Check length of env stack before accessing upvar; fix #3995

19050916 · Yukihiro "Matz" Matsumoto · e340b172 · 19050916
Commit 19050916 authored Apr 11, 2018 by Yukihiro "Matz" Matsumoto
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src/vm.c src/vm.c +3 -3

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--- a/src/vm.c
+++ b/src/vm.c
@@ -1201,11 +1201,11 @@ RETRY_TRY_BLOCK:
      mrb_value *regs_a = regs + a;
      struct REnv *e = uvenv(mrb, c);

-      if (!e) {
-        *regs_a = mrb_nil_value();
+      if (e && b < MRB_ENV_STACK_LEN(e)) {
+        *regs_a = e->stack[b];
      }
      else {
-        *regs_a = e->stack[b];
+        *regs_a = mrb_nil_value();
      }
      NEXT;
    }