sgsn: Remove inactive LLME/MM after inactivity timeout

Currently old LLMEs and MM contexts that haven't been explicitly
detached or cancelled are not removed until another request with the
same IMSI is made. These stale entries may accumulate over time and
severely compromise the operation of the SGSN.

This patch implements age based LLME expiry, when the maximum age has
been reached, the corresponding MM context is cancelled. If such an MM
context doesn't exist, the LLME is unassigned directly.

The implementation works as follows.
 - llme->age_timestamp is reset on each received PTP LLC message
 - sgsn_llme_check_cb is invoked periodically (each 30s)
 - sgsn_llme_check_cb sets the age_timestamp to the current time if
   it has been reset
 - sgsn_llme_check_cb computes the age and expires the LLME if
   it exceeds gprs_max_time_to_idle()

Ticket: OW#1364
Sponsored-by: On-Waves ehf

[hfreyther: Fix typo in comment LMME -> LLME]

1 files changed, 63 insertions, 0 deletions

diff --git a/openbsc/src/gprs/gprs_sgsn.c b/openbsc/src/gprs/gprs_sgsn.c
index 6f706642d..2b78d315c 100644
--- a/openbsc/src/gprs/gprs_sgsn.c
+++ b/openbsc/src/gprs/gprs_sgsn.c
@@ -37,6 +37,10 @@
 #include <openbsc/gprs_gmm.h>
 #include "openbsc/gprs_llc.h"
 
+#include <time.h>
+
+#define GPRS_LLME_CHECK_TICK 30
+
 extern struct sgsn_instance *sgsn;
 
 LLIST_HEAD(sgsn_mm_ctxts);
@@ -508,3 +512,62 @@ void sgsn_update_subscriber_data(struct sgsn_mm_ctx *mmctx,
 
 	sgsn_auth_update(mmctx);
 }
+
+static void sgsn_llme_cleanup_free(struct gprs_llc_llme *llme)
+{
+	struct sgsn_mm_ctx *mmctx = NULL;
+
+	llist_for_each_entry(mmctx, &sgsn_mm_ctxts, list) {
+		if (llme == mmctx->llme) {
+			gsm0408_gprs_access_cancelled(mmctx, SGSN_ERROR_CAUSE_NONE);
+			return;
+		}
+	}
+
+	/* No MM context found */
+	LOGP(DGPRS, LOGL_INFO, "Deleting orphaned LLME, TLLI 0x%08x\n",
+	     llme->tlli);
+	gprs_llgmm_assign(llme, llme->tlli, 0xffffffff, GPRS_ALGO_GEA0, NULL);
+}
+
+static void sgsn_llme_check_cb(void *data_)
+{
+	struct gprs_llc_llme *llme, *llme_tmp;
+	struct timespec now_tp;
+	time_t now, age;
+	time_t max_age = gprs_max_time_to_idle();
+
+	int rc;
+
+	rc = clock_gettime(CLOCK_MONOTONIC, &now_tp);
+	OSMO_ASSERT(rc >= 0);
+	now = now_tp.tv_sec;
+
+	LOGP(DGPRS, LOGL_DEBUG,
+	     "Checking for inactive LLMEs, time = %u\n", (unsigned)now);
+
+	llist_for_each_entry_safe(llme, llme_tmp, &gprs_llc_llmes, list) {
+		if (llme->age_timestamp == GPRS_LLME_RESET_AGE)
+			llme->age_timestamp = now;
+
+		age = now - llme->age_timestamp;
+
+		if (age > max_age || age < 0) {
+			LOGP(DGPRS, LOGL_INFO,
+			     "Inactivity timeout for TLLI 0x%08x, age %d\n",
+			     llme->tlli, (int)age);
+			sgsn_llme_cleanup_free(llme);
+		}
+	}
+
+	osmo_timer_schedule(&sgsn->llme_timer, GPRS_LLME_CHECK_TICK, 0);
+}
+
+void sgsn_inst_init()
+{
+	sgsn->llme_timer.cb = sgsn_llme_check_cb;
+	sgsn->llme_timer.data = NULL;
+
+	osmo_timer_schedule(&sgsn->llme_timer, GPRS_LLME_CHECK_TICK, 0);
+}
+