new module 'pt_chown'

[Bruno Haible]

The next piece of pseudo-terminal support is the ability to chown the slave
side of a pseudo-terminal. The way it's done in 'xterm' or 'openssh' requires
making the main executable setuid root. I much prefer the approach in glibc,
where only a tiny executable with no dependencies needs to be setuid root.

This module ports the glibc code to gnulib.

How to install the program as setuid root, is a TODO. Someone with root
access to a AIX, HP-UX, IRIX, or Solaris machine could try to set it up.

I put the module under LGPL rather GPL, because the modules 'openpty' and
'forkpty' should stay under LGPL and I'm not willing to go into long
discussions about whether a module that uses (and cannot work without) a
GPLed program is a "combined work" based on that GPLed program and
therefore necessarily under GPL or not.

This compiles fine on Solaris, but is otherwise completely untested.


2010-03-21  Bruno Haible  <address@hidden>

        New module 'pt_chown'.
        * lib/pt_chown.c: New file, from glibc with modifications.
        * lib/pty-private.h: New file, from glibc with modifications.
        * modules/pt_chown: New file.
        * config/srclist.txt: Add pt_chown.c, pty-private.h (commented).

=============================== lib/pt_chown.c ===============================
/* pt_chown - helper program for `grantpt'.
   Copyright (C) 1998, 1999, 2009, 2010 Free Software Foundation, Inc.
   Contributed by C. Scott Ananian <address@hidden>, 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 <http://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 "idpriv.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 == 0)
    {
      /* 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. */
  if (idpriv_drop () < 0)
    return EXIT_FAILURE;

  {
    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 <address@hidden>.\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 != 0)
    {
      fprintf (stderr, "pt_chown: needs to be installed setuid 'root'\n");
      return FAIL_EXEC;
    }

  return EXIT_SUCCESS;
}
============================== lib/pty-private.h ==============================
/* Interface to the pt_chown program.
   Copyright (C) 1998, 1999, 2009, 2010 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Zack Weinberg <address@hidden>, 1998.

   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, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#ifndef _PTY_PRIVATE_H
#define _PTY_PRIVATE_H 1

/* The group slave pseudo terminals belong to.  */
#define TTY_GROUP "tty"

/* The file descriptor connected to the master pseudo terminal.  */
#define PTY_FILENO 3

/* Path to the helper program that implements `grantpt' in user space.  */
#define _PATH_PT_CHOWN PKGLIBEXECDIR "/pt_chown"

/* Test whether given TTY is really a Unix98 pseudo terminal.  */
/* #define unix98_pseudo_p(Dev) ... */

/* Exit codes for the helper program.  */
enum  /* failure modes */
{
  FAIL_EBADF = 1,
  FAIL_EINVAL,
  FAIL_EACCES,
  FAIL_EXEC,
  FAIL_ENOMEM
};

#endif /* pty-private.h  */
============================== modules/pt_chown ==============================
Description:
Helper program for setting the owner of the slave side of a pseudo-terminal.

Files:
lib/pt_chown.c
lib/pty-private.h

Depends-on:
idpriv-drop
ptsname

configure.ac:

Makefile.am:
# TODO: Add rules for installing as setuid root (chown root, chmod a=rx,u+s).
pkglibexec_PROGRAMS = pt_chown
pt_chown_LDADD = libgnu.a

Include:

License:
LGPL

Maintainer:
glibc
==============================================================================
--- config/srclist.txt.orig     Sun Mar 21 16:49:58 2010
+++ config/srclist.txt  Sun Mar 21 16:49:05 2010
@@ -174,6 +174,8 @@
 #$LIBCSRC/locale/programs/xmalloc.c    lib gpl
 #$LIBCSRC/locale/programs/xstrdup.c    lib gpl
 #
+#$LIBCSRC/login/programs/pt_chown.c    lib gpl
+#
 # http://sources.redhat.com/bugzilla/show_bug.cgi?id=321
 #$LIBCSRC/malloc/obstack.c             lib gpl
 #
@@ -209,6 +211,7 @@
 #$LIBCSRC/string/strcspn.c             lib gpl
 #$LIBCSRC/string/strpbrk.c             lib gpl
 #$LIBCSRC/string/strstr.c              lib gpl
+#$LIBCSRC/sysdeps/generic/pty-private.h        lib gpl
 #$LIBCSRC/sysdeps/posix/dup2.c         lib gpl
 #$LIBCSRC/sysdeps/posix/euidaccess.c   lib gpl
 #$LIBCSRC/sysdeps/posix/tempname.c     lib gpl