Meaningless answers.

It's certain that Assad has never used chemical weapons. It's probable but unknown for certain if parties in the Syrian military have done so. It's likewise probable but unknown for certain if rebel militias have used chemical weapons. 

It's not illegal for Russia to drop bombs on civilians. Neither is it illegal for the US to drop bombs on civilians. That's why it happens so frequently. Read the Geneva Conventions before you spout off about the legalities.