chsh: Add libuser support

This is based directly on lchsh which is a part of libuser. libuser.{c,h}
exist because exactly the same code is needed for both chsh and chfn.

[kzak@redhat.com: cleanup err() usage]

Signed-off-by: Cody Maloney <cmaloney@theoreticalchaos.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

login-utils/Makemodule.am

@@ -73,6 +73,9 @@ chfn_chsh_ldadd = libcommon.la -lpam -lpam_misc
 if HAVE_USER
 chfn_chsh_ldflags += $(LIBUSER_LIBS)
 chfn_chsh_cflags += $(LIBUSER_CFLAGS)
+chfn_chsh_sources+= \
+	login-utils/libuser.c \
+	login-utils/libuser.h
 endif
 
 if HAVE_SELINUX

login-utils/chsh.c

@@ -1,6 +1,7 @@
 /*
  *   chsh.c -- change your login shell
  *   (c) 1994 by salvatore valente <svalente@athena.mit.edu>
+ *   (c) 2012 by Cody Maloney <cmaloney@theoreticalchaos.com>
  *
  *   this program is free software.  you can redistribute it and
  *   modify it under the terms of the gnu general public license.
@@ -32,7 +33,6 @@
 #include <sys/types.h>
 #include <unistd.h>
 
-#include "auth.h"
 #include "c.h"
 #include "env.h"
 #include "closestream.h"
@@ -48,6 +48,14 @@
 # include "selinux_utils.h"
 #endif
 
+
+#ifdef HAVE_LIBUSER
+# include <libuser/user.h>
+# include "libuser.h"
+#else
+# include "auth.h"
+#endif
+
 struct sinfo {
 	char *username;
 	char *shell;
@@ -131,7 +139,12 @@ int main(int argc, char **argv)
 		oldshell = _PATH_BSHELL;	/* default */
 
 	/* reality check */
+#ifdef HAVE_LIBUSER
+	/* If we're setuid and not really root, disallow the password change. */
+	if (geteuid() != getuid() && uid != pw->pw_uid) {
+#else
 	if (uid != 0 && uid != pw->pw_uid) {
+#endif
 		errno = EACCES;
 		err(EXIT_FAILURE,
 		    _("running UID doesn't match UID of user we're "
@@ -147,9 +160,11 @@ int main(int argc, char **argv)
 
 	printf(_("Changing shell for %s.\n"), pw->pw_name);
 
+#ifndef HAVE_LIBUSER
 	if(!auth_pam("chsh", uid, pw->pw_name)) {
 		return EXIT_FAILURE;
 	}
+#endif
 
 	if (!shell) {
 		shell = prompt(_("New shell"), oldshell);
@@ -162,10 +177,15 @@ int main(int argc, char **argv)
 
 	if (strcmp(oldshell, shell) == 0)
 		errx(EXIT_SUCCESS, _("Shell not changed."));
+
+#ifdef HAVE_LIBUSER
+	set_value_libuser("chsh", pw->pw_name, uid, LU_LOGINSHELL, shell);
+#else
 	pw->pw_shell = shell;
 	if (setpwnam(pw) < 0)
 		err(EXIT_FAILURE, _("setpwnam failed\n"
 			"Shell *NOT* changed.  Try again later."));
+#endif
 
 	printf(_("Shell changed.\n"));
 	return EXIT_SUCCESS;

login-utils/libuser.c

@@ -0,0 +1,71 @@
+/*
+ *   libuser.c -- Utilize libuser to set a user attribute
+ *   (c) 2012 by Cody Maloney <cmaloney@theoreticalchaos.com>
+ *
+ *   this program is free software.  you can redistribute it and
+ *   modify it under the terms of the gnu general public license.
+ *   there is no warranty.
+ *
+ */
+
+#include "libuser.h"
+
+#include <grp.h>
+#include <libuser/user.h>
+#include <unistd.h>
+
+#include "auth.h"
+#include "c.h"
+#include "nls.h"
+
+static int auth_lu(const char *service_name, struct lu_context *ctx, uid_t uid,
+			const char *username);
+
+static int auth_lu(const char *service_name, struct lu_context *ctx, uid_t uid,
+			const char *username) {
+	if(!lu_uses_elevated_privileges(ctx)) {
+		/* Drop privileges */
+		if (setegid(getgid()) == -1)
+			err(EXIT_FAILURE, _("Couldn't drop group privileges"));
+		if (seteuid(getuid()) == -1)
+			err(EXIT_FAILURE, _("Couldn't drop group privileges"));
+		return TRUE;
+	}
+
+	return auth_pam(service_name, uid, username);
+}
+
+int set_value_libuser(const char *service_name, const char *username, uid_t uid,
+			const char *attr, const char *val) {
+	struct lu_context *ctx;
+	struct lu_error *error = NULL;
+	struct lu_ent *ent;
+
+	ctx = lu_start(username, lu_user, NULL, NULL, lu_prompt_console_quiet,
+			NULL, &error);
+	if (ctx == NULL)
+		errx(EXIT_FAILURE, _("libuser initialization failed: %s."),
+			lu_strerror(error));
+
+	if(!auth_lu(service_name, ctx, uid, username)) {
+		errno = EACCES;
+		err(EXIT_FAILURE, _("changing user attribute failed"));
+	}
+
+	/* Look up the user's record. */
+	ent = lu_ent_new();
+	if (lu_user_lookup_name(ctx, username, ent, &error) == FALSE) {
+		lu_end(ctx);
+		errx(EXIT_FAILURE, _("user \"%s\" does not exist."), username);
+	}
+
+	lu_ent_set_string(ent, attr, val);
+	if (!lu_user_modify(ctx, ent, &error)) {
+		lu_ent_free(ent);
+		lu_end(ctx);
+		errx(EXIT_FAILURE, _("user attribute not changed: %s"), lu_strerror(error));
+	}
+	lu_ent_free(ent);
+	lu_end(ctx);
+	return TRUE;
+}

login-utils/libuser.h

@@ -0,0 +1,14 @@
+/*
+ *   libuser.h -- Utilize libuser to set a user attribute
+ *   (c) 2012 by Cody Maloney <cmaloney@theoreticalchaos.com>
+ *
+ *   this program is free software.  you can redistribute it and
+ *   modify it under the terms of the gnu general public license.
+ *   there is no warranty.
+ *
+ */
+
+#include <sys/types.h>
+
+extern int set_value_libuser(const char *service_name, const char *username,
+			uid_t uid, const char *attr, const char *val);