sysdeps/unix/getlogin_r.c

   1 /* Reentrant function to return the current login name.  Unix version.
   2    Copyright (C) 1991-2024 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 <errno.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22 #include <stdio.h>
  23 #include <limits.h>
  24 #include <fcntl.h>
  25
  26 #include <utmp.h>
  27 #include "../login/utmp-private.h"
  28
  29 /* Return at most NAME_LEN characters of the login name of the user in NAME.
  30    If it cannot be determined or some other error occurred, return the error
  31    code.  Otherwise return 0.  */
  32
  33 #ifdef STATIC
  34 STATIC
  35 #endif
  36 int
  37 __getlogin_r (char *name, size_t name_len)
  38 {
  39   char tty_pathname[2 + 2 * NAME_MAX];
  40   char *real_tty_path = tty_pathname;
  41   int result;
  42   struct utmp *ut, line, buffer;
  43
  44   /* Get name of tty connected to fd 0.  Return if not a tty or
  45      if fd 0 isn't open.  Note that a lot of documentation says that
  46      getlogin() is based on the controlling terminal---what they
  47      really mean is "the terminal connected to standard input".  The
  48      getlogin() implementation of DEC Unix, SunOS, Solaris, HP-UX all
  49      return NULL if fd 0 has been closed, so this is the compatible
  50      thing to do.  Note that ttyname(open("/dev/tty")) on those
  51      systems returns /dev/tty, so that is not a possible solution for
  52      getlogin().  */
  53
  54   result = __ttyname_r (0, real_tty_path, sizeof (tty_pathname));
  55
  56   if (result != 0)
  57     return result;
  58
  59   real_tty_path += 5;           /* Remove "/dev/".  */
  60   strncpy (line.ut_line, real_tty_path, sizeof line.ut_line);
  61
  62   /* We don't use the normal entry points __setutent et al, because we
  63      want setutent + getutline_r + endutent all to happen with the lock
  64      held so that our search is thread-safe.  */
  65
  66   __libc_lock_lock (__libc_utmp_lock);
  67   __libc_setutent ();
  68   result = __libc_getutline_r (&line, &buffer, &ut);
  69   if (result < 0)
  70     {
  71       if (errno == ESRCH)
  72         /* The caller expects ENOENT if nothing is found.  */
  73         result = ENOENT;
  74       else
  75         result = errno;
  76     }
  77   __libc_endutent ();
  78   __libc_lock_unlock (__libc_utmp_lock);
  79
  80   if (result == 0)
  81     {
  82       size_t needed = __strnlen (ut->ut_user, UT_NAMESIZE) + 1;
  83
  84       if (needed > name_len)
  85         {
  86           __set_errno (ERANGE);
  87           result = ERANGE;
  88         }
  89       else
  90         {
  91           memcpy (name, ut->ut_user, needed - 1);
  92           name[needed - 1] = 0;
  93           result = 0;
  94         }
  95     }
  96
  97   return result;
  98 }
  99 #ifndef STATIC
 100 libc_hidden_def (__getlogin_r)
 101 weak_alias (__getlogin_r, getlogin_r)
 102 libc_hidden_weak (getlogin_r)
 103 #endif