Prevent path traversal

lib/business/calendar.rb

@@ -8,6 +8,11 @@ module Business
   class Calendar
     VALID_KEYS = %w[holidays working_days extra_working_dates].freeze
 
+    # Calendar names are interpolated into a filesystem path, so restrict them to
+    # plain identifiers: anything containing path separators, "..", or an absolute
+    # path would otherwise load a file from outside the configured load_paths.
+    CALENDAR_NAME_FORMAT = /\A[a-zA-Z0-9_-]+\z/
+
     class << self
       attr_accessor :load_paths
     end
@@ -38,14 +43,25 @@ def self.find_calendar_data(calendar_name)
         if path.is_a?(Hash)
           break path[calendar_name] if path[calendar_name]
         else
-          calendar_path = Pathname.new(path).join("#{calendar_name}.yml")
+          calendar_path = calendar_path_for(path, calendar_name)
           next unless calendar_path.exist?
 
           break YAML.safe_load(calendar_path.read, permitted_classes: [Date])
         end
       end
     end
 
+    # Only applied to directory load_paths; hash load_paths are a plain key
+    # lookup and cannot escape anywhere, so their keys stay unrestricted.
+    def self.calendar_path_for(directory, calendar_name)
+      unless calendar_name.to_s.match?(CALENDAR_NAME_FORMAT)
+        raise ArgumentError, "invalid calendar name: #{calendar_name.inspect}"
+      end
+
+      Pathname.new(directory).join("#{calendar_name}.yml")
+    end
+    private_class_method :calendar_path_for
+
     @lock = Mutex.new
     def self.load_cached(calendar)
       @lock.synchronize do

spec/business/calendar_spec.rb

@@ -2,6 +2,7 @@
 
 require "business/calendar"
 require "time"
+require "fileutils"
 
 RSpec.configure do |config|
   config.mock_with(:rspec) { |mocks| mocks.verify_partial_doubles = true }
@@ -57,6 +58,71 @@
       specify { expect { load_calendar }.to raise_error(/No such calendar/) }
     end
 
+    context "when given a calendar name that escapes the load path" do
+      before do
+        outside = File.join(File.dirname(__FILE__), "../fixtures")
+        FileUtils.mkdir_p(File.join(outside, "outside"))
+        File.write(
+          File.join(outside, "outside", "escaped.yml"),
+          { "working_days" => ["monday"] }.to_yaml,
+        )
+      end
+
+      after do
+        FileUtils.rm_rf(File.join(File.dirname(__FILE__), "../fixtures", "outside"))
+      end
+
+      context "with a relative traversal" do
+        let(:calendar) { "../outside/escaped" }
+
+        specify do
+          expect { load_calendar }.
+            to raise_error(ArgumentError, /invalid calendar name/)
+        end
+      end
+
+      context "with an absolute path" do
+        let(:calendar) do
+          File.join(File.dirname(__FILE__), "../fixtures", "outside", "escaped")
+        end
+
+        specify do
+          expect { load_calendar }.
+            to raise_error(ArgumentError, /invalid calendar name/)
+        end
+      end
+
+      context "with a bare path separator" do
+        let(:calendar) { "outside/escaped" }
+
+        specify do
+          expect { load_calendar }.
+            to raise_error(ArgumentError, /invalid calendar name/)
+        end
+      end
+
+      context "with a name that is only dots" do
+        let(:calendar) { ".." }
+
+        specify do
+          expect { load_calendar }.
+            to raise_error(ArgumentError, /invalid calendar name/)
+        end
+      end
+
+      context "when the escaping name is a key in a hash load path" do
+        before do
+          described_class.load_paths = [{ "../outside/escaped" => dummy_calendar }]
+        end
+
+        let(:calendar) { "../outside/escaped" }
+
+        it "still resolves, since hash lookups touch no filesystem" do
+          expect(load_calendar).to be_a described_class
+        end
+      end
+    end
+
     context "when given a calendar that has invalid keys" do
       let(:calendar) { "invalid-keys" }