Prevent private repo from being accessed via internal API

changelogs/unreleased/security-kubernetes-agent-internal-api.yml

+---
+title: Prevent private repo from being accessed via internal Kubernetes API
+merge_request:
+author:
+type: security

lib/api/internal/kubernetes.rb

@@ -85,7 +85,7 @@ module API
 
             # TODO sort out authorization for real
             # https://gitlab.com/gitlab-org/gitlab/-/issues/220912
-            if !project || !project.public?
+            unless Ability.allowed?(nil, :download_code, project)
               not_found!
             end
 

spec/requests/api/internal/kubernetes_spec.rb

@@ -166,6 +166,16 @@ RSpec.describe API::Internal::Kubernetes do
             )
           )
         end
+
+        context 'repository is for project members only' do
+          let(:project) { create(:project, :public, :repository_private) }
+
+          it 'returns 404' do
+            send_request(params: { id: project.id }, headers: { 'Authorization' => "Bearer #{agent_token.token}" })
+
+            expect(response).to have_gitlab_http_status(:not_found)
+          end
+        end
       end
 
       context 'project is private' do
@@ -190,7 +200,7 @@ RSpec.describe API::Internal::Kubernetes do
 
       context 'project does not exist' do
         it 'returns 404' do
-          send_request(params: { id: 0 }, headers: { 'Authorization' => "Bearer #{agent_token.token}" })
+          send_request(params: { id: non_existing_record_id }, headers: { 'Authorization' => "Bearer #{agent_token.token}" })
 
           expect(response).to have_gitlab_http_status(:not_found)
         end