nghttpx: Disable TLS renegotiation

src/shrpx_client_handler.cc

@@ -48,6 +48,10 @@ namespace {
 void upstream_readcb(bufferevent *bev, void *arg)
 {
   auto handler = reinterpret_cast<ClientHandler*>(arg);
+  if(handler->get_tls_renegotiation()) {
+    delete handler;
+    return;
+  }
   int rv = handler->on_read();
   if(rv != 0) {
     delete handler;
@@ -106,8 +110,9 @@ void upstream_eventcb(bufferevent *bev, short events, void *arg)
     delete handler;
   } else {
     if(events & BEV_EVENT_CONNECTED) {
+      handler->set_tls_handshake(true);
       if(LOG_ENABLED(INFO)) {
-        CLOG(INFO, handler) << "SSL/TLS handleshake completed";
+        CLOG(INFO, handler) << "SSL/TLS handshake completed";
       }
       if(handler->validate_next_proto() != 0) {
         delete handler;
@@ -226,7 +231,9 @@ ClientHandler::ClientHandler(bufferevent *bev, int fd, SSL *ssl,
     ssl_(ssl),
     left_connhd_len_(NGHTTP2_CLIENT_CONNECTION_HEADER_LEN),
     fd_(fd),
-    should_close_after_write_(false)
+    should_close_after_write_(false),
+    tls_handshake_(false),
+    tls_renegotiation_(false)
 {
   int rv;
   rv = bufferevent_set_rate_limit(bev_, get_config()->rate_limit_cfg);
@@ -238,6 +245,7 @@ ClientHandler::ClientHandler(bufferevent *bev, int fd, SSL *ssl,
   set_upstream_timeouts(&get_config()->upstream_read_timeout,
                         &get_config()->upstream_write_timeout);
   if(ssl_) {
+    SSL_set_app_data(ssl_, reinterpret_cast<char*>(this));
     set_bev_cb(nullptr, upstream_writecb, upstream_eventcb);
   } else {
     // For non-TLS version, first create HttpsUpstream. It may be
@@ -254,6 +262,7 @@ ClientHandler::~ClientHandler()
     CLOG(INFO, this) << "Deleting";
   }
   if(ssl_) {
+    SSL_set_app_data(ssl_, nullptr);
     SSL_set_shutdown(ssl_, SSL_RECEIVED_SHUTDOWN);
     SSL_shutdown(ssl_);
   }
@@ -498,4 +507,24 @@ std::string ClientHandler::get_upstream_scheme() const
   }
 }
 
+void ClientHandler::set_tls_handshake(bool f)
+{
+  tls_handshake_ = f;
+}
+
+bool ClientHandler::get_tls_handshake() const
+{
+  return tls_handshake_;
+}
+
+void ClientHandler::set_tls_renegotiation(bool f)
+{
+  tls_renegotiation_ = f;
+}
+
+bool ClientHandler::get_tls_renegotiation() const
+{
+  return tls_renegotiation_;
+}
+
 } // namespace shrpx

src/shrpx_client_handler.h

@@ -77,6 +77,10 @@ public:
   bool get_http2_upgrade_allowed() const;
   // Returns upstream scheme, either "http" or "https"
   std::string get_upstream_scheme() const;
+  void set_tls_handshake(bool f);
+  bool get_tls_handshake() const;
+  void set_tls_renegotiation(bool f);
+  bool get_tls_renegotiation() const;
 private:
   std::set<DownstreamConnection*> dconn_pool_;
   std::unique_ptr<Upstream> upstream_;
@@ -90,6 +94,8 @@ private:
   size_t left_connhd_len_;
   int fd_;
   bool should_close_after_write_;
+  bool tls_handshake_;
+  bool tls_renegotiation_;
 };
 
 } // namespace shrpx

src/shrpx_ssl.cc

@@ -132,6 +132,25 @@ int servername_callback(SSL *ssl, int *al, void *arg)
 }
 } // namespace
 
+namespace {
+void info_callback(const SSL *ssl, int where, int ret)
+{
+  // To mitigate possible DOS attack using lots of renegotiations, we
+  // disable renegotiation. Since OpenSSL does not provide an easy way
+  // to disable it, we check that renegotiation is started in this
+  // callback.
+  if(where & SSL_CB_HANDSHAKE_START) {
+    auto handler = static_cast<ClientHandler*>(SSL_get_app_data(ssl));
+    if(handler && handler->get_tls_handshake()) {
+      handler->set_tls_renegotiation(true);
+      if(LOG_ENABLED(INFO)) {
+        CLOG(INFO, handler) << "TLS renegotiation started";
+      }
+    }
+  }
+}
+} // namespace
+
 #if OPENSSL_VERSION_NUMBER >= 0x10002000L
 namespace {
 int alpn_select_proto_cb(SSL* ssl,
@@ -301,6 +320,7 @@ SSL_CTX* create_ssl_context(const char *private_key_file,
                        verify_callback);
   }
   SSL_CTX_set_tlsext_servername_callback(ssl_ctx, servername_callback);
+  SSL_CTX_set_info_callback(ssl_ctx, info_callback);
 
   // NPN advertisement
   auto proto_list_len = set_npn_prefs(proto_list, get_config()->npn_list,