MultiplexedSocket: refuse channel if id exists

Prevents the peer from hijacking existing channels,
preventing various issues when collisions occur.

Also mark accepted connections as 'answered', allowing
its removal if shutdown by the server.

Change-Id: Ie91d50b0d518cb6621289233bfda2c289deeed5c

src/multiplexed_socket.cpp

@@ -128,7 +128,7 @@ public:
 
     std::shared_ptr<ChannelSocket> makeSocket(const std::string& name,
                                               uint16_t channel,
-                                              bool isInitiator = false)
+                                              bool isInitiator)
     {
         auto& channelSocket = sockets[channel];
         if (not channelSocket)
@@ -143,8 +143,8 @@ public:
                 });
         else {
             if (logger_)
-                logger_->warn("A channel is already present on that socket, accepting "
-                      "the request will close the previous one {}", name);
+                logger_->warn("Received request for existing channel {}", channel);
+            return {};
         }
         return channelSocket;
     }
@@ -393,11 +393,23 @@ MultiplexedSocket::Impl::onVersion(int version)
 void
 MultiplexedSocket::Impl::onRequest(const std::string& name, uint16_t channel)
 {
-    auto accept = onRequest_(endpoint->peerCertificate(), channel, name);
+    bool accept;
+    if (channel == CONTROL_CHANNEL || channel == PROTOCOL_CHANNEL) {
+        if (logger_)
+            logger_->warn("Channel {:d} is reserved, refusing request", channel);
+        accept = false;
+    } else
+        accept = onRequest_(endpoint->peerCertificate(), channel, name);
+
     std::shared_ptr<ChannelSocket> channelSocket;
     if (accept) {
         std::lock_guard<std::mutex> lkSockets(socketsMutex);
-        channelSocket = makeSocket(name, channel);
+        channelSocket = makeSocket(name, channel, false);
+        if (not channelSocket) {
+            if (logger_)
+                logger_->error("Channel {:d} already exists, refusing request", channel);
+            accept = false;
+        }
     }
 
     // Answer to ChannelRequest if accepted
@@ -422,6 +434,11 @@ MultiplexedSocket::Impl::onRequest(const std::string& name, uint16_t channel)
     if (accept) {
         onChannelReady_(deviceId, channelSocket);
         channelSocket->ready(true);
+        if (channelSocket->isRemovable()) {
+            std::lock_guard<std::mutex> lkSockets(socketsMutex);
+            sockets.erase(channel);
+        } else
+            channelSocket->answered();
     }
 }