login/programs/pt_chown.c

   1 /* pt_chmod - helper program for `grantpt'.
   2    Copyright (C) 1998-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <argp.h>
  20 #include <errno.h>
  21 #include <error.h>
  22 #include <grp.h>
  23 #include <libintl.h>
  24 #include <locale.h>
  25 #include <signal.h>
  26 #include <stdio.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29 #include <sys/stat.h>
  30 #include <unistd.h>
  31 #ifdef HAVE_LIBCAP
  32 # include <sys/capability.h>
  33 # include <sys/prctl.h>
  34 #endif
  35
  36 #include "pty-private.h"
  37
  38 /* Get libc version number.  */
  39 #include "../version.h"
  40
  41 #define PACKAGE _libc_intl_domainname
  42
  43 /* Name and version of program.  */
  44 static void print_version (FILE *stream, struct argp_state *state);
  45 void (*argp_program_version_hook) (FILE *, struct argp_state *) = print_version;
  46
  47 /* Function to print some extra text in the help message.  */
  48 static char *more_help (int key, const char *text, void *input);
  49
  50 /* Data structure to communicate with argp functions.  */
  51 static struct argp argp =
  52 {
  53   NULL, NULL, NULL, NULL, NULL, more_help
  54 };
  55
  56
  57 /* Print the version information.  */
  58 static void
  59 print_version (FILE *stream, struct argp_state *state)
  60 {
  61   fprintf (stream, "pt_chown %s%s\n", PKGVERSION, VERSION);
  62   fprintf (stream, gettext ("\
  63 Copyright (C) %s Free Software Foundation, Inc.\n\
  64 This is free software; see the source for copying conditions.  There is NO\n\
  65 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n\
  66 "), "2024");
  67 }
  68
  69 static char *
  70 more_help (int key, const char *text, void *input)
  71 {
  72   char *cp;
  73   char *tp;
  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       if (asprintf (&tp, gettext ("\
  89 For bug reporting instructions, please see:\n\
  90 %s.\n"), REPORT_BUGS_TO) < 0)
  91         return NULL;
  92       if (asprintf (&cp, gettext ("\
  93 The owner is set to the current user, the group is set to `%s',\
  94  and the access permission is set to `%o'.\n\n\
  95 %s"),
  96                     TTY_GROUP, S_IRUSR|S_IWUSR|S_IWGRP, tp) < 0)
  97         {
  98           free (tp);
  99           return NULL;
 100         }
 101       return cp;
 102     default:
 103       break;
 104     }
 105   return (char *) text;
 106 }
 107
 108 static int
 109 do_pt_chown (void)
 110 {
 111   char *pty;
 112   struct stat64 st;
 113   struct group *p;
 114   gid_t gid;
 115
 116   /* Check that PTY_FILENO is a valid master pseudo terminal.  */
 117   pty = ptsname (PTY_FILENO);
 118   if (pty == NULL)
 119     return errno == EBADF ? FAIL_EBADF : FAIL_EINVAL;
 120
 121   /* Check that the returned slave pseudo terminal is a
 122      character device.  */
 123   if (stat64 (pty, &st) < 0 || !S_ISCHR (st.st_mode))
 124     return FAIL_EINVAL;
 125
 126   /* Get the group ID of the special `tty' group.  */
 127   p = getgrnam (TTY_GROUP);
 128   gid = p ? p->gr_gid : getgid ();
 129
 130   /* Set the owner to the real user ID, and the group to that special
 131      group ID.  */
 132   if (chown (pty, getuid (), gid) < 0)
 133     return FAIL_EACCES;
 134
 135   /* Set the permission mode to readable and writable by the owner,
 136      and writable by the group.  */
 137   if ((st.st_mode & ACCESSPERMS) != (S_IRUSR|S_IWUSR|S_IWGRP)
 138       && chmod (pty, S_IRUSR|S_IWUSR|S_IWGRP) < 0)
 139     return FAIL_EACCES;
 140
 141   return 0;
 142 }
 143
 144
 145 int
 146 main (int argc, char *argv[])
 147 {
 148   uid_t euid = geteuid ();
 149   uid_t uid = getuid ();
 150   int remaining;
 151   sigset_t signalset;
 152
 153   /* Clear any signal mask from the parent process.  */
 154   sigemptyset (&signalset);
 155   sigprocmask (SIG_SETMASK, &signalset, NULL);
 156
 157   if (argc == 1 && euid == 0)
 158     {
 159 #ifdef HAVE_LIBCAP
 160   /* Drop privileges.  */
 161       if (uid != euid)
 162         {
 163           static const cap_value_t cap_list[] =
 164             { CAP_CHOWN, CAP_FOWNER     };
 165 # define ncap_list (sizeof (cap_list) / sizeof (cap_list[0]))
 166           cap_t caps = cap_init ();
 167           if (caps == NULL)
 168             return FAIL_ENOMEM;
 169
 170           /* There is no reason why these should not work.  */
 171           cap_set_flag (caps, CAP_PERMITTED, ncap_list, cap_list, CAP_SET);
 172           cap_set_flag (caps, CAP_EFFECTIVE, ncap_list, cap_list, CAP_SET);
 173
 174           int res = cap_set_proc (caps);
 175
 176           cap_free (caps);
 177
 178           if (__glibc_unlikely (res != 0))
 179             return FAIL_EXEC;
 180         }
 181 #endif
 182
 183       /* Normal invocation of this program is with no arguments and
 184          with privileges.  */
 185       return do_pt_chown ();
 186     }
 187
 188   /* We aren't going to be using privileges, so drop them right now. */
 189   setuid (uid);
 190
 191   /* Set locale via LC_ALL.  */
 192   setlocale (LC_ALL, "");
 193
 194   /* Set the text message domain.  */
 195   textdomain (PACKAGE);
 196
 197   /* parse and process arguments.  */
 198   argp_parse (&argp, argc, argv, 0, &remaining, NULL);
 199
 200   if (remaining < argc)
 201     {
 202       /* We should not be called with any non-option parameters.  */
 203       error (0, 0, gettext ("too many arguments"));
 204       argp_help (&argp, stdout, ARGP_HELP_SEE | ARGP_HELP_EXIT_ERR,
 205                  program_invocation_short_name);
 206       return EXIT_FAILURE;
 207     }
 208
 209   /* Check if we are properly installed.  */
 210   if (euid != 0)
 211     error (FAIL_EXEC, 0, gettext ("needs to be installed setuid `root'"));
 212
 213   return EXIT_SUCCESS;
 214 }