- djm@cvs.openbsd.org 2014/04/01 03:34:10

     [sshconnect.c]
     When using VerifyHostKeyDNS with a DNSSEC resolver, down-convert any
     certificate keys to plain keys and attempt SSHFP resolution.

     Prevents a server from skipping SSHFP lookup and forcing a new-hostkey
     dialog by offering only certificate keys.

     Reported by mcv21 AT cam.ac.uk

1 files changed, 27 insertions, 17 deletions

diff --git a/sshconnect.c b/sshconnect.c
index 573d7a8e8..ca6e4cc96 100644
--- a/sshconnect.c
+++ b/sshconnect.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect.c,v 1.246 2014/02/06 22:21:01 djm Exp $ */
+/* $OpenBSD: sshconnect.c,v 1.247 2014/04/01 03:34:10 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1219,29 +1219,39 @@ verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
 {
         int flags = 0;
         char *fp;
+        Key *plain = NULL;
 
         fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
         debug("Server host key: %s %s", key_type(host_key), fp);
         free(fp);
 
-        /* XXX certs are not yet supported for DNS */
-        if (!key_is_cert(host_key) && options.verify_host_key_dns &&
-            verify_host_key_dns(host, hostaddr, host_key, &flags) == 0) {
-                if (flags & DNS_VERIFY_FOUND) {
-
-                        if (options.verify_host_key_dns == 1 &&
-                            flags & DNS_VERIFY_MATCH &&
-                            flags & DNS_VERIFY_SECURE)
-                                return 0;
-
-                        if (flags & DNS_VERIFY_MATCH) {
-                                matching_host_key_dns = 1;
-                        } else {
-                                warn_changed_key(host_key);
-                                error("Update the SSHFP RR in DNS with the new "
-                                    "host key to get rid of this message.");
+        if (options.verify_host_key_dns) {
+                /*
+                 * XXX certs are not yet supported for DNS, so downgrade
+                 * them and try the plain key.
+                 */
+                plain = key_from_private(host_key);
+                if (key_is_cert(plain))
+                        key_drop_cert(plain);
+                if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) {
+                        if (flags & DNS_VERIFY_FOUND) {
+                                if (options.verify_host_key_dns == 1 &&
+                                    flags & DNS_VERIFY_MATCH &&
+                                    flags & DNS_VERIFY_SECURE) {
+                                        key_free(plain);
+                                        return 0;
+                                }
+                                if (flags & DNS_VERIFY_MATCH) {
+                                        matching_host_key_dns = 1;
+                                } else {
+                                        warn_changed_key(plain);
+                                        error("Update the SSHFP RR in DNS "
+                                            "with the new host key to get rid "
+                                            "of this message.");
+                                }
                         }
                 }
+                key_free(plain);
         }
 
         return check_host_key(host, hostaddr, options.port, host_key, RDRW,