RSL: further rtp local bind related fixes

If the CRCX does not indicate the remote IP address, then we still were
binding to 0.0.0.0 and used that address successively in the CRCX_ACK.

As a workaround, we now use the source IP address of the RTP socket,
assuming that the outbound routes to BSC and the MGW are identical.
This is of course not always true, but I don't think there are any
better alternatives...

1 files changed, 49 insertions, 11 deletions

diff --git a/src/common/rsl.c b/src/common/rsl.c
index cab8a56d..5f2dd901 100644
--- a/src/common/rsl.c
+++ b/src/common/rsl.c
@@ -22,6 +22,7 @@
 
 #include <stdio.h>
 #include <errno.h>
+#include <netdb.h>
 #include <sys/types.h>
 #include <arpa/inet.h>
 
@@ -1198,6 +1199,27 @@ static int tx_ipac_XXcx_nack(struct gsm_lchan *lchan, uint8_t cause,
 	return abis_rsl_sendmsg(msg);
 }
 
+static char *get_rsl_local_ip(struct gsm_bts_trx *trx)
+{
+	struct sockaddr_storage ss;
+	socklen_t sa_len = sizeof(ss);
+	static char hostbuf[256];
+	int rc;
+
+	rc = getsockname(trx->rsl_link->bfd.fd, (struct sockaddr *) &ss,
+			 &sa_len);
+	if (rc < 0)
+		return NULL;
+
+	rc = getnameinfo((struct sockaddr *)&ss, sa_len,
+			 hostbuf, sizeof(hostbuf), NULL, 0,
+			 NI_NUMERICHOST);
+	if (rc < 0)
+		return NULL;
+
+	return hostbuf;
+}
+
 static int rsl_rx_ipac_XXcx(struct msgb *msg)
 {
 	struct abis_rsl_dchan_hdr *dch = msgb_l2(msg);
@@ -1207,7 +1229,7 @@ static int rsl_rx_ipac_XXcx(struct msgb *msg)
 	const uint8_t *payload_type, *speech_mode, *payload_type2;
 	const uint32_t *connect_ip;
 	const uint16_t *connect_port;
-	int rc, inc_ip_port = 0;
+	int rc, inc_ip_port = 0, port;
 	char *name;
 
 	if (dch->c.msg_type == RSL_MT_IPAC_CRCX)
@@ -1239,6 +1261,7 @@ static int rsl_rx_ipac_XXcx(struct msgb *msg)
 	}
 
 	if (dch->c.msg_type == RSL_MT_IPAC_CRCX) {
+		char *ipstr = NULL;
 		if (lchan->abis_ip.rtp_socket) {
 			LOGP(DRSL, LOGL_ERROR, "%s Rx RSL IPAC CRCX, "
 				"but we already have socket!\n",
@@ -1263,8 +1286,22 @@ static int rsl_rx_ipac_XXcx(struct msgb *msg)
 		lchan->abis_ip.rtp_socket->priv = lchan;
 		lchan->abis_ip.rtp_socket->rx_cb = &bts_model_rtp_rx_cb;
 
+		if (connect_ip && connect_port) {
+			/* if CRCX specifies a remote IP, we can bind()
+			 * here to 0.0.0.0 and wait for the connect()
+			 * below, after which the kernel will have
+			 * selected the local IP address.  */
+			ipstr = "0.0.0.0";
+		} else {
+			/* if CRCX does not specify a remote IP, we will
+			 * not do any connect() below, and thus the
+			 * local socket will remain bound to 0.0.0.0 -
+			 * which however we cannot legitimately report
+			 * back to the BSC in the CRCX_ACK */
+			ipstr = get_rsl_local_ip(lchan->ts->trx);
+		}
 		rc = osmo_rtp_socket_bind(lchan->abis_ip.rtp_socket,
-					  "0.0.0.0", -1);
+					  ipstr, -1);
 		if (rc < 0) {
 			LOGP(DRSL, LOGL_ERROR,
 			     "%s IPAC Failed to bind RTP/RTCP sockets\n",
@@ -1289,7 +1326,6 @@ static int rsl_rx_ipac_XXcx(struct msgb *msg)
 
 	if (connect_ip && connect_port) {
 		struct in_addr ia;
-		int port;
 
 		/* Special rule: If connect_ip == 0.0.0.0, use RSL IP
 		 * address */
@@ -1315,17 +1351,19 @@ static int rsl_rx_ipac_XXcx(struct msgb *msg)
 		lchan->abis_ip.connect_ip = ntohl(ia.s_addr);
 		lchan->abis_ip.connect_port = ntohs(*connect_port);
 
-		rc = osmo_rtp_get_bound_ip_port(lchan->abis_ip.rtp_socket,
-						&lchan->abis_ip.bound_ip,
-						&port);
-		if (rc < 0)
-			LOGP(DRSL, LOGL_ERROR, "%s IPAC cannot obtain "
-			     "locally bound IP/port: %d\n",
-			     gsm_lchan_name(lchan), rc);
-		lchan->abis_ip.bound_port = port;
 	} else {
 		/* FIXME: discard all codec frames */
 	}
+
+	rc = osmo_rtp_get_bound_ip_port(lchan->abis_ip.rtp_socket,
+					&lchan->abis_ip.bound_ip,
+					&port);
+	if (rc < 0)
+		LOGP(DRSL, LOGL_ERROR, "%s IPAC cannot obtain "
+		     "locally bound IP/port: %d\n",
+		     gsm_lchan_name(lchan), rc);
+	lchan->abis_ip.bound_port = port;
+
 	/* Everything has succeeded, we can store new values in lchan */
 	if (payload_type) {
 		lchan->abis_ip.rtp_payload = *payload_type;