Because a race condition can occur between S6A Diameter and S1AP message,
the following error handling code has been added.
1. InitialUEMessage + Attach Request + PDN Connectivity request
2. Authentication-Information-Request/Authentication-Information-Answer
3. Authentication Request/Response
4. Security-mode command/complete
5. Update-Location-Request/Update-Location-Answer
6. Detach request/accept
In the ULR/ULA process in step 6, the PDN Connectivity request is
pushed to the queue as an ESM_MESSAGE because the NAS-Type is still
an Attach Request.
See the code below in 'mme-s6a-handler.c' for where the queue is pushed.
if (mme_ue->nas_eps.type == MME_EPS_TYPE_ATTACH_REQUEST) {
rv = nas_eps_send_emm_to_esm(mme_ue,
&mme_ue->pdn_connectivity_request);
if (rv != OGS_OK) {
ogs_error("nas_eps_send_emm_to_esm() failed");
return OGS_NAS_EMM_CAUSE_PROTOCOL_ERROR_UNSPECIFIED;
}
} else if (mme_ue->nas_eps.type == MME_EPS_TYPE_TAU_REQUEST) {
r = nas_eps_send_tau_accept(mme_ue,
S1AP_ProcedureCode_id_InitialContextSetup);
ogs_expect(r == OGS_OK);
ogs_assert(r != OGS_ERROR);
} else {
ogs_error("Invalid Type[%d]", mme_ue->nas_eps.type);
return OGS_NAS_EMM_CAUSE_PROTOCOL_ERROR_UNSPECIFIED;
}
If you perform step 7 Detach request/accept here,
the NAS-Type becomes Detach Request and the EMM state changes
to emm_state_de_registered().
Since the PDN, which is an ESM message that was previously queued,
should not be processed in de_registered, the message is ignored
through error handling below.
Otherwise, MME will crash because there is no active bearer
in the initial_context_setup_request build process.
See the code below in 's1ap-build.c' for where the crash occurs.
ogs_list_for_each(&mme_ue->sess_list, sess) {
ogs_list_for_each(&sess->bearer_list, bearer) {
...
if (mme_ue->nas_eps.type == MME_EPS_TYPE_ATTACH_REQUEST) {
} else if (OGS_FSM_CHECK(&bearer->sm, esm_state_inactive)) {
ogs_warn("No active EPS bearer [%d]", bearer->ebi);
ogs_warn(" IMSI[%s] NAS-EPS Type[%d] "
"ENB_UE_S1AP_ID[%d] MME_UE_S1AP_ID[%d]",
mme_ue->imsi_bcd, mme_ue->nas_eps.type,
enb_ue->enb_ue_s1ap_id, enb_ue->mme_ue_s1ap_id);
continue;
}
...
}
}
* [MME] Introduce aging timers
* Creating three new timers
* mirroring work done by gstaa on the AMF
* Implicit detach procedures added
* Fix for detach from unknown UE
* no Purge Timer, no config, expanded code
* Cancel Location while Idle Fix
* Forgot about SGSAP on MME Change.
Added "action" to sgsap_send_detach..
* Make handle_clr uniform with other handlers
* Added Robustness for Any Detach Type
* Memory wasn't freed upon CLR for unknown IMSIs
* Moving MME Detach to new PR
The problem occurred in the following scenario:
1. VLR sent PAGING-REQUEST to the MME
2. MME sent S1-Paging to the UE
3. Paging failed
4. MME responded SERVICE-REQUEST to the VLR
5. VLR sent DOWNLINK-UNITDATA to the MME
6. Even though there is no S1 Context,
MME try to sent DownlinkNASTransport message to the UE.
7. So, the problem occurred.
I've changed the number 4 PAGING-REJECT instead of SERVICE-REQUEST.
* CLR while idle is broken after 7031856cd7
Cancel Location Request arriving while UE is idle will not proceed to paging due to this check for S1 connection. Using new flag "isAnswer" to bypass this check to allow paging to occur when we are not doing a AIA/ULA related procedure.
* No Context Setup is required when sending the detach request. If the paging was due to wanting to send a Detach Request to the UE, then we fast track to sending the detach request.
* emm-sm.c:
In the case of MME initiated detach while UE is idle, there is no initial conext setup. We go right from the service request after paging into sending the detach request. TS23.401
mme-path.c:
Using nas_eps.type in the case of MME Initiated Detach while UE is idle does not work. nas_eps.type would represent the service request.
mme-s11-handler.c:
After S11 action, no action should be taken. We want to wait for the detach accept from the UE before proceeding with the S1 release (detach).
* InitialContextSetup should occur for detach.
In the past only GTPv2C was supported, and had the "gtp" generic prefix.
Later on, GTPv1C support was added, and "gtp1" prefix was used.
Let's move GTPv2C specific bits to have "gtp2" prefix too, and leave
"gtp" prefix for generic stuff among different GTP versions.
All process will be forcely exited if it failed to encode the S1AP/NGAP/GTP/PFCP message. It is to make sure there was no problem with the encoding of open5gs.
Sukchan Lee
Emanuele Di Pascale
jmasterfunk84
Pau Espin