src/shared/dns-domain.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #if HAVE_LIBIDN2
   4 #  include <idn2.h>
   5 #elif HAVE_LIBIDN
   6 #  include <idna.h>
   7 #  include <stringprep.h>
   8 #endif
   9
  10 #include <endian.h>
  11 #include <netinet/in.h>
  12 #include <stdio.h>
  13 #include <string.h>
  14 #include <sys/socket.h>
  15
  16 #include "alloc-util.h"
  17 #include "dns-domain.h"
  18 #include "hashmap.h"
  19 #include "hexdecoct.h"
  20 #include "in-addr-util.h"
  21 #include "macro.h"
  22 #include "parse-util.h"
  23 #include "string-util.h"
  24 #include "strv.h"
  25 #include "utf8.h"
  26
  27 int dns_label_unescape(const char **name, char *dest, size_t sz) {
  28         const char *n;
  29         char *d;
  30         int r = 0;
  31
  32         assert(name);
  33         assert(*name);
  34
  35         n = *name;
  36         d = dest;
  37
  38         for (;;) {
  39                 if (*n == '.') {
  40                         n++;
  41                         break;
  42                 }
  43
  44                 if (*n == 0)
  45                         break;
  46
  47                 if (r >= DNS_LABEL_MAX)
  48                         return -EINVAL;
  49
  50                 if (sz <= 0)
  51                         return -ENOBUFS;
  52
  53                 if (*n == '\\') {
  54                         /* Escaped character */
  55
  56                         n++;
  57
  58                         if (*n == 0)
  59                                 /* Ending NUL */
  60                                 return -EINVAL;
  61
  62                         else if (IN_SET(*n, '\\', '.')) {
  63                                 /* Escaped backslash or dot */
  64
  65                                 if (d)
  66                                         *(d++) = *n;
  67                                 sz--;
  68                                 r++;
  69                                 n++;
  70
  71                         } else if (n[0] >= '0' && n[0] <= '9') {
  72                                 unsigned k;
  73
  74                                 /* Escaped literal ASCII character */
  75
  76                                 if (!(n[1] >= '0' && n[1] <= '9') ||
  77                                     !(n[2] >= '0' && n[2] <= '9'))
  78                                         return -EINVAL;
  79
  80                                 k = ((unsigned) (n[0] - '0') * 100) +
  81                                         ((unsigned) (n[1] - '0') * 10) +
  82                                         ((unsigned) (n[2] - '0'));
  83
  84                                 /* Don't allow anything that doesn't
  85                                  * fit in 8bit. Note that we do allow
  86                                  * control characters, as some servers
  87                                  * (e.g. cloudflare) are happy to
  88                                  * generate labels with them
  89                                  * inside. */
  90                                 if (k > 255)
  91                                         return -EINVAL;
  92
  93                                 if (d)
  94                                         *(d++) = (char) k;
  95                                 sz--;
  96                                 r++;
  97
  98                                 n += 3;
  99                         } else
 100                                 return -EINVAL;
 101
 102                 } else if ((uint8_t) *n >= (uint8_t) ' ' && *n != 127) {
 103
 104                         /* Normal character */
 105
 106                         if (d)
 107                                 *(d++) = *n;
 108                         sz--;
 109                         r++;
 110                         n++;
 111                 } else
 112                         return -EINVAL;
 113         }
 114
 115         /* Empty label that is not at the end? */
 116         if (r == 0 && *n)
 117                 return -EINVAL;
 118
 119         /* More than one trailing dot? */
 120         if (*n == '.')
 121                 return -EINVAL;
 122
 123         if (sz >= 1 && d)
 124                 *d = 0;
 125
 126         *name = n;
 127         return r;
 128 }
 129
 130 /* @label_terminal: terminal character of a label, updated to point to the terminal character of
 131  *                  the previous label (always skipping one dot) or to NULL if there are no more
 132  *                  labels. */
 133 int dns_label_unescape_suffix(const char *name, const char **label_terminal, char *dest, size_t sz) {
 134         const char *terminal;
 135         int r;
 136
 137         assert(name);
 138         assert(label_terminal);
 139         assert(dest);
 140
 141         /* no more labels */
 142         if (!*label_terminal) {
 143                 if (sz >= 1)
 144                         *dest = 0;
 145
 146                 return 0;
 147         }
 148
 149         terminal = *label_terminal;
 150         assert(IN_SET(*terminal, 0, '.'));
 151
 152         /* Skip current terminal character (and accept domain names ending it ".") */
 153         if (*terminal == 0)
 154                 terminal--;
 155         if (terminal >= name && *terminal == '.')
 156                 terminal--;
 157
 158         /* Point name to the last label, and terminal to the preceding terminal symbol (or make it a NULL pointer) */
 159         for (;;) {
 160                 if (terminal < name) {
 161                         /* Reached the first label, so indicate that there are no more */
 162                         terminal = NULL;
 163                         break;
 164                 }
 165
 166                 /* Find the start of the last label */
 167                 if (*terminal == '.') {
 168                         const char *y;
 169                         unsigned slashes = 0;
 170
 171                         for (y = terminal - 1; y >= name && *y == '\\'; y--)
 172                                 slashes++;
 173
 174                         if (slashes % 2 == 0) {
 175                                 /* The '.' was not escaped */
 176                                 name = terminal + 1;
 177                                 break;
 178                         } else {
 179                                 terminal = y;
 180                                 continue;
 181                         }
 182                 }
 183
 184                 terminal--;
 185         }
 186
 187         r = dns_label_unescape(&name, dest, sz);
 188         if (r < 0)
 189                 return r;
 190
 191         *label_terminal = terminal;
 192
 193         return r;
 194 }
 195
 196 int dns_label_escape(const char *p, size_t l, char *dest, size_t sz) {
 197         char *q;
 198
 199         /* DNS labels must be between 1 and 63 characters long. A
 200          * zero-length label does not exist. See RFC 2182, Section
 201          * 11. */
 202
 203         if (l <= 0 || l > DNS_LABEL_MAX)
 204                 return -EINVAL;
 205         if (sz < 1)
 206                 return -ENOBUFS;
 207
 208         assert(p);
 209         assert(dest);
 210
 211         q = dest;
 212         while (l > 0) {
 213
 214                 if (IN_SET(*p, '.', '\\')) {
 215
 216                         /* Dot or backslash */
 217
 218                         if (sz < 3)
 219                                 return -ENOBUFS;
 220
 221                         *(q++) = '\\';
 222                         *(q++) = *p;
 223
 224                         sz -= 2;
 225
 226                 } else if (IN_SET(*p, '_', '-') ||
 227                            (*p >= '0' && *p <= '9') ||
 228                            (*p >= 'a' && *p <= 'z') ||
 229                            (*p >= 'A' && *p <= 'Z')) {
 230
 231                         /* Proper character */
 232
 233                         if (sz < 2)
 234                                 return -ENOBUFS;
 235
 236                         *(q++) = *p;
 237                         sz -= 1;
 238
 239                 } else {
 240
 241                         /* Everything else */
 242
 243                         if (sz < 5)
 244                                 return -ENOBUFS;
 245
 246                         *(q++) = '\\';
 247                         *(q++) = '0' + (char) ((uint8_t) *p / 100);
 248                         *(q++) = '0' + (char) (((uint8_t) *p / 10) % 10);
 249                         *(q++) = '0' + (char) ((uint8_t) *p % 10);
 250
 251                         sz -= 4;
 252                 }
 253
 254                 p++;
 255                 l--;
 256         }
 257
 258         *q = 0;
 259         return (int) (q - dest);
 260 }
 261
 262 int dns_label_escape_new(const char *p, size_t l, char **ret) {
 263         _cleanup_free_ char *s = NULL;
 264         int r;
 265
 266         assert(p);
 267         assert(ret);
 268
 269         if (l <= 0 || l > DNS_LABEL_MAX)
 270                 return -EINVAL;
 271
 272         s = new(char, DNS_LABEL_ESCAPED_MAX);
 273         if (!s)
 274                 return -ENOMEM;
 275
 276         r = dns_label_escape(p, l, s, DNS_LABEL_ESCAPED_MAX);
 277         if (r < 0)
 278                 return r;
 279
 280         *ret = TAKE_PTR(s);
 281
 282         return r;
 283 }
 284
 285 #if HAVE_LIBIDN
 286 int dns_label_apply_idna(const char *encoded, size_t encoded_size, char *decoded, size_t decoded_max) {
 287         _cleanup_free_ uint32_t *input = NULL;
 288         size_t input_size, l;
 289         const char *p;
 290         bool contains_8bit = false;
 291         char buffer[DNS_LABEL_MAX+1];
 292
 293         assert(encoded);
 294         assert(decoded);
 295
 296         /* Converts an U-label into an A-label */
 297
 298         if (encoded_size <= 0)
 299                 return -EINVAL;
 300
 301         for (p = encoded; p < encoded + encoded_size; p++)
 302                 if ((uint8_t) *p > 127)
 303                         contains_8bit = true;
 304
 305         if (!contains_8bit) {
 306                 if (encoded_size > DNS_LABEL_MAX)
 307                         return -EINVAL;
 308
 309                 return 0;
 310         }
 311
 312         input = stringprep_utf8_to_ucs4(encoded, encoded_size, &input_size);
 313         if (!input)
 314                 return -ENOMEM;
 315
 316         if (idna_to_ascii_4i(input, input_size, buffer, 0) != 0)
 317                 return -EINVAL;
 318
 319         l = strlen(buffer);
 320
 321         /* Verify that the result is not longer than one DNS label. */
 322         if (l <= 0 || l > DNS_LABEL_MAX)
 323                 return -EINVAL;
 324         if (l > decoded_max)
 325                 return -ENOBUFS;
 326
 327         memcpy(decoded, buffer, l);
 328
 329         /* If there's room, append a trailing NUL byte, but only then */
 330         if (decoded_max > l)
 331                 decoded[l] = 0;
 332
 333         return (int) l;
 334 }
 335
 336 int dns_label_undo_idna(const char *encoded, size_t encoded_size, char *decoded, size_t decoded_max) {
 337         size_t input_size, output_size;
 338         _cleanup_free_ uint32_t *input = NULL;
 339         _cleanup_free_ char *result = NULL;
 340         uint32_t *output = NULL;
 341         size_t w;
 342
 343         /* To be invoked after unescaping. Converts an A-label into an U-label. */
 344
 345         assert(encoded);
 346         assert(decoded);
 347
 348         if (encoded_size <= 0 || encoded_size > DNS_LABEL_MAX)
 349                 return -EINVAL;
 350
 351         if (!memory_startswith(encoded, encoded_size, IDNA_ACE_PREFIX))
 352                 return 0;
 353
 354         input = stringprep_utf8_to_ucs4(encoded, encoded_size, &input_size);
 355         if (!input)
 356                 return -ENOMEM;
 357
 358         output_size = input_size;
 359         output = newa(uint32_t, output_size);
 360
 361         idna_to_unicode_44i(input, input_size, output, &output_size, 0);
 362
 363         result = stringprep_ucs4_to_utf8(output, output_size, NULL, &w);
 364         if (!result)
 365                 return -ENOMEM;
 366         if (w <= 0)
 367                 return -EINVAL;
 368         if (w > decoded_max)
 369                 return -ENOBUFS;
 370
 371         memcpy(decoded, result, w);
 372
 373         /* Append trailing NUL byte if there's space, but only then. */
 374         if (decoded_max > w)
 375                 decoded[w] = 0;
 376
 377         return w;
 378 }
 379 #endif
 380
 381 int dns_name_concat(const char *a, const char *b, char **_ret) {
 382         _cleanup_free_ char *ret = NULL;
 383         size_t n = 0, allocated = 0;
 384         const char *p;
 385         bool first = true;
 386         int r;
 387
 388         if (a)
 389                 p = a;
 390         else if (b)
 391                 p = TAKE_PTR(b);
 392         else
 393                 goto finish;
 394
 395         for (;;) {
 396                 char label[DNS_LABEL_MAX];
 397
 398                 r = dns_label_unescape(&p, label, sizeof(label));
 399                 if (r < 0)
 400                         return r;
 401                 if (r == 0) {
 402                         if (*p != 0)
 403                                 return -EINVAL;
 404
 405                         if (b) {
 406                                 /* Now continue with the second string, if there is one */
 407                                 p = TAKE_PTR(b);
 408                                 continue;
 409                         }
 410
 411                         break;
 412                 }
 413
 414                 if (_ret) {
 415                         if (!GREEDY_REALLOC(ret, allocated, n + !first + DNS_LABEL_ESCAPED_MAX))
 416                                 return -ENOMEM;
 417
 418                         r = dns_label_escape(label, r, ret + n + !first, DNS_LABEL_ESCAPED_MAX);
 419                         if (r < 0)
 420                                 return r;
 421
 422                         if (!first)
 423                                 ret[n] = '.';
 424                 } else {
 425                         char escaped[DNS_LABEL_ESCAPED_MAX];
 426
 427                         r = dns_label_escape(label, r, escaped, sizeof(escaped));
 428                         if (r < 0)
 429                                 return r;
 430                 }
 431
 432                 if (!first)
 433                         n++;
 434                 else
 435                         first = false;
 436
 437                 n += r;
 438         }
 439
 440 finish:
 441         if (n > DNS_HOSTNAME_MAX)
 442                 return -EINVAL;
 443
 444         if (_ret) {
 445                 if (n == 0) {
 446                         /* Nothing appended? If so, generate at least a single dot, to indicate the DNS root domain */
 447                         if (!GREEDY_REALLOC(ret, allocated, 2))
 448                                 return -ENOMEM;
 449
 450                         ret[n++] = '.';
 451                 } else {
 452                         if (!GREEDY_REALLOC(ret, allocated, n + 1))
 453                                 return -ENOMEM;
 454                 }
 455
 456                 ret[n] = 0;
 457                 *_ret = TAKE_PTR(ret);
 458         }
 459
 460         return 0;
 461 }
 462
 463 void dns_name_hash_func(const char *p, struct siphash *state) {
 464         int r;
 465
 466         assert(p);
 467
 468         for (;;) {
 469                 char label[DNS_LABEL_MAX+1];
 470
 471                 r = dns_label_unescape(&p, label, sizeof(label));
 472                 if (r < 0)
 473                         break;
 474                 if (r == 0)
 475                         break;
 476
 477                 ascii_strlower_n(label, r);
 478                 siphash24_compress(label, r, state);
 479                 siphash24_compress_byte(0, state); /* make sure foobar and foo.bar result in different hashes */
 480         }
 481
 482         /* enforce that all names are terminated by the empty label */
 483         string_hash_func("", state);
 484 }
 485
 486 int dns_name_compare_func(const char *a, const char *b) {
 487         const char *x, *y;
 488         int r, q;
 489
 490         assert(a);
 491         assert(b);
 492
 493         x = a + strlen(a);
 494         y = b + strlen(b);
 495
 496         for (;;) {
 497                 char la[DNS_LABEL_MAX], lb[DNS_LABEL_MAX];
 498
 499                 if (x == NULL && y == NULL)
 500                         return 0;
 501
 502                 r = dns_label_unescape_suffix(a, &x, la, sizeof(la));
 503                 q = dns_label_unescape_suffix(b, &y, lb, sizeof(lb));
 504                 if (r < 0 || q < 0)
 505                         return CMP(r, q);
 506
 507                 r = ascii_strcasecmp_nn(la, r, lb, q);
 508                 if (r != 0)
 509                         return r;
 510         }
 511 }
 512
 513 DEFINE_HASH_OPS(dns_name_hash_ops, char, dns_name_hash_func, dns_name_compare_func);
 514
 515 int dns_name_equal(const char *x, const char *y) {
 516         int r, q;
 517
 518         assert(x);
 519         assert(y);
 520
 521         for (;;) {
 522                 char la[DNS_LABEL_MAX], lb[DNS_LABEL_MAX];
 523
 524                 r = dns_label_unescape(&x, la, sizeof(la));
 525                 if (r < 0)
 526                         return r;
 527
 528                 q = dns_label_unescape(&y, lb, sizeof(lb));
 529                 if (q < 0)
 530                         return q;
 531
 532                 if (r != q)
 533                         return false;
 534                 if (r == 0)
 535                         return true;
 536
 537                 if (ascii_strcasecmp_n(la, lb, r) != 0)
 538                         return false;
 539         }
 540 }
 541
 542 int dns_name_endswith(const char *name, const char *suffix) {
 543         const char *n, *s, *saved_n = NULL;
 544         int r, q;
 545
 546         assert(name);
 547         assert(suffix);
 548
 549         n = name;
 550         s = suffix;
 551
 552         for (;;) {
 553                 char ln[DNS_LABEL_MAX], ls[DNS_LABEL_MAX];
 554
 555                 r = dns_label_unescape(&n, ln, sizeof(ln));
 556                 if (r < 0)
 557                         return r;
 558
 559                 if (!saved_n)
 560                         saved_n = n;
 561
 562                 q = dns_label_unescape(&s, ls, sizeof(ls));
 563                 if (q < 0)
 564                         return q;
 565
 566                 if (r == 0 && q == 0)
 567                         return true;
 568                 if (r == 0 && saved_n == n)
 569                         return false;
 570
 571                 if (r != q || ascii_strcasecmp_n(ln, ls, r) != 0) {
 572
 573                         /* Not the same, let's jump back, and try with the next label again */
 574                         s = suffix;
 575                         n = TAKE_PTR(saved_n);
 576                 }
 577         }
 578 }
 579
 580 int dns_name_startswith(const char *name, const char *prefix) {
 581         const char *n, *p;
 582         int r, q;
 583
 584         assert(name);
 585         assert(prefix);
 586
 587         n = name;
 588         p = prefix;
 589
 590         for (;;) {
 591                 char ln[DNS_LABEL_MAX], lp[DNS_LABEL_MAX];
 592
 593                 r = dns_label_unescape(&p, lp, sizeof(lp));
 594                 if (r < 0)
 595                         return r;
 596                 if (r == 0)
 597                         return true;
 598
 599                 q = dns_label_unescape(&n, ln, sizeof(ln));
 600                 if (q < 0)
 601                         return q;
 602
 603                 if (r != q)
 604                         return false;
 605                 if (ascii_strcasecmp_n(ln, lp, r) != 0)
 606                         return false;
 607         }
 608 }
 609
 610 int dns_name_change_suffix(const char *name, const char *old_suffix, const char *new_suffix, char **ret) {
 611         const char *n, *s, *saved_before = NULL, *saved_after = NULL, *prefix;
 612         int r, q;
 613
 614         assert(name);
 615         assert(old_suffix);
 616         assert(new_suffix);
 617         assert(ret);
 618
 619         n = name;
 620         s = old_suffix;
 621
 622         for (;;) {
 623                 char ln[DNS_LABEL_MAX], ls[DNS_LABEL_MAX];
 624
 625                 if (!saved_before)
 626                         saved_before = n;
 627
 628                 r = dns_label_unescape(&n, ln, sizeof(ln));
 629                 if (r < 0)
 630                         return r;
 631
 632                 if (!saved_after)
 633                         saved_after = n;
 634
 635                 q = dns_label_unescape(&s, ls, sizeof(ls));
 636                 if (q < 0)
 637                         return q;
 638
 639                 if (r == 0 && q == 0)
 640                         break;
 641                 if (r == 0 && saved_after == n) {
 642                         *ret = NULL; /* doesn't match */
 643                         return 0;
 644                 }
 645
 646                 if (r != q || ascii_strcasecmp_n(ln, ls, r) != 0) {
 647
 648                         /* Not the same, let's jump back, and try with the next label again */
 649                         s = old_suffix;
 650                         n = TAKE_PTR(saved_after);
 651                         saved_before = NULL;
 652                 }
 653         }
 654
 655         /* Found it! Now generate the new name */
 656         prefix = strndupa(name, saved_before - name);
 657
 658         r = dns_name_concat(prefix, new_suffix, ret);
 659         if (r < 0)
 660                 return r;
 661
 662         return 1;
 663 }
 664
 665 int dns_name_between(const char *a, const char *b, const char *c) {
 666         /* Determine if b is strictly greater than a and strictly smaller than c.
 667            We consider the order of names to be circular, so that if a is
 668            strictly greater than c, we consider b to be between them if it is
 669            either greater than a or smaller than c. This is how the canonical
 670            DNS name order used in NSEC records work. */
 671
 672         if (dns_name_compare_func(a, c) < 0)
 673                 /*
 674                    a and c are properly ordered:
 675                    a<---b--->c
 676                 */
 677                 return dns_name_compare_func(a, b) < 0 &&
 678                        dns_name_compare_func(b, c) < 0;
 679         else
 680                 /*
 681                    a and c are equal or 'reversed':
 682                    <--b--c         a----->
 683                    or:
 684                    <-----c         a--b-->
 685                 */
 686                 return dns_name_compare_func(b, c) < 0 ||
 687                        dns_name_compare_func(a, b) < 0;
 688 }
 689
 690 int dns_name_reverse(int family, const union in_addr_union *a, char **ret) {
 691         const uint8_t *p;
 692         int r;
 693
 694         assert(a);
 695         assert(ret);
 696
 697         p = (const uint8_t*) a;
 698
 699         if (family == AF_INET)
 700                 r = asprintf(ret, "%u.%u.%u.%u.in-addr.arpa", p[3], p[2], p[1], p[0]);
 701         else if (family == AF_INET6)
 702                 r = asprintf(ret, "%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.%c.ip6.arpa",
 703                              hexchar(p[15] & 0xF), hexchar(p[15] >> 4), hexchar(p[14] & 0xF), hexchar(p[14] >> 4),
 704                              hexchar(p[13] & 0xF), hexchar(p[13] >> 4), hexchar(p[12] & 0xF), hexchar(p[12] >> 4),
 705                              hexchar(p[11] & 0xF), hexchar(p[11] >> 4), hexchar(p[10] & 0xF), hexchar(p[10] >> 4),
 706                              hexchar(p[ 9] & 0xF), hexchar(p[ 9] >> 4), hexchar(p[ 8] & 0xF), hexchar(p[ 8] >> 4),
 707                              hexchar(p[ 7] & 0xF), hexchar(p[ 7] >> 4), hexchar(p[ 6] & 0xF), hexchar(p[ 6] >> 4),
 708                              hexchar(p[ 5] & 0xF), hexchar(p[ 5] >> 4), hexchar(p[ 4] & 0xF), hexchar(p[ 4] >> 4),
 709                              hexchar(p[ 3] & 0xF), hexchar(p[ 3] >> 4), hexchar(p[ 2] & 0xF), hexchar(p[ 2] >> 4),
 710                              hexchar(p[ 1] & 0xF), hexchar(p[ 1] >> 4), hexchar(p[ 0] & 0xF), hexchar(p[ 0] >> 4));
 711         else
 712                 return -EAFNOSUPPORT;
 713         if (r < 0)
 714                 return -ENOMEM;
 715
 716         return 0;
 717 }
 718
 719 int dns_name_address(const char *p, int *family, union in_addr_union *address) {
 720         int r;
 721
 722         assert(p);
 723         assert(family);
 724         assert(address);
 725
 726         r = dns_name_endswith(p, "in-addr.arpa");
 727         if (r < 0)
 728                 return r;
 729         if (r > 0) {
 730                 uint8_t a[4];
 731                 unsigned i;
 732
 733                 for (i = 0; i < ELEMENTSOF(a); i++) {
 734                         char label[DNS_LABEL_MAX+1];
 735
 736                         r = dns_label_unescape(&p, label, sizeof(label));
 737                         if (r < 0)
 738                                 return r;
 739                         if (r == 0)
 740                                 return -EINVAL;
 741                         if (r > 3)
 742                                 return -EINVAL;
 743
 744                         r = safe_atou8(label, &a[i]);
 745                         if (r < 0)
 746                                 return r;
 747                 }
 748
 749                 r = dns_name_equal(p, "in-addr.arpa");
 750                 if (r <= 0)
 751                         return r;
 752
 753                 *family = AF_INET;
 754                 address->in.s_addr = htobe32(((uint32_t) a[3] << 24) |
 755                                              ((uint32_t) a[2] << 16) |
 756                                              ((uint32_t) a[1] << 8) |
 757                                               (uint32_t) a[0]);
 758
 759                 return 1;
 760         }
 761
 762         r = dns_name_endswith(p, "ip6.arpa");
 763         if (r < 0)
 764                 return r;
 765         if (r > 0) {
 766                 struct in6_addr a;
 767                 unsigned i;
 768
 769                 for (i = 0; i < ELEMENTSOF(a.s6_addr); i++) {
 770                         char label[DNS_LABEL_MAX+1];
 771                         int x, y;
 772
 773                         r = dns_label_unescape(&p, label, sizeof(label));
 774                         if (r <= 0)
 775                                 return r;
 776                         if (r != 1)
 777                                 return -EINVAL;
 778                         x = unhexchar(label[0]);
 779                         if (x < 0)
 780                                 return -EINVAL;
 781
 782                         r = dns_label_unescape(&p, label, sizeof(label));
 783                         if (r <= 0)
 784                                 return r;
 785                         if (r != 1)
 786                                 return -EINVAL;
 787                         y = unhexchar(label[0]);
 788                         if (y < 0)
 789                                 return -EINVAL;
 790
 791                         a.s6_addr[ELEMENTSOF(a.s6_addr) - i - 1] = (uint8_t) y << 4 | (uint8_t) x;
 792                 }
 793
 794                 r = dns_name_equal(p, "ip6.arpa");
 795                 if (r <= 0)
 796                         return r;
 797
 798                 *family = AF_INET6;
 799                 address->in6 = a;
 800                 return 1;
 801         }
 802
 803         return 0;
 804 }
 805
 806 bool dns_name_is_root(const char *name) {
 807
 808         assert(name);
 809
 810         /* There are exactly two ways to encode the root domain name:
 811          * as empty string, or with a single dot. */
 812
 813         return STR_IN_SET(name, "", ".");
 814 }
 815
 816 bool dns_name_is_single_label(const char *name) {
 817         int r;
 818
 819         assert(name);
 820
 821         r = dns_name_parent(&name);
 822         if (r <= 0)
 823                 return false;
 824
 825         return dns_name_is_root(name);
 826 }
 827
 828 /* Encode a domain name according to RFC 1035 Section 3.1, without compression */
 829 int dns_name_to_wire_format(const char *domain, uint8_t *buffer, size_t len, bool canonical) {
 830         uint8_t *label_length, *out;
 831         int r;
 832
 833         assert(domain);
 834         assert(buffer);
 835
 836         out = buffer;
 837
 838         do {
 839                 /* Reserve a byte for label length */
 840                 if (len <= 0)
 841                         return -ENOBUFS;
 842                 len--;
 843                 label_length = out;
 844                 out++;
 845
 846                 /* Convert and copy a single label. Note that
 847                  * dns_label_unescape() returns 0 when it hits the end
 848                  * of the domain name, which we rely on here to encode
 849                  * the trailing NUL byte. */
 850                 r = dns_label_unescape(&domain, (char *) out, len);
 851                 if (r < 0)
 852                         return r;
 853
 854                 /* Optionally, output the name in DNSSEC canonical
 855                  * format, as described in RFC 4034, section 6.2. Or
 856                  * in other words: in lower-case. */
 857                 if (canonical)
 858                         ascii_strlower_n((char*) out, (size_t) r);
 859
 860                 /* Fill label length, move forward */
 861                 *label_length = r;
 862                 out += r;
 863                 len -= r;
 864
 865         } while (r != 0);
 866
 867         /* Verify the maximum size of the encoded name. The trailing
 868          * dot + NUL byte account are included this time, hence
 869          * compare against DNS_HOSTNAME_MAX + 2 (which is 255) this
 870          * time. */
 871         if (out - buffer > DNS_HOSTNAME_MAX + 2)
 872                 return -EINVAL;
 873
 874         return out - buffer;
 875 }
 876
 877 static bool srv_type_label_is_valid(const char *label, size_t n) {
 878         size_t k;
 879
 880         assert(label);
 881
 882         if (n < 2) /* Label needs to be at least 2 chars long */
 883                 return false;
 884
 885         if (label[0] != '_') /* First label char needs to be underscore */
 886                 return false;
 887
 888         /* Second char must be a letter */
 889         if (!(label[1] >= 'A' && label[1] <= 'Z') &&
 890             !(label[1] >= 'a' && label[1] <= 'z'))
 891                 return false;
 892
 893         /* Third and further chars must be alphanumeric or a hyphen */
 894         for (k = 2; k < n; k++) {
 895                 if (!(label[k] >= 'A' && label[k] <= 'Z') &&
 896                     !(label[k] >= 'a' && label[k] <= 'z') &&
 897                     !(label[k] >= '0' && label[k] <= '9') &&
 898                     label[k] != '-')
 899                         return false;
 900         }
 901
 902         return true;
 903 }
 904
 905 bool dns_srv_type_is_valid(const char *name) {
 906         unsigned c = 0;
 907         int r;
 908
 909         if (!name)
 910                 return false;
 911
 912         for (;;) {
 913                 char label[DNS_LABEL_MAX];
 914
 915                 /* This more or less implements RFC 6335, Section 5.1 */
 916
 917                 r = dns_label_unescape(&name, label, sizeof(label));
 918                 if (r < 0)
 919                         return false;
 920                 if (r == 0)
 921                         break;
 922
 923                 if (c >= 2)
 924                         return false;
 925
 926                 if (!srv_type_label_is_valid(label, r))
 927                         return false;
 928
 929                 c++;
 930         }
 931
 932         return c == 2; /* exactly two labels */
 933 }
 934
 935 bool dnssd_srv_type_is_valid(const char *name) {
 936         return dns_srv_type_is_valid(name) &&
 937                 ((dns_name_endswith(name, "_tcp") > 0) ||
 938                  (dns_name_endswith(name, "_udp") > 0)); /* Specific to DNS-SD. RFC 6763, Section 7 */
 939 }
 940
 941 bool dns_service_name_is_valid(const char *name) {
 942         size_t l;
 943
 944         /* This more or less implements RFC 6763, Section 4.1.1 */
 945
 946         if (!name)
 947                 return false;
 948
 949         if (!utf8_is_valid(name))
 950                 return false;
 951
 952         if (string_has_cc(name, NULL))
 953                 return false;
 954
 955         l = strlen(name);
 956         if (l <= 0)
 957                 return false;
 958         if (l > 63)
 959                 return false;
 960
 961         return true;
 962 }
 963
 964 int dns_service_join(const char *name, const char *type, const char *domain, char **ret) {
 965         char escaped[DNS_LABEL_ESCAPED_MAX];
 966         _cleanup_free_ char *n = NULL;
 967         int r;
 968
 969         assert(type);
 970         assert(domain);
 971         assert(ret);
 972
 973         if (!dns_srv_type_is_valid(type))
 974                 return -EINVAL;
 975
 976         if (!name)
 977                 return dns_name_concat(type, domain, ret);
 978
 979         if (!dns_service_name_is_valid(name))
 980                 return -EINVAL;
 981
 982         r = dns_label_escape(name, strlen(name), escaped, sizeof(escaped));
 983         if (r < 0)
 984                 return r;
 985
 986         r = dns_name_concat(type, domain, &n);
 987         if (r < 0)
 988                 return r;
 989
 990         return dns_name_concat(escaped, n, ret);
 991 }
 992
 993 static bool dns_service_name_label_is_valid(const char *label, size_t n) {
 994         char *s;
 995
 996         assert(label);
 997
 998         if (memchr(label, 0, n))
 999                 return false;
1000
1001         s = strndupa(label, n);
1002         return dns_service_name_is_valid(s);
1003 }
1004
1005 int dns_service_split(const char *joined, char **_name, char **_type, char **_domain) {
1006         _cleanup_free_ char *name = NULL, *type = NULL, *domain = NULL;
1007         const char *p = joined, *q = NULL, *d = NULL;
1008         char a[DNS_LABEL_MAX], b[DNS_LABEL_MAX], c[DNS_LABEL_MAX];
1009         int an, bn, cn, r;
1010         unsigned x = 0;
1011
1012         assert(joined);
1013
1014         /* Get first label from the full name */
1015         an = dns_label_unescape(&p, a, sizeof(a));
1016         if (an < 0)
1017                 return an;
1018
1019         if (an > 0) {
1020                 x++;
1021
1022                 /* If there was a first label, try to get the second one */
1023                 bn = dns_label_unescape(&p, b, sizeof(b));
1024                 if (bn < 0)
1025                         return bn;
1026
1027                 if (bn > 0) {
1028                         x++;
1029
1030                         /* If there was a second label, try to get the third one */
1031                         q = p;
1032                         cn = dns_label_unescape(&p, c, sizeof(c));
1033                         if (cn < 0)
1034                                 return cn;
1035
1036                         if (cn > 0)
1037                                 x++;
1038                 } else
1039                         cn = 0;
1040         } else
1041                 an = 0;
1042
1043         if (x >= 2 && srv_type_label_is_valid(b, bn)) {
1044
1045                 if (x >= 3 && srv_type_label_is_valid(c, cn)) {
1046
1047                         if (dns_service_name_label_is_valid(a, an)) {
1048                                 /* OK, got <name> . <type> . <type2> . <domain> */
1049
1050                                 name = strndup(a, an);
1051                                 if (!name)
1052                                         return -ENOMEM;
1053
1054                                 type = strjoin(b, ".", c);
1055                                 if (!type)
1056                                         return -ENOMEM;
1057
1058                                 d = p;
1059                                 goto finish;
1060                         }
1061
1062                 } else if (srv_type_label_is_valid(a, an)) {
1063
1064                         /* OK, got <type> . <type2> . <domain> */
1065
1066                         name = NULL;
1067
1068                         type = strjoin(a, ".", b);
1069                         if (!type)
1070                                 return -ENOMEM;
1071
1072                         d = q;
1073                         goto finish;
1074                 }
1075         }
1076
1077         name = NULL;
1078         type = NULL;
1079         d = joined;
1080
1081 finish:
1082         r = dns_name_normalize(d, &domain);
1083         if (r < 0)
1084                 return r;
1085
1086         if (_domain)
1087                 *_domain = TAKE_PTR(domain);
1088
1089         if (_type)
1090                 *_type = TAKE_PTR(type);
1091
1092         if (_name)
1093                 *_name = TAKE_PTR(name);
1094
1095         return 0;
1096 }
1097
1098 static int dns_name_build_suffix_table(const char *name, const char *table[]) {
1099         const char *p;
1100         unsigned n = 0;
1101         int r;
1102
1103         assert(name);
1104         assert(table);
1105
1106         p = name;
1107         for (;;) {
1108                 if (n > DNS_N_LABELS_MAX)
1109                         return -EINVAL;
1110
1111                 table[n] = p;
1112                 r = dns_name_parent(&p);
1113                 if (r < 0)
1114                         return r;
1115                 if (r == 0)
1116                         break;
1117
1118                 n++;
1119         }
1120
1121         return (int) n;
1122 }
1123
1124 int dns_name_suffix(const char *name, unsigned n_labels, const char **ret) {
1125         const char* labels[DNS_N_LABELS_MAX+1];
1126         int n;
1127
1128         assert(name);
1129         assert(ret);
1130
1131         n = dns_name_build_suffix_table(name, labels);
1132         if (n < 0)
1133                 return n;
1134
1135         if ((unsigned) n < n_labels)
1136                 return -EINVAL;
1137
1138         *ret = labels[n - n_labels];
1139         return (int) (n - n_labels);
1140 }
1141
1142 int dns_name_skip(const char *a, unsigned n_labels, const char **ret) {
1143         int r;
1144
1145         assert(a);
1146         assert(ret);
1147
1148         for (; n_labels > 0; n_labels--) {
1149                 r = dns_name_parent(&a);
1150                 if (r < 0)
1151                         return r;
1152                 if (r == 0) {
1153                         *ret = "";
1154                         return 0;
1155                 }
1156         }
1157
1158         *ret = a;
1159         return 1;
1160 }
1161
1162 int dns_name_count_labels(const char *name) {
1163         unsigned n = 0;
1164         const char *p;
1165         int r;
1166
1167         assert(name);
1168
1169         p = name;
1170         for (;;) {
1171                 r = dns_name_parent(&p);
1172                 if (r < 0)
1173                         return r;
1174                 if (r == 0)
1175                         break;
1176
1177                 if (n >= DNS_N_LABELS_MAX)
1178                         return -EINVAL;
1179
1180                 n++;
1181         }
1182
1183         return (int) n;
1184 }
1185
1186 int dns_name_equal_skip(const char *a, unsigned n_labels, const char *b) {
1187         int r;
1188
1189         assert(a);
1190         assert(b);
1191
1192         r = dns_name_skip(a, n_labels, &a);
1193         if (r <= 0)
1194                 return r;
1195
1196         return dns_name_equal(a, b);
1197 }
1198
1199 int dns_name_common_suffix(const char *a, const char *b, const char **ret) {
1200         const char *a_labels[DNS_N_LABELS_MAX+1], *b_labels[DNS_N_LABELS_MAX+1];
1201         int n = 0, m = 0, k = 0, r, q;
1202
1203         assert(a);
1204         assert(b);
1205         assert(ret);
1206
1207         /* Determines the common suffix of domain names a and b */
1208
1209         n = dns_name_build_suffix_table(a, a_labels);
1210         if (n < 0)
1211                 return n;
1212
1213         m = dns_name_build_suffix_table(b, b_labels);
1214         if (m < 0)
1215                 return m;
1216
1217         for (;;) {
1218                 char la[DNS_LABEL_MAX], lb[DNS_LABEL_MAX];
1219                 const char *x, *y;
1220
1221                 if (k >= n || k >= m) {
1222                         *ret = a_labels[n - k];
1223                         return 0;
1224                 }
1225
1226                 x = a_labels[n - 1 - k];
1227                 r = dns_label_unescape(&x, la, sizeof(la));
1228                 if (r < 0)
1229                         return r;
1230
1231                 y = b_labels[m - 1 - k];
1232                 q = dns_label_unescape(&y, lb, sizeof(lb));
1233                 if (q < 0)
1234                         return q;
1235
1236                 if (r != q || ascii_strcasecmp_n(la, lb, r) != 0) {
1237                         *ret = a_labels[n - k];
1238                         return 0;
1239                 }
1240
1241                 k++;
1242         }
1243 }
1244
1245 int dns_name_apply_idna(const char *name, char **ret) {
1246         /* Return negative on error, 0 if not implemented, positive on success. */
1247
1248 #if HAVE_LIBIDN2
1249         int r;
1250         _cleanup_free_ char *t = NULL;
1251
1252         assert(name);
1253         assert(ret);
1254
1255         r = idn2_lookup_u8((uint8_t*) name, (uint8_t**) &t,
1256                            IDN2_NFC_INPUT | IDN2_NONTRANSITIONAL);
1257         log_debug("idn2_lookup_u8: %s → %s", name, t);
1258         if (r == IDN2_OK) {
1259                 if (!startswith(name, "xn--")) {
1260                         _cleanup_free_ char *s = NULL;
1261
1262                         r = idn2_to_unicode_8z8z(t, &s, 0);
1263                         if (r != IDN2_OK) {
1264                                 log_debug("idn2_to_unicode_8z8z(\"%s\") failed: %d/%s",
1265                                           t, r, idn2_strerror(r));
1266                                 return 0;
1267                         }
1268
1269                         if (!streq_ptr(name, s)) {
1270                                 log_debug("idn2 roundtrip failed: \"%s\" → \"%s\" → \"%s\", ignoring.",
1271                                           name, t, s);
1272                                 return 0;
1273                         }
1274                 }
1275
1276                 *ret = TAKE_PTR(t);
1277
1278                 return 1; /* *ret has been written */
1279         }
1280
1281         log_debug("idn2_lookup_u8(\"%s\") failed: %d/%s", name, r, idn2_strerror(r));
1282         if (r == IDN2_2HYPHEN)
1283                 /* The name has two hyphens — forbidden by IDNA2008 in some cases */
1284                 return 0;
1285         if (IN_SET(r, IDN2_TOO_BIG_DOMAIN, IDN2_TOO_BIG_LABEL))
1286                 return -ENOSPC;
1287         return -EINVAL;
1288 #elif HAVE_LIBIDN
1289         _cleanup_free_ char *buf = NULL;
1290         size_t n = 0, allocated = 0;
1291         bool first = true;
1292         int r, q;
1293
1294         assert(name);
1295         assert(ret);
1296
1297         for (;;) {
1298                 char label[DNS_LABEL_MAX];
1299
1300                 r = dns_label_unescape(&name, label, sizeof(label));
1301                 if (r < 0)
1302                         return r;
1303                 if (r == 0)
1304                         break;
1305
1306                 q = dns_label_apply_idna(label, r, label, sizeof(label));
1307                 if (q < 0)
1308                         return q;
1309                 if (q > 0)
1310                         r = q;
1311
1312                 if (!GREEDY_REALLOC(buf, allocated, n + !first + DNS_LABEL_ESCAPED_MAX))
1313                         return -ENOMEM;
1314
1315                 r = dns_label_escape(label, r, buf + n + !first, DNS_LABEL_ESCAPED_MAX);
1316                 if (r < 0)
1317                         return r;
1318
1319                 if (first)
1320                         first = false;
1321                 else
1322                         buf[n++] = '.';
1323
1324                 n += r;
1325         }
1326
1327         if (n > DNS_HOSTNAME_MAX)
1328                 return -EINVAL;
1329
1330         if (!GREEDY_REALLOC(buf, allocated, n + 1))
1331                 return -ENOMEM;
1332
1333         buf[n] = 0;
1334         *ret = TAKE_PTR(buf);
1335
1336         return 1;
1337 #else
1338         return 0;
1339 #endif
1340 }
1341
1342 int dns_name_is_valid_or_address(const char *name) {
1343         /* Returns > 0 if the specified name is either a valid IP address formatted as string or a valid DNS name */
1344
1345         if (isempty(name))
1346                 return 0;
1347
1348         if (in_addr_from_string_auto(name, NULL, NULL) >= 0)
1349                 return 1;
1350
1351         return dns_name_is_valid(name);
1352 }