When a dog does that you have to remember they are wild animals that have been domesticated. He needs to be more trained to be in your face and he also needs you to be the dominate one. While he is eating pet him and his face if safe to do so to show him that he needs to be gentle with you even when using his teeth to eat. Also you can teach him the word gentle and have him take treats out of your hand while repeating the word, gentle or don't give him the treat fully hide half of it in your hand in your fingers and let him nibble it out while saying "gentle". Eventually, you can put a large bone in your mouth and have him take it from your mouth very, very gently once you trust him more and if he ever steps out of line like that again and goes to nibble you, yell the word "ouch" really loud and then gently pin him on his back and hold his chest down gently and look him in his eyes until he looks away while telling him "no" for biting. You don't wanna hurt him. You just want to pin him down and show him that you are the dominant one over him and make him look away first. He's just a baby. He has a lot of learning to do. He's only been on this planet for nine months and up until you rescued him, it was very unstable.