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/* Copyright (C) 2015-2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. */

#include "hashtables.h"
#include "peer.h"
#include "noise.h"

static inline 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. */
	return &table->hashtable[siphash(pubkey, NOISE_PUBLIC_KEY_LEN, &table->key) & (HASH_SIZE(table->hashtable) - 1)];
}

void pubkey_hashtable_init(struct pubkey_hashtable *table)
{
	get_random_bytes(&table->key, sizeof(table->key));
	hash_init(table->hashtable);
	mutex_init(&table->lock);
}

void pubkey_hashtable_add(struct pubkey_hashtable *table, struct wireguard_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 pubkey_hashtable_remove(struct pubkey_hashtable *table, struct wireguard_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 wireguard_peer *pubkey_hashtable_lookup(struct pubkey_hashtable *table, const u8 pubkey[NOISE_PUBLIC_KEY_LEN])
{
	struct wireguard_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 = peer_get(peer);
	rcu_read_unlock_bh();
	return peer;
}

static inline 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 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. TODO: this would not, however, help
 * with the growing hash lengths.
 */

__le32 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)
			goto search_unused_slot; /* If it's already in use, we continue searching. */
	}

	/* 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);
			goto search_unused_slot; /* If it was stolen, we start over. */
		}
	}
	/* 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 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);
	INIT_HLIST_NODE(&old->index_hash);
	spin_unlock_bh(&table->lock);
	return true;
}

void 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 *index_hashtable_lookup(struct index_hashtable *table, const enum index_hashtable_type type_mask, const __le32 index)
{
	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 = peer_get(entry->peer);
		if (unlikely(!entry->peer))
			entry = NULL;
	}
	rcu_read_unlock_bh();
	return entry;
}