lib/getlogin_r.c

   1 /* Provide a working getlogin_r for systems which lack it.
   2
   3    Copyright (C) 2005-2007, 2010-2017 Free Software Foundation, Inc.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2, or (at your option)
   8    any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, see <http://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert, Derek Price, and Bruno Haible.  */
  19
  20 #include <config.h>
  21
  22 /* Specification.  */
  23 #include <unistd.h>
  24
  25 #include <errno.h>
  26 #include <string.h>
  27
  28 #include "malloca.h"
  29
  30 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
  31 # define WIN32_LEAN_AND_MEAN
  32 # include <windows.h>
  33 #else
  34 # if !HAVE_DECL_GETLOGIN
  35 extern char *getlogin (void);
  36 # endif
  37 #endif
  38
  39 /* See unistd.in.h for documentation.  */
  40 int
  41 getlogin_r (char *name, size_t size)
  42 {
  43 #undef getlogin_r
  44 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
  45   /* Native Windows platform.  */
  46   DWORD sz;
  47
  48   /* When size > 0x7fff, the doc says that GetUserName will fail.
  49      Actually, on Windows XP SP3, it succeeds.  But let's be safe,
  50      for the sake of older Windows versions.  */
  51   if (size > 0x7fff)
  52     size = 0x7fff;
  53   sz = size;
  54   if (!GetUserName (name, &sz))
  55     {
  56       if (GetLastError () == ERROR_INSUFFICIENT_BUFFER)
  57         /* In this case, the doc says that sz contains the required size, but
  58            actually, on Windows XP SP3, it contains 2 * the required size.  */
  59         return ERANGE;
  60       else
  61         return ENOENT;
  62     }
  63   return 0;
  64 #elif HAVE_GETLOGIN_R
  65   /* Platform with a getlogin_r() function.  */
  66   int ret = getlogin_r (name, size);
  67
  68   if (ret == 0)
  69     {
  70       const char *nul = memchr (name, '\0', size);
  71       if (nul == NULL)
  72         /* name contains a truncated result.  */
  73         return ERANGE;
  74       if (size > 0 && nul == name + size - 1)
  75         {
  76           /* strlen(name) == size-1.  Determine whether the untruncated result
  77              would have had length size-1 or size.  */
  78           char *room = (char *) malloca (size + 1);
  79           if (room == NULL)
  80             return ENOMEM;
  81           ret = getlogin_r (room, size + 1);
  82           /* The untruncated result should be the same as in the first call.  */
  83           if (ret == 0 && memcmp (name, room, size) != 0)
  84             /* The untruncated result would have been different.  */
  85             ret = ERANGE;
  86           freea (room);
  87         }
  88     }
  89   return ret;
  90 #else
  91   /* Platform with a getlogin() function.  */
  92   char *n;
  93   size_t nlen;
  94
  95   errno = 0;
  96   n = getlogin ();
  97   if (!n)
  98     /* ENOENT is a reasonable errno value if getlogin returns NULL.  */
  99     return (errno != 0 ? errno : ENOENT);
 100
 101   nlen = strlen (n);
 102   if (size <= nlen)
 103     return ERANGE;
 104   memcpy (name, n, nlen + 1);
 105   return 0;
 106 #endif
 107 }