From a992d79f56ad6107e72d279343766f0154f90183 Mon Sep 17 00:00:00 2001
From: Aaron Patterson <aaron.patterson@gmail.com>
Date: Tue, 22 Nov 2016 14:31:17 -0800
Subject: [PATCH] Stop reading past the end of `ivptr` array

If you have code like this:

```ruby
class A
  def initialize
    @a = nil
    @b = nil
    @c = nil
    @d = nil
    @e = nil
  end
end

x = A.new
y = x.clone
100.times { |z| x.instance_variable_set(:"@foo#{z}", nil) }
puts y.inspect
```

`x` and `y` will share `iv_index_tbl` hashes.  However, the size of the
hash will grow larger than the number if entries in `ivptr` in `y`.
Before this commit, `rb_ivar_count` would use the size of the hash to
determine how far to read in to the array, but this means that it could
read past the end of the array and cause the program to segv
---
 variable.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/variable.c b/variable.c
index 79e4c8d..af4ab16 100644
--- a/variable.c
+++ b/variable.c
@@ -1605,7 +1605,7 @@ rb_ivar_count(VALUE obj)
     switch (BUILTIN_TYPE(obj)) {
       case T_OBJECT:
 	if ((tbl = ROBJECT_IV_INDEX_TBL(obj)) != 0) {
-	    st_index_t i, count, num = tbl->num_entries;
+	    st_index_t i, count, num = ROBJECT_NUMIV(obj);
 	    const VALUE *const ivptr = ROBJECT_IVPTR(obj);
 	    for (i = count = 0; i < num; ++i) {
 		if (ivptr[i] != Qundef) {
-- 
2.10.1