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tor/src/or/dnsserv.c

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/* Copyright (c) 2007-2017, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/**
* \file dnsserv.c
* \brief Implements client-side DNS proxy server code.
*
* When a user enables the DNSPort configuration option to have their local
* Tor client handle DNS requests, this module handles it. It functions as a
* "DNS Server" on the client side, which client applications use.
*
* Inbound DNS requests are represented as entry_connection_t here (since
* that's how Tor represents client-side streams), which are kept associated
* with an evdns_server_request structure as exposed by Libevent's
* evdns code.
*
* Upon receiving a DNS request, libevent calls our evdns_server_callback()
* function here, which causes this module to create an entry_connection_t
* request as appropriate. Later, when that request is answered,
* connection_edge.c calls dnsserv_resolved() so we can finish up and tell the
* DNS client.
**/
#include "or.h"
#include "dnsserv.h"
#include "config.h"
#include "connection.h"
#include "connection_edge.h"
#include "control.h"
#include "main.h"
#include "policies.h"
#include <event2/dns.h>
#include <event2/dns_compat.h>
/* XXXX this implies we want an improved evdns */
#include <event2/dns_struct.h>
/** Helper function: called by evdns whenever the client sends a request to our
* DNSPort. We need to eventually answer the request <b>req</b>.
*/
static void
evdns_server_callback(struct evdns_server_request *req, void *data_)
{
const listener_connection_t *listener = data_;
entry_connection_t *entry_conn;
edge_connection_t *conn;
int i = 0;
struct evdns_server_question *q = NULL, *supported_q = NULL;
struct sockaddr_storage addr;
struct sockaddr *sa;
int addrlen;
tor_addr_t tor_addr;
uint16_t port;
int err = DNS_ERR_NONE;
char *q_name;
tor_assert(req);
log_info(LD_APP, "Got a new DNS request!");
req->flags |= 0x80; /* set RA */
/* First, check whether the requesting address matches our SOCKSPolicy. */
if ((addrlen = evdns_server_request_get_requesting_addr(req,
(struct sockaddr*)&addr, (socklen_t)sizeof(addr))) < 0) {
log_warn(LD_APP, "Couldn't get requesting address.");
evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
return;
}
(void) addrlen;
sa = (struct sockaddr*) &addr;
if (tor_addr_from_sockaddr(&tor_addr, sa, &port)<0) {
log_warn(LD_APP, "Requesting address wasn't recognized.");
evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
return;
}
if (!socks_policy_permits_address(&tor_addr)) {
log_warn(LD_APP, "Rejecting DNS request from disallowed IP.");
evdns_server_request_respond(req, DNS_ERR_REFUSED);
return;
}
/* Now, let's find the first actual question of a type we can answer in this
* DNS request. It makes us a little noncompliant to act like this; we
* should fix that eventually if it turns out to make a difference for
* anybody. */
if (req->nquestions == 0) {
log_info(LD_APP, "No questions in DNS request; sending back nil reply.");
evdns_server_request_respond(req, 0);
return;
}
if (req->nquestions > 1) {
log_info(LD_APP, "Got a DNS request with more than one question; I only "
"handle one question at a time for now. Skipping the extras.");
}
for (i = 0; i < req->nquestions; ++i) {
if (req->questions[i]->dns_question_class != EVDNS_CLASS_INET)
continue;
switch (req->questions[i]->type) {
case EVDNS_TYPE_A:
case EVDNS_TYPE_AAAA:
case EVDNS_TYPE_PTR:
/* We always pick the first one of these questions, if there is
one. */
if (! supported_q)
supported_q = req->questions[i];
break;
default:
break;
}
}
if (supported_q)
q = supported_q;
if (!q) {
log_info(LD_APP, "None of the questions we got were ones we're willing "
"to support. Sending NOTIMPL.");
evdns_server_request_respond(req, DNS_ERR_NOTIMPL);
return;
}
/* Make sure the name isn't too long: This should be impossible, I think. */
if (err == DNS_ERR_NONE && strlen(q->name) > MAX_SOCKS_ADDR_LEN-1)
err = DNS_ERR_FORMAT;
if (err != DNS_ERR_NONE || !supported_q) {
/* We got an error? There's no question we're willing to answer? Then
* send back an answer immediately; we're done. */
evdns_server_request_respond(req, err);
return;
}
/* Make a new dummy AP connection, and attach the request to it. */
entry_conn = entry_connection_new(CONN_TYPE_AP, AF_INET);
conn = ENTRY_TO_EDGE_CONN(entry_conn);
CONNECTION_AP_EXPECT_NONPENDING(entry_conn);
TO_CONN(conn)->state = AP_CONN_STATE_RESOLVE_WAIT;
conn->is_dns_request = 1;
tor_addr_copy(&TO_CONN(conn)->addr, &tor_addr);
TO_CONN(conn)->port = port;
TO_CONN(conn)->address = tor_addr_to_str_dup(&tor_addr);
if (q->type == EVDNS_TYPE_A || q->type == EVDNS_TYPE_AAAA ||
q->type == EVDNS_QTYPE_ALL) {
entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE;
} else {
tor_assert(q->type == EVDNS_TYPE_PTR);
entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE_PTR;
}
/* This serves our DNS port so enable DNS request by default. */
entry_conn->entry_cfg.dns_request = 1;
if (q->type == EVDNS_TYPE_A || q->type == EVDNS_QTYPE_ALL) {
entry_conn->entry_cfg.ipv4_traffic = 1;
entry_conn->entry_cfg.ipv6_traffic = 0;
entry_conn->entry_cfg.prefer_ipv6 = 0;
} else if (q->type == EVDNS_TYPE_AAAA) {
entry_conn->entry_cfg.ipv4_traffic = 0;
entry_conn->entry_cfg.ipv6_traffic = 1;
entry_conn->entry_cfg.prefer_ipv6 = 1;
}
strlcpy(entry_conn->socks_request->address, q->name,
sizeof(entry_conn->socks_request->address));
entry_conn->socks_request->listener_type = listener->base_.type;
entry_conn->dns_server_request = req;
entry_conn->entry_cfg.isolation_flags = listener->entry_cfg.isolation_flags;
entry_conn->entry_cfg.session_group = listener->entry_cfg.session_group;
entry_conn->nym_epoch = get_signewnym_epoch();
if (connection_add(ENTRY_TO_CONN(entry_conn)) < 0) {
log_warn(LD_APP, "Couldn't register dummy connection for DNS request");
evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
connection_free_(ENTRY_TO_CONN(entry_conn));
return;
}
control_event_stream_status(entry_conn, STREAM_EVENT_NEW_RESOLVE, 0);
/* Now, unless a controller asked us to leave streams unattached,
* throw the connection over to get rewritten (which will
* answer it immediately if it's in the cache, or completely bogus, or
* automapped), and then attached to a circuit. */
log_info(LD_APP, "Passing request for %s to rewrite_and_attach.",
escaped_safe_str_client(q->name));
q_name = tor_strdup(q->name); /* q could be freed in rewrite_and_attach */
connection_ap_rewrite_and_attach_if_allowed(entry_conn, NULL, NULL);
/* Now, the connection is marked if it was bad. */
log_info(LD_APP, "Passed request for %s to rewrite_and_attach_if_allowed.",
escaped_safe_str_client(q_name));
tor_free(q_name);
}
/** Helper function: called whenever the client sends a resolve request to our
* controller. We need to eventually answer the request <b>req</b>.
* Returns 0 if the controller will be getting (or has gotten) an event in
* response; -1 if we couldn't launch the request.
*/
int
dnsserv_launch_request(const char *name, int reverse,
control_connection_t *control_conn)
{
entry_connection_t *entry_conn;
edge_connection_t *conn;
char *q_name;
/* Make a new dummy AP connection, and attach the request to it. */
entry_conn = entry_connection_new(CONN_TYPE_AP, AF_INET);
entry_conn->entry_cfg.dns_request = 1;
conn = ENTRY_TO_EDGE_CONN(entry_conn);
CONNECTION_AP_EXPECT_NONPENDING(entry_conn);
conn->base_.state = AP_CONN_STATE_RESOLVE_WAIT;
tor_addr_copy(&TO_CONN(conn)->addr, &control_conn->base_.addr);
#ifdef AF_UNIX
/*
* The control connection can be AF_UNIX and if so tor_addr_to_str_dup will
* unhelpfully say "<unknown address type>"; say "(Tor_internal)"
* instead.
*/
if (control_conn->base_.socket_family == AF_UNIX) {
TO_CONN(conn)->port = 0;
TO_CONN(conn)->address = tor_strdup("(Tor_internal)");
} else {
TO_CONN(conn)->port = control_conn->base_.port;
TO_CONN(conn)->address = tor_addr_to_str_dup(&control_conn->base_.addr);
}
#else /* !(defined(AF_UNIX)) */
TO_CONN(conn)->port = control_conn->base_.port;
TO_CONN(conn)->address = tor_addr_to_str_dup(&control_conn->base_.addr);
#endif /* defined(AF_UNIX) */
if (reverse)
entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE_PTR;
else
entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE;
conn->is_dns_request = 1;
strlcpy(entry_conn->socks_request->address, name,
sizeof(entry_conn->socks_request->address));
entry_conn->socks_request->listener_type = CONN_TYPE_CONTROL_LISTENER;
entry_conn->original_dest_address = tor_strdup(name);
entry_conn->entry_cfg.session_group = SESSION_GROUP_CONTROL_RESOLVE;
entry_conn->nym_epoch = get_signewnym_epoch();
entry_conn->entry_cfg.isolation_flags = ISO_DEFAULT;
if (connection_add(TO_CONN(conn))<0) {
log_warn(LD_APP, "Couldn't register dummy connection for RESOLVE request");
connection_free_(TO_CONN(conn));
return -1;
}
control_event_stream_status(entry_conn, STREAM_EVENT_NEW_RESOLVE, 0);
/* Now, unless a controller asked us to leave streams unattached,
* throw the connection over to get rewritten (which will
* answer it immediately if it's in the cache, or completely bogus, or
* automapped), and then attached to a circuit. */
log_info(LD_APP, "Passing request for %s to rewrite_and_attach.",
escaped_safe_str_client(name));
q_name = tor_strdup(name); /* q could be freed in rewrite_and_attach */
connection_ap_rewrite_and_attach_if_allowed(entry_conn, NULL, NULL);
/* Now, the connection is marked if it was bad. */
log_info(LD_APP, "Passed request for %s to rewrite_and_attach_if_allowed.",
escaped_safe_str_client(q_name));
tor_free(q_name);
return 0;
}
/** If there is a pending request on <b>conn</b> that's waiting for an answer,
* send back an error and free the request. */
void
dnsserv_reject_request(entry_connection_t *conn)
{
if (conn->dns_server_request) {
evdns_server_request_respond(conn->dns_server_request,
DNS_ERR_SERVERFAILED);
conn->dns_server_request = NULL;
}
}
/** Look up the original name that corresponds to 'addr' in req. We use this
* to preserve case in order to facilitate clients using 0x20-hacks to avoid
* DNS poisoning. */
static const char *
evdns_get_orig_address(const struct evdns_server_request *req,
int rtype, const char *addr)
{
int i, type;
switch (rtype) {
case RESOLVED_TYPE_IPV4:
type = EVDNS_TYPE_A;
break;
case RESOLVED_TYPE_HOSTNAME:
type = EVDNS_TYPE_PTR;
break;
case RESOLVED_TYPE_IPV6:
type = EVDNS_TYPE_AAAA;
break;
case RESOLVED_TYPE_ERROR:
case RESOLVED_TYPE_ERROR_TRANSIENT:
/* Addr doesn't matter, since we're not sending it back in the reply.*/
return addr;
default:
tor_fragile_assert();
return addr;
}
for (i = 0; i < req->nquestions; ++i) {
const struct evdns_server_question *q = req->questions[i];
if (q->type == type && !strcasecmp(q->name, addr))
return q->name;
}
return addr;
}
/** Tell the dns request waiting for an answer on <b>conn</b> that we have an
* answer of type <b>answer_type</b> (RESOLVE_TYPE_IPV4/IPV6/ERR), of length
* <b>answer_len</b>, in <b>answer</b>, with TTL <b>ttl</b>. Doesn't do
* any caching; that's handled elsewhere. */
void
dnsserv_resolved(entry_connection_t *conn,
int answer_type,
size_t answer_len,
const char *answer,
int ttl)
{
struct evdns_server_request *req = conn->dns_server_request;
const char *name;
int err = DNS_ERR_NONE;
if (!req)
return;
name = evdns_get_orig_address(req, answer_type,
conn->socks_request->address);
/* XXXX Re-do; this is dumb. */
if (ttl < 60)
ttl = 60;
/* The evdns interface is: add a bunch of reply items (corresponding to one
* or more of the questions in the request); then, call
* evdns_server_request_respond. */
if (answer_type == RESOLVED_TYPE_IPV6) {
evdns_server_request_add_aaaa_reply(req,
name,
1, answer, ttl);
} else if (answer_type == RESOLVED_TYPE_IPV4 && answer_len == 4 &&
conn->socks_request->command == SOCKS_COMMAND_RESOLVE) {
evdns_server_request_add_a_reply(req,
name,
1, answer, ttl);
} else if (answer_type == RESOLVED_TYPE_HOSTNAME &&
answer_len < 256 &&
conn->socks_request->command == SOCKS_COMMAND_RESOLVE_PTR) {
char *ans = tor_strndup(answer, answer_len);
evdns_server_request_add_ptr_reply(req, NULL,
name,
ans, ttl);
tor_free(ans);
} else if (answer_type == RESOLVED_TYPE_ERROR) {
err = DNS_ERR_NOTEXIST;
} else { /* answer_type == RESOLVED_TYPE_ERROR_TRANSIENT */
err = DNS_ERR_SERVERFAILED;
}
evdns_server_request_respond(req, err);
conn->dns_server_request = NULL;
}
/** Set up the evdns server port for the UDP socket on <b>conn</b>, which
* must be an AP_DNS_LISTENER */
void
dnsserv_configure_listener(connection_t *conn)
{
listener_connection_t *listener_conn;
tor_assert(conn);
tor_assert(SOCKET_OK(conn->s));
tor_assert(conn->type == CONN_TYPE_AP_DNS_LISTENER);
listener_conn = TO_LISTENER_CONN(conn);
listener_conn->dns_server_port =
tor_evdns_add_server_port(conn->s, 0, evdns_server_callback,
listener_conn);
}
/** Free the evdns server port for <b>conn</b>, which must be an
* AP_DNS_LISTENER. */
void
dnsserv_close_listener(connection_t *conn)
{
listener_connection_t *listener_conn;
tor_assert(conn);
tor_assert(conn->type == CONN_TYPE_AP_DNS_LISTENER);
listener_conn = TO_LISTENER_CONN(conn);
if (listener_conn->dns_server_port) {
evdns_close_server_port(listener_conn->dns_server_port);
listener_conn->dns_server_port = NULL;
}
}
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