upstream commit

add sshd_config HostbasedAcceptedKeyTypes and
 PubkeyAcceptedKeyTypes options to allow sshd to control what public key types
 will be accepted. Currently defaults to all. Feedback & ok markus@

auth2-hostbased.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-hostbased.c,v 1.21 2015/01/08 10:14:08 djm Exp $ */
+/* $OpenBSD: auth2-hostbased.c,v 1.22 2015/01/13 07:39:19 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -48,6 +48,7 @@
 #endif
 #include "monitor_wrap.h"
 #include "pathnames.h"
+#include "match.h"
 
 /* import */
 extern ServerOptions options;
@@ -108,6 +109,14 @@ userauth_hostbased(Authctxt *authctxt)
 		    "signature format");
 		goto done;
 	}
+	if (match_pattern_list(sshkey_ssh_name(key),
+	    options.hostbased_key_types,
+	    strlen(options.hostbased_key_types), 0) != 1) {
+		logit("%s: key type %s not in HostbasedAcceptedKeyTypes",
+		    __func__, sshkey_type(key));
+		goto done;
+	}
+
 	service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
 	    authctxt->service;
 	buffer_init(&b);

auth2-pubkey.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.44 2014/12/22 07:51:30 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.45 2015/01/13 07:39:19 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -127,6 +127,13 @@ userauth_pubkey(Authctxt *authctxt)
 		logit("refusing previously-used %s key", key_type(key));
 		goto done;
 	}
+	if (match_pattern_list(sshkey_ssh_name(key), options.pubkey_key_types,
+	    strlen(options.pubkey_key_types), 0) != 1) {
+		logit("%s: key type %s not in PubkeyAcceptedKeyTypes",
+		    __func__, sshkey_ssh_name(key));
+		goto done;
+	}
+
 	if (have_sig) {
 		sig = packet_get_string(&slen);
 		packet_check_eom();

key.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: key.h,v 1.45 2015/01/08 10:14:08 djm Exp $ */
+/* $OpenBSD: key.h,v 1.46 2015/01/13 07:39:19 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -50,7 +50,6 @@ typedef struct sshkey Key;
 #define key_size		sshkey_size
 #define key_ecdsa_bits_to_nid	sshkey_ecdsa_bits_to_nid
 #define key_ecdsa_key_to_nid	sshkey_ecdsa_key_to_nid
-#define key_names_valid2	sshkey_names_valid2
 #define key_is_cert		sshkey_is_cert
 #define key_type_plain		sshkey_type_plain
 #define key_cert_is_legacy	sshkey_cert_is_legacy

monitor.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: monitor.c,v 1.136 2014/12/22 07:51:30 djm Exp $ */
+/* $OpenBSD: monitor.c,v 1.137 2015/01/13 07:39:19 djm Exp $ */
 /*
  * Copyright 2002 Niels Provos <provos@citi.umich.edu>
  * Copyright 2002 Markus Friedl <markus@openbsd.org>
@@ -100,6 +100,7 @@
 #include "ssh2.h"
 #include "roaming.h"
 #include "authfd.h"
+#include "match.h"
 
 #ifdef GSSAPI
 static Gssctxt *gsscontext = NULL;
@@ -1167,10 +1168,18 @@ mm_answer_keyallowed(int sock, Buffer *m)
 	debug3("%s: key_from_blob: %p", __func__, key);
 
 	if (key != NULL && authctxt->valid) {
+		/* These should not make it past the privsep child */
+		if (key_type_plain(key->type) == KEY_RSA &&
+		    (datafellows & SSH_BUG_RSASIGMD5) != 0)
+			fatal("%s: passed a SSH_BUG_RSASIGMD5 key", __func__);
+
 		switch (type) {
 		case MM_USERKEY:
 			allowed = options.pubkey_authentication &&
 			    !auth2_userkey_already_used(authctxt, key) &&
+			    match_pattern_list(sshkey_ssh_name(key),
+			    options.pubkey_key_types,
+			    strlen(options.pubkey_key_types), 0) == 1 &&
 			    user_key_allowed(authctxt->pw, key);
 			pubkey_auth_info(authctxt, key, NULL);
 			auth_method = "publickey";
@@ -1179,6 +1188,9 @@ mm_answer_keyallowed(int sock, Buffer *m)
 			break;
 		case MM_HOSTKEY:
 			allowed = options.hostbased_authentication &&
+			    match_pattern_list(sshkey_ssh_name(key),
+			    options.hostbased_key_types,
+			    strlen(options.hostbased_key_types), 0) == 1 &&
 			    hostbased_key_allowed(authctxt->pw,
 			    cuser, chost, key);
 			pubkey_auth_info(authctxt, key,

readconf.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.225 2015/01/08 13:44:36 djm Exp $ */
+/* $OpenBSD: readconf.c,v 1.226 2015/01/13 07:39:19 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1116,7 +1116,7 @@ parse_int:
 		arg = strdelim(&s);
 		if (!arg || *arg == '\0')
 			fatal("%.200s line %d: Missing argument.", filename, linenum);
-		if (!key_names_valid2(arg))
+		if (!sshkey_names_valid2(arg, 1))
 			fatal("%.200s line %d: Bad protocol 2 host key algorithms '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 		if (*activep && options->hostkeyalgorithms == NULL)

servconf.c

@@ -1,5 +1,5 @@
 
-/* $OpenBSD: servconf.c,v 1.257 2014/12/22 07:55:51 djm Exp $ */
+/* $OpenBSD: servconf.c,v 1.258 2015/01/13 07:39:19 djm Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -104,8 +104,10 @@ initialize_server_options(ServerOptions *options)
 	options->rhosts_rsa_authentication = -1;
 	options->hostbased_authentication = -1;
 	options->hostbased_uses_name_from_packet_only = -1;
+	options->hostbased_key_types = NULL;
 	options->rsa_authentication = -1;
 	options->pubkey_authentication = -1;
+	options->pubkey_key_types = NULL;
 	options->kerberos_authentication = -1;
 	options->kerberos_or_local_passwd = -1;
 	options->kerberos_ticket_cleanup = -1;
@@ -248,10 +250,14 @@ fill_default_server_options(ServerOptions *options)
 		options->hostbased_authentication = 0;
 	if (options->hostbased_uses_name_from_packet_only == -1)
 		options->hostbased_uses_name_from_packet_only = 0;
+	if (options->hostbased_key_types == NULL)
+		options->hostbased_key_types = xstrdup("*");
 	if (options->rsa_authentication == -1)
 		options->rsa_authentication = 1;
 	if (options->pubkey_authentication == -1)
 		options->pubkey_authentication = 1;
+	if (options->pubkey_key_types == NULL)
+		options->pubkey_key_types = xstrdup("*");
 	if (options->kerberos_authentication == -1)
 		options->kerberos_authentication = 0;
 	if (options->kerberos_or_local_passwd == -1)
@@ -365,8 +371,8 @@ typedef enum {
 	/* Portable-specific options */
 	sUsePAM,
 	/* Standard Options */
-	sPort, sHostKeyFile, sServerKeyBits, sLoginGraceTime, sKeyRegenerationTime,
-	sPermitRootLogin, sLogFacility, sLogLevel,
+	sPort, sHostKeyFile, sServerKeyBits, sLoginGraceTime,
+	sKeyRegenerationTime, sPermitRootLogin, sLogFacility, sLogLevel,
 	sRhostsRSAAuthentication, sRSAAuthentication,
 	sKerberosAuthentication, sKerberosOrLocalPasswd, sKerberosTicketCleanup,
 	sKerberosGetAFSToken,
@@ -379,11 +385,11 @@ typedef enum {
 	sPermitUserEnvironment, sUseLogin, sAllowTcpForwarding, sCompression,
 	sRekeyLimit, sAllowUsers, sDenyUsers, sAllowGroups, sDenyGroups,
 	sIgnoreUserKnownHosts, sCiphers, sMacs, sProtocol, sPidFile,
-	sGatewayPorts, sPubkeyAuthentication, sXAuthLocation, sSubsystem,
-	sMaxStartups, sMaxAuthTries, sMaxSessions,
+	sGatewayPorts, sPubkeyAuthentication, sPubkeyAcceptedKeyTypes,
+	sXAuthLocation, sSubsystem, sMaxStartups, sMaxAuthTries, sMaxSessions,
 	sBanner, sUseDNS, sHostbasedAuthentication,
-	sHostbasedUsesNameFromPacketOnly, sClientAliveInterval,
-	sClientAliveCountMax, sAuthorizedKeysFile,
+	sHostbasedUsesNameFromPacketOnly, sHostbasedAcceptedKeyTypes,
+	sClientAliveInterval, sClientAliveCountMax, sAuthorizedKeysFile,
 	sGssAuthentication, sGssCleanupCreds, sAcceptEnv, sPermitTunnel,
 	sMatch, sPermitOpen, sForceCommand, sChrootDirectory,
 	sUsePrivilegeSeparation, sAllowAgentForwarding,
@@ -430,8 +436,10 @@ static struct {
 	{ "rhostsrsaauthentication", sRhostsRSAAuthentication, SSHCFG_ALL },
 	{ "hostbasedauthentication", sHostbasedAuthentication, SSHCFG_ALL },
 	{ "hostbasedusesnamefrompacketonly", sHostbasedUsesNameFromPacketOnly, SSHCFG_ALL },
+	{ "hostbasedacceptedkeytypes", sHostbasedAcceptedKeyTypes, SSHCFG_ALL },
 	{ "rsaauthentication", sRSAAuthentication, SSHCFG_ALL },
 	{ "pubkeyauthentication", sPubkeyAuthentication, SSHCFG_ALL },
+	{ "pubkeyacceptedkeytypes", sPubkeyAcceptedKeyTypes, SSHCFG_ALL },
 	{ "dsaauthentication", sPubkeyAuthentication, SSHCFG_GLOBAL }, /* alias */
 #ifdef KRB5
 	{ "kerberosauthentication", sKerberosAuthentication, SSHCFG_ALL },
@@ -1111,6 +1119,20 @@ process_server_config_line(ServerOptions *options, char *line,
 		intptr = &options->hostbased_uses_name_from_packet_only;
 		goto parse_flag;
 
+	case sHostbasedAcceptedKeyTypes:
+		charptr = &options->hostbased_key_types;
+ parse_keytypes:
+		arg = strdelim(&cp);
+		if (!arg || *arg == '\0')
+			fatal("%s line %d: Missing argument.",
+			    filename, linenum);
+		if (!sshkey_names_valid2(arg, 1))
+			fatal("%s line %d: Bad key types '%s'.",
+			    filename, linenum, arg ? arg : "<NONE>");
+		if (*activep && *charptr == NULL)
+			*charptr = xstrdup(arg);
+		break;
+
 	case sRSAAuthentication:
 		intptr = &options->rsa_authentication;
 		goto parse_flag;
@@ -1119,6 +1141,10 @@ process_server_config_line(ServerOptions *options, char *line,
 		intptr = &options->pubkey_authentication;
 		goto parse_flag;
 
+	case sPubkeyAcceptedKeyTypes:
+		charptr = &options->pubkey_key_types;
+		goto parse_keytypes;
+
 	case sKerberosAuthentication:
 		intptr = &options->kerberos_authentication;
 		goto parse_flag;
@@ -2142,6 +2168,10 @@ dump_config(ServerOptions *o)
 	dump_cfg_string(sHostKeyAgent, o->host_key_agent);
 	dump_cfg_string(sKexAlgorithms,
 	    o->kex_algorithms ? o->kex_algorithms : KEX_SERVER_KEX);
+	dump_cfg_string(sHostbasedAcceptedKeyTypes, o->hostbased_key_types ?
+	    o->hostbased_key_types : KEX_DEFAULT_PK_ALG);
+	dump_cfg_string(sPubkeyAcceptedKeyTypes, o->pubkey_key_types ?
+	    o->pubkey_key_types : KEX_DEFAULT_PK_ALG);
 
 	/* string arguments requiring a lookup */
 	dump_cfg_string(sLogLevel, log_level_name(o->log_level));

servconf.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: servconf.h,v 1.115 2014/12/21 22:27:56 djm Exp $ */
+/* $OpenBSD: servconf.h,v 1.116 2015/01/13 07:39:19 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -99,8 +99,10 @@ typedef struct {
 						 * authentication. */
 	int     hostbased_authentication;	/* If true, permit ssh2 hostbased auth */
 	int     hostbased_uses_name_from_packet_only; /* experimental */
+	char   *hostbased_key_types;	/* Key types allowed for hostbased */
 	int     rsa_authentication;	/* If true, permit RSA authentication. */
 	int     pubkey_authentication;	/* If true, permit ssh2 pubkey authentication. */
+	char   *pubkey_key_types;	/* Key types allowed for public key */
 	int     kerberos_authentication;	/* If true, permit Kerberos
 						 * authentication. */
 	int     kerberos_or_local_passwd;	/* If true, permit kerberos
@@ -215,6 +217,8 @@ struct connection_info {
 		M_CP_STROPT(authorized_principals_file); \
 		M_CP_STROPT(authorized_keys_command); \
 		M_CP_STROPT(authorized_keys_command_user); \
+		M_CP_STROPT(hostbased_key_types); \
+		M_CP_STROPT(pubkey_key_types); \
 		M_CP_STRARRAYOPT(authorized_keys_files, num_authkeys_files); \
 		M_CP_STRARRAYOPT(allow_users, num_allow_users); \
 		M_CP_STRARRAYOPT(deny_users, num_deny_users); \

sshd_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: sshd_config.5,v 1.188 2014/12/22 09:05:17 djm Exp $
-.Dd $Mdocdate: December 22 2014 $
+.\" $OpenBSD: sshd_config.5,v 1.189 2015/01/13 07:39:19 djm Exp $
+.Dd $Mdocdate: January 13 2015 $
 .Dt SSHD_CONFIG 5
 .Os
 .Sh NAME
@@ -561,6 +561,17 @@ on logout.
 The default is
 .Dq yes .
 Note that this option applies to protocol version 2 only.
+.It Cm HostbasedAcceptedKeyTypes
+Specifies the key types that will be accepted for hostbased authentication
+as a comma-separated pattern list.
+The default
+.Dq *
+will allow all key types.
+The
+.Fl Q
+option of
+.Xr ssh 1
+may be used to list supported key types.
 .It Cm HostbasedAuthentication
 Specifies whether rhosts or /etc/hosts.equiv authentication together
 with successful public key client host authentication is allowed
@@ -962,6 +973,7 @@ Available keywords are
 .Cm ForceCommand ,
 .Cm GatewayPorts ,
 .Cm GSSAPIAuthentication ,
+.Cm HostbasedAcceptedKeyTypes ,
 .Cm HostbasedAuthentication ,
 .Cm HostbasedUsesNameFromPacketOnly ,
 .Cm KbdInteractiveAuthentication ,
@@ -975,6 +987,7 @@ Available keywords are
 .Cm PermitTTY ,
 .Cm PermitTunnel ,
 .Cm PermitUserRC ,
+.Cm PubkeyAcceptedKeyTypes ,
 .Cm PubkeyAuthentication ,
 .Cm RekeyLimit ,
 .Cm RhostsRSAAuthentication ,
@@ -1182,6 +1195,17 @@ Specifying
 .Dq 2,1
 is identical to
 .Dq 1,2 .
+.It Cm PubkeyAcceptedKeyTypes
+Specifies the key types that will be accepted for public key authentication
+as a comma-separated pattern list.
+The default
+.Dq *
+will allow all key types.
+The
+.Fl Q
+option of
+.Xr ssh 1
+may be used to list supported key types.
 .It Cm PubkeyAuthentication
 Specifies whether public key authentication is allowed.
 The default is

sshkey.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.c,v 1.10 2015/01/12 20:13:27 markus Exp $ */
+/* $OpenBSD: sshkey.c,v 1.11 2015/01/13 07:39:19 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Alexander von Gernler.  All rights reserved.
@@ -54,6 +54,7 @@
 #include "digest.h"
 #define SSHKEY_INTERNAL
 #include "sshkey.h"
+#include "match.h"
 
 /* openssh private key file format */
 #define MARK_BEGIN		"-----BEGIN OPENSSH PRIVATE KEY-----\n"
@@ -219,9 +220,11 @@ key_alg_list(int certs_only, int plain_only)
 }
 
 int
-sshkey_names_valid2(const char *names)
+sshkey_names_valid2(const char *names, int allow_wildcard)
 {
 	char *s, *cp, *p;
+	const struct keytype *kt;
+	int type;
 
 	if (names == NULL || strcmp(names, "") == 0)
 		return 0;
@@ -229,9 +232,28 @@ sshkey_names_valid2(const char *names)
 		return 0;
 	for ((p = strsep(&cp, ",")); p && *p != '\0';
 	    (p = strsep(&cp, ","))) {
-		switch (sshkey_type_from_name(p)) {
-		case KEY_RSA1:
-		case KEY_UNSPEC:
+		type = sshkey_type_from_name(p);
+		if (type == KEY_RSA1) {
+			free(s);
+			return 0;
+		}
+		if (type == KEY_UNSPEC) {
+			if (allow_wildcard) {
+				/*
+				 * Try matching key types against the string.
+				 * If any has a positive or negative match then
+				 * the component is accepted.
+				 */
+				for (kt = keytypes; kt->type != -1; kt++) {
+					if (kt->type == KEY_RSA1)
+						continue;
+					if (match_pattern_list(kt->name,
+					    p, strlen(p), 0) != 0)
+						break;
+				}
+				if (kt->type != -1)
+					continue;
+			}
 			free(s);
 			return 0;
 		}

sshkey.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.h,v 1.3 2015/01/08 10:14:08 djm Exp $ */
+/* $OpenBSD: sshkey.h,v 1.4 2015/01/13 07:39:19 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -156,7 +156,7 @@ int		 sshkey_ec_validate_public(const EC_GROUP *, const EC_POINT *);
 int		 sshkey_ec_validate_private(const EC_KEY *);
 const char	*sshkey_ssh_name(const struct sshkey *);
 const char	*sshkey_ssh_name_plain(const struct sshkey *);
-int		 sshkey_names_valid2(const char *);
+int		 sshkey_names_valid2(const char *, int);
 char		*key_alg_list(int, int);
 
 int	 sshkey_from_blob(const u_char *, size_t, struct sshkey **);