Redesign the interaction between DNSSEC vaildation and per-domain servers.

This should just work in all cases now. If the normal chain-of-trust exists into
the delegated domain then whether the domain is signed or not, DNSSEC
validation will function normally. In the case the delgated domain
is an "overlay" on top of the global DNS and no NS and/or DS records
exist connecting it to the global dns, then if the domain is
unsigned the situation will be handled by synthesising a
proof-of-non-existance-of-DS for the domain and queries will be
answered unvalidated; this action will be logged. A signed domain
without chain-of-trust can be validated if a suitable trust-anchor
is provided using --trust-anchor.

Thanks to Uwe Kleine-König for prompting this change, and contributing
valuable insights into what could be improved.

src/dnssec.c

@@ -997,49 +997,57 @@ int dnssec_validate_ds(time_t now, struct dns_header *header, size_t plen, char
   unsigned long ttl;
   union all_addr a;
 
-  if (ntohs(header->qdcount) != 1 ||
-      !(p = skip_name(p, header, plen, 4)))
-    return STAT_BOGUS;
-  
-  GETSHORT(qtype, p);
-  GETSHORT(qclass, p);
-
-  if (qtype != T_DS || qclass != class)
-    return STAT_BOGUS;
-
-  /* A SERVFAIL answer has been seen to a DS query not at start of authority,
+   /* A SERVFAIL answer has been seen to a DS query not at start of authority,
      so treat it as such and continue to search for a DS or proof of no existence
      further down the tree. */
   if (RCODE(header) == SERVFAIL)
     servfail = neganswer = nons = 1;
   else
-    {
-      rc = dnssec_validate_reply(now, header, plen, name, keyname, NULL, 0, &neganswer, &nons, &neg_ttl, validate_counter);
+    rc = dnssec_validate_reply(now, header, plen, name, keyname, NULL, 0, &neganswer, &nons, &neg_ttl, validate_counter);
   
+  p = (unsigned char *)(header+1);
+  if (ntohs(header->qdcount) != 1 ||
+      !extract_name(header, plen, &p, name, EXTR_NAME_EXTRACT, 4))
+    return STAT_BOGUS;
+  
+  GETSHORT(qtype, p);
+  GETSHORT(qclass, p);
+  
+  if (qtype != T_DS || qclass != class)
+    return STAT_BOGUS;
+
+  if (!servfail)
+    {
       if (STAT_ISEQUAL(rc, STAT_INSECURE))
 	{
-	  my_syslog(LOG_WARNING, _("Insecure DS reply received for %s, check domain configuration and upstream DNS server DNSSEC support"), name);
-	  log_query(F_NOEXTRA | F_UPSTREAM, name, NULL, "BOGUS DS - not secure", 0);
-	  return STAT_BOGUS | DNSSEC_FAIL_INDET;
+	  if (lookup_domain(name, F_DOMAINSRV, NULL, NULL))
+	    {
+	      my_syslog(LOG_INFO, _("Insecure reply received for DS %s, assuming non-DNSSEC domain-specific server."), name);
+	      neganswer = 1;
+	      nons = 0; /* If we're faking a DS, fake one with an NS. */
+	      neg_ttl = DNSSEC_ASSUMED_DS_TTL;
+	    }
+	  else
+	    {
+	      my_syslog(LOG_WARNING, _("Insecure DS reply received for %s, check domain configuration and upstream DNS server DNSSEC support"), name);
+	      log_query(F_NOEXTRA | F_UPSTREAM, name, NULL, "BOGUS DS - not secure", 0);
+	      return STAT_BOGUS | DNSSEC_FAIL_INDET;
+	    }
 	}
-      
-      p = (unsigned char *)(header+1);
-      if (!extract_name(header, plen, &p, name, EXTR_NAME_EXTRACT, 4))
-	return STAT_BOGUS;
-
-      p += 4; /* qtype, qclass */
-      
-      /* If the key needed to validate the DS is on the same domain as the DS, we'll
-	 loop getting nowhere. Stop that now. This can happen of the DS answer comes
-	 from the DS's zone, and not the parent zone. */
-      if (STAT_ISEQUAL(rc, STAT_NEED_KEY) && hostname_isequal(name, keyname))
+      else
 	{
-	  log_query(F_NOEXTRA | F_UPSTREAM, name, NULL, "BOGUS DS", 0);
-	  return STAT_BOGUS;
+	  if (STAT_ISEQUAL(rc, STAT_NEED_KEY) && hostname_isequal(name, keyname))
+	    {
+	      /* If the key needed to validate the DS is on the same domain as the DS, we'll
+		 loop getting nowhere. Stop that now. This can happen of the DS answer comes
+		 from the DS's zone, and not the parent zone. */
+	      log_query(F_NOEXTRA | F_UPSTREAM, name, NULL, "BOGUS DS", 0);
+	      return STAT_BOGUS;
+	    }
+
+	  if (!STAT_ISEQUAL(rc, STAT_SECURE))
+	    return rc;
 	}
-  
-      if (!STAT_ISEQUAL(rc, STAT_SECURE))
-	return rc;
     }
   
   if (!neganswer)
@@ -1129,9 +1137,19 @@ int dnssec_validate_ds(time_t now, struct dns_header *header, size_t plen, char
       /* We only cache validated DS records, DNSSECOK flag hijacked 
 	 to store presence/absence of NS. */
       if (nons)
-	flags &= ~F_DNSSECOK;
+	{
+	  if (lookup_domain(name, F_DOMAINSRV, NULL, NULL))
+	    {
+	      my_syslog(LOG_WARNING, _("Negative DS reply without NS record received for %s, assuming non-DNSSEC domain-specific server."), name);
+	      nons = 0;
+	    }
+	  else
+	    /* We only cache validated DS records, DNSSECOK flag hijacked 
+	       to store presence/absence of NS. */
+	    flags &= ~F_DNSSECOK;
+	}
     }
-  
+
   cache_start_insert();
   
   /* Use TTL from NSEC for negative cache entries */
@@ -2155,7 +2173,9 @@ int dnssec_validate_reply(time_t now, struct dns_header *header, size_t plen, ch
 	/* NXDOMAIN or NODATA reply, unanswered question is (name, qclass, qtype) */
 	
 	/* For anything other than a DS record, this situation is OK if either
-	   the answer is in an unsigned zone, or there's a NSEC records. */
+	   the answer is in an unsigned zone, or there's NSEC records.
+	   For a DS record, we return INSECURE, which almost always turns
+	   into BOGUS in the caller. */
 	if ((rc_nsec = prove_non_existence(header, plen, keyname, name, qtype, qclass, NULL, nons, nsec_ttl, validate_counter)) != 0)
 	  {
 	    if (rc_nsec & DNSSEC_FAIL_WORK)
@@ -2163,7 +2183,7 @@ int dnssec_validate_reply(time_t now, struct dns_header *header, size_t plen, ch
 
 	    /* Empty DS without NSECS */
 	    if (qtype == T_DS)
-	      return STAT_BOGUS | rc_nsec;
+	      return STAT_INSECURE;
 	    
 	    if ((rc_nsec & (DNSSEC_FAIL_NONSEC | DNSSEC_FAIL_NSEC3_ITERS)) &&
 		!STAT_ISEQUAL((rc = zone_status(name, qclass, keyname, now)), STAT_SECURE))