From 4c0747a25b39c0925dd0c94071a286a891291751 Mon Sep 17 00:00:00 2001
From: Alex Beregszaszi <alex@rtfs.hu>
Date: Wed, 14 Mar 2018 16:05:47 +0100
Subject: [PATCH 1/3] Add hasWasmPreamble helper

---
 src/hera.cpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/hera.cpp b/src/hera.cpp
index 6d9966461..c711c0068 100644
--- a/src/hera.cpp
+++ b/src/hera.cpp
@@ -56,6 +56,10 @@ struct hera_instance : evm_instance {
 
 namespace {
 
+bool hasWasmPreamble(vector<uint8_t> const& _input) {
+  return _input.size() >= 5 && _input[0] == 0 && _input[1] == 'a' && _input[2] == 's' && _input[3] == 'm' && _input[4] == 1;
+}
+
 #if HERA_METERING_CONTRACT || HERA_EVM2WASM
 vector<uint8_t> callSystemContract(
   evm_context* context,
@@ -259,7 +263,7 @@ evm_result evm_execute(
     vector<uint8_t> _code(code, code + code_size);
 
     // ensure we can only handle WebAssembly version 1
-    if (code_size < 5 || code[0] != 0 || code[1] != 'a' || code[2] != 's' || code[3] != 'm' || code[4] != 1) {
+    if (!hasWasmPreamble(_code)) {
       hera_instance* hera = static_cast<hera_instance*>(instance);
 #if HERA_EVM2WASM
       // Translate EVM bytecode to WASM

From 89e5ea41348567b2cabd2f76ad8dc7d105e29fc9 Mon Sep 17 00:00:00 2001
From: Alex Beregszaszi <alex@rtfs.hu>
Date: Wed, 14 Mar 2018 16:06:20 +0100
Subject: [PATCH 2/3] Run metering on CREATE output only if it returned wasm
 bytecode

---
 src/hera.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/hera.cpp b/src/hera.cpp
index c711c0068..e1b04af09 100644
--- a/src/hera.cpp
+++ b/src/hera.cpp
@@ -292,7 +292,7 @@ evm_result evm_execute(
     if (result.returnValue.size() > 0) {
       vector<uint8_t> returnValue;
 
-      if (msg->kind == EVM_CREATE && !result.isRevert) {
+      if (msg->kind == EVM_CREATE && !result.isRevert && hasWasmPreamble(result.returnValue)) {
         // Meter the deployed code
         returnValue = sentinel(context, result.returnValue);
         heraAssert(returnValue.size() > 5, "Invalid contract or metering failed.");

From 3fdfad7c83eece3ae880d0c9f0f8611ad518975d Mon Sep 17 00:00:00 2001
From: Alex Beregszaszi <alex@rtfs.hu>
Date: Wed, 14 Mar 2018 16:36:41 +0100
Subject: [PATCH 3/3] Ensure that wasm preamble has both fields completely

---
 src/hera.cpp | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/hera.cpp b/src/hera.cpp
index e1b04af09..4e0cc4b52 100644
--- a/src/hera.cpp
+++ b/src/hera.cpp
@@ -57,7 +57,16 @@ struct hera_instance : evm_instance {
 namespace {
 
 bool hasWasmPreamble(vector<uint8_t> const& _input) {
-  return _input.size() >= 5 && _input[0] == 0 && _input[1] == 'a' && _input[2] == 's' && _input[3] == 'm' && _input[4] == 1;
+  return
+    _input.size() >= 8 &&
+    _input[0] == 0 &&
+    _input[1] == 'a' &&
+    _input[2] == 's' &&
+    _input[3] == 'm' &&
+    _input[4] == 1 &&
+    _input[5] == 0 &&
+    _input[6] == 0 &&
+    _input[7] == 0;
 }
 
 #if HERA_METERING_CONTRACT || HERA_EVM2WASM