login/programs/pt_chown.c

   1 /* pt_chmod - helper program for `grantpt'.
   2    Copyright (C) 1998, 1999 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by C. Scott Ananian <cananian@alumni.princeton.edu>, 1998.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <argp.h>
  22 #include <errno.h>
  23 #include <error.h>
  24 #include <grp.h>
  25 #include <libintl.h>
  26 #include <locale.h>
  27 #include <stdio.h>
  28 #include <stdlib.h>
  29 #include <string.h>
  30 #include <sys/stat.h>
  31 #include <unistd.h>
  32 #ifdef HAVE_LIBCAP
  33 # include <sys/capability.h>
  34 # include <sys/prctl.h>
  35 #endif
  36
  37 #include "pty-private.h"
  38
  39 /* Get libc version number.  */
  40 #include "../version.h"
  41
  42 #define PACKAGE _libc_intl_domainname
  43
  44 /* Name and version of program.  */
  45 static void print_version (FILE *stream, struct argp_state *state);
  46 void (*argp_program_version_hook) (FILE *, struct argp_state *) = print_version;
  47
  48 /* Function to print some extra text in the help message.  */
  49 static char *more_help (int key, const char *text, void *input);
  50
  51 /* Data structure to communicate with argp functions.  */
  52 static struct argp argp =
  53 {
  54   NULL, NULL, NULL, NULL, NULL, more_help
  55 };
  56
  57
  58 /* Print the version information.  */
  59 static void
  60 print_version (FILE *stream, struct argp_state *state)
  61 {
  62   fprintf (stream, "pt_chown (GNU %s) %s\n", PACKAGE, VERSION);
  63   fprintf (stream, gettext ("\
  64 Copyright (C) %s Free Software Foundation, Inc.\n\
  65 This is free software; see the source for copying conditions.  There is NO\n\
  66 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n\
  67 "), "1999");
  68 }
  69
  70 static char *
  71 more_help (int key, const char *text, void *input)
  72 {
  73   char *cp;
  74
  75   switch (key)
  76     {
  77     case ARGP_KEY_HELP_PRE_DOC:
  78       asprintf (&cp, gettext ("\
  79 Set the owner, group and access permission of the slave pseudo\
  80  terminal corresponding to the master pseudo terminal passed on\
  81  file descriptor `%d'.  This is the helper program for the\
  82  `grantpt' function.  It is not intended to be run directly from\
  83  the command line.\n"),
  84                 PTY_FILENO);
  85       return cp;
  86     case ARGP_KEY_HELP_EXTRA:
  87       /* We print some extra information.  */
  88       asprintf (&cp, gettext ("\
  89 The owner is set to the current user, the group is set to `%s',\
  90  and the access permission is set to `%o'.\n\n\
  91 %s"),
  92                 TTY_GROUP, S_IRUSR|S_IWUSR|S_IWGRP, gettext ("\
  93 For bug reporting instructions, please see:\n\
  94 <http://www.gnu.org/software/libc/bugs.html>.\n"));
  95       return cp;
  96     default:
  97       break;
  98     }
  99   return (char *) text;
 100 }
 101
 102 static int
 103 do_pt_chown (void)
 104 {
 105   char *pty;
 106   struct stat64 st;
 107   struct group *p;
 108   gid_t gid;
 109
 110   /* Check that PTY_FILENO is a valid master pseudo terminal.  */
 111   pty = ptsname (PTY_FILENO);
 112   if (pty == NULL)
 113     return errno == EBADF ? FAIL_EBADF : FAIL_EINVAL;
 114
 115   /* Check that the returned slave pseudo terminal is a
 116      character device.  */
 117   if (stat64 (pty, &st) < 0 || !S_ISCHR (st.st_mode))
 118     return FAIL_EINVAL;
 119
 120   /* Get the group ID of the special `tty' group.  */
 121   p = getgrnam (TTY_GROUP);
 122   gid = p ? p->gr_gid : getgid ();
 123
 124   /* Set the owner to the real user ID, and the group to that special
 125      group ID.  */
 126   if (chown (pty, getuid (), gid) < 0)
 127     return FAIL_EACCES;
 128
 129   /* Set the permission mode to readable and writable by the owner,
 130      and writable by the group.  */
 131   if (chmod (pty, S_IRUSR|S_IWUSR|S_IWGRP) < 0)
 132     return FAIL_EACCES;
 133
 134   return 0;
 135 }
 136
 137
 138 int
 139 main (int argc, char *argv[])
 140 {
 141   uid_t euid = geteuid ();
 142   uid_t uid = getuid ();
 143   int remaining;
 144
 145   if (argc == 1 && euid == 0)
 146     {
 147 #ifdef HAVE_LIBCAP
 148   /* Drop privileges.  */
 149       if (uid != euid)
 150         {
 151           static const cap_value_t cap_list[] =
 152             { CAP_CHOWN, CAP_FOWNER     };
 153 # define ncap_list (sizeof (cap_list) / sizeof (cap_list[0]))
 154           cap_t caps = cap_init ();
 155           if (caps == NULL)
 156             error (FAIL_ENOMEM, errno,
 157                    _("Failed to initialize drop of capabilities"));
 158
 159           /* There is no reason why these should not work.  */
 160           cap_set_flag (caps, CAP_PERMITTED, ncap_list, cap_list, CAP_SET);
 161           cap_set_flag (caps, CAP_EFFECTIVE, ncap_list, cap_list, CAP_SET);
 162
 163           int res = cap_set_proc (caps);
 164
 165           cap_free (caps);
 166
 167           if (__builtin_expect (res != 0, 0))
 168             error (FAIL_EXEC, errno, _("cap_set_proc failed"));
 169         }
 170 #endif
 171
 172       /* Normal invocation of this program is with no arguments and
 173          with privileges.  */
 174       return do_pt_chown ();
 175     }
 176
 177   /* We aren't going to be using privileges, so drop them right now. */
 178   setuid (uid);
 179
 180   /* Set locale via LC_ALL.  */
 181   setlocale (LC_ALL, "");
 182
 183   /* Set the text message domain.  */
 184   textdomain (PACKAGE);
 185
 186   /* parse and process arguments.  */
 187   argp_parse (&argp, argc, argv, 0, &remaining, NULL);
 188
 189   if (remaining < argc)
 190     {
 191       /* We should not be called with any non-option parameters.  */
 192       error (0, 0, gettext ("too many arguments"));
 193       argp_help (&argp, stdout, ARGP_HELP_SEE | ARGP_HELP_EXIT_ERR,
 194                  program_invocation_short_name);
 195       return EXIT_FAILURE;
 196     }
 197
 198   /* Check if we are properly installed.  */
 199   if (euid != 0)
 200     error (FAIL_EXEC, 0, gettext ("needs to be installed setuid `root'"));
 201
 202   return EXIT_SUCCESS;
 203 }