From: djm <djm@openbsd.org>
Date: Sun, 19 Dec 2021 22:14:47 +0000 (+0000)
Subject: PubkeyAuthentication=yes|no|unbound|host-bound
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=6d12622932a5f47eb782737a758f045b2a3b101b;p=openbsd

PubkeyAuthentication=yes|no|unbound|host-bound

Allow control over which pubkey methods are used. Added out of
concern that some hardware devices may have difficulty signing
the longer pubkey authentication challenges. This provides a
way for them to disable the extension. It's also handy for
testing.

feedback / ok markus@
---

diff --git a/usr.bin/ssh/readconf.c b/usr.bin/ssh/readconf.c
index 5324d4fc87a..0365dc67070 100644
--- a/usr.bin/ssh/readconf.c
+++ b/usr.bin/ssh/readconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.363 2021/09/16 05:36:03 djm Exp $ */
+/* $OpenBSD: readconf.c,v 1.364 2021/12/19 22:14:47 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -876,6 +876,15 @@ static const struct multistate multistate_canonicalizehostname[] = {
 	{ "always",			SSH_CANONICALISE_ALWAYS },
 	{ NULL, -1 }
 };
+static const struct multistate multistate_pubkey_auth[] = {
+	{ "true",			SSH_PUBKEY_AUTH_ALL },
+	{ "false",			SSH_PUBKEY_AUTH_NO },
+	{ "yes",			SSH_PUBKEY_AUTH_ALL },
+	{ "no",				SSH_PUBKEY_AUTH_NO },
+	{ "unbound",			SSH_PUBKEY_AUTH_UNBOUND },
+	{ "host-bound",			SSH_PUBKEY_AUTH_HBOUND },
+	{ NULL, -1 }
+};
 static const struct multistate multistate_compression[] = {
 #ifdef WITH_ZLIB
 	{ "yes",			COMP_ZLIB },
@@ -1088,8 +1097,9 @@ parse_time:
 		goto parse_string;
 
 	case oPubkeyAuthentication:
+		multistate_ptr = multistate_pubkey_auth;
 		intptr = &options->pubkey_authentication;
-		goto parse_flag;
+		goto parse_multistate;
 
 	case oHostbasedAuthentication:
 		intptr = &options->hostbased_authentication;
@@ -2473,7 +2483,7 @@ fill_default_options(Options * options)
 	if (options->fwd_opts.streamlocal_bind_unlink == -1)
 		options->fwd_opts.streamlocal_bind_unlink = 0;
 	if (options->pubkey_authentication == -1)
-		options->pubkey_authentication = 1;
+		options->pubkey_authentication = SSH_PUBKEY_AUTH_ALL;
 	if (options->gss_authentication == -1)
 		options->gss_authentication = 0;
 	if (options->gss_deleg_creds == -1)
@@ -3116,6 +3126,8 @@ fmt_intarg(OpCodes code, int val)
 		return fmt_multistate_int(val, multistate_canonicalizehostname);
 	case oAddKeysToAgent:
 		return fmt_multistate_int(val, multistate_yesnoaskconfirm);
+	case oPubkeyAuthentication:
+		return fmt_multistate_int(val, multistate_pubkey_auth);
 	case oFingerprintHash:
 		return ssh_digest_alg_name(val);
 	default:
diff --git a/usr.bin/ssh/readconf.h b/usr.bin/ssh/readconf.h
index f24719f982d..ded13c943d3 100644
--- a/usr.bin/ssh/readconf.h
+++ b/usr.bin/ssh/readconf.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.h,v 1.145 2021/09/15 06:56:01 djm Exp $ */
+/* $OpenBSD: readconf.h,v 1.146 2021/12/19 22:14:47 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -179,6 +179,11 @@ typedef struct {
 	char	*ignored_unknown; /* Pattern list of unknown tokens to ignore */
 }       Options;
 
+#define SSH_PUBKEY_AUTH_NO	0x00
+#define SSH_PUBKEY_AUTH_UNBOUND	0x01
+#define SSH_PUBKEY_AUTH_HBOUND	0x02
+#define SSH_PUBKEY_AUTH_ALL	0x03
+
 #define SSH_CANONICALISE_NO	0
 #define SSH_CANONICALISE_YES	1
 #define SSH_CANONICALISE_ALWAYS	2
diff --git a/usr.bin/ssh/sshconnect2.c b/usr.bin/ssh/sshconnect2.c
index 02383a415e9..6a6373fcd16 100644
--- a/usr.bin/ssh/sshconnect2.c
+++ b/usr.bin/ssh/sshconnect2.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect2.c,v 1.353 2021/12/19 22:12:54 djm Exp $ */
+/* $OpenBSD: sshconnect2.c,v 1.354 2021/12/19 22:14:47 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Damien Miller.  All rights reserved.
@@ -1338,16 +1338,20 @@ sign_and_send_pubkey(struct ssh *ssh, Identity *id)
 	int r, fallback_sigtype, sent = 0;
 	char *alg = NULL, *fp = NULL;
 	const char *loc = "", *method = "publickey";
+	int hostbound = 0;
 
 	/* prefer host-bound pubkey signatures if supported by server */
-	if ((ssh->kex->flags & KEX_HAS_PUBKEY_HOSTBOUND) != 0)
+	if ((ssh->kex->flags & KEX_HAS_PUBKEY_HOSTBOUND) != 0 &&
+	    (options.pubkey_authentication & SSH_PUBKEY_AUTH_HBOUND) != 0) {
+		hostbound = 1;
 		method = "publickey-hostbound-v00@openssh.com";
+	}
 
 	if ((fp = sshkey_fingerprint(id->key, options.fingerprint_hash,
 	    SSH_FP_DEFAULT)) == NULL)
 		return 0;
 
-	debug3_f("%s %s", sshkey_type(id->key), fp);
+	debug3_f("using %s with %s %s", method, sshkey_type(id->key), fp);
 
 	/*
 	 * If the key is an certificate, try to find a matching private key
@@ -1433,7 +1437,7 @@ sign_and_send_pubkey(struct ssh *ssh, Identity *id)
 		    (r = sshkey_puts(id->key, b)) != 0) {
 			fatal_fr(r, "assemble signed data");
 		}
-		if ((ssh->kex->flags & KEX_HAS_PUBKEY_HOSTBOUND) != 0) {
+		if (hostbound) {
 			if (ssh->kex->initial_hostkey == NULL) {
 				fatal_f("internal error: initial hostkey "
 				    "not recorded");