add AuthorizedPrincipalsCommand that allows getting authorized_principals

from a subprocess rather than a file, which is quite useful in
deployments with large userbases

feedback and ok markus@

5 files changed, 213 insertions, 29 deletions

diff --git a/usr.bin/ssh/auth2-pubkey.c b/usr.bin/ssh/auth2-pubkey.c
index 9b5ad5540d3..102fea8efbf 100644
--- a/usr.bin/ssh/auth2-pubkey.c
+++ b/usr.bin/ssh/auth2-pubkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.50 2015/05/21 06:38:35 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.51 2015/05/21 06:43:30 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -551,19 +551,13 @@ match_principals_option(const char *principal_list, struct sshkey_cert *cert)
 }
 
 static int
-match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert)
+process_principals(FILE *f, char *file, struct passwd *pw,
+    struct sshkey_cert *cert)
 {
-	FILE *f;
 	char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
 	u_long linenum = 0;
 	u_int i;
 
-	temporarily_use_uid(pw);
-	debug("trying authorized principals file %s", file);
-	if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
-		restore_uid();
-		return 0;
-	}
 	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 		/* Skip leading whitespace. */
 		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
@@ -591,24 +585,128 @@ match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert)
 		}
 		for (i = 0; i < cert->nprincipals; i++) {
 			if (strcmp(cp, cert->principals[i]) == 0) {
-				debug3("matched principal \"%.100s\" "
-				    "from file \"%s\" on line %lu",
-				    cert->principals[i], file, linenum);
+				debug3("%s:%lu: matched principal \"%.100s\"",
+				    file == NULL ? "(command)" : file,
+				    linenum, cert->principals[i]);
 				if (auth_parse_options(pw, line_opts,
 				    file, linenum) != 1)
 					continue;
-				fclose(f);
-				restore_uid();
 				return 1;
 			}
 		}
 	}
+	return 0;
+}
+
+static int
+match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert)
+{
+	FILE *f;
+	int success;
+
+	temporarily_use_uid(pw);
+	debug("trying authorized principals file %s", file);
+	if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
+		restore_uid();
+		return 0;
+	}
+	success = process_principals(f, file, pw, cert);
 	fclose(f);
 	restore_uid();
-	return 0;
+	return success;
 }
 
 /*
+ * Checks whether principal is allowed in output of command.
+ * returns 1 if the principal is allowed or 0 otherwise.
+ */
+static int
+match_principals_command(struct passwd *user_pw, struct sshkey *key)
+{
+	FILE *f = NULL;
+	int ok, found_principal = 0;
+	struct passwd *pw;
+	int i, ac = 0, uid_swapped = 0;
+	pid_t pid;
+	char *tmp, *username = NULL, *command = NULL, **av = NULL;
+	void (*osigchld)(int);
+
+	if (options.authorized_principals_command == NULL)
+		return 0;
+	if (options.authorized_principals_command_user == NULL) {
+		error("No user for AuthorizedPrincipalsCommand specified, "
+		    "skipping");
+		return 0;
+	}
+
+	/*
+	 * NB. all returns later this function should go via "out" to
+	 * ensure the original SIGCHLD handler is restored properly.
+	 */
+	osigchld = signal(SIGCHLD, SIG_DFL);
+
+	/* Prepare and verify the user for the command */
+	username = percent_expand(options.authorized_principals_command_user,
+	    "u", user_pw->pw_name, (char *)NULL);
+	pw = getpwnam(username);
+	if (pw == NULL) {
+		error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
+		    username, strerror(errno));
+		goto out;
+	}
+
+	/* Turn the command into an argument vector */
+	if (split_argv(options.authorized_principals_command, &ac, &av) != 0) {
+		error("AuthorizedPrincipalsCommand \"%s\" contains "
+		    "invalid quotes", command);
+		goto out;
+	}
+	if (ac == 0) {
+		error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
+		    command);
+		goto out;
+	}
+	for (i = 1; i < ac; i++) {
+		tmp = percent_expand(av[i],
+		    "u", user_pw->pw_name,
+		    "h", user_pw->pw_dir,
+		    (char *)NULL);
+		if (tmp == NULL)
+			fatal("%s: percent_expand failed", __func__);
+		free(av[i]);
+		av[i] = tmp;
+	}
+	/* Prepare a printable command for logs, etc. */
+	command = assemble_argv(ac, av);
+
+	if ((pid = subprocess("AuthorizedPrincipalsCommand", pw, command,
+	    ac, av, &f)) == 0)
+		goto out;
+
+	uid_swapped = 1;
+	temporarily_use_uid(pw);
+
+	ok = process_principals(f, NULL, pw, key->cert);
+
+	if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command) != 0)
+		goto out;
+
+	/* Read completed successfully */
+	found_principal = ok;
+ out:
+	if (f != NULL)
+		fclose(f);
+	signal(SIGCHLD, osigchld);
+	for (i = 0; i < ac; i++)
+		free(av[i]);
+	free(av);
+	if (uid_swapped)
+		restore_uid();
+	free(command);
+	free(username);
+	return found_principal;
+}
+/*
  * Checks whether key is allowed in authorized_keys-format file,
  * returns 1 if the key is allowed or 0 otherwise.
  */
@@ -730,7 +828,7 @@ user_cert_trusted_ca(struct passwd *pw, Key *key)
 {
 	char *ca_fp, *principals_file = NULL;
 	const char *reason;
-	int ret = 0;
+	int ret = 0, found_principal = 0;
 
 	if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
 		return 0;
@@ -752,14 +850,20 @@ user_cert_trusted_ca(struct passwd *pw, Key *key)
 	 * against the username.
 	 */
 	if ((principals_file = authorized_principals_file(pw)) != NULL) {
-		if (!match_principals_file(principals_file, pw, key->cert)) {
-			reason = "Certificate does not contain an "
-			    "authorized principal";
+		if (match_principals_file(principals_file, pw, key->cert))
+			found_principal = 1;
+	}
+	/* Try querying command if specified */
+	if (!found_principal && match_principals_command(pw, key))
+		found_principal = 1;
+	/* If principals file or command specify, then require a match here */
+	if (!found_principal && (principals_file != NULL ||
+	    options.authorized_principals_command != NULL)) {
+		reason = "Certificate does not contain an authorized principal";
  fail_reason:
-			error("%s", reason);
-			auth_debug_add("%s", reason);
-			goto out;
-		}
+		error("%s", reason);
+		auth_debug_add("%s", reason);
+		goto out;
 	}
 	if (key_cert_check_authority(key, 0, 1,
 	    principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
diff --git a/usr.bin/ssh/servconf.c b/usr.bin/ssh/servconf.c
index 0c471d69ec2..d64ba6b7533 100644
--- a/usr.bin/ssh/servconf.c
+++ b/usr.bin/ssh/servconf.c
@@ -1,5 +1,5 @@
 
-/* $OpenBSD: servconf.c,v 1.269 2015/05/04 06:10:48 djm Exp $ */
+/* $OpenBSD: servconf.c,v 1.270 2015/05/21 06:43:30 djm Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -151,6 +151,8 @@ initialize_server_options(ServerOptions *options)
 	options->revoked_keys_file = NULL;
 	options->trusted_user_ca_keys = NULL;
 	options->authorized_principals_file = NULL;
+	options->authorized_principals_command = NULL;
+	options->authorized_principals_command_user = NULL;
 	options->ip_qos_interactive = -1;
 	options->ip_qos_bulk = -1;
 	options->version_addendum = NULL;
@@ -371,6 +373,7 @@ typedef enum {
 	sUsePrivilegeSeparation, sAllowAgentForwarding,
 	sHostCertificate,
 	sRevokedKeys, sTrustedUserCAKeys, sAuthorizedPrincipalsFile,
+	sAuthorizedPrincipalsCommand, sAuthorizedPrincipalsCommandUser,
 	sKexAlgorithms, sIPQoS, sVersionAddendum,
 	sAuthorizedKeysCommand, sAuthorizedKeysCommandUser,
 	sAuthenticationMethods, sHostKeyAgent, sPermitUserRC,
@@ -491,6 +494,8 @@ static struct {
 	{ "ipqos", sIPQoS, SSHCFG_ALL },
 	{ "authorizedkeyscommand", sAuthorizedKeysCommand, SSHCFG_ALL },
 	{ "authorizedkeyscommanduser", sAuthorizedKeysCommandUser, SSHCFG_ALL },
+	{ "authorizedprincipalscommand", sAuthorizedPrincipalsCommand, SSHCFG_ALL },
+	{ "authorizedprincipalscommanduser", sAuthorizedPrincipalsCommandUser, SSHCFG_ALL },
 	{ "versionaddendum", sVersionAddendum, SSHCFG_GLOBAL },
 	{ "authenticationmethods", sAuthenticationMethods, SSHCFG_ALL },
 	{ "streamlocalbindmask", sStreamLocalBindMask, SSHCFG_ALL },
@@ -1687,6 +1692,34 @@ process_server_config_line(ServerOptions *options, char *line,
 			*charptr = xstrdup(arg);
 		break;
 
+	case sAuthorizedPrincipalsCommand:
+		if (cp == NULL)
+			fatal("%.200s line %d: Missing argument.", filename,
+			    linenum);
+		len = strspn(cp, WHITESPACE);
+		if (*activep &&
+		    options->authorized_principals_command == NULL) {
+			if (cp[len] != '/' && strcasecmp(cp + len, "none") != 0)
+				fatal("%.200s line %d: "
+				    "AuthorizedPrincipalsCommand must be "
+				    "an absolute path", filename, linenum);
+			options->authorized_principals_command =
+			    xstrdup(cp + len);
+		}
+		return 0;
+
+	case sAuthorizedPrincipalsCommandUser:
+		charptr = &options->authorized_principals_command_user;
+
+		arg = strdelim(&cp);
+		if (!arg || *arg == '\0')
+			fatal("%s line %d: missing "
+			    "AuthorizedPrincipalsCommandUser argument.",
+			    filename, linenum);
+		if (*activep && *charptr == NULL)
+			*charptr = xstrdup(arg);
+		break;
+
 	case sAuthenticationMethods:
 		if (options->num_auth_methods == 0) {
 			while ((arg = strdelim(&cp)) && *arg != '\0') {
@@ -2177,6 +2210,8 @@ dump_config(ServerOptions *o)
 	    ? "none" : o->version_addendum);
 	dump_cfg_string(sAuthorizedKeysCommand, o->authorized_keys_command);
 	dump_cfg_string(sAuthorizedKeysCommandUser, o->authorized_keys_command_user);
+	dump_cfg_string(sAuthorizedPrincipalsCommand, o->authorized_principals_command);
+	dump_cfg_string(sAuthorizedPrincipalsCommandUser, o->authorized_principals_command_user);
 	dump_cfg_string(sHostKeyAgent, o->host_key_agent);
 	dump_cfg_string(sKexAlgorithms,
 	    o->kex_algorithms ? o->kex_algorithms : KEX_SERVER_KEX);
diff --git a/usr.bin/ssh/servconf.h b/usr.bin/ssh/servconf.h
index 6886e351ae5..4c4867b010e 100644
--- a/usr.bin/ssh/servconf.h
+++ b/usr.bin/ssh/servconf.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: servconf.h,v 1.117 2015/04/29 03:48:56 dtucker Exp $ */
+/* $OpenBSD: servconf.h,v 1.118 2015/05/21 06:43:31 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -176,9 +176,11 @@ typedef struct {
 	char   *chroot_directory;
 	char   *revoked_keys_file;
 	char   *trusted_user_ca_keys;
-	char   *authorized_principals_file;
 	char   *authorized_keys_command;
 	char   *authorized_keys_command_user;
+	char   *authorized_principals_file;
+	char   *authorized_principals_command;
+	char   *authorized_principals_command_user;
 
 	int64_t rekey_limit;
 	int	rekey_interval;
@@ -214,9 +216,11 @@ struct connection_info {
 		M_CP_STROPT(banner); \
 		M_CP_STROPT(trusted_user_ca_keys); \
 		M_CP_STROPT(revoked_keys_file); \
-		M_CP_STROPT(authorized_principals_file); \
 		M_CP_STROPT(authorized_keys_command); \
 		M_CP_STROPT(authorized_keys_command_user); \
+		M_CP_STROPT(authorized_principals_file); \
+		M_CP_STROPT(authorized_principals_command); \
+		M_CP_STROPT(authorized_principals_command_user); \
 		M_CP_STROPT(hostbased_key_types); \
 		M_CP_STROPT(pubkey_key_types); \
 		M_CP_STRARRAYOPT(authorized_keys_files, num_authkeys_files); \
diff --git a/usr.bin/ssh/sshd.c b/usr.bin/ssh/sshd.c
index 3cb3da41bff..d8ea87599d3 100644
--- a/usr.bin/ssh/sshd.c
+++ b/usr.bin/ssh/sshd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshd.c,v 1.448 2015/04/27 00:21:21 djm Exp $ */
+/* $OpenBSD: sshd.c,v 1.449 2015/05/21 06:43:31 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1598,6 +1598,11 @@ main(int ac, char **av)
 	    strcasecmp(options.authorized_keys_command, "none") != 0))
 		fatal("AuthorizedKeysCommand set without "
 		    "AuthorizedKeysCommandUser");
+	if (options.authorized_principals_command_user == NULL &&
+	    (options.authorized_principals_command != NULL &&
+	    strcasecmp(options.authorized_principals_command, "none") != 0))
+		fatal("AuthorizedPrincipalsCommand set without "
+		    "AuthorizedPrincipalsCommandUser");
 
 	/*
 	 * Check whether there is any path through configured auth methods.
diff --git a/usr.bin/ssh/sshd_config.5 b/usr.bin/ssh/sshd_config.5
index e2e09aa599e..507a8bf3354 100644
--- a/usr.bin/ssh/sshd_config.5
+++ b/usr.bin/ssh/sshd_config.5
@@ -33,7 +33,7 @@
 .\" (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 1.201 2015/05/21 06:38:35 djm Exp $
+.\" $OpenBSD: sshd_config.5,v 1.202 2015/05/21 06:43:31 djm Exp $
 .Dd $Mdocdate: May 21 2015 $
 .Dt SSHD_CONFIG 5
 .Os
@@ -287,6 +287,42 @@ directory.
 Multiple files may be listed, separated by whitespace.
 The default is
 .Dq .ssh/authorized_keys .ssh/authorized_keys2 .
+.It Cm AuthorizedPrincipalsCommand
+Specifies a program to be used to generate the list of allowed
+certificate principals as per
+.Cm AuthorizedPrincipalsFile .
+The program must be owned by root, not writable by group or others and
+specified by an absolute path.
+.Pp
+Arguments to
+.Cm AuthorizedPrincipalsCommand
+may be provided using the following tokens, which will be expanded
+at runtime: %% is replaced by a literal '%', %u is replaced by the
+username being authenticated and %h is replaced by the home directory
+of the user being authenticated.
+.Pp
+The program should produce on standard output zero or
+more lines of
+.Cm AuthorizedPrincipalsFile
+output.
+If either
+.Cm AuthorizedPrincipalsCommand
+or
+.Cm AuthorizedPrincipalsFile
+is specified, then certificates offered by the client for authentication
+must contain a principal that is listed.
+By default, no AuthorizedPrincipalsCommand is run.
+.It Cm AuthorizedPrincipalsCommandUser
+Specifies the user under whose account the AuthorizedPrincipalsCommand is run.
+It is recommended to use a dedicated user that has no other role on the host
+than running authorized principals commands.
+If
+.Cm AuthorizedPrincipalsCommand
+is specified but
+.Cm AuthorizedPrincipalsCommandUser
+is not, then
+.Xr sshd 8
+will refuse to start.
 .It Cm AuthorizedPrincipalsFile
 Specifies a file that lists principal names that are accepted for
 certificate authentication.