From d4c5b0da105206e3e541fb5a8c69ad061ff35cd6 Mon Sep 17 00:00:00 2001
From: Kelvin Fichter <kelvinfichter@gmail.com>
Date: Fri, 9 Apr 2021 15:48:16 -0700
Subject: [PATCH] fix: Check for overflows in safety checker

---
 .../OVM/execution/OVM_SafetyChecker.sol                  | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/contracts/optimistic-ethereum/OVM/execution/OVM_SafetyChecker.sol b/contracts/optimistic-ethereum/OVM/execution/OVM_SafetyChecker.sol
index ff90584a6..8994f2e4f 100644
--- a/contracts/optimistic-ethereum/OVM/execution/OVM_SafetyChecker.sol
+++ b/contracts/optimistic-ethereum/OVM/execution/OVM_SafetyChecker.sol
@@ -57,12 +57,17 @@ contract OVM_SafetyChecker is iOVM_SafetyChecker {
         // PUSH opcodes
         uint256 opcodePushMask = ~uint256(0xffffffff000000000000000000000000);
 
-        uint256 codeLength;
         uint256 _pc;
         assembly {
             _pc := add(_bytecode, 0x20)
         }
-        codeLength = _pc + _bytecode.length;
+        uint256 codeLength = _pc + _bytecode.length;
+
+        // Simple overflow check.
+        if (codeLength < _pc) {
+            return false;
+        }
+
         do {
             // current opcode: 0x00...0xff
             uint256 opNum;