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evdns.c
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/* $Id: evdns.c 6979 2006-08-04 18:31:13Z nickm $ */
/* The original version of this module was written by Adam Langley; for
* a history of modifications, check out the subversion logs.
*
* When editing this module, try to keep it re-mergeable by Adam. Don't
* reformat the whitespace, add Tor dependencies, or so on.
*
* TODO:
* - Support IPv6 and PTR records.
* - Replace all externally visible magic numbers with #defined constants.
* - Write documentation for APIs of all external functions.
*/
/* Async DNS Library
* Adam Langley <[email protected]>
* http://www.imperialviolet.org/eventdns.html
* Public Domain code
*
* This software is Public Domain. To view a copy of the public domain dedication,
* visit http://creativecommons.org/licenses/publicdomain/ or send a letter to
* Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
*
* I ask and expect, but do not require, that all derivative works contain an
* attribution similar to:
* Parts developed by Adam Langley <[email protected]>
*
* You may wish to replace the word "Parts" with something else depending on
* the amount of original code.
*
* (Derivative works does not include programs which link against, run or include
* the source verbatim in their source distributions)
*
* Version: 0.1b
*/
#include <sys/types.h>
#include "event2/event-config.h"
#ifndef _FORTIFY_SOURCE
#define _FORTIFY_SOURCE 3
#endif
#include <string.h>
#include <fcntl.h>
#ifdef _EVENT_HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#ifdef _EVENT_HAVE_STDINT_H
#include <stdint.h>
#endif
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#ifdef _EVENT_HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <limits.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdarg.h>
#ifdef WIN32
#include <winsock2.h>
#include <ws2tcpip.h>
#ifndef _WIN32_IE
#define _WIN32_IE 0x400
#endif
#include <shlobj.h>
#endif
#include "event2/dns.h"
#include "event2/dns_struct.h"
#include "event2/dns_compat.h"
#include "event2/util.h"
#include "event2/event.h"
#include "event2/event_struct.h"
#include "event2/thread.h"
#include "event2/bufferevent.h"
#include "event2/bufferevent_struct.h"
#include "bufferevent-internal.h"
#include "defer-internal.h"
#include "log-internal.h"
#include "mm-internal.h"
#include "strlcpy-internal.h"
#include "ipv6-internal.h"
#include "util-internal.h"
#include "evthread-internal.h"
#ifdef WIN32
#include <ctype.h>
#include <winsock2.h>
#include <windows.h>
#include <iphlpapi.h>
#include <io.h>
#else
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#endif
#ifdef _EVENT_HAVE_NETINET_IN6_H
#include <netinet/in6.h>
#endif
#define EVDNS_LOG_DEBUG 0
#define EVDNS_LOG_WARN 1
#define EVDNS_LOG_MSG 2
#ifndef HOST_NAME_MAX
#define HOST_NAME_MAX 255
#endif
#include <stdio.h>
#undef MIN
#define MIN(a,b) ((a)<(b)?(a):(b))
#define ASSERT_VALID_REQUEST(req) \
EVUTIL_ASSERT((req)->handle && (req)->handle->current_req == (req))
#define u64 ev_uint64_t
#define u32 ev_uint32_t
#define u16 ev_uint16_t
#define u8 ev_uint8_t
/* maximum number of addresses from a single packet */
/* that we bother recording */
#define MAX_V4_ADDRS 32
#define MAX_V6_ADDRS 32
#define TYPE_A EVDNS_TYPE_A
#define TYPE_CNAME 5
#define TYPE_PTR EVDNS_TYPE_PTR
#define TYPE_AAAA EVDNS_TYPE_AAAA
#define CLASS_INET EVDNS_CLASS_INET
/* Persistent handle. We keep this separate from 'struct request' since we
* need some object to last for as long as an evdns_request is outstanding so
* that it can be canceled, whereas a search request can lead to multiple
* 'struct request' instances being created over its lifetime. */
struct evdns_request {
struct request *current_req;
struct evdns_base *base;
int pending_cb; /* Waiting for its callback to be invoked; not
* owned by event base any more. */
/* elements used by the searching code */
int search_index;
struct search_state *search_state;
char *search_origname; /* needs to be free()ed */
int search_flags;
};
struct request {
u8 *request; /* the dns packet data */
u8 request_type; /* TYPE_PTR or TYPE_A or TYPE_AAAA */
unsigned int request_len;
int reissue_count;
int tx_count; /* the number of times that this packet has been sent */
void *user_pointer; /* the pointer given to us for this request */
evdns_callback_type user_callback;
struct nameserver *ns; /* the server which we last sent it */
/* these objects are kept in a circular list */
struct request *next, *prev;
struct event timeout_event;
u16 trans_id; /* the transaction id */
unsigned request_appended :1; /* true if the request pointer is data which follows this struct */
unsigned transmit_me :1; /* needs to be transmitted */
/* XXXX This is a horrible hack. */
char **put_cname_in_ptr; /* store the cname here if we get one. */
struct evdns_base *base;
struct evdns_request *handle;
};
struct reply {
unsigned int type;
unsigned int have_answer : 1;
union {
struct {
u32 addrcount;
u32 addresses[MAX_V4_ADDRS];
} a;
struct {
u32 addrcount;
struct in6_addr addresses[MAX_V6_ADDRS];
} aaaa;
struct {
char name[HOST_NAME_MAX];
} ptr;
} data;
};
struct nameserver {
evutil_socket_t socket; /* a connected UDP socket */
struct sockaddr_storage address;
ev_socklen_t addrlen;
int failed_times; /* number of times which we have given this server a chance */
int timedout; /* number of times in a row a request has timed out */
struct event event;
/* these objects are kept in a circular list */
struct nameserver *next, *prev;
struct event timeout_event; /* used to keep the timeout for */
/* when we next probe this server. */
/* Valid if state == 0 */
/* Outstanding probe request for this nameserver, if any */
struct evdns_request *probe_request;
char state; /* zero if we think that this server is down */
char choked; /* true if we have an EAGAIN from this server's socket */
char write_waiting; /* true if we are waiting for EV_WRITE events */
struct evdns_base *base;
};
/* Represents a local port where we're listening for DNS requests. Right now, */
/* only UDP is supported. */
struct evdns_server_port {
evutil_socket_t socket; /* socket we use to read queries and write replies. */
int refcnt; /* reference count. */
char choked; /* Are we currently blocked from writing? */
char closing; /* Are we trying to close this port, pending writes? */
evdns_request_callback_fn_type user_callback; /* Fn to handle requests */
void *user_data; /* Opaque pointer passed to user_callback */
struct event event; /* Read/write event */
/* circular list of replies that we want to write. */
struct server_request *pending_replies;
struct event_base *event_base;
#ifndef _EVENT_DISABLE_THREAD_SUPPORT
void *lock;
#endif
};
/* Represents part of a reply being built. (That is, a single RR.) */
struct server_reply_item {
struct server_reply_item *next; /* next item in sequence. */
char *name; /* name part of the RR */
u16 type; /* The RR type */
u16 class; /* The RR class (usually CLASS_INET) */
u32 ttl; /* The RR TTL */
char is_name; /* True iff data is a label */
u16 datalen; /* Length of data; -1 if data is a label */
void *data; /* The contents of the RR */
};
/* Represents a request that we've received as a DNS server, and holds */
/* the components of the reply as we're constructing it. */
struct server_request {
/* Pointers to the next and previous entries on the list of replies */
/* that we're waiting to write. Only set if we have tried to respond */
/* and gotten EAGAIN. */
struct server_request *next_pending;
struct server_request *prev_pending;
u16 trans_id; /* Transaction id. */
struct evdns_server_port *port; /* Which port received this request on? */
struct sockaddr_storage addr; /* Where to send the response */
ev_socklen_t addrlen; /* length of addr */
int n_answer; /* how many answer RRs have been set? */
int n_authority; /* how many authority RRs have been set? */
int n_additional; /* how many additional RRs have been set? */
struct server_reply_item *answer; /* linked list of answer RRs */
struct server_reply_item *authority; /* linked list of authority RRs */
struct server_reply_item *additional; /* linked list of additional RRs */
/* Constructed response. Only set once we're ready to send a reply. */
/* Once this is set, the RR fields are cleared, and no more should be set. */
char *response;
size_t response_len;
/* Caller-visible fields: flags, questions. */
struct evdns_server_request base;
};
struct evdns_base {
/* An array of n_req_heads circular lists for inflight requests.
* Each inflight request req is in req_heads[req->trans_id % n_req_heads].
*/
struct request **req_heads;
/* A circular list of requests that we're waiting to send, but haven't
* sent yet because there are too many requests inflight */
struct request *req_waiting_head;
/* A circular list of nameservers. */
struct nameserver *server_head;
int n_req_heads;
struct event_base *event_base;
/* The number of good nameservers that we have */
int global_good_nameservers;
/* inflight requests are contained in the req_head list */
/* and are actually going out across the network */
int global_requests_inflight;
/* requests which aren't inflight are in the waiting list */
/* and are counted here */
int global_requests_waiting;
int global_max_requests_inflight;
struct timeval global_timeout; /* 5 seconds by default */
int global_max_reissues; /* a reissue occurs when we get some errors from the server */
int global_max_retransmits; /* number of times we'll retransmit a request which timed out */
/* number of timeouts in a row before we consider this server to be down */
int global_max_nameserver_timeout;
/* true iff we will use the 0x20 hack to prevent poisoning attacks. */
int global_randomize_case;
/* The first time that a nameserver fails, how long do we wait before
* probing to see if it has returned? */
struct timeval global_nameserver_probe_initial_timeout;
/** Port to bind to for outgoing DNS packets. */
struct sockaddr_storage global_outgoing_address;
/** ev_socklen_t for global_outgoing_address. 0 if it isn't set. */
ev_socklen_t global_outgoing_addrlen;
struct timeval global_getaddrinfo_allow_skew;
int getaddrinfo_ipv4_timeouts;
int getaddrinfo_ipv6_timeouts;
int getaddrinfo_ipv4_answered;
int getaddrinfo_ipv6_answered;
struct search_state *global_search_state;
TAILQ_HEAD(hosts_list, hosts_entry) hostsdb;
#ifndef _EVENT_DISABLE_THREAD_SUPPORT
void *lock;
#endif
};
struct hosts_entry {
TAILQ_ENTRY(hosts_entry) next;
union {
struct sockaddr sa;
struct sockaddr_in sin;
struct sockaddr_in6 sin6;
} addr;
int addrlen;
char hostname[1];
};
static struct evdns_base *current_base = NULL;
struct evdns_base *
evdns_get_global_base(void)
{
return current_base;
}
/* Given a pointer to an evdns_server_request, get the corresponding */
/* server_request. */
#define TO_SERVER_REQUEST(base_ptr) \
((struct server_request*) \
(((char*)(base_ptr) - evutil_offsetof(struct server_request, base))))
#define REQ_HEAD(base, id) ((base)->req_heads[id % (base)->n_req_heads])
static struct nameserver *nameserver_pick(struct evdns_base *base);
static void evdns_request_insert(struct request *req, struct request **head);
static void evdns_request_remove(struct request *req, struct request **head);
static void nameserver_ready_callback(evutil_socket_t fd, short events, void *arg);
static int evdns_transmit(struct evdns_base *base);
static int evdns_request_transmit(struct request *req);
static void nameserver_send_probe(struct nameserver *const ns);
static void search_request_finished(struct evdns_request *const);
static int search_try_next(struct evdns_request *const req);
static struct request *search_request_new(struct evdns_base *base, struct evdns_request *handle, int type, const char *const name, int flags, evdns_callback_type user_callback, void *user_arg);
static void evdns_requests_pump_waiting_queue(struct evdns_base *base);
static u16 transaction_id_pick(struct evdns_base *base);
static struct request *request_new(struct evdns_base *base, struct evdns_request *handle, int type, const char *name, int flags, evdns_callback_type callback, void *ptr);
static void request_submit(struct request *const req);
static int server_request_free(struct server_request *req);
static void server_request_free_answers(struct server_request *req);
static void server_port_free(struct evdns_server_port *port);
static void server_port_ready_callback(evutil_socket_t fd, short events, void *arg);
static int evdns_base_resolv_conf_parse_impl(struct evdns_base *base, int flags, const char *const filename);
static int evdns_base_set_option_impl(struct evdns_base *base,
const char *option, const char *val, int flags);
static void evdns_base_free_and_unlock(struct evdns_base *base, int fail_requests);
static int strtoint(const char *const str);
#ifdef _EVENT_DISABLE_THREAD_SUPPORT
#define EVDNS_LOCK(base) _EVUTIL_NIL_STMT
#define EVDNS_UNLOCK(base) _EVUTIL_NIL_STMT
#define ASSERT_LOCKED(base) _EVUTIL_NIL_STMT
#else
#define EVDNS_LOCK(base) \
EVLOCK_LOCK((base)->lock, 0)
#define EVDNS_UNLOCK(base) \
EVLOCK_UNLOCK((base)->lock, 0)
#define ASSERT_LOCKED(base) \
EVLOCK_ASSERT_LOCKED((base)->lock)
#endif
static void
default_evdns_log_fn(int warning, const char *buf)
{
if (warning == EVDNS_LOG_WARN)
event_warnx("[evdns] %s", buf);
else if (warning == EVDNS_LOG_MSG)
event_msgx("[evdns] %s", buf);
else
event_debug(("[evdns] %s", buf));
}
static evdns_debug_log_fn_type evdns_log_fn = NULL;
void
evdns_set_log_fn(evdns_debug_log_fn_type fn)
{
evdns_log_fn = fn;
}
#ifdef __GNUC__
#define EVDNS_LOG_CHECK __attribute__ ((format(printf, 2, 3)))
#else
#define EVDNS_LOG_CHECK
#endif
static void _evdns_log(int warn, const char *fmt, ...) EVDNS_LOG_CHECK;
static void
_evdns_log(int warn, const char *fmt, ...)
{
va_list args;
char buf[512];
if (!evdns_log_fn)
return;
va_start(args,fmt);
evutil_vsnprintf(buf, sizeof(buf), fmt, args);
va_end(args);
if (evdns_log_fn) {
if (warn == EVDNS_LOG_MSG)
warn = EVDNS_LOG_WARN;
evdns_log_fn(warn, buf);
} else {
default_evdns_log_fn(warn, buf);
}
}
#define log _evdns_log
/* This walks the list of inflight requests to find the */
/* one with a matching transaction id. Returns NULL on */
/* failure */
static struct request *
request_find_from_trans_id(struct evdns_base *base, u16 trans_id) {
struct request *req = REQ_HEAD(base, trans_id);
struct request *const started_at = req;
ASSERT_LOCKED(base);
if (req) {
do {
if (req->trans_id == trans_id) return req;
req = req->next;
} while (req != started_at);
}
return NULL;
}
/* a libevent callback function which is called when a nameserver */
/* has gone down and we want to test if it has came back to life yet */
static void
nameserver_prod_callback(evutil_socket_t fd, short events, void *arg) {
struct nameserver *const ns = (struct nameserver *) arg;
(void)fd;
(void)events;
EVDNS_LOCK(ns->base);
nameserver_send_probe(ns);
EVDNS_UNLOCK(ns->base);
}
/* a libevent callback which is called when a nameserver probe (to see if */
/* it has come back to life) times out. We increment the count of failed_times */
/* and wait longer to send the next probe packet. */
static void
nameserver_probe_failed(struct nameserver *const ns) {
struct timeval timeout;
int i;
ASSERT_LOCKED(ns->base);
(void) evtimer_del(&ns->timeout_event);
if (ns->state == 1) {
/* This can happen if the nameserver acts in a way which makes us mark */
/* it as bad and then starts sending good replies. */
return;
}
#define MAX_PROBE_TIMEOUT 3600
#define TIMEOUT_BACKOFF_FACTOR 3
memcpy(&timeout, &ns->base->global_nameserver_probe_initial_timeout,
sizeof(struct timeval));
for (i=ns->failed_times; i > 0 && timeout.tv_sec < MAX_PROBE_TIMEOUT; --i) {
timeout.tv_sec *= TIMEOUT_BACKOFF_FACTOR;
timeout.tv_usec *= TIMEOUT_BACKOFF_FACTOR;
if (timeout.tv_usec > 1000000) {
timeout.tv_sec += timeout.tv_usec / 1000000;
timeout.tv_usec %= 1000000;
}
}
if (timeout.tv_sec > MAX_PROBE_TIMEOUT) {
timeout.tv_sec = MAX_PROBE_TIMEOUT;
timeout.tv_usec = 0;
}
ns->failed_times++;
if (evtimer_add(&ns->timeout_event, &timeout) < 0) {
char addrbuf[128];
log(EVDNS_LOG_WARN,
"Error from libevent when adding timer event for %s",
evutil_format_sockaddr_port(
(struct sockaddr *)&ns->address,
addrbuf, sizeof(addrbuf)));
}
}
/* called when a nameserver has been deemed to have failed. For example, too */
/* many packets have timed out etc */
static void
nameserver_failed(struct nameserver *const ns, const char *msg) {
struct request *req, *started_at;
struct evdns_base *base = ns->base;
int i;
char addrbuf[128];
ASSERT_LOCKED(base);
/* if this nameserver has already been marked as failed */
/* then don't do anything */
if (!ns->state) return;
log(EVDNS_LOG_MSG, "Nameserver %s has failed: %s",
evutil_format_sockaddr_port(
(struct sockaddr *)&ns->address,
addrbuf, sizeof(addrbuf)),
msg);
base->global_good_nameservers--;
EVUTIL_ASSERT(base->global_good_nameservers >= 0);
if (base->global_good_nameservers == 0) {
log(EVDNS_LOG_MSG, "All nameservers have failed");
}
ns->state = 0;
ns->failed_times = 1;
if (evtimer_add(&ns->timeout_event,
&base->global_nameserver_probe_initial_timeout) < 0) {
log(EVDNS_LOG_WARN,
"Error from libevent when adding timer event for %s",
evutil_format_sockaddr_port(
(struct sockaddr *)&ns->address,
addrbuf, sizeof(addrbuf)));
/* ???? Do more? */
}
/* walk the list of inflight requests to see if any can be reassigned to */
/* a different server. Requests in the waiting queue don't have a */
/* nameserver assigned yet */
/* if we don't have *any* good nameservers then there's no point */
/* trying to reassign requests to one */
if (!base->global_good_nameservers) return;
for (i = 0; i < base->n_req_heads; ++i) {
req = started_at = base->req_heads[i];
if (req) {
do {
if (req->tx_count == 0 && req->ns == ns) {
/* still waiting to go out, can be moved */
/* to another server */
req->ns = nameserver_pick(base);
}
req = req->next;
} while (req != started_at);
}
}
}
static void
nameserver_up(struct nameserver *const ns)
{
char addrbuf[128];
ASSERT_LOCKED(ns->base);
if (ns->state) return;
log(EVDNS_LOG_MSG, "Nameserver %s is back up",
evutil_format_sockaddr_port(
(struct sockaddr *)&ns->address,
addrbuf, sizeof(addrbuf)));
evtimer_del(&ns->timeout_event);
if (ns->probe_request) {
evdns_cancel_request(ns->base, ns->probe_request);
ns->probe_request = NULL;
}
ns->state = 1;
ns->failed_times = 0;
ns->timedout = 0;
ns->base->global_good_nameservers++;
}
static void
request_trans_id_set(struct request *const req, const u16 trans_id) {
req->trans_id = trans_id;
*((u16 *) req->request) = htons(trans_id);
}
/* Called to remove a request from a list and dealloc it. */
/* head is a pointer to the head of the list it should be */
/* removed from or NULL if the request isn't in a list. */
/* when free_handle is one, free the handle as well. */
static void
request_finished(struct request *const req, struct request **head, int free_handle) {
struct evdns_base *base = req->base;
int was_inflight = (head != &base->req_waiting_head);
EVDNS_LOCK(base);
ASSERT_VALID_REQUEST(req);
if (head)
evdns_request_remove(req, head);
log(EVDNS_LOG_DEBUG, "Removing timeout for request %p", req);
if (was_inflight) {
evtimer_del(&req->timeout_event);
base->global_requests_inflight--;
} else {
base->global_requests_waiting--;
}
if (!req->request_appended) {
/* need to free the request data on it's own */
mm_free(req->request);
} else {
/* the request data is appended onto the header */
/* so everything gets free()ed when we: */
}
if (req->handle) {
EVUTIL_ASSERT(req->handle->current_req == req);
if (free_handle) {
search_request_finished(req->handle);
req->handle->current_req = NULL;
if (! req->handle->pending_cb) {
/* If we're planning to run the callback,
* don't free the handle until later. */
mm_free(req->handle);
}
req->handle = NULL; /* If we have a bug, let's crash
* early */
} else {
req->handle->current_req = NULL;
}
}
mm_free(req);
evdns_requests_pump_waiting_queue(base);
EVDNS_UNLOCK(base);
}
/* This is called when a server returns a funny error code. */
/* We try the request again with another server. */
/* */
/* return: */
/* 0 ok */
/* 1 failed/reissue is pointless */
static int
request_reissue(struct request *req) {
const struct nameserver *const last_ns = req->ns;
ASSERT_LOCKED(req->base);
ASSERT_VALID_REQUEST(req);
/* the last nameserver should have been marked as failing */
/* by the caller of this function, therefore pick will try */
/* not to return it */
req->ns = nameserver_pick(req->base);
if (req->ns == last_ns) {
/* ... but pick did return it */
/* not a lot of point in trying again with the */
/* same server */
return 1;
}
req->reissue_count++;
req->tx_count = 0;
req->transmit_me = 1;
return 0;
}
/* this function looks for space on the inflight queue and promotes */
/* requests from the waiting queue if it can. */
static void
evdns_requests_pump_waiting_queue(struct evdns_base *base) {
ASSERT_LOCKED(base);
while (base->global_requests_inflight < base->global_max_requests_inflight &&
base->global_requests_waiting) {
struct request *req;
/* move a request from the waiting queue to the inflight queue */
EVUTIL_ASSERT(base->req_waiting_head);
req = base->req_waiting_head;
evdns_request_remove(req, &base->req_waiting_head);
base->global_requests_waiting--;
base->global_requests_inflight++;
req->ns = nameserver_pick(base);
request_trans_id_set(req, transaction_id_pick(base));
evdns_request_insert(req, &REQ_HEAD(base, req->trans_id));
evdns_request_transmit(req);
evdns_transmit(base);
}
}
/* TODO(nickm) document */
struct deferred_reply_callback {
struct deferred_cb deferred;
struct evdns_request *handle;
u8 request_type;
u8 have_reply;
u32 ttl;
u32 err;
evdns_callback_type user_callback;
struct reply reply;
};
static void
reply_run_callback(struct deferred_cb *d, void *user_pointer)
{
struct deferred_reply_callback *cb =
EVUTIL_UPCAST(d, struct deferred_reply_callback, deferred);
switch (cb->request_type) {
case TYPE_A:
if (cb->have_reply)
cb->user_callback(DNS_ERR_NONE, DNS_IPv4_A,
cb->reply.data.a.addrcount, cb->ttl,
cb->reply.data.a.addresses,
user_pointer);
else
cb->user_callback(cb->err, 0, 0, 0, NULL, user_pointer);
break;
case TYPE_PTR:
if (cb->have_reply) {
char *name = cb->reply.data.ptr.name;
cb->user_callback(DNS_ERR_NONE, DNS_PTR, 1, cb->ttl,
&name, user_pointer);
} else {
cb->user_callback(cb->err, 0, 0, 0, NULL, user_pointer);
}
break;
case TYPE_AAAA:
if (cb->have_reply)
cb->user_callback(DNS_ERR_NONE, DNS_IPv6_AAAA,
cb->reply.data.aaaa.addrcount, cb->ttl,
cb->reply.data.aaaa.addresses,
user_pointer);
else
cb->user_callback(cb->err, 0, 0, 0, NULL, user_pointer);
break;
default:
EVUTIL_ASSERT(0);
}
if (cb->handle && cb->handle->pending_cb) {
mm_free(cb->handle);
}
mm_free(cb);
}
static void
reply_schedule_callback(struct request *const req, u32 ttl, u32 err, struct reply *reply)
{
struct deferred_reply_callback *d = mm_calloc(1, sizeof(*d));
ASSERT_LOCKED(req->base);
d->request_type = req->request_type;
d->user_callback = req->user_callback;
d->ttl = ttl;
d->err = err;
if (reply) {
d->have_reply = 1;
memcpy(&d->reply, reply, sizeof(struct reply));
}
if (req->handle) {
req->handle->pending_cb = 1;
d->handle = req->handle;
}
event_deferred_cb_init(&d->deferred, reply_run_callback,
req->user_pointer);
event_deferred_cb_schedule(
event_base_get_deferred_cb_queue(req->base->event_base),
&d->deferred);
}
/* this processes a parsed reply packet */
static void
reply_handle(struct request *const req, u16 flags, u32 ttl, struct reply *reply) {
int error;
char addrbuf[128];
static const int error_codes[] = {
DNS_ERR_FORMAT, DNS_ERR_SERVERFAILED, DNS_ERR_NOTEXIST,
DNS_ERR_NOTIMPL, DNS_ERR_REFUSED
};
ASSERT_LOCKED(req->base);
ASSERT_VALID_REQUEST(req);
if (flags & 0x020f || !reply || !reply->have_answer) {
/* there was an error */
if (flags & 0x0200) {
error = DNS_ERR_TRUNCATED;
} else {
u16 error_code = (flags & 0x000f) - 1;
if (error_code > 4) {
error = DNS_ERR_UNKNOWN;
} else {
error = error_codes[error_code];
}
}
switch (error) {
case DNS_ERR_NOTIMPL:
case DNS_ERR_REFUSED:
/* we regard these errors as marking a bad nameserver */
if (req->reissue_count < req->base->global_max_reissues) {
char msg[64];
evutil_snprintf(msg, sizeof(msg), "Bad response %d (%s)",
error, evdns_err_to_string(error));
nameserver_failed(req->ns, msg);
if (!request_reissue(req)) return;
}
break;
case DNS_ERR_SERVERFAILED:
/* rcode 2 (servfailed) sometimes means "we
* are broken" and sometimes (with some binds)
* means "that request was very confusing."
* Treat this as a timeout, not a failure.
*/
log(EVDNS_LOG_DEBUG, "Got a SERVERFAILED from nameserver"
"at %s; will allow the request to time out.",
evutil_format_sockaddr_port(
(struct sockaddr *)&req->ns->address,
addrbuf, sizeof(addrbuf)));
break;
default:
/* we got a good reply from the nameserver */
nameserver_up(req->ns);
}
if (req->handle->search_state &&
req->request_type != TYPE_PTR) {
/* if we have a list of domains to search in,
* try the next one */
if (!search_try_next(req->handle)) {
/* a new request was issued so this
* request is finished and */
/* the user callback will be made when
* that request (or a */
/* child of it) finishes. */
return;
}
}
/* all else failed. Pass the failure up */
reply_schedule_callback(req, 0, error, NULL);
request_finished(req, &REQ_HEAD(req->base, req->trans_id), 1);
} else {
/* all ok, tell the user */
reply_schedule_callback(req, ttl, 0, reply);
if (req->handle == req->ns->probe_request)
req->ns->probe_request = NULL; /* Avoid double-free */
nameserver_up(req->ns);
request_finished(req, &REQ_HEAD(req->base, req->trans_id), 1);
}
}
static int
name_parse(u8 *packet, int length, int *idx, char *name_out, int name_out_len) {
int name_end = -1;
int j = *idx;
int ptr_count = 0;
#define GET32(x) do { if (j + 4 > length) goto err; memcpy(&_t32, packet + j, 4); j += 4; x = ntohl(_t32); } while (0)
#define GET16(x) do { if (j + 2 > length) goto err; memcpy(&_t, packet + j, 2); j += 2; x = ntohs(_t); } while (0)
#define GET8(x) do { if (j >= length) goto err; x = packet[j++]; } while (0)
char *cp = name_out;
const char *const end = name_out + name_out_len;
/* Normally, names are a series of length prefixed strings terminated */
/* with a length of 0 (the lengths are u8's < 63). */
/* However, the length can start with a pair of 1 bits and that */
/* means that the next 14 bits are a pointer within the current */
/* packet. */
for (;;) {
u8 label_len;
if (j >= length) return -1;
GET8(label_len);
if (!label_len) break;
if (label_len & 0xc0) {
u8 ptr_low;
GET8(ptr_low);
if (name_end < 0) name_end = j;
j = (((int)label_len & 0x3f) << 8) + ptr_low;
/* Make sure that the target offset is in-bounds. */
if (j < 0 || j >= length) return -1;
/* If we've jumped more times than there are characters in the
* message, we must have a loop. */
if (++ptr_count > length) return -1;
continue;
}
if (label_len > 63) return -1;
if (cp != name_out) {
if (cp + 1 >= end) return -1;
*cp++ = '.';
}
if (cp + label_len >= end) return -1;
memcpy(cp, packet + j, label_len);
cp += label_len;
j += label_len;
}
if (cp >= end) return -1;
*cp = '\0';
if (name_end < 0)
*idx = j;
else
*idx = name_end;
return 0;
err:
return -1;
}
/* parses a raw request from a nameserver */
static int
reply_parse(struct evdns_base *base, u8 *packet, int length) {
int j = 0, k = 0; /* index into packet */
u16 _t; /* used by the macros */
u32 _t32; /* used by the macros */
char tmp_name[256], cmp_name[256]; /* used by the macros */
int name_matches = 0;
u16 trans_id, questions, answers, authority, additional, datalength;
u16 flags = 0;
u32 ttl, ttl_r = 0xffffffff;
struct reply reply;
struct request *req = NULL;
unsigned int i;
ASSERT_LOCKED(base);
GET16(trans_id);
GET16(flags);
GET16(questions);
GET16(answers);
GET16(authority);
GET16(additional);
(void) authority; /* suppress "unused variable" warnings. */
(void) additional; /* suppress "unused variable" warnings. */
req = request_find_from_trans_id(base, trans_id);
if (!req) return -1;
EVUTIL_ASSERT(req->base == base);
memset(&reply, 0, sizeof(reply));
/* If it's not an answer, it doesn't correspond to any request. */
if (!(flags & 0x8000)) return -1; /* must be an answer */
if (flags & 0x020f) {
/* there was an error */
goto err;
}
/* if (!answers) return; */ /* must have an answer of some form */
/* This macro skips a name in the DNS reply. */
#define SKIP_NAME \