AST-2014-015: Fix race condition in chan_pjsip when sending responses after a CANCEL has been received.

Due to the serialized architecture of chan_pjsip there exists a race condition where a CANCEL may
be received and processed before responses (such as 180 Ringing, 183 Session Progress, and 200 OK)
are sent. Since the session is in an unexpected state PJSIP will assert when this is attempted.

This change makes it so that these responses are not sent on disconnected sessions.

ASTERISK-24471 #close
Reported by: yaron nahum
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Merged revisions 428301 from http://svn.asterisk.org/svn/asterisk/branches/12
........

Merged revisions 428302 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@428303 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_pjsip.c

@@ -489,6 +489,11 @@ static int answer(void *data)
 	pjsip_tx_data *packet = NULL;
 	struct ast_sip_session *session = data;
 
+	if (session->inv_session->state == PJSIP_INV_STATE_DISCONNECTED) {
+		ao2_ref(session, -1);
+		return 0;
+	}
+
 	pjsip_dlg_inc_lock(session->inv_session->dlg);
 	if (session->inv_session->invite_tsx) {
 		status = pjsip_inv_answer(session->inv_session, 200, NULL, NULL, &packet);
@@ -1001,7 +1006,8 @@ static int indicate(void *data)
 	struct ast_sip_session *session = ind_data->session;
 	int response_code = ind_data->response_code;
 
-	if (pjsip_inv_answer(session->inv_session, response_code, NULL, NULL, &packet) == PJ_SUCCESS) {
+	if ((session->inv_session->state != PJSIP_INV_STATE_DISCONNECTED) &&
+		(pjsip_inv_answer(session->inv_session, response_code, NULL, NULL, &packet) == PJ_SUCCESS)) {
 		ast_sip_session_send_response(session, packet);
 	}
 
@@ -1053,6 +1059,10 @@ static int update_connected_line_information(void *data)
 	if ((ast_channel_state(session->channel) != AST_STATE_UP) && (session->inv_session->role == PJSIP_UAS_ROLE)) {
 		int response_code = 0;
 
+		if (session->inv_session->state == PJSIP_INV_STATE_DISCONNECTED) {
+			return 0;
+		}
+
 		if (ast_channel_state(session->channel) == AST_STATE_RING) {
 			response_code = !session->endpoint->inband_progress ? 180 : 183;
 		} else if (ast_channel_state(session->channel) == AST_STATE_RINGING) {