I'm running Curse of Strahd, and have reworked Strahd as an actual wizard and not just a vampire with convenient wizard-powers. One of the spells he has is charm person.
If my PCs cast protection from evil and good on themselves, will this protect against charm person as cast by an undead? The specific wording of PfEaG is
Until the spell ends, one willing creature you touch is protected against certain types of creatures: aberrations, celestials, elementals, fey, fiends, and undead.
The protection grants several benefits. Creatures of those types have disadvantage on attack rolls against the target. The target also can't be charmed, frightened, or possessed by them. If the target is already charmed, frightened, or possessed by such a creature, the target has advantage on any new saving throw against the relevant effect.
My thinking is that this is intended to protect against things like innate charm abilities (like a succubus). However, will it also protect against charm person IF the caster of said spell is undead?