MNCC v6: add optional SDP to the socket protocol

Add a char buffer of 1024 characters length as space for SDP to pass to /
receive from MNCC.

Actually support receiving MNCC without such an SDP tail. The main reason for
this is to avoid the need to adjust the ttcn3 implementation of MNCC: it would
stop working for older osmo-msc.

Older or non-SIP MNCC peers could operate the previous MNCC protocol unchanged
(save the protocol number bump) without having to implement SDP.

The SDP part in the MNCC protocol will be used in upcoming patch
I8c3b2de53ffae4ec3a66b9dabf308c290a2c999f.

This patch must be merged at the same time as osmo-sip-connector patch
Iaca9ed6611fc5ca8ca749bbbefc31f54bea5e925, so that both sides have a matching
MNCC protocol version number.

Change-Id: Ie16f0804c4d99760cd4a0c544d0889b6313eebb7

1 files changed, 30 insertions, 8 deletions

diff --git a/src/libmsc/mncc.c b/src/libmsc/mncc.c
index d0b2ff263..0a38997bc 100644
--- a/src/libmsc/mncc.c
+++ b/src/libmsc/mncc.c
@@ -235,6 +235,34 @@ static int mncc_prim_check_sign(const struct gsm_mncc *mncc_prim)
 	return 0;
 }
 
+/* Make sure that the SDP section has a terminating \0. The MNCC message may end after that \0, and if SDP is omitted it
+ * must contain at least one \0 byte. */
+int mncc_check_sdp_termination(const char *label, const struct gsm_mncc *mncc, unsigned int len, const char *sdp)
+{
+	size_t sdp_offset;
+	size_t sdp_data_len;
+	size_t sdp_str_len;
+
+	OSMO_ASSERT(((char*)mncc) < sdp);
+
+	sdp_offset = sdp - (char*)mncc;
+	if (len < sdp_offset)
+		goto too_short;
+
+	sdp_data_len = len - sdp_offset;
+	if (sdp_data_len < 1)
+		goto too_short;
+
+	sdp_str_len = strnlen(sdp, sdp_data_len);
+	/* There must be a \0, so sdp_str_len must be at most sdp_data_len - 1 */
+	if (sdp_str_len >= sdp_data_len)
+		goto too_short;
+	return 0;
+too_short:
+	LOGP(DMNCC, LOGL_ERROR, "Short %s\n", label);
+	return -EINVAL;
+}
+
 int mncc_prim_check(const struct gsm_mncc *mncc_prim, unsigned int len)
 {
 	if (len < sizeof(mncc_prim->msg_type)) {
@@ -262,11 +290,7 @@ int mncc_prim_check(const struct gsm_mncc *mncc_prim, unsigned int len)
 	case MNCC_RTP_FREE:
 	case MNCC_RTP_CONNECT:
 	case MNCC_RTP_CREATE:
-		if (len < sizeof(struct gsm_mncc_rtp)) {
-			LOGP(DMNCC, LOGL_ERROR, "Short MNCC RTP\n");
-			return -EINVAL;
-		}
-		break;
+		return mncc_check_sdp_termination("MNCC RTP", mncc_prim, len, ((struct gsm_mncc_rtp*)mncc_prim)->sdp);
 	case MNCC_LCHAN_MODIFY:
 	case MNCC_FRAME_DROP:
 	case MNCC_FRAME_RECV:
@@ -279,10 +303,8 @@ int mncc_prim_check(const struct gsm_mncc *mncc_prim, unsigned int len)
 		}
 		break;
 	default:
-		if (len < sizeof(struct gsm_mncc)) {
-			LOGP(DMNCC, LOGL_ERROR, "Short MNCC Signalling\n");
+		if (mncc_check_sdp_termination("MNCC Signalling", mncc_prim, len, mncc_prim->sdp))
 			return -EINVAL;
-		}
 		return mncc_prim_check_sign(mncc_prim);
 	}
 	return 0;