Add nss_tacplus, a TACACS+ NSS module.

MFC after:	1 week
Sponsored by:	Klara, Inc.
Reviewed by:	imp
Differential Revision:	https://reviews.freebsd.org/D40133

lib/Makefile

@@ -109,7 +109,8 @@ SUBDIR=	${SUBDIR_BOOTSTRAP} \
 	liby \
 	libz \
 	libzstd \
-	ncurses
+	ncurses \
+	nss_tacplus
 
 # Inter-library dependencies.  When the makefile for a library contains LDADD
 # libraries, those libraries should be listed as build order dependencies here.
@@ -145,6 +146,7 @@ SUBDIR_DEPEND_liblzma= libthr
 .if ${MK_OFED} != "no"
 SUBDIR_DEPEND_libpcap= ofed
 .endif
+SUBDIR_DEPEND_nss_tacplus= libtacplus
 
 .if !defined(COMPAT_32BIT)
 SUBDIR+=	flua

lib/nss_tacplus/Makefile

@@ -0,0 +1,9 @@
+LIB=		nss_tacplus
+SRCS=		${LIB}.8
+SHLIB_MAJOR=	1
+SHLIB_NAME=	${LIB}.so.${SHLIB_MAJOR}
+LIBADD=		tacplus
+MK_INSTALLIB=	no
+MAN=		${LIB}.8
+
+.include <bsd.lib.mk>

lib/nss_tacplus/nss_tacplus.8

@@ -0,0 +1,86 @@
+.\"-
+.\" Copyright (c) 2023 Klara, Inc.
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
+.Dd May 17, 2023
+.Dt NSS_TACPLUS 8
+.Os
+.Sh NAME
+.Nm nss_tacplus
+.Nd TACACS+ nsswitch module
+.Sh SYNOPSIS
+.Ic passwd : files tacplus
+.Sh DESCRIPTION
+The
+.Nm
+module is a loadable NSS module which provides a minimal identity
+service using a TACACS+ backend.
+.Pp
+Due to the limitations of the TACACS+ protocol, the functionality
+provided by the
+.Nm
+module is very limited: it can look up a user by name, but not by uid,
+and it cannot enumerate users.
+.Pp
+To look up a user, the
+.Nm
+module submits an authorization request with authentication method
+.Dv TAC_PLUS_AUTHEN_METH_NOT_SET ,
+authentication type
+.Dv TAC_PLUS_AUTHEN_TYPE_NOT_SET ,
+and authentication service
+.Dv TAC_PLUS_AUTHEN_SVC_LOGIN ,
+for the
+.Dq shell
+service.
+If the response status is either
+.Dv TAC_PLUS_AUTHOR_STATUS_PASS_ADD
+or
+.Dv TAC_PLUS_AUTHOR_STATUS_PASS_REPL ,
+the user is considered to exist and the
+.Nm
+module fills out a
+.Vt struct passwd
+for it.
+.Pp
+The following attributes, if included in the response from the TACACS+
+server, are used to construct the response:
+.Bl -tag -width GECOS
+.It Va UID
+Numeric user ID.
+Must be between 0 and
+.Dv UID_MAX .
+Defaults to 65534.
+.It Va GID
+Numeric primary group ID.
+Must be between 0 and
+.Dv GID_MAX .
+Defaults to 65534.
+.It Va GECOS
+Display name.
+If not provided, the user name is used instead.
+.It Va HOME
+Home directory.
+Defaults to
+.Pa / .
+.It Va SHELL
+Shell.
+Defaults to
+.Pa /bin/sh .
+.El
+.Pp
+Case is ignored when matching attribute names.
+If an attribute is included multiple times, the last value takes
+effect.
+.Sh SEE ALSO
+.Xr libtacplus 3 ,
+.Xr tacplus.conf 5 ,
+.Xr pam_tacplus 8
+.Sh HISTORY
+.An -nosplit
+The
+.Nm
+module and this manual page were written by
+.An Dag-Erling Smørgrav Aq Mt des@FreeBSD.org
+for Klara Systems.

lib/nss_tacplus/nss_tacplus.c

@@ -0,0 +1,273 @@
+/*-
+ * Copyright (c) 2023 Klara, Inc.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <sys/param.h>
+#include <sys/limits.h>
+
+#include <errno.h>
+#include <inttypes.h>
+#include <pthread.h>
+#include <pthread_np.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syslog.h>
+
+#include <nsswitch.h>
+#include <pwd.h>
+#include <taclib.h>
+
+extern int __isthreaded;
+
+#define	DEF_UID		65534
+#define	DEF_GID		65534
+#define	DEF_DIR		"/"
+#define	DEF_SHELL	"/bin/sh"
+
+ns_mtab *nss_module_register(const char *, unsigned int *,
+    nss_module_unregister_fn *);
+
+static void
+tacplus_error(struct tac_handle *h, const char *func)
+{
+	if (h == NULL)
+		syslog(LOG_ERR, "%s(): %m", func);
+	else
+		syslog(LOG_ERR, "%s(): %s", func, tac_strerror(h));
+}
+
+static pthread_key_t tacplus_key;
+
+static void
+tacplus_fini(void *p)
+{
+	struct tac_handle **h = p;
+
+	tac_close(*h);
+	free(h);
+}
+
+static void
+tacplus_keyinit(void)
+{
+	(void)pthread_key_create(&tacplus_key, tacplus_fini);
+}
+
+static struct tac_handle *
+tacplus_get_handle(void)
+{
+	static pthread_once_t keyinit = PTHREAD_ONCE_INIT;
+	static struct tac_handle *sth;
+	struct tac_handle **h = &sth;
+	int ret;
+
+	if (__isthreaded && !pthread_main_np()) {
+		if ((ret = pthread_once(&keyinit, tacplus_keyinit)) != 0)
+			return (NULL);
+		if ((h = pthread_getspecific(tacplus_key)) == NULL) {
+			if ((h = calloc(1, sizeof(*h))) == NULL)
+				return (NULL);
+			if ((pthread_setspecific(tacplus_key, h)) != 0) {
+				free(h);
+				return (NULL);
+			}
+		}
+	}
+	if (*h == NULL) {
+		if ((*h = tac_open()) == NULL) {
+			tacplus_error(*h, "tac_open");
+			return (NULL);
+		}
+		if (tac_config(*h, NULL) != 0) {
+			tacplus_error(*h, "tac_config");
+			tac_close(*h);
+			*h = NULL;
+			return (NULL);
+		}
+	}
+	return (*h);
+}
+
+static char *
+tacplus_copystr(const char *str, char **buffer, size_t *bufsize)
+{
+	char *copy = *buffer;
+	size_t len = strlen(str) + 1;
+
+	if (len > *bufsize) {
+		errno = ERANGE;
+		return (NULL);
+	}
+	memcpy(copy, str, len);
+	*buffer += len;
+	*bufsize -= len;
+	return (copy);
+}
+
+static int
+tacplus_getpwnam_r(const char *name, struct passwd *pwd, char *buffer,
+    size_t bufsize)
+{
+	struct tac_handle *h;
+	char *av, *key, *value, *end;
+	intmax_t num;
+	int i, ret;
+
+	if ((h = tacplus_get_handle()) == NULL)
+		return (NS_UNAVAIL);
+	ret = tac_create_author(h, TAC_AUTHEN_METH_NOT_SET,
+	    TAC_AUTHEN_TYPE_NOT_SET, TAC_AUTHEN_SVC_LOGIN);
+	if (ret < 0) {
+		tacplus_error(h, "tac_create_author");
+		return (NS_TRYAGAIN);
+	}
+	if (tac_set_user(h, name) < 0) {
+		tacplus_error(h, "tac_set_user");
+		return (NS_TRYAGAIN);
+	}
+	if (tac_set_av(h, 0, "service=shell") < 0) {
+		tacplus_error(h, "tac_set_av");
+		return (NS_TRYAGAIN);
+	}
+	ret = tac_send_author(h);
+	switch (TAC_AUTHOR_STATUS(ret)) {
+	case TAC_AUTHOR_STATUS_PASS_ADD:
+	case TAC_AUTHOR_STATUS_PASS_REPL:
+		/* found */
+		break;
+	case TAC_AUTHOR_STATUS_FAIL:
+		return (NS_NOTFOUND);
+	case TAC_AUTHOR_STATUS_ERROR:
+		return (NS_UNAVAIL);
+	default:
+		tacplus_error(h, "tac_send_author");
+		return (NS_UNAVAIL);
+	}
+	memset(pwd, 0, sizeof(*pwd));
+
+	/* copy name */
+	pwd->pw_name = tacplus_copystr(name, &buffer, &bufsize);
+	if (pwd->pw_name == NULL)
+		return (NS_RETURN);
+
+	/* no password */
+	pwd->pw_passwd = tacplus_copystr("*", &buffer, &bufsize);
+	if (2 > bufsize)
+		return (NS_RETURN);
+
+	/* default uid and gid */
+	pwd->pw_uid = DEF_UID;
+	pwd->pw_gid = DEF_GID;
+
+	/* get attribute-value pairs from TACACS+ response */
+	for (i = 0; i < TAC_AUTHEN_AV_COUNT(ret); i++) {
+		if ((av = tac_get_av(h, i)) == NULL) {
+			tacplus_error(h, "tac_get_av");
+			return (NS_UNAVAIL);
+		}
+		key = av;
+		if ((value = strchr(av, '=')) == NULL) {
+			free(av);
+			return (NS_RETURN);
+		}
+		*value++ = '\0';
+		if (strcasecmp(key, "uid") == 0) {
+			num = strtoimax(value, &end, 10);
+			if (end == value || *end != '\0' ||
+			    num < 0 || num > (intmax_t)UID_MAX) {
+				errno = EINVAL;
+				free(av);
+				return (NS_RETURN);
+			}
+			pwd->pw_uid = num;
+		} else if (strcasecmp(key, "gid") == 0) {
+			num = strtoimax(value, &end, 10);
+			if (end == value || *end != '\0' ||
+			    num < 0 || num > (intmax_t)GID_MAX) {
+				errno = EINVAL;
+				free(av);
+				return (NS_RETURN);
+			}
+			pwd->pw_gid = num;
+		} else if (strcasecmp(av, "gecos") == 0) {
+			pwd->pw_gecos = tacplus_copystr(value, &buffer,
+			    &bufsize);
+			if (pwd->pw_gecos == NULL) {
+				free(av);
+				return (NS_RETURN);
+			}
+		} else if (strcasecmp(av, "home") == 0) {
+			pwd->pw_dir = tacplus_copystr(value, &buffer,
+			    &bufsize);
+			if (pwd->pw_dir == NULL) {
+				free(av);
+				return (NS_RETURN);
+			}
+		} else if (strcasecmp(av, "shell") == 0) {
+			pwd->pw_shell = tacplus_copystr(value, &buffer,
+			    &bufsize);
+			if (pwd->pw_shell == NULL) {
+				free(av);
+				return (NS_RETURN);
+			}
+		}
+		free(av);
+	}
+
+	/* gecos equal to name if none was provided */
+	if (pwd->pw_gecos == NULL)
+		pwd->pw_gecos = pwd->pw_name;
+
+	/* default home directory if none was provided */
+	if (pwd->pw_dir == NULL)
+		pwd->pw_dir = tacplus_copystr(DEF_DIR, &buffer, &bufsize);
+	if (pwd->pw_dir == NULL)
+		return (NS_RETURN);
+
+	/* default shell if none was provided */
+	if (pwd->pw_shell == NULL)
+		pwd->pw_shell = tacplus_copystr(DEF_SHELL, &buffer, &bufsize);
+	if (pwd->pw_shell == NULL)
+		return (NS_RETURN);
+
+	/* done! */
+	return (NS_SUCCESS);
+}
+
+static int
+nss_tacplus_getpwnam_r(void *retval, void *mdata __unused, va_list ap)
+{
+	char *name = va_arg(ap, char *);
+	struct passwd *pwd = va_arg(ap, struct passwd *);
+	char *buffer = va_arg(ap, char *);
+	size_t bufsize = va_arg(ap, size_t);
+	int *result = va_arg(ap, int *);
+	int ret;
+
+	errno = 0;
+	ret = tacplus_getpwnam_r(name, pwd, buffer, bufsize);
+	if (ret == NS_SUCCESS) {
+		*(void **)retval = pwd;
+		*result = 0;
+	} else {
+		*(void **)retval = NULL;
+		*result = errno;
+	}
+	return (ret);
+}
+
+ns_mtab *
+nss_module_register(const char *name __unused, unsigned int *plen,
+    nss_module_unregister_fn *unreg)
+{
+	static ns_mtab mtab[] = {
+		{ "passwd", "getpwnam_r", &nss_tacplus_getpwnam_r, NULL },
+	};
+
+	*plen = nitems(mtab);
+	*unreg = NULL;
+	return (mtab);
+}