1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466
|
/* $Id: dns.C,v 1.16 2001/08/19 00:27:16 dm Exp $ */
/*
*
* Copyright (C) 1998 David Mazieres (dm@uun.org)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2, or (at
* your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
* USA
*
*/
/* Asynchronous resolver. This code is easy to understand if and only
* if you also have a copy of RFC 1035. You can get this by anonymous
* ftp from, among other places, ftp.internic.net:/rfc/rfc1035.txt.
*/
#include "dnsparse.h"
#include "arena.h"
#include "vec.h"
#include "ihash.h"
#include "list.h"
#include "backoff.h"
INITFN(dns_start);
#define NSPORT NAMESERVER_PORT
#define QBSIZE 512
class dnsreq {
static u_int16_t lastid; // Last request id
static int ns_idx;
static sockaddr_in srvaddr; // IP address of name server
static int sock; // UDP socket
static bool tcplock;
static int last_good_idx;
static time_t last_resp;
static void tcpcb (int, int);
static void resend (dnsreq *r) { r->xmit (); }
static u_int16_t genid ();
dnsreq ();
virtual void readreply (dnsparse *) = 0;
void fail (int);
void start (bool);
int ntries;
int srchno;
protected:
int error;
public:
static void setsock (bool);
static void pktready ();
u_int16_t id; // DNS query ID
str basename; // Name for which to search
str name; // Name for which to query
u_short type; // Type of query (T_A, T_PTR, etc.)
ihash_entry<dnsreq> hlink; // Per-id hash table link
tmoq_entry<dnsreq> tlink; // Retransmit queue link
dnsreq (str, u_int16_t, bool search = false);
virtual ~dnsreq ();
bool xmit (int = 0);
void timeout ();
};
u_int16_t dnsreq::lastid;
int dnsreq::ns_idx;
sockaddr_in dnsreq::srvaddr;
int dnsreq::sock = -1;
bool dnsreq::tcplock;
int dnsreq::last_good_idx;
time_t dnsreq::last_resp;
static ihash<u_short, dnsreq, &dnsreq::id, &dnsreq::hlink> reqtab;
static tmoq<dnsreq, &dnsreq::tlink, 1, 5> reqtoq;
u_int16_t
dnsreq::genid ()
{
#ifndef HAVE_ARC4RANDOM
static u_short dns_lastid;
return ++dns_lastid;
#else /* HAVE_ARC4RANDOM */
return arc4random () & 0xffff;
#endif /* HAVE_ARC4RANDOM */
}
void
dnsreq::fail (int err)
{
if (!error)
error = err;
readreply (NULL);
delete this;
}
void
dnsreq::start (bool again)
{
if (again && (srchno < 0 || !_res.dnsrch[srchno])) {
fail (NXDOMAIN);
return;
}
if (again) {
reqtab.remove (this);
reqtoq.remove (this);
}
if (srchno >= 0)
name = strbuf ("%s.%s", basename.cstr (), _res.dnsrch[srchno++]);
id = genid ();
reqtab.insert (this);
reqtoq.start (this);
}
dnsreq::dnsreq (str n, u_int16_t t, bool search)
: ntries (0), error (0), type (t)
{
if (!search || strchr (n, '.')) {
srchno = -1;
basename = NULL;
name = n;
}
else {
srchno = 0;
basename = n;
name = NULL;
}
start (false);
}
dnsreq::~dnsreq ()
{
reqtab.remove (this);
reqtoq.remove (this);
}
//* Send a query to the nameserver */
bool
dnsreq::xmit (int retry)
{
u_char qb[QBSIZE];
HEADER *const h = (HEADER *) qb;
int n;
n = res_mkquery (QUERY, name, C_IN, type, NULL, 0, NULL, qb, sizeof (qb));
if (n < 0)
return false;
h->id = htons (id); /* XXX - Why bother with htons? */
if (sendto (sock, reinterpret_cast<char *> (qb), n, 0,
reinterpret_cast<sockaddr *> (&srvaddr), sizeof (srvaddr)) < 0) {
error = ARERR_CANTSEND;
return false;
}
error = 0;
return true;
}
void
dnsreq::timeout ()
{
if (timenow - last_resp > 60) {
if (++ntries < _res.nscount) {
reqtab.remove (this);
reqtoq.remove (this);
setsock (true);
start (false);
return;
}
setsock (true);
}
fail (ARERR_TIMEOUT);
}
void
dnsreq::pktready ()
{
u_char qb[QBSIZE];
ssize_t n;
for (;;) {
sockaddr_in sin;
socklen_t sinlen = sizeof (sin);
bzero (&sin, sizeof (sin));
n = recvfrom (sock, reinterpret_cast<char *> (qb), sizeof (qb),
0, reinterpret_cast<sockaddr *> (&sin), &sinlen);
if (n < 0)
break;
if (!addreq (reinterpret_cast<sockaddr *> (&sin),
reinterpret_cast<sockaddr *> (&srvaddr),
sizeof (sin)))
continue;
last_resp = timenow;
last_good_idx = ns_idx;
dnsparse reply (qb, n);
question q;
if (!reply.qparse (&q))
continue;
dnsreq *r;
for (r = reqtab[ntohs (reply.hdr->id)];
r && (r->type != q.q_type || strcasecmp (r->name, q.q_name));
r = reqtab.nextkeq (r))
;
if (!r)
continue;
if (reply.error && !r->error)
r->error = reply.error;
if (r->error == NXDOMAIN) {
r->error = 0;
r->start (true);
}
else {
r->readreply (r->error ? NULL : &reply);
delete r;
}
}
}
/* Try setting up a TCP connection to name servers, to make sure they
* are really running named. (This is really a kludge because we
* can't see ICMP port unreachable packets without using connected UDP
* sockets, and we can't use connected UDP sockets without failing
* when laptops change their IP addresses.) */
void
dnsreq::tcpcb (int idx, int fd)
{
tcplock = false;
if (fd >= 0) {
close (fd);
last_good_idx = ns_idx;
return;
}
else if (idx == ns_idx && !last_resp)
setsock (true);
}
void
dnsreq::setsock (bool bump)
{
if (sock < 0) {
/* We use a reserved port here to prevent port-capture problems.
* (An unprivileged user can steal packets destined to an INADDR_ANY
* socket by binding to the same port on the more-specific interface
* address. */
if (suidsafe ())
sock = inetsocket_resvport (SOCK_DGRAM);
else
sock = inetsocket (SOCK_DGRAM);
if (sock < 0)
fatal ("dnsreq::setsock: inetsocket: %s\n", strerror (errno));
close_on_exec (sock);
make_async (sock);
fdcb (sock, selread, wrap (pktready));
}
if (bump && _res.nscount) {
ns_idx = (ns_idx + 1) % _res.nscount;
warn ("changing nameserver to %s\n",
inet_ntoa (_res.nsaddr_list[ns_idx].sin_addr));
}
srvaddr = _res.nsaddr_list[ns_idx];
if (!srvaddr.sin_addr.s_addr) // XXX
srvaddr.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
last_resp = 0;
reqtab.traverse (wrap (resend));
if (!tcplock && (!bump || ns_idx != last_good_idx)) {
tcplock = true;
tcpconnect (srvaddr.sin_addr, ntohs (srvaddr.sin_port),
wrap (tcpcb, ns_idx));
}
}
class dnsreq_a : public dnsreq {
bool checkaddr; // Non-zero when arr_addr must be checked
in_addr addr; // Adress of inverse queries (for checking)
cbhent cb; // Callback for hostbyname/addr
dnsreq_a ();
public:
dnsreq_a (str n, cbhent c, bool s = false)
: dnsreq (n, T_A, s), checkaddr (false), cb (c) {}
dnsreq_a (str n, cbhent c, const in_addr &a)
: dnsreq (n, T_A), checkaddr (true), addr (a), cb (c) {}
void readreply (dnsparse *);
};
void
dnsreq_a::readreply (dnsparse *reply)
{
ptr<hostent> h;
if (!error) {
if (!(h = reply->tohostent ()))
error = reply->error;
else if (checkaddr) {
char **ap;
for (ap = h->h_addr_list; *ap && *(in_addr *) *ap != addr; ap++)
;
if (!*ap) {
h = NULL;
error = ARERR_PTRSPOOF;
}
}
}
(*cb) (h, error);
}
void
dns_hostbyname (str name, cbhent cb,
bool search, bool addrok)
{
if (addrok) {
in_addr addr;
if (inet_aton (name.cstr (), &addr)) {
ptr<hostent> h = refcounted<hostent, vsize>::alloc
(sizeof (*h) + 3 * sizeof (void *)
+ sizeof (addr) + strlen (name) + 1);
h->h_aliases = (char **) &h[1];
h->h_addrtype = AF_INET;
h->h_length = sizeof (addr);
h->h_addr_list = &h->h_aliases[1];
h->h_aliases[0] = NULL;
h->h_addr_list[0] = (char *) &h->h_addr_list[2];
h->h_addr_list[1] = NULL;
*(struct in_addr *) h->h_addr_list[0] = addr;
h->h_name = (char *) h->h_addr_list[0] + sizeof (addr);
strcpy ((char *) h->h_name, name);
(*cb) (h, 0);
return;
}
}
vNew dnsreq_a (name, cb, search);
}
class dnsreq_ptr : public dnsreq {
in_addr addr;
cbhent cb; // Callback for hostbyname/addr
dnsreq_ptr ();
public:
static str inaddr_arpa (in_addr);
dnsreq_ptr (in_addr a, cbhent c)
: dnsreq (inaddr_arpa (a), T_PTR), addr (a), cb (c) {}
void readreply (dnsparse *);
};
str
dnsreq_ptr::inaddr_arpa (in_addr addr)
{
u_char *a = reinterpret_cast<u_char *> (&addr);
return strbuf ("%d.%d.%d.%d.in-addr.arpa", a[3], a[2], a[1], a[0]);
}
void
dnsreq_ptr::readreply (dnsparse *reply)
{
if (!error) {
const u_char *cp = reply->getanp ();
for (u_int i = 0; i < reply->ancount; i++) {
resrec rr;
if (!reply->rrparse (&cp, &rr))
break;
if (rr.rr_type == T_PTR && rr.rr_class == C_IN) {
vNew dnsreq_a (rr.rr_ptr, cb, addr);
return;
}
}
}
if (!error && !(error = reply->error))
error = ARERR_NXREC;
(*cb) (NULL, error);
}
void
dns_hostbyaddr (in_addr addr, cbhent cb)
{
vNew dnsreq_ptr (addr, cb);
}
static void
dns_start ()
{
if (!(_res.options & RES_INIT))
res_init ();
dnsreq::setsock (false);
}
const char *
dns_strerror (int no)
{
switch (no) {
case NOERROR:
return "no error";
case FORMERR:
return "DNS format error";
case SERVFAIL:
return "name server failure";
case NXDOMAIN:
return "non-existent domain name";
case NOTIMP:
return "unimplemented DNS request";
case REFUSED:
return "DNS query refused";
case ARERR_NXREC:
return "no DNS records of appropriate type";
case ARERR_TIMEOUT:
return "name lookup timed out";
case ARERR_PTRSPOOF:
return "incorrect PTR record";
case ARERR_BADRESP:
return "malformed DNS reply";
case ARERR_CANTSEND:
return "cannot send to name server";
case ARERR_REQINVAL:
return "malformed domain name";
case ARERR_CNAMELOOP:
return "CNAME records form loop";
default:
return "unknown DNS error";
}
}
int
dns_tmperr (int no)
{
switch (no) {
case SERVFAIL:
case ARERR_TIMEOUT:
case ARERR_CANTSEND:
case ARERR_BADRESP:
return 1;
default:
return 0;
}
}
|