Fix TOCTTOU and avoid to read existing unreadable file

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60900 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/irb/workspace.rb

@@ -111,8 +111,11 @@ EOF
       file, pos = @binding.eval('[__FILE__, __LINE__]')
 
       unless defined?(::SCRIPT_LINES__[file]) && lines = ::SCRIPT_LINES__[file]
-        return unless File.exist?(file)
+        begin
           lines = File.readlines(file)
+        rescue SystemCallError
+          return
+        end
       end
       pos -= 1
 

test/irb/test_workspace.rb

@@ -32,6 +32,19 @@ module TestIRB
       end
     end
 
+    def test_code_around_binding_with_existing_unreadable_file
+      Tempfile.create do |f|
+        code = "IRB::WorkSpace.new(binding)\n"
+        f.print(code)
+        f.close
+
+        File.chmod(0, f.path)
+
+        workspace = eval(code, binding, f.path)
+        assert_equal(nil, workspace.code_around_binding)
+      end
+    end
+
     def test_code_around_binding_with_script_lines__
       with_script_lines do |script_lines|
         Tempfile.create do |f|