/* Copyright (c) 2003-2004, Roger Dingledine. * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson. * Copyright (c) 2007-2020, The Tor Project, Inc. */ /* See LICENSE for licensing information */ /** * \file dns.c * \brief Implements a local cache for DNS results for Tor servers. * This is implemented as a wrapper around Adam Langley's eventdns.c code. * (We can't just use gethostbyname() and friends because we really need to * be nonblocking.) * * There are three main cases when a Tor relay uses dns.c to launch a DNS * request: *
    *
  1. To check whether the DNS server is working more or less correctly. * This happens via dns_launch_correctness_checks(). The answer is * reported in the return value from later calls to * dns_seems_to_be_broken(). *
  2. When a client has asked the relay, in a RELAY_BEGIN cell, to connect * to a given server by hostname. This happens via dns_resolve(). *
  3. When a client has asked the relay, in a RELAY_RESOLVE cell, to look * up a given server's IP address(es) by hostname. This also happens via * dns_resolve(). *
* * Each of these gets handled a little differently. * * To check for correctness, we look up some hostname we expect to exist and * have real entries, some hostnames which we expect to definitely not exist, * and some hostnames that we expect to probably not exist. If too many of * the hostnames that shouldn't exist do exist, that's a DNS hijacking * attempt. If too many of the hostnames that should exist have the same * addresses as the ones that shouldn't exist, that's a very bad DNS hijacking * attempt, or a very naughty captive portal. And if the hostnames that * should exist simply don't exist, we probably have a broken nameserver. * * To handle client requests, we first check our cache for answers. If there * isn't something up-to-date, we've got to launch A or AAAA requests as * appropriate. How we handle responses to those in particular is a bit * complex; see dns_lookup() and set_exitconn_info_from_resolve(). * * When a lookup is finally complete, the inform_pending_connections() * function will tell all of the streams that have been waiting for the * resolve, by calling connection_exit_connect() if the client sent a * RELAY_BEGIN cell, and by calling send_resolved_cell() or * send_hostname_cell() if the client sent a RELAY_RESOLVE cell. **/ #define DNS_PRIVATE #include "core/or/or.h" #include "app/config/config.h" #include "core/mainloop/connection.h" #include "core/mainloop/mainloop.h" #include "core/mainloop/netstatus.h" #include "core/or/circuitlist.h" #include "core/or/circuituse.h" #include "core/or/connection_edge.h" #include "core/or/policies.h" #include "core/or/relay.h" #include "feature/control/control_events.h" #include "feature/relay/dns.h" #include "feature/relay/router.h" #include "feature/relay/routermode.h" #include "lib/crypt_ops/crypto_rand.h" #include "lib/evloop/compat_libevent.h" #include "lib/sandbox/sandbox.h" #include "core/or/edge_connection_st.h" #include "core/or/or_circuit_st.h" #include "ht.h" #ifdef HAVE_SYS_STAT_H #include #endif #include #include /** How long will we wait for an answer from the resolver before we decide * that the resolver is wedged? */ #define RESOLVE_MAX_TIMEOUT 300 /** Our evdns_base; this structure handles all our name lookups. */ static struct evdns_base *the_evdns_base = NULL; /** Have we currently configured nameservers with eventdns? */ static int nameservers_configured = 0; /** Did our most recent attempt to configure nameservers with eventdns fail? */ static int nameserver_config_failed = 0; /** What was the resolv_conf fname we last used when configuring the * nameservers? Used to check whether we need to reconfigure. */ static char *resolv_conf_fname = NULL; /** What was the mtime on the resolv.conf file we last used when configuring * the nameservers? Used to check whether we need to reconfigure. */ static time_t resolv_conf_mtime = 0; static void purge_expired_resolves(time_t now); static void dns_found_answer(const char *address, uint8_t query_type, int dns_answer, const tor_addr_t *addr, const char *hostname, uint32_t ttl); static void add_wildcarded_test_address(const char *address); static int configure_nameservers(int force); static int answer_is_wildcarded(const char *ip); static int evdns_err_is_transient(int err); static void inform_pending_connections(cached_resolve_t *resolve); static void make_pending_resolve_cached(cached_resolve_t *cached); #ifdef DEBUG_DNS_CACHE static void assert_cache_ok_(void); #define assert_cache_ok() assert_cache_ok_() #else #define assert_cache_ok() STMT_NIL #endif /* defined(DEBUG_DNS_CACHE) */ static void assert_resolve_ok(cached_resolve_t *resolve); /** Hash table of cached_resolve objects. */ static HT_HEAD(cache_map, cached_resolve_t) cache_root; /** Global: how many IPv6 requests have we made in all? */ static uint64_t n_ipv6_requests_made = 0; /** Global: how many IPv6 requests have timed out? */ static uint64_t n_ipv6_timeouts = 0; /** Global: Do we think that IPv6 DNS is broken? */ static int dns_is_broken_for_ipv6 = 0; /** Function to compare hashed resolves on their addresses; used to * implement hash tables. */ static inline int cached_resolves_eq(cached_resolve_t *a, cached_resolve_t *b) { /* make this smarter one day? */ assert_resolve_ok(a); // Not b; b may be just a search. return !strncmp(a->address, b->address, MAX_ADDRESSLEN); } /** Hash function for cached_resolve objects */ static inline unsigned int cached_resolve_hash(cached_resolve_t *a) { return (unsigned) siphash24g((const uint8_t*)a->address, strlen(a->address)); } HT_PROTOTYPE(cache_map, cached_resolve_t, node, cached_resolve_hash, cached_resolves_eq); HT_GENERATE2(cache_map, cached_resolve_t, node, cached_resolve_hash, cached_resolves_eq, 0.6, tor_reallocarray_, tor_free_); /** Initialize the DNS cache. */ static void init_cache_map(void) { HT_INIT(cache_map, &cache_root); } /** Helper: called by eventdns when eventdns wants to log something. */ static void evdns_log_cb(int warn, const char *msg) { const char *cp; static int all_down = 0; int severity = warn ? LOG_WARN : LOG_INFO; if (!strcmpstart(msg, "Resolve requested for") && get_options()->SafeLogging) { log_info(LD_EXIT, "eventdns: Resolve requested."); return; } else if (!strcmpstart(msg, "Search: ")) { return; } if (!strcmpstart(msg, "Nameserver ") && (cp=strstr(msg, " has failed: "))) { char *ns = tor_strndup(msg+11, cp-(msg+11)); const char *colon = strchr(cp, ':'); tor_assert(colon); const char *err = colon+2; /* Don't warn about a single failed nameserver; we'll warn with 'all * nameservers have failed' if we're completely out of nameservers; * otherwise, the situation is tolerable. */ severity = LOG_INFO; control_event_server_status(LOG_NOTICE, "NAMESERVER_STATUS NS=%s STATUS=DOWN ERR=%s", ns, escaped(err)); tor_free(ns); } else if (!strcmpstart(msg, "Nameserver ") && (cp=strstr(msg, " is back up"))) { char *ns = tor_strndup(msg+11, cp-(msg+11)); severity = (all_down && warn) ? LOG_NOTICE : LOG_INFO; all_down = 0; control_event_server_status(LOG_NOTICE, "NAMESERVER_STATUS NS=%s STATUS=UP", ns); tor_free(ns); } else if (!strcmp(msg, "All nameservers have failed")) { control_event_server_status(LOG_WARN, "NAMESERVER_ALL_DOWN"); all_down = 1; } else if (!strcmpstart(msg, "Address mismatch on received DNS")) { static ratelim_t mismatch_limit = RATELIM_INIT(3600); const char *src = strstr(msg, " Apparent source"); if (!src || get_options()->SafeLogging) { src = ""; } log_fn_ratelim(&mismatch_limit, severity, LD_EXIT, "eventdns: Received a DNS packet from " "an IP address to which we did not send a request. This " "could be a DNS spoofing attempt, or some kind of " "misconfiguration.%s", src); return; } tor_log(severity, LD_EXIT, "eventdns: %s", msg); } /** Helper: passed to eventdns.c as a callback so it can generate random * numbers for transaction IDs and 0x20-hack coding. */ static void dns_randfn_(char *b, size_t n) { crypto_rand(b,n); } /** Initialize the DNS subsystem; called by the OR process. */ int dns_init(void) { init_cache_map(); evdns_set_random_bytes_fn(dns_randfn_); if (server_mode(get_options())) { int r = configure_nameservers(1); return r; } return 0; } /** Called when DNS-related options change (or may have changed). Returns -1 * on failure, 0 on success. */ int dns_reset(void) { const or_options_t *options = get_options(); if (! server_mode(options)) { if (!the_evdns_base) { if (!(the_evdns_base = evdns_base_new(tor_libevent_get_base(), 0))) { log_err(LD_BUG, "Couldn't create an evdns_base"); return -1; } } evdns_base_clear_nameservers_and_suspend(the_evdns_base); evdns_base_search_clear(the_evdns_base); nameservers_configured = 0; tor_free(resolv_conf_fname); resolv_conf_mtime = 0; } else { if (configure_nameservers(0) < 0) { return -1; } } return 0; } /** Return true iff the most recent attempt to initialize the DNS subsystem * failed. */ int has_dns_init_failed(void) { return nameserver_config_failed; } /** Helper: free storage held by an entry in the DNS cache. */ static void free_cached_resolve_(cached_resolve_t *r) { if (!r) return; while (r->pending_connections) { pending_connection_t *victim = r->pending_connections; r->pending_connections = victim->next; tor_free(victim); } if (r->res_status_hostname == RES_STATUS_DONE_OK) tor_free(r->result_ptr.hostname); r->magic = 0xFF00FF00; tor_free(r); } /** Compare two cached_resolve_t pointers by expiry time, and return * less-than-zero, zero, or greater-than-zero as appropriate. Used for * the priority queue implementation. */ static int compare_cached_resolves_by_expiry_(const void *_a, const void *_b) { const cached_resolve_t *a = _a, *b = _b; if (a->expire < b->expire) return -1; else if (a->expire == b->expire) return 0; else return 1; } /** Priority queue of cached_resolve_t objects to let us know when they * will expire. */ static smartlist_t *cached_resolve_pqueue = NULL; static void cached_resolve_add_answer(cached_resolve_t *resolve, int query_type, int dns_result, const tor_addr_t *answer_addr, const char *answer_hostname, uint32_t ttl) { if (query_type == DNS_PTR) { if (resolve->res_status_hostname != RES_STATUS_INFLIGHT) return; if (dns_result == DNS_ERR_NONE && answer_hostname) { resolve->result_ptr.hostname = tor_strdup(answer_hostname); resolve->res_status_hostname = RES_STATUS_DONE_OK; } else { resolve->result_ptr.err_hostname = dns_result; resolve->res_status_hostname = RES_STATUS_DONE_ERR; } resolve->ttl_hostname = ttl; } else if (query_type == DNS_IPv4_A) { if (resolve->res_status_ipv4 != RES_STATUS_INFLIGHT) return; if (dns_result == DNS_ERR_NONE && answer_addr && tor_addr_family(answer_addr) == AF_INET) { resolve->result_ipv4.addr_ipv4 = tor_addr_to_ipv4h(answer_addr); resolve->res_status_ipv4 = RES_STATUS_DONE_OK; } else { resolve->result_ipv4.err_ipv4 = dns_result; resolve->res_status_ipv4 = RES_STATUS_DONE_ERR; } resolve->ttl_ipv4 = ttl; } else if (query_type == DNS_IPv6_AAAA) { if (resolve->res_status_ipv6 != RES_STATUS_INFLIGHT) return; if (dns_result == DNS_ERR_NONE && answer_addr && tor_addr_family(answer_addr) == AF_INET6) { memcpy(&resolve->result_ipv6.addr_ipv6, tor_addr_to_in6(answer_addr), sizeof(struct in6_addr)); resolve->res_status_ipv6 = RES_STATUS_DONE_OK; } else { resolve->result_ipv6.err_ipv6 = dns_result; resolve->res_status_ipv6 = RES_STATUS_DONE_ERR; } resolve->ttl_ipv6 = ttl; } } /** Return true iff there are no in-flight requests for resolve. */ static int cached_resolve_have_all_answers(const cached_resolve_t *resolve) { return (resolve->res_status_ipv4 != RES_STATUS_INFLIGHT && resolve->res_status_ipv6 != RES_STATUS_INFLIGHT && resolve->res_status_hostname != RES_STATUS_INFLIGHT); } /** Set an expiry time for a cached_resolve_t, and add it to the expiry * priority queue */ static void set_expiry(cached_resolve_t *resolve, time_t expires) { tor_assert(resolve && resolve->expire == 0); if (!cached_resolve_pqueue) cached_resolve_pqueue = smartlist_new(); resolve->expire = expires; smartlist_pqueue_add(cached_resolve_pqueue, compare_cached_resolves_by_expiry_, offsetof(cached_resolve_t, minheap_idx), resolve); } /** Free all storage held in the DNS cache and related structures. */ void dns_free_all(void) { cached_resolve_t **ptr, **next, *item; assert_cache_ok(); if (cached_resolve_pqueue) { SMARTLIST_FOREACH(cached_resolve_pqueue, cached_resolve_t *, res, { if (res->state == CACHE_STATE_DONE) free_cached_resolve_(res); }); } for (ptr = HT_START(cache_map, &cache_root); ptr != NULL; ptr = next) { item = *ptr; next = HT_NEXT_RMV(cache_map, &cache_root, ptr); free_cached_resolve_(item); } HT_CLEAR(cache_map, &cache_root); smartlist_free(cached_resolve_pqueue); cached_resolve_pqueue = NULL; tor_free(resolv_conf_fname); } /** Remove every cached_resolve whose expire time is before or * equal to now from the cache. */ static void purge_expired_resolves(time_t now) { cached_resolve_t *resolve, *removed; pending_connection_t *pend; edge_connection_t *pendconn; assert_cache_ok(); if (!cached_resolve_pqueue) return; while (smartlist_len(cached_resolve_pqueue)) { resolve = smartlist_get(cached_resolve_pqueue, 0); if (resolve->expire > now) break; smartlist_pqueue_pop(cached_resolve_pqueue, compare_cached_resolves_by_expiry_, offsetof(cached_resolve_t, minheap_idx)); if (resolve->state == CACHE_STATE_PENDING) { log_debug(LD_EXIT, "Expiring a dns resolve %s that's still pending. Forgot to " "cull it? DNS resolve didn't tell us about the timeout?", escaped_safe_str(resolve->address)); } else if (resolve->state == CACHE_STATE_CACHED) { log_debug(LD_EXIT, "Forgetting old cached resolve (address %s, expires %lu)", escaped_safe_str(resolve->address), (unsigned long)resolve->expire); tor_assert(!resolve->pending_connections); } else { tor_assert(resolve->state == CACHE_STATE_DONE); tor_assert(!resolve->pending_connections); } if (resolve->pending_connections) { log_debug(LD_EXIT, "Closing pending connections on timed-out DNS resolve!"); while (resolve->pending_connections) { pend = resolve->pending_connections; resolve->pending_connections = pend->next; /* Connections should only be pending if they have no socket. */ tor_assert(!SOCKET_OK(pend->conn->base_.s)); pendconn = pend->conn; /* Prevent double-remove */ pendconn->base_.state = EXIT_CONN_STATE_RESOLVEFAILED; if (!pendconn->base_.marked_for_close) { connection_edge_end(pendconn, END_STREAM_REASON_TIMEOUT); circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn); connection_free_(TO_CONN(pendconn)); } tor_free(pend); } } if (resolve->state == CACHE_STATE_CACHED || resolve->state == CACHE_STATE_PENDING) { removed = HT_REMOVE(cache_map, &cache_root, resolve); if (removed != resolve) { log_err(LD_BUG, "The expired resolve we purged didn't match any in" " the cache. Tried to purge %s (%p); instead got %s (%p).", resolve->address, (void*)resolve, removed ? removed->address : "NULL", (void*)removed); } tor_assert(removed == resolve); } else { /* This should be in state DONE. Make sure it's not in the cache. */ cached_resolve_t *tmp = HT_FIND(cache_map, &cache_root, resolve); tor_assert(tmp != resolve); } if (resolve->res_status_hostname == RES_STATUS_DONE_OK) tor_free(resolve->result_ptr.hostname); resolve->magic = 0xF0BBF0BB; tor_free(resolve); } assert_cache_ok(); } /* argument for send_resolved_cell only, meaning "let the answer type be ipv4 * or ipv6 depending on the connection's address". */ #define RESOLVED_TYPE_AUTO 0xff /** Send a response to the RESOLVE request of a connection. * answer_type must be one of * RESOLVED_TYPE_(AUTO|ERROR|ERROR_TRANSIENT|). * * If circ is provided, and we have a cached answer, send the * answer back along circ; otherwise, send the answer back along * conn's attached circuit. */ MOCK_IMPL(STATIC void, send_resolved_cell,(edge_connection_t *conn, uint8_t answer_type, const cached_resolve_t *resolved)) { char buf[RELAY_PAYLOAD_SIZE], *cp = buf; size_t buflen = 0; uint32_t ttl; buf[0] = answer_type; ttl = clip_dns_ttl(conn->address_ttl); switch (answer_type) { case RESOLVED_TYPE_AUTO: if (resolved && resolved->res_status_ipv4 == RES_STATUS_DONE_OK) { cp[0] = RESOLVED_TYPE_IPV4; cp[1] = 4; set_uint32(cp+2, htonl(resolved->result_ipv4.addr_ipv4)); set_uint32(cp+6, htonl(ttl)); cp += 10; } if (resolved && resolved->res_status_ipv6 == RES_STATUS_DONE_OK) { const uint8_t *bytes = resolved->result_ipv6.addr_ipv6.s6_addr; cp[0] = RESOLVED_TYPE_IPV6; cp[1] = 16; memcpy(cp+2, bytes, 16); set_uint32(cp+18, htonl(ttl)); cp += 22; } if (cp != buf) { buflen = cp - buf; break; } else { answer_type = RESOLVED_TYPE_ERROR; /* We let this fall through and treat it as an error. */ } FALLTHROUGH; case RESOLVED_TYPE_ERROR_TRANSIENT: case RESOLVED_TYPE_ERROR: { const char *errmsg = "Error resolving hostname"; size_t msglen = strlen(errmsg); buf[0] = answer_type; buf[1] = msglen; strlcpy(buf+2, errmsg, sizeof(buf)-2); set_uint32(buf+2+msglen, htonl(ttl)); buflen = 6+msglen; break; } default: tor_assert(0); return; } // log_notice(LD_EXIT, "Sending a regular RESOLVED reply: "); connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen); } /** Send a response to the RESOLVE request of a connection for an in-addr.arpa * address on connection conn which yielded the result hostname. * The answer type will be RESOLVED_HOSTNAME. * * If circ is provided, and we have a cached answer, send the * answer back along circ; otherwise, send the answer back along * conn's attached circuit. */ MOCK_IMPL(STATIC void, send_resolved_hostname_cell,(edge_connection_t *conn, const char *hostname)) { char buf[RELAY_PAYLOAD_SIZE]; size_t buflen; uint32_t ttl; if (BUG(!hostname)) return; size_t namelen = strlen(hostname); tor_assert(namelen < 256); ttl = clip_dns_ttl(conn->address_ttl); buf[0] = RESOLVED_TYPE_HOSTNAME; buf[1] = (uint8_t)namelen; memcpy(buf+2, hostname, namelen); set_uint32(buf+2+namelen, htonl(ttl)); buflen = 2+namelen+4; // log_notice(LD_EXIT, "Sending a reply RESOLVED reply: %s", hostname); connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen); // log_notice(LD_EXIT, "Sent"); } /** See if we have a cache entry for exitconn-\>address. If so, * if resolve valid, put it into exitconn-\>addr and return 1. * If resolve failed, free exitconn and return -1. * * (For EXIT_PURPOSE_RESOLVE connections, send back a RESOLVED error cell * on returning -1. For EXIT_PURPOSE_CONNECT connections, there's no * need to send back an END cell, since connection_exit_begin_conn will * do that for us.) * * If we have a cached answer, send the answer back along exitconn's * circuit. * * Else, if seen before and pending, add conn to the pending list, * and return 0. * * Else, if not seen before, add conn to pending list, hand to * dns farm, and return 0. * * Exitconn's on_circuit field must be set, but exitconn should not * yet be linked onto the n_streams/resolving_streams list of that circuit. * On success, link the connection to n_streams if it's an exit connection. * On "pending", link the connection to resolving streams. Otherwise, * clear its on_circuit field. */ int dns_resolve(edge_connection_t *exitconn) { or_circuit_t *oncirc = TO_OR_CIRCUIT(exitconn->on_circuit); int is_resolve, r; int made_connection_pending = 0; char *hostname = NULL; cached_resolve_t *resolve = NULL; is_resolve = exitconn->base_.purpose == EXIT_PURPOSE_RESOLVE; r = dns_resolve_impl(exitconn, is_resolve, oncirc, &hostname, &made_connection_pending, &resolve); switch (r) { case 1: /* We got an answer without a lookup -- either the answer was * cached, or it was obvious (like an IP address). */ if (is_resolve) { /* Send the answer back right now, and detach. */ if (hostname) send_resolved_hostname_cell(exitconn, hostname); else send_resolved_cell(exitconn, RESOLVED_TYPE_AUTO, resolve); exitconn->on_circuit = NULL; } else { /* Add to the n_streams list; the calling function will send back a * connected cell. */ exitconn->next_stream = oncirc->n_streams; oncirc->n_streams = exitconn; } break; case 0: /* The request is pending: add the connection into the linked list of * resolving_streams on this circuit. */ exitconn->base_.state = EXIT_CONN_STATE_RESOLVING; exitconn->next_stream = oncirc->resolving_streams; oncirc->resolving_streams = exitconn; break; case -2: case -1: /* The request failed before it could start: cancel this connection, * and stop everybody waiting for the same connection. */ if (is_resolve) { send_resolved_cell(exitconn, (r == -1) ? RESOLVED_TYPE_ERROR : RESOLVED_TYPE_ERROR_TRANSIENT, NULL); } exitconn->on_circuit = NULL; dns_cancel_pending_resolve(exitconn->base_.address); if (!made_connection_pending && !exitconn->base_.marked_for_close) { /* If we made the connection pending, then we freed it already in * dns_cancel_pending_resolve(). If we marked it for close, it'll * get freed from the main loop. Otherwise, can free it now. */ connection_free_(TO_CONN(exitconn)); } break; default: tor_assert(0); } tor_free(hostname); return r; } /** Helper function for dns_resolve: same functionality, but does not handle: * - marking connections on error and clearing their on_circuit * - linking connections to n_streams/resolving_streams, * - sending resolved cells if we have an answer/error right away, * * Return -2 on a transient error. If it's a reverse resolve and it's * successful, sets *hostname_out to a newly allocated string * holding the cached reverse DNS value. * * Set *made_connection_pending_out to true if we have placed * exitconn on the list of pending connections for some resolve; set it * to false otherwise. * * Set *resolve_out to a cached resolve, if we found one. */ MOCK_IMPL(STATIC int, dns_resolve_impl,(edge_connection_t *exitconn, int is_resolve, or_circuit_t *oncirc, char **hostname_out, int *made_connection_pending_out, cached_resolve_t **resolve_out)) { cached_resolve_t *resolve; cached_resolve_t search; pending_connection_t *pending_connection; int is_reverse = 0; tor_addr_t addr; time_t now = time(NULL); int r; assert_connection_ok(TO_CONN(exitconn), 0); tor_assert(!SOCKET_OK(exitconn->base_.s)); assert_cache_ok(); tor_assert(oncirc); *made_connection_pending_out = 0; /* first check if exitconn->base_.address is an IP. If so, we already * know the answer. */ if (tor_addr_parse(&addr, exitconn->base_.address) >= 0) { if (tor_addr_family(&addr) == AF_INET || tor_addr_family(&addr) == AF_INET6) { tor_addr_copy(&exitconn->base_.addr, &addr); exitconn->address_ttl = DEFAULT_DNS_TTL; return 1; } else { /* XXXX unspec? Bogus? */ return -1; } } /* If we're a non-exit, don't even do DNS lookups. */ if (router_my_exit_policy_is_reject_star()) return -1; if (address_is_invalid_destination(exitconn->base_.address, 0)) { tor_log(LOG_PROTOCOL_WARN, LD_EXIT, "Rejecting invalid destination address %s", escaped_safe_str(exitconn->base_.address)); return -1; } /* then take this opportunity to see if there are any expired * resolves in the hash table. */ purge_expired_resolves(now); /* lower-case exitconn->base_.address, so it's in canonical form */ tor_strlower(exitconn->base_.address); /* Check whether this is a reverse lookup. If it's malformed, or it's a * .in-addr.arpa address but this isn't a resolve request, kill the * connection. */ if ((r = tor_addr_parse_PTR_name(&addr, exitconn->base_.address, AF_UNSPEC, 0)) != 0) { if (r == 1) { is_reverse = 1; if (tor_addr_is_internal(&addr, 0)) /* internal address? */ return -1; } if (!is_reverse || !is_resolve) { if (!is_reverse) log_info(LD_EXIT, "Bad .in-addr.arpa address \"%s\"; sending error.", escaped_safe_str(exitconn->base_.address)); else if (!is_resolve) log_info(LD_EXIT, "Attempt to connect to a .in-addr.arpa address \"%s\"; " "sending error.", escaped_safe_str(exitconn->base_.address)); return -1; } //log_notice(LD_EXIT, "Looks like an address %s", //exitconn->base_.address); } exitconn->is_reverse_dns_lookup = is_reverse; /* now check the hash table to see if 'address' is already there. */ strlcpy(search.address, exitconn->base_.address, sizeof(search.address)); resolve = HT_FIND(cache_map, &cache_root, &search); if (resolve && resolve->expire > now) { /* already there */ switch (resolve->state) { case CACHE_STATE_PENDING: /* add us to the pending list */ pending_connection = tor_malloc_zero( sizeof(pending_connection_t)); pending_connection->conn = exitconn; pending_connection->next = resolve->pending_connections; resolve->pending_connections = pending_connection; *made_connection_pending_out = 1; log_debug(LD_EXIT,"Connection (fd "TOR_SOCKET_T_FORMAT") waiting " "for pending DNS resolve of %s", exitconn->base_.s, escaped_safe_str(exitconn->base_.address)); return 0; case CACHE_STATE_CACHED: log_debug(LD_EXIT,"Connection (fd "TOR_SOCKET_T_FORMAT") found " "cached answer for %s", exitconn->base_.s, escaped_safe_str(resolve->address)); *resolve_out = resolve; return set_exitconn_info_from_resolve(exitconn, resolve, hostname_out); case CACHE_STATE_DONE: log_err(LD_BUG, "Found a 'DONE' dns resolve still in the cache."); tor_fragile_assert(); } tor_assert(0); } tor_assert(!resolve); /* not there, need to add it */ resolve = tor_malloc_zero(sizeof(cached_resolve_t)); resolve->magic = CACHED_RESOLVE_MAGIC; resolve->state = CACHE_STATE_PENDING; resolve->minheap_idx = -1; strlcpy(resolve->address, exitconn->base_.address, sizeof(resolve->address)); /* add this connection to the pending list */ pending_connection = tor_malloc_zero(sizeof(pending_connection_t)); pending_connection->conn = exitconn; resolve->pending_connections = pending_connection; *made_connection_pending_out = 1; /* Add this resolve to the cache and priority queue. */ HT_INSERT(cache_map, &cache_root, resolve); set_expiry(resolve, now + RESOLVE_MAX_TIMEOUT); log_debug(LD_EXIT,"Launching %s.", escaped_safe_str(exitconn->base_.address)); assert_cache_ok(); return launch_resolve(resolve); } /** Given an exit connection exitconn, and a cached_resolve_t * resolve whose DNS lookups have all either succeeded or failed, * update the appropriate fields (address_ttl and addr) of exitconn. * * The logic can be complicated here, since we might have launched both * an A lookup and an AAAA lookup, and since either of those might have * succeeded or failed, and since we want to answer a RESOLVE cell with * a full answer but answer a BEGIN cell with whatever answer the client * would accept and we could still connect to. * * If this is a reverse lookup, set *hostname_out to a newly allocated * copy of the name resulting hostname. * * Return -2 on a transient error, -1 on a permenent error, and 1 on * a successful lookup. */ MOCK_IMPL(STATIC int, set_exitconn_info_from_resolve,(edge_connection_t *exitconn, const cached_resolve_t *resolve, char **hostname_out)) { int ipv4_ok, ipv6_ok, answer_with_ipv4, r; uint32_t begincell_flags; const int is_resolve = exitconn->base_.purpose == EXIT_PURPOSE_RESOLVE; tor_assert(exitconn); tor_assert(resolve); if (exitconn->is_reverse_dns_lookup) { exitconn->address_ttl = resolve->ttl_hostname; if (resolve->res_status_hostname == RES_STATUS_DONE_OK) { *hostname_out = tor_strdup(resolve->result_ptr.hostname); return 1; } else { return -1; } } /* If we're here then the connection wants one or either of ipv4, ipv6, and * we can give it one or both. */ if (is_resolve) { begincell_flags = BEGIN_FLAG_IPV6_OK; } else { begincell_flags = exitconn->begincell_flags; } ipv4_ok = (resolve->res_status_ipv4 == RES_STATUS_DONE_OK) && ! (begincell_flags & BEGIN_FLAG_IPV4_NOT_OK); ipv6_ok = (resolve->res_status_ipv6 == RES_STATUS_DONE_OK) && (begincell_flags & BEGIN_FLAG_IPV6_OK) && get_options()->IPv6Exit; /* Now decide which one to actually give. */ if (ipv4_ok && ipv6_ok && is_resolve) { answer_with_ipv4 = 1; } else if (ipv4_ok && ipv6_ok) { /* If we have both, see if our exit policy has an opinion. */ const uint16_t port = exitconn->base_.port; int ipv4_allowed, ipv6_allowed; tor_addr_t a4, a6; tor_addr_from_ipv4h(&a4, resolve->result_ipv4.addr_ipv4); tor_addr_from_in6(&a6, &resolve->result_ipv6.addr_ipv6); ipv4_allowed = !router_compare_to_my_exit_policy(&a4, port); ipv6_allowed = !router_compare_to_my_exit_policy(&a6, port); if (ipv4_allowed && !ipv6_allowed) { answer_with_ipv4 = 1; } else if (ipv6_allowed && !ipv4_allowed) { answer_with_ipv4 = 0; } else { /* Our exit policy would permit both. Answer with whichever the user * prefers */ answer_with_ipv4 = !(begincell_flags & BEGIN_FLAG_IPV6_PREFERRED); } } else { /* Otherwise if one is okay, send it back. */ if (ipv4_ok) { answer_with_ipv4 = 1; } else if (ipv6_ok) { answer_with_ipv4 = 0; } else { /* Neither one was okay. Choose based on user preference. */ answer_with_ipv4 = !(begincell_flags & BEGIN_FLAG_IPV6_PREFERRED); } } /* Finally, we write the answer back. */ r = 1; if (answer_with_ipv4) { if (resolve->res_status_ipv4 == RES_STATUS_DONE_OK) { tor_addr_from_ipv4h(&exitconn->base_.addr, resolve->result_ipv4.addr_ipv4); } else { r = evdns_err_is_transient(resolve->result_ipv4.err_ipv4) ? -2 : -1; } exitconn->address_ttl = resolve->ttl_ipv4; } else { if (resolve->res_status_ipv6 == RES_STATUS_DONE_OK) { tor_addr_from_in6(&exitconn->base_.addr, &resolve->result_ipv6.addr_ipv6); } else { r = evdns_err_is_transient(resolve->result_ipv6.err_ipv6) ? -2 : -1; } exitconn->address_ttl = resolve->ttl_ipv6; } return r; } /** Log an error and abort if conn is waiting for a DNS resolve. */ void assert_connection_edge_not_dns_pending(edge_connection_t *conn) { pending_connection_t *pend; cached_resolve_t search; #if 1 cached_resolve_t *resolve; strlcpy(search.address, conn->base_.address, sizeof(search.address)); resolve = HT_FIND(cache_map, &cache_root, &search); if (!resolve) return; for (pend = resolve->pending_connections; pend; pend = pend->next) { tor_assert(pend->conn != conn); } #else /* !(1) */ cached_resolve_t **resolve; HT_FOREACH(resolve, cache_map, &cache_root) { for (pend = (*resolve)->pending_connections; pend; pend = pend->next) { tor_assert(pend->conn != conn); } } #endif /* 1 */ } /** Remove conn from the list of connections waiting for conn-\>address. */ void connection_dns_remove(edge_connection_t *conn) { pending_connection_t *pend, *victim; cached_resolve_t search; cached_resolve_t *resolve; tor_assert(conn->base_.type == CONN_TYPE_EXIT); tor_assert(conn->base_.state == EXIT_CONN_STATE_RESOLVING); strlcpy(search.address, conn->base_.address, sizeof(search.address)); resolve = HT_FIND(cache_map, &cache_root, &search); if (!resolve) { log_notice(LD_BUG, "Address %s is not pending. Dropping.", escaped_safe_str(conn->base_.address)); return; } tor_assert(resolve->pending_connections); assert_connection_ok(TO_CONN(conn),0); pend = resolve->pending_connections; if (pend->conn == conn) { resolve->pending_connections = pend->next; tor_free(pend); log_debug(LD_EXIT, "First connection (fd "TOR_SOCKET_T_FORMAT") no " "longer waiting for resolve of %s", conn->base_.s, escaped_safe_str(conn->base_.address)); return; } else { for ( ; pend->next; pend = pend->next) { if (pend->next->conn == conn) { victim = pend->next; pend->next = victim->next; tor_free(victim); log_debug(LD_EXIT, "Connection (fd "TOR_SOCKET_T_FORMAT") no longer waiting " "for resolve of %s", conn->base_.s, escaped_safe_str(conn->base_.address)); return; /* more are pending */ } } log_warn(LD_BUG, "Connection (fd "TOR_SOCKET_T_FORMAT") was not waiting " "for a resolve of %s, but we tried to remove it.", conn->base_.s, escaped_safe_str(conn->base_.address)); } } /** Mark all connections waiting for address for close. Then cancel * the resolve for address itself, and remove any cached results for * address from the cache. */ MOCK_IMPL(STATIC void, dns_cancel_pending_resolve,(const char *address)) { pending_connection_t *pend; cached_resolve_t search; cached_resolve_t *resolve, *tmp; edge_connection_t *pendconn; circuit_t *circ; strlcpy(search.address, address, sizeof(search.address)); resolve = HT_FIND(cache_map, &cache_root, &search); if (!resolve) return; if (resolve->state != CACHE_STATE_PENDING) { /* We can get into this state if we never actually created the pending * resolve, due to finding an earlier cached error or something. Just * ignore it. */ if (resolve->pending_connections) { log_warn(LD_BUG, "Address %s is not pending but has pending connections!", escaped_safe_str(address)); tor_fragile_assert(); } return; } if (!resolve->pending_connections) { log_warn(LD_BUG, "Address %s is pending but has no pending connections!", escaped_safe_str(address)); tor_fragile_assert(); return; } tor_assert(resolve->pending_connections); /* mark all pending connections to fail */ log_debug(LD_EXIT, "Failing all connections waiting on DNS resolve of %s", escaped_safe_str(address)); while (resolve->pending_connections) { pend = resolve->pending_connections; pend->conn->base_.state = EXIT_CONN_STATE_RESOLVEFAILED; pendconn = pend->conn; assert_connection_ok(TO_CONN(pendconn), 0); tor_assert(!SOCKET_OK(pendconn->base_.s)); if (!pendconn->base_.marked_for_close) { connection_edge_end(pendconn, END_STREAM_REASON_RESOLVEFAILED); } circ = circuit_get_by_edge_conn(pendconn); if (circ) circuit_detach_stream(circ, pendconn); if (!pendconn->base_.marked_for_close) connection_free_(TO_CONN(pendconn)); resolve->pending_connections = pend->next; tor_free(pend); } tmp = HT_REMOVE(cache_map, &cache_root, resolve); if (tmp != resolve) { log_err(LD_BUG, "The cancelled resolve we purged didn't match any in" " the cache. Tried to purge %s (%p); instead got %s (%p).", resolve->address, (void*)resolve, tmp ? tmp->address : "NULL", (void*)tmp); } tor_assert(tmp == resolve); resolve->state = CACHE_STATE_DONE; } /** Return true iff address is one of the addresses we use to verify * that well-known sites aren't being hijacked by our DNS servers. */ static inline int is_test_address(const char *address) { const or_options_t *options = get_options(); return options->ServerDNSTestAddresses && smartlist_contains_string_case(options->ServerDNSTestAddresses, address); } /** Called on the OR side when the eventdns library tells us the outcome of a * single DNS resolve: remember the answer, and tell all pending connections * about the result of the lookup if the lookup is now done. (address * is a NUL-terminated string containing the address to look up; * query_type is one of DNS_{IPv4_A,IPv6_AAAA,PTR}; dns_answer * is DNS_OK or one of DNS_ERR_*, addr is an IPv4 or IPv6 address if we * got one; hostname is a hostname fora PTR request if we got one, and * ttl is the time-to-live of this answer, in seconds.) */ static void dns_found_answer(const char *address, uint8_t query_type, int dns_answer, const tor_addr_t *addr, const char *hostname, uint32_t ttl) { cached_resolve_t search; cached_resolve_t *resolve; assert_cache_ok(); strlcpy(search.address, address, sizeof(search.address)); resolve = HT_FIND(cache_map, &cache_root, &search); if (!resolve) { int is_test_addr = is_test_address(address); if (!is_test_addr) log_info(LD_EXIT,"Resolved unasked address %s; ignoring.", escaped_safe_str(address)); return; } assert_resolve_ok(resolve); if (resolve->state != CACHE_STATE_PENDING) { /* XXXX Maybe update addr? or check addr for consistency? Or let * VALID replace FAILED? */ int is_test_addr = is_test_address(address); if (!is_test_addr) log_notice(LD_EXIT, "Resolved %s which was already resolved; ignoring", escaped_safe_str(address)); tor_assert(resolve->pending_connections == NULL); return; } cached_resolve_add_answer(resolve, query_type, dns_answer, addr, hostname, ttl); if (cached_resolve_have_all_answers(resolve)) { inform_pending_connections(resolve); make_pending_resolve_cached(resolve); } } /** Given a pending cached_resolve_t that we just finished resolving, * inform every connection that was waiting for the outcome of that * resolution. * * Do this by sending a RELAY_RESOLVED cell (if the pending stream had sent us * RELAY_RESOLVE cell), or by launching an exit connection (if the pending * stream had send us a RELAY_BEGIN cell). */ static void inform_pending_connections(cached_resolve_t *resolve) { pending_connection_t *pend; edge_connection_t *pendconn; int r; while (resolve->pending_connections) { char *hostname = NULL; pend = resolve->pending_connections; pendconn = pend->conn; /* don't pass complex things to the connection_mark_for_close macro */ assert_connection_ok(TO_CONN(pendconn),time(NULL)); if (pendconn->base_.marked_for_close) { /* prevent double-remove. */ pendconn->base_.state = EXIT_CONN_STATE_RESOLVEFAILED; resolve->pending_connections = pend->next; tor_free(pend); continue; } r = set_exitconn_info_from_resolve(pendconn, resolve, &hostname); if (r < 0) { /* prevent double-remove. */ pendconn->base_.state = EXIT_CONN_STATE_RESOLVEFAILED; if (pendconn->base_.purpose == EXIT_PURPOSE_CONNECT) { connection_edge_end(pendconn, END_STREAM_REASON_RESOLVEFAILED); /* This detach must happen after we send the end cell. */ circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn); } else { send_resolved_cell(pendconn, r == -1 ? RESOLVED_TYPE_ERROR : RESOLVED_TYPE_ERROR_TRANSIENT, NULL); /* This detach must happen after we send the resolved cell. */ circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn); } connection_free_(TO_CONN(pendconn)); } else { circuit_t *circ; if (pendconn->base_.purpose == EXIT_PURPOSE_CONNECT) { /* prevent double-remove. */ pend->conn->base_.state = EXIT_CONN_STATE_CONNECTING; circ = circuit_get_by_edge_conn(pend->conn); tor_assert(circ); tor_assert(!CIRCUIT_IS_ORIGIN(circ)); /* unlink pend->conn from resolving_streams, */ circuit_detach_stream(circ, pend->conn); /* and link it to n_streams */ pend->conn->next_stream = TO_OR_CIRCUIT(circ)->n_streams; pend->conn->on_circuit = circ; TO_OR_CIRCUIT(circ)->n_streams = pend->conn; connection_exit_connect(pend->conn); } else { /* prevent double-remove. This isn't really an accurate state, * but it does the right thing. */ pendconn->base_.state = EXIT_CONN_STATE_RESOLVEFAILED; if (pendconn->is_reverse_dns_lookup) send_resolved_hostname_cell(pendconn, hostname); else send_resolved_cell(pendconn, RESOLVED_TYPE_AUTO, resolve); circ = circuit_get_by_edge_conn(pendconn); tor_assert(circ); circuit_detach_stream(circ, pendconn); connection_free_(TO_CONN(pendconn)); } } resolve->pending_connections = pend->next; tor_free(pend); tor_free(hostname); } } /** Remove a pending cached_resolve_t from the hashtable, and add a * corresponding cached cached_resolve_t. * * This function is only necessary because of the perversity of our * cache timeout code; see inline comment for ideas on eliminating it. **/ static void make_pending_resolve_cached(cached_resolve_t *resolve) { cached_resolve_t *removed; resolve->state = CACHE_STATE_DONE; removed = HT_REMOVE(cache_map, &cache_root, resolve); if (removed != resolve) { log_err(LD_BUG, "The pending resolve we found wasn't removable from" " the cache. Tried to purge %s (%p); instead got %s (%p).", resolve->address, (void*)resolve, removed ? removed->address : "NULL", (void*)removed); } assert_resolve_ok(resolve); assert_cache_ok(); /* The resolve will eventually just hit the time-out in the expiry queue and * expire. See fd0bafb0dedc7e2 for a brief explanation of how this got that * way. XXXXX we could do better!*/ { cached_resolve_t *new_resolve = tor_memdup(resolve, sizeof(cached_resolve_t)); uint32_t ttl = UINT32_MAX; new_resolve->expire = 0; /* So that set_expiry won't croak. */ if (resolve->res_status_hostname == RES_STATUS_DONE_OK) new_resolve->result_ptr.hostname = tor_strdup(resolve->result_ptr.hostname); new_resolve->state = CACHE_STATE_CACHED; assert_resolve_ok(new_resolve); HT_INSERT(cache_map, &cache_root, new_resolve); if ((resolve->res_status_ipv4 == RES_STATUS_DONE_OK || resolve->res_status_ipv4 == RES_STATUS_DONE_ERR) && resolve->ttl_ipv4 < ttl) ttl = resolve->ttl_ipv4; if ((resolve->res_status_ipv6 == RES_STATUS_DONE_OK || resolve->res_status_ipv6 == RES_STATUS_DONE_ERR) && resolve->ttl_ipv6 < ttl) ttl = resolve->ttl_ipv6; if ((resolve->res_status_hostname == RES_STATUS_DONE_OK || resolve->res_status_hostname == RES_STATUS_DONE_ERR) && resolve->ttl_hostname < ttl) ttl = resolve->ttl_hostname; set_expiry(new_resolve, time(NULL) + clip_dns_ttl(ttl)); } assert_cache_ok(); } /** Eventdns helper: return true iff the eventdns result err is * a transient failure. */ static int evdns_err_is_transient(int err) { switch (err) { case DNS_ERR_SERVERFAILED: case DNS_ERR_TRUNCATED: case DNS_ERR_TIMEOUT: return 1; default: return 0; } } /** * Return number of configured nameservers in the_evdns_base. */ size_t number_of_configured_nameservers(void) { return evdns_base_count_nameservers(the_evdns_base); } #ifdef HAVE_EVDNS_BASE_GET_NAMESERVER_ADDR /** * Return address of configured nameserver in the_evdns_base * at index idx. */ tor_addr_t * configured_nameserver_address(const size_t idx) { struct sockaddr_storage sa; ev_socklen_t sa_len = sizeof(sa); if (evdns_base_get_nameserver_addr(the_evdns_base, (int)idx, (struct sockaddr *)&sa, sa_len) > 0) { tor_addr_t *tor_addr = tor_malloc(sizeof(tor_addr_t)); if (tor_addr_from_sockaddr(tor_addr, (const struct sockaddr *)&sa, NULL) == 0) { return tor_addr; } tor_free(tor_addr); } return NULL; } #endif /* defined(HAVE_EVDNS_BASE_GET_NAMESERVER_ADDR) */ /** Configure eventdns nameservers if force is true, or if the configuration * has changed since the last time we called this function, or if we failed on * our last attempt. On Unix, this reads from /etc/resolv.conf or * options->ServerDNSResolvConfFile; on Windows, this reads from * options->ServerDNSResolvConfFile or the registry. Return 0 on success or * -1 on failure. */ static int configure_nameservers(int force) { const or_options_t *options; const char *conf_fname; struct stat st; int r, flags; options = get_options(); conf_fname = options->ServerDNSResolvConfFile; #ifndef _WIN32 if (!conf_fname) conf_fname = "/etc/resolv.conf"; #endif flags = DNS_OPTIONS_ALL; if (!the_evdns_base) { if (!(the_evdns_base = evdns_base_new(tor_libevent_get_base(), 0))) { log_err(LD_BUG, "Couldn't create an evdns_base"); return -1; } } evdns_set_log_fn(evdns_log_cb); if (conf_fname) { log_debug(LD_FS, "stat()ing %s", conf_fname); int missing_resolv_conf = 0; int stat_res = stat(sandbox_intern_string(conf_fname), &st); if (stat_res) { log_warn(LD_EXIT, "Unable to stat resolver configuration in '%s': %s", conf_fname, strerror(errno)); missing_resolv_conf = 1; } else if (!force && resolv_conf_fname && !strcmp(conf_fname,resolv_conf_fname) && st.st_mtime == resolv_conf_mtime) { log_info(LD_EXIT, "No change to '%s'", conf_fname); return 0; } if (stat_res == 0 && st.st_size == 0) missing_resolv_conf = 1; if (nameservers_configured) { evdns_base_search_clear(the_evdns_base); evdns_base_clear_nameservers_and_suspend(the_evdns_base); } #if defined(DNS_OPTION_HOSTSFILE) && defined(USE_LIBSECCOMP) if (flags & DNS_OPTION_HOSTSFILE) { flags ^= DNS_OPTION_HOSTSFILE; log_debug(LD_FS, "Loading /etc/hosts"); evdns_base_load_hosts(the_evdns_base, sandbox_intern_string("/etc/hosts")); } #endif /* defined(DNS_OPTION_HOSTSFILE) && defined(USE_LIBSECCOMP) */ if (!missing_resolv_conf) { log_info(LD_EXIT, "Parsing resolver configuration in '%s'", conf_fname); if ((r = evdns_base_resolv_conf_parse(the_evdns_base, flags, sandbox_intern_string(conf_fname)))) { log_warn(LD_EXIT, "Unable to parse '%s', or no nameservers " "in '%s' (%d)", conf_fname, conf_fname, r); if (r != 6) // "r = 6" means "no DNS servers were in resolv.conf" - goto err; // in which case we expect libevent to add 127.0.0.1 as // fallback. } if (evdns_base_count_nameservers(the_evdns_base) == 0) { log_warn(LD_EXIT, "Unable to find any nameservers in '%s'.", conf_fname); } tor_free(resolv_conf_fname); resolv_conf_fname = tor_strdup(conf_fname); resolv_conf_mtime = st.st_mtime; } else { log_warn(LD_EXIT, "Could not read your DNS config from '%s' - " "please investigate your DNS configuration. " "This is possibly a problem. Meanwhile, falling" " back to local DNS at 127.0.0.1.", conf_fname); evdns_base_nameserver_ip_add(the_evdns_base, "127.0.0.1"); } if (nameservers_configured) evdns_base_resume(the_evdns_base); } #ifdef _WIN32 else { if (nameservers_configured) { evdns_base_search_clear(the_evdns_base); evdns_base_clear_nameservers_and_suspend(the_evdns_base); } if (evdns_base_config_windows_nameservers(the_evdns_base)) { log_warn(LD_EXIT,"Could not config nameservers."); goto err; } if (evdns_base_count_nameservers(the_evdns_base) == 0) { log_warn(LD_EXIT, "Unable to find any platform nameservers in " "your Windows configuration."); goto err; } if (nameservers_configured) evdns_base_resume(the_evdns_base); tor_free(resolv_conf_fname); resolv_conf_mtime = 0; } #endif /* defined(_WIN32) */ #define SET(k,v) evdns_base_set_option(the_evdns_base, (k), (v)) // If we only have one nameserver, it does not make sense to back off // from it for a timeout. Unfortunately, the value for max-timeouts is // currently clamped by libevent to 255, but it does not hurt to set // it higher in case libevent gets a patch for this. Higher-than- // default maximum of 3 with multiple nameservers to avoid spuriously // marking one down on bursts of timeouts resulting from scans/attacks // against non-responding authoritative DNS servers. if (evdns_base_count_nameservers(the_evdns_base) == 1) { SET("max-timeouts:", "1000000"); } else { SET("max-timeouts:", "10"); } // Elongate the queue of maximum inflight dns requests, so if a bunch // remain pending at the resolver (happens commonly with Unbound) we won't // stall every other DNS request. This potentially means some wasted // CPU as there's a walk over a linear queue involved, but this is a // much better tradeoff compared to just failing DNS requests because // of a full queue. SET("max-inflight:", "8192"); // Two retries at 5 and 10 seconds for bind9/named which relies on // clients to handle retries. Second retry for retried circuits with // extended 15 second timeout. Superfluous with local-system Unbound // instance--has its own elaborate retry scheme. SET("timeout:", "5"); SET("attempts:","3"); if (options->ServerDNSRandomizeCase) SET("randomize-case:", "1"); else SET("randomize-case:", "0"); #undef SET dns_servers_relaunch_checks(); nameservers_configured = 1; if (nameserver_config_failed) { nameserver_config_failed = 0; /* XXX the three calls to republish the descriptor might be producing * descriptors that are only cosmetically different, especially on * non-exit relays! -RD */ mark_my_descriptor_dirty("dns resolvers back"); } return 0; err: nameservers_configured = 0; if (! nameserver_config_failed) { nameserver_config_failed = 1; mark_my_descriptor_dirty("dns resolvers failed"); } return -1; } /** For eventdns: Called when we get an answer for a request we launched. * See eventdns.h for arguments; 'arg' holds the address we tried to resolve. */ static void evdns_callback(int result, char type, int count, int ttl, void *addresses, void *arg) { char *arg_ = arg; uint8_t orig_query_type = arg_[0]; char *string_address = arg_ + 1; tor_addr_t addr; const char *hostname = NULL; int was_wildcarded = 0; tor_addr_make_unspec(&addr); /* Keep track of whether IPv6 is working */ if (type == DNS_IPv6_AAAA) { if (result == DNS_ERR_TIMEOUT) { ++n_ipv6_timeouts; } if (n_ipv6_timeouts > 10 && n_ipv6_timeouts > n_ipv6_requests_made / 2) { if (! dns_is_broken_for_ipv6) { log_notice(LD_EXIT, "More than half of our IPv6 requests seem to " "have timed out. I'm going to assume I can't get AAAA " "responses."); dns_is_broken_for_ipv6 = 1; } } } if (result == DNS_ERR_NONE) { if (type == DNS_IPv4_A && count) { char answer_buf[INET_NTOA_BUF_LEN+1]; char *escaped_address; uint32_t *addrs = addresses; tor_addr_from_ipv4n(&addr, addrs[0]); tor_addr_to_str(answer_buf, &addr, sizeof(answer_buf), 0); escaped_address = esc_for_log(string_address); if (answer_is_wildcarded(answer_buf)) { log_debug(LD_EXIT, "eventdns said that %s resolves to ISP-hijacked " "address %s; treating as a failure.", safe_str(escaped_address), escaped_safe_str(answer_buf)); was_wildcarded = 1; tor_addr_make_unspec(&addr); result = DNS_ERR_NOTEXIST; } else { log_debug(LD_EXIT, "eventdns said that %s resolves to %s", safe_str(escaped_address), escaped_safe_str(answer_buf)); } tor_free(escaped_address); } else if (type == DNS_IPv6_AAAA && count) { char answer_buf[TOR_ADDR_BUF_LEN]; char *escaped_address; const char *ip_str; struct in6_addr *addrs = addresses; tor_addr_from_in6(&addr, &addrs[0]); ip_str = tor_inet_ntop(AF_INET6, &addrs[0], answer_buf, sizeof(answer_buf)); escaped_address = esc_for_log(string_address); if (BUG(ip_str == NULL)) { log_warn(LD_EXIT, "tor_inet_ntop() failed!"); result = DNS_ERR_NOTEXIST; } else if (answer_is_wildcarded(answer_buf)) { log_debug(LD_EXIT, "eventdns said that %s resolves to ISP-hijacked " "address %s; treating as a failure.", safe_str(escaped_address), escaped_safe_str(answer_buf)); was_wildcarded = 1; tor_addr_make_unspec(&addr); result = DNS_ERR_NOTEXIST; } else { log_debug(LD_EXIT, "eventdns said that %s resolves to %s", safe_str(escaped_address), escaped_safe_str(answer_buf)); } tor_free(escaped_address); } else if (type == DNS_PTR && count) { char *escaped_address; hostname = ((char**)addresses)[0]; escaped_address = esc_for_log(string_address); log_debug(LD_EXIT, "eventdns said that %s resolves to %s", safe_str(escaped_address), escaped_safe_str(hostname)); tor_free(escaped_address); } else if (count) { log_info(LD_EXIT, "eventdns returned only unrecognized answer types " " for %s.", escaped_safe_str(string_address)); } else { log_info(LD_EXIT, "eventdns returned no addresses or error for %s.", escaped_safe_str(string_address)); } } if (was_wildcarded) { if (is_test_address(string_address)) { /* Ick. We're getting redirected on known-good addresses. Our DNS * server must really hate us. */ add_wildcarded_test_address(string_address); } } if (orig_query_type && type && orig_query_type != type) { log_warn(LD_BUG, "Weird; orig_query_type == %d but type == %d", (int)orig_query_type, (int)type); } if (result != DNS_ERR_SHUTDOWN) dns_found_answer(string_address, orig_query_type, result, &addr, hostname, ttl); tor_free(arg_); } /** Start a single DNS resolve for address (if query_type is * DNS_IPv4_A or DNS_IPv6_AAAA) ptr_address (if query_type is * DNS_PTR). Return 0 if we launched the request, -1 otherwise. */ static int launch_one_resolve(const char *address, uint8_t query_type, const tor_addr_t *ptr_address) { const int options = get_options()->ServerDNSSearchDomains ? 0 : DNS_QUERY_NO_SEARCH; const size_t addr_len = strlen(address); struct evdns_request *req = 0; char *addr = tor_malloc(addr_len + 2); addr[0] = (char) query_type; memcpy(addr+1, address, addr_len + 1); switch (query_type) { case DNS_IPv4_A: req = evdns_base_resolve_ipv4(the_evdns_base, address, options, evdns_callback, addr); break; case DNS_IPv6_AAAA: req = evdns_base_resolve_ipv6(the_evdns_base, address, options, evdns_callback, addr); ++n_ipv6_requests_made; break; case DNS_PTR: if (tor_addr_family(ptr_address) == AF_INET) req = evdns_base_resolve_reverse(the_evdns_base, tor_addr_to_in(ptr_address), DNS_QUERY_NO_SEARCH, evdns_callback, addr); else if (tor_addr_family(ptr_address) == AF_INET6) req = evdns_base_resolve_reverse_ipv6(the_evdns_base, tor_addr_to_in6(ptr_address), DNS_QUERY_NO_SEARCH, evdns_callback, addr); else log_warn(LD_BUG, "Called with PTR query and unexpected address family"); break; default: log_warn(LD_BUG, "Called with unexpectd query type %d", (int)query_type); break; } if (req) { return 0; } else { tor_free(addr); return -1; } } /** For eventdns: start resolving as necessary to find the target for * exitconn. Returns -1 on error, -2 on transient error, * 0 on "resolve launched." */ MOCK_IMPL(STATIC int, launch_resolve,(cached_resolve_t *resolve)) { tor_addr_t a; int r; if (net_is_disabled()) return -1; /* What? Nameservers not configured? Sounds like a bug. */ if (!nameservers_configured) { log_warn(LD_EXIT, "(Harmless.) Nameservers not configured, but resolve " "launched. Configuring."); if (configure_nameservers(1) < 0) { return -1; } } r = tor_addr_parse_PTR_name( &a, resolve->address, AF_UNSPEC, 0); tor_assert(the_evdns_base); if (r == 0) { log_info(LD_EXIT, "Launching eventdns request for %s", escaped_safe_str(resolve->address)); resolve->res_status_ipv4 = RES_STATUS_INFLIGHT; if (get_options()->IPv6Exit) resolve->res_status_ipv6 = RES_STATUS_INFLIGHT; if (launch_one_resolve(resolve->address, DNS_IPv4_A, NULL) < 0) { resolve->res_status_ipv4 = 0; r = -1; } if (r==0 && get_options()->IPv6Exit) { /* We ask for an IPv6 address for *everything*. */ if (launch_one_resolve(resolve->address, DNS_IPv6_AAAA, NULL) < 0) { resolve->res_status_ipv6 = 0; r = -1; } } } else if (r == 1) { r = 0; log_info(LD_EXIT, "Launching eventdns reverse request for %s", escaped_safe_str(resolve->address)); resolve->res_status_hostname = RES_STATUS_INFLIGHT; if (launch_one_resolve(resolve->address, DNS_PTR, &a) < 0) { resolve->res_status_hostname = 0; r = -1; } } else if (r == -1) { log_warn(LD_BUG, "Somehow a malformed in-addr.arpa address reached here."); } if (r < 0) { log_fn(LOG_PROTOCOL_WARN, LD_EXIT, "eventdns rejected address %s.", escaped_safe_str(resolve->address)); } return r; } /** How many requests for bogus addresses have we launched so far? */ static int n_wildcard_requests = 0; /** Map from dotted-quad IP address in response to an int holding how many * times we've seen it for a randomly generated (hopefully bogus) address. It * would be easier to use definitely-invalid addresses (as specified by * RFC2606), but see comment in dns_launch_wildcard_checks(). */ static strmap_t *dns_wildcard_response_count = NULL; /** If present, a list of dotted-quad IP addresses that we are pretty sure our * nameserver wants to return in response to requests for nonexistent domains. */ static smartlist_t *dns_wildcard_list = NULL; /** True iff we've logged about a single address getting wildcarded. * Subsequent warnings will be less severe. */ static int dns_wildcard_one_notice_given = 0; /** True iff we've warned that our DNS server is wildcarding too many failures. */ static int dns_wildcard_notice_given = 0; /** List of supposedly good addresses that are getting wildcarded to the * same addresses as nonexistent addresses. */ static smartlist_t *dns_wildcarded_test_address_list = NULL; /** True iff we've warned about a test address getting wildcarded */ static int dns_wildcarded_test_address_notice_given = 0; /** True iff all addresses seem to be getting wildcarded. */ static int dns_is_completely_invalid = 0; /** Called when we see id (a dotted quad or IPv6 address) in response * to a request for a hopefully bogus address. */ static void wildcard_increment_answer(const char *id) { int *ip; if (!dns_wildcard_response_count) dns_wildcard_response_count = strmap_new(); ip = strmap_get(dns_wildcard_response_count, id); // may be null (0) if (!ip) { ip = tor_malloc_zero(sizeof(int)); strmap_set(dns_wildcard_response_count, id, ip); } ++*ip; if (*ip > 5 && n_wildcard_requests > 10) { if (!dns_wildcard_list) dns_wildcard_list = smartlist_new(); if (!smartlist_contains_string(dns_wildcard_list, id)) { tor_log(dns_wildcard_notice_given ? LOG_INFO : LOG_NOTICE, LD_EXIT, "Your DNS provider has given \"%s\" as an answer for %d different " "invalid addresses. Apparently they are hijacking DNS failures. " "I'll try to correct for this by treating future occurrences of " "\"%s\" as 'not found'.", id, *ip, id); smartlist_add_strdup(dns_wildcard_list, id); } if (!dns_wildcard_notice_given) control_event_server_status(LOG_NOTICE, "DNS_HIJACKED"); dns_wildcard_notice_given = 1; } } /** Note that a single test address (one believed to be good) seems to be * getting redirected to the same IP as failures are. */ static void add_wildcarded_test_address(const char *address) { int n, n_test_addrs; if (!dns_wildcarded_test_address_list) dns_wildcarded_test_address_list = smartlist_new(); if (smartlist_contains_string_case(dns_wildcarded_test_address_list, address)) return; n_test_addrs = get_options()->ServerDNSTestAddresses ? smartlist_len(get_options()->ServerDNSTestAddresses) : 0; smartlist_add_strdup(dns_wildcarded_test_address_list, address); n = smartlist_len(dns_wildcarded_test_address_list); if (n > n_test_addrs/2) { tor_log(dns_wildcarded_test_address_notice_given ? LOG_INFO : LOG_NOTICE, LD_EXIT, "Your DNS provider tried to redirect \"%s\" to a junk " "address. It has done this with %d test addresses so far. I'm " "going to stop being an exit node for now, since our DNS seems so " "broken.", address, n); if (!dns_is_completely_invalid) { dns_is_completely_invalid = 1; mark_my_descriptor_dirty("dns hijacking confirmed"); } if (!dns_wildcarded_test_address_notice_given) control_event_server_status(LOG_WARN, "DNS_USELESS"); dns_wildcarded_test_address_notice_given = 1; } } /** Callback function when we get an answer (possibly failing) for a request * for a (hopefully) nonexistent domain. */ static void evdns_wildcard_check_callback(int result, char type, int count, int ttl, void *addresses, void *arg) { (void)ttl; const char *ip_str; ++n_wildcard_requests; if (result == DNS_ERR_NONE && count) { char *string_address = arg; int i; if (type == DNS_IPv4_A) { const uint32_t *addrs = addresses; for (i = 0; i < count; ++i) { char answer_buf[INET_NTOA_BUF_LEN+1]; struct in_addr in; int ntoa_res; in.s_addr = addrs[i]; ntoa_res = tor_inet_ntoa(&in, answer_buf, sizeof(answer_buf)); tor_assert_nonfatal(ntoa_res >= 0); if (ntoa_res > 0) wildcard_increment_answer(answer_buf); } } else if (type == DNS_IPv6_AAAA) { const struct in6_addr *addrs = addresses; for (i = 0; i < count; ++i) { char answer_buf[TOR_ADDR_BUF_LEN+1]; ip_str = tor_inet_ntop(AF_INET6, &addrs[i], answer_buf, sizeof(answer_buf)); tor_assert_nonfatal(ip_str); if (ip_str) wildcard_increment_answer(answer_buf); } } tor_log(dns_wildcard_one_notice_given ? LOG_INFO : LOG_NOTICE, LD_EXIT, "Your DNS provider gave an answer for \"%s\", which " "is not supposed to exist. Apparently they are hijacking " "DNS failures. Trying to correct for this. We've noticed %d " "possibly bad address%s so far.", string_address, strmap_size(dns_wildcard_response_count), (strmap_size(dns_wildcard_response_count) == 1) ? "" : "es"); dns_wildcard_one_notice_given = 1; } tor_free(arg); } /** Launch a single request for a nonexistent hostname consisting of between * min_len and max_len random (plausible) characters followed by * suffix */ static void launch_wildcard_check(int min_len, int max_len, int is_ipv6, const char *suffix) { char *addr; struct evdns_request *req; addr = crypto_random_hostname(min_len, max_len, "", suffix); log_info(LD_EXIT, "Testing whether our DNS server is hijacking nonexistent " "domains with request for bogus hostname \"%s\"", addr); tor_assert(the_evdns_base); if (is_ipv6) req = evdns_base_resolve_ipv6( the_evdns_base, /* This "addr" tells us which address to resolve */ addr, DNS_QUERY_NO_SEARCH, evdns_wildcard_check_callback, /* This "addr" is an argument to the callback*/ addr); else req = evdns_base_resolve_ipv4( the_evdns_base, /* This "addr" tells us which address to resolve */ addr, DNS_QUERY_NO_SEARCH, evdns_wildcard_check_callback, /* This "addr" is an argument to the callback*/ addr); if (!req) { /* There is no evdns request in progress; stop addr from getting leaked */ tor_free(addr); } } /** Launch attempts to resolve a bunch of known-good addresses (configured in * ServerDNSTestAddresses). [Callback for a libevent timer] */ static void launch_test_addresses(evutil_socket_t fd, short event, void *args) { const or_options_t *options = get_options(); (void)fd; (void)event; (void)args; if (net_is_disabled()) return; log_info(LD_EXIT, "Launching checks to see whether our nameservers like to " "hijack *everything*."); /* This situation is worse than the failure-hijacking situation. When this * happens, we're no good for DNS requests at all, and we shouldn't really * be an exit server.*/ if (options->ServerDNSTestAddresses) { tor_assert(the_evdns_base); SMARTLIST_FOREACH_BEGIN(options->ServerDNSTestAddresses, const char *, address) { if (launch_one_resolve(address, DNS_IPv4_A, NULL) < 0) { log_info(LD_EXIT, "eventdns rejected test address %s", escaped_safe_str(address)); } if (launch_one_resolve(address, DNS_IPv6_AAAA, NULL) < 0) { log_info(LD_EXIT, "eventdns rejected test address %s", escaped_safe_str(address)); } } SMARTLIST_FOREACH_END(address); } } #define N_WILDCARD_CHECKS 2 /** Launch DNS requests for a few nonexistent hostnames and a few well-known * hostnames, and see if we can catch our nameserver trying to hijack them and * map them to a stupid "I couldn't find ggoogle.com but maybe you'd like to * buy these lovely encyclopedias" page. */ static void dns_launch_wildcard_checks(void) { int i, ipv6; log_info(LD_EXIT, "Launching checks to see whether our nameservers like " "to hijack DNS failures."); for (ipv6 = 0; ipv6 <= 1; ++ipv6) { for (i = 0; i < N_WILDCARD_CHECKS; ++i) { /* RFC2606 reserves these. Sadly, some DNS hijackers, in a silly * attempt to 'comply' with rfc2606, refrain from giving A records for * these. This is the standards-compliance equivalent of making sure * that your crackhouse's elevator inspection certificate is up to date. */ launch_wildcard_check(2, 16, ipv6, ".invalid"); launch_wildcard_check(2, 16, ipv6, ".test"); /* These will break specs if there are ever any number of * 8+-character top-level domains. */ launch_wildcard_check(8, 16, ipv6, ""); /* Try some random .com/org/net domains. This will work fine so long as * not too many resolve to the same place. */ launch_wildcard_check(8, 16, ipv6, ".com"); launch_wildcard_check(8, 16, ipv6, ".org"); launch_wildcard_check(8, 16, ipv6, ".net"); } } } /** If appropriate, start testing whether our DNS servers tend to lie to * us. */ void dns_launch_correctness_checks(void) { static struct event *launch_event = NULL; struct timeval timeout; if (!get_options()->ServerDNSDetectHijacking) return; dns_launch_wildcard_checks(); /* Wait a while before launching requests for test addresses, so we can * get the results from checking for wildcarding. */ if (!launch_event) launch_event = tor_evtimer_new(tor_libevent_get_base(), launch_test_addresses, NULL); timeout.tv_sec = 30; timeout.tv_usec = 0; if (evtimer_add(launch_event, &timeout) < 0) { log_warn(LD_BUG, "Couldn't add timer for checking for dns hijacking"); } } /** Return true iff our DNS servers lie to us too much to be trusted. */ int dns_seems_to_be_broken(void) { return dns_is_completely_invalid; } /** Return true iff we think that IPv6 hostname lookup is broken */ int dns_seems_to_be_broken_for_ipv6(void) { return dns_is_broken_for_ipv6; } /** Forget what we've previously learned about our DNS servers' correctness. */ void dns_reset_correctness_checks(void) { strmap_free(dns_wildcard_response_count, tor_free_); dns_wildcard_response_count = NULL; n_wildcard_requests = 0; n_ipv6_requests_made = n_ipv6_timeouts = 0; if (dns_wildcard_list) { SMARTLIST_FOREACH(dns_wildcard_list, char *, cp, tor_free(cp)); smartlist_clear(dns_wildcard_list); } if (dns_wildcarded_test_address_list) { SMARTLIST_FOREACH(dns_wildcarded_test_address_list, char *, cp, tor_free(cp)); smartlist_clear(dns_wildcarded_test_address_list); } dns_wildcard_one_notice_given = dns_wildcard_notice_given = dns_wildcarded_test_address_notice_given = dns_is_completely_invalid = dns_is_broken_for_ipv6 = 0; } /** Return true iff we have noticed that the dotted-quad ip has been * returned in response to requests for nonexistent hostnames. */ static int answer_is_wildcarded(const char *ip) { return dns_wildcard_list && smartlist_contains_string(dns_wildcard_list, ip); } /** Exit with an assertion if resolve is corrupt. */ static void assert_resolve_ok(cached_resolve_t *resolve) { tor_assert(resolve); tor_assert(resolve->magic == CACHED_RESOLVE_MAGIC); tor_assert(strlen(resolve->address) < MAX_ADDRESSLEN); tor_assert(tor_strisnonupper(resolve->address)); if (resolve->state != CACHE_STATE_PENDING) { tor_assert(!resolve->pending_connections); } if (resolve->state == CACHE_STATE_PENDING || resolve->state == CACHE_STATE_DONE) { #if 0 tor_assert(!resolve->ttl); if (resolve->is_reverse) tor_assert(!resolve->hostname); else tor_assert(!resolve->result_ipv4.addr_ipv4); #endif /* 0 */ /*XXXXX ADD MORE */ } } /** Return the number of DNS cache entries as an int */ static int dns_cache_entry_count(void) { return HT_SIZE(&cache_root); } /* Return the total size in bytes of the DNS cache. */ size_t dns_cache_total_allocation(void) { return sizeof(struct cached_resolve_t) * dns_cache_entry_count() + HT_MEM_USAGE(&cache_root); } /** Log memory information about our internal DNS cache at level 'severity'. */ void dump_dns_mem_usage(int severity) { /* This should never be larger than INT_MAX. */ int hash_count = dns_cache_entry_count(); size_t hash_mem = dns_cache_total_allocation(); /* Print out the count and estimated size of our &cache_root. It undercounts hostnames in cached reverse resolves. */ tor_log(severity, LD_MM, "Our DNS cache has %d entries.", hash_count); tor_log(severity, LD_MM, "Our DNS cache size is approximately %u bytes.", (unsigned)hash_mem); } /* Do a round of OOM cleanup on all DNS entries. Return the amount of removed * bytes. It is possible that the returned value is lower than min_remove_bytes * if the caches get emptied out so the caller should be aware of this. */ size_t dns_cache_handle_oom(time_t now, size_t min_remove_bytes) { time_t time_inc = 0; size_t total_bytes_removed = 0; size_t current_size = dns_cache_total_allocation(); do { /* If no DNS entries left, break loop. */ if (!dns_cache_entry_count()) break; /* Get cutoff interval and remove entries. */ time_t cutoff = now + time_inc; purge_expired_resolves(cutoff); /* Update amount of bytes removed and array size. */ size_t bytes_removed = current_size - dns_cache_total_allocation(); current_size -= bytes_removed; total_bytes_removed += bytes_removed; /* Increase time_inc by a reasonable fraction. */ time_inc += (MAX_DNS_TTL / 4); } while (total_bytes_removed < min_remove_bytes); return total_bytes_removed; } #ifdef DEBUG_DNS_CACHE /** Exit with an assertion if the DNS cache is corrupt. */ static void assert_cache_ok_(void) { cached_resolve_t **resolve; int bad_rep = HT_REP_IS_BAD_(cache_map, &cache_root); if (bad_rep) { log_err(LD_BUG, "Bad rep type %d on dns cache hash table", bad_rep); tor_assert(!bad_rep); } HT_FOREACH(resolve, cache_map, &cache_root) { assert_resolve_ok(*resolve); tor_assert((*resolve)->state != CACHE_STATE_DONE); } if (!cached_resolve_pqueue) return; smartlist_pqueue_assert_ok(cached_resolve_pqueue, compare_cached_resolves_by_expiry_, offsetof(cached_resolve_t, minheap_idx)); SMARTLIST_FOREACH(cached_resolve_pqueue, cached_resolve_t *, res, { if (res->state == CACHE_STATE_DONE) { cached_resolve_t *found = HT_FIND(cache_map, &cache_root, res); tor_assert(!found || found != res); } else { cached_resolve_t *found = HT_FIND(cache_map, &cache_root, res); tor_assert(found); } }); } #endif /* defined(DEBUG_DNS_CACHE) */ cached_resolve_t * dns_get_cache_entry(cached_resolve_t *query) { return HT_FIND(cache_map, &cache_root, query); } void dns_insert_cache_entry(cached_resolve_t *new_entry) { HT_INSERT(cache_map, &cache_root, new_entry); }