- Make ports be less predictable.

runtime/vm/port.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 "vm/port.h"
 
 #include "platform/utils.h"
 #include "vm/dart_api_impl.h"
 #include "vm/isolate.h"
 #include "vm/message_handler.h"
 #include "vm/thread.h"
 
 namespace dart {
 
 DECLARE_FLAG(bool, trace_isolates);
 
 Mutex* PortMap::mutex_ = NULL;
 PortMap::Entry* PortMap::map_ = NULL;
 MessageHandler* PortMap::deleted_entry_ = reinterpret_cast<MessageHandler*>(1);
 intptr_t PortMap::capacity_ = 0;
 intptr_t PortMap::used_ = 0;
 intptr_t PortMap::deleted_ = 0;
-Dart_Port PortMap::next_port_ = 7111;
+Random* PortMap::prng_ = NULL;
 
 
 intptr_t PortMap::FindPort(Dart_Port port) {
   intptr_t index = port % capacity_;
   intptr_t start_index = index;
   Entry entry = map_[index];
   while (entry.handler != NULL) {
     if (entry.port == port) {
       return index;
     }
@@ skipping 22 matching lines @@
     }
   }
   delete[] map_;
   map_ = new_ports;
   capacity_ = new_capacity;
   deleted_ = 0;
 }
 
 
 Dart_Port PortMap::AllocatePort() {
-  Dart_Port result = next_port_;
+  const Dart_Port kMASK = 0x3fffffff;
+  Dart_Port result = prng_->NextUInt32() & kMASK;
 
-  do {
-    // TODO(iposva): Use an approved hashing function to have less predictable
-    // port ids, or make them not accessible from Dart code or both.
-    next_port_++;
-  } while (FindPort(next_port_) >= 0);
+  // Keep getting new values while we have an illegal port number or the port
+  // number is already in use.
+  while ((result == 0) || (FindPort(result) >= 0)) {

[hausner, 2014/03/28 23:27:30]

You could turn this into a do { } while() loop.

[Ivan Posva, 2014/03/28 23:39:26]

I tried to write it as an repeat-until, but that somehow did not work.

+    result = prng_->NextUInt32() & kMASK;
+  }
 
   ASSERT(result != 0);
+  ASSERT(FindPort(result) < 0);
   return result;
 }
 
 
 void PortMap::SetLive(Dart_Port port) {
   MutexLocker ml(mutex_);
   intptr_t index = FindPort(port);
   ASSERT(index >= 0);
   map_[index].live = true;
   map_[index].handler->increment_live_ports();
@@ skipping 166 matching lines @@
     return NULL;
   }
 
   MessageHandler* handler = map_[index].handler;
   return handler->GetIsolate();
 }
 
 
 void PortMap::InitOnce() {
   mutex_ = new Mutex();
+  prng_ = new Random();
 
   static const intptr_t kInitialCapacity = 8;
   // TODO(iposva): Verify whether we want to keep exponentially growing.
   ASSERT(Utils::IsPowerOfTwo(kInitialCapacity));
   map_ = new Entry[kInitialCapacity];
   memset(map_, 0, kInitialCapacity * sizeof(Entry));
   capacity_ = kInitialCapacity;
   used_ = 0;
   deleted_ = 0;
 }
 
 }  // namespace dart