src/src/lookups/dnsdb.c

   1 /* $Cambridge: exim/src/src/lookups/dnsdb.c,v 1.8 2005/01/04 10:00:44 ph10 Exp $ */
   2
   3 /*************************************************
   4 *     Exim - an Internet mail transport agent    *
   5 *************************************************/
   6
   7 /* Copyright (c) University of Cambridge 1995 - 2005 */
   8 /* See the file NOTICE for conditions of use and distribution. */
   9
  10 #include "../exim.h"
  11 #include "lf_functions.h"
  12 #include "dnsdb.h"
  13
  14
  15
  16 /* Ancient systems (e.g. SunOS4) don't appear to have T_TXT defined in their
  17 header files. */
  18
  19 #ifndef T_TXT
  20 #define T_TXT 16
  21 #endif
  22
  23 /* Table of recognized DNS record types and their integer values. */
  24
  25 static char *type_names[] = {
  26   "a",
  27 #if HAVE_IPV6
  28   "aaaa",
  29   #ifdef SUPPORT_A6
  30   "a6",
  31   #endif
  32 #endif
  33   "cname",
  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_MX,
  53   T_MXH,     /* Private type for "MX hostnames" */
  54   T_NS,
  55   T_PTR,
  56   T_SRV,
  57   T_TXT,
  58   T_ZNS      /* Private type for "zone nameservers" */
  59 };
  60
  61
  62 /*************************************************
  63 *              Open entry point                  *
  64 *************************************************/
  65
  66 /* See local README for interface description. */
  67
  68 void *
  69 dnsdb_open(uschar *filename, uschar **errmsg)
  70 {
  71 filename = filename;   /* Keep picky compilers happy */
  72 errmsg = errmsg;       /* Ditto */
  73 return (void *)(-1);   /* Any non-0 value */
  74 }
  75
  76
  77
  78 /*************************************************
  79 *           Find entry point for dnsdb           *
  80 *************************************************/
  81
  82 /* See local README for interface description. The query in the "keystring" may
  83 consist of a number of parts.
  84
  85 (a) If the first significant character is '>' then the next character is the
  86 separator character that is used when multiple records are found. The default
  87 separator is newline.
  88
  89 (b) If the next sequence of characters is 'defer_FOO' followed by a comma,
  90 the defer behaviour is set to FOO. The possible behaviours are: 'strict', where
  91 any defer causes the whole lookup to defer; 'lax', where a defer causes the
  92 whole lookup to defer only if none of the DNS queries succeeds; and 'never',
  93 where all defers are as if the lookup failed. The default is 'lax'.
  94
  95 (c) If the next sequence of characters is a sequence of letters and digits
  96 followed by '=', it is interpreted as the name of the DNS record type. The
  97 default is "TXT".
  98
  99 (d) Then there follows list of domain names. This is a generalized Exim list,
 100 which may start with '<' in order to set a specific separator. The default
 101 separator, as always, is colon. */
 102
 103 int
 104 dnsdb_find(void *handle, uschar *filename, uschar *keystring, int length,
 105   uschar **result, uschar **errmsg, BOOL *do_cache)
 106 {
 107 int rc;
 108 int size = 256;
 109 int ptr = 0;
 110 int sep = 0;
 111 int defer_mode = PASS;
 112 int type = T_TXT;
 113 int failrc = FAIL;
 114 uschar *outsep = US"\n";
 115 uschar *equals, *domain;
 116 uschar buffer[256];
 117
 118 /* Because we're the working in the search pool, we try to reclaim as much
 119 store as possible later, so we preallocate the result here */
 120
 121 uschar *yield = store_get(size);
 122
 123 dns_record *rr;
 124 dns_answer dnsa;
 125 dns_scan dnss;
 126
 127 handle = handle;           /* Keep picky compilers happy */
 128 filename = filename;
 129 length = length;
 130 do_cache = do_cache;
 131
 132 /* If the string starts with '>' we change the output separator */
 133
 134 while (isspace(*keystring)) keystring++;
 135 if (*keystring == '>')
 136   {
 137   outsep = keystring + 1;
 138   keystring += 2;
 139   while (isspace(*keystring)) keystring++;
 140   }
 141
 142 /* Check for a defer behaviour keyword. */
 143
 144 if (strncmpic(keystring, US"defer_", 6) == 0)
 145   {
 146   keystring += 6;
 147   if (strncmpic(keystring, US"strict", 6) == 0)
 148     {
 149     defer_mode = DEFER;
 150     keystring += 6;
 151     }
 152   else if (strncmpic(keystring, US"lax", 3) == 0)
 153     {
 154     defer_mode = PASS;
 155     keystring += 3;
 156     }
 157   else if (strncmpic(keystring, US"never", 5) == 0)
 158     {
 159     defer_mode = OK;
 160     keystring += 5;
 161     }
 162   else
 163     {
 164     *errmsg = US"unsupported dnsdb defer behaviour";
 165     return DEFER;
 166     }
 167   while (isspace(*keystring)) keystring++;
 168   if (*keystring++ != ',')
 169     {
 170     *errmsg = US"dnsdb defer behaviour syntax error";
 171     return DEFER;
 172     }
 173   while (isspace(*keystring)) keystring++;
 174   }
 175
 176 /* If the keystring contains an = this must be preceded by a valid type name. */
 177
 178 if ((equals = Ustrchr(keystring, '=')) != NULL)
 179   {
 180   int i, len;
 181   uschar *tend = equals;
 182
 183   while (tend > keystring && isspace(tend[-1])) tend--;
 184   len = tend - keystring;
 185
 186   for (i = 0; i < sizeof(type_names)/sizeof(uschar *); i++)
 187     {
 188     if (len == Ustrlen(type_names[i]) &&
 189         strncmpic(keystring, US type_names[i], len) == 0)
 190       {
 191       type = type_values[i];
 192       break;
 193       }
 194     }
 195
 196   if (i >= sizeof(type_names)/sizeof(uschar *))
 197     {
 198     *errmsg = US"unsupported DNS record type";
 199     return DEFER;
 200     }
 201
 202   keystring = equals + 1;
 203   while (isspace(*keystring)) keystring++;
 204   }
 205
 206 /* Initialize the resolver in case this is the first time it has been used. */
 207
 208 dns_init(FALSE, FALSE);
 209
 210 /* The remainder of the string must be a list of domains. As long as the lookup
 211 for at least one of them succeeds, we return success. Failure means that none
 212 of them were found.
 213
 214 The original implementation did not support a list of domains. Adding the list
 215 feature is compatible, except in one case: when PTR records are being looked up
 216 for a single IPv6 address. Fortunately, we can hack in a compatibility feature
 217 here: If the type is PTR and no list separator is specified, and the entire
 218 remaining string is valid as an IP address, set an impossible separator so that
 219 it is treated as one item. */
 220
 221 if (type == T_PTR && keystring[0] != '<' &&
 222     string_is_ip_address(keystring, NULL) > 0)
 223   sep = -1;
 224
 225 /* Now scan the list and do a lookup for each item */
 226
 227 while ((domain = string_nextinlist(&keystring, &sep, buffer, sizeof(buffer)))
 228         != NULL)
 229   {
 230   uschar rbuffer[256];
 231   int searchtype = (type == T_ZNS)? T_NS :          /* record type we want */
 232                    (type == T_MXH)? T_MX : type;
 233
 234   /* If the type is PTR, we have to construct the relevant magic lookup key if
 235   the original is an IP address (some experimental protocols are using PTR
 236   records for different purposes where the key string is a host name). This
 237   code for doing the reversal is now in a separate function. */
 238
 239   if (type == T_PTR && string_is_ip_address(domain, NULL))
 240     {
 241     dns_build_reverse(domain, rbuffer);
 242     domain = rbuffer;
 243     }
 244
 245   DEBUG(D_lookup) debug_printf("dnsdb key: %s\n", domain);
 246
 247   /* Do the lookup and sort out the result. There are two special types that
 248   are handled specially: T_ZNS and T_MXH. The former is handled in a special
 249   lookup function so that the facility could be used from other parts of the
 250   Exim code. The latter affects only what happens later on in this function,
 251   but for tidiness it is handled in a similar way. If the lookup fails,
 252   continue with the next domain. In the case of DEFER, adjust the final
 253   "nothing found" result, but carry on to the next domain. */
 254
 255   rc = dns_special_lookup(&dnsa, domain, type, NULL);
 256
 257   if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
 258   if (rc != DNS_SUCCEED)
 259     {
 260     if (defer_mode == DEFER) return DEFER;          /* always defer */
 261       else if (defer_mode == PASS) failrc = DEFER;  /* defer only if all do */
 262     continue;                                       /* treat defer as fail */
 263     }
 264
 265   /* Search the returned records */
 266
 267   for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
 268        rr != NULL;
 269        rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
 270     {
 271     if (rr->type != searchtype) continue;
 272
 273     /* There may be several addresses from an A6 record. Put the configured
 274     separator between them, just as for between several records. However, A6
 275     support is not normally configured these days. */
 276
 277     if (type == T_A ||
 278         #ifdef SUPPORT_A6
 279         type == T_A6 ||
 280         #endif
 281         type == T_AAAA)
 282       {
 283       dns_address *da;
 284       for (da = dns_address_from_rr(&dnsa, rr); da != NULL; da = da->next)
 285         {
 286         if (ptr != 0) yield = string_cat(yield, &size, &ptr, outsep, 1);
 287         yield = string_cat(yield, &size, &ptr, da->address,
 288           Ustrlen(da->address));
 289         }
 290       continue;
 291       }
 292
 293     /* Other kinds of record just have one piece of data each, but there may be
 294     several of them, of course. */
 295
 296     if (ptr != 0) yield = string_cat(yield, &size, &ptr, outsep, 1);
 297
 298     if (type == T_TXT)
 299       {
 300       yield = string_cat(yield, &size, &ptr, (uschar *)(rr->data+1),
 301         (rr->data)[0]);
 302       }
 303     else   /* T_CNAME, T_MX, T_MXH, T_NS, T_SRV, T_PTR */
 304       {
 305       int num;
 306       uschar s[264];
 307       uschar *p = (uschar *)(rr->data);
 308
 309       if (type == T_MXH)
 310         {
 311         /* mxh ignores the priority number and includes only the hostnames */
 312         GETSHORT(num, p);            /* pointer is advanced */
 313         }
 314       else if (type == T_MX)
 315         {
 316         GETSHORT(num, p);            /* pointer is advanced */
 317         sprintf(CS s, "%d ", num);
 318         yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 319         }
 320       else if (type == T_SRV)
 321         {
 322         int weight, port;
 323         GETSHORT(num, p);            /* pointer is advanced */
 324         GETSHORT(weight, p);
 325         GETSHORT(port, p);
 326         sprintf(CS s, "%d %d %d ", num, weight, port);
 327         yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 328         }
 329
 330       rc = dn_expand(dnsa.answer, dnsa.answer + dnsa.answerlen, p,
 331         (DN_EXPAND_ARG4_TYPE)(s), sizeof(s));
 332
 333       /* If an overlong response was received, the data will have been
 334       truncated and dn_expand may fail. */
 335
 336       if (rc < 0)
 337         {
 338         log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
 339           "domain=%s", dns_text_type(type), domain);
 340         break;
 341         }
 342       else yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 343       }
 344     }    /* Loop for list of returned records */
 345   }      /* Loop for list of domains */
 346
 347 /* Reclaim unused memory */
 348
 349 store_reset(yield + ptr + 1);
 350
 351 /* If ptr == 0 we have not found anything. Otherwise, insert the terminating
 352 zero and return the result. */
 353
 354 if (ptr == 0) return failrc;
 355 yield[ptr] = 0;
 356 *result = yield;
 357 return OK;
 358 }
 359
 360 /* End of lookups/dnsdb.c */