Prohibit setting class variable on frozen module through inheritance

Setting class varibles goes through the ancestor list which can
contain iclasses. Iclasses share a lot of information with the
module they are made from, but not the frozen status.

Check the frozen status of the module instead of the iclass.

1 files changed, 3 insertions, 0 deletions

diff --git a/variable.c b/variable.c
index ebf23fab67..0d8a424438 100644
--- a/variable.c
+++ b/variable.c
@@ -3143,6 +3143,9 @@ rb_cvar_set(VALUE klass, ID id, VALUE val)
 	target = tmp;
     }
 
+    if (RB_TYPE_P(target, T_ICLASS)) {
+        target = RBASIC(target)->klass;
+    }
     check_before_mod_set(target, id, val, "class variable");
     if (!RCLASS_IV_TBL(target)) {
 	RCLASS_IV_TBL(target) = st_init_numtable();