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feat(s3): Reduce notifications handler permissions (#5925) #27274

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feat(s3): Reduce notifications handler permissions (#5925) #27274

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27 changes: 16 additions & 11 deletions packages/aws-cdk-lib/aws-s3/lib/notifications-resource/notifications-resource-handler.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -52,24 +52,28 @@ export class NotificationsResourceHandler extends Construct {
public readonly functionArn: string;

/**
* The role of the handler's lambda function.
* The default policy of role of the handler's lambda function.
*/
public readonly role: iam.IRole;
private readonly policy: iam.Policy;
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This is breaking. A user could be using this property which now would become private


constructor(scope: Construct, id: string, props: NotificationsResourceHandlerProps = {}) {
super(scope, id);

this.role = props.role ?? new iam.Role(this, 'Role', {
const role = props.role ?? new iam.Role(this, 'Role', {
assumedBy: new iam.ServicePrincipal('lambda.amazonaws.com'),
});

this.role.addManagedPolicy(
role.addManagedPolicy(
iam.ManagedPolicy.fromAwsManagedPolicyName('service-role/AWSLambdaBasicExecutionRole'),
);
this.role.addToPrincipalPolicy(new iam.PolicyStatement({
actions: ['s3:PutBucketNotification'],
resources: ['*'],
}));

// We create our own default policy so we can set minimize to true and statements size
// remain small
const policy = new iam.Policy(this, 'DefaultPolicy', {
document: new iam.PolicyDocument({ minimize: true }),
});
role.attachInlinePolicy(policy);
this.policy = policy;

const resourceType = 'AWS::Lambda::Function';
class InLineLambda extends cdk.CfnResource {
Expand Down Expand Up @@ -97,17 +101,18 @@ export class NotificationsResourceHandler extends Construct {
Description: 'AWS CloudFormation handler for "Custom::S3BucketNotifications" resources (@aws-cdk/aws-s3)',
Code: { ZipFile: handlerSourceWithoutComments },
Handler: 'index.handler',
Role: this.role.roleArn,
Role: role.roleArn,
Runtime: 'python3.9',
Timeout: 300,
},
});
resource.node.addDependency(this.role);
resource.node.addDependency(role);
resource.node.addDependency(policy);

this.functionArn = resource.getAtt('Arn').toString();
}

public addToRolePolicy(statement: iam.PolicyStatement) {
this.role.addToPrincipalPolicy(statement);
this.policy.addStatements(statement);
}
}
6 changes: 5 additions & 1 deletion packages/aws-cdk-lib/aws-s3/lib/notifications-resource/notifications-resource.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -116,13 +116,17 @@ export class BucketNotifications extends Construct {
const handler = NotificationsResourceHandler.singleton(this, {
role: this.handlerRole,
});
handler.addToRolePolicy(new iam.PolicyStatement({
actions: ['s3:PutBucketNotification'],
resources: [this.bucket.bucketArn],
}));

const managed = this.bucket instanceof Bucket;

if (!managed) {
handler.addToRolePolicy(new iam.PolicyStatement({
actions: ['s3:GetBucketNotification'],
resources: ['*'],
resources: [this.bucket.bucketArn],
}));
}

Expand Down
120 changes: 119 additions & 1 deletion packages/aws-cdk-lib/aws-s3/test/notification.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -116,7 +116,7 @@ describe('notification', () => {
],
},
},
DependsOn: ['BucketNotificationsHandler050a0587b7544547bf325f094a3db834RoleDefaultPolicy2CF63D36',
DependsOn: ['BucketNotificationsHandler050a0587b7544547bf325f094a3db834DefaultPolicy8DF38B44',
'BucketNotificationsHandler050a0587b7544547bf325f094a3db834RoleB6FB88EC'],
});
});
Expand Down Expand Up @@ -185,4 +185,122 @@ describe('notification', () => {
Runtime: 'python3.9',
});
});
test('Check notifications handler permissions for single imported bucket', () => {
const stack = new cdk.Stack();

const bucket = s3.Bucket.fromBucketAttributes(stack, 'MyBucket', {
bucketName: 'foo-bar',
});

bucket.addEventNotification(s3.EventType.OBJECT_CREATED, {
bind: () => ({
arn: 'ARN',
type: s3.BucketNotificationDestinationType.TOPIC,
}),
});

Template.fromStack(stack).hasResourceProperties('AWS::IAM::Policy', {
PolicyDocument: {
Statement: [
{
Action: [
's3:GetBucketNotification',
's3:PutBucketNotification',
],
Effect: 'Allow',
Resource: {
'Fn::Join':
['', [
'arn:',
{ Ref: 'AWS::Partition' },
':s3:::foo-bar',
]],
},
},
],
},
});
});
test('Check notifications handler permissions for two imported bucket', () => {
const stack = new cdk.Stack();

const bucket = s3.Bucket.fromBucketAttributes(stack, 'MyBucket', {
bucketName: 'foo-bar',
});

bucket.addEventNotification(s3.EventType.OBJECT_CREATED, {
bind: () => ({
arn: 'ARN',
type: s3.BucketNotificationDestinationType.TOPIC,
}),
});

const bucket2 = s3.Bucket.fromBucketAttributes(stack, 'MyBucket2', {
bucketName: 'foo-bar2',
});

bucket2.addEventNotification(s3.EventType.OBJECT_CREATED, {
bind: () => ({
arn: 'ARN',
type: s3.BucketNotificationDestinationType.TOPIC,
}),
});

Template.fromStack(stack).hasResourceProperties('AWS::IAM::Policy', {
PolicyDocument: {
Statement: [
{
Action: [
's3:GetBucketNotification',
's3:PutBucketNotification',
],
Effect: 'Allow',
Resource: [{
'Fn::Join':
['', [
'arn:',
{ Ref: 'AWS::Partition' },
':s3:::foo-bar',
]],
}, {
'Fn::Join':
['', [
'arn:',
{ Ref: 'AWS::Partition' },
':s3:::foo-bar2',
]],
}],
},
],
},
});
});
test('Check notifications handler permissions for single bucket', () => {
const stack = new cdk.Stack();

const bucket = new s3.Bucket(stack, 'MyBucket', {
bucketName: 'foo-bar',
});

bucket.addEventNotification(s3.EventType.OBJECT_CREATED, {
bind: () => ({
arn: 'ARN',
type: s3.BucketNotificationDestinationType.TOPIC,
}),
});

Template.fromStack(stack).hasResourceProperties('AWS::IAM::Policy', {
PolicyDocument: {
Statement: [
{
Action: 's3:PutBucketNotification',
Effect: 'Allow',
Resource: {
'Fn::GetAtt': ['MyBucketF68F3FF0', 'Arn'],
},
},
],
},
});
});
});
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