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, 12 insertions, 73 deletions

diff --git a/apps/app_dial.c b/apps/app_dial.c
index 0390cfe7f..895d4b883 100644
--- a/apps/app_dial.c
+++ b/apps/app_dial.c
@@ -58,7 +58,6 @@ ASTERISK_REGISTER_FILE()
 #include "asterisk/manager.h"
 #include "asterisk/privacy.h"
 #include "asterisk/stringfields.h"
-#include "asterisk/global_datastores.h"
 #include "asterisk/dsp.h"
 #include "asterisk/aoc.h"
 #include "asterisk/ccss.h"
@@ -68,6 +67,7 @@ ASTERISK_REGISTER_FILE()
 #include "asterisk/stasis_channels.h"
 #include "asterisk/bridge_after.h"
 #include "asterisk/features_config.h"
+#include "asterisk/max_forwards.h"
 
 /*** DOCUMENTATION
 	<application name="Dial" language="en_US">
@@ -881,6 +881,7 @@ static void do_forward(struct chanlist *o, struct cause_args *num,
 			ast_channel_lock_both(in, o->chan);
 			ast_channel_inherit_variables(in, o->chan);
 			ast_channel_datastore_inherit(in, o->chan);
+			ast_max_forwards_decrement(o->chan);
 			ast_channel_unlock(in);
 			ast_channel_unlock(o->chan);
 			/* When a call is forwarded, we don't want to track new interfaces
@@ -2074,7 +2075,6 @@ static int dial_exec_full(struct ast_channel *chan, const char *data, struct ast
 	);
 	struct ast_flags64 opts = { 0, };
 	char *opt_args[OPT_ARG_ARRAY_SIZE];
-	struct ast_datastore *datastore = NULL;
 	int fulldial = 0, num_dialed = 0;
 	int ignore_cc = 0;
 	char device_name[AST_CHANNEL_NAME];
@@ -2101,6 +2101,7 @@ static int dial_exec_full(struct ast_channel *chan, const char *data, struct ast
 	 * \note This will not have any malloced strings so do not free it.
 	 */
 	struct ast_party_caller caller;
+	int max_forwards;
 
 	/* Reset all DIAL variables back to blank, to prevent confusion (in case we don't reset all of them). */
 	ast_channel_lock(chan);
@@ -2111,8 +2112,16 @@ static int dial_exec_full(struct ast_channel *chan, const char *data, struct ast
 	pbx_builtin_setvar_helper(chan, "ANSWEREDTIME", "");
 	pbx_builtin_setvar_helper(chan, "DIALEDTIME", "");
 	ast_channel_stage_snapshot_done(chan);
+	max_forwards = ast_max_forwards_get(chan);
 	ast_channel_unlock(chan);
 
+	if (max_forwards <= 0) {
+		ast_log(LOG_WARNING, "Cannot place outbound call from channel '%s'. Max forwards exceeded\n",
+				ast_channel_name(chan));
+		pbx_builtin_setvar_helper(chan, "DIALSTATUS", "BUSY");
+		return -1;
+	}
+
 	if (ast_strlen_zero(data)) {
 		ast_log(LOG_WARNING, "Dial requires an argument (technology/resource)\n");
 		pbx_builtin_setvar_helper(chan, "DIALSTATUS", pa.status);
@@ -2314,9 +2323,6 @@ static int dial_exec_full(struct ast_channel *chan, const char *data, struct ast
 		char *tech = strsep(&number, "/");
 		size_t tech_len;
 		size_t number_len;
-		/* find if we already dialed this interface */
-		struct ast_dialed_interface *di;
-		AST_LIST_HEAD(,ast_dialed_interface) *dialed_interfaces;
 
 		num_dialed++;
 		if (ast_strlen_zero(number)) {
@@ -2360,7 +2366,6 @@ static int dial_exec_full(struct ast_channel *chan, const char *data, struct ast
 		/* Request the peer */
 
 		ast_channel_lock(chan);
-		datastore = ast_channel_datastore_find(chan, &dialed_interface_info, NULL);
 		/*
 		 * Seed the chanlist's connected line information with previously
 		 * acquired connected line info from the incoming channel.  The
@@ -2370,61 +2375,6 @@ static int dial_exec_full(struct ast_channel *chan, const char *data, struct ast
 		ast_party_connected_line_copy(&tmp->connected, ast_channel_connected(chan));
 		ast_channel_unlock(chan);
 
-		if (datastore)
-			dialed_interfaces = datastore->data;
-		else {
-			if (!(datastore = ast_datastore_alloc(&dialed_interface_info, NULL))) {
-				ast_log(LOG_WARNING, "Unable to create channel datastore for dialed interfaces. Aborting!\n");
-				chanlist_free(tmp);
-				goto out;
-			}
-			datastore->inheritance = DATASTORE_INHERIT_FOREVER;
-
-			if (!(dialed_interfaces = ast_calloc(1, sizeof(*dialed_interfaces)))) {
-				ast_datastore_free(datastore);
-				chanlist_free(tmp);
-				goto out;
-			}
-
-			datastore->data = dialed_interfaces;
-			AST_LIST_HEAD_INIT(dialed_interfaces);
-
-			ast_channel_lock(chan);
-			ast_channel_datastore_add(chan, datastore);
-			ast_channel_unlock(chan);
-		}
-
-		AST_LIST_LOCK(dialed_interfaces);
-		AST_LIST_TRAVERSE(dialed_interfaces, di, list) {
-			if (!strcasecmp(di->interface, tmp->interface)) {
-				ast_log(LOG_WARNING, "Skipping dialing interface '%s' again since it has already been dialed\n",
-					di->interface);
-				break;
-			}
-		}
-		AST_LIST_UNLOCK(dialed_interfaces);
-		if (di) {
-			fulldial++;
-			chanlist_free(tmp);
-			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 (strcasecmp(tmp->tech, "Local")) {
-			if (!(di = ast_calloc(1, sizeof(*di) + strlen(tmp->interface)))) {
-				chanlist_free(tmp);
-				goto out;
-			}
-			strcpy(di->interface, tmp->interface);
-
-			AST_LIST_LOCK(dialed_interfaces);
-			AST_LIST_INSERT_TAIL(dialed_interfaces, di, list);
-			AST_LIST_UNLOCK(dialed_interfaces);
-		}
-
 		tc = ast_request(tmp->tech, ast_channel_nativeformats(chan), NULL, chan, tmp->number, &cause);
 		if (!tc) {
 			/* If we can't, just go on to the next call */
@@ -2465,6 +2415,7 @@ static int dial_exec_full(struct ast_channel *chan, const char *data, struct ast
 		/* Inherit specially named variables from parent channel */
 		ast_channel_inherit_variables(chan, tc);
 		ast_channel_datastore_inherit(chan, tc);
+		ast_max_forwards_decrement(tc);
 
 		ast_channel_appl_set(tc, "AppDial");
 		ast_channel_data_set(tc, "(Outgoing Line)");
@@ -2680,18 +2631,6 @@ static int dial_exec_full(struct ast_channel *chan, const char *data, struct ast
 	peer = wait_for_answer(chan, &out_chans, &to, peerflags, opt_args, &pa, &num, &result,
 		dtmf_progress, ignore_cc, &forced_clid, &stored_clid);
 
-	/* 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(chan);
-	datastore = ast_channel_datastore_find(chan, &dialed_interface_info, NULL); /* make sure we weren't cleaned up already */
-	if (datastore && !ast_channel_datastore_remove(chan, datastore)) {
-		ast_datastore_free(datastore);
-	}
-	ast_channel_unlock(chan);
 	if (!peer) {
 		if (result) {
 			res = result;