+/*************************************************
+* Perform a single dnsbl lookup *
+*************************************************/
+
+/* This function is called from verify_check_dnsbl() below.
+
+Arguments:
+ domain the outer dnsbl domain (for debug message)
+ keydomain the current keydomain (for debug message)
+ query the domain to be looked up
+ iplist the list of matching IP addresses
+ bitmask true if bitmask matching is wanted
+ invert_result true if result to be inverted
+ defer_return what to return for a defer
+
+Returns: OK if lookup succeeded
+ FAIL if not
+*/
+
+static int
+one_check_dnsbl(uschar *domain, uschar *keydomain, uschar *query,
+ uschar *iplist, BOOL bitmask, BOOL invert_result, int defer_return)
+{
+dns_answer dnsa;
+dns_scan dnss;
+tree_node *t;
+dnsbl_cache_block *cb;
+int old_pool = store_pool;
+
+/* Look for this query in the cache. */
+
+t = tree_search(dnsbl_cache, query);
+
+/* If not cached from a previous lookup, we must do a DNS lookup, and
+cache the result in permanent memory. */
+
+if (t == NULL)
+ {
+ store_pool = POOL_PERM;
+
+ /* Set up a tree entry to cache the lookup */
+
+ t = store_get(sizeof(tree_node) + Ustrlen(query));
+ Ustrcpy(t->name, query);
+ t->data.ptr = cb = store_get(sizeof(dnsbl_cache_block));
+ (void)tree_insertnode(&dnsbl_cache, t);
+
+ /* Do the DNS loopup . */
+
+ HDEBUG(D_dnsbl) debug_printf("new DNS lookup for %s\n", query);
+ cb->rc = dns_basic_lookup(&dnsa, query, T_A);
+ cb->text_set = FALSE;
+ cb->text = NULL;
+ cb->rhs = NULL;
+
+ /* If the lookup succeeded, cache the RHS address. The code allows for
+ more than one address - this was for complete generality and the possible
+ use of A6 records. However, A6 records have been reduced to experimental
+ status (August 2001) and may die out. So they may never get used at all,
+ let alone in dnsbl records. However, leave the code here, just in case.
+
+ Quite apart from one A6 RR generating multiple addresses, there are DNS
+ lists that return more than one A record, so we must handle multiple
+ addresses generated in that way as well. */
+
+ if (cb->rc == DNS_SUCCEED)
+ {
+ dns_record *rr;
+ dns_address **addrp = &(cb->rhs);
+ for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
+ rr != NULL;
+ rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
+ {
+ if (rr->type == T_A)
+ {
+ dns_address *da = dns_address_from_rr(&dnsa, rr);
+ if (da != NULL)
+ {
+ *addrp = da;
+ while (da->next != NULL) da = da->next;
+ addrp = &(da->next);
+ }
+ }
+ }
+
+ /* If we didn't find any A records, change the return code. This can
+ happen when there is a CNAME record but there are no A records for what
+ it points to. */
+
+ if (cb->rhs == NULL) cb->rc = DNS_NODATA;
+ }
+
+ store_pool = old_pool;
+ }
+
+/* Previous lookup was cached */
+
+else
+ {
+ HDEBUG(D_dnsbl) debug_printf("using result of previous DNS lookup\n");
+ cb = t->data.ptr;
+ }
+
+/* We now have the result of the DNS lookup, either newly done, or cached
+from a previous call. If the lookup succeeded, check against the address
+list if there is one. This may be a positive equality list (introduced by
+"="), a negative equality list (introduced by "!="), a positive bitmask
+list (introduced by "&"), or a negative bitmask list (introduced by "!&").*/
+
+if (cb->rc == DNS_SUCCEED)
+ {
+ dns_address *da = NULL;
+ uschar *addlist = cb->rhs->address;
+
+ /* For A and AAAA records, there may be multiple addresses from multiple
+ records. For A6 records (currently not expected to be used) there may be
+ multiple addresses from a single record. */
+
+ for (da = cb->rhs->next; da != NULL; da = da->next)
+ addlist = string_sprintf("%s, %s", addlist, da->address);
+
+ HDEBUG(D_dnsbl) debug_printf("DNS lookup for %s succeeded (yielding %s)\n",
+ query, addlist);
+
+ /* Address list check; this can be either for equality, or via a bitmask.
+ In the latter case, all the bits must match. */
+
+ if (iplist != NULL)
+ {
+ int ipsep = ',';
+ uschar ip[46];
+ uschar *ptr = iplist;
+
+ while (string_nextinlist(&ptr, &ipsep, ip, sizeof(ip)) != NULL)
+ {
+ /* Handle exact matching */
+ if (!bitmask)
+ {
+ for (da = cb->rhs; da != NULL; da = da->next)
+ {
+ if (Ustrcmp(CS da->address, ip) == 0) break;
+ }
+ }
+ /* Handle bitmask matching */
+ else
+ {
+ int address[4];
+ int mask = 0;
+
+ /* At present, all known DNS blocking lists use A records, with
+ IPv4 addresses on the RHS encoding the information they return. I
+ wonder if this will linger on as the last vestige of IPv4 when IPv6
+ is ubiquitous? Anyway, for now we use paranoia code to completely
+ ignore IPv6 addresses. The default mask is 0, which always matches.
+ We change this only for IPv4 addresses in the list. */
+
+ if (host_aton(ip, address) == 1) mask = address[0];
+
+ /* Scan the returned addresses, skipping any that are IPv6 */
+
+ for (da = cb->rhs; da != NULL; da = da->next)
+ {
+ if (host_aton(da->address, address) != 1) continue;
+ if ((address[0] & mask) == mask) break;
+ }
+ }
+
+ /* Break out if a match has been found */
+
+ if (da != NULL) break;
+ }
+
+ /* If either
+
+ (a) No IP address in a positive list matched, or
+ (b) An IP address in a negative list did match
+
+ then behave as if the DNSBL lookup had not succeeded, i.e. the host is
+ not on the list. */
+
+ if (invert_result != (da == NULL))
+ {
+ HDEBUG(D_dnsbl)
+ {
+ debug_printf("=> but we are not accepting this block class because\n");
+ debug_printf("=> there was %s match for %c%s\n",
+ invert_result? "an exclude":"no", bitmask? '&' : '=', iplist);
+ }
+ return FAIL;
+ }
+ }
+
+ /* Either there was no IP list, or the record matched. Look up a TXT record
+ if it hasn't previously been done. */
+
+ if (!cb->text_set)
+ {
+ cb->text_set = TRUE;
+ if (dns_basic_lookup(&dnsa, query, T_TXT) == DNS_SUCCEED)
+ {
+ dns_record *rr;
+ for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
+ rr != NULL;
+ rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
+ if (rr->type == T_TXT) break;
+ if (rr != NULL)
+ {
+ int len = (rr->data)[0];
+ if (len > 511) len = 127;
+ store_pool = POOL_PERM;
+ cb->text = string_sprintf("%.*s", len, (const uschar *)(rr->data+1));
+ store_pool = old_pool;
+ }
+ }
+ }
+
+ dnslist_value = addlist;
+ dnslist_text = cb->text;
+ return OK;
+ }
+
+/* There was a problem with the DNS lookup */
+
+if (cb->rc != DNS_NOMATCH && cb->rc != DNS_NODATA)
+ {
+ log_write(L_dnslist_defer, LOG_MAIN,
+ "DNS list lookup defer (probably timeout) for %s: %s", query,
+ (defer_return == OK)? US"assumed in list" :
+ (defer_return == FAIL)? US"assumed not in list" :
+ US"returned DEFER");
+ return defer_return;
+ }
+
+/* No entry was found in the DNS; continue for next domain */
+
+HDEBUG(D_dnsbl)
+ {
+ debug_printf("DNS lookup for %s failed\n", query);
+ debug_printf("=> that means %s is not listed at %s\n",
+ keydomain, domain);
+ }
+
+return FAIL;
+}
+
+
+
+
projects / exim.git / commitdiff