lib/getlogin_r.c

   1 /* Provide a working getlogin_r for systems which lack it.
   2
   3    Copyright (C) 2005-2007, 2010-2020 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 <https://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 __CYGWIN__
  31 # define WIN32_LEAN_AND_MEAN
  32 # include <windows.h>
  33 /* Don't assume that UNICODE is not defined.  */
  34 # undef GetUserName
  35 # define GetUserName GetUserNameA
  36 #else
  37 # if !HAVE_DECL_GETLOGIN
  38 extern char *getlogin (void);
  39 # endif
  40 #endif
  41
  42 /* See unistd.in.h for documentation.  */
  43 int
  44 getlogin_r (char *name, size_t size)
  45 {
  46 #undef getlogin_r
  47 #if defined _WIN32 && ! defined __CYGWIN__
  48   /* Native Windows platform.  */
  49   DWORD sz;
  50
  51   /* When size > 0x7fff, the doc says that GetUserName will fail.
  52      Actually, on Windows XP SP3, it succeeds.  But let's be safe,
  53      for the sake of older Windows versions.  */
  54   if (size > 0x7fff)
  55     size = 0x7fff;
  56   sz = size;
  57   if (!GetUserName (name, &sz))
  58     {
  59       if (GetLastError () == ERROR_INSUFFICIENT_BUFFER)
  60         /* In this case, the doc says that sz contains the required size, but
  61            actually, on Windows XP SP3, it contains 2 * the required size.  */
  62         return ERANGE;
  63       else
  64         return ENOENT;
  65     }
  66   return 0;
  67 #elif HAVE_GETLOGIN_R
  68   /* Platform with a getlogin_r() function.  */
  69   int ret = getlogin_r (name, size);
  70
  71   if (ret == 0)
  72     {
  73       const char *nul = memchr (name, '\0', size);
  74       if (nul == NULL)
  75         /* name contains a truncated result.  */
  76         return ERANGE;
  77       if (size > 0 && nul == name + size - 1)
  78         {
  79           /* strlen(name) == size-1.  Determine whether the untruncated result
  80              would have had length size-1 or size.  */
  81           char *room = (char *) malloca (size + 1);
  82           if (room == NULL)
  83             return ENOMEM;
  84           ret = getlogin_r (room, size + 1);
  85           /* The untruncated result should be the same as in the first call.  */
  86           if (ret == 0 && memcmp (name, room, size) != 0)
  87             /* The untruncated result would have been different.  */
  88             ret = ERANGE;
  89           freea (room);
  90         }
  91     }
  92   return ret;
  93 #else
  94   /* Platform with a getlogin() function.  */
  95   char *n;
  96   size_t nlen;
  97
  98   errno = 0;
  99   n = getlogin ();
 100   if (!n)
 101     /* ENOENT is a reasonable errno value if getlogin returns NULL.  */
 102     return (errno != 0 ? errno : ENOENT);
 103
 104   nlen = strlen (n);
 105   if (size <= nlen)
 106     return ERANGE;
 107   memcpy (name, n, nlen + 1);
 108   return 0;
 109 #endif
 110 }