shadow/libmisc/chowntty.c

/*
 * Copyright (c) 1989 - 1994, Julianne Frances Haugh
 * Copyright (c) 1996 - 2001, Marek Michałkiewicz
 * Copyright (c) 2003 - 2005, Tomasz Kłoczko
 * Copyright (c) 2007 - 2008, Nicolas François
 * 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. The name of the copyright holders or contributors may not be used to
 *    endorse or promote products derived from this software without
 *    specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 THE COPYRIGHT
 * HOLDERS 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>

#ident "$Id$"

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <errno.h>
#include <grp.h>
#include "prototypes.h"
#include "defines.h"
#include <pwd.h>
#include "getdef.h"
/*
 * is_my_tty -- determine if "tty" is the same as TTY stdin is using
 */
static bool is_my_tty (const char *tty)
{
	struct stat by_name, by_fd;

	if ((stat (tty, &by_name) != 0) || (fstat (0, &by_fd) != 0)) {
		return false;
	}

	if (by_name.st_rdev != by_fd.st_rdev) {
		return false;
	} else {
		return true;
	}
}

/*
 *	chown_tty() sets the login tty to be owned by the new user ID
 *	with TTYPERM modes
 */

void chown_tty (const char *tty, const struct passwd *info)
{
	char buf[200], full_tty[200];
	char *group;		/* TTY group name or number */
	struct group *grent;
	gid_t gid;

	/*
	 * See if login.defs has some value configured for the port group
	 * ID.  Otherwise, use the user's primary group ID.
	 */

	group = getdef_str ("TTYGROUP");
	if (NULL == group) {
		gid = info->pw_gid;
	} else if ((group[0] >= '0') && (group[0] <= '9')) {
		gid = (gid_t) atol (group);
	} else {
		grent = getgrnam (group); /* local, no need for xgetgrnam */
		if (NULL != grent) {
			gid = grent->gr_gid;
		} else {
			gid = info->pw_gid;
		}
	}

	/*
	 * Change the permissions on the TTY to be owned by the user with
	 * the group as determined above.
	 */

	if ('/' != *tty) {
		snprintf (full_tty, sizeof full_tty, "/dev/%s", tty);
		tty = full_tty;
	}

	if (!is_my_tty (tty)) {
		SYSLOG ((LOG_WARN,
			 "unable to determine TTY name, got %s\n", tty));
		closelog ();
		exit (1);
	}

	if (   (fchown (STDIN_FILENO, info->pw_uid, gid) != 0)
	    || (fchmod (STDIN_FILENO, getdef_num ("TTYPERM", 0600)) != 0)) {
		int err = errno;

		snprintf (buf, sizeof buf, _("Unable to change tty stdin"));
		perror (buf);
		SYSLOG ((LOG_WARN,
			 "unable to change tty stdin for user `%s'\n",
			 info->pw_name));
		closelog ();

		if (EROFS != err) {
			exit (1);
		}
	}
#ifdef __linux__
	/*
	 * Please don't add code to chown /dev/vcs* to the user logging in -
	 * it's a potential security hole.  I wouldn't like the previous user
	 * to hold the file descriptor open and watch my screen.  We don't
	 * have the *BSD revoke() system call yet, and vhangup() only works
	 * for tty devices (which vcs* is not).  --marekm
	 */
#endif
}