Use mrb_ptr instead of mrb_cptr in Kernel#to_s

This is to avoid segfault when WORD_BOXING is enabled

Reported by https://hackerone.com/brakhane

1 files changed, 15 insertions, 0 deletions

diff --git a/test/t/kernel.rb b/test/t/kernel.rb
index d240e59dc..e59bd6a10 100644
--- a/test/t/kernel.rb
+++ b/test/t/kernel.rb
@@ -520,6 +520,21 @@ assert('Kernel#to_s', '15.3.1.3.46') do
   assert_equal to_s.class, String
 end
 
+assert('Kernel#to_s on primitives') do
+  begin
+    Fixnum.alias_method :to_s_, :to_s
+    Fixnum.remove_method :to_s
+
+    assert_nothing_raised do
+      # segfaults if mrb_cptr is used
+      1.to_s
+    end
+  ensure
+    Fixnum.alias_method :to_s, :to_s_
+    Fixnum.remove_method :to_s_
+  end
+end
+
 assert('Kernel.local_variables', '15.3.1.2.7') do
   a, b = 0, 1
   a += b