src/src/lookups/dnsdb.c

   1 /* $Cambridge: exim/src/src/lookups/dnsdb.c,v 1.6 2004/12/20 15:24:28 ph10 Exp $ */
   2
   3 /*************************************************
   4 *     Exim - an Internet mail transport agent    *
   5 *************************************************/
   6
   7 /* Copyright (c) University of Cambridge 1995 - 2004 */
   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
 235   key. This code is now in a separate function. */
 236
 237   if (type == T_PTR)
 238     {
 239     dns_build_reverse(domain, rbuffer);
 240     domain = rbuffer;
 241     }
 242
 243   DEBUG(D_lookup) debug_printf("dnsdb key: %s\n", domain);
 244
 245   /* Do the lookup and sort out the result. There are two special types that
 246   are handled specially: T_ZNS and T_MXH. The former is handled in a special
 247   lookup function so that the facility could be used from other parts of the
 248   Exim code. The latter affects only what happens later on in this function,
 249   but for tidiness it is handled in a similar way. If the lookup fails,
 250   continue with the next domain. In the case of DEFER, adjust the final
 251   "nothing found" result, but carry on to the next domain. */
 252
 253   rc = dns_special_lookup(&dnsa, domain, type, NULL);
 254
 255   if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
 256   if (rc != DNS_SUCCEED)
 257     {
 258     if (defer_mode == DEFER) return DEFER;          /* always defer */
 259       else if (defer_mode == PASS) failrc = DEFER;  /* defer only if all do */
 260     continue;                                       /* treat defer as fail */
 261     }
 262
 263   /* Search the returned records */
 264
 265   for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
 266        rr != NULL;
 267        rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
 268     {
 269     if (rr->type != searchtype) continue;
 270
 271     /* There may be several addresses from an A6 record. Put the configured
 272     separator between them, just as for between several records. However, A6
 273     support is not normally configured these days. */
 274
 275     if (type == T_A ||
 276         #ifdef SUPPORT_A6
 277         type == T_A6 ||
 278         #endif
 279         type == T_AAAA)
 280       {
 281       dns_address *da;
 282       for (da = dns_address_from_rr(&dnsa, rr); da != NULL; da = da->next)
 283         {
 284         if (ptr != 0) yield = string_cat(yield, &size, &ptr, outsep, 1);
 285         yield = string_cat(yield, &size, &ptr, da->address,
 286           Ustrlen(da->address));
 287         }
 288       continue;
 289       }
 290
 291     /* Other kinds of record just have one piece of data each, but there may be
 292     several of them, of course. */
 293
 294     if (ptr != 0) yield = string_cat(yield, &size, &ptr, outsep, 1);
 295
 296     if (type == T_TXT)
 297       {
 298       yield = string_cat(yield, &size, &ptr, (uschar *)(rr->data+1),
 299         (rr->data)[0]);
 300       }
 301     else   /* T_CNAME, T_MX, T_MXH, T_NS, T_SRV, T_PTR */
 302       {
 303       int num;
 304       uschar s[264];
 305       uschar *p = (uschar *)(rr->data);
 306
 307       if (type == T_MXH)
 308         {
 309         /* mxh ignores the priority number and includes only the hostnames */
 310         GETSHORT(num, p);            /* pointer is advanced */
 311         }
 312       else if (type == T_MX)
 313         {
 314         GETSHORT(num, p);            /* pointer is advanced */
 315         sprintf(CS s, "%d ", num);
 316         yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 317         }
 318       else if (type == T_SRV)
 319         {
 320         int weight, port;
 321         GETSHORT(num, p);            /* pointer is advanced */
 322         GETSHORT(weight, p);
 323         GETSHORT(port, p);
 324         sprintf(CS s, "%d %d %d ", num, weight, port);
 325         yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 326         }
 327
 328       rc = dn_expand(dnsa.answer, dnsa.answer + dnsa.answerlen, p,
 329         (DN_EXPAND_ARG4_TYPE)(s), sizeof(s));
 330
 331       /* If an overlong response was received, the data will have been
 332       truncated and dn_expand may fail. */
 333
 334       if (rc < 0)
 335         {
 336         log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
 337           "domain=%s", dns_text_type(type), domain);
 338         break;
 339         }
 340       else yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 341       }
 342     }    /* Loop for list of returned records */
 343   }      /* Loop for list of domains */
 344
 345 /* Reclaim unused memory */
 346
 347 store_reset(yield + ptr + 1);
 348
 349 /* If ptr == 0 we have not found anything. Otherwise, insert the terminating
 350 zero and return the result. */
 351
 352 if (ptr == 0) return failrc;
 353 yield[ptr] = 0;
 354 *result = yield;
 355 return OK;
 356 }
 357
 358 /* End of lookups/dnsdb.c */