/*

 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")

 *

 * SPDX-License-Identifier: MPL-2.0

 *

 * This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, you can obtain one at https://mozilla.org/MPL/2.0/.

 *

 * See the COPYRIGHT file distributed with this work for additional

 * information regarding copyright ownership.

 */

/*! \file */

#include <inttypes.h>

#include <stdbool.h>

#include <isc/buffer.h>

#include <isc/hash.h>

#include <isc/log.h>

#include <isc/loop.h>

#include <isc/mem.h>

#include <isc/mutex.h>

#include <isc/sockaddr.h>

#include <isc/stdtime.h>

#include <isc/string.h>

#include <isc/thread.h>

#include <isc/time.h>

#include <isc/urcu.h>

#include <isc/util.h>

#include <dns/fixedname.h>

#include <dns/name.h>

#include <dns/rdatatype.h>

#include <dns/types.h>

#include <dns/unreachcache.h>

typedef struct dns_ucentry dns_ucentry_t;

typedef struct dns_uckey {

  const isc_sockaddr_t *remote;

  const isc_sockaddr_t *local;

} dns__uckey_t;

struct dns_unreachcache {

  unsigned int magic;

  isc_mem_t *mctx;

  uint16_t expire_min_s;

  uint16_t expire_max_s;

  uint16_t backoff_eligible_s;

  struct cds_lfht *ht;

  isc_mutex_t lru_lock;

  struct cds_list_head lru;

};

#define UNREACHCACHE_MAGIC    ISC_MAGIC('U', 'R', 'C', 'a')

#define VALID_UNREACHCACHE(m) ISC_MAGIC_VALID(m, UNREACHCACHE_MAGIC)

#define UNREACHCACHE_INIT_SIZE (1 << 4) /* Must be power of 2 */

#define UNREACHCACHE_MIN_SIZE  (1 << 5) /* Must be power of 2 */

struct dns_ucentry {

  isc_mem_t *mctx;

  isc_stdtime_t expire;

  unsigned int exp_backoff_n;

  uint16_t wait_time;

  bool confirmed;

  struct cds_lfht_node ht_node;

  struct rcu_head rcu_head;

  struct cds_list_head lru_head;

  isc_sockaddr_t remote;

  isc_sockaddr_t local;

};

static void

ucentry_destroy(struct rcu_head *rcu_head);

static bool

ucentry_alive(dns_unreachcache_t *uc, dns_ucentry_t *unreach, isc_stdtime_t now,

        bool alive_or_waiting);

dns_unreachcache_t *

dns_unreachcache_new(isc_mem_t *mctx, const uint16_t expire_min_s,

         const uint16_t expire_max_s,

         const uint16_t backoff_eligible_s) {

  REQUIRE(expire_min_s > 0);

  REQUIRE(expire_min_s <= expire_max_s);

  dns_unreachcache_t *uc = isc_mem_get(mctx, sizeof(*uc));

  *uc = (dns_unreachcache_t){

    .magic = UNREACHCACHE_MAGIC,

    .expire_min_s = expire_min_s,

    .expire_max_s = expire_max_s,

    .backoff_eligible_s = backoff_eligible_s,

  };

  uc->ht = cds_lfht_new(UNREACHCACHE_INIT_SIZE, UNREACHCACHE_MIN_SIZE, 0,

            CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);

  INSIST(uc->ht != NULL);

  isc_mutex_init(&uc->lru_lock);

  CDS_INIT_LIST_HEAD(&uc->lru);

  isc_mem_attach(mctx, &uc->mctx);

  return uc;

}

void

dns_unreachcache_destroy(dns_unreachcache_t **ucp) {

  REQUIRE(ucp != NULL && *ucp != NULL);

  REQUIRE(VALID_UNREACHCACHE(*ucp));

  dns_unreachcache_t *uc = *ucp;

  *ucp = NULL;

  uc->magic = 0;

  dns_ucentry_t *unreach = NULL;

  struct cds_lfht_iter iter;

  cds_lfht_for_each_entry(uc->ht, &iter, unreach, ht_node) {

    INSIST(!cds_lfht_del(uc->ht, &unreach->ht_node));

    ucentry_destroy(&unreach->rcu_head);

  }

  RUNTIME_CHECK(!cds_lfht_destroy(uc->ht, NULL));

  isc_mutex_destroy(&uc->lru_lock);

  isc_mem_putanddetach(&uc->mctx, uc, sizeof(dns_unreachcache_t));

}

static int

ucentry_match(struct cds_lfht_node *ht_node, const void *key0) {

  const dns__uckey_t *key = key0;

  dns_ucentry_t *unreach = caa_container_of(ht_node, dns_ucentry_t,

              ht_node);

  return isc_sockaddr_equal(&unreach->remote, key->remote) &&

         isc_sockaddr_equal(&unreach->local, key->local);

}

static uint32_t

ucentry_hash(const dns__uckey_t *key) {

  return isc_sockaddr_hash(key->remote, false) ^

         isc_sockaddr_hash(key->local, false);

}

static dns_ucentry_t *

ucentry_lookup(struct cds_lfht *ht, uint32_t hashval, dns__uckey_t *key) {

  struct cds_lfht_iter iter;

  cds_lfht_lookup(ht, hashval, ucentry_match, key, &iter);

  return cds_lfht_entry(cds_lfht_iter_get_node(&iter), dns_ucentry_t,

            ht_node);

}

static dns_ucentry_t *

ucentry_new(isc_loop_t *loop, const isc_sockaddr_t *remote,

      const isc_sockaddr_t *local, const isc_stdtime_t expire,

      const isc_stdtime_t wait_time) {

  isc_mem_t *mctx = isc_loop_getmctx(loop);

  dns_ucentry_t *unreach = isc_mem_get(mctx, sizeof(*unreach));

  *unreach = (dns_ucentry_t){

    .remote = *remote,

    .local = *local,

    .expire = expire,

    .wait_time = wait_time,

    .mctx = isc_mem_ref(mctx),

    .lru_head = CDS_LIST_HEAD_INIT(unreach->lru_head),

  };

  return unreach;

}

static void

ucentry_destroy(struct rcu_head *rcu_head) {

  dns_ucentry_t *unreach = caa_container_of(rcu_head, dns_ucentry_t,

              rcu_head);

  isc_mem_putanddetach(&unreach->mctx, unreach, sizeof(*unreach));

}

static void

ucentry_evict_locked(dns_unreachcache_t *uc, dns_ucentry_t *unreach) {

  if (!cds_lfht_del(uc->ht, &unreach->ht_node)) {

    cds_list_del_rcu(&unreach->lru_head);

    call_rcu(&unreach->rcu_head, ucentry_destroy);

  }

}

static void

ucentry_evict(dns_unreachcache_t *uc, dns_ucentry_t *unreach) {

  LOCK(&uc->lru_lock);

  ucentry_evict_locked(uc, unreach);

  UNLOCK(&uc->lru_lock);

}

static bool

ucentry_alive(dns_unreachcache_t *uc, dns_ucentry_t *unreach, isc_stdtime_t now,

        bool alive_or_waiting) {

  if (cds_lfht_is_node_deleted(&unreach->ht_node)) {

    return false;

  } else if (unreach->expire < now) {

    bool is_waiting = unreach->expire + unreach->wait_time >= now;

    if (is_waiting) {

      /*

       * Wait some minimum time before evicting an expired

       * entry so we can support exponential backoff for

       * nodes which enter again shortly after expiring.

       *

       * The return value depends on whether the caller is

       * interested to know if the node is in either active or

       * waiting state (i.e. not eviceted), or is interested

       * only if it's still alive (i.e. not expired).

       */

      return alive_or_waiting;

    }

    /* The entry is already expired, evict it before returning. */

    ucentry_evict(uc, unreach);

    return false;

  }

  return true;

}

static void

ucentry_purge(dns_unreachcache_t *uc, isc_stdtime_t now) {

  size_t count = 10;

  dns_ucentry_t *unreach;

  cds_list_for_each_entry_rcu(unreach, &uc->lru, lru_head) {

    if (ucentry_alive(uc, unreach, now, true)) {

      break;

    }

    if (--count == 0) {

      break;

    }

  }

}

static void

ucentry_backoff(const dns_unreachcache_t *uc, const isc_stdtime_t now,

    dns_ucentry_t *new, const dns_ucentry_t *old) {

  /*

   * Perform exponential backoff if this is an expired entry waiting to be

   * evicted. Otherwise it's a duplicate entry and no backoff is required

   * as we will just update the cache with a new entry that has the same

   * expiration time as the old one, but calculated freshly, based on the

   * current time.

   */

  if (old->expire < now) {

    new->exp_backoff_n = old->exp_backoff_n + 1;

  } else {

    new->exp_backoff_n = old->exp_backoff_n;

  }

  for (size_t i = 0; i < new->exp_backoff_n; i++) {

    new->expire += uc->expire_min_s;

    if (new->expire > now + uc->expire_max_s) {

      new->expire = now + uc->expire_max_s;

      break;

    }

  }

}

void

dns_unreachcache_add(dns_unreachcache_t *uc, const isc_sockaddr_t *remote,

         const isc_sockaddr_t *local) {

  REQUIRE(VALID_UNREACHCACHE(uc));

  REQUIRE(remote != NULL);

  REQUIRE(local != NULL);

  isc_loop_t *loop = isc_loop();

  isc_stdtime_t now = isc_stdtime_now();

  isc_stdtime_t expire = now + uc->expire_min_s;

  bool exp_backoff_activated = false;

  rcu_read_lock();

  dns__uckey_t key = {

    .remote = remote,

    .local = local,

  };

  uint32_t hashval = ucentry_hash(&key);

  dns_ucentry_t *unreach = ucentry_new(loop, remote, local, expire,

               uc->backoff_eligible_s);

  LOCK(&uc->lru_lock);

  struct cds_lfht_node *ht_node;

  do {

    ht_node = cds_lfht_add_unique(uc->ht, hashval, ucentry_match,

                &key, &unreach->ht_node);

    if (ht_node != &unreach->ht_node) {

      /* The entry already exists, get it. */

      dns_ucentry_t *found = caa_container_of(

        ht_node, dns_ucentry_t, ht_node);

      /*

       * Consider unreachability as confirmed only if

       * an entry is submitted at least twice, i.e. there

       * was an older entry (which is exactly this case).

       */

      unreach->confirmed = true;

      /*

       * Recalculate the expire time of the new entry based

       * on the old entry's exponential backoff value.

       */

      if (!exp_backoff_activated) {

        exp_backoff_activated = true;

        ucentry_backoff(uc, now, unreach, found);

      }

      /*

       * Evict the old entry, so we can try to insert the new

       * one again.

       */

      ucentry_evict_locked(uc, found);

    }

  } while (ht_node != &unreach->ht_node);

  cds_list_add_tail_rcu(&unreach->lru_head, &uc->lru);

  UNLOCK(&uc->lru_lock);

  ucentry_purge(uc, now);

  rcu_read_unlock();

}

isc_result_t

dns_unreachcache_find(dns_unreachcache_t *uc, const isc_sockaddr_t *remote,

          const isc_sockaddr_t *local) {

  REQUIRE(VALID_UNREACHCACHE(uc));

  REQUIRE(remote != NULL);

  REQUIRE(local != NULL);

  isc_result_t result = ISC_R_NOTFOUND;

  isc_stdtime_t now = isc_stdtime_now();

  rcu_read_lock();

  dns__uckey_t key = {

    .remote = remote,

    .local = local,

  };

  uint32_t hashval = ucentry_hash(&key);

  dns_ucentry_t *found = ucentry_lookup(uc->ht, hashval, &key);

  if (found != NULL && found->confirmed &&

      ucentry_alive(uc, found, now, false))

  {

    result = ISC_R_SUCCESS;

  }

  ucentry_purge(uc, now);

  rcu_read_unlock();

  return result;

}

void

dns_unreachcache_remove(dns_unreachcache_t *uc, const isc_sockaddr_t *remote,

      const isc_sockaddr_t *local) {

  REQUIRE(VALID_UNREACHCACHE(uc));

  REQUIRE(remote != NULL);

  REQUIRE(local != NULL);

  isc_stdtime_t now = isc_stdtime_now();

  rcu_read_lock();

  dns__uckey_t key = {

    .remote = remote,

    .local = local,

  };

  uint32_t hashval = ucentry_hash(&key);

  dns_ucentry_t *found = ucentry_lookup(uc->ht, hashval, &key);

  if (found != NULL) {

    ucentry_evict(uc, found);

  }

  ucentry_purge(uc, now);

  rcu_read_unlock();

}

void

dns_unreachcache_flush(dns_unreachcache_t *uc) {

  REQUIRE(VALID_UNREACHCACHE(uc));

  rcu_read_lock();

  /* Flush the hash table */

  dns_ucentry_t *unreach;

  struct cds_lfht_iter iter;

  cds_lfht_for_each_entry(uc->ht, &iter, unreach, ht_node) {

    ucentry_evict(uc, unreach);

  }

  rcu_read_unlock();

}