Detect potential forwarding loops based on count.

A potential problem that can arise is the following:

* Bob's phone is programmed to automatically forward to Carol.
* Carol's phone is programmed to automatically forward to Bob.
* Alice calls Bob.

If left unchecked, this results in an endless loops of call forwards
that would eventually result in some sort of fiery crash.

Asterisk's method of solving this issue was to track which interfaces
had been dialed. If a destination were dialed a second time, then
the attempt to call that destination would fail since a loop was
detected.

The problem with this method is that call forwarding has evolved. Some
SIP phones allow for a user to manually forward an incoming call to an
ad-hoc destination. This can mean that:

* There are legitimate use cases where a device may be dialed multiple
times, or
* There can be human error when forwarding calls.

This change removes the old method of detecting forwarding loops in
favor of keeping a count of the number of destinations a channel has
dialed on a particular branch of a call. If the number exceeds the
set number of max forwards, then the call fails. This approach has
the following advantages over the old:

* It is much simpler.
* It can detect loops involving local channels.
* It is user configurable.

The only disadvantage it has is that in the case where there is a
legitimate forwarding loop present, it takes longer to detect it.
However, the forwarding loop is still properly detected and the
call is cleaned up as it should be.

Address review feedback on gerrit.

* Correct "mfgium" to "Digium"
* Decrement max forwards by one in the case where allocation of the
  max forwards datastore is required.
* Remove irrelevant code change from pjsip_global_headers.c

ASTERISK-24958 #close

Change-Id: Ia7e4b7cd3bccfbd34d9a859838356931bba56c23

1 files changed, 15 insertions, 81 deletions

diff --git a/apps/app_queue.c b/apps/app_queue.c
index 6d45be370..df5ff306e 100644
--- a/apps/app_queue.c
+++ b/apps/app_queue.c
@@ -98,7 +98,6 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 #include "asterisk/stringfields.h"
 #include "asterisk/astobj2.h"
 #include "asterisk/strings.h"
-#include "asterisk/global_datastores.h"
 #include "asterisk/taskprocessor.h"
 #include "asterisk/aoc.h"
 #include "asterisk/callerid.h"
@@ -113,6 +112,7 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 #include "asterisk/mixmonitor.h"
 #include "asterisk/core_unreal.h"
 #include "asterisk/bridge_basic.h"
+#include "asterisk/max_forwards.h"
 
 /*!
  * \par Please read before modifying this file.
@@ -4260,6 +4260,7 @@ static int ring_entry(struct queue_ent *qe, struct callattempt *tmp, int *busies
 	/* Inherit specially named variables from parent channel */
 	ast_channel_inherit_variables(qe->chan, tmp->chan);
 	ast_channel_datastore_inherit(qe->chan, tmp->chan);
+	ast_max_forwards_decrement(tmp->chan);
 
 	/* Presense of ADSI CPE on outgoing channel follows ours */
 	ast_channel_adsicpe_set(tmp->chan, ast_channel_adsicpe(qe->chan));
@@ -4753,6 +4754,7 @@ static struct callattempt *wait_for_answer(struct queue_ent *qe, struct callatte
 						ast_channel_lock_both(o->chan, in);
 						ast_channel_inherit_variables(in, o->chan);
 						ast_channel_datastore_inherit(in, o->chan);
+						ast_max_forwards_decrement(o->chan);
 
 						if (o->pending_connected_update) {
 							/*
@@ -6234,10 +6236,7 @@ static void setup_mixmonitor(struct queue_ent *qe, const char *filename)
  *
  * Here is the process of this function
  * 1. Process any options passed to the Queue() application. Options here mean the third argument to Queue()
- * 2. Iterate trough the members of the queue, creating a callattempt corresponding to each member. During this
- *    iteration, we also check the dialed_interfaces datastore to see if we have already attempted calling this
- *    member. If we have, we do not create a callattempt. This is in place to prevent call forwarding loops. Also
- *    during each iteration, we call calc_metric to determine which members should be rung when.
+ * 2. Iterate trough the members of the queue, creating a callattempt corresponding to each member.
  * 3. Call ring_one to place a call to the appropriate member(s)
  * 4. Call wait_for_answer to wait for an answer. If no one answers, return.
  * 5. Take care of any holdtime announcements, member delays, or other options which occur after a call has been answered.
@@ -6290,13 +6289,8 @@ static int try_calling(struct queue_ent *qe, struct ast_flags opts, char **opt_a
 	int block_connected_line = 0;
 	int callcompletedinsl;
 	struct ao2_iterator memi;
-	struct ast_datastore *datastore;
 	struct queue_end_bridge *queue_end_bridge = NULL;
 
-	ast_channel_lock(qe->chan);
-	datastore = ast_channel_datastore_find(qe->chan, &dialed_interface_info, NULL);
-	ast_channel_unlock(qe->chan);
-
 	memset(&bridge_config, 0, sizeof(bridge_config));
 	tmpid[0] = 0;
 	time(&now);
@@ -6383,73 +6377,12 @@ static int try_calling(struct queue_ent *qe, struct ast_flags opts, char **opt_a
 	memi = ao2_iterator_init(qe->parent->members, 0);
 	while ((cur = ao2_iterator_next(&memi))) {
 		struct callattempt *tmp = ast_calloc(1, sizeof(*tmp));
-		struct ast_dialed_interface *di;
-		AST_LIST_HEAD(,ast_dialed_interface) *dialed_interfaces;
 		if (!tmp) {
 			ao2_ref(cur, -1);
 			ao2_iterator_destroy(&memi);
 			ao2_unlock(qe->parent);
 			goto out;
 		}
-		if (!datastore) {
-			if (!(datastore = ast_datastore_alloc(&dialed_interface_info, NULL))) {
-				callattempt_free(tmp);
-				ao2_ref(cur, -1);
-				ao2_iterator_destroy(&memi);
-				ao2_unlock(qe->parent);
-				goto out;
-			}
-			datastore->inheritance = DATASTORE_INHERIT_FOREVER;
-			if (!(dialed_interfaces = ast_calloc(1, sizeof(*dialed_interfaces)))) {
-				callattempt_free(tmp);
-				ao2_ref(cur, -1);
-				ao2_iterator_destroy(&memi);
-				ao2_unlock(qe->parent);
-				goto out;
-			}
-			datastore->data = dialed_interfaces;
-			AST_LIST_HEAD_INIT(dialed_interfaces);
-
-			ast_channel_lock(qe->chan);
-			ast_channel_datastore_add(qe->chan, datastore);
-			ast_channel_unlock(qe->chan);
-		} else
-			dialed_interfaces = datastore->data;
-
-		AST_LIST_LOCK(dialed_interfaces);
-		AST_LIST_TRAVERSE(dialed_interfaces, di, list) {
-			if (!strcasecmp(cur->interface, di->interface)) {
-				ast_debug(1, "Skipping dialing interface '%s' since it has already been dialed\n",
-					di->interface);
-				break;
-			}
-		}
-		AST_LIST_UNLOCK(dialed_interfaces);
-
-		if (di) {
-			callattempt_free(tmp);
-			ao2_ref(cur, -1);
-			continue;
-		}
-
-		/* It is always ok to dial a Local interface.  We only keep track of
-		 * which "real" interfaces have been dialed.  The Local channel will
-		 * inherit this list so that if it ends up dialing a real interface,
-		 * it won't call one that has already been called. */
-		if (strncasecmp(cur->interface, "Local/", 6)) {
-			if (!(di = ast_calloc(1, sizeof(*di) + strlen(cur->interface)))) {
-				callattempt_free(tmp);
-				ao2_ref(cur, -1);
-				ao2_iterator_destroy(&memi);
-				ao2_unlock(qe->parent);
-				goto out;
-			}
-			strcpy(di->interface, cur->interface);
-
-			AST_LIST_LOCK(dialed_interfaces);
-			AST_LIST_INSERT_TAIL(dialed_interfaces, di, list);
-			AST_LIST_UNLOCK(dialed_interfaces);
-		}
 
 		/*
 		 * Seed the callattempt's connected line information with previously
@@ -6508,16 +6441,7 @@ static int try_calling(struct queue_ent *qe, struct ast_flags opts, char **opt_a
 	lpeer = wait_for_answer(qe, outgoing, &to, &digit, numbusies,
 		ast_test_flag(&(bridge_config.features_caller), AST_FEATURE_DISCONNECT),
 		forwardsallowed, ringing);
-	/* The ast_channel_datastore_remove() function could fail here if the
-	 * datastore was moved to another channel during a masquerade. If this is
-	 * the case, don't free the datastore here because later, when the channel
-	 * to which the datastore was moved hangs up, it will attempt to free this
-	 * datastore again, causing a crash
-	 */
-	ast_channel_lock(qe->chan);
-	if (datastore && !ast_channel_datastore_remove(qe->chan, datastore)) {
-		ast_datastore_free(datastore);
-	}
+
 	ast_channel_unlock(qe->chan);
 	ao2_lock(qe->parent);
 	if (qe->parent->strategy == QUEUE_STRATEGY_RRMEMORY || qe->parent->strategy == QUEUE_STRATEGY_RRORDERED) {
@@ -7709,12 +7633,22 @@ static int queue_exec(struct ast_channel *chan, const char *data)
 	struct queue_ent qe = { 0 };
 	struct ast_flags opts = { 0, };
 	char *opt_args[OPT_ARG_ARRAY_SIZE];
+	int max_forwards;
 
 	if (ast_strlen_zero(data)) {
 		ast_log(LOG_WARNING, "Queue requires an argument: queuename[,options[,URL[,announceoverride[,timeout[,agi[,macro[,gosub[,rule[,position]]]]]]]]]\n");
 		return -1;
 	}
 
+	ast_channel_lock(chan);
+	max_forwards = ast_max_forwards_get(chan);
+	ast_channel_unlock(chan);
+
+	if (max_forwards <= 0) {
+		ast_log(LOG_WARNING, "Channel '%s' cannot enter queue. Max forwards exceeded\n", ast_channel_name(chan));
+		return -1;
+	}
+
 	parse = ast_strdupa(data);
 	AST_STANDARD_APP_ARGS(args, parse);