Implement fork network mirroring rule [RUN ALL RSPEC] [RUN AS-IF-FOSS]

app/models/project.rb

@@ -825,6 +825,21 @@ class Project < ApplicationRecord
 
       from_union([with_issues_enabled, with_merge_requests_enabled]).select(:id)
     end
+
+    def find_by_url(url)
+      uri = URI(url)
+
+      return unless uri.host == Gitlab.config.gitlab.host
+
+      match = Rails.application.routes.recognize_path(url)
+
+      return if match[:unmatched_route].present?
+      return if match[:namespace_id].blank? || match[:id].blank?
+
+      find_by_full_path(match.values_at(:namespace_id, :id).join("/"))
+    rescue ActionController::RoutingError, URI::InvalidURIError
+      nil
+    end
   end
 
   def initialize(attributes = nil)

config/feature_flags/development/block_external_fork_network_mirrors.yml

+---
+name: block_external_fork_network_mirrors
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60735
+rollout_issue_url: 
+milestone: '14.0'
+type: development
+group: group::source code
+default_enabled: false

ee/app/models/ee/project.rb

@@ -218,6 +218,7 @@ module EE
                         less_than: ::Gitlab::Pages::MAX_SIZE / 1.megabyte }
 
       validates :approvals_before_merge, numericality: true, allow_blank: true
+      validate :import_url_inside_fork_network, if: :import_url_changed?
 
       with_options if: :mirror? do
         validates :import_url, presence: true
@@ -852,5 +853,19 @@ module EE
       pipeline_scope.with_reports(::Ci::JobArtifact.security_reports).first ||
         pipeline_scope.with_legacy_security_reports.first
     end
+
+    # If the project is inside a fork network, the mirror URL must
+    # also belong to a member of that fork network
+    def import_url_inside_fork_network
+      return unless ::Feature.enabled?(:block_external_fork_network_mirrors, self, default_enabled: :yaml)
+
+      if forked?
+        mirror_project = ::Project.find_by_url(import_url)
+
+        unless mirror_project.present? && fork_network_projects.include?(mirror_project)
+          errors.add(:url, _("must be inside the fork network"))
+        end
+      end
+    end
   end
 end

ee/spec/models/project_spec.rb

@@ -2412,6 +2412,61 @@ RSpec.describe Project do
         expect(project.reload.import_url).to eq('http://user:pass@test.com')
       end
     end
+
+    context 'project is inside a fork network' do
+      subject { project }
+
+      let(:project) { create(:project, fork_network: fork_network) }
+      let(:fork_network) { create(:fork_network) }
+
+      before do
+        stub_config_setting(host: 'gitlab.com')
+      end
+
+      context 'feature flag is disabled' do
+        before do
+          stub_feature_flags(block_external_fork_network_mirrors: false)
+          project.import_url = "https://customgitlab.com/foo/bar.git"
+        end
+
+        it { is_expected.to be_valid }
+      end
+
+      context 'the project is the root of the fork network' do
+        before do
+          project.import_url = "https://customgitlab.com/foo/bar.git"
+          expect(fork_network).to receive(:root_project).and_return(project)
+        end
+
+        it { is_expected.to be_valid }
+      end
+
+      context 'the URL is inside the fork network' do
+        before do
+          project.import_url = "https://#{Gitlab.config.gitlab.host}/#{project.fork_network.root_project.full_path}.git"
+        end
+
+        it { is_expected.to be_valid }
+      end
+
+      context 'the URL is external but the project exists' do
+        it 'raises an error' do
+          project.import_url = "https://customgitlab.com/#{project.fork_network.root_project.full_path}.git"
+          project.validate
+
+          expect(project.errors[:url]).to include('must be inside the fork network')
+        end
+      end
+
+      context 'the URL is not inside the fork network' do
+        it 'raises an error' do
+          project.import_url = "https://customgitlab.com/foo/bar.git"
+          project.validate
+
+          expect(project.errors[:url]).to include('must be inside the fork network')
+        end
+      end
+    end
   end
 
   describe '#add_import_job' do

locale/gitlab.pot

@@ -39189,6 +39189,9 @@ msgstr ""
 msgid "must be greater than start date"
 msgstr ""
 
+msgid "must be inside the fork network"
+msgstr ""
+
 msgid "must have a unique schedule, status, and elapsed time"
 msgstr ""
 

spec/models/project_spec.rb

@@ -1661,6 +1661,45 @@ RSpec.describe Project, factory_default: :keep do
     end
   end
 
+  describe '.find_by_url' do
+    subject { described_class.find_by_url(url) }
+
+    let_it_be(:project) { create(:project) }
+
+    before do
+      stub_config_setting(host: 'gitlab.com')
+    end
+
+    context 'url is internal' do
+      let(:url) { "https://#{Gitlab.config.gitlab.host}/#{path}" }
+
+      context 'path is recognised as a project path' do
+        let(:path) { project.full_path }
+
+        it { is_expected.to eq(project) }
+
+        it 'returns nil if the path detection throws an error' do
+          expect(Rails.application.routes).to receive(:recognize_path).with(url) { raise ActionController::RoutingError, 'test' }
+
+          expect { subject }.not_to raise_error(ActionController::RoutingError)
+          expect(subject).to be_nil
+        end
+      end
+
+      context 'path is not a project path' do
+        let(:path) { 'probably/missing.git' }
+
+        it { is_expected.to be_nil }
+      end
+    end
+
+    context 'url is external' do
+      let(:url) { "https://foo.com/bar/baz.git" }
+
+      it { is_expected.to be_nil }
+    end
+  end
+
   context 'repository storage by default' do
     let(:project) { build(:project) }