Adding upstream version 4.94.2.upstream/4.94.2upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1344 insertions, 0 deletions

diff --git a/src/dns.c b/src/dns.c
new file mode 100644
index 0000000..806838e
--- /dev/null
+++ b/src/dns.c
@@ -0,0 +1,1344 @@
+/*************************************************
+*     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 for interfacing with the DNS. */
+
+#include "exim.h"
+
+
+/*************************************************
+*               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 suite 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(const uschar *domain, int type, uschar *answerptr, int size)
+{
+int len = Ustrlen(domain);
+int asize = size;                  /* Locally modified */
+uschar * name;
+uschar utilname[256];
+uschar *aptr = answerptr;          /* Locally modified */
+struct stat statbuf;
+
+/* Remove terminating dot. */
+
+if (domain[len - 1] == '.') len--;
+name = string_copyn(domain, len);
+
+/* Look for the fakens utility, and if it exists, call it. */
+
+(void)string_format(utilname, sizeof(utilname), "%s/bin/fakens",
+  config_main_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] = config_main_directory;
+  argv[2] = name;
+  argv[3] = dns_text_type(type);
+  argv[4] = NULL;
+
+  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));
+
+  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 we ran out of output buffer before exhausting the return,
+  carry on reading and counting it. */
+
+  if (asize == 0)
+    while ((rc = read(outfd, name, sizeof(name))) > 0)
+      len += rc;
+
+  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");
+    }
+  }
+else
+  {
+  DEBUG(D_dns) debug_printf("fakens (%s) not found\n", utilname);
+  }
+
+/* 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
+  use_dnssec        TRUE to set the RES_USE_DNSSEC option
+
+Returns:            nothing
+*/
+
+void
+dns_init(BOOL qualify_single, BOOL search_parents, BOOL use_dnssec)
+{
+res_state resp = os_get_dns_resolver_res();
+
+if ((resp->options & RES_INIT) == 0)
+  {
+  DEBUG(D_resolver) resp->options |= RES_DEBUG;     /* For Cygwin */
+  os_put_dns_resolver_res(resp);
+  res_init();
+  DEBUG(D_resolver) resp->options |= RES_DEBUG;
+  os_put_dns_resolver_res(resp);
+  }
+
+resp->options &= ~(RES_DNSRCH | RES_DEFNAMES);
+resp->options |= (qualify_single? RES_DEFNAMES : 0) |
+                (search_parents? RES_DNSRCH : 0);
+if (dns_retrans > 0) resp->retrans = dns_retrans;
+if (dns_retry > 0) resp->retry = dns_retry;
+
+#ifdef RES_USE_EDNS0
+if (dns_use_edns0 >= 0)
+  {
+  if (dns_use_edns0)
+    resp->options |= RES_USE_EDNS0;
+  else
+    resp->options &= ~RES_USE_EDNS0;
+  DEBUG(D_resolver)
+    debug_printf("Coerced resolver EDNS0 support %s.\n",
+        dns_use_edns0 ? "on" : "off");
+  }
+#else
+if (dns_use_edns0 >= 0)
+  DEBUG(D_resolver)
+    debug_printf("Unable to %sset EDNS0 without resolver support.\n",
+        dns_use_edns0 ? "" : "un");
+#endif
+
+#ifndef DISABLE_DNSSEC
+# ifdef RES_USE_DNSSEC
+#  ifndef RES_USE_EDNS0
+#   error Have RES_USE_DNSSEC but not RES_USE_EDNS0?  Something hinky ...
+#  endif
+if (use_dnssec)
+  resp->options |= RES_USE_DNSSEC;
+if (dns_dnssec_ok >= 0)
+  {
+  if (dns_use_edns0 == 0 && dns_dnssec_ok != 0)
+    {
+    DEBUG(D_resolver)
+      debug_printf("CONFLICT: dns_use_edns0 forced false, dns_dnssec_ok forced true, ignoring latter!\n");
+    }
+  else
+    {
+    if (dns_dnssec_ok)
+      resp->options |= RES_USE_DNSSEC;
+    else
+      resp->options &= ~RES_USE_DNSSEC;
+    DEBUG(D_resolver) debug_printf("Coerced resolver DNSSEC support %s.\n",
+        dns_dnssec_ok ? "on" : "off");
+    }
+  }
+# else
+if (dns_dnssec_ok >= 0)
+  DEBUG(D_resolver)
+    debug_printf("Unable to %sset DNSSEC without resolver support.\n",
+        dns_dnssec_ok ? "" : "un");
+if (use_dnssec)
+  DEBUG(D_resolver)
+    debug_printf("Unable to set DNSSEC without resolver support.\n");
+# endif
+#endif /* DISABLE_DNSSEC */
+
+os_put_dns_resolver_res(resp);
+}
+
+
+
+/*************************************************
+*       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
+
+Returns:     an allocated string
+*/
+
+uschar *
+dns_build_reverse(const uschar * string)
+{
+const uschar * p = string + Ustrlen(string);
+gstring * g = NULL;
+
+/* Handle IPv4 address */
+
+#if HAVE_IPV6
+if (Ustrchr(string, ':') == NULL)
+#endif
+  {
+  for (int i = 0; i < 4; i++)
+    {
+    const uschar * ppp = p;
+    while (ppp > string && ppp[-1] != '.') ppp--;
+    g = string_catn(g, ppp, p - ppp);
+    g = string_catn(g, US".", 1);
+    p = ppp - 1;
+    }
+  g = string_catn(g, US"in-addr.arpa", 12);
+  }
+
+/* Handle IPv6 address; convert to binary so as to fill out any
+abbreviation in the textual form. */
+
+#if HAVE_IPV6
+else
+  {
+  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 (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
+  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 (int i = 0; i < 4; i++)
+    {
+    sprintf(pp, "%08X", v6[i]);
+    pp += 8;
+    }
+  Ustrcpy(pp, US"].ip6.arpa.");
+  **************************************************/
+
+  }
+#endif
+return string_from_gstring(g);
+}
+
+
+
+
+/* Increment the aptr in dnss, checking against dnsa length.
+Return: TRUE for a bad result
+*/
+static BOOL
+dnss_inc_aptr(const dns_answer * dnsa, dns_scan * dnss, unsigned delta)
+{
+return (dnss->aptr += delta) >= dnsa->answer + dnsa->answerlen;
+}
+
+/*************************************************
+*       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 specifying what portion to scan, as described above
+
+Returns:    next dns record, or NULL when no more
+*/
+
+dns_record *
+dns_next_rr(const dns_answer *dnsa, dns_scan *dnss, int reset)
+{
+const HEADER * h = (const HEADER *)dnsa->answer;
+int namelen;
+
+char * trace = NULL;
+#ifdef rr_trace
+# define TRACE DEBUG(D_dns)
+#else
+trace = trace;
+# define TRACE if (FALSE)
+#endif
+
+/* Reset the saved data when requested to, and skip to the first required RR */
+
+if (reset != RESET_NEXT)
+  {
+  dnss->rrcount = ntohs(h->qdcount);
+  TRACE debug_printf("%s: reset (Q rrcount %d)\n", __FUNCTION__, dnss->rrcount);
+  dnss->aptr = dnsa->answer + sizeof(HEADER);
+
+  /* Skip over questions; failure to expand the name just gives up */
+
+  while (dnss->rrcount-- > 0)
+    {
+    TRACE trace = "Q-namelen";
+    namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
+      dnss->aptr, (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME);
+    if (namelen < 0) goto null_return;
+    /* skip name & type & class */
+    TRACE trace = "Q-skip";
+    if (dnss_inc_aptr(dnsa, dnss, namelen+4)) goto null_return;
+    }
+
+  /* Get the number of answer records. */
+
+  dnss->rrcount = ntohs(h->ancount);
+  TRACE debug_printf("%s: reset (A rrcount %d)\n", __FUNCTION__, dnss->rrcount);
+
+  /* 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)
+    {
+    TRACE debug_printf("%s: additional\n", __FUNCTION__);
+    dnss->rrcount += ntohs(h->nscount);
+    TRACE debug_printf("%s: reset (NS rrcount %d)\n", __FUNCTION__, dnss->rrcount);
+    }
+
+  if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL)
+    {
+    TRACE if (reset == RESET_AUTHORITY)
+      debug_printf("%s: authority\n", __FUNCTION__);
+    while (dnss->rrcount-- > 0)
+      {
+      TRACE trace = "A-namelen";
+      namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
+        dnss->aptr, (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME);
+      if (namelen < 0) goto null_return;
+      /* skip name, type, class & TTL */
+      TRACE trace = "A-hdr";
+      if (dnss_inc_aptr(dnsa, dnss, namelen+8)) goto null_return;
+      GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */
+      /* skip over it */
+      TRACE trace = "A-skip";
+      if (dnss_inc_aptr(dnsa, dnss, dnss->srr.size)) goto null_return;
+      }
+    dnss->rrcount = reset == RESET_AUTHORITY
+      ? ntohs(h->nscount) : ntohs(h->arcount);
+    TRACE debug_printf("%s: reset (%s rrcount %d)\n", __FUNCTION__,
+      reset == RESET_AUTHORITY ? "NS" : "AR", dnss->rrcount);
+    }
+  TRACE debug_printf("%s: %d RRs to read\n", __FUNCTION__, dnss->rrcount);
+  }
+else
+  TRACE debug_printf("%s: next (%d left)\n", __FUNCTION__, dnss->rrcount);
+
+/* 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). */
+
+TRACE trace = "R-namelen";
+namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr,
+  (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME);
+if (namelen < 0) goto null_return;
+
+/* Move the pointer past the name and fill in the rest of the data structure
+from the following bytes. */
+
+TRACE trace = "R-name";
+if (dnss_inc_aptr(dnsa, dnss, namelen)) goto null_return;
+
+GETSHORT(dnss->srr.type, dnss->aptr);		/* Record type */
+TRACE trace = "R-class";
+if (dnss_inc_aptr(dnsa, dnss, 2)) goto null_return;	/* Don't want class */
+GETLONG(dnss->srr.ttl, dnss->aptr);		/* TTL */
+GETSHORT(dnss->srr.size, dnss->aptr);		/* Size of data portion */
+dnss->srr.data = dnss->aptr;			/* The record's data follows */
+
+/* Unchecked increment ok here since no further access on this iteration;
+will be checked on next at "R-name". */
+
+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. */
+
+TRACE debug_printf("%s: return %s\n", __FUNCTION__, dns_text_type(dnss->srr.type));
+return &dnss->srr;
+
+null_return:
+  TRACE debug_printf("%s: terminate (%d RRs left). Last op: %s; errno %d %s\n",
+    __FUNCTION__, dnss->rrcount, trace, errno, strerror(errno));
+  dnss->rrcount = 0;
+  return NULL;
+}
+
+
+/* Extract the AUTHORITY information from the answer. If the answer isn't
+authoritative (AA not set), we do not extract anything.
+
+The AUTHORITY section contains NS records if the name in question was found,
+it contains a SOA record otherwise. (This is just from experience and some
+tests, is there some spec?)
+
+Scan the whole AUTHORITY section, since it may contain other records
+(e.g. NSEC3) too.
+
+Return: name for the authority, in an allocated string, or NULL if none found */
+
+static const uschar *
+dns_extract_auth_name(const dns_answer * dnsa)	/* FIXME: const dns_answer */
+{
+dns_scan dnss;
+const HEADER * h = (const HEADER *) dnsa->answer;
+
+if (h->nscount && h->aa)
+  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);
+return NULL;
+}
+
+
+
+
+/*************************************************
+*    Return whether AD bit set in DNS result     *
+*************************************************/
+
+/* We do not perform DNSSEC work ourselves; if the administrator has installed
+a verifying resolver which sets AD as appropriate, though, we'll use that.
+(AD = Authentic Data, AA = Authoritative Answer)
+
+Argument:   pointer to dns answer block
+Returns:    bool indicating presence of AD bit
+*/
+
+BOOL
+dns_is_secure(const dns_answer * dnsa)
+{
+#ifdef DISABLE_DNSSEC
+DEBUG(D_dns)
+  debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n");
+return FALSE;
+#else
+const HEADER * h = (const HEADER *) dnsa->answer;
+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 (  !h->aa
+   || !dns_trust_aa
+   || !(trusted = expand_string(dns_trust_aa))
+   || !*trusted
+   || !(auth_name = dns_extract_auth_name(dnsa))
+   || OK != match_isinlist(auth_name, &trusted, 0, &domainlist_anchor, NULL,
+			    MCL_DOMAIN, TRUE, NULL)
+   )
+  return FALSE;
+
+DEBUG(D_dns) debug_printf("DNS faked the AD bit "
+  "(got AA and matched with dns_trust_aa (%s in %s))\n",
+  auth_name, dns_trust_aa);
+
+return TRUE;
+#endif
+}
+
+static void
+dns_set_insecure(dns_answer * dnsa)
+{
+#ifndef DISABLE_DNSSEC
+HEADER * h = (HEADER *)dnsa->answer;
+h->aa = h->ad = 0;
+#endif
+}
+
+/************************************************
+ *	Check whether the AA bit is set		*
+ *	We need this to warn if we requested AD *
+ *	from an authoritative server		*
+ ************************************************/
+
+BOOL
+dns_is_aa(const dns_answer * dnsa)
+{
+#ifdef DISABLE_DNSSEC
+return FALSE;
+#else
+return dnsa->answerlen >= 0 && ((const HEADER *)dnsa->answer)->aa;
+#endif
+}
+
+
+
+/*************************************************
+*            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_SPF:   return US"SPF";
+  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_TLSA:  return US"TLSA";
+  default:      return US"?";
+  }
+}
+
+
+
+/*************************************************
+*        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
+caching.
+
+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_fail_return(const uschar * name, int type, time_t expiry, int rc)
+{
+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               *
+*************************************************/
+
+/* 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-
+Authoritative 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.
+
+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
+  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, const uschar * name, int type)
+{
+int rc;
+#ifndef STAND_ALONE
+const uschar * save_domain;
+#endif
+
+/* 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.
+*/
+
+if ((rc = dns_fail_cache_hit(name, type)) > 0)
+  {
+  dnsa->answerlen = -1;
+  return rc;
+  }
+
+#ifdef SUPPORT_I18N
+/* Convert all names to a-label form before doing lookup */
+  {
+  uschar * alabel;
+  uschar * errstr = NULL;
+  DEBUG(D_dns) if (string_is_utf8(name))
+    debug_printf("convert utf8 '%s' to alabel for for lookup\n", name);
+  if ((alabel = string_domain_utf8_to_alabel(name, &errstr)), errstr)
+    {
+    DEBUG(D_dns)
+      debug_printf("DNS name '%s' utf8 conversion to alabel failed: %s\n", name,
+        errstr);
+    f.host_find_failed_syntax = TRUE;
+    return DNS_NOMATCH;
+    }
+  name = alabel;
+  }
+#endif
+
+/* If configured, check the hygiene 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 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)
+  {
+  int ovector[3*(EXPAND_MAXN+1)];
+
+  dns_pattern_init();
+  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));
+    f.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 ((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. */
+
+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));
+
+if (dnsa->answerlen > (int) sizeof(dnsa->answer))
+  {
+  DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet"
+    " (size %d), truncating to %u.\n",
+    name, dns_text_type(type), dnsa->answerlen, (unsigned int) sizeof(dnsa->answer));
+  dnsa->answerlen = sizeof(dnsa->answer);
+  }
+
+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_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",
+      name, dns_text_type(type));
+
+    /* Cut this out for various test programs */
+#ifndef STAND_ALONE
+    save_domain = deliver_domain;
+    deliver_domain = string_copy(name);  /* set $domain */
+    rc = match_isinlist(name, CUSS &dns_again_means_nonexist, 0,
+      &domainlist_anchor, NULL, MCL_DOMAIN, TRUE, NULL);
+    deliver_domain = save_domain;
+    if (rc != OK)
+      {
+      DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
+      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_fail_return(name, type, dns_expire_from_soa(dnsa, type), DNS_NOMATCH);
+
+#else   /* For stand-alone tests */
+    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_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_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_fail_return(name, type, 0, 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.
+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
+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.  In international mode "different" means "alabel
+forms are different".
+
+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, const uschar *name, int type,
+  const uschar **fully_qualified_name)
+{
+const uschar *orig_name = name;
+BOOL secure_so_far = TRUE;
+
+/* 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 (int i = 0; i <= dns_cname_loops; i++)
+  {
+  uschar * data;
+  dns_record cname_rr, type_rr;
+  dns_scan dnss;
+  int 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 (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
+       rr; 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)
+    {
+    uschar * rr_name = cname_rr.data
+      ? cname_rr.name : type_rr.data ? type_rr.name : NULL;
+    if (  rr_name
+       && Ustrcmp(rr_name, *fully_qualified_name) != 0
+       && rr_name[0] != '*'
+#ifdef SUPPORT_I18N
+       && (  !string_is_utf8(*fully_qualified_name)
+	  || Ustrcmp(rr_name,
+	       string_domain_utf8_to_alabel(*fully_qualified_name, NULL)) != 0
+	  )
+#endif
+       )
+        *fully_qualified_name = string_copy_dnsdomain(rr_name);
+    }
+
+  /* If any data records of the correct type were found, we are done. */
+
+  if (type_rr.data)
+    {
+    if (!secure_so_far)	/* mark insecure if any element of CNAME chain was */
+      dns_set_insecure(dnsa);
+    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)
+    return DNS_FAIL;
+
+  /* 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;
+
+  if (!dns_is_secure(dnsa))
+    secure_so_far = FALSE;
+
+  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 features
+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, const uschar *name, int type,
+  const uschar **fully_qualified_name)
+{
+switch (type)
+  {
+  /* The "mx hosts only" type doesn't require any special action here */
+  case 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. */
+  case T_ZNS:
+    type = T_NS;
+    /* FALLTHROUGH */
+  case T_SOA:
+    {
+    const uschar *d = name;
+    while (d != 0)
+      {
+      int rc = dns_lookup(dnsa, d, type, 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. */
+  case T_CSA:
+    {
+    uschar *srvname, *namesuff, *tld;
+    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 = string_copy(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)
+      {
+      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)
+	  )
+	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; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) if (rr->type == T_SRV)
+	{
+	const uschar * p = rr->data;
+
+	/* Extract the numerical SRV fields (p is incremented) */
+	GETSHORT(priority, p);
+	GETSHORT(weight, p);	weight = weight; /* compiler quietening */
+	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;
+    }
+
+  default:
+    if (type >= 0)
+      return dns_lookup(dnsa, name, type, fully_qualified_name);
+  }
+
+/* Control should never reach here */
+
+return DNS_FAIL;
+}
+
+
+
+
+
+/*************************************************
+*          Get address(es) from DNS record       *
+*************************************************/
+
+/* The record type is either T_A for an IPv4 address or T_AAAA for an IPv6 address.
+
+Argument:
+  dnsa       the DNS answer block
+  rr         the RR
+
+Returns:     pointer to a chain of dns_address items; NULL when the dnsa was overrun
+*/
+
+dns_address *
+dns_address_from_rr(dns_answer *dnsa, dns_record *rr)
+{
+dns_address * yield = NULL;
+uschar * dnsa_lim = dnsa->answer + dnsa->answerlen;
+
+if (rr->type == T_A)
+  {
+  uschar *p = US rr->data;
+  if (p + 4 <= dnsa_lim)
+    {
+    /* 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 HAVE_IPV6
+
+else
+  {
+  if (rr->data + 16 <= dnsa_lim)
+    {
+    struct in6_addr in6;
+    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;
+    }
+  }
+#endif  /* HAVE_IPV6 */
+
+return yield;
+}
+
+
+
+void
+dns_pattern_init(void)
+{
+if (check_dns_names_pattern[0] != 0 && !regex_check_dns_names)
+  regex_check_dns_names =
+    regex_must_compile(check_dns_names_pattern, FALSE, TRUE);
+}
+
+/* vi: aw ai sw=2
+*/
+/* End of dns.c */