pt_chown.tproj/pt_chown.c

   1 /*
   2  * Copyright (c) 2002 The FreeBSD Project, Inc.
   3  * All rights reserved.
   4  *
   5  * This software includes code contributed to the FreeBSD Project
   6  * by Ryan Younce of North Carolina State University.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of the FreeBSD Project nor the names of its
  17  *    contributors may be used to endorse or promote products derived from
  18  *    this software without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE FREEBSD PROJECT AND CONTRIBUTORS ``AS IS''
  21  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE FREEBSD PROJECT OR ITS CONTRIBUTORS
  24  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  25  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  26  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  27  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  28  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  29  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  30  * POSSIBILITY OF SUCH DAMAGE.
  31  */
  32
  33 #include <sys/cdefs.h>
  34 #ifndef lint
  35 __FBSDID("$FreeBSD: /repoman/r/ncvs/src/libexec/pt_chown/pt_chown.c,v 1.1 2003/01/02 20:44:41 jmallett Exp $");
  36 #endif /* not lint */
  37
  38 #include <sys/stat.h>
  39
  40 #include <grp.h>
  41 #include <stdlib.h>
  42 #include <sysexits.h>
  43 #include <unistd.h>
  44
  45 /*
  46  * pt_chown
  47  * Utility support routine for grantpt(3).
  48  *
  49  * According to IEEE Std 1003.1-2001, grantpt(3) changes ownership and
  50  * permission bits of a slave pseudo-terminal device associated with a
  51  * master.
  52  *
  53  * Since doing this if we are not the owner of the slave (which would
  54  * rarely happen) cannot be done by conventional methods, grantpt(3)
  55  * has to rely on this support program, which is setuid root, to change
  56  * the slave's owner, group, and permission mode attributes.  It's
  57  * a rather undesirable approach, but Digital Unix and Solaris also seem
  58  * to rely on this approach to pull this off.
  59  *
  60  * This program hangs around long enough to do just these things upon
  61  * its standard input (which is set up by grantpt(3) to be the master's
  62  * descriptor, the one passed to it).  The rationale behind this
  63  * approach not allowing somebody to modify ownership of another active
  64  * pseudo terminal is:
  65  *
  66  * 1)  This program only operates on its standard input.  If STDIN_FILENO
  67  *     is not open or is not a pseudo-terminal master, no action is
  68  *     taken and the program exits (ptsname() is called for a non-NULL
  69  *     return).
  70  * 2)  Only one active file description for a pseudo-terminal master
  71  *     can exist at a time (attempting to open an active PTY returns with
  72  *     EIO - I/O Error).  Thus, if the pseudo-terminal is already in
  73  *     use by somebody else, it could not have been opened to begin
  74  *     with, and thus this program would be useless in such situations.
  75  */
  76 int
  77 main(int argc, char *argv[])
  78 {
  79         int retcode;
  80         char *slave;
  81         gid_t gid;
  82         struct group *grp;
  83
  84         retcode = EX_OK;
  85
  86         if ((slave = ptsname(STDIN_FILENO)) == NULL)
  87                 retcode = EX_USAGE;
  88         else {
  89                 gid = (grp = getgrnam("tty")) ? grp->gr_gid : -1;
  90                 if (chown(slave, getuid(), gid) == 0 &&
  91                     chmod(slave, S_IRUSR | S_IWUSR | S_IWGRP) == 0)
  92                         retcode = 0;
  93                 else
  94                         retcode = EX_NOPERM;
  95         }
  96
  97         /*
  98          * grantpt(3) checks the retcode for being either zero or
  99          * nonzero.  Any nonzero return results in errno being set
 100          * to EACCES.
 101          */
 102         exit(retcode);
 103 }