/* Copyright (c) 2003-2004, Roger Dingledine. * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson. * Copyright (c) 2007-2009, 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.) **/ #include "or.h" #include "ht.h" #ifdef HAVE_EVENT2_DNS_H #include #include #else #include #include "eventdns.h" #ifndef HAVE_EVDNS_SET_DEFAULT_OUTGOING_BIND_ADDRESS #define HAVE_EVDNS_SET_DEFAULT_OUTGOING_BIND_ADDRESS #endif #endif #ifndef HAVE_EVENT2_DNS_H struct evdns_base; struct evdns_request; #define evdns_base_new(x,y) tor_malloc(1) #define evdns_base_clear_nameservers_and_suspend(base) \ evdns_clear_nameservers_and_suspend() #define evdns_base_search_clear(base) evdns_search_clear() #define evdns_base_set_default_outgoing_bind_address(base, a, len) \ evdns_set_default_outgoing_bind_address((a),(len)) #define evdns_base_resolv_conf_parse(base, options, fname) \ evdns_resolv_conf_parse((options), (fname)) #define evdns_base_count_nameservers(base) \ evdns_count_nameservers() #define evdns_base_resume(base) \ evdns_resume() #define evdns_base_config_windows_nameservers(base) \ evdns_config_windows_nameservers() #define evdns_base_set_option(base, opt, val, flags) \ evdns_set_option((opt),(val),(flags)) #define evdns_base_resolve_ipv4(base, addr, options, cb, ptr) \ ((evdns_resolve_ipv4(addr, options, cb, ptr)<0) ? NULL : ((void*)1)) #define evdns_base_resolve_reverse(base, addr, options, cb, ptr) \ ((evdns_resolve_reverse(addr, options, cb, ptr)<0) ? NULL : ((void*)1)) #define evdns_base_resolve_reverse_ipv6(base, addr, options, cb, ptr) \ ((evdns_resolve_reverse_ipv6(addr, options, cb, ptr)<0) ? NULL : ((void*)1)) #endif /** Longest hostname we're willing to resolve. */ #define MAX_ADDRESSLEN 256 /** How long will we wait for an answer from the resolver before we decide * that the resolver is wedged? */ #define RESOLVE_MAX_TIMEOUT 300 /** Possible outcomes from hostname lookup: permanent failure, * transient (retryable) failure, and success. */ #define DNS_RESOLVE_FAILED_TRANSIENT 1 #define DNS_RESOLVE_FAILED_PERMANENT 2 #define DNS_RESOLVE_SUCCEEDED 3 /** 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; /** Linked list of connections waiting for a DNS answer. */ typedef struct pending_connection_t { edge_connection_t *conn; struct pending_connection_t *next; } pending_connection_t; /** Value of 'magic' field for cached_resolve_t. Used to try to catch bad * pointers and memory stomping. */ #define CACHED_RESOLVE_MAGIC 0x1234F00D /* Possible states for a cached resolve_t */ /** We are waiting for the resolver system to tell us an answer here. * When we get one, or when we time out, the state of this cached_resolve_t * will become "DONE" and we'll possibly add a CACHED_VALID or a CACHED_FAILED * entry. This cached_resolve_t will be in the hash table so that we will * know not to launch more requests for this addr, but rather to add more * connections to the pending list for the addr. */ #define CACHE_STATE_PENDING 0 /** This used to be a pending cached_resolve_t, and we got an answer for it. * Now we're waiting for this cached_resolve_t to expire. This should * have no pending connections, and should not appear in the hash table. */ #define CACHE_STATE_DONE 1 /** We are caching an answer for this address. This should have no pending * connections, and should appear in the hash table. */ #define CACHE_STATE_CACHED_VALID 2 /** We are caching a failure for this address. This should have no pending * connections, and should appear in the hash table */ #define CACHE_STATE_CACHED_FAILED 3 /** A DNS request: possibly completed, possibly pending; cached_resolve * structs are stored at the OR side in a hash table, and as a linked * list from oldest to newest. */ typedef struct cached_resolve_t { HT_ENTRY(cached_resolve_t) node; uint32_t magic; char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */ union { struct { struct in6_addr addr6; /**< IPv6 addr for address. */ uint32_t addr; /**< IPv4 addr for address. */ } a; char *hostname; /**< Hostname for address (if a reverse lookup) */ } result; uint8_t state; /**< Is this cached entry pending/done/valid/failed? */ uint8_t is_reverse; /**< Is this a reverse (addr-to-hostname) lookup? */ time_t expire; /**< Remove items from cache after this time. */ uint32_t ttl; /**< What TTL did the nameserver tell us? */ /** Connections that want to know when we get an answer for this resolve. */ pending_connection_t *pending_connections; /** Position of this element in the heap*/ int minheap_idx; } cached_resolve_t; static void purge_expired_resolves(time_t now); static void dns_found_answer(const char *address, uint8_t is_reverse, uint32_t addr, const char *hostname, char outcome, uint32_t ttl); static void send_resolved_cell(edge_connection_t *conn, uint8_t answer_type); static int launch_resolve(edge_connection_t *exitconn); 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 dns_resolve_impl(edge_connection_t *exitconn, int is_resolve, or_circuit_t *oncirc, char **resolved_to_hostname); #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 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; /** 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 ht_string_hash(a->address); } HT_PROTOTYPE(cache_map, cached_resolve_t, node, cached_resolve_hash, cached_resolves_eq) HT_GENERATE(cache_map, cached_resolve_t, node, cached_resolve_hash, cached_resolves_eq, 0.6, malloc, realloc, 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(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 *err = strchr(cp, ':')+2; tor_assert(err); /* 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; } 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) { or_options_t *options = get_options(); if (! server_mode(options)) { 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: Given a TTL from a DNS response, determine what TTL to give the * OP that asked us to resolve it. */ uint32_t dns_clip_ttl(uint32_t ttl) { if (ttl < MIN_DNS_TTL) return MIN_DNS_TTL; else if (ttl > MAX_DNS_TTL) return MAX_DNS_TTL; else return ttl; } /** Helper: Given a TTL from a DNS response, determine how long to hold it in * our cache. */ static uint32_t dns_get_expiry_ttl(uint32_t ttl) { if (ttl < MIN_DNS_TTL) return MIN_DNS_TTL; else if (ttl > MAX_DNS_ENTRY_AGE) return MAX_DNS_ENTRY_AGE; else return ttl; } /** 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->is_reverse) tor_free(r->result.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; /** 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_create(); resolve->expire = expires; smartlist_pqueue_add(cached_resolve_pqueue, _compare_cached_resolves_by_expiry, STRUCT_OFFSET(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, STRUCT_OFFSET(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_VALID || resolve->state == CACHE_STATE_CACHED_FAILED) { 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!"); tor_fragile_assert(); 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(pend->conn->_base.s == -1); pendconn = pend->conn; 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_VALID || resolve->state == CACHE_STATE_CACHED_FAILED || 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*)remove); } 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->is_reverse) tor_free(resolve->result.hostname); resolve->magic = 0xF0BBF0BB; tor_free(resolve); } assert_cache_ok(); } /** Send a response to the RESOLVE request of a connection. * answer_type must be one of * RESOLVED_TYPE_(IPV4|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. */ static void send_resolved_cell(edge_connection_t *conn, uint8_t answer_type) { char buf[RELAY_PAYLOAD_SIZE]; size_t buflen; uint32_t ttl; buf[0] = answer_type; ttl = dns_clip_ttl(conn->address_ttl); switch (answer_type) { case RESOLVED_TYPE_IPV4: buf[1] = 4; set_uint32(buf+2, tor_addr_to_ipv4n(&conn->_base.addr)); set_uint32(buf+6, htonl(ttl)); buflen = 10; break; /*XXXX IP6 need ipv6 implementation */ case RESOLVED_TYPE_ERROR_TRANSIENT: case RESOLVED_TYPE_ERROR: { const char *errmsg = "Error resolving hostname"; size_t msglen = strlen(errmsg); 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. */ static void send_resolved_hostname_cell(edge_connection_t *conn, const char *hostname) { char buf[RELAY_PAYLOAD_SIZE]; size_t buflen; uint32_t ttl; size_t namelen = strlen(hostname); tor_assert(hostname); tor_assert(namelen < 256); ttl = dns_clip_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; char *hostname = NULL; is_resolve = exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE; r = dns_resolve_impl(exitconn, is_resolve, oncirc, &hostname); 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_IPV4); 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); } exitconn->on_circuit = NULL; dns_cancel_pending_resolve(exitconn->_base.address); if (!exitconn->_base.marked_for_close) { connection_free(TO_CONN(exitconn)); // XXX ... and we just leak exitconn otherwise? -RD // If it's marked for close, it's on closeable_connection_lst in // main.c. If it's on the closeable list, it will get freed from // main.c. -NM // " If that's true, there are other bugs around, where we // don't check if it's marked, and will end up double-freeing." // On the other hand, I don't know of any actual bugs here, so this // shouldn't be holding up the rc. -RD } 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. */ static int dns_resolve_impl(edge_connection_t *exitconn, int is_resolve, or_circuit_t *oncirc, char **hostname_out) { cached_resolve_t *resolve; cached_resolve_t search; pending_connection_t *pending_connection; routerinfo_t *me; tor_addr_t addr; time_t now = time(NULL); uint8_t is_reverse = 0; int r; assert_connection_ok(TO_CONN(exitconn), 0); tor_assert(exitconn->_base.s == -1); assert_cache_ok(); tor_assert(oncirc); /* first check if exitconn->_base.address is an IP. If so, we already * know the answer. */ if (tor_addr_from_str(&addr, exitconn->_base.address) >= 0) { if (tor_addr_family(&addr) == AF_INET) { tor_addr_assign(&exitconn->_base.addr, &addr); exitconn->address_ttl = DEFAULT_DNS_TTL; return 1; } else { /* XXXX IPv6 */ return -1; } } /* If we're a non-exit, don't even do DNS lookups. */ if (!(me = router_get_my_routerinfo()) || policy_is_reject_star(me->exit_policy)) { return -1; } if (address_is_invalid_destination(exitconn->_base.address, 0)) { 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_reverse_lookup_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); } /* 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; log_debug(LD_EXIT,"Connection (fd %d) waiting for pending DNS " "resolve of %s", exitconn->_base.s, escaped_safe_str(exitconn->_base.address)); return 0; case CACHE_STATE_CACHED_VALID: log_debug(LD_EXIT,"Connection (fd %d) found cached answer for %s", exitconn->_base.s, escaped_safe_str(resolve->address)); exitconn->address_ttl = resolve->ttl; if (resolve->is_reverse) { tor_assert(is_resolve); *hostname_out = tor_strdup(resolve->result.hostname); } else { tor_addr_from_ipv4h(&exitconn->_base.addr, resolve->result.a.addr); } return 1; case CACHE_STATE_CACHED_FAILED: log_debug(LD_EXIT,"Connection (fd %d) found cached error for %s", exitconn->_base.s, escaped_safe_str(exitconn->_base.address)); return -1; 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; resolve->is_reverse = is_reverse; 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; /* 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(exitconn); } /** 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 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 } /** Log an error and abort if any connection waiting for a DNS resolve is * corrupted. */ void assert_all_pending_dns_resolves_ok(void) { pending_connection_t *pend; cached_resolve_t **resolve; HT_FOREACH(resolve, cache_map, &cache_root) { for (pend = (*resolve)->pending_connections; pend; pend = pend->next) { assert_connection_ok(TO_CONN(pend->conn), 0); tor_assert(pend->conn->_base.s == -1); tor_assert(!connection_in_array(TO_CONN(pend->conn))); } } } /** 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 %d) 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 %d) no longer waiting for resolve of %s", conn->_base.s, escaped_safe_str(conn->_base.address)); return; /* more are pending */ } } tor_assert(0); /* not reachable unless onlyconn not in pending list */ } } /** 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. */ 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(pendconn->_base.s == -1); 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; } /** Helper: adds an entry to the DNS cache mapping address to the ipv4 * address addr (if is_reverse is 0) or the hostname hostname (if * is_reverse is 1). ttl is a cache ttl; outcome is one of * DNS_RESOLVE_{FAILED_TRANSIENT|FAILED_PERMANENT|SUCCEEDED}. **/ static void add_answer_to_cache(const char *address, uint8_t is_reverse, uint32_t addr, const char *hostname, char outcome, uint32_t ttl) { cached_resolve_t *resolve; if (outcome == DNS_RESOLVE_FAILED_TRANSIENT) return; //log_notice(LD_EXIT, "Adding to cache: %s -> %s (%lx, %s), %d", // address, is_reverse?"(reverse)":"", (unsigned long)addr, // hostname?hostname:"NULL",(int)outcome); resolve = tor_malloc_zero(sizeof(cached_resolve_t)); resolve->magic = CACHED_RESOLVE_MAGIC; resolve->state = (outcome == DNS_RESOLVE_SUCCEEDED) ? CACHE_STATE_CACHED_VALID : CACHE_STATE_CACHED_FAILED; strlcpy(resolve->address, address, sizeof(resolve->address)); resolve->is_reverse = is_reverse; if (is_reverse) { if (outcome == DNS_RESOLVE_SUCCEEDED) { tor_assert(hostname); resolve->result.hostname = tor_strdup(hostname); } else { tor_assert(! hostname); resolve->result.hostname = NULL; } } else { tor_assert(!hostname); resolve->result.a.addr = addr; } resolve->ttl = ttl; assert_resolve_ok(resolve); HT_INSERT(cache_map, &cache_root, resolve); set_expiry(resolve, time(NULL) + dns_get_expiry_ttl(ttl)); } /** 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) { or_options_t *options = get_options(); return options->ServerDNSTestAddresses && smartlist_string_isin_case(options->ServerDNSTestAddresses, address); } /** Called on the OR side when a DNS worker or the eventdns library tells us * the outcome of a DNS resolve: tell all pending connections about the result * of the lookup, and cache the value. (address is a NUL-terminated * string containing the address to look up; addr is an IPv4 address in * host order; outcome is one of * DNS_RESOLVE_{FAILED_TRANSIENT|FAILED_PERMANENT|SUCCEEDED}. */ static void dns_found_answer(const char *address, uint8_t is_reverse, uint32_t addr, const char *hostname, char outcome, uint32_t ttl) { pending_connection_t *pend; cached_resolve_t search; cached_resolve_t *resolve, *removed; edge_connection_t *pendconn; circuit_t *circ; 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; caching anyway.", escaped_safe_str(address)); add_answer_to_cache(address, is_reverse, addr, hostname, outcome, ttl); 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; } /* Removed this assertion: in fact, we'll sometimes get a double answer * to the same question. This can happen when we ask one worker to resolve * X.Y.Z., then we cancel the request, and then we ask another worker to * resolve X.Y.Z. */ /* tor_assert(resolve->state == CACHE_STATE_PENDING); */ while (resolve->pending_connections) { 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)); tor_addr_from_ipv4h(&pendconn->_base.addr, addr); pendconn->address_ttl = ttl; if (outcome != DNS_RESOLVE_SUCCEEDED) { /* 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, outcome == DNS_RESOLVE_FAILED_PERMANENT ? RESOLVED_TYPE_ERROR : RESOLVED_TYPE_ERROR_TRANSIENT); /* 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 { if (pendconn->_base.purpose == EXIT_PURPOSE_CONNECT) { tor_assert(!is_reverse); /* 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 (is_reverse) send_resolved_hostname_cell(pendconn, hostname); else send_resolved_cell(pendconn, RESOLVED_TYPE_IPV4); 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); } resolve->state = CACHE_STATE_DONE; removed = HT_REMOVE(cache_map, &cache_root, &search); 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(); add_answer_to_cache(address, is_reverse, addr, hostname, outcome, 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; } } /** 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) { or_options_t *options; const char *conf_fname; struct stat st; int r; options = get_options(); conf_fname = options->ServerDNSResolvConfFile; #ifndef MS_WINDOWS if (!conf_fname) conf_fname = "/etc/resolv.conf"; #endif 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; } } #ifdef HAVE_EVDNS_SET_DEFAULT_OUTGOING_BIND_ADDRESS if (options->OutboundBindAddress) { tor_addr_t addr; if (tor_addr_from_str(&addr, options->OutboundBindAddress) < 0) { log_warn(LD_CONFIG,"Outbound bind address '%s' didn't parse. Ignoring.", options->OutboundBindAddress); } else { int socklen; struct sockaddr_storage ss; socklen = tor_addr_to_sockaddr(&addr, 0, (struct sockaddr *)&ss, sizeof(ss)); if (socklen < 0) { log_warn(LD_BUG, "Couldn't convert outbound bind address to sockaddr." " Ignoring."); } else { evdns_base_set_default_outgoing_bind_address(the_evdns_base, (struct sockaddr *)&ss, socklen); } } } #endif evdns_set_log_fn(evdns_log_cb); if (conf_fname) { if (stat(conf_fname, &st)) { log_warn(LD_EXIT, "Unable to stat resolver configuration in '%s': %s", conf_fname, strerror(errno)); goto err; } 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 (nameservers_configured) { evdns_base_search_clear(the_evdns_base); evdns_base_clear_nameservers_and_suspend(the_evdns_base); } log_info(LD_EXIT, "Parsing resolver configuration in '%s'", conf_fname); if ((r = evdns_base_resolv_conf_parse(the_evdns_base, DNS_OPTIONS_ALL, conf_fname))) { log_warn(LD_EXIT, "Unable to parse '%s', or no nameservers in '%s' (%d)", conf_fname, conf_fname, r); goto err; } if (evdns_base_count_nameservers(the_evdns_base) == 0) { log_warn(LD_EXIT, "Unable to find any nameservers in '%s'.", conf_fname); goto err; } tor_free(resolv_conf_fname); resolv_conf_fname = tor_strdup(conf_fname); resolv_conf_mtime = st.st_mtime; if (nameservers_configured) evdns_base_resume(the_evdns_base); } #ifdef MS_WINDOWS 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 #define SET(k,v) \ evdns_base_set_option(the_evdns_base, (k), (v), DNS_OPTIONS_ALL) if (evdns_base_count_nameservers(the_evdns_base) == 1) { SET("max-timeouts:", "16"); SET("timeout:", "10"); } else { SET("max-timeouts:", "3"); SET("timeout:", "5"); } 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; mark_my_descriptor_dirty(); } return 0; err: nameservers_configured = 0; if (! nameserver_config_failed) { nameserver_config_failed = 1; mark_my_descriptor_dirty(); } 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 *string_address = arg; uint8_t is_reverse = 0; int status = DNS_RESOLVE_FAILED_PERMANENT; uint32_t addr = 0; const char *hostname = NULL; int was_wildcarded = 0; if (result == DNS_ERR_NONE) { if (type == DNS_IPv4_A && count) { char answer_buf[INET_NTOA_BUF_LEN+1]; struct in_addr in; char *escaped_address; uint32_t *addrs = addresses; in.s_addr = addrs[0]; addr = ntohl(addrs[0]); status = DNS_RESOLVE_SUCCEEDED; tor_inet_ntoa(&in, answer_buf, sizeof(answer_buf)); 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; addr = 0; status = DNS_RESOLVE_FAILED_PERMANENT; } 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; is_reverse = 1; hostname = ((char**)addresses)[0]; status = DNS_RESOLVE_SUCCEEDED; 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_warn(LD_EXIT, "eventdns returned only non-IPv4 answers for %s.", escaped_safe_str(string_address)); } else { log_warn(LD_BUG, "eventdns returned no addresses or error for %s!", escaped_safe_str(string_address)); } } else { if (evdns_err_is_transient(result)) status = DNS_RESOLVE_FAILED_TRANSIENT; } 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 (result != DNS_ERR_SHUTDOWN) dns_found_answer(string_address, is_reverse, addr, hostname, status, ttl); tor_free(string_address); } /** For eventdns: start resolving as necessary to find the target for * exitconn. Returns -1 on error, -2 on transient error, * 0 on "resolve launched." */ static int launch_resolve(edge_connection_t *exitconn) { char *addr = tor_strdup(exitconn->_base.address); struct evdns_request *req = NULL; tor_addr_t a; int r; int options = get_options()->ServerDNSSearchDomains ? 0 : DNS_QUERY_NO_SEARCH; /* 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_reverse_lookup_name( &a, exitconn->_base.address, AF_UNSPEC, 0); if (r == 0) { log_info(LD_EXIT, "Launching eventdns request for %s", escaped_safe_str(exitconn->_base.address)); req = evdns_base_resolve_ipv4(the_evdns_base, exitconn->_base.address, options, evdns_callback, addr); } else if (r == 1) { log_info(LD_EXIT, "Launching eventdns reverse request for %s", escaped_safe_str(exitconn->_base.address)); if (tor_addr_family(&a) == AF_INET) req = evdns_base_resolve_reverse(the_evdns_base, tor_addr_to_in(&a), DNS_QUERY_NO_SEARCH, evdns_callback, addr); else req = evdns_base_resolve_reverse_ipv6(the_evdns_base, tor_addr_to_in6(&a), DNS_QUERY_NO_SEARCH, evdns_callback, addr); } else if (r == -1) { log_warn(LD_BUG, "Somehow a malformed in-addr.arpa address reached here."); } r = 0; if (!req) { log_warn(LD_EXIT, "eventdns rejected address %s.", escaped_safe_str(addr)); r = -1; tor_free(addr); /* There is no evdns request in progress; stop * addr from getting leaked. */ } 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) 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_create(); if (!smartlist_string_isin(dns_wildcard_list, id)) { 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(dns_wildcard_list, tor_strdup(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_create(); if (smartlist_string_isin_case(dns_wildcarded_test_address_list, address)) return; n_test_addrs = get_options()->ServerDNSTestAddresses ? smartlist_len(get_options()->ServerDNSTestAddresses) : 0; smartlist_add(dns_wildcarded_test_address_list, tor_strdup(address)); n = smartlist_len(dns_wildcarded_test_address_list); if (n > n_test_addrs/2) { 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(); } 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; ++n_wildcard_requests; if (result == DNS_ERR_NONE && type == DNS_IPv4_A && count) { uint32_t *addrs = addresses; int i; char *string_address = arg; for (i = 0; i < count; ++i) { char answer_buf[INET_NTOA_BUF_LEN+1]; struct in_addr in; in.s_addr = addrs[i]; tor_inet_ntoa(&in, answer_buf, sizeof(answer_buf)); wildcard_increment_answer(answer_buf); } 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, 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); 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(int fd, short event, void *args) { or_options_t *options = get_options(); struct evdns_request *req; (void)fd; (void)event; (void)args; 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) return; SMARTLIST_FOREACH_BEGIN(options->ServerDNSTestAddresses, const char *, address) { char *a = tor_strdup(address); req = evdns_base_resolve_ipv4(the_evdns_base, address, DNS_QUERY_NO_SEARCH, evdns_callback, a); if (!req) { log_info(LD_EXIT, "eventdns rejected test address %s", escaped_safe_str(address)); tor_free(a); } } 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; log_info(LD_EXIT, "Launching checks to see whether our nameservers like " "to hijack DNS failures."); 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, ".invalid"); launch_wildcard_check(2, 16, ".test"); /* These will break specs if there are ever any number of * 8+-character top-level domains. */ launch_wildcard_check(8, 16, ""); /* 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, ".com"); launch_wildcard_check(8, 16, ".org"); launch_wildcard_check(8, 16, ".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; } /** 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; 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 = 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_string_isin(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) { tor_assert(!resolve->ttl); if (resolve->is_reverse) tor_assert(!resolve->result.hostname); else tor_assert(!resolve->result.a.addr); } } /** Return the number of DNS cache entries as an int */ static int dns_cache_entry_count(void) { return HT_SIZE(&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 = sizeof(struct cached_resolve_t) * hash_count; hash_mem += HT_MEM_USAGE(&cache_root); /* Print out the count and estimated size of our &cache_root. It undercounts hostnames in cached reverse resolves. */ log(severity, LD_MM, "Our DNS cache has %d entries.", hash_count); log(severity, LD_MM, "Our DNS cache size is approximately %u bytes.", (unsigned)hash_mem); } #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 = _cache_map_HT_REP_IS_BAD(&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, STRUCT_OFFSET(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