glibc/sysdeps/unix/getlogin_r.c

/* Reentrant function to return the current login name.  Unix version.
   Copyright (C) 1991-2024 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 <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <limits.h>
#include <fcntl.h>

#include <utmp.h>
#include "../login/utmp-private.h"

/* Return at most NAME_LEN characters of the login name of the user in NAME.
   If it cannot be determined or some other error occurred, return the error
   code.  Otherwise return 0.  */

#ifdef STATIC
STATIC
#endif
int
__getlogin_r (char *name, size_t name_len)
{
  char tty_pathname[2 + 2 * NAME_MAX];
  char *real_tty_path = tty_pathname;
  int result;
  struct utmp *ut, line, buffer;

  /* Get name of tty connected to fd 0.  Return if not a tty or
     if fd 0 isn't open.  Note that a lot of documentation says that
     getlogin() is based on the controlling terminal---what they
     really mean is "the terminal connected to standard input".  The
     getlogin() implementation of DEC Unix, SunOS, Solaris, HP-UX all
     return NULL if fd 0 has been closed, so this is the compatible
     thing to do.  Note that ttyname(open("/dev/tty")) on those
     systems returns /dev/tty, so that is not a possible solution for
     getlogin().  */

  result = __ttyname_r (0, real_tty_path, sizeof (tty_pathname));

  if (result != 0)
    return result;

  real_tty_path += 5;		/* Remove "/dev/".  */
  strncpy (line.ut_line, real_tty_path, sizeof line.ut_line);

  /* We don't use the normal entry points __setutent et al, because we
     want setutent + getutline_r + endutent all to happen with the lock
     held so that our search is thread-safe.  */

  __libc_lock_lock (__libc_utmp_lock);
  __libc_setutent ();
  result = __libc_getutline_r (&line, &buffer, &ut);
  if (result < 0)
    {
      if (errno == ESRCH)
	/* The caller expects ENOENT if nothing is found.  */
	result = ENOENT;
      else
	result = errno;
    }
  __libc_endutent ();
  __libc_lock_unlock (__libc_utmp_lock);

  if (result == 0)
    {
      size_t needed = __strnlen (ut->ut_user, UT_NAMESIZE) + 1;

      if (needed > name_len)
	{
	  __set_errno (ERANGE);
	  result = ERANGE;
	}
      else
	{
	  memcpy (name, ut->ut_user, needed - 1);
	  name[needed - 1] = 0;
	  result = 0;
	}
    }

  return result;
}
#ifndef STATIC
libc_hidden_def (__getlogin_r)
weak_alias (__getlogin_r, getlogin_r)
libc_hidden_weak (getlogin_r)
#endif