DNS_RR *smtp_host_addr(const char *host, int misc_flags, DSN_BUF *why)
{
DNS_RR *addr_list;
dsb_reset(why); /* Paranoia */
/*
* If the host is specified by numerical address, just convert the
* address to internal form. Otherwise, the host is specified by name.
*/
#define PREF0 0
addr_list = smtp_addr_one((DNS_RR *) 0, host, PREF0, why);
if (addr_list
&& (misc_flags & SMTP_MISC_FLAG_LOOP_DETECT)
&& smtp_find_self(addr_list) != 0) {
dns_rr_free(addr_list);
dsb_simple(why, "5.4.6", "mail for %s loops back to myself", host);
return (0);
}
if (addr_list && addr_list->next) {
if (var_smtp_rand_addr)
addr_list = dns_rr_shuffle(addr_list);
/* The following changes the order of equal-preference hosts. */
if (inet_proto_info()->ai_family_list[1] != 0)
addr_list = dns_rr_sort(addr_list, SMTP_COMPARE_ADDR(misc_flags));
}
if (msg_verbose)
smtp_print_addr(host, addr_list);
return (addr_list);
}
DNS_RR *smtp_host_addr(const char *host, int misc_flags, DSN_BUF *why)
{
DNS_RR *addr_list;
int res_opt = 0;
const char *ahost;
dsb_reset(why); /* Paranoia */
if (smtp_dns_support == SMTP_DNS_DNSSEC)
res_opt |= RES_USE_DNSSEC;
/*
* IDNA support.
*/
#ifndef NO_EAI
if (!allascii(host) && (ahost = midna_domain_to_ascii(host)) != 0) {
if (msg_verbose)
msg_info("%s asciified to %s", host, ahost);
} else
#endif
ahost = host;
/*
* If the host is specified by numerical address, just convert the
* address to internal form. Otherwise, the host is specified by name.
*/
#define PREF0 0
addr_list = smtp_addr_one((DNS_RR *) 0, ahost, res_opt, PREF0, why);
if (addr_list
&& (misc_flags & SMTP_MISC_FLAG_LOOP_DETECT)
&& smtp_find_self(addr_list) != 0) {
dns_rr_free(addr_list);
dsb_simple(why, "5.4.6", "mail for %s loops back to myself", host);
return (0);
}
if (addr_list && addr_list->next) {
if (var_smtp_rand_addr)
addr_list = dns_rr_shuffle(addr_list);
/* The following changes the order of equal-preference hosts. */
if (inet_proto_info()->ai_family_list[1] != 0)
addr_list = dns_rr_sort(addr_list, SMTP_COMPARE_ADDR(misc_flags));
}
if (msg_verbose)
smtp_print_addr(host, addr_list);
return (addr_list);
}
static DNS_RR *smtp_truncate_self(DNS_RR *addr_list, unsigned pref)
{
DNS_RR *addr;
DNS_RR *last;
for (last = 0, addr = addr_list; addr; last = addr, addr = addr->next) {
if (pref == addr->pref) {
if (msg_verbose)
smtp_print_addr("truncated", addr);
dns_rr_free(addr);
if (last == 0) {
addr_list = 0;
} else {
last->next = 0;
}
break;
}
}
return (addr_list);
}
DNS_RR *smtp_domain_addr(char *name, int misc_flags, DSN_BUF *why,
int *found_myself)
{
DNS_RR *mx_names;
DNS_RR *addr_list = 0;
DNS_RR *self = 0;
unsigned best_pref;
unsigned best_found;
dsb_reset(why); /* Paranoia */
/*
* Preferences from DNS use 0..32767, fall-backs use 32768+.
*/
#define IMPOSSIBLE_PREFERENCE (~0)
/*
* Sanity check.
*/
if (var_disable_dns)
msg_panic("smtp_domain_addr: DNS lookup is disabled");
/*
* Look up the mail exchanger hosts listed for this name. Sort the
* results by preference. Look up the corresponding host addresses, and
* truncate the list so that it contains only hosts that are more
* preferred than myself. When no MX resource records exist, look up the
* addresses listed for this name.
*
* According to RFC 974: "It is possible that the list of MXs in the
* response to the query will be empty. This is a special case. If the
* list is empty, mailers should treat it as if it contained one RR, an
* MX RR with a preference value of 0, and a host name of REMOTE. (I.e.,
* REMOTE is its only MX). In addition, the mailer should do no further
* processing on the list, but should attempt to deliver the message to
* REMOTE."
*
* Normally it is OK if an MX host cannot be found in the DNS; we'll just
* use a backup one, and silently ignore the better MX host. However, if
* the best backup that we can find in the DNS is the local machine, then
* we must remember that the local machine is not the primary MX host, or
* else we will claim that mail loops back.
*
* XXX Optionally do A lookups even when the MX lookup didn't complete.
* Unfortunately with some DNS servers this is not a transient problem.
*
* XXX Ideally we would perform A lookups only as far as needed. But as long
* as we're looking up all the hosts, it would be better to look up the
* least preferred host first, so that DNS lookup error messages make
* more sense.
*
* XXX 2821: RFC 2821 says that the sender must shuffle equal-preference MX
* hosts, whereas multiple A records per hostname must be used in the
* order as received. They make the bogus assumption that a hostname with
* multiple A records corresponds to one machine with multiple network
* interfaces.
*
* XXX 2821: Postfix recognizes the local machine by looking for its own IP
* address in the list of mail exchangers. RFC 2821 says one has to look
* at the mail exchanger hostname as well, making the bogus assumption
* that an IP address is listed only under one hostname. However, looking
* at hostnames provides a partial solution for MX hosts behind a NAT
* gateway.
*/
switch (dns_lookup(name, T_MX, 0, &mx_names, (VSTRING *) 0, why->reason)) {
default:
dsb_status(why, "4.4.3");
if (var_ign_mx_lookup_err)
addr_list = smtp_host_addr(name, misc_flags, why);
break;
case DNS_INVAL:
dsb_status(why, "5.4.4");
if (var_ign_mx_lookup_err)
addr_list = smtp_host_addr(name, misc_flags, why);
break;
case DNS_FAIL:
dsb_status(why, "5.4.3");
if (var_ign_mx_lookup_err)
addr_list = smtp_host_addr(name, misc_flags, why);
break;
case DNS_OK:
mx_names = dns_rr_sort(mx_names, dns_rr_compare_pref_any);
best_pref = (mx_names ? mx_names->pref : IMPOSSIBLE_PREFERENCE);
addr_list = smtp_addr_list(mx_names, why);
dns_rr_free(mx_names);
if (addr_list == 0) {
/* Text does not change. */
if (var_smtp_defer_mxaddr) {
/* Don't clobber the null terminator. */
if (SMTP_HAS_HARD_DSN(why))
SMTP_SET_SOFT_DSN(why); /* XXX */
/* Require some error status. */
else if (!SMTP_HAS_SOFT_DSN(why))
msg_panic("smtp_domain_addr: bad status");
}
msg_warn("no MX host for %s has a valid address record", name);
break;
}
best_found = (addr_list ? addr_list->pref : IMPOSSIBLE_PREFERENCE);
if (msg_verbose)
smtp_print_addr(name, addr_list);
if ((misc_flags & SMTP_MISC_FLAG_LOOP_DETECT)
&& (self = smtp_find_self(addr_list)) != 0) {
addr_list = smtp_truncate_self(addr_list, self->pref);
if (addr_list == 0) {
if (best_pref != best_found) {
dsb_simple(why, "4.4.4",
"unable to find primary relay for %s", name);
} else {
dsb_simple(why, "5.4.6", "mail for %s loops back to myself",
name);
}
}
}
#define SMTP_COMPARE_ADDR(flags) \
(((flags) & SMTP_MISC_FLAG_PREF_IPV6) ? dns_rr_compare_pref_ipv6 : \
((flags) & SMTP_MISC_FLAG_PREF_IPV4) ? dns_rr_compare_pref_ipv4 : \
dns_rr_compare_pref_any)
if (addr_list && addr_list->next && var_smtp_rand_addr) {
addr_list = dns_rr_shuffle(addr_list);
addr_list = dns_rr_sort(addr_list, SMTP_COMPARE_ADDR(misc_flags));
}
break;
case DNS_NOTFOUND:
addr_list = smtp_host_addr(name, misc_flags, why);
break;
}
/*
* Clean up.
*/
*found_myself |= (self != 0);
return (addr_list);
}
