lock channel during datastore removal

On channel destruction the channel's datastores are removed and
destroyed.  Since there are public API calls to find and remove
datastores on a channel, a lock should be held whenever datastores are
removed and destroyed.  This resolves a crash caused by a race
condition in app_chanspy.c.

(closes issue #16678)
Reported by: tim_ringenbach
Patches:
      datastore_destroy_race.diff uploaded by tim ringenbach (license 540)
Tested by: dvossel




git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@246545 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/channel.c

@@ -1286,9 +1286,11 @@ void ast_channel_free(struct ast_channel *chan)
 	}
 
 	/* Get rid of each of the data stores on the channel */
+	ast_channel_lock(chan);
 	while ((datastore = AST_LIST_REMOVE_HEAD(&chan->datastores, entry)))
 		/* Free the data store */
 		ast_channel_datastore_free(datastore);
+	ast_channel_unlock(chan);
 
 	/* Lock and unlock the channel just to be sure nobody has it locked still
 	   due to a reference that was stored in a datastore. (i.e. app_chanspy) */