GetDefaultLocalAddress should return the bestIP

webrtc/base/network.cc

Index: webrtc/base/network.cc
diff --git a/webrtc/base/network.cc b/webrtc/base/network.cc
index 001877947046e2d7f5bcdd06c7b08a8ed75d9345..c9ad181776507b063e8e3f87aa5ca927c1f5ef8c 100644
--- a/webrtc/base/network.cc
+++ b/webrtc/base/network.cc
@@ -357,12 +357,34 @@ bool NetworkManagerBase::GetDefaultLocalAddress(int family,
     *ipaddr = default_local_ipv4_address_;
     return true;
   } else if (family == AF_INET6 && !default_local_ipv6_address_.IsNil()) {
-    *ipaddr = default_local_ipv6_address_;
+    Network* ipv6_network = GetNetworkFromAddress(default_local_ipv6_address_);
+    if (ipv6_network) {
+      // If the default ipv6 network's BestIP is different than
+      // default_local_ipv6_address_, use it instead.
+      // This is to prevent potential IP address leakage. See WebRTC bug 5376.
+      *ipaddr = ipv6_network->GetBestIP();
+    } else {
+      *ipaddr = default_local_ipv6_address_;
+    }
     return true;
   }
   return false;
 }
 
+Network* NetworkManagerBase::GetNetworkFromAddress(
+    const rtc::IPAddress& ip) const {
+  for (Network* network : networks_) {
+    const auto& ips = network->GetIPs();
+    if (std::find_if(ips.begin(), ips.end(),
+                     [ip](const InterfaceAddress& existing_ip) {
+                       return ip == static_cast<rtc::IPAddress>(existing_ip);
+                     }) != ips.end()) {
+      return network;
+    }
+  }
+  return nullptr;
+}
+
 BasicNetworkManager::BasicNetworkManager()
     : thread_(NULL), sent_first_update_(false), start_count_(0),
       ignore_non_default_routes_(false) {