From 4cf1da9542d6554ec23de6324c5f2d5eebe138c9 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Tue, 1 Sep 2020 18:06:49 +0900
Subject: Separate jump destination check in `OP_R_RETURN`.

In the past code, the current `callinfo (ci)` was modified, thus it was
possible to pop `ci` beyond the `cibase`, that could cause out of memory
bound access for the code like the following:

```ruby
def m2
  lambda {
    Proc.new {
      return :return # return from the method
    }
  }.call.call
  :never_reached
end

p m2
```
---
 src/vm.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

(limited to 'src')

diff --git a/src/vm.c b/src/vm.c
index bff13af10..b282af260 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -2029,11 +2029,20 @@ RETRY_TRY_BLOCK:
                 goto L_RAISE;
               }
             }
+            /* check jump destination */
             while (cibase <= ci && ci->proc != dst) {
-              if (ci->acc < 0) {
+              if (ci->acc < 0) { /* jump cross C boudary */
                 localjump_error(mrb, LOCALJUMP_ERROR_RETURN);
                 goto L_RAISE;
               }
+              ci--;
+            }
+            if (ci <= cibase) { /* no jump destination */
+              localjump_error(mrb, LOCALJUMP_ERROR_RETURN);
+              goto L_RAISE;
+            }
+            ci = mrb->c->ci;
+            while (cibase <= ci && ci->proc != dst) {
               CHECKPOINT_RESTORE(RBREAK_TAG_RETURN_BLOCK) {
                 cibase = mrb->c->cibase;
                 dst = top_proc(mrb, proc);
@@ -2045,12 +2054,8 @@ RETRY_TRY_BLOCK:
               pc = ci->pc;
               ci = cipop(mrb);
             }
-            mrb->exc = NULL; /* clear break object */
             proc = ci->proc;
-            if (ci <= cibase) {
-              localjump_error(mrb, LOCALJUMP_ERROR_RETURN);
-              goto L_RAISE;
-            }
+            mrb->exc = NULL; /* clear break object */
             break;
           }
           /* fallthrough */
-- 
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