/* Copyright 2003-2004 Roger Dingledine.
* Copyright 2004-2006 Roger Dingledine, Nick Mathewson. */
/* See LICENSE for licensing information */
/* $Id$ */
const char dns_c_id[] =
"$Id$";
/**
* \file dns.c
* \brief Implements a local cache for DNS results for Tor servers.
* We provide two asynchrounous backend implementations:
* 1) A farm of 'DNS worker' threads or processes to perform DNS lookups for
* onion routers and cache the results.
* 2) A wrapper around Adam Langley's eventdns.c code, to send requests
* to the nameservers asynchronously.
* (We can't just use gethostbyname() and friends because we really need to
* be nonblocking.)
**/
#include "or.h"
#include "../common/ht.h"
#ifdef USE_EVENTDNS
#include "eventdns.h"
#endif
/** Longest hostname we're willing to resolve. */
#define MAX_ADDRESSLEN 256
/** Maximum DNS processes to spawn. */
#define MAX_DNSWORKERS 100
/** 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
/** 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
#ifndef USE_EVENTDNS
/** 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;
#endif
/** 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;
#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. */
uint32_t addr; /**< IPv4 addr for <b>address</b>. */
uint8_t state; /**< Is this cached entry pending/done/valid/failed? */
time_t expire; /**< Remove items from cache after this time. */
uint32_t ttl; /**< What TTL did the nameserver tell us? */
pending_connection_t *pending_connections;
} cached_resolve_t;
static void purge_expired_resolves(time_t now);
static void dns_found_answer(const char *address, uint32_t addr, 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);
#ifndef USE_EVENTDNS
static int dnsworker_main(void *data);
static int spawn_dnsworker(void);
static int spawn_enough_dnsworkers(void);
#else
static void configure_nameservers(void);
#endif
static void assert_cache_ok(void);
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);
}
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_root);
}
#ifdef USE_EVENTDNS
static void
eventdns_log_cb(const char *msg)
{
if (!strcmpstart(msg, "Resolve requested for") &&
get_options()->SafeLogging) {
log(LOG_INFO, LD_EXIT, "eventdns: Resolve requested.");
return;
}
log(LOG_INFO, LD_EXIT, "eventdns: %s", msg);
}
#endif
/** Initialize the DNS subsystem; called by the OR process. */
void
dns_init(void)
{
init_cache_map();
dnsworkers_rotate();
#ifdef USE_EVENTDNS
if (server_mode(get_options()))
configure_nameservers();
#endif
}
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;
}
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)
{
while (r->pending_connections) {
pending_connection_t *victim = r->pending_connections;
r->pending_connections = victim->next;
tor_free(victim);
}
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,
resolve);
}
/** Free all storage held in the DNS cache */
void
dns_free_all(void)
{
cached_resolve_t **ptr, **next, *item;
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);
if (cached_resolve_pqueue)
smartlist_free(cached_resolve_pqueue);
cached_resolve_pqueue = NULL;
}
/** Remove every cached_resolve whose <b>expire</b> time is before <b>now</b>
* 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);
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,
pendconn->cpath_layer);
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, resolve,
removed ? removed->address : "NULL", remove);
}
tor_assert(removed == resolve);
resolve->magic = 0xF0BBF0BB;
tor_free(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);
}
}
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) */
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, htonl(conn->_base.addr));
set_uint32(buf+6, htonl(ttl));
buflen = 10;
break;
case RESOLVED_TYPE_ERROR_TRANSIENT:
case RESOLVED_TYPE_ERROR:
{
const char *errmsg = "Error resolving hostname";
int 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);
}
connection_edge_send_command(conn, circuit_get_by_edge_conn(conn),
RELAY_COMMAND_RESOLVED, buf, buflen,
conn->cpath_layer);
}
/** See if we have a cache entry for <b>exitconn</b>-\>address. if so,
* if resolve valid, put it into <b>exitconn</b>-\>addr and return 1.
* If resolve failed, unlink exitconn if needed, free it, and 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(edge_connection_t *exitconn)
{
cached_resolve_t *resolve;
cached_resolve_t search;
pending_connection_t *pending_connection;
struct in_addr in;
circuit_t *circ;
time_t now = time(NULL);
assert_connection_ok(TO_CONN(exitconn), 0);
tor_assert(exitconn->_base.s == -1);
assert_cache_ok();
/* first check if exitconn->_base.address is an IP. If so, we already
* know the answer. */
if (tor_inet_aton(exitconn->_base.address, &in) != 0) {
exitconn->_base.addr = ntohl(in.s_addr);
exitconn->address_ttl = DEFAULT_DNS_TTL;
if (exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE)
send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4);
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);
/* 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));
exitconn->_base.state = EXIT_CONN_STATE_RESOLVING;
return 0;
case CACHE_STATE_CACHED_VALID:
exitconn->_base.addr = resolve->addr;
exitconn->address_ttl = resolve->ttl;
log_debug(LD_EXIT,"Connection (fd %d) found cached answer for %s",
exitconn->_base.s,
escaped_safe_str(exitconn->_base.address));
if (exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE)
send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4);
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));
if (exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE)
send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR);
circ = circuit_get_by_edge_conn(exitconn);
if (circ)
circuit_detach_stream(circ, exitconn);
if (!exitconn->_base.marked_for_close)
connection_free(TO_CONN(exitconn));
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);
}
/* not there, need to add it */
resolve = tor_malloc_zero(sizeof(cached_resolve_t));
resolve->magic = CACHED_RESOLVE_MAGIC;
resolve->state = CACHE_STATE_PENDING;
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;
exitconn->_base.state = EXIT_CONN_STATE_RESOLVING;
/* 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 **resolve;
HT_FOREACH(resolve, cache_map, &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)
{
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 <b>conn</b> 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 <b>address</b> for close. Then cancel
* the resolve for <b>address</b> itself, and remove any cached results for
* <b>address</b> from the cache.
*/
void
dns_cancel_pending_resolve(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 || resolve->state != CACHE_STATE_PENDING) {
log_notice(LD_BUG,"Address %s is not pending. Dropping.",
escaped_safe_str(address));
return;
}
if (!resolve->pending_connections) {
/* XXX this should never trigger, but sometimes it does */
log_warn(LD_BUG,
"Bug: Address %s is pending but has no pending connections!",
escaped_safe_str(address));
tor_fragile_assert();
return;
}
tor_assert(resolve->pending_connections);
tor_assert(! resolve->expire);
/* 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_RESOURCELIMIT,
pendconn->cpath_layer);
}
circ = circuit_get_by_edge_conn(pendconn);
if (circ)
circuit_detach_stream(circ, pendconn);
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, resolve,
tmp ? tmp->address : "NULL", tmp);
}
tor_assert(tmp == resolve);
resolve->magic = 0xABABABAB;
tor_free(resolve);
}
static void
add_answer_to_cache(const char *address, uint32_t addr, char outcome,
uint32_t ttl)
{
cached_resolve_t *resolve;
if (outcome == DNS_RESOLVE_FAILED_TRANSIENT)
return;
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->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));
}
/** 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. (<b>address</b> is a NUL-terminated string containing the
* address to look up; <b>addr</b> is an IPv4 address in host order;
* <b>outcome</b> is one of
* DNS_RESOLVE_{FAILED_TRANSIENT|FAILED_PERMANENT|SUCCEEDED}.
*/
static void
dns_found_answer(const char *address, uint32_t addr, 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) {
log_info(LD_EXIT,"Resolved unasked address %s; caching anyway.",
escaped_safe_str(address));
add_answer_to_cache(address, addr, 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? */
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));
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,
pendconn->cpath_layer);
/* 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, RESOLVED_TYPE_ERROR);
/* 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) {
/* 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;
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, resolve,
removed ? removed->address : "NULL", removed);
}
assert_resolve_ok(resolve);
assert_cache_ok();
add_answer_to_cache(address, addr, outcome, ttl);
assert_cache_ok();
}
#ifndef USE_EVENTDNS
/** Find or spawn a dns worker process to handle resolving
* <b>exitconn</b>-\>address; tell that dns worker to begin resolving.
*/
static int
launch_resolve(edge_connection_t *exitconn)
{
connection_t *dnsconn;
unsigned char len;
tor_assert(exitconn->_base.state == EXIT_CONN_STATE_RESOLVING);
assert_connection_ok(TO_CONN(exitconn), 0);
tor_assert(exitconn->_base.s == -1);
/* respawn here, to be sure there are enough */
if (spawn_enough_dnsworkers() < 0) {
goto err;
}
dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER,
DNSWORKER_STATE_IDLE);
if (!dnsconn) {
log_warn(LD_EXIT,"no idle dns workers. Failing.");
if (exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE)
send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR_TRANSIENT);
goto err;
}
log_debug(LD_EXIT,
"Connection (fd %d) needs to resolve %s; assigning "
"to DNSWorker (fd %d)", exitconn->_base.s,
escaped_safe_str(exitconn->_base.address), dnsconn->s);
tor_free(dnsconn->address);
dnsconn->address = tor_strdup(exitconn->_base.address);
dnsconn->state = DNSWORKER_STATE_BUSY;
/* touch the lastwritten timestamp, since that's how we check to
* see how long it's been since we asked the question, and sometimes
* we check before the first call to connection_handle_write(). */
dnsconn->timestamp_lastwritten = time(NULL);
num_dnsworkers_busy++;
len = strlen(dnsconn->address);
connection_write_to_buf((char*)&len, 1, dnsconn);
connection_write_to_buf(dnsconn->address, len, dnsconn);
return 0;
err:
/* also sends end and frees */
dns_cancel_pending_resolve(exitconn->_base.address);
return -1;
}
/******************************************************************/
/*
* 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);
tor_assert(conn->type == CONN_TYPE_DNSWORKER);
connection_stop_writing(conn);
return 0;
}
int
connection_dns_reached_eof(connection_t *conn)
{
log_warn(LD_EXIT,"Read eof. Worker died unexpectedly.");
if (conn->state == DNSWORKER_STATE_BUSY) {
/* don't cancel the resolve here -- it would be cancelled in
* connection_about_to_close_connection(), since conn is still
* in state BUSY
*/
num_dnsworkers_busy--;
}
num_dnsworkers--;
connection_mark_for_close(conn);
return 0;
}
/** Read handler: called when we get data from a dnsworker. 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;
int ttl;
tor_assert(conn);
tor_assert(conn->type == CONN_TYPE_DNSWORKER);
if (conn->state != DNSWORKER_STATE_BUSY && buf_datalen(conn->inbuf)) {
log_warn(LD_BUG,
"Bug: read data (%d bytes) from an idle dns worker (fd %d, "
"address %s). Please report.", (int)buf_datalen(conn->inbuf),
conn->s, escaped_safe_str(conn->address));
tor_fragile_assert();
/* Pull it off the buffer anyway, or it will just stay there.
* Keep pulling things off because sometimes we get several
* answers at once (!). */
while (buf_datalen(conn->inbuf)) {
connection_fetch_from_buf(&success,1,conn);
connection_fetch_from_buf((char *)&addr,sizeof(uint32_t),conn);
log_warn(LD_EXIT,"Discarding idle dns answer (success %d, addr %d.)",
success, addr);
}
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_debug(LD_EXIT, "DNSWorker (fd %d) returned answer for %s",
conn->s, escaped_safe_str(conn->address));
tor_assert(success >= DNS_RESOLVE_FAILED_TRANSIENT);
tor_assert(success <= DNS_RESOLVE_SUCCEEDED);
ttl = (success == DNS_RESOLVE_FAILED_TRANSIENT) ? 0 : MAX_DNS_ENTRY_AGE;
dns_found_answer(conn->address, ntohl(addr), success, ttl);
tor_free(conn->address);
conn->address = tor_strdup("<idle>");
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);
if (server_mode(get_options()))
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 *log_address;
char answer[5];
uint32_t ip;
int *fdarray = data;
int fd;
int result;
/* log_fn(LOG_NOTICE,"After spawn: fdarray @%d has %d:%d", (int)fdarray,
* fdarray[0],fdarray[1]); */
fd = fdarray[1]; /* this side is ours */
#ifndef TOR_IS_MULTITHREADED
tor_close_socket(fdarray[0]); /* this is the side of the socketpair the
* parent uses */
tor_free_all(1); /* so the child doesn't hold the parent's fd's open */
handle_signals(0); /* ignore interrupts from the keyboard, etc */
#endif
tor_free(data);
for (;;) {
int r;
if ((r = recv(fd, &address_len, 1, 0)) != 1) {
if (r == 0) {
log_info(LD_EXIT,"DNS worker exiting because Tor process closed "
"connection (either pruned idle dnsworker or died).");
} else {
log_info(LD_EXIT,"DNS worker exiting because of error on connection "
"to Tor process.");
log_info(LD_EXIT,"(Error on %d was %s)", fd,
tor_socket_strerror(tor_socket_errno(fd)));
}
tor_close_socket(fd);
crypto_thread_cleanup();
spawn_exit();
}
if (address_len && read_all(fd, address, address_len, 1) != address_len) {
log_err(LD_BUG,"read hostname failed. Child exiting.");
tor_close_socket(fd);
crypto_thread_cleanup();
spawn_exit();
}
address[address_len] = 0; /* nul terminate it */
log_address = esc_for_log(safe_str(address));
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:
/* XXX result can never be 1, because we set it to -1 above on error */
log_info(LD_NET,"Could not resolve dest addr %s (transient).",
log_address);
answer[0] = DNS_RESOLVE_FAILED_TRANSIENT;
break;
case -1:
log_info(LD_NET,"Could not resolve dest addr %s (permanent).",
log_address);
answer[0] = DNS_RESOLVE_FAILED_PERMANENT;
break;
case 0:
log_info(LD_NET,"Resolved address %s.", log_address);
answer[0] = DNS_RESOLVE_SUCCEEDED;
break;
}
tor_free(log_address);
set_uint32(answer+1, ip);
if (write_all(fd, answer, 5, 1) != 5) {
log_err(LD_NET,"writing answer failed. Child exiting.");
tor_close_socket(fd);
crypto_thread_cleanup();
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 *fdarray;
int fd;
connection_t *conn;
int err;
fdarray = tor_malloc(sizeof(int)*2);
if ((err = tor_socketpair(AF_UNIX, SOCK_STREAM, 0, fdarray)) < 0) {
log_warn(LD_NET, "Couldn't construct socketpair: %s",
tor_socket_strerror(-err));
tor_free(fdarray);
return -1;
}
tor_assert(fdarray[0] >= 0);
tor_assert(fdarray[1] >= 0);
/* log_fn(LOG_NOTICE,"Before spawn: fdarray @%d has %d:%d",
(int)fdarray, fdarray[0],fdarray[1]); */
fd = fdarray[0]; /* We copy this out here, since dnsworker_main may free
* fdarray */
spawn_func(dnsworker_main, (void*)fdarray);
log_debug(LD_EXIT,"just spawned a dns worker.");
#ifndef TOR_IS_MULTITHREADED
tor_close_socket(fdarray[1]); /* don't need the worker's side of the pipe */
tor_free(fdarray);
#endif
conn = connection_new(CONN_TYPE_DNSWORKER);
set_socket_nonblocking(fd);
/* set up conn so it's got all the data we need to remember */
conn->s = fd;
conn->address = tor_strdup("<unused>");
if (connection_add(conn) < 0) { /* no space, forget it */
log_warn(LD_NET,"connection_add failed. Giving up.");
connection_free(conn); /* this closes fd */
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.
* Return 0 if we are happy, return -1 if we tried to spawn more but
* we couldn't.
*/
static int
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_warn(LD_EXIT, "%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_warn(LD_EXIT,"Spawn failed. Will try again later.");
return -1;
}
num_dnsworkers++;
}
while (num_dnsworkers > num_dnsworkers_busy+MAX_IDLE_DNSWORKERS) {
/* too many idle? */
/* cull excess workers */
log_info(LD_EXIT,"%d of %d dnsworkers are idle. Killing one.",
num_dnsworkers-num_dnsworkers_busy, num_dnsworkers);
dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER,
DNSWORKER_STATE_IDLE);
tor_assert(dnsconn);
connection_mark_for_close(dnsconn);
num_dnsworkers--;
}
return 0;
}
#else /* !USE_EVENTDNS */
static int
eventdns_err_is_transient(int err)
{
switch (err)
{
case DNS_ERR_SERVERFAILED:
case DNS_ERR_TRUNCATED:
case DNS_ERR_TIMEOUT:
return 1;
default:
return 0;
}
}
void
dnsworkers_rotate(void)
{
}
int
connection_dns_finished_flushing(connection_t *conn)
{
(void)conn;
tor_assert(0);
return 0;
}
int
connection_dns_process_inbuf(connection_t *conn)
{
(void)conn;
tor_assert(0);
return 0;
}
int
connection_dns_reached_eof(connection_t *conn)
{
(void)conn;
tor_assert(0);
return 0;
}
static int nameservers_configured = 0;
static void
configure_nameservers(void)
{
or_options_t *options;
if (nameservers_configured)
return;
options = get_options();
eventdns_set_log_fn(eventdns_log_cb);
if (options->Nameservers && smartlist_len(options->Nameservers)) {
log_info(LD_EXIT, "Configuring nameservers from Tor configuration");
SMARTLIST_FOREACH(options->Nameservers, const char *, ip,
{
struct in_addr in;
if (tor_inet_aton(ip, &in)) {
log_info(LD_EXIT, "Adding nameserver '%s'", ip);
eventdns_nameserver_add(in.s_addr);
}
});
} else {
#ifdef MS_WINDOWS
eventdns_config_windows_nameservers();
#else
log_info(LD_EXIT, "Parsing /etc/resolv.conf");
eventdns_resolv_conf_parse(DNS_OPTION_NAMESERVERS|DNS_OPTION_MISC,
"/etc/resolv.conf");
#endif
}
nameservers_configured = 1;
}
static void
eventdns_callback(int result, char type, int count, int ttl, void *addresses,
void *arg)
{
char *string_address = arg;
int status = DNS_RESOLVE_FAILED_PERMANENT;
uint32_t addr = 0;
if (result == DNS_ERR_NONE) {
if (type == DNS_IPv4_A && count) {
char answer_buf[INET_NTOA_BUF_LEN+1];
struct in_addr in;
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));
log_debug(LD_EXIT, "eventdns said that %s resolves to %s",
escaped_safe_str(string_address),
escaped_safe_str(answer_buf));
} 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 (eventdns_err_is_transient(result))
status = DNS_RESOLVE_FAILED_TRANSIENT;
}
dns_found_answer(string_address, addr, status, ttl);
tor_free(string_address);
}
static int
launch_resolve(edge_connection_t *exitconn)
{
char *addr = tor_strdup(exitconn->_base.address);
int r;
if (!nameservers_configured)
configure_nameservers();
log_info(LD_EXIT, "Launching eventdns request for %s",
escaped_safe_str(exitconn->_base.address));
r = eventdns_resolve(exitconn->_base.address, DNS_QUERY_NO_SEARCH,
eventdns_callback, addr);
if (r) {
log_warn(LD_EXIT, "eventdns rejected address %s: error %d.",
escaped_safe_str(addr), r);
if (exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE) {
if (eventdns_err_is_transient(r))
send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR_TRANSIENT);
else {
exitconn->address_ttl = DEFAULT_DNS_TTL;
send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR);
}
}
dns_cancel_pending_resolve(addr);/* also sends end and frees */
tor_free(addr);
}
return r ? -1 : 0;
}
#endif /* USE_EVENTDNS */
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);
tor_assert(!resolve->addr);
}
}
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);
}