222 lines
6.3 KiB
C
222 lines
6.3 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
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*/
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#include "peerlookup.h"
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#include "peer.h"
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#include "noise.h"
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static struct hlist_head *pubkey_bucket(struct pubkey_hashtable *table,
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const u8 pubkey[NOISE_PUBLIC_KEY_LEN])
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{
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/* siphash gives us a secure 64bit number based on a random key. Since
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* the bits are uniformly distributed, we can then mask off to get the
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* bits we need.
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*/
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const u64 hash = siphash(pubkey, NOISE_PUBLIC_KEY_LEN, &table->key);
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return &table->hashtable[hash & (HASH_SIZE(table->hashtable) - 1)];
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}
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struct pubkey_hashtable *wg_pubkey_hashtable_alloc(void)
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{
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struct pubkey_hashtable *table = kvmalloc(sizeof(*table), GFP_KERNEL);
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if (!table)
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return NULL;
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get_random_bytes(&table->key, sizeof(table->key));
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hash_init(table->hashtable);
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mutex_init(&table->lock);
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return table;
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}
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void wg_pubkey_hashtable_add(struct pubkey_hashtable *table,
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struct wg_peer *peer)
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{
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mutex_lock(&table->lock);
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hlist_add_head_rcu(&peer->pubkey_hash,
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pubkey_bucket(table, peer->handshake.remote_static));
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mutex_unlock(&table->lock);
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}
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void wg_pubkey_hashtable_remove(struct pubkey_hashtable *table,
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struct wg_peer *peer)
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{
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mutex_lock(&table->lock);
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hlist_del_init_rcu(&peer->pubkey_hash);
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mutex_unlock(&table->lock);
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}
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/* Returns a strong reference to a peer */
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struct wg_peer *
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wg_pubkey_hashtable_lookup(struct pubkey_hashtable *table,
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const u8 pubkey[NOISE_PUBLIC_KEY_LEN])
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{
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struct wg_peer *iter_peer, *peer = NULL;
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rcu_read_lock_bh();
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hlist_for_each_entry_rcu_bh(iter_peer, pubkey_bucket(table, pubkey),
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pubkey_hash) {
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if (!memcmp(pubkey, iter_peer->handshake.remote_static,
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NOISE_PUBLIC_KEY_LEN)) {
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peer = iter_peer;
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break;
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}
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}
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peer = wg_peer_get_maybe_zero(peer);
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rcu_read_unlock_bh();
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return peer;
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}
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static struct hlist_head *index_bucket(struct index_hashtable *table,
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const __le32 index)
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{
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/* Since the indices are random and thus all bits are uniformly
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* distributed, we can find its bucket simply by masking.
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*/
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return &table->hashtable[(__force u32)index &
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(HASH_SIZE(table->hashtable) - 1)];
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}
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struct index_hashtable *wg_index_hashtable_alloc(void)
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{
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struct index_hashtable *table = kvmalloc(sizeof(*table), GFP_KERNEL);
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if (!table)
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return NULL;
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hash_init(table->hashtable);
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spin_lock_init(&table->lock);
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return table;
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}
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/* At the moment, we limit ourselves to 2^20 total peers, which generally might
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* amount to 2^20*3 items in this hashtable. The algorithm below works by
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* picking a random number and testing it. We can see that these limits mean we
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* usually succeed pretty quickly:
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*
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* >>> def calculation(tries, size):
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* ... return (size / 2**32)**(tries - 1) * (1 - (size / 2**32))
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* ...
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* >>> calculation(1, 2**20 * 3)
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* 0.999267578125
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* >>> calculation(2, 2**20 * 3)
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* 0.0007318854331970215
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* >>> calculation(3, 2**20 * 3)
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* 5.360489012673497e-07
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* >>> calculation(4, 2**20 * 3)
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* 3.9261394135792216e-10
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*
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* At the moment, we don't do any masking, so this algorithm isn't exactly
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* constant time in either the random guessing or in the hash list lookup. We
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* could require a minimum of 3 tries, which would successfully mask the
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* guessing. this would not, however, help with the growing hash lengths, which
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* is another thing to consider moving forward.
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*/
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__le32 wg_index_hashtable_insert(struct index_hashtable *table,
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struct index_hashtable_entry *entry)
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{
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struct index_hashtable_entry *existing_entry;
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spin_lock_bh(&table->lock);
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hlist_del_init_rcu(&entry->index_hash);
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spin_unlock_bh(&table->lock);
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rcu_read_lock_bh();
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search_unused_slot:
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/* First we try to find an unused slot, randomly, while unlocked. */
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entry->index = (__force __le32)get_random_u32();
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hlist_for_each_entry_rcu_bh(existing_entry,
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index_bucket(table, entry->index),
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index_hash) {
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if (existing_entry->index == entry->index)
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/* If it's already in use, we continue searching. */
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goto search_unused_slot;
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}
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/* Once we've found an unused slot, we lock it, and then double-check
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* that nobody else stole it from us.
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*/
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spin_lock_bh(&table->lock);
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hlist_for_each_entry_rcu_bh(existing_entry,
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index_bucket(table, entry->index),
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index_hash) {
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if (existing_entry->index == entry->index) {
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spin_unlock_bh(&table->lock);
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/* If it was stolen, we start over. */
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goto search_unused_slot;
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}
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}
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/* Otherwise, we know we have it exclusively (since we're locked),
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* so we insert.
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*/
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hlist_add_head_rcu(&entry->index_hash,
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index_bucket(table, entry->index));
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spin_unlock_bh(&table->lock);
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rcu_read_unlock_bh();
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return entry->index;
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}
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bool wg_index_hashtable_replace(struct index_hashtable *table,
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struct index_hashtable_entry *old,
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struct index_hashtable_entry *new)
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{
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if (unlikely(hlist_unhashed(&old->index_hash)))
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return false;
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spin_lock_bh(&table->lock);
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new->index = old->index;
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hlist_replace_rcu(&old->index_hash, &new->index_hash);
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/* Calling init here NULLs out index_hash, and in fact after this
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* function returns, it's theoretically possible for this to get
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* reinserted elsewhere. That means the RCU lookup below might either
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* terminate early or jump between buckets, in which case the packet
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* simply gets dropped, which isn't terrible.
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*/
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INIT_HLIST_NODE(&old->index_hash);
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spin_unlock_bh(&table->lock);
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return true;
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}
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void wg_index_hashtable_remove(struct index_hashtable *table,
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struct index_hashtable_entry *entry)
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{
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spin_lock_bh(&table->lock);
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hlist_del_init_rcu(&entry->index_hash);
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spin_unlock_bh(&table->lock);
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}
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/* Returns a strong reference to a entry->peer */
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struct index_hashtable_entry *
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wg_index_hashtable_lookup(struct index_hashtable *table,
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const enum index_hashtable_type type_mask,
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const __le32 index, struct wg_peer **peer)
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{
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struct index_hashtable_entry *iter_entry, *entry = NULL;
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rcu_read_lock_bh();
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hlist_for_each_entry_rcu_bh(iter_entry, index_bucket(table, index),
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index_hash) {
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if (iter_entry->index == index) {
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if (likely(iter_entry->type & type_mask))
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entry = iter_entry;
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break;
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}
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}
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if (likely(entry)) {
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entry->peer = wg_peer_get_maybe_zero(entry->peer);
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if (likely(entry->peer))
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*peer = entry->peer;
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else
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entry = NULL;
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}
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rcu_read_unlock_bh();
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return entry;
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}
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