commit 20a3f611057cb81c489ccf9d40438bc5d930d766 Author: Mike Perry mikeperry-git@torproject.org Date: Fri Dec 22 05:43:44 2017 +0000
Implement layer 2 and layer 3 guard pinning via torrc.
Block circuit canibalization when HSRendezvousMiddleNodes is active. Also make it apply to all HS circuits, not just rends. --- changes/bug13837 | 4 + doc/tor.1.txt | 94 ++++++++++++++++++ src/or/circuitbuild.c | 257 +++++++++++++++++++++++++++++++++++++++++++++++--- src/or/circuituse.c | 66 ++++++++++++- src/or/circuituse.h | 3 + src/or/config.c | 8 ++ src/or/or.h | 8 ++ 7 files changed, 426 insertions(+), 14 deletions(-)
diff --git a/changes/bug13837 b/changes/bug13837 new file mode 100644 index 000000000..5791dcee5 --- /dev/null +++ b/changes/bug13837 @@ -0,0 +1,4 @@ + o Major features (Onion Services): + - Provide torrc options to pin the second and third hops of onion service + circuits to a list of nodes. The option HSLayer2Guards pins the second hop, + and the option HSLayer3Guards pins the third hop. Closes ticket 13837. diff --git a/doc/tor.1.txt b/doc/tor.1.txt index 115f09bc3..8e27a25de 100644 --- a/doc/tor.1.txt +++ b/doc/tor.1.txt @@ -1531,6 +1531,100 @@ The following options are useful only for clients (that is, if If no nodes in Tor2webRendezvousPoints are currently available for use, Tor will choose a random node when building HS circuits.
+[[_HSLayer2Nodes]] **_HSLayer2Nodes** __node__,__node__,__...__:: + A list of identity fingerprints, nicknames, country codes, and + address patterns of nodes that are allowed to be used as the + second hop in all client or service-side Onion Service circuits. + This option mitigates attacks where the adversary runs middle nodes + and induces your client or service to create many circuits, in order + to discover your primary guard node. + (Default: Any node in the network may be used in the second hop.) + + + (Example: + _HSLayer2Nodes ABCD1234CDEF5678ABCD1234CDEF5678ABCD1234, {cc}, 255.254.0.0/8) + + + + When this is set, the resulting hidden service paths will + look like: + + + C - G - L2 - M - Rend + + C - G - L2 - M - HSDir + + C - G - L2 - M - Intro + + S - G - L2 - M - Rend + + S - G - L2 - M - HSDir + + S - G - L2 - M - Intro + + + + where C is this client, S is the service, G is the Guard node, + L2 is a node from this option, and M is a random middle node. + Rend, HSDir, and Intro point selection is not affected by this + option. + + + This option may be combined with _HSLayer3Nodes to create + paths of the form: + + + C - G - L2 - L3 - Rend + + C - G - L2 - L3 - M - HSDir + + C - G - L2 - L3 - M - Intro + + S - G - L2 - L3 - M - Rend + + S - G - L2 - L3 - HSDir + + S - G - L2 - L3 - Intro + + + + ExcludeNodes have higher priority than _HSLayer2Nodes, + which means that nodes specified in ExcludeNodes will not be + picked. + + + This option is meant to be managed by a Tor controller such as + https://github.com/mikeperry-tor/vanguards that selects and + updates this set of nodes for you. Hence it does not do load + balancing if fewer than 20 nodes are selected, and if no nodes in + _HSLayer2Nodes are currently available for use, Tor will not work. + Please use extreme care if you are setting this option manually. + +[[_HSLayer3Nodes]] **_HSLayer3Nodes** __node__,__node__,__...__:: + A list of identity fingerprints, nicknames, country codes, and + address patterns of nodes that are allowed to be used as the + third hop in all client and service-side Onion Service circuits. + This option mitigates attacks where the adversary runs middle nodes + and induces your client or service to create many circuits, in order + to discover your primary or Layer2 guard nodes. + (Default: Any node in the network may be used in the third hop.) + + + (Example: + _HSLayer3Nodes ABCD1234CDEF5678ABCD1234CDEF5678ABCD1234, {cc}, 255.254.0.0/8) + + + + When this is set by itself, the resulting hidden service paths + will look like: + + C - G - M - L3 - Rend + + C - G - M - L3 - M - HSDir + + C - G - M - L3 - M - Intro + + S - G - M - L3 - M - Rend + + S - G - M - L3 - HSDir + + S - G - M - L3 - Intro + + where C is this client, S is the service, G is the Guard node, + L2 is a node from this option, and M is a random middle node. + Rend, HSDir, and Intro point selection is not affected by this + option. + + + While it is possible to use this option by itself, it should be + combined with _HSLayer2Nodes to create paths of the form: + + + C - G - L2 - L3 - Rend + + C - G - L2 - L3 - M - HSDir + + C - G - L2 - L3 - M - Intro + + S - G - L2 - L3 - M - Rend + + S - G - L2 - L3 - HSDir + + S - G - L2 - L3 - Intro + + + + ExcludeNodes have higher priority than _HSLayer3Nodes, + which means that nodes specified in ExcludeNodes will not be + picked. + + + This option is meant to be managed by a Tor controller such as + https://github.com/mikeperry-tor/vanguards that selects and + updates this set of nodes for you. Hence it does not do load + balancing if fewer than 20 nodes are selected, and if no nodes in + _HSLayer3Nodes are currently available for use, Tor will not work. + Please use extreme care if you are setting this option manually. + [[UseMicrodescriptors]] **UseMicrodescriptors** **0**|**1**|**auto**:: Microdescriptors are a smaller version of the information that Tor needs in order to build its circuits. Using microdescriptors makes Tor clients diff --git a/src/or/circuitbuild.c b/src/or/circuitbuild.c index a350f6c14..707654adf 100644 --- a/src/or/circuitbuild.c +++ b/src/or/circuitbuild.c @@ -1659,6 +1659,37 @@ route_len_for_purpose(uint8_t purpose, extend_info_t *exit_ei) int routelen = DEFAULT_ROUTE_LEN; int known_purpose = 0;
+ if (circuit_should_use_vanguards(purpose)) { + /* Clients want an extra hop for rends to avoid linkability. + * Services want it for intro points to avoid publishing their + * layer3 guards. + * Ex: C - G - L2 - L3 - R + * S - G - L2 - L3 - I + */ + if (purpose == CIRCUIT_PURPOSE_C_ESTABLISH_REND || + purpose == CIRCUIT_PURPOSE_S_ESTABLISH_INTRO) + return routelen+1; + + /* If we only have Layer2 vanguards, then we do not need + * the extra hop for linkabilty reasons (see below). + * This means all hops can be of the form: + * S/C - G - L2 - M - R/HSDir/I + */ + if (get_options()->HSLayer2Nodes && !get_options()->HSLayer3Nodes) + return routelen+1; + + /* For connections to hsdirs, clients want two extra hops + * when using layer3 guards, to avoid linkability. + * Same goes for intro points. Note that the route len + * includes the intro point or hsdir, hence the +2. + * Ex: C - G - L2 - L3 - M - I + * S - G - L2 - L3 - M - R + */ + if (purpose == CIRCUIT_PURPOSE_S_CONNECT_REND || + purpose == CIRCUIT_PURPOSE_C_INTRODUCING) + return routelen+2; + } + if (!exit_ei) return routelen;
@@ -2123,6 +2154,98 @@ pick_rendezvous_node(router_crn_flags_t flags) return router_choose_random_node(NULL, options->ExcludeNodes, flags); }
+/* + * Helper function to pick a configured restricted middle node + * (either HSLayer2Nodes or HSLayer3Nodes). + * + * Make sure that the node we chose is alive, and not excluded, + * and return it. + * + * The exclude_set is a routerset of nodes that the selected node + * must not match, and the exclude_list is a simple list of nodes + * that the selected node must not be in. Either or both may be + * NULL. + * + * Return NULL if no usable nodes could be found. */ +static const node_t * +pick_restricted_middle_node(router_crn_flags_t flags, + const routerset_t *pick_from, + const routerset_t *exclude_set, + const smartlist_t *exclude_list, + int position_hint) +{ + const node_t *middle_node = NULL; + + smartlist_t *whitelisted_live_middles = smartlist_new(); + smartlist_t *all_live_nodes = smartlist_new(); + + tor_assert(pick_from); + + /* Add all running nodes to all_live_nodes */ + router_add_running_nodes_to_smartlist(all_live_nodes, + (flags & CRN_NEED_UPTIME) != 0, + (flags & CRN_NEED_CAPACITY) != 0, + (flags & CRN_NEED_GUARD) != 0, + (flags & CRN_NEED_DESC) != 0, + (flags & CRN_PREF_ADDR) != 0, + (flags & CRN_DIRECT_CONN) != 0); + + /* Filter all_live_nodes to only add live *and* whitelisted middles + * to the list whitelisted_live_middles. */ + SMARTLIST_FOREACH_BEGIN(all_live_nodes, node_t *, live_node) { + if (routerset_contains_node(pick_from, live_node)) { + smartlist_add(whitelisted_live_middles, live_node); + } + } SMARTLIST_FOREACH_END(live_node); + + /* Honor ExcludeNodes */ + if (exclude_set) { + routerset_subtract_nodes(whitelisted_live_middles, exclude_set); + } + + if (exclude_list) { + smartlist_subtract(whitelisted_live_middles, exclude_list); + } + + /** + * Max number of restricted nodes before we alert the user and try + * to load balance for them. + * + * The most agressive vanguard design had 16 nodes at layer3. + * Let's give a small ceiling above that. */ +#define MAX_SANE_RESTRICTED_NODES 20 + /* If the user (or associated tor controller) selected only a few nodes, + * assume they took load balancing into account and don't do it for them. + * + * If there are a lot of nodes in here, assume they did not load balance + * and do it for them, but also warn them that they may be Doing It Wrong. + */ + if (smartlist_len(whitelisted_live_middles) <= + MAX_SANE_RESTRICTED_NODES) { + middle_node = smartlist_choose(whitelisted_live_middles); + } else { + static ratelim_t pinned_notice_limit = RATELIM_INIT(24*3600); + log_fn_ratelim(&pinned_notice_limit, LOG_NOTICE, LD_CIRC, + "Your _HSLayer%dNodes setting has resulted " + "in %d total nodes. This is a lot of nodes. " + "You may want to consider using a Tor controller " + "to select and update a smaller set of nodes instead.", + position_hint, smartlist_len(whitelisted_live_middles)); + + /* NO_WEIGHTING here just means don't take node flags into account + * (ie: use consensus measurement only). This is done so that + * we don't further surprise the user by not using Exits that they + * specified at all */ + middle_node = node_sl_choose_by_bandwidth(whitelisted_live_middles, + NO_WEIGHTING); + } + + smartlist_free(whitelisted_live_middles); + smartlist_free(all_live_nodes); + + return middle_node; +} + /** Return a pointer to a suitable router to be the exit node for the * circuit of purpose <b>purpose</b> that we're about to build (or NULL * if no router is suitable). @@ -2410,6 +2533,118 @@ cpath_get_n_hops(crypt_path_t **head_ptr)
#endif /* defined(TOR_UNIT_TESTS) */
+/** + * Build a list of nodes to exclude from the choice of this middle + * hop, based on already chosen nodes. + * + * XXX: At present, this function does not exclude any nodes from + * the vanguard circuits. See + * https://trac.torproject.org/projects/tor/ticket/24487 + */ +static smartlist_t * +build_middle_exclude_list(uint8_t purpose, + cpath_build_state_t *state, + crypt_path_t *head, + int cur_len) +{ + smartlist_t *excluded; + const node_t *r; + crypt_path_t *cpath; + int i; + + excluded = smartlist_new(); + + /* Add the exit to the exclude list (note that the exit/last hop is always + * chosen first in circuit_establish_circuit()). */ + if ((r = build_state_get_exit_node(state))) { + nodelist_add_node_and_family(excluded, r); + } + + /* XXX: We don't apply any other previously selected node restrictions for + * vanguards, and allow nodes to be reused for those hop positions in the + * same circuit. This is because after many rotations, you get to learn + * inner guard nodes through the nodes that are not selected for outer + * hops. + * + * The alternative is building the circuit in reverse. Reverse calls to + * onion_extend_cpath() (ie: select outer hops first) would then have the + * property that you don't gain information about inner hops by observing + * outer ones. See https://trac.torproject.org/projects/tor/ticket/24487 + * for this. + * + * (Note further that we can and do still exclude the exit in the block + * above, because it is chosen first in circuit_establish_circuit()..) */ + if (circuit_should_use_vanguards(purpose)) { + return excluded; + } + + for (i = 0, cpath = head; cpath && i < cur_len; ++i, cpath=cpath->next) { + if ((r = node_get_by_id(cpath->extend_info->identity_digest))) { + nodelist_add_node_and_family(excluded, r); + } + } + + return excluded; +} + +/** Return true if we MUST use vanguards for picking this middle node. */ +static int +middle_node_must_be_vanguard(const or_options_t *options, + uint8_t purpose, int cur_len) +{ + /* If this is not a hidden service circuit, don't use vanguards */ + if (!circuit_purpose_is_hidden_service(purpose)) { + return 0; + } + + /* If we have sticky L2 nodes, and this is an L2 pick, use vanguards */ + if (options->HSLayer2Nodes && cur_len == 1) { + return 1; + } + + /* If we have sticky L3 nodes, and this is an L3 pick, use vanguards */ + if (options->HSLayer3Nodes && cur_len == 2) { + return 1; + } + + return 0; +} + +/** Pick a sticky vanguard middle node or return NULL if not found. + * See doc of pick_restricted_middle_node() for argument details. */ +static const node_t * +pick_vanguard_middle_node(const or_options_t *options, + router_crn_flags_t flags, int cur_len, + const smartlist_t *excluded) +{ + const routerset_t *vanguard_routerset = NULL; + const node_t *node = NULL; + + /* Pick the right routerset based on the current hop */ + if (cur_len == 1) { + vanguard_routerset = options->HSLayer2Nodes; + } else if (cur_len == 2) { + vanguard_routerset = options->HSLayer3Nodes; + } else { + /* guaranteed by middle_node_should_be_vanguard() */ + tor_assert_nonfatal_unreached(); + return NULL; + } + + node = pick_restricted_middle_node(flags, vanguard_routerset, + options->ExcludeNodes, excluded, + cur_len+1); + + if (!node) { + static ratelim_t pinned_warning_limit = RATELIM_INIT(300); + log_fn_ratelim(&pinned_warning_limit, LOG_WARN, LD_CIRC, + "Could not find a node that matches the configured " + "_HSLayer%dNodes set", cur_len+1); + } + + return node; +} + /** A helper function used by onion_extend_cpath(). Use <b>purpose</b> * and <b>state</b> and the cpath <b>head</b> (currently populated only * to length <b>cur_len</b> to decide a suitable middle hop for a @@ -2422,9 +2657,7 @@ choose_good_middle_server(uint8_t purpose, crypt_path_t *head, int cur_len) { - int i; - const node_t *r, *choice; - crypt_path_t *cpath; + const node_t *choice; smartlist_t *excluded; const or_options_t *options = get_options(); router_crn_flags_t flags = CRN_NEED_DESC; @@ -2433,20 +2666,20 @@ choose_good_middle_server(uint8_t purpose,
log_debug(LD_CIRC, "Contemplating intermediate hop #%d: random choice.", cur_len+1); - excluded = smartlist_new(); - if ((r = build_state_get_exit_node(state))) { - nodelist_add_node_and_family(excluded, r); - } - for (i = 0, cpath = head; i < cur_len; ++i, cpath=cpath->next) { - if ((r = node_get_by_id(cpath->extend_info->identity_digest))) { - nodelist_add_node_and_family(excluded, r); - } - } + + excluded = build_middle_exclude_list(purpose, state, head, cur_len);
if (state->need_uptime) flags |= CRN_NEED_UPTIME; if (state->need_capacity) flags |= CRN_NEED_CAPACITY; + + /** If a hidden service circuit wants a specific middle node, pin it. */ + if (middle_node_must_be_vanguard(options, purpose, cur_len)) { + log_debug(LD_GENERAL, "Picking a sticky node (cur_len = %d)", cur_len); + return pick_vanguard_middle_node(options, flags, cur_len, excluded); + } + choice = router_choose_random_node(excluded, options->ExcludeNodes, flags); smartlist_free(excluded); return choice; diff --git a/src/or/circuituse.c b/src/or/circuituse.c index f04448ffc..e7be8fa22 100644 --- a/src/or/circuituse.c +++ b/src/or/circuituse.c @@ -1762,8 +1762,22 @@ circuit_build_failed(origin_circuit_t *circ) TO_CIRCUIT(circ)->n_circ_id, circ->global_identifier); } if (n_chan_id && !already_marked) { - /* New guard API: we failed. */ - if (circ->guard_state) + /* + * If we have guard state (new guard API) and our path selection + * code actually chose a full path, then blame the failure of this + * circuit on the guard. + * + * Note that we deliberately use circuit_get_cpath_len() (and not + * circuit_get_cpath_opened_len()) because we only want to ensure + * that a full path is *chosen*. This is different than a full path + * being *built*. We only want to blame *build* failures on this + * guard. Path selection failures can happen spuriously for a number + * of reasons (such as aggressive/invalid user-specified path + * restrictions in the torrc, as well as non-user reasons like + * exitpolicy issues), and so should not be counted here. + */ + if (circ->guard_state && + circuit_get_cpath_len(circ) >= circ->build_state->desired_path_len) entry_guard_failed(&circ->guard_state); /* if there are any one-hop streams waiting on this circuit, fail * them now so they can retry elsewhere. */ @@ -1856,6 +1870,53 @@ have_enough_path_info(int need_exit) return router_have_consensus_path() != CONSENSUS_PATH_UNKNOWN; }
+/** + * Tell us if a circuit is a hidden service circuit. + */ +int +circuit_purpose_is_hidden_service(uint8_t purpose) +{ + /* Client-side purpose */ + if (purpose >= CIRCUIT_PURPOSE_C_INTRODUCING && + purpose <= CIRCUIT_PURPOSE_C_REND_JOINED) { + return 1; + } + + /* Service-side purpose */ + if (purpose >= CIRCUIT_PURPOSE_S_ESTABLISH_INTRO && + purpose <= CIRCUIT_PURPOSE_S_REND_JOINED) { + return 1; + } + + return 0; +} + +/** + * Return true if this circuit purpose should use vanguards + * or pinned Layer2 or Layer3 guards. + * + * This function takes both the circuit purpose and the + * torrc options for pinned middles/vanguards into account + * (ie: the circuit must be a hidden service circuit and + * vanguards/pinned middles must be enabled for it to return + * true). + */ +int +circuit_should_use_vanguards(uint8_t purpose) +{ + const or_options_t *options = get_options(); + + /* Only hidden service circuits use vanguards */ + if (!circuit_purpose_is_hidden_service(purpose)) + return 0; + + /* Pinned middles are effectively vanguards */ + if (options->HSLayer2Nodes || options->HSLayer3Nodes) + return 1; + + return 0; +} + /** Launch a new circuit with purpose <b>purpose</b> and exit node * <b>extend_info</b> (or NULL to select a random exit node). If flags * contains CIRCLAUNCH_NEED_UPTIME, choose among routers with high uptime. If @@ -1892,6 +1953,7 @@ circuit_launch_by_extend_info(uint8_t purpose,
if ((extend_info || purpose != CIRCUIT_PURPOSE_C_GENERAL) && purpose != CIRCUIT_PURPOSE_TESTING && + !circuit_should_use_vanguards(purpose) && !onehop_tunnel && !need_specific_rp) { /* see if there are appropriate circs available to cannibalize. */ /* XXX if we're planning to add a hop, perhaps we want to look for diff --git a/src/or/circuituse.h b/src/or/circuituse.h index 2b0f983f1..71c818b97 100644 --- a/src/or/circuituse.h +++ b/src/or/circuituse.h @@ -63,6 +63,9 @@ int hostname_in_track_host_exits(const or_options_t *options, const char *address); void mark_circuit_unusable_for_new_conns(origin_circuit_t *circ);
+int circuit_purpose_is_hidden_service(uint8_t); +int circuit_should_use_vanguards(uint8_t); + #ifdef TOR_UNIT_TESTS /* Used only by circuituse.c and test_circuituse.c */
diff --git a/src/or/config.c b/src/or/config.c index e5c10498c..ebb536b0f 100644 --- a/src/or/config.c +++ b/src/or/config.c @@ -404,6 +404,8 @@ static config_var_t option_vars_[] = { V(Socks5ProxyPassword, STRING, NULL), VAR("KeyDirectory", FILENAME, KeyDirectory_option, NULL), V(KeyDirectoryGroupReadable, BOOL, "0"), + VAR("_HSLayer2Nodes", ROUTERSET, HSLayer2Nodes, NULL), + VAR("_HSLayer3Nodes", ROUTERSET, HSLayer3Nodes, NULL), V(KeepalivePeriod, INTERVAL, "5 minutes"), V(KeepBindCapabilities, AUTOBOOL, "auto"), VAR("Log", LINELIST, Logs, NULL), @@ -1647,6 +1649,8 @@ options_need_geoip_info(const or_options_t *options, const char **reason_out) routerset_needs_geoip(options->ExitNodes) || routerset_needs_geoip(options->ExcludeExitNodes) || routerset_needs_geoip(options->ExcludeNodes) || + routerset_needs_geoip(options->HSLayer2Nodes) || + routerset_needs_geoip(options->HSLayer3Nodes) || routerset_needs_geoip(options->Tor2webRendezvousPoints);
if (routerset_usage && reason_out) { @@ -2088,6 +2092,10 @@ options_act(const or_options_t *old_options) options->ExcludeExitNodes) || !routerset_equal(old_options->EntryNodes, options->EntryNodes) || !routerset_equal(old_options->ExitNodes, options->ExitNodes) || + !routerset_equal(old_options->HSLayer2Nodes, + options->HSLayer2Nodes) || + !routerset_equal(old_options->HSLayer3Nodes, + options->HSLayer3Nodes) || !routerset_equal(old_options->Tor2webRendezvousPoints, options->Tor2webRendezvousPoints) || options->StrictNodes != old_options->StrictNodes) { diff --git a/src/or/or.h b/src/or/or.h index 2617d2d87..54e9786c7 100644 --- a/src/or/or.h +++ b/src/or/or.h @@ -3876,6 +3876,14 @@ typedef struct { /** A routerset that should be used when picking RPs for HS circuits. */ routerset_t *Tor2webRendezvousPoints;
+ /** A routerset that should be used when picking middle nodes for HS + * circuits. */ + routerset_t *HSLayer2Nodes; + + /** A routerset that should be used when picking third-hop nodes for HS + * circuits. */ + routerset_t *HSLayer3Nodes; + /** Onion Services in HiddenServiceSingleHopMode make one-hop (direct) * circuits between the onion service server, and the introduction and * rendezvous points. (Onion service descriptors are still posted using