The rhashtable's bucket_table struct stores a random seed (the hash_rnd field) that is folded into the calculation of the hash. Without knowing what the seed is

The rhashtable's bucket_table struct stores a random seed (the hash_rnd field) that is folded into the calculation of the hash. Without knowing what the seed is going to be, an attacker has no way to precompute keys with colliding hashes.