better validate CASignatureAlgorithms in ssh_config and sshd_config.

Previously this directive would accept certificate algorithm names, but
these were unusable in practice as OpenSSH does not support CA chains.

part of bz3577; ok dtucker@

4 files changed, 22 insertions, 9 deletions

diff --git a/usr.bin/ssh/readconf.c b/usr.bin/ssh/readconf.c
index 7c1b1b1f434..de70683e558 100644
--- a/usr.bin/ssh/readconf.c
+++ b/usr.bin/ssh/readconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.376 2023/03/31 04:23:02 djm Exp $ */
+/* $OpenBSD: readconf.c,v 1.377 2023/06/21 05:10:26 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -931,7 +931,7 @@ process_config_line_depth(Options *options, struct passwd *pw, const char *host,
 	char **cpptr, ***cppptr, fwdarg[256];
 	u_int i, *uintptr, uvalue, max_entries = 0;
 	int r, oactive, negated, opcode, *intptr, value, value2, cmdline = 0;
-	int remotefwd, dynamicfwd;
+	int remotefwd, dynamicfwd, ca_only = 0;
 	LogLevel *log_level_ptr;
 	SyslogFacility *log_facility_ptr;
 	long long val64;
@@ -1427,6 +1427,7 @@ parse_int:
 
 	case oHostKeyAlgorithms:
 		charptr = &options->hostkeyalgorithms;
+		ca_only = 0;
 parse_pubkey_algos:
 		arg = argv_next(&ac, &av);
 		if (!arg || *arg == '\0') {
@@ -1436,7 +1437,7 @@ parse_pubkey_algos:
 		}
 		if (*arg != '-' &&
 		    !sshkey_names_valid2(*arg == '+' || *arg == '^' ?
-		    arg + 1 : arg, 1)) {
+		    arg + 1 : arg, 1, ca_only)) {
 			error("%s line %d: Bad key types '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 			goto out;
@@ -1447,6 +1448,7 @@ parse_pubkey_algos:
 
 	case oCASignatureAlgorithms:
 		charptr = &options->ca_sign_algorithms;
+		ca_only = 1;
 		goto parse_pubkey_algos;
 
 	case oLogLevel:
@@ -2103,10 +2105,12 @@ parse_pubkey_algos:
 
 	case oHostbasedAcceptedAlgorithms:
 		charptr = &options->hostbased_accepted_algos;
+		ca_only = 0;
 		goto parse_pubkey_algos;
 
 	case oPubkeyAcceptedAlgorithms:
 		charptr = &options->pubkey_accepted_algos;
+		ca_only = 0;
 		goto parse_pubkey_algos;
 
 	case oAddKeysToAgent:
diff --git a/usr.bin/ssh/servconf.c b/usr.bin/ssh/servconf.c
index 862b02068cb..1cf33162943 100644
--- a/usr.bin/ssh/servconf.c
+++ b/usr.bin/ssh/servconf.c
@@ -1,5 +1,5 @@
 
-/* $OpenBSD: servconf.c,v 1.394 2023/06/05 13:24:36 millert Exp $ */
+/* $OpenBSD: servconf.c,v 1.395 2023/06/21 05:10:26 djm Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -1282,6 +1282,7 @@ process_server_config_line_depth(ServerOptions *options, char *line,
 {
 	char *str, ***chararrayptr, **charptr, *arg, *arg2, *p, *keyword;
 	int cmdline = 0, *intptr, value, value2, n, port, oactive, r, found;
+	int ca_only = 0;
 	SyslogFacility *log_facility_ptr;
 	LogLevel *log_level_ptr;
 	ServerOpCodes opcode;
@@ -1517,6 +1518,7 @@ process_server_config_line_depth(ServerOptions *options, char *line,
 
 	case sHostbasedAcceptedAlgorithms:
 		charptr = &options->hostbased_accepted_algos;
+		ca_only = 0;
  parse_pubkey_algos:
 		arg = argv_next(&ac, &av);
 		if (!arg || *arg == '\0')
@@ -1524,7 +1526,7 @@ process_server_config_line_depth(ServerOptions *options, char *line,
 			    filename, linenum);
 		if (*arg != '-' &&
 		    !sshkey_names_valid2(*arg == '+' || *arg == '^' ?
-		    arg + 1 : arg, 1))
+		    arg + 1 : arg, 1, ca_only))
 			fatal("%s line %d: Bad key types '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 		if (*activep && *charptr == NULL)
@@ -1533,18 +1535,22 @@ process_server_config_line_depth(ServerOptions *options, char *line,
 
 	case sHostKeyAlgorithms:
 		charptr = &options->hostkeyalgorithms;
+		ca_only = 0;
 		goto parse_pubkey_algos;
 
 	case sCASignatureAlgorithms:
 		charptr = &options->ca_sign_algorithms;
+		ca_only = 1;
 		goto parse_pubkey_algos;
 
 	case sPubkeyAuthentication:
 		intptr = &options->pubkey_authentication;
+		ca_only = 0;
 		goto parse_flag;
 
 	case sPubkeyAcceptedAlgorithms:
 		charptr = &options->pubkey_accepted_algos;
+		ca_only = 0;
 		goto parse_pubkey_algos;
 
 	case sPubkeyAuthOptions:
diff --git a/usr.bin/ssh/sshkey.c b/usr.bin/ssh/sshkey.c
index eac9c866ebe..3b07c92de12 100644
--- a/usr.bin/ssh/sshkey.c
+++ b/usr.bin/ssh/sshkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.c,v 1.135 2023/03/31 03:22:49 djm Exp $ */
+/* $OpenBSD: sshkey.c,v 1.136 2023/06/21 05:10:26 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Alexander von Gernler.  All rights reserved.
@@ -319,7 +319,7 @@ sshkey_alg_list(int certs_only, int plain_only, int include_sigonly, char sep)
 }
 
 int
-sshkey_names_valid2(const char *names, int allow_wildcard)
+sshkey_names_valid2(const char *names, int allow_wildcard, int plain_only)
 {
 	char *s, *cp, *p;
 	const struct sshkey_impl *impl;
@@ -352,6 +352,9 @@ sshkey_names_valid2(const char *names, int allow_wildcard)
 			}
 			free(s);
 			return 0;
+		} else if (plain_only && sshkey_type_is_cert(type)) {
+			free(s);
+			return 0;
 		}
 	}
 	free(s);
diff --git a/usr.bin/ssh/sshkey.h b/usr.bin/ssh/sshkey.h
index e90a1eec8cb..2be16d19611 100644
--- a/usr.bin/ssh/sshkey.h
+++ b/usr.bin/ssh/sshkey.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.h,v 1.61 2022/10/28 00:44:44 djm Exp $ */
+/* $OpenBSD: sshkey.h,v 1.62 2023/06/21 05:10:26 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -258,7 +258,7 @@ 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);
+int		 sshkey_names_valid2(const char *, int, int);
 char		*sshkey_alg_list(int, int, int, char);
 
 int	 sshkey_from_blob(const u_char *, size_t, struct sshkey **);