From 6e01a628384a450beaad4d1e65275dd5fd78f4f4 Mon Sep 17 00:00:00 2001
From: Robert Schmidt <robert.schmidt@openairinterface.org>
Date: Mon, 13 Mar 2023 12:30:59 +0100
Subject: [PATCH] Decode Registration Accept to receive GUTI

---
 .../NAS/COMMON/EMM/MSG/RegistrationAccept.c   | 17 ++++++++++++
 .../NAS/COMMON/EMM/MSG/RegistrationAccept.h   |  4 +++
 openair3/NAS/NR_UE/nr_nas_msg_sim.c           | 26 +++++++++++++++++++
 openair3/NAS/NR_UE/nr_nas_msg_sim.h           |  1 +
 4 files changed, 48 insertions(+)

diff --git a/openair3/NAS/COMMON/EMM/MSG/RegistrationAccept.c b/openair3/NAS/COMMON/EMM/MSG/RegistrationAccept.c
index d8fde7e2cc..c34d777bd5 100644
--- a/openair3/NAS/COMMON/EMM/MSG/RegistrationAccept.c
+++ b/openair3/NAS/COMMON/EMM/MSG/RegistrationAccept.c
@@ -50,6 +50,16 @@ int decode_registration_accept(registration_accept_msg *registration_accept, uin
 
   decoded += decoded_result;
 
+  if (decoded < len && buffer[decoded] == 0x77) {
+    registration_accept->guti = calloc(1, sizeof(*registration_accept->guti));
+    if (!registration_accept->guti)
+      return -1;
+    int mi_dec = decode_5gs_mobile_identity(registration_accept->guti, 0x77, buffer + decoded, len - decoded);
+    if (mi_dec < 0)
+      return -1;
+    decoded += mi_dec;
+  }
+
   // todo ,Decoding optional fields
   return decoded;
 }
@@ -64,6 +74,13 @@ int encode_registration_accept(registration_accept_msg *registration_accept, uin
   *(buffer + encoded) = encode_fgs_registration_result(&registration_accept->fgsregistrationresult);
   encoded = encoded + 2;
 
+  if (registration_accept->guti) {
+    int mi_enc = encode_5gs_mobile_identity(registration_accept->guti, 0x77, buffer + encoded, len - encoded);
+    if (mi_enc < 0)
+      return mi_enc;
+    encoded += mi_enc;
+  }
+
   // todo ,Encoding optional fields
   LOG_FUNC_RETURN(encoded);
 }
diff --git a/openair3/NAS/COMMON/EMM/MSG/RegistrationAccept.h b/openair3/NAS/COMMON/EMM/MSG/RegistrationAccept.h
index 08daec2646..e0d3ade23a 100644
--- a/openair3/NAS/COMMON/EMM/MSG/RegistrationAccept.h
+++ b/openair3/NAS/COMMON/EMM/MSG/RegistrationAccept.h
@@ -38,6 +38,7 @@
 #include "SpareHalfOctet.h"
 #include "MessageType.h"
 #include "FGSRegistrationResult.h"
+#include "FGSMobileIdentity.h"
 
 #ifndef REGISTRATION_ACCEPT_H_
 #define REGISTRATION_ACCEPT_H_
@@ -56,6 +57,9 @@ typedef struct registration_accept_msg_tag {
   SpareHalfOctet                          sparehalfoctet:4;
   MessageType                             messagetype;
   FGSRegistrationResult                   fgsregistrationresult;
+
+  /* Optional fields */
+  FGSMobileIdentity *guti;
 } registration_accept_msg;
 
 int decode_registration_accept(registration_accept_msg *registrationaccept, uint8_t *buffer, uint32_t len);
diff --git a/openair3/NAS/NR_UE/nr_nas_msg_sim.c b/openair3/NAS/NR_UE/nr_nas_msg_sim.c
index d415242324..443fb8d06c 100644
--- a/openair3/NAS/NR_UE/nr_nas_msg_sim.c
+++ b/openair3/NAS/NR_UE/nr_nas_msg_sim.c
@@ -42,6 +42,7 @@
 #include "kdf.h"
 #include "PduSessionEstablishRequest.h"
 #include "PduSessionEstablishmentAccept.h"
+#include "RegistrationAccept.h"
 #include "intertask_interface.h"
 #include "openair2/RRC/NAS/nas_config.h"
 #include <openair3/NAS/COMMON/NR_NAS_defs.h>
@@ -613,6 +614,30 @@ static void generateSecurityModeComplete(nr_ue_nas_t *nas, as_nas_info_t *initia
   }
 }
 
+static void decodeRegistrationAccept(uint8_t *buf, int len, nr_ue_nas_t *nas)
+{
+  registration_accept_msg reg_acc = {0};
+  /* it seems there is no 5G corresponding emm_msg_decode() function, so here
+   * we just jump to the right decision */
+  buf += 7; /* skip security header */
+  buf += 2; /* skip prot discriminator, security header, half octet */
+  AssertFatal(*buf == 0x42, "this is not a NAS Registration Accept\n");
+  buf++;
+  int decoded = decode_registration_accept(&reg_acc, buf, len);
+  AssertFatal(decoded > 0, "could not decode registration accept\n");
+  if (reg_acc.guti) {
+     AssertFatal(reg_acc.guti->guti.typeofidentity == FGS_MOBILE_IDENTITY_5G_GUTI,
+                 "registration accept 5GS Mobile Identity is not GUTI, but %d\n",
+                 reg_acc.guti->guti.typeofidentity);
+     nas->guti = malloc(sizeof(nas->guti));
+     AssertFatal(nas->guti, "out of memory\n");
+     *nas->guti = reg_acc.guti->guti;
+     free(reg_acc.guti); /* no proper memory management for NAS decoded messages */
+  } else {
+    LOG_W(NAS, "no GUTI in registration accept\n");
+  }
+}
+
 static void generateRegistrationComplete(nr_ue_nas_t *nas, as_nas_info_t *initialNasMsg, SORTransparentContainer *sortransparentcontainer)
 {
   //wait send RRCReconfigurationComplete and InitialContextSetupResponse
@@ -909,6 +934,7 @@ void *nas_nrue_task(void *args_p)
 
           if (msg_type == REGISTRATION_ACCEPT) {
             LOG_I(NAS, "[UE] Received REGISTRATION ACCEPT message\n");
+            decodeRegistrationAccept(pdu_buffer, NAS_CONN_ESTABLI_CNF(msg_p).nasMsg.length, nas);
 
             as_nas_info_t initialNasMsg;
             memset(&initialNasMsg, 0, sizeof(as_nas_info_t));
diff --git a/openair3/NAS/NR_UE/nr_nas_msg_sim.h b/openair3/NAS/NR_UE/nr_nas_msg_sim.h
index 8ca655ad9d..86cc4f856d 100644
--- a/openair3/NAS/NR_UE/nr_nas_msg_sim.h
+++ b/openair3/NAS/NR_UE/nr_nas_msg_sim.h
@@ -84,6 +84,7 @@ typedef struct {
 typedef struct {
   uicc_t *uicc;
   ue_sa_security_key_t security;
+  Guti5GSMobileIdentity_t *guti;
 } nr_ue_nas_t;
 
 typedef enum fgs_protocol_discriminator_e {