fs: validate fd on fs.write

PR-URL: nodejs#1553
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

src/node_file.cc

@@ -779,7 +779,9 @@ static void Open(const FunctionCallbackInfo<Value>& args) {
 static void WriteBuffer(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
-  CHECK(args[0]->IsInt32());
+  if (!args[0]->IsInt32())
+    return env->ThrowTypeError("First argument must be file descriptor");
+
   CHECK(Buffer::HasInstance(args[1]));
 
   int fd = args[0]->Int32Value();

test/parallel/test-fs-write-no-fd.js

@@ -0,0 +1,11 @@
+const common = require('../common');
+const fs = require('fs');
+const assert = require('assert');
+
+assert.throws(function() {
+  fs.write(null, new Buffer(1), 0, 1);
+}, /TypeError/);
+
+assert.throws(function() {
+  fs.write(null, '1', 0, 1);
+}, /TypeError/);