Fix for issue 24487951 (heap buffer overflow problem)

runtime/bin/dartutils.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/dartutils.h"
 
 #include "include/dart_api.h"
 #include "include/dart_tools_api.h"
 #include "include/dart_native_api.h"
 
@@ skipping 446 matching lines @@
                               url,
                               library_url,
                               builtin_lib);
 }
 
 
 const uint8_t* DartUtils::SniffForMagicNumber(const uint8_t* text_buffer,
                                               intptr_t* buffer_len,
                                               bool* is_snapshot) {
   intptr_t len = sizeof(magic_number);
+  if (*buffer_len <= len) {
+    *is_snapshot = false;
+    return text_buffer;
+  }
   for (intptr_t i = 0; i < len; i++) {
     if (text_buffer[i] != magic_number[i]) {
       *is_snapshot = false;
       return text_buffer;
     }
   }
   *is_snapshot = true;
   ASSERT(*buffer_len > len);
   *buffer_len -= len;
   return text_buffer + len;
@@ skipping 759 matching lines @@
       new CObjectString(CObject::NewString(os_error->message()));
   CObjectArray* result = new CObjectArray(CObject::NewArray(3));
   result->SetAt(0, new CObjectInt32(CObject::NewInt32(kOSError)));
   result->SetAt(1, new CObjectInt32(CObject::NewInt32(os_error->code())));
   result->SetAt(2, error_message);
   return result;
 }
 
 }  // namespace bin
 }  // namespace dart