shadow/src/newgrp.c

/*
 * Copyright 1990 - 1994, Julianne Frances Haugh
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of Julianne F. Haugh nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY JULIE HAUGH AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL JULIE HAUGH OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <config.h>

#include "rcsid.h"
RCSID (PKG_VER "$Id: newgrp.c,v 1.32 2005/06/20 10:17:08 kloczek Exp $")
#include <stdio.h>
#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include "prototypes.h"
#include "defines.h"
#include "getdef.h"
extern char **environ;

#ifdef HAVE_SETGROUPS
static int ngroups;
static GETGROUPS_T *grouplist;
#endif

static char *Prog;
static int is_newgrp;

/* local function prototypes */
static void usage (void);

/*
 * usage - print command usage message
 */

static void usage (void)
{
	if (is_newgrp)
		fprintf (stderr, _("Usage: newgrp [-] [group]\n"));
	else
		fprintf (stderr, _("Usage: sg group [[-c] command]\n"));
}

/*
 * newgrp - change the invokers current real and effective group id
 */

int main (int argc, char **argv)
{
	int initflag = 0;
	int needspasswd = 0;
	int i;
	int cflag = 0;
	gid_t gid;
	char *cp;
	const char *cpasswd, *name, *prog;
	char *group = NULL;
	char *command = NULL;
	char **envp = environ;
	struct passwd *pwd;
	struct group *grp;

	struct spwd *spwd;

#ifdef SHADOWGRP
	struct sgrp *sgrp;
#endif

	setlocale (LC_ALL, "");
	bindtextdomain (PACKAGE, LOCALEDIR);
	textdomain (PACKAGE);

	/*
	 * Save my name for error messages and save my real gid incase of
	 * errors. If there is an error i have to exec a new login shell for
	 * the user since her old shell won't have fork'd to create the
	 * process. Skip over the program name to the next command line
	 * argument.
	 *
	 * This historical comment, and the code itself, suggest that the
	 * behavior of the system/shell on which it was written differed
	 * significantly from the one I am using. If this process was
	 * started from a shell (including the login shell), it was fork'ed
	 * and exec'ed as a child by that shell. In order to get the user
	 * back to that shell, it is only necessary to exit from this
	 * process which terminates the child of the fork. The parent shell,
	 * which is blocked waiting for a signal, will then receive a
	 * SIGCHLD and will continue; any changes made to the process
	 * persona or the environment after the fork never occurred in the
	 * parent process.
	 *
	 * Bottom line: we want to save the name and real gid for messages,
	 * but we do not need to restore the previous process persona and we
	 * don't need to re-exec anything.  -- JWP
	 */

	Prog = Basename (argv[0]);
	is_newgrp = (strcmp (Prog, "newgrp") == 0);
	OPENLOG (is_newgrp ? "newgrp" : "sg");
	gid = getgid ();
	argc--;
	argv++;

	initenv ();

	pwd = get_my_pwent ();
	if (!pwd) {
		fprintf (stderr, _("unknown UID: %u\n"), getuid ());
		SYSLOG ((LOG_WARN, "unknown UID %u", getuid ()));
		closelog ();
		exit (1);
	}
	name = pwd->pw_name;

	/*
	 * Parse the command line. There are two accepted flags. The first
	 * is "-", which for newgrp means to re-create the entire
	 * environment as though a login had been performed, and "-c", which
	 * for sg causes a command string to be executed.
	 *
	 * The next argument, if present, must be the new group name. Any
	 * remaining remaining arguments will be used to execute a command
	 * as the named group. If the group name isn't present, I just use
	 * the login group ID of the current user.
	 *
	 * The valid syntax are
	 *      newgrp [-] [groupid]
	 *      newgrp [-l] [groupid]
	 *      sg [-]
	 *      sg [-] groupid [[-c command]
	 */

	if (argc > 0 && (!strcmp (argv[0], "-") || !strcmp (argv[0], "-l"))) {
		argc--;
		argv++;
		initflag = 1;
	}
	if (!is_newgrp) {
		/* 
		 * Do the command line for everything that is
		 * not "newgrp".
		 */

		if (argc > 0 && argv[0][0] != '-') {
			group = argv[0];
			argc--;
			argv++;
		} else {
			usage ();
			closelog ();
			exit (1);
		}
		if (argc > 0) {

			/*
			 * skip -c if specified so both forms work:
			 * "sg group -c command" (as in the man page) or
			 * "sg group command" (as in the usage message).
			 */

			if (argc > 1 && strcmp (argv[0], "-c") == 0)
				command = argv[1];
			else
				command = argv[0];
			cflag++;
		}
	} else {

		/*
		 * Do the command line for "newgrp". It's just making sure
		 * there aren't any flags and getting the new group name.
		 */

		if (argc > 0 && argv[0][0] == '-') {
			usage ();
			goto failure;
		} else if (argv[0] != (char *) 0) {
			group = argv[0];
		} else {

			/*
			 * get the group file entry for her login group id. 
			 * the entry must exist, simply to be annoying.
			 *
			 * Perhaps in the past, but the default behavior now depends on the
			 * group entry, so it had better exist.  -- JWP
			 */

			if (!(grp = getgrgid (pwd->pw_gid))) {
				fprintf (stderr, _("unknown GID: %lu\n"),
					 (unsigned long) pwd->pw_gid);
				SYSLOG ((LOG_CRIT, "unknown GID: %lu",
					 (unsigned long) pwd->pw_gid));
				goto failure;
			} else
				group = grp->gr_name;
		}
	}

#ifdef HAVE_SETGROUPS
	/*
	 * get the current users groupset. The new group will be added to
	 * the concurrent groupset if there is room, otherwise you get a
	 * nasty message but at least your real and effective group id's are
	 * set.
	 */

	/* don't use getgroups(0, 0) - it doesn't work on some systems */
	i = 16;
	for (;;) {
		grouplist = (GETGROUPS_T *) xmalloc (i * sizeof (GETGROUPS_T));
		ngroups = getgroups (i, grouplist);
		if (i > ngroups && !(ngroups == -1 && errno == EINVAL))
			break;
		/* not enough room, so try allocating a larger buffer */
		free (grouplist);
		i *= 2;
	}
	if (ngroups < 0) {
		perror ("getgroups");
		exit (1);
	}
#endif				/* HAVE_SETGROUPS */

	/*
	 * now we put her in the new group. The password file entry for her
	 * current user id has been gotten. If there was no optional group
	 * argument she will have her real and effective group id set to the
	 * set to the value from her password file entry.  
	 *
	 * If run as newgrp, or as sg with no command, this process exec's
	 * an interactive subshell with the effective GID of the new group. 
	 * If run as sg with a command, that command is exec'ed in this
	 * subshell. When this process terminates, either because the user
	 * exits, or the command completes, the parent of this process
	 * resumes with the current GID.
	 *
	 * If a group is explicitly specified on the command line, the
	 * interactive shell or command is run with that effective GID. 
	 * Access will be denied if no entry for that group can be found in
	 * /etc/group. If the current user name appears in the members list
	 * for that group, access will be granted immediately; if not, the
	 * user will be challenged for that group's password. If the
	 * password response is incorrect, if the specified group does not
	 * have a password, or if that group has been locked by gpasswd -R,
	 * access will be denied. This is true even if the group specified
	 * has the user's login GID (as shown in /etc/passwd). If no group
	 * is explicitly specified on the command line, the effect is
	 * exactly the same as if a group name matching the user's login GID
	 * had been explicitly specified. Root, however, is never
	 * challenged for passwords, and is always allowed access.
	 *
	 * The previous behavior was to allow access to the login group if
	 * no explicit group was specified, irrespective of the group
	 * control file(s). This behavior is usually not desirable. A user
	 * wishing to return to the login group has only to exit back to the
	 * login shell. Generating yet more shell levels in order to
	 * provide a convenient "return" to the default group has the
	 * undesirable side effects of confusing the user, scrambling the
	 * history file, and consuming system resources. The default now is
	 * to lock out such behavior. A sys admin can allow it by explicitly
	 * including the user's name in the member list of the user's login
	 * group.  -- JWP
	 */

	if (!(grp = getgrnam (group))) {
		fprintf (stderr, _("unknown group: %s\n"), group);
		goto failure;
	}
#ifdef SHADOWGRP
	if ((sgrp = getsgnam (group))) {
		grp->gr_passwd = sgrp->sg_passwd;
		grp->gr_mem = sgrp->sg_mem;
	}
#endif

	/*
	 * see if she is a member of this group. If she isn't a member, she
	 * needs to provide the group password. If there is no group
	 * password, she will be denied access anyway.
	 *
	 */

	if (!is_on_list (grp->gr_mem, name))
		needspasswd = 1;

	/*
	 * If she does not have either a shadowed password, or a regular
	 * password, and the group has a password, she needs to give the
	 * group password.
	 */

	if ((spwd = getspnam (name)))
		pwd->pw_passwd = spwd->sp_pwdp;

	if (pwd->pw_passwd[0] == '\0' && grp->gr_passwd[0])
		needspasswd = 1;

	/*
	 * Now i see about letting her into the group she requested. If she
	 * is the root user, i'll let her in without having to prompt for
	 * the password. Otherwise i ask for a password if she flunked one
	 * of the tests above.
	 *
	 * Note that she now has to provide the password to her own group,
	 * unless she is listed as a member.  -- JWP
	 */

	if (getuid () != 0 && needspasswd) {

		/*
		 * get the password from her, and set the salt for
		 * the decryption from the group file.
		 */

		if (!(cp = getpass (_("Password: "))))
			goto failure;

		/*
		 * encrypt the key she gave us using the salt from the
		 * password in the group file. The result of this encryption
		 * must match the previously encrypted value in the file.
		 */

		cpasswd = pw_encrypt (cp, grp->gr_passwd);
		strzero (cp);

		if (grp->gr_passwd[0] == '\0') {
			/*
			 * there is no password, print out "Sorry" and give up
			 */
			sleep (1);
			fputs (_("Sorry.\n"), stderr);
			goto failure;
		}

		if (strcmp (cpasswd, grp->gr_passwd) != 0) {
			SYSLOG ((LOG_INFO,
				 "Invalid password for group `%s' from `%s'",
				 group, name));
			sleep (1);
			fputs (_("Sorry.\n"), stderr);
			goto failure;
		}
	}

	/*
	 * all successful validations pass through this point. The group id
	 * will be set, and the group added to the concurrent groupset.
	 */

#ifdef	USE_SYSLOG
	if (getdef_bool ("SYSLOG_SG_ENAB"))
		SYSLOG ((LOG_INFO, "user `%s' switched to group `%s'",
			 name, group));
	if (getdef_bool ("SYSLOG_SG_ENAB")) {
		char *loginname = getlogin ();
		char *tty = ttyname (0);

		if (loginname != NULL)
			loginname = xstrdup (loginname);
		if (tty != NULL)
			tty = xstrdup (tty);

		if (loginname == NULL)
			loginname = "???";
		if (tty == NULL)
			tty = "???";
		else if (strncmp (tty, "/dev/", 5) == 0)
			tty += 5;
		SYSLOG ((LOG_INFO,
			 "user `%s' (login `%s' on %s) switched to group `%s'",
			 name, loginname, tty, group));
#ifdef USE_PAM
		if (getdef_bool ("CLOSE_SESSIONS")) {
			/*
			 * We want to fork and exec the new shell in the child, leaving the
			 * parent waiting to log the session close.
			 *
			 * The parent must ignore signals generated from the console
			 * (SIGINT, SIGQUIT, SIGHUP) which might make the parent terminate
			 * before its child. When bash is exec'ed as the subshell, it
			 * generates a new process group id for itself, and consequently
			 * only SIGHUP, which is sent to all process groups in the session,
			 * can reach the parent. However, since arbitrary programs can be
			 * specified as login shells, there is no such guarantee in general.
			 * For the same reason, we must also ignore stop signals generated
			 * from the console (SIGTSTP, SIGTTIN, and SIGTTOU) in order to
			 * avoid any possibility of the parent being stopped when it
			 * receives SIGCHLD from the terminating subshell.  -- JWP
			 */
			pid_t child, pid;

			signal (SIGINT, SIG_IGN);
			signal (SIGQUIT, SIG_IGN);
			signal (SIGHUP, SIG_IGN);
			signal (SIGTSTP, SIG_IGN);
			signal (SIGTTIN, SIG_IGN);
			signal (SIGTTOU, SIG_IGN);
			child = fork ();
			if (child < 0) {
				/* error in fork() */
				fprintf (stderr, "%s: failure forking: %s",
					 is_newgrp ? "newgrp" : "sg",
					 strerror (errno));
				exit (1);
			} else if (child) {
				/* parent - wait for child to finish, then log session close */
				do {
					pid = waitpid (child, NULL, 0);
				} while (pid != child);
				SYSLOG ((LOG_INFO,
					 "user `%s' (login `%s' on %s) returned to group `%s'",
					 name, loginname, tty,
					 getgrgid (gid)->gr_name));
				closelog ();
				exit (0);
			}
			/* child - restore signals to their default state */
			signal (SIGINT, SIG_DFL);
			signal (SIGQUIT, SIG_DFL);
			signal (SIGHUP, SIG_DFL);
			signal (SIGTSTP, SIG_DFL);
			signal (SIGTTIN, SIG_DFL);
			signal (SIGTTOU, SIG_DFL);
		}
#endif				/* USE_PAM */
	}
#endif				/* USE_SYSLOG */

	gid = grp->gr_gid;

#ifdef HAVE_SETGROUPS
	/*
	 * I am going to try to add her new group id to her concurrent group
	 * set. If the group id is already present i'll just skip this part. 
	 * If the group doesn't fit, i'll complain loudly and skip this
	 * part.
	 */

	for (i = 0; i < ngroups; i++) {
		if (gid == grouplist[i])
			break;
	}
	if (i == ngroups) {
		if (ngroups >= sysconf (_SC_NGROUPS_MAX)) {
			fprintf (stderr, _("too many groups\n"));
		} else {
			grouplist[ngroups++] = gid;
			if (setgroups (ngroups, grouplist)) {
				perror ("setgroups");
			}
		}
	}
#endif

	/*
	 * Set the effective GID to the new group id and the effective UID
	 * to the real UID. For root, this also sets the real GID to the
	 * new group id.
	 */

	if (setgid (gid))
		perror ("setgid");

	if (setuid (getuid ())) {
		perror ("setuid");
		exit (1);
	}

	/*
	 * See if the "-c" flag was used. If it was, i just create a shell
	 * command for her using the argument that followed the "-c" flag.
	 */

	if (cflag) {
		closelog ();
		execl ("/bin/sh", "sh", "-c", command, (char *) 0);
		if (errno == ENOENT) {
			perror ("/bin/sh");
			exit (127);
		} else {
			perror ("/bin/sh");
			exit (126);
		}
	}

	/*
	 * I have to get the pathname of her login shell. As a favor, i'll
	 * try her environment for a $SHELL value first, and then try the
	 * password file entry. Obviously this shouldn't be in the
	 * restricted command directory since it could be used to leave the
	 * restricted environment.
	 *
	 * Note that the following assumes this user's entry in /etc/passwd
	 * does not have a chroot * prefix. If it does, the * will be copied
	 * verbatim into the exec path. This is probably not an issue
	 * because if this user is operating in a chroot jail, her entry in
	 * the version of /etc/passwd that is accessible here should
	 * probably never have a chroot shell entry (but entries for other
	 * users might). If I have missed something, and this causes you a
	 * problem, try using $SHELL as a workaround; also please notify me
	 * at jparmele@wildbear.com -- JWP
	 */

	if (!initflag && (cp = getenv ("SHELL")))
		prog = cp;
	else if (pwd->pw_shell && pwd->pw_shell[0])
		prog = pwd->pw_shell;
	else
		prog = "/bin/sh";

	/*
	 * Now i try to find the basename of the login shell. This will
	 * become argv[0] of the spawned command.
	 */

	cp = Basename ((char *) prog);

	endspent ();
#ifdef	SHADOWGRP
	endsgent ();
#endif
	endpwent ();
	endgrent ();

	/*
	 * Switch back to her home directory if i am doing login
	 * initialization.
	 */

	if (initflag) {
		if (chdir (pwd->pw_dir))
			perror ("chdir");

		while (*envp) {
			if (strncmp (*envp, "PATH=", 5) == 0 ||
			    strncmp (*envp, "HOME=", 5) == 0 ||
			    strncmp (*envp, "SHELL=", 6) == 0 ||
			    strncmp (*envp, "TERM=", 5) == 0)
				addenv (*envp, NULL);

			envp++;
		}
	} else {
		while (*envp)
			addenv (*envp++, NULL);
	}

	/*
	 * Exec the login shell and go away. We are trying to get back to
	 * the previous environment which should be the user's login shell.
	 */

	shell (prog, initflag ? (char *) 0 : cp);
	/* NOTREACHED */
      failure:

	/*
	 * The previous code, when run as newgrp, re-exec'ed the shell in
	 * the current process with the original gid on error conditions. 
	 * See the comment above. This historical behavior now has the
	 * effect of creating unlogged extraneous shell layers when the
	 * command line has an error or there is an authentication failure.
	 * We now just want to exit with error status back to the parent
	 * process. The closelog is probably unnecessary, but it does no
	 * harm.  -- JWP
	 */

	closelog ();
	exit (1);
}