sgsn/test: Really parse received DL LLC messages

Currently just the number of intercepted downlink messages is counted
and eventually checked. The contents of the messages is lost. The
PTMSI contained in ATTACH/RAU Accept messages is just 'guessed' by
resetting the random number generator after reference PTMSIs have
been generated. While this works with rand_r, RAND_bytes cannot be
forced to recreate a certain number sequence this way (unless the
backend is replaced).

This commit changes that behaviour so that the last received msgb is
kept and decoded. The PTMSI that has been assigned by the SGSN is
then taken in the affected test cases and used instead of a 'guessed'
one. This is similar to how a real MS would react to the Accept
message.

Sponsored-by: On-Waves ehf

2 files changed, 61 insertions, 27 deletions

diff --git a/openbsc/tests/sgsn/Makefile.am b/openbsc/tests/sgsn/Makefile.am
index 3c202ddf2..2782d9e1f 100644
--- a/openbsc/tests/sgsn/Makefile.am
+++ b/openbsc/tests/sgsn/Makefile.am
@@ -28,6 +28,7 @@ sgsn_test_LDADD = \
 	$(top_builddir)/src/gprs/gprs_utils.o \
 	$(top_builddir)/src/gprs/gprs_subscriber.o \
 	$(top_builddir)/src/gprs/gsm_04_08_gprs.o \
+	$(top_builddir)/src/gprs/gprs_gb_parse.o \
 	$(top_builddir)/src/libcommon/libcommon.a \
 	$(LIBOSMOABIS_LIBS) \
 	$(LIBOSMOCORE_LIBS) \
diff --git a/openbsc/tests/sgsn/sgsn_test.c b/openbsc/tests/sgsn/sgsn_test.c
index d66983040..859223f7a 100644
--- a/openbsc/tests/sgsn/sgsn_test.c
+++ b/openbsc/tests/sgsn/sgsn_test.c
@@ -27,6 +27,7 @@
 #include <openbsc/gprs_gsup_messages.h>
 #include <openbsc/gprs_gsup_client.h>
 #include <openbsc/gprs_utils.h>
+#include <openbsc/gprs_gb_parse.h>
 
 #include <osmocom/gprs/gprs_bssgp.h>
 
@@ -51,17 +52,53 @@ static struct sgsn_instance sgsn_inst = {
 };
 struct sgsn_instance *sgsn = &sgsn_inst;
 unsigned sgsn_tx_counter = 0;
+struct msgb *last_msg = NULL;
+struct gprs_gb_parse_context last_dl_parse_ctx;
+
+static void reset_last_msg()
+{
+	if (last_msg)
+		msgb_free(last_msg);
+
+	last_msg = NULL;
+	memset(&last_dl_parse_ctx, 0, sizeof(last_dl_parse_ctx));
+}
 
 static void cleanup_test()
 {
+	reset_last_msg();
+}
+
+static uint32_t get_new_ptmsi(const struct gprs_gb_parse_context *parse_ctx)
+{
+	uint32_t new_ptmsi = GSM_RESERVED_TMSI;
+
+	if (parse_ctx->new_ptmsi_enc)
+		gprs_parse_tmsi(parse_ctx->new_ptmsi_enc, &new_ptmsi);
+
+	return new_ptmsi;
 }
 
 /* override */
 int bssgp_tx_dl_ud(struct msgb *msg, uint16_t pdu_lifetime,
 		   struct bssgp_dl_ud_par *dup)
 {
+	int rc;
+
+	reset_last_msg();
+
+	last_msg = msg;
+	OSMO_ASSERT(msgb_data(last_msg) != NULL);
+
+	rc = gprs_gb_parse_llc(msgb_data(last_msg), msgb_length(last_msg),
+		&last_dl_parse_ctx);
+
+	fprintf(stderr, "Got DL LLC message: %s\n",
+		gprs_gb_message_name(&last_dl_parse_ctx, "UNKNOWN"));
+
+	OSMO_ASSERT(rc > 0);
+
 	sgsn_tx_counter += 1;
-	msgb_free(msg);
 	return 0;
 }
 
@@ -153,6 +190,7 @@ static void send_0408_message(struct gprs_llc_llme *llme, uint32_t tlli,
 {
 	struct msgb *msg;
 
+	reset_last_msg();
 	sgsn_tx_counter = 0;
 
 	msg = create_msg(data, data_len);
@@ -911,16 +949,6 @@ static void test_gmm_attach(int retry)
 
 	printf("Testing GMM attach%s\n", retry ? " with retry" : "");
 
-	/* reset the PRNG used by sgsn_alloc_ptmsi */
-	srand(1);
-
-	ptmsi1 = sgsn_alloc_ptmsi();
-	OSMO_ASSERT(ptmsi1 != GSM_RESERVED_TMSI);
-
-	/* reset the PRNG, so that the same P-TMSI sequence will be generated
-	 * again */
-	srand(1);
-
 	foreign_tlli = gprs_tmsi2tlli(0xc0000023, TLLI_FOREIGN);
 
 	/* Create a LLE/LLME */
@@ -984,6 +1012,8 @@ retry_attach_req:
 
 	/* we expect an attach accept/reject */
 	OSMO_ASSERT(sgsn_tx_counter == 1);
+	ptmsi1 = get_new_ptmsi(&last_dl_parse_ctx);
+	OSMO_ASSERT(ptmsi1 != GSM_RESERVED_TMSI);
 
 	/* this has been randomly assigned by the SGSN */
 	local_tlli = gprs_tmsi2tlli(ptmsi1, TLLI_LOCAL);
@@ -1507,16 +1537,6 @@ static void test_gmm_cancel(void)
 
 	sgsn_inst.cfg.auth_policy = SGSN_AUTH_POLICY_OPEN;
 
-	/* reset the PRNG used by sgsn_alloc_ptmsi */
-	srand(1);
-
-	ptmsi1 = sgsn_alloc_ptmsi();
-	OSMO_ASSERT(ptmsi1 != GSM_RESERVED_TMSI);
-
-	/* reset the PRNG, so that the same P-TMSI sequence will be generated
-	 * again */
-	srand(1);
-
 	foreign_tlli = gprs_tmsi2tlli(0xc0000023, TLLI_FOREIGN);
 
 	/* Create a LLE/LLME */
@@ -1554,6 +1574,8 @@ static void test_gmm_cancel(void)
 
 	/* we expect an attach accept/reject */
 	OSMO_ASSERT(sgsn_tx_counter == 1);
+	ptmsi1 = get_new_ptmsi(&last_dl_parse_ctx);
+	OSMO_ASSERT(ptmsi1 != GSM_RESERVED_TMSI);
 
 	/* this has been randomly assigned by the SGSN */
 	local_tlli = gprs_tmsi2tlli(ptmsi1, TLLI_LOCAL);
@@ -1591,6 +1613,7 @@ static void test_gmm_ptmsi_allocation(void)
 	uint32_t foreign_tlli;
 	uint32_t ptmsi1;
 	uint32_t ptmsi2;
+	uint32_t received_ptmsi;
 	uint32_t old_ptmsi;
 	uint32_t local_tlli = 0;
 	struct gprs_llc_lle *lle;
@@ -1658,11 +1681,9 @@ static void test_gmm_ptmsi_allocation(void)
 
 	OSMO_ASSERT(ptmsi1 != ptmsi2);
 
-	printf("  - Repeated Attach Request\n");
+	ptmsi1 = ptmsi2 = GSM_RESERVED_TMSI;
 
-	/* reset the PRNG, so that the same P-TMSI will be generated
-	 * again */
-	srand(1);
+	printf("  - Repeated Attach Request\n");
 
 	foreign_tlli = gprs_tmsi2tlli(0xc0000023, TLLI_FOREIGN);
 
@@ -1678,7 +1699,8 @@ static void test_gmm_ptmsi_allocation(void)
 	ctx = sgsn_mm_ctx_by_tlli(foreign_tlli, &raid);
 	OSMO_ASSERT(ctx != NULL);
 	OSMO_ASSERT(ctx->mm_state == GMM_COMMON_PROC_INIT);
-	OSMO_ASSERT(ctx->p_tmsi == ptmsi1);
+	OSMO_ASSERT(ctx->p_tmsi != GSM_RESERVED_TMSI);
+	ptmsi1 = ctx->p_tmsi;
 
 	old_ptmsi = ctx->p_tmsi_old;
 
@@ -1698,6 +1720,8 @@ static void test_gmm_ptmsi_allocation(void)
 
 	/* we expect an attach accept */
 	OSMO_ASSERT(sgsn_tx_counter == 1);
+	received_ptmsi = get_new_ptmsi(&last_dl_parse_ctx);
+	OSMO_ASSERT(received_ptmsi == ptmsi1);
 
 	/* we ignore this and send the attach again */
 	send_0408_message(lle->llme, foreign_tlli,
@@ -1710,6 +1734,11 @@ static void test_gmm_ptmsi_allocation(void)
 	OSMO_ASSERT(ctx->p_tmsi_old == old_ptmsi);
 	OSMO_ASSERT(ctx->p_tmsi == ptmsi1);
 
+	/* we expect an attach accept */
+	OSMO_ASSERT(sgsn_tx_counter == 1);
+	received_ptmsi = get_new_ptmsi(&last_dl_parse_ctx);
+	OSMO_ASSERT(received_ptmsi == ptmsi1);
+
 	/* inject the attach complete */
 	local_tlli = gprs_tmsi2tlli(ptmsi1, TLLI_LOCAL);
 	send_0408_message(ctx->llme, local_tlli,
@@ -1733,7 +1762,9 @@ static void test_gmm_ptmsi_allocation(void)
 
 	OSMO_ASSERT(ctx->mm_state == GMM_COMMON_PROC_INIT);
 	OSMO_ASSERT(ctx->p_tmsi_old == ptmsi1);
-	OSMO_ASSERT(ctx->p_tmsi == ptmsi2);
+	OSMO_ASSERT(ctx->p_tmsi != GSM_RESERVED_TMSI);
+	OSMO_ASSERT(ctx->p_tmsi != ptmsi1);
+	ptmsi2 = ctx->p_tmsi;
 
 	/* repeat the RA update request */
 	send_0408_message(ctx->llme, local_tlli,
@@ -1741,6 +1772,8 @@ static void test_gmm_ptmsi_allocation(void)
 
 	/* we expect an RA update accept */
 	OSMO_ASSERT(sgsn_tx_counter == 1);
+	received_ptmsi = get_new_ptmsi(&last_dl_parse_ctx);
+	OSMO_ASSERT(received_ptmsi == ptmsi2);
 
 	OSMO_ASSERT(ctx->mm_state == GMM_COMMON_PROC_INIT);
 	OSMO_ASSERT(ctx->p_tmsi_old == ptmsi1);