Despite an international arms embargo on Syria, both sides are getting weapons. The rebels get weapons smuggled in via Turkey and Jordan while the Assad government gets all that and heavier stuff (armored vehicles, smart bombs. Aircraft spare parts and UAVs) via ship or flights from Russia. Most of the weapons for the rebels are paid for by the Arab Gulf oil states while the stuff for the Assads is paid for by Iran. Technically Russia is selling the military equipment to Syria but the major source of financial aid for Syria is from Iran. This breaks all sorts of rules because Iran is under more stringent arms embargoes than Syria. Russia and China use their permanent seats on the UN Security Council to block any efforts to enforce the prohibitions against sending weapons to Syria.
Iran is also flying in a lot of weapons and personnel. Sending anything by ship is too risky as the Americans have apparently gotten too good at detecting seaborne weapons smuggling efforts into or out of Iran. Air freight is another matter, at least as long as Iraq continues to ignore the illegal flights. The Iranian transports have been seen landing at several different Syrian airports and even some rural airfields.
Russia also provides electronic warfare and monitoring equipment along with personnel to operate this gear. Russia also provides operators for the UAVs while Iran provides lots of military trainers and security advisors and technical experts. The U.S. and NATO provide the rebels with electronic warfare assistance and the benefits of satellite reconnaissance photos.