https://git.ruby-lang.org/ruby.git/commit/?id=b61e82eac9

From b61e82eac9fb5ac247b204dd4fbf09ac49fce530 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=8D=9C=E9=83=A8=E6=98=8C=E5=B9=B3?=
 <shyouhei@r...>
Date: Sun, 31 May 2020 16:44:42 +0900
Subject: vm_call_symbol: check stack overflow

VM stack could overflow here.  The condition is when a symbol is passed
to a block-taking method via &variable, and that symbol has never been
used for actual method names (thus yielding that results in calling
method_missing), and the VM stack is full (no single word left).  This
is a once-in-a-blue-moon event.  Yet there is a very tiny room of stack
overflow.  We need to check that.

diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index e36ce10..bd6b0a2 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -2708,6 +2708,7 @@ vm_call_symbol( https://github.com/ruby/ruby/blob/trunk/vm_insnhelper.c#L2708
          * --+------+--------+------+------
          */
         int i = argc;
+        CHECK_VM_STACK_OVERFLOW(reg_cfp, 1);
         INC_SP(1);
         MEMMOVE(&TOPN(i - 1), &TOPN(i), VALUE, i);
         argc = ++calling->argc;
-- 
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