[rubygems/rubygems] Check requirements classes

Mitigate the security risk:
https://devcraft.io/2021/01/07/universal-deserialisation-gadget-for-ruby-2-x-3-x.html

https://github.com/rubygems/rubygems/commit/141c2f4388

lib/rubygems/requirement.rb

@@ -199,6 +199,8 @@ class Gem::Requirement
 
   def marshal_load(array) # :nodoc:
     @requirements = array[0]
+
+    raise TypeError, "wrong @requirements" unless Array === @requirements
   end
 
   def yaml_initialize(tag, vals) # :nodoc:

test/rubygems/test_gem_requirement.rb

@@ -422,6 +422,40 @@ class TestGemRequirement < Gem::TestCase
     assert_requirement_hash_equal "1", "1.0.0"
   end
 
+  class Exploit < RuntimeError
+  end
+
+  def self.exploit(arg)
+    raise Exploit, "arg = #{arg}"
+  end
+
+  def test_marshal_load_attack
+    wa = Net::WriteAdapter.allocate
+    wa.instance_variable_set(:@socket, self.class)
+    wa.instance_variable_set(:@method_id, :exploit)
+    request_set = Gem::RequestSet.allocate
+    request_set.instance_variable_set(:@git_set, "id")
+    request_set.instance_variable_set(:@sets, wa)
+    wa = Net::WriteAdapter.allocate
+    wa.instance_variable_set(:@socket, request_set)
+    wa.instance_variable_set(:@method_id, :resolve)
+    ent = Gem::Package::TarReader::Entry.allocate
+    ent.instance_variable_set(:@read, 0)
+    ent.instance_variable_set(:@header, "aaa")
+    io = Net::BufferedIO.allocate
+    io.instance_variable_set(:@io, ent)
+    io.instance_variable_set(:@debug_output, wa)
+    reader = Gem::Package::TarReader.allocate
+    reader.instance_variable_set(:@io, io)
+    requirement = Gem::Requirement.allocate
+    requirement.instance_variable_set(:@requirements, reader)
+    m = [Gem::SpecFetcher, Gem::Installer, requirement]
+    e = assert_raise(TypeError) do
+      Marshal.load(Marshal.dump(m))
+    end
+    assert_equal(e.message, "wrong @requirements")
+  end
+
   # Assert that two requirements are equal. Handles Gem::Requirements,
   # strings, arrays, numbers, and versions.