[kazinator]

What if Alice leave her home directory permissions open? Mallory can then move a large file there and have it assigned to Alice's quota.

I suppose it could work, but Mallory would then risk Alice blowing that file away (perhaps innocently, not even realizing it was Mallory's file).

[IshKebab]

If I leave my front door unlocked and you put a large cow in my house, it's taking up space in my house.