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/* pt_chown - helper program for 'grantpt'.
Copyright (C) 1998-1999, 2009-2020 Free Software Foundation, Inc.
Contributed by C. Scott Ananian <cananian@alumni.princeton.edu>, 1998.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
#include <errno.h>
#include <grp.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#include "root-uid.h"
#include "pty-private.h"
/* For security reasons, we try to minimize the dependencies on libraries
outside libc. This means, in particular:
- No use of gettext(), since it's usually implemented in libintl.
- No use of error() or argp, since they rely on gettext by default. */
static int
do_pt_chown (void)
{
char *pty;
struct stat st;
struct group *p;
gid_t gid;
/* Check that PTY_FILENO is a valid master pseudo terminal. */
pty = ptsname (PTY_FILENO);
if (pty == NULL)
return errno == EBADF ? FAIL_EBADF : FAIL_EINVAL;
/* Check that the returned slave pseudo terminal is a
character device. */
if (stat (pty, &st) < 0 || !S_ISCHR (st.st_mode))
return FAIL_EINVAL;
/* Get the group ID of the special 'tty' group. */
p = getgrnam (TTY_GROUP);
gid = p ? p->gr_gid : getgid ();
/* Set the owner to the real user ID, and the group to that special
group ID. */
if (st.st_gid != gid && chown (pty, getuid (), gid) < 0)
return FAIL_EACCES;
/* Set the permission mode to readable and writable by the owner,
and writable by the group. */
if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != (S_IRUSR|S_IWUSR|S_IWGRP)
&& chmod (pty, S_IRUSR|S_IWUSR|S_IWGRP) < 0)
return FAIL_EACCES;
return 0;
}
int
main (int argc, char *argv[])
{
uid_t euid = geteuid ();
if (argc == 1 && euid == ROOT_UID)
{
/* Normal invocation of this program is with no arguments and
with privileges. */
return do_pt_chown ();
}
/* It would be possible to drop setuid/setgid privileges here. But it is not
really needed, since the code below only calls strcmp and [f]printf. */
{
int do_help = 0;
int do_version = 0;
int remaining;
for (remaining = 1; remaining < argc; remaining++)
{
const char *arg = argv[remaining];
if (arg[0] == '-')
{
if (strcmp (arg, "--") == 0)
{
remaining++;
break;
}
else if (strcmp (arg, "--help") == 0)
do_help = 1;
else if (strcmp (arg, "--version") == 0)
do_version = 1;
else
{
fprintf (stderr, "pt_chown: invalid option: %s\n", arg);
return EXIT_FAILURE;
}
}
else
break;
}
if (remaining < argc)
{
fprintf (stderr, "pt_chown: too many arguments\n");
return EXIT_FAILURE;
}
if (do_help)
{
printf ("Usage: pt_chown [OPTION...]\n");
printf ("Set the owner, group and access permission of the slave pseudo terminal\n"
"corresponding to the master pseudo terminal passed on file descriptor %d.\n"
"This is the helper program for the 'grantpt' function. It is not intended\n"
"to be run directly from the command line.\n",
PTY_FILENO);
printf ("\n");
printf (" --help Give this help list\n");
printf (" --version Print program version\n");
printf ("\n");
printf ("The owner is set to the current user, the group is set to '%s', and the\n"
"access permission is set to '%o'.\n",
TTY_GROUP, S_IRUSR|S_IWUSR|S_IWGRP);
printf ("Please report bugs to <bug-gnulib@gnu.org>.\n");
return EXIT_SUCCESS;
}
if (do_version)
{
printf ("pt_chown (GNU %s) %s\n", "libc", "2.11");
printf ("Copyright (C) %s Free Software Foundation, Inc.\n"
"This is free software; see the source for copying conditions. There is NO\n"
"warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n",
"1999");
return EXIT_SUCCESS;
}
}
/* Check if we are properly installed. */
if (euid != ROOT_UID)
{
fprintf (stderr, "pt_chown: needs to be installed setuid 'root'\n");
return FAIL_EXEC;
}
return EXIT_SUCCESS;
}
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