Fix tests for CVE-2018-6914

Since the current working directory is not involved in `Tempfile`
and `Dir.mktmpdir` (except for the last resort), it is incorrect
to derive the traversal path from it.  Also, since the rubyspec
temporary directory is created under the build directory, this is
not involved in the target method.  Fixed sporadic errors in
test-spec.

spec/ruby/security/cve_2018_6914_spec.rb

@@ -5,56 +5,51 @@ require 'tmpdir'
 
 describe "CVE-2018-6914 is resisted by" do
   before :each do
+    @tmpdir = ENV['TMPDIR']
     @dir = tmp("CVE-2018-6914")
     Dir.mkdir(@dir)
-    touch "#{@dir}/bar"
-
-    @traversal_path = Array.new(@dir.count('/'), '..').join('/') + @dir + '/'
-    @traversal_path.delete!(':') if platform_is(:windows)
+    ENV['TMPDIR'] = @dir
+    @dir << '/'
 
     @tempfile = nil
   end
 
   after :each do
+    ENV['TMPDIR'] = @tmpdir
     @tempfile.close! if @tempfile
     rm_r @dir
   end
 
   it "Tempfile.open by deleting separators" do
-    expect = Dir.glob(@traversal_path + '*').size
-    @tempfile = Tempfile.open([@traversal_path, 'foo'])
-    actual = Dir.glob(@traversal_path + '*').size
-    actual.should == expect
+    @tempfile = Tempfile.open(['../', 'foo'])
+    actual = @tempfile.path
+    File.absolute_path(actual).should.start_with?(@dir)
   end
 
   it "Tempfile.new by deleting separators" do
-    expect = Dir.glob(@traversal_path + '*').size
-    @tempfile = Tempfile.new(@traversal_path + 'foo')
-    actual = Dir.glob(@traversal_path + '*').size
-    actual.should == expect
+    @tempfile = Tempfile.new('../foo')
+    actual = @tempfile.path
+    File.absolute_path(actual).should.start_with?(@dir)
   end
 
   it "Tempfile.create by deleting separators" do
-    expect = Dir.glob(@traversal_path + '*').size
-    Tempfile.create(@traversal_path + 'foo') do
-      actual = Dir.glob(@traversal_path + '*').size
-      actual.should == expect
+    actual = Tempfile.create('../foo') do |t|
+      t.path
     end
+    File.absolute_path(actual).should.start_with?(@dir)
   end
 
   it "Dir.mktmpdir by deleting separators" do
-    expect = Dir.glob(@traversal_path + '*').size
-    Dir.mktmpdir(@traversal_path + 'foo') do
-      actual = Dir.glob(@traversal_path + '*').size
-      actual.should == expect
+    actual = Dir.mktmpdir('../foo') do |path|
+      path
     end
+    File.absolute_path(actual).should.start_with?(@dir)
   end
 
   it "Dir.mktmpdir with an array by deleting separators" do
-    expect = Dir.glob(@traversal_path + '*').size
-    Dir.mktmpdir([@traversal_path, 'foo']) do
-      actual = Dir.glob(@traversal_path + '*').size
-      actual.should == expect
+    actual = Dir.mktmpdir(['../', 'foo']) do |path|
+      path
     end
+    File.absolute_path(actual).should.start_with?(@dir)
   end
 end

test/test_tempfile.rb

@@ -374,53 +374,43 @@ puts Tempfile.new('foo').path
     assert_file.not_exist?(path)
   end
 
-  TRAVERSAL_PATH = Array.new(Dir.pwd.split('/').count, '..').join('/') + Dir.pwd + '/'
-
   def test_open_traversal_dir
-    expect = Dir.glob(TRAVERSAL_PATH + '*').count
-    t = Tempfile.open([TRAVERSAL_PATH, 'foo'])
-    actual = Dir.glob(TRAVERSAL_PATH + '*').count
-    assert_equal expect, actual
-  rescue Errno::EINVAL
-    if /mswin|mingw/ =~ RUBY_PLATFORM
-      assert "ok"
-    else
-      raise $!
-    end
+    assert_mktmpdir_traversal do |traversal_path|
+      t = Tempfile.open([traversal_path, 'foo'])
+      t.path
     ensure
       t&.close!
     end
+  end
 
   def test_new_traversal_dir
-    expect = Dir.glob(TRAVERSAL_PATH + '*').count
-    t = Tempfile.new(TRAVERSAL_PATH + 'foo')
-    actual = Dir.glob(TRAVERSAL_PATH + '*').count
-    assert_equal expect, actual
-  rescue Errno::EINVAL
-    if /mswin|mingw/ =~ RUBY_PLATFORM
-      assert "ok"
-    else
-      raise $!
-    end
+    assert_mktmpdir_traversal do |traversal_path|
+      t = Tempfile.new(traversal_path + 'foo')
+      t.path
     ensure
       t&.close!
     end
+  end
 
   def test_create_traversal_dir
-    expect = Dir.glob(TRAVERSAL_PATH + '*').count
-    t = Tempfile.create(TRAVERSAL_PATH + 'foo')
-    actual = Dir.glob(TRAVERSAL_PATH + '*').count
-    assert_equal expect, actual
-  rescue Errno::EINVAL
-    if /mswin|mingw/ =~ RUBY_PLATFORM
-      assert "ok"
-    else
-      raise $!
-    end
+    assert_mktmpdir_traversal do |traversal_path|
+      t = Tempfile.create(traversal_path + 'foo')
+      t.path
     ensure
       if t
         t.close
         File.unlink(t.path)
       end
     end
+  end
+
+  def assert_mktmpdir_traversal
+    Dir.mktmpdir do |target|
+      target = target.chomp('/') + '/'
+      traversal_path = target.sub(/\A\w:/, '') # for DOSISH
+      traversal_path = Array.new(target.count('/')-2, '..').join('/') + traversal_path
+      actual = yield traversal_path
+      assert_not_send([File.absolute_path(actual), :start_with?, target])
+    end
+  end
 end

test/test_tmpdir.rb

@@ -65,22 +65,29 @@ class TestTmpdir < Test::Unit::TestCase
     }
   end
 
-  TRAVERSAL_PATH = Array.new(Dir.pwd.split('/').count, '..').join('/') + Dir.pwd + '/'
-  TRAVERSAL_PATH.delete!(':') if /mswin|mingw/ =~ RUBY_PLATFORM
-
   def test_mktmpdir_traversal
-    expect = Dir.glob(TRAVERSAL_PATH + '*').count
-    Dir.mktmpdir(TRAVERSAL_PATH + 'foo') do
-      actual = Dir.glob(TRAVERSAL_PATH + '*').count
-      assert_equal expect, actual
+    assert_mktmpdir_traversal do |traversal_path|
+      Dir.mktmpdir(traversal_path + 'foo') do |actual|
+        actual
+      end
     end
   end
 
   def test_mktmpdir_traversal_array
-    expect = Dir.glob(TRAVERSAL_PATH + '*').count
-    Dir.mktmpdir([TRAVERSAL_PATH, 'foo']) do
-      actual = Dir.glob(TRAVERSAL_PATH + '*').count
-      assert_equal expect, actual
+    assert_mktmpdir_traversal do |traversal_path|
+      Dir.mktmpdir([traversal_path, 'foo']) do |actual|
+        actual
+      end
+    end
+  end
+
+  def assert_mktmpdir_traversal
+    Dir.mktmpdir do |target|
+      target = target.chomp('/') + '/'
+      traversal_path = target.sub(/\A\w:/, '') # for DOSISH
+      traversal_path = Array.new(target.count('/')-2, '..').join('/') + traversal_path
+      actual = yield traversal_path
+      assert_not_send([File.absolute_path(actual), :start_with?, target])
     end
   end
 end