buffer: prevent abort on bad proto

If an object's prototype is munged it's possible to bypass the
instanceof check and cause the application to abort. Instead now use
HasInstance() to verify that the object is a Buffer, and throw if not.

This check will not work for JS only methods. So while the application
won't abort, it also won't throw.

In order to properly throw in all cases with toString() the JS
optimization of checking that length is zero has been removed. In its
place the native methods will now return early if a zero length string
is detected.

Ref: https://github.com/nodejs/io.js/pull/1486
Ref: https://github.com/nodejs/io.js/pull/1922
Fixes: https://github.com/nodejs/io.js/issues/1485
PR-URL: https://github.com/nodejs/io.js/pull/2012
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

3 files changed, 88 insertions, 6 deletions

diff --git a/lib/buffer.js b/lib/buffer.js
index 4625515c6..6732ecdee 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -380,8 +380,6 @@ function slowToString(encoding, start, end) {
 
 Buffer.prototype.toString = function() {
   const length = this.length | 0;
-  if (length === 0)
-    return '';
   if (arguments.length === 0)
     return this.utf8Slice(0, length);
   return slowToString.apply(this, arguments);
diff --git a/src/node_buffer.cc b/src/node_buffer.cc
index fca08599e..5133140a8 100644
--- a/src/node_buffer.cc
+++ b/src/node_buffer.cc
@@ -18,6 +18,12 @@
     if (!(r)) return env->ThrowRangeError("out of range index");            \
   } while (0)
 
+#define THROW_AND_RETURN_UNLESS_BUFFER(env, obj)                            \
+  do {                                                                      \
+    if (!HasInstance(obj))                                                  \
+      return env->ThrowTypeError("argument should be a Buffer");            \
+  } while (0)
+
 #define ARGS_THIS(argT)                                                     \
   Local<Object> obj = argT;                                                 \
   size_t obj_length = obj->GetIndexedPropertiesExternalArrayDataLength();   \
@@ -223,7 +229,12 @@ template <encoding encoding>
 void StringSlice(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
+  THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
   ARGS_THIS(args.This())
+
+  if (obj_length == 0)
+    return args.GetReturnValue().SetEmptyString();
+
   SLICE_START_END(args[0], args[1], obj_length)
 
   args.GetReturnValue().Set(
@@ -235,7 +246,12 @@ template <>
 void StringSlice<UCS2>(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
+  THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
   ARGS_THIS(args.This())
+
+  if (obj_length == 0)
+    return args.GetReturnValue().SetEmptyString();
+
   SLICE_START_END(args[0], args[1], obj_length)
   length /= 2;
 
@@ -306,8 +322,9 @@ void Copy(const FunctionCallbackInfo<Value> &args) {
   if (!HasInstance(args[0]))
     return env->ThrowTypeError("first arg should be a Buffer");
 
-  Local<Object> target = args[0]->ToObject(env->isolate());
+  Local<Object> target = args[0].As<Object>();
 
+  THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
   ARGS_THIS(args.This())
   size_t target_length = target->GetIndexedPropertiesExternalArrayDataLength();
   char* target_data = static_cast<char*>(
@@ -340,6 +357,7 @@ void Copy(const FunctionCallbackInfo<Value> &args) {
 
 
 void Fill(const FunctionCallbackInfo<Value>& args) {
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   ARGS_THIS(args[0].As<Object>())
 
   size_t start = args[2]->Uint32Value();
@@ -383,6 +401,7 @@ template <encoding encoding>
 void StringWrite(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
+  THROW_AND_RETURN_UNLESS_BUFFER(env, args.This());
   ARGS_THIS(args.This())
 
   if (!args[0]->IsString())
@@ -459,6 +478,7 @@ static inline void Swizzle(char* start, unsigned int len) {
 
 template <typename T, enum Endianness endianness>
 void ReadFloatGeneric(const FunctionCallbackInfo<Value>& args) {
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   ARGS_THIS(args[0].As<Object>());
 
   uint32_t offset = args[1]->Uint32Value();
@@ -522,21 +542,25 @@ uint32_t WriteFloatGeneric(const FunctionCallbackInfo<Value>& args) {
 
 
 void WriteFloatLE(const FunctionCallbackInfo<Value>& args) {
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   args.GetReturnValue().Set(WriteFloatGeneric<float, kLittleEndian>(args));
 }
 
 
 void WriteFloatBE(const FunctionCallbackInfo<Value>& args) {
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   args.GetReturnValue().Set(WriteFloatGeneric<float, kBigEndian>(args));
 }
 
 
 void WriteDoubleLE(const FunctionCallbackInfo<Value>& args) {
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   args.GetReturnValue().Set(WriteFloatGeneric<double, kLittleEndian>(args));
 }
 
 
 void WriteDoubleBE(const FunctionCallbackInfo<Value>& args) {
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   args.GetReturnValue().Set(WriteFloatGeneric<double, kBigEndian>(args));
 }
 
@@ -550,6 +574,10 @@ void ByteLengthUtf8(const FunctionCallbackInfo<Value> &args) {
 
 
 void Compare(const FunctionCallbackInfo<Value> &args) {
+  Environment* env = Environment::GetCurrent(args);
+  THROW_AND_RETURN_UNLESS_BUFFER(env, args[0]);
+  THROW_AND_RETURN_UNLESS_BUFFER(env, args[1]);
+
   Local<Object> obj_a = args[0].As<Object>();
   char* obj_a_data =
       static_cast<char*>(obj_a->GetIndexedPropertiesExternalArrayData());
@@ -599,10 +627,10 @@ int32_t IndexOf(const char* haystack,
 
 
 void IndexOfString(const FunctionCallbackInfo<Value>& args) {
-  ASSERT(args[0]->IsObject());
   ASSERT(args[1]->IsString());
   ASSERT(args[2]->IsNumber());
 
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   ARGS_THIS(args[0].As<Object>());
   node::Utf8Value str(args.GetIsolate(), args[1]);
   int32_t offset_i32 = args[2]->Int32Value();
@@ -630,10 +658,10 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
 
 
 void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
-  ASSERT(args[0]->IsObject());
   ASSERT(args[1]->IsObject());
   ASSERT(args[2]->IsNumber());
 
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   ARGS_THIS(args[0].As<Object>());
   Local<Object> buf = args[1].As<Object>();
   int32_t offset_i32 = args[2]->Int32Value();
@@ -667,10 +695,10 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
 
 
 void IndexOfNumber(const FunctionCallbackInfo<Value>& args) {
-  ASSERT(args[0]->IsObject());
   ASSERT(args[1]->IsNumber());
   ASSERT(args[2]->IsNumber());
 
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   ARGS_THIS(args[0].As<Object>());
   uint32_t needle = args[1]->Uint32Value();
   int32_t offset_i32 = args[2]->Int32Value();
diff --git a/test/parallel/test-buffer-fakes.js b/test/parallel/test-buffer-fakes.js
new file mode 100644
index 000000000..d473d16e9
--- /dev/null
+++ b/test/parallel/test-buffer-fakes.js
@@ -0,0 +1,56 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const Buffer = require('buffer').Buffer;
+const Bp = Buffer.prototype;
+
+function FakeBuffer() { }
+FakeBuffer.__proto__ = Buffer;
+FakeBuffer.prototype.__proto__ = Buffer.prototype;
+
+const fb = new FakeBuffer();
+
+assert.throws(function() {
+  new Buffer(fb);
+}, TypeError);
+
+assert.throws(function() {
+  +Buffer.prototype;
+}, TypeError);
+
+assert.throws(function() {
+  Buffer.compare(fb, new Buffer(0));
+}, TypeError);
+
+assert.throws(function() {
+  fb.write('foo');
+}, TypeError);
+
+assert.throws(function() {
+  Buffer.concat([fb, fb]);
+}, TypeError);
+
+assert.throws(function() {
+  fb.toString();
+}, TypeError);
+
+assert.throws(function() {
+  fb.equals(new Buffer(0));
+}, TypeError);
+
+assert.throws(function() {
+  fb.indexOf(5);
+}, TypeError);
+
+assert.throws(function() {
+  fb.readFloatLE(0);
+}, TypeError);
+
+assert.throws(function() {
+  fb.writeFloatLE(0);
+}, TypeError);
+
+assert.throws(function() {
+  fb.fill(0);
+}, TypeError);