Remove implicit conversion using `to_int` method.

The ISO standard does not include implicit type conversion using
`to_int`. This implicit conversion often causes vulnerability.
There will be no more attacks like #4120.

In addition, we have added internal convenience method `__to_int` which
does type check and conversion (from floats).

3 files changed, 18 insertions, 45 deletions

diff --git a/src/kernel.c b/src/kernel.c
index db681d510..195594d6b 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -830,6 +830,7 @@ mrb_obj_ceqq(mrb_state *mrb, mrb_value self)
 }
 
 mrb_value mrb_obj_equal_m(mrb_state *mrb, mrb_value);
+
 void
 mrb_init_kernel(mrb_state *mrb)
 {
@@ -871,6 +872,7 @@ mrb_init_kernel(mrb_state *mrb)
   mrb_define_method(mrb, krn, "respond_to?",                obj_respond_to,                  MRB_ARGS_ANY());     /* 15.3.1.3.43 */
   mrb_define_method(mrb, krn, "to_s",                       mrb_any_to_s,                    MRB_ARGS_NONE());    /* 15.3.1.3.46 */
   mrb_define_method(mrb, krn, "__case_eqq",                 mrb_obj_ceqq,                    MRB_ARGS_REQ(1));    /* internal */
+  mrb_define_method(mrb, krn, "__to_int",                   mrb_to_int,                      MRB_ARGS_NONE()); /* internal */
 
   mrb_define_method(mrb, krn, "class_defined?",             mrb_krn_class_defined,           MRB_ARGS_REQ(1));
 
diff --git a/src/numeric.c b/src/numeric.c
index f7f0318e8..3624831cc 100644
--- a/src/numeric.c
+++ b/src/numeric.c
@@ -674,7 +674,6 @@ flo_round(mrb_state *mrb, mrb_value num)
 /*
  *  call-seq:
  *     flt.to_i      ->  integer
- *     flt.to_int    ->  integer
  *     flt.truncate  ->  integer
  *
  *  Returns <i>flt</i> truncated to an <code>Integer</code>.
@@ -714,7 +713,6 @@ flo_nan_p(mrb_state *mrb, mrb_value num)
 /*
  *  call-seq:
  *     int.to_i      ->  integer
- *     int.to_int    ->  integer
  *
  *  As <i>int</i> is already an <code>Integer</code>, all these
  *  methods simply return the receiver.
@@ -1513,7 +1511,6 @@ mrb_init_numeric(mrb_state *mrb)
   MRB_SET_INSTANCE_TT(integer, MRB_TT_FIXNUM);
   mrb_undef_class_method(mrb, integer, "new");
   mrb_define_method(mrb, integer, "to_i",     int_to_i,        MRB_ARGS_NONE()); /* 15.2.8.3.24 */
-  mrb_define_method(mrb, integer, "to_int",   int_to_i,        MRB_ARGS_NONE());
 #ifndef MRB_WITHOUT_FLOAT
   mrb_define_method(mrb, integer, "ceil",     int_to_i,        MRB_ARGS_REQ(1)); /* 15.2.8.3.8 (x) */
   mrb_define_method(mrb, integer, "floor",    int_to_i,        MRB_ARGS_REQ(1)); /* 15.2.8.3.10 (x) */
@@ -1565,7 +1562,6 @@ mrb_init_numeric(mrb_state *mrb)
   mrb_define_method(mrb, fl,      "round",     flo_round,      MRB_ARGS_OPT(1)); /* 15.2.9.3.12 */
   mrb_define_method(mrb, fl,      "to_f",      flo_to_f,       MRB_ARGS_NONE()); /* 15.2.9.3.13 */
   mrb_define_method(mrb, fl,      "to_i",      flo_truncate,   MRB_ARGS_NONE()); /* 15.2.9.3.14 */
-  mrb_define_method(mrb, fl,      "to_int",    flo_truncate,   MRB_ARGS_NONE());
   mrb_define_method(mrb, fl,      "truncate",  flo_truncate,   MRB_ARGS_NONE()); /* 15.2.9.3.15 */
   mrb_define_method(mrb, fl,      "divmod",    flo_divmod,     MRB_ARGS_REQ(1));
   mrb_define_method(mrb, fl,      "eql?",      flo_eql,        MRB_ARGS_REQ(1)); /* 15.2.8.3.16 */
diff --git a/src/object.c b/src/object.c
index 8724c5416..ba6fa3947 100644
--- a/src/object.c
+++ b/src/object.c
@@ -323,19 +323,6 @@ convert_type(mrb_state *mrb, mrb_value val, const char *tname, const char *metho
 }
 
 MRB_API mrb_value
-mrb_check_to_integer(mrb_state *mrb, mrb_value val, const char *method)
-{
-  mrb_value v;
-
-  if (mrb_fixnum_p(val)) return val;
-  v = convert_type(mrb, val, "Integer", method, FALSE);
-  if (mrb_nil_p(v) || !mrb_fixnum_p(v)) {
-    return mrb_nil_value();
-  }
-  return v;
-}
-
-MRB_API mrb_value
 mrb_convert_type(mrb_state *mrb, mrb_value val, enum mrb_vtype type, const char *tname, const char *method)
 {
   mrb_value v;
@@ -505,25 +492,22 @@ mrb_obj_is_kind_of(mrb_state *mrb, mrb_value obj, struct RClass *c)
   return FALSE;
 }
 
-static mrb_value
-mrb_to_integer(mrb_state *mrb, mrb_value val, const char *method)
-{
-  mrb_value v;
-
-  if (mrb_fixnum_p(val)) return val;
-  v = convert_type(mrb, val, "Integer", method, TRUE);
-  if (!mrb_obj_is_kind_of(mrb, v, mrb->fixnum_class)) {
-    mrb_value type = inspect_type(mrb, val);
-    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S to Integer (%S#%S gives %S)",
-               type, type, mrb_str_new_cstr(mrb, method), inspect_type(mrb, v));
-  }
-  return v;
-}
-
 MRB_API mrb_value
 mrb_to_int(mrb_state *mrb, mrb_value val)
 {
-  return mrb_to_integer(mrb, val, "to_int");
+
+  if (!mrb_fixnum_p(val)) {
+    mrb_value type;
+
+#ifndef MRB_WITHOUT_FLOAT
+    if (mrb_float_p(val)) {
+      return mrb_flo_to_fixnum(mrb, val);
+    }
+#endif
+    type = inspect_type(mrb, val);
+    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S to Integer", type);
+  }
+  return val;
 }
 
 MRB_API mrb_value
@@ -533,18 +517,12 @@ mrb_convert_to_integer(mrb_state *mrb, mrb_value val, mrb_int base)
 
   if (mrb_nil_p(val)) {
     if (base != 0) goto arg_error;
-      mrb_raise(mrb, E_TYPE_ERROR, "can't convert nil into Integer");
+    mrb_raise(mrb, E_TYPE_ERROR, "can't convert nil into Integer");
   }
   switch (mrb_type(val)) {
 #ifndef MRB_WITHOUT_FLOAT
     case MRB_TT_FLOAT:
       if (base != 0) goto arg_error;
-      else {
-        mrb_float f = mrb_float(val);
-        if (FIXABLE_FLOAT(f)) {
-          break;
-        }
-      }
       return mrb_flo_to_fixnum(mrb, val);
 #endif
 
@@ -568,11 +546,8 @@ mrb_convert_to_integer(mrb_state *mrb, mrb_value val, mrb_int base)
 arg_error:
     mrb_raise(mrb, E_ARGUMENT_ERROR, "base specified for non string value");
   }
-  tmp = convert_type(mrb, val, "Integer", "to_int", FALSE);
-  if (mrb_nil_p(tmp) || !mrb_fixnum_p(tmp)) {
-    tmp = mrb_to_integer(mrb, val, "to_i");
-  }
-  return tmp;
+  /* to raise TypeError */
+  return mrb_to_int(mrb, val);
 }
 
 MRB_API mrb_value