lib/putenv.c

   1 /* Copyright (C) 1991, 1994, 1997-1998, 2000, 2003-2024 Free Software
   2    Foundation, Inc.
   3
   4    NOTE: The canonical source of this file is maintained with the GNU C
   5    Library.  Bugs can be reported to bug-glibc@prep.ai.mit.edu.
   6
   7    This file is free software: you can redistribute it and/or modify
   8    it under the terms of the GNU Lesser General Public License as
   9    published by the Free Software Foundation, either version 3 of the
  10    License, or (at your option) any later version.
  11
  12    This file is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public License
  18    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  19
  20 #include <config.h>
  21
  22 /* Specification.  */
  23 #include <stdlib.h>
  24
  25 #include <stddef.h>
  26
  27 /* Include errno.h *after* sys/types.h to work around header problems
  28    on AIX 3.2.5.  */
  29 #include <errno.h>
  30 #ifndef __set_errno
  31 # define __set_errno(ev) ((errno) = (ev))
  32 #endif
  33
  34 #include <string.h>
  35 #include <unistd.h>
  36
  37 #if defined _WIN32 && ! defined __CYGWIN__
  38 # define WIN32_LEAN_AND_MEAN
  39 # include <windows.h>
  40 #endif
  41
  42 #if _LIBC
  43 # if HAVE_GNU_LD
  44 #  define environ __environ
  45 # else
  46 extern char **environ;
  47 # endif
  48 #endif
  49
  50 #if _LIBC
  51 /* This lock protects against simultaneous modifications of 'environ'.  */
  52 # include <bits/libc-lock.h>
  53 __libc_lock_define_initialized (static, envlock)
  54 # define LOCK   __libc_lock_lock (envlock)
  55 # define UNLOCK __libc_lock_unlock (envlock)
  56 #else
  57 # define LOCK
  58 # define UNLOCK
  59 #endif
  60
  61 #if defined _WIN32 && ! defined __CYGWIN__
  62 /* Don't assume that UNICODE is not defined.  */
  63 # undef SetEnvironmentVariable
  64 # define SetEnvironmentVariable SetEnvironmentVariableA
  65 #endif
  66
  67 /* Put STRING, which is of the form "NAME=VALUE", in the environment.
  68    If STRING contains no '=', then remove STRING from the environment.  */
  69 int
  70 putenv (char *string)
  71 {
  72   const char *name_end = strchr (string, '=');
  73   char **ep;
  74
  75   if (name_end == NULL)
  76     {
  77       /* Remove the variable from the environment.  */
  78       return unsetenv (string);
  79     }
  80
  81 #if HAVE_DECL__PUTENV /* native Windows */
  82   /* The Microsoft documentation
  83      <https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/putenv-wputenv>
  84      says:
  85        "Don't change an environment entry directly: instead,
  86         use _putenv or _wputenv to change it."
  87      Note: Microsoft's _putenv updates not only the contents of _environ but
  88      also the contents of _wenviron, so that both are in kept in sync.
  89
  90      If we didn't follow this advice, our code and other parts of the
  91      application (that use _putenv) would fight over who owns the environ vector
  92      and thus cause a crash.  */
  93   if (name_end[1])
  94     return _putenv (string);
  95   else
  96     {
  97       /* _putenv ("NAME=") unsets NAME, so invoke _putenv ("NAME= ")
  98          to allocate the environ vector and then replace the new
  99          entry with "NAME=".  */
 100       int putenv_result;
 101       char *name_x = malloc (name_end - string + sizeof "= ");
 102       if (!name_x)
 103         return -1;
 104       memcpy (name_x, string, name_end - string + 1);
 105       name_x[name_end - string + 1] = ' ';
 106       name_x[name_end - string + 2] = 0;
 107       putenv_result = _putenv (name_x);
 108       for (ep = environ; *ep; ep++)
 109         if (strcmp (*ep, name_x) == 0)
 110           {
 111             *ep = string;
 112             break;
 113           }
 114 # if defined _WIN32 && ! defined __CYGWIN__
 115       if (putenv_result == 0)
 116         {
 117           /* _putenv propagated "NAME= " into the subprocess environment;
 118              fix that by calling SetEnvironmentVariable directly.  */
 119           name_x[name_end - string] = 0;
 120           putenv_result = SetEnvironmentVariable (name_x, "") ? 0 : -1;
 121           errno = ENOMEM; /* ENOMEM is the only way to fail.  */
 122         }
 123 # endif
 124       free (name_x);
 125       return putenv_result;
 126     }
 127 #else
 128   for (ep = environ; *ep; ep++)
 129     if (strncmp (*ep, string, name_end - string) == 0
 130         && (*ep)[name_end - string] == '=')
 131       break;
 132
 133   if (*ep)
 134     *ep = string;
 135   else
 136     {
 137       static char **last_environ = NULL;
 138       size_t size = ep - environ;
 139       char **new_environ = malloc ((size + 2) * sizeof *new_environ);
 140       if (! new_environ)
 141         return -1;
 142       new_environ[0] = string;
 143       memcpy (new_environ + 1, environ, (size + 1) * sizeof *new_environ);
 144       free (last_environ);
 145       last_environ = new_environ;
 146       environ = new_environ;
 147     }
 148
 149   return 0;
 150 #endif
 151 }