// SPDX-License-Identifier: GPL-2.0 /* * Copyright (C) 2015-2019 Jason A. Donenfeld . All Rights Reserved. */ #include "peerlookup.h" #include "peer.h" #include "noise.h" static struct hlist_head *pubkey_bucket(struct pubkey_hashtable *table, const u8 pubkey[NOISE_PUBLIC_KEY_LEN]) { /* siphash gives us a secure 64bit number based on a random key. Since * the bits are uniformly distributed, we can then mask off to get the * bits we need. */ const u64 hash = siphash(pubkey, NOISE_PUBLIC_KEY_LEN, &table->key); return &table->hashtable[hash & (HASH_SIZE(table->hashtable) - 1)]; } struct pubkey_hashtable *wg_pubkey_hashtable_alloc(void) { struct pubkey_hashtable *table = kvmalloc(sizeof(*table), GFP_KERNEL); if (!table) return NULL; get_random_bytes(&table->key, sizeof(table->key)); hash_init(table->hashtable); mutex_init(&table->lock); return table; } void wg_pubkey_hashtable_add(struct pubkey_hashtable *table, struct wg_peer *peer) { mutex_lock(&table->lock); hlist_add_head_rcu(&peer->pubkey_hash, pubkey_bucket(table, peer->handshake.remote_static)); mutex_unlock(&table->lock); } void wg_pubkey_hashtable_remove(struct pubkey_hashtable *table, struct wg_peer *peer) { mutex_lock(&table->lock); hlist_del_init_rcu(&peer->pubkey_hash); mutex_unlock(&table->lock); } /* Returns a strong reference to a peer */ struct wg_peer * wg_pubkey_hashtable_lookup(struct pubkey_hashtable *table, const u8 pubkey[NOISE_PUBLIC_KEY_LEN]) { struct wg_peer *iter_peer, *peer = NULL; rcu_read_lock_bh(); hlist_for_each_entry_rcu_bh(iter_peer, pubkey_bucket(table, pubkey), pubkey_hash) { if (!memcmp(pubkey, iter_peer->handshake.remote_static, NOISE_PUBLIC_KEY_LEN)) { peer = iter_peer; break; } } peer = wg_peer_get_maybe_zero(peer); rcu_read_unlock_bh(); return peer; } static struct hlist_head *index_bucket(struct index_hashtable *table, const __le32 index) { /* Since the indices are random and thus all bits are uniformly * distributed, we can find its bucket simply by masking. */ return &table->hashtable[(__force u32)index & (HASH_SIZE(table->hashtable) - 1)]; } struct index_hashtable *wg_index_hashtable_alloc(void) { struct index_hashtable *table = kvmalloc(sizeof(*table), GFP_KERNEL); if (!table) return NULL; hash_init(table->hashtable); spin_lock_init(&table->lock); return table; } /* At the moment, we limit ourselves to 2^20 total peers, which generally might * amount to 2^20*3 items in this hashtable. The algorithm below works by * picking a random number and testing it. We can see that these limits mean we * usually succeed pretty quickly: * * >>> def calculation(tries, size): * ... return (size / 2**32)**(tries - 1) * (1 - (size / 2**32)) * ... * >>> calculation(1, 2**20 * 3) * 0.999267578125 * >>> calculation(2, 2**20 * 3) * 0.0007318854331970215 * >>> calculation(3, 2**20 * 3) * 5.360489012673497e-07 * >>> calculation(4, 2**20 * 3) * 3.9261394135792216e-10 * * At the moment, we don't do any masking, so this algorithm isn't exactly * constant time in either the random guessing or in the hash list lookup. We * could require a minimum of 3 tries, which would successfully mask the * guessing. this would not, however, help with the growing hash lengths, which * is another thing to consider moving forward. */ __le32 wg_index_hashtable_insert(struct index_hashtable *table, struct index_hashtable_entry *entry) { struct index_hashtable_entry *existing_entry; spin_lock_bh(&table->lock); hlist_del_init_rcu(&entry->index_hash); spin_unlock_bh(&table->lock); rcu_read_lock_bh(); search_unused_slot: /* First we try to find an unused slot, randomly, while unlocked. */ entry->index = (__force __le32)get_random_u32(); hlist_for_each_entry_rcu_bh(existing_entry, index_bucket(table, entry->index), index_hash) { if (existing_entry->index == entry->index) /* If it's already in use, we continue searching. */ goto search_unused_slot; } /* Once we've found an unused slot, we lock it, and then double-check * that nobody else stole it from us. */ spin_lock_bh(&table->lock); hlist_for_each_entry_rcu_bh(existing_entry, index_bucket(table, entry->index), index_hash) { if (existing_entry->index == entry->index) { spin_unlock_bh(&table->lock); /* If it was stolen, we start over. */ goto search_unused_slot; } } /* Otherwise, we know we have it exclusively (since we're locked), * so we insert. */ hlist_add_head_rcu(&entry->index_hash, index_bucket(table, entry->index)); spin_unlock_bh(&table->lock); rcu_read_unlock_bh(); return entry->index; } bool wg_index_hashtable_replace(struct index_hashtable *table, struct index_hashtable_entry *old, struct index_hashtable_entry *new) { if (unlikely(hlist_unhashed(&old->index_hash))) return false; spin_lock_bh(&table->lock); new->index = old->index; hlist_replace_rcu(&old->index_hash, &new->index_hash); /* Calling init here NULLs out index_hash, and in fact after this * function returns, it's theoretically possible for this to get * reinserted elsewhere. That means the RCU lookup below might either * terminate early or jump between buckets, in which case the packet * simply gets dropped, which isn't terrible. */ INIT_HLIST_NODE(&old->index_hash); spin_unlock_bh(&table->lock); return true; } void wg_index_hashtable_remove(struct index_hashtable *table, struct index_hashtable_entry *entry) { spin_lock_bh(&table->lock); hlist_del_init_rcu(&entry->index_hash); spin_unlock_bh(&table->lock); } /* Returns a strong reference to a entry->peer */ struct index_hashtable_entry * wg_index_hashtable_lookup(struct index_hashtable *table, const enum index_hashtable_type type_mask, const __le32 index, struct wg_peer **peer) { struct index_hashtable_entry *iter_entry, *entry = NULL; rcu_read_lock_bh(); hlist_for_each_entry_rcu_bh(iter_entry, index_bucket(table, index), index_hash) { if (iter_entry->index == index) { if (likely(iter_entry->type & type_mask)) entry = iter_entry; break; } } if (likely(entry)) { entry->peer = wg_peer_get_maybe_zero(entry->peer); if (likely(entry->peer)) *peer = entry->peer; else entry = NULL; } rcu_read_unlock_bh(); return entry; }