gbproxy: Change creation of tlli_info for SGSN originated messages

Currently tlli_info are created for SGSN originated messages when
the SGSN TLLI cannot be found and P-TMSI patching is active. This
doesn't make much sense, since the BSS side TLLI is not known in this
case. Given that the SGSN is working properly, that can only happen
if either the tlli_info has expired or the gbproxy has been
restarted.

This patch disables the creation of a tlli_info in this case.

Note that these messages are passed unmodified to the MS so far.

Sponsored-by: On-Waves ehf

1 files changed, 51 insertions, 30 deletions

diff --git a/openbsc/src/gprs/gb_proxy_tlli.c b/openbsc/src/gprs/gb_proxy_tlli.c
index 2074308cf..4c97f8abe 100644
--- a/openbsc/src/gprs/gb_proxy_tlli.c
+++ b/openbsc/src/gprs/gb_proxy_tlli.c
@@ -440,8 +440,8 @@ struct gbproxy_tlli_info *gbproxy_update_tlli_state_dl(
 	if (parse_ctx->tlli_enc)
 		tlli_info = gbproxy_find_tlli_by_sgsn_tlli(peer, parse_ctx->tlli);
 
-	if (parse_ctx->tlli_enc && parse_ctx->new_ptmsi_enc) {
-		/* A new PTMSI has been signaled in the message,
+	if (parse_ctx->tlli_enc && parse_ctx->new_ptmsi_enc && tlli_info) {
+		/* A new P-TMSI has been signalled in the message,
 		 * register new TLLI */
 		uint32_t new_sgsn_ptmsi;
 		uint32_t new_sgsn_tlli;
@@ -461,46 +461,67 @@ struct gbproxy_tlli_info *gbproxy_update_tlli_state_dl(
 		LOGP(DGPRS, LOGL_INFO,
 		     "Got new TLLI(PTMSI) %08x(%08x) from SGSN, using %08x(%08x)\n",
 		     new_sgsn_tlli, new_sgsn_ptmsi, new_bss_tlli, new_bss_ptmsi);
-		if (tlli_info) {
-			gbproxy_reassign_tlli(&tlli_info->sgsn_tlli,
-					      peer, new_sgsn_tlli);
-			gbproxy_reassign_tlli(&tlli_info->tlli,
-					      peer, new_bss_tlli);
-			gbproxy_touch_tlli(peer, tlli_info, now);
-		} else {
-			tlli_info = gbproxy_tlli_info_alloc(peer);
-			LOGP(DGPRS, LOGL_INFO,
-			     "Adding TLLI %08x to list (SGSN, new P-TMSI)\n",
-			     new_sgsn_tlli);
 
-			gbproxy_attach_tlli_info(peer, now, tlli_info);
-			/* Setup TLLIs */
-			tlli_info->sgsn_tlli.current = new_sgsn_tlli;
-		}
+		gbproxy_reassign_tlli(&tlli_info->sgsn_tlli,
+				      peer, new_sgsn_tlli);
+		gbproxy_reassign_tlli(&tlli_info->tlli,
+				      peer, new_bss_tlli);
+		gbproxy_touch_tlli(peer, tlli_info, now);
 		/* Setup PTMSIs */
 		tlli_info->sgsn_tlli.ptmsi = new_sgsn_ptmsi;
 		tlli_info->tlli.ptmsi = new_bss_ptmsi;
-	} else if (parse_ctx->tlli_enc && parse_ctx->llc && !tlli_info) {
-		/* Unknown SGSN TLLI */
+	} else if (parse_ctx->tlli_enc && parse_ctx->new_ptmsi_enc && !tlli_info &&
+		   !peer->cfg->patch_ptmsi) {
+		/* A new P-TMSI has been signalled in the message with an unknown
+		 * TLLI, create a new tlli_info */
+		uint32_t new_ptmsi;
+		if (!gprs_parse_mi_tmsi(parse_ctx->new_ptmsi_enc, GSM48_TMSI_LEN,
+					&new_ptmsi)) {
+			LOGP(DGPRS, LOGL_ERROR,
+			     "Failed to parse new PTMSI (TLLI is %08x)\n",
+			     parse_ctx->tlli);
+			return tlli_info;
+		}
+
+		LOGP(DGPRS, LOGL_INFO,
+		     "Adding TLLI %08x to list (SGSN, new P-TMSI is %08x)\n",
+		     parse_ctx->tlli, new_ptmsi);
+
+		tlli_info = gbproxy_tlli_info_alloc(peer);
+		tlli_info->sgsn_tlli.current = parse_ctx->tlli;;
+		tlli_info->tlli.current = parse_ctx->tlli;;
+		tlli_info->sgsn_tlli.ptmsi = new_ptmsi;
+		tlli_info->tlli.ptmsi = new_ptmsi;
+	} else if (parse_ctx->tlli_enc && parse_ctx->llc && !tlli_info &&
+		   !peer->cfg->patch_ptmsi) {
+		/* Unknown SGSN TLLI, create a new tlli_info */
+		uint32_t new_ptmsi;
 		tlli_info = gbproxy_tlli_info_alloc(peer);
 		LOGP(DGPRS, LOGL_INFO, "Adding TLLI %08x to list (SGSN)\n",
 		     parse_ctx->tlli);
 
 		gbproxy_attach_tlli_info(peer, now, tlli_info);
+
 		/* Setup TLLIs */
 		tlli_info->sgsn_tlli.current = parse_ctx->tlli;
-		if (peer->cfg->patch_ptmsi) {
-			/* TODO: We don't know the local TLLI here, perhaps add
-			 * a workaround that derives a PTMSI from the SGSN TLLI
-			 * and use that to get the missing values. This may
-			 * only happen when the gbproxy has been restarted or a
-			 * tlli_info has been discarded due to age or queue
-			 * length.
-			 */
-			tlli_info->tlli.current = 0;
-		} else {
-			tlli_info->tlli.current = tlli_info->sgsn_tlli.current;
+		tlli_info->tlli.current = parse_ctx->tlli;
+
+		if (!parse_ctx->new_ptmsi_enc)
+			return tlli_info;
+		/* A new P-TMSI has been signalled in the message */
+
+		if (!gprs_parse_mi_tmsi(parse_ctx->new_ptmsi_enc,
+					GSM48_TMSI_LEN, &new_ptmsi)) {
+			LOGP(DGPRS, LOGL_ERROR,
+			     "Failed to parse new PTMSI (TLLI is %08x)\n",
+			     parse_ctx->tlli);
+			return tlli_info;
 		}
+		LOGP(DGPRS, LOGL_INFO,
+		     "Assigning new P-TMSI %08x\n", new_ptmsi);
+		/* Setup P-TMSIs */
+		tlli_info->sgsn_tlli.ptmsi = new_ptmsi;
+		tlli_info->tlli.ptmsi = new_ptmsi;
 	} else if (parse_ctx->tlli_enc && parse_ctx->llc && tlli_info) {
 		uint32_t bss_tlli = gbproxy_map_tlli(parse_ctx->tlli,
 						     tlli_info, 1);