- Make ports be less predictable.

runtime/vm/port.cc

Index: runtime/vm/port.cc
===================================================================
--- runtime/vm/port.cc	(revision 34525)
+++ runtime/vm/port.cc	(working copy)
@@ -20,7 +20,7 @@
 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) {
@@ -63,15 +63,17 @@
 
 
 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;
 }
 
@@ -258,6 +260,7 @@
 
 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.