4 files changed, 52 insertions, 22 deletions

diff --git a/readconf.c b/readconf.c
index b11c628f9..4f38b27cf 100644
--- a/readconf.c
+++ b/readconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.277 2017/05/30 18:58:37 bluhm Exp $ */
+/* $OpenBSD: readconf.c,v 1.278 2017/09/03 23:33:13 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -751,6 +751,16 @@ static const struct multistate multistate_yesnoask[] = {
         { "ask",                        2 },
         { NULL, -1 }
 };
+static const struct multistate multistate_strict_hostkey[] = {
+        { "true",                       SSH_STRICT_HOSTKEY_YES },
+        { "false",                      SSH_STRICT_HOSTKEY_OFF },
+        { "yes",                        SSH_STRICT_HOSTKEY_YES },
+        { "no",                         SSH_STRICT_HOSTKEY_OFF },
+        { "ask",                        SSH_STRICT_HOSTKEY_ASK },
+        { "off",                        SSH_STRICT_HOSTKEY_OFF },
+        { "accept-new",                 SSH_STRICT_HOSTKEY_NEW },
+        { NULL, -1 }
+};
 static const struct multistate multistate_yesnoaskconfirm[] = {
         { "true",                       1 },
         { "false",                      0 },
@@ -984,7 +994,7 @@ parse_time:
 
         case oStrictHostKeyChecking:
                 intptr = &options->strict_host_key_checking;
-                multistate_ptr = multistate_yesnoask;
+                multistate_ptr = multistate_strict_hostkey;
                 goto parse_multistate;
 
         case oCompression:
@@ -1927,7 +1937,7 @@ fill_default_options(Options * options)
         if (options->check_host_ip == -1)
                 options->check_host_ip = 1;
         if (options->strict_host_key_checking == -1)
-                options->strict_host_key_checking = 2;  /* 2 is default */
+                options->strict_host_key_checking = SSH_STRICT_HOSTKEY_ASK;
         if (options->compression == -1)
                 options->compression = 0;
         if (options->tcp_keep_alive == -1)
@@ -2329,9 +2339,10 @@ fmt_intarg(OpCodes code, int val)
         case oAddressFamily:
                 return fmt_multistate_int(val, multistate_addressfamily);
         case oVerifyHostKeyDNS:
-        case oStrictHostKeyChecking:
         case oUpdateHostkeys:
                 return fmt_multistate_int(val, multistate_yesnoask);
+        case oStrictHostKeyChecking:
+                return fmt_multistate_int(val, multistate_strict_hostkey);
         case oControlMaster:
                 return fmt_multistate_int(val, multistate_controlmaster);
         case oTunnel:
diff --git a/readconf.h b/readconf.h
index 94dd427f5..22fe5c187 100644
--- a/readconf.h
+++ b/readconf.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.h,v 1.122 2017/05/30 18:58:37 bluhm Exp $ */
+/* $OpenBSD: readconf.h,v 1.123 2017/09/03 23:33:13 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -190,6 +190,11 @@ typedef struct {
 #define SSH_UPDATE_HOSTKEYS_YES 1
 #define SSH_UPDATE_HOSTKEYS_ASK 2
 
+#define SSH_STRICT_HOSTKEY_OFF  0
+#define SSH_STRICT_HOSTKEY_NEW  1
+#define SSH_STRICT_HOSTKEY_YES  2
+#define SSH_STRICT_HOSTKEY_ASK  3
+
 void     initialize_options(Options *);
 void     fill_default_options(Options *);
 void     fill_default_options_for_canonicalization(Options *);
diff --git a/ssh_config.5 b/ssh_config.5
index 15ca0b4f9..3823da6f3 100644
--- a/ssh_config.5
+++ b/ssh_config.5
@@ -33,8 +33,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh_config.5,v 1.253 2017/07/23 23:37:02 djm Exp $
-.Dd $Mdocdate: July 23 2017 $
+.\" $OpenBSD: ssh_config.5,v 1.254 2017/09/03 23:33:13 djm Exp $
+.Dd $Mdocdate: September 3 2017 $
 .Dt SSH_CONFIG 5
 .Os
 .Sh NAME
@@ -1459,9 +1459,17 @@ frequently made.
 This option forces the user to manually
 add all new hosts.
 If this flag is set to
-.Cm no ,
-ssh will automatically add new host keys to the
-user known hosts files.
+.Dq accept-new
+then ssh will automatically add new new host keys to the user
+known hosts files, but will not permit connections to hosts with
+changed host keys.
+If this flag is set to
+.Dq no
+or
+.Dq off ,
+ssh will automatically add new host keys to the user known hosts files,
+and allow connections to hosts with changed hostkeys to proceed subject
+to some restrictions.
 If this flag is set to
 .Cm ask
 (the default),
diff --git a/sshconnect.c b/sshconnect.c
index 4013ec7db..2842d9e59 100644
--- a/sshconnect.c
+++ b/sshconnect.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect.c,v 1.284 2017/09/01 05:53:56 djm Exp $ */
+/* $OpenBSD: sshconnect.c,v 1.285 2017/09/03 23:33:13 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -891,7 +891,8 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
                 if (readonly || want_cert)
                         goto fail;
                 /* The host is new. */
-                if (options.strict_host_key_checking == 1) {
+                if (options.strict_host_key_checking ==
+                    SSH_STRICT_HOSTKEY_YES) {
                         /*
                          * User has requested strict host key checking.  We
                          * will not add the host key automatically.  The only
@@ -900,7 +901,8 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
                         error("No %s host key is known for %.200s and you "
                             "have requested strict checking.", type, host);
                         goto fail;
-                } else if (options.strict_host_key_checking == 2) {
+                } else if (options.strict_host_key_checking ==
+                    SSH_STRICT_HOSTKEY_ASK) {
                         char msg1[1024], msg2[1024];
 
                         if (show_other_keys(host_hostkeys, host_key))
@@ -944,8 +946,8 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
                         hostkey_trusted = 1; /* user explicitly confirmed */
                 }
                 /*
-                 * If not in strict mode, add the key automatically to the
-                 * local known_hosts file.
+                 * If in "new" or "off" strict mode, add the key automatically
+                 * to the local known_hosts file.
                  */
                 if (options.check_host_ip && ip_status == HOST_NEW) {
                         snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
@@ -987,7 +989,8 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
                  * If strict host key checking is in use, the user will have
                  * to edit the key manually and we can only abort.
                  */
-                if (options.strict_host_key_checking) {
+                if (options.strict_host_key_checking !=
+                    SSH_STRICT_HOSTKEY_OFF) {
                         error("%s host key for %.200s was revoked and you have "
                             "requested strict checking.", type, host);
                         goto fail;
@@ -1040,7 +1043,8 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
                  * If strict host key checking is in use, the user will have
                  * to edit the key manually and we can only abort.
                  */
-                if (options.strict_host_key_checking) {
+                if (options.strict_host_key_checking !=
+                    SSH_STRICT_HOSTKEY_OFF) {
                         error("%s host key for %.200s has changed and you have "
                             "requested strict checking.", type, host);
                         goto fail;
@@ -1127,15 +1131,17 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
                             "\nMatching host key in %s:%lu",
                             host_found->file, host_found->line);
                 }
-                if (options.strict_host_key_checking == 1) {
-                        logit("%s", msg);
-                        error("Exiting, you have requested strict checking.");
-                        goto fail;
-                } else if (options.strict_host_key_checking == 2) {
+                if (options.strict_host_key_checking ==
+                    SSH_STRICT_HOSTKEY_ASK) {
                         strlcat(msg, "\nAre you sure you want "
                             "to continue connecting (yes/no)? ", sizeof(msg));
                         if (!confirm(msg))
                                 goto fail;
+                } else if (options.strict_host_key_checking !=
+                    SSH_STRICT_HOSTKEY_OFF) {
+                        logit("%s", msg);
+                        error("Exiting, you have requested strict checking.");
+                        goto fail;
                 } else {
                         logit("%s", msg);
                 }