lib/pt_chown.c

   1 /* pt_chown - helper program for `grantpt'.
   2    Copyright (C) 1998-1999, 2009-2011 Free Software Foundation, Inc.
   3    Contributed by C. Scott Ananian <cananian@alumni.princeton.edu>, 1998.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  17
  18 #include <config.h>
  19
  20 #include <errno.h>
  21 #include <grp.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/stat.h>
  26 #include <unistd.h>
  27
  28 #include "pty-private.h"
  29
  30 /* For security reasons, we try to minimize the dependencies on libraries
  31    outside libc.  This means, in particular:
  32      - No use of gettext(), since it's usually implemented in libintl.
  33      - No use of error() or argp, since they rely on gettext by default.  */
  34
  35
  36 static int
  37 do_pt_chown (void)
  38 {
  39   char *pty;
  40   struct stat st;
  41   struct group *p;
  42   gid_t gid;
  43
  44   /* Check that PTY_FILENO is a valid master pseudo terminal.  */
  45   pty = ptsname (PTY_FILENO);
  46   if (pty == NULL)
  47     return errno == EBADF ? FAIL_EBADF : FAIL_EINVAL;
  48
  49   /* Check that the returned slave pseudo terminal is a
  50      character device.  */
  51   if (stat (pty, &st) < 0 || !S_ISCHR (st.st_mode))
  52     return FAIL_EINVAL;
  53
  54   /* Get the group ID of the special `tty' group.  */
  55   p = getgrnam (TTY_GROUP);
  56   gid = p ? p->gr_gid : getgid ();
  57
  58   /* Set the owner to the real user ID, and the group to that special
  59      group ID.  */
  60   if (st.st_gid != gid && chown (pty, getuid (), gid) < 0)
  61     return FAIL_EACCES;
  62
  63   /* Set the permission mode to readable and writable by the owner,
  64      and writable by the group.  */
  65   if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != (S_IRUSR|S_IWUSR|S_IWGRP)
  66       && chmod (pty, S_IRUSR|S_IWUSR|S_IWGRP) < 0)
  67     return FAIL_EACCES;
  68
  69   return 0;
  70 }
  71
  72
  73 int
  74 main (int argc, char *argv[])
  75 {
  76   uid_t euid = geteuid ();
  77
  78   if (argc == 1 && euid == 0)
  79     {
  80       /* Normal invocation of this program is with no arguments and
  81          with privileges.  */
  82       return do_pt_chown ();
  83     }
  84
  85   /* It would be possible to drop setuid/setgid privileges here.  But it is not
  86      really needed, since the code below only calls strcmp and [f]printf.  */
  87
  88   {
  89     int do_help = 0;
  90     int do_version = 0;
  91     int remaining;
  92
  93     for (remaining = 1; remaining < argc; remaining++)
  94       {
  95         const char *arg = argv[remaining];
  96
  97         if (arg[0] == '-')
  98           {
  99             if (strcmp (arg, "--") == 0)
 100               {
 101                 remaining++;
 102                 break;
 103               }
 104             else if (strcmp (arg, "--help") == 0)
 105               do_help = 1;
 106             else if (strcmp (arg, "--version") == 0)
 107               do_version = 1;
 108             else
 109               {
 110                 fprintf (stderr, "pt_chown: invalid option: %s\n", arg);
 111                 return EXIT_FAILURE;
 112               }
 113           }
 114         else
 115           break;
 116       }
 117
 118     if (remaining < argc)
 119       {
 120         fprintf (stderr, "pt_chown: too many arguments\n");
 121         return EXIT_FAILURE;
 122       }
 123
 124     if (do_help)
 125       {
 126         printf ("Usage: pt_chown [OPTION...]\n");
 127         printf ("Set the owner, group and access permission of the slave pseudo terminal\n"
 128                 "corresponding to the master pseudo terminal passed on file descriptor %d.\n"
 129                 "This is the helper program for the 'grantpt' function.  It is not intended\n"
 130                 "to be run directly from the command line.\n",
 131                 PTY_FILENO);
 132         printf ("\n");
 133         printf ("  --help                     Give this help list\n");
 134         printf ("  --version                  Print program version\n");
 135         printf ("\n");
 136         printf ("The owner is set to the current user, the group is set to '%s', and the\n"
 137                 "access permission is set to '%o'.\n",
 138                 TTY_GROUP, S_IRUSR|S_IWUSR|S_IWGRP);
 139         printf ("Please report bugs to <bug-gnulib@gnu.org>.\n");
 140         return EXIT_SUCCESS;
 141       }
 142
 143     if (do_version)
 144       {
 145         printf ("pt_chown (GNU %s) %s\n", "libc", "2.11");
 146         printf ("Copyright (C) %s Free Software Foundation, Inc.\n"
 147                 "This is free software; see the source for copying conditions.  There is NO\n"
 148                 "warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n",
 149                 "1999");
 150         return EXIT_SUCCESS;
 151       }
 152   }
 153
 154   /* Check if we are properly installed.  */
 155   if (euid != 0)
 156     {
 157       fprintf (stderr, "pt_chown: needs to be installed setuid 'root'\n");
 158       return FAIL_EXEC;
 159     }
 160
 161   return EXIT_SUCCESS;
 162 }