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tor/src/or/dns.c

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/* Copyright (c) 2003-2004, Roger Dingledine.
* Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
* Copyright (c) 2007-2008, The Tor Project, Inc. */
/* 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.
* 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"
#include "eventdns.h"
/** 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
/** Have we currently configured nameservers with eventdns? */
static int nameservers_configured = 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 <b>address</b>. */
uint32_t addr; /**< IPv4 addr for <b>address</b>. */
} a;
char *hostname; /**< Hostname for <b>address</b> (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;
} 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: generate a good random transaction ID. */
static uint16_t
dns_get_transaction_id(void)
{
uint16_t result;
crypto_rand((void*)&result, sizeof(result));
return result;
}
/** Initialize the DNS subsystem; called by the OR process. */
int
dns_init(void)
{
init_cache_map();
evdns_set_transaction_id_fn(dns_get_transaction_id);
if (server_mode(get_options()))
return configure_nameservers(1);
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_clear_nameservers_and_suspend();
evdns_search_clear();
nameservers_configured = 0;
tor_free(resolv_conf_fname);
resolv_conf_mtime = 0;
} else {
if (configure_nameservers(0) < 0)
return -1;
}
return 0;
}
/** 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)
{
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,
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);
if (cached_resolve_pqueue)
smartlist_free(cached_resolve_pqueue);
cached_resolve_pqueue = NULL;
tor_free(resolv_conf_fname);
}
/** Remove every cached_resolve whose <b>expire</b> time is before or
* equal to <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);
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.
* <b>answer_type</b> must be one of
* RESOLVED_TYPE_(IPV4|ERROR|ERROR_TRANSIENT).
*
* If <b>circ</b> is provided, and we have a cached answer, send the
* answer back along circ; otherwise, send the answer back along
* <b>conn</b>'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;
/*XXXX021 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 <b>conn</b> which yielded the result <b>hostname</b>.
* The answer type will be RESOLVED_HOSTNAME.
*
* If <b>circ</b> is provided, and we have a cached answer, send the
* answer back along circ; otherwise, send the answer back along
* <b>conn</b>'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");
}
/** Given a lower-case <b>address</b>, check to see whether it's a
* 1.2.3.4.in-addr.arpa address used for reverse lookups. If so,
* parse it and place the address in <b>in</b> if present. Return 1 on success;
* 0 if the address is not in in-addr.arpa format, and -1 if the address is
* malformed. */
/* XXXX021 move this to util.c. */
int
parse_inaddr_arpa_address(const char *address, struct in_addr *in)
{
char buf[INET_NTOA_BUF_LEN];
char *cp;
size_t len;
struct in_addr inaddr;
cp = strstr(address, ".in-addr.arpa");
if (!cp || *(cp+strlen(".in-addr.arpa")))
return 0; /* not an .in-addr.arpa address */
len = cp - address;
if (len >= INET_NTOA_BUF_LEN)
return -1; /* Too long. */
memcpy(buf, address, len);
buf[len] = '\0';
if (tor_inet_aton(buf, &inaddr) == 0)
return -1; /* malformed. */
if (in) {
uint32_t a;
/* reverse the bytes */
a = (uint32_t) ( ((inaddr.s_addr & 0x000000fful) << 24)
|((inaddr.s_addr & 0x0000ff00ul) << 8)
|((inaddr.s_addr & 0x00ff0000ul) >> 8)
|((inaddr.s_addr & 0xff000000ul) >> 24));
inaddr.s_addr = a;
memcpy(in, &inaddr, sizeof(inaddr));
}
return 1;
}
/** 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, 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 <b>exitconn</b>'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));
//XXX020 ... 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
// "<armadev> 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 *<b>hostname_out</b> 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;
struct in_addr in;
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_inet_aton(exitconn->_base.address, &in) != 0) {
tor_addr_from_ipv4n(&exitconn->_base.addr, in.s_addr);
exitconn->address_ttl = DEFAULT_DNS_TTL;
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 = parse_inaddr_arpa_address(exitconn->_base.address, &in)) != 0) {
if (r == 1) {
is_reverse = 1;
if (is_internal_IP(ntohl(in.s_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->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 **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(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 <b>address</b> to the ipv4
* address <b>addr</b> (if is_reverse is 0) or the hostname <b>hostname</b> (if
* is_reverse is 1). <b>ttl</b> is a cache ttl; <b>outcome</b> 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 <b>address</b> 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. (<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, 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) {
/* XXXX020 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 <b>err</b> 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. On Unix, this
* reads from options->ServerDNSResolvConfFile or /etc/resolv.conf; 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
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));
return options->ServerDNSAllowBrokenResolvConf ? 0 : -1;
}
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_search_clear();
evdns_clear_nameservers_and_suspend();
}
log_info(LD_EXIT, "Parsing resolver configuration in '%s'", conf_fname);
if ((r = evdns_resolv_conf_parse(DNS_OPTIONS_ALL, conf_fname))) {
log_warn(LD_EXIT, "Unable to parse '%s', or no nameservers in '%s' (%d)",
conf_fname, conf_fname, r);
return options->ServerDNSAllowBrokenResolvConf ? 0 : -1;
}
if (evdns_count_nameservers() == 0) {
log_warn(LD_EXIT, "Unable to find any nameservers in '%s'.", conf_fname);
return options->ServerDNSAllowBrokenResolvConf ? 0 : -1;
}
tor_free(resolv_conf_fname);
resolv_conf_fname = tor_strdup(conf_fname);
resolv_conf_mtime = st.st_mtime;
if (nameservers_configured)
evdns_resume();
}
#ifdef MS_WINDOWS
else {
if (nameservers_configured) {
evdns_search_clear();
evdns_clear_nameservers_and_suspend();
}
if (evdns_config_windows_nameservers()) {
log_warn(LD_EXIT,"Could not config nameservers.");
return options->ServerDNSAllowBrokenResolvConf ? 0 : -1;
}
if (evdns_count_nameservers() == 0) {
log_warn(LD_EXIT, "Unable to find any platform nameservers in "
"your Windows configuration. Perhaps you should list a "
"ServerDNSResolvConfFile file in your torrc?");
return options->ServerDNSAllowBrokenResolvConf ? 0 : -1;
}
if (nameservers_configured)
evdns_resume();
tor_free(resolv_conf_fname);
resolv_conf_mtime = 0;
}
#endif
if (evdns_count_nameservers() == 1) {
evdns_set_option("max-timeouts:", "16", DNS_OPTIONS_ALL);
evdns_set_option("timeout:", "10", DNS_OPTIONS_ALL);
} else {
evdns_set_option("max-timeouts:", "3", DNS_OPTIONS_ALL);
evdns_set_option("timeout:", "5", DNS_OPTIONS_ALL);
}
dns_servers_relaunch_checks();
nameservers_configured = 1;
return 0;
}
/** 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
* <b>exitconn</b>. 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 in_addr in;
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 = parse_inaddr_arpa_address(exitconn->_base.address, &in);
if (r == 0) {
log_info(LD_EXIT, "Launching eventdns request for %s",
escaped_safe_str(exitconn->_base.address));
r = evdns_resolve_ipv4(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));
r = evdns_resolve_reverse(&in, DNS_QUERY_NO_SEARCH,
evdns_callback, addr);
} else if (r == -1) {
log_warn(LD_BUG, "Somehow a malformed in-addr.arpa address reached here.");
}
if (r) {
log_warn(LD_EXIT, "eventdns rejected address %s: error %d.",
escaped_safe_str(addr), r);
r = evdns_err_is_transient(r) ? -2 : -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 <b>id</b> (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
* <b>min_len</b> and <b>max_len</b> random (plausible) characters followed by
* <b>suffix</b> */
static void
launch_wildcard_check(int min_len, int max_len, const char *suffix)
{
char *addr;
int r;
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);
r = evdns_resolve_ipv4(/* 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 (r) {
/* 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();
(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(options->ServerDNSTestAddresses, const char *, address,
{
int r = evdns_resolve_ipv4(address, DNS_QUERY_NO_SEARCH, evdns_callback,
tor_strdup(address));
if (r)
log_info(LD_EXIT, "eventdns rejected test address %s: error %d",
escaped_safe_str(address), r);
});
}
#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;
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. */
evtimer_set(&launch_event, 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 trustd. */
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)
{
if (dns_wildcard_response_count) {
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 <b>ip</b> 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 <b>resolve</b> 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);
}
}
#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);
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
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