Move literally everything out of src/or

This commit won't build yet -- it just puts everything in a slightly
more logical place.

The reasoning here is that "src/core" will hold the stuff that every (or
nearly every) tor instance will need in order to do onion routing.
Other features (including some necessary ones) will live in
"src/feature".  The "src/app" directory will hold the stuff needed
to have Tor be an application you can actually run.

This commit DOES NOT refactor the former contents of src/or into a
logical set of acyclic libraries, or change any code at all.  That
will have to come in the future.

We will continue to move things around and split them in the future,
but I hope this lays a reasonable groundwork for doing so.

1 files changed, 801 insertions, 0 deletions

diff --git a/src/core/or/dos.c b/src/core/or/dos.c
new file mode 100644
index 0000000000..d86ede02cb
--- /dev/null
+++ b/src/core/or/dos.c
@@ -0,0 +1,801 @@
+/* Copyright (c) 2018-2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/*
+ * \file dos.c
+ * \brief Implement Denial of Service mitigation subsystem.
+ */
+
+#define DOS_PRIVATE
+
+#include "or/or.h"
+#include "or/channel.h"
+#include "or/config.h"
+#include "or/connection.h"
+#include "or/connection_or.h"
+#include "lib/crypt_ops/crypto_rand.h"
+#include "or/geoip.h"
+#include "or/main.h"
+#include "or/networkstatus.h"
+#include "or/nodelist.h"
+#include "or/relay.h"
+#include "or/router.h"
+
+#include "or/dos.h"
+
+#include "or/or_connection_st.h"
+
+/*
+ * Circuit creation denial of service mitigation.
+ *
+ * Namespace used for this mitigation framework is "dos_cc_" where "cc" is for
+ * Circuit Creation.
+ */
+
+/* Is the circuit creation DoS mitigation enabled? */
+static unsigned int dos_cc_enabled = 0;
+
+/* Consensus parameters. They can be changed when a new consensus arrives.
+ * They are initialized with the hardcoded default values. */
+static uint32_t dos_cc_min_concurrent_conn;
+static uint32_t dos_cc_circuit_rate;
+static uint32_t dos_cc_circuit_burst;
+static dos_cc_defense_type_t dos_cc_defense_type;
+static int32_t dos_cc_defense_time_period;
+
+/* Keep some stats for the heartbeat so we can report out. */
+static uint64_t cc_num_rejected_cells;
+static uint32_t cc_num_marked_addrs;
+
+/*
+ * Concurrent connection denial of service mitigation.
+ *
+ * Namespace used for this mitigation framework is "dos_conn_".
+ */
+
+/* Is the connection DoS mitigation enabled? */
+static unsigned int dos_conn_enabled = 0;
+
+/* Consensus parameters. They can be changed when a new consensus arrives.
+ * They are initialized with the hardcoded default values. */
+static uint32_t dos_conn_max_concurrent_count;
+static dos_conn_defense_type_t dos_conn_defense_type;
+
+/* Keep some stats for the heartbeat so we can report out. */
+static uint64_t conn_num_addr_rejected;
+
+/*
+ * General interface of the denial of service mitigation subsystem.
+ */
+
+/* Keep stats for the heartbeat. */
+static uint64_t num_single_hop_client_refused;
+
+/* Return true iff the circuit creation mitigation is enabled. We look at the
+ * consensus for this else a default value is returned. */
+MOCK_IMPL(STATIC unsigned int,
+get_param_cc_enabled, (const networkstatus_t *ns))
+{
+  if (get_options()->DoSCircuitCreationEnabled != -1) {
+    return get_options()->DoSCircuitCreationEnabled;
+  }
+
+  return !!networkstatus_get_param(ns, "DoSCircuitCreationEnabled",
+                                   DOS_CC_ENABLED_DEFAULT, 0, 1);
+}
+
+/* Return the parameter for the minimum concurrent connection at which we'll
+ * start counting circuit for a specific client address. */
+STATIC uint32_t
+get_param_cc_min_concurrent_connection(const networkstatus_t *ns)
+{
+  if (get_options()->DoSCircuitCreationMinConnections) {
+    return get_options()->DoSCircuitCreationMinConnections;
+  }
+  return networkstatus_get_param(ns, "DoSCircuitCreationMinConnections",
+                                 DOS_CC_MIN_CONCURRENT_CONN_DEFAULT,
+                                 1, INT32_MAX);
+}
+
+/* Return the parameter for the time rate that is how many circuits over this
+ * time span. */
+static uint32_t
+get_param_cc_circuit_rate(const networkstatus_t *ns)
+{
+  /* This is in seconds. */
+  if (get_options()->DoSCircuitCreationRate) {
+    return get_options()->DoSCircuitCreationRate;
+  }
+  return networkstatus_get_param(ns, "DoSCircuitCreationRate",
+                                 DOS_CC_CIRCUIT_RATE_DEFAULT,
+                                 1, INT32_MAX);
+}
+
+/* Return the parameter for the maximum circuit count for the circuit time
+ * rate. */
+STATIC uint32_t
+get_param_cc_circuit_burst(const networkstatus_t *ns)
+{
+  if (get_options()->DoSCircuitCreationBurst) {
+    return get_options()->DoSCircuitCreationBurst;
+  }
+  return networkstatus_get_param(ns, "DoSCircuitCreationBurst",
+                                 DOS_CC_CIRCUIT_BURST_DEFAULT,
+                                 1, INT32_MAX);
+}
+
+/* Return the consensus parameter of the circuit creation defense type. */
+static uint32_t
+get_param_cc_defense_type(const networkstatus_t *ns)
+{
+  if (get_options()->DoSCircuitCreationDefenseType) {
+    return get_options()->DoSCircuitCreationDefenseType;
+  }
+  return networkstatus_get_param(ns, "DoSCircuitCreationDefenseType",
+                                 DOS_CC_DEFENSE_TYPE_DEFAULT,
+                                 DOS_CC_DEFENSE_NONE, DOS_CC_DEFENSE_MAX);
+}
+
+/* Return the consensus parameter of the defense time period which is how much
+ * time should we defend against a malicious client address. */
+static int32_t
+get_param_cc_defense_time_period(const networkstatus_t *ns)
+{
+  /* Time in seconds. */
+  if (get_options()->DoSCircuitCreationDefenseTimePeriod) {
+    return get_options()->DoSCircuitCreationDefenseTimePeriod;
+  }
+  return networkstatus_get_param(ns, "DoSCircuitCreationDefenseTimePeriod",
+                                 DOS_CC_DEFENSE_TIME_PERIOD_DEFAULT,
+                                 0, INT32_MAX);
+}
+
+/* Return true iff connection mitigation is enabled. We look at the consensus
+ * for this else a default value is returned. */
+MOCK_IMPL(STATIC unsigned int,
+get_param_conn_enabled, (const networkstatus_t *ns))
+{
+  if (get_options()->DoSConnectionEnabled != -1) {
+    return get_options()->DoSConnectionEnabled;
+  }
+  return !!networkstatus_get_param(ns, "DoSConnectionEnabled",
+                                   DOS_CONN_ENABLED_DEFAULT, 0, 1);
+}
+
+/* Return the consensus parameter for the maximum concurrent connection
+ * allowed. */
+STATIC uint32_t
+get_param_conn_max_concurrent_count(const networkstatus_t *ns)
+{
+  if (get_options()->DoSConnectionMaxConcurrentCount) {
+    return get_options()->DoSConnectionMaxConcurrentCount;
+  }
+  return networkstatus_get_param(ns, "DoSConnectionMaxConcurrentCount",
+                                 DOS_CONN_MAX_CONCURRENT_COUNT_DEFAULT,
+                                 1, INT32_MAX);
+}
+
+/* Return the consensus parameter of the connection defense type. */
+static uint32_t
+get_param_conn_defense_type(const networkstatus_t *ns)
+{
+  if (get_options()->DoSConnectionDefenseType) {
+    return get_options()->DoSConnectionDefenseType;
+  }
+  return networkstatus_get_param(ns, "DoSConnectionDefenseType",
+                                 DOS_CONN_DEFENSE_TYPE_DEFAULT,
+                                 DOS_CONN_DEFENSE_NONE, DOS_CONN_DEFENSE_MAX);
+}
+
+/* Set circuit creation parameters located in the consensus or their default
+ * if none are present. Called at initialization or when the consensus
+ * changes. */
+static void
+set_dos_parameters(const networkstatus_t *ns)
+{
+  /* Get the default consensus param values. */
+  dos_cc_enabled = get_param_cc_enabled(ns);
+  dos_cc_min_concurrent_conn = get_param_cc_min_concurrent_connection(ns);
+  dos_cc_circuit_rate = get_param_cc_circuit_rate(ns);
+  dos_cc_circuit_burst = get_param_cc_circuit_burst(ns);
+  dos_cc_defense_time_period = get_param_cc_defense_time_period(ns);
+  dos_cc_defense_type = get_param_cc_defense_type(ns);
+
+  /* Connection detection. */
+  dos_conn_enabled = get_param_conn_enabled(ns);
+  dos_conn_max_concurrent_count = get_param_conn_max_concurrent_count(ns);
+  dos_conn_defense_type = get_param_conn_defense_type(ns);
+}
+
+/* Free everything for the circuit creation DoS mitigation subsystem. */
+static void
+cc_free_all(void)
+{
+  /* If everything is freed, the circuit creation subsystem is not enabled. */
+  dos_cc_enabled = 0;
+}
+
+/* Called when the consensus has changed. Do appropriate actions for the
+ * circuit creation subsystem. */
+static void
+cc_consensus_has_changed(const networkstatus_t *ns)
+{
+  /* Looking at the consensus, is the circuit creation subsystem enabled? If
+   * not and it was enabled before, clean it up. */
+  if (dos_cc_enabled && !get_param_cc_enabled(ns)) {
+    cc_free_all();
+  }
+}
+
+/** Return the number of circuits we allow per second under the current
+ *  configuration. */
+STATIC uint64_t
+get_circuit_rate_per_second(void)
+{
+  return dos_cc_circuit_rate;
+}
+
+/* Given the circuit creation client statistics object, refill the circuit
+ * bucket if needed. This also works if the bucket was never filled in the
+ * first place. The addr is only used for logging purposes. */
+STATIC void
+cc_stats_refill_bucket(cc_client_stats_t *stats, const tor_addr_t *addr)
+{
+  uint32_t new_circuit_bucket_count;
+  uint64_t num_token, elapsed_time_last_refill = 0, circuit_rate = 0;
+  time_t now;
+  int64_t last_refill_ts;
+
+  tor_assert(stats);
+  tor_assert(addr);
+
+  now = approx_time();
+  last_refill_ts = (int64_t)stats->last_circ_bucket_refill_ts;
+
+  /* If less than a second has elapsed, don't add any tokens.
+   * Note: If a relay's clock is ever 0, any new clients won't get a refill
+   * until the next second. But a relay that thinks it is 1970 will never
+   * validate the public consensus. */
+  if ((int64_t)now == last_refill_ts) {
+    goto done;
+  }
+
+  /* At this point, we know we might need to add token to the bucket. We'll
+   * first get the circuit rate that is how many circuit are we allowed to do
+   * per second. */
+  circuit_rate = get_circuit_rate_per_second();
+
+  /* We've never filled the bucket so fill it with the maximum being the burst
+   * and we are done.
+   * Note: If a relay's clock is ever 0, all clients that were last refilled
+   * in that zero second will get a full refill here. */
+  if (last_refill_ts == 0) {
+    num_token = dos_cc_circuit_burst;
+    goto end;
+  }
+
+  /* Our clock jumped backward so fill it up to the maximum. Not filling it
+   * could trigger a detection for a valid client. Also, if the clock jumped
+   * negative but we didn't notice until the elapsed time became positive
+   * again, then we potentially spent many seconds not refilling the bucket
+   * when we should have been refilling it. But the fact that we didn't notice
+   * until now means that no circuit creation requests came in during that
+   * time, so the client doesn't end up punished that much from this hopefully
+   * rare situation.*/
+  if ((int64_t)now < last_refill_ts) {
+    /* Use the maximum allowed value of token. */
+    num_token = dos_cc_circuit_burst;
+    goto end;
+  }
+
+  /* How many seconds have elapsed between now and the last refill?
+   * This subtraction can't underflow, because now >= last_refill_ts.
+   * And it can't overflow, because INT64_MAX - (-INT64_MIN) == UINT64_MAX. */
+  elapsed_time_last_refill = (uint64_t)now - last_refill_ts;
+
+  /* If the elapsed time is very large, it means our clock jumped forward.
+   * If the multiplication would overflow, use the maximum allowed value. */
+  if (elapsed_time_last_refill > UINT32_MAX) {
+    num_token = dos_cc_circuit_burst;
+    goto end;
+  }
+
+  /* Compute how many circuits we are allowed in that time frame which we'll
+   * add to the bucket. This can't overflow, because both multiplicands
+   * are less than or equal to UINT32_MAX, and num_token is uint64_t. */
+  num_token = elapsed_time_last_refill * circuit_rate;
+
+ end:
+  /* If the sum would overflow, use the maximum allowed value. */
+  if (num_token > UINT32_MAX - stats->circuit_bucket) {
+    new_circuit_bucket_count = dos_cc_circuit_burst;
+  } else {
+    /* We cap the bucket to the burst value else this could overflow uint32_t
+     * over time. */
+    new_circuit_bucket_count = MIN(stats->circuit_bucket + (uint32_t)num_token,
+                                   dos_cc_circuit_burst);
+  }
+
+  /* This function is not allowed to make the bucket count larger than the
+   * burst value */
+  tor_assert_nonfatal(new_circuit_bucket_count <= dos_cc_circuit_burst);
+  /* This function is not allowed to make the bucket count smaller, unless it
+   * is decreasing it to a newly configured, lower burst value. We allow the
+   * bucket to stay the same size, in case the circuit rate is zero. */
+  tor_assert_nonfatal(new_circuit_bucket_count >= stats->circuit_bucket ||
+                      new_circuit_bucket_count == dos_cc_circuit_burst);
+
+  log_debug(LD_DOS, "DoS address %s has its circuit bucket value: %" PRIu32
+                    ". Filling it to %" PRIu32 ". Circuit rate is %" PRIu64
+                    ". Elapsed time is %" PRIi64,
+            fmt_addr(addr), stats->circuit_bucket, new_circuit_bucket_count,
+            circuit_rate, (int64_t)elapsed_time_last_refill);
+
+  stats->circuit_bucket = new_circuit_bucket_count;
+  stats->last_circ_bucket_refill_ts = now;
+
+ done:
+  return;
+}
+
+/* Return true iff the circuit bucket is down to 0 and the number of
+ * concurrent connections is greater or equal the minimum threshold set the
+ * consensus parameter. */
+static int
+cc_has_exhausted_circuits(const dos_client_stats_t *stats)
+{
+  tor_assert(stats);
+  return stats->cc_stats.circuit_bucket == 0 &&
+         stats->concurrent_count >= dos_cc_min_concurrent_conn;
+}
+
+/* Mark client address by setting a timestamp in the stats object which tells
+ * us until when it is marked as positively detected. */
+static void
+cc_mark_client(cc_client_stats_t *stats)
+{
+  tor_assert(stats);
+  /* We add a random offset of a maximum of half the defense time so it is
+   * less predictable. */
+  stats->marked_until_ts =
+    approx_time() + dos_cc_defense_time_period +
+    crypto_rand_int_range(1, dos_cc_defense_time_period / 2);
+}
+
+/* Return true iff the given channel address is marked as malicious. This is
+ * called a lot and part of the fast path of handling cells. It has to remain
+ * as fast as we can. */
+static int
+cc_channel_addr_is_marked(channel_t *chan)
+{
+  time_t now;
+  tor_addr_t addr;
+  clientmap_entry_t *entry;
+  cc_client_stats_t *stats = NULL;
+
+  if (chan == NULL) {
+    goto end;
+  }
+  /* Must be a client connection else we ignore. */
+  if (!channel_is_client(chan)) {
+    goto end;
+  }
+  /* Without an IP address, nothing can work. */
+  if (!channel_get_addr_if_possible(chan, &addr)) {
+    goto end;
+  }
+
+  /* We are only interested in client connection from the geoip cache. */
+  entry = geoip_lookup_client(&addr, NULL, GEOIP_CLIENT_CONNECT);
+  if (entry == NULL) {
+    /* We can have a connection creating circuits but not tracked by the geoip
+     * cache. Once this DoS subsystem is enabled, we can end up here with no
+     * entry for the channel. */
+    goto end;
+  }
+  now = approx_time();
+  stats = &entry->dos_stats.cc_stats;
+
+ end:
+  return stats && stats->marked_until_ts >= now;
+}
+
+/* Concurrent connection private API. */
+
+/* Free everything for the connection DoS mitigation subsystem. */
+static void
+conn_free_all(void)
+{
+  dos_conn_enabled = 0;
+}
+
+/* Called when the consensus has changed. Do appropriate actions for the
+ * connection mitigation subsystem. */
+static void
+conn_consensus_has_changed(const networkstatus_t *ns)
+{
+  /* Looking at the consensus, is the connection mitigation subsystem enabled?
+   * If not and it was enabled before, clean it up. */
+  if (dos_conn_enabled && !get_param_conn_enabled(ns)) {
+    conn_free_all();
+  }
+}
+
+/* General private API */
+
+/* Return true iff we have at least one DoS detection enabled. This is used to
+ * decide if we need to allocate any kind of high level DoS object. */
+static inline int
+dos_is_enabled(void)
+{
+  return (dos_cc_enabled || dos_conn_enabled);
+}
+
+/* Circuit creation public API. */
+
+/* Called when a CREATE cell is received from the given channel. */
+void
+dos_cc_new_create_cell(channel_t *chan)
+{
+  tor_addr_t addr;
+  clientmap_entry_t *entry;
+
+  tor_assert(chan);
+
+  /* Skip everything if not enabled. */
+  if (!dos_cc_enabled) {
+    goto end;
+  }
+
+  /* Must be a client connection else we ignore. */
+  if (!channel_is_client(chan)) {
+    goto end;
+  }
+  /* Without an IP address, nothing can work. */
+  if (!channel_get_addr_if_possible(chan, &addr)) {
+    goto end;
+  }
+
+  /* We are only interested in client connection from the geoip cache. */
+  entry = geoip_lookup_client(&addr, NULL, GEOIP_CLIENT_CONNECT);
+  if (entry == NULL) {
+    /* We can have a connection creating circuits but not tracked by the geoip
+     * cache. Once this DoS subsystem is enabled, we can end up here with no
+     * entry for the channel. */
+    goto end;
+  }
+
+  /* General comment. Even though the client can already be marked as
+   * malicious, we continue to track statistics. If it keeps going above
+   * threshold while marked, the defense period time will grow longer. There
+   * is really no point at unmarking a client that keeps DoSing us. */
+
+  /* First of all, we'll try to refill the circuit bucket opportunistically
+   * before we assess. */
+  cc_stats_refill_bucket(&entry->dos_stats.cc_stats, &addr);
+
+  /* Take a token out of the circuit bucket if we are above 0 so we don't
+   * underflow the bucket. */
+  if (entry->dos_stats.cc_stats.circuit_bucket > 0) {
+    entry->dos_stats.cc_stats.circuit_bucket--;
+  }
+
+  /* This is the detection. Assess at every CREATE cell if the client should
+   * get marked as malicious. This should be kept as fast as possible. */
+  if (cc_has_exhausted_circuits(&entry->dos_stats)) {
+    /* If this is the first time we mark this entry, log it a info level.
+     * Under heavy DDoS, logging each time we mark would results in lots and
+     * lots of logs. */
+    if (entry->dos_stats.cc_stats.marked_until_ts == 0) {
+      log_debug(LD_DOS, "Detected circuit creation DoS by address: %s",
+                fmt_addr(&addr));
+      cc_num_marked_addrs++;
+    }
+    cc_mark_client(&entry->dos_stats.cc_stats);
+  }
+
+ end:
+  return;
+}
+
+/* Return the defense type that should be used for this circuit.
+ *
+ * This is part of the fast path and called a lot. */
+dos_cc_defense_type_t
+dos_cc_get_defense_type(channel_t *chan)
+{
+  tor_assert(chan);
+
+  /* Skip everything if not enabled. */
+  if (!dos_cc_enabled) {
+    goto end;
+  }
+
+  /* On an OR circuit, we'll check if the previous channel is a marked client
+   * connection detected by our DoS circuit creation mitigation subsystem. */
+  if (cc_channel_addr_is_marked(chan)) {
+    /* We've just assess that this circuit should trigger a defense for the
+     * cell it just seen. Note it down. */
+    cc_num_rejected_cells++;
+    return dos_cc_defense_type;
+  }
+
+ end:
+  return DOS_CC_DEFENSE_NONE;
+}
+
+/* Concurrent connection detection public API. */
+
+/* Return true iff the given address is permitted to open another connection.
+ * A defense value is returned for the caller to take appropriate actions. */
+dos_conn_defense_type_t
+dos_conn_addr_get_defense_type(const tor_addr_t *addr)
+{
+  clientmap_entry_t *entry;
+
+  tor_assert(addr);
+
+  /* Skip everything if not enabled. */
+  if (!dos_conn_enabled) {
+    goto end;
+  }
+
+  /* We are only interested in client connection from the geoip cache. */
+  entry = geoip_lookup_client(addr, NULL, GEOIP_CLIENT_CONNECT);
+  if (entry == NULL) {
+    goto end;
+  }
+
+  /* Need to be above the maximum concurrent connection count to trigger a
+   * defense. */
+  if (entry->dos_stats.concurrent_count > dos_conn_max_concurrent_count) {
+    conn_num_addr_rejected++;
+    return dos_conn_defense_type;
+  }
+
+ end:
+  return DOS_CONN_DEFENSE_NONE;
+}
+
+/* General API */
+
+/* Take any appropriate actions for the given geoip entry that is about to get
+ * freed. This is called for every entry that is being freed.
+ *
+ * This function will clear out the connection tracked flag if the concurrent
+ * count of the entry is above 0 so if those connections end up being seen by
+ * this subsystem, we won't try to decrement the counter for a new geoip entry
+ * that might have been added after this call for the same address. */
+void
+dos_geoip_entry_about_to_free(const clientmap_entry_t *geoip_ent)
+{
+  tor_assert(geoip_ent);
+
+  /* The count is down to 0 meaning no connections right now, we can safely
+   * clear the geoip entry from the cache. */
+  if (geoip_ent->dos_stats.concurrent_count == 0) {
+    goto end;
+  }
+
+  /* For each connection matching the geoip entry address, we'll clear the
+   * tracked flag because the entry is about to get removed from the geoip
+   * cache. We do not try to decrement if the flag is not set. */
+  SMARTLIST_FOREACH_BEGIN(get_connection_array(), connection_t *, conn) {
+    if (conn->type == CONN_TYPE_OR) {
+      or_connection_t *or_conn = TO_OR_CONN(conn);
+      if (!tor_addr_compare(&geoip_ent->addr, &or_conn->real_addr,
+                            CMP_EXACT)) {
+        or_conn->tracked_for_dos_mitigation = 0;
+      }
+    }
+  } SMARTLIST_FOREACH_END(conn);
+
+ end:
+  return;
+}
+
+/* Note down that we've just refused a single hop client. This increments a
+ * counter later used for the heartbeat. */
+void
+dos_note_refuse_single_hop_client(void)
+{
+  num_single_hop_client_refused++;
+}
+
+/* Return true iff single hop client connection (ESTABLISH_RENDEZVOUS) should
+ * be refused. */
+int
+dos_should_refuse_single_hop_client(void)
+{
+  /* If we aren't a public relay, this shouldn't apply to anything. */
+  if (!public_server_mode(get_options())) {
+    return 0;
+  }
+
+  if (get_options()->DoSRefuseSingleHopClientRendezvous != -1) {
+    return get_options()->DoSRefuseSingleHopClientRendezvous;
+  }
+
+  return (int) networkstatus_get_param(NULL,
+                                       "DoSRefuseSingleHopClientRendezvous",
+                                       0 /* default */, 0, 1);
+}
+
+/* Log a heartbeat message with some statistics. */
+void
+dos_log_heartbeat(void)
+{
+  char *conn_msg = NULL;
+  char *cc_msg = NULL;
+  char *single_hop_client_msg = NULL;
+  char *circ_stats_msg = NULL;
+
+  /* Stats number coming from relay.c append_cell_to_circuit_queue(). */
+  tor_asprintf(&circ_stats_msg,
+               " %" PRIu64 " circuits killed with too many cells.",
+               stats_n_circ_max_cell_reached);
+
+  if (dos_cc_enabled) {
+    tor_asprintf(&cc_msg,
+                 " %" PRIu64 " circuits rejected,"
+                 " %" PRIu32 " marked addresses.",
+                 cc_num_rejected_cells, cc_num_marked_addrs);
+  }
+
+  if (dos_conn_enabled) {
+    tor_asprintf(&conn_msg,
+                 " %" PRIu64 " connections closed.",
+                 conn_num_addr_rejected);
+  }
+
+  if (dos_should_refuse_single_hop_client()) {
+    tor_asprintf(&single_hop_client_msg,
+                 " %" PRIu64 " single hop clients refused.",
+                 num_single_hop_client_refused);
+  }
+
+  log_notice(LD_HEARTBEAT,
+             "DoS mitigation since startup:%s%s%s%s",
+             circ_stats_msg,
+             (cc_msg != NULL) ? cc_msg : " [cc not enabled]",
+             (conn_msg != NULL) ? conn_msg : " [conn not enabled]",
+             (single_hop_client_msg != NULL) ? single_hop_client_msg : "");
+
+  tor_free(conn_msg);
+  tor_free(cc_msg);
+  tor_free(single_hop_client_msg);
+  tor_free(circ_stats_msg);
+  return;
+}
+
+/* Called when a new client connection has been established on the given
+ * address. */
+void
+dos_new_client_conn(or_connection_t *or_conn)
+{
+  clientmap_entry_t *entry;
+
+  tor_assert(or_conn);
+
+  /* Past that point, we know we have at least one DoS detection subsystem
+   * enabled so we'll start allocating stuff. */
+  if (!dos_is_enabled()) {
+    goto end;
+  }
+
+  /* We ignore any known address meaning an address of a known relay. The
+   * reason to do so is because network reentry is possible where a client
+   * connection comes from an Exit node. Even when we'll fix reentry, this is
+   * a robust defense to keep in place. */
+  if (nodelist_probably_contains_address(&or_conn->real_addr)) {
+    goto end;
+  }
+
+  /* We are only interested in client connection from the geoip cache. */
+  entry = geoip_lookup_client(&or_conn->real_addr, NULL,
+                              GEOIP_CLIENT_CONNECT);
+  if (BUG(entry == NULL)) {
+    /* Should never happen because we note down the address in the geoip
+     * cache before this is called. */
+    goto end;
+  }
+
+  entry->dos_stats.concurrent_count++;
+  or_conn->tracked_for_dos_mitigation = 1;
+  log_debug(LD_DOS, "Client address %s has now %u concurrent connections.",
+            fmt_addr(&or_conn->real_addr),
+            entry->dos_stats.concurrent_count);
+
+ end:
+  return;
+}
+
+/* Called when a client connection for the given IP address has been closed. */
+void
+dos_close_client_conn(const or_connection_t *or_conn)
+{
+  clientmap_entry_t *entry;
+
+  tor_assert(or_conn);
+
+  /* We have to decrement the count on tracked connection only even if the
+   * subsystem has been disabled at runtime because it might be re-enabled
+   * after and we need to keep a synchronized counter at all time. */
+  if (!or_conn->tracked_for_dos_mitigation) {
+    goto end;
+  }
+
+  /* We are only interested in client connection from the geoip cache. */
+  entry = geoip_lookup_client(&or_conn->real_addr, NULL,
+                              GEOIP_CLIENT_CONNECT);
+  if (entry == NULL) {
+    /* This can happen because we can close a connection before the channel
+     * got to be noted down in the geoip cache. */
+    goto end;
+  }
+
+  /* Extra super duper safety. Going below 0 means an underflow which could
+   * lead to most likely a false positive. In theory, this should never happen
+   * but lets be extra safe. */
+  if (BUG(entry->dos_stats.concurrent_count == 0)) {
+    goto end;
+  }
+
+  entry->dos_stats.concurrent_count--;
+  log_debug(LD_DOS, "Client address %s has lost a connection. Concurrent "
+                    "connections are now at %u",
+            fmt_addr(&or_conn->real_addr),
+            entry->dos_stats.concurrent_count);
+
+ end:
+  return;
+}
+
+/* Called when the consensus has changed. We might have new consensus
+ * parameters to look at. */
+void
+dos_consensus_has_changed(const networkstatus_t *ns)
+{
+  /* There are two ways to configure this subsystem, one at startup through
+   * dos_init() which is called when the options are parsed. And this one
+   * through the consensus. We don't want to enable any DoS mitigation if we
+   * aren't a public relay. */
+  if (!public_server_mode(get_options())) {
+    return;
+  }
+
+  cc_consensus_has_changed(ns);
+  conn_consensus_has_changed(ns);
+
+  /* We were already enabled or we just became enabled but either way, set the
+   * consensus parameters for all subsystems. */
+  set_dos_parameters(ns);
+}
+
+/* Return true iff the DoS mitigation subsystem is enabled. */
+int
+dos_enabled(void)
+{
+  return dos_is_enabled();
+}
+
+/* Free everything from the Denial of Service subsystem. */
+void
+dos_free_all(void)
+{
+  /* Free the circuit creation mitigation subsystem. It is safe to do this
+   * even if it wasn't initialized. */
+  cc_free_all();
+
+  /* Free the connection mitigation subsystem. It is safe to do this even if
+   * it wasn't initialized. */
+  conn_free_all();
+}
+
+/* Initialize the Denial of Service subsystem. */
+void
+dos_init(void)
+{
+  /* To initialize, we only need to get the parameters. */
+  set_dos_parameters(NULL);
+}