negative bounds checking on realm calls

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 76ff4f94318890a4cd3b23b3b42208fec4c3d409..564aafe0050263b5128c1693ac9a0845bd2fab1e 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -119,6 +119,8 @@ class PerIsolateData {
   Persistent<Context>* realms_;
   Persistent<Value> realm_shared_;
 
+  int RealmIndexOrThrow(const v8::FunctionCallbackInfo<v8::Value>& args,
+                        int arg_offset);
   int RealmFind(Handle<Context> context);
 };
 
@@ -288,6 +290,24 @@ int PerIsolateData::RealmFind(Handle<Context> context) {
 }
 
 
+int PerIsolateData::RealmIndexOrThrow(
+    const v8::FunctionCallbackInfo<v8::Value>& args,
+    int arg_offset) {
+  if (args.Length() < arg_offset || !args[arg_offset]->IsNumber()) {
+    Throw(args.GetIsolate(), "Invalid argument");
+    return -1;
+  }
+  int index = args[arg_offset]->Int32Value();
+  if (index < 0 ||
+      index >= realm_count_ ||
+      realms_[index].IsEmpty()) {
+    Throw(args.GetIsolate(), "Invalid realm index");
+    return -1;
+  }
+  return index;
+}
+
+
 #ifndef V8_SHARED
 // performance.now() returns a time stamp as double, measured in milliseconds.
 void Shell::PerformanceNow(const v8::FunctionCallbackInfo<v8::Value>& args) {
@@ -325,15 +345,8 @@ void Shell::RealmOwner(const v8::FunctionCallbackInfo<v8::Value>& args) {
 // (Note that properties of global objects cannot be read/written cross-realm.)
 void Shell::RealmGlobal(const v8::FunctionCallbackInfo<v8::Value>& args) {
   PerIsolateData* data = PerIsolateData::Get(args.GetIsolate());
-  if (args.Length() < 1 || !args[0]->IsNumber()) {
-    Throw(args.GetIsolate(), "Invalid argument");
-    return;
-  }
-  int index = args[0]->Uint32Value();
-  if (index >= data->realm_count_ || data->realms_[index].IsEmpty()) {
-    Throw(args.GetIsolate(), "Invalid realm index");
-    return;
-  }
+  int index = data->RealmIndexOrThrow(args, 0);
+  if (index == -1) return;
   args.GetReturnValue().Set(
       Local<Context>::New(args.GetIsolate(), data->realms_[index])->Global());
 }
@@ -361,13 +374,9 @@ void Shell::RealmCreate(const v8::FunctionCallbackInfo<v8::Value>& args) {
 void Shell::RealmDispose(const v8::FunctionCallbackInfo<v8::Value>& args) {
   Isolate* isolate = args.GetIsolate();
   PerIsolateData* data = PerIsolateData::Get(isolate);
-  if (args.Length() < 1 || !args[0]->IsNumber()) {
-    Throw(args.GetIsolate(), "Invalid argument");
-    return;
-  }
-  int index = args[0]->Uint32Value();
-  if (index >= data->realm_count_ || data->realms_[index].IsEmpty() ||
-      index == 0 ||
+  int index = data->RealmIndexOrThrow(args, 0);
+  if (index == -1) return;
+  if (index == 0 ||
       index == data->realm_current_ || index == data->realm_switch_) {
     Throw(args.GetIsolate(), "Invalid realm index");
     return;
@@ -380,15 +389,8 @@ void Shell::RealmDispose(const v8::FunctionCallbackInfo<v8::Value>& args) {
 void Shell::RealmSwitch(const v8::FunctionCallbackInfo<v8::Value>& args) {
   Isolate* isolate = args.GetIsolate();
   PerIsolateData* data = PerIsolateData::Get(isolate);
-  if (args.Length() < 1 || !args[0]->IsNumber()) {
-    Throw(args.GetIsolate(), "Invalid argument");
-    return;
-  }
-  int index = args[0]->Uint32Value();
-  if (index >= data->realm_count_ || data->realms_[index].IsEmpty()) {
-    Throw(args.GetIsolate(), "Invalid realm index");
-    return;
-  }
+  int index = data->RealmIndexOrThrow(args, 0);
+  if (index == -1) return;
   data->realm_switch_ = index;
 }
 
@@ -397,15 +399,12 @@ void Shell::RealmSwitch(const v8::FunctionCallbackInfo<v8::Value>& args) {
 void Shell::RealmEval(const v8::FunctionCallbackInfo<v8::Value>& args) {
   Isolate* isolate = args.GetIsolate();
   PerIsolateData* data = PerIsolateData::Get(isolate);
-  if (args.Length() < 2 || !args[0]->IsNumber() || !args[1]->IsString()) {
+  int index = data->RealmIndexOrThrow(args, 0);
+  if (index == -1) return;
+  if (args.Length() < 2 || !args[1]->IsString()) {
     Throw(args.GetIsolate(), "Invalid argument");
     return;
   }
-  int index = args[0]->Uint32Value();
-  if (index >= data->realm_count_ || data->realms_[index].IsEmpty()) {
-    Throw(args.GetIsolate(), "Invalid realm index");
-    return;
-  }
   Handle<Script> script = Script::New(args[1]->ToString());
   if (script.IsEmpty()) return;
   Local<Context> realm = Local<Context>::New(isolate, data->realms_[index]);