gprs: Use RAND_bytes for p-tmsi

[hfreyther: Link to libcrypto, include header, add uint8_t* cast]

openbsc/src/gprs/Makefile.am

@@ -30,4 +30,5 @@ osmo_sgsn_SOURCES =	gprs_gmm.c gprs_sgsn.c gprs_sndcp.c gprs_sndcp_vty.c \
 			gsm_04_08_gprs.c sgsn_cdr.c sgsn_ares.c
 osmo_sgsn_LDADD = 	\
 			$(top_builddir)/src/libcommon/libcommon.a \
-			-lgtp $(OSMO_LIBS) $(LIBOSMOABIS_LIBS) $(LIBCARES_LIBS) -lrt
+			-lgtp $(OSMO_LIBS) $(LIBOSMOABIS_LIBS) $(LIBCARES_LIBS) \
+			$(LIBCRYPTO_LIBS) -lrt

openbsc/src/gprs/gprs_sgsn.c

@@ -41,6 +41,8 @@
 
 #include <time.h>
 
+#include <openssl/rand.h>
+
 #define GPRS_LLME_CHECK_TICK 30
 
 extern struct sgsn_instance *sgsn;
@@ -525,7 +527,9 @@ uint32_t sgsn_alloc_ptmsi(void)
 	int max_retries = 100;
 
 restart:
-	ptmsi = rand();
+	if (RAND_bytes((uint8_t *) &ptmsi, sizeof(ptmsi)) != 1)
+		goto failed;
+
 	/* Enforce that the 2 MSB are set without loosing the distance between
 	 * identical values. Since rand() has no duplicate values within a
 	 * period (because the size of the state is the same like the size of

openbsc/tests/sgsn/Makefile.am

@@ -34,5 +34,6 @@ sgsn_test_LDADD = \
 	$(LIBOSMOGSM_LIBS) \
 	$(LIBOSMOGB_LIBS) \
 	$(LIBCARES_LIBS) \
+	$(LIBCRYPTO_LIBS) \
 	-lgtp -lrt