Backport #7557: Module#initialize_copy allows to change the superclass of a class

• Status: Closed
• Assignee: usa (Usaku NAKAMURA)

=begin

You can abuse (({Module#initialize_copy})) to change the superclass of a class, because of this line of code in (({rb_mod_init_copy})):

RCLASS_SUPER(clone) = RCLASS_SUPER(orig);

(({Class#initialize_copy})) does perform some checks to stop you calling (({#initialize})) on an already initialized class, but this can be subverted by redefining it to call (({super})) from Ruby-land.

Here's an example:

class Class
def initialize_copy(*)
super
end

def superclass=(klass)
  initialize_copy(Class.new(klass))
end

end

Symbol.superclass = String

p :hello.class.ancestors

=> [Symbol, String, Comparable, Object, Kernel, BasicObject]

• Status changed from Open to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r38364.
Charlie, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• object.c (Init_Object): use rb_mod_init_copy for Class#initialize_copy
  • class.c (rb_class_init_copy): rename to class_init_copy_check, performs type
    checks on arguments to prevent reinitialization of initialized class
    [ruby-core:50869] [Bug #7557]
  • class.c (rb_mod_init_copy): use class_init_copy_check if receiver is T_CLASS
  • test/ruby/test_class.rb (class TestClass): related test

[nobu (Nobuyoshi Nakada)]

• Tracker changed from Bug to Backport
• Project changed from Ruby to 13
• Category deleted (core)
• Status changed from Closed to Assigned
• Priority changed from Normal to 5
• Assignee changed from Anonymous to usa (Usaku NAKAMURA)

[usa (Usaku NAKAMURA)]

• Status changed from Assigned to Closed

This issue was solved with changeset r38507.
Charlie, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

merge revision(s) 38364,38366: [Backport #7557]

* object.c (Init_Object): use rb_mod_init_copy for Class#initialize_copy

* class.c (rb_class_init_copy): rename to class_init_copy_check, performs type
  checks on arguments to prevent reinitialization of initialized class
  [ruby-core:50869] [Bug #7557]

* class.c (rb_mod_init_copy): use class_init_copy_check if receiver is T_CLASS

* test/ruby/test_class.rb (class TestClass): related test