src/src/lookups/dnsdb.c

   1 /* $Cambridge: exim/src/src/lookups/dnsdb.c,v 1.20 2010/05/29 19:23:26 nm4 Exp $ */
   2
   3 /*************************************************
   4 *     Exim - an Internet mail transport agent    *
   5 *************************************************/
   6
   7 /* Copyright (c) University of Cambridge 1995 - 2009 */
   8 /* See the file NOTICE for conditions of use and distribution. */
   9
  10 #include "../exim.h"
  11 #include "lf_functions.h"
  12
  13
  14
  15 /* Ancient systems (e.g. SunOS4) don't appear to have T_TXT defined in their
  16 header files. */
  17
  18 #ifndef T_TXT
  19 #define T_TXT 16
  20 #endif
  21
  22 /* Table of recognized DNS record types and their integer values. */
  23
  24 static char *type_names[] = {
  25   "a",
  26 #if HAVE_IPV6
  27   "aaaa",
  28   #ifdef SUPPORT_A6
  29   "a6",
  30   #endif
  31 #endif
  32   "cname",
  33   "csa",
  34   "mx",
  35   "mxh",
  36   "ns",
  37   "ptr",
  38   "srv",
  39   "txt",
  40   "zns"
  41 };
  42
  43 static int type_values[] = {
  44   T_A,
  45 #if HAVE_IPV6
  46   T_AAAA,
  47   #ifdef SUPPORT_A6
  48   T_A6,
  49   #endif
  50 #endif
  51   T_CNAME,
  52   T_CSA,     /* Private type for "Client SMTP Authorization". */
  53   T_MX,
  54   T_MXH,     /* Private type for "MX hostnames" */
  55   T_NS,
  56   T_PTR,
  57   T_SRV,
  58   T_TXT,
  59   T_ZNS      /* Private type for "zone nameservers" */
  60 };
  61
  62
  63 /*************************************************
  64 *              Open entry point                  *
  65 *************************************************/
  66
  67 /* See local README for interface description. */
  68
  69 static void *
  70 dnsdb_open(uschar *filename, uschar **errmsg)
  71 {
  72 filename = filename;   /* Keep picky compilers happy */
  73 errmsg = errmsg;       /* Ditto */
  74 return (void *)(-1);   /* Any non-0 value */
  75 }
  76
  77
  78
  79 /*************************************************
  80 *           Find entry point for dnsdb           *
  81 *************************************************/
  82
  83 /* See local README for interface description. The query in the "keystring" may
  84 consist of a number of parts.
  85
  86 (a) If the first significant character is '>' then the next character is the
  87 separator character that is used when multiple records are found. The default
  88 separator is newline.
  89
  90 (b) If the next character is ',' then the next character is the separator
  91 character used for multiple items of text in "TXT" records. Alternatively,
  92 if the next character is ';' then these multiple items are concatenated with
  93 no separator. With neither of these options specified, only the first item
  94 is output.
  95
  96 (c) If the next sequence of characters is 'defer_FOO' followed by a comma,
  97 the defer behaviour is set to FOO. The possible behaviours are: 'strict', where
  98 any defer causes the whole lookup to defer; 'lax', where a defer causes the
  99 whole lookup to defer only if none of the DNS queries succeeds; and 'never',
 100 where all defers are as if the lookup failed. The default is 'lax'.
 101
 102 (d) If the next sequence of characters is a sequence of letters and digits
 103 followed by '=', it is interpreted as the name of the DNS record type. The
 104 default is "TXT".
 105
 106 (e) Then there follows list of domain names. This is a generalized Exim list,
 107 which may start with '<' in order to set a specific separator. The default
 108 separator, as always, is colon. */
 109
 110 static int
 111 dnsdb_find(void *handle, uschar *filename, uschar *keystring, int length,
 112   uschar **result, uschar **errmsg, BOOL *do_cache)
 113 {
 114 int rc;
 115 int size = 256;
 116 int ptr = 0;
 117 int sep = 0;
 118 int defer_mode = PASS;
 119 int type = T_TXT;
 120 int failrc = FAIL;
 121 uschar *outsep = US"\n";
 122 uschar *outsep2 = NULL;
 123 uschar *equals, *domain, *found;
 124 uschar buffer[256];
 125
 126 /* Because we're the working in the search pool, we try to reclaim as much
 127 store as possible later, so we preallocate the result here */
 128
 129 uschar *yield = store_get(size);
 130
 131 dns_record *rr;
 132 dns_answer dnsa;
 133 dns_scan dnss;
 134
 135 handle = handle;           /* Keep picky compilers happy */
 136 filename = filename;
 137 length = length;
 138 do_cache = do_cache;
 139
 140 /* If the string starts with '>' we change the output separator.
 141 If it's followed by ';' or ',' we set the TXT output separator. */
 142
 143 while (isspace(*keystring)) keystring++;
 144 if (*keystring == '>')
 145   {
 146   outsep = keystring + 1;
 147   keystring += 2;
 148   if (*keystring == ',')
 149     {
 150     outsep2 = keystring + 1;
 151     keystring += 2;
 152     }
 153   else if (*keystring == ';')
 154     {
 155     outsep2 = US"";
 156     keystring++;
 157     }
 158   while (isspace(*keystring)) keystring++;
 159   }
 160
 161 /* Check for a defer behaviour keyword. */
 162
 163 if (strncmpic(keystring, US"defer_", 6) == 0)
 164   {
 165   keystring += 6;
 166   if (strncmpic(keystring, US"strict", 6) == 0)
 167     {
 168     defer_mode = DEFER;
 169     keystring += 6;
 170     }
 171   else if (strncmpic(keystring, US"lax", 3) == 0)
 172     {
 173     defer_mode = PASS;
 174     keystring += 3;
 175     }
 176   else if (strncmpic(keystring, US"never", 5) == 0)
 177     {
 178     defer_mode = OK;
 179     keystring += 5;
 180     }
 181   else
 182     {
 183     *errmsg = US"unsupported dnsdb defer behaviour";
 184     return DEFER;
 185     }
 186   while (isspace(*keystring)) keystring++;
 187   if (*keystring++ != ',')
 188     {
 189     *errmsg = US"dnsdb defer behaviour syntax error";
 190     return DEFER;
 191     }
 192   while (isspace(*keystring)) keystring++;
 193   }
 194
 195 /* If the keystring contains an = this must be preceded by a valid type name. */
 196
 197 if ((equals = Ustrchr(keystring, '=')) != NULL)
 198   {
 199   int i, len;
 200   uschar *tend = equals;
 201
 202   while (tend > keystring && isspace(tend[-1])) tend--;
 203   len = tend - keystring;
 204
 205   for (i = 0; i < sizeof(type_names)/sizeof(uschar *); i++)
 206     {
 207     if (len == Ustrlen(type_names[i]) &&
 208         strncmpic(keystring, US type_names[i], len) == 0)
 209       {
 210       type = type_values[i];
 211       break;
 212       }
 213     }
 214
 215   if (i >= sizeof(type_names)/sizeof(uschar *))
 216     {
 217     *errmsg = US"unsupported DNS record type";
 218     return DEFER;
 219     }
 220
 221   keystring = equals + 1;
 222   while (isspace(*keystring)) keystring++;
 223   }
 224
 225 /* Initialize the resolver in case this is the first time it has been used. */
 226
 227 dns_init(FALSE, FALSE);
 228
 229 /* The remainder of the string must be a list of domains. As long as the lookup
 230 for at least one of them succeeds, we return success. Failure means that none
 231 of them were found.
 232
 233 The original implementation did not support a list of domains. Adding the list
 234 feature is compatible, except in one case: when PTR records are being looked up
 235 for a single IPv6 address. Fortunately, we can hack in a compatibility feature
 236 here: If the type is PTR and no list separator is specified, and the entire
 237 remaining string is valid as an IP address, set an impossible separator so that
 238 it is treated as one item. */
 239
 240 if (type == T_PTR && keystring[0] != '<' &&
 241     string_is_ip_address(keystring, NULL) != 0)
 242   sep = -1;
 243
 244 /* Now scan the list and do a lookup for each item */
 245
 246 while ((domain = string_nextinlist(&keystring, &sep, buffer, sizeof(buffer)))
 247         != NULL)
 248   {
 249   uschar rbuffer[256];
 250   int searchtype = (type == T_CSA)? T_SRV :         /* record type we want */
 251                    (type == T_MXH)? T_MX :
 252                    (type == T_ZNS)? T_NS : type;
 253
 254   /* If the type is PTR or CSA, we have to construct the relevant magic lookup
 255   key if the original is an IP address (some experimental protocols are using
 256   PTR records for different purposes where the key string is a host name, and
 257   Exim's extended CSA can be keyed by domains or IP addresses). This code for
 258   doing the reversal is now in a separate function. */
 259
 260   if ((type == T_PTR || type == T_CSA) &&
 261       string_is_ip_address(domain, NULL) != 0)
 262     {
 263     dns_build_reverse(domain, rbuffer);
 264     domain = rbuffer;
 265     }
 266
 267   DEBUG(D_lookup) debug_printf("dnsdb key: %s\n", domain);
 268
 269   /* Do the lookup and sort out the result. There are three special types that
 270   are handled specially: T_CSA, T_ZNS and T_MXH. The former two are handled in
 271   a special lookup function so that the facility could be used from other
 272   parts of the Exim code. The latter affects only what happens later on in
 273   this function, but for tidiness it is handled in a similar way. If the
 274   lookup fails, continue with the next domain. In the case of DEFER, adjust
 275   the final "nothing found" result, but carry on to the next domain. */
 276
 277   found = domain;
 278   rc = dns_special_lookup(&dnsa, domain, type, &found);
 279
 280   if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
 281   if (rc != DNS_SUCCEED)
 282     {
 283     if (defer_mode == DEFER) return DEFER;          /* always defer */
 284       else if (defer_mode == PASS) failrc = DEFER;  /* defer only if all do */
 285     continue;                                       /* treat defer as fail */
 286     }
 287
 288   /* Search the returned records */
 289
 290   for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
 291        rr != NULL;
 292        rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
 293     {
 294     if (rr->type != searchtype) continue;
 295
 296     /* There may be several addresses from an A6 record. Put the configured
 297     separator between them, just as for between several records. However, A6
 298     support is not normally configured these days. */
 299
 300     if (type == T_A ||
 301         #ifdef SUPPORT_A6
 302         type == T_A6 ||
 303         #endif
 304         type == T_AAAA)
 305       {
 306       dns_address *da;
 307       for (da = dns_address_from_rr(&dnsa, rr); da != NULL; da = da->next)
 308         {
 309         if (ptr != 0) yield = string_cat(yield, &size, &ptr, outsep, 1);
 310         yield = string_cat(yield, &size, &ptr, da->address,
 311           Ustrlen(da->address));
 312         }
 313       continue;
 314       }
 315
 316     /* Other kinds of record just have one piece of data each, but there may be
 317     several of them, of course. */
 318
 319     if (ptr != 0) yield = string_cat(yield, &size, &ptr, outsep, 1);
 320
 321     if (type == T_TXT)
 322       {
 323       if (outsep2 == NULL)
 324         {
 325         /* output only the first item of data */
 326         yield = string_cat(yield, &size, &ptr, (uschar *)(rr->data+1),
 327           (rr->data)[0]);
 328         }
 329       else
 330         {
 331         /* output all items */
 332         int data_offset = 0;
 333         while (data_offset < rr->size)
 334           {
 335           uschar chunk_len = (rr->data)[data_offset++];
 336           if (outsep2[0] != '\0' && data_offset != 1)
 337             yield = string_cat(yield, &size, &ptr, outsep2, 1);
 338           yield = string_cat(yield, &size, &ptr,
 339                              (uschar *)((rr->data)+data_offset), chunk_len);
 340           data_offset += chunk_len;
 341           }
 342         }
 343       }
 344     else   /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SRV */
 345       {
 346       int priority, weight, port;
 347       uschar s[264];
 348       uschar *p = (uschar *)(rr->data);
 349
 350       if (type == T_MXH)
 351         {
 352         /* mxh ignores the priority number and includes only the hostnames */
 353         GETSHORT(priority, p);
 354         }
 355       else if (type == T_MX)
 356         {
 357         GETSHORT(priority, p);
 358         sprintf(CS s, "%d ", priority);
 359         yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 360         }
 361       else if (type == T_SRV)
 362         {
 363         GETSHORT(priority, p);
 364         GETSHORT(weight, p);
 365         GETSHORT(port, p);
 366         sprintf(CS s, "%d %d %d ", priority, weight, port);
 367         yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 368         }
 369       else if (type == T_CSA)
 370         {
 371         /* See acl_verify_csa() for more comments about CSA. */
 372
 373         GETSHORT(priority, p);
 374         GETSHORT(weight, p);
 375         GETSHORT(port, p);
 376
 377         if (priority != 1) continue;      /* CSA version must be 1 */
 378
 379         /* If the CSA record we found is not the one we asked for, analyse
 380         the subdomain assertions in the port field, else analyse the direct
 381         authorization status in the weight field. */
 382
 383         if (found != domain)
 384           {
 385           if (port & 1) *s = 'X';         /* explicit authorization required */
 386           else *s = '?';                  /* no subdomain assertions here */
 387           }
 388         else
 389           {
 390           if (weight < 2) *s = 'N';       /* not authorized */
 391           else if (weight == 2) *s = 'Y'; /* authorized */
 392           else if (weight == 3) *s = '?'; /* unauthorizable */
 393           else continue;                  /* invalid */
 394           }
 395
 396         s[1] = ' ';
 397         yield = string_cat(yield, &size, &ptr, s, 2);
 398         }
 399
 400       /* GETSHORT() has advanced the pointer to the target domain. */
 401
 402       rc = dn_expand(dnsa.answer, dnsa.answer + dnsa.answerlen, p,
 403         (DN_EXPAND_ARG4_TYPE)(s), sizeof(s));
 404
 405       /* If an overlong response was received, the data will have been
 406       truncated and dn_expand may fail. */
 407
 408       if (rc < 0)
 409         {
 410         log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
 411           "domain=%s", dns_text_type(type), domain);
 412         break;
 413         }
 414       else yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 415       }
 416     }    /* Loop for list of returned records */
 417   }      /* Loop for list of domains */
 418
 419 /* Reclaim unused memory */
 420
 421 store_reset(yield + ptr + 1);
 422
 423 /* If ptr == 0 we have not found anything. Otherwise, insert the terminating
 424 zero and return the result. */
 425
 426 if (ptr == 0) return failrc;
 427 yield[ptr] = 0;
 428 *result = yield;
 429 return OK;
 430 }
 431
 432
 433
 434 /*************************************************
 435 *         Version reporting entry point          *
 436 *************************************************/
 437
 438 /* See local README for interface description. */
 439
 440 #include "../version.h"
 441
 442 void
 443 dnsdb_version_report(FILE *f)
 444 {
 445 #ifdef DYNLOOKUP
 446 fprintf(f, "Library version: DNSDB: Exim version %s\n", EXIM_VERSION_STR);
 447 #endif
 448 }
 449
 450
 451 static lookup_info _lookup_info = {
 452   US"dnsdb",                     /* lookup name */
 453   lookup_querystyle,             /* query style */
 454   dnsdb_open,                    /* open function */
 455   NULL,                          /* check function */
 456   dnsdb_find,                    /* find function */
 457   NULL,                          /* no close function */
 458   NULL,                          /* no tidy function */
 459   NULL,                          /* no quoting function */
 460   dnsdb_version_report           /* version reporting */
 461 };
 462
 463 #ifdef DYNLOOKUP
 464 #define dnsdb_lookup_module_info _lookup_module_info
 465 #endif
 466
 467 static lookup_info *_lookup_list[] = { &_lookup_info };
 468 lookup_module_info dnsdb_lookup_module_info = { LOOKUP_MODULE_INFO_MAGIC, _lookup_list, 1 };
 469
 470 /* End of lookups/dnsdb.c */