prevent double masqurading channels when one is been hung up and deadlock avoidance is used.

There is a race condition in ast_do_masquerade / ast_hangup (at least)

Reported by me signed off by schmidts with input from David Vossel

Review: https://reviewboard.asterisk.org/r/1323/


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@330311 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/channel.c

@@ -6320,10 +6320,18 @@ int ast_do_masquerade(struct ast_channel *original)
 	 * for deadlock avoidance will not result in any sort of masquerade race condition.
 	 * If masq is called by a different thread while this happens, it will be stuck waiting
 	 * until we unlock the container. */
-	while (ast_channel_trylock(clonechan)) {
+	while ((clonechan = original->masq) && ast_channel_trylock(clonechan)) {
 		CHANNEL_DEADLOCK_AVOIDANCE(original);
 	}
 
+	/* recheck if masq has been done the deadlock avoidance above could cause a double masq
+	 * this is posible with at least ast_hangup*/
+	if (!original->masq) {
+		ast_channel_unlock(original);
+		ao2_unlock(channels);
+		return 0; /* masq already completed by another thread, or never needed to be done to begin with */
+	}
+
 	/* Get any transfer masquerade connected line exchange data. */
 	xfer_ds = ast_channel_datastore_find(original, &xfer_ds_info, NULL);
 	if (xfer_ds) {