commit 94b56eaa7597e4a091a5b51d2c9032ea046631e3 Author: David Goulet dgoulet@torproject.org Date: Tue Jan 26 11:42:52 2021 -0500
dos: New client connect rate detection
This is a new detection type which is that a relay can now control the rate of client connections from a single address.
The mechanism is pretty simple, if the rate/burst is reached, the address is marked for a period of time and any connection from that address is denied.
Closes #40253
Signed-off-by: David Goulet dgoulet@torproject.org --- changes/ticket40253 | 3 + doc/man/tor.1.txt | 24 ++++++++ src/core/or/dos.c | 122 ++++++++++++++++++++++++++++++++++++++++ src/core/or/dos.h | 30 +++++++++- src/core/or/dos_options.inc | 12 ++++ src/feature/stats/geoip_stats.c | 2 + 6 files changed, 192 insertions(+), 1 deletion(-)
diff --git a/changes/ticket40253 b/changes/ticket40253 new file mode 100644 index 0000000000..ca7c207bb3 --- /dev/null +++ b/changes/ticket40253 @@ -0,0 +1,3 @@ + o Major feature (relay, denial of service): + - Add a new DoS subsystem feature to control the rate of client connections + for relays. Closes ticket 40253. diff --git a/doc/man/tor.1.txt b/doc/man/tor.1.txt index 3538d94b8e..3756d26522 100644 --- a/doc/man/tor.1.txt +++ b/doc/man/tor.1.txt @@ -2936,6 +2936,30 @@ Denial of Service mitigation subsystem described above. consensus, the value is 100. (Default: 0)
+[[DoSConnectionConnectRate]] **DoSConnectionConnectRate** __NUM__:: + + The allowed rate of client connection from a single address per second. + Coupled with the burst (see below), if the limit is reached, the address + is marked and a defense is applied (DoSConnectionDefenseType) for a period + of time defined by DoSConnectionConnectDefenseTimePeriod. If not defined + or set to 0, it is controlled by a consensus parameter. + (Default: 0) + +[[DoSConnectionConnectBurst]] **DoSConnectionConnectBurst** __NUM__:: + + The allowed burst of client connection from a single address per second. + See the DoSConnectionConnectRate for more details on this detection. If + not defined or set to 0, it is controlled by a consensus parameter. + (Default: 0) + +[[DoSConnectionConnectDefenseTimePeriod]] **DoSConnectionConnectDefenseTimePeriod** __N__ **seconds**|**minutes**|**hours**:: + + The base time period in seconds that the client connection defense is + activated for. The actual value is selected randomly for each activation + from N+1 to 3/2 * N. If not defined or set to 0, it is controlled by a + consensus parameter. + (Default: 24 hours) + [[DoSRefuseSingleHopClientRendezvous]] **DoSRefuseSingleHopClientRendezvous** **0**|**1**|**auto**::
Refuse establishment of rendezvous points for single hop clients. In other diff --git a/src/core/or/dos.c b/src/core/or/dos.c index a761082be0..8b3dccc871 100644 --- a/src/core/or/dos.c +++ b/src/core/or/dos.c @@ -63,9 +63,14 @@ static unsigned int dos_conn_enabled = 0; * 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; +static uint32_t dos_conn_connect_rate = DOS_CONN_CONNECT_RATE_DEFAULT; +static uint32_t dos_conn_connect_burst = DOS_CONN_CONNECT_BURST_DEFAULT; +static int32_t dos_conn_connect_defense_time_period = + DOS_CONN_CONNECT_DEFENSE_TIME_PERIOD_DEFAULT;
/* Keep some stats for the heartbeat so we can report out. */ static uint64_t conn_num_addr_rejected; +static uint64_t conn_num_addr_connect_rejected;
/* * General interface of the denial of service mitigation subsystem. @@ -190,6 +195,47 @@ get_param_conn_defense_type(const networkstatus_t *ns) DOS_CONN_DEFENSE_NONE, DOS_CONN_DEFENSE_MAX); }
+/* Return the connection connect rate parameters either from the configuration + * file or, if not found, consensus parameter. */ +static uint32_t +get_param_conn_connect_rate(const networkstatus_t *ns) +{ + if (dos_get_options()->DoSConnectionConnectRate) { + return dos_get_options()->DoSConnectionConnectRate; + } + return networkstatus_get_param(ns, "DoSConnectionConnectRate", + DOS_CONN_CONNECT_RATE_DEFAULT, + 1, INT32_MAX); +} + +/* Return the connection connect burst parameters either from the + * configuration file or, if not found, consensus parameter. */ +static uint32_t +get_param_conn_connect_burst(const networkstatus_t *ns) +{ + if (dos_get_options()->DoSConnectionConnectBurst) { + return dos_get_options()->DoSConnectionConnectBurst; + } + return networkstatus_get_param(ns, "DoSConnectionConnectBurst", + DOS_CONN_CONNECT_BURST_DEFAULT, + 1, INT32_MAX); +} + +/* Return the connection connect defense time period from the configuration + * file or, if not found, the consensus parameter. */ +static int32_t +get_param_conn_connect_defense_time_period(const networkstatus_t *ns) +{ + /* Time in seconds. */ + if (dos_get_options()->DoSConnectionConnectDefenseTimePeriod) { + return dos_get_options()->DoSConnectionConnectDefenseTimePeriod; + } + return networkstatus_get_param(ns, "DoSConnectionConnectDefenseTimePeriod", + DOS_CONN_CONNECT_DEFENSE_TIME_PERIOD_DEFAULT, + DOS_CONN_CONNECT_DEFENSE_TIME_PERIOD_MIN, + INT32_MAX); +} + /* Set circuit creation parameters located in the consensus or their default * if none are present. Called at initialization or when the consensus * changes. */ @@ -208,6 +254,10 @@ set_dos_parameters(const networkstatus_t *ns) 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); + dos_conn_connect_rate = get_param_conn_connect_rate(ns); + dos_conn_connect_burst = get_param_conn_connect_burst(ns); + dos_conn_connect_defense_time_period = + get_param_conn_connect_defense_time_period(ns); }
/* Free everything for the circuit creation DoS mitigation subsystem. */ @@ -405,6 +455,20 @@ cc_channel_addr_is_marked(channel_t *chan)
/* Concurrent connection private API. */
+/* Mark client connection stats by setting a timestamp which tells us until + * when it is marked as positively detected. */ +static void +conn_mark_client(conn_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 and thus more difficult to game. */ + stats->marked_until_ts = + approx_time() + dos_conn_connect_defense_time_period + + crypto_rand_int_range(1, dos_conn_connect_defense_time_period / 2); +} + /* Free everything for the connection DoS mitigation subsystem. */ static void conn_free_all(void) @@ -424,6 +488,32 @@ conn_consensus_has_changed(const networkstatus_t *ns) } }
+/** Called when a new client connection has arrived. The following will update + * the client connection statistics. + * + * If the connect counter reaches its limit, it is marked. */ +static void +conn_update_on_connect(conn_client_stats_t *stats) +{ + tor_assert(stats); + + /* Refill connect connection count. */ + token_bucket_ctr_refill(&stats->connect_count, (uint32_t) approx_time()); + + /* Decrement counter for this new connection. */ + if (token_bucket_ctr_get(&stats->connect_count) > 0) { + token_bucket_ctr_dec(&stats->connect_count, 1); + } + + /* Assess connect counter. Mark it if counter is down to 0 and we haven't + * marked it before or it was reset. This is to avoid to re-mark it over and + * over again extending continously the blocked time. */ + if (token_bucket_ctr_get(&stats->connect_count) == 0 && + stats->marked_until_ts == 0) { + conn_mark_client(stats); + } +} + /* General private API */
/* Return true iff we have at least one DoS detection enabled. This is used to @@ -549,6 +639,16 @@ dos_conn_addr_get_defense_type(const tor_addr_t *addr) goto end; }
+ /* Is this address marked as making too many client connections? */ + if (entry->dos_stats.conn_stats.marked_until_ts >= approx_time()) { + conn_num_addr_connect_rejected++; + return dos_conn_defense_type; + } + /* Reset it to 0 here so that if the marked timestamp has expired that is + * we've gone beyond it, we have to reset it so the detection can mark it + * again in the future. */ + entry->dos_stats.conn_stats.marked_until_ts = 0; + /* Need to be above the maximum concurrent connection count to trigger a * defense. */ if (entry->dos_stats.concurrent_count > dos_conn_max_concurrent_count) { @@ -597,6 +697,22 @@ dos_geoip_entry_about_to_free(const clientmap_entry_t *geoip_ent) return; }
+/** A new geoip client entry has been allocated, initialize its DoS object. */ +void +dos_geoip_entry_init(clientmap_entry_t *geoip_ent) +{ + tor_assert(geoip_ent); + + /* Initialize the connection count counter with the rate and burst + * parameters taken either from configuration or consensus. + * + * We do this even if the DoS connection detection is not enabled because it + * can be enabled at runtime and these counters need to be valid. */ + token_bucket_ctr_init(&geoip_ent->dos_stats.conn_stats.connect_count, + dos_conn_connect_rate, dos_conn_connect_burst, + (uint32_t) approx_time()); +} + /* Note down that we've just refused a single hop client. This increments a * counter later used for the heartbeat. */ void @@ -650,6 +766,9 @@ dos_log_heartbeat(void) tor_asprintf(&conn_msg, " %" PRIu64 " connections closed.", conn_num_addr_rejected); + tor_asprintf(&conn_msg, + " %" PRIu64 " connect() connections closed.", + conn_num_addr_connect_rejected); }
if (dos_should_refuse_single_hop_client()) { @@ -711,6 +830,9 @@ dos_new_client_conn(or_connection_t *or_conn, const char *transport_name) goto end; }
+ /* Update stats from this new connect. */ + conn_update_on_connect(&entry->dos_stats.conn_stats); + entry->dos_stats.concurrent_count++; or_conn->tracked_for_dos_mitigation = 1; log_debug(LD_DOS, "Client address %s has now %u concurrent connections.", diff --git a/src/core/or/dos.h b/src/core/or/dos.h index 62c3857409..9dba63531b 100644 --- a/src/core/or/dos.h +++ b/src/core/or/dos.h @@ -11,7 +11,9 @@
#include "core/or/or.h"
-/* Structure that keeps stats of client connection per-IP. */ +#include "lib/evloop/token_bucket.h" + +/* Structure that keeps stats of circuit creation per client connection IP. */ typedef struct cc_client_stats_t { /* Number of allocated circuits remaining for this address. It is * decremented every time a new circuit is seen for this client address and @@ -30,6 +32,18 @@ typedef struct cc_client_stats_t { time_t marked_until_ts; } cc_client_stats_t;
+/* Structure that keeps stats of client connection per-IP. */ +typedef struct conn_client_stats_t { + /* Connect count from the specific address. We use a token bucket here to + * track the rate and burst of connections from the same IP address.*/ + token_bucket_ctr_t connect_count; + + /* The client address attempted too many connections, per the connect_count + * rules, and thus is marked so defense(s) can be applied. It is + * synchronized using the approx_time(). */ + time_t marked_until_ts; +} conn_client_stats_t; + /* This object is a top level object that contains everything related to the * per-IP client DoS mitigation. Because it is per-IP, it is used in the geoip * clientmap_entry_t object. */ @@ -38,6 +52,9 @@ typedef struct dos_client_stats_t { * likely way too big for the amount of allowed file descriptors. */ uint32_t concurrent_count;
+ /* Client connection statistics. */ + conn_client_stats_t conn_stats; + /* Circuit creation statistics. This is only used if the circuit creation * subsystem has been enabled (dos_cc_enabled). */ cc_client_stats_t cc_stats; @@ -53,6 +70,7 @@ void dos_free_all(void); void dos_consensus_has_changed(const networkstatus_t *ns); int dos_enabled(void); void dos_log_heartbeat(void); +void dos_geoip_entry_init(struct clientmap_entry_t *geoip_ent); void dos_geoip_entry_about_to_free(const struct clientmap_entry_t *geoip_ent);
void dos_new_client_conn(or_connection_t *or_conn, @@ -104,6 +122,16 @@ dos_cc_defense_type_t dos_cc_get_defense_type(channel_t *chan); #define DOS_CONN_MAX_CONCURRENT_COUNT_DEFAULT 100 /* DoSConnectionDefenseType maps to the dos_conn_defense_type_t enum. */ #define DOS_CONN_DEFENSE_TYPE_DEFAULT DOS_CONN_DEFENSE_CLOSE +/* DoSConnectionConnectRate default. Per second. */ +#define DOS_CONN_CONNECT_RATE_DEFAULT 20 +/* DoSConnectionConnectBurst default. Per second. */ +#define DOS_CONN_CONNECT_BURST_DEFAULT 40 +/* DoSConnectionConnectDefenseTimePeriod default. Set to 24 hours. */ +#define DOS_CONN_CONNECT_DEFENSE_TIME_PERIOD_DEFAULT (24 * 60 * 60) +/* DoSCircuitCreationDefenseTimePeriod minimum value. Because we add a random + * offset to the marked timestamp, we need the minimum value to be non zero. + * We consider that 10 seconds is an acceptable lower bound. */ +#define DOS_CONN_CONNECT_DEFENSE_TIME_PERIOD_MIN (10)
/* Type of defense that we can use for the concurrent connection DoS * mitigation. */ diff --git a/src/core/or/dos_options.inc b/src/core/or/dos_options.inc index 063a739939..9baa7a35b8 100644 --- a/src/core/or/dos_options.inc +++ b/src/core/or/dos_options.inc @@ -44,4 +44,16 @@ CONF_VAR(DoSConnectionDefenseType, INT, 0, "0") /** Autobool: Do we refuse single hop client rendezvous? */ CONF_VAR(DoSRefuseSingleHopClientRendezvous, AUTOBOOL, 0, "auto")
+/** Allowed burst of client connection allowed per address. */ +CONF_VAR(DoSConnectionConnectBurst, POSINT, 0, "0") + +/** Allowed rate of client connection allowed per address. */ +CONF_VAR(DoSConnectionConnectRate, POSINT, 0, "0") + +/** For how much time (in seconds) the connection connect rate defense is +* applicable for a malicious address. A random time delta is added to the +* defense time of an address which will be between 1 second and half of this +* value. */ +CONF_VAR(DoSConnectionConnectDefenseTimePeriod, INTERVAL, 0, "0") + END_CONF_STRUCT(dos_options_t) diff --git a/src/feature/stats/geoip_stats.c b/src/feature/stats/geoip_stats.c index a733653dde..aa9f91c136 100644 --- a/src/feature/stats/geoip_stats.c +++ b/src/feature/stats/geoip_stats.c @@ -196,6 +196,8 @@ clientmap_entry_new(geoip_client_action_t action, const tor_addr_t *addr, if (transport_name) { entry->transport_name = tor_strdup(transport_name); } + /* Initialize the DoS object. */ + dos_geoip_entry_init(entry);
/* Allocated and initialized, note down its size for the OOM handler. */ geoip_increment_client_history_cache_size(clientmap_entry_size(entry));