/* Copyright 2003 Roger Dingledine. */ /* See LICENSE for licensing information */ /* $Id$ */ /** * \file dns.c * \brief Resolve hostnames in separate processes. **/ /* See http://elvin.dstc.com/ListArchive/elvin-dev/archive/2001/09/msg00027.html * for some approaches to asynchronous dns. We will want to switch once one of * them becomes more commonly available. */ #include "or.h" #include "tree.h" extern or_options_t options; /* command-line and config-file options */ /** Longest hostname we're willing to resolve. */ #define MAX_ADDRESSLEN 256 /** Maximum DNS processes to spawn. */ #define MAX_DNSWORKERS 50 /** Minimum DNS processes to spawn. */ #define MIN_DNSWORKERS 3 /** If more than this many processes are idle, shut down the extras. */ #define MAX_IDLE_DNSWORKERS 10 /** 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 /** How many dnsworkers we have running right now. */ static int num_dnsworkers=0; /** How many of the running dnsworkers have an assigned task right now. */ static int num_dnsworkers_busy=0; /** When did we last rotate the dnsworkers? */ static time_t last_rotation_time=0; /** Linked list of connections waiting for a DNS answer. */ struct pending_connection_t { struct connection_t *conn; struct pending_connection_t *next; }; /** A DNS request: possibly completed, possibly pending; cached_resolve * structs are stored at the OR side in a splay tree, and as a linked * list from oldest to newest. */ struct cached_resolve { SPLAY_ENTRY(cached_resolve) node; char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */ uint32_t addr; /**< IPv4 addr for address. */ char state; /**< 0 is pending; 1 means answer is valid; 2 means resolve failed. */ #define CACHE_STATE_PENDING 0 #define CACHE_STATE_VALID 1 #define CACHE_STATE_FAILED 2 uint32_t expire; /**< Remove items from cache after this time. */ struct pending_connection_t *pending_connections; struct cached_resolve *next; }; static void purge_expired_resolves(uint32_t now); static int assign_to_dnsworker(connection_t *exitconn); static void dns_purge_resolve(struct cached_resolve *resolve); static void dns_found_answer(char *address, uint32_t addr, char outcome); static int dnsworker_main(void *data); static int spawn_dnsworker(void); static void spawn_enough_dnsworkers(void); static void send_resolved_cell(connection_t *conn, uint8_t answer_type); /** Splay tree of cached_resolve objects. */ static SPLAY_HEAD(cache_tree, cached_resolve) cache_root; /** Function to compare hashed resolves on their addresses; used to * implement splay trees. */ static int compare_cached_resolves(struct cached_resolve *a, struct cached_resolve *b) { /* make this smarter one day? */ return strncasecmp(a->address, b->address, MAX_ADDRESSLEN); } SPLAY_PROTOTYPE(cache_tree, cached_resolve, node, compare_cached_resolves); SPLAY_GENERATE(cache_tree, cached_resolve, node, compare_cached_resolves); /** Initialize the DNS cache. */ static void init_cache_tree(void) { SPLAY_INIT(&cache_root); } /** Initialize the DNS subsystem; called by the OR process. */ void dns_init(void) { init_cache_tree(); last_rotation_time=time(NULL); spawn_enough_dnsworkers(); } /** Linked list of resolved addresses, oldest to newest. */ static struct cached_resolve *oldest_cached_resolve = NULL; static struct cached_resolve *newest_cached_resolve = NULL; /** Remove every cached_resolve whose expire time is before now * from the cache. */ static void purge_expired_resolves(uint32_t now) { struct cached_resolve *resolve; struct pending_connection_t *pend; connection_t *pendconn; /* this is fast because the linked list * oldest_cached_resolve is ordered by when they came in. */ while(oldest_cached_resolve && (oldest_cached_resolve->expire < now)) { resolve = oldest_cached_resolve; log(LOG_DEBUG,"Forgetting old cached resolve (expires %lu)", (unsigned long)resolve->expire); if(resolve->state == CACHE_STATE_PENDING) { log_fn(LOG_WARN,"Expiring a dns resolve that's still pending. Forgot to cull it?"); } if (resolve->pending_connections) { log_fn(LOG_WARN, "Closing pending connections on expiring 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(pend->conn->s == -1); pendconn = pend->conn; connection_edge_end(pendconn, END_STREAM_REASON_MISC, pendconn->cpath_layer); circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn); connection_free(pendconn); tor_free(pend); } } oldest_cached_resolve = resolve->next; if(!oldest_cached_resolve) /* if there are no more, */ newest_cached_resolve = NULL; /* then make sure the list's tail knows that too */ SPLAY_REMOVE(cache_tree, &cache_root, resolve); tor_free(resolve); } } static void send_resolved_cell(connection_t *conn, uint8_t answer_type) { char buf[RELAY_PAYLOAD_SIZE]; int buflen; buf[0] = answer_type; switch (answer_type) { case RESOLVED_TYPE_IPV4: buf[1] = 4; set_uint32(buf+2, htonl(conn->addr)); buflen = 6; break; case RESOLVED_TYPE_ERROR_TRANSIENT: case RESOLVED_TYPE_ERROR: buf[1] = 24; /* length of "error resolving hostname" */ strcpy(buf+2, "error resolving hostname"); buflen = 26; break; default: tor_assert(0); } connection_edge_send_command(conn, circuit_get_by_conn(conn), RELAY_COMMAND_RESOLVED, buf, buflen, conn->cpath_layer); } /** 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, return -1. * * 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. */ int dns_resolve(connection_t *exitconn) { struct cached_resolve *resolve; struct cached_resolve search; struct pending_connection_t *pending_connection; struct in_addr in; uint32_t now = time(NULL); assert_connection_ok(exitconn, 0); tor_assert(exitconn->s == -1); /* first check if exitconn->address is an IP. If so, we already * know the answer. */ if (tor_inet_aton(exitconn->address, &in) != 0) { exitconn->addr = ntohl(in.s_addr); return 1; } /* then take this opportunity to see if there are any expired * resolves in the tree. */ purge_expired_resolves(now); /* now check the tree to see if 'address' is already there. */ strncpy(search.address, exitconn->address, MAX_ADDRESSLEN); search.address[MAX_ADDRESSLEN-1] = 0; resolve = SPLAY_FIND(cache_tree, &cache_root, &search); if(resolve) { /* already there */ switch(resolve->state) { case CACHE_STATE_PENDING: /* add us to the pending list */ pending_connection = tor_malloc_zero( sizeof(struct pending_connection_t)); pending_connection->conn = exitconn; pending_connection->next = resolve->pending_connections; resolve->pending_connections = pending_connection; log_fn(LOG_DEBUG,"Connection (fd %d) waiting for pending DNS resolve of '%s'", exitconn->s, exitconn->address); exitconn->state = EXIT_CONN_STATE_RESOLVING; return 0; case CACHE_STATE_VALID: exitconn->addr = resolve->addr; log_fn(LOG_DEBUG,"Connection (fd %d) found cached answer for '%s'", exitconn->s, exitconn->address); if (exitconn->purpose == EXIT_PURPOSE_RESOLVE) send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4); return 1; case CACHE_STATE_FAILED: if (exitconn->purpose == EXIT_PURPOSE_RESOLVE) send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR); return -1; } tor_assert(0); } /* not there, need to add it */ resolve = tor_malloc_zero(sizeof(struct cached_resolve)); resolve->state = CACHE_STATE_PENDING; resolve->expire = now + MAX_DNS_ENTRY_AGE; strncpy(resolve->address, exitconn->address, MAX_ADDRESSLEN); resolve->address[MAX_ADDRESSLEN-1] = 0; /* add us to the pending list */ pending_connection = tor_malloc_zero(sizeof(struct pending_connection_t)); pending_connection->conn = exitconn; pending_connection->next = NULL; resolve->pending_connections = pending_connection; exitconn->state = EXIT_CONN_STATE_RESOLVING; /* add us to the linked list of resolves */ if (!oldest_cached_resolve) { oldest_cached_resolve = resolve; } else { newest_cached_resolve->next = resolve; } newest_cached_resolve = resolve; SPLAY_INSERT(cache_tree, &cache_root, resolve); return assign_to_dnsworker(exitconn); } /** Find or spawn a dns worker process to handle resolving * exitconn-\>address; tell that dns worker to begin resolving. */ static int assign_to_dnsworker(connection_t *exitconn) { connection_t *dnsconn; unsigned char len; tor_assert(exitconn->state == EXIT_CONN_STATE_RESOLVING); tor_assert(exitconn->s == -1); spawn_enough_dnsworkers(); /* respawn here, to be sure there are enough */ dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE); if(!dnsconn) { log_fn(LOG_WARN,"no idle dns workers. Failing."); dns_cancel_pending_resolve(exitconn->address); send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR_TRANSIENT); return -1; } log_fn(LOG_DEBUG, "Connection (fd %d) needs to resolve '%s'; assigning to DNSWorker (fd %d)", exitconn->s, exitconn->address, dnsconn->s); tor_free(dnsconn->address); dnsconn->address = tor_strdup(exitconn->address); dnsconn->state = DNSWORKER_STATE_BUSY; num_dnsworkers_busy++; len = strlen(dnsconn->address); connection_write_to_buf(&len, 1, dnsconn); connection_write_to_buf(dnsconn->address, len, dnsconn); // log_fn(LOG_DEBUG,"submitted '%s'", exitconn->address); return 0; } /** Remove conn from the list of connections waiting for conn-\>address. */ void connection_dns_remove(connection_t *conn) { struct pending_connection_t *pend, *victim; struct cached_resolve search; struct cached_resolve *resolve; tor_assert(conn->type == CONN_TYPE_EXIT); tor_assert(conn->state == EXIT_CONN_STATE_RESOLVING); strncpy(search.address, conn->address, MAX_ADDRESSLEN); search.address[MAX_ADDRESSLEN-1] = 0; resolve = SPLAY_FIND(cache_tree, &cache_root, &search); if(!resolve) { log_fn(LOG_WARN,"Address '%s' is not pending. Dropping.", conn->address); return; } tor_assert(resolve->pending_connections); assert_connection_ok(conn,0); pend = resolve->pending_connections; if(pend->conn == conn) { resolve->pending_connections = pend->next; tor_free(pend); log_fn(LOG_DEBUG, "First connection (fd %d) no longer waiting for resolve of '%s'", conn->s, conn->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_fn(LOG_DEBUG, "Connection (fd %d) no longer waiting for resolve of '%s'", conn->s, conn->address); return; /* more are pending */ } } tor_assert(0); /* not reachable unless onlyconn not in pending list */ } } /** Log an error and abort if conn is waiting for a DNS resolve. */ void assert_connection_edge_not_dns_pending(connection_t *conn) { struct pending_connection_t *pend; struct cached_resolve *resolve; SPLAY_FOREACH(resolve, cache_tree, &cache_root) { for(pend = resolve->pending_connections; pend; pend = pend->next) { tor_assert(pend->conn != conn); } } } /** Log an error and abort if any connection waiting for a DNS resolve is * corrupted. */ void assert_all_pending_dns_resolves_ok(void) { struct pending_connection_t *pend; struct cached_resolve *resolve; SPLAY_FOREACH(resolve, cache_tree, &cache_root) { for(pend = resolve->pending_connections; pend; pend = pend->next) { assert_connection_ok(pend->conn, 0); tor_assert(pend->conn->s == -1); tor_assert(!connection_in_array(pend->conn)); } } } /** 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(char *address) { struct pending_connection_t *pend; struct cached_resolve search; struct cached_resolve *resolve; connection_t *pendconn; strncpy(search.address, address, MAX_ADDRESSLEN); search.address[MAX_ADDRESSLEN-1] = 0; resolve = SPLAY_FIND(cache_tree, &cache_root, &search); if(!resolve) { log_fn(LOG_WARN,"Address '%s' is not pending. Dropping.", address); return; } tor_assert(resolve->pending_connections); /* mark all pending connections to fail */ log_fn(LOG_DEBUG, "Failing all connections waiting on DNS resolve of '%s'", address); while(resolve->pending_connections) { pend = resolve->pending_connections; pend->conn->state = EXIT_CONN_STATE_RESOLVEFAILED; pendconn = pend->conn; tor_assert(pendconn->s == -1); if(!pendconn->marked_for_close) { connection_edge_end(pendconn, END_STREAM_REASON_MISC, pendconn->cpath_layer); } circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn); connection_free(pendconn); resolve->pending_connections = pend->next; tor_free(pend); } dns_purge_resolve(resolve); } /** Remove resolve from the cache. */ static void dns_purge_resolve(struct cached_resolve *resolve) { struct cached_resolve *tmp; /* remove resolve from the linked list */ if(resolve == oldest_cached_resolve) { oldest_cached_resolve = resolve->next; if(oldest_cached_resolve == NULL) newest_cached_resolve = NULL; } else { /* FFFF make it a doubly linked list if this becomes too slow */ for(tmp=oldest_cached_resolve; tmp && tmp->next != resolve; tmp=tmp->next) ; tor_assert(tmp); /* it's got to be in the list, or we screwed up somewhere else */ tmp->next = resolve->next; /* unlink it */ if(newest_cached_resolve == resolve) newest_cached_resolve = tmp; } /* remove resolve from the tree */ SPLAY_REMOVE(cache_tree, &cache_root, resolve); tor_free(resolve); } /** Called on the OR side when a DNS worker 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(char *address, uint32_t addr, char outcome) { struct pending_connection_t *pend; struct cached_resolve search; struct cached_resolve *resolve; connection_t *pendconn; circuit_t *circ; strncpy(search.address, address, MAX_ADDRESSLEN); search.address[MAX_ADDRESSLEN-1] = 0; resolve = SPLAY_FIND(cache_tree, &cache_root, &search); if(!resolve) { log_fn(LOG_INFO,"Resolved unasked address '%s'? Dropping.", address); /* XXX Why drop? Just because we don't care now doesn't mean we shouldn't * XXX cache the result for later. */ return; } if (resolve->state != CACHE_STATE_PENDING) { /* XXXX Maybe update addr? or check addr for consistency? Or let * VALID replace FAILED? */ log_fn(LOG_WARN, "Resolved '%s' which was already resolved; ignoring", 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); */ resolve->addr = ntohl(addr); if(outcome == DNS_RESOLVE_SUCCEEDED) resolve->state = CACHE_STATE_VALID; else resolve->state = CACHE_STATE_FAILED; while(resolve->pending_connections) { pend = resolve->pending_connections; assert_connection_ok(pend->conn,time(NULL)); pend->conn->addr = resolve->addr; pendconn = pend->conn; /* don't pass complex things to the connection_mark_for_close macro */ if(resolve->state == CACHE_STATE_FAILED) { /* prevent double-remove. */ pendconn->state = EXIT_CONN_STATE_RESOLVEFAILED; if (pendconn->purpose == EXIT_PURPOSE_CONNECT) { /*XXXX can we safely raise the detach here to happen after we * send the end cell? */ circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn); connection_edge_end(pendconn, END_STREAM_REASON_MISC, pendconn->cpath_layer); } else { send_resolved_cell(pendconn, RESOLVED_TYPE_ERROR); /* This detach must happen after we send the resolved cell. */ circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn); } connection_free(pendconn); } else { if (pendconn->purpose == EXIT_PURPOSE_CONNECT) { /* prevent double-remove. */ pend->conn->state = EXIT_CONN_STATE_CONNECTING; circ = circuit_get_by_conn(pend->conn); tor_assert(circ); /* unlink pend->conn from resolving_streams, */ circuit_detach_stream(circ, pend->conn); /* and link it to n_streams */ pend->conn->next_stream = circ->n_streams; 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->state = EXIT_CONN_STATE_RESOLVEFAILED; send_resolved_cell(pendconn, RESOLVED_TYPE_IPV4); circ = circuit_get_by_conn(pendconn); tor_assert(circ); circuit_detach_stream(circ, pendconn); connection_free(pendconn); } } resolve->pending_connections = pend->next; tor_free(pend); } if(outcome == DNS_RESOLVE_FAILED_TRANSIENT) { /* remove from cache */ dns_purge_resolve(resolve); } } /******************************************************************/ /* * Connection between OR and dnsworker */ /** Write handler: called when we've pushed a request to a dnsworker. */ int connection_dns_finished_flushing(connection_t *conn) { tor_assert(conn && conn->type == CONN_TYPE_DNSWORKER); connection_stop_writing(conn); return 0; } /** Read handler: called when we get data from a dnsworker. If the * connection is closed, mark the dnsworker as dead. Otherwise, see * if we have a complete answer. If so, call dns_found_answer on the * result. If not, wait. Returns 0. */ int connection_dns_process_inbuf(connection_t *conn) { char success; uint32_t addr; tor_assert(conn && conn->type == CONN_TYPE_DNSWORKER); if(conn->inbuf_reached_eof) { log_fn(LOG_WARN,"Read eof. Worker died unexpectedly."); if(conn->state == DNSWORKER_STATE_BUSY) { dns_cancel_pending_resolve(conn->address); num_dnsworkers_busy--; } num_dnsworkers--; connection_mark_for_close(conn); return 0; } if(conn->state != DNSWORKER_STATE_BUSY) { log_fn(LOG_WARN,"Bug: poll() indicated than an idle dns worker was readable. Please report."); return 0; } if(buf_datalen(conn->inbuf) < 5) /* entire answer available? */ return 0; /* not yet */ tor_assert(conn->state == DNSWORKER_STATE_BUSY); tor_assert(buf_datalen(conn->inbuf) == 5); connection_fetch_from_buf(&success,1,conn); connection_fetch_from_buf((char *)&addr,sizeof(uint32_t),conn); log_fn(LOG_DEBUG, "DNSWorker (fd %d) returned answer for '%s'", conn->s, conn->address); tor_assert(success >= DNS_RESOLVE_FAILED_TRANSIENT); tor_assert(success <= DNS_RESOLVE_SUCCEEDED); dns_found_answer(conn->address, addr, success); tor_free(conn->address); conn->address = tor_strdup(""); conn->state = DNSWORKER_STATE_IDLE; num_dnsworkers_busy--; if (conn->timestamp_created < last_rotation_time) { connection_mark_for_close(conn); num_dnsworkers--; spawn_enough_dnsworkers(); } return 0; } /** Close and re-open all idle dnsworkers; schedule busy ones to be closed * and re-opened once they're no longer busy. **/ void dnsworkers_rotate(void) { connection_t *dnsconn; while ((dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE))) { connection_mark_for_close(dnsconn); num_dnsworkers--; } last_rotation_time = time(NULL); spawn_enough_dnsworkers(); } /** Implementation for DNS workers; this code runs in a separate * execution context. It takes as its argument an fdarray as returned * by socketpair(), and communicates via fdarray[1]. The protocol is * as follows: * - The OR says: * - ADDRESSLEN [1 byte] * - ADDRESS [ADDRESSLEN bytes] * - The DNS worker does the lookup, and replies: * - OUTCOME [1 byte] * - IP [4 bytes] * * OUTCOME is one of DNS_RESOLVE_{FAILED_TRANSIENT|FAILED_PERMANENT|SUCCEEDED}. * IP is in host order. * * The dnsworker runs indefinitely, until its connection is closed or an error * occurs. */ static int dnsworker_main(void *data) { char address[MAX_ADDRESSLEN]; unsigned char address_len; char answer[5]; uint32_t ip; int *fdarray = data; int fd; int result; tor_close_socket(fdarray[0]); /* this is the side of the socketpair the parent uses */ fd = fdarray[1]; /* this side is ours */ #ifndef MS_WINDOWS connection_free_all(); /* so the child doesn't hold the parent's fd's open */ #endif handle_signals(0); /* ignore interrupts from the keyboard, etc */ for(;;) { if(recv(fd, &address_len, 1, 0) != 1) { log_fn(LOG_INFO,"dnsworker exiting because tor process closed connection (either pruned idle dnsworker or died)."); spawn_exit(); } if(address_len && read_all(fd, address, address_len, 1) != address_len) { log_fn(LOG_ERR,"read hostname failed. Child exiting."); spawn_exit(); } address[address_len] = 0; /* null terminate it */ result = tor_lookup_hostname(address, &ip); /* Make 0.0.0.0 an error, so that we can use "0" to mean "no addr") */ if (!ip) result = -1; switch (result) { case 1: /* XXX008 result can never be 1, because we set it to -1 above on error */ log_fn(LOG_INFO,"Could not resolve dest addr %s (transient).",address); answer[0] = DNS_RESOLVE_FAILED_TRANSIENT; break; case -1: log_fn(LOG_INFO,"Could not resolve dest addr %s (permanent).",address); answer[0] = DNS_RESOLVE_FAILED_PERMANENT; break; case 0: log_fn(LOG_INFO,"Resolved address '%s'.",address); answer[0] = DNS_RESOLVE_SUCCEEDED; break; } set_uint32(answer+1, ip); if(write_all(fd, answer, 5, 1) != 5) { log_fn(LOG_ERR,"writing answer failed. Child exiting."); spawn_exit(); } } return 0; /* windows wants this function to return an int */ } /** Launch a new DNS worker; return 0 on success, -1 on failure. */ static int spawn_dnsworker(void) { int fd[2]; connection_t *conn; if(tor_socketpair(AF_UNIX, SOCK_STREAM, 0, fd) < 0) { log(LOG_ERR, "Couldn't construct socketpair: %s", tor_socket_strerror(tor_socket_errno(-1))); tor_cleanup(); exit(1); } spawn_func(dnsworker_main, (void*)fd); log_fn(LOG_DEBUG,"just spawned a worker."); tor_close_socket(fd[1]); /* we don't need the worker's side of the pipe */ conn = connection_new(CONN_TYPE_DNSWORKER); set_socket_nonblocking(fd[0]); /* set up conn so it's got all the data we need to remember */ conn->s = fd[0]; conn->address = tor_strdup(""); if(connection_add(conn) < 0) { /* no space, forget it */ log_fn(LOG_WARN,"connection_add failed. Giving up."); connection_free(conn); /* this closes fd[0] */ return -1; } conn->state = DNSWORKER_STATE_IDLE; connection_start_reading(conn); return 0; /* success */ } /** If we have too many or too few DNS workers, spawn or kill some. */ static void spawn_enough_dnsworkers(void) { int num_dnsworkers_needed; /* aim to have 1 more than needed, * but no less than min and no more than max */ connection_t *dnsconn; /* XXX This may not be the best strategy. Maybe we should queue pending * requests until the old ones finish or time out: otherwise, if * the connection requests come fast enough, we never get any DNS done. -NM * XXX But if we queue them, then the adversary can pile even more * queries onto us, blocking legitimate requests for even longer. * Maybe we should compromise and only kill if it's been at it for * more than, e.g., 2 seconds. -RD */ if(num_dnsworkers_busy == MAX_DNSWORKERS) { /* We always want at least one worker idle. * So find the oldest busy worker and kill it. */ dnsconn = connection_get_by_type_state_lastwritten(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_BUSY); tor_assert(dnsconn); log_fn(LOG_WARN, "%d DNS workers are spawned; all are busy. Killing one.", MAX_DNSWORKERS); connection_mark_for_close(dnsconn); num_dnsworkers_busy--; num_dnsworkers--; } if(num_dnsworkers_busy >= MIN_DNSWORKERS) num_dnsworkers_needed = num_dnsworkers_busy+1; else num_dnsworkers_needed = MIN_DNSWORKERS; while(num_dnsworkers < num_dnsworkers_needed) { if(spawn_dnsworker() < 0) { log(LOG_WARN,"spawn_enough_dnsworkers(): spawn failed!"); return; } num_dnsworkers++; } while(num_dnsworkers > num_dnsworkers_busy+MAX_IDLE_DNSWORKERS) { /* too many idle? */ /* cull excess workers */ log_fn(LOG_WARN,"%d of %d dnsworkers are idle. Killing one.", num_dnsworkers-num_dnsworkers_needed, num_dnsworkers); dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE); tor_assert(dnsconn); connection_mark_for_close(dnsconn); num_dnsworkers--; } } /* Local Variables: mode:c indent-tabs-mode:nil c-basic-offset:2 End: */