+/*************************************************
+* Exim - an Internet mail transport agent *
+*************************************************/
+
+/* Copyright (c) University of Cambridge 1995 - 2018 */
+/* Copyright (c) The Exim Maintainers 2020 */
+/* See the file NOTICE for conditions of use and distribution. */
+
+/* Functions concerned with dnsbls */
+
+
+#include "exim.h"
+
+/* Structure for caching DNSBL lookups */
+
+typedef struct dnsbl_cache_block {
+ time_t expiry;
+ dns_address *rhs;
+ uschar *text;
+ int rc;
+ BOOL text_set;
+} dnsbl_cache_block;
+
+
+/* Anchor for DNSBL cache */
+
+static tree_node *dnsbl_cache = NULL;
+
+
+/* Bits for match_type in one_check_dnsbl() */
+
+#define MT_NOT 1
+#define MT_ALL 2
+
+
+/*************************************************
+* Perform a single dnsbl lookup *
+*************************************************/
+
+/* This function is called from verify_check_dnsbl() below. It is also called
+recursively from within itself when domain and domain_txt are different
+pointers, in order to get the TXT record from the alternate domain.
+
+Arguments:
+ domain the outer dnsbl domain
+ domain_txt alternate domain to lookup TXT record on success; when the
+ same domain is to be used, domain_txt == domain (that is,
+ the pointers must be identical, not just the text)
+ keydomain the current keydomain (for debug message)
+ prepend subdomain to lookup (like keydomain, but
+ reversed if IP address)
+ iplist the list of matching IP addresses, or NULL for "any"
+ bitmask true if bitmask matching is wanted
+ match_type condition for 'succeed' result
+ 0 => Any RR in iplist (=)
+ 1 => No RR in iplist (!=)
+ 2 => All RRs in iplist (==)
+ 3 => Some RRs not in iplist (!==)
+ the two bits are defined as MT_NOT and MT_ALL
+ defer_return what to return for a defer
+
+Returns: OK if lookup succeeded
+ FAIL if not
+*/
+
+static int
+one_check_dnsbl(uschar *domain, uschar *domain_txt, uschar *keydomain,
+ uschar *prepend, uschar *iplist, BOOL bitmask, int match_type,
+ int defer_return)
+{
+dns_answer * dnsa = store_get_dns_answer();
+dns_scan dnss;
+tree_node *t;
+dnsbl_cache_block *cb;
+int old_pool = store_pool;
+uschar * query;
+int qlen;
+
+/* Construct the specific query domainname */
+
+query = string_sprintf("%s.%s", prepend, domain);
+if ((qlen = Ustrlen(query)) >= 256)
+ {
+ log_write(0, LOG_MAIN|LOG_PANIC, "dnslist query is too long "
+ "(ignored): %s...", query);
+ return FAIL;
+ }
+
+/* Look for this query in the cache. */
+
+if ( (t = tree_search(dnsbl_cache, query))
+ && (cb = t->data.ptr)->expiry > time(NULL)
+ )
+
+/* Previous lookup was cached */
+
+ {
+ HDEBUG(D_dnsbl) debug_printf("dnslists: using result of previous lookup\n");
+ }
+
+/* If not cached from a previous lookup, we must do a DNS lookup, and
+cache the result in permanent memory. */
+
+else
+ {
+ uint ttl = 3600; /* max TTL for positive cache entries */
+
+ store_pool = POOL_PERM;
+
+ if (t)
+ {
+ HDEBUG(D_dnsbl) debug_printf("cached data found but past valid time; ");
+ }
+
+ else
+ { /* Set up a tree entry to cache the lookup */
+ t = store_get(sizeof(tree_node) + qlen + 1 + 1, is_tainted(query));
+ Ustrcpy(t->name, query);
+ t->data.ptr = cb = store_get(sizeof(dnsbl_cache_block), FALSE);
+ (void)tree_insertnode(&dnsbl_cache, t);
+ }
+
+ /* Do the DNS lookup . */
+
+ 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 are no longer supported. 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.
+
+ Mark the cache entry with the "now" plus the minimum of the address TTLs,
+ or the RFC 2308 negative-cache value from the SOA if none were found. */
+
+ switch (cb->rc)
+ {
+ case DNS_SUCCEED:
+ {
+ dns_address ** addrp = &cb->rhs;
+ dns_address * da;
+ for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
+ rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
+ if (rr->type == T_A && (da = dns_address_from_rr(dnsa, rr)))
+ {
+ *addrp = da;
+ while (da->next) da = da->next;
+ addrp = &da->next;
+ if (ttl > rr->ttl) ttl = rr->ttl;
+ }
+
+ if (cb->rhs)
+ {
+ cb->expiry = time(NULL) + ttl;
+ break;
+ }
+
+ /* 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. */
+
+ cb->rc = DNS_NODATA;
+ }
+ /*FALLTHROUGH*/
+
+ case DNS_NOMATCH:
+ case DNS_NODATA:
+ {
+ /* Although there already is a neg-cache layer maintained by
+ dns_basic_lookup(), we have a dnslist cache entry allocated and
+ tree-inserted. So we may as well use it. */
+
+ time_t soa_negttl = dns_expire_from_soa(dnsa, T_A);
+ cb->expiry = soa_negttl ? soa_negttl : time(NULL) + ttl;
+ break;
+ }
+
+ default:
+ cb->expiry = time(NULL) + ttl;
+ break;
+ }
+
+ store_pool = old_pool;
+ HDEBUG(D_dnsbl) debug_printf("dnslists: wrote cache entry, ttl=%d\n",
+ (int)(cb->expiry - time(NULL)));
+ }
+
+/* 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; 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)
+ {
+ for (da = cb->rhs; da; da = da->next)
+ {
+ int ipsep = ',';
+ const uschar *ptr = iplist;
+ uschar *res;
+
+ /* Handle exact matching */
+
+ if (!bitmask)
+ {
+ while ((res = string_nextinlist(&ptr, &ipsep, NULL, 0)))
+ if (Ustrcmp(CS da->address, res) == 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(da->address, address) == 1) mask = address[0];
+
+ /* Scan the returned addresses, skipping any that are IPv6 */
+
+ while ((res = string_nextinlist(&ptr, &ipsep, NULL, 0)))
+ if (host_aton(res, address) == 1)
+ if ((address[0] & mask) == address[0])
+ break;
+ }
+
+ /* If either
+
+ (a) An IP address in an any ('=') list matched, or
+ (b) No IP address in an all ('==') list matched
+
+ then we're done searching. */
+
+ if (((match_type & MT_ALL) != 0) == (res == NULL)) break;
+ }
+
+ /* If da == NULL, either
+
+ (a) No IP address in an any ('=') list matched, or
+ (b) An IP address in an all ('==') list didn't match
+
+ so behave as if the DNSBL lookup had not succeeded, i.e. the host is not on
+ the list. */
+
+ if ((match_type == MT_NOT || match_type == MT_ALL) != (da == NULL))
+ {
+ HDEBUG(D_dnsbl)
+ {
+ uschar *res = NULL;
+ switch(match_type)
+ {
+ case 0:
+ res = US"was no match"; break;
+ case MT_NOT:
+ res = US"was an exclude match"; break;
+ case MT_ALL:
+ res = US"was an IP address that did not match"; break;
+ case MT_NOT|MT_ALL:
+ res = US"were no IP addresses that did not match"; break;
+ }
+ debug_printf("=> but we are not accepting this block class because\n");
+ debug_printf("=> there %s for %s%c%s\n",
+ res,
+ match_type & MT_ALL ? "=" : "",
+ bitmask ? '&' : '=', iplist);
+ }
+ return FAIL;
+ }
+ }
+
+ /* Either there was no IP list, or the record matched, implying that the
+ domain is on the list. We now want to find a corresponding TXT record. If an
+ alternate domain is specified for the TXT record, call this function
+ recursively to look that up; this has the side effect of re-checking that
+ there is indeed an A record at the alternate domain. */
+
+ if (domain_txt != domain)
+ return one_check_dnsbl(domain_txt, domain_txt, keydomain, prepend, NULL,
+ FALSE, match_type, defer_return);
+
+ /* If there is no alternate domain, look up a TXT record in the main domain
+ if it has not previously been cached. */
+
+ if (!cb->text_set)
+ {
+ cb->text_set = TRUE;
+ if (dns_basic_lookup(dnsa, query, T_TXT) == DNS_SUCCEED)
+ for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
+ rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
+ if (rr->type == T_TXT)
+ {
+ int len = (rr->data)[0];
+ if (len > 511) len = 127;
+ store_pool = POOL_PERM;
+ cb->text = string_sprintf("%.*s", len, CUS (rr->data+1));
+ store_pool = old_pool;
+ break;
+ }
+ }
+
+ 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;
+}
+
+
+
+
+/*************************************************
+* Check host against DNS black lists *
+*************************************************/
+
+/* This function runs checks against a list of DNS black lists, until one
+matches. Each item on the list can be of the form
+
+ domain=ip-address/key
+
+The domain is the right-most domain that is used for the query, for example,
+blackholes.mail-abuse.org. If the IP address is present, there is a match only
+if the DNS lookup returns a matching IP address. Several addresses may be
+given, comma-separated, for example: x.y.z=127.0.0.1,127.0.0.2.
+
+If no key is given, what is looked up in the domain is the inverted IP address
+of the current client host. If a key is given, it is used to construct the
+domain for the lookup. For example:
+
+ dsn.rfc-ignorant.org/$sender_address_domain
+
+After finding a match in the DNS, the domain is placed in $dnslist_domain, and
+then we check for a TXT record for an error message, and if found, save its
+value in $dnslist_text. We also cache everything in a tree, to optimize
+multiple lookups.
+
+The TXT record is normally looked up in the same domain as the A record, but
+when many lists are combined in a single DNS domain, this will not be a very
+specific message. It is possible to specify a different domain for looking up
+TXT records; this is given before the main domain, comma-separated. For
+example:
+
+ dnslists = http.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.2 : \
+ socks.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.3
+
+The caching ensures that only one lookup in dnsbl.sorbs.net is done.
+
+Note: an address for testing RBL is 192.203.178.39
+Note: an address for testing DUL is 192.203.178.4
+Note: a domain for testing RFCI is example.tld.dsn.rfc-ignorant.org
+
+Arguments:
+ where the acl type
+ listptr the domain/address/data list
+ log_msgptr log message on error
+
+Returns: OK successful lookup (i.e. the address is on the list), or
+ lookup deferred after +include_unknown
+ FAIL name not found, or no data found for the given type, or
+ lookup deferred after +exclude_unknown (default)
+ DEFER lookup failure, if +defer_unknown was set
+*/
+
+int
+verify_check_dnsbl(int where, const uschar ** listptr, uschar ** log_msgptr)
+{
+int sep = 0;
+int defer_return = FAIL;
+const uschar *list = *listptr;
+uschar *domain;
+uschar revadd[128]; /* Long enough for IPv6 address */
+
+/* Indicate that the inverted IP address is not yet set up */
+
+revadd[0] = 0;
+
+/* In case this is the first time the DNS resolver is being used. */
+
+dns_init(FALSE, FALSE, FALSE); /*XXX dnssec? */
+
+/* Loop through all the domains supplied, until something matches */
+
+while ((domain = string_nextinlist(&list, &sep, NULL, 0)))
+ {
+ int rc;
+ BOOL bitmask = FALSE;
+ int match_type = 0;
+ uschar *domain_txt;
+ uschar *comma;
+ uschar *iplist;
+ uschar *key;
+
+ HDEBUG(D_dnsbl) debug_printf("dnslists check: %s\n", domain);
+
+ /* Deal with special values that change the behaviour on defer */
+
+ if (domain[0] == '+')
+ {
+ if (strcmpic(domain, US"+include_unknown") == 0) defer_return = OK;
+ else if (strcmpic(domain, US"+exclude_unknown") == 0) defer_return = FAIL;
+ else if (strcmpic(domain, US"+defer_unknown") == 0) defer_return = DEFER;
+ else
+ log_write(0, LOG_MAIN|LOG_PANIC, "unknown item in dnslist (ignored): %s",
+ domain);
+ continue;
+ }
+
+ /* See if there's explicit data to be looked up */
+
+ if ((key = Ustrchr(domain, '/'))) *key++ = 0;
+
+ /* See if there's a list of addresses supplied after the domain name. This is
+ introduced by an = or a & character; if preceded by = we require all matches
+ and if preceded by ! we invert the result. */
+
+ if (!(iplist = Ustrchr(domain, '=')))
+ {
+ bitmask = TRUE;
+ iplist = Ustrchr(domain, '&');
+ }
+
+ if (iplist) /* Found either = or & */
+ {
+ if (iplist > domain && iplist[-1] == '!') /* Handle preceding ! */
+ {
+ match_type |= MT_NOT;
+ iplist[-1] = 0;
+ }
+
+ *iplist++ = 0; /* Terminate domain, move on */
+
+ /* If we found = (bitmask == FALSE), check for == or =& */
+
+ if (!bitmask && (*iplist == '=' || *iplist == '&'))
+ {
+ bitmask = *iplist++ == '&';
+ match_type |= MT_ALL;
+ }
+ }
+
+
+ /* If there is a comma in the domain, it indicates that a second domain for
+ looking up TXT records is provided, before the main domain. Otherwise we must
+ set domain_txt == domain. */
+
+ domain_txt = domain;
+ if ((comma = Ustrchr(domain, ',')))
+ {
+ *comma++ = 0;
+ domain = comma;
+ }
+
+ /* Check that what we have left is a sensible domain name. There is no reason
+ why these domains should in fact use the same syntax as hosts and email
+ domains, but in practice they seem to. However, there is little point in
+ actually causing an error here, because that would no doubt hold up incoming
+ mail. Instead, I'll just log it. */
+
+ for (uschar * s = domain; *s; s++)
+ if (!isalnum(*s) && *s != '-' && *s != '.' && *s != '_')
+ {
+ log_write(0, LOG_MAIN, "dnslists domain \"%s\" contains "
+ "strange characters - is this right?", domain);
+ break;
+ }
+
+ /* Check the alternate domain if present */
+
+ if (domain_txt != domain) for (uschar * s = domain_txt; *s; s++)
+ if (!isalnum(*s) && *s != '-' && *s != '.' && *s != '_')
+ {
+ log_write(0, LOG_MAIN, "dnslists domain \"%s\" contains "
+ "strange characters - is this right?", domain_txt);
+ break;
+ }
+
+ /* If there is no key string, construct the query by adding the domain name
+ onto the inverted host address, and perform a single DNS lookup. */
+
+ if (!key)
+ {
+ if (where == ACL_WHERE_NOTSMTP_START || where == ACL_WHERE_NOTSMTP)
+ {
+ *log_msgptr = string_sprintf
+ ("cannot test auto-keyed dnslists condition in %s ACL",
+ acl_wherenames[where]);
+ return ERROR;
+ }
+ if (!sender_host_address) return FAIL; /* can never match */
+ if (revadd[0] == 0) invert_address(revadd, sender_host_address);
+ rc = one_check_dnsbl(domain, domain_txt, sender_host_address, revadd,
+ iplist, bitmask, match_type, defer_return);
+ if (rc == OK)
+ {
+ dnslist_domain = string_copy(domain_txt);
+ dnslist_matched = string_copy(sender_host_address);
+ HDEBUG(D_dnsbl) debug_printf("=> that means %s is listed at %s\n",
+ sender_host_address, dnslist_domain);
+ }
+ if (rc != FAIL) return rc; /* OK or DEFER */
+ }
+
+ /* If there is a key string, it can be a list of domains or IP addresses to
+ be concatenated with the main domain. */
+
+ else
+ {
+ int keysep = 0;
+ BOOL defer = FALSE;
+ uschar *keydomain;
+ uschar keyrevadd[128];
+
+ while ((keydomain = string_nextinlist(CUSS &key, &keysep, NULL, 0)))
+ {
+ uschar *prepend = keydomain;
+
+ if (string_is_ip_address(keydomain, NULL) != 0)
+ {
+ invert_address(keyrevadd, keydomain);
+ prepend = keyrevadd;
+ }
+
+ rc = one_check_dnsbl(domain, domain_txt, keydomain, prepend, iplist,
+ bitmask, match_type, defer_return);
+ if (rc == OK)
+ {
+ dnslist_domain = string_copy(domain_txt);
+ dnslist_matched = string_copy(keydomain);
+ HDEBUG(D_dnsbl) debug_printf("=> that means %s is listed at %s\n",
+ keydomain, dnslist_domain);
+ return OK;
+ }
+
+ /* If the lookup deferred, remember this fact. We keep trying the rest
+ of the list to see if we get a useful result, and if we don't, we return
+ DEFER at the end. */
+
+ if (rc == DEFER) defer = TRUE;
+ } /* continue with next keystring domain/address */
+
+ if (defer) return DEFER;
+ }
+ } /* continue with next dnsdb outer domain */
+
+return FAIL;
+}
+
+/* vi: aw ai sw=2
+*/
+/* End of dnsbl.c.c */
git://git.exim.org / users / heiko / exim.git / commitdiff