Merge remote-tracking branch 'origin/fix-drb-integrity' into integration_2025_w48 (!3767)

Fix DRB integrity failures during handover and re-establishment

This MR fixes DRB integrity protection failures that occur during N2 handover
and connection re-establishment scenarios. The issues were caused by incorrect
security key handling and ciphering configuration during these procedures with
DRB integity enabled.

See merge request !3767 for more details.

ci-scripts/conf_files/gnb-cu.sa.f1.ho.conf

@@ -53,7 +53,7 @@ security = {
   # preferred ciphering algorithms
   # the first one of the list that an UE supports in chosen
   # valid values: nea0, nea1, nea2, nea3
-  ciphering_algorithms = ( "nea0" );
+  ciphering_algorithms = ( "nea2", "nea0" );
 
   # preferred integrity algorithms
   # the first one of the list that an UE supports in chosen
@@ -63,7 +63,7 @@ security = {
   # setting 'drb_ciphering' to "no" disables ciphering for DRBs, no matter
   # what 'ciphering_algorithms' configures; same thing for 'drb_integrity'
   drb_ciphering = "yes";
-  drb_integrity = "no";
+  drb_integrity = "yes";
 };
 
 log_config :

ci-scripts/conf_files/gnb.sa.band77.51prb.usrpb200.n2-ho.conf

@@ -209,7 +209,7 @@ security = {
   # preferred ciphering algorithms
   # the first one of the list that an UE supports in chosen
   # valid values: nea0, nea1, nea2, nea3
-  ciphering_algorithms = ( "nea0" );
+  ciphering_algorithms = ( "nea2", "nea0" );
 
   # preferred integrity algorithms
   # the first one of the list that an UE supports in chosen
@@ -219,7 +219,7 @@ security = {
   # setting 'drb_ciphering' to "no" disables ciphering for DRBs, no matter
   # what 'ciphering_algorithms' configures; same thing for 'drb_integrity'
   drb_ciphering = "yes";
-  drb_integrity = "no";
+  drb_integrity = "yes";
 };
 
 log_config :

openair2/RRC/NR/rrc_gNB.c

@@ -1063,15 +1063,10 @@ static void cuup_notify_reestablishment(gNB_RRC_INST *rrc, gNB_RRC_UE_t *ue_p)
     }
   }
 
-#if 0
-  /* According to current understanding of E1 specifications, it is not needed
-   * to send security information because this does not change.
-   * But let's keep the code here in case it's needed.
-   */
-  // Always send security information
+  /* During reestablishment, for DRB integrity protection security keys change (KgNB* is derived),
+   * so security information MUST be sent to CU-UP to update DRB security keys. */
   req.secInfo = malloc_or_fail(sizeof(*req.secInfo));
   fill_security_info(rrc, ue_p, req.secInfo);
-#endif
 
   /* Send E1 Bearer Context Modification Request (3GPP TS 38.463) */
   sctp_assoc_t assoc_id = get_existing_cuup_for_ue(rrc, ue_p);

openair2/RRC/NR/rrc_gNB_NGAP.c

@@ -1192,7 +1192,11 @@ int rrc_gNB_process_Handover_Request(gNB_RRC_INST *rrc, instance_t instance, nga
   // Activate SRBs
   activate_srb(UE, SRB1);
   activate_srb(UE, SRB2);
-  nr_rrc_pdcp_config_security(UE, false);
+  // During N2 handover, the UE continues using the old security context from the source gNB
+  // until it receives and processes the RRC Reconfiguration with masterKeyUpdate. The first
+  // PDUs sent after CFRA are still ciphered with the old keys. The target gNB must enable
+  // ciphering during handover setup to correctly decipher and verify integrity of these PDUs.
+  nr_rrc_pdcp_config_security(UE, true);
 
   // Process all PDU Session Resource Setup items from handover request
   DevAssert(msg->nb_of_pdusessions <= NGAP_MAX_PDU_SESSION);