core_local: local channel data not being properly unref'ed and unlocked

In an earlier version of Asterisk a local channel [un]lock all functions were
added in order to keep a crash from occurring when a channel hung up too early
during an attended transfer. Unfortunately, when a transfer failure occurs and
depending on the timing, the local channels sometime do not get properly
unlocked and deref'ed after being locked and ref'ed. This happens because the
underlying local channel structure gets NULLed out before unlocking.

This patch reworks those [un]lock functions and makes sure the values that get
locked and ref'ed later get unlocked and deref'ed.

ASTERISK-27074 #close

Change-Id: Ice96653e29bd9d6674ed5f95feb6b448ab148b09

include/asterisk/core_local.h

@@ -42,36 +42,37 @@ struct stasis_message_type;
 /* ------------------------------------------------------------------- */
 
 /*!
- * \brief Lock the "chan" and "owner" channels (and return them) on the base
- *        private structure as well as the base private structure itself.
+ * \brief Add a reference to the local channel's private tech, lock the local channel's
+ *        private base, and add references and lock both sides of the local channel.
  *
- * \note This also adds references to each of the above mentioned elements and
- *       also the underlying private local structure.
  * \note None of these locks should be held prior to calling this function.
- * \note To undo this process call ast_local_unlock_all.
+ * \note To undo this process call ast_local_unlock_all2.
  *
- * \since 13.8.0
+ * \since 13.17.0, 14.6.0
  *
  * \param chan Must be a local channel
- * \param outchan The local channel's "chan" channel
- * \param outowner The local channel's "owner" channel
+ * \param tech_pvt [out] channel's private tech (ref and lock added)
+ * \param base_chan [out] One side of the local channel (ref and lock added)
+ * \param base_owner [out] Other side of the local channel (ref and lock added)
  */
-void ast_local_lock_all(struct ast_channel *chan, struct ast_channel **outchan,
-			struct ast_channel **outowner);
+void ast_local_lock_all(struct ast_channel *chan, void **tech_pvt,
+	struct ast_channel **base_chan, struct ast_channel **base_owner);
 
 /*!
- * \brief Unlock the "chan" and "owner" channels on the base private structure
- *        as well as the base private structure itself.
+ * \brief Remove a reference to the given local channel's private tech, unlock the given
+ *        local channel's private base, and remove references and unlock both sides of
+ *        given the local channel.
  *
- * \note This also removes references to each of the above mentioned elements and
- *       also the underlying private local structure.
- * \note This function should be used in conjunction with ast_local_lock_all.
+ * \note This function should be used in conjunction with ast_local_lock_all2.
  *
- * \since 13.8.0
+ * \since 13.17.0, 14.6.0
  *
- * \param chan Must be a local channel
+ * \param tech_pvt channel's private tech (ref and lock removed)
+ * \param base_chan One side of the local channel (ref and lock removed)
+ * \param base_owner Other side of the local channel (ref and lock removed)
  */
-void ast_local_unlock_all(struct ast_channel *chan);
+void ast_local_unlock_all(void *tech_pvt, struct ast_channel *base_chan,
+	struct ast_channel *base_owner);
 
 /*!
  * \brief Get the other local channel in the pair.

main/bridge.c

@@ -4276,14 +4276,15 @@ static enum ast_transfer_result attended_transfer_bridge(struct ast_channel *cha
 	BRIDGE_LOCK_ONE_OR_BOTH(bridge1, bridge2);
 
 	if (bridge2) {
+		void *tech;
 		struct ast_channel *locals[2];
 
 		/* Have to lock everything just in case a hangup comes in early */
-		ast_local_lock_all(local_chan, &locals[0], &locals[1]);
+		ast_local_lock_all(local_chan, &tech, &locals[0], &locals[1]);
 		if (!locals[0] || !locals[1]) {
 			ast_log(LOG_ERROR, "Transfer failed probably due to an early hangup - "
 				"missing other half of '%s'\n", ast_channel_name(local_chan));
-			ast_local_unlock_all(local_chan);
+			ast_local_unlock_all(tech, locals[0], locals[1]);
 			ao2_cleanup(local_chan);
 			return AST_BRIDGE_TRANSFER_FAIL;
 		}
@@ -4294,7 +4295,7 @@ static enum ast_transfer_result attended_transfer_bridge(struct ast_channel *cha
 		}
 
 		ast_attended_transfer_message_add_link(transfer_msg, locals);
-		ast_local_unlock_all(local_chan);
+		ast_local_unlock_all(tech, locals[0], locals[1]);
 	} else {
 		ast_attended_transfer_message_add_app(transfer_msg, app, local_chan);
 	}

main/core_local.c

@@ -233,43 +233,39 @@ struct local_pvt {
 	char exten[AST_MAX_EXTENSION];
 };
 
-void ast_local_lock_all(struct ast_channel *chan, struct ast_channel **outchan,
-			struct ast_channel **outowner)
+void ast_local_lock_all(struct ast_channel *chan, void **tech_pvt,
+	struct ast_channel **base_chan, struct ast_channel **base_owner)
 {
 	struct local_pvt *p = ast_channel_tech_pvt(chan);
 
-	*outchan = NULL;
-	*outowner = NULL;
+	*tech_pvt = NULL;
+	*base_chan = NULL;
+	*base_owner = NULL;
 
 	if (p) {
-		ao2_ref(p, 1);
-		ast_unreal_lock_all(&p->base, outchan, outowner);
+		*tech_pvt = ao2_bump(p);
+		ast_unreal_lock_all(&p->base, base_chan, base_owner);
 	}
 }
 
-void ast_local_unlock_all(struct ast_channel *chan)
+void ast_local_unlock_all(void *tech_pvt, struct ast_channel *base_chan,
+	struct ast_channel *base_owner)
 {
-	struct local_pvt *p = ast_channel_tech_pvt(chan);
-	struct ast_unreal_pvt *base;
-
-	if (!p) {
-		return;
+	if (base_chan) {
+		ast_channel_unlock(base_chan);
+		ast_channel_unref(base_chan);
 	}
 
-	base = &p->base;
-
-	if (base->owner) {
-		ast_channel_unlock(base->owner);
-		ast_channel_unref(base->owner);
+	if (base_owner) {
+		ast_channel_unlock(base_owner);
+		ast_channel_unref(base_owner);
 	}
 
-	if (base->chan) {
-		ast_channel_unlock(base->chan);
-		ast_channel_unref(base->chan);
+	if (tech_pvt) {
+		struct local_pvt *p = tech_pvt;
+		ao2_unlock(&p->base);
+		ao2_ref(tech_pvt, -1);
 	}
-
-	ao2_unlock(base);
-	ao2_ref(p, -1);
 }
 
 struct ast_channel *ast_local_get_peer(struct ast_channel *ast)