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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*/
#include "hashtables.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)];
}
void wg_pubkey_hashtable_init(struct pubkey_hashtable *table)
{
get_random_bytes(&table->key, sizeof(table->key));
hash_init(table->hashtable);
mutex_init(&table->lock);
}
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)];
}
void wg_index_hashtable_init(struct index_hashtable *table)
{
hash_init(table->hashtable);
spin_lock_init(&table->lock);
}
/* 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;
}
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