One news source claims the missile was an S-300 and another says it was an SA-5. I checked the specs on both of those missiles. Some variants have a maximum range approaching 300 kilometers. The airliner was reported as being 114 miles (~184 kilometers) off shore, so it's possible that one of these missiles could've reached the plane if the missile was launched very close to the shore. The exercises were taking place 160 miles (~258 kilometers) from the crash site.

Some Urkranian military officials have stated that they didn't launch in the direction of the plane, that the time between the launch and the explosion was too short for the missile to have reached the plane, and that they would've self-destructed the missile had it gone astray. I'm still somewhat skeptical about this one.

ABC News report saying it was an S-300

CNN Report claiming it was an SA-5 / S-200

MSNBC Report stating the exercises were 160 miles (258 kilometers) from the airliner.