1 /* $Id: evdns.c 6979 2006-08-04 18:31:13Z nickm $ */
2
3 /* The original version of this module was written by Adam Langley; for
4 * a history of modifications, check out the subversion logs.
5 *
6 * When editing this module, try to keep it re-mergeable by Adam. Don't
7 * reformat the whitespace, add Tor dependencies, or so on.
8 *
9 * TODO:
10 * - Support IPv6 and PTR records.
11 * - Replace all externally visible magic numbers with #defined constants.
12 * - Write doccumentation for APIs of all external functions.
13 */
14
15 /* Async DNS Library
16 * Adam Langley <agl@imperialviolet.org>
17 * http://www.imperialviolet.org/eventdns.html
18 * Public Domain code
19 *
20 * This software is Public Domain. To view a copy of the public domain dedication,
21 * visit http://creativecommons.org/licenses/publicdomain/ or send a letter to
22 * Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
23 *
24 * I ask and expect, but do not require, that all derivative works contain an
25 * attribution similar to:
26 * Parts developed by Adam Langley <agl@imperialviolet.org>
27 *
28 * You may wish to replace the word "Parts" with something else depending on
29 * the amount of original code.
30 *
31 * (Derivative works does not include programs which link against, run or include
32 * the source verbatim in their source distributions)
33 *
34 * Version: 0.1b
35 */
36
37 #include <sys/types.h>
38 #ifdef HAVE_CONFIG_H
39 #include "config.h"
40 #endif
41
42 #ifdef DNS_USE_FTIME_FOR_ID
43 #include <sys/timeb.h>
44 #endif
45
46 #ifndef DNS_USE_CPU_CLOCK_FOR_ID
47 #ifndef DNS_USE_GETTIMEOFDAY_FOR_ID
48 #ifndef DNS_USE_OPENSSL_FOR_ID
49 #ifndef DNS_USE_FTIME_FOR_ID
50 #error Must configure at least one id generation method.
51 #error Please see the documentation.
52 #endif
53 #endif
54 #endif
55 #endif
56
57 /* #define _POSIX_C_SOURCE 200507 */
58 #define _GNU_SOURCE
59
60 #ifdef DNS_USE_CPU_CLOCK_FOR_ID
61 #ifdef DNS_USE_OPENSSL_FOR_ID
62 #error Multiple id options selected
63 #endif
64 #ifdef DNS_USE_GETTIMEOFDAY_FOR_ID
65 #error Multiple id options selected
66 #endif
67 #include <time.h>
68 #endif
69
70 #ifdef DNS_USE_OPENSSL_FOR_ID
71 #ifdef DNS_USE_GETTIMEOFDAY_FOR_ID
72 #error Multiple id options selected
73 #endif
74 #include <openssl/rand.h>
75 #endif
76
77 #ifndef _FORTIFY_SOURCE
78 #define _FORTIFY_SOURCE 3
79 #endif
80
81 #include <string.h>
82 #include <fcntl.h>
83 #ifdef HAVE_SYS_TIME_H
84 #include <sys/time.h>
85 #endif
86 #ifdef HAVE_STDINT_H
87 #include <stdint.h>
88 #endif
89 #include <stdlib.h>
90 #include <string.h>
91 #include <errno.h>
92 #include <assert.h>
93 #ifdef HAVE_UNISTD_H
94 #include <unistd.h>
95 #endif
96 #include <limits.h>
97 #include <sys/stat.h>
98 #include <ctype.h>
99 #include <stdio.h>
100 #include <stdarg.h>
101
102 #include "evdns.h"
103 #include "evutil.h"
104 #include "log.h"
105 #ifdef WIN32
106 #include <winsock2.h>
107 #include <windows.h>
108 #include <iphlpapi.h>
109 #include <io.h>
110 #else
111 #include <sys/socket.h>
112 #include <netinet/in.h>
113 #include <arpa/inet.h>
114 #endif
115
116 #ifdef HAVE_NETINET_IN6_H
117 #include <netinet/in6.h>
118 #endif
119
120 #define EVDNS_LOG_DEBUG 0
121 #define EVDNS_LOG_WARN 1
122
123 #ifndef HOST_NAME_MAX
124 #define HOST_NAME_MAX 255
125 #endif
126
127 #include <stdio.h>
128
129 #undef MIN
130 #define MIN(a,b) ((a)<(b)?(a):(b))
131
132 #ifdef __USE_ISOC99B
133 /* libevent doesn't work without this */
134 typedef ev_uint8_t u_char;
135 typedef unsigned int uint;
136 #endif
137 #include <event.h>
138
139 #define u64 ev_uint64_t
140 #define u32 ev_uint32_t
141 #define u16 ev_uint16_t
142 #define u8 ev_uint8_t
143
144 #ifdef WIN32
145 #define open _open
146 #define read _read
147 #define close _close
148 #define strdup _strdup
149 #endif
150
151 #define MAX_ADDRS 32 /* maximum number of addresses from a single packet */
152 /* which we bother recording */
153
154 #define TYPE_A EVDNS_TYPE_A
155 #define TYPE_CNAME 5
156 #define TYPE_PTR EVDNS_TYPE_PTR
157 #define TYPE_AAAA EVDNS_TYPE_AAAA
158
159 #define CLASS_INET EVDNS_CLASS_INET
160
161 struct request {
162 u8 *request; /* the dns packet data */
163 unsigned int request_len;
164 int reissue_count;
165 int tx_count; /* the number of times that this packet has been sent */
166 unsigned int request_type; /* TYPE_PTR or TYPE_A */
167 void *user_pointer; /* the pointer given to us for this request */
168 evdns_callback_type user_callback;
169 struct nameserver *ns; /* the server which we last sent it */
170
171 /* elements used by the searching code */
172 int search_index;
173 struct search_state *search_state;
174 char *search_origname; /* needs to be free()ed */
175 int search_flags;
176
177 /* these objects are kept in a circular list */
178 struct request *next, *prev;
179
180 struct event timeout_event;
181
182 u16 trans_id; /* the transaction id */
183 char request_appended; /* true if the request pointer is data which follows this struct */
184 char transmit_me; /* needs to be transmitted */
185 };
186
187 #ifndef HAVE_STRUCT_IN6_ADDR
188 struct in6_addr {
189 u8 s6_addr[16];
190 };
191 #endif
192
193 struct reply {
194 unsigned int type;
195 unsigned int have_answer;
196 union {
197 struct {
198 u32 addrcount;
199 u32 addresses[MAX_ADDRS];
200 } a;
201 struct {
202 u32 addrcount;
203 struct in6_addr addresses[MAX_ADDRS];
204 } aaaa;
205 struct {
206 char name[HOST_NAME_MAX];
207 } ptr;
208 } data;
209 };
210
211 struct nameserver {
212 int socket; /* a connected UDP socket */
213 u32 address;
214 u16 port;
215 int failed_times; /* number of times which we have given this server a chance */
216 int timedout; /* number of times in a row a request has timed out */
217 struct event event;
218 /* these objects are kept in a circular list */
219 struct nameserver *next, *prev;
220 struct event timeout_event; /* used to keep the timeout for */
221 /* when we next probe this server. */
222 /* Valid if state == 0 */
223 char state; /* zero if we think that this server is down */
224 char choked; /* true if we have an EAGAIN from this server's socket */
225 char write_waiting; /* true if we are waiting for EV_WRITE events */
226 };
227
228 static struct request *req_head = NULL, *req_waiting_head = NULL;
229 static struct nameserver *server_head = NULL;
230
231 /* Represents a local port where we're listening for DNS requests. Right now, */
232 /* only UDP is supported. */
233 struct evdns_server_port {
234 int socket; /* socket we use to read queries and write replies. */
235 int refcnt; /* reference count. */
236 char choked; /* Are we currently blocked from writing? */
237 char closing; /* Are we trying to close this port, pending writes? */
238 evdns_request_callback_fn_type user_callback; /* Fn to handle requests */
239 void *user_data; /* Opaque pointer passed to user_callback */
240 struct event event; /* Read/write event */
241 /* circular list of replies that we want to write. */
242 struct server_request *pending_replies;
243 };
244
245 /* Represents part of a reply being built. (That is, a single RR.) */
246 struct server_reply_item {
247 struct server_reply_item *next; /* next item in sequence. */
248 char *name; /* name part of the RR */
249 u16 type : 16; /* The RR type */
250 u16 class : 16; /* The RR class (usually CLASS_INET) */
251 u32 ttl; /* The RR TTL */
252 char is_name; /* True iff data is a label */
253 u16 datalen; /* Length of data; -1 if data is a label */
254 void *data; /* The contents of the RR */
255 };
256
257 /* Represents a request that we've received as a DNS server, and holds */
258 /* the components of the reply as we're constructing it. */
259 struct server_request {
260 /* Pointers to the next and previous entries on the list of replies */
261 /* that we're waiting to write. Only set if we have tried to respond */
262 /* and gotten EAGAIN. */
263 struct server_request *next_pending;
264 struct server_request *prev_pending;
265
266 u16 trans_id; /* Transaction id. */
267 struct evdns_server_port *port; /* Which port received this request on? */
268 struct sockaddr_storage addr; /* Where to send the response */
269 socklen_t addrlen; /* length of addr */
270
271 int n_answer; /* how many answer RRs have been set? */
272 int n_authority; /* how many authority RRs have been set? */
273 int n_additional; /* how many additional RRs have been set? */
274
275 struct server_reply_item *answer; /* linked list of answer RRs */
276 struct server_reply_item *authority; /* linked list of authority RRs */
277 struct server_reply_item *additional; /* linked list of additional RRs */
278
279 /* Constructed response. Only set once we're ready to send a reply. */
280 /* Once this is set, the RR fields are cleared, and no more should be set. */
281 char *response;
282 size_t response_len;
283
284 /* Caller-visible fields: flags, questions. */
285 struct evdns_server_request base;
286 };
287
288 /* helper macro */
289 #define OFFSET_OF(st, member) ((off_t) (((char*)&((st*)0)->member)-(char*)0))
290
291 /* Given a pointer to an evdns_server_request, get the corresponding */
292 /* server_request. */
293 #define TO_SERVER_REQUEST(base_ptr) \
294 ((struct server_request*) \
295 (((char*)(base_ptr) - OFFSET_OF(struct server_request, base))))
296
297 /* The number of good nameservers that we have */
298 static int global_good_nameservers = 0;
299
300 /* inflight requests are contained in the req_head list */
301 /* and are actually going out across the network */
302 static int global_requests_inflight = 0;
303 /* requests which aren't inflight are in the waiting list */
304 /* and are counted here */
305 static int global_requests_waiting = 0;
306
307 static int global_max_requests_inflight = 64;
308
309 static struct timeval global_timeout = {5, 0}; /* 5 seconds */
310 static int global_max_reissues = 1; /* a reissue occurs when we get some errors from the server */
311 static int global_max_retransmits = 3; /* number of times we'll retransmit a request which timed out */
312 /* number of timeouts in a row before we consider this server to be down */
313 static int global_max_nameserver_timeout = 3;
314
315 /* These are the timeout values for nameservers. If we find a nameserver is down */
316 /* we try to probe it at intervals as given below. Values are in seconds. */
317 static const struct timeval global_nameserver_timeouts[] = {{10, 0}, {60, 0}, {300, 0}, {900, 0}, {3600, 0}};
318 static const int global_nameserver_timeouts_length = sizeof(global_nameserver_timeouts)/sizeof(struct timeval);
319
320 static struct nameserver *nameserver_pick(void);
321 static void evdns_request_insert(struct request *req, struct request **head);
322 static void nameserver_ready_callback(int fd, short events, void *arg);
323 static int evdns_transmit(void);
324 static int evdns_request_transmit(struct request *req);
325 static void nameserver_send_probe(struct nameserver *const ns);
326 static void search_request_finished(struct request *const);
327 static int search_try_next(struct request *const req);
328 static int search_request_new(int type, const char *const name, int flags, evdns_callback_type user_callback, void *user_arg);
329 static void evdns_requests_pump_waiting_queue(void);
330 static u16 transaction_id_pick(void);
331 static struct request *request_new(int type, const char *name, int flags, evdns_callback_type callback, void *ptr);
332 static void request_submit(struct request *const req);
333
334 static int server_request_free(struct server_request *req);
335 static void server_request_free_answers(struct server_request *req);
336 static void server_port_free(struct evdns_server_port *port);
337 static void server_port_ready_callback(int fd, short events, void *arg);
338
339 static int strtoint(const char *const str);
340
341 #ifdef WIN32
342 static int
last_error(int sock)343 last_error(int sock)
344 {
345 int optval, optvallen=sizeof(optval);
346 int err = WSAGetLastError();
347 if (err == WSAEWOULDBLOCK && sock >= 0) {
348 if (getsockopt(sock, SOL_SOCKET, SO_ERROR, (void*)&optval,
349 &optvallen))
350 return err;
351 if (optval)
352 return optval;
353 }
354 return err;
355
356 }
357 static int
error_is_eagain(int err)358 error_is_eagain(int err)
359 {
360 return err == EAGAIN || err == WSAEWOULDBLOCK;
361 }
362 static int
inet_aton(const char * c,struct in_addr * addr)363 inet_aton(const char *c, struct in_addr *addr)
364 {
365 ev_uint32_t r;
366 if (strcmp(c, "255.255.255.255") == 0) {
367 addr->s_addr = 0xffffffffu;
368 } else {
369 r = inet_addr(c);
370 if (r == INADDR_NONE)
371 return 0;
372 addr->s_addr = r;
373 }
374 return 1;
375 }
376 #else
377 #define last_error(sock) (errno)
378 #define error_is_eagain(err) ((err) == EAGAIN)
379 #endif
380 #define CLOSE_SOCKET(s) EVUTIL_CLOSESOCKET(s)
381
382 #define ISSPACE(c) isspace((int)(unsigned char)(c))
383 #define ISDIGIT(c) isdigit((int)(unsigned char)(c))
384
385 static const char *
debug_ntoa(u32 address)386 debug_ntoa(u32 address)
387 {
388 static char buf[32];
389 u32 a = ntohl(address);
390 evutil_snprintf(buf, sizeof(buf), "%d.%d.%d.%d",
391 (int)(u8)((a>>24)&0xff),
392 (int)(u8)((a>>16)&0xff),
393 (int)(u8)((a>>8 )&0xff),
394 (int)(u8)((a )&0xff));
395 return buf;
396 }
397
398 static evdns_debug_log_fn_type evdns_log_fn = NULL;
399
400 void
evdns_set_log_fn(evdns_debug_log_fn_type fn)401 evdns_set_log_fn(evdns_debug_log_fn_type fn)
402 {
403 evdns_log_fn = fn;
404 }
405
406 #ifdef __GNUC__
407 #define EVDNS_LOG_CHECK __attribute__ ((format(printf, 2, 3)))
408 #else
409 #define EVDNS_LOG_CHECK
410 #endif
411
412 static void _evdns_log(int warn, const char *fmt, ...) EVDNS_LOG_CHECK;
413 static void
_evdns_log(int warn,const char * fmt,...)414 _evdns_log(int warn, const char *fmt, ...)
415 {
416 va_list args;
417 static char buf[512];
418 if (!evdns_log_fn)
419 return;
420 va_start(args,fmt);
421 evutil_vsnprintf(buf, sizeof(buf), fmt, args);
422 buf[sizeof(buf)-1] = '\0';
423 evdns_log_fn(warn, buf);
424 va_end(args);
425 }
426
427 #define log _evdns_log
428
429 /* This walks the list of inflight requests to find the */
430 /* one with a matching transaction id. Returns NULL on */
431 /* failure */
432 static struct request *
request_find_from_trans_id(u16 trans_id)433 request_find_from_trans_id(u16 trans_id) {
434 struct request *req = req_head, *const started_at = req_head;
435
436 if (req) {
437 do {
438 if (req->trans_id == trans_id) return req;
439 req = req->next;
440 } while (req != started_at);
441 }
442
443 return NULL;
444 }
445
446 /* a libevent callback function which is called when a nameserver */
447 /* has gone down and we want to test if it has came back to life yet */
448 static void
nameserver_prod_callback(int fd,short events,void * arg)449 nameserver_prod_callback(int fd, short events, void *arg) {
450 struct nameserver *const ns = (struct nameserver *) arg;
451 (void)fd;
452 (void)events;
453
454 nameserver_send_probe(ns);
455 }
456
457 /* a libevent callback which is called when a nameserver probe (to see if */
458 /* it has come back to life) times out. We increment the count of failed_times */
459 /* and wait longer to send the next probe packet. */
460 static void
nameserver_probe_failed(struct nameserver * const ns)461 nameserver_probe_failed(struct nameserver *const ns) {
462 const struct timeval * timeout;
463 (void) evtimer_del(&ns->timeout_event);
464 if (ns->state == 1) {
465 /* This can happen if the nameserver acts in a way which makes us mark */
466 /* it as bad and then starts sending good replies. */
467 return;
468 }
469
470 timeout =
471 &global_nameserver_timeouts[MIN(ns->failed_times,
472 global_nameserver_timeouts_length - 1)];
473 ns->failed_times++;
474
475 if (evtimer_add(&ns->timeout_event, (struct timeval *) timeout) < 0) {
476 log(EVDNS_LOG_WARN,
477 "Error from libevent when adding timer event for %s",
478 debug_ntoa(ns->address));
479 /* ???? Do more? */
480 }
481 }
482
483 /* called when a nameserver has been deemed to have failed. For example, too */
484 /* many packets have timed out etc */
485 static void
nameserver_failed(struct nameserver * const ns,const char * msg)486 nameserver_failed(struct nameserver *const ns, const char *msg) {
487 struct request *req, *started_at;
488 /* if this nameserver has already been marked as failed */
489 /* then don't do anything */
490 if (!ns->state) return;
491
492 log(EVDNS_LOG_WARN, "Nameserver %s has failed: %s",
493 debug_ntoa(ns->address), msg);
494 global_good_nameservers--;
495 assert(global_good_nameservers >= 0);
496 if (global_good_nameservers == 0) {
497 log(EVDNS_LOG_WARN, "All nameservers have failed");
498 }
499
500 ns->state = 0;
501 ns->failed_times = 1;
502
503 if (evtimer_add(&ns->timeout_event, (struct timeval *) &global_nameserver_timeouts[0]) < 0) {
504 log(EVDNS_LOG_WARN,
505 "Error from libevent when adding timer event for %s",
506 debug_ntoa(ns->address));
507 /* ???? Do more? */
508 }
509
510 /* walk the list of inflight requests to see if any can be reassigned to */
511 /* a different server. Requests in the waiting queue don't have a */
512 /* nameserver assigned yet */
513
514 /* if we don't have *any* good nameservers then there's no point */
515 /* trying to reassign requests to one */
516 if (!global_good_nameservers) return;
517
518 req = req_head;
519 started_at = req_head;
520 if (req) {
521 do {
522 if (req->tx_count == 0 && req->ns == ns) {
523 /* still waiting to go out, can be moved */
524 /* to another server */
525 req->ns = nameserver_pick();
526 }
527 req = req->next;
528 } while (req != started_at);
529 }
530 }
531
532 static void
nameserver_up(struct nameserver * const ns)533 nameserver_up(struct nameserver *const ns) {
534 if (ns->state) return;
535 log(EVDNS_LOG_WARN, "Nameserver %s is back up",
536 debug_ntoa(ns->address));
537 evtimer_del(&ns->timeout_event);
538 ns->state = 1;
539 ns->failed_times = 0;
540 ns->timedout = 0;
541 global_good_nameservers++;
542 }
543
544 static void
request_trans_id_set(struct request * const req,const u16 trans_id)545 request_trans_id_set(struct request *const req, const u16 trans_id) {
546 req->trans_id = trans_id;
547 *((u16 *) req->request) = htons(trans_id);
548 }
549
550 /* Called to remove a request from a list and dealloc it. */
551 /* head is a pointer to the head of the list it should be */
552 /* removed from or NULL if the request isn't in a list. */
553 static void
request_finished(struct request * const req,struct request ** head)554 request_finished(struct request *const req, struct request **head) {
555 if (head) {
556 if (req->next == req) {
557 /* only item in the list */
558 *head = NULL;
559 } else {
560 req->next->prev = req->prev;
561 req->prev->next = req->next;
562 if (*head == req) *head = req->next;
563 }
564 }
565
566 log(EVDNS_LOG_DEBUG, "Removing timeout for request %lx",
567 (unsigned long) req);
568 evtimer_del(&req->timeout_event);
569
570 search_request_finished(req);
571 global_requests_inflight--;
572
573 if (!req->request_appended) {
574 /* need to free the request data on it's own */
575 free(req->request);
576 } else {
577 /* the request data is appended onto the header */
578 /* so everything gets free()ed when we: */
579 }
580
581 free(req);
582
583 evdns_requests_pump_waiting_queue();
584 }
585
586 /* This is called when a server returns a funny error code. */
587 /* We try the request again with another server. */
588 /* */
589 /* return: */
590 /* 0 ok */
591 /* 1 failed/reissue is pointless */
592 static int
request_reissue(struct request * req)593 request_reissue(struct request *req) {
594 const struct nameserver *const last_ns = req->ns;
595 /* the last nameserver should have been marked as failing */
596 /* by the caller of this function, therefore pick will try */
597 /* not to return it */
598 req->ns = nameserver_pick();
599 if (req->ns == last_ns) {
600 /* ... but pick did return it */
601 /* not a lot of point in trying again with the */
602 /* same server */
603 return 1;
604 }
605
606 req->reissue_count++;
607 req->tx_count = 0;
608 req->transmit_me = 1;
609
610 return 0;
611 }
612
613 /* this function looks for space on the inflight queue and promotes */
614 /* requests from the waiting queue if it can. */
615 static void
evdns_requests_pump_waiting_queue(void)616 evdns_requests_pump_waiting_queue(void) {
617 while (global_requests_inflight < global_max_requests_inflight &&
618 global_requests_waiting) {
619 struct request *req;
620 /* move a request from the waiting queue to the inflight queue */
621 assert(req_waiting_head);
622 if (req_waiting_head->next == req_waiting_head) {
623 /* only one item in the queue */
624 req = req_waiting_head;
625 req_waiting_head = NULL;
626 } else {
627 req = req_waiting_head;
628 req->next->prev = req->prev;
629 req->prev->next = req->next;
630 req_waiting_head = req->next;
631 }
632
633 global_requests_waiting--;
634 global_requests_inflight++;
635
636 req->ns = nameserver_pick();
637 request_trans_id_set(req, transaction_id_pick());
638
639 evdns_request_insert(req, &req_head);
640 evdns_request_transmit(req);
641 evdns_transmit();
642 }
643 }
644
645 static void
reply_callback(struct request * const req,u32 ttl,u32 err,struct reply * reply)646 reply_callback(struct request *const req, u32 ttl, u32 err, struct reply *reply) {
647 switch (req->request_type) {
648 case TYPE_A:
649 if (reply)
650 req->user_callback(DNS_ERR_NONE, DNS_IPv4_A,
651 reply->data.a.addrcount, ttl,
652 reply->data.a.addresses,
653 req->user_pointer);
654 else
655 req->user_callback(err, 0, 0, 0, NULL, req->user_pointer);
656 return;
657 case TYPE_PTR:
658 if (reply) {
659 char *name = reply->data.ptr.name;
660 req->user_callback(DNS_ERR_NONE, DNS_PTR, 1, ttl,
661 &name, req->user_pointer);
662 } else {
663 req->user_callback(err, 0, 0, 0, NULL,
664 req->user_pointer);
665 }
666 return;
667 case TYPE_AAAA:
668 if (reply)
669 req->user_callback(DNS_ERR_NONE, DNS_IPv6_AAAA,
670 reply->data.aaaa.addrcount, ttl,
671 reply->data.aaaa.addresses,
672 req->user_pointer);
673 else
674 req->user_callback(err, 0, 0, 0, NULL, req->user_pointer);
675 return;
676 }
677 assert(0);
678 }
679
680 /* this processes a parsed reply packet */
681 static void
reply_handle(struct request * const req,u16 flags,u32 ttl,struct reply * reply)682 reply_handle(struct request *const req, u16 flags, u32 ttl, struct reply *reply) {
683 int error;
684 static const int error_codes[] = {
685 DNS_ERR_FORMAT, DNS_ERR_SERVERFAILED, DNS_ERR_NOTEXIST,
686 DNS_ERR_NOTIMPL, DNS_ERR_REFUSED
687 };
688
689 if (flags & 0x020f || !reply || !reply->have_answer) {
690 /* there was an error */
691 if (flags & 0x0200) {
692 error = DNS_ERR_TRUNCATED;
693 } else {
694 u16 error_code = (flags & 0x000f) - 1;
695 if (error_code > 4) {
696 error = DNS_ERR_UNKNOWN;
697 } else {
698 error = error_codes[error_code];
699 }
700 }
701
702 switch(error) {
703 case DNS_ERR_NOTIMPL:
704 case DNS_ERR_REFUSED:
705 /* we regard these errors as marking a bad nameserver */
706 if (req->reissue_count < global_max_reissues) {
707 char msg[64];
708 evutil_snprintf(msg, sizeof(msg),
709 "Bad response %d (%s)",
710 error, evdns_err_to_string(error));
711 nameserver_failed(req->ns, msg);
712 if (!request_reissue(req)) return;
713 }
714 break;
715 case DNS_ERR_SERVERFAILED:
716 /* rcode 2 (servfailed) sometimes means "we
717 * are broken" and sometimes (with some binds)
718 * means "that request was very confusing."
719 * Treat this as a timeout, not a failure.
720 */
721 log(EVDNS_LOG_DEBUG, "Got a SERVERFAILED from nameserver %s; "
722 "will allow the request to time out.",
723 debug_ntoa(req->ns->address));
724 break;
725 default:
726 /* we got a good reply from the nameserver */
727 nameserver_up(req->ns);
728 }
729
730 if (req->search_state && req->request_type != TYPE_PTR) {
731 /* if we have a list of domains to search in,
732 * try the next one */
733 if (!search_try_next(req)) {
734 /* a new request was issued so this
735 * request is finished and */
736 /* the user callback will be made when
737 * that request (or a */
738 /* child of it) finishes. */
739 request_finished(req, &req_head);
740 return;
741 }
742 }
743
744 /* all else failed. Pass the failure up */
745 reply_callback(req, 0, error, NULL);
746 request_finished(req, &req_head);
747 } else {
748 /* all ok, tell the user */
749 reply_callback(req, ttl, 0, reply);
750 nameserver_up(req->ns);
751 request_finished(req, &req_head);
752 }
753 }
754
755 static int
name_parse(u8 * packet,int length,int * idx,char * name_out,int name_out_len)756 name_parse(u8 *packet, int length, int *idx, char *name_out, int name_out_len) {
757 int name_end = -1;
758 int j = *idx;
759 int ptr_count = 0;
760 #define GET32(x) do { if (j + 4 > length) goto err; memcpy(&_t32, packet + j, 4); j += 4; x = ntohl(_t32); } while(0)
761 #define GET16(x) do { if (j + 2 > length) goto err; memcpy(&_t, packet + j, 2); j += 2; x = ntohs(_t); } while(0)
762 #define GET8(x) do { if (j >= length) goto err; x = packet[j++]; } while(0)
763
764 char *cp = name_out;
765 const char *const end = name_out + name_out_len;
766
767 /* Normally, names are a series of length prefixed strings terminated */
768 /* with a length of 0 (the lengths are u8's < 63). */
769 /* However, the length can start with a pair of 1 bits and that */
770 /* means that the next 14 bits are a pointer within the current */
771 /* packet. */
772
773 for(;;) {
774 u8 label_len;
775 if (j >= length) return -1;
776 GET8(label_len);
777 if (!label_len) break;
778 if (label_len & 0xc0) {
779 u8 ptr_low;
780 GET8(ptr_low);
781 if (name_end < 0) name_end = j;
782 j = (((int)label_len & 0x3f) << 8) + ptr_low;
783 /* Make sure that the target offset is in-bounds. */
784 if (j < 0 || j >= length) return -1;
785 /* If we've jumped more times than there are characters in the
786 * message, we must have a loop. */
787 if (++ptr_count > length) return -1;
788 continue;
789 }
790 if (label_len > 63) return -1;
791 if (cp != name_out) {
792 if (cp + 1 >= end) return -1;
793 *cp++ = '.';
794 }
795 if (cp + label_len >= end) return -1;
796 memcpy(cp, packet + j, label_len);
797 cp += label_len;
798 j += label_len;
799 }
800 if (cp >= end) return -1;
801 *cp = '\0';
802 if (name_end < 0)
803 *idx = j;
804 else
805 *idx = name_end;
806 return 0;
807 err:
808 return -1;
809 }
810
811 /* parses a raw request from a nameserver */
812 static int
reply_parse(u8 * packet,int length)813 reply_parse(u8 *packet, int length) {
814 int j = 0, k = 0; /* index into packet */
815 u16 _t; /* used by the macros */
816 u32 _t32; /* used by the macros */
817 char tmp_name[256], cmp_name[256]; /* used by the macros */
818
819 u16 trans_id, questions, answers, authority, additional, datalength;
820 u16 flags = 0;
821 u32 ttl, ttl_r = 0xffffffff;
822 struct reply reply;
823 struct request *req = NULL;
824 unsigned int i;
825
826 GET16(trans_id);
827 GET16(flags);
828 GET16(questions);
829 GET16(answers);
830 GET16(authority);
831 GET16(additional);
832 (void) authority; /* suppress "unused variable" warnings. */
833 (void) additional; /* suppress "unused variable" warnings. */
834
835 req = request_find_from_trans_id(trans_id);
836 if (!req) return -1;
837
838 memset(&reply, 0, sizeof(reply));
839
840 /* If it's not an answer, it doesn't correspond to any request. */
841 if (!(flags & 0x8000)) return -1; /* must be an answer */
842 if (flags & 0x020f) {
843 /* there was an error */
844 goto err;
845 }
846 /* if (!answers) return; */ /* must have an answer of some form */
847
848 /* This macro skips a name in the DNS reply. */
849 #define SKIP_NAME \
850 do { tmp_name[0] = '\0'; \
851 if (name_parse(packet, length, &j, tmp_name, sizeof(tmp_name))<0)\
852 goto err; \
853 } while(0)
854 #define TEST_NAME \
855 do { tmp_name[0] = '\0'; \
856 cmp_name[0] = '\0'; \
857 k = j; \
858 if (name_parse(packet, length, &j, tmp_name, sizeof(tmp_name))<0)\
859 goto err; \
860 if (name_parse(req->request, req->request_len, &k, cmp_name, sizeof(cmp_name))<0) \
861 goto err; \
862 if (memcmp(tmp_name, cmp_name, strlen (tmp_name)) != 0) \
863 return (-1); /* we ignore mismatching names */ \
864 } while(0)
865
866 reply.type = req->request_type;
867
868 /* skip over each question in the reply */
869 for (i = 0; i < questions; ++i) {
870 /* the question looks like
871 * <label:name><u16:type><u16:class>
872 */
873 TEST_NAME;
874 j += 4;
875 if (j > length) goto err;
876 }
877
878 /* now we have the answer section which looks like
879 * <label:name><u16:type><u16:class><u32:ttl><u16:len><data...>
880 */
881
882 for (i = 0; i < answers; ++i) {
883 u16 type, class;
884
885 SKIP_NAME;
886 GET16(type);
887 GET16(class);
888 GET32(ttl);
889 GET16(datalength);
890
891 if (type == TYPE_A && class == CLASS_INET) {
892 int addrcount, addrtocopy;
893 if (req->request_type != TYPE_A) {
894 j += datalength; continue;
895 }
896 if ((datalength & 3) != 0) /* not an even number of As. */
897 goto err;
898 addrcount = datalength >> 2;
899 addrtocopy = MIN(MAX_ADDRS - reply.data.a.addrcount, (unsigned)addrcount);
900
901 ttl_r = MIN(ttl_r, ttl);
902 /* we only bother with the first four addresses. */
903 if (j + 4*addrtocopy > length) goto err;
904 memcpy(&reply.data.a.addresses[reply.data.a.addrcount],
905 packet + j, 4*addrtocopy);
906 j += 4*addrtocopy;
907 reply.data.a.addrcount += addrtocopy;
908 reply.have_answer = 1;
909 if (reply.data.a.addrcount == MAX_ADDRS) break;
910 } else if (type == TYPE_PTR && class == CLASS_INET) {
911 if (req->request_type != TYPE_PTR) {
912 j += datalength; continue;
913 }
914 if (name_parse(packet, length, &j, reply.data.ptr.name,
915 sizeof(reply.data.ptr.name))<0)
916 goto err;
917 ttl_r = MIN(ttl_r, ttl);
918 reply.have_answer = 1;
919 break;
920 } else if (type == TYPE_AAAA && class == CLASS_INET) {
921 int addrcount, addrtocopy;
922 if (req->request_type != TYPE_AAAA) {
923 j += datalength; continue;
924 }
925 if ((datalength & 15) != 0) /* not an even number of AAAAs. */
926 goto err;
927 addrcount = datalength >> 4; /* each address is 16 bytes long */
928 addrtocopy = MIN(MAX_ADDRS - reply.data.aaaa.addrcount, (unsigned)addrcount);
929 ttl_r = MIN(ttl_r, ttl);
930
931 /* we only bother with the first four addresses. */
932 if (j + 16*addrtocopy > length) goto err;
933 memcpy(&reply.data.aaaa.addresses[reply.data.aaaa.addrcount],
934 packet + j, 16*addrtocopy);
935 reply.data.aaaa.addrcount += addrtocopy;
936 j += 16*addrtocopy;
937 reply.have_answer = 1;
938 if (reply.data.aaaa.addrcount == MAX_ADDRS) break;
939 } else {
940 /* skip over any other type of resource */
941 j += datalength;
942 }
943 }
944
945 reply_handle(req, flags, ttl_r, &reply);
946 return 0;
947 err:
948 if (req)
949 reply_handle(req, flags, 0, NULL);
950 return -1;
951 }
952
953 /* Parse a raw request (packet,length) sent to a nameserver port (port) from */
954 /* a DNS client (addr,addrlen), and if it's well-formed, call the corresponding */
955 /* callback. */
956 static int
request_parse(u8 * packet,int length,struct evdns_server_port * port,struct sockaddr * addr,socklen_t addrlen)957 request_parse(u8 *packet, int length, struct evdns_server_port *port, struct sockaddr *addr, socklen_t addrlen)
958 {
959 int j = 0; /* index into packet */
960 u16 _t; /* used by the macros */
961 char tmp_name[256]; /* used by the macros */
962
963 int i;
964 u16 trans_id, flags, questions, answers, authority, additional;
965 struct server_request *server_req = NULL;
966
967 /* Get the header fields */
968 GET16(trans_id);
969 GET16(flags);
970 GET16(questions);
971 GET16(answers);
972 GET16(authority);
973 GET16(additional);
974
975 if (flags & 0x8000) return -1; /* Must not be an answer. */
976 flags &= 0x0110; /* Only RD and CD get preserved. */
977
978 server_req = malloc(sizeof(struct server_request));
979 if (server_req == NULL) return -1;
980 memset(server_req, 0, sizeof(struct server_request));
981
982 server_req->trans_id = trans_id;
983 memcpy(&server_req->addr, addr, addrlen);
984 server_req->addrlen = addrlen;
985
986 server_req->base.flags = flags;
987 server_req->base.nquestions = 0;
988 server_req->base.questions = malloc(sizeof(struct evdns_server_question *) * questions);
989 if (server_req->base.questions == NULL)
990 goto err;
991
992 for (i = 0; i < questions; ++i) {
993 u16 type, class;
994 struct evdns_server_question *q;
995 int namelen;
996 if (name_parse(packet, length, &j, tmp_name, sizeof(tmp_name))<0)
997 goto err;
998 GET16(type);
999 GET16(class);
1000 namelen = strlen(tmp_name);
1001 q = malloc(sizeof(struct evdns_server_question) + namelen);
1002 if (!q)
1003 goto err;
1004 q->type = type;
1005 q->dns_question_class = class;
1006 memcpy(q->name, tmp_name, namelen+1);
1007 server_req->base.questions[server_req->base.nquestions++] = q;
1008 }
1009
1010 /* Ignore answers, authority, and additional. */
1011
1012 server_req->port = port;
1013 port->refcnt++;
1014
1015 /* Only standard queries are supported. */
1016 if (flags & 0x7800) {
1017 evdns_server_request_respond(&(server_req->base), DNS_ERR_NOTIMPL);
1018 return -1;
1019 }
1020
1021 port->user_callback(&(server_req->base), port->user_data);
1022
1023 return 0;
1024 err:
1025 if (server_req) {
1026 if (server_req->base.questions) {
1027 for (i = 0; i < server_req->base.nquestions; ++i)
1028 free(server_req->base.questions[i]);
1029 free(server_req->base.questions);
1030 }
1031 free(server_req);
1032 }
1033 return -1;
1034
1035 #undef SKIP_NAME
1036 #undef GET32
1037 #undef GET16
1038 #undef GET8
1039 }
1040
1041 static u16
default_transaction_id_fn(void)1042 default_transaction_id_fn(void)
1043 {
1044 u16 trans_id;
1045 #ifdef DNS_USE_CPU_CLOCK_FOR_ID
1046 struct timespec ts;
1047 static int clkid = -1;
1048 if (clkid == -1) {
1049 clkid = CLOCK_REALTIME;
1050 #ifdef CLOCK_MONOTONIC
1051 if (clock_gettime(CLOCK_MONOTONIC, &ts) != -1)
1052 clkid = CLOCK_MONOTONIC;
1053 #endif
1054 }
1055 if (clock_gettime(clkid, &ts) == -1)
1056 event_err(1, "clock_gettime");
1057 trans_id = ts.tv_nsec & 0xffff;
1058 #endif
1059
1060 #ifdef DNS_USE_FTIME_FOR_ID
1061 struct _timeb tb;
1062 _ftime(&tb);
1063 trans_id = tb.millitm & 0xffff;
1064 #endif
1065
1066 #ifdef DNS_USE_GETTIMEOFDAY_FOR_ID
1067 struct timeval tv;
1068 evutil_gettimeofday(&tv, NULL);
1069 trans_id = tv.tv_usec & 0xffff;
1070 #endif
1071
1072 #ifdef DNS_USE_OPENSSL_FOR_ID
1073 if (RAND_pseudo_bytes((u8 *) &trans_id, 2) == -1) {
1074 /* in the case that the RAND call fails we back */
1075 /* down to using gettimeofday. */
1076 /*
1077 struct timeval tv;
1078 evutil_gettimeofday(&tv, NULL);
1079 trans_id = tv.tv_usec & 0xffff;
1080 */
1081 abort();
1082 }
1083 #endif
1084 return trans_id;
1085 }
1086
1087 static ev_uint16_t (*trans_id_function)(void) = default_transaction_id_fn;
1088
1089 void
evdns_set_transaction_id_fn(ev_uint16_t (* fn)(void))1090 evdns_set_transaction_id_fn(ev_uint16_t (*fn)(void))
1091 {
1092 if (fn)
1093 trans_id_function = fn;
1094 else
1095 trans_id_function = default_transaction_id_fn;
1096 }
1097
1098 /* Try to choose a strong transaction id which isn't already in flight */
1099 static u16
transaction_id_pick(void)1100 transaction_id_pick(void) {
1101 for (;;) {
1102 const struct request *req = req_head, *started_at;
1103 u16 trans_id = trans_id_function();
1104
1105 if (trans_id == 0xffff) continue;
1106 /* now check to see if that id is already inflight */
1107 req = started_at = req_head;
1108 if (req) {
1109 do {
1110 if (req->trans_id == trans_id) break;
1111 req = req->next;
1112 } while (req != started_at);
1113 }
1114 /* we didn't find it, so this is a good id */
1115 if (req == started_at) return trans_id;
1116 }
1117 }
1118
1119 /* choose a namesever to use. This function will try to ignore */
1120 /* nameservers which we think are down and load balance across the rest */
1121 /* by updating the server_head global each time. */
1122 static struct nameserver *
nameserver_pick(void)1123 nameserver_pick(void) {
1124 struct nameserver *started_at = server_head, *picked;
1125 if (!server_head) return NULL;
1126
1127 /* if we don't have any good nameservers then there's no */
1128 /* point in trying to find one. */
1129 if (!global_good_nameservers) {
1130 server_head = server_head->next;
1131 return server_head;
1132 }
1133
1134 /* remember that nameservers are in a circular list */
1135 for (;;) {
1136 if (server_head->state) {
1137 /* we think this server is currently good */
1138 picked = server_head;
1139 server_head = server_head->next;
1140 return picked;
1141 }
1142
1143 server_head = server_head->next;
1144 if (server_head == started_at) {
1145 /* all the nameservers seem to be down */
1146 /* so we just return this one and hope for the */
1147 /* best */
1148 assert(global_good_nameservers == 0);
1149 picked = server_head;
1150 server_head = server_head->next;
1151 return picked;
1152 }
1153 }
1154 }
1155
1156 static int
address_is_correct(struct nameserver * ns,struct sockaddr * sa,socklen_t slen)1157 address_is_correct(struct nameserver *ns, struct sockaddr *sa, socklen_t slen)
1158 {
1159 struct sockaddr_in *sin = (struct sockaddr_in*) sa;
1160 if (sa->sa_family != AF_INET || slen != sizeof(struct sockaddr_in))
1161 return 0;
1162 if (sin->sin_addr.s_addr != ns->address)
1163 return 0;
1164 return 1;
1165 }
1166
1167 /* this is called when a namesever socket is ready for reading */
1168 static void
nameserver_read(struct nameserver * ns)1169 nameserver_read(struct nameserver *ns) {
1170 u8 packet[1500];
1171 struct sockaddr_storage ss;
1172 socklen_t addrlen = sizeof(ss);
1173
1174 for (;;) {
1175 const int r = recvfrom(ns->socket, packet, sizeof(packet), 0,
1176 (struct sockaddr*)&ss, &addrlen);
1177 if (r < 0) {
1178 int err = last_error(ns->socket);
1179 if (error_is_eagain(err)) return;
1180 nameserver_failed(ns, strerror(err));
1181 return;
1182 }
1183 if (!address_is_correct(ns, (struct sockaddr*)&ss, addrlen)) {
1184 log(EVDNS_LOG_WARN, "Address mismatch on received "
1185 "DNS packet.");
1186 return;
1187 }
1188 ns->timedout = 0;
1189 reply_parse(packet, r);
1190 }
1191 }
1192
1193 /* Read a packet from a DNS client on a server port s, parse it, and */
1194 /* act accordingly. */
1195 static void
server_port_read(struct evdns_server_port * s)1196 server_port_read(struct evdns_server_port *s) {
1197 u8 packet[1500];
1198 struct sockaddr_storage addr;
1199 socklen_t addrlen;
1200 int r;
1201
1202 for (;;) {
1203 addrlen = sizeof(struct sockaddr_storage);
1204 r = recvfrom(s->socket, packet, sizeof(packet), 0,
1205 (struct sockaddr*) &addr, &addrlen);
1206 if (r < 0) {
1207 int err = last_error(s->socket);
1208 if (error_is_eagain(err)) return;
1209 log(EVDNS_LOG_WARN, "Error %s (%d) while reading request.",
1210 strerror(err), err);
1211 return;
1212 }
1213 request_parse(packet, r, s, (struct sockaddr*) &addr, addrlen);
1214 }
1215 }
1216
1217 /* Try to write all pending replies on a given DNS server port. */
1218 static void
server_port_flush(struct evdns_server_port * port)1219 server_port_flush(struct evdns_server_port *port)
1220 {
1221 while (port->pending_replies) {
1222 struct server_request *req = port->pending_replies;
1223 int r = sendto(port->socket, req->response, req->response_len, 0,
1224 (struct sockaddr*) &req->addr, req->addrlen);
1225 if (r < 0) {
1226 int err = last_error(port->socket);
1227 if (error_is_eagain(err))
1228 return;
1229 log(EVDNS_LOG_WARN, "Error %s (%d) while writing response to port; dropping", strerror(err), err);
1230 }
1231 if (server_request_free(req)) {
1232 /* we released the last reference to req->port. */
1233 return;
1234 }
1235 }
1236
1237 /* We have no more pending requests; stop listening for 'writeable' events. */
1238 (void) event_del(&port->event);
1239 event_set(&port->event, port->socket, EV_READ | EV_PERSIST,
1240 server_port_ready_callback, port);
1241 if (event_add(&port->event, NULL) < 0) {
1242 log(EVDNS_LOG_WARN, "Error from libevent when adding event for DNS server.");
1243 /* ???? Do more? */
1244 }
1245 }
1246
1247 /* set if we are waiting for the ability to write to this server. */
1248 /* if waiting is true then we ask libevent for EV_WRITE events, otherwise */
1249 /* we stop these events. */
1250 static void
nameserver_write_waiting(struct nameserver * ns,char waiting)1251 nameserver_write_waiting(struct nameserver *ns, char waiting) {
1252 if (ns->write_waiting == waiting) return;
1253
1254 ns->write_waiting = waiting;
1255 (void) event_del(&ns->event);
1256 event_set(&ns->event, ns->socket, EV_READ | (waiting ? EV_WRITE : 0) | EV_PERSIST,
1257 nameserver_ready_callback, ns);
1258 if (event_add(&ns->event, NULL) < 0) {
1259 log(EVDNS_LOG_WARN, "Error from libevent when adding event for %s",
1260 debug_ntoa(ns->address));
1261 /* ???? Do more? */
1262 }
1263 }
1264
1265 /* a callback function. Called by libevent when the kernel says that */
1266 /* a nameserver socket is ready for writing or reading */
1267 static void
nameserver_ready_callback(int fd,short events,void * arg)1268 nameserver_ready_callback(int fd, short events, void *arg) {
1269 struct nameserver *ns = (struct nameserver *) arg;
1270 (void)fd;
1271
1272 if (events & EV_WRITE) {
1273 ns->choked = 0;
1274 if (!evdns_transmit()) {
1275 nameserver_write_waiting(ns, 0);
1276 }
1277 }
1278 if (events & EV_READ) {
1279 nameserver_read(ns);
1280 }
1281 }
1282
1283 /* a callback function. Called by libevent when the kernel says that */
1284 /* a server socket is ready for writing or reading. */
1285 static void
server_port_ready_callback(int fd,short events,void * arg)1286 server_port_ready_callback(int fd, short events, void *arg) {
1287 struct evdns_server_port *port = (struct evdns_server_port *) arg;
1288 (void) fd;
1289
1290 if (events & EV_WRITE) {
1291 port->choked = 0;
1292 server_port_flush(port);
1293 }
1294 if (events & EV_READ) {
1295 server_port_read(port);
1296 }
1297 }
1298
1299 /* This is an inefficient representation; only use it via the dnslabel_table_*
1300 * functions, so that is can be safely replaced with something smarter later. */
1301 #define MAX_LABELS 128
1302 /* Structures used to implement name compression */
1303 struct dnslabel_entry { char *v; off_t pos; };
1304 struct dnslabel_table {
1305 int n_labels; /* number of current entries */
1306 /* map from name to position in message */
1307 struct dnslabel_entry labels[MAX_LABELS];
1308 };
1309
1310 /* Initialize dnslabel_table. */
1311 static void
dnslabel_table_init(struct dnslabel_table * table)1312 dnslabel_table_init(struct dnslabel_table *table)
1313 {
1314 table->n_labels = 0;
1315 }
1316
1317 /* Free all storage held by table, but not the table itself. */
1318 static void
dnslabel_clear(struct dnslabel_table * table)1319 dnslabel_clear(struct dnslabel_table *table)
1320 {
1321 int i;
1322 for (i = 0; i < table->n_labels; ++i)
1323 free(table->labels[i].v);
1324 table->n_labels = 0;
1325 }
1326
1327 /* return the position of the label in the current message, or -1 if the label */
1328 /* hasn't been used yet. */
1329 static int
dnslabel_table_get_pos(const struct dnslabel_table * table,const char * label)1330 dnslabel_table_get_pos(const struct dnslabel_table *table, const char *label)
1331 {
1332 int i;
1333 for (i = 0; i < table->n_labels; ++i) {
1334 if (!strcmp(label, table->labels[i].v))
1335 return table->labels[i].pos;
1336 }
1337 return -1;
1338 }
1339
1340 /* remember that we've used the label at position pos */
1341 static int
dnslabel_table_add(struct dnslabel_table * table,const char * label,off_t pos)1342 dnslabel_table_add(struct dnslabel_table *table, const char *label, off_t pos)
1343 {
1344 char *v;
1345 int p;
1346 if (table->n_labels == MAX_LABELS)
1347 return (-1);
1348 v = strdup(label);
1349 if (v == NULL)
1350 return (-1);
1351 p = table->n_labels++;
1352 table->labels[p].v = v;
1353 table->labels[p].pos = pos;
1354
1355 return (0);
1356 }
1357
1358 /* Converts a string to a length-prefixed set of DNS labels, starting */
1359 /* at buf[j]. name and buf must not overlap. name_len should be the length */
1360 /* of name. table is optional, and is used for compression. */
1361 /* */
1362 /* Input: abc.def */
1363 /* Output: <3>abc<3>def<0> */
1364 /* */
1365 /* Returns the first index after the encoded name, or negative on error. */
1366 /* -1 label was > 63 bytes */
1367 /* -2 name too long to fit in buffer. */
1368 /* */
1369 static off_t
dnsname_to_labels(u8 * const buf,size_t buf_len,off_t j,const char * name,const int name_len,struct dnslabel_table * table)1370 dnsname_to_labels(u8 *const buf, size_t buf_len, off_t j,
1371 const char *name, const int name_len,
1372 struct dnslabel_table *table) {
1373 const char *end = name + name_len;
1374 int ref = 0;
1375 u16 _t;
1376
1377 #define APPEND16(x) do { \
1378 if (j + 2 > (off_t)buf_len) \
1379 goto overflow; \
1380 _t = htons(x); \
1381 memcpy(buf + j, &_t, 2); \
1382 j += 2; \
1383 } while (0)
1384 #define APPEND32(x) do { \
1385 if (j + 4 > (off_t)buf_len) \
1386 goto overflow; \
1387 _t32 = htonl(x); \
1388 memcpy(buf + j, &_t32, 4); \
1389 j += 4; \
1390 } while (0)
1391
1392 if (name_len > 255) return -2;
1393
1394 for (;;) {
1395 const char *const start = name;
1396 if (table && (ref = dnslabel_table_get_pos(table, name)) >= 0) {
1397 APPEND16(ref | 0xc000);
1398 return j;
1399 }
1400 name = strchr(name, '.');
1401 if (!name) {
1402 const unsigned int label_len = end - start;
1403 if (label_len > 63) return -1;
1404 if ((size_t)(j+label_len+1) > buf_len) return -2;
1405 if (table) dnslabel_table_add(table, start, j);
1406 buf[j++] = label_len;
1407
1408 memcpy(buf + j, start, end - start);
1409 j += end - start;
1410 break;
1411 } else {
1412 /* append length of the label. */
1413 const unsigned int label_len = name - start;
1414 if (label_len > 63) return -1;
1415 if ((size_t)(j+label_len+1) > buf_len) return -2;
1416 if (table) dnslabel_table_add(table, start, j);
1417 buf[j++] = label_len;
1418
1419 memcpy(buf + j, start, name - start);
1420 j += name - start;
1421 /* hop over the '.' */
1422 name++;
1423 }
1424 }
1425
1426 /* the labels must be terminated by a 0. */
1427 /* It's possible that the name ended in a . */
1428 /* in which case the zero is already there */
1429 if (!j || buf[j-1]) buf[j++] = 0;
1430 return j;
1431 overflow:
1432 return (-2);
1433 }
1434
1435 /* Finds the length of a dns request for a DNS name of the given */
1436 /* length. The actual request may be smaller than the value returned */
1437 /* here */
1438 static int
evdns_request_len(const int name_len)1439 evdns_request_len(const int name_len) {
1440 return 96 + /* length of the DNS standard header */
1441 name_len + 2 +
1442 4; /* space for the resource type */
1443 }
1444
1445 /* build a dns request packet into buf. buf should be at least as long */
1446 /* as evdns_request_len told you it should be. */
1447 /* */
1448 /* Returns the amount of space used. Negative on error. */
1449 static int
evdns_request_data_build(const char * const name,const int name_len,const u16 trans_id,const u16 type,const u16 class,u8 * const buf,size_t buf_len)1450 evdns_request_data_build(const char *const name, const int name_len,
1451 const u16 trans_id, const u16 type, const u16 class,
1452 u8 *const buf, size_t buf_len) {
1453 off_t j = 0; /* current offset into buf */
1454 u16 _t; /* used by the macros */
1455
1456 APPEND16(trans_id);
1457 APPEND16(0x0100); /* standard query, recusion needed */
1458 APPEND16(1); /* one question */
1459 APPEND16(0); /* no answers */
1460 APPEND16(0); /* no authority */
1461 APPEND16(0); /* no additional */
1462
1463 j = dnsname_to_labels(buf, buf_len, j, name, name_len, NULL);
1464 if (j < 0) {
1465 return (int)j;
1466 }
1467
1468 APPEND16(type);
1469 APPEND16(class);
1470
1471 return (int)j;
1472 overflow:
1473 return (-1);
1474 }
1475
1476 /* exported function */
1477 struct evdns_server_port *
evdns_add_server_port(int socket,int is_tcp,evdns_request_callback_fn_type cb,void * user_data)1478 evdns_add_server_port(int socket, int is_tcp, evdns_request_callback_fn_type cb, void *user_data)
1479 {
1480 struct evdns_server_port *port;
1481 if (!(port = malloc(sizeof(struct evdns_server_port))))
1482 return NULL;
1483 memset(port, 0, sizeof(struct evdns_server_port));
1484
1485 assert(!is_tcp); /* TCP sockets not yet implemented */
1486 port->socket = socket;
1487 port->refcnt = 1;
1488 port->choked = 0;
1489 port->closing = 0;
1490 port->user_callback = cb;
1491 port->user_data = user_data;
1492 port->pending_replies = NULL;
1493
1494 event_set(&port->event, port->socket, EV_READ | EV_PERSIST,
1495 server_port_ready_callback, port);
1496 event_add(&port->event, NULL); /* check return. */
1497 return port;
1498 }
1499
1500 /* exported function */
1501 void
evdns_close_server_port(struct evdns_server_port * port)1502 evdns_close_server_port(struct evdns_server_port *port)
1503 {
1504 if (--port->refcnt == 0)
1505 server_port_free(port);
1506 port->closing = 1;
1507 }
1508
1509 /* exported function */
1510 int
evdns_server_request_add_reply(struct evdns_server_request * _req,int section,const char * name,int type,int class,int ttl,int datalen,int is_name,const char * data)1511 evdns_server_request_add_reply(struct evdns_server_request *_req, int section, const char *name, int type, int class, int ttl, int datalen, int is_name, const char *data)
1512 {
1513 struct server_request *req = TO_SERVER_REQUEST(_req);
1514 struct server_reply_item **itemp, *item;
1515 int *countp;
1516
1517 if (req->response) /* have we already answered? */
1518 return (-1);
1519
1520 switch (section) {
1521 case EVDNS_ANSWER_SECTION:
1522 itemp = &req->answer;
1523 countp = &req->n_answer;
1524 break;
1525 case EVDNS_AUTHORITY_SECTION:
1526 itemp = &req->authority;
1527 countp = &req->n_authority;
1528 break;
1529 case EVDNS_ADDITIONAL_SECTION:
1530 itemp = &req->additional;
1531 countp = &req->n_additional;
1532 break;
1533 default:
1534 return (-1);
1535 }
1536 while (*itemp) {
1537 itemp = &((*itemp)->next);
1538 }
1539 item = malloc(sizeof(struct server_reply_item));
1540 if (!item)
1541 return -1;
1542 item->next = NULL;
1543 if (!(item->name = strdup(name))) {
1544 free(item);
1545 return -1;
1546 }
1547 item->type = type;
1548 item->dns_question_class = class;
1549 item->ttl = ttl;
1550 item->is_name = is_name != 0;
1551 item->datalen = 0;
1552 item->data = NULL;
1553 if (data) {
1554 if (item->is_name) {
1555 if (!(item->data = strdup(data))) {
1556 free(item->name);
1557 free(item);
1558 return -1;
1559 }
1560 item->datalen = (u16)-1;
1561 } else {
1562 if (!(item->data = malloc(datalen))) {
1563 free(item->name);
1564 free(item);
1565 return -1;
1566 }
1567 item->datalen = datalen;
1568 memcpy(item->data, data, datalen);
1569 }
1570 }
1571
1572 *itemp = item;
1573 ++(*countp);
1574 return 0;
1575 }
1576
1577 /* exported function */
1578 int
evdns_server_request_add_a_reply(struct evdns_server_request * req,const char * name,int n,void * addrs,int ttl)1579 evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl)
1580 {
1581 return evdns_server_request_add_reply(
1582 req, EVDNS_ANSWER_SECTION, name, TYPE_A, CLASS_INET,
1583 ttl, n*4, 0, addrs);
1584 }
1585
1586 /* exported function */
1587 int
evdns_server_request_add_aaaa_reply(struct evdns_server_request * req,const char * name,int n,void * addrs,int ttl)1588 evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl)
1589 {
1590 return evdns_server_request_add_reply(
1591 req, EVDNS_ANSWER_SECTION, name, TYPE_AAAA, CLASS_INET,
1592 ttl, n*16, 0, addrs);
1593 }
1594
1595 /* exported function */
1596 int
evdns_server_request_add_ptr_reply(struct evdns_server_request * req,struct in_addr * in,const char * inaddr_name,const char * hostname,int ttl)1597 evdns_server_request_add_ptr_reply(struct evdns_server_request *req, struct in_addr *in, const char *inaddr_name, const char *hostname, int ttl)
1598 {
1599 u32 a;
1600 char buf[32];
1601 assert(in || inaddr_name);
1602 assert(!(in && inaddr_name));
1603 if (in) {
1604 a = ntohl(in->s_addr);
1605 evutil_snprintf(buf, sizeof(buf), "%d.%d.%d.%d.in-addr.arpa",
1606 (int)(u8)((a )&0xff),
1607 (int)(u8)((a>>8 )&0xff),
1608 (int)(u8)((a>>16)&0xff),
1609 (int)(u8)((a>>24)&0xff));
1610 inaddr_name = buf;
1611 }
1612 return evdns_server_request_add_reply(
1613 req, EVDNS_ANSWER_SECTION, inaddr_name, TYPE_PTR, CLASS_INET,
1614 ttl, -1, 1, hostname);
1615 }
1616
1617 /* exported function */
1618 int
evdns_server_request_add_cname_reply(struct evdns_server_request * req,const char * name,const char * cname,int ttl)1619 evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl)
1620 {
1621 return evdns_server_request_add_reply(
1622 req, EVDNS_ANSWER_SECTION, name, TYPE_CNAME, CLASS_INET,
1623 ttl, -1, 1, cname);
1624 }
1625
1626
1627 static int
evdns_server_request_format_response(struct server_request * req,int err)1628 evdns_server_request_format_response(struct server_request *req, int err)
1629 {
1630 unsigned char buf[1500];
1631 size_t buf_len = sizeof(buf);
1632 off_t j = 0, r;
1633 u16 _t;
1634 u32 _t32;
1635 int i;
1636 u16 flags;
1637 struct dnslabel_table table;
1638
1639 if (err < 0 || err > 15) return -1;
1640
1641 /* Set response bit and error code; copy OPCODE and RD fields from
1642 * question; copy RA and AA if set by caller. */
1643 flags = req->base.flags;
1644 flags |= (0x8000 | err);
1645
1646 dnslabel_table_init(&table);
1647 APPEND16(req->trans_id);
1648 APPEND16(flags);
1649 APPEND16(req->base.nquestions);
1650 APPEND16(req->n_answer);
1651 APPEND16(req->n_authority);
1652 APPEND16(req->n_additional);
1653
1654 /* Add questions. */
1655 for (i=0; i < req->base.nquestions; ++i) {
1656 const char *s = req->base.questions[i]->name;
1657 j = dnsname_to_labels(buf, buf_len, j, s, strlen(s), &table);
1658 if (j < 0) {
1659 dnslabel_clear(&table);
1660 return (int) j;
1661 }
1662 APPEND16(req->base.questions[i]->type);
1663 APPEND16(req->base.questions[i]->dns_question_class);
1664 }
1665
1666 /* Add answer, authority, and additional sections. */
1667 for (i=0; i<3; ++i) {
1668 struct server_reply_item *item;
1669 if (i==0)
1670 item = req->answer;
1671 else if (i==1)
1672 item = req->authority;
1673 else
1674 item = req->additional;
1675 while (item) {
1676 r = dnsname_to_labels(buf, buf_len, j, item->name, strlen(item->name), &table);
1677 if (r < 0)
1678 goto overflow;
1679 j = r;
1680
1681 APPEND16(item->type);
1682 APPEND16(item->dns_question_class);
1683 APPEND32(item->ttl);
1684 if (item->is_name) {
1685 off_t len_idx = j, name_start;
1686 j += 2;
1687 name_start = j;
1688 r = dnsname_to_labels(buf, buf_len, j, item->data, strlen(item->data), &table);
1689 if (r < 0)
1690 goto overflow;
1691 j = r;
1692 _t = htons( (short) (j-name_start) );
1693 memcpy(buf+len_idx, &_t, 2);
1694 } else {
1695 APPEND16(item->datalen);
1696 if (j+item->datalen > (off_t)buf_len)
1697 goto overflow;
1698 memcpy(buf+j, item->data, item->datalen);
1699 j += item->datalen;
1700 }
1701 item = item->next;
1702 }
1703 }
1704
1705 if (j > 512) {
1706 overflow:
1707 j = 512;
1708 buf[2] |= 0x02; /* set the truncated bit. */
1709 }
1710
1711 req->response_len = j;
1712
1713 if (!(req->response = malloc(req->response_len))) {
1714 server_request_free_answers(req);
1715 dnslabel_clear(&table);
1716 return (-1);
1717 }
1718 memcpy(req->response, buf, req->response_len);
1719 server_request_free_answers(req);
1720 dnslabel_clear(&table);
1721 return (0);
1722 }
1723
1724 /* exported function */
1725 int
evdns_server_request_respond(struct evdns_server_request * _req,int err)1726 evdns_server_request_respond(struct evdns_server_request *_req, int err)
1727 {
1728 struct server_request *req = TO_SERVER_REQUEST(_req);
1729 struct evdns_server_port *port = req->port;
1730 int r;
1731 if (!req->response) {
1732 if ((r = evdns_server_request_format_response(req, err))<0)
1733 return r;
1734 }
1735
1736 r = sendto(port->socket, req->response, req->response_len, 0,
1737 (struct sockaddr*) &req->addr, req->addrlen);
1738 if (r<0) {
1739 int sock_err = last_error(port->socket);
1740 if (! error_is_eagain(sock_err))
1741 return -1;
1742
1743 if (port->pending_replies) {
1744 req->prev_pending = port->pending_replies->prev_pending;
1745 req->next_pending = port->pending_replies;
1746 req->prev_pending->next_pending =
1747 req->next_pending->prev_pending = req;
1748 } else {
1749 req->prev_pending = req->next_pending = req;
1750 port->pending_replies = req;
1751 port->choked = 1;
1752
1753 (void) event_del(&port->event);
1754 event_set(&port->event, port->socket, (port->closing?0:EV_READ) | EV_WRITE | EV_PERSIST, server_port_ready_callback, port);
1755
1756 if (event_add(&port->event, NULL) < 0) {
1757 log(EVDNS_LOG_WARN, "Error from libevent when adding event for DNS server");
1758 }
1759
1760 }
1761
1762 return 1;
1763 }
1764 if (server_request_free(req))
1765 return 0;
1766
1767 if (port->pending_replies)
1768 server_port_flush(port);
1769
1770 return 0;
1771 }
1772
1773 /* Free all storage held by RRs in req. */
1774 static void
server_request_free_answers(struct server_request * req)1775 server_request_free_answers(struct server_request *req)
1776 {
1777 struct server_reply_item *victim, *next, **list;
1778 int i;
1779 for (i = 0; i < 3; ++i) {
1780 if (i==0)
1781 list = &req->answer;
1782 else if (i==1)
1783 list = &req->authority;
1784 else
1785 list = &req->additional;
1786
1787 victim = *list;
1788 while (victim) {
1789 next = victim->next;
1790 free(victim->name);
1791 if (victim->data)
1792 free(victim->data);
1793 free(victim);
1794 victim = next;
1795 }
1796 *list = NULL;
1797 }
1798 }
1799
1800 /* Free all storage held by req, and remove links to it. */
1801 /* return true iff we just wound up freeing the server_port. */
1802 static int
server_request_free(struct server_request * req)1803 server_request_free(struct server_request *req)
1804 {
1805 int i, rc=1;
1806 if (req->base.questions) {
1807 for (i = 0; i < req->base.nquestions; ++i)
1808 free(req->base.questions[i]);
1809 free(req->base.questions);
1810 }
1811
1812 if (req->port) {
1813 if (req->port->pending_replies == req) {
1814 if (req->next_pending)
1815 req->port->pending_replies = req->next_pending;
1816 else
1817 req->port->pending_replies = NULL;
1818 }
1819 rc = --req->port->refcnt;
1820 }
1821
1822 if (req->response) {
1823 free(req->response);
1824 }
1825
1826 server_request_free_answers(req);
1827
1828 if (req->next_pending && req->next_pending != req) {
1829 req->next_pending->prev_pending = req->prev_pending;
1830 req->prev_pending->next_pending = req->next_pending;
1831 }
1832
1833 if (rc == 0) {
1834 server_port_free(req->port);
1835 free(req);
1836 return (1);
1837 }
1838 free(req);
1839 return (0);
1840 }
1841
1842 /* Free all storage held by an evdns_server_port. Only called when */
1843 static void
server_port_free(struct evdns_server_port * port)1844 server_port_free(struct evdns_server_port *port)
1845 {
1846 assert(port);
1847 assert(!port->refcnt);
1848 assert(!port->pending_replies);
1849 if (port->socket > 0) {
1850 CLOSE_SOCKET(port->socket);
1851 port->socket = -1;
1852 }
1853 (void) event_del(&port->event);
1854 /* XXXX actually free the port? -NM */
1855 }
1856
1857 /* exported function */
1858 int
evdns_server_request_drop(struct evdns_server_request * _req)1859 evdns_server_request_drop(struct evdns_server_request *_req)
1860 {
1861 struct server_request *req = TO_SERVER_REQUEST(_req);
1862 server_request_free(req);
1863 return 0;
1864 }
1865
1866 /* exported function */
1867 int
evdns_server_request_get_requesting_addr(struct evdns_server_request * _req,struct sockaddr * sa,int addr_len)1868 evdns_server_request_get_requesting_addr(struct evdns_server_request *_req, struct sockaddr *sa, int addr_len)
1869 {
1870 struct server_request *req = TO_SERVER_REQUEST(_req);
1871 if (addr_len < (int)req->addrlen)
1872 return -1;
1873 memcpy(sa, &(req->addr), req->addrlen);
1874 return req->addrlen;
1875 }
1876
1877 #undef APPEND16
1878 #undef APPEND32
1879
1880 /* this is a libevent callback function which is called when a request */
1881 /* has timed out. */
1882 static void
evdns_request_timeout_callback(int fd,short events,void * arg)1883 evdns_request_timeout_callback(int fd, short events, void *arg) {
1884 struct request *const req = (struct request *) arg;
1885 (void) fd;
1886 (void) events;
1887
1888 log(EVDNS_LOG_DEBUG, "Request %lx timed out", (unsigned long) arg);
1889
1890 req->ns->timedout++;
1891 if (req->ns->timedout > global_max_nameserver_timeout) {
1892 req->ns->timedout = 0;
1893 nameserver_failed(req->ns, "request timed out.");
1894 }
1895
1896 (void) evtimer_del(&req->timeout_event);
1897 if (req->tx_count >= global_max_retransmits) {
1898 /* this request has failed */
1899 reply_callback(req, 0, DNS_ERR_TIMEOUT, NULL);
1900 request_finished(req, &req_head);
1901 } else {
1902 /* retransmit it */
1903 evdns_request_transmit(req);
1904 }
1905 }
1906
1907 /* try to send a request to a given server. */
1908 /* */
1909 /* return: */
1910 /* 0 ok */
1911 /* 1 temporary failure */
1912 /* 2 other failure */
1913 static int
evdns_request_transmit_to(struct request * req,struct nameserver * server)1914 evdns_request_transmit_to(struct request *req, struct nameserver *server) {
1915 struct sockaddr_in sin;
1916 int r;
1917 memset(&sin, 0, sizeof(sin));
1918 sin.sin_addr.s_addr = req->ns->address;
1919 sin.sin_port = req->ns->port;
1920 sin.sin_family = AF_INET;
1921
1922 r = sendto(server->socket, req->request, req->request_len, 0,
1923 (struct sockaddr*)&sin, sizeof(sin));
1924 if (r < 0) {
1925 int err = last_error(server->socket);
1926 if (error_is_eagain(err)) return 1;
1927 nameserver_failed(req->ns, strerror(err));
1928 return 2;
1929 } else if (r != (int)req->request_len) {
1930 return 1; /* short write */
1931 } else {
1932 return 0;
1933 }
1934 }
1935
1936 /* try to send a request, updating the fields of the request */
1937 /* as needed */
1938 /* */
1939 /* return: */
1940 /* 0 ok */
1941 /* 1 failed */
1942 static int
evdns_request_transmit(struct request * req)1943 evdns_request_transmit(struct request *req) {
1944 int retcode = 0, r;
1945
1946 /* if we fail to send this packet then this flag marks it */
1947 /* for evdns_transmit */
1948 req->transmit_me = 1;
1949 if (req->trans_id == 0xffff) abort();
1950
1951 if (req->ns->choked) {
1952 /* don't bother trying to write to a socket */
1953 /* which we have had EAGAIN from */
1954 return 1;
1955 }
1956
1957 r = evdns_request_transmit_to(req, req->ns);
1958 switch (r) {
1959 case 1:
1960 /* temp failure */
1961 req->ns->choked = 1;
1962 nameserver_write_waiting(req->ns, 1);
1963 return 1;
1964 case 2:
1965 /* failed in some other way */
1966 retcode = 1;
1967 /* fall through */
1968 default:
1969 /* all ok */
1970 log(EVDNS_LOG_DEBUG,
1971 "Setting timeout for request %lx", (unsigned long) req);
1972 if (evtimer_add(&req->timeout_event, &global_timeout) < 0) {
1973 log(EVDNS_LOG_WARN,
1974 "Error from libevent when adding timer for request %lx",
1975 (unsigned long) req);
1976 /* ???? Do more? */
1977 }
1978 req->tx_count++;
1979 req->transmit_me = 0;
1980 return retcode;
1981 }
1982 }
1983
1984 static void
nameserver_probe_callback(int result,char type,int count,int ttl,void * addresses,void * arg)1985 nameserver_probe_callback(int result, char type, int count, int ttl, void *addresses, void *arg) {
1986 struct nameserver *const ns = (struct nameserver *) arg;
1987 (void) type;
1988 (void) count;
1989 (void) ttl;
1990 (void) addresses;
1991
1992 if (result == DNS_ERR_NONE || result == DNS_ERR_NOTEXIST) {
1993 /* this is a good reply */
1994 nameserver_up(ns);
1995 } else nameserver_probe_failed(ns);
1996 }
1997
1998 static void
nameserver_send_probe(struct nameserver * const ns)1999 nameserver_send_probe(struct nameserver *const ns) {
2000 struct request *req;
2001 /* here we need to send a probe to a given nameserver */
2002 /* in the hope that it is up now. */
2003
2004 log(EVDNS_LOG_DEBUG, "Sending probe to %s", debug_ntoa(ns->address));
2005
2006 req = request_new(TYPE_A, "www.google.com", DNS_QUERY_NO_SEARCH, nameserver_probe_callback, ns);
2007 if (!req) return;
2008 /* we force this into the inflight queue no matter what */
2009 request_trans_id_set(req, transaction_id_pick());
2010 req->ns = ns;
2011 request_submit(req);
2012 }
2013
2014 /* returns: */
2015 /* 0 didn't try to transmit anything */
2016 /* 1 tried to transmit something */
2017 static int
evdns_transmit(void)2018 evdns_transmit(void) {
2019 char did_try_to_transmit = 0;
2020
2021 if (req_head) {
2022 struct request *const started_at = req_head, *req = req_head;
2023 /* first transmit all the requests which are currently waiting */
2024 do {
2025 if (req->transmit_me) {
2026 did_try_to_transmit = 1;
2027 evdns_request_transmit(req);
2028 }
2029
2030 req = req->next;
2031 } while (req != started_at);
2032 }
2033
2034 return did_try_to_transmit;
2035 }
2036
2037 /* exported function */
2038 int
evdns_count_nameservers(void)2039 evdns_count_nameservers(void)
2040 {
2041 const struct nameserver *server = server_head;
2042 int n = 0;
2043 if (!server)
2044 return 0;
2045 do {
2046 ++n;
2047 server = server->next;
2048 } while (server != server_head);
2049 return n;
2050 }
2051
2052 /* exported function */
2053 int
evdns_clear_nameservers_and_suspend(void)2054 evdns_clear_nameservers_and_suspend(void)
2055 {
2056 struct nameserver *server = server_head, *started_at = server_head;
2057 struct request *req = req_head, *req_started_at = req_head;
2058
2059 if (!server)
2060 return 0;
2061 while (1) {
2062 struct nameserver *next = server->next;
2063 (void) event_del(&server->event);
2064 if (evtimer_initialized(&server->timeout_event))
2065 (void) evtimer_del(&server->timeout_event);
2066 if (server->socket >= 0)
2067 CLOSE_SOCKET(server->socket);
2068 free(server);
2069 if (next == started_at)
2070 break;
2071 server = next;
2072 }
2073 server_head = NULL;
2074 global_good_nameservers = 0;
2075
2076 while (req) {
2077 struct request *next = req->next;
2078 req->tx_count = req->reissue_count = 0;
2079 req->ns = NULL;
2080 /* ???? What to do about searches? */
2081 (void) evtimer_del(&req->timeout_event);
2082 req->trans_id = 0;
2083 req->transmit_me = 0;
2084
2085 global_requests_waiting++;
2086 evdns_request_insert(req, &req_waiting_head);
2087 /* We want to insert these suspended elements at the front of
2088 * the waiting queue, since they were pending before any of
2089 * the waiting entries were added. This is a circular list,
2090 * so we can just shift the start back by one.*/
2091 req_waiting_head = req_waiting_head->prev;
2092
2093 if (next == req_started_at)
2094 break;
2095 req = next;
2096 }
2097 req_head = NULL;
2098 global_requests_inflight = 0;
2099
2100 return 0;
2101 }
2102
2103
2104 /* exported function */
2105 int
evdns_resume(void)2106 evdns_resume(void)
2107 {
2108 evdns_requests_pump_waiting_queue();
2109 return 0;
2110 }
2111
2112 static int
_evdns_nameserver_add_impl(unsigned long int address,int port)2113 _evdns_nameserver_add_impl(unsigned long int address, int port) {
2114 /* first check to see if we already have this nameserver */
2115
2116 const struct nameserver *server = server_head, *const started_at = server_head;
2117 struct nameserver *ns;
2118 int err = 0;
2119 if (server) {
2120 do {
2121 if (server->address == address) return 3;
2122 server = server->next;
2123 } while (server != started_at);
2124 }
2125
2126 ns = (struct nameserver *) malloc(sizeof(struct nameserver));
2127 if (!ns) return -1;
2128
2129 memset(ns, 0, sizeof(struct nameserver));
2130
2131 evtimer_set(&ns->timeout_event, nameserver_prod_callback, ns);
2132
2133 ns->socket = socket(PF_INET, SOCK_DGRAM, 0);
2134 if (ns->socket < 0) { err = 1; goto out1; }
2135 evutil_make_socket_nonblocking(ns->socket);
2136
2137 ns->address = address;
2138 ns->port = htons(port);
2139 ns->state = 1;
2140 event_set(&ns->event, ns->socket, EV_READ | EV_PERSIST, nameserver_ready_callback, ns);
2141 if (event_add(&ns->event, NULL) < 0) {
2142 err = 2;
2143 goto out2;
2144 }
2145
2146 log(EVDNS_LOG_DEBUG, "Added nameserver %s", debug_ntoa(address));
2147
2148 /* insert this nameserver into the list of them */
2149 if (!server_head) {
2150 ns->next = ns->prev = ns;
2151 server_head = ns;
2152 } else {
2153 ns->next = server_head->next;
2154 ns->prev = server_head;
2155 server_head->next = ns;
2156 if (server_head->prev == server_head) {
2157 server_head->prev = ns;
2158 }
2159 }
2160
2161 global_good_nameservers++;
2162
2163 return 0;
2164
2165 out2:
2166 CLOSE_SOCKET(ns->socket);
2167 out1:
2168 free(ns);
2169 log(EVDNS_LOG_WARN, "Unable to add nameserver %s: error %d", debug_ntoa(address), err);
2170 return err;
2171 }
2172
2173 /* exported function */
2174 int
evdns_nameserver_add(unsigned long int address)2175 evdns_nameserver_add(unsigned long int address) {
2176 return _evdns_nameserver_add_impl(address, 53);
2177 }
2178
2179 /* exported function */
2180 int
evdns_nameserver_ip_add(const char * ip_as_string)2181 evdns_nameserver_ip_add(const char *ip_as_string) {
2182 struct in_addr ina;
2183 int port;
2184 char buf[20];
2185 const char *cp;
2186 cp = strchr(ip_as_string, ':');
2187 if (! cp) {
2188 cp = ip_as_string;
2189 port = 53;
2190 } else {
2191 port = strtoint(cp+1);
2192 if (port < 0 || port > 65535) {
2193 return 4;
2194 }
2195 if ((cp-ip_as_string) >= (int)sizeof(buf)) {
2196 return 4;
2197 }
2198 memcpy(buf, ip_as_string, cp-ip_as_string);
2199 buf[cp-ip_as_string] = '\0';
2200 cp = buf;
2201 }
2202 if (!inet_aton(cp, &ina)) {
2203 return 4;
2204 }
2205 return _evdns_nameserver_add_impl(ina.s_addr, port);
2206 }
2207
2208 /* insert into the tail of the queue */
2209 static void
evdns_request_insert(struct request * req,struct request ** head)2210 evdns_request_insert(struct request *req, struct request **head) {
2211 if (!*head) {
2212 *head = req;
2213 req->next = req->prev = req;
2214 return;
2215 }
2216
2217 req->prev = (*head)->prev;
2218 req->prev->next = req;
2219 req->next = *head;
2220 (*head)->prev = req;
2221 }
2222
2223 static int
string_num_dots(const char * s)2224 string_num_dots(const char *s) {
2225 int count = 0;
2226 while ((s = strchr(s, '.'))) {
2227 s++;
2228 count++;
2229 }
2230 return count;
2231 }
2232
2233 static struct request *
request_new(int type,const char * name,int flags,evdns_callback_type callback,void * user_ptr)2234 request_new(int type, const char *name, int flags,
2235 evdns_callback_type callback, void *user_ptr) {
2236 const char issuing_now =
2237 (global_requests_inflight < global_max_requests_inflight) ? 1 : 0;
2238
2239 const int name_len = strlen(name);
2240 const int request_max_len = evdns_request_len(name_len);
2241 const u16 trans_id = issuing_now ? transaction_id_pick() : 0xffff;
2242 /* the request data is alloced in a single block with the header */
2243 struct request *const req =
2244 (struct request *) malloc(sizeof(struct request) + request_max_len);
2245 int rlen;
2246 (void) flags;
2247
2248 if (!req) return NULL;
2249 memset(req, 0, sizeof(struct request));
2250
2251 evtimer_set(&req->timeout_event, evdns_request_timeout_callback, req);
2252
2253 /* request data lives just after the header */
2254 req->request = ((u8 *) req) + sizeof(struct request);
2255 /* denotes that the request data shouldn't be free()ed */
2256 req->request_appended = 1;
2257 rlen = evdns_request_data_build(name, name_len, trans_id,
2258 type, CLASS_INET, req->request, request_max_len);
2259 if (rlen < 0)
2260 goto err1;
2261 req->request_len = rlen;
2262 req->trans_id = trans_id;
2263 req->tx_count = 0;
2264 req->request_type = type;
2265 req->user_pointer = user_ptr;
2266 req->user_callback = callback;
2267 req->ns = issuing_now ? nameserver_pick() : NULL;
2268 req->next = req->prev = NULL;
2269
2270 return req;
2271 err1:
2272 free(req);
2273 return NULL;
2274 }
2275
2276 static void
request_submit(struct request * const req)2277 request_submit(struct request *const req) {
2278 if (req->ns) {
2279 /* if it has a nameserver assigned then this is going */
2280 /* straight into the inflight queue */
2281 evdns_request_insert(req, &req_head);
2282 global_requests_inflight++;
2283 evdns_request_transmit(req);
2284 } else {
2285 evdns_request_insert(req, &req_waiting_head);
2286 global_requests_waiting++;
2287 }
2288 }
2289
2290 /* exported function */
evdns_resolve_ipv4(const char * name,int flags,evdns_callback_type callback,void * ptr)2291 int evdns_resolve_ipv4(const char *name, int flags,
2292 evdns_callback_type callback, void *ptr) {
2293 log(EVDNS_LOG_DEBUG, "Resolve requested for %s", name);
2294 if (flags & DNS_QUERY_NO_SEARCH) {
2295 struct request *const req =
2296 request_new(TYPE_A, name, flags, callback, ptr);
2297 if (req == NULL)
2298 return (1);
2299 request_submit(req);
2300 return (0);
2301 } else {
2302 return (search_request_new(TYPE_A, name, flags, callback, ptr));
2303 }
2304 }
2305
2306 /* exported function */
evdns_resolve_ipv6(const char * name,int flags,evdns_callback_type callback,void * ptr)2307 int evdns_resolve_ipv6(const char *name, int flags,
2308 evdns_callback_type callback, void *ptr) {
2309 log(EVDNS_LOG_DEBUG, "Resolve requested for %s", name);
2310 if (flags & DNS_QUERY_NO_SEARCH) {
2311 struct request *const req =
2312 request_new(TYPE_AAAA, name, flags, callback, ptr);
2313 if (req == NULL)
2314 return (1);
2315 request_submit(req);
2316 return (0);
2317 } else {
2318 return (search_request_new(TYPE_AAAA, name, flags, callback, ptr));
2319 }
2320 }
2321
evdns_resolve_reverse(const struct in_addr * in,int flags,evdns_callback_type callback,void * ptr)2322 int evdns_resolve_reverse(const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr) {
2323 char buf[32];
2324 struct request *req;
2325 u32 a;
2326 assert(in);
2327 a = ntohl(in->s_addr);
2328 evutil_snprintf(buf, sizeof(buf), "%d.%d.%d.%d.in-addr.arpa",
2329 (int)(u8)((a )&0xff),
2330 (int)(u8)((a>>8 )&0xff),
2331 (int)(u8)((a>>16)&0xff),
2332 (int)(u8)((a>>24)&0xff));
2333 log(EVDNS_LOG_DEBUG, "Resolve requested for %s (reverse)", buf);
2334 req = request_new(TYPE_PTR, buf, flags, callback, ptr);
2335 if (!req) return 1;
2336 request_submit(req);
2337 return 0;
2338 }
2339
evdns_resolve_reverse_ipv6(const struct in6_addr * in,int flags,evdns_callback_type callback,void * ptr)2340 int evdns_resolve_reverse_ipv6(const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr) {
2341 /* 32 nybbles, 32 periods, "ip6.arpa", NUL. */
2342 char buf[73];
2343 char *cp;
2344 struct request *req;
2345 int i;
2346 assert(in);
2347 cp = buf;
2348 for (i=15; i >= 0; --i) {
2349 u8 byte = in->s6_addr[i];
2350 *cp++ = "0123456789abcdef"[byte & 0x0f];
2351 *cp++ = '.';
2352 *cp++ = "0123456789abcdef"[byte >> 4];
2353 *cp++ = '.';
2354 }
2355 assert(cp + strlen("ip6.arpa") < buf+sizeof(buf));
2356 memcpy(cp, "ip6.arpa", strlen("ip6.arpa")+1);
2357 log(EVDNS_LOG_DEBUG, "Resolve requested for %s (reverse)", buf);
2358 req = request_new(TYPE_PTR, buf, flags, callback, ptr);
2359 if (!req) return 1;
2360 request_submit(req);
2361 return 0;
2362 }
2363
2364 /*/////////////////////////////////////////////////////////////////// */
2365 /* Search support */
2366 /* */
2367 /* the libc resolver has support for searching a number of domains */
2368 /* to find a name. If nothing else then it takes the single domain */
2369 /* from the gethostname() call. */
2370 /* */
2371 /* It can also be configured via the domain and search options in a */
2372 /* resolv.conf. */
2373 /* */
2374 /* The ndots option controls how many dots it takes for the resolver */
2375 /* to decide that a name is non-local and so try a raw lookup first. */
2376
2377 struct search_domain {
2378 int len;
2379 struct search_domain *next;
2380 /* the text string is appended to this structure */
2381 };
2382
2383 struct search_state {
2384 int refcount;
2385 int ndots;
2386 int num_domains;
2387 struct search_domain *head;
2388 };
2389
2390 static struct search_state *global_search_state = NULL;
2391
2392 static void
search_state_decref(struct search_state * const state)2393 search_state_decref(struct search_state *const state) {
2394 if (!state) return;
2395 state->refcount--;
2396 if (!state->refcount) {
2397 struct search_domain *next, *dom;
2398 for (dom = state->head; dom; dom = next) {
2399 next = dom->next;
2400 free(dom);
2401 }
2402 free(state);
2403 }
2404 }
2405
2406 static struct search_state *
search_state_new(void)2407 search_state_new(void) {
2408 struct search_state *state = (struct search_state *) malloc(sizeof(struct search_state));
2409 if (!state) return NULL;
2410 memset(state, 0, sizeof(struct search_state));
2411 state->refcount = 1;
2412 state->ndots = 1;
2413
2414 return state;
2415 }
2416
2417 static void
search_postfix_clear(void)2418 search_postfix_clear(void) {
2419 search_state_decref(global_search_state);
2420
2421 global_search_state = search_state_new();
2422 }
2423
2424 /* exported function */
2425 void
evdns_search_clear(void)2426 evdns_search_clear(void) {
2427 search_postfix_clear();
2428 }
2429
2430 static void
search_postfix_add(const char * domain)2431 search_postfix_add(const char *domain) {
2432 int domain_len;
2433 struct search_domain *sdomain;
2434 while (domain[0] == '.') domain++;
2435 domain_len = strlen(domain);
2436
2437 if (!global_search_state) global_search_state = search_state_new();
2438 if (!global_search_state) return;
2439 global_search_state->num_domains++;
2440
2441 sdomain = (struct search_domain *) malloc(sizeof(struct search_domain) + domain_len);
2442 if (!sdomain) return;
2443 memcpy( ((u8 *) sdomain) + sizeof(struct search_domain), domain, domain_len);
2444 sdomain->next = global_search_state->head;
2445 sdomain->len = domain_len;
2446
2447 global_search_state->head = sdomain;
2448 }
2449
2450 /* reverse the order of members in the postfix list. This is needed because, */
2451 /* when parsing resolv.conf we push elements in the wrong order */
2452 static void
search_reverse(void)2453 search_reverse(void) {
2454 struct search_domain *cur, *prev = NULL, *next;
2455 cur = global_search_state->head;
2456 while (cur) {
2457 next = cur->next;
2458 cur->next = prev;
2459 prev = cur;
2460 cur = next;
2461 }
2462
2463 global_search_state->head = prev;
2464 }
2465
2466 /* exported function */
2467 void
evdns_search_add(const char * domain)2468 evdns_search_add(const char *domain) {
2469 search_postfix_add(domain);
2470 }
2471
2472 /* exported function */
2473 void
evdns_search_ndots_set(const int ndots)2474 evdns_search_ndots_set(const int ndots) {
2475 if (!global_search_state) global_search_state = search_state_new();
2476 if (!global_search_state) return;
2477 global_search_state->ndots = ndots;
2478 }
2479
2480 static void
search_set_from_hostname(void)2481 search_set_from_hostname(void) {
2482 char hostname[HOST_NAME_MAX + 1], *domainname;
2483
2484 search_postfix_clear();
2485 if (gethostname(hostname, sizeof(hostname))) return;
2486 domainname = strchr(hostname, '.');
2487 if (!domainname) return;
2488 search_postfix_add(domainname);
2489 }
2490
2491 /* warning: returns malloced string */
2492 static char *
search_make_new(const struct search_state * const state,int n,const char * const base_name)2493 search_make_new(const struct search_state *const state, int n, const char *const base_name) {
2494 const int base_len = strlen(base_name);
2495 const char need_to_append_dot = base_name[base_len - 1] == '.' ? 0 : 1;
2496 struct search_domain *dom;
2497
2498 for (dom = state->head; dom; dom = dom->next) {
2499 if (!n--) {
2500 /* this is the postfix we want */
2501 /* the actual postfix string is kept at the end of the structure */
2502 const u8 *const postfix = ((u8 *) dom) + sizeof(struct search_domain);
2503 const int postfix_len = dom->len;
2504 char *const newname = (char *) malloc(base_len + need_to_append_dot + postfix_len + 1);
2505 if (!newname) return NULL;
2506 memcpy(newname, base_name, base_len);
2507 if (need_to_append_dot) newname[base_len] = '.';
2508 memcpy(newname + base_len + need_to_append_dot, postfix, postfix_len);
2509 newname[base_len + need_to_append_dot + postfix_len] = 0;
2510 return newname;
2511 }
2512 }
2513
2514 /* we ran off the end of the list and still didn't find the requested string */
2515 abort();
2516 return NULL; /* unreachable; stops warnings in some compilers. */
2517 }
2518
2519 static int
search_request_new(int type,const char * const name,int flags,evdns_callback_type user_callback,void * user_arg)2520 search_request_new(int type, const char *const name, int flags, evdns_callback_type user_callback, void *user_arg) {
2521 assert(type == TYPE_A || type == TYPE_AAAA);
2522 if ( ((flags & DNS_QUERY_NO_SEARCH) == 0) &&
2523 global_search_state &&
2524 global_search_state->num_domains) {
2525 /* we have some domains to search */
2526 struct request *req;
2527 if (string_num_dots(name) >= global_search_state->ndots) {
2528 req = request_new(type, name, flags, user_callback, user_arg);
2529 if (!req) return 1;
2530 req->search_index = -1;
2531 } else {
2532 char *const new_name = search_make_new(global_search_state, 0, name);
2533 if (!new_name) return 1;
2534 req = request_new(type, new_name, flags, user_callback, user_arg);
2535 free(new_name);
2536 if (!req) return 1;
2537 req->search_index = 0;
2538 }
2539 req->search_origname = strdup(name);
2540 req->search_state = global_search_state;
2541 req->search_flags = flags;
2542 global_search_state->refcount++;
2543 request_submit(req);
2544 return 0;
2545 } else {
2546 struct request *const req = request_new(type, name, flags, user_callback, user_arg);
2547 if (!req) return 1;
2548 request_submit(req);
2549 return 0;
2550 }
2551 }
2552
2553 /* this is called when a request has failed to find a name. We need to check */
2554 /* if it is part of a search and, if so, try the next name in the list */
2555 /* returns: */
2556 /* 0 another request has been submitted */
2557 /* 1 no more requests needed */
2558 static int
search_try_next(struct request * const req)2559 search_try_next(struct request *const req) {
2560 if (req->search_state) {
2561 /* it is part of a search */
2562 char *new_name;
2563 struct request *newreq;
2564 req->search_index++;
2565 if (req->search_index >= req->search_state->num_domains) {
2566 /* no more postfixes to try, however we may need to try */
2567 /* this name without a postfix */
2568 if (string_num_dots(req->search_origname) < req->search_state->ndots) {
2569 /* yep, we need to try it raw */
2570 newreq = request_new(req->request_type, req->search_origname, req->search_flags, req->user_callback, req->user_pointer);
2571 log(EVDNS_LOG_DEBUG, "Search: trying raw query %s", req->search_origname);
2572 if (newreq) {
2573 request_submit(newreq);
2574 return 0;
2575 }
2576 }
2577 return 1;
2578 }
2579
2580 new_name = search_make_new(req->search_state, req->search_index, req->search_origname);
2581 if (!new_name) return 1;
2582 log(EVDNS_LOG_DEBUG, "Search: now trying %s (%d)", new_name, req->search_index);
2583 newreq = request_new(req->request_type, new_name, req->search_flags, req->user_callback, req->user_pointer);
2584 free(new_name);
2585 if (!newreq) return 1;
2586 newreq->search_origname = req->search_origname;
2587 req->search_origname = NULL;
2588 newreq->search_state = req->search_state;
2589 newreq->search_flags = req->search_flags;
2590 newreq->search_index = req->search_index;
2591 newreq->search_state->refcount++;
2592 request_submit(newreq);
2593 return 0;
2594 }
2595 return 1;
2596 }
2597
2598 static void
search_request_finished(struct request * const req)2599 search_request_finished(struct request *const req) {
2600 if (req->search_state) {
2601 search_state_decref(req->search_state);
2602 req->search_state = NULL;
2603 }
2604 if (req->search_origname) {
2605 free(req->search_origname);
2606 req->search_origname = NULL;
2607 }
2608 }
2609
2610 /*/////////////////////////////////////////////////////////////////// */
2611 /* Parsing resolv.conf files */
2612
2613 static void
evdns_resolv_set_defaults(int flags)2614 evdns_resolv_set_defaults(int flags) {
2615 /* if the file isn't found then we assume a local resolver */
2616 if (flags & DNS_OPTION_SEARCH) search_set_from_hostname();
2617 if (flags & DNS_OPTION_NAMESERVERS) evdns_nameserver_ip_add("127.0.0.1");
2618 }
2619
2620 #ifndef HAVE_STRTOK_R
2621 static char *
strtok_r(char * s,const char * delim,char ** state)2622 strtok_r(char *s, const char *delim, char **state) {
2623 return strtok(s, delim);
2624 }
2625 #endif
2626
2627 /* helper version of atoi which returns -1 on error */
2628 static int
strtoint(const char * const str)2629 strtoint(const char *const str) {
2630 char *endptr;
2631 const int r = strtol(str, &endptr, 10);
2632 if (*endptr) return -1;
2633 return r;
2634 }
2635
2636 /* helper version of atoi that returns -1 on error and clips to bounds. */
2637 static int
strtoint_clipped(const char * const str,int min,int max)2638 strtoint_clipped(const char *const str, int min, int max)
2639 {
2640 int r = strtoint(str);
2641 if (r == -1)
2642 return r;
2643 else if (r<min)
2644 return min;
2645 else if (r>max)
2646 return max;
2647 else
2648 return r;
2649 }
2650
2651 /* exported function */
2652 int
evdns_set_option(const char * option,const char * val,int flags)2653 evdns_set_option(const char *option, const char *val, int flags)
2654 {
2655 if (!strncmp(option, "ndots:", 6)) {
2656 const int ndots = strtoint(val);
2657 if (ndots == -1) return -1;
2658 if (!(flags & DNS_OPTION_SEARCH)) return 0;
2659 log(EVDNS_LOG_DEBUG, "Setting ndots to %d", ndots);
2660 if (!global_search_state) global_search_state = search_state_new();
2661 if (!global_search_state) return -1;
2662 global_search_state->ndots = ndots;
2663 } else if (!strncmp(option, "timeout:", 8)) {
2664 const int timeout = strtoint(val);
2665 if (timeout == -1) return -1;
2666 if (!(flags & DNS_OPTION_MISC)) return 0;
2667 log(EVDNS_LOG_DEBUG, "Setting timeout to %d", timeout);
2668 global_timeout.tv_sec = timeout;
2669 } else if (!strncmp(option, "max-timeouts:", 12)) {
2670 const int maxtimeout = strtoint_clipped(val, 1, 255);
2671 if (maxtimeout == -1) return -1;
2672 if (!(flags & DNS_OPTION_MISC)) return 0;
2673 log(EVDNS_LOG_DEBUG, "Setting maximum allowed timeouts to %d",
2674 maxtimeout);
2675 global_max_nameserver_timeout = maxtimeout;
2676 } else if (!strncmp(option, "max-inflight:", 13)) {
2677 const int maxinflight = strtoint_clipped(val, 1, 65000);
2678 if (maxinflight == -1) return -1;
2679 if (!(flags & DNS_OPTION_MISC)) return 0;
2680 log(EVDNS_LOG_DEBUG, "Setting maximum inflight requests to %d",
2681 maxinflight);
2682 global_max_requests_inflight = maxinflight;
2683 } else if (!strncmp(option, "attempts:", 9)) {
2684 int retries = strtoint(val);
2685 if (retries == -1) return -1;
2686 if (retries > 255) retries = 255;
2687 if (!(flags & DNS_OPTION_MISC)) return 0;
2688 log(EVDNS_LOG_DEBUG, "Setting retries to %d", retries);
2689 global_max_retransmits = retries;
2690 }
2691 return 0;
2692 }
2693
2694 static void
resolv_conf_parse_line(char * const start,int flags)2695 resolv_conf_parse_line(char *const start, int flags) {
2696 char *strtok_state;
2697 static const char *const delims = " \t";
2698 #define NEXT_TOKEN strtok_r(NULL, delims, &strtok_state)
2699
2700 char *const first_token = strtok_r(start, delims, &strtok_state);
2701 if (!first_token) return;
2702
2703 if (!strcmp(first_token, "nameserver") && (flags & DNS_OPTION_NAMESERVERS)) {
2704 const char *const nameserver = NEXT_TOKEN;
2705 struct in_addr ina;
2706
2707 if (inet_aton(nameserver, &ina)) {
2708 /* address is valid */
2709 evdns_nameserver_add(ina.s_addr);
2710 }
2711 } else if (!strcmp(first_token, "domain") && (flags & DNS_OPTION_SEARCH)) {
2712 const char *const domain = NEXT_TOKEN;
2713 if (domain) {
2714 search_postfix_clear();
2715 search_postfix_add(domain);
2716 }
2717 } else if (!strcmp(first_token, "search") && (flags & DNS_OPTION_SEARCH)) {
2718 const char *domain;
2719 search_postfix_clear();
2720
2721 while ((domain = NEXT_TOKEN)) {
2722 search_postfix_add(domain);
2723 }
2724 search_reverse();
2725 } else if (!strcmp(first_token, "options")) {
2726 const char *option;
2727 while ((option = NEXT_TOKEN)) {
2728 const char *val = strchr(option, ':');
2729 evdns_set_option(option, val ? val+1 : "", flags);
2730 }
2731 }
2732 #undef NEXT_TOKEN
2733 }
2734
2735 /* exported function */
2736 /* returns: */
2737 /* 0 no errors */
2738 /* 1 failed to open file */
2739 /* 2 failed to stat file */
2740 /* 3 file too large */
2741 /* 4 out of memory */
2742 /* 5 short read from file */
2743 int
evdns_resolv_conf_parse(int flags,const char * const filename)2744 evdns_resolv_conf_parse(int flags, const char *const filename) {
2745 struct stat st;
2746 int fd, n, r;
2747 u8 *resolv;
2748 char *start;
2749 int err = 0;
2750
2751 log(EVDNS_LOG_DEBUG, "Parsing resolv.conf file %s", filename);
2752
2753 fd = open(filename, O_RDONLY);
2754 if (fd < 0) {
2755 evdns_resolv_set_defaults(flags);
2756 return 1;
2757 }
2758
2759 if (fstat(fd, &st)) { err = 2; goto out1; }
2760 if (!st.st_size) {
2761 evdns_resolv_set_defaults(flags);
2762 err = (flags & DNS_OPTION_NAMESERVERS) ? 6 : 0;
2763 goto out1;
2764 }
2765 if (st.st_size > 65535) { err = 3; goto out1; } /* no resolv.conf should be any bigger */
2766
2767 resolv = (u8 *) malloc((size_t)st.st_size + 1);
2768 if (!resolv) { err = 4; goto out1; }
2769
2770 n = 0;
2771 while ((r = read(fd, resolv+n, (size_t)st.st_size-n)) > 0) {
2772 n += r;
2773 if (n == st.st_size)
2774 break;
2775 assert(n < st.st_size);
2776 }
2777 if (r < 0) { err = 5; goto out2; }
2778 resolv[n] = 0; /* we malloced an extra byte; this should be fine. */
2779
2780 start = (char *) resolv;
2781 for (;;) {
2782 char *const newline = strchr(start, '\n');
2783 if (!newline) {
2784 resolv_conf_parse_line(start, flags);
2785 break;
2786 } else {
2787 *newline = 0;
2788 resolv_conf_parse_line(start, flags);
2789 start = newline + 1;
2790 }
2791 }
2792
2793 if (!server_head && (flags & DNS_OPTION_NAMESERVERS)) {
2794 /* no nameservers were configured. */
2795 evdns_nameserver_ip_add("127.0.0.1");
2796 err = 6;
2797 }
2798 if (flags & DNS_OPTION_SEARCH && (!global_search_state || global_search_state->num_domains == 0)) {
2799 search_set_from_hostname();
2800 }
2801
2802 out2:
2803 free(resolv);
2804 out1:
2805 close(fd);
2806 return err;
2807 }
2808
2809 #ifdef WIN32
2810 /* Add multiple nameservers from a space-or-comma-separated list. */
2811 static int
evdns_nameserver_ip_add_line(const char * ips)2812 evdns_nameserver_ip_add_line(const char *ips) {
2813 const char *addr;
2814 char *buf;
2815 int r;
2816 while (*ips) {
2817 while (ISSPACE(*ips) || *ips == ',' || *ips == '\t')
2818 ++ips;
2819 addr = ips;
2820 while (ISDIGIT(*ips) || *ips == '.' || *ips == ':')
2821 ++ips;
2822 buf = malloc(ips-addr+1);
2823 if (!buf) return 4;
2824 memcpy(buf, addr, ips-addr);
2825 buf[ips-addr] = '\0';
2826 r = evdns_nameserver_ip_add(buf);
2827 free(buf);
2828 if (r) return r;
2829 }
2830 return 0;
2831 }
2832
2833 typedef DWORD(WINAPI *GetNetworkParams_fn_t)(FIXED_INFO *, DWORD*);
2834
2835 /* Use the windows GetNetworkParams interface in iphlpapi.dll to */
2836 /* figure out what our nameservers are. */
2837 static int
load_nameservers_with_getnetworkparams(void)2838 load_nameservers_with_getnetworkparams(void)
2839 {
2840 /* Based on MSDN examples and inspection of c-ares code. */
2841 FIXED_INFO *fixed;
2842 HMODULE handle = 0;
2843 ULONG size = sizeof(FIXED_INFO);
2844 void *buf = NULL;
2845 int status = 0, r, added_any;
2846 IP_ADDR_STRING *ns;
2847 GetNetworkParams_fn_t fn;
2848
2849 if (!(handle = LoadLibrary("iphlpapi.dll"))) {
2850 log(EVDNS_LOG_WARN, "Could not open iphlpapi.dll");
2851 status = -1;
2852 goto done;
2853 }
2854 if (!(fn = (GetNetworkParams_fn_t) GetProcAddress(handle, "GetNetworkParams"))) {
2855 log(EVDNS_LOG_WARN, "Could not get address of function.");
2856 status = -1;
2857 goto done;
2858 }
2859
2860 buf = malloc(size);
2861 if (!buf) { status = 4; goto done; }
2862 fixed = buf;
2863 r = fn(fixed, &size);
2864 if (r != ERROR_SUCCESS && r != ERROR_BUFFER_OVERFLOW) {
2865 status = -1;
2866 goto done;
2867 }
2868 if (r != ERROR_SUCCESS) {
2869 free(buf);
2870 buf = malloc(size);
2871 if (!buf) { status = 4; goto done; }
2872 fixed = buf;
2873 r = fn(fixed, &size);
2874 if (r != ERROR_SUCCESS) {
2875 log(EVDNS_LOG_DEBUG, "fn() failed.");
2876 status = -1;
2877 goto done;
2878 }
2879 }
2880
2881 assert(fixed);
2882 added_any = 0;
2883 ns = &(fixed->DnsServerList);
2884 while (ns) {
2885 r = evdns_nameserver_ip_add_line(ns->IpAddress.String);
2886 if (r) {
2887 log(EVDNS_LOG_DEBUG,"Could not add nameserver %s to list,error: %d",
2888 (ns->IpAddress.String),(int)GetLastError());
2889 status = r;
2890 goto done;
2891 } else {
2892 log(EVDNS_LOG_DEBUG,"Succesfully added %s as nameserver",ns->IpAddress.String);
2893 }
2894
2895 added_any++;
2896 ns = ns->Next;
2897 }
2898
2899 if (!added_any) {
2900 log(EVDNS_LOG_DEBUG, "No nameservers added.");
2901 status = -1;
2902 }
2903
2904 done:
2905 if (buf)
2906 free(buf);
2907 if (handle)
2908 FreeLibrary(handle);
2909 return status;
2910 }
2911
2912 static int
config_nameserver_from_reg_key(HKEY key,const char * subkey)2913 config_nameserver_from_reg_key(HKEY key, const char *subkey)
2914 {
2915 char *buf;
2916 DWORD bufsz = 0, type = 0;
2917 int status = 0;
2918
2919 if (RegQueryValueEx(key, subkey, 0, &type, NULL, &bufsz)
2920 != ERROR_MORE_DATA)
2921 return -1;
2922 if (!(buf = malloc(bufsz)))
2923 return -1;
2924
2925 if (RegQueryValueEx(key, subkey, 0, &type, (LPBYTE)buf, &bufsz)
2926 == ERROR_SUCCESS && bufsz > 1) {
2927 status = evdns_nameserver_ip_add_line(buf);
2928 }
2929
2930 free(buf);
2931 return status;
2932 }
2933
2934 #define SERVICES_KEY "System\\CurrentControlSet\\Services\\"
2935 #define WIN_NS_9X_KEY SERVICES_KEY "VxD\\MSTCP"
2936 #define WIN_NS_NT_KEY SERVICES_KEY "Tcpip\\Parameters"
2937
2938 static int
load_nameservers_from_registry(void)2939 load_nameservers_from_registry(void)
2940 {
2941 int found = 0;
2942 int r;
2943 #define TRY(k, name) \
2944 if (!found && config_nameserver_from_reg_key(k,name) == 0) { \
2945 log(EVDNS_LOG_DEBUG,"Found nameservers in %s/%s",#k,name); \
2946 found = 1; \
2947 } else if (!found) { \
2948 log(EVDNS_LOG_DEBUG,"Didn't find nameservers in %s/%s", \
2949 #k,#name); \
2950 }
2951
2952 if (((int)GetVersion()) > 0) { /* NT */
2953 HKEY nt_key = 0, interfaces_key = 0;
2954
2955 if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, WIN_NS_NT_KEY, 0,
2956 KEY_READ, &nt_key) != ERROR_SUCCESS) {
2957 log(EVDNS_LOG_DEBUG,"Couldn't open nt key, %d",(int)GetLastError());
2958 return -1;
2959 }
2960 r = RegOpenKeyEx(nt_key, "Interfaces", 0,
2961 KEY_QUERY_VALUE|KEY_ENUMERATE_SUB_KEYS,
2962 &interfaces_key);
2963 if (r != ERROR_SUCCESS) {
2964 log(EVDNS_LOG_DEBUG,"Couldn't open interfaces key, %d",(int)GetLastError());
2965 return -1;
2966 }
2967 TRY(nt_key, "NameServer");
2968 TRY(nt_key, "DhcpNameServer");
2969 TRY(interfaces_key, "NameServer");
2970 TRY(interfaces_key, "DhcpNameServer");
2971 RegCloseKey(interfaces_key);
2972 RegCloseKey(nt_key);
2973 } else {
2974 HKEY win_key = 0;
2975 if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, WIN_NS_9X_KEY, 0,
2976 KEY_READ, &win_key) != ERROR_SUCCESS) {
2977 log(EVDNS_LOG_DEBUG, "Couldn't open registry key, %d", (int)GetLastError());
2978 return -1;
2979 }
2980 TRY(win_key, "NameServer");
2981 RegCloseKey(win_key);
2982 }
2983
2984 if (found == 0) {
2985 log(EVDNS_LOG_WARN,"Didn't find any nameservers.");
2986 }
2987
2988 return found ? 0 : -1;
2989 #undef TRY
2990 }
2991
2992 int
evdns_config_windows_nameservers(void)2993 evdns_config_windows_nameservers(void)
2994 {
2995 if (load_nameservers_with_getnetworkparams() == 0)
2996 return 0;
2997 return load_nameservers_from_registry();
2998 }
2999 #endif
3000
3001 int
evdns_init(void)3002 evdns_init(void)
3003 {
3004 int res = 0;
3005 #ifdef WIN32
3006 res = evdns_config_windows_nameservers();
3007 #else
3008 res = evdns_resolv_conf_parse(DNS_OPTIONS_ALL, "/etc/resolv.conf");
3009 #endif
3010
3011 return (res);
3012 }
3013
3014 const char *
evdns_err_to_string(int err)3015 evdns_err_to_string(int err)
3016 {
3017 switch (err) {
3018 case DNS_ERR_NONE: return "no error";
3019 case DNS_ERR_FORMAT: return "misformatted query";
3020 case DNS_ERR_SERVERFAILED: return "server failed";
3021 case DNS_ERR_NOTEXIST: return "name does not exist";
3022 case DNS_ERR_NOTIMPL: return "query not implemented";
3023 case DNS_ERR_REFUSED: return "refused";
3024
3025 case DNS_ERR_TRUNCATED: return "reply truncated or ill-formed";
3026 case DNS_ERR_UNKNOWN: return "unknown";
3027 case DNS_ERR_TIMEOUT: return "request timed out";
3028 case DNS_ERR_SHUTDOWN: return "dns subsystem shut down";
3029 default: return "[Unknown error code]";
3030 }
3031 }
3032
3033 void
evdns_shutdown(int fail_requests)3034 evdns_shutdown(int fail_requests)
3035 {
3036 struct nameserver *server, *server_next;
3037 struct search_domain *dom, *dom_next;
3038
3039 while (req_head) {
3040 if (fail_requests)
3041 reply_callback(req_head, 0, DNS_ERR_SHUTDOWN, NULL);
3042 request_finished(req_head, &req_head);
3043 }
3044 while (req_waiting_head) {
3045 if (fail_requests)
3046 reply_callback(req_waiting_head, 0, DNS_ERR_SHUTDOWN, NULL);
3047 request_finished(req_waiting_head, &req_waiting_head);
3048 }
3049 global_requests_inflight = global_requests_waiting = 0;
3050
3051 for (server = server_head; server; server = server_next) {
3052 server_next = server->next;
3053 if (server->socket >= 0)
3054 CLOSE_SOCKET(server->socket);
3055 (void) event_del(&server->event);
3056 if (server->state == 0)
3057 (void) event_del(&server->timeout_event);
3058 free(server);
3059 if (server_next == server_head)
3060 break;
3061 }
3062 server_head = NULL;
3063 global_good_nameservers = 0;
3064
3065 if (global_search_state) {
3066 for (dom = global_search_state->head; dom; dom = dom_next) {
3067 dom_next = dom->next;
3068 free(dom);
3069 }
3070 free(global_search_state);
3071 global_search_state = NULL;
3072 }
3073 evdns_log_fn = NULL;
3074 }
3075
3076 #ifdef EVDNS_MAIN
3077 void
main_callback(int result,char type,int count,int ttl,void * addrs,void * orig)3078 main_callback(int result, char type, int count, int ttl,
3079 void *addrs, void *orig) {
3080 char *n = (char*)orig;
3081 int i;
3082 for (i = 0; i < count; ++i) {
3083 if (type == DNS_IPv4_A) {
3084 printf("%s: %s\n", n, debug_ntoa(((u32*)addrs)[i]));
3085 } else if (type == DNS_PTR) {
3086 printf("%s: %s\n", n, ((char**)addrs)[i]);
3087 }
3088 }
3089 if (!count) {
3090 printf("%s: No answer (%d)\n", n, result);
3091 }
3092 fflush(stdout);
3093 }
3094 void
evdns_server_callback(struct evdns_server_request * req,void * data)3095 evdns_server_callback(struct evdns_server_request *req, void *data)
3096 {
3097 int i, r;
3098 (void)data;
3099 /* dummy; give 192.168.11.11 as an answer for all A questions,
3100 * give foo.bar.example.com as an answer for all PTR questions. */
3101 for (i = 0; i < req->nquestions; ++i) {
3102 u32 ans = htonl(0xc0a80b0bUL);
3103 if (req->questions[i]->type == EVDNS_TYPE_A &&
3104 req->questions[i]->dns_question_class == EVDNS_CLASS_INET) {
3105 printf(" -- replying for %s (A)\n", req->questions[i]->name);
3106 r = evdns_server_request_add_a_reply(req, req->questions[i]->name,
3107 1, &ans, 10);
3108 if (r<0)
3109 printf("eeep, didn't work.\n");
3110 } else if (req->questions[i]->type == EVDNS_TYPE_PTR &&
3111 req->questions[i]->dns_question_class == EVDNS_CLASS_INET) {
3112 printf(" -- replying for %s (PTR)\n", req->questions[i]->name);
3113 r = evdns_server_request_add_ptr_reply(req, NULL, req->questions[i]->name,
3114 "foo.bar.example.com", 10);
3115 } else {
3116 printf(" -- skipping %s [%d %d]\n", req->questions[i]->name,
3117 req->questions[i]->type, req->questions[i]->dns_question_class);
3118 }
3119 }
3120
3121 r = evdns_request_respond(req, 0);
3122 if (r<0)
3123 printf("eeek, couldn't send reply.\n");
3124 }
3125
3126 void
logfn(int is_warn,const char * msg)3127 logfn(int is_warn, const char *msg) {
3128 (void) is_warn;
3129 fprintf(stderr, "%s\n", msg);
3130 }
3131 int
main(int c,char ** v)3132 main(int c, char **v) {
3133 int idx;
3134 int reverse = 0, verbose = 1, servertest = 0;
3135 if (c<2) {
3136 fprintf(stderr, "syntax: %s [-x] [-v] hostname\n", v[0]);
3137 fprintf(stderr, "syntax: %s [-servertest]\n", v[0]);
3138 return 1;
3139 }
3140 idx = 1;
3141 while (idx < c && v[idx][0] == '-') {
3142 if (!strcmp(v[idx], "-x"))
3143 reverse = 1;
3144 else if (!strcmp(v[idx], "-v"))
3145 verbose = 1;
3146 else if (!strcmp(v[idx], "-servertest"))
3147 servertest = 1;
3148 else
3149 fprintf(stderr, "Unknown option %s\n", v[idx]);
3150 ++idx;
3151 }
3152 event_init();
3153 if (verbose)
3154 evdns_set_log_fn(logfn);
3155 evdns_resolv_conf_parse(DNS_OPTION_NAMESERVERS, "/etc/resolv.conf");
3156 if (servertest) {
3157 int sock;
3158 struct sockaddr_in my_addr;
3159 sock = socket(PF_INET, SOCK_DGRAM, 0);
3160 evutil_make_socket_nonblocking(sock);
3161 my_addr.sin_family = AF_INET;
3162 my_addr.sin_port = htons(10053);
3163 my_addr.sin_addr.s_addr = INADDR_ANY;
3164 if (bind(sock, (struct sockaddr*)&my_addr, sizeof(my_addr))<0) {
3165 perror("bind");
3166 exit(1);
3167 }
3168 evdns_add_server_port(sock, 0, evdns_server_callback, NULL);
3169 }
3170 for (; idx < c; ++idx) {
3171 if (reverse) {
3172 struct in_addr addr;
3173 if (!inet_aton(v[idx], &addr)) {
3174 fprintf(stderr, "Skipping non-IP %s\n", v[idx]);
3175 continue;
3176 }
3177 fprintf(stderr, "resolving %s...\n",v[idx]);
3178 evdns_resolve_reverse(&addr, 0, main_callback, v[idx]);
3179 } else {
3180 fprintf(stderr, "resolving (fwd) %s...\n",v[idx]);
3181 evdns_resolve_ipv4(v[idx], 0, main_callback, v[idx]);
3182 }
3183 }
3184 fflush(stdout);
3185 event_dispatch();
3186 return 0;
3187 }
3188 #endif
3189