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nrUE NAS: implement downlink security processing

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Maybe not totally ok (code has some comments). To be refined if needed.
This commit is contained in:
Cedric Roux
2024-05-27 17:39:35 +02:00
parent 4cc1bb5433
commit 075f8330f6
1 changed files with 79 additions and 1 deletions
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openair3/NAS/NR_UE/nr_nas_msg_sim.c
+79 -1
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@@ -60,6 +60,76 @@ extern uint16_t NB_UE_INST;
static nr_ue_nas_t nr_ue_nas = {0};
static nr_nas_msg_snssai_t nas_allowed_nssai[8];
typedef enum {
NAS_SECURITY_NO_SECURITY_CONTEXT,
NAS_SECURITY_INTEGRITY_FAILED,
NAS_SECURITY_INTEGRITY_PASSED,
NAS_SECURITY_BAD_INPUT
} security_state_t;
security_state_t nas_security_rx_process(nr_ue_nas_t *nas, uint8_t *pdu_buffer, int pdu_length)
{
if (nas->security_container == NULL)
return NAS_SECURITY_NO_SECURITY_CONTEXT;
/* header is 7 bytes, require at least one byte of payload */
if (pdu_length < 8)
return NAS_SECURITY_BAD_INPUT;
/* only accept "integrity protected and ciphered" messages */
if (pdu_buffer[1] != 2) {
LOG_E(NAS, "todo: unhandled security type %d\n", pdu_buffer[2]);
return NAS_SECURITY_BAD_INPUT;
}
/* synchronize NAS SQN, based on 24.501 4.4.3.1 */
int nas_sqn = pdu_buffer[6];
int target_sqn = nas->security.nas_count_dl & 0xff;
if (nas_sqn != target_sqn) {
if (nas_sqn < target_sqn)
nas->security.nas_count_dl += 256;
nas->security.nas_count_dl &= ~255;
nas->security.nas_count_dl |= nas_sqn;
}
if (nas->security.nas_count_dl > 0x00ffffff) {
/* it's doubtful that this will happen, so let's simply exit for the time being */
/* to be refined if needed */
LOG_E(NAS, "max NAS COUNT DL reached\n");
exit(1);
}
/* check integrity */
uint8_t computed_mac[4];
nas_stream_cipher_t stream_cipher;
stream_cipher.context = nas->security_container->integrity_context;
stream_cipher.count = nas->security.nas_count_dl;
stream_cipher.bearer = 1; /* todo: don't hardcode */
stream_cipher.direction = 1;
stream_cipher.message = pdu_buffer + 6;
/* length in bits */
stream_cipher.blength = (pdu_length - 6) << 3;
stream_compute_integrity(nas->security_container->integrity_algorithm, &stream_cipher, computed_mac);
uint8_t *received_mac = pdu_buffer + 2;
if (memcmp(received_mac, computed_mac, 4) != 0)
return NAS_SECURITY_INTEGRITY_FAILED;
/* decipher */
uint8_t buf[pdu_length - 7];
stream_cipher.context = nas->security_container->ciphering_context;
stream_cipher.count = nas->security.nas_count_dl;
stream_cipher.bearer = 1; /* todo: don't hardcode */
stream_cipher.direction = 1;
stream_cipher.message = pdu_buffer + 7;
/* length in bits */
stream_cipher.blength = (pdu_length - 7) << 3;
stream_compute_encrypt(nas->security_container->ciphering_algorithm, &stream_cipher, buf);
memcpy(pdu_buffer + 7, buf, pdu_length - 7);
nas->security.nas_count_dl++;
return NAS_SECURITY_INTEGRITY_PASSED;
}
static int nas_protected_security_header_encode(
char *buffer,
const fgs_nas_message_security_header_t *header,
@@ -1234,11 +1304,19 @@ void *nas_nrue(void *args_p)
NAS_DOWNLINK_DATA_IND(msg_p).nasMsg.length,
NAS_DOWNLINK_DATA_IND(msg_p).nasMsg.data);
as_nas_info_t initialNasMsg = {0};
nr_ue_nas_t *nas = get_ue_nas_info(0);
uint8_t *pdu_buffer = NAS_DOWNLINK_DATA_IND(msg_p).nasMsg.data;
int pdu_length = NAS_DOWNLINK_DATA_IND(msg_p).nasMsg.length;
security_state_t security_state = nas_security_rx_process(nas, pdu_buffer, pdu_length);
if (security_state != NAS_SECURITY_INTEGRITY_PASSED
&& security_state != NAS_SECURITY_NO_SECURITY_CONTEXT) {
LOG_E(NAS, "NAS integrity failed, discard incoming message\n");
break;
}
int msg_type = get_msg_type(pdu_buffer, pdu_length);
nr_ue_nas_t *nas = get_ue_nas_info(0);
switch (msg_type) {
case FGS_IDENTITY_REQUEST: