Add feature flag to apply upload API size enforcement

This adds the `enforce_max_attachment_size_upload_api` feature flag to
enable enforcement of max attachment size in the upload API.  If the
feature is not enabled, we limit to 1 GB by
default. `GITLAB_UPLOAD_API_ALLOWLIST` can be set in the environment to
allow certain project IDs to bypass enforcement.

app/services/upload_service.rb

 # frozen_string_literal: true
 
 class UploadService
+  # Temporarily introduced for upload API: https://gitlab.com/gitlab-org/gitlab/-/issues/325788
+  attr_accessor :override_max_attachment_size
+
   def initialize(model, file, uploader_class = FileUploader, **uploader_context)
     @model, @file, @uploader_class, @uploader_context = model, file, uploader_class, uploader_context
   end
@@ -19,6 +22,6 @@ class UploadService
   attr_reader :model, :file, :uploader_class, :uploader_context
 
   def max_attachment_size
-    Gitlab::CurrentSettings.max_attachment_size.megabytes.to_i
+    override_max_attachment_size || Gitlab::CurrentSettings.max_attachment_size.megabytes.to_i
   end
 end

config/feature_flags/development/enforce_max_attachment_size_upload_api.yml

+---
+name: enforce_max_attachment_size_upload_api
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/57250
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/325787
+milestone: '13.11'
+type: development
+group: group::source code
+default_enabled: false

lib/api/projects.rb

@@ -13,6 +13,8 @@ module API
 
     feature_category :projects, ['/projects/:id/custom_attributes', '/projects/:id/custom_attributes/:key']
 
+    PROJECT_ATTACHMENT_SIZE_EXEMPT = 1.gigabyte
+
     helpers do
       # EE::API::Projects would override this method
       def apply_filters(projects)
@@ -52,6 +54,19 @@ module API
 
         accepted!
       end
+
+      def exempt_from_global_attachment_size?(user_project)
+        list = ::Gitlab::RackAttack::UserAllowlist.new(ENV['GITLAB_UPLOAD_API_ALLOWLIST'])
+        list.include?(user_project.id)
+      end
+
+      # Temporarily introduced for upload API: https://gitlab.com/gitlab-org/gitlab/-/issues/325788
+      def project_attachment_size(user_project)
+        return PROJECT_ATTACHMENT_SIZE_EXEMPT if exempt_from_global_attachment_size?(user_project)
+        return user_project.max_attachment_size if Feature.enabled?(:enforce_max_attachment_size_upload_api, user_project)
+
+        PROJECT_ATTACHMENT_SIZE_EXEMPT
+      end
     end
 
     helpers do
@@ -553,7 +568,7 @@ module API
 
         status 200
         content_type Gitlab::Workhorse::INTERNAL_API_CONTENT_TYPE
-        FileUploader.workhorse_authorize(has_length: false, maximum_size: user_project.max_attachment_size)
+        FileUploader.workhorse_authorize(has_length: false, maximum_size: project_attachment_size(user_project))
       end
 
       desc 'Upload a file'
@@ -561,7 +576,9 @@ module API
         requires :file, types: [Rack::Multipart::UploadedFile, ::API::Validations::Types::WorkhorseFile], desc: 'The attachment file to be uploaded'
       end
       post ":id/uploads", feature_category: :not_owned do
-        upload = UploadService.new(user_project, params[:file]).execute
+        service = UploadService.new(user_project, params[:file])
+        service.override_max_attachment_size = project_attachment_size(user_project)
+        upload = service.execute
 
         present upload, with: Entities::ProjectUpload
       end

spec/features/file_uploads/attachment_spec.rb

@@ -9,7 +9,7 @@ RSpec.describe 'Upload an attachment', :api, :js do
   let_it_be(:user) { project.owner }
   let_it_be(:personal_access_token) { create(:personal_access_token, user: user) }
 
-  let(:api_path) { "/projects/#{project.id}/uploads" }
+  let(:api_path) { "/projects/#{project_id}/uploads" }
   let(:url) { capybara_url(api(api_path)) }
   let(:file) { fixture_file_upload('spec/fixtures/dk.png') }
 
@@ -22,7 +22,7 @@ RSpec.describe 'Upload an attachment', :api, :js do
   end
 
   shared_examples 'for an attachment' do
-    it 'creates package files' do
+    it 'creates files' do
       expect { subject }
         .to change { Upload.count }.by(1)
     end
@@ -30,5 +30,15 @@ RSpec.describe 'Upload an attachment', :api, :js do
     it { expect(subject.code).to eq(201) }
   end
 
-  it_behaves_like 'handling file uploads', 'for an attachment'
+  context 'with an integer project ID' do
+    let(:project_id) { project.id }
+
+    it_behaves_like 'handling file uploads', 'for an attachment'
+  end
+
+  context 'with an encoded project ID' do
+    let(:project_id) { "#{project.namespace.path}%2F#{project.path}" }
+
+    it_behaves_like 'handling file uploads', 'for an attachment'
+  end
 end

spec/requests/api/projects_spec.rb

@@ -1471,7 +1471,6 @@ RSpec.describe API::Projects do
         post api("/projects/#{project.id}/uploads/authorize", user), headers: headers
 
         expect(response).to have_gitlab_http_status(:ok)
-
         expect(json_response['MaximumSize']).to eq(project.max_attachment_size)
       end
     end
@@ -1484,6 +1483,32 @@ RSpec.describe API::Projects do
       end
     end
 
+    context 'with exempted project' do
+      before do
+        stub_env('GITLAB_UPLOAD_API_ALLOWLIST', project.id)
+      end
+
+      it "returns 200" do
+        post api("/projects/#{project.id}/uploads/authorize", user), headers: headers
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(json_response['MaximumSize']).to eq(1.gigabyte)
+      end
+    end
+
+    context 'with upload size enforcement disabled' do
+      before do
+        stub_feature_flags(enforce_max_attachment_size_upload_api: false)
+      end
+
+      it "returns 200" do
+        post api("/projects/#{project.id}/uploads/authorize", user), headers: headers
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(json_response['MaximumSize']).to eq(1.gigabyte)
+      end
+    end
+
     context 'with no Workhorse headers' do
       it "returns 403" do
         post api("/projects/#{project.id}/uploads/authorize", user)
@@ -1499,6 +1524,10 @@ RSpec.describe API::Projects do
     end
 
     it "uploads the file and returns its info" do
+      expect_next_instance_of(UploadService) do |instance|
+        expect(instance).to receive(:override_max_attachment_size=).with(project.max_attachment_size).and_call_original
+      end
+
       post api("/projects/#{project.id}/uploads", user), params: { file: fixture_file_upload("spec/fixtures/dk.png", "image/png") }
 
       expect(response).to have_gitlab_http_status(:created)
@@ -1508,6 +1537,34 @@ RSpec.describe API::Projects do
 
       expect(json_response['full_path']).to start_with("/#{project.namespace.path}/#{project.path}/uploads")
     end
+
+    shared_examples 'capped upload attachments' do
+      it "limits the upload to 1 GB" do
+        expect_next_instance_of(UploadService) do |instance|
+          expect(instance).to receive(:override_max_attachment_size=).with(1.gigabyte).and_call_original
+        end
+
+        post api("/projects/#{project.id}/uploads", user), params: { file: fixture_file_upload("spec/fixtures/dk.png", "image/png") }
+
+        expect(response).to have_gitlab_http_status(:created)
+      end
+    end
+
+    context 'with exempted project' do
+      before do
+        stub_env('GITLAB_UPLOAD_API_ALLOWLIST', project.id)
+      end
+
+      it_behaves_like 'capped upload attachments'
+    end
+
+    context 'with upload size enforcement disabled' do
+      before do
+        stub_feature_flags(enforce_max_attachment_size_upload_api: false)
+      end
+
+      it_behaves_like 'capped upload attachments'
+    end
   end
 
   describe "GET /projects/:id/groups" do

spec/services/upload_service_spec.rb

@@ -67,6 +67,29 @@ RSpec.describe UploadService do
 
       it { expect(@link_to_file).to eq({}) }
     end
+
+    describe '#override_max_attachment_size' do
+      let(:txt) { fixture_file_upload('spec/fixtures/doc_sample.txt', 'text/plain') }
+      let(:service) { described_class.new(@project, txt, FileUploader) }
+
+      subject { service.execute.to_h }
+
+      before do
+        allow(txt).to receive(:size) { 100.megabytes.to_i }
+      end
+
+      it 'allows the upload' do
+        service.override_max_attachment_size = 101.megabytes
+
+        expect(subject.keys).to eq(%i(alt url markdown))
+      end
+
+      it 'disallows the upload' do
+        service.override_max_attachment_size = 99.megabytes
+
+        expect(subject).to eq({})
+      end
+    end
   end
 
   def upload_file(project, file)