kdc: get_pa_etype_info_both comply with RFC4120

Heimdal's current behavior regarding the generation of PA-ETYPE-INFO2
and PA-ETYPE-INFO violates RFC4120 in two ways:

 1. when generating responding both PA-ETYPE-INFO2 and PA-ETYPE-INFO
    the hints returned in the inverse order: INFO then INFO2 instead
    of INFO2 then INFO.

 2. the determination that both PA-ETYPE-INFO2 and PA-ETYPE-INFO is
    currently based upon the KDC selected enctype when it should be
    determine based upon examining the entire enctype list specified
    by the requesting client.

This change corrects the behavior to follow the RFC4120 guidance.

Change-Id: I6ebda8a813c25f9296f10314e32e93a22380ca72

kdc/kerberos5.c

@@ -1221,28 +1221,55 @@ get_pa_etype_info2(krb5_context context,
     return 0;
 }
 
+static int
+newer_enctype_present(struct KDC_REQ_BODY_etype *etype_list)
+{
+    size_t i;
+
+    for (i = 0; i < etype_list->len; i++) {
+	if (!older_enctype(etype_list->val[i]))
+	    return 1;
+    }
+    return 0;
+}
+
 static krb5_error_code
 get_pa_etype_info_both(krb5_context context,
 		       krb5_kdc_configuration *config,
+		       struct KDC_REQ_BODY_etype *etype_list,
 		       METHOD_DATA *md, Key *ckey)
 {
     krb5_error_code ret;
 
     /*
      * RFC4120 requires:
-     * - If the client only knows about old enctypes, then send
-     *   both info replies (we send 'info' first in the list).
-     * - If the client is 'modern', because it knows about 'new'
-     *   enctype types, then only send the 'info2' reply.
+     *   When the AS server is to include pre-authentication data in a
+     *   KRB-ERROR or in an AS-REP, it MUST use PA-ETYPE-INFO2, not
+     *   PA-ETYPE-INFO, if the etype field of the client's AS-REQ lists
+     *   at least one "newer" encryption type.  Otherwise (when the etype
+     *   field of the client's AS-REQ does not list any "newer" encryption
+     *   types), it MUST send both PA-ETYPE-INFO2 and PA-ETYPE-INFO (both
+     *   with an entry for each enctype).  A "newer" enctype is any enctype
+     *   first officially specified concurrently with or subsequent to the
+     *   issue of this RFC.  The enctypes DES, 3DES, or RC4 and any defined
+     *   in [RFC1510] are not "newer" enctypes.
+     *
+     * It goes on to state:
+     *   The preferred ordering of the "hint" pre-authentication data that
+     *   affect client key selection is: ETYPE-INFO2, followed by ETYPE-INFO,
+     *   followed by PW-SALT.  As noted in Section 3.1.3, a KDC MUST NOT send
+     *   ETYPE-INFO or PW-SALT when the client's AS-REQ includes at least one
+     *   "newer" etype.
      */
 
-    if (older_enctype(ckey->key.keytype)) {
+    ret = get_pa_etype_info2(context, config, md, ckey);
+    if (ret)
+	return ret;
+
+    if (!newer_enctype_present(etype_list))
 	ret = get_pa_etype_info(context, config, md, ckey);
-	if (ret)
-	    return ret;
-    }
 
-    return get_pa_etype_info2(context, config, md, ckey);
+    return ret;
 }
 
 /*
@@ -1852,7 +1879,7 @@ _kdc_as_rep(kdc_request_t r,
 					   TRUE, r->client, b->etype.val,
 					   b->etype.len, NULL, &ckey);
 		    if (ret2 == 0) {
-			ret2 = get_pa_etype_info_both(context, config,
+			ret2 = get_pa_etype_info_both(context, config, &b->etype,
 						      &error_method, ckey);
 			if (ret2 != 0)
 			    ret = ret2;
@@ -1888,7 +1915,8 @@ _kdc_as_rep(kdc_request_t r,
 			      config->preauth_use_strongest_session_key, TRUE,
 			      r->client, b->etype.val, b->etype.len, NULL, &ckey);
 	if (ret == 0) {
-	    ret = get_pa_etype_info_both(context, config, &error_method, ckey);
+	    ret = get_pa_etype_info_both(context, config, &b->etype,
+					 &error_method, ckey);
 	    if (ret)
 		goto out;
 	}