* Exim - an Internet mail transport agent *
*************************************************/
-/* Copyright (c) University of Cambridge 1995 - 2017 */
+/* Copyright (c) University of Cambridge 1995 - 2018 */
/* See the file NOTICE for conditions of use and distribution. */
/* Functions for interfacing with the DNS. */
#include "exim.h"
-
/*************************************************
* Fake DNS resolver *
*************************************************/
{
int len = Ustrlen(domain);
int asize = size; /* Locally modified */
-uschar name[256];
+uschar * name;
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;
+name = string_copyn(domain, len);
/* Look for the fakens utility, and if it exists, call it. */
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));
+ DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n",
+ name, dns_text_type(type));
argv[0] = utilname;
argv[1] = config_main_directory;
argv[3] = dns_text_type(type);
argv[4] = NULL;
- pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE);
+ pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE, US"fakens-search");
if (pid < 0)
log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s",
strerror(errno));
Arguments:
string the IP address as a string
- buffer a suitable buffer, long enough to hold the result
-Returns: nothing
+Returns: an allocated string
*/
-void
-dns_build_reverse(const uschar *string, uschar *buffer)
+uschar *
+dns_build_reverse(const uschar * string)
{
-const uschar *p = string + Ustrlen(string);
-uschar *pp = buffer;
+const uschar * p = string + Ustrlen(string);
+gstring * g = NULL;
/* Handle IPv4 address */
if (Ustrchr(string, ':') == NULL)
#endif
{
- int i;
- for (i = 0; i < 4; i++)
+ for (int i = 0; i < 4; i++)
{
- const uschar *ppp = p;
+ const uschar * ppp = p;
while (ppp > string && ppp[-1] != '.') ppp--;
- Ustrncpy(pp, ppp, p - ppp);
- pp += p - ppp;
- *pp++ = '.';
+ g = string_catn(g, ppp, p - ppp);
+ g = string_catn(g, US".", 1);
p = ppp - 1;
}
- Ustrcpy(pp, "in-addr.arpa");
+ g = string_catn(g, US"in-addr.arpa", 12);
}
/* Handle IPv6 address; convert to binary so as to fill out any
#if HAVE_IPV6
else
{
- int i;
int v6[4];
+
+ g = string_get_tainted(32, is_tainted(string));
(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.");
+ for (int i = 3; i >= 0; i--)
+ for (int j = 0; j < 32; j += 4)
+ g = string_fmt_append(g, "%x.", (v6[i] >> j) & 15);
+ g = string_catn(g, US"ip6.arpa.", 9);
/* Another way of doing IPv6 reverse lookups was proposed in conjunction
with A6 records. However, it fell out of favour when they did. The
Ustrcpy(pp, "\\[x");
pp += 3;
- for (i = 0; i < 4; i++)
+ for (int i = 0; i < 4; i++)
{
sprintf(pp, "%08X", v6[i]);
pp += 8;
}
- Ustrcpy(pp, "].ip6.arpa.");
+ Ustrcpy(pp, US"].ip6.arpa.");
**************************************************/
}
#endif
+return string_from_gstring(g);
}
/* 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. */
+TRACE debug_printf("%s: return %s\n", __FUNCTION__, dns_text_type(dnss->srr.type));
return &dnss->srr;
null_return:
dns_extract_auth_name(const dns_answer * dnsa) /* FIXME: const dns_answer */
{
dns_scan dnss;
-dns_record * rr;
const HEADER * h = (const HEADER *) dnsa->answer;
if (h->nscount && h->aa)
- for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
+ for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
if (rr->type == (h->ancount ? T_NS : T_SOA))
return string_copy(rr->name);
const uschar * auth_name;
const uschar * trusted;
+if (dnsa->answerlen < 0) return FALSE;
+/* Beware that newer versions of glibc on Linux will filter out the ad bit
+unless their shiny new RES_TRUSTAD bit is set for the resolver. */
if (h->ad) return TRUE;
-/* If the resolver we ask is authoritative for the domain in question, it
-* may not set the AD but the AA bit. If we explicitly trust
-* the resolver for that domain (via a domainlist in dns_trust_aa),
-* we return TRUE to indicate a secure answer.
-*/
+/* If the resolver we ask is authoritative for the domain in question, it may
+not set the AD but the AA bit. If we explicitly trust the resolver for that
+domain (via a domainlist in dns_trust_aa), we return TRUE to indicate a secure
+answer. */
if ( !h->aa
|| !dns_trust_aa
************************************************/
BOOL
-dns_is_aa(const dns_answer *dnsa)
+dns_is_aa(const dns_answer * dnsa)
{
#ifdef DISABLE_DNSSEC
return FALSE;
#else
-return ((const HEADER*)dnsa->answer)->aa;
+return dnsa->answerlen >= 0 && ((const HEADER *)dnsa->answer)->aa;
#endif
}
* Cache a failed DNS lookup result *
*************************************************/
+static void
+dns_fail_tag(uschar * buf, const uschar * name, int dns_type)
+{
+res_state resp = os_get_dns_resolver_res();
+
+/*XX buf needs to be 255 +1 + (max(typetext) == 5) +1 + max(chars_for_long-max) +1
+We truncate the name here for safety... could use a dynamic string. */
+
+sprintf(CS buf, "%.255s-%s-%lx", name, dns_text_type(dns_type),
+ (unsigned long) resp->options);
+}
+
+
/* 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
Arguments:
name the domain name
type the lookup type
+ expiry time TTL expires, or zero for unlimited
rc the return code
Returns: the return code
*/
+/* we need: 255 +1 + (max(typetext) == 5) +1 + max(chars_for_long-max) +1 */
+#define DNS_FAILTAG_MAX 290
+#define DNS_FAILNODE_SIZE \
+ (sizeof(expiring_data) + sizeof(tree_node) + DNS_FAILTAG_MAX)
+
static int
-dns_return(const uschar * name, int type, int rc)
+dns_fail_return(const uschar * name, int type, time_t expiry, int rc)
{
-res_state resp = os_get_dns_resolver_res();
-tree_node *node = store_get_perm(sizeof(tree_node) + 290);
-sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type),
- (unsigned long) resp->options);
-node->data.val = rc;
-(void)tree_insertnode(&tree_dns_fails, node);
+uschar node_name[DNS_FAILTAG_MAX];
+tree_node * previous, * new;
+expiring_data * e;
+
+dns_fail_tag(node_name, name, type);
+if ((previous = tree_search(tree_dns_fails, node_name)))
+ e = previous->data.ptr;
+else
+ {
+ e = store_get_perm(DNS_FAILNODE_SIZE, is_tainted(name));
+ new = (void *)(e+1);
+ dns_fail_tag(new->name, name, type);
+ new->data.ptr = e;
+ (void)tree_insertnode(&tree_dns_fails, new);
+ }
+
+DEBUG(D_dns) debug_printf(" %s neg-cache entry for %s, ttl %d\n",
+ previous ? "update" : "writing",
+ node_name, expiry ? (int)(expiry - time(NULL)) : -1);
+e->expiry = expiry;
+e->data.val = rc;
return rc;
}
+
+/* Return the cached result of a known-bad lookup, or -1.
+*/
+static int
+dns_fail_cache_hit(const uschar * name, int type)
+{
+uschar node_name[DNS_FAILTAG_MAX];
+tree_node * previous;
+expiring_data * e;
+int val, rc;
+
+dns_fail_tag(node_name, name, type);
+if (!(previous = tree_search(tree_dns_fails, node_name)))
+ return -1;
+
+e = previous->data.ptr;
+val = e->data.val;
+rc = e->expiry && e->expiry <= time(NULL) ? -1 : val;
+
+DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: %scached value %s%s\n",
+ name, dns_text_type(type),
+ rc == -1 ? "" : "using ",
+ val == DNS_NOMATCH ? "DNS_NOMATCH" :
+ val == DNS_NODATA ? "DNS_NODATA" :
+ val == DNS_AGAIN ? "DNS_AGAIN" :
+ val == DNS_FAIL ? "DNS_FAIL" : "??",
+ rc == -1 ? " past valid time" : "");
+
+return rc;
+}
+
+
+
+/* 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. */
+
+static void
+fake_dnsa_len_for_fail(dns_answer * dnsa, int type)
+{
+const HEADER * h = (const HEADER *)dnsa->answer;
+
+if ( h->qr == 1 /* a response */
+ && h->opcode == QUERY
+ && h->tc == 0 /* nmessage not truncated */
+ && (h->rcode == NOERROR || h->rcode == NXDOMAIN)
+ && ( ntohs(h->qdcount) == 1 /* one question record */
+ || f.running_in_test_harness)
+ && ntohs(h->ancount) == 0 /* no answer records */
+ && ntohs(h->nscount) >= 1) /* authority records */
+ {
+ DEBUG(D_dns) debug_printf("faking res_search(%s) response length as %d\n",
+ dns_text_type(type), (int)sizeof(dnsa->answer));
+ dnsa->answerlen = sizeof(dnsa->answer);
+ }
+}
+
+
+/* Return the TTL suitable for an NXDOMAIN result, which is given
+in the SOA. We hope that one was returned in the lookup, and do not
+bother doing a separate lookup; if not found return a forever TTL.
+*/
+
+time_t
+dns_expire_from_soa(dns_answer * dnsa, int type)
+{
+dns_scan dnss;
+
+fake_dnsa_len_for_fail(dnsa, type);
+
+for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
+ rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)
+ ) if (rr->type == T_SOA)
+ {
+ const uschar * p = rr->data;
+ uschar discard_buf[256];
+ int len;
+ unsigned long ttl;
+
+ /* Skip the mname & rname strings */
+
+ if ((len = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
+ p, (DN_EXPAND_ARG4_TYPE)discard_buf, 256)) < 0)
+ break;
+ p += len;
+ if ((len = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
+ p, (DN_EXPAND_ARG4_TYPE)discard_buf, 256)) < 0)
+ break;
+ p += len;
+
+ /* Skip the SOA serial, refresh, retry & expire. Grab the TTL */
+
+ if (p > dnsa->answer + dnsa->answerlen - 5 * INT32SZ)
+ break;
+ p += 4 * INT32SZ;
+ GETLONG(ttl, p);
+
+ return time(NULL) + ttl;
+ }
+DEBUG(D_dns) debug_printf("DNS: no SOA record found for neg-TTL\n");
+return 0;
+}
+
+
/*************************************************
* Do basic DNS lookup *
*************************************************/
providing a list of domains for which this is treated as a non-existent
host.
+The dns_answer structure is pretty big; enough to hold a max-sized DNS message
+- so best allocated from fast-release memory. As of writing, all our callers
+use a stack-auto variable.
+
Arguments:
dnsa pointer to dns_answer structure
name name to look up
*/
int
-dns_basic_lookup(dns_answer *dnsa, const uschar *name, int type)
+dns_basic_lookup(dns_answer * dnsa, const uschar * name, int type)
{
+int rc;
#ifndef STAND_ALONE
-int rc = -1;
-const uschar *save_domain;
+const uschar * save_domain;
#endif
-res_state resp = os_get_dns_resolver_res();
-
-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. */
+caching for successful lookups.
+*/
-sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type),
- (unsigned long) resp->options);
-if ((previous = tree_search(tree_dns_fails, node_name)))
+if ((rc = dns_fail_cache_hit(name, type)) > 0)
{
- 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;
+ dnsa->answerlen = -1;
+ return rc;
}
#ifdef SUPPORT_I18N
DEBUG(D_dns)
debug_printf("DNS name '%s' utf8 conversion to alabel failed: %s\n", name,
errstr);
- host_find_failed_syntax = TRUE;
+ f.host_find_failed_syntax = TRUE;
return DNS_NOMATCH;
}
name = alabel;
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. */
+bitstring labels don't conform to normal name syntax. (But they aren't used any
+more.) */
#ifndef STAND_ALONE /* Omit this for stand-alone tests */
if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT)
{
- const uschar *checkname = name;
int ovector[3*(EXPAND_MAXN+1)];
dns_pattern_init();
-
- /* 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 || type == T_TLSA)
- {
- while (*checkname++ != '.');
- while (*checkname++ != '.');
- }
-
- if (pcre_exec(regex_check_dns_names, NULL, CCS checkname, Ustrlen(checkname),
+ if (pcre_exec(regex_check_dns_names, NULL, CCS name, Ustrlen(name),
0, PCRE_EOPT, ovector, nelem(ovector)) < 0)
{
DEBUG(D_dns)
debug_printf("DNS name syntax check failed: %s (%s)\n", name,
dns_text_type(type));
- host_find_failed_syntax = TRUE;
+ f.host_find_failed_syntax = TRUE;
return DNS_NOMATCH;
}
}
(res_search), we call fakens_search(), which recognizes certain special
domains, and interfaces to a fake nameserver for certain special zones. */
-dnsa->answerlen = running_in_test_harness
+h_errno = 0;
+dnsa->answerlen = f.running_in_test_harness
? fakens_search(name, type, dnsa->answer, sizeof(dnsa->answer))
: res_search(CCS name, C_IN, type, dnsa->answer, sizeof(dnsa->answer));
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);
+ return dns_fail_return(name, type, dns_expire_from_soa(dnsa, type), DNS_NOMATCH);
case TRY_AGAIN:
DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n",
if (rc != OK)
{
DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
- return dns_return(name, type, DNS_AGAIN);
+ return dns_fail_return(name, type, 0, 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);
+ return dns_fail_return(name, type, dns_expire_from_soa(dnsa, type), DNS_NOMATCH);
#else /* For stand-alone tests */
- return dns_return(name, type, DNS_AGAIN);
+ return dns_fail_return(name, type, 0, 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);
+ return dns_fail_return(name, type, 0, 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);
+ return dns_fail_return(name, type, dns_expire_from_soa(dnsa, 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);
+ return dns_fail_return(name, type, 0, DNS_FAIL);
}
DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n",
/* 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.
+By default, follow one CNAME since a resolver has been seen, faced with
+an MX request and a CNAME (to an A) but no MX present, returning the CNAME.
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
dns_lookup(dns_answer *dnsa, const uschar *name, int type,
const uschar **fully_qualified_name)
{
-int i;
const uschar *orig_name = name;
BOOL secure_so_far = TRUE;
-/* Loop to follow CNAME chains so far, but no further... */
+/* By default, assume the resolver follows CNAME chains (and returns NODATA for
+an unterminated one). If it also does that for a CNAME loop, fine; if it returns
+a CNAME (maybe the last?) whine about it. However, retain the coding for dumb
+resolvers hiding behind a config variable. Loop to follow CNAME chains so far,
+but no further... The testsuite tests the latter case, mostly assuming that the
+former will work. */
-for (i = 0; i < 10; i++)
+for (int i = 0; i <= dns_cname_loops; i++)
{
uschar * data;
- dns_record *rr, cname_rr, type_rr;
+ dns_record cname_rr, type_rr;
dns_scan dnss;
- int datalen, rc;
+ int rc;
/* DNS lookup failures get passed straight back. */
area in the dnsa block. */
cname_rr.data = type_rr.data = NULL;
- for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
+ for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
if (rr->type == type)
{
if (!cname_rr.data)
return DNS_FAIL;
- data = store_get(256);
- if ((datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
- cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256)) < 0)
+ /* DNS data comes from the outside, hence tainted */
+ data = store_get(256, TRUE);
+ if (dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
+ cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256) < 0)
return DNS_FAIL;
name = data;
assertion field. */
case T_CSA:
{
- uschar *srvname, *namesuff, *tld, *p;
+ uschar *srvname, *namesuff, *tld;
int priority, weight, port;
int limit, rc, i;
BOOL ipv6;
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. */
-
- const HEADER * h = (const 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;
+ fake_dnsa_len_for_fail(dnsa, T_CSA);
for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)
uschar *p = US rr->data;
if (p + 4 <= dnsa_lim)
{
- yield = store_get(sizeof(dns_address) + 20);
+ /* the IP is not regarded as tainted */
+ yield = store_get(sizeof(dns_address) + 20, FALSE);
(void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
yield->next = NULL;
}
if (rr->data + 16 <= dnsa_lim)
{
struct in6_addr in6;
- int i;
- for (i = 0; i < 16; i++) in6.s6_addr[i] = rr->data[i];
- yield = store_get(sizeof(dns_address) + 50);
+ for (int i = 0; i < 16; i++) in6.s6_addr[i] = rr->data[i];
+ yield = store_get(sizeof(dns_address) + 50, FALSE);
inet_ntop(AF_INET6, &in6, CS yield->address, 50);
yield->next = NULL;
}
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