Is it normal for frost to accumulate on nails in my attic?
I'm late to the game, but this is obviously frost due to condensation. Leaks would appear as icicles. I've witnessed this phenomenon personally in very cold climates, and it's often just the result of seasonal changes that leave moist air in place from warmer days. 

You may have a ventilation deficiency, but there's no evidence of roof leaks here, at least what's visible in the photos. Of course, you could have a leak elsewhere that contributes water vapor.