Disallow opening of directories as files.

runtime/bin/file.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "bin/file.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 
 #include "include/dart_api.h"
@@ skipping 41 matching lines @@
       DartUtils::GetStringValue(Dart_GetNativeArgument(args, 0));
   int mode = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 1));
   ASSERT(mode == kRead || mode == kWrite || mode == kAppend);
   File::FileOpenMode file_mode = File::kRead;
   if (mode == kWrite) {
     file_mode = File::kWriteTruncate;
   }
   if (mode == kAppend) {
     file_mode = File::kWrite;
   }
-  File* file = File::Open(filename, file_mode);
+  // Check that the file exists before opening it only for
+  // reading. This is to prevent the opening of directories as
+  // files. Directories can be opened for reading using the posix
+  // 'open' call.
+  File* file = NULL;
+  if (((file_mode & File::kWrite) != 0) || File::Exists(filename)) {
+    file = File::Open(filename, file_mode);
+  }
   Dart_SetReturnValue(args, Dart_NewInteger(reinterpret_cast<intptr_t>(file)));
   Dart_ExitScope();
 }
 
 
 void FUNCTION_NAME(File_Exists)(Dart_NativeArguments args) {
   Dart_EnterScope();
   const char* filename =
       DartUtils::GetStringValue(Dart_GetNativeArgument(args, 0));
   bool exists = File::Exists(filename);
@@ skipping 262 matching lines @@
 }
 
 
 void FUNCTION_NAME(File_GetStdioHandleType)(Dart_NativeArguments args) {
   Dart_EnterScope();
   int fd = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 0));
   File::StdioHandleType type = File::GetStdioHandleType(fd);
   Dart_SetReturnValue(args, Dart_NewInteger(type));
   Dart_ExitScope();
 }