Limit identity packets to 8KiB

Healthy identity packages shouldn't be that big and we don't want to
allow systems around us to send us ever humongous packages that will
just leave us without any memory.

Thanks Matthias Gerstner <mgerstner@suse.de> for reporting this.

core/backends/lan/lanlinkprovider.cpp

@@ -399,6 +399,14 @@ void LanLinkProvider::newConnection()
 void LanLinkProvider::dataReceived()
 {
     QSslSocket* socket = qobject_cast<QSslSocket*>(sender());
+    //the size here is arbitrary and is now at 8192 bytes. It needs to be considerably long as it includes the capabilities but there needs to be a limit
+    //Tested between my systems and I get around 2000 per identity package.
+    if (socket->bytesAvailable() > 8192) {
+        qCWarning(KDECONNECT_CORE) << "LanLinkProvider/newConnection: Suspiciously long identity package received. Closing connection." << socket->peerAddress() << socket->bytesAvailable();
+        socket->disconnectFromHost();
+        return;
+    }
+
 #if QT_VERSION < QT_VERSION_CHECK(5,7,0)
     if (!socket->canReadLine())
         return;