Fix uninitialized memory read in CJS_Object::GetEmbedObject()

The expected way to create native PDFium objects for JS is via
the NewFxDynamicObject() call in C++, but that doesn't mean that the
corresponding constructors won't be called from JS. In that case,
the internal fields will be uninitialized, and subsequent method
calls may try to use them.

Add a constructor callback for all PDFium objects that nulls out
these fields (shame that v8 doesn't do this by default, but probably
saves some cycles).  Then ensure that we check for this possibility
in all the places it might turn up.

Conversely, if we've just gotten a successful return from
NewFxDynamicObject(), we know the CJS_Object/EmbedObj are good,
so avoid checking there.

BUG=695826

Change-Id: Iadad644c4af937def967ddc83daac1dad7544d69
Reviewed-on: https://pdfium-review.googlesource.com/2839
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

1 files changed, 52 insertions, 30 deletions

diff --git a/fpdfsdk/javascript/JS_Define.h b/fpdfsdk/javascript/JS_Define.h
index ee7448c649..375ca3ac35 100644
--- a/fpdfsdk/javascript/JS_Define.h
+++ b/fpdfsdk/javascript/JS_Define.h
@@ -45,6 +45,8 @@ void JSPropGetter(const char* prop_name_string,
     return;
   CJS_Object* pJSObj =
       static_cast<CJS_Object*>(pRuntime->GetObjectPrivate(info.Holder()));
+  if (!pJSObj)
+    return;
   C* pObj = reinterpret_cast<C*>(pJSObj->GetEmbedObject());
   CFX_WideString sError;
   CJS_PropValue value(pRuntime);
@@ -69,6 +71,8 @@ void JSPropSetter(const char* prop_name_string,
     return;
   CJS_Object* pJSObj =
       static_cast<CJS_Object*>(pRuntime->GetObjectPrivate(info.Holder()));
+  if (!pJSObj)
+    return;
   C* pObj = reinterpret_cast<C*>(pJSObj->GetEmbedObject());
   CFX_WideString sError;
   CJS_PropValue propValue(pRuntime, CJS_Value(pRuntime, value));
@@ -111,6 +115,8 @@ void JSMethod(const char* method_name_string,
   }
   CJS_Object* pJSObj =
       static_cast<CJS_Object*>(pRuntime->GetObjectPrivate(info.Holder()));
+  if (!pJSObj)
+    return;
   C* pObj = reinterpret_cast<C*>(pJSObj->GetEmbedObject());
   CFX_WideString sError;
   CJS_Value valueRes(pRuntime);
@@ -210,33 +216,31 @@ void JSMethod(const char* method_name_string,
   static JSPropertySpec PropertySpecs[];                                       \
   static JSMethodSpec MethodSpecs[];
 
-#define IMPLEMENT_JS_CLASS_RICH_PART(js_class_name, class_alternate,   \
-                                     class_name)                       \
-  void js_class_name::JSConstructor(CFXJS_Engine* pEngine,             \
-                                    v8::Local<v8::Object> obj) {       \
-    CJS_Object* pObj = new js_class_name(obj);                         \
-    pObj->SetEmbedObject(new class_alternate(pObj));                   \
-    pEngine->SetObjectPrivate(obj, (void*)pObj);                       \
-    pObj->InitInstance(static_cast<CJS_Runtime*>(pEngine));            \
-  }                                                                    \
-  void js_class_name::JSDestructor(CFXJS_Engine* pEngine,              \
-                                   v8::Local<v8::Object> obj) {        \
-    js_class_name* pObj =                                              \
-        static_cast<js_class_name*>(pEngine->GetObjectPrivate(obj));   \
-    delete pObj;                                                       \
-  }                                                                    \
-  void js_class_name::DefineProps(CFXJS_Engine* pEngine) {             \
-    for (size_t i = 0; i < FX_ArraySize(PropertySpecs) - 1; ++i) {     \
-      pEngine->DefineObjProperty(g_nObjDefnID, PropertySpecs[i].pName, \
-                                 PropertySpecs[i].pPropGet,            \
-                                 PropertySpecs[i].pPropPut);           \
-    }                                                                  \
-  }                                                                    \
-  void js_class_name::DefineMethods(CFXJS_Engine* pEngine) {           \
-    for (size_t i = 0; i < FX_ArraySize(MethodSpecs) - 1; ++i) {       \
-      pEngine->DefineObjMethod(g_nObjDefnID, MethodSpecs[i].pName,     \
-                               MethodSpecs[i].pMethodCall);            \
-    }                                                                  \
+#define IMPLEMENT_JS_CLASS_RICH_PART(js_class_name, class_alternate,    \
+                                     class_name)                        \
+  void js_class_name::JSConstructor(CFXJS_Engine* pEngine,              \
+                                    v8::Local<v8::Object> obj) {        \
+    CJS_Object* pObj = new js_class_name(obj);                          \
+    pObj->SetEmbedObject(new class_alternate(pObj));                    \
+    pEngine->SetObjectPrivate(obj, (void*)pObj);                        \
+    pObj->InitInstance(static_cast<CJS_Runtime*>(pEngine));             \
+  }                                                                     \
+  void js_class_name::JSDestructor(CFXJS_Engine* pEngine,               \
+                                   v8::Local<v8::Object> obj) {         \
+    delete static_cast<js_class_name*>(pEngine->GetObjectPrivate(obj)); \
+  }                                                                     \
+  void js_class_name::DefineProps(CFXJS_Engine* pEngine) {              \
+    for (size_t i = 0; i < FX_ArraySize(PropertySpecs) - 1; ++i) {      \
+      pEngine->DefineObjProperty(g_nObjDefnID, PropertySpecs[i].pName,  \
+                                 PropertySpecs[i].pPropGet,             \
+                                 PropertySpecs[i].pPropPut);            \
+    }                                                                   \
+  }                                                                     \
+  void js_class_name::DefineMethods(CFXJS_Engine* pEngine) {            \
+    for (size_t i = 0; i < FX_ArraySize(MethodSpecs) - 1; ++i) {        \
+      pEngine->DefineObjMethod(g_nObjDefnID, MethodSpecs[i].pName,      \
+                               MethodSpecs[i].pMethodCall);             \
+    }                                                                   \
   }
 
 // Special JS classes implement methods, props, and queries, but not consts.
@@ -310,12 +314,18 @@ void JSSpecialPropQuery(const char*,
                         const v8::PropertyCallbackInfo<v8::Integer>& info) {
   CJS_Runtime* pRuntime =
       CJS_Runtime::CurrentRuntimeFromIsolate(info.GetIsolate());
-  v8::String::Utf8Value utf8_value(property);
-  CFX_WideString propname = CFX_WideString::FromUTF8(
-      CFX_ByteStringC(*utf8_value, utf8_value.length()));
+  if (!pRuntime)
+    return;
+
   CJS_Object* pJSObj =
       static_cast<CJS_Object*>(pRuntime->GetObjectPrivate(info.Holder()));
+  if (!pJSObj)
+    return;
+
   Alt* pObj = reinterpret_cast<Alt*>(pJSObj->GetEmbedObject());
+  v8::String::Utf8Value utf8_value(property);
+  CFX_WideString propname = CFX_WideString::FromUTF8(
+      CFX_ByteStringC(*utf8_value, utf8_value.length()));
   bool bRet = pObj->QueryProperty(propname.c_str());
   info.GetReturnValue().Set(bRet ? 4 : 0);
 }
@@ -328,8 +338,12 @@ void JSSpecialPropGet(const char* class_name,
       CJS_Runtime::CurrentRuntimeFromIsolate(info.GetIsolate());
   if (!pRuntime)
     return;
+
   CJS_Object* pJSObj =
       static_cast<CJS_Object*>(pRuntime->GetObjectPrivate(info.Holder()));
+  if (!pJSObj)
+    return;
+
   Alt* pObj = reinterpret_cast<Alt*>(pJSObj->GetEmbedObject());
   v8::String::Utf8Value utf8_value(property);
   CFX_WideString propname = CFX_WideString::FromUTF8(
@@ -353,8 +367,12 @@ void JSSpecialPropPut(const char* class_name,
       CJS_Runtime::CurrentRuntimeFromIsolate(info.GetIsolate());
   if (!pRuntime)
     return;
+
   CJS_Object* pJSObj =
       static_cast<CJS_Object*>(pRuntime->GetObjectPrivate(info.Holder()));
+  if (!pJSObj)
+    return;
+
   Alt* pObj = reinterpret_cast<Alt*>(pJSObj->GetEmbedObject());
   v8::String::Utf8Value utf8_value(property);
   CFX_WideString propname = CFX_WideString::FromUTF8(
@@ -375,8 +393,12 @@ void JSSpecialPropDel(const char* class_name,
       CJS_Runtime::CurrentRuntimeFromIsolate(info.GetIsolate());
   if (!pRuntime)
     return;
+
   CJS_Object* pJSObj =
       static_cast<CJS_Object*>(pRuntime->GetObjectPrivate(info.Holder()));
+  if (!pJSObj)
+    return;
+
   Alt* pObj = reinterpret_cast<Alt*>(pJSObj->GetEmbedObject());
   v8::String::Utf8Value utf8_value(property);
   CFX_WideString propname = CFX_WideString::FromUTF8(