glibc/login/programs/pt_chown.c

/* pt_chmod - helper program for `grantpt'.
   Copyright (C) 1998-2022 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <argp.h>
#include <errno.h>
#include <error.h>
#include <grp.h>
#include <libintl.h>
#include <locale.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#ifdef HAVE_LIBCAP
# include <sys/capability.h>
# include <sys/prctl.h>
#endif

#include "pty-private.h"

/* Get libc version number.  */
#include "../version.h"

#define PACKAGE _libc_intl_domainname

/* Name and version of program.  */
static void print_version (FILE *stream, struct argp_state *state);
void (*argp_program_version_hook) (FILE *, struct argp_state *) = print_version;

/* Function to print some extra text in the help message.  */
static char *more_help (int key, const char *text, void *input);

/* Data structure to communicate with argp functions.  */
static struct argp argp =
{
  NULL, NULL, NULL, NULL, NULL, more_help
};


/* Print the version information.  */
static void
print_version (FILE *stream, struct argp_state *state)
{
  fprintf (stream, "pt_chown %s%s\n", PKGVERSION, VERSION);
  fprintf (stream, gettext ("\
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\
"), "2022");
}

static char *
more_help (int key, const char *text, void *input)
{
  char *cp;
  char *tp;

  switch (key)
    {
    case ARGP_KEY_HELP_PRE_DOC:
      asprintf (&cp, gettext ("\
Set the owner, group and access permission of the slave pseudo\
 terminal corresponding to the master pseudo terminal passed on\
 file descriptor `%d'.  This is the helper program for the\
 `grantpt' function.  It is not intended to be run directly from\
 the command line.\n"),
		PTY_FILENO);
      return cp;
    case ARGP_KEY_HELP_EXTRA:
      /* We print some extra information.  */
      if (asprintf (&tp, gettext ("\
For bug reporting instructions, please see:\n\
%s.\n"), REPORT_BUGS_TO) < 0)
	return NULL;
      if (asprintf (&cp, gettext ("\
The owner is set to the current user, the group is set to `%s',\
 and the access permission is set to `%o'.\n\n\
%s"),
		    TTY_GROUP, S_IRUSR|S_IWUSR|S_IWGRP, tp) < 0)
	{
	  free (tp);
	  return NULL;
	}
      return cp;
    default:
      break;
    }
  return (char *) text;
}

static int
do_pt_chown (void)
{
  char *pty;
  struct stat64 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 (stat64 (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 (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 & ACCESSPERMS) != (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 ();
  uid_t uid = getuid ();
  int remaining;
  sigset_t signalset;

  /* Clear any signal mask from the parent process.  */
  sigemptyset (&signalset);
  sigprocmask (SIG_SETMASK, &signalset, NULL);

  if (argc == 1 && euid == 0)
    {
#ifdef HAVE_LIBCAP
  /* Drop privileges.  */
      if (uid != euid)
	{
	  static const cap_value_t cap_list[] =
	    { CAP_CHOWN, CAP_FOWNER	};
# define ncap_list (sizeof (cap_list) / sizeof (cap_list[0]))
	  cap_t caps = cap_init ();
	  if (caps == NULL)
	    return FAIL_ENOMEM;

	  /* There is no reason why these should not work.  */
	  cap_set_flag (caps, CAP_PERMITTED, ncap_list, cap_list, CAP_SET);
	  cap_set_flag (caps, CAP_EFFECTIVE, ncap_list, cap_list, CAP_SET);

	  int res = cap_set_proc (caps);

	  cap_free (caps);

	  if (__glibc_unlikely (res != 0))
	    return FAIL_EXEC;
	}
#endif

      /* Normal invocation of this program is with no arguments and
	 with privileges.  */
      return do_pt_chown ();
    }

  /* We aren't going to be using privileges, so drop them right now. */
  setuid (uid);

  /* Set locale via LC_ALL.  */
  setlocale (LC_ALL, "");

  /* Set the text message domain.  */
  textdomain (PACKAGE);

  /* parse and process arguments.  */
  argp_parse (&argp, argc, argv, 0, &remaining, NULL);

  if (remaining < argc)
    {
      /* We should not be called with any non-option parameters.  */
      error (0, 0, gettext ("too many arguments"));
      argp_help (&argp, stdout, ARGP_HELP_SEE | ARGP_HELP_EXIT_ERR,
		 program_invocation_short_name);
      return EXIT_FAILURE;
    }

  /* Check if we are properly installed.  */
  if (euid != 0)
    error (FAIL_EXEC, 0, gettext ("needs to be installed setuid `root'"));

  return EXIT_SUCCESS;
}