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Add callback for generation of NAS Security Mode Reject message

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This is necessary to indicate to the Core network, that
the security mode command procedure has failed.

Check for the security context presence when generating the Security Mode
reject message: according to 3GPP TS 24.501 5.4.2.5 "NAS security mode command
not accepted by the UE" The UE shall send a SECURITY MODE REJECT containing
a 5GMM cause that typically indicates one of the following cause values:
(23) UE security capabilities mismatch
(24) security mode rejected, unspecified
The message shall be protected if a security context is available

Signed-off-by: Eduard Vlad <eduard.vlad@rwth-aachen.de>
Co-authored-by: Guido Casati <hello@guidocasati.com>
This commit is contained in:
Eduard Vlad
2025-06-12 09:49:33 +02:00
committed by Guido Casati
co-authored by Guido Casati
parent 98c458fa2c
commit 6399d93be8
1 changed files with 62 additions and 0 deletions
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openair3/NAS/NR_UE/nr_nas_msg.c
+62
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@@ -1042,6 +1042,68 @@ static void generateSecurityModeComplete(nr_ue_nas_t *nas, as_nas_info_t *initia
}
}
/** @brief Generates the Security Mode Reject message to be sent by the UE to the AMF
* to indicate that the corresponding security mode command has been rejected */
static void generateSecurityModeReject(nr_ue_nas_t *nas, as_nas_info_t *initialNasMsg, cause_id_t cause)
{
LOG_I(NAS, "Send Security Mode Reject\n");
fgmm_msg_header_t plain_header = set_mm_header(FGS_SECURITY_MODE_REJECT, PLAIN_5GS_MSG);
int size = sizeof(plain_header);
fgs_security_mode_reject_msg msg = {.cause = cause};
size += 1;
/** The UE shall apply the 5G NAS security context in use
* before the initiation of the security mode control procedure,
* if any, to protect the SECURITY MODE REJECT message */
bool has_security_context = nas->security_container && nas->security_container->integrity_context;
if (has_security_context) {
fgmm_nas_msg_security_protected_t sp = {0};
sp.header.protocol_discriminator = FGS_MOBILITY_MANAGEMENT_MESSAGE;
sp.header.security_header_type = INTEGRITY_PROTECTED;
sp.header.sequence_number = nas->security.nas_count_ul & 0xff;
size += sizeof(sp.header);
sp.plain.header = plain_header;
sp.plain.mm_msg.fgs_security_mode_reject = msg;
// Security protected header encoding
int security_header_len = nas_protected_security_header_encode(initialNasMsg->nas_data, &sp.header, size);
initialNasMsg->length =
security_header_len + mm_msg_encode(&sp.plain, initialNasMsg->nas_data + security_header_len, size - security_header_len);
/* ciphering */
uint8_t buf[initialNasMsg->length - 7];
nas_stream_cipher_t stream_cipher;
stream_cipher.context = nas->security_container->ciphering_context;
AssertFatal(nas->security.nas_count_ul <= 0xffffff, "fatal: NAS COUNT UL too big (todo: fix that)\n");
stream_cipher.count = nas->security.nas_count_ul;
stream_cipher.bearer = 1;
stream_cipher.direction = 0;
stream_cipher.message = (unsigned char *)(initialNasMsg->nas_data + 7);
/* length in bits */
stream_cipher.blength = (initialNasMsg->length - 7) << 3;
stream_compute_encrypt(nas->security_container->ciphering_algorithm, &stream_cipher, buf);
memcpy(stream_cipher.message, buf, initialNasMsg->length - 7);
/* integrity protection */
uint8_t mac[4];
stream_cipher.context = nas->security_container->integrity_context;
stream_cipher.count = nas->security.nas_count_ul++;
stream_cipher.bearer = 1;
stream_cipher.direction = 0;
stream_cipher.message = (unsigned char *)(initialNasMsg->nas_data + 6);
/* length in bits */
stream_cipher.blength = (initialNasMsg->length - 6) << 3;
stream_compute_integrity(nas->security_container->integrity_algorithm, &stream_cipher, mac);
LOG_D(NAS, "Integrity protected initial NAS message: mac = %x %x %x %x \n", mac[0], mac[1], mac[2], mac[3]);
for (int i = 0; i < 4; i++)
initialNasMsg->nas_data[2 + i] = mac[i];
} else {
fgmm_nas_message_plain_t plain = {0};
plain.header = plain_header;
plain.mm_msg.fgs_security_mode_reject = msg;
// encode the message
initialNasMsg->nas_data = malloc_or_fail(size);
initialNasMsg->length = mm_msg_encode(&plain, initialNasMsg->nas_data, size);
}
}
static void handle_security_mode_command(nr_ue_nas_t *nas, as_nas_info_t *initialNasMsg, uint8_t *pdu, int pdu_length)
{
/* retrieve integrity and ciphering algorithms */