Merge remote-tracking branch 'origin/ue_nas_simulator' into integration_2026_w13 (!3973)

Introduce UE NAS Simulator

This MR introduces a simple standalone tester for 5G UE NAS signaling and NGAP
messages. It connects to the AMF to perform NGAP and NAS encoding/decoding and
validates the UE Registration and PDU Session Establishment processes without
the overhead of a full Radio Access Network (PHY/MAC/RLC).

The motivation for this tester is as follows,
- This tester is a lightweight, deterministic tool to test the UE NAS layer
directly.
- Developers can easily inject specific NAS messages depending on the use-case.
- Developers can validate custom NAS/NGAP messages without the need to implement
complete RRC/MAC etc procedures.

Start the 5G Core network to test the UE NAS simulator. The compiling and
testing procedure is described below.
To compile:
mkdir build && cd build && cmake .. -GNinja && ninja nr-ue-nas-simulator-test

To run:
  LD_LIBRARY_PATH=. ./tests/nr-ue-nas-simulator/nr-ue-nas-simulator-test -O ../tests/nr-ue-nas-simulator/test.conf

openair3/NAS/NR_UE/nr_nas_msg.c

@@ -78,6 +78,12 @@
 
 static nr_ue_nas_t nr_ue_nas[MAX_NUM_NR_UE_INST] = {0};
 
+nr_ue_nas_t *get_nr_ue_nas_info(uint8_t ue_inst)
+{
+  AssertFatal(ue_inst >= 0 && ue_inst < MAX_NUM_NR_UE_INST, "Invalid UE instance\n");
+  return &nr_ue_nas[ue_inst];
+}
+
 #define FOREACH_STATE(TYPE_DEF)                  \
   TYPE_DEF(NAS_SECURITY_NO_SECURITY_CONTEXT, 0)  \
   TYPE_DEF(NAS_SECURITY_UNPROTECTED, 1)          \
@@ -1166,6 +1172,10 @@ static void generateSecurityModeComplete(nr_ue_nas_t *nas, as_nas_info_t *initia
       security_header_len
       + mm_msg_encode(plain, (uint8_t *)(initialNasMsg->nas_data + security_header_len), size - security_header_len);
 
+  if (rr.nas_data) {
+    free(rr.nas_data);
+  }
+
   /* ciphering */
   uint8_t buf[initialNasMsg->length - 7];
   stream_cipher.context = nas->security_container->ciphering_context;

openair3/NAS/NR_UE/nr_nas_msg.h

@@ -113,5 +113,6 @@ void *nas_nrue(void *args_p);
 void nas_init_nrue(int num_ues);
 void nr_ue_create_ip_if(const char *ifnameprefix, const char *ipv4, const char *ipv6, int ue_id, int pdu_session_id);
 void request_pdusession(nr_ue_nas_t *nas, const pdu_session_config_t *pdu);
+nr_ue_nas_t *get_nr_ue_nas_info(uint8_t ue_inst);
 
 #endif /* __NR_NAS_MSG_SIM_H__*/