mDNSMacOSX/DNS64.c

   1 /*
   2  * Copyright (c) 2017 Apple Inc. All rights reserved.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <TargetConditionals.h>
  18
  19 // DNS64 code is only for iOS, which is currently the only Apple OS that supports DNS proxy network extensions.
  20
  21 #if TARGET_OS_IOS
  22 #include "DNS64.h"
  23
  24 #include <AssertMacros.h>
  25
  26 #if __has_include(<nw/private.h>)
  27     #include <nw/private.h>
  28 #else
  29     #include <network/nat64.h>
  30 #endif
  31
  32 #include <stdlib.h>
  33 #include <string.h>
  34
  35 #include "dns_sd.h"
  36 #include "dns_sd_internal.h"
  37 #include "uDNS.h"
  38
  39 //===========================================================================================================================
  40 //  Constants
  41 //===========================================================================================================================
  42
  43 #define kDNS64IPv4OnlyFQDNString    "\x8" "ipv4only" "\x4" "arpa"
  44 #define kDNS64IPv4OnlyFQDN          ((const domainname *) kDNS64IPv4OnlyFQDNString)
  45 #define kDNS64IPv4OnlyFQDNLength    15  // 9 bytes for first label, 5 bytes for second label, and 1 byte for the root label.
  46
  47 #define sizeof_field(TYPE, FIELD)   sizeof(((TYPE *)0)->FIELD)    // From CoreUtils.h
  48
  49 check_compile_time(sizeof(kDNS64IPv4OnlyFQDNString) == kDNS64IPv4OnlyFQDNLength);
  50 check_compile_time(sizeof_field(DNSQuestion, qname) >= kDNS64IPv4OnlyFQDNLength);
  51 check_compile_time(sizeof_field(DNS64, qnameStash)  == kDNS64IPv4OnlyFQDNLength);
  52
  53 //===========================================================================================================================
  54 //  Local Prototypes
  55 //===========================================================================================================================
  56
  57 mDNSlocal mStatus   DNS64GetIPv6Addrs(mDNS *m, mDNSu16 inResGroupID, struct in6_addr **outAddrs, uint32_t *outAddrCount);
  58 mDNSlocal mStatus   DNS64GetPrefixes(mDNS *m, mDNSu16 inResGroupID, nw_nat64_prefix_t **outPrefixes, uint32_t *outPrefixCount);
  59 mDNSlocal mDNSBool  DNS64GetReverseIPv6Addr(const domainname *inQName, struct in6_addr *outAddr);
  60 mDNSlocal mDNSu32   DNS64IPv4OnlyFQDNHash(void);
  61 mDNSlocal void      DNS64RestartQuestion(mDNS *m, DNSQuestion *q, DNS64State newState);
  62 mDNSlocal mDNSBool  DNS64TestIPv6Synthesis(mDNS *m, mDNSu16 inResGroupID, const mDNSv4Addr *inV4Addr);
  63
  64 //===========================================================================================================================
  65 //  DNS64StateMachine
  66 //===========================================================================================================================
  67
  68 mDNSexport mDNSBool DNS64StateMachine(mDNS *m, DNSQuestion *inQ, const ResourceRecord *inRR, QC_result inResult)
  69 {
  70     // If this is an mDNS question, then exit early. DNS64 is only for unicast DNS questions.
  71
  72     if (mDNSOpaque16IsZero(inQ->TargetQID)) return (mDNSfalse);
  73
  74     switch (inQ->dns64.state)
  75     {
  76     // If this question is going to be answered with a negative AAAA record and the question is not for "ipv4only.arpa." and
  77     // the question's DNS server's interface supports NAT64, then restart the question as an "ipv4only.arpa." AAAA question.
  78     // Otherwise, do nothing.
  79
  80     case kDNS64State_Initial:
  81         if ((inRR->RecordType == kDNSRecordTypePacketNegative) && (inResult == QC_add))
  82         {
  83             if ((inQ->qtype      == kDNSType_AAAA) &&
  84                 (inRR->rrtype    == kDNSType_AAAA) &&
  85                 (inRR->rrclass   == kDNSClass_IN) &&
  86                 ((inQ->qnamehash != DNS64IPv4OnlyFQDNHash()) || !SameDomainName(&inQ->qname, kDNS64IPv4OnlyFQDN)) &&
  87                 inQ->qDNSServer &&
  88                 nw_nat64_does_interface_index_support_nat64((uint32_t)(uintptr_t)inQ->qDNSServer->interface))
  89             {
  90                 DNS64RestartQuestion(m, inQ, kDNS64State_PrefixDiscovery);
  91                 return (mDNStrue);
  92             }
  93             else if ((inQ->qtype == kDNSType_PTR) &&
  94                 (inRR->rrtype    == kDNSType_PTR) &&
  95                 (inRR->rrclass   == kDNSClass_IN) &&
  96                 inQ->qDNSServer &&
  97                 nw_nat64_does_interface_index_support_nat64((uint32_t)(uintptr_t)inQ->qDNSServer->interface) &&
  98                 DNS64GetReverseIPv6Addr(&inQ->qname, NULL))
  99             {
 100                 DNS64RestartQuestion(m, inQ, kDNS64State_PrefixDiscoveryPTR);
 101                 return (mDNStrue);
 102             }
 103         }
 104         break;
 105
 106     // If the "ipv4only.arpa." question is going to be answered with a positive AAAA record, then restart it as a question
 107     // for an A record with the original AAAA qname.
 108     // Otherwise, restart the question for the original AAAA record.
 109
 110     case kDNS64State_PrefixDiscovery:
 111         if ((inRR->RecordType != kDNSRecordTypePacketNegative) &&
 112             (inResult         == QC_add) &&
 113             (inRR->rrtype     == kDNSType_AAAA) &&
 114             (inRR->rrclass    == kDNSClass_IN))
 115         {
 116             DNS64RestartQuestion(m, inQ, kDNS64State_QueryA);
 117             return (mDNStrue);
 118         }
 119         else
 120         {
 121             DNS64RestartQuestion(m, inQ, kDNS64State_QueryAAAA);
 122             return (mDNStrue);
 123         }
 124         break;
 125
 126     // The "ipv4only.arpa." question is going to be answered. Restart the question now. DNS64HandleNewQuestion() will decide
 127     // whether or not to change it to a reverse IPv4 question.
 128
 129     case kDNS64State_PrefixDiscoveryPTR:
 130         DNS64RestartQuestion(m, inQ, kDNS64State_QueryPTR);
 131         return (mDNStrue);
 132         break;
 133
 134     // If this question is going to be answered with a CNAME, then do nothing.
 135     // If this question is going to be answered with a positive A record that's synthesizable, then set the state to
 136     // QueryARecord2.
 137     // Otherwise, restart the question for the original AAAA record.
 138
 139     case kDNS64State_QueryA:
 140         if (inRR->rrtype != kDNSType_CNAME)
 141         {
 142             if ((inRR->RecordType != kDNSRecordTypePacketNegative) &&
 143                 (inResult         == QC_add) &&
 144                 (inRR->rrtype     == kDNSType_A) &&
 145                 (inRR->rrclass    == kDNSClass_IN) &&
 146                 inQ->qDNSServer &&
 147                 DNS64TestIPv6Synthesis(m, inQ->qDNSServer->resGroupID, &inRR->rdata->u.ipv4))
 148             {
 149                 inQ->dns64.state = kDNS64State_QueryA2;
 150             }
 151             else
 152             {
 153                 DNS64RestartQuestion(m, inQ, kDNS64State_QueryAAAA);
 154                 return (mDNStrue);
 155             }
 156         }
 157         break;
 158
 159     // For all other states, do nothing.
 160
 161     case kDNS64State_QueryA2:
 162     case kDNS64State_QueryAAAA:
 163     case kDNS64State_QueryPTR:
 164     case kDNS64State_ReverseIPv4:
 165     case kDNS64State_ReverseIPv6:
 166         break;
 167
 168     default:
 169         LogMsg("DNS64StateMachine: unrecognized DNS64 state %d", inQ->dns64.state);
 170         break;
 171     }
 172
 173     return (mDNSfalse);
 174 }
 175
 176 //===========================================================================================================================
 177 //  DNS64AnswerQuestion
 178 //===========================================================================================================================
 179
 180 mDNSexport mStatus DNS64AnswerQuestion(mDNS *m, DNSQuestion *inQ, const ResourceRecord *inRR, QC_result inResult)
 181 {
 182     mStatus                 err;
 183     ResourceRecord          newRR;
 184     RData                   rdata;
 185     nw_nat64_prefix_t *     prefixes = NULL;
 186     uint32_t                prefixCount;
 187     uint32_t                i;
 188     struct in_addr          v4Addr;
 189     struct in6_addr         synthV6;
 190
 191     require_action_quiet(inQ->qDNSServer, exit, err = mStatus_BadParamErr);
 192
 193     err = DNS64GetPrefixes(m, inQ->qDNSServer->resGroupID, &prefixes, &prefixCount);
 194     require_noerr_quiet(err, exit);
 195
 196     newRR               = *inRR;
 197     newRR.rrtype        = kDNSType_AAAA;
 198     newRR.rdlength      = 16;
 199     rdata.MaxRDLength   = newRR.rdlength;
 200     newRR.rdata         = &rdata;
 201
 202     memcpy(&v4Addr.s_addr, inRR->rdata->u.ipv4.b, 4);
 203     for (i = 0; i < prefixCount; i++)
 204     {
 205         if (nw_nat64_synthesize_v6(&prefixes[i], &v4Addr, &synthV6))
 206         {
 207             memcpy(rdata.u.ipv6.b, synthV6.s6_addr, 16);
 208             inQ->QuestionCallback(m, inQ, &newRR, inResult);
 209         }
 210     }
 211     err = mStatus_NoError;
 212
 213 exit:
 214     if (prefixes) free(prefixes);
 215     return (err);
 216 }
 217
 218 //===========================================================================================================================
 219 //  DNS64HandleNewQuestion
 220 //===========================================================================================================================
 221
 222 mDNSexport void DNS64HandleNewQuestion(mDNS *m, DNSQuestion *inQ)
 223 {
 224     if (inQ->dns64.state == kDNS64State_QueryPTR)
 225     {
 226         struct in6_addr     v6Addr;
 227
 228         inQ->dns64.state = kDNS64State_ReverseIPv6;
 229         if (inQ->qDNSServer && DNS64GetReverseIPv6Addr(&inQ->qname, &v6Addr))
 230         {
 231             mStatus                 err;
 232             nw_nat64_prefix_t *     prefixes;
 233             uint32_t                prefixCount;
 234             uint32_t                i;
 235             struct in_addr          v4Addr;
 236             char                    qnameStr[MAX_REVERSE_MAPPING_NAME_V4];
 237
 238             err = DNS64GetPrefixes(m, inQ->qDNSServer->resGroupID, &prefixes, &prefixCount);
 239             require_noerr_quiet(err, exit);
 240
 241             for (i = 0; i < prefixCount; i++)
 242             {
 243                 if (nw_nat64_extract_v4(&prefixes[i], &v6Addr, &v4Addr))
 244                 {
 245                     const mDNSu8 * const        a = (const mDNSu8 *)&v4Addr.s_addr;
 246
 247                     snprintf(qnameStr, sizeof(qnameStr), "%u.%u.%u.%u.in-addr.arpa.", a[3], a[2], a[1], a[0]);
 248                     MakeDomainNameFromDNSNameString(&inQ->qname, qnameStr);
 249                     inQ->qnamehash   = DomainNameHashValue(&inQ->qname);
 250                     inQ->dns64.state = kDNS64State_ReverseIPv4;
 251                     break;
 252                 }
 253             }
 254             free(prefixes);
 255         }
 256     }
 257
 258 exit:
 259     return;
 260 }
 261
 262 //===========================================================================================================================
 263 //  DNS64ResetState
 264 //===========================================================================================================================
 265
 266 // Called from mDNS_StopQuery_internal().
 267
 268 mDNSexport void DNS64ResetState(DNSQuestion *inQ)
 269 {
 270     switch (inQ->dns64.state)
 271     {
 272     case kDNS64State_PrefixDiscoveryPTR:
 273         inQ->qtype = kDNSType_PTR;  // Restore qtype to PTR and fall through.
 274
 275     case kDNS64State_PrefixDiscovery:
 276         memcpy(&inQ->qname, inQ->dns64.qnameStash, sizeof(inQ->dns64.qnameStash));  // Restore the previous qname.
 277         inQ->qnamehash = DomainNameHashValue(&inQ->qname);
 278         break;
 279
 280     case kDNS64State_QueryA:
 281     case kDNS64State_QueryA2:
 282         inQ->qtype = kDNSType_AAAA; // Restore qtype to AAAA.
 283         break;
 284
 285     // Do nothing for the other states.
 286
 287     case kDNS64State_Initial:
 288     case kDNS64State_QueryAAAA:
 289     case kDNS64State_QueryPTR:
 290     case kDNS64State_ReverseIPv4:
 291     case kDNS64State_ReverseIPv6:
 292         break;
 293
 294     default:
 295         LogMsg("DNS64ResetState: unrecognized DNS64 state %d", inQ->dns64.state);
 296         break;
 297     }
 298     inQ->dns64.state = kDNS64State_Initial;
 299 }
 300
 301 //===========================================================================================================================
 302 //  DNS64RestartQuestions
 303 //===========================================================================================================================
 304
 305 mDNSexport void DNS64RestartQuestions(mDNS *m)
 306 {
 307     DNSQuestion *       q;
 308     DNSQuestion *       restartList = NULL;
 309     DNSServer *         newServer;
 310
 311     m->RestartQuestion = m->Questions;
 312     while (m->RestartQuestion)
 313     {
 314         q = m->RestartQuestion;
 315         m->RestartQuestion = q->next;
 316         if (q->dns64.state != kDNS64State_Initial)
 317         {
 318             SetValidDNSServers(m, q);
 319             q->triedAllServersOnce = 0;
 320             newServer = GetServerForQuestion(m, q);
 321             if (q->qDNSServer != newServer)
 322             {
 323                 if (!CacheRecordRmvEventsForQuestion(m, q))
 324                 {
 325                     LogInfo("DNS64RestartQuestions: Question deleted while delivering RMV events from cache");
 326                 }
 327                 else
 328                 {
 329                     LogInfo("DNS64RestartQuestions: Stop question %p %##s (%s)", q, q->qname.c, DNSTypeName(q->qtype));
 330                     mDNS_StopQuery_internal(m, q);
 331                     q->next = restartList;
 332                     restartList = q;
 333                 }
 334             }
 335         }
 336     }
 337     while ((q = restartList) != NULL)
 338     {
 339         restartList = restartList->next;
 340         q->next = NULL;
 341         LogInfo("DNS64RestartQuestions: Start question %p %##s (%s)", q, q->qname.c, DNSTypeName(q->qtype));
 342         mDNS_StartQuery_internal(m, q);
 343     }
 344 }
 345
 346 //===========================================================================================================================
 347 //  DNS64GetIPv6Addrs
 348 //===========================================================================================================================
 349
 350 #define IsPositiveAAAAFromResGroup(RR, RES_GROUP_ID)        \
 351     ((RR)->rDNSServer &&                                    \
 352     ((RR)->rDNSServer->resGroupID == RES_GROUP_ID) &&       \
 353     ((RR)->rrtype == kDNSType_AAAA) &&                      \
 354     ((RR)->RecordType != kDNSRecordTypePacketNegative) &&   \
 355     !(RR)->InterfaceID)
 356
 357 mDNSlocal mStatus DNS64GetIPv6Addrs(mDNS *m, const mDNSu16 inResGroupID, struct in6_addr **outAddrs, uint32_t *outAddrCount)
 358 {
 359     mStatus                 err;
 360     const CacheGroup *      cg;
 361     const CacheRecord *     cr;
 362     struct in6_addr *       addrs = NULL;
 363     uint32_t                addrCount;
 364     uint32_t                recordCount;
 365
 366     cg = CacheGroupForName(m, DNS64IPv4OnlyFQDNHash(), kDNS64IPv4OnlyFQDN);
 367     require_action_quiet(cg, exit, err = mStatus_NoSuchRecord);
 368
 369     recordCount = 0;
 370     for (cr = cg->members; cr; cr = cr->next)
 371     {
 372         if (IsPositiveAAAAFromResGroup(&cr->resrec, inResGroupID))
 373         {
 374             recordCount++;
 375         }
 376     }
 377     require_action_quiet(recordCount > 0, exit, err = mStatus_NoSuchRecord);
 378
 379     addrs = (struct in6_addr *)calloc(recordCount, sizeof(*addrs));
 380     require_action_quiet(addrs, exit, err = mStatus_NoMemoryErr);
 381
 382     addrCount = 0;
 383     for (cr = cg->members; cr && (addrCount < recordCount); cr = cr->next)
 384     {
 385         if (IsPositiveAAAAFromResGroup(&cr->resrec, inResGroupID))
 386         {
 387             memcpy(addrs[addrCount].s6_addr, cr->resrec.rdata->u.ipv6.b, 16);
 388             addrCount++;
 389         }
 390     }
 391
 392     *outAddrs = addrs;
 393     addrs = NULL;
 394     *outAddrCount = addrCount;
 395     err = mStatus_NoError;
 396
 397 exit:
 398     if (addrs) free(addrs);
 399     return (err);
 400 }
 401
 402 //===========================================================================================================================
 403 //  DNS64GetPrefixes
 404 //===========================================================================================================================
 405
 406 mDNSlocal mStatus DNS64GetPrefixes(mDNS *m, mDNSu16 inResGroupID, nw_nat64_prefix_t **outPrefixes, uint32_t *outPrefixCount)
 407 {
 408     mStatus                 err;
 409     struct in6_addr *       v6Addrs;
 410     uint32_t                v6AddrCount;
 411     nw_nat64_prefix_t *     prefixes;
 412     int32_t                 prefixCount;
 413
 414     err = DNS64GetIPv6Addrs(m, inResGroupID, &v6Addrs, &v6AddrCount);
 415     require_noerr_quiet(err, exit);
 416
 417     prefixCount = nw_nat64_copy_prefixes_from_ipv4only_records(v6Addrs, v6AddrCount, &prefixes);
 418     free(v6Addrs);
 419     require_action_quiet(prefixCount > 0, exit, err = mStatus_UnknownErr);
 420
 421     *outPrefixes    = prefixes;
 422     *outPrefixCount = prefixCount;
 423
 424 exit:
 425     return (err);
 426 }
 427
 428 //===========================================================================================================================
 429 //  DNS64GetReverseIPv6Addr
 430 //===========================================================================================================================
 431
 432 #define kReverseIPv6Domain  ((const domainname *) "\x3" "ip6" "\x4" "arpa")
 433
 434 mDNSlocal mDNSBool DNS64GetReverseIPv6Addr(const domainname *inQName, struct in6_addr *outAddr)
 435 {
 436     const mDNSu8 *      ptr;
 437     int                 i;
 438     unsigned int        c;
 439     unsigned int        nl;
 440     unsigned int        nu;
 441
 442     // If the name is of the form "x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.ip6.arpa.", where each x
 443     // is a hex digit, then the sequence of 32 hex digit labels represents the nibbles of an IPv6 address in reverse order.
 444     // See <https://tools.ietf.org/html/rfc3596#section-2.5>.
 445
 446     ptr = (const mDNSu8 *)inQName;
 447     for (i = 0; i < 16; i++)
 448     {
 449         if (*ptr++ != 1) return (mDNSfalse);                    // If this label's length is not 1, then fail.
 450         c = *ptr++;                                             // Get label byte.
 451         if (     (c >= '0') && (c <= '9')) nl =  c - '0';       // If it's a hex digit, get its numeric value.
 452         else if ((c >= 'a') && (c <= 'f')) nl = (c - 'a') + 10;
 453         else if ((c >= 'A') && (c <= 'F')) nl = (c - 'A') + 10;
 454         else                               return (mDNSfalse);  // Otherwise, fail.
 455
 456         if (*ptr++ != 1) return (mDNSfalse);                    // If this label's length is not 1, then fail.
 457         c = *ptr++;                                             // Get label byte.
 458         if (     (c >= '0') && (c <= '9')) nu =  c - '0';       // If it's a hex digit, get its numeric value.
 459         else if ((c >= 'a') && (c <= 'f')) nu = (c - 'a') + 10;
 460         else if ((c >= 'A') && (c <= 'F')) nu = (c - 'A') + 10;
 461         else                               return (mDNSfalse);  // Otherwise, fail.
 462
 463         if (outAddr) outAddr->s6_addr[15 - i] = (mDNSu8)((nu << 4) | nl);
 464     }
 465
 466     // The rest of the name needs to be "ip6.arpa.". If it isn't, fail.
 467
 468     if (!SameDomainName((const domainname *)ptr, kReverseIPv6Domain)) return (mDNSfalse);
 469
 470     return (mDNStrue);
 471 }
 472
 473 //===========================================================================================================================
 474 //  DNS64IPv4OnlyFQDNHash
 475 //===========================================================================================================================
 476
 477 mDNSlocal mDNSu32 DNS64IPv4OnlyFQDNHash(void)
 478 {
 479     static dispatch_once_t      sHashOnce;
 480     static mDNSu32              sHash;
 481
 482     dispatch_once(&sHashOnce, ^{ sHash = DomainNameHashValue(kDNS64IPv4OnlyFQDN); });
 483
 484     return (sHash);
 485 }
 486
 487 //===========================================================================================================================
 488 //  DNS64RestartQuestion
 489 //===========================================================================================================================
 490
 491 mDNSlocal void DNS64RestartQuestion(mDNS *const m, DNSQuestion *inQ, DNS64State inNewState)
 492 {
 493     mDNS_StopQuery_internal(m, inQ);
 494
 495     inQ->dns64.state = inNewState;
 496     switch (inQ->dns64.state)
 497     {
 498     case kDNS64State_Initial:
 499         break;
 500
 501     case kDNS64State_PrefixDiscovery:
 502     case kDNS64State_PrefixDiscoveryPTR:
 503         // Save the first 15 bytes from the original qname that are displaced by setting qname to "ipv4only.arpa.".
 504
 505         memcpy(inQ->dns64.qnameStash, &inQ->qname, sizeof(inQ->dns64.qnameStash));
 506         AssignDomainName(&inQ->qname, kDNS64IPv4OnlyFQDN);
 507         inQ->qnamehash = DNS64IPv4OnlyFQDNHash();
 508         inQ->qtype = kDNSType_AAAA;
 509         break;
 510
 511     case kDNS64State_QueryA:
 512     case kDNS64State_QueryA2:
 513         inQ->qtype = kDNSType_A;
 514         break;
 515
 516     case kDNS64State_QueryPTR:
 517     case kDNS64State_ReverseIPv4:
 518     case kDNS64State_ReverseIPv6:
 519         inQ->qtype = kDNSType_PTR;
 520         break;
 521
 522     case kDNS64State_QueryAAAA:
 523         inQ->qtype = kDNSType_AAAA;
 524         break;
 525
 526     default:
 527         LogMsg("DNS64RestartQuestion: unrecognized DNS64 state %d", inQ->dns64.state);
 528         break;
 529     }
 530
 531     mDNS_StartQuery_internal(m, inQ);
 532 }
 533
 534 //===========================================================================================================================
 535 //  DNS64TestIPv6Synthesis
 536 //===========================================================================================================================
 537
 538 mDNSlocal mDNSBool DNS64TestIPv6Synthesis(mDNS *m, mDNSu16 inResGroupID, const mDNSv4Addr *inV4Addr)
 539 {
 540     mStatus                 err;
 541     nw_nat64_prefix_t *     prefixes    = NULL;
 542     uint32_t                prefixCount;
 543     uint32_t                i;
 544     struct in_addr          v4Addr;
 545     struct in6_addr         synthV6;
 546     mDNSBool                result      = mDNSfalse;
 547
 548     err = DNS64GetPrefixes(m, inResGroupID, &prefixes, &prefixCount);
 549     require_noerr_quiet(err, exit);
 550
 551     memcpy(&v4Addr.s_addr, inV4Addr->b, 4);
 552     for (i = 0; i < prefixCount; i++)
 553     {
 554         if (nw_nat64_synthesize_v6(&prefixes[i], &v4Addr, &synthV6))
 555         {
 556             result = mDNStrue;
 557             break;
 558         }
 559     }
 560
 561 exit:
 562     if (prefixes) free(prefixes);
 563     return (result);
 564 }
 565 #endif  // TARGET_OS_IOS