Fix use-after-free in ep in Proc#dup for ifunc procs

[Bug #20950]

ifunc proc has the ep allocated in the cfunc_proc_t which is the data of
the TypedData object. If an ifunc proc is duplicated, the ep points to
the ep of the source object. If the source object is freed, then the ep
of the duplicated object now points to a freed memory region. If we try
to use the ep we could crash.

For example, the following script crashes:

    p = { a: 1 }.to_proc
    100.times do
      p = p.dup
      GC.start
      p.call
    rescue ArgumentError
    end

This commit changes ifunc proc to also duplicate the ep when it is duplicated.

1 files changed, 12 insertions, 0 deletions

diff --git a/test/ruby/test_proc.rb b/test/ruby/test_proc.rb
index b9b10c932c..6ca9e0cfb4 100644
--- a/test/ruby/test_proc.rb
+++ b/test/ruby/test_proc.rb
@@ -469,6 +469,18 @@ class TestProc < Test::Unit::TestCase
     assert_throw(:initialize_dup) {c1.new{}.dup}
   end
 
+  def test_dup_ifunc_proc_bug_20950
+    assert_normal_exit(<<~RUBY, "[Bug #20950]")
+      p = { a: 1 }.to_proc
+      100.times do
+        p = p.dup
+        GC.start
+        p.call
+      rescue ArgumentError
+      end
+    RUBY
+  end
+
   def test_clone_subclass
     c1 = Class.new(Proc)
     assert_equal c1, c1.new{}.clone.class, '[Bug #17545]'