Prevent BLF subscriptions from causing deadlocks

Fix a locking inversion in sip_send_mwi_to_peer that was causing deadlocks.
This function now requires that both the peer and associated pvt be unlocked
before it is called for cases where peer and peer->mwipvt form a circular
reference.

(closes issue ASTERISK-18663)
Review: https://reviewboard.asterisk.org/r/1563/


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@343621 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -24345,7 +24345,9 @@ static int handle_request_subscribe(struct sip_pvt *p, struct sip_request *req,
 
 		p->subscribed = MWI_NOTIFICATION;
 		if (ast_test_flag(&authpeer->flags[1], SIP_PAGE2_SUBSCRIBEMWIONLY)) {
+			ao2_unlock(p);
 			add_peer_mwi_subs(authpeer);
+			ao2_lock(p);
 		}
 		if (authpeer->mwipvt && authpeer->mwipvt != p) {	/* Destroy old PVT if this is a new one */
 			/* We only allow one subscription per peer */
@@ -24421,7 +24423,12 @@ static int handle_request_subscribe(struct sip_pvt *p, struct sip_request *req,
 			ast_set_flag(&p->flags[1], SIP_PAGE2_DIALOG_ESTABLISHED);
 			transmit_response(p, "200 OK", req);
 			if (p->relatedpeer) {	/* Send first notification */
-				sip_send_mwi_to_peer(p->relatedpeer, 0);
+				struct sip_peer *peer = p->relatedpeer;
+				ref_peer(peer, "ensure a peer ref is held during MWI sending");
+				ao2_unlock(p);
+				sip_send_mwi_to_peer(peer, 0);
+				ao2_lock(p);
+				unref_peer(peer, "release a peer ref now that MWI is sent");
 			}
 		} else if (p->subscribed != CALL_COMPLETION) {
 			if ((firststate = ast_extension_state(NULL, p->context, p->exten)) < 0) {
@@ -25132,36 +25139,49 @@ static int get_cached_mwi(struct sip_peer *peer, int *new, int *old)
 	return in_cache;
 }
 
-/*! \brief Send message waiting indication to alert peer that they've got voicemail */
+/*! \brief Send message waiting indication to alert peer that they've got voicemail
+ *  \note Both peer and associated sip_pvt must be unlocked prior to calling this function
+*/
 static int sip_send_mwi_to_peer(struct sip_peer *peer, int cache_only)
 {
 	/* Called with peerl lock, but releases it */
 	struct sip_pvt *p;
 	int newmsgs = 0, oldmsgs = 0;
+	const char *vmexten;
 
-	if (ast_test_flag((&peer->flags[1]), SIP_PAGE2_SUBSCRIBEMWIONLY) && !peer->mwipvt)
+	ao2_lock(peer);
+
+	vmexten = ast_strdupa(peer->vmexten);
+
+	if (ast_test_flag((&peer->flags[1]), SIP_PAGE2_SUBSCRIBEMWIONLY) && !peer->mwipvt) {
+		ao2_unlock(peer);
 		return 0;
+	}
 
 	/* Do we have an IP address? If not, skip this peer */
-	if (ast_sockaddr_isnull(&peer->addr) && ast_sockaddr_isnull(&peer->defaddr))
+	if (ast_sockaddr_isnull(&peer->addr) && ast_sockaddr_isnull(&peer->defaddr)) {
+		ao2_unlock(peer);
 		return 0;
+	}
 
 	/* Attempt to use cached mwi to get message counts. */
 	if (!get_cached_mwi(peer, &newmsgs, &oldmsgs) && !cache_only) {
 		/* Fall back to manually checking the mailbox if not cache_only and get_cached_mwi failed */
 		struct ast_str *mailbox_str = ast_str_alloca(512);
 		peer_mailboxes_to_str(&mailbox_str, peer);
+		ao2_unlock(peer);
 		ast_app_inboxcount(mailbox_str->str, &newmsgs, &oldmsgs);
+		ao2_lock(peer);
 	}
-	ao2_lock(peer);
 
 	if (peer->mwipvt) {
 		/* Base message on subscription */
-		p = dialog_ref(peer->mwipvt, "sip_send_mwi_to_peer: Setting dialog ptr p from peer->mwipvt-- should this be done?");
+		p = dialog_ref(peer->mwipvt, "sip_send_mwi_to_peer: Setting dialog ptr p from peer->mwipvt");
+		ao2_unlock(peer);
 	} else {
+		ao2_unlock(peer);
 		/* Build temporary dialog for this message */
 		if (!(p = sip_alloc(NULL, NULL, 0, SIP_NOTIFY, NULL))) {
-			ao2_unlock(peer);
 			return -1;
 		}
 
@@ -25175,7 +25195,6 @@ static int sip_send_mwi_to_peer(struct sip_peer *peer, int cache_only)
 			dialog_unlink_all(p);
 			dialog_unref(p, "unref dialog p just created via sip_alloc");
 			/* sip_destroy(p); */
-			ao2_unlock(peer);
 			return 0;
 		}
 		/* Recalculate our side, and recalculate Call ID */
@@ -25183,11 +25202,15 @@ static int sip_send_mwi_to_peer(struct sip_peer *peer, int cache_only)
 		build_via(p);
 		ao2_t_unlink(dialogs, p, "About to change the callid -- remove the old name");
 		build_callid_pvt(p);
+
+		ao2_lock(peer);
 		if (!ast_strlen_zero(peer->mwi_from)) {
 			ast_string_field_set(p, mwi_from, peer->mwi_from);
 		} else if (!ast_strlen_zero(default_mwi_from)) {
 			ast_string_field_set(p, mwi_from, default_mwi_from);
 		}
+		ao2_unlock(peer);
+
 		ao2_t_link(dialogs, p, "Linking in under new name");
 		/* Destroy this session after 32 secs */
 		sip_scheddestroy(p, DEFAULT_TRANS_TIMEOUT);
@@ -25200,10 +25223,10 @@ static int sip_send_mwi_to_peer(struct sip_peer *peer, int cache_only)
 	/* Send MWI */
 	ast_set_flag(&p->flags[0], SIP_OUTGOING);
 	/* the following will decrement the refcount on p as it finishes */
-	transmit_notify_with_mwi(p, newmsgs, oldmsgs, peer->vmexten);
+	transmit_notify_with_mwi(p, newmsgs, oldmsgs, vmexten);
 	sip_pvt_unlock(p);
 	dialog_unref(p, "unref dialog ptr p just before it goes out of scope at the end of sip_send_mwi_to_peer.");
-	ao2_unlock(peer);
+
 	return 0;
 }