cu_cp,rrc: await security mode command complete before sending rrc reconfiguration

Author: FabianEckermann

include/srsran/rrc/rrc_ue.h

@@ -198,6 +198,11 @@ class rrc_ue_control_message_handler
   /// \returns The Security Mode Command context.
   virtual rrc_ue_security_mode_command_context get_security_mode_command_context() = 0;
 
+  /// \brief Await a RRC Security Mode Command Complete for a handover.
+  /// \param[in] transaction_id The transaction ID of the RRC Security Mode Command Complete.
+  /// \returns True if the RRC Security Mode Command Complete was received, false otherwise.
+  virtual async_task<bool> handle_security_mode_command_complete_expected(uint8_t transaction_id) = 0;
+
   /// \brief Handle an RRC Reconfiguration Request.
   /// \param[in] msg The new RRC Reconfiguration Request.
   /// \returns The result of the rrc reconfiguration.

lib/cu_cp/routines/initial_context_setup_routine.cpp

@@ -76,6 +76,16 @@ void initial_context_setup_routine::operator()(
     }
   }
 
+  // Await Security Mode Command Complete from RRC UE
+  {
+    CORO_AWAIT_VALUE(security_mode_command_result,
+                     rrc_ue.handle_security_mode_command_complete_expected(rrc_smc_ctxt.transaction_id));
+    if (!security_mode_command_result) {
+      handle_failure();
+      CORO_EARLY_RETURN(make_unexpected(fail_msg));
+    }
+  }
+
   // Start UE Capability Enquiry Procedure
   {
     /// TODO: Move UE Capability Enquiry Procedure here

lib/cu_cp/routines/initial_context_setup_routine.h

@@ -52,7 +52,8 @@ class initial_context_setup_routine
   // (sub-)routine results
   f1ap_ue_context_setup_response            ue_context_setup_response;
   cu_cp_pdu_session_resource_setup_response pdu_session_setup_response;
-  bool                                      rrc_reconfig_result = false; // the final UE reconfiguration
+  bool                                      security_mode_command_result = false;
+  bool                                      rrc_reconfig_result          = false; // the final UE reconfiguration
   ngap_init_context_setup_failure           fail_msg;
   ngap_init_context_setup_response          resp_msg;
 };

lib/rrc/ue/rrc_ue_impl.h

@@ -62,6 +62,7 @@ class rrc_ue_impl final : public rrc_ue_interface, public rrc_ue_controller
 
   // rrc_ue_control_message_handler
   rrc_ue_security_mode_command_context get_security_mode_command_context() override;
+  async_task<bool>                     handle_security_mode_command_complete_expected(uint8_t transaction_id) override;
   async_task<bool> handle_rrc_reconfiguration_request(const rrc_reconfiguration_procedure_request& msg) override;
   rrc_ue_handover_reconfiguration_context
   get_rrc_ue_handover_reconfiguration_context(const rrc_reconfiguration_procedure_request& request) override;

lib/rrc/ue/rrc_ue_message_handlers.cpp

@@ -150,7 +150,7 @@ void rrc_ue_impl::handle_pdu(const srb_id_t srb_id, byte_buffer rrc_pdu)
       handle_rrc_transaction_complete(ul_dcch_msg, ul_dcch_msg.msg.c1().rrc_setup_complete().rrc_transaction_id);
       break;
     case ul_dcch_msg_type_c::c1_c_::types_opts::security_mode_complete:
-      handle_security_mode_complete(ul_dcch_msg.msg.c1().security_mode_complete());
+      handle_rrc_transaction_complete(ul_dcch_msg, ul_dcch_msg.msg.c1().security_mode_complete().rrc_transaction_id);
       break;
     case ul_dcch_msg_type_c::c1_c_::types_opts::ue_cap_info:
       handle_rrc_transaction_complete(ul_dcch_msg, ul_dcch_msg.msg.c1().ue_cap_info().rrc_transaction_id);
@@ -309,6 +309,34 @@ rrc_ue_security_mode_command_context rrc_ue_impl::get_security_mode_command_cont
   return smc_ctxt;
 }
 
+async_task<bool> rrc_ue_impl::handle_security_mode_command_complete_expected(uint8_t transaction_id)
+{
+  // arbitrary timeout for RRC Reconfig procedure, UE will be removed if timer fires
+  const std::chrono::milliseconds timeout_ms{1000};
+
+  return launch_async(
+      [this, timeout_ms, transaction_id, transaction = rrc_transaction{}](coro_context<async_task<bool>>& ctx) mutable {
+        CORO_BEGIN(ctx);
+
+        logger.log_debug("Awaiting RRC Security Mode Command Complete (timeout={}ms)", timeout_ms.count());
+        // create new transaction for RRC Security Mode Command procedure
+        transaction = event_mng->transactions.create_transaction(transaction_id, timeout_ms);
+
+        CORO_AWAIT(transaction);
+
+        bool procedure_result = false;
+        if (transaction.has_response()) {
+          logger.log_debug("Received RRC Security Mode Command Complete");
+          procedure_result = true;
+          handle_security_mode_complete(transaction.response().msg.c1().security_mode_complete());
+        } else {
+          logger.log_debug("Did not receive RRC Security Mode Command Complete. Cause: timeout");
+        }
+
+        CORO_RETURN(procedure_result);
+      });
+}
+
 async_task<bool> rrc_ue_impl::handle_rrc_reconfiguration_request(const rrc_reconfiguration_procedure_request& msg)
 {
   return launch_async<rrc_reconfiguration_procedure>(