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

6 files changed, 17 insertions, 29 deletions

diff --git a/channels/chan_dahdi.c b/channels/chan_dahdi.c
index 6958e5be5..953561ce4 100644
--- a/channels/chan_dahdi.c
+++ b/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
diff --git a/channels/chan_iax2.c b/channels/chan_iax2.c
index a5f86e188..dc30d9fe7 100644
--- a/channels/chan_iax2.c
+++ b/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);
 		}
 	}
 
diff --git a/channels/chan_mgcp.c b/channels/chan_mgcp.c
index 08c4dc2e2..b75cd43af 100644
--- a/channels/chan_mgcp.c
+++ b/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());
diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index 1307a9342..b1fbd6e9b 100644
--- a/channels/chan_sip.c
+++ b/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);
 }
diff --git a/channels/chan_skinny.c b/channels/chan_skinny.c
index ed82c7d1f..be9f9b67e 100644
--- a/channels/chan_skinny.c
+++ b/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);
diff --git a/channels/sig_pri.c b/channels/sig_pri.c
index 2815dac13..4b9139101 100644
--- a/channels/sig_pri.c
+++ b/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) */