-/* $Cambridge: exim/src/src/dns.c,v 1.2 2004/11/19 09:45:54 ph10 Exp $ */
+/* $Cambridge: exim/src/src/dns.c,v 1.13 2006/02/07 11:19:00 ph10 Exp $ */
/*************************************************
* Exim - an Internet mail transport agent *
*************************************************/
-/* Copyright (c) University of Cambridge 1995 - 2004 */
+/* Copyright (c) University of Cambridge 1995 - 2006 */
/* See the file NOTICE for conditions of use and distribution. */
/* Functions for interfacing with the DNS. */
#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 *
*************************************************/
/* Call this with reset == RESET_ANSWERS to scan the answer block, 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.
+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->rrcount = ntohs(h->ancount);
- /* Skip over answers and NS records if wanting to look at the additional
+ /* 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)
+ if (reset == RESET_ADDITIONAL) dnss->rrcount += ntohs(h->nscount);
+
+ if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL)
{
- dnss->rrcount += ntohs(h->nscount);
while (dnss->rrcount-- > 0)
{
namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */
dnss->aptr += dnss->srr.size; /* skip over it */
}
- dnss->rrcount = ntohs(h->arcount);
+ 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. */
* Turn DNS type into text *
*************************************************/
-/* Turn the coded record type into a string for printing.
+/* 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
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";
+ case T_CNAME: return US"CNAME";
default: return US"?";
}
}
int
dns_basic_lookup(dns_answer *dnsa, uschar *name, int type)
{
+int rc = -1;
#ifndef STAND_ALONE
-int rc;
uschar *save;
#endif
return previous->data.val;
}
-/* If we are running in the test harness, recognize a couple of special
-names that always give error returns. This makes it straightforward to
-test the handling of DNS errors. */
-
-if (running_in_test_harness)
- {
- uschar *endname = name + Ustrlen(name);
- if (Ustrcmp(endname - 14, "test.again.dns") == 0)
- {
- int delay = Uatoi(name); /* digits at the start of the name */
- DEBUG(D_dns) debug_printf("Real DNS lookup of %s (%s) bypassed for testing\n",
- name, dns_text_type(type));
- if (delay > 0)
- {
- DEBUG(D_dns) debug_printf("delaying %d seconds\n", delay);
- sleep(delay);
- }
- DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
- return dns_return(name, type, DNS_AGAIN);
- }
- if (Ustrcmp(endname - 13, "test.fail.dns") == 0)
- {
- DEBUG(D_dns) debug_printf("Real DNS lookup of %s (%s) bypassed for testing\n",
- name, dns_text_type(type));
- DEBUG(D_dns) debug_printf("returning DNS_FAIL\n");
- return dns_return(name, type, DNS_FAIL);
- }
- }
-
/* 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
#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. */
+number of bytes the message would need, so we need to check for this case. The
+effect is to truncate overlong data.
+
+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);
-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)
* 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.
+/* 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:
*/
int
-dns_special_lookup(dns_answer *dnsa, uschar *name, int type,
+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);
-/* Find nameservers for the domain or the nearest enclosing zone, excluding the
+/* 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)
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;
+ 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;
+ }
}
- return DNS_NOMATCH;
- }
+
+ 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 */
projects / exim.git / blobdiff