// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 */

#include "peer.h"
#include "device.h"
#include "queueing.h"
#include "timers.h"
#include "peerlookup.h"
#include "noise.h"

#include <linux/kref.h>
#include <linux/lockdep.h>
#include <linux/rcupdate.h>
#include <linux/list.h>

static struct kmem_cache *peer_cache;
static atomic64_t peer_counter = ATOMIC64_INIT(0);

struct wg_peer *wg_peer_create(struct wg_device *wg,
                               const u8 public_key[NOISE_PUBLIC_KEY_LEN],
                               const u8 preshared_key[NOISE_SYMMETRIC_KEY_LEN])
{
        struct wg_peer *peer;
        int ret = -ENOMEM;

        lockdep_assert_held(&wg->device_update_lock);

        if (wg->num_peers >= MAX_PEERS_PER_DEVICE)
                return ERR_PTR(ret);

        peer = kmem_cache_zalloc(peer_cache, GFP_KERNEL);
        if (unlikely(!peer))
                return ERR_PTR(ret);
        if (unlikely(dst_cache_init(&peer->endpoint_cache, GFP_KERNEL)))
                goto err;

        peer->device = wg;
        wg_noise_handshake_init(&peer->handshake, &wg->static_identity,
                                public_key, preshared_key, peer);
        peer->internal_id = atomic64_inc_return(&peer_counter);
        peer->serial_work_cpu = nr_cpumask_bits;
        wg_cookie_init(&peer->latest_cookie);
        wg_timers_init(peer);
        wg_cookie_checker_precompute_peer_keys(peer);
        spin_lock_init(&peer->keypairs.keypair_update_lock);
        INIT_WORK(&peer->transmit_handshake_work, wg_packet_handshake_send_worker);
        INIT_WORK(&peer->transmit_packet_work, wg_packet_tx_worker);
        wg_prev_queue_init(&peer->tx_queue);
        wg_prev_queue_init(&peer->rx_queue);
        rwlock_init(&peer->endpoint_lock);
        kref_init(&peer->refcount);
        skb_queue_head_init(&peer->staged_packet_queue);
        wg_noise_reset_last_sent_handshake(&peer->last_sent_handshake);
        set_bit(NAPI_STATE_NO_BUSY_POLL, &peer->napi.state);
        netif_napi_add(wg->dev, &peer->napi, wg_packet_rx_poll,
                       NAPI_POLL_WEIGHT);
        napi_enable(&peer->napi);
        list_add_tail(&peer->peer_list, &wg->peer_list);
        INIT_LIST_HEAD(&peer->allowedips_list);
        wg_pubkey_hashtable_add(wg->peer_hashtable, peer);
        ++wg->num_peers;
        pr_debug("%s: Peer %llu created\n", wg->dev->name, peer->internal_id);
        return peer;

err:
        kmem_cache_free(peer_cache, peer);
        return ERR_PTR(ret);
}

struct wg_peer *wg_peer_get_maybe_zero(struct wg_peer *peer)
{
        RCU_LOCKDEP_WARN(!rcu_read_lock_bh_held(),
                         "Taking peer reference without holding the RCU read lock");
        if (unlikely(!peer || !kref_get_unless_zero(&peer->refcount)))
                return NULL;
        return peer;
}

static void peer_make_dead(struct wg_peer *peer)
{
        /* Remove from configuration-time lookup structures. */
        list_del_init(&peer->peer_list);
        wg_allowedips_remove_by_peer(&peer->device->peer_allowedips, peer,
                                     &peer->device->device_update_lock);
        wg_pubkey_hashtable_remove(peer->device->peer_hashtable, peer);

        /* Mark as dead, so that we don't allow jumping contexts after. */
        WRITE_ONCE(peer->is_dead, true);

        /* The caller must now synchronize_net() for this to take effect. */
}

static void peer_remove_after_dead(struct wg_peer *peer)
{
        WARN_ON(!peer->is_dead);

        /* No more keypairs can be created for this peer, since is_dead protects
         * add_new_keypair, so we can now destroy existing ones.
         */
        wg_noise_keypairs_clear(&peer->keypairs);

        /* Destroy all ongoing timers that were in-flight at the beginning of
         * this function.
         */
        wg_timers_stop(peer);

        /* The transition between packet encryption/decryption queues isn't
         * guarded by is_dead, but each reference's life is strictly bounded by
         * two generations: once for parallel crypto and once for serial
         * ingestion, so we can simply flush twice, and be sure that we no
         * longer have references inside these queues.
         */

        /* a) For encrypt/decrypt. */
        flush_workqueue(peer->device->packet_crypt_wq);
        /* b.1) For send (but not receive, since that's napi). */
        flush_workqueue(peer->device->packet_crypt_wq);
        /* b.2.1) For receive (but not send, since that's wq). */
        napi_disable(&peer->napi);
        /* b.2.1) It's now safe to remove the napi struct, which must be done
         * here from process context.
         */
        netif_napi_del(&peer->napi);

        /* Ensure any workstructs we own (like transmit_handshake_work or
         * clear_peer_work) no longer are in use.
         */
        flush_workqueue(peer->device->handshake_send_wq);

        /* After the above flushes, a peer might still be active in a few
         * different contexts: 1) from xmit(), before hitting is_dead and
         * returning, 2) from wg_packet_consume_data(), before hitting is_dead
         * and returning, 3) from wg_receive_handshake_packet() after a point
         * where it has processed an incoming handshake packet, but where
         * all calls to pass it off to timers fails because of is_dead. We won't
         * have new references in (1) eventually, because we're removed from
         * allowedips; we won't have new references in (2) eventually, because
         * wg_index_hashtable_lookup will always return NULL, since we removed
         * all existing keypairs and no more can be created; we won't have new
         * references in (3) eventually, because we're removed from the pubkey
         * hash table, which allows for a maximum of one handshake response,
         * via the still-uncleared index hashtable entry, but not more than one,
         * and in wg_cookie_message_consume, the lookup eventually gets a peer
         * with a refcount of zero, so no new reference is taken.
         */

        --peer->device->num_peers;
        wg_peer_put(peer);
}

/* We have a separate "remove" function make sure that all active places where
 * a peer is currently operating will eventually come to an end and not pass
 * their reference onto another context.
 */
void wg_peer_remove(struct wg_peer *peer)
{
        if (unlikely(!peer))
                return;
        lockdep_assert_held(&peer->device->device_update_lock);

        peer_make_dead(peer);
        synchronize_net();
        peer_remove_after_dead(peer);
}

void wg_peer_remove_all(struct wg_device *wg)
{
        struct wg_peer *peer, *temp;
        LIST_HEAD(dead_peers);

        lockdep_assert_held(&wg->device_update_lock);

        /* Avoid having to traverse individually for each one. */
        wg_allowedips_free(&wg->peer_allowedips, &wg->device_update_lock);

        list_for_each_entry_safe(peer, temp, &wg->peer_list, peer_list) {
                peer_make_dead(peer);
                list_add_tail(&peer->peer_list, &dead_peers);
        }
        synchronize_net();
        list_for_each_entry_safe(peer, temp, &dead_peers, peer_list)
                peer_remove_after_dead(peer);
}

static void rcu_release(struct rcu_head *rcu)
{
        struct wg_peer *peer = container_of(rcu, struct wg_peer, rcu);

        dst_cache_destroy(&peer->endpoint_cache);
        WARN_ON(wg_prev_queue_peek(&peer->tx_queue) || wg_prev_queue_peek(&peer->rx_queue));

        /* The final zeroing takes care of clearing any remaining handshake key
         * material and other potentially sensitive information.
         */
        memzero_explicit(peer, sizeof(*peer));
        kmem_cache_free(peer_cache, peer);
}

static void kref_release(struct kref *refcount)
{
        struct wg_peer *peer = container_of(refcount, struct wg_peer, refcount);

        pr_debug("%s: Peer %llu (%pISpfsc) destroyed\n",
                 peer->device->dev->name, peer->internal_id,
                 &peer->endpoint.addr);

        /* Remove ourself from dynamic runtime lookup structures, now that the
         * last reference is gone.
         */
        wg_index_hashtable_remove(peer->device->index_hashtable,
                                  &peer->handshake.entry);

        /* Remove any lingering packets that didn't have a chance to be
         * transmitted.
         */
        wg_packet_purge_staged_packets(peer);

        /* Free the memory used. */
        call_rcu(&peer->rcu, rcu_release);
}

void wg_peer_put(struct wg_peer *peer)
{
        if (unlikely(!peer))
                return;
        kref_put(&peer->refcount, kref_release);
}

int __init wg_peer_init(void)
{
        peer_cache = KMEM_CACHE(wg_peer, 0);
        return peer_cache ? 0 : -ENOMEM;
}

void wg_peer_uninit(void)
{
        kmem_cache_destroy(peer_cache);
}