the statement was deleted. But, to fix that, I manually changed that ID with the IAM Role ARN.

"AWS": "AROAQ2VQR17XTKL6QP3WA" --> "AWS": "arn:aws:iam::123456789123:role/my-cool-role"

This move equalised both the AWS and IAC sides. Here is my input for the statement:

topic_policy_statements = {
    AllowPublish = {
      actions = ["sns:Publish"]
      principals = [{
        type = "AWS"
        identifiers = [
          "arn:aws:iam::123456789123:role/my-cool-role"
        ]
      }]
    }

And, when I reapplied the terraform, I saw the error was fixed. At least this was my workaround.