gbproxy: Patch BSSGP P-TMSI in PAGING PS messages

Currently the P-TMSI IE in PAGING_PS is not patched.

This commit adds code to patch BSSGP P-TMSI IE in
gbproxy_patch_bssgp independently from the P-TMSI patching at the LLC
layer. It also extends gbproxy_update_link_state_dl to use the IMSI
to find the link_info if the TLLI is not present in the message.

Note that the spec (GSM 08.18, 7.2) requires to use of the P-TMSI
instead of the IMSI to select the MS if that IE is available.
Nevertheless as long as the IMSI is always present in downlink BSSGP
messages and as long as the optional P-TMSI refers to the same MS
(which is the case currently), this is not an issue.

Sponsored-by: On-Waves ehf

3 files changed, 47 insertions, 4 deletions

diff --git a/openbsc/src/gprs/gb_proxy_patch.c b/openbsc/src/gprs/gb_proxy_patch.c
index b14809495..c1d2497db 100644
--- a/openbsc/src/gprs/gb_proxy_patch.c
+++ b/openbsc/src/gprs/gb_proxy_patch.c
@@ -327,6 +327,19 @@ void gbproxy_patch_bssgp(struct msgb *msg, uint8_t *bssgp, size_t bssgp_len,
 		}
 	}
 
+	if (parse_ctx->bssgp_ptmsi_enc && peer->cfg->patch_ptmsi) {
+		uint32_t ptmsi;
+		if (parse_ctx->to_bss)
+			ptmsi = link_info->tlli.ptmsi;
+		else
+			ptmsi = link_info->sgsn_tlli.ptmsi;
+
+		if (ptmsi != GSM_RESERVED_TMSI)
+			gbproxy_patch_ptmsi(
+				parse_ctx->bssgp_ptmsi_enc, peer,
+				ptmsi, parse_ctx->to_bss, "BSSGP P-TMSI");
+	}
+
 	if (parse_ctx->llc) {
 		uint8_t *llc = parse_ctx->llc;
 		size_t llc_len = parse_ctx->llc_len;
diff --git a/openbsc/src/gprs/gb_proxy_tlli.c b/openbsc/src/gprs/gb_proxy_tlli.c
index 467006e87..54e41e9e0 100644
--- a/openbsc/src/gprs/gb_proxy_tlli.c
+++ b/openbsc/src/gprs/gb_proxy_tlli.c
@@ -542,6 +542,30 @@ struct gbproxy_link_info *gbproxy_update_link_state_ul(
 	return link_info;
 }
 
+static struct gbproxy_link_info *gbproxy_get_link_info_dl(
+	struct gbproxy_peer *peer,
+	struct gprs_gb_parse_context *parse_ctx)
+{
+	struct gbproxy_link_info *link_info = NULL;
+
+	/* Which key to use depends on its availability only, if that fails, do
+	 * not retry it with another key (e.g. IMSI). */
+	if (parse_ctx->tlli_enc)
+		link_info = gbproxy_link_info_by_sgsn_tlli(peer, parse_ctx->tlli,
+							   parse_ctx->peer_nsei);
+
+	/* TODO: Get link_info by (SGSN) P-TMSI if that is available (see
+	 * GSM 08.18, 7.2) instead of using the IMSI as key. */
+	else if (parse_ctx->imsi)
+		link_info = gbproxy_link_info_by_imsi(
+			peer, parse_ctx->imsi, parse_ctx->imsi_len);
+
+	if (link_info)
+		link_info->is_deregistered = 0;
+
+	return link_info;
+}
+
 struct gbproxy_link_info *gbproxy_update_link_state_dl(
 	struct gbproxy_peer *peer,
 	time_t now,
@@ -549,9 +573,7 @@ struct gbproxy_link_info *gbproxy_update_link_state_dl(
 {
 	struct gbproxy_link_info *link_info = NULL;
 
-	if (parse_ctx->tlli_enc)
-		link_info = gbproxy_link_info_by_sgsn_tlli(
-			peer, parse_ctx->tlli, parse_ctx->peer_nsei);
+	link_info = gbproxy_get_link_info_dl(peer, parse_ctx);
 
 	if (parse_ctx->tlli_enc && parse_ctx->new_ptmsi_enc && link_info) {
 		/* A new P-TMSI has been signalled in the message,
diff --git a/openbsc/src/gprs/gprs_gb_parse.c b/openbsc/src/gprs/gprs_gb_parse.c
index 8e72cc819..6c6371ca0 100644
--- a/openbsc/src/gprs/gprs_gb_parse.c
+++ b/openbsc/src/gprs/gprs_gb_parse.c
@@ -596,7 +596,7 @@ int gprs_gb_parse_bssgp(uint8_t *bssgp, size_t bssgp_len,
 	}
 
 	if (TLVP_PRESENT(tp, BSSGP_IE_TMSI) && pdu_type == BSSGP_PDUT_PAGING_PS)
-		parse_ctx->ptmsi_enc = (uint8_t *)TLVP_VAL(tp, BSSGP_IE_TMSI);
+		parse_ctx->bssgp_ptmsi_enc = (uint8_t *)TLVP_VAL(tp, BSSGP_IE_TMSI);
 
 	if (TLVP_PRESENT(tp, BSSGP_IE_LLC_PDU)) {
 		uint8_t *llc = (uint8_t *)TLVP_VAL(tp, BSSGP_IE_LLC_PDU);
@@ -633,6 +633,7 @@ void gprs_gb_log_parse_context(int log_level,
 	if (!parse_ctx->tlli_enc &&
 	    !parse_ctx->ptmsi_enc &&
 	    !parse_ctx->new_ptmsi_enc &&
+	    !parse_ctx->bssgp_ptmsi_enc &&
 	    !parse_ctx->imsi)
 		return;
 
@@ -681,6 +682,13 @@ void gprs_gb_log_parse_context(int log_level,
 		sep = ",";
 	}
 
+	if (parse_ctx->bssgp_ptmsi_enc) {
+		uint32_t ptmsi = GSM_RESERVED_TMSI;
+		gprs_parse_tmsi(parse_ctx->bssgp_ptmsi_enc, &ptmsi);
+		LOGPC(DGPRS, log_level, "%s BSSGP PTMSI %08x", sep, ptmsi);
+		sep = ",";
+	}
+
 	if (parse_ctx->ptmsi_enc) {
 		uint32_t ptmsi = GSM_RESERVED_TMSI;
 		gprs_parse_tmsi(parse_ctx->ptmsi_enc, &ptmsi);