res/res_pjsip_pubsub: Gracefully handle errors when re-creating subscriptions

A subscription that has been persisted can - for various reasons - fail to be
re-created on startup. This patch resolves a number of crashes that occurred
when a subscription cannot be re-created on several off-nominal paths.

#SIPit31

ASTERISK-24368 #close
Reported by: Matt Jordan


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@424601 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_pjsip_pubsub.c

@@ -1038,8 +1038,10 @@ static void remove_subscription(struct sip_subscription_tree *obj)
 	AST_RWLIST_TRAVERSE_SAFE_BEGIN(&subscriptions, i, next) {
 		if (i == obj) {
 			AST_RWLIST_REMOVE_CURRENT(next);
+			if (i->root) {
 				ast_debug(1, "Removing subscription to resource %s from list of subscriptions\n",
 						ast_sip_subscription_get_resource_name(i->root));
+			}
 			break;
 		}
 	}
@@ -1142,6 +1144,10 @@ static void shutdown_subscriptions(struct ast_sip_subscription *sub)
 {
 	int i;
 
+	if (!sub) {
+		return;
+	}
+
 	if (AST_VECTOR_SIZE(&sub->children) > 0) {
 		for (i = 0; i < AST_VECTOR_SIZE(&sub->children); ++i) {
 			shutdown_subscriptions(AST_VECTOR_GET(&sub->children, i));
@@ -1357,6 +1363,11 @@ static int subscription_persistence_recreate(void *obj, void *arg, int flags)
 		ast_sip_pubsub_has_eventlist_support(&rdata));
 	if (PJSIP_IS_STATUS_IN_CLASS(resp, 200)) {
 		sub_tree = create_subscription_tree(handler, endpoint, &rdata, resource, generator, &tree);
+		if (!sub_tree) {
+			ast_sorcery_delete(ast_sip_get_sorcery(), persistence);
+			ast_log(LOG_WARNING, "Failed to re-create subscription for %s\n", persistence->endpoint);
+			return 0;
+		}
 		sub_tree->persistence = ao2_bump(persistence);
 		subscription_persistence_update(sub_tree, &rdata);
 	} else {