login/programs/pt_chown.c

   1 /* Copyright (C) 1998 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by C. Scott Ananian <cananian@alumni.princeton.edu>, 1998.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 /* pt_chmod.c ... securely implement grantpt in user-land.  */
  21
  22 #include <sys/stat.h>
  23 #include <sys/types.h>
  24 #include <stdlib.h>
  25 #include <unistd.h>
  26 #include <errno.h>
  27 #include <stdio.h>
  28 #include <grp.h>
  29
  30 #include "pty-internal.h"
  31 #define Str(x) _Str(x)
  32 #define _Str(x) #x
  33
  34 void
  35 usage (void)
  36 {
  37   fprintf (stderr, _("usage: pt_chown FD>&%s\n"
  38                      "This program is used internally by grantpt(3).\n"),
  39            Str (PTY_FD));
  40   exit (0);
  41 }
  42
  43 void
  44 bad_installation (void)
  45 {
  46   fputs (_("pt_chown: installation problem: "
  47            "This program needs to be setuid root.\n"), stderr);
  48   exit (FAIL_EXEC);
  49 }
  50
  51 int
  52 main (int argc, char **argv)
  53 {
  54   struct group *grp;
  55   struct stat s;
  56   char *pty;
  57   gid_t gid;
  58   uid_t uid;
  59
  60   if (argc != 1)
  61     usage ();
  62   if (geteuid () != 0)
  63     bad_installation ();
  64
  65   grp = getgrnam (TTY_GROUP);
  66   gid = grp ? grp->gr_gid : getgid ();
  67   uid = getuid ();
  68
  69   /* Check that fd is a valid pty master -- call ptsname().  */
  70   pty = ptsname (PTY_FD);
  71   if (pty == NULL)
  72     return errno == EBADF ? FAIL_EBADF : FAIL_EINVAL;
  73   close (PTY_FD);
  74
  75   /* Check that target file is a character device.  */
  76   if (stat (pty, &s))
  77     return FAIL_EINVAL; /* This should only fail if pty doesn't exist.  */
  78   if (!S_ISCHR (s.st_mode))
  79     return FAIL_EINVAL;
  80
  81   if (chmod (pty, 0620))
  82     return FAIL_EACCES;  /* XXX: Probably not true. */
  83
  84   if (chown (pty, uid, gid))
  85     return FAIL_EACCES;
  86
  87   return 0;
  88 }