Iran is using Syrian arms purchases from Russia, as a way to get around a UN and U.S. arms embargo. The latest example of this is a billion dollar purchase of Russian MiG-31 and MiG-29 fighters.
Strategypage also notes that Syria has agreed to be Iran's poodle. As I noted here.
Assad thinks he is using Iran to survive, but Iran is Hell-bent on glory and will sacrifice Syria to achieve their dream of a Heaven-creating end time.