asp: Monitor SCTP_PEER_ADDR_CHANGE events to re-apply configured Primary Address

The kernel doesn't store state about a "always-preferred" Primary
address, it simply applies the requested one at the time the request is
done. If afterwards the remote address becomes unavailable, the kernel
will end up giving up on it and selecting anoter one as primary address.

If the VTY-configured Primary Address become available after a while
(signaled by the kernel in the SCTP_PEER_ADDR_CHANGE), make sure to
apply it again.

Similary, if the peer sends us an ASCONF changing our Primary Address,
we should discard that and apply/overwrite *iff* the user explicitly
VTY-configured one (kernel announces the change through
SCTP_ADDR_MADE_PRIM in this scenario).

Related: OS#6076
Change-Id: I2e54e6f9e424350474db6dec6ab604b33a03f88b

1 files changed, 72 insertions, 0 deletions

diff --git a/src/osmo_ss7.c b/src/osmo_ss7.c
index 7882bc2..b8124d1 100644
--- a/src/osmo_ss7.c
+++ b/src/osmo_ss7.c
@@ -1478,6 +1478,76 @@ static int asp_apply_primary_address(const struct osmo_ss7_asp *asp)
 	return rc;
 }
 
+/* Returns whether the address signalled in the SCTP_PEER_ADDR_CHANGE matches
+ * the user-configured Primary Address. */
+static bool sctp_peer_addr_change_ev_addr_matches_our_primary(const struct osmo_ss7_asp *asp,
+							      const union sctp_notification *notif)
+{
+	const char *primary_str;
+	int primary_str_type;
+	struct osmo_sockaddr ev_addr, primary;
+
+	OSMO_ASSERT(asp->cfg.remote.idx_primary >= 0);
+
+	primary_str = asp->cfg.remote.host[asp->cfg.remote.idx_primary];
+	primary_str_type = osmo_ip_str_type(primary_str);
+	memcpy(&ev_addr.u.sas, &notif->sn_paddr_change.spc_aaddr, sizeof(ev_addr.u.sas));
+
+	/* This whole switch is to properly compare addresses (take into account v6mapped IPv4 addresses): */
+	switch (ev_addr.u.sa.sa_family) {
+	case AF_INET:
+		switch (primary_str_type) {
+		case AF_INET:
+			primary = ev_addr; /* Copy AF + port */
+			inet_pton(AF_INET, primary_str, &primary.u.sin.sin_addr);
+			return (osmo_sockaddr_cmp(&primary, &ev_addr) == 0);
+		case AF_INET6:
+			/* for sure not the same */
+			return false;
+		}
+		return false;
+	case AF_INET6:
+		/* "ev_addr" can either be a IPv6 addr or a v6-mapped IPv4
+		 * address. Compare both as IPv6 (or v6-mapped IPv4) addresses. */
+		primary = ev_addr; /* Copy AF + port */
+		inet_pton(AF_INET6, primary_str, &primary.u.sin6.sin6_addr);
+		return (osmo_sockaddr_cmp(&primary, &ev_addr) == 0);
+	default:
+		return false;
+	}
+}
+
+/* Simple SCTP Path-manager tracking/driving the VTY-user-configured primary
+ * address against the kernel when assoc state changes: */
+static void asp_handle_sctp_notif_monitor_primary_address(const struct osmo_ss7_asp *asp,
+							  const union sctp_notification *notif)
+{
+	bool match;
+
+	if (asp->cfg.remote.idx_primary == -1)
+		return;
+	if (notif->sn_header.sn_type != SCTP_PEER_ADDR_CHANGE)
+		return;
+
+	switch (notif->sn_paddr_change.spc_state) {
+	case SCTP_ADDR_AVAILABLE:
+	case SCTP_ADDR_ADDED:
+	case SCTP_ADDR_CONFIRMED:
+		/* If our primary addr became available/added/confirmed, set it */
+		match = sctp_peer_addr_change_ev_addr_matches_our_primary(asp, notif);
+		if (match)
+			asp_apply_primary_address(asp);
+		break;
+	case SCTP_ADDR_MADE_PRIM:
+		/* If another primary addr was made primary, overwrite it by setting it again */
+		match = sctp_peer_addr_change_ev_addr_matches_our_primary(asp, notif);
+		if (!match)
+			asp_apply_primary_address(asp);
+	default:
+		break;
+	}
+}
+
 static bool ipv6_sctp_supported(const char *host, bool bind)
 {
 	int rc;
@@ -2001,6 +2071,7 @@ static int xua_srv_conn_cb(struct osmo_stream_srv *conn)
 	if (flags & OSMO_STREAM_SCTP_MSG_FLAGS_NOTIFICATION) {
 		union sctp_notification *notif = (union sctp_notification *) msgb_data(msg);
 		log_sctp_notification(asp, "xUA CLNT", notif);
+		asp_handle_sctp_notif_monitor_primary_address(asp, notif);
 
 		switch (notif->sn_header.sn_type) {
 		case SCTP_ASSOC_CHANGE:
@@ -2147,6 +2218,7 @@ static int xua_cli_read_cb(struct osmo_stream_cli *conn)
 	if (flags & OSMO_STREAM_SCTP_MSG_FLAGS_NOTIFICATION) {
 		union sctp_notification *notif = (union sctp_notification *) msgb_data(msg);
 		log_sctp_notification(asp, "xUA CLNT", notif);
+		asp_handle_sctp_notif_monitor_primary_address(asp, notif);
 
 		switch (notif->sn_header.sn_type) {
 		case SCTP_ASSOC_CHANGE: