/* $Cambridge: exim/exim-src/src/dns.c,v 1.17 2007/01/08 10:50:18 ph10 Exp $ */
/*************************************************
* Exim - an Internet mail transport agent *
*************************************************/
/* Copyright (c) University of Cambridge 1995 - 2007 */
/* See the file NOTICE for conditions of use and distribution. */
/* Functions for interfacing with the DNS. */
#include "exim.h"
/* Function declaration needed for mutual recursion when A6 records
are supported. */
#if HAVE_IPV6
#ifdef SUPPORT_A6
static void dns_complete_a6(dns_address ***, dns_answer *, dns_record *,
int, uschar *);
#endif
#endif
/*************************************************
* Fake DNS resolver *
*************************************************/
/* This function is called instead of res_search() when Exim is running in its
test harness. It recognizes some special domain names, and uses them to force
failure and retry responses (optionally with a delay). Otherwise, it calls an
external utility that mocks-up a nameserver, if it can find the utility.
If not, it passes its arguments on to res_search(). The fake nameserver may
also return a code specifying that the name should be passed on.
Background: the original test suite required a real nameserver to carry the
test zones, whereas the new test suit has the fake server for portability. This
code supports both.
Arguments:
domain the domain name
type the DNS record type
answerptr where to put the answer
size size of the answer area
Returns: length of returned data, or -1 on error (h_errno set)
*/
static int
fakens_search(uschar *domain, int type, uschar *answerptr, int size)
{
int len = Ustrlen(domain);
int asize = size; /* Locally modified */
uschar *endname;
uschar name[256];
uschar utilname[256];
uschar *aptr = answerptr; /* Locally modified */
struct stat statbuf;
/* Remove terminating dot. */
if (domain[len - 1] == '.') len--;
Ustrncpy(name, domain, len);
name[len] = 0;
endname = name + len;
/* This code, for forcing TRY_AGAIN and NO_RECOVERY, is here so that it works
for the old test suite that uses a real nameserver. When the old test suite is
eventually abandoned, this code could be moved into the fakens utility. */
if (len >= 14 && Ustrcmp(endname - 14, "test.again.dns") == 0)
{
int delay = Uatoi(name); /* digits at the start of the name */
DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n",
name, dns_text_type(type));
if (delay > 0)
{
DEBUG(D_dns) debug_printf("delaying %d seconds\n", delay);
sleep(delay);
}
h_errno = TRY_AGAIN;
return -1;
}
if (len >= 13 && Ustrcmp(endname - 13, "test.fail.dns") == 0)
{
DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n",
name, dns_text_type(type));
h_errno = NO_RECOVERY;
return -1;
}
/* Look for the fakens utility, and if it exists, call it. */
(void)string_format(utilname, sizeof(utilname), "%s/../bin/fakens",
spool_directory);
if (stat(CS utilname, &statbuf) >= 0)
{
pid_t pid;
int infd, outfd, rc;
uschar *argv[5];
DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n",
name, dns_text_type(type));
argv[0] = utilname;
argv[1] = spool_directory;
argv[2] = name;
argv[3] = dns_text_type(type);
argv[4] = NULL;
pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE);
if (pid < 0)
log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s",
strerror(errno));
len = 0;
rc = -1;
while (asize > 0 && (rc = read(outfd, aptr, asize)) > 0)
{
len += rc;
aptr += rc; /* Don't modify the actual arguments, because they */
asize -= rc; /* may need to be passed on to res_search(). */
}
if (rc < 0)
log_write(0, LOG_MAIN|LOG_PANIC_DIE, "read from fakens failed: %s",
strerror(errno));
switch(child_close(pid, 0))
{
case 0: return len;
case 1: h_errno = HOST_NOT_FOUND; return -1;
case 2: h_errno = TRY_AGAIN; return -1;
default:
case 3: h_errno = NO_RECOVERY; return -1;
case 4: h_errno = NO_DATA; return -1;
case 5: /* Pass on to res_search() */
DEBUG(D_dns) debug_printf("fakens returned PASS_ON\n");
}
}
/* fakens utility not found, or it returned "pass on" */
DEBUG(D_dns) debug_printf("passing %s on to res_search()\n", domain);
return res_search(CS domain, C_IN, type, answerptr, size);
}
/*************************************************
* Initialize and configure resolver *
*************************************************/
/* Initialize the resolver and the storage for holding DNS answers if this is
the first time we have been here, and set the resolver options.
Arguments:
qualify_single TRUE to set the RES_DEFNAMES option
search_parents TRUE to set the RES_DNSRCH option
Returns: nothing
*/
void
dns_init(BOOL qualify_single, BOOL search_parents)
{
if ((_res.options & RES_INIT) == 0)
{
DEBUG(D_resolver) _res.options |= RES_DEBUG; /* For Cygwin */
res_init();
DEBUG(D_resolver) _res.options |= RES_DEBUG;
}
_res.options &= ~(RES_DNSRCH | RES_DEFNAMES);
_res.options |= (qualify_single? RES_DEFNAMES : 0) |
(search_parents? RES_DNSRCH : 0);
if (dns_retrans > 0) _res.retrans = dns_retrans;
if (dns_retry > 0) _res.retry = dns_retry;
}
/*************************************************
* Build key name for PTR records *
*************************************************/
/* This function inverts an IP address and adds the relevant domain, to produce
a name that can be used to look up PTR records.
Arguments:
string the IP address as a string
buffer a suitable buffer, long enough to hold the result
Returns: nothing
*/
void
dns_build_reverse(uschar *string, uschar *buffer)
{
uschar *p = string + Ustrlen(string);
uschar *pp = buffer;
/* Handle IPv4 address */
#if HAVE_IPV6
if (Ustrchr(string, ':') == NULL)
#endif
{
int i;
for (i = 0; i < 4; i++)
{
uschar *ppp = p;
while (ppp > string && ppp[-1] != '.') ppp--;
Ustrncpy(pp, ppp, p - ppp);
pp += p - ppp;
*pp++ = '.';
p = ppp - 1;
}
Ustrcpy(pp, "in-addr.arpa");
}
/* Handle IPv6 address; convert to binary so as to fill out any
abbreviation in the textual form. */
#if HAVE_IPV6
else
{
int i;
int v6[4];
(void)host_aton(string, v6);
/* The original specification for IPv6 reverse lookup was to invert each
nibble, and look in the ip6.int domain. The domain was subsequently
changed to ip6.arpa. */
for (i = 3; i >= 0; i--)
{
int j;
for (j = 0; j < 32; j += 4)
{
sprintf(CS pp, "%x.", (v6[i] >> j) & 15);
pp += 2;
}
}
Ustrcpy(pp, "ip6.arpa.");
/* Another way of doing IPv6 reverse lookups was proposed in conjunction
with A6 records. However, it fell out of favour when they did. The
alternative was to construct a binary key, and look in ip6.arpa. I tried
to make this code do that, but I could not make it work on Solaris 8. The
resolver seems to lose the initial backslash somehow. However, now that
this style of reverse lookup has been dropped, it doesn't matter. These
lines are left here purely for historical interest. */
/**************************************************
Ustrcpy(pp, "\\[x");
pp += 3;
for (i = 0; i < 4; i++)
{
sprintf(pp, "%08X", v6[i]);
pp += 8;
}
Ustrcpy(pp, "].ip6.arpa.");
**************************************************/
}
#endif
}
/*************************************************
* Get next DNS record from answer block *
*************************************************/
/* Call this with reset == RESET_ANSWERS to scan the answer block, reset ==
RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to
scan the additional records, and reset == RESET_NEXT to get the next record.
The result is in static storage which must be copied if it is to be preserved.
Arguments:
dnsa pointer to dns answer block
dnss pointer to dns scan block
reset option specifing what portion to scan, as described above
Returns: next dns record, or NULL when no more
*/
dns_record *
dns_next_rr(dns_answer *dnsa, dns_scan *dnss, int reset)
{
HEADER *h = (HEADER *)dnsa->answer;
int namelen;
/* Reset the saved data when requested to, and skip to the first required RR */
if (reset != RESET_NEXT)
{
dnss->rrcount = ntohs(h->qdcount);
dnss->aptr = dnsa->answer + sizeof(HEADER);
/* Skip over questions; failure to expand the name just gives up */
while (dnss->rrcount-- > 0)
{
namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
if (namelen < 0) { dnss->rrcount = 0; return NULL; }
dnss->aptr += namelen + 4; /* skip name & type & class */
}
/* Get the number of answer records. */
dnss->rrcount = ntohs(h->ancount);
/* Skip over answers if we want to look at the authority section. Also skip
the NS records (i.e. authority section) if wanting to look at the additional
records. */
if (reset == RESET_ADDITIONAL) dnss->rrcount += ntohs(h->nscount);
if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL)
{
while (dnss->rrcount-- > 0)
{
namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
if (namelen < 0) { dnss->rrcount = 0; return NULL; }
dnss->aptr += namelen + 8; /* skip name, type, class & TTL */
GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */
dnss->aptr += dnss->srr.size; /* skip over it */
}
dnss->rrcount = (reset == RESET_AUTHORITY)
? ntohs(h->nscount) : ntohs(h->arcount);
}
}
/* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount
contains the number of RR records left. */
if (dnss->rrcount-- <= 0) return NULL;
/* If expanding the RR domain name fails, behave as if no more records
(something safe). */
namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr,
(DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
if (namelen < 0) { dnss->rrcount = 0; return NULL; }
/* Move the pointer past the name and fill in the rest of the data structure
from the following bytes. */
dnss->aptr += namelen;
GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */
dnss->aptr += 6; /* Don't want class or TTL */
GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */
dnss->srr.data = dnss->aptr; /* The record's data follows */
dnss->aptr += dnss->srr.size; /* Advance to next RR */
/* Return a pointer to the dns_record structure within the dns_answer. This is
for convenience so that the scans can use nice-looking for loops. */
return &(dnss->srr);
}
/*************************************************
* Turn DNS type into text *
*************************************************/
/* Turn the coded record type into a string for printing. All those that Exim
uses should be included here.
Argument: record type
Returns: pointer to string
*/
uschar *
dns_text_type(int t)
{
switch(t)
{
case T_A: return US"A";
case T_MX: return US"MX";
case T_AAAA: return US"AAAA";
case T_A6: return US"A6";
case T_TXT: return US"TXT";
case T_PTR: return US"PTR";
case T_SOA: return US"SOA";
case T_SRV: return US"SRV";
case T_NS: return US"NS";
case T_CNAME: return US"CNAME";
default: return US"?";
}
}
/*************************************************
* Cache a failed DNS lookup result *
*************************************************/
/* We cache failed lookup results so as not to experience timeouts many
times for the same domain. We need to retain the resolver options because they
may change. For successful lookups, we rely on resolver and/or name server
caching.
Arguments:
name the domain name
type the lookup type
rc the return code
Returns: the return code
*/
static int
dns_return(uschar *name, int type, int rc)
{
tree_node *node = store_get_perm(sizeof(tree_node) + 290);
sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type),
_res.options);
node->data.val = rc;
(void)tree_insertnode(&tree_dns_fails, node);
return rc;
}
/*************************************************
* Do basic DNS lookup *
*************************************************/
/* Call the resolver to look up the given domain name, using the given type,
and check the result. The error code TRY_AGAIN is documented as meaning "non-
Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set
up nameservers that produce this error continually, so there is the option of
providing a list of domains for which this is treated as a non-existent
host.
Arguments:
dnsa pointer to dns_answer structure
name name to look up
type type of DNS record required (T_A, T_MX, etc)
Returns: DNS_SUCCEED successful lookup
DNS_NOMATCH name not found (NXDOMAIN)
or name contains illegal characters (if checking)
or name is an IP address (for IP address lookup)
DNS_NODATA domain exists, but no data for this type (NODATA)
DNS_AGAIN soft failure, try again later
DNS_FAIL DNS failure
*/
int
dns_basic_lookup(dns_answer *dnsa, uschar *name, int type)
{
int rc = -1;
#ifndef STAND_ALONE
uschar *save;
#endif
tree_node *previous;
uschar node_name[290];
/* DNS lookup failures of any kind are cached in a tree. This is mainly so that
a timeout on one domain doesn't happen time and time again for messages that
have many addresses in the same domain. We rely on the resolver and name server
caching for successful lookups. */
sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type),
_res.options);
previous = tree_search(tree_dns_fails, node_name);
if (previous != NULL)
{
DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n",
name, dns_text_type(type),
(previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" :
(previous->data.val == DNS_NODATA)? "DNS_NODATA" :
(previous->data.val == DNS_AGAIN)? "DNS_AGAIN" :
(previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??");
return previous->data.val;
}
/* If configured, check the hygene of the name passed to lookup. Otherwise,
although DNS lookups may give REFUSED at the lower level, some resolvers
turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such
domains cannot be in the DNS. The check is now done by a regular expression;
give it space for substring storage to save it having to get its own if the
regex has substrings that are used - the default uses a conditional.
This test is omitted for PTR records. These occur only in calls from the dnsdb
lookup, which constructs the names itself, so they should be OK. Besides,
bitstring labels don't conform to normal name syntax. (But the aren't used any
more.)
For SRV records, we omit the initial _smtp._tcp. components at the start. */
#ifndef STAND_ALONE /* Omit this for stand-alone tests */
if (check_dns_names_pattern[0] != 0 && type != T_PTR)
{
uschar *checkname = name;
int ovector[3*(EXPAND_MAXN+1)];
if (regex_check_dns_names == NULL)
regex_check_dns_names =
regex_must_compile(check_dns_names_pattern, FALSE, TRUE);
/* For an SRV lookup, skip over the first two components (the service and
protocol names, which both start with an underscore). */
if (type == T_SRV)
{
while (*checkname++ != '.');
while (*checkname++ != '.');
}
if (pcre_exec(regex_check_dns_names, NULL, CS checkname, Ustrlen(checkname),
0, PCRE_EOPT, ovector, sizeof(ovector)/sizeof(int)) < 0)
{
DEBUG(D_dns)
debug_printf("DNS name syntax check failed: %s (%s)\n", name,
dns_text_type(type));
host_find_failed_syntax = TRUE;
return DNS_NOMATCH;
}
}
#endif /* STAND_ALONE */
/* Call the resolver; for an overlong response, res_search() will return the
number of bytes the message would need, so we need to check for this case. The
effect is to truncate overlong data.
On some systems, res_search() will recognize "A-for-A" queries and return
the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some
nameservers are also believed to do this. It is, of course, contrary to the
specification of the DNS, so we lock it out. */
if ((
#ifdef SUPPORT_A6
type == T_A6 ||
#endif
type == T_A || type == T_AAAA) &&
string_is_ip_address(name, NULL) != 0)
return DNS_NOMATCH;
/* If we are running in the test harness, instead of calling the normal resolver
(res_search), we call fakens_search(), which recognizes certain special
domains, and interfaces to a fake nameserver for certain special zones. */
if (running_in_test_harness)
dnsa->answerlen = fakens_search(name, type, dnsa->answer, MAXPACKET);
else
dnsa->answerlen = res_search(CS name, C_IN, type, dnsa->answer, MAXPACKET);
if (dnsa->answerlen > MAXPACKET) dnsa->answerlen = MAXPACKET;
if (dnsa->answerlen < 0) switch (h_errno)
{
case HOST_NOT_FOUND:
DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n"
"returning DNS_NOMATCH\n", name, dns_text_type(type));
return dns_return(name, type, DNS_NOMATCH);
case TRY_AGAIN:
DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n",
name, dns_text_type(type));
/* Cut this out for various test programs */
#ifndef STAND_ALONE
save = deliver_domain;
deliver_domain = name; /* set $domain */
rc = match_isinlist(name, &dns_again_means_nonexist, 0, NULL, NULL,
MCL_DOMAIN, TRUE, NULL);
deliver_domain = save;
if (rc != OK)
{
DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
return dns_return(name, type, DNS_AGAIN);
}
DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning "
"DNS_NOMATCH\n", name);
return dns_return(name, type, DNS_NOMATCH);
#else /* For stand-alone tests */
return dns_return(name, type, DNS_AGAIN);
#endif
case NO_RECOVERY:
DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n"
"returning DNS_FAIL\n", name, dns_text_type(type));
return dns_return(name, type, DNS_FAIL);
case NO_DATA:
DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n"
"returning DNS_NODATA\n", name, dns_text_type(type));
return dns_return(name, type, DNS_NODATA);
default:
DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n"
"returning DNS_FAIL\n", name, dns_text_type(type), h_errno);
return dns_return(name, type, DNS_FAIL);
}
DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n",
name, dns_text_type(type));
return DNS_SUCCEED;
}
/************************************************
* Do a DNS lookup and handle CNAMES *
************************************************/
/* Look up the given domain name, using the given type. Follow CNAMEs if
necessary, but only so many times. There aren't supposed to be CNAME chains in
the DNS, but you are supposed to cope with them if you find them.
The assumption is made that if the resolver gives back records of the
requested type *and* a CNAME, we don't need to make another call to look up
the CNAME. I can't see how it could return only some of the right records. If
it's done a CNAME lookup in the past, it will have all of them; if not, it
won't return any.
If fully_qualified_name is not NULL, set it to point to the full name
returned by the resolver, if this is different to what it is given, unless
the returned name starts with "*" as some nameservers seem to be returning
wildcards in this form.
Arguments:
dnsa pointer to dns_answer structure
name domain name to look up
type DNS record type (T_A, T_MX, etc)
fully_qualified_name if not NULL, return the returned name here if its
contents are different (i.e. it must be preset)
Returns: DNS_SUCCEED successful lookup
DNS_NOMATCH name not found
DNS_NODATA no data found
DNS_AGAIN soft failure, try again later
DNS_FAIL DNS failure
*/
int
dns_lookup(dns_answer *dnsa, uschar *name, int type, uschar **fully_qualified_name)
{
int i;
uschar *orig_name = name;
/* Loop to follow CNAME chains so far, but no further... */
for (i = 0; i < 10; i++)
{
uschar data[256];
dns_record *rr, cname_rr, type_rr;
dns_scan dnss;
int datalen, rc;
/* DNS lookup failures get passed straight back. */
if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) return rc;
/* We should have either records of the required type, or a CNAME record,
or both. We need to know whether both exist for getting the fully qualified
name, but avoid scanning more than necessary. Note that we must copy the
contents of any rr blocks returned by dns_next_rr() as they use the same
area in the dnsa block. */
cname_rr.data = type_rr.data = NULL;
for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
rr != NULL;
rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
{
if (rr->type == type)
{
if (type_rr.data == NULL) type_rr = *rr;
if (cname_rr.data != NULL) break;
}
else if (rr->type == T_CNAME) cname_rr = *rr;
}
/* For the first time round this loop, if a CNAME was found, take the fully
qualified name from it; otherwise from the first data record, if present. */
if (i == 0 && fully_qualified_name != NULL)
{
if (cname_rr.data != NULL)
{
if (Ustrcmp(cname_rr.name, *fully_qualified_name) != 0 &&
cname_rr.name[0] != '*')
*fully_qualified_name = string_copy_dnsdomain(cname_rr.name);
}
else if (type_rr.data != NULL)
{
if (Ustrcmp(type_rr.name, *fully_qualified_name) != 0 &&
type_rr.name[0] != '*')
*fully_qualified_name = string_copy_dnsdomain(type_rr.name);
}
}
/* If any data records of the correct type were found, we are done. */
if (type_rr.data != NULL) return DNS_SUCCEED;
/* If there are no data records, we need to re-scan the DNS using the
domain given in the CNAME record, which should exist (otherwise we should
have had a failure from dns_lookup). However code against the possibility of
its not existing. */
if (cname_rr.data == NULL) return DNS_FAIL;
datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256);
if (datalen < 0) return DNS_FAIL;
name = data;
DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name);
} /* Loop back to do another lookup */
/*Control reaches here after 10 times round the CNAME loop. Something isn't
right... */
log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name);
return DNS_FAIL;
}
/************************************************
* Do a DNS lookup and handle virtual types *
************************************************/
/* This function handles some invented "lookup types" that synthesize feature
not available in the basic types. The special types all have negative values.
Positive type values are passed straight on to dns_lookup().
Arguments:
dnsa pointer to dns_answer structure
name domain name to look up
type DNS record type (T_A, T_MX, etc or a "special")
fully_qualified_name if not NULL, return the returned name here if its
contents are different (i.e. it must be preset)
Returns: DNS_SUCCEED successful lookup
DNS_NOMATCH name not found
DNS_NODATA no data found
DNS_AGAIN soft failure, try again later
DNS_FAIL DNS failure
*/
int
dns_special_lookup(dns_answer *dnsa, uschar *name, int type,
uschar **fully_qualified_name)
{
if (type >= 0) return dns_lookup(dnsa, name, type, fully_qualified_name);
/* The "mx hosts only" type doesn't require any special action here */
if (type == T_MXH) return dns_lookup(dnsa, name, T_MX, fully_qualified_name);
/* Find nameservers for the domain or the nearest enclosing zone, excluding the
root servers. */
if (type == T_ZNS)
{
uschar *d = name;
while (d != 0)
{
int rc = dns_lookup(dnsa, d, T_NS, fully_qualified_name);
if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc;
while (*d != 0 && *d != '.') d++;
if (*d++ == 0) break;
}
return DNS_NOMATCH;
}
/* Try to look up the Client SMTP Authorization SRV record for the name. If
there isn't one, search from the top downwards for a CSA record in a parent
domain, which might be making assertions about subdomains. If we find a record
we set fully_qualified_name to whichever lookup succeeded, so that the caller
can tell whether to look at the explicit authorization field or the subdomain
assertion field. */
if (type == T_CSA)
{
uschar *srvname, *namesuff, *tld, *p;
int priority, weight, port;
int limit, rc, i;
BOOL ipv6;
dns_record *rr;
dns_scan dnss;
DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name);
srvname = string_sprintf("_client._smtp.%s", name);
rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
if (rc == DNS_SUCCEED || rc == DNS_AGAIN)
{
if (rc == DNS_SUCCEED) *fully_qualified_name = name;
return rc;
}
/* Search for CSA subdomain assertion SRV records from the top downwards,
starting with the 2nd level domain. This order maximizes cache-friendliness.
We skip the top level domains to avoid loading their nameservers and because
we know they'll never have CSA SRV records. */
namesuff = Ustrrchr(name, '.');
if (namesuff == NULL) return DNS_NOMATCH;
tld = namesuff + 1;
ipv6 = FALSE;
limit = dns_csa_search_limit;
/* Use more appropriate search parameters if we are in the reverse DNS. */
if (strcmpic(namesuff, US".arpa") == 0)
{
if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0)
{
namesuff -= 8;
tld = namesuff + 1;
limit = 3;
}
else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0)
{
namesuff -= 4;
tld = namesuff + 1;
ipv6 = TRUE;
limit = 3;
}
}
DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld);
/* Do not perform the search if the top level or 2nd level domains do not
exist. This is quite common, and when it occurs all the search queries would
go to the root or TLD name servers, which is not friendly. So we check the
AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then
the TLD or the 2LD (respectively) doesn't exist and we can skip the search.
If the TLD and the 2LD exist but the explicit CSA record lookup failed, then
the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */
if (rc == DNS_NOMATCH)
{
/* This is really gross. The successful return value from res_search() is
the packet length, which is stored in dnsa->answerlen. If we get a
negative DNS reply then res_search() returns -1, which causes the bounds
checks for name decompression to fail when it is treated as a packet
length, which in turn causes the authority search to fail. The correct
packet length has been lost inside libresolv, so we have to guess a
replacement value. (The only way to fix this properly would be to
re-implement res_search() and res_query() so that they don't muddle their
success and packet length return values.) For added safety we only reset
the packet length if the packet header looks plausible. */
HEADER *h = (HEADER *)dnsa->answer;
if (h->qr == 1 && h->opcode == QUERY && h->tc == 0
&& (h->rcode == NOERROR || h->rcode == NXDOMAIN)
&& ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0
&& ntohs(h->nscount) >= 1)
dnsa->answerlen = MAXPACKET;
for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
rr != NULL;
rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
if (rr->type != T_SOA) continue;
else if (strcmpic(rr->name, US"") == 0 ||
strcmpic(rr->name, tld) == 0) return DNS_NOMATCH;
else break;
}
for (i = 0; i < limit; i++)
{
if (ipv6)
{
/* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP
address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */
namesuff -= 8;
if (namesuff <= name) return DNS_NOMATCH;
}
else
/* Find the start of the preceding domain name label. */
do
if (--namesuff <= name) return DNS_NOMATCH;
while (*namesuff != '.');
DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1);
srvname = string_sprintf("_client._smtp.%s", namesuff + 1);
rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
if (rc == DNS_AGAIN) return rc;
if (rc != DNS_SUCCEED) continue;
/* Check that the SRV record we have found is worth returning. We don't
just return the first one we find, because some lower level SRV record
might make stricter assertions than its parent domain. */
for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
rr != NULL;
rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
{
if (rr->type != T_SRV) continue;
/* Extract the numerical SRV fields (p is incremented) */
p = rr->data;
GETSHORT(priority, p);
GETSHORT(weight, p);
GETSHORT(port, p);
/* Check the CSA version number */
if (priority != 1) continue;
/* If it's making an interesting assertion, return this response. */
if (port & 1)
{
*fully_qualified_name = namesuff + 1;
return DNS_SUCCEED;
}
}
}
return DNS_NOMATCH;
}
/* Control should never reach here */
return DNS_FAIL;
}
/* Support for A6 records has been commented out since they were demoted to
experimental status at IETF 51. */
#if HAVE_IPV6 && defined(SUPPORT_A6)
/*************************************************
* Search DNS block for prefix RRs *
*************************************************/
/* Called from dns_complete_a6() to search an additional section or a main
answer section for required prefix records to complete an IPv6 address obtained
from an A6 record. For each prefix record, a recursive call to dns_complete_a6
is made, with a new copy of the address so far.
Arguments:
dnsa the DNS answer block
which RESET_ADDITIONAL or RESET_ANSWERS
name name of prefix record
yptrptr pointer to the pointer that points to where to hang the next
dns_address structure
bits number of bits we have already got
bitvec the bits we have already got
Returns: TRUE if any records were found
*/
static BOOL
dns_find_prefix(dns_answer *dnsa, int which, uschar *name, dns_address
***yptrptr, int bits, uschar *bitvec)
{
BOOL yield = FALSE;
dns_record *rr;
dns_scan dnss;
for (rr = dns_next_rr(dnsa, &dnss, which);
rr != NULL;
rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
{
uschar cbitvec[16];
if (rr->type != T_A6 || strcmpic(rr->name, name) != 0) continue;
yield = TRUE;
memcpy(cbitvec, bitvec, sizeof(cbitvec));
dns_complete_a6(yptrptr, dnsa, rr, bits, cbitvec);
}
return yield;
}
/*************************************************
* Follow chains of A6 records *
*************************************************/
/* A6 records may be incomplete, with pointers to other records containing more
bits of the address. There can be a tree structure, leading to a number of
addresses originating from a single initial A6 record.
Arguments:
yptrptr pointer to the pointer that points to where to hang the next
dns_address structure
dnsa the current DNS answer block
rr the RR we have at present
bits number of bits we have already got
bitvec the bits we have already got
Returns: nothing
*/
static void
dns_complete_a6(dns_address ***yptrptr, dns_answer *dnsa, dns_record *rr,
int bits, uschar *bitvec)
{
static uschar bitmask[] = { 0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80 };
uschar *p = (uschar *)(rr->data);
int prefix_len, suffix_len;
int i, j, k;
uschar *chainptr;
uschar chain[264];
dns_answer cdnsa;
/* The prefix length is the first byte. It defines the prefix which is missing
from the data in this record as a number of bits. Zero means this is the end of
a chain. The suffix is the data in this record; only sufficient bytes to hold
it are supplied. There may be zero bytes. We have to ignore trailing bits that
we have already obtained from earlier RRs in the chain. */
prefix_len = *p++; /* bits */
suffix_len = (128 - prefix_len + 7)/8; /* bytes */
/* If the prefix in this record is greater than the prefix in the previous
record in the chain, we have to ignore the record (RFC 2874). */
if (prefix_len > 128 - bits) return;
/* In this little loop, the number of bits up to and including the current byte
is held in k. If we have none of the bits in this byte, we can just or it into
the current data. If we have all of the bits in this byte, we skip it.
Otherwise, some masking has to be done. */
for (i = suffix_len - 1, j = 15, k = 8; i >= 0; i--)
{
int required = k - bits;
if (required >= 8) bitvec[j] |= p[i];
else if (required > 0) bitvec[j] |= p[i] & bitmask[required];
j--; /* I tried putting these in the "for" statement, but gcc muttered */
k += 8; /* about computed values not being used. */
}
/* If the prefix_length is zero, we are at the end of a chain. Build a
dns_address item with the current data, hang it onto the end of the chain,
adjust the hanging pointer, and we are done. */
if (prefix_len == 0)
{
dns_address *new = store_get(sizeof(dns_address) + 50);
inet_ntop(AF_INET6, bitvec, CS new->address, 50);
new->next = NULL;
**yptrptr = new;
*yptrptr = &(new->next);
return;
}
/* Prefix length is not zero. Reset the number of bits that we have collected
so far, and extract the chain name. */
bits = 128 - prefix_len;
p += suffix_len;
chainptr = chain;
while ((i = *p++) != 0)
{
if (chainptr != chain) *chainptr++ = '.';
memcpy(chainptr, p, i);
chainptr += i;
p += i;
}
*chainptr = 0;
chainptr = chain;
/* Now scan the current DNS response record to see if the additional section
contains the records we want. This processing can be cut out for testing
purposes. */
if (dns_find_prefix(dnsa, RESET_ADDITIONAL, chainptr, yptrptr, bits, bitvec))
return;
/* No chain records were found in the current DNS response block. Do a new DNS
lookup to try to find these records. This opens up the possibility of DNS
failures. We ignore them at this point; if all branches of the tree fail, there
will be no addresses at the end. */
if (dns_lookup(&cdnsa, chainptr, T_A6, NULL) == DNS_SUCCEED)
(void)dns_find_prefix(&cdnsa, RESET_ANSWERS, chainptr, yptrptr, bits, bitvec);
}
#endif /* HAVE_IPV6 && defined(SUPPORT_A6) */
/*************************************************
* Get address(es) from DNS record *
*************************************************/
/* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when
supported) for an IPv6 address. In the A6 case, there may be several addresses,
generated by following chains. A recursive function does all the hard work. A6
records now look like passing into history, so the code is only included when
explicitly asked for.
Argument:
dnsa the DNS answer block
rr the RR
Returns: pointer a chain of dns_address items
*/
dns_address *
dns_address_from_rr(dns_answer *dnsa, dns_record *rr)
{
dns_address *yield = NULL;
#if HAVE_IPV6 && defined(SUPPORT_A6)
dns_address **yieldptr = &yield;
uschar bitvec[16];
#else
dnsa = dnsa; /* Stop picky compilers warning */
#endif
if (rr->type == T_A)
{
uschar *p = (uschar *)(rr->data);
yield = store_get(sizeof(dns_address) + 20);
(void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
yield->next = NULL;
}
#if HAVE_IPV6
#ifdef SUPPORT_A6
else if (rr->type == T_A6)
{
memset(bitvec, 0, sizeof(bitvec));
dns_complete_a6(&yieldptr, dnsa, rr, 0, bitvec);
}
#endif /* SUPPORT_A6 */
else
{
yield = store_get(sizeof(dns_address) + 50);
inet_ntop(AF_INET6, (uschar *)(rr->data), CS yield->address, 50);
yield->next = NULL;
}
#endif /* HAVE_IPV6 */
return yield;
}
/* End of dns.c */
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