Add NAS Security Mode Reject enc/dec lib and unit test

This 5GMM message is required for an invalid security mode command,
e.g. when the MAC integrity fails, or the wrong Security Header is set.

* Add encode/decode functions for common IEs in fgmm_lib: this library
  provides encoding/decoding helpers for IEs shared across multiple
  NAS messages. The goal is to avoid the legacy approach of creating
  separate files per IE
* add NAS Cause enc/dec lib
* Adopted byte_array_t to handle the buffer

Co-authored-by: Eduard Vlad <eduard.vlad@rwth-aachen.de>

openair3/NAS/NR_UE/5GS/5GMM/MSG/CMakeLists.txt

@@ -9,6 +9,7 @@ add_library(fgs_5gmm_lib OBJECT
     FGSIdentityResponse.c
     FGSAuthenticationResponse.c
     FGSNASSecurityModeComplete.c
+    FGSNASSecurityModeReject.c
     RegistrationComplete.c
     FGSUplinkNasTransport.c
     FGSDeregistrationRequestUEOriginating.c

openair3/NAS/NR_UE/5GS/5GMM/MSG/FGSNASSecurityModeReject.c

@@ -0,0 +1,50 @@
+/*
+ * Licensed to the OpenAirInterface (OAI) Software Alliance under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The OpenAirInterface Software Alliance licenses this file to You under
+ * the OAI Public License, Version 1.1  (the "License"); you may not use this file
+ * except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.openairinterface.org/?page_id=698
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *-------------------------------------------------------------------------------
+ * For more information about the OpenAirInterface (OAI) Software Alliance:
+ *      contact@openairinterface.org
+ */
+
+#include <stdint.h>
+#include "FGSNASSecurityModeReject.h"
+#include "common/utils/ds/byte_array.h"
+#include "fgmm_lib.h"
+
+int encode_fgs_security_mode_reject(byte_array_t *buffer, const fgs_security_mode_reject_msg *msg)
+{
+  if (buffer->len < 1)
+    return -1; // nothing to encode
+
+  // 5GMM cause (Mandatory)
+  return encode_fgs_nas_cause(buffer, &msg->cause);
+}
+
+/** @brief Decode Security Mode Reject (8.2.18 of 3GPP TS 24.501) */
+int decode_fgs_security_mode_reject(fgs_security_mode_reject_msg *msg, const byte_array_t *buffer)
+{
+  if (buffer->len < 1)
+    return -1; // nothing to decode
+
+  // 5GMM cause (Mandatory)
+  return decode_fgs_nas_cause(&msg->cause, buffer);
+}
+
+bool eq_sec_mode_reject(const fgs_security_mode_reject_msg *a, const fgs_security_mode_reject_msg *b)
+{
+  _NAS_EQ_CHECK_INT(a->cause, b->cause);
+  return true;
+}

openair3/NAS/NR_UE/5GS/5GMM/MSG/FGSNASSecurityModeReject.h

@@ -0,0 +1,47 @@
+/*
+ * Licensed to the OpenAirInterface (OAI) Software Alliance under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The OpenAirInterface Software Alliance licenses this file to You under
+ * the OAI Public License, Version 1.1  (the "License"); you may not use this file
+ * except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.openairinterface.org/?page_id=698
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *-------------------------------------------------------------------------------
+ * For more information about the OpenAirInterface (OAI) Software Alliance:
+ *      contact@openairinterface.org
+ */
+
+#ifndef FGS_NAS_security_mode_reject_H_
+#define FGS_NAS_security_mode_reject_H_
+
+#include <stdint.h>
+#include "fgmm_lib.h"
+
+/*
+ * Message name: security mode reject
+ * Description: The SECURITY MODE REJECT message is sent by the UE to the AMF to
+ * indicate that the corresponding security mode command has been rejected.
+ * See 3GPP TS 24.501 table 8.2.27.1.1
+ *
+ * Significance: dual
+ * Direction: UE to AMF
+ */
+
+typedef struct {
+  // 5GMM cause (Mandatory)
+  cause_id_t cause;
+} fgs_security_mode_reject_msg;
+
+int encode_fgs_security_mode_reject(byte_array_t *buffer, const fgs_security_mode_reject_msg *msg);
+int decode_fgs_security_mode_reject(fgs_security_mode_reject_msg *msg, const byte_array_t *buffer);
+bool eq_sec_mode_reject(const fgs_security_mode_reject_msg *a, const fgs_security_mode_reject_msg *b);
+
+#endif /* ! defined(FGS_NAS_security_mode_reject_H_) */

openair3/NAS/NR_UE/5GS/tests/nas_lib_test.c

@@ -8,6 +8,7 @@
 #include "fgmm_service_accept.h"
 #include "fgmm_service_reject.h"
 #include "fgmm_authentication_failure.h"
+#include "FGSNASSecurityModeReject.h"
 #include "nr_nas_msg.h"
 
 void exit_function(const char *file, const char *function, const int line, const char *s, const int assert)
@@ -266,6 +267,37 @@ static void test_auth_failure(void)
   free_fgmm_auth_failure(&dec);
 }
 
+/** @brief Test NAS Security Mode Reject enc/dec */
+static void test_security_mode_reject(void)
+{
+  // Dummy NAS Security Mode Reject message
+  const fgs_security_mode_reject_msg orig = {
+      .cause = Illegal_UE,
+  };
+
+  // Expected encoded data
+  uint8_t expected_enc[] = {0x03};
+
+  // Buffer
+  uint8_t buf[8] = {0};
+  byte_array_t buffer = {.buf = buf, .len = sizeof(buf)};
+
+  // Encode
+  int encoded_length = encode_fgs_security_mode_reject(&buffer, &orig);
+  AssertFatal(encoded_length == sizeofArray(expected_enc), "encode_fgs_security_mode_reject() failed\n");
+
+  // Compare the raw encoded buffer with expected encoded data
+  AssertFatal(memcmp(buffer.buf, expected_enc, encoded_length) == 0, "Encoding mismatch!\n");
+
+  // Decode
+  fgs_security_mode_reject_msg dec = {0};
+  int decoded_length = decode_fgs_security_mode_reject(&dec, &buffer);
+  AssertFatal(decoded_length >= 0, "decode_fgs_security_mode_reject() failed\n");
+
+  // Compare original and decoded messages
+  AssertFatal(eq_sec_mode_reject(&orig, &dec), "test_sec_mode_reject() failed: original and decoded messages do not match\n");
+}
+
 int main()
 {
   test_regression_registration_accept();
@@ -273,5 +305,6 @@ int main()
   test_service_accept();
   test_service_reject();
   test_auth_failure();
+  test_security_mode_reject();
   return 0;
 }