fix(cdk): grant observed EB deploy reads

infra/cdk/README.md

@@ -40,15 +40,18 @@ The role grants only:
   describe actions are not reliably constrained by resource ARN.
 - `elasticbeanstalk:CreateApplicationVersion` on application `shoc-backend`.
 - `elasticbeanstalk:UpdateEnvironment` on environment `shoc-backend-dev` only.
-- `s3:ListBucket` on `elasticbeanstalk-us-east-1-396287094661` (the official
-  action's ownership-safe `HeadBucket` check), plus `s3:CreateBucket` on the
-  same bucket-level ARN. Under the `shoc-backend/` object prefix only:
-  `s3:PutObject` plus `s3:GetObject` and `s3:GetObjectVersion`, which the
-  pinned official deployment action requires to validate the
-  `CreateApplicationVersion` source bundle after upload.
+- `s3:ListBucket` and `s3:GetBucketLocation` on
+  `elasticbeanstalk-us-east-1-396287094661` (the official action's
+  ownership-safe bucket checks), plus `s3:CreateBucket` and
+  `s3:PutBucketOwnershipControls` on the same bucket-level ARN. Under the
+  `shoc-backend/` object prefix only:
+  `s3:PutObject`, `s3:GetObject`, `s3:GetObjectAcl`, and
+  `s3:GetObjectVersion`, which the pinned official deployment action and
+  Elastic Beanstalk require to validate the `CreateApplicationVersion` source
+  bundle after upload.
 
   `s3:CreateBucket` is part of the pinned
-  `aws-actions/aws-elasticbeanstalk-deploy@cfad3e5e...` (v1.0.6) IAM
+  `aws-actions/aws-elastic-beanstalk-deploy@cfad3e5e...` (v1.0.6) IAM
   contract even though the workflow sets
   `create-s3-bucket-if-not-exists: "false"`. That input prevents the
   action's explicit bucket-creation helper; it does not remove the permission
@@ -59,9 +62,53 @@ The role grants only:
   exact bucket-level ARN only (no object prefix, no wildcard resource), so it
   cannot create any other bucket.
 
-It grants **no** IAM mutation or `PassRole`, **no** RDS / EC2 / Secrets Manager
-access, and **no** administrator policy. There are no wildcard mutation
-surfaces.
+  `s3:PutBucketOwnershipControls` was added after a second live deployment
+  (run 30375409934) failed at `UpdateEnvironment` with `AccessDenied` for
+  `s3:PutBucketOwnershipControls` on the same service bucket. That call is
+  emitted by Elastic Beanstalk's `UpdateEnvironment` path after the source
+  bundle upload succeeds; AWS classifies it as a bucket-level permission, so
+  it is scoped to the same exact bucket-level ARN (no object prefix, no
+  wildcard resource). It does not widen object-prefix permissions, does not
+  grant `PutBucketPolicy`, `PutBucketPublicAccessBlock`, or any object-level write,
+  and does not change `create-s3-bucket-if-not-exists: "false"`.
+
+  `s3:GetBucketLocation` was added after CloudTrail showed that run
+  `30375409934` attempt 4 invoked it as
+  `githubdeploy-shoc-backend-dev/GitHubActions` and was denied. It is scoped to
+  the exact bucket-level ARN and grants no object access.
+
+- `cloudformation:GetTemplate`, `cloudformation:DescribeStackResources`, and
+  `cloudformation:ListStackResources` on the Elastic Beanstalk-managed
+  CloudFormation stack `awseb-e-hehnrqjjrt-stack`, scoped to
+  `arn:aws:cloudformation:us-east-1:396287094661:stack/awseb-e-hehnrqjjrt-stack/*`.
+  These read-only calls are emitted by Elastic Beanstalk's
+  `UpdateEnvironment` path under the GitHub deploy role. `GetTemplate` was
+  added after run `30375409934` attempt 2 advanced past the S3
+  ownership-controls step and was denied on the EB-managed stack instance
+  `awseb-e-hehnrqjjrt-stack/112f77c0-7718-11f1-a1a9-0e48750aef13`.
+  CloudTrail then showed attempt 4 denied `DescribeStackResources` and
+  `ListStackResources` on that same stack instance.
+  CloudFormation stack ARNs carry a random GUID instance suffix, so the
+  permission is scoped to that one stack-name prefix (`/*`) rather than a
+  single instance ARN. The statement grants no CloudFormation mutation, no
+  `Resource: "*"`, and no access to any other stack. CDK does not own or
+  mutate that stack; it is owned by Elastic Beanstalk and referenced by
+  identifier only.
+
+- `ec2:DescribeSubnets` as a read-only account-level query. Elastic Beanstalk
+  emitted this call during run 30375409934 attempt 3 after the environment
+  update started. EC2 does not support resource-level constraints for this
+  Describe action, so IAM requires `Resource: "*"`. No EC2 mutation action is
+  granted.
+- `s3:GetObjectAcl` under the existing
+  `elasticbeanstalk-us-east-1-396287094661/shoc-backend/*` object prefix.
+  Elastic Beanstalk emitted this read during the same attempt while validating
+  the uploaded application bundle. It grants no bucket-wide or cross-prefix
+  object access.
+
+It grants **no** IAM mutation or `PassRole`, **no** RDS / Secrets Manager
+access, no EC2 mutation, and **no** administrator policy. There are no wildcard
+mutation surfaces.
 
 ## Prerequisites
 
@@ -92,7 +139,10 @@ All commands run from `infra/cdk/`.
 
 - Trust policy `StringEquals` matches the exact audience and subject above.
 - The inline policy contains no `Resource: "*"` mutation action and no service
-  outside `elasticbeanstalk` / `s3`.
+  outside `elasticbeanstalk` / `s3` / `cloudformation` / `ec2`. The
+  `cloudformation` grants are the three observed read-only actions on the
+  single EB-managed stack prefix; the only EC2 grant is the read-only
+  `DescribeSubnets` action whose IAM resource model requires `Resource: "*"`.
 
 The workflow's `AWS_DEPLOY_ROLE_ARN` repository secret (environment `dev`) must
 hold the ARN output by this stack (`GithubDeployRoleArn`).

infra/cdk/deploy-dev-stack.ts

@@ -73,7 +73,34 @@ export class DeployDevStack extends cdk.Stack {
     deployRole.addToPolicy(
       new iam.PolicyStatement({
         effect: iam.Effect.ALLOW,
-        actions: ['s3:ListBucket', 's3:CreateBucket'],
+        actions: [
+          'cloudformation:GetTemplate',
+          'cloudformation:DescribeStackResources',
+          'cloudformation:ListStackResources',
+        ],
+        resources: [
+          `arn:aws:cloudformation:${REGION}:${ACCOUNT_ID}:stack/awseb-e-hehnrqjjrt-stack/*`,
+        ],
+      }),
+    );
+
+    deployRole.addToPolicy(
+      new iam.PolicyStatement({
+        effect: iam.Effect.ALLOW,
+        actions: ['ec2:DescribeSubnets'],
+        resources: ['*'],
+      }),
+    );
+
+    deployRole.addToPolicy(
+      new iam.PolicyStatement({
+        effect: iam.Effect.ALLOW,
+        actions: [
+          's3:ListBucket',
+          's3:CreateBucket',
+          's3:PutBucketOwnershipControls',
+          's3:GetBucketLocation',
+        ],
         resources: [bucketArn],
       }),
     );
@@ -81,7 +108,7 @@ export class DeployDevStack extends cdk.Stack {
     deployRole.addToPolicy(
       new iam.PolicyStatement({
         effect: iam.Effect.ALLOW,
-        actions: ['s3:GetObject', 's3:GetObjectVersion', 's3:PutObject'],
+        actions: ['s3:GetObject', 's3:GetObjectAcl', 's3:GetObjectVersion', 's3:PutObject'],
         resources: [`${bucketArn}/${APPLICATION_NAME}/*`],
       }),
     );