1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
4 */
5
6#include "peerlookup.h"
7#include "peer.h"
8#include "noise.h"
9
10static struct hlist_head *pubkey_bucket(struct pubkey_hashtable *table,
11 const u8 pubkey[NOISE_PUBLIC_KEY_LEN])
12{
13 /* siphash gives us a secure 64bit number based on a random key. Since
14 * the bits are uniformly distributed, we can then mask off to get the
15 * bits we need.
16 */
17 const u64 hash = siphash(data: pubkey, len: NOISE_PUBLIC_KEY_LEN, key: &table->key);
18
19 return &table->hashtable[hash & (HASH_SIZE(table->hashtable) - 1)];
20}
21
22struct pubkey_hashtable *wg_pubkey_hashtable_alloc(void)
23{
24 struct pubkey_hashtable *table = kvmalloc(size: sizeof(*table), GFP_KERNEL);
25
26 if (!table)
27 return NULL;
28
29 get_random_bytes(buf: &table->key, len: sizeof(table->key));
30 hash_init(table->hashtable);
31 mutex_init(&table->lock);
32 return table;
33}
34
35void wg_pubkey_hashtable_add(struct pubkey_hashtable *table,
36 struct wg_peer *peer)
37{
38 mutex_lock(&table->lock);
39 hlist_add_head_rcu(n: &peer->pubkey_hash,
40 h: pubkey_bucket(table, pubkey: peer->handshake.remote_static));
41 mutex_unlock(lock: &table->lock);
42}
43
44void wg_pubkey_hashtable_remove(struct pubkey_hashtable *table,
45 struct wg_peer *peer)
46{
47 mutex_lock(&table->lock);
48 hlist_del_init_rcu(n: &peer->pubkey_hash);
49 mutex_unlock(lock: &table->lock);
50}
51
52/* Returns a strong reference to a peer */
53struct wg_peer *
54wg_pubkey_hashtable_lookup(struct pubkey_hashtable *table,
55 const u8 pubkey[NOISE_PUBLIC_KEY_LEN])
56{
57 struct wg_peer *iter_peer, *peer = NULL;
58
59 rcu_read_lock_bh();
60 hlist_for_each_entry_rcu_bh(iter_peer, pubkey_bucket(table, pubkey),
61 pubkey_hash) {
62 if (!memcmp(p: pubkey, q: iter_peer->handshake.remote_static,
63 size: NOISE_PUBLIC_KEY_LEN)) {
64 peer = iter_peer;
65 break;
66 }
67 }
68 peer = wg_peer_get_maybe_zero(peer);
69 rcu_read_unlock_bh();
70 return peer;
71}
72
73static struct hlist_head *index_bucket(struct index_hashtable *table,
74 const __le32 index)
75{
76 /* Since the indices are random and thus all bits are uniformly
77 * distributed, we can find its bucket simply by masking.
78 */
79 return &table->hashtable[(__force u32)index &
80 (HASH_SIZE(table->hashtable) - 1)];
81}
82
83struct index_hashtable *wg_index_hashtable_alloc(void)
84{
85 struct index_hashtable *table = kvmalloc(size: sizeof(*table), GFP_KERNEL);
86
87 if (!table)
88 return NULL;
89
90 hash_init(table->hashtable);
91 spin_lock_init(&table->lock);
92 return table;
93}
94
95/* At the moment, we limit ourselves to 2^20 total peers, which generally might
96 * amount to 2^20*3 items in this hashtable. The algorithm below works by
97 * picking a random number and testing it. We can see that these limits mean we
98 * usually succeed pretty quickly:
99 *
100 * >>> def calculation(tries, size):
101 * ... return (size / 2**32)**(tries - 1) * (1 - (size / 2**32))
102 * ...
103 * >>> calculation(1, 2**20 * 3)
104 * 0.999267578125
105 * >>> calculation(2, 2**20 * 3)
106 * 0.0007318854331970215
107 * >>> calculation(3, 2**20 * 3)
108 * 5.360489012673497e-07
109 * >>> calculation(4, 2**20 * 3)
110 * 3.9261394135792216e-10
111 *
112 * At the moment, we don't do any masking, so this algorithm isn't exactly
113 * constant time in either the random guessing or in the hash list lookup. We
114 * could require a minimum of 3 tries, which would successfully mask the
115 * guessing. this would not, however, help with the growing hash lengths, which
116 * is another thing to consider moving forward.
117 */
118
119__le32 wg_index_hashtable_insert(struct index_hashtable *table,
120 struct index_hashtable_entry *entry)
121{
122 struct index_hashtable_entry *existing_entry;
123
124 spin_lock_bh(lock: &table->lock);
125 hlist_del_init_rcu(n: &entry->index_hash);
126 spin_unlock_bh(lock: &table->lock);
127
128 rcu_read_lock_bh();
129
130search_unused_slot:
131 /* First we try to find an unused slot, randomly, while unlocked. */
132 entry->index = (__force __le32)get_random_u32();
133 hlist_for_each_entry_rcu_bh(existing_entry,
134 index_bucket(table, entry->index),
135 index_hash) {
136 if (existing_entry->index == entry->index)
137 /* If it's already in use, we continue searching. */
138 goto search_unused_slot;
139 }
140
141 /* Once we've found an unused slot, we lock it, and then double-check
142 * that nobody else stole it from us.
143 */
144 spin_lock_bh(lock: &table->lock);
145 hlist_for_each_entry_rcu_bh(existing_entry,
146 index_bucket(table, entry->index),
147 index_hash) {
148 if (existing_entry->index == entry->index) {
149 spin_unlock_bh(lock: &table->lock);
150 /* If it was stolen, we start over. */
151 goto search_unused_slot;
152 }
153 }
154 /* Otherwise, we know we have it exclusively (since we're locked),
155 * so we insert.
156 */
157 hlist_add_head_rcu(n: &entry->index_hash,
158 h: index_bucket(table, index: entry->index));
159 spin_unlock_bh(lock: &table->lock);
160
161 rcu_read_unlock_bh();
162
163 return entry->index;
164}
165
166bool wg_index_hashtable_replace(struct index_hashtable *table,
167 struct index_hashtable_entry *old,
168 struct index_hashtable_entry *new)
169{
170 bool ret;
171
172 spin_lock_bh(lock: &table->lock);
173 ret = !hlist_unhashed(h: &old->index_hash);
174 if (unlikely(!ret))
175 goto out;
176
177 new->index = old->index;
178 hlist_replace_rcu(old: &old->index_hash, new: &new->index_hash);
179
180 /* Calling init here NULLs out index_hash, and in fact after this
181 * function returns, it's theoretically possible for this to get
182 * reinserted elsewhere. That means the RCU lookup below might either
183 * terminate early or jump between buckets, in which case the packet
184 * simply gets dropped, which isn't terrible.
185 */
186 INIT_HLIST_NODE(h: &old->index_hash);
187out:
188 spin_unlock_bh(lock: &table->lock);
189 return ret;
190}
191
192void wg_index_hashtable_remove(struct index_hashtable *table,
193 struct index_hashtable_entry *entry)
194{
195 spin_lock_bh(lock: &table->lock);
196 hlist_del_init_rcu(n: &entry->index_hash);
197 spin_unlock_bh(lock: &table->lock);
198}
199
200/* Returns a strong reference to a entry->peer */
201struct index_hashtable_entry *
202wg_index_hashtable_lookup(struct index_hashtable *table,
203 const enum index_hashtable_type type_mask,
204 const __le32 index, struct wg_peer **peer)
205{
206 struct index_hashtable_entry *iter_entry, *entry = NULL;
207
208 rcu_read_lock_bh();
209 hlist_for_each_entry_rcu_bh(iter_entry, index_bucket(table, index),
210 index_hash) {
211 if (iter_entry->index == index) {
212 if (likely(iter_entry->type & type_mask))
213 entry = iter_entry;
214 break;
215 }
216 }
217 if (likely(entry)) {
218 entry->peer = wg_peer_get_maybe_zero(peer: entry->peer);
219 if (likely(entry->peer))
220 *peer = entry->peer;
221 else
222 entry = NULL;
223 }
224 rcu_read_unlock_bh();
225 return entry;
226}
227

source code of linux/drivers/net/wireguard/peerlookup.c