ciphering: Handle ciphering support for A5/3 correctly

This was found and debugged by Sylvain. The BTS will always support
A5/0 so we do not keep track of that, the first bit of the flags is
used for A5/1, second for A5/2... but for RSL there is an offset to
go from RSL to A5(x). Add a testcase and change the code.

.gitignore

@@ -26,6 +26,7 @@ src/osmo-bts-sysmo/sysmobts-mgr
 tests/atconfig
 tests/package.m4
 tests/paging/paging_test
+tests/cipher/cipher_test
 tests/testsuite
 tests/testsuite.log
 

configure.ac

@@ -59,4 +59,5 @@ dnl    src/osmo-bts-bb/Makefile
     include/osmo-bts/Makefile
     tests/Makefile
     tests/paging/Makefile
+    tests/cipher/Makefile
     Makefile)

include/osmo-bts/gsm_data.h

@@ -56,7 +56,7 @@ struct gsm_bts_role_bts {
 	char *rtp_bind_host;
 	unsigned int rtp_jitter_buf_ms;
 	struct {
-		uint8_t ciphers;
+		uint8_t ciphers;	/* flags A5/1==0x1, A5/2==0x2, A5/3==0x4 */
 	} support;
 	struct {
 		uint8_t tc4_ctr;
@@ -85,4 +85,10 @@ static inline struct femtol1_hdl *trx_femtol1_hdl(struct gsm_bts_trx *trx)
 
 void lchan_set_state(struct gsm_lchan *lchan, enum gsm_lchan_state state);
 
+/* cipher code */
+#define CIPHER_A5(x) (1 << (x-1))
+
+int bts_supports_cipher(struct gsm_bts_role_bts *bts, int rsl_cipher);
+
+
 #endif /* _GSM_DATA_H */

src/common/bts.c

@@ -213,3 +213,18 @@ struct msgb *bts_agch_dequeue(struct gsm_bts *bts)
 
 	return msgb_dequeue(&btsb->agch_queue);
 }
+
+int bts_supports_cipher(struct gsm_bts_role_bts *bts, int rsl_cipher)
+{
+	int sup;
+
+	if (rsl_cipher < 1 || rsl_cipher > 8)
+		return -ENOTSUP;
+
+	/* No encryption is always supported */
+	if (rsl_cipher == 1)
+		return 1;
+
+	sup =  (1 << (rsl_cipher - 2)) & bts->support.ciphers;
+	return sup > 0;
+}

src/common/rsl.c

@@ -593,11 +593,13 @@ static void copy_sacch_si_to_lchan(struct gsm_lchan *lchan)
 static int encr_info2lchan(struct gsm_lchan *lchan,
 			   const uint8_t *val, uint8_t len)
 {
+	int rc;
 	struct gsm_bts_role_bts *btsb = bts_role_bts(lchan->ts->trx->bts);
 
 	/* check if the encryption algorithm sent by BSC is supported! */
-	if (!((1 << *val) & btsb->support.ciphers))
-		 return -ENOTSUP;
+	rc = bts_supports_cipher(btsb, *val);
+	if (rc != 1)
+		return rc;
 
 	/* length can be '1' in case of no ciphering */
 	if (len < 1)

src/osmo-bts-sysmo/main.c

@@ -257,7 +257,7 @@ int main(int argc, char **argv)
 		exit(1);
 	}
 	btsb = bts_role_bts(bts);
-	btsb->support.ciphers = (1 << 0) | (1 << 1) | (1 << 2);
+	btsb->support.ciphers = CIPHER_A5(1) | CIPHER_A5(2) | CIPHER_A5(3);
 
 	rc = vty_read_config_file(config_file, NULL);
 	if (rc < 0) {

tests/Makefile.am

@@ -1,4 +1,4 @@
-SUBDIRS = paging
+SUBDIRS = paging cipher
 
 # The `:;' works around a Bash 3.2 bug when the output is not writeable.
 $(srcdir)/package.m4: $(top_srcdir)/configure.ac

tests/cipher/Makefile.am

@@ -0,0 +1,8 @@
+INCLUDES = $(all_includes) -I$(top_srcdir)/include -I$(OPENBSC_INCDIR)
+AM_CFLAGS = -Wall $(LIBOSMOCORE_CFLAGS) $(LIBOSMOGSM_CFLAGS) $(LIBOSMOVTY_CFLAGS) $(LIBOSMOTRAU_CFLAGS)
+LDADD = $(LIBOSMOCORE_LIBS) $(LIBOSMOGSM_LIBS) $(LIBOSMOVTY_LIBS) $(LIBOSMOTRAU_LIBS) -lortp
+noinst_PROGRAMS = cipher_test
+EXTRA_DIST = cipher_test.ok
+
+cipher_test_SOURCES = cipher_test.c
+cipher_test_LDADD = $(top_builddir)/src/common/libbts.a $(LDADD)

tests/cipher/cipher_test.c

@@ -0,0 +1,130 @@
+/* (C) 2012 by Holger Hans Peter Freyther
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <osmo-bts/bts.h>
+#include <osmo-bts/logging.h>
+#include <osmo-bts/paging.h>
+#include <osmo-bts/gsm_data.h>
+
+#include <osmocom/core/talloc.h>
+
+#include <errno.h>
+#include <unistd.h>
+
+static struct gsm_bts *bts;
+static struct gsm_bts_role_bts *btsb;
+int pcu_direct = 0;
+
+#define ASSERT_TRUE(rc) \
+	if (!(rc)) { \
+		printf("Assert failed in %s:%d.\n",  \
+		       __FILE__, __LINE__);          \
+		abort();			     \
+	}
+
+static void test_cipher_parsing(void)
+{
+	int i;
+
+	btsb->support.ciphers = 0;
+
+	/* always support A5/0 */
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x0) == -ENOTSUP);
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x1) == 1); /* A5/0 */
+	for (i = 2; i <= 8; ++i) {
+		ASSERT_TRUE(bts_supports_cipher(btsb, i) == 0);
+	}
+
+	/* checking default A5/1 to A5/3 support */
+	btsb->support.ciphers = CIPHER_A5(1) | CIPHER_A5(2) | CIPHER_A5(3);
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x0) == -ENOTSUP);
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x1) == 1); /* A5/0 */
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x2) == 1); /* A5/1 */
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x3) == 1); /* A5/2 */
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x4) == 1); /* A5/3 */
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x5) == 0); /* A5/4 */
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x6) == 0); /* A5/5 */
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x7) == 0); /* A5/6 */
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x8) == 0); /* A5/7 */
+	ASSERT_TRUE(bts_supports_cipher(btsb, 0x9) == -ENOTSUP);
+}
+
+int main(int argc, char **argv)
+{
+	void *tall_msgb_ctx;
+
+	tall_bts_ctx = talloc_named_const(NULL, 1, "OsmoBTS context");
+	tall_msgb_ctx = talloc_named_const(tall_bts_ctx, 1, "msgb");
+	msgb_set_talloc_ctx(tall_msgb_ctx);
+
+	bts_log_init(NULL);
+
+	bts = gsm_bts_alloc(tall_bts_ctx);
+	if (bts_init(bts) < 0) {
+		fprintf(stderr, "unable to to open bts\n");
+		exit(1);
+	}
+
+	btsb = bts_role_bts(bts);
+	test_cipher_parsing();
+	printf("Success\n");
+
+	return 0;
+}
+
+/* stub to link */
+const uint8_t abis_mac[6] = { 0,1,2,3,4,5 };
+const char *software_version = "0815";
+
+int bts_model_chg_adm_state(struct gsm_bts *bts, struct gsm_abis_mo *mo,
+			    void *obj, uint8_t adm_state)
+{ return 0; }
+int bts_model_init(struct gsm_bts *bts)
+{ return 0; }
+int bts_model_apply_oml(struct gsm_bts *bts, struct msgb *msg,
+			struct tlv_parsed *new_attr, void *obj)
+{ return 0; }
+int bts_model_rsl_chan_rel(struct gsm_lchan *lchan)
+{ return 0;}
+
+int bts_model_rsl_deact_sacch(struct gsm_lchan *lchan)
+{ return 0; }
+
+int bts_model_trx_deact_rf(struct gsm_bts_trx *trx)
+{ return 0; }
+int bts_model_check_oml(struct gsm_bts *bts, uint8_t msg_type,
+			struct tlv_parsed *old_attr, struct tlv_parsed *new_attr,
+			void *obj)
+{ return 0; }
+int bts_model_opstart(struct gsm_bts *bts, struct gsm_abis_mo *mo,
+		      void *obj)
+{ return 0; }
+int bts_model_rsl_chan_act(struct gsm_lchan *lchan, struct tlv_parsed *tp)
+{ return 0; }
+int bts_model_rsl_mode_modify(struct gsm_lchan *lchan)
+{ return 0; }
+void bts_model_rtp_rx_cb(struct osmo_rtp_socket *rs, const uint8_t *rtp_pl,
+			 unsigned int rtp_pl_len) {}
+
+int l1if_pdch_req(struct gsm_bts_trx_ts *ts, int is_ptcch, uint32_t fn,
+        uint16_t arfcn, uint8_t block_nr, uint8_t *data, uint8_t len)
+{ return 0; }
+
+uint32_t trx_get_hlayer1(struct gsm_bts_trx *trx)
+{ return 0; }

tests/cipher/cipher_test.ok

@@ -0,0 +1 @@
+Success

tests/testsuite.at

@@ -6,3 +6,9 @@ AT_KEYWORDS([paging])
 cat $abs_srcdir/paging/paging_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/paging/paging_test], [], [expout], [ignore])
 AT_CLEANUP
+
+AT_SETUP([cipher])
+AT_KEYWORDS([cipher])
+cat $abs_srcdir/cipher/cipher_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/cipher/cipher_test], [], [expout], [ignore])
+AT_CLEANUP