Stasis: Fix unsafe use of stasis_unsubscribe in modules.

Many uses of stasis_unsubscribe in modules can be reached through unload.
These have been switched to stasis_unsubscribe_and_join.

Some subscription callbacks do nothing, for these I've created a noop
callback function in stasis.c.  This is used by some modules that monitor
MWI topics in order to enable cache, since the callback does not become
invalid after dlclose it is safe to use stasis_unsubscribe on these, even
during module unload.

ASTERISK-25121 #close

Change-Id: Ifc2549fbd8eef7d703c222978e8f452e2972189c

channels/chan_dahdi.c

@@ -600,14 +600,6 @@ static int restart_monitor(void);
 
 static int dahdi_sendtext(struct ast_channel *c, const char *text);
 
-static void mwi_event_cb(void *userdata, struct stasis_subscription *sub, struct stasis_message *msg)
-{
-	/* This module does not handle MWI in an event-based manner.  However, it
-	 * subscribes to MWI for each mailbox that is configured so that the core
-	 * knows that we care about it.  Then, chan_dahdi will get the MWI from the
-	 * event cache instead of checking the mailbox directly. */
-}
-
 /*! \brief Avoid the silly dahdi_getevent which ignores a bunch of events */
 static inline int dahdi_get_event(int fd)
 {
@@ -12594,7 +12586,11 @@ static struct dahdi_pvt *mkintf(int channel, const struct dahdi_chan_conf *conf,
 
 			mailbox_specific_topic = ast_mwi_topic(tmp->mailbox);
 			if (mailbox_specific_topic) {
-				tmp->mwi_event_sub = stasis_subscribe_pool(mailbox_specific_topic, mwi_event_cb, NULL);
+				/* This module does not handle MWI in an event-based manner.  However, it
+				 * subscribes to MWI for each mailbox that is configured so that the core
+				 * knows that we care about it.  Then, chan_dahdi will get the MWI from the
+				 * event cache instead of checking the mailbox directly. */
+				tmp->mwi_event_sub = stasis_subscribe_pool(mailbox_specific_topic, stasis_subscription_cb_noop, NULL);
 			}
 		}
 #ifdef HAVE_DAHDI_LINEREVERSE_VMWI

channels/chan_iax2.c

@@ -1438,13 +1438,6 @@ static int iax2_is_control_frame_allowed(int subtype)
 	return is_allowed;
 }
 
-static void mwi_event_cb(void *userdata, struct stasis_subscription *sub, struct stasis_message *msg)
-{
-	/* The MWI subscriptions exist just so the core knows we care about those
-	 * mailboxes.  However, we just grab the events out of the cache when it
-	 * is time to send MWI, since it is only sent with a REGACK. */
-}
-
 static void network_change_stasis_subscribe(void)
 {
 	if (!network_change_sub) {
@@ -13029,7 +13022,10 @@ static struct iax2_peer *build_peer(const char *name, struct ast_variable *v, st
 
 		mailbox_specific_topic = ast_mwi_topic(peer->mailbox);
 		if (mailbox_specific_topic) {
-			peer->mwi_event_sub = stasis_subscribe_pool(mailbox_specific_topic, mwi_event_cb, NULL);
+			/* The MWI subscriptions exist just so the core knows we care about those
+			 * mailboxes.  However, we just grab the events out of the cache when it
+			 * is time to send MWI, since it is only sent with a REGACK. */
+			peer->mwi_event_sub = stasis_subscribe_pool(mailbox_specific_topic, stasis_subscription_cb_noop, NULL);
 		}
 	}
 

channels/chan_mgcp.c

@@ -489,14 +489,6 @@ static struct ast_channel_tech mgcp_tech = {
 	.func_channel_read = acf_channel_read,
 };
 
-static void mwi_event_cb(void *userdata, struct stasis_subscription *sub, struct stasis_message *msg)
-{
-	/* This module does not handle MWI in an event-based manner.  However, it
-	 * subscribes to MWI for each mailbox that is configured so that the core
-	 * knows that we care about it.  Then, chan_mgcp will get the MWI from the
-	 * event cache instead of checking the mailbox directly. */
-}
-
 static int has_voicemail(struct mgcp_endpoint *p)
 {
 	int new_msgs;
@@ -4237,7 +4229,11 @@ static struct mgcp_gateway *build_gateway(char *cat, struct ast_variable *v)
 
 					mailbox_specific_topic = ast_mwi_topic(e->mailbox);
 					if (mailbox_specific_topic) {
-						e->mwi_event_sub = stasis_subscribe_pool(mailbox_specific_topic, mwi_event_cb, NULL);
+						/* This module does not handle MWI in an event-based manner.  However, it
+						 * subscribes to MWI for each mailbox that is configured so that the core
+						 * knows that we care about it.  Then, chan_mgcp will get the MWI from the
+						 * event cache instead of checking the mailbox directly. */
+						e->mwi_event_sub = stasis_subscribe_pool(mailbox_specific_topic, stasis_subscription_cb_noop, NULL);
 					}
 				}
 				snprintf(e->rqnt_ident, sizeof(e->rqnt_ident), "%08lx", (unsigned long)ast_random());

channels/chan_sip.c

@@ -5004,7 +5004,7 @@ static void register_peer_exten(struct sip_peer *peer, int onoff)
 static void destroy_mailbox(struct sip_mailbox *mailbox)
 {
 	if (mailbox->event_sub) {
-		mailbox->event_sub = stasis_unsubscribe(mailbox->event_sub);
+		mailbox->event_sub = stasis_unsubscribe_and_join(mailbox->event_sub);
 	}
 	ast_free(mailbox);
 }

channels/chan_skinny.c

@@ -8749,7 +8749,7 @@ static int unload_module(void)
 				skinny_unlocksub(sub);
 			}
 			if (l->mwi_event_sub) {
-				l->mwi_event_sub = stasis_unsubscribe(l->mwi_event_sub);
+				l->mwi_event_sub = stasis_unsubscribe_and_join(l->mwi_event_sub);
 			}
 			ast_mutex_unlock(&l->lock);
 			unregister_exten(l);

channels/sig_pri.c

@@ -8991,7 +8991,7 @@ void sig_pri_stop_pri(struct sig_pri_span *pri)
 #if defined(HAVE_PRI_MWI)
 	for (idx = 0; idx < ARRAY_LEN(pri->mbox); ++idx) {
 		if (pri->mbox[idx].sub) {
-			pri->mbox[idx].sub = stasis_unsubscribe(pri->mbox[idx].sub);
+			pri->mbox[idx].sub = stasis_unsubscribe_and_join(pri->mbox[idx].sub);
 		}
 	}
 #endif	/* defined(HAVE_PRI_MWI) */

include/asterisk/stasis.h

@@ -520,6 +520,17 @@ void stasis_publish_sync(struct stasis_subscription *sub, struct stasis_message
  */
 typedef void (*stasis_subscription_cb)(void *data, struct stasis_subscription *sub, struct stasis_message *message);
 
+/*!
+ * \brief Stasis subscription callback function that does nothing.
+ *
+ * \note This callback should be used for events are not directly processed, but need
+ * to be generated so data can be retrieved from cache later.  Subscriptions with this
+ * callback can be released with \ref stasis_unsubscribe, even during module unload.
+ *
+ * \since 13.5
+ */
+void stasis_subscription_cb_noop(void *data, struct stasis_subscription *sub, struct stasis_message *message);
+
 /*!
  * \brief Create a subscription.
  *

main/stasis.c

@@ -444,6 +444,10 @@ static void subscription_invoke(struct stasis_subscription *sub,
 static void send_subscription_subscribe(struct stasis_topic *topic, struct stasis_subscription *sub);
 static void send_subscription_unsubscribe(struct stasis_topic *topic, struct stasis_subscription *sub);
 
+void stasis_subscription_cb_noop(void *data, struct stasis_subscription *sub, struct stasis_message *message)
+{
+}
+
 struct stasis_subscription *internal_stasis_subscribe(
 	struct stasis_topic *topic,
 	stasis_subscription_cb callback,

res/res_hep_rtcp.c

@@ -131,7 +131,7 @@ static int load_module(void)
 static int unload_module(void)
 {
 	if (stasis_rtp_subscription) {
-		stasis_rtp_subscription = stasis_unsubscribe(stasis_rtp_subscription);
+		stasis_rtp_subscription = stasis_unsubscribe_and_join(stasis_rtp_subscription);
 	}
 
 	return 0;

res/res_pjsip_mwi.c

@@ -471,7 +471,7 @@ static int unsubscribe_stasis(void *obj, void *arg, int flags)
 	struct mwi_stasis_subscription *mwi_stasis = obj;
 	if (mwi_stasis->stasis_sub) {
 		ast_debug(3, "Removing stasis subscription to mailbox %s\n", mwi_stasis->mailbox);
-		mwi_stasis->stasis_sub = stasis_unsubscribe(mwi_stasis->stasis_sub);
+		mwi_stasis->stasis_sub = stasis_unsubscribe_and_join(mwi_stasis->stasis_sub);
 	}
 	return CMP_MATCH;
 }

res/res_security_log.c

@@ -152,7 +152,7 @@ static int load_module(void)
 static int unload_module(void)
 {
 	if (security_stasis_sub) {
-		security_stasis_sub = stasis_unsubscribe(security_stasis_sub);
+		security_stasis_sub = stasis_unsubscribe_and_join(security_stasis_sub);
 	}
 
 	ast_logger_unregister_level(LOG_SECURITY_NAME);

res/res_stasis_device_state.c

@@ -105,7 +105,7 @@ static int device_state_subscriptions_cmp(void *obj, void *arg, int flags)
 static void device_state_subscription_destroy(void *obj)
 {
 	struct device_state_subscription *sub = obj;
-	sub->sub = stasis_unsubscribe(sub->sub);
+	sub->sub = stasis_unsubscribe_and_join(sub->sub);
 	ast_string_field_free_memory(sub);
 }
 

res/res_xmpp.c

@@ -3568,12 +3568,12 @@ int ast_xmpp_client_disconnect(struct ast_xmpp_client *client)
 	}
 
 	if (client->mwi_sub) {
-		client->mwi_sub = stasis_unsubscribe(client->mwi_sub);
+		client->mwi_sub = stasis_unsubscribe_and_join(client->mwi_sub);
 		xmpp_pubsub_unsubscribe(client, "message_waiting");
 	}
 
 	if (client->device_state_sub) {
-		client->device_state_sub = stasis_unsubscribe(client->device_state_sub);
+		client->device_state_sub = stasis_unsubscribe_and_join(client->device_state_sub);
 		xmpp_pubsub_unsubscribe(client, "device_state");
 	}